Anterior knee pain, also known as patellofemoral pain syndrome, is characterized by knee pain around the patella and patella tendon. It’s quite common in females, and has been associated with muscle imbalances at the hip. Recently, researchers found inadequate control of weight-bearing activities, reporting increased femoral adduction and internal rotation, which may affect patellar movement (Magalhaes et al. 2010). Brazilian researchers examined 50 sedentary females with patellofemoral pain syndrome and compared their hip strength to 50 control subjects without knee pain. They used a handheld dynamometer (Nicholas, Lafayette Instrument Co) to quantify the strength of 6 major hip muscles on both the right and left sides. Their results were published in the Journal of Orthopedic and Sports Physical Therapy.
They found that sedentary females with unilateral anterior knee pain had 15 to 20% less strength in hip extension, external rotation, abduction and flexion, compared to a control group. Females with bilateral pain had weakness in all 6 hip muscles, ranging from 12 to 30% deficits. Subjects with anterior knee pain had 20% less hip abduction strength compared to the uninjured side. This was the first study to demonstrate weakness in sedentary females; most other studies have been completed on female athletes.
This study had a few minor limitations. The examiner was not blinded to the control or experimental group. This study was also retrospective, leaving us unable to determine cause-and-effect. More studies are needed to determine if hip weakness is a cause or result of patellofemoral pain syndrome. Furthermore, this study did not investigate the effects of a strengthening program.
This study supports Dr. Janda’s classification of muscle weakness, noting decreased strength of phasic extension, abduction, and external rotation. It also noted weakness of hip flexors and remaining muscles in females with bilateral knee pain. Janda noted that flexion, internal rotation, and adduction were tonic motions, prone to tightness. This study did not assess muscle length; however, it’s possible that the muscle weakness may be related to short muscle length-tension. Exercises including hip extension may be effective at improving anterior knee pain in females.
REFERENCE: Magalhães E, Fukuda TY, Sacramento SN, Forgas A, Cohen M, Abdalla RJ. A comparison of hip strength between sedentary females with and without patellofemoral pain syndrome.J Orthop Sports Phys Ther. 2010 Oct;40(10):641-7.
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