Observations concerning the limited mobilisation cast after anterior cruciate ligament surgery.

A limited mobilisation cast (LMC) with hinges locked at 20 and 60 degrees has been advocated for the care after anterior cruciate ligament (ACL) surgery. The brace presumably limits motion to 20 and 60 degrees and prevents straining of the ACL. Extension of more than 20 degrees as well as anterior drawer forces are known to strain the ACL. We have therefore tested whether the LMC reliably limits the desired range of motion: Extension of more than 20 degrees was found in 11 of 12 patients and averaged 12 degrees. The long leg cast reduced a 30 degree anterior drawer in unstable knees by 70%, a Lenox-Hill-Derotation Brace by 53% and the LMC by only 14%. It was concluded that a modified Lenox-Hill Brace locked at 30 and 60 degrees of flexion provides better stress-protection of the ACL than a LMC and that the safety of the conventional long leg cast should be remembered in legs with unfavourable soft tissue configurations. If a LMC is used, it should be fixed to the trunk with a waist- or shoulder-strap and the hinges must be freely adjustable.