Purpose: To determine the displacement forces across a lateral meniscal tear during motion.
Type of study: Experimental laboratory biomechanical study.
Methods: A middle third longitudinal lateral meniscal cut was created arthroscopically at the "red-white" junction in 5 intact porcine knees. With a pressure transducer in the tear, the knees were repeatedly cycled through a full range of motion. Pressure data were gathered with the knees held at neutral, internal rotation (IRot), and external rotation (ERot) and matched to the specific flexion angle measured by electronic goniometer. Averaged pressure measurements were calculated at each 5 degrees interval.
Results: The highest pressures were seen at full extension (neutral, 589 mm Hg; IRot, 1,110 mm Hg; ERot, 337 mm Hg) and declined to a low at 90 degrees of flexion (neutral, 133 mm Hg; IRot, 314 mm Hg; ERot, 187 mm Hg). Then the pressures increased steadily after 100 degrees as the knees were further flexed. The highest pressure was always seen with IRot. IRot during flexion resulted in higher lateral meniscus compressive loads than ERot.
Conclusions: This model demonstrated that a middle third longitudinal lateral meniscal cut is compressed throughout the full range of knee motion. At no time were negative intrameniscal tear pressures registered that would suggest meniscal cut separation.
Clinical relevance: These data suggest that meniscal compressive loads, not distractive loads, occur throughout knee flexion and extension. The absence of distractive loads across a meniscal cut suggests that the ability of a repair to align the meniscal fragment may be more important than a high load to failure strength.