Publications by authors named "Lawrence D Dorr"

111 Publications

How much change in pelvic sagittal tilt can result in hip dislocation due to prosthetic impingement? A computer simulation study.

J Orthop Res 2021 Dec 22;39(12):2604-2614. Epub 2021 Mar 22.

Dorr Institute for Arthritis Research and Education, Los Angeles, California, USA.

Developing spinal pathologies and spinal fusion after total hip arthroplasty (THA) can result in increased pelvic retroversion (e.g., flat back deformity) or increased anterior pelvic tilt (caused by spinal stenosis, spinal fusion or other pathologies) while bending forward. This change in sagittal pelvic tilt (SPT) can result in prosthetic impingement and dislocation. Our aim was to determine the magnitude of SPT change that could lead to prosthetic impingement. We hypothesized that the magnitude of SPT change that could lead to THA dislocation is less than 10° and it varies for different hip motions. Hip motion was simulated in standing, sitting, sit-to-stand, bending forward, squatting and pivoting in Matlab software. The implant orientations and SPT angle were modified by 1° increments. The risk of prosthetic impingement in pivoting caused by increased pelvic retroversion (reciever operating characteristic [ROC] threshold as low as 1-3°) is higher than the risk of prosthetic impingement with increased pelvic anteversion (ROC threshold as low as 16-18°). Larger femoral heads decrease the risk of prosthetic impingement (odds ratio {OR}: 0.08 [932 mm head]; OR: 0.01 [36 mm head]; OR: 0.002 [40 mm head]). Femoral stems with a higher neck-shaft angle decrease the prosthetic impingement due to SPT change in motions requiring hip flexion (OR: 1.16 [132° stem]; OR: 4.94 [135° stem]). Our results show that overall, the risk of prosthetic impingement due to SPT change is low. In particular, this risk is very low when a larger diameter head is used and femoral offset and length are recreated to prevent bone on bone impingement.
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http://dx.doi.org/10.1002/jor.25022DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8455710PMC
December 2021

Is Combined Anteversion Equally Affected by Acetabular Cup and Femoral Stem Anteversion?

J Arthroplasty 2021 07 9;36(7):2393-2401. Epub 2021 Feb 9.

Dorr Institute for Arthritis Research and Education, Los Angeles, CA.

Background: To create a safe zone, an understanding of the combined femoral and acetabular mating during hip motion is required. We investigated the position of the femoral head inside the acetabular liner during simulated hip motion. We hypothesized that cup and stem anteversions do not equally affect hip motion and combined hip anteversion.

Methods: Hip implant motion was simulated in standing, sitting, sit-to-stand, bending forward, squatting, and pivoting positions using the MATLAB software. A line passing through the center of the stem neck and the center of the prosthetic head exits at the polar axis (PA) of the prosthetic head. When the prosthetic head and liner are parallel, the PA faces the center of the liner (PA position = 0, 0). By simulating hip motion in 1-degree increments, the maximum distance of the PA from the liner center and the direction of its movement were measured (polar coordination system).

Results: The effect of modifying cup and stem anteversion on the direction and distance of the PA's change inside the acetabular liner was different. Stem anteversion influenced the PA position inside the liner more than cup anteversion during sitting, sit-to-stand, squatting, and bending forward (P = .0001). This effect was evident even when comparing stems with different neck angles (P = .0001).

Conclusion: Cup anteversion, stem anteversion, and stem neck-shaft angle affected the PA position inside the liner and combined anteversion in different ways. Thus, focusing on cup orientation alone when assessing hip motion during different daily activities is inadequate.
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http://dx.doi.org/10.1016/j.arth.2021.02.017DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8197737PMC
July 2021

The Effect of Functional Pelvic Tilt on the Three-Dimensional Acetabular Cup Orientation in Total Hip Arthroplasty Dislocations.

J Arthroplasty 2021 06 8;36(6):2184-2188.e1. Epub 2021 Jan 8.

Department of Orthopedic Surgery, Keck Medical Center of the University of Southern California, Los Angeles, CA.

