Hamstrings loading contributes to lateral patellofemoral malalignment and elevated cartilage pressures: An in vitro study.

Elias JJ, Kirkpatrick MS, Saranathan A, Mani S, Smith LG, Tanaka MJ. Clin Biomech (Bristol, Avon). 2011 May 2. [Epub ahead of print]

Patellofemoral syndrome is an injury that continually plagues athletes of all shapes and sizes. It is a very challenging condition to treat and reoccurrences are almost inevitable. We have had several posts (see below links) related to this condition that mainly discussed focused rehabilitation at the hip. Hamstring loading has also been thought to contribute to patellofemoral syndrome by causing posterior tibial translation and external rotation, which will cause patellar malalignment and increase contact pressures. However, this has never been scientifically evaluated. Therefore, this study used 10 cadaver knees to examine patellar alignment and contact pressures with and without hamstring loading. Cadaver knees were tested in 3 knee flexion positions (40°, 60°, and 80°) with the quadriceps loaded to 586 N and the hamstring either not loaded or loaded to 200 N. Patellar motion was measured (patellar flexion, lateral rotation, lateral tilt, and lateral translation) using a magnetic sensor system. Contact pressures were measured using thin film pressure sensors between the femur and patella. They found that with hamstrings loading the patella had an increase in patellar flexion, lateral tilt, and lateral shift. These altered kinematics caused increases in total contact force applied to the lateral cartilage.

This study evaluated another mechanism that can contribute to patellofemoral syndrome (as if there weren’t enough!). Hamstrings loading can manipulate the tibia during knee flexion which will alter both the kinematics and the joint forces. This can lead to significant pain and if left untreated it can cause cartilage injury. Hamstrings loading can be caused by two mechanisms; 1) hamstrings tightness and 2) altered hamstring neuromuscular control. Hamstring tightness is something we commonly treat to minimize hamstring strains, but now suggests that it may contribute to patellofemoral syndrome. This is further reason for focusing on hamstring flexibility with both injury prevention and rehabilitation. Altered hamstring neuromuscular control can occur and has been identified in patients after ACL tears and reconstructions, along with other lower extremity injuries. Clinically it is difficult to determine if an athlete has altered neuromuscular control without EMG analysis. However, it may be beneficial when rehabilitating a patient with patellofemoral syndrome to focus on both open and closed chain exercises that minimize hamstrings activity. This continues to reiterate the importance of quadriceps activation and strength, both at the knee and the hip, when treating patellofemoral syndrome. What are your thoughts on hamstrings loading and patellofemoral syndrome? Is this something that you commonly consider?

Written by: Stephen Thomas
Reviewed by: Joseph Zeni, Jr.

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