A Gore-Tex prosthetic ligament was inserted, with an over-the-top
femoral placement, into thirteen fresh-frozen cadaver knees as a substitute
for the anterior cruciate ligament. The femoral eyelet was screwed into
bone and the tibial eyelet was attached to a force-transducer, which was
positioned and locked on a tibial slider track to record forces in the
ligament as the tibia was externally loaded. A reference position was
established for the tibial eyelet so that, after the Gore-Tex ligament was
implanted, the total anterior-posterior laxity of the knee (at 200 newtons
of applied tibial force) matched that of the intact knee (that is, before
the anterior cruciate ligament had been cut) at 20 degrees of flexion. With
both ends of the ligament secured in the knee, repeated 200-newton
anterior-posterior load cycles produced an increase of five to seven
millimeters in the total laxity. This apparent stretch-out of the ligament
could be worked out of the knee by manually flexing and extending the knee
thirty times between zero and 90 degrees of flexion while a constant
200-newton force was applied to the tibial eyelet. After implantation of
the Gore-Tex ligament, the laxity of the knee matched that of the intact
specimen at 20 degrees of flexion and matched it within one millimeter at
zero, 5, and 10 degrees of flexion. For each millimeter that the tibial
eyelet was moved distally, the total anterior-posterior laxity decreased by
the same amount. The anterior stiffness of the knee after implantation of
the Gore-Tex ligament was always less than that of the intact specimen.
With an applied extension moment of ten newton-meters, section of the
anterior cruciate ligament increased hyperextension of the knee by 2.3
degrees; implantation of the Gore-Tex ligament did not restore full
extension, even when the ligament was over-tightened by using a distal
location for the tibial eyelet. When the eyelet was in the reference
position, the ligament forces ranged from three to 319 newtons when the
knee was in full extension, they rose dramatically as the knee was
hyperextended, and they decreased to zero in most specimens as the knee was
flexed more than 15 degrees. The pull of the quadriceps tendon against
fixed resistance always increased the ligament forces. The application of
tibiofemoral contact force reduced the ligament forces that were generated
during a straight anterior tibial pull.(ABSTRACT TRUNCATED AT 400
WORDS)