|Abstract / Summary
The concept of adult spinal deformity (ASD) constitutes very heterogeneous radiographic presentations in the coronal and/or sagittal plane with severe impact on health related quality of life (HRQOL). The prevalence of ASD increases with age and with the demographic development in Western societies an increasing number of elderly individuals with high quality of life expectations can be anticipated and thus increase the demand for surgical intervention. Treatment of adult deformity primarily aims at reducing pain and disability and while most patients offered surgical intervention benefit, many experience complications and require revision procedures, which adversely affect recovery and increase the cost of treatment.
Numerous technical options are available to spine surgeons, but development of an evidence-based approach to operative as well as non-operative treatment has been limited by the lack of a systematic categorisation that enables comparison of similar disorders. During the past decade extensive work has been performed to better understand the clinical impact of regional and global spinal deformity as well as compensating mechanisms and recently the Scoliosis Research Society (SRS)-Schwab classification was proposed.
The objectives of the present thesis were to investigate the reliability; clinical discriminating ability and prognostic value of the SRS-Schwab classification as well as to identify risk factors and protective construct features for mechanical failure following adult spinal deformity surgery.
The first paper investigated the agreement and reliability of the classification among four spine surgeons with varied experience who classified 67 sets of radiographs twice. We found acceptable agreement and reliability for each of the classification parameters.
The second paper addressed the ability of the classification to discriminate ASD patients according to pain and disability. A consecutive cohort of 292 patients with radiographic evaluation of spinal deformity was prospectively enrolled from our outpatient clinic. We found that the classification did not discriminate consistently according to either general health, regional or disease specific HRQOL instruments. However, if the three levels of deformity for each sagittal parameter in the classification were dichotomised, patients categorised as “abnormal” had significantly worse HRQOL than the “normal”.
The third paper set out to investigate the prognostic value of pre- and immediate postoperative classification as well as change in classification parameters. 138 consecutive patients were retrospectively reviewed for mechanical failure at minimum two years following spine deformity surgery. No statistically significant prognostic effects from the original classification or dichotomised parameters were detected, however use of 3-column osteotomies, ending the instrumentation at L5 or S1 and postoperative thoracic kyphosis > 50° were associate with higher hazard of failure, while postoperative sacral slope >30° was associated with lower hazard of failure.
The fourth paper was designed to evaluate the efficacy of three different construct features proposed to reduce rod fracture rates in patients who undergo 3-column osteotomy. A total of eight surgical constructs were tested in each of five human spine specimens using a custom 6 degrees of freedom motion simulator. We found that addition of two short rods across the osteotomy site to the standard two-rod construct and selection of cobalt chromium over titanium rods significantly reduced motion and surface rod strain, while anterior column support immediate above and below the osteotomy level had only minimal effect in a biomechanical model.
In conclusion the SRS-Schwab ASD classification is reliable, but only dichotomised classification parameters discriminated patients significantly according to HRQOL and no prognostic values in terms of mechanical failure were detected. This indicates the need for further work on classification development and some researchers suggest that the variation in spinal shapes among asymptomatic adults should be considered. Among other factors 3-column osteotomy showed significant association with higher hazard of mechanical failure, while additional rods and selection of cobalt chromium could potentially reduce the hazard from this surgical procedure in ASD patients.