Diagnosis and treatment of Pipkin type IV femoral head fracture : a finite element analysis

To use FEA(finite element analysis) to elucidate the biomechanical mechanisms and stress distribution patterns leading to Pipkin type IV femoral head fractures under different loading conditions and to evaluate the biomechanical stability of different internal fixation methods for Pipkin type IV femoral head fractures and correlate the findings with clinical outcomes. Finite element models of normal hip joints and Pipkin type IV femoral head fractures were separately established, and the stress distribution and displacement of each model were simulated using FEA. Clinical data were retrospectively collected from 15 patients with Pipkin type IV femoral head fractures who underwent surgical treatment at Xijing Hospital, Air Force Medical University, between March 2013 and April 2019. Their hip joint function was evaluated during follow-up, and the findings from the FEA were validated through comparison with the clinical follow-up results. The results of the FEA were as follows: (1) When a load is applied to the normal hip joint model in the upright position, the femoral head bears the largest stress, followed by the posterior wall and top of the acetabulum, and the anterior column of the acetabulum experiences the largest displacement, followed by the femoral neck, which suggests that Pipkin type IV femoral head fractures are prone to occur when the lower limbs hit the ground after falling from a height. When a load is applied to the normal hip joint model in 90°, 120° flexion and 10° internal rotation, the stress is concentrated on the top and posterior wall of the acetabulum and the femoral neck and the displacement is mainly distributed along the posterior column and posterior wall of the acetabulum, which indicates that the patient is prone to Pipkin type IV femoral head fracture if the dashboard is damaged in a car accident. (2) In the model of Pipkin type IV femoral head fracture, acetabular fractures are fixed with lag screws and reconstruction plates, resulting in the smallest stress and displacement, which suggests that this method of internal fixation is the most reliable. The clinical follow-up results were as follows: a total of 15 patients were followed up for 12–86 months, with a mean of 34.4 months and Majeed functional scoring was performed to evaluate the hip joint at the last follow-up after their femoral head fractures were fixed with double-head compression screws. Among them, 5 cases of acetabular fracture were fixed with lag screws and reconstruction plates, and their hip joint function was graded excellent; 5 cases of acetabular fracture were fixed with reconstruction plates, and their hip joint function was graded good; another 5 cases of acetabular fractures were fixed with lag screws, and their hip joint function was graded as good. The results of FEA in the normal hip joint model are consistent with the clinical data of patients with injuries caused by falling from a height and car accidents, so FEA can provide evidence for the early diagnosis of Pipkin type IV femoral head fractures. The results of the FEA in the model of Pipkin type IV femoral head fracture with internal fixation are consistent with the hip function scores in the clinical evaluation, so FEA can provide guidance for selecting optimal internal fixation. In short, FEA can play an important role in the clinical diagnosis and treatment of Pipkin type IV femoral head fractures.