Background: Anterior and posterior pelvic tilt appears to play a role in total hip arthroplasty (THA) stability. When changing from the standing to the sitting position, the pelvis typically rotates posteriorly while the hips flex and this affects the femoro-acetabular positions. This case-control study compares changes in 3-D acetabular cup orientation during functional pelvic tilt between posterior THA dislocations vs stable THAs.

Methods: Standing and sitting 3-D cup orientation was compared between fifteen posterior dislocations vs 233 prospectively followed stable THAs. 3-D cup orientation was calculated using previously validated trigonometric algorithms on biplanar radiographs. Those algorithms combine the angles in the three anatomical planes (coronal inclination, transverse version, and sagittal ante-inclination) in the standing position with the change in sagittal pelvic tilt from standing to sitting to calculate the 3-D orientation in the sitting position.

Results: The standing cup orientation of the dislocated THAs was only characterized by a lower coronal inclination (P = .039). Compared with the controls, from standing to sitting, they showed less posterior pelvic tilt (P < .001). This led to a significant lower coronal inclination (P < .001) and sagittal ante-inclination (P < .001) in the sitting position but similar transverse version (P = .366).

Conclusions: Comparing posterior THA dislocations to stable THAs, there is a lower increase of all three orientation angles from standing to sitting. This leads to a decreased sitting coronal inclination and sagittal ante-inclination which may lead to an increased risk of impingement ensued by THA instability. By contrast, the transverse version was not significantly different in both positions. This confirms the importance of biplanar data on functional cup orientation.

Level Of Evidence: Diagnostic, Level III.
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http://dx.doi.org/10.1016/j.arth.2020.12.055DOI Listing
June 2021

Functional Anatomy of the Hip Joint.

J Arthroplasty 2021 01 31;36(1):374-378. Epub 2020 Jul 31.

Dorr Institute for Arthritis Research and Education, Pasadena, CA.

Background: The functional anatomy of the osteoarthritic hip joint in the sagittal plane has not been defined. The purpose of this study was to define the functional anatomy of the hip using clinical and radiographic analyses.

Methods: 320 hips had preoperative standing and sitting lateral spine-pelvis-hip X-rays. Radiographic pelvic measurements were pelvic incidence (PI) and sacral slope (SS), and hip measurements were anteinclination (AI) and pelvic femoral angle (PFA). Pelvic tilt (PT) was calculated as PI-SS. A triangle model was created from the clinical data that illustrates the functional motion of the hip during postural changes from standing to sitting.

Results: Pelvic motion was coordinated with hip motion, even with spinopelvic imbalance and stiffness. Pelvic motion (ΔSS) varied for all 5 types of imbalance, but pelvic motion (ΔSS) and acetabular motion (ΔAI) changed with a 1:1 ratio and inversely with femoral motion (ΔPFA) with a 1:1 ratio. The triangle model showed similar results with ΔSS, ΔPT, and ΔAI changing in a 1:1:1 ratio, and femur motion inversely changing with a 1:1 ratio.

Conclusion: The functional anatomy of the hip joint can be visually illustrated using a triangle model. Pelvic angles SS, PT, and AI change in unison, whereas femoral motion (ΔPFA) changes inversely with pelvic motion (ΔSS) in a 1:1 ratio. This coordinated mobility explains the limitations of the Lewinnek safe zone, which include only the acetabulum.
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http://dx.doi.org/10.1016/j.arth.2020.07.065DOI Listing
January 2021

The Effects of Pelvic Incidence in the Functional Anatomy of the Hip Joint.

J Bone Joint Surg Am 2020 Jun;102(11):991-999

Dorr Institute for Arthritis Research and Education, Pasadena, California.

Background: The spine-pelvis-hip interaction during postural change should be considered in the functional anatomy of the hip. The component parts of this anatomy and how they influence hip function are important to know. Pelvic incidence (PI) is one of these components. We studied if PI was preoperatively predictive of impingement risk and if it postoperatively influences hip position, which could cause outliers from the functional safe zone of hip replacement.

