Abstract
PurposeAs yet, there are no studies describing a relationship between radiographic subsidence after lumbar total disc replacement (TDR) and patient symptoms. To investigate if subsidence, in terms of penetrated bone volume or angular rotation over time (ΔPBV and ΔAR), is related to clinical outcome. To assess if subsidence can be predicted by position implant asymmetry (IA) or relative size of the TDR, areal undersizing index (AUI) on direct post-operative radiographs.MethodsRetrospective cohort study consists of 209 consecutive patients with lumbar TDR for degenerative disc disease. A three-dimensional graphical representation of the implant in relation to the bony endplates was created on conventional radiographs. Consequently, the PBV, AR, IA and AUI were calculated, direct post-operative (DPO) and at last follow-up (LFU). For clinical evaluation, patients with substantial pain (VAS ≥ 50) and malfunction (ODI ≥ 40) were considered failures.ResultsAt a mean follow-up of 16.7 years, 152 patients (73%) were available for analysis. In 32 patients, revision by spinal fusion had been performed. Both ΔAR (4.33° vs. 1.83°, p = 0.019) and ΔPBV (1448.4 mm3 vs. 747.3 mm3, p = 0.003) were significantly higher in the failure-compared to the success-group. Using ROC curves, thresholds for symptomatic subsidence were defined as ΔPBV ≥ 829 mm3 or PBV-LFU ≥ 1223 mm3 [area under the curve (AUC) 0.723, p = 0.003 and 0.724, p = 0.005, respectively]. Associations between symptomatic subsidence and AUI-DPO ≥ 0.50 (AUC 0.750, p = 0.002) and AR-DPO ≥ 3.95° (AUC 0.690, p = 0.022) were found.ConclusionSubsidence of a TDR is associated with a worse clinical outcome. The occurrence of subsidence is higher in case of incorrect placement or shape mismatch.
Highlights
Fusion of a symptomatic lumbar spinal motion segment is the most commonly used operative treatment for patients with degenerative disc disease (DDD) not responding to conservative care [1]
The measurements were done for the upper and lower part of the total disc replacement (TDR), and the highest value was used for Altogether 225 patients who had undergone a TDR at level L4–L5 and/or L5–S1 were identified, 16 patients had deceased (7.1%)
To investigate whether subsidence could be predicted by the position and relative size of the TDR on the direct post-operative radiographs, we investigated associations between position as measured from these radiographs and symptomatic subsidence as outcome
Summary
Fusion of a symptomatic lumbar spinal motion segment is the most commonly used operative treatment for patients with degenerative disc disease (DDD) not responding to conservative care [1]. Spinal fusion is associated with negative side effects such as proximal facet-joint violation, pseudarthrosis and symptomatic adjacent level disease (ASD) [2,3,4,5,6,7,8,9]. In order to avoid those fusion-related side effects, lumbar total disc replacement (TDR) has been introduced. TDR has been associated with drawbacks, such as subsidence, dislocation, or malposition of the implant [10,11,12]. All patients were contacted with the request to visit the outpatient clinic for clinical evaluation and AP and lateral radiographs
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