Publications by authors named "Kevin McGill"

47 Publications

Rigorous performance assessment of the algorithms for resolving motor unit action potential superpositions.

J Electromyogr Kinesiol 2021 Feb 13;56:102510. Epub 2020 Dec 13.

Department of Automatic Control, Biomedical Engineering Research Center, Universitat Politècnica de Catalunya, BarcelonaTech (UPC), Barcelona, Spain; Biomedical Research Networking Center in Bioengineering, Biomaterials, and Nanomedicine (CIBER-BBN), Barcelona, Spain. Electronic address:

It is necessary to decompose the intra-muscular EMG signal to extract motor unit action potential (MUAP) waveforms and firing times. Some algorithms were proposed in the literature to resolve superimposed MUAPs, including Peel-Off (PO), branch and bound (BB), genetic algorithm (GA), and particle swarm optimization (PSO). This study aimed to compare these algorithms in terms of overall accuracy and running time. Two sets of two-to-five MUAP templates (set1: a wide range of energies, and set2: a high degree of similarity) were used. Such templates were time-shifted, and white Gaussian noise was added. A total of 1000 superpositions were simulated for each template and were resolved using PO (also, POI: interpolated PO), BB, GA, and PSO algorithms. The generalized estimating equation was used to identify which method significantly outperformed, while the overall rank product was used for overall ranking. The rankings were PSO, BB, GA, PO, and POI in the first, and BB, PSO, GA, PO, POI in the second set. The overall ranking was BB, PSO, GA, PO, and POI in the entire dataset. Although the BB algorithm is generally fast, there are cases where the BB algorithm is too slow and it is thus not suitable for real-time applications.
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http://dx.doi.org/10.1016/j.jelekin.2020.102510DOI Listing
February 2021

Quantitative electrodiagnostic patterns of damage and recovery after spinal cord injury: a pilot study.

Spinal Cord Ser Cases 2019 Dec 12;5(1):101. Epub 2019 Dec 12.

Spinal Cord Injury Center, VA Palo Alto Health Care System, Palo Alto, CA, USA.

Study Design: Prospective observational pilot study.

Objectives: To compare quantitative electromyographic (EMG), imaging and strength data at two time points in individuals with cervical spinal cord injury (SCI).

Setting: SCI center, Veterans Affairs Health Care System, Palo Alto, California, USA.

Methods: Subjects without suspected peripheral nerve injury were recruited within 3 months of injury. Needle EMG examination was performed in myotomes above, at, and below the SCI level around 11- and 12-months post injury. EMG data were decomposed using custom software into constituent motor unit trains and each distinct motor unit was analyzed for firing rate and amplitude. Strength measurements were made with dynamometry and according to the International Standard of Neurologic Classification of SCI (ISNCSCI). Cervical magnetic resonance images (MRI) were evaluated by two neuroradiologists for gray and white matter damage around the SCI. Here, we compare the EMG, strength, and imaging findings of the one of the four participants who completed both 3- and 12-month EMG evaluations.

Results: There was an increase in force generation in all muscles tested at 1 year. Localized findings of very fast firing motor units helped localize spinal cord damage and revealed gray matter damage in spinal segments where MRI was normal. Meanwhile, improvement in strength over time corresponded with different electrophysiologic patterns.

Conclusions: Electromyographic decomposition at two time points provides valuable information about localization of spinal cord damage, integrity of motor neuron pools and may provide a unique understanding of neural recovery mechanisms.
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http://dx.doi.org/10.1038/s41394-019-0246-0DOI Listing
December 2019

Genomic Profiling of Low-grade Intramedullary Cartilage Tumors Can Distinguish Enchondroma From Chondrosarcoma.

Am J Surg Pathol 2020 Nov 24. Epub 2020 Nov 24.

Departments of Pathology.

Low-grade intramedullary cartilage tumors include enchondroma and grade 1 chondrosarcoma. Classification based on radiopathologic correlation guides treatment, typically observation for asymptomatic enchondroma and surgery for chondrosarcoma. However, some tumors elude classification because radiographic and morphologic findings are equivocal. To date, no ancillary tests are available to aid the diagnosis of such indeterminate or suspicious tumors. We investigated the genomic landscape of low-grade cartilage tumors to determine the profile. We studied 10 each enchondroma, grade 1 chondrosarcoma, and suspicious cartilage neoplasms, respectively, by capture-based next-generation sequencing targeting 479 cancer genes and copy number. In enchondroma, IDH1 or IDH2 hotspot activating mutations and/or COL2A1 alterations were identified in 70% and 60% of cases, respectively; copy number changes were rare (20%). Suspicious cartilage neoplasms had frequent hotspot mutations in IDH1 or IDH2 and alterations in COL2A1 (90% and 70%, respectively); copy number changes were rare (20%). Overall, 80% of suspicious cartilage neoplasms were genomically indistinguishable from enchondroma. In contrast, 20% of chondrosarcoma had IDH1 or IDH2 alterations, 100% demonstrated alteration of COL2A1, and 70% had genomes with numerous copy number gains and losses. In total, 80% of chondrosarcomas demonstrated additional pathogenic mutations, deep deletions, or focal amplifications in cancer genes, predominantly CDKN2A. These results demonstrate distinct genomic profiles of enchondroma and grade 1 chondrosarcoma. Further, sequencing may aid in the correct classification of diagnostically challenging tumors. Additional pathogenic alterations (such as in CDKN2A) or numerous copy number gains or losses would support a diagnosis of chondrosarcoma although the absence of such findings does not exclude the diagnosis.
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http://dx.doi.org/10.1097/PAS.0000000000001626DOI Listing
November 2020

Pleomorphic Sarcoma in a Patient with Osteopetrosis.

J Radiol Case Rep 2020 Jul 31;14(7):1-9. Epub 2020 Jul 31.

Department of Orthopaedic Surgery, University of California, San Francisco, USA.

Osteopetrosis comprises a rare, heterogeneous group of heritable conditions that are characterized by a defect in bone resorption by osteoclasts. We report the case of a 53-year-old woman with previously undiagnosed osteopetrosis who presented with a pathologic proximal humeral fracture secondary to pleomorphic sarcoma, which is previously undescribed in the English literature. Management of the primary lesion necessitated ablative surgery, but the malignancy nonetheless was associated with rapidly progressive metastatic disease.
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http://dx.doi.org/10.3941/jrcr.v14i7.3920DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7536008PMC
July 2020

Consensus for experimental design in electromyography (CEDE) project: Amplitude normalization matrix.

