Isolated Hip Exercise Reduces Anterior Knee Pain

Anterior knee pain is often associated with hip muscle weakness of the abductors, extensors and external rotators. Dr. Vladimir Janda noted these muscles were particularly susceptible to inhibition and weakness. Patellofemoral pain is often associated with muscle imbalance. Hip weakness is particularly prevalent in females with anterior knee pain.

This hip weakness is thought to result in abnormal forces occurring at the knee during stance, allowing the femur to adduct more than normal, possibly leading to excessive force and/or abnormal tracking of the patellofemoral joint.

Traditionally, anterior knee pain was thought to result from quadriceps weakness, particularly from the vastus medialis muscle. Recent biomechanical and epidemiological data suggest however, that hip weakness may play a more important role in the etiology of patellofemoral pain.

Dr. Khalil Khayambashi and colleagues performed a randomized controlled trial of hip exercise on females with patellofemoral pain. The experimental exercise group performed hip strengthening exercises 3 times a day for 8 weeks. Hip extension and external rotation exercises were performed on both legs using Thera-Band® elastic tubing.

The control group did not exercise. Both groups were tested before and after the program for hip strength, pain, and self-report WOMAC scores. There were 14 participants in each group, and no significant differences at baseline between groups.

After the 8 week intervention, the hip exercise group significantly decreased in knee pain and significantly improved their health status, whereas the control group did not improve. In addition, the exercise group improved in hip strength significantly more than the control group, between 32 and 56%. These improvements were maintained at the 6 month follow-up as well.

While these results are impressive given the simplicity of the exercise program, the study had a few limitations. Subjects were not categorized as having hip weakness before the program; it would be interesting to know if their knee pain was actually associated with hip weakness. The researchers didn’t evaluate kinematics in subjects; therefore, it’s not clear if the strengthening program had a biomechanical effect. Finally, the relatively small sample size limits the generalizability of the findings.

In summary, a simple 8 week Thera-Band exercise program with only 2 hip exercises significantly reduces pain in females with anterior knee pain.

REFERENCE: Khayambashi K, et al.The Effects of Isolated Hip Abductor and External Rotator Muscle Strengthening on Pain, Health Status, and Hip Strength in Females With Patellofemoral Pain.J Orthop Sports Phys Ther. 2012. 42(1):22-29.

Hip weakness again associated with anterior knee pain

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.

by Dr. Phil on January 24, 2011