29 – THE ROLE OF HEMARTHROSIS IN JOINT CONTRACTURES

Purpose: The presence of hemarthrosis during joint injury is a potential inciting stimulus in the genesis of joint capsule fibrosis. Using a rabbit model of posttraumatic knee joint contracture, our hypothesis was that, bone marrow-derived elements of hemarthrosis rather than simply the presence of blood in the joint, trigger the induction of capsule fibrosis in post-traumatic joint contracture. Method: 35 Skeletally mature New Zealand White female rabbits (12–18 months old, 5.5 ± 0.5 kg) were randomly assigned to one of five groups: Immobilization-Only (IMO), Immobilization+ Bone Marrow (IMBM), Immobilization+ Peripheral Blood (IMPB), Bone Marrow-Only (BMO), and Controls. Surgeries: Immobilization groups had one knee joint fixed at full flexion with a Kirschner wire drilled through the tibia, passed posterior (extra-articular) to the knee joint and bent around the femur. Bone marrow groups had cortical windows removed from the non-articular cartilage portion of the medial and lateral femoral condyles. In the IMPB group, autologous peripheral venous blood was injected into the immobilized knee joint to recreate a non-traumatic hemarthrosis. The control group did not have any intervention. Joint angle measurements: After 8 weeks, rabbits were euthanized, all muscular tissue was removed and maximum extension angle of the joints with intact capsule was measured using a standard torque applied via a custom made rabbit knee gripping device attached to a MTS TestStar II. Each joint was cycled 5 times (0.2 Nm) and the average of 5 cycles was calculated. Statistical analysis consisted of a one-way ANOVA with posthoc Scheffe test (significance p < 0.05). Data are presented as mean +/ − standard deviation. Results: The IMBM (n=8) and IMPB (n=7) groups had significantly greater contractures (52 +/ − 12 and 58 +/ − 13 degrees, respectively) when compared to the BMO (n=7) and control (n=6) groups (32 +/ − 10 and 32 +/ − 13 degrees, respectively). The IMO group had average contracture measures of 44 +/ − 15 degrees. There was no statistically significant difference between the IMBM and IMPB groups. Conclusion: The present study showed differences in the contracture severity of the immobilized knees associated with hemarthrosis compared to other experimental and control groups. There does not appear to be a difference whether the hemarthrosis arose from a fracture (bone marrow) versus peripheral blood in rabbits. Future work will look at reversibility of contractures in the various groups. Studies on the joint capsule will evaluate myofibroblast numbers in concert with mast cell and neuropeptide distribution based on our previous work. Such knowledge will aid the prevention and treatment of the difficult and disabling problem of contracture formation after joint injury.