Summary

During dynamic activity, the addition of LET to ACLR may affect the cartilage contact location in the early post-operation phase, but this effect is lost in the longer term, which suggests that healing and neuromuscular adaptation diminish the effect of LET over time.

Abstract

Purpose

The aim of this study was to investigate the effect of lateral extra-articular tenodesis (LET) in combination with ACLR (ACLR+LET) on in vivo cartilage contact kinematics compared to isolated ACLR (ACLR) during downhill running. It was hypothesized that cartilage contact area in the lateral compartment would be larger in ACLR+LET compared with ACLR, and that the anterior-posterior (AP) location of the center of the cartilage contact on the lateral tibia would be more anterior after ACLR+LET than after ACLR.

Methods

Twenty patients with rotary laxity, determined by PIVOT technology and inertial sensor, were randomly assigned into ACLR+LET or ACLR during surgery. At 6 months and 12 months after surgery, participants were imaged during downhill running (2.0m/s, 10 degree slope) on an instrumented treadmill using dynamic biplane radiography. A validated volumetric model-based tracking technique was used to match digitally reconstructed radiographs (created from subject-specific CT scans) to the biplane radiographs to track femur and tibia motion with accuracy better than 1° and 1 mm. Patient-specific cartilage models, obtained from 3T MRI, were registered to tracked bone models. Cartilage contact area in the medial and lateral compartments was calculated from the outline of overlapping areas of femoral and tibial cartilage models and normalized to the total tibial cartilage area in the corresponding compartment. The center of cartilage contact on the tibia in both the medial and lateral compartment was calculated in the AP and medial-lateral (ML) directions. At each 10% increment of the gait cycle from 0% (foot-strike) to 40% (toe off), the side-to-side differences (SSD) ([Operated knee] – [Contralateral healthy knee]) of the cartilage contact area and center of cartilage contact location were compared between groups using a Mann-Whitney U test.

Results

Eighteen participants (9 ACLR+LET, 9 ACLR) completed the testing at 6 months and 16 participants (8 ACLR+LET, 8 ACLR) completed the testing at 12 months. There were no significant SSD in cartilage contact area on the tibia between groups at 6 months and 12 months after surgery in either the medial or lateral compartment. The SSD in the AP location of the center of cartilage contact of the lateral compartment was larger in the ACLR+LET group than in the ACLR group at 10% (3.9±2.6 mm vs.1.2±1.6 mm, p <0.01 ) and 20% (4.4±3.1 mm vs. 1.5±2.0 mm, p <0.05 ) of gait cycle at 6 months, however, no significant SSD were observed at 12 months. There were no differences between groups in the SSD of the center of contact at 6 months and 12 months in the medial compartment. There were no differences in the SSD of the ML location of the center of cartilage contact between groups at 6 months and 12 months after surgery in either the medial or lateral compartment.

Conclusion

LET in combination with ACLR may affect the cartilage contact location during downhill running in the early post-operation phase, but this effect is lost in the longer term. This suggests that healing and neuromuscular adaptation occur and may diminish the effect of LET over time.