Clinical StudyReoperation rates and risk factors for revision 4 years after dynamic stabilization of the lumbar spine
Introduction
Rigid stabilization and fusion has become a well-accepted procedure for the treatment of painful degenerative segmental instability in the lumbar spine with or without spinal stenosis [1], [2]. Nevertheless, initially good clinical results might be extenuated by adjacent segment degeneration (ASD) [3], [4], with reported rates of symptomatic ASD of 2.0%–5.5% per year after lumbar fusion surgery [5], [6], [7]. Especially in the elderly, ASD in the cranial segment is a common problem after lumbar stabilization [4]. Relative hypermobility of the adjacent segment in relation to the rigid fixation was considered to be a relevant factor predisposing ASD [4], [8]. In an attempt to reduce relative hypermobility in adjacent segments by allowing motion in stabilized segments and thereby diminishing altered biomechanical stress at adjacent segments, the concept of dynamic stabilization (DS) of the lumbar spine for treatment of degenerative instability has been introduced almost two decades ago [9], [10], [11]. Dynamic stabilization is based on the principle of controlling the movement by providing load transfer of spinal segments without fusion and, at the same time, reducing relative movements of the adjacent segment, when compared with rigid fixation [12]. Thus, the concept of DS is following the objective of reducing side effects such as ASD [13]. Morishita et al. [14] found significantly lower disc degeneration after DS of the lumbar spine in comparison to rigid fixation. By allowing movement in the spinal segment without fusion, the transmission of forces will be mainly dependent on the bone-screw interface, leading to higher forces in the transition zone at the bone-screw interface possibly inducing different side effects such as loosening of the screw [10], [12].
The objective of the present study is therefore to determine the longitudinal reoperation rates after DS of the lumbar spine focusing on ASD and SL. Additionally, various risk factors including age, gender, body mass index (BMI), number of segments, postoperative lordosis, and previous surgery, potentially predicting the probability of revision surgery, are evaluated. Screw angles (SAs) in the axial plane within a segment, as well as intersegmental and in-segmental delta angles, are assessed as independent risk factors for ASD and SL.
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Ethics
The analysis was approved by our local ethics committee (registration number: 159/16S) and was conducted in accordance with the Declaration of Helsinki.
Patients
We performed a post hoc analysis of our prospectively collected database for all patients that underwent DS of the lumbar spine (including levels T12 to S1) using the dynamic Cosmic system (Ulrich Medical, Ulm, Germany). Between January 2008 and December 2011, 283 patients (151 [53.4%] female and 132 [46.6%] male) were operated on and included
Results
Overall reoperation rate for ASD and SL of dynamic lumbar pedicle screw stabilization after 1 year was 7.4%, after 2 years was 15.0%, and after a mean follow-up of 51.4±15 months (range 27–92 months) was 22.6% (Table 2). During follow-up, 31 (10.9%) patients were revised for other reasons: 6 for chronic pain (2.1%) within the first 2 years, 2 for postoperative hematomas (0.7%), 3 for postoperative cerebrospinal fluid fistulae (1.1%), 6 for infections (2.1%) (5 early wound infections, 1 late
Comparison with other dynamic and rigid stabilization cohorts
Our detailed analysis revealed age, gender, LL postsurgery, and previous surgery as main risk factors of indication for revision on the patient level. To the best of our knowledge, this is the first and largest study presenting the longitudinal reoperation rates for SL and ASD after DS of the lumbar spine. So far, only little information is available on specific risk factors for reoperation rates following dynamic pedicle screw stabilization of the lumbar spine.
On the patient level, we found an
Conclusions
The large cohort and considerably long follow-up presented in this work demonstrates that DS is a suitable option for the treatment of degenerative instability in the lumbar spine. Thus, despite no bone grafting for fusion was performed in conjunction with this DS technique, revision rates are comparable with the literature for conventional rigid instrumentation with spinal fusion. For clear clinical indication and careful evaluation of preoperative imaging data, DS is a possible option.
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Author disclosures: ACR: Ulrich Medical (B, Paid directly to institution/employer), outside the submitted work. SMK: Consulting: Brainlab AG (B), Nexstim Plc (B); Speaking and/or Teaching Arrangements: Brainlab AG (B), Nexstim Plc (B); Trips: Nexstim Plc (B), outside the submitted work. FAS: Nothing to disclose. ELM: Nothing to disclose. BM: Consulting: Brainlab AG (B), Ulrich Medical (B), Medtronic (B); Speaking and/or Teaching Arrangements: Brainlab (B), Ulrich Medical; Trips/Travel: Nexstim (B); Grants: Ulrich Medical (G, Paid directly to institution/employer), outside the submitted work.
The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com.
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These authors contributed equally to this work.