The knee joints of mice can be used as a model for studying the effect
s of interventions on knee laxity. The goal of this study was to quant
ify knee joint laxity in vitro. Three devices were developed: a positi
oning- and cementing device, an anterior-posterior (AP) laxity tester
and a varus-valgus (VV) laxity tester. The positioning- and cementing
device was used to position the joint in a reproducible way and to att
ach clamping pins to the proximal femur and distal tibia using PMMA. T
he clamping pins were used to fix the joint to the AP- and VV-testers.
In both testers the load was applied by means of a spindle-actuated s
pring while load and displacements were measured simultaneously. The l
oad-displacement data were used to calculate displacement and complian
ce parameters. The performance of the testers was evaluated by testing
5 normal knee joints of 5 mice. Total AP-translation at +/-0.8 N was
0.43 (+/-0.16 S.D.) mm with compliances of 0.14 (+/-0.05 S.D.) mm N-1
and 0.12 (+/-0.05 S.D.) mmN(-1) at 0.8 N posterior and anterior force,
respectively. Total VV-rotation at +/-4 Nmm was 17.2 (+/-2.6 S.D.) de
grees with compliances of 0.9 degrees Nmm(-1) (+/-0.2 degrees Nmm(-1)
S.D.) and 1.0 degrees Nmm(-1) (+/-0.4 degrees Nmm(-1) S.D.) at 4 Nmm v
algus and varus moment, respectively. The contributions of the deforma
tions of the bones and the fixtures to the rotations were negligible i
n the VV-test. In the AP-test they account for approximately 0.07 (+/-
0.03 S.D.) mm of the total AP-translation. This will not affect the ut
ilization of the device for comparative analysis. It is concluded that
in vitro evaluation of AP- and VV-laxity in knees of mice is feasible
with sufficient accuracy for evaluation of changes after ligament dam
age. (C) 1996 Elsevier Science Ltd.