Variations in medial-lateral hamstring force and force ratio influence tibiofemoral kinematics

Area of Science:

• Biomechanics
• Orthopaedic Research
• Kinesiology

Background:

• Hamstring strength and activation changes are common after knee injuries and surgeries like anterior cruciate reconstruction or total knee replacement.
• Previous research has focused on isometric hamstring loading, with limited understanding of how medial-lateral force ratios affect knee kinematics.

Purpose of the Study:

• To quantify changes in knee joint kinematics resulting from variations in the medial to lateral hamstring force ratio during an open-chain deep knee bend.
• To investigate the impact of altered hamstring loading on tibiofemoral translation, axial rotation, and quadriceps load.

Main Methods:

• Eight cadaveric knees underwent deep knee bends under six loading conditions, including unloaded and five configurations varying medial (semimembranosus) to lateral (biceps femoris) hamstring force ratios (total 175 N).
• Measurements included anterior-posterior translation of femoral condyles, tibial axial rotation, and quadriceps load at various flexion angles.

Main Results:

• Unloading hamstrings led to posterior femoral condyle translation and increased tibial internal rotation.
• Higher lateral hamstring force resulted in greater posterior medial condyle translation, anterior lateral condyle translation, and external tibial rotation.
• Increasing medial hamstring force ratio caused anterior medial condyle shift, posterior lateral condyle shift, and increased tibial internal rotation.

Conclusions:

• Variations in medial-lateral hamstring force ratios significantly influence tibiofemoral transverse plane kinematics (rotation and translation).
• Altered hamstring force distribution impacts the quadriceps load required for knee extension, particularly at deeper flexion angles.