Fusion rates and SF-36 outcomes after multilevel laminectomy and noninstrumented lumbar fusions in a predominantly geriatric population. ACTA ACUST UNITED AC. 2008;21:159-164. [PMID: 18458584 DOI: 10.1097/bsd.0b013e318074ddaa]

Surgical risk factors associated with the development of adjacent segment pathology in the lumbar spine

Adjacent segment pathology (ASP) is a major cause of disability, and the recognition of the surgical risk factors associated with the development of this condition is essential for its prevention.

Different surgical approaches, from decompression without fusion to non-instrumented and instrumented fusion, have distinct contributions to the development of ASP.

Although motion-preservation procedures could reduce the prevalence of ASP, these are also associated with a higher percentage of complications.

Several risk factors associated with previous surgery, namely the chosen surgical approach and anatomical dissection, the choice of interbody fusion, the increment and length of the fusion, and the restoration of sagittal alignment, may influence the development of ASP.

Cite this article: EFORT Open Rev 2021;6:966-972. DOI: 10.1302/2058-5241.6.210050

Current Updates on Bone Grafting Biomaterials and Recombinant Human Growth Factors Implanted Biotherapy for Spinal Fusion: A Review of Human Clinical Studies

BACKGROUND

Owing to their great promise in the spinal surgeries, bone graft substitutes have been widely investigated for their safety and clinical potential. By the current advances in the spinal surgery, an understanding of the precise biological mechanism of each bone graft substitute is mandatory for upholding the induction of solid spinal fusion.

OBJECTIVE

The aim of the present review is to critically discuss various surgical implications and level of evidence of most commonly employed bone graft substitutes for spinal fusion.

METHOD

Data was collected via electronic search using "PubMed", "SciFinder", "ScienceDirect", "Google Scholar", "Web of Science" and a library search for articles published in peer-reviewed journals, conferences, and e-books.

RESULTS

Despite having exceptional inherent osteogenic, osteoinductive, and osteoconductive features, clinical acceptability of autografts (patient's own bone) is limited due to several perioperative and postoperative complications i.e., donor-site morbidities and limited graft supply. Alternatively, allografts (bone harvested from cadaver) have shown great promise in achieving acceptable bone fusion rate while alleviating the donor-site morbidities associated with implantation of autografts. As an adjuvant to allograft, demineralized bone matrix (DBM) has shown remarkable efficacy of bone fusion, when employed as graft extender or graft enhancer. Recent advances in recombinant technologies have made it possible to implant growth and differentiation factors (bone morphogenetic proteins) for spinal fusion.

CONCLUSION

Selection of a particular bone grafting biotherapy can be rationalized based on the level of spine fusion, clinical experience and preference of orthopaedic surgeon, and prevalence of donor-site morbidities.

Allograft Versus Demineralized Bone Matrix in Instrumented and Noninstrumented Lumbar Fusion: A Systematic Review

STUDY DESIGN

Systematic review.

OBJECTIVES

The aim was to determine the fusion efficacy of allograft and demineralized bone matrix (DBM) in lumbar instrumented and noninstrumented fusion procedures for degenerative lumbar disorders.

METHODS

A literature search was conducted using the PubMed and Cochrane databases. To be considered, publications had to meet 4 criteria: patients were treated for a degenerative lumbar disorder, a minimum group size of 10 patients, use of allograft or DBM, and at least a 2-year follow-up. Data on the study population, follow-up time, surgery type, grafting material, fusion rates, and its definition were collected.

RESULTS

The search yielded 692 citations with 17 studies meeting the criteria including 4 retrospective and 13 prospective studies. Six studies used DBM and 11 employed allograft alone or in the combination with autograft. For the allograft, fusion rates ranged from 58% to 68% for noninstrumented and from 68% to 98% for instrumented procedures. For DBM, fusion rates were 83% for noninstrumented and between 60% and 100% for instrumented lumbar fusion procedures.

CONCLUSIONS

Both allograft and DBM appeared to provide similar fusion rates in instrumented fusions. On the other hand, in noninstrumented procedures DBM was superior. However, a large variation in the type of surgery, outcomes collection, lack of control groups, and follow-up time prevented any significant conclusions. Thus, studies comparing the performance of allograft and DBM to adequate controls in large, well-defined patient populations and with a sufficient follow-up time are needed to establish the efficacy of these materials as adjuncts to fusion.

