Contributions of flexion-extension cyclic loads to the lumbar spinal segment stability following different discectomy procedures

An in vitro comparison of three nucleus pulposus removal techniques for partial intervertebral disc replacement: An ultra-high resolution MRI study

Background

Nuclectomy, also known as nucleotomy, is a percutaneous surgical procedure performed to remove nucleus material from the center of the disc. Multiple techniques have been considered to perform a nuclectomy, however, the advantages and disadvantages of each are not well understood.

Aims

This in vitro biomechanical investigation on human cadaveric specimens aimed to quantitatively compare three nuclectomy techniques performed using an automated shaver, rongeurs, and laser.

Material & Methods

Comparisons were made in terms of mass, volume and location of material removal, changes in disc height, and stiffness. Fifteen vertebra-disc-vertebra lumbar specimens were acquired from six donors (40 ± 13 years) and split into three groups. Before and after nucleotomy axial mechanical tests were performed and T2-weighted 9.4T MRIs were acquired for each specimen.

Results

When using the automated shaver and rongeurs similar volumes of disc material were removed (2.51 ± 1.10% and 2.76 ± 1.39% of the total disc volume, respectively), while considerably less material was removed using the laser (0.12 ± 0.07%). Nuclectomy using the automated shaver and rongeurs significantly reduced the toe-region stiffness (p = 0.036), while the reduction in the linear region stiffness was significant only for the rongeurs group (p = 0.011). Post-nuclectomy, 60% of the rongeurs group specimens showed changes in the endplate profile while 40% from the laser group showed subchondral marrow changes.

Discussion

From the MRIs, homogeneous cavities were seen in the center of the disc when using the automated shaver. When using rongeurs, material was removed non-homogeneously both from the nucleus and annulus regions. Laser ablation formed small and localized cavities suggesting that the technique is not suitable to remove large volumes of material unless it is developed and optimized for this application.

Conclusion

The results demonstrate that both rongeurs and automated shavers can be used to remove large volumes of NP material but the reduced risk of collateral damage to surrounding tissues suggests that the automated shaver may be more suitable.

The degenerative lumbar disc: not a disease, but still an important consideration for OMPT practice: a review of the history and science of discogenic instability

BACKGROUND

A recent AAOMPT position paper was published that opposed the use of the term 'degenerative disc disease' (DDD), in large part because it appears to be a common age-related finding. While common, there are significant physiologic and biomechanical changes that occur as a result of discogenic degeneration, which are relevant to consider during the practice of manual therapy.

METHODS

A narrative review provides an overview of these considerations, including a historical perspective of discogenic instability, the role of the disc as a pain generator, the basic science of a combined biomechanical and physiologic cycle of degeneration and subsequent discogenic instability, the influence of rotation on the degenerative segment, the implications of these factors for manual therapy practice, and a perspective on an evidence-based treatment approach to patients with concurrent low back pain and discogenic degeneration.

CONCLUSIONS

As we consider the role of imaging findings such as DDD, we pose the following question: Do our manual interventions reflect the scientifically proven biomechanical aspects of DDD, or have we chosen to ignore the helpful science as we discard the harmful diagnostic label?

Percutaneous endoscopic discectomy in adolescent lumbar disc herniation: a 3- to 5-year study

OBJECTIVEThe authors sought to investigate the efficiency of percutaneous endoscopic discectomy (PED) in adolescent patients with lumbar disc herniation (LDH), compare PED outcomes in adolescent patients with those in young adult LDH patients as controls, and discuss relevant technical notes.METHODSThis was a retrospective study involving 19 adolescent LDH patients (age > 13 and < 18 years, 20 discectomies) and 38 young adults (age < 40 years, 38 discectomies) who also had LDH and were matched to the adolescent group for sex and body mass index. The combined cohort included 51 male patients (89.5%) and 6 female patients (10.5%), with an average age of 26.7 years (range 14-39 years). The operated levels included L3-4 in 1 patient (1.7%), L4-5 in 22 patients (37.9%), and L5-S1 in 35 patients (60.4%). Two adolescents (10.5%) exhibited apophyseal ring separation and one (5.3%) had had previous PED. All patients underwent PED under local anesthesia. Outcomes were evaluated through a visual analog scale (VAS), the Japanese Orthopaedic Association (JOA) scoring system, and the modified MacNab grading system.RESULTSThe mean duration of follow-up was 41.7 months (range 36-65 months). The outcomes in adolescents were satisfactory and comparable with previously reported outcomes of microsurgical discectomy (MD) and conventional open discectomy (COD). The adolescent patients had a faster and better recovery course than the adult patients (p < 0.01). One adolescent patient (5.3%) exhibited recurrence and 2 adults (5.3%) experienced transient dysesthesia; the complication rates were comparable in the 2 age groups (p = 0.47). Prolonged duration of symptoms (p < 0.01) and disc degeneration (p = 0.01) were correlated with lower postoperative JOA values; patients with extrusions had higher postoperative JOA values than those with protrusions (p = 0.01).CONCLUSIONSPED may yield favorable results in the treatment of adolescent LDH in terms of short- to medium-term follow-up; restricted discectomy and a conservative rehabilitation program might be advisable. Further long-term studies are warranted to address this rare disease entity.

