An in vivo strain gage study of elongation of the anterior cruciate ligament

Abstract

The purpose of this paper is to study the load-elonga tion characteristics of a Grade II sprain of the anterior cruciate ligament (ACL) at the time of local anesthesia arthroscopy. The data may be used to increase diag nostic and prognostic accuracy when evaluating Grade II ACL sprains and to structure properly a rehabilitation program following ACL injury. This report is based on the data from two in vivo strain gage studies of Grade II ACL sprains. Following instrumentation of the ligament, several events com mon to physical examination and rehabilitation pro grams were tested. The Lachman test produced greater elongation of the anteromedial fibers than did the anterior drawer or pivot shift test. A fairly high force of 80 pounds may be required by the examiner's hands to test satisfactorily the anteromedial fibers in the acutely injured large athlete. The proper order for a rehabilitation program should be crutch walking, cycling, walking, slow running, and faster running. Patients should be cautioned to run on a perfectly level surface. Cycling produced 7% as much elongation as an 80 pound Lachman test, and the one leg half squat 21 % as much. Quadriceps rehabilitation can be done more safely using these exercises. Quadriceps exercises by knee extension against a 20 pound weight boot in the range of full extension to 22° flexion created peak elongation of the anteromedial fibers ranging from 87 to 121% of that produced by an 80 pound Lachman test. We recommend that quadri ceps exercises and testing by knee extension through a full range of motion not be done during the first year following ACL injury or reconstruction. Quadriceps contraction against a 20 pound weight boot at 45° flexion produced 50% as much elongation as an 80 pound Lachman test. Beginning at 9 months post-ACL reconstruction, we do measure quadriceps strength isometrically with the knee flexed 45°.