Summary
Objectives: The bone-patellar tendon-bone complex is routinely harvested for anterior cruciate
ligament reconstruction in humans. Patella infera may ensue. However, the contribution
from resection of the central one-third of the patellar tendon (PT) to potentially
altered patellofemoral kinematics, in addition to those induced by a positional shift
of the patella, are yet to be distinguished. Objectives of this study were to characterize
changes in intraoperative patellar kinematics and PT length in nine sheep immediately
following unilateral resection of the central one-third PT, and again at six, 12 and
24 weeks postoperatively.
Methods: Following implantation of bone-screws into the patella and tibia, electromagnetic
receivers were anchored to these, and then passively-induced, unloaded patellar kinematics
were captured. Patellar kinematics were referenced to the tibial coordinate frame
and analysed using non-parametric tests (Wilcoxon Signed Rank Test).
Results: Resection alone did cause significant alteration in kinematics at the time of surgery
(p <0.05). Postoperatively, a mean increase in PT length of 2.6 mm was detected in
the operated stifles, reflected partly as a net 2.8 mm proximal patellar shift (p
<0.001). This was accompanied by a mean net six degree medial shift in the patellar
tilt pattern (p <0.001). Significant changes to patellar spin in the latter parts
of flexion were also observed (p <0.005). Kinematic and length changes did not recover
up to 24 weeks postoperatively.
Clinical significance: The data obtained in this study suggests that both the patellar height and integrity
of the PT are important determinants of patellar kinematics in the ovine stifle joint.
Keywords
Anterior cruciate ligament - patella infera - ovine stifle - bone-patellar tendon-bone
auto-graft - cranial cruciate ligament