Biological cages

Restoring a stable anterior column is essential to achieve normal spinal biomechanics. A variety of mechanical spacers have been developed and advocated for both anterior and posterior approaches. The ability to radiographically assess the "biology" of bone incorporation in these mechanical (metal) spacers is an inherent limitation. The femoral ring allograft (FRA) and posterior lumbar interbody fusion (PLIF) spacers have been developed as biological cages that permit restoration of the anterior column with a machined allograft bone (biological cage). Test results demonstrate that the FRA and PLIF Spacers have a compressive strength over 25,000 N. The pyramid shaped teeth on the surfaces and the geometry of the implant increase the resistance to expulsion at clinically relevant loads (1053 and 1236 N). The technique of anterior column reconstruction with both the FRA and the PLIF biological cages are discussed. Clinical experience with the PLIF biological cage (10 patients) and the FRA biological cage (90 patients) has not revealed any graft migration, infection, or subsidence. Additional posterior instrumentation may increase the stability of the motion segment, but the degree of stability necessary to achieve a biological union remains unclear. The incorporation of these biological cages can be monitored by conventional radiographic techniques. The method of insertion preserves the vertebral end-plates and can be performed by a minimally invasive or standard open procedure.     

Segmental stability and compressive strength of posterior lumbar interbody fusion implants

STUDY DESIGN: Human cadaveric study on initial segmental stability and compressive strength of posterior lumbar interbody fusion implants. OBJECTIVES: To compare the initial segmental stability and compressive strength of a posterior lumbar interbody fusion construct using a new cortical bone spacer machined from allograft to that of titanium threaded and nonthreaded posterior lumbar interbody fusion cages, tested as stand-alone and with supplemental pedicle screw fixation. SUMMARY OF BACKGROUND DATA: Cages were introduced to overcome the limitations of conventional allografts. Radiodense cage materials impede radiographic assessment of the fusion, however, and may cause stress shielding of the graft. METHODS: Multisegmental specimens were tested intact, with posterior lumbar interbody fusion implants inserted into the L4/L5 interbody space and with supplemental pedicle screw fixation. Three posterior lumbar interbody fusion implant constructs (Ray Threaded Fusion Cage, Contact Fusion Cage, and PLIF Allograft Spacer) were tested nondestructively in axial rotation, flexion-extension, and lateral bending. The implant-specimen constructs then were isolated and compressed to failure. Changes in the neutral zone, range of motion, yield strength, and ultimate compressive strength were analyzed. RESULTS: None of the stand-alone implant constructs reduced the neutral zone. Supplemental pedicle screw fixation decreased the neutral zone in flexion-extension and lateral bending. Stand-alone implant constructs decreased the range of motion in flexion and lateral bending. Differences in the range of motion between stand-alone cage constructs were found in flexion and extension (marginally significant). Supplemental posterior fixation further decreased the range of motion in all loading directions with no differences between implant constructs. The Contact Fusion Cage and PLIF Allograft Spacer constructs had a higher ultimate compressive strength than the Ray Threaded Fusion Cage. CONCLUSIONS: The biomechanical data did not suggest any implant construct to behave superiorly either as a stand-alone or with supplemental posterior fixation. The PLIF Allograph Spacer is biomechanically equivalent to titanium cages but is devoid of the deficiencies associated with other cage technologies. Therefore, the PLIF Allograft Spacer is a valid alternative to conventional cages.     

Are 2 cages needed with instrumented PLIF? A comparison of 1 versus 2 interbody cages in a military population

Bovine biomechanical data have demonstrated adequate stability of a single threaded interbody cage when combined with a unilateral facet screw during posterior lumbar disc excision and interbody fusion (PLIF). Instrumented PLIF surgery using 1 versus 2 interbody cages was studied in 35 military men with disc disease and chronic low back pain. All patients underwent instrumented PLIF with bilateral diskectomy and partial facetectomy, pedicle screws, autogenous iliac crest bone graft, 1 or 2 interbody cages, and posterior lateral fusion. After an average of 15 months' follow-up, the 2-cage group had a higher rate of dural tear, but rates of other complications, hospital stay, fusion rates, pain levels, functional outcomes, and patient satisfaction were good and did not differ between groups. Costs were higher for the 2-cage group by 1728 dollars per patient.     