Kinematic and fatigue biomechanics of an interpositional facet arthroplasty device

BACKGROUND CONTEXT

Although approximately 30% of chronic lumbar pain can be attributed to the facets, limited surgical options exist for patients. Interpositional facet arthroplasty (IFA) is a novel treatment for lumbar facetogenic pain designed to provide patients who gain insufficient relief from medical interventional treatment options with long-term relief, filling a void in the facet pain treatment continuum.

PURPOSE

This study aimed to quantify the effect of IFA on segmental range of motion (ROM) compared with the intact state, and to observe device position and condition after 10,000 cycles of worst-case loading.

STUDY DESIGN/SETTING

In situ biomechanical analysis of the lumbar spine following implantation of a novel IFA device was carried out.

METHODS

Twelve cadaveric functional spinal units (L2-L3 and L5-S1) were tested in 7.5 Nm flexion-extension, lateral bending, and torsion while intact and following device implantation. Additionally, specimens underwent 10,000 cycles of worst-case complex loading and were testing in ROM again. Load-displacement and fluoroscopic data were analyzed to determine ROM and to evaluate device position during cyclic testing. Devices and facets were evaluated post testing. Institutional support for implant evaluation was received by Zyga Technology.

RESULTS

Range of motion post implantation decreased versus intact, and then was restored post cyclic-testing. Of the tested devices, 6.5% displayed slight movement (0.5-2 mm), all from tight L2-L3 facet joints with misplaced devices or insufficient cartilage. No damage was observed on the devices, and wear patterns were primarily linear.

CONCLUSIONS

The results from this in situ cadaveric biomechanics and cyclic fatigue study demonstrate that a low-profile, conformable IFA device can maintain position and facet functionality post implantation and through 10,000 complex loading cycles. In vivo conditions were not accounted for in this model, which may affect implant behavior not predictable via a biomechanical study. However, these data along with published 1-year clinical results suggest that IFA may be a valid treatment option in patients with chronic lumbar zygapophysial pain who have exhausted medical interventional options.

Primary Versus Revision Single-level Minimally Invasive Lumbar Discectomy: Analysis of Clinical Outcomes and Narcotic Utilization

STUDY DESIGN

Retrospective cohort analysis of a prospectively maintained registry.

OBJECTIVE

To compare the intraoperative variables, surgical outcomes, and narcotic utilization between primary and revision 1-level minimally invasive (MIS) lumbar discectomies.

SUMMARY OF BACKGROUND DATA

Revision spine surgery may be associated with longer procedural time and greater soft tissue disruption. Few studies have analyzed the surgical outcomes and narcotic utilization associated with MIS revision lumbar discectomies.

METHODS

A retrospective analysis of 227 consecutive cases of MIS 1-level lumbar discectomy for degenerative spinal pathology between 2009 and 2014 by a single surgeon was performed. Patients were stratified into primary and revision cohorts. Demographics, comorbidity, intraoperative parameters, peri- and postoperative outcomes, and reoperations were assessed. Postoperative narcotic utilization was compared between cohorts. Statistical analyses were performed using Student t-test and Pearson χ test. A P < 0.05 denoted statistical significance.

RESULTS

Of the 227 cases included, 186 patients (81.9%) and 41 patients (18.1%) were included in the primary and revision cohorts, respectively. Demographics, comorbidity, smoking status, preoperative visual analogue scale (VAS) scores, and estimated blood loss did not differ between cohorts. However, the revision cohort demonstrated a longer procedural time, increased length of hospitalization, and higher postoperative narcotic utilization. Although not statistically significant, revision patients trended toward higher 6-week postoperative VAS scores and reherniation rates. In addition, revision patients were more likely to undergo subsequent lumbar fusion than primary patients.