High lumbar noninstrumented fusion rates using lamina autograft and Nanoss/bone marrow aspirate

BACKGROUND

Patients with marked osteoporosis and/or obesity/morbid obesity and severe multilevel lumbar stenosis and other pathology often undergo multilevel laminectomies with non instrumented posterolateral fusions (PLF). The other pathology may include combinations of degenerative spondylolisthesis/lysis, foraminal/far lateral discs, and/or synovial cysts requiring more extensive facet resections. Presently, spine surgeons often use bone graft expanders to supplement the lamina autograft harvested in the course of laminectomy/decompressions for the PLF mass.

METHODS

In 59 patients, we prospectively analyzed the fusion rates following multilevel laminectomies/noninstrumented fusions using lamina autograft and the bone graft expander Nanoss (RTI Surgical Alachua, FL, and USA) with autogenous bone marrow aspirate (BMA). Patients averaged 66.1 years of age; many exhibited marked osteoporosis (48 patients) and obesity (13 of 27 morbidly obese). Magnetic resonance (MR) and computed tomography (CT) studies documented stenosis/ossified yellow ligament (OYL) and degenerative spondylolisthesis (51 patients)/lysis (2 patients), synovial cysts (32 patients), and disc herniations (10 of 21 far lateral). Patients were followed remove up for an average of 3.12 years.

RESULTS

Average 4.0 level laminectomies/1.2 level noninstrumented fusions utilized lamina autograft and Nanoss/BMA. Both X-ray/CT studies performed an average of 4.9 months postoperatively documented a 97% fusion rate (57 of 59 patients). Two patients with severe osteoporosis, morbid obesity, and smoking histories exhibited pseudarthroses; neither was sufficiently symptomatic to require secondary surgery.

CONCLUSIONS

Fifty-nine patients with multilevel lumbar stenosis/OYL and other pathology underwent multilevel lumbar laminectomies/noninstrumented fusions using lamina autograft and Nanoss/BMA. Both dynamic X-ray/CT studies confirmed a 97% fusion rate an average of 4.9 months postoperatively. Nanoss/BMA contributed to a high posterolateral lumbar non instrumented fusion rate without complciations.

Bone substitutes and expanders in Spine Surgery: A review of their fusion efficacies

STUDY DESIGN

A narrative review of literature.

OBJECTIVE

This manuscript intends to provide a review of clinically relevant bone substitutes and bone expanders for spinal surgery in terms of efficacy and associated clinical outcomes, as reported in contemporary spine literature.

SUMMARY OF BACKGROUND DATA

Ever since the introduction of allograft as a substitute for autologous bone in spinal surgery, a sea of literature has surfaced, evaluating both established and newly emerging fusion alternatives. An understanding of the available fusion options and an organized evidence-based approach to their use in spine surgery is essential for achieving optimal results.

METHODS

A Medline search of English language literature published through March 2016 discussing bone graft substitutes and fusion extenders was performed. All clinical studies reporting radiological and/or patient outcomes following the use of bone substitutes were reviewed under the broad categories of Allografts, Demineralized Bone Matrices (DBM), Ceramics, Bone Morphogenic proteins (BMPs), Autologous growth factors (AGFs), Stem cell products and Synthetic Peptides. These were further grouped depending on their application in lumbar and cervical spine surgeries, deformity correction or other miscellaneous procedures viz. trauma, infection or tumors; wherever data was forthcoming. Studies in animal populations and experimental in vitro studies were excluded. Primary endpoints were radiological fusion rates and successful clinical outcomes.

RESULTS

A total of 181 clinical studies were found suitable to be included in the review. More than a third of the published articles (62 studies, 34.25%) focused on BMP. Ceramics (40 studies) and Allografts (39 studies) were the other two highly published groups of bone substitutes. Highest radiographic fusion rates were observed with BMPs, followed by allograft and DBM. There were no significant differences in the reported clinical outcomes across all classes of bone substitutes.

CONCLUSIONS

There is a clear publication bias in the literature, mostly favoring BMP. Based on the available data, BMP is however associated with the highest radiographic fusion rate. Allograft is also very well corroborated in the literature. The use of DBM as a bone expander to augment autograft is supported, especially in the lumbar spine. Ceramics are also utilized as bone graft extenders and results are generally supportive, although limited. The use of autologous growth factors is not substantiated at this time. Cell matrix or stem cell-based products and the synthetic peptides have inadequate data. More comparative studies are needed to evaluate the efficacy of bone graft substitutes overall.

