Anchor loop plate fixation for the treatment of sleeve avulsion fracture of the inferior pole of the patella : finite element analysis and case series

Objective The purpose of this study was to compare the biomechanical stability of the Kirschner wire tension band combined with patellar cerclage and anchor loop plate ( ALP ) in the treatment of inferior patellar fracture with different fracture lines and to provide a new solution for the treatment of sleeve avulsion fracture of the inferior pole of the patella. Methods The finite element model was established, and the lower pole fractures of different fracture block sizes were graded according to the distribution of the lower pole fracture line. The model was subjected to finite element mechanical test under 500 N pressure to test the biomechanical properties of Kirschner wire tension band combined with patellar cerclage anchor nail loop plate fixation for the treatment of patellar lower pole fractures with different fracture lines. The clinical data of 8 patients with sleeve avulsion fracture of the inferior pole of the patella admitted to our hospital from June 2018 to June 2022 were retrospectively analyzed. All patients were treated with a newly designed anchor loop plate. The safety and effectiveness of this new technique in the treatment of sleeve avulsion fracture of the inferior pole of the patella were analyzed. The safety activity of passive flexion and extension of the knee joint during the operation was observed by consulting the medical records and follow-up results. The fracture healing, knee function recovery and postoperative complications were observed. Bostman score was used to evaluate knee joint function 3 and 9 months after operation. Results The biomechanical analysis of the finite element model showed that the maximum displacement of the Kirschner wire group was 1.77 times that of the ALP group at I-degree of the lower pole bone, the maximum stress of the Kirschner wire group was 1.21 times that of the ALP group, and the maximum stress of the Kirschner wire group was 13.29 times that of the ALP group. The maximum displacement of the II-degree of the lower pole bone in the Kirschner wire group was 2.22 times that of the ALP group, the maximum stress in the Kirschner wire group was 1.53 times that of the ALP group, and the maximum stress in the Kirschner wire group was 15.34 times that of the ALP group. The maximum displacement of the III-degree of the lower pole bone in the Kirschner wire group was 3.43 times that of the ALP group, the maximum stress in the Kirschner wire group was 1.60 times that of the ALP group, and the maximum stress in the Kirschner wire group was 16.86 times that of the ALP group. All avulsion fractures of the inferior patellar pole healed well without serious complications such as internal fixation failure or infection. The average operation time was 81.87 min ( 72–87 min ), the average final knee range of motion ( ROM ) was 124.50 ° ( 118 ° -130 ° ), the average Bostman score was 26.38 ( 24–29 ) in the third month, and the average Bostman score was 28.63 ( 27–30 ) in the ninth month. All patients showed good knee function one year after the operation. Conclusions With the change of fracture line to the distal end, the biomechanical stability of anchor loop plate was less affected by the change of fracture line, while the influence of Kirschner wire tension band combined with patellar cerclage technology tended to be unstable. Therefore, for sleeve avulsion fracture of the inferior pole of the patella, anchor loop plate has more biomechanical stability. In clinical practice, sleeve avulsion fracture of the inferior pole of the patella can be firmly fixed, and early functional exercise of knee joint can be allowed to bring good knee joint function to patients with sleeve avulsion fracture of the inferior pole of the patella.