Laxity, instability, and functional outcome after ACL injury: copers versus noncopers

Purpose: The purpose of this study was to determine the relationship among laxity, quadriceps strength, instability, and function in subjects with com plete rupture of the anterior cruciate ligament (ACL) who compensate well f or the injury (copers) and those who require surgical stabilization(noncope rs). Methods: Forty-five patients with unilateral ACL rupture (confirmed vi a arthroscopy or magnetic resonance imaging (MRI) and arthrometer measureme nts) participated in this study. Subjects were divided into two groups: cop ers (N = 12), and subacute noncopers (N = Is) and chronic noncopers (N = 15 ). All copers had returned to all preinjury activity (including index sport ) without limitation. Maximum manual anterior tibiofemoral laxity measureme nts, quadriceps femoris muscle strength measurements, and a series of hop t ests were performed. Lysholm Scale, Knee Outcome Survey (KOS), global ratin g of knee function, and the International Knee Documentation Committee (IKD C) form were completed. Results: There was, no significant difference in la xity between copers ((X) over bar = 5.5 +/- 2.7 mm) and noncopers (chronic, (X) over bar = 5.1 +/- 2.8 mm and subacute, (X) over bar = 4.2 +/- 2.2 mm) or in IKDC scores among the;groups. The copers, however, scored significan tly better than the chronic and subacute ACL-deficient subsets on all other measures. Measurements of laxity were not correlated to any functional out come measure or to episodes of instability. Conclusions: Copers were not di fferent in any meaningful way from the. noncopers before injury, had equal or greater side-to-side laxity differences, and functioned normally. A batt ery of tests was identified that accurately discriminated noncopers from co pers even early after injury. Thus, measurements of laxity alone are insuff icient for determining functional status after ACL injury.