Methods: This was a prospective radiographic study of 187 consecutive patients (200 hips) who had lateral spinopelvis-hip radiographs before and after primary total hip arthroplasty with measurements of the component factors that influence mobility and position of the functional anatomy. The predictive value of PI for risk of impingement of the hip and its postoperative relationship to functional safe-zone outliers were assessed. Forty-one dislocations from our clinical practice were also reviewed.

Results: Of 200 hips, the PI was normal in 145 hips (73%), low in 18 hips (9%), and high in 37 hips (19%). Eighty-two hips had spinopelvic imbalance: 12 (67%) of the 18 hips with low PI, 56 (39%) of the 145 hips with normal PI, and 14 (38%) of the 37 hips with high PI. Low-PI hips was the most predictive of the risk of impingement and postoperatively these hips had the most outliers from the functional safe zone.

Conclusions: PI is an anatomical component that is predictive of both impingement risk and functional safe-zone outliers. Preoperative risk, based on factors such as the Lewinnek zones and combined anteversion, is an established guide in determining cup position in hip replacement. Low-PI hips that have the "terrible triad" of a posteriorly tilted pelvis, stiff pelvic mobility, and increased femoral flexion therefore have no functional safe zone.

Level Of Evidence: Prognostic Level IV. See Instructions for Authors for a complete description of levels of evidence.
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http://dx.doi.org/10.2106/JBJS.19.00300DOI Listing
June 2020

Letter to the Editor on "Low-Dose Aspirin is Adequate for Venous Thromboembolism Prevention Following Total Joint Arthroplasty: A Systemic Review".

Authors:
Lawrence D Dorr

J Arthroplasty 2020 08 6;35(8):2296. Epub 2020 Apr 6.

Dorr Institute for Arthritis Research and Education, Pasadena, CA.

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http://dx.doi.org/10.1016/j.arth.2020.03.056DOI Listing
August 2020

CORR Insights®: What Factors Are Associated With Neck Fracture in One Commonly Used Bimodular THA Design? A Multicenter, Nationwide Study in Slovenia.

Authors:
Lawrence D Dorr

Clin Orthop Relat Res 2019 06;477(6):1333-1334

L. D. Dorr Keck Medical Center of USC, Department of Orthopaedics, Los Angeles, CA, USA.

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http://dx.doi.org/10.1097/CORR.0000000000000708DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6554128PMC
June 2019

Spinopelvic Motion and Impingement in Total Hip Arthroplasty.

J Arthroplasty 2019 Jul 24;34(7S):S53-S56. Epub 2019 Jan 24.

Department of Orthopaedic Surgery, Keck School of Medicine of USC, Los Angeles, CA.

The stability of a total hip arthroplasty relies on proper positioning of the acetabular cup. Recent research has shown that this cup position is more dynamic than previously thought. The 3-dimensional orientation of the acetabular cup changes when the pelvis tilts anteriorly or posteriorly. These changes in pelvic tilt are directly related to the biomechanics of the lumbosacral junction. In normal physiology, the lumbar spine straightens with sitting and becomes more lordotic with standing. This directly translates to posterior or anterior pelvic tilt due to the rigid sacroiliac attachments. During sitting, increased posterior pelvic tilt opens the acetabulum to accommodate flexion and internal rotation of the hip. This helps prevent anterior impingement and posterior hip dislocation. During standing, anterior pelvic tilt increases superior coverage of the acetabulum. This helps prevent posterior impingement and anterior hip dislocations. When lumbosacral motion becomes pathologic, spinopelvic motion changes and acetabular cup orientation is affected. In cases of decreased lumbosacral motion, patients rely on greater hip motion to reach standing or sitting positions. This can cause pathologic impingement. In addition, traditional safe zones for cup position may not apply in the presence of pathologic spinopelvic motion. This article discusses the normal physiology of spinopelvic motion, the patterns of pathologic change, and the clinical implications therein.
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http://dx.doi.org/10.1016/j.arth.2019.01.033DOI Listing
July 2019

Death of the Lewinnek "Safe Zone".

J Arthroplasty 2019 01;34(1):1-2

Professor, University of Iowa, Department of Orthopedics and Rehabilitation, Iowa City, IA.

