Medial collateral ligament reconstruction graft isometry is effected by femoral position more than tibial position

Abstract

Purpose The purpose of this study was to examine the length change patterns of the native medial structures of the knee and determine the effect on graft length change patterns for different tibial and femoral attachment points for previously described medial reconstructions. Methods Eight cadaveric knee specimens were prepared by removing the skin and subcutaneous fat. The sartorius fascia was divided to allow clear identification of the medial ligamentous structures. Knees were then mounted in a custom-made rig and the quadriceps muscle and the iliotibial tract were loaded, using cables and hanging weights. Threads were mounted between tibial and femoral pins positioned in the anterior, middle, and posterior parts of the attachment sites of the native superficial medial collateral ligament (sMCL) and posterior oblique ligament (POL). Pins were also placed at the attachment sites relating to two commonly used medial reconstructions (Bosworth/Lind and LaPrade). Length changes between the tibiofemoral pin combinations were measured using a rotary encoder as the knee was flexed through an arc of 0–120°. Results With knee flexion, the anterior fibres of the sMCL tightened (increased in length 7.4% ± 2.9%) whilst the posterior fibres slackened (decreased in length 8.3% ± 3.1%). All fibre regions of the POL displayed a uniform lengthening of approximately 25% between 0 and 120° knee flexion. The most isometric tibiofemoral combination was between pins placed representing the middle fibres of the sMCL (Length change = 5.4% ± 2.1% with knee flexion). The simulated sMCL reconstruction that produced the least length change was the Lind/Bosworth reconstruction with the tibial attachment at the insertion of the semitendinosus and the femoral attachment in the posterior part of the native sMCL attachment side (5.4 ± 2.2%). This appeared more isometric than using the attachment positions described for the LaPrade reconstruction (10.0 ± 4.8%). Conclusion The complex behaviour of the native MCL could not be imitated by a single point-to-point combination and surgeons should be aware that small changes in the femoral MCL graft attachment position will significantly effect graft length change patterns. Reconstructing the sMCL with a semitendinosus autograft, left attached distally to its tibial insertion, would appear to have a minimal effect on length change compared to detaching it and using the native tibial attachment site. A POL graft must always be tensioned near extension to avoid capturing the knee or graft failure.

Elongation Patterns of the Superficial Medial Collateral Ligament and the Posterior Oblique Ligament: A 3-Dimensional, Weightbearing Computed Tomography Simulation

“…Because of the nearly isometric behavior of the native sMCL center, the computed most isometric point is located in direct proximity posteroinferior to the described anatomical insertion in accordance with previous studies. 21 , 32 While the elongation patterns of the center of the sMCL are in line with previous studies, it is important to consider the reciprocal behavior of tensioning of anterior fibers and slackening of posterior fibers of the MCL during flexion because of the fan-shaped wide anatomical structure. 2 , 21 , 30 However, most commonly performed MCL reconstruction techniques use a single graft strand for the sMCL, 24 , 25 , 33 and therefore guidance to reconstruct the sMCL and preventing lengthening or slackening of the graft strand is of high clinical relevance.…”

“… 21 , 32 While the elongation patterns of the center of the sMCL are in line with previous studies, it is important to consider the reciprocal behavior of tensioning of anterior fibers and slackening of posterior fibers of the MCL during flexion because of the fan-shaped wide anatomical structure. 2 , 21 , 30 However, most commonly performed MCL reconstruction techniques use a single graft strand for the sMCL, 24 , 25 , 33 and therefore guidance to reconstruct the sMCL and preventing lengthening or slackening of the graft strand is of high clinical relevance. The relatively small length changes of the sMCL during flexion support the role as a primary valgus stabilizer throughout the full ROM, whereas the slackening of the POL during flexion suggests that its primary role is to provide additional stability near full extension, as previously described.…”

“…Regarding the POL graft strand, significant shortening occurred during knee flexion from 30° to 120°. As the main function is the constraint of tibial internal rotation near full extension 24 and ligament lengthening of the POL has been described toward knee extension in previous studies, 21 , 24 tightening of the POL graft strand in extension has been proposed. 24 This is supported by our results.…”

“…Despite the inclusion of in vivo tibiofemoral kinematics by analyzing CT under weightbearing load, our findings are similar to those of previous studies that have not considered the weightbearing state. 21 , 32 This is most likely because the main anteroposterior translation as a result of weightbearing occurs at the lateral knee compartment and has only a limited effect on graft lengths at the medial side of the knee.…”

“… 11 , 22 , 29 Although length changes of the native medial ligament complex and also reconstruction techniques have been described investigating the full range of motion (ROM), 21 , 32 we are only aware of 1 study investigating ligament elongation under in vivo weightbearing conditions. 18 Previous studies either have not considered the weightbearing state 21 , 32 or have not reported quantitative radiographic landmarks that allow the clear identification of the insertion sites that demonstrate the smallest length changes during flexion. 18 However, the axial rotation of the native knee joint during flexion under weightbearing load might influence ligament elongation patterns and therefore should be accounted for.…”