Anterior lumbar fusion using a hybrid interbody graft. A preliminary radiographic report

Primary anterior lumbar interbody fusion, with and without posterior instrumentation: a 1,377-patient cohort from a multicenter spine registry

BACKGROUND CONTEXT

Lumbar interbody instrumentation techniques are common and effective surgical options for a variety of lumbar degenerative pathologies. Anterior lumbar interbody fusion (ALIF) has become a versatile and powerful means of decompression, stabilization, and reconstruction. As an anterior only technique, the integrity of the posterior muscle and ligaments remain intact. Adding posterior instrumentation to ALIF is common and may confer benefits in terms of higher fusion rate but could contribute to adjacent segment degeneration due to additional rigidity. Large clinical studies comparing stand-alone ALIF with and without posterior supplementary fixation (ALIF+PSF) are lacking.

PURPOSE

To compare rates of operative nonunion and adjacent segment disease (ASD) in ALIF with or without posterior instrumentation.

STUDY DESIGN

Retrospective cohort study.

PATIENT SAMPLE

Adult patients (≥18 years old) who underwent primary ALIF for lumbar degenerative pathology between levels L4 to S1 over a 12-year period. Exclusion criteria included trauma, cancer, infection, supplemental decompression, noncontiguous fusions, prior lumbar fusions, and other interbody devices.

OUTCOME MEASURES

Reoperation for nonunion and ASD compared between ALIF only and ALIF+PSF.

METHODS

Reoperations were modeled as time-to-events where the follow-up time was defined as the difference between the primary ALIF procedure and the date of the outcome of interest. Crude cumulative reoperation probabilities were reported at 5-years follow-up. Multivariable Cox proportional hazard regression was used to evaluate risk of operative nonunion and for ASD adjusting for patient characteristics.

RESULTS

The study consisted of 1,377 cases; 307 ALIF only and 1070 ALIF+PSF. Mean follow-up time was 5.6 years. The 5-year crude nonunion incidence was 2.4% for ALIF only and 0.5% for ALIF+PSF; after adjustment for covariates, a lower operative nonunion risk was observed for ALIF+PSF (HR=0.22, 95% CI=0.06-0.76). Of the patients who are deemed potentially suitable for ALIF alone, one would need to add posterior instrumentation in 53 patients to prevent one case of operative nonunion at a 5-year follow-up (number needed to treat). Five-year operative ASD incidence was 4.3% for ALIF only and 6.2% for ALIF+PSF; with adjustments, no difference was observed between the cohorts (HR=0.96, 95% CI=0.54-1.71).

CONCLUSIONS

While the addition of posterior instrumentation in ALIFs is associated with lower risk of operative nonunion compared with ALIF alone, operative nonunion is rare in both techniques (<5%). Accordingly, surgeons should evaluate the added risks associated with the addition of posterior instrumentation and reserve the supplemental posterior fixation for patients that might be at higher risk for operative nonunion. Rates of operative ASD were not statistically higher with the addition of posterior instrumentation suggesting concern regarding future risk of ASD perhaps should not play a role in considering supplemental posterior instrumentation in ALIF.

Lumbar disc arthroplasty versus anterior lumbar interbody fusion: 5-year outcomes for patients in the Maverick disc investigational device exemption study

OBJECTIVE

Despite evidence of its safety and effectiveness, the use of lumbar disc arthroplasty has been slow to expand due in part to concerns about late complications and the risks of revision surgery associated with early devices. More recently, FDA approval of newer devices and improving reimbursements have reversed this trend in the United States. Additional long-term data on lumbar disc arthroplasty are still needed. This study reports the 5-year results of the FDA investigational device exemption clinical trial of the Medtronic Spinal and Biologics' Maverick total disc replacement.

METHODS

Patients with single-level degenerative disc disease from L4 to S1 were randomized 2:1 at 31 investigational sites. In the period from April 2003 to August 2004, 405 patients received the investigational device and 172 patients underwent the control procedure of anterior lumbar interbody fusion. Outcome measures included the Oswestry Disability Index (ODI), numeric rating scales (NRSs) for back and leg pain, the SF-36, disc height, interbody motion, heterotopic ossification (investigational device), adverse events (AEs), additional surgeries, and neurological status. Treatment was considered an overall success when all of the following criteria were met: 1) ODI score improvement ≥ 15 points over the preoperative score; 2) maintenance or improvement in neurological status compared with preoperatively; 3) disc height success, that is, no more than a 2-mm reduction in anterior or posterior height; 4) no serious AEs caused by the implant or by the implant and the surgical procedure; and 5) no additional surgery classified as a failure.

RESULTS

Compared to that in the control group, improvement in the investigational group was statistically greater according to the ODI and SF-36 Physical Component Summary (PCS) at 1, 2, and 5 years; the NRS for back pain at 1 and 2 years; and the NRS for leg pain at 1 year. The rates of heterotopic ossification increased over time: 1.0% (4/382) at 1 year, 2.6% (9/345) at 2 years, and 5.9% (11/187) at 5 years. Investigational patients had fewer device-related AEs and serious device-related AEs than the control patients at both 2 and 5 years postoperatively. Noninferiority of the composite measure overall success was demonstrated at all follow-up intervals; superiority was demonstrated at 1 and 2 years.

CONCLUSIONS

Lumbar disc arthroplasty is a safe and effective treatment for single-level lumbar degenerative disc disease, resulting in improved physical function and reduced pain up to 5 years after surgery.Clinical trial registration no.: NCT00635843 (clinicaltrials.gov).

Quality of Life Following Prestige LP Cervical Disc Arthroplasty in a Prospective Multicountry Study

Background

To describe routine surgical practice using Prestige LP Cervical Disc (Prestige disc) and patient outcomes for degenerative cervical disc disease in a multicenter 2-year prospective, observational study.

Methods

Patient demographics and intraoperative data were collected; quality of life (QoL) (EQ-5D, EQ-VAS, and neck disability index), average disc height, and adverse events were assessed pre- and postoperatively at 3, 6, 12, and 24 months.

Results

One hundred and ninety-four patients were enrolled (190 patients implanted; female: 67%; mean age: 44.0 years; mean body mass index: 25.6). Disc herniation was the most frequent indication for cervical arthroplasty (80.5%). Thirty-seven percent of patients experienced pain for >1 year prior to baseline assessment. Mean procedure duration was 87.1 minutes, and mean blood loss was 43.8 mL. The majority (71.0%) of Prestige discs were implanted at level C5 to C6, while 16.3% of patients received implants at 2 levels. There was a significant improvement from baseline to 3, 6, 12, and 24 months of follow-up in all QoL assessments. After implantation, the mean disc height at the affected level increased by 0.19 from baseline (0.22) to 3 months (0.41) and remained constant up to 24 months (P < .001). Mean disc height of levels above and below the implant remained comparable at baseline and follow-up. A total of 63 adverse events (44 patients) was recorded, of which 7 (11.1%) were related to the Prestige disc, instrumentation, or procedure; 41 (65.1%) were unrelated; and 15 (23.8%) had an unknown relation.

Conclusions

In line with published findings, our study shows significant improvement in outcomes in the first 3 months after Prestige disc implantation with improvements maintained throughout the study.

The effect of interbody fusion cage design on the stability of the instrumented spine in response to cyclic loading: an experimental study

BACKGROUND CONTEXT

In the lumbar spine, end plate preparation for the interbody fusion cages may critically affect the cage's long-term performance. This study investigated the effect of the interbody cage design on the compliance and cage subsidence of instrumented spines under cyclic compression.

PURPOSE

We aimed to quantify the role of cage geometry and bone density on the stability of the spinal construct in response to cyclic compressive loads.

STUDY DESIGN

Changes in the cage-bone interface and the effect of bone density on these changes were evaluated in a human cadaveric model for three intervertebral cage designs.

METHODS

The intervertebral space of 27 functional cadaveric spinal units was instrumented with bilateral linear cages, single anterior conformal cages, or single unilateral oblique cages. Once augmented with a pedicle screw fixation system, the instrumented spine unit was tested under cyclic compression loads (400-1,200 N) to 20,000 cycles at a rate of 2 Hz. Compliance of the cage-bone interface and cage subsidence was computed. Two-way repeated multivariate analysis of variance was used to test the effects of cage design and bone density on the compliance and subsidence of the cages.

RESULTS

The anterior conformal shaped cage showed reduced interface stiffness (p<.01) and higher hysteresis (p<.01) and subsidence rate (10%-30%) than the bilateral linear and unilateral oblique-shaped cages. Bone density was not associated with the initial compliance of the cage-bone interface or the rate of cage subsidence. Higher bone density did decrease the rate of reduction in cage-bone interface stiffness under higher cyclic loads for the anterior conformal shaped and unilateral oblique cages.

CONCLUSIONS

Cage design and position significantly affected the degradation of the cage-bone interface under cyclic loading. Comparisons of subsidence rate between the different cage designs suggest the peripheral location of the cages, using the stronger peripheral subchondral bone of the apophyseal ring, to be advantageous in preventing the subsidence and failure of the cage-bone interface.

