Lower Extremity Kinematics in Runners with Patellofemoral Pain during a Prolonged Run.
Dierks TA, Manal KT, Hamill J, Davis I. Med Sci Sports Exerc. 2011 Apr;43(4):693-700.
Over the past few weeks we have had several posts related to the diagnosis and treatment of patellofemoral pain (PFP). A lot of the focus has been on detecting functional weakness in the hip abductors and trying to address this functional strength deficit. A unique aspect of PFP, which we have not addressed on this site, is that runners with PFP typically do not experience pain at the beginning of a run. This raises the question: Is something changing as the patient runs a long distance? The purpose of this study was to evaluate 20 runners with PFP and 20 runners without knee pain to investigate the influence of prolonged running on lower extremity kinematics during the weight-bearing (stance) phase in running. All participants were recreational runners. The running protocol was performed at a self-selected speed and was completed when one of three criteria were met (target hear rate, perceived exertion, knee pain). Overall the PFP runners showed less joint motion (peak knee flexion, peak hip adduction, and eversion) as well as less peak joint velocity (knee flexion, hip adduction, and hip internal rotation) compared to controls (regardless of time). Both groups experienced increases in most kinematic variables at the end of the run compared to the beginning. The two groups did not show different changes over time. During data analysis the authors noticed that some of the PFP runners were using distinct movement patterns. Therefore, the authors created 3 subsets of PFP runners: 1) 7 runners who had a “typical frontal-plane movement pattern” (knee and hip adduction followed by abduction at both joints), 2) 5 runners that exhibited early knee abduction (valgus) as well as decreased peak movements at other joints, and 3) 8 runners that exhibited early hip abduction and less joint motion at other joints. Even the subset with typical frontal-plane movement patterns had increased hip internal rotation and decreased knee internal rotation compared to controls.
Overall the PFP runners showed decreased joint motion including knee flexion. The authors suggest that this may be a protective mechanism against knee pain (less flexion should lead to less compressive forces on the patellofemoral joint). We should be cautious though because it is unclear if the decreased knee flexion is a protective mechanism that runners adapt in response to PFP or if this is a movement pattern that predisposed them to PFP. This becomes especially important when discussing interventions. If this is an adaptation to pain then as we rehabilitate the runner they may return to a movement pattern like the control runners but if the kinematics were what predisposed them to PFP then the therapeutic exercises might not restore “normal kinematics”. In the second case, we need to consider the runner’s experience: for a novice runner we may want to help them establish mechanics similar to a control runner but for an experienced runner we need to consider that if this is their normal mechanics then why did they start to have problems (what’s changed recently?). In regards to selecting therapeutic exercises, the three subgroups warrant further study because of their potential implications. The authors hypothesized that the “valgus” subgroup of runners with PFP may have weak hip abductors. Upon closer evaluation of the “hip abduction” subgroup the authors noticed it was not the femur abducting but the pelvis elevating on the contralateral side (coincidentally males tended to adopt this running pattern) which may suggest hip and trunk (core) weakness. The authors note that the third subgroup, which showed normal frontal plane movements but irregular knee and hip rotations, most likely had weak hip internal rotators. This study raised a lot of interesting questions. What’s your thoughts?
Written by: Jeffrey Driban