Posterior lumbar interbody fusion

Posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) create intervertebral fusion by means of a posterior approach. Both techniques are useful in managing degenerative disk disease, severe instability, spondylolisthesis, deformity, and pseudarthrosis. Successful results have been reported with allograft, various cages (for interbody support), autograft, and recombinant human bone morphogenetic protein-2. Interbody fusion techniques may facilitate reduction and enhance fusion. The rationale for PLIF and TLIF is biomechanically sound. However, clinical outcomes of different anterior and posterior spinal fusion techniques tend to be similar. PLIF has a high complication rate (dural tear, 5.4% to 10%; neurologic injury, 9% to 16%). These findings, coupled with the versatility of TLIF throughout the entire lumbar spine, may make TLIF the ideal choice for an all-posterior interbody fusion.     

Posterior lumbar interbody fusion (PLIF) with cages and local bone graft in the treatment of spinal stenosis

Posterior lumbar interbody fusion (PLIF) implants are increasingly being used for 360 degrees fusion after decompression of lumbar spinal stenosis combined with degenerative instability. Both titanium and PEEK (PolyEtherEtherKetone) implants are commonly used. Assessing the clinical and radiological results as well as typical complications, such as migration of the cages, is important. In addition, questions such as which radiological parameters can be used to assess successful fusion, and whether the exclusive use of local bone graft is sufficient, are frequently debated. We prospectively evaluated 30 patients after PLIF instrumentation for degenerative lumbar spinal canal stenosis, over a course of 42 months. In all cases, titanium cages and local bone graft were used for spondylodesis. The follow-up protocol of these 30 cases included standardised clinical and radiological evaluation at 3, 6, 12 and 42 months after surgery. Overall satisfactory results were achieved. With one exception, a stable result was achieved with restoration of the intervertebral space in the anterior column. After 42 months of follow-up in most cases, a radiologically visible loss of disc space height can be demonstrated. Clinically relevant migration of the cage in the dorsal direction was detected in one case. Based on our experience, posterior lumbar interbody fusion (PLIF) can be recommended for the treatment of monosegmental and bisegmental spinal stenosis, with or without segmental instability. Postoperative evaluation is mainly based on clinical parameters since the titanium implant affects the diagnostic value of imaging studies and is responsible for artefacts. The results observed in our group of patients suggest that local autologous bone graft procured from the posterior elements after decompression is an adequate material for bone grafting in this procedure.     

Radiographic assessment of anterior titanium mesh cages

Carbon fiber and titanium cage implantation for anterior column support during spinal fusions is an alternative to the use of more traditional structural allografts and autografts. The authors report instrumentation and cage failure for patients who underwent spinal fusion with structural titanium mesh cages implanted into the anterior column a minimum of 2 years after surgery. They wanted to determine whether plain radiographic techniques can be used to critically assess disk space and corpectomy fusions after implantation of these radioopaque cages. Fifty patients having undergone spinal fusions using structural titanium mesh cages in the anterior column had 99 anterior levels fused with at least 1 (maximum of 2) titanium mesh cage, resulting in a total of 131 cages used. The cages were examined for evidence of settling, migration, or failure. The anterior and posterior instrumentation was assessed for evidence of failure, and the spine was examined for evidence of successful fusion. Radiographic cage settling (>2 mm) into the vertebral body end plates was observed, but cage migration or failure were not. An average lordotic correction of 10 degrees was observed, with loss of correction into kyphosis from immediately after operation to final follow-up averaging 2 degrees. As an average of all reviewers, using a strict radiographic fusion assessment, definite or probable anterior fusion was graded at 81% of the levels, probably not or no at 5% of the levels, and could not be assessed at 14% of the levels. Definite or probable posterior fusion as an average of all reviewers was graded at 44% of the posterior fusion levels, questionable at 4%, no at 5%, and could not be assessed at 47%. The use of anterior-only, posterior-only, or anterior and posterior instrumentation with structural titanium mesh cages in the anterior spine along with proper autogenous bone grafting techniques provided anterior column support with a low rate of radiographic complications. Acceptable anterior spinal fusion rates, as assessed by a consensus agreement of reviewers, were observed primarily by evaluation of the fusion mass around the cages (extracage fusion), because intracage fusion was difficult to assess.     

