gms | German Medical Science

Objectives: Combined slope reduction and anterior cruciate ligament reconstruction has become established in the context of primary reconstruction and revision surgery with promising results. However, it remains unclear whether an anterior slope-modifying osteotomy affects the length change pattern and isometry behavior of the medial ligamentous structures.

The aim of this study was to examine the length change pattern of the medial collateral ligament complex following an anterior slope-modifying osteotomy. It was hypothesized that (1) an slope decreasing (increasing) osteotomy slackens (tightens) the fibers of the superficial medial collateral ligament (sMCL) and (2) that the fibers of the posterior oblique ligament (POL) remain unaffected.

Methods: Eight cadaveric knee specimens underwent anatomical dissection to precisely identify the medial ligamentous structures. The knees were mounted in a custom-made kinematics rig with loaded quadriceps muscle and iliotibial tract using cables and hanging weights. An anterior slope-modifying osteotomy was performed and fixed using an external fixator, which allowed a gradual slope modification from +10° to -15° in steps of five degrees. Threads were mounted between tibial and femoral pins positioned along the anterior, middle and posterior parts of the attachments of the sMCL and POL. The resulting length changes between the tibiofemoral pin combinations were recorded using a rotary encoder from 0° to 120° knee flexion. The level of isometry was determined by the total strain range (TSR). A one-way repeated-measures ANOVA was performed for each structure to compare the length change and TSR across flexion angles and degrees of slope modification with the initial measure at 0° knee flexion. Statistical significance was set to p<0.05.

Results and conclusion: During knee flexion, the sMCL progressively slackened with increasing slope reduction (p<0.01), while a slope-increasing osteotomy caused a tightening of the sMCL (p<0.01). The anterior fibers of the sMCL (decrease/increase in length of -7.4 ± 2.2% and 5.7 ± 1.1%) were more affected by anterior slope-modifying osteotomy than the posterior fibers (decrease/increase of length -2.8 ± 0.7 % and 1.9 ± 0.7 %, p<0.01). Regardless of slope modification, all fiber regions of the POL displayed a continuously shortening to knee flexion to 50 % towards knee flexion. The most isometric behavior was shown for the medium fibers of the sMCL (TSR 1.65 ± 0.56 to 2.89 ± 1.12), whereas the anterior fibers of the sMCL became less isometric with increasing slope reduction and showed a continuously increase of TSR (+10°: 7.49 ± 7.73; -15°: 11.44 ± 3.99).

In conclusion, a slope reduction slackened and slope increase tightened the fibers of the sMCL, which was most pronounced for the anterior fibers of the sMCL. The length change pattern of the POL remained unaffected. Regardless of slope-modification, the reciprocal behavior of the sMCL to knee flexion was maintained.