J Electromyogr Kinesiol 2020 Aug 10;53:102438. Epub 2020 Jun 10.

School of Health and Rehabilitation Sciences, The University of Queensland, Brisbane, Australia; School of Biomedical Sciences, The University of Queensland, Brisbane, Australia.

The general purpose of normalization of EMG amplitude is to enable comparisons between participants, muscles, measurement sessions or electrode positions. Normalization is necessary to reduce the impact of differences in physiological and anatomical characteristics of muscles and surrounding tissues. Normalization of the EMG amplitude provides information about the magnitude of muscle activation relative to a reference value. It is essential to select an appropriate method for normalization with specific reference to how the EMG signal will be interpreted, and to consider how the normalized EMG amplitude may change when interpreting it under specific conditions. This matrix, developed by the Consensus for Experimental Design in Electromyography (CEDE) project, presents six approaches to EMG normalization: (1) Maximal voluntary contraction (MVC) in same task/context as the task of interest, (2) Standardized isometric MVC (which is not necessarily matched to the contraction type in the task of interest), (3) Standardized submaximal task (isometric/dynamic) that can be task-specific, (4) Peak/mean EMG amplitude in task, (5) Non-normalized, and (6) Maximal M-wave. General considerations for normalization, features that should be reported, definitions, and "pros and cons" of each normalization approach are presented first. This information is followed by recommendations for specific experimental contexts, along with an explanation of the factors that determine the suitability of a method, and frequently asked questions. This matrix is intended to help researchers when selecting, reporting and interpreting EMG amplitude data.
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http://dx.doi.org/10.1016/j.jelekin.2020.102438DOI Listing
August 2020

Quantitative electrodiagnostic patterns of damage and recovery after spinal cord injury: a pilot study.

Spinal Cord Ser Cases 2019 12;5:101. Epub 2019 Dec 12.

Spinal Cord Injury Center, VA Palo Alto Health Care System, Palo Alto, CA USA.

Study Design: Prospective observational pilot study.

Objectives: To compare quantitative electromyographic (EMG), imaging and strength data at two time points in individuals with cervical spinal cord injury (SCI).

Setting: SCI center, Veterans Affairs Health Care System, Palo Alto, California, USA.

Methods: Subjects without suspected peripheral nerve injury were recruited within 3 months of injury. Needle EMG examination was performed in myotomes above, at, and below the SCI level around 11- and 12-months post injury. EMG data were decomposed using custom software into constituent motor unit trains and each distinct motor unit was analyzed for firing rate and amplitude. Strength measurements were made with dynamometry and according to the International Standard of Neurologic Classification of SCI (ISNCSCI). Cervical magnetic resonance images (MRI) were evaluated by two neuroradiologists for gray and white matter damage around the SCI. Here, we compare the EMG, strength, and imaging findings of the one of the four participants who completed both 3- and 12-month EMG evaluations.

Results: There was an increase in force generation in all muscles tested at 1 year. Localized findings of very fast firing motor units helped localize spinal cord damage and revealed gray matter damage in spinal segments where MRI was normal. Meanwhile, improvement in strength over time corresponded with different electrophysiologic patterns.

Conclusions: Electromyographic decomposition at two time points provides valuable information about localization of spinal cord damage, integrity of motor neuron pools and may provide a unique understanding of neural recovery mechanisms.
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http://dx.doi.org/10.1038/s41394-019-0246-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6908655PMC
September 2020

Consensus for experimental design in electromyography (CEDE) project: Electrode selection matrix.

J Electromyogr Kinesiol 2019 Oct 19;48:128-144. Epub 2019 Jul 19.

Centre for Health, Exercise and Sports Medicine, Department of Physiotherapy, University of Melbourne, Parkville, Australia.

The Consensus for Experimental Design in Electromyography (CEDE) project is an international initiative which aims to guide decision-making in recording, analysis, and interpretation of electromyographic (EMG) data. The quality of the EMG recording, and validity of its interpretation depend on many characteristics of the recording set-up and analysis procedures. Different electrode types (i.e., surface and intramuscular) will influence the recorded signal and its interpretation. This report presents a matrix to consider the best electrode type selection for recording EMG, and the process undertaken to achieve consensus. Four electrode types were considered: (1) conventional surface electrode, (2) surface matrix or array electrode, (3) fine-wire electrode, and (4) needle electrode. General features, pros, and cons of each electrode type are presented first. This information is followed by recommendations for specific types of muscles, the information that can be estimated, the typical representativeness of the recording and the types of contractions for which the electrode is best suited. This matrix is intended to help researchers when selecting and reporting the electrode type in EMG studies.
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http://dx.doi.org/10.1016/j.jelekin.2019.07.008DOI Listing
October 2019

Quantifying Distance Overestimation From Global Positioning System in Urban Spaces.

Am J Public Health 2016 Apr 18;106(4):651-3. Epub 2016 Feb 18.

Stephen J. Mooney, Daniel M. Sheehan, Garazi Zulaika, Andrew G. Rundle, and Gina Schellenbaum Lovasi are with Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY. Kevin McGill is with State University of New York at New Paltz. Melika R. Behrooz is with Barnard College, New York.

Objectives: To investigate accuracy of distance measures computed from Global Positioning System (GPS) points in New York City.

Methods: We performed structured walks along urban streets carrying Globalsat DG-100 GPS Data Logger devices in highest and lowest quartiles of building height and tree canopy cover. We used ArcGIS version 10.1 to select walks and compute the straight-line distance (Geographic Information System-measured) and sum of distances between consecutive GPS waypoints (GPS-measured) for each walk.

Results: GPS distance overestimates were associated with building height (median overestimate = 97% for high vs 14% for low building height) and to a lesser extent tree canopy (43% for high vs 28% for low tree canopy).

Conclusions: Algorithms using distances between successive GPS points to infer speed or travel mode may misclassify trips differentially by context. Researchers studying urban spaces may prefer alternative mode identification techniques.
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http://dx.doi.org/10.2105/AJPH.2015.303036DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4815998PMC
April 2016

Myotonic discharges discriminate chloride from sodium muscle channelopathies.

Neuromuscul Disord 2015 Jan 6;25(1):73-80. Epub 2014 Oct 6.

Rehabilitation R&D Center, VA Palo Alto Health Care System, Palo Alto, CA, USA.