Use of an autologous cortical bone graft sandwiched between two intervertebral spacers in posterior lumbar interbody fusion

Various intervertebral spacers with or without posterior instrumentation use pedicle screw fixation in posterior lumbar interbody fusion (PLIF). Recently we harvested an autologous cortical bone graft from a spinous process by en bloc resection and inserted it between two intervertebral spacers during PLIF surgery. Due to better balance, this procedure provides greater mechanical strength, larger contact area, and better bilateral restoration of disc height than PLIF using intervertebral spacers only, and there is no need to take a bone graft from the iliac crest. This technique appears to result in effective spinal fusion in PLIF surgery. Received: 19 September 2000 / Accepted: 15 November 2000     

Advances in Spinal Interbody Cages

Since the late 1980s, spinal interbody cages (ICs) have been used to aid bone fusion in a variety of spinal disorders. Utilized to restore intervertebral height, enable bone graft containment for arthrodesis, and restore anterior column biomechanical stability, ICs have since evolved to become a highly successful means of achieving fusion, being associated with less postoperative pain, shorter hospital stay, fewer complications and higher rates of fusion when than bone graft only spinal fusion. IC design and materials have changed considerably over the past two decades. The threaded titanium‐alloy cylindrical screw cages, typically filled with autologous bone graft, of the mid‐1990s achieved greater fusion rates than bone grafts and non‐threaded cages. Threaded screw cages, however, were soon found to be less stable in extension and flexion; additionally, they had a high incidence of cage subsidence. As of the early 2000s, non‐threaded box‐shaped titanium or polyether ether ketone IC designs have become increasingly more common. This modern design continues to achieve greater cage stability in flexion, axial rotation and bending. However, cage stability and subsidence, bone fusion rates and surgical complications still require optimization. Thus, this review provides an update of recent research findings relevant to ICs over the past 3 years, highlighting trends in optimization of cage design, materials, alternatives to bone grafts, and coatings that may enhance fusion.     

Radiological analysis of titanium mesh cages used after corpectomy in the thoracic and lumbar spine: minimum 3 years' follow-up

This study analyses radiological outcome of titanium mesh cages used for anterior column support following corpectomy in the thoracic and lumbar spine in 34 patients with a minimum three-year follow-up. The aim of the study was to assess the complications and radiological outcomes of patients with structural cages implanted into the anterior column. Titanium mesh cages for the anterior column became popular for anterior column reconstruction following discectomy and corpectomy. Few clinical studies are published assessing their efficacy as a structural graft after corpectomy and factors for the development of settling and correction loss are not investigated enough. Thirty-four patients with minimum 3-year follow-up were analysed radiologically for correction achievement, cage settling and fusion inside the mesh cage. The effect of fixation technique, anatomical localisation and diagnosis for the development of settling were analysed. Measurements of preoperative and early postoperative local kyphotic angle revealed that a mean correction of 27 degrees (range: 8 to 60) was obtained. While no dislodgement or fracture of titanium mesh cages was observed, there was a mean correction loss of 4 degrees and settling (> 2 mm) was noted in 6 patients. Short posterior and only anterior instrumentation systems were associated with settling. The anatomical location and diagnosis did not affect the development of cage settling. Following corpectomy and mesh cage implantation, isolated anterior fixation or short posterior fixation do not provide enough stability, and correction loss and settling can occur.     

Massive acetabular bone loss: Limits of trabecular metal cages

Massive acetabular bone loss (more than 50% of the acetabular area) can result in insufficient native bone for stable fixation and long-term bone ingrowth of conventional porous cups. The development of trabecular metal cages with osteoconductive properties may allow a more biological and versatile approach that will help restore bone loss, thus reducing the frequency of implant failure in the short-to-medium term. We report a case of massive bone loss affecting the dome of the acetabulum and the ilium, which was treated with a trabecular metal cage and particulate allograft. Although the trabecular metal components had no intrinsic stability, they did enhance osseointegration and incorporation of a non-impacted particulate graft, thus preventing failure of the reconstruction. The minimum 50% contact area between the native bone and the cup required for osseointegration with the use of porous cups may not hold for new trabecular metal cups, thus reducing the need for antiprotrusio cages. The osteoconductive properties of trabecular metal enhanced allograft incorportation and iliac bone rebuilding without the need to fill the defect with multiple wedges nor protect the reconstruction with an antiprotrusio cage.     

