Michael N. Tzermiadianos

The pathophysiology of disc degeneration: A CRITICAL REVIEW

The pathophysiology of intervertebral disc degeneration has been extensively studied. Various factors have been suggested as influencing its aetiology, including mechanical factors, such as compressive loading, shear stress and vibration, as well as ageing, genetic, systemic and toxic factors, which can lead to degeneration of the disc through biochemical reactions. How are these factors linked? What is their individual importance? There is no clear evidence indicating whether ageing in the presence of repetitive injury or repetitive injury in the absence of ageing plays a greater role in the degenerative process. Mechanical factors can trigger biochemical reactions which, in turn, may promote the normal biological changes of ageing, which can also be accelerated by genetic factors. Degradation of the molecular structure of the disc during ageing renders it more susceptible to superimposed mechanical injuries. This review supports the theory that degeneration of the disc has a complex multifactorial aetiology. Which factors initiate the events in the degenerative cascade is a question that remains unanswered, but most evidence points to an age-related process influenced primarily by mechanical and genetic factors.

Percutaneous transpedicular discectomy and drainage in pyogenic spondylodiscitis.

The natural history of uncomplicated hematogenous pyogenic spondylodiscitis is self-limiting healing. However, a variable degree of bone destruction frequently occurs, predisposing the spine to painful kyphosis. Delayed treatment may result in serious neurologic complications. Early debridement of these infections by percutaneous transpedicular discectomy can accelerate the natural process of healing and prevent progression to bone destruction and epidural abscess. The purpose of this manuscript is to present our technique of percutaneous transpedicular discectomy (PTD), to revisit this minimally invasive surgical technique with stricter patient selection, and to exclude cases of extensive vertebral body destruction with kyphosis and neurocompression by epidural abscess, infected disc herniation, and foraminal stenosis. In a previously published report of 28 unselected patients with primary hematogenous pyogenic spondylodiscitis, the immediate relief of pain after PTD was 75%, and in the longterm follow-up, the success rate was 68%. Applying stricter patient selection criteria in a second series of six patients (five with primary hematogenous spondylodiscitis and one with secondary postlaminectomydiscectomy spondylodiscitis), all patients with primary hematogenous spondylodiskitis (5/5) experienced immediate relief of pain that remained sustained at 12–18 months follow-up. This procedure was not very effective, however, in the patient who suffered from postlaminectomy infection. This lack of response was attributed to postlaminectomydiscitis instability. The immediate success rate after surgery for unselected patients in this combined series of 34 patients was 76%. This technique can be impressively effective and the results sustained when applied in the early stages of uncomplicated spondylodiscitis and contraindicated in the presence of instability, kyphosis from bone destruction, and neurological deficit. The special point of this procedure is a minimally invasive technique with high diagnostic and therapeutic effectiveness.

Effect of the Total Facet Arthroplasty System after complete laminectomy-facetectomy on the biomechanics of implanted and adjacent segments.

BACKGROUND CONTEXT Lumbar fusion is traditionally used to restore stability after wide surgical decompression for spinal stenosis. The Total Facet Arthroplasty System (TFAS) is a motion-restoring implant suggested as an alternative to rigid fixation after complete facetectomy. PURPOSE To investigate the effect of TFAS on the kinematics of the implanted and adjacent lumbar segments. STUDY DESIGN Biomechanical in vitro study. METHODS Nine human lumbar spines (L1 to sacrum) were tested in flexion-extension (+8 to -6Nm), lateral bending (+/-6Nm), and axial rotation (+/-5Nm). Flexion-extension was tested under 400 N follower preload. Specimens were tested intact, after complete L3 laminectomy with L3-L4 facetectomy, after L3-L4 pedicle screw fixation, and after L3-L4 TFAS implantation. Range of motion (ROM) was assessed in all tested directions. Neutral zone and stiffness in flexion and extension were calculated to assess quality of motion. RESULTS Complete laminectomy-facetectomy increased L3-L4 ROM compared with intact in flexion-extension (8.7+/-2.0 degrees to 12.2+/-3.2 degrees, p<.05) lateral bending (9.0+/-2.5 degrees to 12.6+/-3.2 degrees, p=.09), and axial rotation (3.8+/-2.7 degrees to 7.8+/-4.5 degrees p<.05). Pedicle screw fixation decreased ROM compared with intact, resulting in 1.7+/-0.5 degrees flexion-extension (p<.05), 3.3+/-1.4 degrees lateral bending (p<.05), and 1.8+/-0.6 degrees axial rotation (p=.09). TFAS restored intact ROM (p>.05) resulting in 7.9+/-2.1 degrees flexion-extension, 10.1+/-3.0 degrees lateral bending, and 4.7+/-1.6 degrees axial rotation. Fusion significantly increased the normalized ROM at all remaining lumbar segments, whereas TFAS implantation resulted in near-normal distribution of normalized ROM at the implanted and remaining lumbar segments. Flexion and extension stiffness in the high-flexibility zone decreased after facetectomy (p<.05) and increased after simulated fusion (p<.05). TFAS restored quality of motion parameters (load-displacement curves) to intact (p>.05). The quality of motion parameters for the whole lumbar spine mimicked L3-L4 segmental results. CONCLUSIONS TFAS restored range and quality of motion at the operated segment to intact values and restored near-normal motion at the adjacent segments.

