Vasti Control of Patellofemoral Kinematics in Patients with chronic Patellofemoral pain

Clinical Center

Investigators

Abstract

The most widely accepted model addressing the source of PF pain is that a force imbalance in the muscles controlling the knee joint leads to static patellofemoral (PF) malalignment and dynamic PF maltracking. In turn, this malalignment and maltracking leads to elevated joint contact stresses, which ultimately leads to PF pain and potentially OA. This model has been substantiated by a recent study that demonstrated a direct correlation between the degree of pain at the PF joint and patellofemoral kinematics. In addition, studies focused on McConnell taping have consistently shown that by adding a medializing force through taping an immediate reduction in pain can be seen. Yet, the source of the force imbalance around the knee is still open to debate with some postulating the cause to be delayed timing in the vastus medialis oblique (VMO) muscle, imbalance in the passive structures, or a loss of strength in the VMO. Numerous studies refute these claims as well. Therefore, the goal of this current protocol is to determine if a temporary immediate medialization of the quadriceps force can reduce excessive lateral shift and tilt in individuals with PF pain and by doing so provide immediate pain relief. This will be accomplished by using bupivacaine to create a short-term, instantaneous loss of function in the VL muscle in patients with PF pain. Bupivacaine is a local anesthetic which is closely related to lidocaine and commonly used for peripheral nerve blocks. Cine-PC (CPC) MR imaging will be the primary measurement tool to assess the PF kinematics pre- and post-block. This is the only non-invasive technique that can accurately (<0.33mm) measure three-dimensional skeletal and muscular motion simultaneously. The two specific primary hypotheses and the secondary hypothesis to be addressed are: 1) A short-term loss of function in the VL in patients with PF pain will result in a reduction in their PF lateral shift and tilt; 2) A short-term loss of function in the VL in patients with PF pain will result in a reduction of pain; and 3) A short-term loss of function in the VL will result in a no change in the maximum isometric extensor strength of the quadriceps muscles. Ultimately, we hope to establish direct links between medialization of the quadriceps force, normalization of knee kinematics, and a reduction in pain. In order to better understand potential confounding variables, this protocol plans to enroll 10 healthy control subjects prior to evaluating individuals with PF pain. To date, five asymptomatic volunteers with no prior history of knee pain, trauma, leg surgery, or contraindications to having an MRI have been enrolled. For all subjects, the PF and tibiofemoral (TF) kinematics will be derived from dynamic cine phase contrast velocity data during the first visit. The subject will then be asked to return within a week for the second segment of the study. For the second visit, the subject's isometric strength and level of pain during various activities will be assessed first. Then, the vasti lateralis block will be performed using 1-5 cc of 0.5% solution of bupivacaine. After it has been confirmed that the block is effective, the subject's strength and level of pain will be reassessed. Following this, cine-phase contrast data will be again collected during a flexion-extension exercise in order to quantify the subject patellofemoral kinematics. A repeated measures analysis of variance (ANOVA) will be used to test the null hypothesis that the post- and pre-injection kinematics were no different across the knee angles of extension. A Kolmogorov-Smirnov test for normality will be run. If the data are normally distributed a repeated measures ANOVA will be run using Hotellings T2 test statistic; if not, the non-parametric Friedman's test statistic will be used. Upon rejection of the null hypothesis a post-hoc analysis (Wilcoxon signed rank test) will be completed to determine at which knee angles the null hypothesis could be rejected. Pearsons correlations between the change in kinematics post-injection and the pre-injection kinematics will quantified at these same knee angles. This will followed by a step-wise linear regression. Significance is set at p less than or equal to 0.05. This project remains in the data collection phase.