THE MENISCOFEMORAL LIGAMENT AS A SECONDARY RESTRAINT: A SHEEP STUDY

Abstract

The aim of this study was to determine the function of the meniscofemoral ligament in the cranio-caudal and rotatory laxity of the ovine stifle.

Twenty fresh cadaveric ovine stifles were harvested from fully mature sheep, average weight 25kg. The joint was denuded of its muscular attachments leaving the capsule, including the patella and patellar tendon undisturbed. The femur and tibia were divided 10 cm from the joint line, positioned in cylindrical pots, and secured in polymethylmethacrylate bone cement. The stifles were tested in a four-degree-of-freedom rig positioned in an Instron materials testing machine. This allowed unconstrained coupled tibial rotations and translations during application of cranial (anterior) and caudal (posterior) draw forces. Forces up to a maximum of 100Nm were applied in the anterior and posterior directions, and the resultant translations were measured. These parameters were assessed at 30, 60, 90, and 110 degrees of flexion in ten intact stifles. Similar measurements were carried out after division of the caudal (posterior) cruciate ligament, followed by division of the meniscofemoral ligament. The sequence of division was reversed for a further ten stifles.

Division of the meniscofemoral ligament resulted in an 18–38% increase in posterior translation at all angles of flexion, both in the intact and in the caudal cruciate ligament-deficient stifle (p< 0.05). There was no significant increase in anterior translation. This effect was largest with the joint relatively extended (at 30°). Division of the meniscofemoral ligament also resulted in a 5–32% increase in internal rotation of the tibia after application of a 6Nm torque in the caudal cruciate-deficient knee. This was significant at 30° and 110° flexion (p< 0.05).

The meniscofemoral ligament is a significant secondary restraint in resisting the posterior draw and internal tibial rotation in the sheep stifle joint. This is the first study demonstrating a functional role for this structure in any animal. Its counterpart in the human is the posterior meniscofemoral ligament of Wrisberg. Several studies have demonstrated similarities between the sheep stifle and the human knee. Confirmation of a similar role for the ligament of Wrisberg in the human knee would have a significant bearing on the prognosis and management of the posterior cruciate ligament injured knee.