Contribution of the Medial Hamstrings to Valgus Stability of the Knee

Background: Multiligament knee injuries involving the medial side are common. When performing surgical reconstruction, use of the medial hamstrings (HS) as grafts remains controversial in this setting. Purpose: To determine the role of the medial HS in stabilizing the valgus knee for different types of medial-sided knee injury. Study Design: Controlled laboratory study. Methods: A biomechanical study on 10 cadaveric knees was performed. Valgus load (force moment of 10 N/m) was applied at 0°, 30°, and 60° of flexion, and the resultant rotation was recorded using an optoelectronic motion analysis system. Measurements were repeated for 4 different knee states: intact knee, superficial medial collateral ligament (sMCL) injury, deep medial collateral ligament (dMCL) injury, and posterior oblique ligament (POL) injury. For each state, 4 loading conditions (+ loaded; – unloaded) of the semitendinosus (ST) and gracilis (GRA) tendons were tested: ST+/GRA+, ST+/GRA–, ST–/GRA+, and ST–/GRA–. Results: At 0° of flexion, combined unloading of the ST and GRA (ST–/GRA–) increased valgus laxity on the intact knee compared with the ST+/GRA+ condition ( P < .05). For all medial-sided injury states (isolated sMCL; combined sMCL and dMCL; and combined sMCL, dMCL, and POL damage), ST–/GRA– increased valgus laxity at 0° and 30° of flexion versus ST+/GRA+ ( P < .05 for all). The absolute value of valgus laxity increased with the severity of medial-sided ligament injury. Isolated ST unloading increased valgus laxity for the intact knee and the MCL-injured knee (combined sMCL and dMCL) at 0° of flexion ( P < .05 vs ST+/GRA+). Isolated unloading of the GRA had no effect on valgus knee stability. Conclusion: The medial HS tendons contributed to the stabilization of the knee in valgus, and this was even more important when the medial side was severely affected (POL damage). This stabilizing effect was greater between 0° and 30°, in which the POL is the main valgus stabilizer. Clinical Relevance: When deciding on graft selection for multiligament knee injury reconstruction, the surgeon should be aware of the effect of harvesting the medial HS tendon on valgus laxity.