Length-change patterns of the medial collateral ligament and posterior oblique ligament in relation to their function and surgery

Abstract

Purpose: To define the length-change patterns of the superficial medial collateral ligament (sMCL), deep MCL (dMCL), and posterior oblique ligament (POL) across knee flexion and with applied anterior and rotational loads, and to relate these findings to their functions in knee stability and to surgical repair or reconstruction.

Methods: Ten cadaveric knees were mounted in a kinematics rig with loaded quadriceps, ITB, and hamstrings. Length changes of the anterior and posterior fibres of the sMCL, dMCL, and POL were recorded from 0° to 100° flexion by use of a linear displacement transducer and normalised to lengths at 0° flexion. Measurements were repeated with no external load, 90 N anterior draw force, and 5 Nm internal and 5 Nm external rotation torque applied.

Results: The anterior sMCL lengthened with flexion (p < 0.01) and further lengthened by external rotation (p < 0.001). The posterior sMCL slackened with flexion (p < 0.001), but was lengthened by internal rotation (p < 0.05). External rotation lengthened the anterior dMCL fibres by 10% throughout flexion (p < 0.001). sMCL release allowed the dMCL to become taut with valgus rotation (p < 0.001). The anterior and posterior POL fibres slackened with flexion (p < 0.001), but were elongated by internal rotation (p < 0.001).

Conclusion: The structures of the medial ligament complex react differently to knee flexion and applied loads. Structures attaching posterior to the medial epicondyle are taut in extension, whereas the anterior sMCL, attaching anterior to the epicondyle, is tensioned during flexion. The anterior dMCL is elongated by external rotation. These data offer the basis for MCL repair and reconstruction techniques regarding graft positioning and tensioning.

Keywords: Isometry; Length change; Medial collateral ligament; Posterior oblique ligament; Reconstruction.

Fig. 1

Medial aspect of a right knee: a near extension and b at 90° flexion. The four staples in the femur are, from anterior to posterior: the anterior edge of the sMCL, the posterior edge of the sMCL, the anterior edge of the POL, and the posterior edge of the POL. They were hammered completely into the bone after attaching a suture to each of them. The staple loops which guided the anterior and posterior sMCL sutures are visible distally, at the sMCL tibial attachment. The anterior margin of the sMCL wraps around the femoral medial epicondyle with knee flexion. The femoral medial epicondyle is located midway between the anterior and posterior fibre attachments of the sMCL. Note that the distal staples of the POL, in the posterior rim of the tibial plateau, are obscured by the semimembranosus tendon

Fig. 2

a The dMCL of an extended right knee, anterior to the left of the picture and the long axis of the tibia vertically downwards. The red pin head is at the most prominent point of the femoral medial epicondyle (ME): the sMCL attaches anterior and posterior to it. The sMCL femoral attachment is intact, showing the anterior fibres passing anterior to the epicondyle. Distally, the sMCL has been reflected posteriorly (but not released completely) as far as the green line where the sMCL and dMCL blend together to form the PMC, revealing the dMCL, with its most-posterior fibres marked by the green line. The femoral attachment of the dMCL is distal and posterior to the epicondyle, so it is obscured by the sMCL. The most-anterior fibres of the dMCL—the blue line highlighted by the arrows—are oriented anterior/distal from the femur to the tibia. The wrinkle/buckling across the width of the dMCL indicates that it is slack when the sMCL is intact. MTP: medial tibial plateau. b The sMCL has been removed: the most prominent point of the medial epicondyle (black dot) is at the centre of the sMCL attachment (black dashed circle). The oblique antero-distal orientation of the dMCL in neutral tibial rotation is evident, with the anterior and posterior borders indicated by the white arrows. SM direct head of semimembranosus muscle, MGH medial head of gastrocnemius muscle, MTP medial tibia plateau

Fig. 3

The knee was secured in a 6-DOF kinematics rig which allowed testing across knee flexion between 0° and 100° and applying anterior draw and rotational loads. Muscle loads were applied by hanging weights via a cord and pulley system. A linear variable displacement transducer was mounted alongside the tibial rod with a customised 3D-printed fixture (see inset)

Fig. 4

Length changes of the anterior fibres of the superficial MCL across knee flexion, with the tibia unloaded and with anterior translation force, internal rotation torque, and external rotation torque applied to the tibia. Shown as mean values with ± SD; n = 10. Significant length changes are described in the text

Fig. 5

Length changes of the posterior fibres of the superficial MCL across knee flexion, with the tibia unloaded and with anterior translation force, internal rotation torque, and external rotation torque applied to the tibia. Shown as mean values with ± SD; n = 10. Significant length changes are described in the text

Fig. 6

Length changes of the anterior fibres of the deep MCL across knee flexion, with the tibia unloaded and with anterior translation force, internal rotation torque, and external rotation torque applied to the tibia. Shown as means with ± SD; n = 10. Significant length changes are described in the text

Fig. 7

Length changes of the posterior fibres of the deep MCL across knee flexion, with the tibia unloaded and with anterior translation force, internal rotation torque, and external rotation torque applied to the tibia. Shown as mean values with ± SD; n = 10. Significant length changes are described in the text

Fig. 8

Length changes of the anterior fibres of the POL across knee flexion, with the tibia unloaded and with anterior translation force, internal rotation torque, and external rotation torque applied to the tibia. Shown as means with ± SD; n = 10. Significant length changes are described in the text

Fig. 9

Length changes of the posterior fibres of the POL across knee flexion, with the tibia unloaded and with anterior translation force, internal rotation torque, and external rotation torque applied to the tibia. Shown as means with ± SD; n = 10. Significant length changes are described in the text