Stand-alone anterior lumbar interbody fusion: indications, techniques, surgical outcomes and complications

INTRODUCTION

Anterior lumbar interbody fusion (ALIF) is a well-established technique to achieve lumbar spine fusion with various indications including degenerative disk disease, spondylolisthesis, recurrent disk herniation, adjacent level disease, pseudoarthrosis, as well as being used as part of the overall strategy to restore sagittal balance. ALIF can be an extremely useful tool in any spine surgeon's armamentarium. However, like any surgical procedure, proper patient selection is key to success. A solid understanding of the biomechanics, careful surgical planning, along with clear knowledge of the advantages and disadvantages of stand-alone ALIF will ensure optimal clinical outcome. Stand-alone ALIF may be a suitable surgical option in carefully selected patients that can provide good clinical results and adequate fusion rates without the need for posterior instrumentation. Areas covered: A brief overview of the indications, techniques, biomechanics, surgical outcome and complications of stand-alone ALIF is provided in this article with a review of the pertinent literature. Expert commentary: In this review we discuss the clinical evidence of using a stand-alone ALIF compared to other fusion techniques of the lumbar spine. The development of interbody cages with integrated screws has increased the arthrodesis rate and improved clinical outcomes while decreasing morbidity and operative time.

Evolution of Design of Interbody Cages for Anterior Lumbar Interbody Fusion

Anterior lumbar interbody fusion (ALIF) is one of the surgical procedures for the relief of chronic back pain, radiculopathy and neurogenic claudication in patients with degenerative lumbar spine disease that is refractory to conservative therapy, low-grade spondylolisthesis and pseudo arthrosis. Over the past half century, both the surgical techniques and instrumentation required for ALIF have changed significantly. In particular, the designs of ALIF cage and the materials used have evolved dramatically, the common goal being to improve fusion rates and optimize clinical outcomes. The increasing popularity of ALIF is reflected by the increasing abundance of published studies reporting clinical outcomes, surgical techniques and grafting options for ALIF. Developments in cage designs include cylindrical Bagby and Kuslich, cylindrical ray, cylindrical mesh, lumbar-tapered, polyethyl-etherketone cage and integral fixation cages. Biologic implants include bone dowels and femoral ring allografts. Methods for optimization of cage design have included cage dimensions, use of novel composite cage materials and integral fixation technologies. However, the historical development and evolution of cages used for ALIF has not been extensively documented. This article therefore aims to provide an overview of the historical basis for the anterior approach, evolution in design of ALIF cage implants and potential future research directions.

New cage for posterior minimally invasive lumbar interbody fusion: a study in vitro and in vivo

OBJECTIVE

To design a new type of interbody fusion device made of nickel titanium NiTi shape memory alloy and to compare segmental stiffness after various posterior lumbar interbody fusion (PLIF) procedures in vitro and in vivo.

METHODS

Twelve sheep lumbar functional spinal units were randomly allocated to four groups. One acted as controls (N); the other three were treated with autogenous iliac crest bone dowel graft (L), a threaded cylindrical titanium (KC) interbody fusion device (TFC) or a new type of interbody fusion device made of NiTi shape memory alloy (NT) containing autogenous iliac crest graft. In addition, 15 sheep were allocated to three groups; one served as controls and the other two underwent TFC (KC) or NiTi-FC (NT). Nondestructive mechanical tests were performed in pure compression, extension, lateral bending and torsion. The operated spines were photographed regularly to assess changes in interbody height and degree of fusion. The animals were killed at 6 months for histologic testing.

RESULTS

Biomechanical tests showed both the strength and axial stiffness of the NT and KC groups were significantly higher than those of the control group and L group (P < 0.05). When the mechanical performance in torque and torsion of each group were compared, the same results could be obtained. The maximal destructive load of the NiTi-TFC was 11 200 N and the safety coefficient was above 1.2. Radiological observations revealed that the bone callus around the interbody fusion device were gradually increased postoperatively (2 months, no obvious; 4 months, poorly define; 6 months, dense). The KC and NT group had lost 16% and 16.5% of their postoperative height but remained well above normal disc height (P < 0.05). Histologic examination showed new trabeculation connected with that of the host.

CONCLUSION

The mechanical characteristics of the NiTi-TFC are excellent and it is safe and reliable.

Bone graft substitutes for anterior lumbar interbody fusion

The procedure of anterior lumbar interbody fusion (ALIF) is commonly performed on patients suffering from pain and/or neurological symptoms associated with disorders of the lumbar spine caused by disc degeneration and trauma. Surgery is indicated when prolonged conservative management proves ineffective. Because an important objective of the ALIF procedure is solid arthrodesis of the degenerative spinal segment, bone graft selection is critical. Iliac crest bone grafts (ICBG) remain the "gold standard" for achieving lumbar fusion. However, patient dissatisfaction stemming from donor site morbidity, lengthier operating times and finite supply of ICBG has prompted a search for better alternatives. Here presented is a literature review evaluating available bone graft options assessed within the clinical setting. These options include autografts, allograft-based, synthetic and cell-based technologies. The emphasis is on the contentious use of recombinant human bone morphogenetic proteins, which is in widespread use and has demonstrated both significant osteogenic potential and risk of complications.

Microscopic anterior foraminal decompression combined with anterior lumbar interbody fusion

BACKGROUND CONTEXT

Anterior lumbar interbody fusion (ALIF) with percutaneous pedicle screw fixation (PPF) provides successful surgical outcomes to isthmic spondylolisthesis patients with indirect decompression through foraminal volume expansion. However, indirect decompression through ALIF followed by PPF may not obtain a successful surgical outcome in patients with isthmic spondylolisthesis accompanied by foraminal stenosis caused by a posterior osteophyte or foraminal sequestrated disc herniation. Thus far, there has been no report of foraminal decompression through anterior direct access in the lumbar spine.

PURPOSE

This study aims to describe the new surgical technique of microscopic anterior foraminal decompression and to analyze the clinical outcomes and radiologic results of the microscopic anterior decompression during ALIF followed by PPF.

STUDY DESIGN/SETTING

We conducted a multisurgeon, retrospective, clinical series from a single institution.

PATIENT SAMPLE

This study was carried out from March 2007 to July 2010 and included 40 consecutive patients with isthmic spondylolisthesis accompanied by foraminal stenosis caused by posterior osteophyte or foraminal sequestrated disc herniation undergoing microscopic anterior foraminal decompression during ALIF followed by PPF.

OUTCOME MEASURES

The visual analog scales (VAS) of back and leg pain and the Oswestry disability index were measured preoperatively and at the last follow-up.

METHODS

Postoperative computed tomography and magnetic resonance imaging measured whether decompression of neural structure had been made and morphometric change of the foramen and the amount of resected bone. Moreover, segmental lordosis, whole lumbar lordosis, disc height, and degree of listhesis were measured through X-ray examination before the operation and at the last follow-up; we also verified whether fusion had been achieved.

RESULTS

Successful decompression was confirmed in both patients with foraminal stenosis caused by posterior osteophyte and those with foraminal sequestrated disc herniation. Clinically, compared with before the surgery, the VAS (leg and back) and the Oswestry disability index significantly decreased at the last follow-up (p=.000). With regard to radiology, at the last follow-up all patients had bone fusion on X-ray examination, and an increase in disc height, a reduction in the degree of listhesis, an increase in segmental lordosis, and an increase in whole lumbar lordosis were significant in both groups (p=.000) compared with before the surgery. Foraminal volume, foraminal width, and foraminal height also significantly increased postoperatively compared with before the operation (p=.000). The height, width, and dimension of resected body were 4.61±1.05 mm, 7.92±1.42 mm, 17.15±4.96 mm(2), respectively, in patients with foraminal stenosis caused by a posterior osteophyte, and 3.88±0.92 mm, 6.8±1.29 mm, and 13.12±2.25 mm(2), respectively, in patients with foraminal sequestrated disc.

CONCLUSIONS

The microscopic anterior foraminal approach provides successful foraminal decompression. Combined with ALIF and PPF, this approach shows a good surgical outcome in patients with isthmic spondylolisthesis accompanied by foraminal stenosis caused by a posterior osteophyte or those with foraminal sequestrated disc herniation.

Indications for anterior lumbar interbody fusion

Anterior lumbar interbody fusion (ALIF) has become a widely recognized surgical technique for degenerative pathology of the lumbar spine. Spinal fusion has evolved dramatically ever since the first successful internal fixation by Hadra in 1891 who used a posterior approach to wire adjacent cervical vertebrae in the treatment of fracture-dislocation. Advancements were made to reduce morbidity including bone grafting substitutes, metallic hardware instrumentation and improved surgical technique. The controversy regarding which surgical approach is best for treating various pathologies of the lumbar spine still exists. Despite being an established treatment modality, current indications of ALIF are yet to be clearly defined in the literature. This article discusses the current literature on indications on ALIF surgery.

Brachial plexus reconstruction following resection of a malignant peripheral nerve sheath tumor: case report

BACKGROUND AND IMPORTANCE

The main therapeutic approach for malignant peripheral nerve sheath tumors (MPNSTs) of the brachial plexus is wide local excision. Sacrifice of some--occasionally all--elements of the brachial plexus often is required to obtain complete resection, and therefore can be associated with significant morbidity. While peripheral nerve repair is commonly used in the setting of traumatic nerve injury, little is known about its potential use in the treatment of MPNST.

CLINICAL PRESENTATION

We present a patient with an enlarging right neck mass who was diagnosed with MPNST of the brachial plexus. The patient underwent gross total resection of the tumor, requiring sectioning of the upper trunk of the brachial plexus, as well as associated divisions. Following resection, sural nerve grafts were used to connect the C5 nerve root to the anterior division of the upper trunk and the spinal accessory nerve to the suprascapular nerve, whereas a triceps branch of the radial nerve was coapted directly to the anterior division of the axillary nerve.

CONCLUSION

By 20 months after surgery, the patient had regained significant strength in her upper trunk distribution and demonstrated no evidence of tumor recurrence. Brachial plexus reconstruction offers a potentially valuable surgical adjunct to MPNST treatment.