Effect of uncovertebral joint excision on the motion response of the cervical spine after total disc replacement

Study Design. In vitro biomechanical study. Objective. To quantify the effects of uncinatectomy on cervical motion after total disc replacement (TDR). Summary of Background Data. The effect of uncinatectomy on TDR motion is unknown. Partial uncinatectomy may be required to decompress the foramen; however, the residual uncinates can potentially limit TDR motion and serve as a source of progressive spondylosis. Complete resection of the uncinates may decrease this risk yet endanger destabilizing the segment. Methods. Seven human cervical spines (C3–C7) (age, 63.4 ± 6.9 years) were tested first intact and then after implantation of a metal-on-polyethylene ball-and-socket semiconstrained prosthesis at C5–C6. Following this, gradually increased uncinatectomy was performed in the following order: 1) right partial-posteromedial (two thirds), 2) right complete, and 3) bilateral complete resection. Specimens were tested in flexion-extension, lateral bending, and axial rotation (±1.5 Nm). Flexion-extension was tested under 150 N follower preload. Results. TDR without uncinatectomy increased C5–C6 flexion-extension range of motion from 8.4° ± 3.5° to 11.6° ± 3.4°, but statistical significance was not reached (P > 0.05). Lateral bending decreased from 6.2° ± 2.2° to 3.1° ± 1.4°, with a trend for statistical significance (P = 0.07). Axial rotation decreased from 5.5° ± 2.4° to 4.3° ± 1.4° after the implantation (P > 0.05). Both right partial and right complete uncinatectomy resulted in nearly symmetrical restoration of lateral bending to intact values and significantly increased flexion-extension compared with intact (P ≤ 0.05); however, axial rotation still did not differ from intact (P > 0.05). Complete bilateral resection also restored lateral bending to intact values (7.3° ± 2.7°, P > 0.05); however, it resulted in significant increase in range of motion in flexion-extension (14.1° ± 3.0°, P ≤ 0.05) and axial rotation (8.7° ± 2.4°, P ≤ 0.05). Conclusion. Unilateral complete or even partial uncinatectomy can normalize lateral bending after TDR. Bilateral complete uncinatectomy is not necessary to restore lateral bending and may result in significantly increased range of motion in flexion-extension and axial rotation compared with intact values.

An evidence-based medicine approach in determining factors that may affect outcome in lumbar total disc replacement.

Study Design. Literature research. Objective. To analyze the available evidence about a variety of factors that might affect outcome of lumbar artificial disc replacement. Summary of Background Data. Evaluating the scientific merit of new technology is important for a clinician considering incorporating these techniques. An evidence-based medicine approach can aid in this decision-making process. Methods. Eleven questions were asked about patient selection issues, surgical accuracy of placement, and evidence that motion preservation alters the natural history of degeneration. Studies where answers were found were ranked according to their level of evidence. Results. The majority of studies found were level IV, with only limited numbers of higher level studies. Only lower level studies with conflicting results assess the effect on outcomes of single versus multilevel surgery, L4–L5 versus L5–S1 implantations, patient’s age, and history of previous surgery. One lower level study suggests that mild-to-moderate facet degeneration does not influence outcomes. The extent of preoperative facet degeneration that can be accepted remains unclear, as level IV studies report degradation of facet degeneration after implantation. Higher level studies support the importance of surgical precision on clinical outcome and lower level studies give mixed results on the same issue. A level III prognostic study suggests that higher range of motion of the implanted segment may be associated with better outcomes, whereas 2 level IV therapeutic studies provide conflicting results. The incidence of adjacent level degeneration in lower level studies ranges between 17% and 28.6%, and can require additional surgery in 2% to 3% of patients. Two level IV studies suggest that preservation of motion may have a prophylactic effect on adjacent discs. Conclusion. Existing evidence does not provide definite conclusions in the majority of the questions regarding indications and factors that may affect outcomes. Where feasible, conclusions are mainly drawn from lower level, least reliable evidence. Highest quality data are short-term whereas longer-term data are of lower quality and in many instances conflicting. More high level studies with long-term follow-up are necessary to shed light to important clinical issues.