CONCLUSION

The findings suggest that revision MIS lumbar discectomy may be associated with increased procedural time, increased length of hospitalization, and increased postoperative narcotic utilization. Whereas revision patients trended toward higher postoperative VAS scores at 6 weeks, both cohorts demonstrated similar pain levels at final follow-up. Finally, revision patients may be at a greater risk of reherniation and subsequent reoperation. Further studies are warranted to characterize the independent risk factors for a revision lumbar discectomy.

LEVEL OF EVIDENCE

3.

Surgical treatment for posterior rim separation of the lumbar and sacral vertebrae

OBJECTIVE

The posterior rim separation of the lumbar and sacral vertebrae has been ascribed to various mechanisms. The procedure of operative treatment is still controversial. The authors' objective was to study the therapeutic methods of posterior vertebral rim separation.

METHODS

Thirty-four patients, including 23 males and 11 females whose ages ranged from 24 to 65 years (mean 41.3 years), were treated for posterior vertebral rim separation by various methods. All patients had discectomy and removal of bony fragment. Wide fenestration or hemilaminectomy was performed for 24 type I-III lesions, laminectomy for four type II and one type III lesion, and bilateral fenestration for 5 of 17 type II lesions. Posterior lumbar interbody fusion (PLIF) was performed in 11 patients using autogenous iliac bone or poly (ether-ether-ketone) (PEEK) spacer implant.

RESULTS

Follow-up studies were performed for all patients ranging from 11 months to 4.6 years with an average period of 2.7 years. There were no serious intra-operative or postoperative complications. Satisfactory results were achieved in all patients except two with type III lesions, mostly because of a long history of hypaesthesia of the leg and a drop foot. Eleven patients who had PLIF exhibited bony fusion at final follow-up.

CONCLUSIONS

Early operative treatment should be performed on patients after a brief trial of conservative treatment. A proper surgical operation must be based on the type and location of the separated bony fragment and clinical symptoms.

An injectable nucleus pulposus implant restores compressive range of motion in the ovine disc

STUDY DESIGN

Investigation of injectable nucleus pulposus (NP) implant.

OBJECTIVE

To assess the ability of a recently developed injectable hydrogel implant to restore nondegenerative disc mechanics through support of NP functional mechanics.

SUMMARY OF BACKGROUND DATA

Although surgical intervention for low back pain is effective for some patients, treated discs undergo altered biomechanics and adjacent levels are at increased risk for accelerated degeneration. One potential treatment as an alternative to surgery for degenerated disc includes the percutaneous delivery of agents to support NP functional mechanics. The implants are delivered in a minimally invasive fashion, potentially on an outpatient basis, and do not preclude later surgical options. One of the challenges in designing such implants includes the need to match key NP mechanical behavior and mimic the role of native nondegenerate NP in spinal motion.

METHODS

The oxidized hyaluronic acid gelatin implant material was prepared. In vitro mechanical testing was performed in mature ovine bone-disc-bone units in 3 stages: intact, discectomy, and implantation versus sham. Tested samples were cut axially for qualitative structural observations.

RESULTS

Discectomy increased axial range of motion (ROM) significantly compared with intact. Hydrogel implantation reduced ROM 17% (P < 0.05) compared with discectomy and returned ROM to intact levels (ROM intact 0.71 mm, discectomy 0.87 mm, postimplantation 0.72 mm). Although ROM for the hydrogel implant group was statistically unchanged compared with the intact disc, ROM for sham discs, which received a discectomy and no implant, was significantly increased compared with intact. The compression and tension stiffness were decreased with discectomy and remained unchanged for both implant and sham groups as expected because the annulus fibrosus was not repaired. Gross morphology images confirmed no ejection of NP implant.

CONCLUSION

An injectable implant that mimics nondegenerate NP has the potential to return motion segment ROM to normal subsequent to injury.

Transarticular facet screw stabilization and dorsal laminectomy in 26 dogs with degenerative lumbosacral stenosis with instability

OBJECTIVE

To describe outcome after transarticular facet screw stabilization and dorsal laminectomy for treatment of dynamic degenerative lumbosacral stenosis (DLS) in 26 dogs.

STUDY DESIGN

Retrospective case series.

ANIMALS

Dogs (n = 26) with dynamic DLS.

