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.