Non-dystrophic myotonic syndromes represent a heterogeneous group of clinically quite similar diseases sharing the feature of myotonia. These syndromes can be separated into chloride and sodium channelopathies, with gene-defects in chloride or sodium channel proteins of the sarcolemmal membrane. Myotonia has its basis in an electrical instability of the sarcolemmal membrane. In the present study we examine the discriminative power of the resulting myotonic discharges for these disorders. Needle electromyography was performed by an electromyographer blinded for genetic diagnosis in 66 non-dystrophic myotonia patients (32 chloride and 34 sodium channelopathy). Five muscles in each patient were examined. Individual trains of myotonic discharges were extracted and analyzed with respect to firing characteristics. Myotonic discharge characteristics in the rectus femoris muscle almost perfectly discriminated chloride from sodium channelopathy patients. The first interdischarge interval as a single variable was longer than 30 ms in all but one of the chloride channelopathy patients and shorter than 30 ms in all of the sodium channelopathy patients. This resulted in a detection rate of over 95%. Myotonic discharges of a single muscle can be used to better guide toward a molecular diagnosis in non-dystrophic myotonic syndromes.
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http://dx.doi.org/10.1016/j.nmd.2014.09.014DOI Listing
January 2015

Cross-comparison of three electromyogram decomposition algorithms assessed with experimental and simulated data.

IEEE Trans Neural Syst Rehabil Eng 2015 Jan 22;23(1):32-40. Epub 2014 May 22.

The reliability of clinical and scientific information provided by algorithms that automatically decompose the electromyogram (EMG) depends on the algorithms' accuracies. We used experimental and simulated data to assess the agreement and accuracy of three publicly available decomposition algorithms-EMGlab (McGill , 2005) (single channel data only), Fuzzy Expert (Erim and Lim, 2008) and Montreal (Florestal , 2009). Data consisted of quadrifilar needle EMGs from the tibialis anterior of 12 subjects at 10%, 20% and 50% maximum voluntary contraction (MVC); single channel needle EMGs from the biceps brachii of 10 controls and 10 patients during contractions just above threshold; and matched simulated data. Performance was assessed via agreement between pairs of algorithms for experimental data and accuracy with respect to the known decomposition for simulated data. For the quadrifilar experimental data, median agreements between the Montreal and Fuzzy Expert algorithms at 10%, 20%, and 50% MVC were 95%, 86%, and 64%, respectively. For the single channel control and patient data, median agreements between the three algorithm pairs were statistically similar at ∼ 97% and ∼ 92%, respectively. Accuracy on the simulated data exceeded this performance. Agreement/accuracy was strongly related to the Decomposability Index (Florestal , 2009). When agreement was high between algorithm pairs applied to simulated data, so was accuracy.
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http://dx.doi.org/10.1109/TNSRE.2014.2322586DOI Listing
January 2015

Magnetic resonance imaging evaluation of normal glenoid length and width: an anatomic study.

Arthroscopy 2014 Aug 10;30(8):915-20. Epub 2014 May 10.

Division of Sports Medicine, Department of Orthopedic Surgery, Rush University Medical Center, Chicago, Illinois, U.S.A.. Electronic address:

Purpose: The purpose of this study was to evaluate the measured dimensions of the normal glenoid on sagittal magnetic resonance (MR) imaging to determine whether a fixed ratio of glenoid length and width can be determined.

Methods: MR images of 90 glenoids in 84 patients were analyzed. The mean age was 54.8 years, with 44 male and 40 female patients. Glenoid length and width at the widest dimension were measured and recorded by 3 independent examiners. The ratio of length to width and the ratio of the length of the superior pole at the widest point to the total length were calculated. Intraclass correlation coefficients, Spearman and Pearson correlations, regression analysis with cross validation, and coefficients of variation were calculated.

Results: The mean glenoid length was 37.5 ± 3.8 mm, whereas the mean width was 24.4 ± 2.9 mm. The mean ratio of length to width was 1.55 ± 0.1, whereas the mean ratio of the distance from the superior pole to the widest point to the total glenoid length was 0.64 ± 0.03. The calculated ratios were less variable than the absolute length and width. Cross validation of length for width showed a 95% prediction band width of 4.48 mm, with an average absolute error of prediction of 1.46 mm, and was equally specific when separated by gender. The width was equal to 0.65 times the length.

Conclusions: Measurement of glenoid length and width using MR imaging results in a consistent ratio of length to width independent of patient age and gender, where the width was equal to 0.65 times the length at a point two-thirds along the inferosuperior axis.

Level Of Evidence: Level IV, case series.
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http://dx.doi.org/10.1016/j.arthro.2014.03.006DOI Listing
August 2014

Triceps Brachii in Incomplete Tetraplegia: EMG and Dynamometer Evaluation of Residual Motor Resources and Capacity for Strengthening.

Top Spinal Cord Inj Rehabil 2013 ;19(4):300-10

Rehabilitation Research and Development Center, VA Palo Alto Health Care System , Palo Alto, California ; Spinal Cord Injury Service, VA Palo Alto Health Care System , Palo Alto, California.

Background: Candidates for activity-based therapy after spinal cord injury (SCI) are often selected on the basis of manual muscle test scores and the classification of the injury as complete or incomplete. However, these scores may not adequately predict which individuals have sufficient residual motor resources for the therapy to be beneficial.

Objective: We performed a preliminary study to see whether dynamometry and quantitative electromyography (EMG) can provide a more detailed assessment of residual motor resources.

Methods: We measured elbow extension strength using a hand-held dynamometer and recorded fine-wire EMG from the triceps brachii muscles of 4 individuals with C5, C6, or C7 level SCI and 2 able-bodied controls. We used EMG decomposition to measure motor unit action potential (MUAP) amplitudes and motor unit (MU) recruitment and firing-rate profiles during constant and ramp contractions.

Results: All 4 subjects with cervical SCI (cSCI) had increased MUAP amplitudes indicative of denervation. Two of the subjects with cSCI had very weak elbow extension strength (<4 kg), dramatically reduced recruitment, and excessive firing rates (>40 pps), suggesting profound loss of motoneurons. The other 2 subjects with cSCI had stronger elbow extension (>6 kg), more normal recruitment, and more normal firing rates, suggesting a substantial remaining motoneuron population.

Conclusions: Dynamometry and quantitative EMG may provide information about the extent of gray matter loss in cSCI to help guide rehabilitation strategies.
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http://dx.doi.org/10.1310/sci1904-300DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3816724PMC
November 2013

Effect of interference screw depth on fixation strength in biceps tenodesis.