Percutaneous facet screw fixation of lumbar spine with CT and fluoroscopic guidance: a feasibility study

PURPOSE

To assess the feasibility of computed tomography (CT)- and fluoroscopy-guided percutaneous facet screw fixation following anterior lumbar interbody fusion (ALIF) or anterior pseudarthrosis in adults.

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained for this study. One hundred seven consecutive adult patients (46 men, 61 women; mean age ± standard deviation: 56.3 years ± 12.9) with ALIF (n = 79) or anterior pseudarthrosis (n = 28) were prospectively treated by means of percutaneous facet screw fixation with CT and fluoroscopic guidance. Two 4.0-mm cannulated screws were placed per level to fix facet joints by using either a translaminar facet or transfacet pedicle pathway. Only local anesthesia was used during these procedures. Procedural time was noted for each patient. Postoperative follow-up ranging from 1 year to 3 years was assessed by using Macnab and radiologic criteria.

RESULTS

The mean procedure times for a lumbar single-level and a double-level fusion ranged from 15 to 25 minutes and from 40 to 50 minutes, respectively. All the transfacet pedicle (n = 182) and translaminar facet (n = 56) screws were successfully placed in one attempt. Radiographic fusion was observed within the year following posterior fixation in all patients despite one translaminar screw failure. According to the Macnab criteria, the clinical results were classified as excellent in 92 (86%) and good in 15 (14%) of 107 patients at the time of their last follow-up examination.

CONCLUSION

This feasibility study showed that CT- and fluoroscopy-guided percutaneous facet screw fixation is a rapid, safe, and effective method.

Reconstruction of massive uncontained glenoid defects using a combined autograft-allograft construct with reverse shoulder arthroplasty: preliminary results

BACKGROUND

This report documents our experiences with a new technique for reconstructing massive uncontained defects of the glenoid with reverse total shoulder arthroplasty.

MATERIALS AND METHODS

We use a modified deltopectoral approach to perform the combined allograft-autograft construct glenoid reconstruction. We make use of a peripherally seated cortical allograft acting as a sleeve bushing to provide a stable ring under compression in which to house impacted cancellous autograft centrally for early incorporation and in-growth with the long-peg Aequalis (Tornier, Saint-Ismier Cedex, France) reverse total shoulder arthroplasty baseplate.

RESULTS

Our case series now comprises 10 patients with postoperative follow-up of up to 36 months. We report the first 5 patients here, all of whom have more than 12 months of follow-up. Computed tomography scanning demonstrates incorporation of the graft as early as 6 months. None of these patients have had loosening, implant failures, dislocations, periprosthetic fractures, or infections. One patient sustained an acromial stress fracture that was successfully treated nonoperatively, and 1 patient has nonprogressive grade I notching.

CONCLUSION

The hybrid graft glenoid reconstruction is a useful and versatile technique in the setting of massive uncontained defects of the glenoid and permits the implantation of a reverse total shoulder arthroplasty. We believe this technique is reproducible and uses materials that are both readily available and familiar.

The memory metal minimal access cage: a new concept in lumbar interbody fusion-a prospective, noncomparative study to evaluate the safety and performance

Study Design/Objective. A single-centre, prospective, non-comparative study of 25 patients to evaluate the performance and safety of the Memory Metal Minimal Access Cage (MAC) in Lumbar Interbody Fusion. Summary of Background Data. Interbody fusion cages in general are designed to withstand high axial loads and in the meantime to allow ingrowth of new bone for bony fusion. In many cages the contact area with the endplate is rather large leaving a relatively small contact area for the bone graft with the adjacent host bone. MAC is constructed from the memory metal Nitinol and builds on the concept of sufficient axial support in combination with a large contact area of the graft facilitating bony ingrowth and ease in minimal access implantation due to its high deformability. Methods. Twenty five subjects with a primary diagnosis of disabling back and radicular leg pain from a single level degenerative lumbar disc underwent an interbody fusion using MAC and pedicle screws. Clinical performance was evaluated prospectively over 2 years using the Oswestry Disability Index (ODI), Short Form 36 questionnaire (SF-36) and pain visual analogue scale (VAS) scores. The interbody fusion status was assessed using conventional radiographs and CT scan. Safety of the device was studied by registration of intra- and post-operative adverse effects. Results. Clinical performance improved significantly (P < .0018), CT scan confirmed solid fusion in all 25 patients at two year follow-up. In two patients migration of the cage occurred, which was resolved uneventfully by placing a larger size at the subsequent revision. Conclusions. We conclude that the Memory Metal Minimal Access Cage (MAC) resulted in 100% solid fusions in 2 years and proved to be safe, although two patients required revision surgery in order to achieve solid fusion.

Replicating interbody device subsidence with lumbar vertebrae surrogates

Bone surrogates are proposed alternatives to human cadaveric vertebrae for assessing interbody device subsidence. A synthetic vertebra with representations of cortices, endplates and cancellous bone was recently developed as an alternative surrogate to polyurethane foam blocks. The ability of the two surrogates to replicate subsidence has not been fully assessed, and was evaluated by indenting them with ring-shaped indenters and comparing their performance with human cadaveric vertebrae using qualitative characteristics and indentation metrics. The sensitivity of each surrogate to a centrally or peripherally placed indenter was of particular interest. Many indentation characteristics of the foam blocks were similar to those of human cadaveric vertebrae, except their insensitivity to centrally and peripherally placed indenters, owing to their homogeneous mechanical properties. This is distinctly different from the cadaveric vertebrae, where a peripherally placed indenter indented significantly less than a centrally placed indenter, because of endplates. By contrast, the synthetic vertebra was sensitive to peripherally placed indenters owing to its bi-material composition, including a thickened peripheral endplate. However, an overly strong synthetic endplate resulted in unrepresentative indentation shape and depth. Both surrogates produced similar results to human cadaveric vertebrae in certain respects, but neither is accurate enough in terms of material property distribution to model subsidence completely in human cadaveric vertebrae.

Biomechanical differences between transfacet and lateral mass screw-rod constructs for multilevel posterior cervical spine stabilization

STUDY DESIGN

In vitro biomechanical investigation using human cadaveric cervical spines.

OBJECTIVE

Evaluate differences in biomechanical stability between typical lateral mass screw + rod constructs compared to transfacet screw fixation with and without rods.

SUMMARY OF BACKGROUND DATA

Lateral mass screw + rod constructs have reported efficacious arthrodesis rates/quality but risk damaging the lateral neurovascular structures. Transfacet screw fixation has been studied in the lumbar spine, but little data exists regarding its potential utility in the cervical spine.

METHODS

Sixteen human cadaveric cervical spines were stripped of soft tissue leaving the occiput and ligamentous structures intact. Spines were randomized to lateral mass or transfacet groups (n = 8/group). Spines were prepared in typical surgical fashion and instrumented with the appropriate devices. In the case of the transfacet constructs, the occiput was left intact to simulate the potential surgical difficulty of screw insertion. The transfacet screw group was initially instrumented with rods. Once instrumented (C3-C6) for each group, spines were further dissected to isolate the instrumented levels. End vertebral bodies were rigidly fixed and constructs biomechanically tested in flexion/extension, lateral bending, and axial torsion between +/-2 Nm. After testing for the transfacet screw + rod group, rods were removed and spines retested. All instrumentation was then removed and spines tested in their destabilized state as would occur with surgical preparation. Stiffness data were calculated for each test direction for all groups. Raw and normalized data were each compared across techniques with a 1-way ANOVA (P < 0.05).

RESULTS

The transfacet screw groups (with and without rods) were found to have statistically similar biomechanical stability to lateral mass screw + rod constructs for each test direction.

CONCLUSION

Transfacet screws (without rods) were found to have similar biomechanical stability compared to typical lateral mass screw + rod constructs. However, transfacet fixation eliminates the risk to the neurovascular structures and lowers the overall implant profile.

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 degrees and 5.1 +/- 2.2 degrees 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 degrees and 0.9 +/- 0.6 degrees , 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.

A comparison of long-term outcomes of translaminar facet screw fixation and pedicle screw fixation: a prospective study

Object

In this paper, the authors compare the long-term outcomes of translaminar facet screw fixation (TFSF) and pedicle screw fixation (PSF) in the treatment of degenerative lumbosacral disease.

Methods

This prospective analytical study was performed to compare the long-term outcomes of TFSF and PSF for degenerative lumbosacral disease. Outcomes were defined as the need for reoperation for the development of a nonunion, end-fusion degeneration, or for explantation of hardware.

Results

A total of 77 patients were analyzed. Thirty-seven patients underwent PSF and 40 received TFSF. Twenty-three of the 77 patients required a reoperation: 13 (32.5%) of the 40 patients in the TFSF group and 10 (27%) of the 37 the patients in the PSF group. The overall mean time to reoperation (regardless of outcome) was 4.05 years. For patients in the TFSF group the mean time to reoperation was 2.94 years, whereas it was 4.35 years in the PSF group (p = 0.34). Nonunion was noted in seven of the 40 patients in the TFSF group and one of 37 in the PSF group. The mean time to surgery for nonunion for patients in the TFSF group was 3.46 years and for those in the PSF group it was 6.27 years (p = 0.04). Surgery for end-fusion degeneration was performed in two patients in the TFSF group and five in the PSF group (p = 0.43). Explantation of hardware was performed in two patients with TFSF and four patients with PSF.

Multivariable analysis revealed a statistically significant difference in the time to surgery for nonunion between PSF and TFSF (p = 0.048), with a hazard ratio of 0.097 (95% confidence interval 0.01–0.98).

Conclusions

Findings from the current prospective study suggest that there is an increased risk of requirement for a reoperation for nonunion among TFSF cases compared with PSF cases.

Initial results of anterior interbody fusion achieved with a less invasive bone harvesting technique

STUDY DESIGN

A retrospective review.

