The design of a locking compression plate for periprosthetic proximal femur fractures

Abstract

Objective To design a locking compression plate (LCP) for fixation of periprosthetic proximal femur fractures(PPFF) in Chinese. Methods (1)The imaging data of 90 patients that had primary total hip arthroplasty (THA) in Department of Orthopaedics, the Traditional Chinese Medicine of Changzhou, the Affiliated Hospital of Nanjing University of Chinese Medicine from September 2012 to December 2013 were retrospectively analyzed. The vertical distance between the edge of femur prosthesis and anterior or posterior femoral outer cortex was measured on the postoperative lateral X-rays films of hip of all cases. (2)Twenty cadaver femoral specimens were selected and their length and circumference were measured. Next to it, these specimens were implanted with femoral prosthesis stem, established the cadaveric femoral prosthesis model. Then 5 femoral prosthesis models underwent gemstone CT spectral scan and three-dimensional reconstruction. The vertical distance between the edge of femoral prosthesis stem and anterior or posterior femoral outer cortex and the length of femur for the vertical distance greater than 6 mm between the femoral prosthesis stem and femoral outer cortex were measured. The sagittal curve of femur was also assessed. (3)The LCP was digital customized according to the measured data of 90 patients and 5 femoral prosthesis models. After that, they were used to fix 5 cadaveric femur prosthesis models, and the relation of the locking screws on the LCP and the femoral prosthesis stem were observed by general view and image. The angle of locking screw which maybe contacted the femoral prosthesis was adjusted again. Then the improved LCP were used for fixing 10 cadaveric femur prosthesis models, the relation between the locking screws and the femoral prosthesis stem was evaluated. Finally, the design of the LCP was determined. Results (1)The measured data from the postoperative lateral X-rays films of hip of 90 cases were shown as follows: the average minimum and maximum vertical distance were (11.26±3.58)mm and (17.97±6.94)mm between the proximal half of the prosthesis and the outer posterior cortex of the femur, and they were (9.18±2.32)mm and (14.22±3.10)mm between the distal half of the prosthesis stem and the outer anterior femoral cortex respectively. (2)The average length and circumference of 20 cadaver femoral specimens were (41.67±0.24)cm and(9.19±0.74)cm respectively. The measured data from gemstone CT of femoral prosthesis models were showed as below: the average vertical distance between the proximal half of the prosthesis and the outer posterior cortex of the femur was (12.36±3.24) mm, and it was (8.14±1.21 )mm between the distal half of the prosthesis stem and the outer anterior femoral cortex. The length of femur was (69.20 ± 4.53)mm corresponding with the vertical distance over 6mm between proximal half prosthesis and femoral cortex, and that was (57.31±3.82)mm between distal half prosthesis and femur cortex. (3)The length of the LCP corresponding to proximal half femur prosthesis was designed with 3 locking holes which can be angulated in a specific angle in posterior of the prosthesis stem, and the length corresponding to distal half femur prosthesis was designed with 3 locking holes that can be angulated in a specific angle in anterior of the prosthesis stem. The curve of LCP was consistent with the curve of the femur. All locking screws achieved double cortical fixation by appropriate angle posterior or anterior the femoral prosthesis. Conclusions Although the LCP designed according to the anatomical data of Chinese femur can obtain adequate fixed space for femoral prosthesis models, and provide a new solution for treatment of PPFF, it still needs further clinical verification. Key words: Femoral fractures; Periprosthetic fractures; Arthroplasty, replacement, hip; Bone plates; Bone screw