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.