BACKGROUND AND PURPOSE: Patellar instability can be a source of pain and functional disability. Aspects of patellar dislocations explored in the literature include demographics, radiographic findings, physical features, and quadriceps and hamstring strength. A lack of information exists on muscular strength as a predisposing factor for recurrent patellar dislocations. The aim of this study was to determine the influence of hip strength and core endurance on recurrent patellar dislocations. It was hypothesized that decreased hip strength and core endurance would be associated with this injury.
METHODS: In this case control study, cases with recurrent patellar dislocation at a rehabilitation clinic were all offered the chance to participate. Healthy controls without any current knee injuries or previous surgeries were matched by sex and age. Participants provided anthropometric and demographic data and filled out the International Physical Activity Questionnaire, KOOS Knee Survey, Kujala Knee Pain Scale, and a patellofemoral instability form. Cases underwent a patellofemoral exam and joint testing protocol. Both groups completed the forward step down test, strength of hip external rotation and abduction using a dynamometer, and bilateral side plank endurance. Recordings of the forward step down test were reviewed by six researchers to determine inter-rater reliability.
RESULTS: Side plank endurance and hip external rotation strength were significantly decreased in the cases compared to the controls. There was no statistical difference for hip abduction strength between the two groups. Moderate to good inter-rater reliability was found for the forward step down test.
CONCLUSIONS: Weak hip external rotators and core endurance could lead to an increased risk for patellar dislocations. While hip abduction strength was not statistically significant between cases and controls, it was 4% less in the case group. The gluteus medius is active during side plank exercise and may contribute to significant results observed in core endurance testing. The forward step down test could be used to assess dynamic weakness in hip abductors and external rotators across providers based on reliability findings. This pilot study was the first to investigate hip strength and core endurance as a risk factor for recurrent patellar dislocations and further research is needed to confirm findings