OBJECTIVE

To review the initial experience using a trephine bone harvesting system from the local lumbar spine for use in anterior interbody fusions, analyzing fusion rates and complications.

SUMMARY OF BACKGROUND DATA

Historically, autogenous bone for lumbar spine fusions has been procured from the iliac crest. No data exist regarding the use of a trephine bone harvesting system for obtaining cancellous bone locally from the lumbar spine for use in anterior interbody fusions. In this technique, the donor site is replaced with a corticocancellous humeral dowel.

METHODS

A total of 36 patients who underwent anterior lumbar interbody fusion were retrospectively reviewed. There were 56 interbody fusions performed using 36 trephine donor sites. Twenty individuals had the bone divided between 2 fusion levels, placed within allograft femoral rings, and 16 had the bone applied to 1 fusion level. Radiographs were analyzed for complications associated with the fibular dowel and time to interbody fusion.

RESULTS

By 6 months, 35 of 36 (97%) of the corticocancellous fibular dowels had incorporated. Two dowels migrated 3 mm, each without sequelae. Of 56 of interbody spaces, 50 (89%) were fused. Two eventually fused at 9 and 11 months, and 4 (7%) failed to unite by 15 months.

CONCLUSION

Harvesting cancellous autograft anteriorly from the lumbar spine using a trephine technique appears to be safe and reliable, with satisfactory fusion rates. Iliac crest graft harvesting with its attendant morbidity is avoided.

A prospective, randomised controlled trial of femoral ring allograft versus a titanium cage in circumferential lumbar spinal fusion with minimum 2-year clinical results

The literature reports on the safety and efficacy of titanium cages (TCs) with additional posterior fixation for anterior lumbar interbody fusion. However, these papers are limited to prospective cohort studies. The introduction of TCs for spinal fusion has resulted in increased costs, without evidence of superiority over the established practice. There are currently no prospective controlled trials comparing TCs to femoral ring allografts (FRAs) for circumferential fusion in the literature. In this prospective, randomised controlled trial, our objective was to compare the clinical outcome following the use of FRA (current practice) to the use of TC in circumferential lumbar spinal fusion. Full ethical committee approval and institutional research and development departmental approval were obtained. Power calculations estimated a total of 80 patients (40 in each arm) would be required to detect clinically relevant differences in functional outcome. Eighty-three patients were recruited for the study fulfilling strict entry requirements (>6 months chronic discogenic low back pain, failure of conservative treatment, one- or two-level discographically proven discogenic low back pain). The patients completed the Oswestry Disability Index (ODI), Visual Analogue Score (VAS) for back and leg pain and the Short-Form 36 (SF-36) preoperatively and also postoperatively at 6, 12 and 24 months, respectively. The results were available for all the 83 patients with a mean follow-up of 28 months (range 24-75 months). Five patients were excluded on the basis of technical infringements (unable to insert TC in four patients and FRA in one patient due to the narrowing of the disc space). From the remaining 78 patients randomised, 37 received the FRA and 41 received the TC. Posterior stabilisation was achieved with translaminar or pedicle screws. Baseline demographic data (age, sex, smoking history, number of operated levels and preoperative outcome measures) showed no statistical difference between groups (p<0.05) other than for the vitality domain of the SF-36. For patients who received the FRA, mean VAS (back pain) improved by 2.0 points (p<0.01), mean ODI improved by 15 points (p=<0.01) and mean SF-36 scores improved by >11 points in all domains (p<0.03) except that of general health and emotional role. For patients who received the TC, mean VAS improved by 1.1 points (p=0.004), mean ODI improved by 6 points (p=0.01) and SF-36 improved significantly in only two of the eight domains (bodily pain and physical function). Revision procedures and complications were similar in both groups. In conclusion, this prospective, randomised controlled clinical trial shows the use of FRA in circumferential lumbar fusion to be associated with superior clinical outcomes when compared to those observed following the use of TCs. The use of TCs for circumferential lumbar spinal fusion is not justified on the basis of inferior clinical outcome and the tenfold increase in cost.

Interkorporelle Metallimplantate („Cages“) bei lumbalen Spondylodesen

Over the last 15 years, interbody metal implants have become commonly used worldwide for lumbar interbody fusion. The so called "cages" are made of metal or absorbable materials. By using different surgical techniques, they can be implanted either regularly or via endoscopy. The published results on surgical techniques using cages for the lumbar spine show, in most cases and with or without additional instrumentation, rates of fusion of more than 90%. It seems that the use of osteoinductive substances (especially BMP) leads to even better results. Dorsoventral fusion with internal fixation and bone show the same rate of consolidation, but the advantages of cages are primarily in the maintenance of the distraction and the possibility of a single surgical procedure without additional instrumentation (including endoscopy), and in a lower donor side morbidity.

Primary stability of anterior lumbar stabilization: interdependence of implant type and endplate retention or removal

This is a comparative in vitro biomechanical study of the primary stability of an anterior lumbar interbody stabilization. The objective was to compare the stability of a interbody stabilizing titanium cage with and without the retention of the bordering vertebral endplates, as well as to compare the titanium cage with a tricalcium phosphate block when the endplates are removed. An adequate blood supply is critical for interbody fusion, which suggests surgical treatment of the bordering endplates. On the other hand, primary stability is improved by the retention of the endplates. Furthermore, bone substitute materials are finding more frequent use due to complications associated with autologous bone grafts. Ten bovine lumbar spine motion segments (average age 6 months) were investigated. Pure bending loadings as well as eccentric axial compression loadings were applied. A titanium cage and tricalcium phosphate block, were tested in conjunction with an anterior augmentation (MACS). Range of motion, neutral zone (NZ) and bending stiffness were measured under pure bending to 10 Nm, and bending stiffness under axial loads of up to 1,500 N. Range of motion of both implants in flexion-extension was significantly smaller than physiologic (cage without endplates 4.3 degrees , cage with 2.8 degrees , block without 3.4 degrees , and physiologic 6.6 degrees , all p<0.001). The cage with endplates and the block without endplates were both significantly stiffer than physiologic in all directions except left lateral bending. The block without endplates and the cage with endplates were both stiffer than the cage without endplates. The results suggest that the use of the bone substitute block provides better stability than the cage when the endplates are removed.

Pedicle screw fixation enhances anterior lumbar interbody fusion with porous tantalum cages: an experimental study in pigs

STUDY DESIGN

A porous tantalum implant (Hedrocel, Implex Corp., Allendale, NJ), designed to assist interbody lumbar fusion, was tested biologically in an experimental model. A total of 11 female Danish landrace pigs received 3 levels of anterior lumbar interbody fusion at L2-L3, L4-L5, and L6-L7. Each level was randomly assigned one of the procedures: (1) implantation of PT-ring with pedicle screw fixation (PSF), (2) implantation of a porous tantalum ring (PT-ring) stabilized anteriorly with staples, or (3) implantation of carbon fiber cage (CF-cage) stabilized anteriorly with 2 staples. Each implant was filled with autogenous iliac crest bone graft.

OBJECTIVES

To evaluate the effects of PSF on the incorporation of autologous bone in a porous tantalum interbody device and to compare healing in PT-rings to that in CF-cages of autologous bone.

SUMMARY OF BACKGROUND DATA

Despite the promising results that early clinical trials have shown, interbody fusion cage technology is still under debate because of uncertainties that include indications for surgery, criteria for fusion, material, cage design, cage subsidence, and the effect of immediate stabilization.

METHODS

Pigs were euthanized 6 months after surgery. Fusion segments were evaluated by plain radiography, conventional radiograph tomography, and histology.

RESULTS

Fusion segments with PSF had significantly fewer radiolucencies than the other 2 levels (P = 0.002). Improved interface healing and fusion rate were observed in PT-rings when supplemented with PSF (P = 0.03). His tomorphometric results showed that the percentage of bone and bone marrow space in the center of a PT-ring was not significantly different from that of its adjacent vertebral body, but PSF increased bone marrow and decreased fibrous tissue formation in a tantalum cage. However, a CF-cage had higher bone volume and lower bone marrow space inside the cage compared with its adjacent vertebral body (P < 0.001). Fibrous tissue formation inside and around a CF-cage was more than that of a PT-ring (P < 0.05).

CONCLUSION

Interbody fusion using a PT-ring cage packed with autologous bone achieved higher interface healing and more reliable fusion when fixated with supplementary pedicle screws than did fixated anteriorly with 2 staples. A lesser amount of bone graft was required, and bone remodeling was enhanced in the PT-ring when compared to the CF-cage.

Clinical analysis of percutaneous facet screw fixation after anterior lumbar interbody fusion

Object. The authors performed a retrospective study to evaluate the results of percutaneous facet screw fixation (PFSF) after anterior lumbar interbody fusion (ALIF) in comparison with the gold standard, post-ALIF pedicle screw fixation (PSF).

Methods. Of 84 patients treated for degenerative spondylolisthesis or degenerative disc disease at the authors' institution, 44 underwent PFSF (Group 1) and 40 underwent PSF (Group 2 [control population]) after ALIF. Function was assessed using the Oswestry Disability Index (ODI) scoring system, and outcome was measured using the Macnab criteria. At 3, 6, 12, and 24 months after surgery, dynamic lateral (flexion—extension) radiography and computerized tomography scanning were conducted to evaluate the osseous union status. After a minimum follow-up period of 2 years, analysis showed no intergroup statistical difference in terms of ODI score and Macnab outcome criteria (p > 0.05).

