Stable, anatomical fixation of acetabular fractures gives the best chance of a good outcome. We performed a biomechanical study to compare fracture stability and construct stiffness of three methods of fixation of posterior wall acetabular fractures.

Two-dimensional motion analysis was used to measure fracture fragment displacement and the construct stiffness for each fixation method was calculated from the force / displacement data.

Following 2 cyclic loading protocols of 6000 cycles, to a maximum 1.5kN, the mean fracture displacement was 0.154mm for the rim plate model, 0.326mm for the buttress plate and 0.254mm for the spring plate model. Mean maximum displacement was significantly less for the rim plate fixation than the buttress plate (p=0.015) and spring plate fixation (p=0.02).

The rim plate was the stiffest construct 10962N/mm (SD 3351.8), followed by the spring plate model 5637N/mm (SD 832.6) and the buttress plate model 4882N/mm (SD 387.3).

Where possible a rim plate with inter-fragmentary lag screws should be used for isolated posterior wall fracture fixation as this is the most stable and stiffest construct. However, when this method is not possible, spring plate fixation is a safe and superior alternative to a posterior buttress plate method.

Posterior lumber interbody fusion (PLIF) has the theoretical advantage of optimising foraminal decompression, improving sagittal alignment and providing a more consistent fusion mass in adult patients with isthmic spondylolisthesis (IS) compared to posterolateral fusion (PLF). Previous studies with only short-term follow-up have not shown a difference between fusion techniques.

An observational cohort study was performed of a single surgeon's patients treating IS over a ten year period (52 patients), using either PLF (21 pts) or PLIF (31pts). Preoperative and 12-month data were collected prospectively, and long-term follow-up was by mailed questionnaire. Preoperative patient characteristics between the two groups were not significantly different. Average follow-up was 7 years, 10 months, and 81% of questionnaires were returned. Outcome measures were Roland Morris Disability Questionnaire (RMDQ), Low Back Outcome Score (LBOS), SF-12v2 and SF-6D R2. The SF-6D R2 is a “whole of health” measure.

PLIF provided better short- and long-term results than PLF. The PLIF group had significantly better LBOS scores in the long term, and non-significantly better RMDQ scores in the long term. As measured by RMDQ Minimum Clinically Important Difference (MCID) short term set at 4, RMDQ MCID set at 8, the LBOS MCID set at 7.5 points and by SF-12v2 physical component score (PCS), PLIF patients performed better than PLF patients. When analysing single level fusions alone, the difference is more pronounced, with PCS, mental component scores and SF-6D R2 all being significantly better in the PLIF group rather than the PLF group.

This paper strongly supports the use of PLIF to obtain equivalent or superior clinical outcomes when compared to PLF for spinal fusion for lumbar isthmic spondylolisthesis. The results of this study are the first to report to such long-term follow-up comparing these two procedures.