Cortical Button Fixation: A Better Patellar Tendon Repair?

OBJECTIVES: Patella tendon rupture requires surgical repair for optimal outcomes yet there is no consensus regarding appropriate repair technique or duration of post-operative immobilization. Cortical button fixation is a secure method for tendon repair but has not been studied in patellar tendons. This study evaluates a novel patellar tendon repair technique using cortical button fixation. METHODS: Twenty-two fresh frozen cadaveric knees compared three techniques of patellar tendon repair following a simulated rupture at the inferior pole of the patella. Specimens were divided into three groups such that mean donor age, weight and height were closely matched. Repairs were performed at 45 degrees flexion using a standard suture only (SO) repair (n=7), PEEK suture anchor (SA) repair (n=7) or cortical button (CB) repair (n=8). A standard suture size and type (#2 Fiberwire) and suture technique (Krackow) was used for each repair. The details of the CB repair are illustrated in Figure 1. All specimens were tested on a custom apparatus based on an established biomechanical protocol, which simulated cyclic open kinetic chain quadriceps contraction from extension to 90 degrees flexion. Outcomes of interest were gap formation up to 250 cycles, maximum load to failure and mode of failure. Secondary analysis evaluated the effect of bone volume on construct failure. All patellae were CT scanned and the bone volume was estimated in mean Hounsfield units (HU) using MIMICS Software (Materialise, Leuven, Belgium). All values are presented in the form of mean + standard deviation. One-way analysis of variance using Tukey-Kramer multiple comparisons test was performed and a p value of <0.05 was used for statistical significance. RESULTS: Results are summarized in Table 1. CB had significantly less gap formation than SA after 1 cycle (p<0.001) and 20 cycles (p<0.01) and significantly less gap formation than SO from 1-250 cycles (p<0.05) CB repairs sustained significantly higher loads to failure than SA and SO (p <0.001). All SO repairs failed through the suture. SA repairs failed at the suture anchor eyelet interface (n= 4) or by anchor pullout (n=3). CB repairs either failed through the suture (n=4), secondary failure of the patella tendon (n=2) or pullout of the button through the anterior cortex of the patella. For each group, there was no significant difference between failure load and bone volume. However, the three SA specimens that failed by anchor pullout had 3 of the four lowest bone volumes for that group (9.3, 10.4, 14.3 cm3). The CB construct that failed through the patella had the lowest bone volume (10.3 cm3) of that group. Best-estimate wholesale cost for suture only, suture anchor and CB instrumentation was $37, $570 and $677, respectively. CONCLUSION: Patellar tendon repair using CB fixation has mechanical advantages over suture and anchor repair in cadaveric specimens. CB fixation showed less cyclic gap formation and withstood at least twice the load to catastrophic failure of the construct. The theoretical cost difference between CB and SA repair is minimal but SA patellar tendon repair in osteoporotic patients may be suboptimal due to risk of anchor pullout. This may translate to clinical advantages of CB fixation in accelerating post-operative rehabilitation or with ensuring adequate fixation in patients with poor bone density.