Houston Methodist. Leading Medicine

Knee News

Hip Weakness Linked to Patellofemoral Pain Syndrome

Patellofemoral pain syndrome (PFPS) is a common cause of knee pain in athletes. Active teens and adults are affected most often. The exact cause of this problem remains under investigation.

Studies have linked hip muscle weakness with PFPS. Weakness of the hip abductor and hip external rotator muscles may be one cause of PFPS. When there's weakness of these muscles, then there's too much hip adduction (movement toward the midline) and internal rotation. These motions put increased stress on the patellofemoral joint.

A recent study by a group of physical therapists showed that the Q-angle of the knee in patients with PFPS is increased during dynamic movements. The Q-angle is a measure of the angle between the femur (thigh) and the tibia (lower leg). An increased Q-angle means there is an increased lateral pull (sideways away from the knee) of the quadriceps (thigh) muscle.

In this study, changes in knee alignment during movement were measured and compared between two groups of women. One group had a known PFPS knee problem. But there was no known cause except overuse. The second (control) group did not have any known knee pain or problems.

Pain levels and hip strength were measured and recorded. Motion analysis was done using a video-based motion capture system. This system allows for measurement of hip and knee joint angles, muscle strength, and analysis of kinematics. Kinematic studies show how the position of the joints changes with time.

The women walked down two 20-cm-high steps. Everyone walked at the same rate by using a metronome set at 96 beats per minute. Five practice trials were allowed. Then 10 test trials were performed. The stair-stepping task was chosen because it is a common activity that brings on pain with PFPS.

The results of this study did not support the idea that hip weakness alters leg kinematics resulting in PFPS. At least not while going down stairs at the 96-beats per minute pace.

The women with PFPS did have lower hip muscle strength compared to the control group. So there may be something else going on to explain these findings. It's not clear if the hip weakness in patients with PFPS is the cause or the result of this condition. The authors suggest further studies to help identify other factors at play.

Lori A. Bolgla, PT, PhD, ATC, et al. Hip Strength and Hip and Knee Kinematics During Stair Descent in Females With and Without Patellofemoral Pain syndrome. In Journal of Orthopaedic & Sports Physical Therapy. January 2008. Vol. 38. No. 1. Pp. 12-18.


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