Low reoperation rate following 336 multilevel lumbar laminectomies with noninstrumented fusions

Background:

Few reoperations are required in older patients undergoing multilevel lumbar laminectomy with noninstrumented fusions for spinal stenosis with/without spondylolisthesis/instability, and they rarely require instrumentation.

Methods:

We reviewed 336 patients averaging 66.5 years of age undergoing initial average 4.7 level lumbar laminectomies with average 1.4 level noninstrumented fusions over an average 7.1-year period (range 2.0–16.5 years). Patients uniformly exhibited spinal stenosis, instability (Grade I [195 patients] or Grade II spondylolisthesis [67 patients]), disc herniations (154 patients), and/or synovial cysts (66 patients). Reoperations, including for adjacent segment disease (ASD), addressed new/recurrent pathology.

Results:

Nine (2.7%) of 336 patients required reoperations, including for ASD, an average of 6.3 years (range 2–15 years) following initial 4.7 level laminectomies with 1.4 level noninstrumented fusions. Second operations warranted average 4.8 level (range 3–6) laminectomies and average 1.1 level non instrumented fusions addressing stenosis with instability (Grade I [7 patients] or Grade II [1 patient] spondylolisthesis), new disc herniations (2 patients), and/or a synovial cyst (1 patient).

Conclusions:

Only 9 (2.7%) of 336 patients required reoperations (including for ASD) consisting of multilevel laminectomies with noninstrumented fusions for recurrent/new stenosis even with instability; these older patients were not typically unstable, or were likely already fused, and did not require instrumentation. Alternatively, reoperation rates following instrumented fusions in other series approached 80% at 5 postoperative years. Therefore, we as spinal surgeons should realize that older patients even with instability rarely require instrumentation and that the practice of performing instrumented fusions in everyone, irrespective of age, needs to stop.

A review: Reduced reoperation rate for multilevel lumbar laminectomies with noninstrumented versus instrumented fusions

Background:

The reoperation rate, including for adjacent segment disease (ASD), is lower following multilevel lumbar laminectomy with noninstrumented versus instrumented fusions.

Methods:

This study reviews selected literature focusing on the reoperation rate, including for ASD, following multilevel laminectomies with noninstrumented versus instrumented fusions. Several prior studies document a 1.3–5.6% reoperation rate following multilevel laminectomy with/without noninstrumented fusions.

Results:

The reoperation rates for instrumented fusions, including for ASD, are substantially higher. One study cited a 12.2–18.5% frequency for reoperation following instrumented transforaminal lumbar and posterior lumbar interbody fusions (TLIF and PLIFs) at an average of 164 postoperative months. Another study cited a 9.9% reoperation rate for ASD 1 year following PLIF; this increased to 80% at 5 postoperative years. A further study compared 380 patients variously undergoing laminectomies/noninstrumented posterolateral fusions, laminectomies with instrumented fusions (PLFs), and laminectomies with instrumented PLF plus an interbody fusions; this study documented no significant differences in outcomes for any of these operations at 4 postoperative years. Furthermore, other series showed fusion rates for 1–2 level procedures which were often similar with or without instrumentation, while instrumentation increased reoperation rates and morbidity.

Conclusions:

Many studies document no benefit for adding instrumentation to laminectomies performed for degenerative disease, including spondylolisthesis. Reoperation rates for laminectomy alone/laminectomy with noninstrumented fusions vary from 1.3% to 5.6% whereas reoperation rates for ASD after instrumented PLIF was 80% at 5 postoperative years. This review should prompt spinal surgeons to reexamine when, why, and whether instrumentation is really necessary, particularly for treating degenerative lumbar disease.

Does fusion status after posterior lumbar interbody fusion affect patient-based QOL outcomes? An evaluation performed using a patient-based outcome measure

BACKGROUND

Although delayed union or pseudoarthrosis after lumbar arthrodesis has been recognized as a major radiographic complication, little has been known about the effect of fusion status on the patient's quality-of-life (QOL) outcome. The purpose of this study was to investigate the effects of fusion status after posterior lumbar interbody fusion (PLIF) on QOL outcomes by using the Japanese Orthopaedic Association Back Pain Evaluation Questionnaire (JOABPEQ).