Posterior lumbar interbody fusion using posterolateral placement of a single cylindrical threaded cage

STUDY DESIGN: An in vitro biomechanical study of posterior lumbar interbody fusion (PLIF) with threaded cages was performed on 18 bovine lumbar functional spinal units. OBJECTIVES: To compare the segmental stiffness among PLIF with a single long posterolateral cage, PLIF with a single long posterolateral cage and simultaneous facet joint fixation, and PLIF with two posterior cages. SUMMARY OF BACKGROUND DATA: In most cases, PLIF with threaded cage techniques needs bilateral facetectomy, extensive exposure, and retraction of the cauda equina. Posterior element deficiency is detrimental to postoperative segmental stiffness. METHODS: All specimens were tested intact and with cage insertion. Group 1 (n = 12) had a long threaded cage (15 x 36 mm) inserted posterolaterally and oriented counter anterolaterally on the left side by posterior approach with left unilateral facetectomy. Group 2 (n = 6) had two regular-length cages (15 x 24 mm) inserted posteriorly with bilateral facetectomy. Six specimens from Group 1 were then retested after unilateral facet joint screw fixation in neutral (Group 3). Similarly, the other six specimens from Group 1 were retested after fixation with a facet joint screw in an extended position (Group 4). Nondestructive tests were performed in pure compression, flexion, extension, lateral bending, and torsion. RESULTS: The PLIF procedure involving a single cage (Group 1) had a significantly higher stiffness than PLIF with two cages (Group 2) in left and right torsion (P < 0.05). Group 1 had higher stiffness values than Group 2 in pure compression, flexion, and left and right bending, but differences were not significant. Group 3 had a significant increase in stiffness in comparison with Group 1 for pure compression, extension, left bending, and right torsion (P < 0.05). For Group 4, the stiffness significantly increased in comparison with Group 1 for extension, flexion, and right torsion (P < 0.05). Although there was no significant difference between Groups 3 and 4, Group 4 had increased stiffness in extension, flexion, right bending, and torsion. CONCLUSIONS: Posterior lumbar interbody fusion with a single posterolateral long threaded cage with unilateral facetectomy enabled sufficient decompression while maintaining most of the posterior elements. In combination with a facet joint screw, adequate postoperative stability was achieved.     

Are stand‐alone cages sufficient for anterior lumbar interbody fusion?

Anterior lumbar interbody fusion (ALIF) has increased in popularity because it has advantages over posterior fusion. Because there is disagreement about the stability of stand‐alone cage ALIF, some surgeons use various types of supplementary fixation, including anterior plates, pedicle screw systems and translaminar screws, to increase segmental stability. Many factors associated with both the cages and endplates influence the time of onset and extent of subsidence after use of stand‐alone cage ALIF. A large round cage with an adequate central opening is recommended to facilitate maximum contact with the periphery of the endplate. With regard to the relationship between radiographic fusion and recurrence of symptoms with the development of subsidence, most researchers have reported finding no correlation. Subsidence may be due to a process of bone incorporation between cages and endplates. Does subsidence or nonfusion really matter clinically? Further prospective, randomized controlled trials are very much needed to answer these questions.     

