Abstract
Introduction: Anterior cruciate ligament (ACL) rupture impairs knee stability. Reconstruction of the ACL is therefore performed to restore knee stability and avert risk of subsequent ligament and meniscal injury. Bone-patellar tendon-bone autograft is the most commonly employed technique for ACL reconstruction and considered the “gold standard”. Although 10% postoperative patellar tendon shortening has been reported with this technique, there are no systematic studies assessing the effect of this shortening on patellofemoral joint (PFJ) biomechanics under loading conditions simulating normal physiologic activity. The purpose of this study was to determine if 10% shortening of the patellar tendon affected PFJ biomechanics.
Methods: Patellofemoral contact characteristics were evaluated in cadaveric knees before and after patellar tendon shortening. Tendon shortening was performed using a specifically designed device that shortened the tendon without interfering with its anatomic and physiologic integrity. Conditions simulating light physical activity such as level walking were recreated by applying physiological quadriceps loads and corresponding angles of tibial rotation to the PFJ at 15°, 30° and 60° of knee flexion. PFJ contact areas were measured at each position of knee flexion before and after patellar tendon shortening using the silicone oil-carbon black powder suspension squeeze technique (3S technique, Yao & Seedhom, Proc Instn Mech Engrs1991;205:69–72). Differences were compared using the Wilcoxon signed rank t-test, with p< 0.05 required for statistical significance.
Results: Twelve unembalmed cadaveric knees (median age 81.8 years, 8 female: 4 male) were available for study. Five knees had evidence of osteoarthritic changes, and were rejected. The remaining 7 knees were macroscopically intact and were considered adequate for the experimental procedure. The mean patellofemoral contact areas and stresses determined preoperatively were comparable to those reported in normal knees in previous studies. Following patellar tendon shortening, PFJ contact areas were displaced superiorly on the patellar articular surface and distally on the femoral articular surface. Although the PFJ contact area increased by 17% at 15° of knee flexion (p=0.04), no significant change occurred at 30° or 60° of knee flexion (p> 0.05). Patellofemoral contact stress did not differ before and after patellar tendon shortening (p> 0.05) at any angle of knee flexion.
Conclusions: Our results suggest that with light activity such as level walking, a 10% postoperative shortening of the patellar tendon does not alter patellar tracking (in particular contact stresses) and therefore may not impact biomechanics of the patellofemoral joint. Extrapolating these results to the clinical scenario, deleterious consequences on the patellofemoral joint are unlikely after bone-patellar tendon-bone autograft reconstruction of the ACL despite the possibility of postoperative patellar tendon shortening.
Correspondence should be addressed to Mr Carlos Wigderowitz, Honorary Secretary BORS, University Dept of Orthopaedic & Trauma Surgery, Ninewells Hospital & Medical School, Dundee DD1 9SY.
