IMPROVEMENTS IN KNEE EXTENSION STRENGTH ARE ASSOCIATED WITH IMPROVEMENTS IN SELF-REPORTED HIP FUNCTION FOLLOWING ARTHROSCOPY FOR FEMOROACETABULAR IMPINGEMENT SYNDROME

Abstract

Background: Recovery of strength is critical for return to sport, and is a known predictor of functional outcomes in post-surgical orthopedic populations. Muscle weakness is a known impairment in patients with femoroacetabular impingement syndrome (FAIS) but whether improvements in muscle strength after arthroscopy are associated with improved hip function is unknown.

Hypothesis/purpose: To examine the relationships between changes in hip and thigh muscle strength and self-reported function in athletes undergoing arthroscopy for FAIS.

Study design: Single cohort descriptive and correlational study.

Methods: Twenty-eight athletes underwent strength testing and completed the Hip Outcome Score Activities of Daily Living (HOS-ADL) and Sports (HOS-S) subscales prior to and six months after surgery. Isokinetic knee extension and flexion strength were measured using a Biodex dynamometer at 60 °/s and 300 °/s. Isometric hip abduction strength was measured using a custom dynamometer. Changes in strength, limb symmetry, and HOS scores were assessed using paired t-tests. Spearman's rank correlations were used to examine relationships between change in involved limb strength and change in HOS scores.

Results: Subjects were tested an average of 32 days before and 178 days after surgery. HOS-ADL and HOS-S subscales improved by a mean of 19.0 ± 21.1 and 23.8 ± 31.9, respectively, over time (p < 0.001). Hip abduction strength did not increase over time in either limb (p ≥ 0.27). Involved limb knee flexion and extension strength did not increase significantly over time (p-values: 0.10-0.48) with the exception of knee extension at 300 °/s (p = 0.04). Uninvolved limb knee extension strength at both velocities and knee flexion strength at 60 °/s improved significantly over time (p < 0.012). Increases in knee extension strength (60 °/s) of the involved limb were significantly correlated with improvements on the HOS-ADL (r = 0.431; 0 = 0.025) and HOS-S (r = 0.439; p = 0.025). There were no significant relationships between changes in involved limb hip abduction or knee flexion strength and HOS subscales (p≥0.123).

Conclusion: Improvements in knee extension strength were associated with improvements in self-reported hip function in athletes following arthroscopy for FAIS. Individuals with knee extension strength deficits prior to surgery may benefit from targeted knee extension strengthening during post-operative rehabilitation to improve functional outcomes.

Level of evidence: Level III (non-randomized controlled cohort study).

Keywords: femoroacetabular impingement syndrome; hip strength; knee strength.

Figures

Figure 1.

Hip abduction strength testing set up.

Figure 2.

Limb symmetry indexes (%) of peak strength values for hip abduction, knee flexion, and knee extension pre- and post-operatively. No statistically significant changes (P ≥ 0.115). Bars represent standard deviation values. Abbreviations: SLR, straight leg raise; 6 mo, 6 month post-operative; abd, abduction; ext, extension; flex, flexion; s, second.

Figure 3.

Change in Normalized Knee Extension Strength at 60 deg/s and HOS-ADL and HOS-S over Time. Torque measured in ft-lbs and normalized to subject weight (lbs). Abbreviations: deg, degrees; s, second.

Figure 4.

Change in Normalized Knee Extension Strength at 300 deg/s and HOS-ADL and HOS-S over Time. Torque measured in ft-lbs and normalized to subject weight (lbs). Abbreviations: deg, degrees; s, second.