METHODS

Among 100 patients who underwent single level PLIF for spinal canal stenosis, 29 who had not achieved fusion (incomplete fusion group) and 29 age- and sex ratio-matched patients who had achieved fusion (fusion group) 6 months after surgery were enrolled. Overall clinical evaluation was performed before and 6 months after surgery: the physician determined the Japanese Orthopaedic Association Score for Low Back Pain (JOA score); the JOABPEQ and visual analogue scale (VAS) values were collected. The recovery rate of the JOA score, changes in all JOABPEQ subdomain scores and in the VAS values were calculated. All variables were compared between the groups.

RESULTS

The preoperative JOA scores, JOABPEQ scores of all subdomains, and VAS values of all categories did not differ between the groups. The recovery rate was higher in the fusion group than the incomplete fusion group (p = 0.0185). The changes in the JOABPEQ scores for walking ability and social life function were significantly greater in the fusion group than the incomplete fusion group (walking ability, p = 0.0172; social life function, p = 0.0191). The postoperative VAS values and changes in the VAS values for all categories did not differ between the groups.

CONCLUSIONS

Incomplete fusion after PLIF correlated with poor improvement in walking ability and social life function. Therefore, the achievement of fusion after PLIF is essential to obtain better patient QOL outcomes.

Use of demineralized bone matrix in spinal fusion

Spinal fusion remains the gold-standard treatment for several pathological spine conditions. Although, autologous Iliac Crest Bone Grafting is considered the gold-standard graft choice to promote spinal fusion; however, it is associated with significant donor site morbidity and a limited graft quantity. Therefore, several bone graft alternatives have been developed, to augment arthrodesis. The purpose of this review is to present the results of clinical studies concerning the use of demineralized bone matrix (DBM), alone or as a composite graft, in the spinal fusion. A critical review of the English-language literature was conducted on Pubmed, using key word “demineralized bone matrix”, “DBM”, “spinal fusion”, and “scoliosis”. Results had been restricted to clinical studies. The majority of clinical trials demonstrate satisfactory fusion rates when DBM is employed as a graft extender or a graft enhancer. Limited number of prospective randomized controlled trials (4 studies), have been performed comparing DBM to autologous iliac crest bone graft in spine fusion. The majority of the clinical trials demonstrate comparable efficacy of DBM when it used as a graft extender in combination with autograft, but there is no clinical evidence to support its use as a standalone graft material. Additionally, high level of evidence studies are required, in order to optimize and clarify the indications of its use and the appropriate patient population that will benefit from DBM in spine arthrodesis.

Clinical and radiographic outcomes of extreme lateral approach to interbody fusion with β-tricalcium phosphate and hydroxyapatite composite for lumbar degenerative conditions

Background

Historically, iliac crest bone graft has been used as the graft of choice for lumbar spine fusion procedures. Because fusion techniques have become less invasive, the demand for minimally disruptive grafting options has increased. This prospective study was performed to assess clinical and radiographic outcomes of patients treated with an iliac crest bone graft alternative and lateral lumbar interbody fusion.

Methods

Fifty degenerative lumbar patients were treated with the extreme lateral approach to interbody fusion and a β-tricalcium phosphate–hydroxyapatite graft with bone marrow aspirate (BMA) at 1 or 2 adjacent levels. BMA was collected from the iliac crest with a bone aspiration needle and applied to the FormaGraft (NuVasive, Inc., San Diego, California) in a 1:1 ratio. Radiolucent cages were filled with FormaGraft strips, granules, or blocks and implanted in a standard fashion. Clinical data were collected at baseline, 6 weeks, and 3, 6, and 12 months and included visual analog scale, Oswestry Disability Index, and Short Form 36 patient-reported assessments. Fusion assessments were made from neutral anteroposterior/lateral radiographs, lateral flexion/extension radiographs, and computed tomography images taken at least 12 months after surgery.

Results

Forty-four patients treated at 49 levels completed follow-up. The mean patient age was 54.7 ± 10.8 years, and mean body mass index was 30.8 ± 7.7 kg/m². Radiographic fusion was observed in 41 of 44 assessed levels (93.2%). Blood loss was less than 100 mL in 95.5% of patients. Of the patients, 93.2% spent 1 night or less in the hospital. By the 6-week follow-up, all clinical outcomes were significantly improved (P < .05). Improvements were maintained or increased throughout the course of follow-up.

