Defining Muscular Weakness and Gait Alterations in Chronic Patelleofemoral Instability

Background: Patellar instability is a common, yet understudied condition that affects primarily younger active individuals. A diagnosis of patellar instability earlier in life is considered a significant risk factor for the development of patellofemoral osteoarthritis. Unlike those with patellofemoral pain, the gait and strength deficits in this cohort of patients have not been studied. Defining the impairments that make up specific cohorts of those with patellofemoral pain is essential to the development of effective evidence based interventions. We anticipate that those with patellar instability will have a similar pattern of gait and strength reductions as seen in those with patellofemoral pain. Specifically, we expect that those with patellar instability will have greater hip adduction, hip internal rotation, knee external rotation, knee joint stiffness during walking, as well as decreased quadriceps and gluteal muscle strength as compared to a healthy control group. Moreover, we expect the pattern of gait and strength reductions to be similar to those who have patellofemoral pain without instability. Purpose: The purpose of this study is to determine the gait and strength deficits between those with chronic patellofemoral instability, healthy control subjects, and those with patellofemoral pain and no instability. Design: Cross sectional. Methods: 60 subjects (20 with patllofemoral instability, 20 with patellofemoral pain, and 20 healthy control subjects) will be recruited for this study. To qualify subjects in the patellofemoral instability group must meet speci'fic clinical and radiographic criteria. Subjects will initially have retroreflective markers placed on their trunk, and lower extremities. The markers will be tracked with a 3D motion capture system while the subject walks on a instrumented treadmill at 1.5 m\s. Joint angles and forces will then be calculated. We will also record the subjects eccentric and concentric muscle strength on a dynamometer at a speed of 600s. Statistics: Differences in gait mechanics and strength between groups will be assessed with an ANOVA. A linear mixed model may also be used taking into potential covariates such as 8MI, gender, and leg dominance. Significance: The results from this study will provide the field with some of the first evidence if a unique pattern of weakness and gait exists within a sub-population of those with patellofemoral pain. Furthermore, these results will direct future studies developing interventions that specifically target these impairments. If the pattern of weakness and gait deviations are similar between those with patellofemoral pain irregardless of instability, then future studies will explore the possibility of the effects of subtle instability in the larger population of those with patellofemoral pain. In addition, a similar pattern would suggest that rehabilitation techniques used in those with patellofemoral pain maybe effective for those with patellar instability. Ultimately, this may help reduce the risk for future joint degeneration, disability, and chronic pain in this population