Stability of internal versus external fixation in osteoporotic pelvic fractures - a biomechanical analysis

Osteoporosis-related fragility fractures of the pelvic ring (FFP) differ fundamentally from pelvic fractures in younger patients. However, very little is known about biomechanical stability of different osteosynthesis procedures addressing the anterior pelvic ring in these fractures. The aim of this study was to compare standard external fixation with internal fixation using a novel screw-and-rod system in osteoporotic fractures of the pelvic ring in terms of stiffness, plastic deformation and maximum load under cyclic loading in a human cadaveric model.

A total of 18 embalmed osteoporotic cadaver pelvis specimens were randomized based on the T-score into a group for external fixation and a group for internal fixation. FFP type-IIB fractures were created. In addition to the external or internal fixator, a cement-augmented sacroiliac screw was implanted. Afterwards, axial cyclic loading was performed in a testing setup simulating one-leg stand.

Mean plastic deformation and stiffness both were significantly better in the internal fixation group than in the external fixation group (plastic deformation: 0.37 mm (SD: 0.23) versus 0.71 mm (SD: 0.26), p = 0.011; stiffness: 43.69 N/mm (SD: 18.39) versus 26.52 N/mm (SD: 9.76), p = 0.029). Maximum load did not differ significantly between internal fixator (506.3 N; SD: 129.4) and external fixator (461.1 N; SD: 147.4) (p = 0.515).

Submuscular internal fixation might be an interesting alternative to external fixation in clinical practice because of better biomechanical properties as well as several advantages in clinical use.