Excellent or good outcome was obtained in 40 (90.9%) of the 44 patients in Group 1 and 37 (92.5%) of the 40 patients in the control Group 2 (p > 0.05). No patient required a blood transfusion in either group. At 24 months after surgery fusion rates were 95.8% in Group 1 and 97.5% in Group 2.

Conclusions. The results of PFSF following ALIF appear to be clinically equivalent to those achieved after PSF, and the procedure represents a safe and minimally invasive modality with which to achieve solid fusion in the lumbar spine.

Comparative biomechanical testing of anterior and posterior stabilization procedures

STUDY DESIGN

This is a comparative in vitro biomechanical study in a calf lumbar spine model.

OBJECTIVES

The objective was to compare the primary stability of an anterior instrumentation, an intercorporal cage in combination with an anterior instrumentation, and a posterior instrumentation for monosegmental spondylodesis.

SUMMARY OF BACKGROUND DATA

Spondylodesis can be achieved through a posterior lumbar fusion, posterior lumbar intercorporal fusion, or an anterior lumbar intercorporal fusion. The posterior lumbar fusion is the gold standard, although the anterior approach offers some potential advantages to the transpedicular posterior techniques.

METHODS

Stability testing was performed on 30 calf lumbar spine motion segments in a physiologic state (n = 30), with either an isolated anterior (MACS) or posterior instrumentation (SOCON), and with an anterior instrumentation augmented with an intercorporal cage (MACS-Cage, n = 10, respectively). Range of motion, neutral zone, and bending stiffness were measured under pure bending to 10 Nm, and bending stiffness under axial loads of up to 1500 N.

RESULTS

The isolated posterior instrumentation was found to be more stable than the isolated or augmented anterior instrumentation in flexion/extension, although no significant differences were observed in lateral bending or axial rotation. The results of this biomechanical study suggest that an augmented anterior instrumentation provides similar stability for bony fusion as does the golden standard posterior instrumentation, with the exception of flexion/extension.

CONCLUSION

An augmented anterior instrumentation may provide similar stability for bony fusion as does the posterior instrumentation.

Biomechanical comparison of transarticular facet screws to lateral mass plates in two-level instrumentations of the cervical spine

STUDY DESIGN

In vitro biomechanical comparison of transarticular facet screws to lateral mass plates in two level instrumentations of the cervical spine.

OBJECTIVE

Lateral mass plates are costly, and screw placement is difficult. Facet screws have never been tested as an alternative in the cervical spine. This biomechanical study compared cervical transarticular facet screws to lateral mass plates in two-level instrumentations of human cadaveric cervical spines.

SUMMARY OF BACKGROUND DATA

Translaminar facet screws have been shown to have similar biomechanical performance to pedicle screw fixation in the lumbar spine, especially in flexion. They have proven to be fast, safe, and effective, with authors reporting 94% to 100% fusion rates in single-level lumbar fusions. However, a biomechanical comparison of transarticular facet screws to lateral mass plates in cervical spine instrumentations has not been reported.

METHODS

Thirteen human cadaveric cervical motion segments (C2-C4, C5-C7) were tested before and after instrumentation, with either transarticular facet screws or lateral mass plates, in flexion, extension, lateral bending, and torsion. Specimens were subjected to six cycles under a load of 2 Nm.

RESULTS

Both fixation systems significantly reduced range of motion (ROM) and increased stiffness compared with the intact state in flexion, extension, lateral bending, and torsion. There were also no significant differences between the facet screws and plates in any of the four directions. To compare the two systems, ROM of each was analyzed relative to the uninstrumented state. Flexion was 0.26 (or 26% of the intact state) for the transarticular facet screws versus 0.20 for the lateral mass plates (P = 0.34), extension was 0.10 versus 0.07 (P = 0.43), lateral bending was 0.17 versus 0.15 (P = 0.52), and torque was 0.25 versus 0.38 (P = 0.12). Load to failure testing failed to indicate any differences between the two methods of fixation because all the specimens failed elsewhere.

CONCLUSION

This study proves that transarticular facet screws and lateral mass plates are equivalent in two-level instrumentations of the cervical spine. This is the first biomechanical study to test transarticular facet screws in this context.

Biomechanical comparison: stability of lateral-approach anterior lumbar interbody fusion and lateral fixation compared with anterior-approach anterior lumbar interbody fusion and posterior fixation in the lower lumbar spine

Object. The stability of lateral lumbar interbody graft—augmented fusion and supplementary lateral plate fixation in human cadavers has not been determined. The purpose of this study was to investigate the immediate biomechanical stabilities of the following: 1) femoral ring allograft (FRA)—augmented anterior lumbar interbody fusion (ALIF) after left lateral discectomy combined with additional lateral MACS HMA plate and screw fixation; and 2) ALIF combined with posterior transpedicular fixation after anterior discectomy.

Methods. Sixteen human lumbosacral spines were loaded with six modes of motion. The intervertebral motion was measured using a video-based motion-capturing system. The range of motion (ROM) and the neutral zone (NZ) in each loading mode were compared with a maximum of 7.5 Nm.

The ROM values for both stand-alone ALIF approaches were similar to those of the intact spine, whereas NZ measurements were higher in most loading modes. No significant intergroup differences were found. The ROM and NZ values for lateral fixation in all modes were significantly lower than those of intact spine, except when NZ was measured in lateral bending. All ROM and NZ values for transpedicular fixation were significantly lower than those for stand-alone anterior ALIF. Transpedicular fixation conferred better stabilization than lateral fixation in flexion, extension, and lateral bending modes.

Conclusions. Neither approach to stand-alone FRA-augmented ALIF provided sufficient stabilization, but supplementary instrumentation conferred significant stabilization. The MACS HMA plate and screw fixation system, although inferior to posterior transpedicular fixation, provided adequate stability compared with the intact spine and can serve as a sound alternative to supplementary spinal stabilization.

Stabilisation surgery for chronic low back pain: indications, surgical procedures, and outcome

Spinal fusion was introduced as a treatment option for chronic low back pain >70 years ago. However, few areas of spinal surgery have caused as much controversy. The debate about whether to use an anterior-, posterior- or anterior + posterior approach has persisted since the 1930s. Within the last 10 years, the effects of different spinal fusion procedures have been tested in 10 randomized controlled trails (RCT). A highly significant improvement over preoperative status was found in all 10 studies. Two recent RCTs have dealt with the question of conservative versus operative treatment of patients with low back pain, and both studies have shown a significant better functional outcome for spinal fusion in situ, compared with a more or less organized exercise programme at 2-year follow-up. The choice of postoperative rehabilitation strategy has also been shown to be of importance for overall functional outcome. One study has demonstrated the importance of the inclusion of coping schemes, and questioned the role of intensive exercises in a rehabilitation programme for spinal fusion patients.

Posterior augmentation of an anterior lumbar interbody fusion: minimally invasive fixation versus pedicle screws in vitro

STUDY DESIGN

An in vitro biomechanical comparison of four posterior fixation techniques in the setting of an anterior lumbar interbody fusion (ALIF).

OBJECTIVE

To compare the initial stability, in terms of range of motion and neutral zone, provided by pedicle screws, facet screws, translaminar facet screws, and H-graft plus interspinous cables in the presence of an anteriorly placed femoral ring allograft.

SUMMARY OF BACKGROUND DATA

Pedicular fixation has been used to increase ALIF fusion rates but has also been linked with increased morbidity. Alternative posterior fixation options are available, but comprehensive biomechanical comparisons of these techniques do not exist. METHODS.: Twelve cadaveric lumbar motion segments were loaded to 5 Nm in unconstrained flexion-extension, lateral bending, and axial torsion. Specimens were tested intact, after ALIF, and after applying pedicle screws, translaminar screws, facet screws, and H-graft plus cables. The resulting neutral zones and ranges of motion were measured.

RESULTS

The mean (+/-SEM) range of motion for each construct in flexion-extension was as follows: intact: 6.39 degrees (+/-0.47 degrees); ALIF alone: 3.31 degrees (+/-0.22 degrees); (ALIF+) pedicle screws: 0.6 degrees (+/-0.06 degrees); facet screws: 0.75 degrees (+/-0.12 degrees); translaminar screws: 0.61 degrees (+/-0.09 degrees); and H-graft: 1.74 degrees (+/-0.26 degrees). Pedicle, translaminar facet, and facet screws significantly decreased range of motion and neutral zone compared to ALIF alone in flexion-extension, lateral bending, and axial torsion (all at P < 0.04, except translaminar screws in torsion neutral zone where P = 0.09). H-graft decreasedflexion-extension range of motion and neutral zone only (P < 0.01) and resulted in a significantly greater neutral zone than pedicle and facet screws in torsion and lateral bending neutral zones (P < 0.03).

CONCLUSIONS

In the ALIF setting, facet screw and translaminar screw techniques, which may be associated with less morbidity than pedicle screws clinically, provided initial posterior stabilization similar to pedicular fixation in this in vitro study.

A biomechanical comparison of supplementary posterior translaminar facet and transfacetopedicular screw fixation after anterior lumbar interbody fusion

Object. Facet screw fixation is the lowest profile lumbar stabilization method. In this study the immediate biomechanical stability provided by the two different types of fixation are compared: translaminar facet screw (TLFS) and transfacetopedicular screw (TFPS) placement after anterior lumbar interbody fusion (ALIF) using a femoral ring allograft. Both facet screw fixation types were also compared with the gold standard, transpedicular screw and rod (TSR) fixation.

Methods. Twenty-four human lumbosacral spines were tested in the following sequence: intact state, after discectomy, after ALIF, and after TLFS, TFPS, or TSR fixation. Intervertebral motions were measured by a video-based motion capture system. The range of motion (ROM) and neutral zone (NZ) were compared for each loading to a maximum of 7.5 Nm.