Enhancing the stability of anterior lumbar interbody fusion: A biomechanical comparison of anterior plate versus posterior transpedicular instrumentation

Study Design. Biomechanical study using human cadaver spines. Objective. To assess the stabilizing effect of a supplemental anterior tension band (ATB, Synthes) plate on L5–S1 anterior lumbar interbody fusion (ALIF) using a femoral ring allograft (FRA) under physiologic compressive preloads, and to compare the results with the stability achieved using FRA with supplemental transpedicular instrumentation. Summary of Background Data. Posterior instrumentation can improve the stability of ALIF cages. Anterior plates have been proposed as an alternative to avoid the additional posterior approach. Methods. Eight human specimens (L3 to sacrum) were tested in the following sequence: (i) intact, (ii) after anterior insertion of an FRA at L5–S1, (iii) after instrumentation with the ATB plate, and (iv) after removal of the plate and adding transpedicular instrumentation at the same level. Specimens were tested in flexion-extension, lateral bending, and axial rotation. Flexion-extension was tested under 0 N, 400 N, and 800 N compressive follower preload to simulate physiologic compressive preloads on the lumbar spine. Results. Stand-alone FRAs significantly decreased the range of motion (ROM) in all tested directions (P < 0.05); however, the resultant ROM was large in flexion-extension ranging between 6.1 ± 3.1° and 5.1 ± 2.2° under 0 N to 800 N preloads. The ATB plate resulted in a significant additional decrease in flexion-extension ROM under 400 N and 800 N preloads (P < 0.05). The flexion-extension ROM with the ATB plate was 4.1 ± 2.3 under 0 N preload and ranged from 3.1 ± 1.8 to 2.4 ± 1.3 under 400 N to 800 N preloads. The plate did not significantly decrease lateral bending or axial rotation ROM compared with stand-alone FRA (P > 0.05), but the resultant ROM was 2.7 ±1.9° and 0.9 ± 0.6°, respectively. Compared with the ATB plate, the transpedicular instrumentation resulted in significantly less ROM in flexion-extension and lateral bending (P < 0.05), but not in axial rotation (P > 0.05). Conclusion. The ATB plate can significantly increase the stability of the anterior FRA at L5–S1 level. Although supplemental transpedicular instrumentation results in a more stable biomechanical environment, the resultant ROM with the addition of a plate is small, especially under physiologic preload, suggesting that the plate can sufficiently resist motion. Therefore, clinical assessment of the ATB plate as an alternative to transpedicular instrumentation to enhance ALIF cage stability is considered reasonable.

Plaster of Paris as bone substitute in spinal surgery

Abstract. In order to assess the effectiveness of calcium sulphate (plaster of Paris; POP) as a substitute for autologous bone graft, we performed lumbar intervertebral fusion in mature sheep using POP and a variety of other graft materials, and reviewed the literature. The osteoconductivity of the POP grafts was compared to that of grafts carried out with autogenous iliac crest, frozen allogeneic bone, and ProOsteon 500 coralline bone. We also compared the osteogenicity of POP to admixtures of autogenous iliac crest bone with POP and coralline bone, and to an osteoinductive demineralized sheep bone preparation (DBM). The substrates were loaded into tubular titanium mesh, implanted into excavated disc spaces and recovered after a period of 4 months. Fusion mass segments tested in flexion and tension showed that POP was equal to autogenous bone and most other substrates. The POP fusions were significantly tougher than the DBM fusions, even though histomorphometry failed to reveal differences in the amount of trabecular bone. We conclude that POP can be used to achieve a biomechanically stable interbody lumbar vertebral fusion. In addition, our literature review indicated that POP can be used as a vehicle for local delivery of antibiotics in bone infections.

Kinematics of cervical total disc replacement adjacent to a two-level, straight versus lordotic fusion.

Study Design. In vitro biomechanical study. Objective. To characterize cervical total disc replacement (TDR) kinematics above two-level fusion, and to determine the effect of fusion alignment on TDR response. Summary of Background Data. Cervical TDR may be a promising alternative for a symptomatic adjacent level after prior multilevel cervical fusion. However, little is known about the TDR kinematics in this setting. Methods. Eight human cadaveric cervical spines (C2–T1, age: 59 ± 8.6 years) were tested intact, after simulated two-level fusion (C4–C6) in lordotic alignment and then in straight alignment, and after C3–C4 TDR above the C4–C6 fusion in lordotic and straight alignments. Fusion was simulated using an external fixator apparatus, allowing easy adjustment of C4–C6 fusion alignment, and restoration to intact state upon disassembly. Specimens were tested in flexion-extension using hybrid testing protocols. Results. The external fixator device significantly reduced range of motion (ROM) at C4–C6 to 2.0 ± 0.6°, a reduction of 89 ± 3.0% (P < 0.05). Removal of the fusion construct restored the motion response of the spinal segments to their intact state. The C3–C4 TDR resulted in less motion as compared to the intact segment when the disc prosthesis was implanted either as a stand-alone procedure or above a two-level fusion. The decrease in motion of C3–C4 TDR was significant for both lordotic and straight fusions across C4–C6 (P < 0.05). Flexion and extension moments needed to bring the cervical spine to similar C2 motion endpoints significantly increased for the TDR above a two-level fusion compared to TDR alone (P < 0.05). Lordotic fusion required significantly greater flexion moment, whereas straight fusion required significantly greater extension moment (P < 0.05). Conclusion. TDR placed adjacent to a two-level fusion is subjected to a more challenging biomechanical environment as compared to a stand-alone TDR. An artificial disc used in such a clinical scenario should be able to accommodate the increased moment loads without causing impingement of its endplates or undue wear during the expected life of the prosthesis.