Arthroscopy 2014 Jan 31;30(1):11-5. Epub 2013 Oct 31.

Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, Illinois, U.S.A.

Purpose: The purpose of this study was to assess the biomechanical performance of the long head of the biceps tenodesis with an interference screw with respect to screw depth.

Methods: Twenty-one human cadaveric shoulders were randomized into 3 treatment groups (7 each): interference screw placed flush to the humeral cortex, 50% proud, or fully recessed. Bone density was determined, and subpectoral biceps tenodesis was performed with 8 × 12 mm Bio-Tenodesis screws (Arthrex, Naples, FL). Each construct was cyclically loaded from 5 to 70 N for 500 cycles at 1 Hz and then pulled to failure at 1 mm/s. Relative actuator displacement was calculated from cyclic testing. Maximum load, elongation, linear stiffness, and failure mode were recorded from pull-to-failure testing. Because of numerous failures during cyclic testing, the final load data from the fully recessed group were not statistically analyzed. The remaining groups were compared by use of a 2-tailed, Student unpaired t test and χ(2) analysis.

Results: There was no significant difference in displacement among groups during cyclic testing. Five specimens in the recessed group failed during cyclic testing, whereas 2 specimens and 0 specimens failed in the proud and flush groups, respectively. The maximum loads sustained were 281.6 ± 77.8 N, 184.5 ± 56.3 N, and 209.1 ± 57.0 N for the flush group, 50% proud group, and recessed group (in those specimens surviving cyclical loading), respectively.

Conclusions: Placement of a Bio-Tenodesis screw flush to the humeral cortex is preferred for maximum fixation strength in subpectoral biceps tenodesis. A screw placed to 50% depth may be effective in the laboratory setting, but recessed placement is more variable and requires additional fixation. The fully recessed group resulted in 5 of 7 failures during cyclical loading, with no specimens failing in the flush group.

Clinical Relevance: This study shows the importance of determining the optimal depth of interference screw placement during biceps tenodesis to obtain optimal biomechanical performance and reduce the risk of fixation failure.
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http://dx.doi.org/10.1016/j.arthro.2013.08.033DOI Listing
January 2014

Low accuracy of interpretation of rotator cuff MRI in patients with osteoarthritis.

Acta Orthop 2013 Oct 31;84(5):479-82. Epub 2013 Oct 31.

Division of Sports Medicine , Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL , USA.

Background: Magnetic resonance imaging (MRI) is considered to be a valuable tool for the diagnosis of rotator cuff tears in patients with severe glenohumeral osteoarthritis who are indicated for total shoulder arthroplasty (TSA). We determined the sensitivity, specificity, and positive predictive value of MRI in diagnosing rotator cuff tears in such patients.

Methods: MRI reports of 100 patients who had completed a shoulder MRI prior to TSA were reviewed to determine the radiologists' interpretation of the MRI including the diagnosis, presence of a full-thickness cuff tear, and the presence of atrophy and/or fatty infiltration within the rotator cuff muscle bellies. Operative reports were used as a gold standard to determine whether a full-thickness rotator cuff tear was present.

Results: Preoperative MRI reports noted 33 of the 100 patients as having a full-thickness rotator cuff tear, 17 of which had multiple tendon tears. 2 of the 33 patients with full tears on MRI were found to have full-thickness tears at surgery. The sensitivity, specificity, and positive predictive value for MRI detection of full-thickness tears were 100%, 68%, and 6% respectively, with a false-positive rate of 32% and an accuracy of 69%.

Interpretation: The study suggests that although MRI is highly sensitive, it has a low positive predictive value and moderately low specificity and accuracy in detecting full-thickness rotator cuff tears in patients with severe glenohumeral osteoarthritis.
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http://dx.doi.org/10.3109/17453674.2013.850012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3822133PMC
October 2013

Clinical outcomes of reverse total shoulder arthroplasty in patients aged younger than 60 years.

J Shoulder Elbow Surg 2014 Mar 12;23(3):395-400. Epub 2013 Oct 12.

Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL, USA.

Background: Reverse total shoulder arthroplasty (RTSA) has been indicated primarily for patients aged older than 65 years with symptomatic rotator cuff deficiency, poor function, and pain. However, conditions that benefit from RTSA are not restricted to an elderly population. This study evaluates a consecutive series of RTSA patients aged younger than 60 years.

Methods: We evaluated 36 shoulders (mean age, 54 years) at a mean follow-up of 2.8 years (range, 24-48 months). Of these shoulders, 30 (83%) had previous surgery, averaging 2.5 procedures per patient. The preoperative conditions compelling RTSA were as follows: failed rotator cuff repair (12), fracture sequelae (11), failed arthroplasty (5), instability sequelae (4), cuff tear arthropathy (CTA) (4), and rheumatoid arthritis (2). Follow-up examinations included range-of-motion and strength testing, as well as Single Assessment Numeric Evaluation, visual analog scale, Simple Shoulder Test, American Shoulder and Elbow Surgeons (ASES), and Constant scores. Preoperative and postoperative radiographs were reviewed for component loosening and scapular notching. Failure criteria were defined as undergoing revision, having gross loosening, or having an ASES score below 50.

Results: The mean Single Assessment Numeric Evaluation score improved from 24.4 to 72.0; the visual analog scale pain score improved from 6 to 2.1. The Simple Shoulder Test score improved from 1.4 to 6.2, and the ASES score improved from 31.4 to 65.8. Active forward elevation improved from 56° to 121°. The normalized postoperative mean Constant score was 54.3. In 9 patients (25.0%), we recorded an ASES score below 50, and these cases were considered failures.

Conclusion: RTSA can improve shoulder function in a younger, complex patient population with poor preoperative functional ability. This study's success rate was 75% at 2.8 years. This is a limited-goals procedure, and longer-term studies are required to determine whether similar results are maintained over time.
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http://dx.doi.org/10.1016/j.jse.2013.07.047DOI Listing
March 2014

Role of the superior labrum after biceps tenodesis in glenohumeral stability.

J Shoulder Elbow Surg 2014 Apr 30;23(4):485-91. Epub 2013 Sep 30.

Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL, USA.

Background: Little is known about the role that a torn superior labrum (SLAP) plays in glenohumeral stability after biceps tenodesis. This biomechanical study evaluated the contribution of a type II SLAP lesion to glenohumeral translation in the presence of biceps tenodesis. The authors hypothesize that subsequent to biceps tenodesis, a torn superior labrum does not affect glenohumeral stability and therefore does not require anatomic repair in an overhead throwing athlete.