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http://dx.doi.org/10.1016/j.arth.2018.10.035DOI Listing
January 2019

Functional Safe Zone Is Superior to the Lewinnek Safe Zone for Total Hip Arthroplasty: Why the Lewinnek Safe Zone Is Not Always Predictive of Stability.

J Arthroplasty 2019 01 2;34(1):3-8. Epub 2018 Nov 2.

Department of Orthopaedic Surgery, Keck Medical Center of USC, Los Angeles, CA.

Background: The Lewinnek "safe zone" is not always predictive of stability after total hip arthroplasty (THA). Recent studies have focused on functional hip motion as observed on lateral spine-pelvis-hip x-rays. The purpose of this study was to assess the correlation between the Lewinnek safe zone and the functional safe zone based on hip and pelvic motion in the sagittal plane.

Methods: Three hundred twenty hips (291 patients) underwent primary THA using computer navigation. Two hundred ninety-six of these hips (92.5%) were within the Lewinnek safe zone as determined by inclination of 40° ± 10° and anteversion of 15° ± 10°. All patients had preoperative and postoperative standing and sitting lateral spinopelvic x-rays. The combined sagittal index (CSI), a combination of sagittal acetabular and femoral position, was measured for each patient and used to assess the functional safe zone. Data analysis was performed to identify hips in the Lewinnek safe zone inside and outside the sagittal functional safe zone. Predictive factors for hips outside the functional safe zone were identified.

Results: Of the 296 hips within the Lewinnek safe zone, 254 (85.8%) were also in the functional safe zone. Forty-two patients were outside the functional safe zone based on CSI; 19 had an increased standing CSI and 23 had a decreased sitting CSI, all were considered at risk for dislocation. Predictive factors for falling outside the functional safe zone were increased femoral mobility (P < .001, r = 0.632), decreased spinopelvic mobility (P < .001, r = 0.455), and pelvic incidence (P < .001, r = 0.400).

Conclusion: In this study, 14.2% of hips within the Lewinnek safe zone were outside the functional safe zone, identifying a potential reason hips dislocate despite having "normal" cup angles. The best predictor for falling outside the functional safe zone, both preoperatively and postoperatively, was femoral mobility, not the sagittal cup position (ie, cup anteinclination).

Level Of Evidence: Level III, retrospective review.
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http://dx.doi.org/10.1016/j.arth.2018.10.034DOI Listing
January 2019

Late Dislocation Following Total Hip Arthroplasty: Spinopelvic Imbalance as a Causative Factor.

J Bone Joint Surg Am 2018 Nov;100(21):1845-1853

Department of Orthopaedic Surgery, Keck Medical Center of the University of Southern California, Los Angeles, California.

Background: Late dislocations after total hip arthroplasty (THA) are challenging for the hip surgeon because the cause is often not evident and recurrence is common. Recently, decreased spinopelvic motion has been implicated as a cause of dislocation. The purpose of this study was to assess the mechanical causes of late dislocation, including the influence of spinopelvic motion.

Methods: Twenty consecutive patients were studied to identify the cause of their late dislocation. Cup inclination and anteversion were measured on standard pelvic radiographs. Lateral standing and sitting spine-pelvis-hip radiographs were used to measure pelvic motion, femoral mobility, and sagittal cup position by assessing sacral slope, pelvic-femoral angle, and cup ante-inclination. Spinopelvic motion was defined as the difference between the standing and sitting sacral slopes (Δsacral slope). A new measurement, the combined sagittal index, which measures the sagittal acetabular and femoral positions, was used to assess the functional motion of the hip joint and risk of impingement.

Results: There were 9 anterior dislocations (45%) and 11 posterior dislocations (55%) at a mean of 8.3 years after a primary THA. Eight of the 9 patients with an anterior dislocation had spinopelvic abnormalities such as fixed posterior pelvic tilt when standing, increased standing femoral extension, and an increased standing combined sagittal index. Ten of the 11 patients with a posterior dislocation had abnormal spinopelvic measurements such as decreased spinopelvic motion (average Δsacral slope [and standard error] = 9.0° ± 2.4°), increased femoral flexion, and a decreased sitting combined sagittal index. For every 1° decrease in spinopelvic motion, there was an associated 0.9° increase in femoral motion and, in some patients, this resulted in osseous impingement and dislocation.

