The Deep Medial Collateral Ligament: Part 2, Structural Properties and Failure Characteristics

BACKGROUND: The deep medial collateral ligament (dMCL) has traditionally been described as a capsular thickening deep to the superficial medial collateral ligament; however, recent investigations suggest a more extensive anteromedial course with a more important role in knee stability. Despite this, its structural properties and failure characteristics are not well described. PURPOSE: To quantify the structural properties of the dMCL, including load to failure, stiffness, displacement, and failure location. STUDY DESIGN: Descriptive laboratory study. METHODS: ) were dissected to isolate the dMCL while preserving its meniscofemoral and meniscotibial attachments. Specimens were mounted in a 6 degrees of freedom robotic system and subjected to preconditioning and then uniaxial load-to-failure testing. Load, displacement, stiffness, and failure location were recorded. RESULTS: The mean load to failure of the dMCL was 242.9 ± 86.6 N, with a mean stiffness of 25.3 ± 14.3 N/mm and a median displacement at failure of 12.4 mm (range, 8.9-31.8 mm). Failure occurred predominantly within the meniscotibial portion (9/10 specimens), with only 1 failure in the meniscofemoral portion, and none of the specimens failed at the femoral or tibial osseous attachments. CONCLUSION: When the expanded anteromedial course of the dMCL is included, its measured load to failure was higher than values previously reported using more restricted anatomic definitions. Failure occurred predominantly within the meniscotibial portion. These findings characterize the isolated structural properties and predominant failure pattern of the dMCL and may provide reference data for future biomechanical evaluation of medial knee reconstruction techniques. CLINICAL RELEVANCE: Quantification of the structural properties of the dMCL provides a biomechanical basis for surgical reconstruction and fixation strategies. These data may assist in graft selection and fixation strength requirements in anatomic medial knee reconstructions, particularly in patients with anteromedial rotatory instability.