Methods: Baseline anterior, posterior, and abduction and maximal external rotation glenohumeral translation data were collected from 20 cadaveric shoulders. Translation testing was repeated after the creation of anterior (n = 10) and posterior (n = 10) type II SLAP lesions. Translation re-evaluation after biceps tenodesis was performed for each specimen. Finally, anatomic SLAP lesion repair and testing were performed.

Results: Anterior and posterior SLAP lesions led to significant increases in glenohumeral translation in all directions (P < .0125). Biceps tenodesis showed no significance in stability compared with SLAP alone (P > .0125). Arthroscopic repair of anterior SLAP lesions did not restore anterior translation compared with the baseline state (P = .0011) but did restore posterior (P = .823) and abduction and maximal external rotation (P = .806) translations. Repair of posterior SLAP lesions demonstrated no statistical difference compared with the baseline state (P > .0125).

Conclusions: With no detrimental effect on glenohumeral stability in the presence of a SLAP lesion, biceps tenodesis may be considered a valid primary or revision surgery for patients suffering from symptomatic type II SLAP tears. However, biceps tenodesis should be considered with caution as the primary treatment of SLAP lesions in overhead throwing athletes secondary to its inability to completely restore translational stability.
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http://dx.doi.org/10.1016/j.jse.2013.07.036DOI Listing
April 2014

The high failure rate of biologic resurfacing of the glenoid in young patients with glenohumeral arthritis.

J Shoulder Elbow Surg 2014 Mar 4;23(3):409-19. Epub 2013 Sep 4.

New York University Hospital for Joint Diseases, New York, NY, USA.

Background: The current study evaluated the outcomes of biologic resurfacing of the glenoid using a lateral meniscus allograft or human acellular dermal tissue matrix at intermediate-term follow-up.

Methods: Forty-five patients (mean age, 42.2 years) underwent biologic resurfacing of the glenoid, and 41 were available for follow-up at a mean of 2.8 years. Lateral meniscal allograft resurfacing was used in 31 patients and human acellular dermal tissue matrix interposition in 10. Postoperative range of motion and clinical outcomes were assessed at the final follow-up.

Results: The overall clinical failure rate was 51.2%. The lateral meniscal allograft cohort had a failure rate of 45.2%, with a mean time to failure of 3.4 years. Human acellular dermal tissue matrix interposition had a failure rate of 70.0%, with a mean time to failure of 2.2 years. Overall, significant improvements were seen compared with baseline with respect to the visual analog pain score (3.0 vs. 6.3), American Shoulder and Elbow Surgeons score (62.0 vs. 36.8), and Simple Shoulder Test score (7.0 vs. 4.0). Significant improvements were seen for forward elevation (106° to 138°) and external rotation (31° to 51°).

Conclusion: Despite significant improvements compared with baseline values, biologic resurfacing of the glenoid resulted in a high rate of clinical failure at intermediate follow-up. Our results suggest that biologic resurfacing of the glenoid may have a minimal and as yet undefined role in the management of glenohumeral arthritis in the young active patient over more traditional methods of hemiarthroplasty or total shoulder arthroplasty.
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http://dx.doi.org/10.1016/j.jse.2013.06.001DOI Listing
March 2014

Retrospective analysis of arthroscopic superior labrum anterior to posterior repair: prognostic factors associated with failure.

Adv Orthop 2013 25;2013:125960. Epub 2013 Mar 25.

Division of Sports Medicine, Department of Orthopaedic Surgery, Rush University Medical Center, 1611 West Harrison Street, Suite 300, Chicago, IL 60612, USA.

Background. The purpose of this study was to report on any prognostic factors that had a significant effect on clinical outcomes following arthroscopic Type II SLAP repairs. Methods. Consecutive patients who underwent arthroscopic Type II SLAP repair were retrospectively identified and invited to return for follow-up examination and questionnaire. Statistical analysis was performed to determine associations between potential prognostic factors and failure of SLAP repair as defined by ASES of less than 50 and/or revision surgery. Results. Sixty-two patients with an average age of 36 ± 13 years met the study criteria with a mean followup of 3.3 years. There were statistically significant improvements in mean ASES score, forward elevation, and external rotation among patients. Significant associations were identified between ASES score less than 50 and age greater than 40 years; alcohol/tobacco use; coexisting diabetes; pain in the bicipital groove on examination; positive O'Brien's, Speed's, and/or Yergason's tests; and high levels of lifting required at work. There was a significant improvement in ASES at final followup. Conclusions. Patients younger than 20 and overhead throwers had significant associations with cases requiring revision surgery. The results from this study may be used to assist in patient selection for SLAP surgery.
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http://dx.doi.org/10.1155/2013/125960DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3621156PMC
April 2013

Arthroscopic primary rotator cuff repairs in patients aged younger than 45 years.

Arthroscopy 2013 May 16;29(5):811-7. Epub 2013 Mar 16.

Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, Illinois, USA.

Purpose: The purpose of this study was to evaluate the mechanism of injury, patient characteristics, tear size, and clinical outcomes after arthroscopic primary rotator cuff repair of full-thickness tears in patients aged younger than 45 years.

Methods: A total of 70 consecutive patients were reviewed in a retrospective, multicenter (2 institutions) study evaluating prospectively collected data. Fifty-three patients, with a mean age of 37.5 years (range, 16.2 to 44.9 years), were available for follow-up at a mean of 35.8 months (range, 13.8 to 59.1 months). Exclusion criteria included patients with revision procedures, repair of partial tears, and follow-up of less than 12 months. Follow-up evaluation included physical examination with dynamometer strength testing and clinical outcome measures including the Single Assessment Numeric Evaluation score, American Shoulder and Elbow Surgeons (ASES) score, Constant-Murley score, pain score on a visual analog scale, and Simple Shoulder Test score.

Results: A total of 60% of the patients (32 of 53) had a traumatic etiology, with 38% (12 of 32) of these related to an athletic event. Of the tears, 36 (68%) were medium tears. Concomitant procedures performed at the time of rotator cuff repair included acromioplasty (51), biceps tenodesis or tenotomy (24), distal clavicle excision (10), anteroinferior stabilization (2), and labral repair (1). The mean postoperative ASES score was 84.6 (range, 21.6 to 100.0), with 2 patients recording ASES scores of less than 50 (21.7 and 41.7) at final follow-up. In the 38 patients available for clinical follow-up examination, forward flexion improved from 158.7° (range, 45° to 180°) to 168.4° (range, 120° to 180°) (P = .014). At the time of follow-up, no patients had undergone revision surgery. On the basis of poor clinical outcome scores, 2 patients (4.0%) were considered failures.

