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Athletes with anterior cruciate ligament (ACL) deficiencies exert decreased knee extension moments during level walking (quadriceps avoidance gait), and yet within a few months of ACL reconstruction they are often expected to return to competitive sport. To investigate this issue further, 10 normal subjects and seven ACL deficient patients were evaluated both pre- and post-operatively (mean follow-up of 6 months), and each performed multiple trials ascending a staircase which consisted of three steps. Bilateral joint angles, moments, powers, and work were measured and the data were ensemble averaged and statistically analyzed (repeated measures ANOVA with significance level set at 0.05). Anterior-posterior knee laxity decreased significantly (from 7.9 mm to 5.8 mm) while subjective knee function also improved following ACL reconstruction (knee score increased from 70.4 to 88.5). Pre-operatively, there were no statistically significant differences in biomechanical parameters between the patients' ACL-deficient and intact sides and the normal subjects. Post-operatively, however, statistically significant reductions were seen for the peak moment (91.9 vs 22.5 Nm), power (181 vs 84 W), and work performed (28.0 vs -5.6 J) at the injured knee, which was also the knee from which the patellar tendon graft had been harvested. These reductions were accommodated by significant increases in excursion, moment, and power at the contralateral ankle joint. The results indicate that while the ACL reconstruction were successful in restoring anterior-posterior knee stability, the decrease in knee power and work performed post-operatively by the injured (i.e., donor) knee suggests that donor site morbidity may need to be critically evaluated over a long-term period.

The KT-1000 arthrometer was evaluated in vitro and in vivo to determine accuracy and quantify effects of potential error sources in clinical application. The KT-1000 arthrometer in vitro accuracy was evaluated by making 30 measurements of 13 known displacements (range, +15 to -15 mm). The effect of applied force on malalignment measurements was evaluated in vitro by making repeated measurements with force applied 5 degrees, 10 degrees, and 15 degrees from the vertical position. The effect of malpositioning the device along the joint line was evaluated in vivo by making repeated measurements 1 cm proximal and 1 cm distal to the joint line. The KT-1000 arthrometer was accurate in vitro (average error, 0.13 mm; SD, 0.12 mm). The range of measurements increased when the angle of force application was increased. Positioning the device 1 cm proximal to the joint line produced larger anterior translation measurements in vivo than those at the joint line (5.8 versus 5.4 mm), while positioning it 1 cm distal produced smaller measurements (4.4 mm). The KT-1000 arthrometer's accuracy indicates great potential for clinical application, but one must ensure that the displacing force is directed properly and the device is positioned accurately over the joint line.

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