The ROMs for stand-alone ALIFs were less than but similar to those of the intact spine, but NZs were slightly increased in all modes. The ROMs for both TLFS and TFPS fixation were significantly decreased from those of the intact spine in all modes and those of the stand-alone ALIF in flexion and extension. The TLFS and TFPS fixations significantly reduced NZs to below that of the intact spine in all modes. Compared with NZs for ALIF, both types of fixation revealed significantly lower values, except for TLFS placement in lateral bending and TFPS fixation in lateral bending and rotation. There were no significant differences between TLFS and TFPS fixation. There were also no significant differences among both TLFS and TFPS and TSR fixations, except that TFPS was inferior to TSR in lateral bending.

Conclusions. Stand-alone ALIF may not provide sufficient stability. Both facet fixations produced significant additional stability and both are comparable to TSR fixation. Although TFPS fixation revealed a slightly inferior result, TFPSs can be placed percutaneously with the assistance of fluoroscopic guidance and it makes the posterior facet fixation minimally invasive. Therefore, the TFPS fixation can be considered as a good alternative to TLFS fixation.

Direct current stimulation of titanium interbody fusion devices in primates

BACKGROUND CONTEXT

The fusion rate for anterior lumbar interbody fusion (ALIF) varies widely with the use of different interbody devices and bone graft options. Adjunctive techniques such as electrical stimulation may improve the rate of bony fusion.

PURPOSE

To determine if direct current (DC) electrical stimulation of a metallic interbody fusion device enhanced the incidence or extent of anterior bony fusion.

STUDY DESIGN/SETTING

ALIF was performed using titanium alloy interbody fusion devices with and without adjunctive DC electrical stimulation in nonhuman primates.

METHODS

ALIF was performed through an anterolateral approach in 35 macaques with autogenous bone graft and either a titanium alloy (Ti-6Al-4V) fusion device or femoral allograft ring. The fusion devices of 19 animals received high (current density 19.6 microA/cm2) or low (current density 5.4 microA/cm2) DC electrical stimulation using an implanted generator for a 12- or 26-week evaluation period. Fusion sites were studied using serial radiographs, computed tomography imaging, nondestructive mechanical testing and qualitative and semiquantitative histology.

RESULTS

Fusion was achieved with the titanium fusion device and autogenous bone graft. At 12 weeks, the graft was consolidating and early to moderate bridging callus was observed in and around the device. By 26 weeks, the anterior callus formation was more advanced with increased evidence of bridging trabeculations and early bone remodeling. The callus formation was not as advanced or abundant for the allograft ring group. Histology revealed the spinal fusion device had an 86% incidence of bony fusion at 26 weeks compared with a 50% fusion rate for the allograft rings. DC electrical stimulation of the fusion device had a positive effect on anterior interbody fusion by increasing both the presence and extent of bony fusion in a current density-dependent manner.

CONCLUSIONS

Adjunctive DC electrical stimulation of the fusion device improved the rate and extent of bony fusion compared with a nonstimulated device. The fusion device was equivalent to or better than the femoral allograft ring in all evaluations. The use of adjunctive direct current electrical stimulation may provide a means of improving anterior interbody fusion.

Comparative study of laparoscopic L5-S1 fusion versus open mini-ALIF, with a minimum 2-year follow-up

Anterior lumbar interbody fusion (ALIF) is a widely accepted tool for management of painful degenerative disc disease. Recently, the modern laparoscopic surgical technique has been combined with ALIF procedure, with good early postoperative results being reported. However, the benefit of laparoscopic fusion is poorly defined compared with its open counterpart. This study aimed to compare perioperative parameters and minimum 2-year follow-up outcome for laparoscopic and open anterior surgical approach for L5-S1 fusion. The data of 54 consecutive patients who underwent anterior lumbar interbody fusion (ALIF) of L5-S1 from 1997 to 1999 were collected prospectively. More than 2-years' follow-up data were available for 47 of these patients. In all cases, carbon cage and autologous bone graft were used for fusion. Twenty-five patients underwent a laparoscopic procedure and 22 an open mini-ALIF. Three laparoscopic procedures were converted to open ones. For perioperative parameters only, the operative time was statistically different (P=0.001), while length of postoperative hospital stay and blood loss were not. The incidence of operative complications was three in the laparoscopic group and two in the open mini-ALIF group. After a follow-up period of at least 2 years, the two groups showed no statistical difference in pain, measured by visual analog scale, in the Oswestry Disability Index or in the Patient Satisfaction Index. The fusion rate was 91% in both groups. The laparoscopic ALIF for L5-S1 showed similar clinical and radiological outcome when compared with open mini-ALIF, but significant advantages were not identified, despite its technical difficulty.

Comparison of instrumented anterior interbody fusion with instrumented circumferential lumbar fusion

Posterior lumbar interbody fusion (PLIF) restores disc height, the load bearing ability of anterior ligaments and muscles, root canal dimensions, and spinal balance. It immobilizes the painful degenerate spinal segment and decompresses the nerve roots. Anterior lumbar interbody fusion (ALIF) does the same, but could have complications of graft extrusion, compression and instability contributing to pseudarthrosis in the absence of instrumentation. The purpose of this study was to assess and compare the outcome of instrumented circumferential fusion through a posterior approach [PLIF and posterolateral fusion (PLF)] with instrumented ALIF using the Hartshill horseshoe cage, for comparable degrees of internal disc disruption and clinical disability. It was designed as a prospective study, comparing the outcome of two methods of instrumented interbody fusion for internal disc disruption. Between April 1994 and June 1998, the senior author (N.R.B.) performed 39 instrumented ALIF procedures and 35 instrumented circumferential fusion with PLIF procedures. The second author, an independent assessor (S.M.), performed the entire review. Preoperative radiographic assessment included plain radiographs, magnetic resonance imaging (MRI) and provocative discography in all the patients. The outcome in the two groups was compared in terms of radiological improvement and clinical improvement, measured on the basis of improvement of back pain and work capacity. Preoperatively, patients were asked to fill out a questionnaire giving their demographic details, maximum walking distance and current employment status in order to establish the comparability of the two groups. Patient assessment was with the Oswestry Disability Index, quality of life questionnaire (subjective), pain drawing, visual analogue scale, disability benefit, compensation status, and psychological profile. The results of the study showed a satisfactory outcome (score< or =30) on the subjective (quality of life questionnaire) score of 71.8% (28 patients) in the ALIF group and 74.3% (26 patients) in the PLIF group (P>0.05). On categorising Oswestry Index scores into "excellent", "better", "same", and "worse", we found no difference in outcome between the two groups: 79.5% (n=31) had satisfactory outcome with ALIF and 80% (n=28) had satisfactory outcome with PLIF. The rate of return to work was no different in the two groups. On radiological assessment, we found two nonunions in the circumferential fusion (PLIF) group (94.3% fusion rate) and indirect evidence of no nonunions in the ALIF group. There was no significant difference between the compensation rate and disability benefit rate between the two groups. There were three complications in ALIF group and four in the PLIF (circumferential) group. On the basis of these results, we conclude that it is possible to treat discogenic back pain by anterior interbody fusion with Hartshill horseshoe cage or with circumferential fusion using instrumented PLIF.

Threaded cortical bone dowels in lumbosacral arthrodesis: a review

Lumbar fusion is a common spinal surgery, for which numerous devices have been developed to aid in segment stabilization. A threaded cortical bone dowel is a machined and processed bone allograft which is one such development. Threaded cortical bone dowels are attractive because of their osteoconductive nature and the opportunity to load them with osteogenic morselized bone autograft or osteoinductive growth factors, such as bone morphogenetic proteins. Although threaded cortical bone dowels have been in clinical use for more than 5 years, they have not been the subject of a comprehensive review. The current article covers the history, preparation, uses, safety, and efficacy of threaded cortical bone dowels in lumbosacral interbody fusion.

Comparison of plain radiographs with CT scan to evaluate interbody fusion following the use of titanium interbody cages and transpedicular instrumentation

The availability of lumbar interbody cages has fuelled renewed interest in interbody fusion. Despite this, there is no consensus regarding the best non-invasive method for evaluation of interbody fusion, especially where cages have been used. The purpose of this study was to determine whether high-quality thin-slice (1- to 3-mm) computed tomography (CT) scans allow proper evaluation of interbody fusion through titanium cages. Patients undergoing lumbar interbody fusion were prospectively evaluated with CT scan and plain radiographs 6 months following surgery. These images were blindly and independently evaluated by a consultant radiologist and a spine research fellow, for bridging bony trabeculation both through and surrounding the cages as well as for changes at the cage endplate interface. Fifty-three patients (156 cages) undergoing posterior lumbar interbody fusion using titanium interbody cages were evaluated. Posterior elements were used to pack the cages and no graft was packed outside the cages. The outcome data were analysed using the Kappa co-efficient and chi-squared analysis. On CT scan, both observers noted bridging trabeculation in 95% of the cages (Kappa 0.85), while on radiographs this was present in only 4% (Kappa 0.74). Both observers also identified bridging trabeculation surrounding the cages on CT scan in 90% of cages (Kappa 0.82), while on the radiographs this was 8% (Kappa 0.86). Radiographs also failed to demonstrate all the loose cages. The results of the study show that high-quality CT scans show images suggesting bridging bony trabeculae following the use of titanium interbody cages. They also appear to show consistent bone outside the cages in spite of no bone graft having been used, and they appear to be better than plain radiographs in the early detection of cage loosening.

Anterior lumbar interbody fusion: does stable anterior fixation matter?

