Clinical and radiological indicators of outcome in the use of X-Stops were sought by evaluating patient-centred outcomes alongside radiographic scrutiny of changes around implants with correlation to outcome.

Prospectively collated outcome scores were correlated to outcome, with retrospective analysis of pre-operative MRI scans and 117 post-operative radiographs.

Single surgeon series of 44 patients(52 implants).

Clinical - ODI, walking distance, Low Back Outcome Score, MZDI and MSP. Radiographic - lucency(anterior and cranio-caudal to implant), coronal rotation, dorsal migration of implant. Failure defined by persistent symptoms requiring removal+/−decompression.

Pre-operative features of success: lower ODI(p<0.05), higher LBOS(p<0.01), higher walking distance(p<0.01), lower MZDI(p<0.01).

Marked differences were noted in post-operative scores for the two cohorts. An eight-fold improvement in walking distance in success patients compared to an increase to 1.8 times the baseline in failures. ODI improved ten times more in the success group at 20 cf2(failure). MZDI improvement was greater in the revisions at 2.2 cf 0.9 in successes.

Ranking Pearson's coefficient of radiograph measurements in success and failure cohorts, revealed failure associated most to anterior lucency(R=0.93), rotation(R=-0.61), cranio-caudal lucency (R=-0.29) and migration (R=-0.25). Success most associated to rotation (R=-0.22). Failure radiographs revealed greater lucency cranio-caudal and ventral to the implant, more coronal rotation, and pronounced dorsal migration.

Clinical features of success are older patients with no co-morbidities, unilateral leg pain and multi-level insertion. Males, those with bilateral leg pain, and scoliosis or spondylolistheses are more likely to fail.