Surgical treatment of spinal brucellosis.

We retrospectively reviewed 10 patients with spinal brucellosis of the thoracic and lumbar spine who were treated successfully with a combination of surgery and antibiotics. All patients had back pain; six patients had radiculopathy and one patient had paraparesis. Patients with spondylodiscitis without epidural abscesses (n = 3) had transpedicle discectomy and drainage. Epidural abscesses in the lumbar area caused by spondylodiscitis (n = 3), spondylitis (n = 2), and discitis with infected disc herniation (n = 1), were drained using a posterior approach combined with posterolateral fusion in two patients with spondylodiscitis and discectomy in the patient with a herniated disc. One patient presented with a pathologic fracture and neural compression and was treated with anterior corpectomy and reconstruction. Antibiotic treatment was given for 3 to 9 months. Mean followup was 3 years. Back pain improved soon after surgery. Recovery from radiculopathy and paraparesis was complete. One patient had recurrence of infection 9 months after initial treatment. Clinical manifestation of spinal brucellosis can include spondylitis, spondylodiscitis, discitis, epidural abscess, paraspinal abscess, and vertebral collapse. Transpedicle drainage allows tissue diagnosis and facilitates treatment. Because brucellosis usually responds to antibiotics, surgery is considered as the last resort in treating spinal brucellosis, but severe neurologic deficit and incapacitating back pain often necessitate surgical intervention.Level of Evidence: Therapeutic study, level IV (case series). Please see the Guidelines for Authors for a complete description of levels of evidence.

Biomechanical evaluation of segmental occipitoatlantoaxial stabilization techniques.

Study Design. Biomechanical study using human cadaveric cervical spines. Objective. To evaluate the construct stability of 3 different segmental occipitoatlantoaxial (C0–C1–C2) stabilization techniques. Summary of Background Data. Different C0–C1–C2 stabilization techniques are used for unstable conditions in the upper cervical spine, all with different degrees of risk to the vertebral artery. Techniques with similar stability but less risk to the vertebral artery may be advantageous. Methods. Six human cadaveric cervical spines (C0–C5) (age: 74 ± 5.0 years) were used. After testing the intact spines, instability was created by transecting the transverse and alar ligaments. The spines were instrumented from the occiput to C2 using 3 different techniques which varied in their attachment to C2. All spines had 6 screws placed into the occiput along with lateral mass screws at C1. The 3 variations used in attachment to C2 were (1) C2 crossing laminar screws, (2) C2 pedicle screws, and (3) C1–C2 transarticular screws. The C1 lateral mass screws were removed before placement of the C1–C2 transarticular screws. Range of motion across C0–C2 was measured for each construct. The data were analyzed using repeated measures ANOVA. The following post hoc comparisons were made: (1) intact spine versus each of the 3 techniques, (2) laminar screw technique versus the pedicle screw technique, and (3) laminar screw technique versus the transarticular screw technique. The level of significance was α = 0.01 (after Bonferroni correction for 5 comparisons). Results. All 3 stabilization techniques significantly decreased range of motion across C0–C2 compared to the intact spine (P < 0.01). There was no statistical difference among the 3 stabilization methods in flexion/extension and axial rotation. In lateral bending, the technique using C2 crossing laminar screws demonstrated a trend toward increased range of motion compared to the other 2 techniques. CT scans in both axial and sagittal views demonstrated greater proximity to the vertebral artery in the pedicle and transarticular screw techniques compared to the crossing laminar screw technique. Conclusion. Occipitoatlantoaxial stabilization techniques using C2 crossing laminar screws, C2 pedicles screws, and C1–C2 transarticular screws offer similar biomechanical stability. Using the C2 crossing laminar screw technique may offer an advantage over the other techniques due to the reduction of the risk to the vertebral artery during C2 screw placement.