Asymptomatic Construct Failure after Metastatic Spine Tumor Surgery: A New Entity or a Continuum with Symptomatic Failure?

STUDY DESIGN: Retrospective cohort study. PURPOSE: To study the incidence, onset, underlying mechanism, clinical course, and factors leading to asymptomatic construct failure (AsCF) after metastatic spinal tumor surgery (MSTS). OVERVIEW OF LITERATURE: The reported incidence rates for implant and/or construct failure after MSTS are low (1.9%-16%) and based on clinical presentations and revisions required for symptomatic failures (SFs). AsCF after MSTS has not been reported. METHODS: We conducted a retrospective analysis of 288 patients (246 for final analysis) who underwent MSTS between 2005-2015. Data collected were demographics and peri/postoperative clinical and radiological features. Early and late radiological AsCF were defined as presentation before and after 3 months, respectively. We analyzed patients with AsCF for risk factors and survival duration by performing competing risk regression analyses where AsCF was the event of interest, with SF and death as competing events. RESULTS: We observed AsCF in 41/246 patients (16.7%). The mean time to onset of AsCF after MSTS was 2 months (range, 1-9 months). Median survival of patients with AsCF was 20 and 41 months for early and late failures, respectively. Early AsCF accounted for 80.5% of cases, while late AsCF accounted for 19.5%. The commonest radiologically detectable AsCF mechanism was angular deformity (increase in kyphus) in 29 patients. Increasing age (p<0.02) and primary breast (13/41, 31.7%) (p<0.01) tumors were associated with higher AsCF rates. There was a non-significant trend towards AsCF in patients with a spinal instability neoplastic score ≥7, instrumentation across junctional regions, and construct lengths of 6-9 levels. None of the patients with AsCF underwent revision surgery. CONCLUSIONS: AsCF after MSTS is a distinct entity. Most patients with early AsCF did not require intervention. Patients who survived and maintained ambulation for longer periods had late failure. Increasing age and tumors with a better prognosis have a higher likelihood of developing AsCF. AsCF is not necessarily an indication for aggressive/urgent intervention.