Conclusions: Patients with a late dislocation have abnormal spinopelvic motion that precipitates the dislocation, especially when combined with cup malposition or soft-tissue abnormalities. Spinopelvic stiffness is associated with increased age and increased femoral motion, which may lead to impingement and dislocation. Lateral spine-pelvis-hip radiographs may predict the risk and direction of dislocation.

Level Of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.
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http://dx.doi.org/10.2106/JBJS.18.00078DOI Listing
November 2018

CORR Insights®: No Increase in Survival for 36-mm versus 32-mm Femoral Heads in Metal-on-polyethylene THA: A Registry Study.

Authors:
Lawrence D Dorr

Clin Orthop Relat Res 2018 12;476(12):2379-2380

L. D. Dorr, Professor of Orthopaedics, Department of Orthopaedics, USC Keck Medical Center, Los Angeles, CA, USA.

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http://dx.doi.org/10.1097/CORR.0000000000000546DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6259905PMC
December 2018

Spine-Pelvis-Hip Relationship in the Functioning of a Total Hip Replacement.

J Bone Joint Surg Am 2018 Sep;100(18):1606-1615

Department of Orthopaedic Surgery, Keck School of Medicine of the University of Southern California, Los Angeles, California.

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http://dx.doi.org/10.2106/JBJS.17.00403DOI Listing
September 2018

Restoration of center of rotation and balance of THR.

J Orthop 2018 Dec 6;15(4):992-996. Epub 2018 Sep 6.

Keck Medical Center of University of Southern California, 1520 San Pablo Street, Suite 2000, Department of Orthopedics, Los Angeles, CA, 90033, USA.

Improvements in early hip arthroplasties focused on surgical techniques with subsequent studies emphasizing restoration of the hip center of rotation for longevity of the implant. Current literature suggests femoral stem anteversion of 10-20°, cup anteversion of 20-25° and a combined anteversion of 25-40° in males, 30-45° in females. Inclination goal appears to be 45° precisely to balance between impingement & dislocation versus edge loading & accelerated wear. Restoration of the acetabular center of rotation will improve joint reactive forces and reduce wear. Here we describe techniques to achieve a well balanced total hip with restoration of the center of rotation.
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http://dx.doi.org/10.1016/j.jor.2018.08.040DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6138845PMC
December 2018

The Opioid Crisis and the Orthopedic Surgeon.

J Arthroplasty 2018 11 11;33(11):3379-3382.e1. Epub 2018 Jul 11.

Department of Orthopedics, Keck Medical Center of USC, Los Angeles, California.

Opioid use and abuse has become a national crisis in the United States. Many opioid abusers become addicted through an initial course of legal, physician-prescribed medications. Consequently, there has been increased pressure on medical care providers to be better stewards of these medications. In orthopedic surgery and total joint arthroplasty, pain control after surgery is critical for restoring mobility and maintaining patient satisfaction in the early postoperative period. Before the opioid misuse epidemic, orthopedic surgeons were frequently influenced to "treat pain with pain medications." Long-acting opioids, such as OxyContin were used commonly. In the past decade, there has been a paradigm shift in favor of multimodal pain control with limited opioid use. This review will discuss 4 major topics. First, we will describe the pressures on orthopedic surgeons to prescribe narcotic pain medications. We will then discuss the major and minor complications and side effects associated with these prescriptions. Second, we will review how these factors motivated the development of alternative pain management strategies and a multimodal approach. Third, we will look at perioperative interventions that can reduce postoperative opioid consumption, including wound injections and peripheral nerve blocks, which have shown superb clinical results. Finally, we will recommend an evidence-based program that avoids parenteral narcotics and facilitates rapid discharge home without readmissions for pain-related complaints.
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http://dx.doi.org/10.1016/j.arth.2018.07.002DOI Listing
November 2018

Why total knees fail-A modern perspective review.

World J Orthop 2018 Apr 18;9(4):60-64. Epub 2018 Apr 18.

Department of Orthopaedic Surgery, Keck Medical Center of University of Southern California, Los Angeles, CA 90033, United States.