Healing properties of allograft from alendronate-treated animal in lumbar spine interbody cage fusion

This study investigated the healing potential of allograft from bisphosphonate-treated animals in anterior lumbar spine interbody fusion. Three levels of anterior lumbar interbody fusion with Brantigan cages were performed in two groups of five landrace pigs. Empty Brantigan cages or cages filled with either autograft or allograft were located randomly at different levels. The allograft materials for the treatment group were taken from the pigs that had been fed with alendronate, 10 mg daily for 3 months. The histological fusion rate was 2/5 in alendronate-treated allograft and 3/5 in non-treated allograft. The mean bone volume was 39% and 37.2% in alendronate-treated or non-treated allograft (NS), respectively. No statistical difference was found between the same grafted cage comparing two groups. The histological fusion rate was 7/10 in all autograft cage levels and 5/10 in combined allograft cage levels. No fusion was found at all in empty cage levels. With the numbers available, no statistically significant difference was found in histological fusion between autograft and allograft applications. There was a significant difference of mean bone volume between autograft (49.2%) and empty cage (27.5%) (P<0.01). In conclusion, this study did not demonstrate different healing properties of alendronate-treated and non-treated allograft for anterior lumbar interbody fusion in pigs.     

Anterior cervical reconstruction using titanium cages with anterior plating.

STUDY DESIGN: A preliminary outcome assessment study of titanium cage implants with anterior cervical plating in anterior cervical reconstruction. OBJECTIVES: To evaluate the efficacy and safety of using titanium cage implants and anterior plating in cervical reconstruction. SUMMARY OF BACKGROUND DATA: Anterior decompression and interbody fusion is a widely accepted surgical treatment for patients with cervical spondylosis. Tricortical iliac crest autograft has been the gold standard but is associated with morbidity at the bone graft donor site, whereas allograft fibula is associated with pseudarthrosis. Problems such as pseudarthrosis, graft collapse, and extrusion still persist with the accepted method of harvesting and implanting bone autografts. METHODS: Thirty-four patients were treated by channel corpectomy followed by placement of a titanium cage packed with autogenous bone graft from the vertebral bodies to reconstruct the anterior column. An anterior cervical plate was added in 30 of 34 cases that involved decompression of two or more levels. The follow-up period ranged from 24 to 56 months, with an average follow-up period of 32 months, and included examination and radiography. RESULTS: Six months after surgery, there was radiographic evidence of fusion in 97% of the patients. Eighty-eight percent of the patients (30 of 34) did not experience any complications (neither cage dislodgment nor hardware failure). Four patients had complications that included pseudarthrosis (1), extruded cage (1), cage in kyphosis (1), and radiculopathy (1). CONCLUSIONS: Titanium cages provide immediate strong anterior column support with minimum hardware complications and avoid bone graft-site morbidity. Titanium cages, with concomitant use of anterior plating, offer an effective and safe alternative to bone autografts.     

Biomechanical effect of anterior grafting devices on the rotational stability of spinal constructs

In the thoracolumbar spine, frequently strut grafting is used to restore the anterior and middle column defects. Biomechanical stability of the surgical construct may be altered significantly depending on the type of anterior grafting devices. In this study, a biomechanical flexibility test was conducted to compare the stabilizing role of various types of anterior grafting devices, such as a polymethylmethacrylate block, tricortical iliac crest bone graft, one large Harms cage, and two small Harms cages using a calf lumbar corpectomy model. The Harms cage, especially one large cage, improved the axial rotational stability significantly in both anterior and posterior fixation groups as compared with the iliac bone or polymethylmethacrylate. No significant difference in the stabilizing role was found among different grafting devices in lateral bending, flexion, and extension. These results suggest that a more rigid spinal construct can be obtained by using a metal cage with improved friction at the cage-bone interface.     

Antiprotrusio cages for acetabular revision

The purpose of this review was to explore the results of antiprotrusio cages and present indications for these devices. The role of antiprotrusio cages has had several reassessments in North America during the past decade. Currently, the primary indication for antiprotrusio cages are: (1) circumstances in which a stable, uncemented hemispheric acetabular component cannot be gained; and (2) circumstances in which there is so little remaining host bone that biologic fixation of a porous implant is very unlikely. Antiprotrusio cages have been reported to have a mechanical failure rate between 0% and 15% at midterm followup but most series do not report selective results of using cages only for the most severe bone defects. Key technical points when using antiprotrusio cages include: (1) wide exposure of the acetabular bone while protecting surrounding neurovascular structures; (2) positioning the antiprotrusio cage so as to span from host bone to host bone, thereby bridging acetabular defects; (3) appropriate bone grafting of acetabular bone deficiencies; and (4) secure fixation of the cage with good dome and posterior column support.     

