Background context: Total lumbar disc replacement (TDR) intends to avoid fusion-related negative side effects by means of motion preservation. Despite their widespread use, the adequate quality and quantity of motion, as well as the correlation between radiographic data with the patient's clinical symptomatology, remains to be established. Long-term data are lacking in particular.
Purpose: This study aimed to perform a clinical and radiographic long-term investigation following TDR with special emphasis on motion preservation assessment and to establish any potential correlation with patient-reported outcome parameters.
Study design/setting: A prospective, single-center, clinical, and radiological investigation following TDR with ProDisc II (Synthes, Paoli, PA, USA) was carried out.
Patient sample: Patients with a minimum 5-year follow-up (FU) after TDR performed for the treatment of intractable and predominant (≥80%) axial low back pain resulting from single-level degenerative disc disease without instabilities or deformities at the lumbosacral junction (L5-S1) comprised the sample.
Outcome measures: Visual analogue scale (VAS), Oswestry Disability Index (ODI), and patient satisfaction rates (three-scale outcome rating), range of motion (ROM) at the index- and cranially adjacent level as well as segmental lumbar lordosis (SLL) and global lumbar lordosis (GLL) were the outcome measures.
Methods: All data were acquired within the framework of an ongoing prospective clinical trial. Patients were examined preoperatively, 3, 6, and 12 months postoperatively, and annually thereafter. X-rays were performed in antero-posterior and lateral views as well as functional flexion/extension images. Radiological examinations included ROM at the index and cranially adjacent level as well as SLL and GLL. X-ray measurements were correlated with the clinical outcome parameters. A longitudinal analysis was performed between baseline data with those from the early (3-6 months), mid- (12-24 months), and late FU stages (≥5 years).
Results: Results from 51 patients with a mean FU of 7.8 years (range 5.0-13.3 years) were available for the final analysis. X-ray measurements revealed a maintained mobility with a trend toward gradually declining ROM values. Although no statistically significant difference in ROM was detected between the preoperative and early FU (6.8° vs. 5.8°, p=.1), a further reduction in ROM became statistically significant at the mid- and final FU, with mean ROM of 5.2° and 4.4°, respectively (p<.001). Global lumbar lordosis increased from 48.8° to 54.4° (p<.0001) which was attributed to a lordotic shift from 18.2° to 28.0° at the index segment (p<.00001) and which was positively correlated with the applied implant lordosis (p<.05). A compensatory reduction of lordosis was observed at the cranially adjacent segment (p<.0001). The mobility of the cranially adjacent level remained unchanged (p>.05). The clinical outcome scores (VAS, ODI) revealed a significant improvement from baseline levels (p<.05). The reduction in ROM was not negatively correlated with the patient's clinical symptomatology (p>.05).
Conclusion: The present data reveal an increased GLL resulting from a lordotic shift of the index segment, which was strongly correlated with the applied implant lordosis. This lordotic shift was accompanied by a compensatory reduction of lordosis at the cranially adjacent segment. A gradual and statistically significant decline of the device mobility was noted over time which, however, did not negatively impact the patient's clinical symptomatology. Although the present long-term investigation provides additional insight into longitudinal radiographic changes and their influence on the patient's clinical symptomatology following TDR, the adequate quality and quantity of motion with artificial motion-preserving implants remains to be established, which will aid in defining more refined treatment concepts for both fusion and motion preserving techniques alike.
Keywords: Disc arthroplasty; Long-term results; Lumbar disc replacement; Mobility; Motion preservation; Range of motion.
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