Historically, the most common mechanism of total knee arthroplasty (TKA) failures included aseptic loosening, instability and malalignment. As polyethylene production improved, modes of failure from polyethylene wear and subsequent osteolysis became less prevalent. Newer longitudinal studies report that infection has become the primary acute cause of failure with loosening and instability remaining as the overall greatest reasons for revision. Clinical database and worldwide national registries confirm these reports. With an increasing amount of TKA operations performed in the United States, and with focus on value-based healthcare, it is imperative to understand why total knees fail.
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http://dx.doi.org/10.5312/wjo.v9.i4.60DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5908984PMC
April 2018

The Current Knowledge on Spinopelvic Mobility.

J Arthroplasty 2018 01 24;33(1):291-296. Epub 2017 Aug 24.

Keck Medical Center of University of Southern California, Department of Orthopaedic Surgery, Los Angeles, CA.

Recent studies may suggest that our conventional knowledge of risk factors for dislocation may need rethinking. Previous studies have demonstrated a large majority of total hip arthroplasty instability with acetabular cups implanted in safe zones. Recently discovered spinopelvic motion is a coordinated biomechanical relationship among acetabular anteversion, pelvic tilt, and lumbar lordosis. Classification includes normal, hypermobile, stiff, stuck standing, stuck sitting, and fused. Normal spinopelvic motion from standing to sitting occurs with hip flexion, posterior sacral tilt, and decreased lumbar lordosis to accommodate a flexed femur and prevent impingement and dislocation. Acetabular cup implantation ideally is adapted based on spinopelvic interactions. This may lower the rate of impingement and subsequent dislocation. These new biomechanical interactions may provide a better understanding of the safe zones of anteversion and inclination.
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http://dx.doi.org/10.1016/j.arth.2017.08.013DOI Listing
January 2018

What's Important: Giving Back.

Authors:
Lawrence D Dorr

J Bone Joint Surg Am 2017 08;99(15):e81

1Department of Orthopaedics, Keck School of Medicine, University of Southern California, Los Angeles, California.

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http://dx.doi.org/10.2106/JBJS.17.00536DOI Listing
August 2017

Letter to the Editor: Editor's Spotlight/Take 5: No Benefit after THA Performed with Computer-assisted Cup Placement: 10-year Results of a Randomized Controlled Study.

Authors:
Lawrence D Dorr

Clin Orthop Relat Res 2017 02 17;475(2):565-566. Epub 2016 Nov 17.

Orthopedic Department, Keck Medical Center of USC, 1520 San Pablo Street, #2000, Los Angeles, CA, 90033, USA.

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http://dx.doi.org/10.1007/s11999-016-5163-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5213954PMC
February 2017

CORR Insights(®): Does Degenerative Lumbar Spine Disease Influence Femoroacetabular Flexion in Patients Undergoing Total Hip Arthroplasty?

Authors:
Lawrence D Dorr

Clin Orthop Relat Res 2016 08 10;474(8):1798-801. Epub 2016 May 10.

Keck Medical Center of USC, 1520 San Pablo Street, #2000, Los Angeles, CA, 90033, USA.

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http://dx.doi.org/10.1007/s11999-016-4877-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4925420PMC
August 2016

Outpatient Arthroplasty is Here Now.

Instr Course Lect 2016 ;65:531-46

President, Joint Implant Surgeons, New Albany, Ohio.

Substantial advances have been made in arthroplasty to minimize surgical trauma and maximize perioperative pain control, which has enabled patients to regain mobility within hours of surgical intervention and be safely discharged to home the same day. Surgeons should understand the indications and contraindications for the safe performance of outpatient arthroplasty in a hospital and ambulatory surgical center setting as well as know how to optimize, medically manage, prepare, and rehabilitate patients. To undertake outpatient arthroplasty, surgeons must be knowledgeable in multimodal anesthesia techniques, effective venous thromboembolism prophylaxis, blood management, and wound management. In addition, surgeons must learn the subtle nuances of specialized surgical techniques that lend themselves to outpatient arthroplasty, including partial knee, muscle-sparing total hip, less invasive total knee, and total shoulder techniques.
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July 2016

Posterior Mini-Incision Approach for Total Hip Replacement.

