The Effects of Anterolateral Tenodesis on Tibiofemoral Contact Pressures and Kinematics.

BACKGROUND: Anterolateral tenodeses are increasingly popular in combination with intra-articular anterior cruciate ligament reconstructions. Despite the perception of risk of overconstraint and lateral osteoarthritis, evidence is lacking regarding the effect of graft tensioning on knee kinematics and intra-articular compartmental joint pressures.

PURPOSE: To investigate tibiofemoral joint contact pressures and kinematics related to an anterolateral lesion and the effectiveness of a MacIntosh tenodesis in restoring these when varying (1) graft tension and (2) tibial rotation during graft fixation.

STUDY DESIGN: Controlled laboratory study.

METHODS: Eight fresh-frozen cadaveric knees were tested in a customized rig with femur fixed and tibia free to move from 0° to 90° of flexion. The quadriceps and iliotibial band were loaded by means of a weighted pulley system. At 30° intervals of knee flexion, tibiofemoral contact pressures were measured with a Tekscan sensor and tibiofemoral kinematics were recorded by use of an optical tracking system. The knee was tested intact and then with an anterolateral soft tissue transection. MacIntosh tenodeses were then tested in a randomized order with 20 N or 80 N of graft tension, each with the tibia held in neutral intact alignment or free to rotate.

RESULTS: Tibial anterior translation and internal rotation were significantly increased and lateral contact pressures significantly reduced compared with the intact knee following anterolateral soft tissue cutting ( P < .05). Contact pressures were restored with fixed neutral tibial rotation combined with 20 N or 80 N of graft tension or by a free-hanging tibia with 20 N of graft tension (all P values > .5). Grafts tensioned with 80 N caused significant overconstraint both when the tibia was fixed and free hanging (all P values < .05). Increases in the lateral tibiofemoral contact pressures were also seen when the tibia was free hanging and 80 N was used for graft tension ( P < .05).

CONCLUSION: Anterolateral soft tissue injury caused reduced lateral tibiofemoral contact pressures and altered tibiofemoral kinematics; these were restored with a MacIntosh procedure performed with 20 N of graft tension. If 80 N of graft tension was used, increased lateral contact pressures and overconstraint in internal rotation were seen. With the tibia free hanging, intact contact biomechanics were restored when 20 N of graft tension was applied, but 80 N of graft tension significantly increased lateral tibiofemoral pressures and overconstrained internal rotation. The kinematic and contact pressure effects were significantly correlated: Changes in tibial rotation caused by increased graft tension correlated with elevated lateral articular contact pressure.

CLINICAL RELEVANCE: Controlling tibial position appears important when tensioning anterolateral tenodeses. However, the identified changes were subtle and may not be clinically significant in a fully loaded knee.