Purpose: Lumbosacral dislocation injuries are rare. Severe trauma disrupts the mechanically stable lumbosacral junction, rendering the injuries particularly unstable. Aggressive surgical management has been recommended. We present a review of our experience with these uncommon injuries defining injury patterns, surgical strategies and outcomes.

Methodology: Six patients were treated at Auckland Hospital in the last decade. Thorough review and literature search were performed to revise recommendations for management.

Results: All injuries were associated with high-energy trauma. In two cases there was evidence of previous spondylolysis, with dramatic progression after injury. All cases were surgically treated with decompression, reduction as indicated, and fusion with instrumentation. The only instrumentation failure occurred when reduction reconstituted disc height without attention to reconstruction of the severely mechanically compromised intervertebral disc. Satisfactory recovery of nerve root injury occurred in all but one case. Major cauda equina damage did not occur. Correlations with previously described classification systems for this injury were poor, and often showed injuries to span grades.

Conclusions: These highly unstable injuries require a high index of suspicion, and aggressive surgical management of these highly unstable injuries is warranted, yielding satisfactory outcomes. Existing classification systems are of little value prognostically, or in planning treatment, and it is better to classify and treat these injuries specifically relating to the anatomical injury patterns. The severe disruption to the intervertebral disc warrants special consideration with attention to a stable reduction position or three-column reconstruction. Spondylolysis may represent a predisposing factor.

Aim: To investigate, quantify and model the influence of three biomechanical factors on the severity of mechanically induced nuclear disruption in healthy bovine, caudal, intervertebral discs.

Method: A preliminary study was conducted with a fully divided annular wall to investigate the cohesive nature of the isolated nucleus and its tendency to form clefts when loaded. A second more clinically relevant model using whole bovine discs was then conducted to investigate whether significant clefts could be induced in healthy discs by controlling flexion, hydration and rate of compressive loading.. A finite element model of the bovine caudal disc was constructed to predict the complex stress conditions that exist within the disc.

Results: We found that high degrees of flexion and hydration were significant risk factors in nuclear disruption (P < 0.005), while the rate of loading showed no significant effect (P = 0.37). The intact disc study also showed that flexion and hydration are significant risk factors (P < 0.002). In contrast with the preliminary study, the rate of loading was also shown to be mildly significant (P < 0.1). The finite element model predicted relatively high concentrations of stress and strain energy density within the nucleus. This is consistent with the experimental observations of cleft formation.

Conclusions: While it is well established that dehydration of the nucleus is a symptom of degeneration this study suggested that the healthy nucleus, when maximally hydrated, is more susceptible to nuclear disruption when loaded. This supports the hypothesis that the histologically abnormal and degenerate nuclear material removed at surgery, may well have attained this state as a result of biomechanical and biochemical changes occurring in the disc following rather than preceding a prolapse. This study further defined the rôle of trauma in disc injury and prolapse of the normal disc.

Introduction: Age related histological and radiological changes are widespread in the lumbar spine. The correlation with symptoms is poor and there is good evidence that in later decades the incidence of back symptoms decreases, despite the relentless progression of radiological abnormalities. Much confusion exists regarding Accident Compensation Corporation (ACC) insurance entitlement following injuries in the presence of asymptomatic but existing radiological ageing changes (spondylosis) and existing but asymptomatic spondylolysis/isthmic spondylolisthesis.

Aim: To review the relevant literature and ACC Acts to clarify the ACC Act definition of injury/accident and exclusion criteria and the natural history of spondylosis/spondylolysis/spondylolisthesis, in relation to patients sustaining new lumbar spine injuries in the presence of existing but asymptomatic radiological abnormalities.

Method: The relevant literature and legislation (1992 ARCI and 1998 AI Acts) were reviewed.

Results: Regarding spondylolysis and low grade isthmic spondylolisthesis the literature is conflicting in relation to the incidence of back symptoms. The ACC Acts do not discuss existing disorders or degenerative conditions, but focus on exclusion of cover for ‘personal injury caused wholly or substantially by the ageing process’.

Conclusions: As with clinical decision making medico-legal assessment requires a meticulous history as the primary focus. It is inappropriate to apportion undue weight to radiological abnormalities that correlate poorly with symptoms.