Authors:
Lawrence D Dorr

JBJS Essent Surg Tech 2016 Mar 10;6(1):e5. Epub 2016 Feb 10.

Orthopaedic Department, Keck Medical Center of USC, 1520 San Pablo Street, Suite 2000, Los Angeles, CA 90033.

We developed a modification of the posterior mini-incision for total hip arthroplasty, which was initially used by Sculco at The Hospital for Special Surgery, in response to the movement in the orthopaedic community to perform total hip arthroplasty with smaller incisions. Our approach preserves the piriformis and quadratus femoris muscles of the external rotators, uses three incisions into the capsule but does not excise the capsule, does not incise the tensor fascia/iliotibial band, and leaves intact the insertion of the gluteus maximus onto the femur. We have used this incision since 2004, and our published results and those of others show that the greatest advantage is cosmetic and patients' perception of less violation of their body. It is a contributor to the same-day surgery program and rapid recovery protocol on which we have reported. The steps of the procedure include (1) an incision made along the posterior edge of the greater trochanter from the level of the vastus tubercle to one fingerbreadth from the tip of the greater trochanter; (2) a deep L-shaped incision parallel to the piriformis tendon, and along the posterior edge of the greater trochanter through the small external rotator muscles and hip capsule to the proximal edge of the quadratus to expose the femoral head and neck; (3) measurement of the neck cut from the distal edge of the femoral head and amputation of the femoral head; (4) exposure of the cut neck of the femur with retractors and broaching of the femur; (5) exposure of the acetabulum with retractors and acetabular reaming to prepare it for the cup; (6) implantation of the cup and stem and a femoral head of the correct length to restore lower-limb length and offset; and (7) closure of the wound in layers with the skin with subcutaneous sutures and sealing of the wound with a DERMABOND dressing (Ethicon). The expected outcome is that the patient will walk with full weight-bearing on the day of the operation and be discharged home that day or the next. Patients with occupations that do not require physical labor can return to work in one week, and according to our data 98% of patients under sixty-five can walk one mile (1.6 km) by three weeks. Recovery is in three phases: for the first month, the patient has soreness and swelling from the surgical trauma to the tissues; at three months, the muscles are well healed; and at six months, bone healing is mature. The hip is "forgotten" (the patient goes days without thinking about it) after six months.
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http://dx.doi.org/10.2106/JBJS.ST.N.00119DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6145620PMC
March 2016

Posterior Mini-Incision With Primary Total Hip Arthroplasty: A Nine to Ten Year Follow Up Study.

J Arthroplasty 2016 Jan 17;31(1):168-71. Epub 2015 Jul 17.

Keck Medical Center of USC, Department of Orthopedic Surgery, Los Angeles, California.

The question has been raised as to whether small incision surgery will compromise long term results of total hip arthroplasty. We report nine to ten years' outcome with posterior mini-incision. Radiographs were measured for component position, polyethylene wear, fixation, and osteolysis. Sixty-two of the original 86 patients (76 of 100 hips) were alive and available for study with 17 patients deceased (with known results) and seven (8%) lost to follow-up. The result was rated as excellent in 70 of 75 remaining hips (93%). Eighty-nine of 93 hips (96%) with known results had the original implants. Radiographically, wear was a mean 0.015 ± 0.009 mm/year, and no hip had impending failure. There were four revisions, 2 for dislocation, 1 for fracture, and 1 for loose cup.
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http://dx.doi.org/10.1016/j.arth.2015.07.023DOI Listing
January 2016

Early Postoperative Femur Fracture After Uncemented Collarless Primary Total Hip Arthroplasty: Characterization and Results of Treatment.

J Arthroplasty 2015 Nov 29;30(11):2008-11. Epub 2015 May 29.

Mayo Graduate School of Medicine, Mayo Clinic, Rochester, Minnesota.