The purpose of this study was to compare the outcome of anterior lumbar interbody fusion without instrumentation (uninstrumented ALIF) against that with stable anterior cage fixation using Hartshill horseshoe instrumentation (ALIF-HH) for similar severity of disc disease. Between April 1994 and June 1998 the senior author N.R.B. performed 29 instrumented ALIF procedures with a Hartshill horseshoe cage (ALIF-HH). Between 1990 and 1998, the other senior author (J.M.H.), together with another senior consultant orthopaedic surgeon, performed 27 noninstrumented ALIF procedures using corticocancellous iliac crest autograft. All the patients in both groups had single-level fusion. An independent assessor (S.M.) performed the entire review. The mean follow-up was 4.7 years (2.3-7.9 years) in the uninstrumented ALIF group and 3.0 years (2.1-4.4 years) in the ALIF-HH group. There was subsidence of graft in four patients in the uninstrumented ALIF group. It is reasonable to assume that there was no pseudarthrosis in the ALIF-HH group. This difference was statistically significant (two-sided P-value =0.0425). On subjective score assessment, there was a satisfactory outcome (score0.05). On classification by the Oswestry Index into four categories, we found no difference in outcome between the two groups: 83.3% ( n=20) had a satisfactory outcome (defined as Excellent or Better) with ALIF and 77.8% ( n=21) had a satisfactory outcome with ALIF-HH using the Oswestry Disability Index for post-operative assessment ( P>0.05). The results of this study indicate that the Hartshill horseshoe cage does improve the fusion rate, but does not affect clinical outcome.

The effect of bone graft extenders to enhance the performance of iliac crest bone grafts in instrumented lumbar spine fusion

Allograft bone extenders are commonly used in spinal surgery to increase the available graft volume, thereby promoting and achieving a solid fusion mass. We report a single surgeon's use and early results of autologous bone graft and allograft demineralized bone matrix in 65 patients undergoing lumbar spinal fusion. Of the patients included in this study, 59 (91%) patients underwent surgical intervention for lumbar spinal stenosis, three (5%) patients had lumbar spondylolisthesis, two (3%) patients had stenosis, and one (1%) patient had bilateral spondylolysis. Forty-three (64%) women and 22 (36%) men were included in the study. The average patient age was 56 years (20-85 years, SD= +/- 16). Independent radiographic evaluation was performed. Each subsequent radiographic follow-up revealed increased improvement in average Lenke score and was statistically significant between the early (1 month) and recent (12 month) follow-ups. There were statistically significant changes in Lenke score between 1 month and 3 months follow-up (P<.01), between 3 months and 6 months follow-up (P<.001), and between 6 months and 12 months follow-up (P<.01). The gradual and constant increment of improvement in radiographic measurements in this preliminary series may indicate a positive effect of the use of bone graft extenders that may decrease the required amount of autologous bone graft. Bone graft extenders also may minimize the risks and complications associated with the harvesting procedure.

Guide device for percutaneous placement of translaminar facet screws after anterior lumbar interbody fusion. Technical note

Because the degree of immediate stabilization provided by cage-assisted anterior lumbar interbody fusion (ALIF) has been shown by several studies to be inadequate, supplementary posterior fixation, such as that created by translaminar or transpedicle screw fixation, is necessary. In this study, the authors studied the ALIF-augmentation procedure in which a special guide device is used to place percutaneously translaminar facet screws in 18 patients with degenerative lumbar disease. The minimum follow-up period was 1 month (mean 6 months, range 1-13 months). Degenerative spondylolisthesis with foraminal stenosis was diagnosed in nine patients, associated degenerative disc disease alone or combined with foraminal stenosis in eight, and recurrent disc herniation in one. Following screw placement, computerized tomography scanning was conducted to evaluate the accuracy of the facet screw positioning. All screws were properly placed. No screw penetrated the spinal canal or injured the neural structures. Excellent or good clinical outcomes were demonstrated in all patients at the last follow up. The use of this guide device for post-ALIF percutaneous translaminar facet screw fixation represents a safe, accurate, and minimally invasive modality with which to achieve immediate solid fixation in the lumbar spine.

Circumferential lumbar spinal fusion with Brantigan cage versus posterolateral fusion with titanium Cotrel-Dubousset instrumentation: a prospective, randomized clinical study of 146 patients

STUDY DESIGN

A prospective randomized clinical study with a 2-year follow-up period was conducted.

OBJECTIVE

To analyze the effects of circumferential fusion using ALIF radiolucent carbon fiber cages and titanium posterior instrumentation on functional outcome, fusion rate, complications, and lumbar lordosis.

SUMMARY OF BACKGROUND DATA

Circumferential fusion has become a common procedure in lumbar spine fusion, both as a primary and salvage procedure. However, the claimed advantages of ALIF plus PLF over conventional PLF lack scientific documentation.

METHODS

From April 1996 through November 1999, a total of 148 patients with severe chronic low back pain were randomly selected for either posterolateral lumbar fusion with titanium CD-Horizon (posterolateral group) or circumferential fusion with a ALIF Brantigan cage plus posterior instrumentation. The Dallas Pain Questionnaire (DPQ), the Low Back Pain Rating Scale (LBPR), and a questionnaire concerning work status assessed their outcomes.

RESULTS

Both groups showed highly significant improvement in all four categories of life quality (DPQ) as well as in the back pain and leg pain index (LBPR), as compared with preoperative status. There was a clear tendency toward better overall functional outcome for patients with the circumferential procedure ( < 0.08), and this patient group also showed significantly less leg pain at the 1-year follow-up evaluation ( < 0.03) and less peak back pain at 2 years ( < 0.04). Sagittal lordosis was restored and maintained in the circumferential group ( < 0.01). The circumferential fusion patients showed a higher posterolateral fusion rate (92%) than the posterolateral group (80%)( < 0.04). The repeat operation rate including implant removal was significantly lower in the circumferential group (7%) ( < 0.009) than in the posterolateral group (22%).

CONCLUSIONS

Circumferential lumbar fusion restored lordosis, provided a higher union rate with significantly fewer repeat operations, showed a tendency toward better functional outcome, and resulted in less peak back pain and leg pain than instrumented posterolateral fusion. The clinical perspective of the current study implies a recommendation to favor circumferential fusion as a definitive surgical procedure in complex lumbar pathology involving major instability, flatback, and previous disc surgery in younger patients, as compared with posterolateral fusion with pedicle screws alone.

Pullout test with three lumbar interbody fusion cages

STUDY DESIGN

In vitro biomechanical testing was performed on 12 cadaveric human lumbar spines.

OBJECTIVE

To determine the initial dislocation resistance, as quantified by the pullout force of three different cage designs.

SUMMARY OF BACKGROUND DATA

Interbody cage devices frequently are used as stand-alone cages in the surgical treatment of degenerative conditions in the lumbar spine. In contrast to the wide clinical acceptance of interbody fusion cages, there are only a few biomechanical studies of posterior pullout trials.

METHODS

Cylindrical threaded cages (Ray TFC Surgical Dynamics), bullet-shaped cages (Stryker), and newly designed rectangular titanium cages with an endplate anchorage device (Marquardt) were used for posterior interbody implants. For each device, the pullout test was performed in four specimens on both sides (L3-L4).

RESULTS

In the pullout test, the Stryker cages required a median pullout force of 130 N (minimum, 100 N; maximum, 220 N), as compared with the higher pullout force of the Marquardt cages (median, 605 N; minimum, 450 N; maximum, 680 N), and the Ray cages (median, 945 N; minimum, 125 N; maximum, 2230 N).

CONCLUSIONS

Differences in pullout resistance were noted depending on the cage design. A cage design with threads or a hook device provides superior stability, as compared with ridges. The initial pullout resistance was highest for the Ray cages and lowest for the Stryker cages.

In vitro stability of FRA spacers with integrated crossed screws for anterior lumbar interbody fusion

STUDY DESIGN

Mechanical testing of human lumbar functional spine units was carried out after instrumenting the disc space with femoral ring allografts (FRAs) with and without integrated crossed anterior screws applied into the adjacent bodies.

OBJECTIVES

To assess the stability of FRA construct with and without the integrated crossed anterior screws and to compare that with the intact specimen.

SUMMARY OF BACKGROUND DATA

Most modern methods of achieving anterior lumbar intervertebral fusion rely on the use of interbody spacers to restore and maintain intervertebral height, overall alignment, and stability while facilitating arthrodesis. The FRAs have the advantage of biologic compatibility but may not have enough stability when used as stand-alone devices. FRA spacers alone are less stiff in torsion and extension compared with other instrumented constructs. Increased motion could lead to higher failure rates because of graft migration and pseudarthrosis. This makes the use of supplementary anterior or posterior fixation necessary. The current authors hypothesized that the addition of anterior integrated crossed screws applied through the FRA spacer into the adjacent vertebral bodies would increase the stability of the FRA spacer in extension and torsion in the absence of further posterior instrumentation.

METHODS

Seven fresh-frozen human cadaveric lumbar spine functional spine units were tested applying cantilever bending moments in flexion, lateral bending, torsion, and extension. The specimens were tested in the following sequence: intact, with FRA spacer alone and with FRA spacer and integrated crossed screws. The stiffness of each construct was then compared with the intact specimen. Specimens with obvious deformity on radiographs or dual-energy radiograph absorptiometry t score values <-1.2 were excluded.

RESULTS

The addition of the integrated crossed metal screw system improved the stiffness of the construct by 53% over the intact (P = 0.02) and by 31% over the FRA alone in extension (P = 0.01), whereas it improved the stiffness by 40% over the intact (P = 0.03) and by 18% over the FRA alone in torsion (P = 0.21). The crossed screw system did not improve the stiffness compared with intact in either flexion or lateral bending modes.