Posterior lumbar interbody fusion using one diagonal fusion cage with transpedicular screw/rod fixation

Posterior lumbar interbody fusion (PLIF) using threaded cages has gained wide popularity for lumbosacral spinal disease. Our biomechanical tests showed that PLIF using a single diagonal cage with unilateral facetectomy does add a little to spinal stability and provides equal or even higher postoperative stability than PLIF using two posterior cages with bilateral facetectomy. Studies also demonstrated that cages placed using a posterior approach did not cause the same increase in spinal stiffness seen with pedicle screw instrumentation, and we concluded that cages should not be used posteriorly without other forms of fixation. On the other hand, placement of two cages using a posterior approach does have the disadvantage of risk to the bilateral nerve roots. We therefore performed a prospective study to determine whether PLIF can be accomplished by utilizing a single diagonal fusion cage with the application of supplemental transpedicular screw/rod instrumentation. Twenty-seven patients underwent a PLIF using one single fusion cage (BAK, Sulzer Spine-Tech, Minneapolis, MN, USA) inserted posterolaterally and oriented anteromedially on the symptomatic side with unilateral facetectomy and at the same level supplemental fixation with a transpedicular screw/rod system. The internal fixation systems included 12 SOCON spinal systems (Aesculap AG, Germany) and 15 TSRH spinal systems (Medtronic Sofamor Danek, USA). The inclusion criteria were grade 1 to 2 lumbar isthmic spondylolisthesis, lumbar degenerative spondylolisthesis, and recurrent lumbar disc herniations with instability. Patients had at least 1 year of low back pain and/or unilateral sciatica and a severely restricted functional ability in individuals aged 28-55 years. Patients with more than grade 2 spondylolisthesis or adjacent-level degeneration were excluded from the study. Patients were clinically assessed prior to surgery by an independent assessor; they were then reassessed at 1, 3, 6, 12, 18, and 24 months postoperatively by the same assessor and put into four categories: excellent, good, fair, and poor. Operative time, blood loss, hospital expense, and complications were also recorded. All patients achieved successful radiographic fusion at 2 years, and this was achieved at 1 year in 25 out of 27 patients. At 2 years, clinical results were excellent in 15 patients, good in 10, fair in 1, and poor in 1. Regarding complications, one patient had a postoperative motor and sensory deficit of the nerve root. Reoperation was required in one patient due to migration of pedicle screws. No implant fractures or deformities occurred in any of the patients. PLIF using diagonal insertion of a single threaded cage with supplemental transpedicular screw/rod instrumentation enables sufficient decompression and solid interbody fusion to be achieved with minimal invasion of the posterior spinal elements. It is a clinically safer, easier, and more economical means of accomplishing PLIF.     

Complications of anterior cervical discectomy and fusion using recombinant human bone morphogenetic protein-2

The use of bone morphogenetic protein-2 (rhBMP-2) in spinal fusion has increased dramatically since an FDA approval for its use in anterior lumbar fusion with the LT cage. There are several reports of its use in transforaminal lumbar interbody fusion, posterolateral fusion, and anterior cervical fusion. Reports on adverse effects of rhBMP-2 when used in spinal fusion are scarce in literature. An Institutional Review Board approved retrospective study was conducted in patients undergoing anterior spinal fusion and instrumentation following diskectomy at a single center. Forty-six consecutive patients were included. Twenty-two patients treated with rhBMP-2 and PEEK cages were compared to 24 in whom allograft spacers and demineralized bone matrix was used. Patients filled out Cervical Oswestry Scores, VAS for arm pain, neck pain, and had radiographs preoperatively as well at every follow up visit. Radiographic examination following surgery revealed end plate resorption in all patients in whom rhBMP-2 was used. This was followed by a period of new bone formation commencing at 6 weeks. In contrast, allograft patients showed a progressive blurring of end plate-allograft junction. Dysphagia was a common complication and it was significantly more frequent and more severe in patients in whom rhBMP-2 was used. Post operative swelling anterior to the vertebral body on lateral cervical spine X-ray was significantly larger in the rhBMP-2 group when measured from 1 to 6 weeks after which it was similar. These effects are possibly due to an early inflammatory response to rhBMP-2 and were observed to be dose related. With the parameters we used, there was no significant difference in the clinical outcome of patients in the two groups at 2 years. The cost of implants in patients treated with rhBMP-2 and PEEK spacers was more than three times the cost of allograft spacers and demineralized bone matrix in 1, 2, and 3-level cases. Despite providing consistently good fusion rates, we have abandoned using rhBMP-2 and PEEK cages for anterior cervical fusion, due to the side effects, high cost, and the availability of a suitable alternative.     