Conclusions

This report shows that the technique of extreme lateral approach to interbody fusion in combination with FormaGraft and BMA in the interbody space is a safe and effective treatment option for interbody fusion of the lumbar spine when compared with other approaches and biologic options.

A review of demineralized bone matrices for spinal fusion: the evidence for efficacy

BACKGROUND AND PURPOSE

Autologous Iliac Crest Bone Grafting (ICBG) is considered the gold-standard graft choice for spinal arthrodesis; however, it is associated with donor site morbidity and a limited graft supply. Bone graft alternatives to replace autograft and augment arthrodesis are a topic of ongoing research. This article will review properties of Demineralized Bone Matrix (DBM) and review the evidence for its use, including animal models and human clinical trials.

METHODS

A systematic and critical review of the English-language literature was conducted on Pubmed, Cochrane, CINAHL, and Google Scholar using search key terms such as 'Demineralized Bone Matrix', 'Spine' and 'Fusion'. Papers that were included were original research articles in peer-reviewed journals that investigated fusion outcomes. Scientific validity of articles was appraised using the PRISMA methodology. Articles were critically examined and compared according to study design, DBM type, outcomes, and results. Primary outcome of interest was fusion rate. Secondary outcomes included Oswestry Disability Index; Short Form-36 survey; Odom's criteria; Visual Analog Scale neurologic pain score; Japanese Orthopedic Association myelopathy score; Neck Disability and Ishihara Curvature Indices; and pseudarthrosis and surgical failure rates.

RESULTS

Demineralized Bone Matrix has been evaluated in animal models and human clinical trials of spine fusion. Results of animal studies indicate variation in performance within and among DBM products. The majority of human clinical trials report high fusion rates when DBM is employed as a graft extender or a graft enhancer. Few prospective randomized controlled trials have been performed comparing DBM to autologous iliac crest bone graft in spine fusion.

CONCLUSIONS

Although many animal and human studies demonstrate comparable efficacy of DBM when combined with autograft or compared to autograft alone, additional high level of evidence studies are required to clearly define the indications for its use in spine fusion surgeries and the appropriate patient population that will benefit from DBM.

Mid-range outcomes in 64 consecutive cases of multilevel fusion for degenerative diseases of the lumbar spine

In the treatment of multilevel degenerative disorders of the lumbar spine, spondylodesis plays a controversial role. Most patients can be treated conservatively with success. Multilevel lumbar fusion with instrumentation is associated with severe complications like failed back surgery syndrome, implant failure, and adjacent segment disease (ASD). This retrospective study examines the records of 70 elderly patients with degenerative changes or instability of the lumbar spine treated between 2002 and 2007 with spondylodesis of more than two segments. Sixty-four patients were included; 5 patients had died and one patient was lost to follow-up. We evaluated complications, clinical/radiological outcomes, and success of fusion. Flexion-extension and standing X-rays in two planes, MRI, and/or CT scans were obtained pre-operatively. Patients were assessed clinically using the Oswestry disability index (ODI) and a Visual Analogue Scale (VAS). Surgery performed was dorsolateral fusion (46.9%) or dorsal fusion with anterior lumbar interbody fusion (ALIF; 53.1%). Additional decompression was carried out in 37.5% of patients. Mean follow-up was 29.4±5.4 months. Average patient age was 64.7±4.3 years. Clinical outcomes were not satisfactory for all patients. VAS scores improved from 8.6±1.3 to 5.6±3.0 pre- to post-operatively, without statistical significance. ODI was also not significantly improved (56.1±22.3 pre- and 45.1±26.4 post-operatively). Successful fusion, defined as adequate bone mass with trabeculation at the facets and transverse processes or in the intervertebral segments, did not correlate with good clinical outcomes. Thirty-five of 64 patients (54%) showed signs of pedicle screw loosening, especially of the screws at S1. However, only 7 of these 35 (20%) complained of corresponding back pain. Revision surgery was required in 24 of 64 patients (38%). Of these, indications were adjacent segment disease (16 cases), pedicle screw loosening (7 cases), and infection (one case). At follow-up of 29.4 months, patients with radiographic ASD had worse ODI scores than patients without (54.7 vs. 36.6; P<0.001). Multilevel fusion for degenerative disease still has a high rate of complications, up to 50%. The problem of adjacent segment disease after fusion surgery has not yet been solved. This study underscores the need for strict indication guidelines to perform lumbar spine fusion of more than two levels.