METHODS

Medical records (2004-2009) of dogs treated with transarticular facet screw stabilization and dorsal laminectomy were reviewed. Dogs (n = 26) were available for immediate postoperative follow-up, 21 dogs at 6 weeks, and 15 at greater than 6 months. Dogs were evaluated by radiographic assessment and owner questionnaire. Lumbosacral (LS) intervertebral disc (IVD) spaces were measured on pre and postoperative 6-week and 6-month radiographs.

RESULTS

In 23 dogs, improvement in clinical signs occurred within 7 days of surgery. Overall postsurgical complication rate directly related to the surgical procedure was 15.4%. LS IVD space measurements taken immediately postoperatively, at 6 weeks, and ≥ 6 months were all significantly increased compared with preoperative measurements. All working dogs (4) returned to full work within 14 months. Most owners (85%) reported their dog was ambulating normally at 6 months with no perceptible lameness during normal activity. All owners perceived their dog's ability to walk, run, and jump after surgery to be improved.

CONCLUSIONS

Transarticular facet screw stabilization and dorsal laminectomy maintains distraction of the LS IVD space for medium-to-large breed dogs with dynamic DLS with a high degree of owner satisfaction, and is comparable to other reported surgical techniques for DLS.

The effect of nucleotomy and the dependence of degeneration of human intervertebral disc strain in axial compression

STUDY DESIGN

Biomechanics of human intervertebral discs before and after nucleotomy.

OBJECTIVE

To noninvasively quantify the effect of nucleotomy on internal strains under axial compression in flexion, neutral, and extension positions, and to determine whether the change in strains depended on degeneration.

SUMMARY OF BACKGROUND DATA

Herniation and nucleotomy may accelerate the progression of disc degeneration. Removal of nucleus pulposus (NP) tissue has resulted in altered disc mechanics in vitro, including a decrease in internal pressure and an increase in the deformations at physiologically relevant strains. We recently presented a technique to quantify internal disc strains using magnetic resonance imaging (MRI).

METHODS

Degeneration was quantitatively assessed by the T1ρ relaxation time in the NP. Samples were prepared from human levels L3-L4 and/or L4-L5. A 1000-N compressive load was applied while in the magnetic resonance scanner. Nucleotomy was performed by removing 2 g of NP through the posterior-lateral annulus fibrosus (AF). The discs were rehydrated, reimaged, and retested. The analyzed parameters include axial deformation, AF radial bulge, and strains. RESULTS.: The axial deformation was more compressive after nucleotomy. In the neutral position, the axial deformation after nucleotomy correlated with degeneration (as quantified by T1ρ in the NP), with minimal alteration in nondegenerated discs. Nucleotomy altered the radial displacements and strains in the neutral position, such that the inner AF radial bulge decreased and the radial strains were more tensile in the lateral AF and less tensile in the posterior AF. In the bending loading positions the radial strains were not affected by nucleotomy.

CONCLUSION

Nucleotomy alters the internal radial and axial AF strains in the neutral position, which may leave the AF vulnerable to damage and microfractures. In bending, the effects of nucleotomy were minimal, likely due to more of the applied load being directed over the AF. Some of the nucleotomy effects are modulated by degeneration, where the mechanical effect of nucleotomy was magnified in degenerated discs and may further induce mechanical damage and degeneration.

Effects of compressive loading on biomechanical properties of disc and peripheral tissue in a rat tail model

Intervertebral disc degeneration induced by mechanical compression is an important issue in spinal disorder research. In this study, the biomechanical aspect of the rat tail model was investigated. An external loading device equipped with super-elastic TiNi springs was developed to apply a precise load to the rat tail. By using this device, rat tail discs were subjected to compressive stress of 0.5 or 1.0 MPa for 2 weeks. Discs in the sham group received an attachment of the device but no loading. After the experimental period, first the intact tail with peripheral tissues (PT) such as tendon and skin and then the retrieved disc without PT were subjected to a uniaxial tension-compression test; biomechanical characteristics such as range of motion (ROM), neutral zone (NZ), and hysteresis loss (HL) were evaluated. Furthermore, the load-bearing contribution of PT in the intact tail was estimated by comparing the load-displacement curves obtained by the mechanical tests performed with and without PT. The experimental findings revealed that the continuous compressive stress induced reduction in disc thickness. The intact tail demonstrated decreases in ROM and NZ as well as increases in HL. On the other hand, the retrieved disc demonstrated increases in ROM, NZ, and HL. Further, a significant increase in the load-bearing contribution of PT was indicated. These findings suggest that the load-bearing capacity of the disc was seriously deteriorated by the application of compressive stress of 0.5 or 1.0 MPa for 2 weeks.

