INTRODUCTION: Flexion distraction injuries (FDI) of the thoracic and lumbar spine can be stabilised with a short construct spanning one motion-segment. This fracture is functionally defined by failure of the posterior and middle columns in tension and the anterior column in compression or tension. Treatment of a predominantly bony injury with minimal deformity (Chance type) is usually non-operative. Intra-abdominal pathology, and ligamentous spinal instability are relative indications for surgery. Deformity of greater than 17 degrees of kyphosis has a poor prognosis when treated conservatively, and represents true instability in vitro. Surgical treatment is mainly through a posterior approach with instrumentation. Which construct to use and the number of motion segments to include is controversial. Multi-level instrumentation techniques both in distraction and compression have been used as well as shorter constructs, particularly in the lumbar spine. We addressed the efficacy of single motion-segment fixation by evaluating the radiographic and functional results of this treatment technique.

METHODS: All patients diagnosed with a FDI were prospectively identified over a 48 months period. Non-operatively treated fractures were excluded. Other spine fractures were excluded. Demographics, co-morbidity, neurological status, operative details and complications were recorded. Radiographic reviewers were blinded to the functional outcome of the patient and the time of follow-up. The Oswestry Functional Assessment Questionnaire was administered by mail.

RESULTS: Twenty-one eligible patients were identified. A significant (p< 0.0001) correction of deformity was achieved, from a mean pre-operative kyphosis of 10.1 degrees to a mean post-operative lordosis of 0.9 degrees. No loss of correction occurred. The mean Oswestry score was 11.5, with 88% of patients having minimal disability. One patient died from unrelated morbidity.

CONCLUSIONS: Hoshikawa et al showed in vitro how compression forces alone can create FDI. Compression without flexion causes burst fractures. With moderate flexion there is FDI with anterior body compression. With increasing flexion FDI becomes entirely distractive. As the forces are concentrated at a single point, reconstruction only requires that this location be addressed. As all FDI are created by the same mechanism, regardless of structures injured only short segment fixation is required.

We have demonstrated in FDI, single level fixation is biomechanically sound. Multilevel instrumentation creates loss of adjacent level motion segments. This is not necessary. The absence of a control group precludes absolute conclusions. Nonetheless most patients reported minimal disability related to their back and had excellent radiological outcomes. This study demonstrates that posterior reduction and stabilisation of a single motion-segment for FDI can adequately stabilise the spine and lead to excellent functional outcomes.