Is Pedicle Screw Dynamic Stabilisation a Possible Management of Lumbar Diseases with A Low-Grade Instability?

Background: A dynamic stabilisation of the lumbar spine can be performed in selected cases of degenerative disc diseases as an alternative to the established but more invasive rigid fusion surgery. The purpose of our study was to assess the clinical and radiological results of dynamic stabilisation of the lumbar spine with pedicle screws and polyetheretherketone (PEEK) rods. Methods: Between March 2018 and March 2020, forty-two patients underwent forty-three consecutive operations for a dynamic lumbar stabilisation. Pre- and postoperative radiological assessment, operative reports and pre- and postoperative clinical documents were analysed retrospectively. Results: The clinical assessment showed on average a postoperative reduction of the back pain from 5.2 to 3.1(visual analogue scale, 0 to 10) and of the leg pain from 6.4 to 1.8 (visual analogue scale, 0 to 10). The radiological controls provided stable results except in one asymptomatic case where a possible mobilisation of a pedicle screw was observed. Three patients (7%) needed a reoperation and in three patients (7%) intraoperative complications have been observed. Conclusion: With the retrospective analysis of the clinical and radiological results of a population of 42 patients (43 operations) consecutively treated with a dynamic lumbar stabilisation surgery the safety of the system can be confirmed. No significant radiological complications have been observed. The pain level of back and leg pain decreased after the operation and remained stable in the controls. this to assess the clinical results of dynamic stabilisation of the lumbar spine with Viper SC and Polyetheretherketone (PEEK) rods. The retrospective analysis of the radiological control studies in a cohort of forty-two patients concerning the of the The of the through the analysis of the perioperative and postoperative complication rate.


Introduction
Degenerative diseases of the lumbar spine can cause different degrees of instability. The treatment of these pathologies often needs a decompression and, in some cases, a stabilisation of the involved segments. Rigid spinal fusion is considered the gold standard to treat degenerative diseases of the lumbar spine associated with instability. The increased load on the adjacent segment with a risk of developing a segmental instability and stenosis is however a well-known long-term side effect of rigid fusion surgery.
Sometimes the instability associated with the degenerative pathology is not so severe to require a rigid stabilisation including postero-lateral pedicle screwing and interbody fusion. Especially in elderly patients, a dynamic stabilising system can be considered to minimize the surgical risks reducing operating time and blood loss. Dynamic stabilisation avoids moreover to perform an extensive discectomy reducing the risks of interbody cages' subsidence and other complications associated with poor bone quality. The dynamic stabilisation can provide an acceleration of the degenerative cascade according to [1] tending to a spontaneous fusion of the spine in a more progressive way compared to a rigid fusion. This delayed fusion could be achieved through a facet joints ankylosis and a progressive dehydration of the intervertebral discs.

Objective
The aim of this study is to assess the clinical results of dynamic stabilisation of the lumbar spine with Viper SC and Polyetheretherketone (PEEK) rods. The retrospective analysis of the radiological control studies in a cohort of forty-two patients provides also information concerning the stability of the segments before and after the operation. The safety of the procedure is, besides, evaluated through the analysis of the perioperative and postoperative complication rate. In some patients a standing X-Ray of the entire spine and a CT were also performed. Control X-Rays were performed 2, 6 and 12 months after surgery. Further radiological investigations were performed just in selected indications. All participants provided written informed consent.

Results
The population consisted of 42 patients consecutively operated during a period of 2 years by the same spinal surgeon in the same Hospital. A total number of 43 surgical procedures using Viper SC were performed as one patient underwent two operations at two different levels. A preoperative pain syndrome was present at least  (Table 1). Preoperative neurological deficit 12 (28%)

SD: Standard Deviation
All the patients were treated with the combination of Viper SC and PEEK rods. In one patient a three-level surgery was performed (L2-L5), six patients were treated at two levels (4 times L3-L5 and 2 times L4-S1) and in 36 cases (84%). a dynamic mono-segmental stabilisation was realized. The most treated level was L4/L5 (34 cases, 79%). L3/L4 was treated in 9 cases, L5/S1 in 5 cases and   PEEK rod systems are well-known devices introduced with the aim to achieve a pedicle-based posterolateral stabilisation avoiding increasing the mechanical stress at the adjacent segment of the fusion level [4,9,10]. PEEK rod systems were approved by the FDA in 2007 and many clinical studies concerning the use of PEEK for fusion procedures are available in literature [11,12]. PEEK rods have an elastic modulus between that of the cancellous and cortical bone and present full biocompatibility in vivo [13].
Hoppe et al. [14] reported comparable long-term results for