Conclusions: Arthroscopic primary rotator cuff repair of full-thickness tears in patients aged younger than 45 years results in improved outcomes with regard to pain, subjective patient satisfaction, and shoulder function.

Level Of Evidence: Level IV, therapeutic case series.
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http://dx.doi.org/10.1016/j.arthro.2013.01.015DOI Listing
May 2013

An institution-specific analysis of ACL reconstruction failure.

J Knee Surg 2012 May;25(2):143-9

Division of Sports Medicine, Department of Orthopedics, Rush University Medical Center, Chicago, Illinois 60612, USA.

The purpose of this study was to determine the most common causes of failed anterior cruciate ligament reconstruction (ACLR) using modern reconstructive techniques at a single, high-volume institution. In addition, the clinical outcomes of patients undergoing revision ACLR will be reported. The surgical logs of four senior knee surgeons were retrospectively reviewed for all patients who had undergone ACLR between 2002 and 2009. Patients were excluded if they did not have both the primary and revision surgery on the same knee with the same surgeon. Out of 1944 ACL reconstructions, 28 patients (56 reconstructions) were included in the study. Radiographic studies, operative reports, KT-1000 scores, and chart notes were used to identify all potential factors that may have led to failure. All patients were invited to return for a follow-up examination and survey. Of the 28 patients, the mean age at the index and revision procedure was 22 +/- 11 (range, 12 to 50) and 24 +/- 11 (range, 14 to 57), respectively. In 20 cases, the cause of failure was determined to be acute trauma (sports, work, or accident); in 1 case, the cause was biologic failure; while in 7 cases, the cause was technical error. During the study period the surgeons performed a combined total of 1944 procedures, for an overall failure rate of 1.8%. Twenty patients (71%) were available for follow-up at a mean 30.2 +/- 17.7 months. The overall postrevision outcomes were good to excellent for a majority of patients, with an average Lysholm score of 84 +/- 15.5 and International Knee Documentation Committee score of 77.2 +/- 13.8. The pre- and postoperative KT-1000 scores were 12.1 +/- 2.8 and 6.7 +/- 2.8, respectively. The results from this study suggest that traumatic re-injury, and not surgical/surgeon error, is the most common cause of ACLR failure using anatomic reconstructive principles and strong fixation. In addition, good to excellent outcomes following revision ACLR can be expected in the majority of patients.
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http://dx.doi.org/10.1055/s-0031-1286196DOI Listing
May 2012

Robust decomposition of single-channel intramuscular EMG signals at low force levels.

J Neural Eng 2011 Dec 8;8(6):066015. Epub 2011 Nov 8.

Biomedical Engineering Department, University of Isfahan, Isfahan, Iran.

This paper presents a density-based method to automatically decompose single-channel intramuscular electromyogram (EMG) signals into their component motor unit action potential (MUAP) trains. In contrast to most previous decomposition methods, which require pre-setting and (or) tuning of multiple parameters, the proposed method takes advantage of the data-dependent strategies in the pattern recognition procedures. In this method, outliers (superpositions) are excluded prior to classification and MUAP templates are identified by an adaptive density-based clustering procedure. MUAP trains are then identified by a novel density-based classifier that incorporates MUAP shape and discharge time information. MUAP trains are merged by a fuzzy system that incorporates expert human knowledge. Finally, superimpositions are resolved to fill the gaps in the MUAP trains. The proposed decomposition algorithm has been experimentally tested on signals from low-force (≤30% maximal) isometric contractions of the vastus medialis obliquus, vastus lateralis, biceps femoris long-head and tibialis anterior muscles. Comparison with expert manual decomposition that had been verified using a rigorous statistical analysis showed that the algorithm identified 80% of the total 229 motor unit trains with an accuracy greater than 90%. The algorithm is robust and accurate, and therefore it is a promising new tool for decomposing single-channel multi-unit signals.
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http://dx.doi.org/10.1088/1741-2560/8/6/066015DOI Listing
December 2011

History dependence of human muscle-fiber conduction velocity during voluntary isometric contractions.

J Appl Physiol (1985) 2011 Sep 12;111(3):630-41. Epub 2011 May 12.

Rehabilitation R&D Center, VA Palo Alto Health Care System, 3801 Miranda Ave., Palo Alto, CA 94304, USA.

The conduction velocity (CV) of a muscle fiber is affected by the fiber's discharge history going back ∼1 s. We investigated this dependence by measuring CV fluctuations during voluntary isometric contractions of the human brachioradialis muscle. We recorded electromyogram (EMG) signals simultaneously from multiple intramuscular electrodes, identified potentials belonging to the same motor unit using EMG decomposition, and estimated the CV of each discharge from the interpotential interval. In 12 of 14 subjects, CV increased by ∼10% during the first second after recruitment and then fluctuated by about ±2% in a way that mirrored the fluctuations in the instantaneous firing rate. The CV profile could be precisely described in terms of the discharge history by a simple mathematical model. In the other two subjects, and one subject retested after cooling the arm, the CV fluctuations were inversely correlated with instantaneous firing rate. In all subjects, CV was additionally affected by very short interdischarge intervals (<25 ms): it was increased in doublets at recruitment, but decreased in doublets during continuous firing and after short interdischarge intervals in doubly innervated fibers. CV also exhibited a slow trend of about -0.05%/s that did not depend on the immediate discharge history. We suggest that measurements of CV fluctuations during voluntary contractions, or during stimulation protocols that involve longer and more complex stimulation patterns than are currently being used, may provide a sensitive approach for estimating the dynamic characteristics of ion channels in the human muscle-fiber membrane.
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http://dx.doi.org/10.1152/japplphysiol.00208.2011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3174799PMC
September 2011

Chronic ankle pain and swelling in a 25-year-old woman: an unusual case.

Clin Orthop Relat Res 2011 May 15;469(5):1517-21. Epub 2011 Mar 15.

Department of Orthopaedic Surgery, Rush University Medical Center, 1611 West Harrison Street, #300, Chicago, IL 60612, USA.