Thirty Vancouver type B periprosthetic fractures occurred within 90 days of total hip arthroplasty were identified using two institutional databases. Twenty-eight of these fractures were of a stereotyped fracture pattern consisting of a displaced fracture of the femoral neck including the lesser trochanter and a variable amount of the proximal medial femoral cortex creating a roughly triangular fragment. Time from operation until fracture was 2-88 days (mean 28). Mechanism of injury was fall from standing height in 12, no defined trauma in 11, stumble without fall in 5, and twisting motion in 2. Fracture treatment consisted of femoral revision in 24, fracture fixation in two, and nonoperative in four. Of the 24 treated with revision, 21 had healed fractures and stable revision stems.
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http://dx.doi.org/10.1016/j.arth.2015.05.044DOI Listing
November 2015

Precision of robotic guided instrumentation for acetabular component positioning.

J Arthroplasty 2015 Mar 22;30(3):392-7. Epub 2014 Oct 22.

Orthopedic Department, Keck Medical Center of USC, Los Angeles, California.

Robotic computerized instrumentation that guides bone preparation and cup implantation in total hip arthroplasty was studied. In 38 patients (43 hips) intraoperative cup inclination and anteversion were validated by postoperative CT scans. Planned inclination was 39.9°±0.8° and with robotic instrumentation was 38. 0°±1.6° with no outliers of 5°; on the postoperative CT scan there were 5 outliers (12%). Planned anteversion was 21.2°±2.4° and intraoperatively was 20.7°±2.4° with no outlier of 5°; on the CT there were 7 outliers (16%). The center of rotation (COR) was superior by a mean 0.9±4.2 mm and medial by 2.7±2.9 mm. This robotic instrumentation achieved precision of inclination in 88%, anteversion in 84% and COR in 81.5%.
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http://dx.doi.org/10.1016/j.arth.2014.10.021DOI Listing
March 2015

Predictability of Acetabular Component Angular Change with Postural Shift from Standing to Sitting Position.

J Bone Joint Surg Am 2014 Jun;96(12):978-986

Orthopedic Department, Keck Medical Center of USC, 1520 San Pablo Street, Suite 2000, Los Angeles, CA 90033. E-mail address for L.D. Dorr:

Background: The angles of the acetabular component of a total hip replacement change with body postural changes, and this change can affect stability and wear. We sought to correlate the intraoperative angles of inclination and anteversion of the cup with the changes in these angles when patients moved from standing to sitting and determine if these changes were predictable.

Methods: Eighty-five patients (eighty-five hips) had sagittal (lateral) spinopelvic radiographs made while they were standing and while they were sitting before and after undergoing total hip replacement. The spinosacral tilt and the pelvic tilt were measured on these radiographs. The angles of acetabular inclination and anteversion achieved at surgery changed during sitting. Each patient was classified according to the stiffness of the spine/pelvis as measured by the change in posterior sacral or pelvic tilt between the standing and sitting positions. The magnitude of change of the sagittal cup position (termed ante-inclination) was correlated to the stiffness classification of the pelvis. An experimental phantom model reproduced possible combinations of intraoperative inclination and anteversion and correlated them to sagittal ante-inclination according to pelvic tilt.

Results: The pelves with normal stiffness tilted posteriorly 20° to 35° with the postural change from standing to sitting. Ante-inclination of the acetabular cup averaged 29.6° ± 8.4° (95% confidence interval [CI] = 13.1° to 46°) with standing and 54.6° ± 10.2° (95% CI = 44.4° to 64.8°) with sitting. The stiff pelves had a mean of 4° less tilt than those with normal stiffness and 13° less than the hypermobile pelves with the postoperative sitting position. The phantom model showed ante-inclination could be predicted by measuring the preoperative degrees of change in sacral/pelvic tilt from standing to sitting.

Conclusions: Ante-inclination during sitting results in a more vertical acetabular cup, which can result in hip instability, especially drop-out dislocation, and edge-loading wear. Patients with supine coronal cup inclination of ≥50° and anteversion of ≥25° and those with a hypermobile pelvis are at risk. It is the pelvic spatial position during postural change that creates the postoperative consequences of the surgical cup placement.
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http://dx.doi.org/10.2106/JBJS.M.00765DOI Listing
June 2014
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