CONCLUSIONS

Although there is a trend toward improved stability of the FRA spacers in torsion with the addition of the metal screws, this is not statistically significant. The integrated crossed anterior metal screw system significantly improves the stability of the FRA spacers in extension when used for anterior lumbar interbody fusion.

Lumbar interbody fusion using the Brantigan I/F cage for posterior lumbar interbody fusion and the variable pedicle screw placement system: two-year results from a Food and Drug Administration investigational device exemption clinical trial

STUDY DESIGN

A carbon fiber-reinforced polymer cage implant filled with autologous bone was designed to separate the mechanical and biologic functions of posterior lumbar interbody fusion.

OBJECTIVES

To test the safety and efficacy of the carbon cage with pedicle screw fixation in a 2-year prospective study performed at six centers under a protocol approved by the Food and Drug Administration, and to present the data supporting the Food and Drug Administration approved indications.

SUMMARY OF BACKGROUND DATA

The success of posterior lumbar interbody fusion has been limited by mechanical and biologic deficiencies of the donor bone. Some failures of pedicle screw fixation may be attributable to the absence of adequate load sharing through the anterior column. Combining an interbody fusion device with pedicle screw fixation may address some limitations of posterior lumbar interbody fusion or pedicle screw fixation in cases that are more complex mechanically.

METHODS

This clinical study of posterior lumbar interbody fusion with pedicle screw fixation involved a prospective group of 221 patients.

RESULTS

Fusion success was achieved in 176 (98.9%) of 178 patients. In the management of degenerative disc disease in patients with prior failed discectomy surgery, clinical success was achieved in 79 (86%) of 92 patients, and radiographic bony arthrodesis in 91 (100%) of 91 patients. Disc space height, averaging 7.9 mm before surgery, was increased to 12.3 mm at surgery and maintained at 11.7 mm at 2 years. Fusion success was notdiminished over multiple fusion levels. These results were significantly better than those reported in prior literature. Although significant surgical complications occurred, those attributable to the implant devices occurred less frequently and generally were minor.

CONCLUSIONS

The Brantigan I/F Cage for posterior lumbar interbody fusion and the Variable Screw Placement System are safe and effective for the management of degenerative disc disease.

Autogenic versus allogenic bone grafts in anterior lumbar interbody fusion

Between 1987 and 1993, 94 consecutive patients with painful spondylolisthesis underwent combined anterior and posterior fusion. The average age at operation was 40 years (range, 16-65 years). Posterior fusion was performed in all patients using pedicle screw systems, and anterior fusion was accomplished with autogenic or allogenic bone grafts. Patients retrospectively were assigned to two groups. In Group 1, anterior fusion was performed with autogenic bone grafts harvested from the iliac crest (n = 65; 146 segments) and in Group 2 allogenic bone grafts were taken from femoral heads (n = 39; 86 segments). The incidence of pseudarthrosis was evaluated on lateral tomograms 24 months after surgery. The mean clinical followup time was 4 years (range, 3-8 years). Pseudarthrosis was found in seven fused levels (3%) managed with autogenic bone grafts (Group 1) and in seven patients (8%) managed with allogenic bone grafts (Group 2). This incidence of pseudarthrosis was not significantly different between the two groups. Considering the possible complications associated with harvesting iliac crest bone, the use of allogenic bone appears justified.

Spinal fusion: a combined anterior and supplementary interspinous technique

"Standard", noninstrumented, techniques of anterior interbody fusion are frequently followed by nonunion and collapse of the intervertebral space, probably because of persistent rocking movements, particularly in the sagittal plane. Elimination of these theoretical movements by supplementing an anterior interbody fusion with a posterior interspinous H-graft and a cerclage wire was considered to be biomechanically attractive without having the disadvantages associated with posterior instrumentation. In a prospective study a solid fusion was obtained at 16 of 17 operated levels, with a mediocre (+/- 50%) fusion as the exception. The height of the intervertebral space was increased at the majority of the fused levels. The technique is only applicable where neural arches are intact. The technique proved to be safe, simple, effective and inexpensive.

Management of iatrogenic spinal stenosis complicating placement of a fusion cage. A case report

STUDY DESIGN

A case of iatrogenic spinal stenosis secondary to fusion cage retropulsion is presented.

OBJECTIVES

To highlight fusion cage retropulsion, a potential complication that may become more prevalent as the use of fusion cage instrumentation expands. The difficulty in management of this complication is emphasized.

SUMMARY OF BACKGROUND DATA

Early reports regarding fusion cage instrumentation have been encouraging. At this point, however, the potential benefits are better defined than the potential complications.

METHODS

A significant complication of fusion cage instrumentation and the limited literature on this subject are reviewed.

RESULTS

The patient underwent successful revision surgery after retropulsion of a fusion cage, however, an extensive surgical procedure including partial vertebral body resection was required.

CONCLUSIONS

The frequency and severity of complications related to fusion cage instrumentation remain poorly defined. Caution should be used in patient selection until additional experience more clearly defines the risk-to-benefit ratio for a given application of this new technology.

Radiological and functional outcome after anterior lumbar interbody spinal fusion

Outcome after anterior spinal fusion has mainly been studied radiologically and reported fusion rates vary greatly. The aim of this study was to investigate radiological and long-term clinical outcome. The study comprised 120 consecutive patients, operated on during the period 1979-1987, with single-or two-level anterior interbody spinal fusion due to disc degeneration or isthmic spondylolisthesis with lumbar instability. In 64 patients a supplemental facet joint fusion was performed. Clinical outcome was evaluated 5-13 years after surgery using the patient-administered Dallas Pain Questionnaire (DPQ). Radiological outcome was determined on the basis of radiographs taken at a 2-year follow-up assessed by independent observers. The radiological follow-up rate was 98%. Complete fusion was found in 52%, questionable fusion in 24%, and definitive pseudoarthrosis in 24% of patients. Radiological results were poor in patients who had undergone previous spinal surgery (P < 0.05) and in those with two-level fusion (P < 0.05). The DPQ reply rate was 80%. Sixty-six patients claimed improvement in all functional groups. Patients with complete or questionable union had significantly better results than did those with non-union (P < 0.01). Poorer functional outcome was found in patients who had undergone previous spinal surgery (P < 0.01) or fusion at the L4/L5 level (P < 0.05), in those who had responded poorly to the preoperative test brace (P < 0.05), and in those above 45 years old at the time of surgery (P < 0.05). Radiological and functional outcome did not vary according to whether patients were treated postoperatively with a plaster jacket or with facet screw fixation. The study demonstrated a functional success rate of approximately 66% following anterior lumbar spinal fusion after a mean follow-up of 8 years. There was a clear tendency for poorer prognosis for patients who had undergone previous spinal surgery, those aged above 45 years, those operated at the L4/L5 level and those who had responded poorly to the preoperative test brace. DPQ scores correlated well with radiological outcome.

Standardized evaluation of long-term results after anterior lumbar interbody fusion

A total of 113 patients, excluding those with tumor, spondylitis, and idiopathic scoliosis, underwent anterior lumbar interbody fusion (ALIF) with autologous iliac crest graft between 1984 and 1991 at our department. The proportion of these who were failed back patients was higher than that reported in the literature. Evaluation of functional outcome was feasible in 80 patients, utilizing Oswestry and Marburg scores, which were closely intercorrelated. The overall results yielded an improvement in the Oswestry score of 35.7 percentage points. A subset of 52 patients who were evaluated twice, showed the same results at an average of 6.6 years as they did at 2.3 years following surgery. Functional results showed a weak correlation with postoperative height loss of the intervertebral space. Influencing factors for the functional result were: postoperative compensation claim, age, and obesity. Of the professional people involved, 19.4% did not return to any occupation. Patients satisfied with the result had significantly greater functional improvement. Younger patients with additional dorsal distraction prior to ALIF for reduction of severe spondylolisthesis fared better than patients with ALIF alone. The rate of complications was low and did not contribute to the postoperative functional result. On the basis of these results further prospective studies have been designed and are currently underway.

Distractive properties of a threaded interbody fusion device. An in vivo model

STUDY DESIGN

Twenty sheep underwent anterior lumbar interbody fusions with either a threaded titanium interbody fusion device (cage, n = 8), autogenous iliac crest dowel graft (autograft, n = 6), or interbody decortication only (sham, n = 6). Two sheep had misplaced cages and were excluded. Sheep were killed after 6 months.

OBJECTIVES

To determine whether this model is useful for examining the distractive and fixation properties of interbody fusion cages.

SUMMARY OF BACKGROUND DATA

Interbody fusion cages are used in anterior lumbar interbody fusion procedures to provide immediate intersegmental fixation and to distract and preserve interbody height. The process of physiologic anchorage by bone ingrowth into such devices is under investigation.

METHODS

Sheep were radiographed immediately after surgery and 2, 4, and 6 months after surgery. Interbody distraction and angulation were measured with a digital photo image analyzer at each time point. After the sheep were killed, stiffness to flexion, extension, and lateral bending moments were measured. Twelve untreated cadaver spines were also tested for comparison.

RESULTS

After surgery, interbody distraction successfully occurred in cage and autograft-implanted sites. Loss of interbody height ensued, however, in all groups during the first 2 months. Percentage loss of height was lowest in cage sites. By 6 months, only cage sites remained distracted beyond normal. Fusions in all groups were stiffer than untreated spines. Autograft sites were stiffer than cage sites to lateral bending. Sham sites were stiffer than cage and autograft sites to flexion, but this likely resulted from complete intervertebral collapse.

CONCLUSION

Despite early subsidence, interbody fusion cages successfully distracted and preserved interbody spaces. This model is useful for investigating methods of improving distraction and stabilization.