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http://dx.doi.org/10.1007/s11999-011-1851-9DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3069290PMC
May 2011

Can anatomic femoral tunnel placement be achieved using a transtibial technique for hamstring anterior cruciate ligament reconstruction?

Am J Sports Med 2011 Jun 18;39(6):1263-9. Epub 2011 Feb 18.

Division of Sports Medicine, Rush University Medical Center, Chicago, IL 60612, USA.

Background: Recent studies have emphasized the importance of anatomic tunnel placement during anterior cruciate ligament (ACL) reconstruction in an effort to restore normal knee kinematics and stability. Secondary to the constraints imposed by a coupled drilling technique, the ability to achieve an anatomic femoral tunnel during transtibial hamstring ACL reconstruction may be limited.

Hypothesis: The size limitations imposed by the small-diameter tibial tunnel used in hamstring ACL reconstruction would preclude the ability to place an anatomic femoral tunnel.

Study Design: Descriptive laboratory study.

Methods: In a descriptive laboratory study, fresh-frozen human cadaveric knees fixed at 90° of flexion were dissected to expose the centers of the native femoral and tibial ACL insertions. The geometry and location of each insertion were evaluated. Using a standardized starting point, tibial tunnels were drilled to the center of the tibial insertion using an 8-mm reamer. Next, a 6-mm over-the-top guide was used to position as close as possible to the anatomic femoral ACL insertion on the lateral wall, and femoral tunnels were drilled with the 8-mm reamer. For each tunnel, the location, geometry, and percentage overlap with the native insertion site were evaluated using a 3-dimensional laser scanner.

Results: The reamed tibial tunnel was central within the insertion site, occupying 40.4% ± 2.0% of the native tibial insertion. Transtibial drilling resulted in femoral tunnels that were superior and posterior compared with the native femoral insertion. Thefemoral tunnel had a mean ± SD overlap of 30.0% ± 12.6% with the femoral insertion, with the center of the tunnel 7.6± 0.5 mm from the center of the native ACL femoral insertion.

Conclusion: Based on our data using our specific starting point, during hamstring ACL reconstructions, the constraints imposed by a coupled drilling technique result in nonanatomic femoral tunnels that are superior and posterior to the native femoral insertion.

Clinical Relevance: Anatomic femoral tunnel placement during hamstring ACL reconstructions may not be possible using a coupled, transtibial drilling approach.
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http://dx.doi.org/10.1177/0363546510395488DOI Listing
June 2011

Multimedia article. The arthroscopic management of partial-thickness rotator cuff tears: a systematic review of the literature.

Arthroscopy 2011 Apr;27(4):568-80

Division of Sports Medicine, Rush University Medical Center, Chicago, Illinois, USA.

Purpose: There is currently limited information available in the orthopaedic surgery literature regarding the appropriate management of symptomatic partial-thickness rotator cuff tears.

Methods: A systematic search was performed in PubMed, EMBASE, CINAHL (Cumulative Index to Nursing and Allied Health Literature), and the Cochrane Central Register of Controlled Trials of all published literature pertaining to the arthroscopic management of partial-thickness rotator cuff tears. Inclusion criteria were all studies that reported clinical outcomes after arthroscopic treatment of both articular-sided and bursal-sided lesions using a validated outcome scoring system and a minimum of 12 months of follow-up. Data abstracted from the selected studies included tear type and location (articular v bursal sided), treatment approach, postoperative rehabilitation protocol, outcome scores, patient satisfaction, and postoperative imaging results.

Results: Sixteen studies met the inclusion criteria and were included for the final analysis. Seven of the studies treated partial-thickness rotator cuff tears with debridement with or without an associated subacromial decompression, 3 performed a takedown and repair, 5 used a transtendon repair technique, and 1 used a transosseous repair method. Among the 16 studies reviewed, excellent postoperative outcomes were reported in 28.7% to 93% of patients treated. In all 12 studies with available preoperative baseline data, treatment resulted in significant improvement in shoulder symptoms and function. For high-grade lesions, the data support arthroscopic takedown and repair, transtendon repairs, and transosseous repairs, with all 3 techniques providing a high percentage of excellent results. Debridement of partial-thickness tears of less than 50% of the tendon's thickness with or without a concomitant acromioplasty also results in good to excellent surgical outcomes; however, a 6.5% to 34.6% incidence of progression to full-thickness tears is present.

Conclusions: This systematic review of 16 clinical studies showed that significant variation is present in the results obtained after the arthroscopic management of partial-thickness rotator cuff tears. What can be supported by the available data is that tears that involve less than 50% of the tendon can be treated with good results by debridement of the tendon with or without a formal acromioplasty, although subsequent tear progression may occur. When the tear is greater than 50%, surgical intervention focusing on repair has been successful. There is no evidence to suggest a differential in outcome for tear completion and repair versus transtendon repair of these lesions because both methods have been shown to result in favorable outcomes.

Level Of Evidence: Level IV, systematic review of Level IV studies.
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http://dx.doi.org/10.1016/j.arthro.2010.09.019DOI Listing
April 2011

The evaluation and management of failed distal clavicle excision.

Sports Med Arthrosc Rev 2010 Sep;18(3):213-9

Section of Sports Medicine, Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL 60612, USA.

Excision of the distal clavicle (DCE) is a commonly carried out surgical procedure used in the management of acromioclavicular joint pathology. Although successful outcomes after both open and arthroscopic distal clavicle excision occur in a high percentage of patients, treatment failures have been reported, creating a difficult clinical scenario for the treating orthopedic surgeon. The most common mode of failure after DCE is persistent pain and potential etiologies include under-resection, over-resection leading to joint instability, postoperative stiffness, heterotopic ossification, untreated concomitant shoulder pathology, and postoperative infection. Less common causes of failure include distal clavicle fracture, reossification or fusion across the acromioclavicular joint, suprascapular neuropathy, and psychiatric illness. Persistent symptoms and disability after distal clavicle excision require a careful assessment of these potential causes of treatment failure and the formulation of a treatment plan, which may include conservative care, revision surgery, or coracoclavicular ligament reconstruction. Although careful patient selection, preoperative planning, proper surgical technique, and appropriate rehabilitation during the index procedure can minimize the likelihood of poor outcome, this paper reviews the work-up and management of cases of failed distal clavicle excision.
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http://dx.doi.org/10.1097/JSA.0b013e3181e892daDOI Listing
September 2010

Rigorous a posteriori assessment of accuracy in EMG decomposition.

