Factors Associated with Patellofemoral Pain Syndrome; A Systematic Review
Lankhorst NE, Bierma-Zeinstra SM, van Middelkoop M. Br J Sports Med. 2012 Jul 19. [Epub ahead of print]
Patellofemoral pain syndrome (PFPS) is a very common diagnosis, making up about 25% of all running injuries. It can also be a very frustrating diagnosis for both patients and clinicians. Whereas short-term treatments can be successful in alleviating symptoms, long-term results are variable, and there is no definitive operative management for PFPS. Several studies have examined risk factors for the development of PFPS with the goal of directing treatments at modifiable factors. The purpose of this comprehensive, systematic review was to summarize which risk factors have been associated with PFPS. The authors used several online research databases to identify case-control or cross-sectional studies including a minimum of 20 patients with PFPS that examined at least 1 possible risk factor for PFPS. The search yielded 4,664 potentially relevant articles, of which a meta-analysis was performed on 47 studies, which examined 523 variables. The authors were able to combine data from multiple studies for 8 factors - which is one benefit of performing a meta-analysis. Six of the eight factors were associated with PFPS. Three anatomic risk factors were associated with PFPS including a larger Q-angle, a larger sulcus angle, and a larger patellar tilt angle. In addition, there were three muscle imbalances which were associated with PFPS including less hip abduction strength, lower knee extension peak torque, and less hip external rotation strength in PFPS patients compared with controls. The authors also evaluated foot arch height index and patellar congruence angle but these were not associated with PFPS after the meta-analysis.
This study is important because it uses the strength of a meta-analysis to examine factors associated with PFPS. However, it is important to note that, because of the case-control and cross-sectional nature of the studies included, conclusions cannot be made about whether the risk factors are causative. Biomechanical risk factors, as the authors’ point out, are subject to measurement error. In particular, there is an ongoing debate regarding how Q-angle should be measured. And, although biomechanical factors are thought to be associated with PFPS, surgical correction with patellofemoral realignment techniques has not been found to reliably treat PFPS symptoms. Several physical therapy techniques have been focused on the muscle imbalances which are associated with PFPS and are the cornerstone of current PFPS treatment. A good therapy program focused on increasing vastus medialis (VMO) strength and addressing hip abductor and external rotator weakness may help treat PFPS. However, more research is needed to determine if the muscle weakness is a cause or effect of PFPS. The authors suggest that since females are more commonly affected by PFPS, then this might explain the findings of decreased muscle strength in general depending on how the studies were completed. In addition, if patients with PFPS stop exercising secondary to the PFPS symptoms, then this may also explain decreased strength compared with controls. Another potential limitation of this study is that PFPS does not have clear diagnostic criteria and there may be subtle differences in factors associated with PFPS compared with interchangeable diagnoses that may have been included in the studies such as patellar chondromalacia, patellar tendonosis, and quadriceps tendonosis. Despite these important limitations, the data from this study may be used to further our understanding of PFPS and identifies some modifiable factors which may improve treatment. What has your experience with PFPS been? Do you find PFPS affects a certain “type” of patient? Have you found effective treatments?
Written By: Hallie Labrador, MD MS
Reviewed by: Jeffrey Driban
Related Posts:Lankhorst NE, Bierma-Zeinstra SM, & van Middelkoop M (2012). Factors associated with patellofemoral pain syndrome: a systematic review. British Journal of Sports Medicine PMID: 22815424