The efficacy of rhBMP-2 versus autograft for posterolateral lumbar spine fusion in elderly patients

Few studies have specifically examined the outcomes following rhBMP-2 usage in patients 65 years and older. The purpose of this retrospective study is to evaluate the efficacy of rhBMP-2 with allograft versus autograft for posterolateral lumbar fusion in patients 65 years and older. One hundred twenty-seven patients were divided into three groups based on fusion material and age. Subjects in group A (n = 34) consisted of patients 65 years and older who received rhBMP-2 and allograft. Group B (n = 52) was composed of patients under 65 years of age with rhBMP-2 and allograft. Subjects in group C (n = 41) were 65 years and older with autograft use. A comparison was made of fusion rate, fusion time (noticed, solid), clinical outcome, VAS, perioperative complications and revision rate between each group. The fusion rate and fusion time were similar in groups A and C; however, these were lower than that observed in group B. Clinical outcomes were similar amongst the groups. There were no significant differences in VAS and perioperative complication rate between groups A and C. In patients 65 years and older, rhBMP-2 with allograft may lead to acceptable fusion rates and fusion times, good clinical outcomes and reduced perioperative complications. The combination of rhBMP-2 with allograft yields equivalent outcomes as autograft in elderly patients undergoing instrumented posterolateral lumbar fusion. Additionally, when compared to patients under 65 years of age undergoing posterolateral lumbar fusion, the use of rhBMP-2 was not sufficient to overcome all aspects of the age-related weakened osteoinductive capacity encountered in elderly patients.

Beta tricalcium phosphate: observation of use in 100 posterolateral lumbar instrumented fusions

BACKGROUND

Beta tricalcium phosphate (B-TCP) is increasingly used to supplement lamina autograft to perform posterolateral lumbar-instrumented arthrodesis.

PURPOSE

To determine the radiographic arthrodesis and pseudarthrosis rates after multisegment lumbar laminectomies and one- or two-segment posterolateral instrumented fusion using lamina autograft and an artificial bone graft expander B-TCP (Vitoss; Orthovita, Malvern, PA, USA).

STUDY DESIGN/SETTING

To document radiographic arthrodesis/pseudarthrosis rates using lamina autograft and B-TCP.

PATIENT SAMPLE

One hundred patients with lumbar spinal stenosis underwent multisegment laminectomies (average 3.6 segments) and one- (78 patients) or two- (22 patients) segment posterolateral instrumented arthrodesis.

OUTCOME MEASURES

Two-year postoperative outcomes were assessed using Short-Form 36 questionnaires.

METHODS

The arthrodesis mass consisted of lamina autograft and B-TCP. Two independent neuroradiologists, using both dynamic X-rays and 2D-CT studies performed 3, 4.5, 6, and up to 12 months postoperatively, documented radiographic arthrodesis progression.

RESULTS

One-segment arthrodesis was performed in 79 patients; 74 (93.7%) were radiographically fused "early" (6.5 postoperative months), 2 (2.5%) fused "late" (6.5-12 months), and 3 (3.8%) exhibited pseudarthrosis. Two-segment arthrodesis was performed in 21 patients; 14 (66.7%) radiographically fused "early," 5 (23.8%) fused "late," and 2 (9.5%) exhibited pseudarthrosis. Although chi-square analyses revealed a significant increase in the number of "late" radiographic fusions occurring for patients undergoing two-level arthrodesis, no significant difference in radiographic pseudarthrosis rates was noted between the two patient populations. In both groups, Short-Form 36 questionnaires revealed nearly comparable maximal improvement on seven of eight Health Scales by the second postoperative year.

CONCLUSIONS

At 6.5 months after multisegment lumbar laminectomies with posterolateral instrumented lumbar arthrodesis using lamina autograft/B-TCP, more one-segment (93.7%) versus two-segment (66.7%) radiographic arthrodesis occurred. By 1 year after operation, there was no significant difference in fusion rates between one- and two-segment radiographic arthrodeses.