Summary

Controlling tibial position during graft fixation is essential to avoid increases in lateral compartment pressures according an investigation of tibiofemoral joint kinematics and lateral compartment pressures following a MacIntosh lateral tenodesis.

Abstract

Background

Anterolateral Complex (ALC) injuries may occur at the time of Anterior Cruciate Ligament (ACL) tear. This provides a rationale for combining anterolateral procedures with the intra-articular ACL reconstruction. Despite the perceived risk of lateral osteoarthritis in these procedures, evidence is lacking regarding the effect of graft tensioning and position of tibial rotation during graft fixation on compartmental joint pressures. The aims were to investigate (1) tibiofemoral joint (TFJ) contact pressures and kinematics with an ALC lesion and (2) their restoration by a MacIntosh tenodesis when varying graft tension and tibial rotation during graft fixation.

Methods

Eight fresh-frozen cadaveric knees were placed on a testing rig, where the femur was fixed but the tibia could move freely from 0-90° flexion. Individual quadriceps heads and the iliotibial band were separated and loaded with 205N using a weighted pulley system. Tibiofemoral contact pressures were measured using a Tekscan pressure sensor inserted proximal to the patella and deep to the quadriceps, which did not alter knee kinematics. The sensor was guided into the TFJ arthroscopically, and sutured into position to prevent movements during testing. Measurements were taken at 0°, 30°, 60° and 90°, and tibial kinematics were measured simultaneously using an Optical Tracking System.

The ACL was left intact to represent a ‘perfect’ reconstruction. The knee was tested intact, then with ALC transection. Four tenodesis protocols were tested in a randomised order: 20N and 80N graft tension each with the tibia held in its neutral intact alignment and also with the tibia free to rotate. During graft fixation 10N and 2N loads were applied to the central quadriceps and ITB respectively to simulate the tension in an anesthetised leg. Full loading was then applied throughout testing. Statistical analysis used a repeated-measures ANOVA, Bonferroni post hoc analysis and paired t-tests.

Results

Tibial anterior translation and internal rotation were significantly increased and lateral contact pressures significantly reduced compared to the intact knee following anterolateral soft tissue cutting (P<0.05). These were restored with fixed neutral tibial rotation combined with a 20N or 80N graft tension or by a free hanging tibia tensioned with 20N (All: P>0.5). However grafts tensioned with 80N whilst the tibia was free hanging resulted in significant increases in lateral TFJ pressures and reduced tibial internal rotation (P<0.05).

Conclusions

Injury to the ALC reduced lateral TFJ contact pressures, (presumed due to distraction by gravity after cutting the soft tissue) and increased anterior translation and internal tibial rotation; these were restored with both 20N and 80N graft tensions when the tibial rotation was held in neutral during graft fixation. With the tibia free to rotate externally intact contact biomechanics were restored when 20N graft tension was applied, but 80N graft tension pulled the tibia into external rotation, resulting in a significant increase in lateral TFJ pressures and overconstraint of internal rotation. Controlling tibial position appears to be important during anterolateral tenodeses. However, note that although consistent, the identified changes were subtle and may not be clinically significant in a fully-loaded knee.