Reduced anterior tibial translation associated with adaptive changes in the anterior cruciate ligament-deficient joint: goat model.

Adaptive changes in the menisci and adjacent posterior capsule were documented within anterior cruciate ligament-deficient knee (stifle) joints in the goat model. These physical changes in the menisci and capsule developed over time and were associated with reduction in the initial (time zero) abnormal anterior tibial translation following transection of the anterior cruciate ligament. At 50 N of applied force, the normal goat knee joint has a total anterior-posterior translation of 0.6+/-0.1 mm (+/- SEM) at 45 degrees of flexion and 0.3+/-0.1 mm at 90 degrees. The translation immediately after transection (time zero) with 50 N of force was 8.2+/-0.5 mm at 45 degrees and 4.9+/-0.9 mm at 90 degrees. Within 8 months after transection and at 50 N of force, the treated knees had reduced translation values of 5.3+/-0.6 mm at 45 degrees of flexion and 2.9+/-0.5 mm at 90 degrees, or 35 (p<0.001) and 40% reductions, respectively, compared with the values at time zero. Magnetic resonance images of the ligament-deficient stifle joints, as well as gross measurements and image analysis after dissection, consistently demonstrated increases in cross-sectional area and volume of the menisci compared with the contralateral controls. These secondary changes were most pronounced in the posterior portion of the medial menisci, and histologic evaluation demonstrated hypercellularity with the accumulation of poorly organized collagen, reduced safranin O staining (proteoglycan matrix synthesis), a thickened capsule and capsule attachment, and increased vascularity at the meniscal capsule interface.