Publications by authors named "A Ruhdorfer"

23 Publications

Association of infra-patellar fat pad size with age and body weight in children and adolescents.

Ann Anat 2020 Nov 2;232:151533. Epub 2020 Jul 2.

Department of Imaging and Functional Musculoskeletal Research, Institute of Anatomy, Paracelsus Medical University Salzburg & Nuremberg, Salzburg, Austria; Department of Orthopedic Surgery & Traumatology, Landesklinik Tamsweg, Paracelsus Medical University, Tamsweg, Austria.

Background: The infra-patellar fat pad (IPFP) represents a potential mediator between obesity, low grade inflammation, and knee osteoarthritis via endocrine pathways. Yet, not only in adults, but also in childhood obesity negatively impacts knee structures.

Objective: The current study therefore investigated the sex-specific growth of the IPFP with age and body weight in healthy children and adolescents.

Materials And Methods: Thirty young healthy subjects (60% girls; age 4-17 years, body weight 14-90 kg in girls and 29-105 kg in boys; BMI 12.2-32.4 kg/m) without magnetic resonance imaging (MRI) knee pathology were studied. The IPFP volume was determined from sagittal T-1 weighted and proton-density spectral attenuated inversion recovery MRIs. The primary analysis focused on the sex-specific IPFP volume/body weight ratio as dependent, and age as independent variable, using linear regression models. A secondary analytic focus was the slope of the age-dependence of IPFP volume, without normalization to body weight.

Results: There was no statistically significant association of the IPFP volume/body weight ratio with age in girls (p = 0.57) or boys (p = 0.31), the R of ranging from -0.32 to 0.14. The ratio was greater in boys (0.54 ± 0.10 cm/kg) than in girls (0.45 ± 0.07 cm/kg) (p < 0.01). The IPFP volume increased by approx. 2 cm per annum in both girls and boys, without any indication of a non-linear relationship.

Conclusion: Our findings reveal that the ratio of the IPFP volume and body weight remains constant between age 4 and 17 in both normal weight girls and boys, and that the IPFP volume increases linearly with age throughout this period.
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November 2020

Clinical evaluation of fully automated thigh muscle and adipose tissue segmentation using a U-Net deep learning architecture in context of osteoarthritic knee pain.

MAGMA 2020 Aug 23;33(4):483-493. Epub 2019 Dec 23.

ETH, Zurich, Switzerland.

Objective: Segmentation of thigh muscle and adipose tissue is important for the understanding of musculoskeletal diseases such as osteoarthritis. Therefore, the purpose of this work is (a) to evaluate whether a fully automated approach provides accurate segmentation of muscles and adipose tissue cross-sectional areas (CSA) compared with manual segmentation and (b) to evaluate the validity of this method based on a previous clinical study.

Materials And Methods: The segmentation method is based on U-Net architecture trained on 250 manually segmented thighs from the Osteoarthritis Initiative (OAI). The clinical evaluation is performed on a hold-out test set bilateral thighs of 48 subjects with unilateral knee pain.

Results: The segmentation time of the method is < 1 s and demonstrated high agreement with the manual method (dice similarity coeffcient: 0.96 ± 0.01). In the clinical study, the automated method shows that similar to manual segmentation (- 5.7 ± 7.9%, p < 0.001, effect size: 0.69), painful knees display significantly lower quadriceps CSAs than contralateral painless knees (- 5.6 ± 7.6%, p < 0.001, effect size: 0.73).

Discussion: Automated segmentation of thigh muscle and adipose tissues has high agreement with manual segmentations and can replicate the effect size seen in a clinical study on osteoarthritic pain.
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August 2020

Reduction in Thigh Muscle Strength Occurs Concurrently but Does Not Seem to Precede Incident Knee Pain in Women: Data From the Osteoarthritis Initiative Cohort.

Am J Phys Med Rehabil 2020 01;99(1):33-40

From the Institute of Anatomy, Department of Imaging and Functional Musculoskeletal Research, Paracelsus Medical University Salzburg & Nuremberg, Salzburg, Austria (AR, WW, AGC, FE); Department of Orthopedic Surgery and Traumatology, Landesklinik Tamsweg, Tamsweg, Austria (AR); and La Trobe Sport and Exercise Medicine Research Centre, La Trobe University, School of Allied Health, Bundoora, Melbourne, Victoria, Australia (AGC).

Objective: The aim of the study was to investigate whether muscle strength declines before or concurrent with incident knee pain in subjects with and without radiographic knee osteoarthritis.

Design: Osteoarthritis initiative participants with incident knee pain (occurrence of infrequent/frequent knee pain during the past 12 mos at two consecutive follow-up time points (either years Y3 + Y4 or Y4 + Y5) were compared with controls (no incident knee pain) with 2-yr changes in knee extensor strength during BL➔Y2 (before) and Y2➔Y4 (concurrent).

