People with patellofemoral osteoarthritis have smaller hip muscle volumes than healthy controls

Abstract

Purpose: The patellofemoral joint (PFJ) is a frequently affected by the osteoarthritis (OA) process and contributes significantly to the OA-related pain and reduced physical function. Due to the unique biomechanics of the PFJ, it is likely that rehabilitation strategies tailored to PFJ OA will optimise clinical outcomes. However, currently there is limited knowledge of the modifiable impairments associated with PFJOA, which could be targeted in rehabilitation programs. Hip muscle dysfunction has been proposed to influence PFJ stress and hence, may play a role in the development or progression of PFJOA. Specifically, weakness of hip abductor muscles may result in excessive femoral adduction, which may increase contact pressure in the lateral PFJ. Therefore, the aim of this study was to compare the volumes of the primary hip-abductors (gluteus medius, gluteus minimus and tensor fasciae latae) of individuals with PFJOA, with those of healthy controls.Methods: 50 individuals with radiographic evidence of PFJ OA and symptoms stereotypical of PFJ involvement, aged > 40 years and 13 people aged > 40, with no lower limb problems were recruited. Magnetic Resonance (MR) images of the hip region were obtained. The cross-sectional area of the hip-abductor muscles were manually segmented from each axial MR slice, and were used to calculate muscle volume. A test-retest reliability study was performed to assess the intra-investigator reliability of this procedure. The muscle volumes of were normalised to body weight and analyses were performed with and without gender as a co-variate.Results: There were no differences in participant characteristics between the PFJ OA group (female 40 (63%); age 55 ± 10 yrs; height 1.69±0.09m; weight 76±13 kg) and control group (female 10 (62%); age 52±6yrs; height 1.68±0.10; weight 71±13kg). The techniques for assessing muscle volume were shown to be reliable (ICC ≥ 0.997). Comparisons of mean normalised muscle volumes revealed significant between-group differences for gluteus medius (mean difference: 95% confidence interval 0.47: 0.08 to 0.86 cm3.kg-1; p = 0.02), gluteus minimus (0.21; 0.09 to 0.33 cm3.kg-1; p = 0.001) and tensor fasciae latae (0.23; 0.03 to 0.42 cm3.kg-1; 0.024). Inclusion of gender as a covariate did not change the significant findings.Conclusions: Individuals with PFJOA had significantly smaller gluteus medius, gluteus minimus and tensor fasciae latae muscles when compared with healthy control individuals. As muscle volume is directly related to peak isometric force output, smaller muscles will tend to be weaker. It is unclear whether hip-abductor weakness is a cause or an effect of PFJOA. Regardless, the present study provides several directions for future research on this relationship