IEEE Trans Neural Syst Rehabil Eng 2011 Feb 15;19(1):54-63. Epub 2010 Jul 15.

Rehabilitation Research and Development Center, VA Palo Alto Health Care System, Palo Alto, CA 94304, USA.

If electromyography (EMG) decomposition is to be a useful tool for scientific investigation, it is essential to know that the results are accurate. Because of background noise, waveform variability, motor-unit action potential (MUAP) indistinguishability, and perplexing superpositions, accuracy assessment is not straightforward. This paper presents a rigorous statistical method for assessing decomposition accuracy based only on evidence from the signal itself. The method uses statistical decision theory in a Bayesian framework to integrate all the shape- and firing-time-related information in the signal to compute an objective a posteriori measure of confidence in the accuracy of each discharge in the decomposition. The assessment is based on the estimated statistical properties of the MUAPs and noise and takes into account the relative likelihood of every other possible decomposition. The method was tested on 3 pairs of real EMG signals containing 4-7 active MUAP trains per signal that had been decomposed by a human expert. It rated 97% of the identified MUAP discharges as accurate to within ± 0.5 ms with a confidence level of 99%, and detected six decomposition errors. Cross-checking between signal pairs verified all but two of these assertions. These results demonstrate that the approach is reliable and practical for real EMG signals.
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http://dx.doi.org/10.1109/TNSRE.2010.2056390DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3434971PMC
February 2011

The effects of a three-week use of lumbosacral orthoses on trunk muscle activity and on the muscular response to trunk perturbations.

BMC Musculoskelet Disord 2010 Jul 7;11:154. Epub 2010 Jul 7.

Department of Surgical Specialties, College of Osteopathic Medicine, Michigan State University, East Lansing, MI, USA.

Background: The effects of lumbosacral orthoses (LSOs) on neuromuscular control of the trunk are not known. There is a concern that wearing LSOs for a long period may adversely alter muscle control, making individuals more susceptible to injury if they discontinue wearing the LSOs. The purpose of this study was to document neuromuscular changes in healthy subjects during a 3-week period while they regularly wore a LSO.

Methods: Fourteen subjects wore LSOs 3 hrs a day for 3 weeks. Trunk muscle activity prior to and following a quick force release (trunk perturbation) was measured with EMG in 3 sessions on days 0, 7, and 21. A longitudinal, repeated-measures, factorial design was used. Muscle reflex response to trunk perturbations, spine compression force, as well as effective trunk stiffness and damping were dependent variables. The LSO, direction of perturbation, and testing session were the independent variables.

Results: The LSO significantly (P < 0.001) increased the effective trunk stiffness by 160 Nm/rad (27%) across all directions and testing sessions. The number of antagonist muscles that responded with an onset activity was significantly reduced after 7 days of wearing the LSO, but this difference disappeared on day 21 and is likely not clinically relevant. The average number of agonist muscles switching off following the quick force release was significantly greater with the LSO, compared to without the LSO (P = 0.003).

Conclusions: The LSO increased trunk stiffness and resulted in a greater number of agonist muscles shutting-off in response to a quick force release. However, these effects did not result in detrimental changes to the neuromuscular function of trunk muscles after 3 weeks of wearing a LSO 3 hours a day by healthy subjects.
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http://dx.doi.org/10.1186/1471-2474-11-154DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2912792PMC
July 2010

The innervation and organization of motor units in a series-fibered human muscle: the brachioradialis.

J Appl Physiol (1985) 2010 Jun 1;108(6):1530-41. Epub 2010 Apr 1.

Rehabilitation Research and Development Center, Department of Veterans Affairs Palo Alto Health Care System, 3801 Miranda Ave., Palo Alto, CA 94304, USA.

We studied the innervation and organization of motor units in the brachioradialis muscle of 25 normal human subjects. We recorded intramuscular EMG signals at points separated by 15 mm along the proximodistal muscle axis during moderate isometric contractions, identified from 27 to 61 (mean 39) individual motor units per subject using EMG decomposition, and estimated the locations of the endplates and distal muscle/tendon junctions from the motor-unit action potential (MUAP) propagation patterns and terminal standing waves. In three subjects all the motor units were innervated in a single endplate zone. In the other 22 subjects, the motor units were innervated in 3-6 (mean 4) distinct endplate zones separated by 15-55 mm along the proximodistal axis. One-third of the motor units had fibers innervated in more than one zone. The more distally innervated motor units had distinct terminal waves indicating tendonous termination, while the more proximal motor units lacked terminal waves, indicating intrafascicular termination. Analysis of blocked MUAP components revealed that 19% of the motor units had at least one doubly innervated fiber, i.e., a fiber innervated in two different endplate zones by two different motoneurons, and thus belonging to two different motor units. These results are consistent with the brachioradialis muscle having a series-fibered architecture consisting of multiple, overlapping bands of muscle fibers in most individuals and a simple parallel-fibered architecture in some individuals.
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http://dx.doi.org/10.1152/japplphysiol.01163.2009DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2886675PMC
June 2010

Hip Microfracture: Indications, Technique, and Outcomes.

Cartilage 2010 Apr;1(2):127-36

Section of Sports Medicine, Department of Orthopedic Surgery, Rush Medical College, Rush University Medical Center, Chicago, Illinois, USA.

Microfracture is a marrow-stimulating technique used in the hip to treat cartilage defects associated with femoro-acetabular impingement, instability, or traumatic hip injury. These defects have a low probability of healing spontaneously and therefore often require surgical intervention. Originally adapted from the knee, microfracture is part of a spectrum of cartilage repair options that include palliative procedures such as debridement and lavage, reparative procedures such as marrow-stimulating techniques (abrasion arthroplasty and microfracture), and restorative procedures such as autologous chondrocyte implantation and osteochondral allograft/autografts. The basic indications for microfracture of the hip include focal and contained lesions typically less than 4 cm in diameter, full-thickness (Outerbridge grade IV) defects in weightbearing areas, unstable lesions with intact subchondral bone, and focal lesions without evidence of surrounding chondromalacia. Although not extensively studied in the hip, there are some small clinical series with promising early outcomes. Although the widespread use of microfracture in the hip is hindered by difficulties in identifying lesions on preoperative imaging and instrumentation to circumvent the femoral head, this technique continues to gain acceptance as an initial treatment for small, focal cartilage defects.
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http://dx.doi.org/10.1177/1947603510366028DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4297043PMC
April 2010