Disc Mechanics With Trans-Endplate Partial Nucleotomy are not Fully Restored Following Cyclic Compressive Loading and Unloaded Recovery

Mechanical function of the intervertebral disc is maintained through the interaction between the hydrated nucleus pulposus, the surrounding annulus fibrosus, and the superior and inferior endplates. In disc degeneration the normal transfer of load between disc substructures is compromised. The objective of this study was to explore the mechanical role of the nucleus pulposus in support of axial compressive loads over time. This was achieved by measuring the elastic slow ramp and viscoelastic stress-relaxation mechanical behaviors of cadaveric sheep motion segments before and after partial nucleotomy through the endplate (keeping the annulus fibrosus intact). Mechanics were evaluated at five conditions: Intact, intact after 10,000cycles of compression, acutely after nucleotomy, following nucleotomy and 10,000cycles of compression, and following unloaded recovery. Radiographs and magnetic resonance images were obtained to examine structure. Only the short time constant of the stress relaxation was altered due to nucleotomy. In contrast, cyclic loading resulted in significant and large changes to both the stiffness and stress relaxation behaviors. Moreover, the nucleotomy had little to no effect on the disc mechanics after cyclic loading, as there were no significant differences comparing mechanics after cyclic loading with or without the nucleotomy. Following unloaded recovery the mechanical changes that had occurred as a consequence of cyclic loading were restored, leaving only a sustained change in the short time constant due to the trans-endplate nucleotomy. Thus the swelling and redistribution of the remaining nucleus pulposus was not able to fully restore mechanical behaviors. This study reveals insights into the role of the nucleus pulposus in disc function, and provides new information toward the potential role of altered nucleus pulpous function in the degenerative cascade.

Trans-Endplate Nucleotomy Increases Deformation and Creep Response in Axial Loading

Knowledge of the functional role of the nucleus pulposus is critical for the development and evaluation of disc treatment strategies to restore mechanical function. While previous motion segment studies have shown that nucleotomy alters disc mechanics, disruption of the annulus fibrosus may have influenced these experiments. The objective of this study was to determine the mechanical role of the nucleus pulposus in support of axial loads via a trans-endplate nucleotomy procedure. Sheep motion segments were randomly assigned to three groups: control, limited nucleotomy, and radical nucleotomy. Mechanical testing consisted of 20 cycles of compression-tension, a 1-h creep, and a slow constant-rate compressive ramp test. Nucleotomy led to increased axial deformations, in particular an elongated neutral zone, a greater range of motion, and altered creep behavior. In general, the elastic properties exhibited a graded response with respect to the amount of nucleus material removed. This graded effect can be attributed to swelling of the nucleus pulposus in the limited nucleotomy group, whereas little swelling was observed in the radical group. The findings of the present study indicate that functional evaluation of nucleus pulposus replacements and disc implants should include range of motion measures (including neutral zone) and viscoelastic creep experiments in addition to considering compressive stiffness.

Biomechanical comparison of lumbar spine with or without spina bifida occulta. A finite element analysis

STUDY DESIGN

Biomechanical study using finite element model (FEM) of lumbar spine.

OBJECTIVES

Very high coincidence of spina bifida occulta (SBO) has been reported more than in 60% of lumbar spondylolysis. The altered biomechanics due to SBO is one considerable factor for this coincidence. Thus, in this study, the biomechanical changes in the lumbar spine due to the presence of SBO were evaluated.

SETTING

United States of America (USA).

METHODS

An experimentally validated three-dimensional nonlinear FEM of the intact ligamentous L3-S1 segment was used and modified to simulate two kinds of SBO at L5. One model had SBO with no change in the length of the spinous process and the other had a small dysplastic spinous process. Von Mises stresses at pars interarticularis were analyzed in the six degrees of lumbar motion with 400 N axial compression, which simulates the standing position. The range of motion at L4/5 and L5/S1 were also calculated.

RESULTS

It was observed that the stresses in all the models were similar, and there was no change in the highest stress value when compared to the intact model. The range of motion was also similar in all the models. The lumbar kinematics of SBO was thus shown to be similar to the intact model.

CONCLUSION

SBO does not alter lumbar biomechanics with respect to stress and range of motion. The high coincidence of spondylolysis in spines with SBO may not be due to the mechanical factors.