Gap Formation in Transpatellar Patellar Tendon Repair

BACKGROUND: Postfixation loosening within the Krackow stitch-tendon construct may be associated with gap formation in patellar tendon repair. HYPOTHESIS: Pretensioning the Krackow stitch-tendon construct decreases postfixation gap formation in transpatellar patellar tendon repair. STUDY DESIGN: Controlled laboratory study. METHODS: Patellar tendon rupture was simulated in 8 pairs of cadaveric knees. Standard manual traction was used in all specimens to remove Krackow stitch slack. In the experimental group, specimens were pretensioned with a simulated active concentric quadriceps contraction with cycling of the knee 10 times from 90 degrees to 5 degrees of flexion. All specimens were then cycled at 0.25 Hz from 90 degrees to 5 degrees for 1000 cycles until failure, which was defined as 3 or 5 mm of gap formation. RESULTS: A 3-mm gap occurred at 1 cycle (mean, 3.5 mm) and 35 cycles (4.0 mm) in the control and experimental groups, respectively. Gapping of 5 mm occurred at 35 (5.9 mm) and 100 cycles (5.0 mm) in the control and experimental specimens, respectively. Gap formation was smaller in the experimental group through 100 cycles (P < .05). CONCLUSION: Gapping was lower with pretensioning in the early cycling stages. However, significant gapping occurred in both groups with repetitive concentric active loading ranging from 90 degrees to 5 degrees of flexion. CLINICAL RELEVANCE: Tightening of the Krackow stitch as done in this study does not result in a clinically important decrease in gapping. This observation may be generalizable to other applications of the Krackow stitch.