Comparison of the Biomechanical Stability of Two Fix-and-Replace Techniques in an Acetabular Fracture Model with Pelvic Discontinuity

Background/Objectives: Managing acetabular fractures remains a surgical challenge, particularly in cases involving traumatic pelvic discontinuity (PD). The optimal method for achieving primary stability is unclear, and biomechanical evidence comparing established techniques is limited. The goal of this biomechanical study is to evaluate if a Ganz reinforcement ring with the addition of a posterior-column plate and anterior-column screw (GRP) provides stability comparable to a Burch-Schneider reinforcement ring (BSR) with an additional anterior- and posterior-column screws construct. Methods: The primary biomechanical stability of two acetabular “fix-and-replace” techniques—BSR versus GRP—using standardized 4th-generation Sawbones® hemipelvis models with T-type fractures (PD) was compared. Relative 3D micromotions at the fracture site (Zone 1: Posterior-column; Zone 2: Anterior-column; Zone 3: Oblique to transverse fracture, and Zone 4: Ischiopubic ramus) were measured under increasing cyclic loading (100 cycles per load level) at 200 N, 400 N, 800 N, and 1200 N using an optical motion tracking system. A detected fracture gap of 1000 µm or more during/after the cyclic load was defined as fixation failure. Results: Fixation failure was not observed in any of the six artificial hemipelves with treated (3 BSR, 3 GRP) T-type acetabular fractures. Under cyclic, increasing load (200–1200 N), the mean fracture gap remained small at 200 N and 400 N with no significant differences between techniques. At 800 N, GRP fixation showed a non-significant increase in micromotion. At 1200 N, significantly greater displacements were observed in Zones 2–4 with GRP compared to BSR (p < 0.005), whereas no difference was found in Zone 1 (p = 0.424). Modelled slope and intercept comparisons confirmed a significantly steeper increase in fracture gap with GRP in zones 2–4 at higher loads (≥800 N, p < 0.01) while remaining under 1000 µm. Conclusions: Both fixation methods demonstrated sufficient construct stability without catastrophic failure, with minimal displacement (