Results: Two hundred two knees (49% women, 40% radiographic knee osteoarthritis) displayed incident pain, and 439 did not (46% women, 23% radiographic knee osteoarthritis). Women with radiographic knee osteoarthritis displayed a significantly greater (P = 0.04) reduction in knee extensor strength concurrent with incident pain compared with controls (mean = -17.6 N vs. +4.5 N), but men did not. A similar trend was observed in women without radiographic knee osteoarthritis, but this was not statistically significant (P = 0.08). There was no significant relationship with change in extensor strength before incident pain (P ≥ 0.43).

Conclusions: These results suggest that in women, incident knee pain is accompanied by a concurrent reduction in knee extensor strength, whereas loss in strength does not precede incident knee pain. The findings encourage interventional studies that attempt to attenuate a decline in extensor strength once knee symptoms occur.
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January 2020

Relationship Between Knee Pain and Infrapatellar Fat Pad Morphology: A Within- and Between-Person Analysis From the Osteoarthritis Initiative.

Arthritis Care Res (Hoboken) 2018 04 11;70(4):550-557. Epub 2018 Mar 11.

Paracelsus Medical University Salzburg and Nuremberg, Salzburg, Austria.

Objective: Inflammation is known to be strongly associated with knee pain in osteoarthritis. The infrapatellar fat pad represents a potential source of proinflammatory cytokines. Yet the relationship between infrapatellar fat pad morphology and osteoarthritis symptoms is unclear.

Methods: Here we investigate quantitative imaging parameters of infrapatellar fat pad morphology between painful versus contralateral pain-free legs of subjects with unilateral knee pain and patients with chronic knee pain versus those of matched pain-free control subjects. A total of 46 subjects with strictly unilateral frequent knee pain and bilateral radiographic osteoarthritis (Kellgren/Lawrence grade 2/3) were drawn from the Osteoarthritis Initiative. Further, 43 subjects with chronic knee pain over 4 years and 43 matched pain-free controls without pain over this period were studied. Infrapatellar fat pad morphology (volume, surface area, and depth) was determined by manual segmentation of sagittal magnetic resonance images.

Results: No significant differences in infrapatellar fat pad morphology were observed between painful versus painless knees of persons with strictly unilateral knee pain (mean difference -0.7% (95% confidence interval [95% CI] -0.6, 0.9; P = 0.64) or between chronically painful knees versus matched painless controls (-2.1% [95% CI -2.2, 1.1]; P = 0.51).

Conclusion: Independent of the ambiguous role of the infrapatellar fat pad in knee osteoarthritis (a potential source of proinflammatory cytokines or a mechanical shock absorber), the size of the infrapatellar fat pad does not appear to be related to knee pain.
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April 2018

Longitudinal change in thigh muscle strength prior to and concurrent with symptomatic and radiographic knee osteoarthritis progression: data from the Osteoarthritis Initiative.

Osteoarthritis Cartilage 2017 10 8;25(10):1633-1640. Epub 2017 Jul 8.

Paracelsus Medical University, Institute of Anatomy Salzburg & Nuremberg, Salzburg, Austria; La Trobe Sports and Exercise Medicine Research Centre, La Trobe University, School of Allied Health, Bundoora, Australia. Electronic address:

Objective: To investigate whether symptomatic and/or radiographic knee osteoarthritis (KOA) progression is associated with prior and/or concurrent change in thigh muscle strength in men or women.

Design: Osteoarthritis Initiative (OAI) participants with isometric muscle strength measurements at baseline, 2- and 4-year follow-up (n = 1785: 1016 women) were grouped into 1) those with vs without symptomatic progression (i.e., increase ≥9 in WOMAC-pain [scale: 0-100]); and 2) those with vs without radiographic progression (i.e., decrease in minimum joint space width (JSW) ≥0.7 mm) between year-two and year-four follow-up. Sex-specific changes in thigh muscle strength concurrent (between year-two and year-four follow-up) and prior to (between baseline and year-two follow-up) symptomatic and radiographic progression were compared between groups (progression vs no progression) using analysis of covariance, with adjustment for age and body mass index.

Results: In women, but not in men, loss in knee extensor and flexor strength was greater concurrent with symptomatic progression (extensors: -3.7%, 95% confidence interval [CI] -6.4, -0.9; flexors: -7.2% 95% CI -10.7, -3.7) than in women without symptomatic progression (extensors: -0.3%, 95% CI -1.9, 1.3, P = 0.030; flexors: -2.6%, 95% CI -4.7, -0.6, P = 0.018). No association was found between extensor or flexor strength loss concurrent to radiographic progression, in either men or women, nor any statistically significant association between prior change in muscle strength with symptomatic or radiographic progression.

Conclusion: These findings suggest that there is concurrent but not prior longitudinal association between loss in muscle strength and symptomatic KOA progression that is specific to women.
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October 2017