Purpose: The purpose of this study is to compare biomechanical characteristics of tension band wiring using Kirschner wires (TBWKW), cannulated screws (TBWCS), and ring pins (TBWRP) for transverse fracture of the patella.
Methods: A total of 48 polyurethane synthetic patellae were biomechanically tested. All patellae were osteotomized to create a transverse fracture. Each TBWKW, TBWCS, and TBWRP fixed 16 broken patellae. A specially designed fixation board simulated a knee with 90° flexion. Ten static tests and six dynamic tests were performed on each method. The static test is measuring maximum strength (N) during traction until breakage of the fixation. The dynamic test consisted of measuring the fracture gap (mm) after 10,000 repetitive loading cycles between 100 N and 300 N that simulated actual daily activity. A gap of 2 mm or more was defined as a failure in both tests.
Result: The failure load was 438.6 ± 138.6 N, 422.2 ± 72.7 N, and 1106.8 ± 230.3 N for TBWKW, TBWRP, and TBWCS, respectively. TBWCS showed a statistically significant difference compared to TBWKW and TBWRP in the static test (p < 0.001). All the groups had no failure in the dynamic test. The mean fracture gap after completion of the dynamic test was 0.3267 ± 0.3395 mm, 0.2938 ± 0.2165 mm, and 0.0360 ± 0.0570 mm for TBWKW, TBWRP, and TBWCS, respectively (p = 0.044). The mean values in the dynamic test showed no statistical difference. There was a significant difference between TBWRP and TBWCS (p = 0.009), but others showed no difference with statistical significance.
Conclusion: All three methods have sufficient stability at a daily activity. TBWCS showed a better failure load compared with TBWKW and TBWRP. TBWRP showed compatible mechanical characteristics with traditional tension band wiring. TBWRP could be an alternative method for TBWKW.
Keywords: biomechanics; fracture fixation; internal/methods; patella/surgery; tension band.