Implantation of Signus ROTAIO-Prosthesis maintains ROM in cervical spine and results in physiological iCOR

The new trend is towards motion-preserving surgical procedures, such as cervical total disc replacement (cTDR). The aim of this technique is to replace the intervertebral disc, releasing and decompressing the corresponding nerve roots while maintaining and restoring segmental and overall range of motion (ROM).

The instantaneous center of rotation (iCOR) of a motion segment has been shown to correlate with its total ROM. Importantly, a correlation of the correct placement of cTDR to preserve a physiological iCOR has been previously identified. However, changes of these parameters and the corresponding clinical relevance have hardly been analyzed.

Anna Lang et al conducted a study to assesses the radiological and clinical correlation of iCOR and ROM following cTDR. The article has been published in ‘European Spine Journal.’

The ROTAIO® prosthesis is an unconstrained prosthesis enabling an uncoupled translation of the vertebral bodies with a variable center of rotation. The special design is intended to mimic physiological motion of the index segment aiming to reduce the biomechanical load on the adjacent levels.

A retrospective multi-center observational study was conducted and radiological as well as clinical parameters were evaluated preoperatively and 1 year after cTDR with an unconstrained device. Radiographic parameters including flexion/extension X-rays (fex/ex), ROM, iCOR and the implant position in anterior–posterior direction (IP ap), as well as corresponding clinical parameters [(Neck Disability Index (NDI) and the visual analogue scale (VAS)] were assessed.

Key findings of the study:

• The authors analyzed 53 patients treated with a uni- or bilevel cTDR from 5 different neurosurgical centers.

• 49 patients (92.5%) received a one level cTDR and 4 patients (7.5%) were treated by two-level cTDR.

• 32 females (60.4%) and 21 males (39.6%) with a mean age of 47.4 years (range: 27–65 years) received a ROTAIO® prosthesis in a total of 57 index segments.

• Pre- and post-operative ROM showed no signifcant changes (8.0° vs. 10.9°; p>0.05).

• Significant correlations between iCOR and IP (Pearson’s R: 0.6; p<0.01) as well as between ROM and IP ap (Pearson’s R: − 0.3; p=0.04) were identified.

• NDI and VAS improved significantly (p<0.01).

• A significant correlation between NDI and IP ap after 12 months (Pearson’s R: − 0.39; p<0.01) was found.

The authors concluded that - Implantation of unconstrained prostheses with the opportunity of uncoupled translation maintains the physiologi cal ROM and iCOR. However, special attention should be paid on implant positioning. Accordingly, comparable data should be available for all cTDR designs, in order to improve the device function through optimal surgical handling and positioning.

Further reading:

Clinical and radiological outcome 1 year after cervical total disc replacement using the Signus ROTAIO – Prosthesis Anna Lang, Sara Lener et al European Spine Journal (2022) 31:3477–3483https://doi.org/10.1007/s00586-022-07416-3