MCL internal brace does not fully recapitulate normal MCL function in valgus stress.

purposeThe null hypothesis is that there would be no difference in medial gapping under valgus load between the intact MCL and the ruptured MCL with an internal brace in place.

methodsEight pairs of cadaver knees were used (16 knees). Alternating sides, one knee from each pair was used for one of two "internal brace" constructs. The constructs involved different methods of fixation for securing FiberTape (Arthrex, Naples, FL) to both the femur and tibia in an effort to brace the MCL. The knees were then subjected to valgus stress by applying 10 N m of torque with the knee at 20 degrees of flexion. The amount of medial joint space opening was measured on radiographs. The stress testing was conducted with three MCL states: intact, grade 2 tear, and grade 3 tear.

resultsIn the Construct I specimens, gapping increased from 0.7 mm with the MCL intact to 1.1 mm with grade 2 tearing (p < 0.01), and to 1.3 mm with grade 3 tearing (p < 0.01). In the Construct II specimens, gapping increased from 0.7 mm with the MCL intact to 1.0 mm with grade 2 tearing (p < 0.01), and to 1.1 mm with grade 3 tearing (n.s.). Construct I specimens failed primarily at the femoral attachment. All Construct II specimens survived the valgus stress testing.

conclusionConstruct I did not maintain tension. Construct II did maintain tension during application of valgus load, but did not restore valgus opening to the intact state. It is important for clinicians who are considering using this commercially available technique to be aware of how the construct performs under valgus stress testing compared to the intact MCL.