Increasing posterior condyle cut for high-flex knee prosthesis may injure popliteus tendon origin: a cadaveric study

Background: High-flex total knee prosthesis designs were proposed to improve flexion in total knee replacement (TKA). One of high-flex features is increasing posterior condyle cut which put popliteal tendon in higher risk of injury and may result in gap changes. Methods: Thirty-six popliteal origin sites from eighteen fresh cadavers were measured distances between the posterior rim of popliteal tendon origin and posterior border of the lateral femoral condyle (distance A) using digital “Vernier caliper”. The mean distances were compared to posterior condyle thickness of different prosthesis designs. Results: The mean of distance A on the right knee was 9.59 ±1.66 mm (6.03-12.70) while the mean of distance A on the left knee was 9.13 ± 1.78 mm (5.80-11.07). Posterior condyle thickness of the femoral prostheses varies upon their design and size from 7.4 to 10 mm for standard model and from 8.2 to 12.5 mm for high-flex design. Possibilities of popliteal tendon injury during posterior condyle bone cut were 16.7% to 66.7% for standard model and 27.8% to 97.2% for the high-flex design. Conclusion: High-flex TKA prosthesis with thicker posterior condyle relates to higher possibility of popliteal tendon origin injury compared to standard one.