Patellofemoral pain (aka EMM, patellar chondromalacia, PFPS, anterior knee pain, etc) is a common diagnosis that I see in the clinic. The problem is, we are not exactly sure what causes it (or if there or many causes) and what is best for remedying it (strengthening, stretching, neuromuscular re-education, bracing, even spinal mobilizations). In the past, PFP was attributed to lateral patellar tracking caused by poor VMO strength/activation and tight lateral structures such as the IT Band. While it is still commonly believed that PFP is from excessive lateral patellar tracking, it is thought that this is caused by poor lower extremity pronation/valgus control by the hip musculature. Specifically the hip abductors and external rotators. This has been preliminarily supported by research that shows, in weight bearing, in those with PFP the femur tends to internally rotate under the patella rather the the patella being pulled laterally (Salsich, GB - JOSPT Sept 2007).
The following article done by Lori Bolgla, PT, PhD, ATC et al looked at hip strength and lower extremity kinematics in those with PFP vs. those with out. Here is the abstract:
Hip Strength and Hip and Knee Kinematics During Stair Descent in Females With and Without Patellofemoral Pain Syndrome
STUDY DESIGN: Cross-sectional. OBJECTIVE: To determine if females presenting with patellofemoral pain syndrome (PFPS) from no discernable cause other than overuse demonstrate hip weakness and increased hip internal rotation, hip adduction, and knee valgus during stair descent. BACKGROUND: Historically, PFPS has been viewed exclusively as a knee problem. Recent findings have indicated an association between hip weakness and PFPS. Researchers have hypothesized that patients who demonstrate hip weakness would exhibit increased hip internal rotation, hip adduction, and knee valgus during functional activities. To date, researchers have not simultaneously examined hip and knee strength and kinematics in subjects with PFPS to make this determination. METHODS AND MEASURES: Eighteen females diagnosed with PFPS and 18 matched controls participated. Strength measures were taken for the hip external rotators and hip abductors. Hip and knee kinematics were collected as subjects completed a standardized stair-stepping task. Independent t tests were used to determine between-group differences in strength and kinematics during stair descent. RESULTS: Subjects with PFPS generated 24% less hip external rotator (P = .002) and 26% less hip abductor (P =. 006) torque. No between-group differences (P > .05) were found for average hip and knee transverse and frontal plane angles during stair descent. CONCLUSION: Subjects with PFPS had significant hip weakness but did not demonstrate altered hip and knee kinematics as previously theorized. Additional investigations are needed to better understand the association between hip weakness and PFPS etiology. LEVEL OF EVIDENCE: Symptom Prevalence, Level 4.
J Orthop Sports Phys Ther. 2008;38(1):12-18, published online 21 November 2007, doi:10.2519/jospt.2008.2462
I commend the authors for doing this study. Treatment in the clinic is dependent on clinical theories and basic science being "put to the test" in RTC with actual patients. It is important to note that hip muscle weakness was found in the symptomatic group; however, significantly altered lower extremity mechanics were not. An admitted limitation is that they only looked at stair stepping (a common pain provoking activity with those with PFP) and this specific activity may not have been challenging enough.
I treat most of my patients with PFP using hip strengthening, lower extremity stretching, and proprioceptive exercises in general. But this study reminds us that we were wrong before about the cause of PFP and most certainly could be wrong about the hip weakness leading to increased pronation/valgus theory most of us currently abide by.