Fixation of transforaminal sacrum fractures: a biomechanical study

A transforaminal fracture of the sacrum usually represents the posterior part of an unstable pelvic ring fracture and is associated with a high rate of neurological complications. Nerve root decompression combined with open reduction and internal fixation (ORIF) can be beneficial. Present fixation methods have the disadvantage of extensive bilateral posterior approaches and fixation across the sacroiliac joint. Three methods of internal fixation of the sacrum were compared in a biomechanical study using six fresh pelvic specimens. A fracture model consisting of a transforaminal osteotomy combined with a symphysis disruption in a single-leg stance was used. Standard Harrington sacral bars, an internal fixator, and a newly developed stabilization technique using adapted standard AO/ASIF small-fragment implants ("local osteosynthesis") were compared. Three-dimensional measurement of the fragment movement (goniometer system) showed a maximum displacement of 4.0-4.5 mm after maximal loading (990-1,181 N) and no differences among the implants. The failure load related to body weight was 85% for sacral bars, 74% for the local osteosynthesis, and 58% for the internal fixator. Major displacement under loading was observed in the direction of the foramen axis. The new osteosynthesis technique showed strength comparable to the clinically successfully applied method of stabilization with sacral bars. It adds the theoretical advantage of a minimized approach, without fixation and thus without involvement of the SI joints.