Background: Primary total hip arthroplasty (THA) has been suggested for posterior wall (PW) fractures with unfavorable features in the geriatric population. There is a paucity of studies reporting on postoperative protocols for primary THA after PW fractures. The purpose of this study was to test the biomechanical effect of immediate assisted weight-bearing on acetabulum THA cup fixation in an osteoporotic PW fracture model.
Methods: Computed tomography scans of 18 geriatric PW fractures (mean age, 77 ± 8 years) were used to generate representative PW fracture. This fracture pattern, comprising 50% of the PW and 25% of the acetabulum rim, was then created in 6 female cadaveric pelves. A multihole acetabulum THA cup was implanted with line-to-line reaming and fixed with four 5-mm screws. The pelves were cyclically loaded to up to 1.8× body weight (BW) in the intact form, after fracture creation and fracture fixation. Optical markers were used to determine acceptable cup motion of less than 150 μm.
Results: Five specimens withstood 3.6× BW loading after implantation and before fracture creation. At 1.8× BW load, cup motion was nonfractured: 50 ± 24 µm (range, 5-128 µm), fractured with no fixation: 37 ± 22 µm (range, 8-74 µm), or fractured with fixation: 62 ± 39 µm (range, 5-120 µm) (P = 0.0097). Cup motion was <150 µm for all groups.
Conclusion: This study supports the practice of allowing immediate assisted weight-bearing in patients undergoing THA with PW fractures involving up to 50% of the PW and up to 25% of the acetabular rim, with or without fixation of the PW fragment.