The strain behavior of the anterior cruciate ligament during stair climbing: An in vivo study

Stair climbing is a closed kinetic chain exercise that is thought to be use ful for knee rehabilitation following anterior cruciate ligament (ACL) reco nstruction while protecting the graft from excessive strain. The objectives of this study were to measure the strain produced in the anteromedial band (AMB) of the normal ACL during stair climbing in vivo. We have previously shown that the normal AMB strain pattern during knee passive flexion-extens ion motion is similar to that of an ACL graft immediately after graft fixat ion. We successfully tested five subjects with normal ACLs, who were candid ates for arthroscopic meniscectomy under local anesthesia. AMB strain was m easured in vivo using the Differential Variable Reluctance Transducer (Micr oStrain, Burlington, VT). The stair climbing activities were performed on a StairMaster 4000PT (Randall Sports Medicine, Kirkland, WA). Two different climbing cadences were evaluated; 80 and 112 steps per minute. Consistent w ith our previous studies of ACL biomechanics, strain values increased as th e knee was moved from a flexed to an extended position. The mean peak AMB s train values for the 80 and 112 steps per minute conditions were 2.69% (+/- 2.89&) and 2.76% (+/-2.68%), respectively. These values were not significan tly different. Compared with other rehabilitation activities previously tes ted in the same manner, the AMB strain values produced during stair climbin g were highly variable across subjects. High strain values were observed in some patients but not in others.