Analysis of titanium mesh cages in adults with minimum two-year follow-up

STUDY DESIGN: This is a study of 66 consecutive adult patients (ages 20-81 years) with sagittal deformities who underwent surgery in which structural titanium mesh cages were implanted into the anterior column during posterior instrumentation and fusion. Follow-up ranged from 24 to 62 months (mean, 33 months). OBJECTIVES: To assess the complications and outcomes of patients with structural cages implanted into the anterior column. SUMMARY OF BACKGROUND DATA: Structural cages for the anterior column are popular in the treatment of adult spinal disorders. Few studies to determine their efficacy have a minimum 2-year follow-up. METHODS: Sixty-six patients with minimum 2-year follow-up were analyzed for cage, spinal fusion, and instrumentation status. Outcomes were assessed by analysis of responses to questionnaires administered to the patients at latest follow-up. RESULTS: No cage failure or extrusion was observed. The average segmental improvement in lordosis with cage implantation was 11 degrees with a loss of correction of less than 1 degrees at latest follow-up. The readability of plain radiographs for assessment of anterior fusions was better than for posterior fusions. The agreement level for judging spines to be fused was two of three for 78% of the anterior levels and 47% of the posterior levels. The remaining posterior fusion levels were unassessable. No statistical difference was found in outcome between the group of patients with suspected nonfused anterior levels and the group with all levels fused. CONCLUSIONS: Structural titanium mesh cages implanted into the anterior column function appropriately to maintain sagittal correction, with rare radiographic complications. Seventy-eight percent of the anterior levels were judged to be fused by observers examining plain radiographs. The outcome at latest follow-up for patients with suspected nonfused anterior levels was similar to that in the group of patients with fusions rated solid at every level.     

Problems of posterior lumbar interbody fusion (PLIF) for the rheumatoid spondylitis of the lumbar spine

We performed posterior lumbar interbody fusion (PLIF) on 7 patients with rheumatoid spondylitis (RA) of the lumbar spine with severe low-back pain and/or cauda equina symptoms, and evaluated the effectiveness of PLIF for the lumbar spinal instability in RA secondary to destruction of the anterior elements, including vertebral endplates and the apophyseal joint. The subjects were 7 patients with classic RA, 2 men and 5 women, mean age 65 years old, and the mean duration of RA was 21 years. All had severe low-back pain and difficulty with walking. According to the ARA classification, the patients were at stage 3 or worse and in class 3. Diagnostic imaging including magnetic resonance imaging (MRI), tomography, myelography, and computed tomographic myelography (CTM) of the lumbar spine clearly delineated pathology, destruction of the vertebral endplate, subluxation, and cauda compression which can be well treated with PLIF. We performed L4/5PLIF (5 cases), L3/4 and L4/5 PLIF (2 cases), and posterior fixation with instruments for anterior column repair and stabilization and posterior decompression. Autografts (all cases) and Brantigan IF cage (2 cases) were used. Stable fixation of the lumbar spine was achieved after surgery, and improvement in gait and activities of daily living were achieved through the relief of low-back pain and radicular pain; the mean duration of follow-up was 22 months. Postoperative, plain radiography, CT, and MRI revealed the enlargement of the lumbar canal and fusion and incorporation of grafted bone, but in some cases, collapse of graft, migration of pedicle screw, instability of adjacent level, and collapse of adjacent vertebra were noted. PLIF with spinal instruments is a preferred treatment for rheumatoid spondylitis of the lumbar spine, but in the mutilating type of RA with severe osteoporosis, PLIF in combination with a long fixation system and/or augmentation of the vertebral bodies might be needed.