Bone graft incorporation in radiographically successful human intervertebral body fusion cages.

STUDY DESIGN: Biopsies were obtained from within radiographically successful human intervertebral body fusion cages to document the histology of remodeling bone graft. OBJECTIVES: The purpose of this study is to describe the tissue within successful human interbody cages with special reference to the viability of bone and the presence or absence of debris particles. SUMMARY OF BACKGROUND DATA: The use of interbody fusion cages is gaining rapid acceptance, but there is little histologic documentation of the nature of tissue within successful human interbody fusion cages. METHODS: Needle biopsies were obtained of tissue within radiographically successful intervertebral body fusion cages at the time of pedicle screw removal for back pain or fusion of adjacent spinal level in nine spinal levels of eight patients. Preoperative diagnoses of these eight adult patients included disease conditions in the sagittal plane: spondylosis (5), degenerative disc disease (6), failed laminectomy and discectomy (2), radiculopathy (1), and spondylolisthesis (1). In all cases the cages had been packed with autograft (iliac crest 7, local 1) at the time of insertion. Cage implantation was performed with anterior (anterior lumbar interbody fusion 4, corpectomy and plate fixation 1), and posterior (posterior lumbar interbody fusion 4), segmental instrumentation (plate 1, or pedicle screws 8). All cases except one cervical case had posterolateral fusion or bilateral facet fusion. The cages were composed of carbon fiber-reinforced polymer (Brantigan cage; DePuy AcroMed, Raynham, MA, n = 5) or titanium mesh (Harms Cage; DePuy AcroMed, Raynham, MA, n = 4). Cages had been in situ from 8 to 72 months (mean 28 months). All nine biopsies from eight patients were obtained from within the center of the cages. Specimens were decalcified, routinely embedded in paraffin, stained with hematoxylin and eosin, and viewed qualitatively with transmitted and polarized light. RESULTS: All needle biopsies were obtained from within the center of the cages, and no patient developed spinal instability after the biopsy. All nine biopsies showed small fragments of necrotic bone associated with viable bone and restoration of hematopoietic bone marrow. Numerous cement lines demarcated the edges of previous cycles of remodeling. The ratio of necrotic to viable bone varied greatly among cases. Small particles of debris were associated with four of the five carbon-fiber cages and one of the four specimens from titanium cages, but there was no visible bone resorption or inflammation. CONCLUSIONS: Autogenous bone graft was incorporated in these radiographically successful human intervertebral body fusion cages. A few debris particles were observed, but there was no histologic evidence of particle-induced bone resorption or inflammation.

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.

Interbody lumbar fusion using a carbon fiber cage implant versus allograft bone. An investigational study in the Spanish goat.

STUDY DESIGN: A carbon fiber-reinforced polymer implant, designed to aid interbody lumbar fusion, was tested biologically in an experimental surgical model. Twenty-seven Spanish goats had interbody lumbar fusion surgery in a randomized protocol. Seventeen goats were implanted with the carbon fiber-reinforced polymer cage packed with autologous bone, and 10 goats were implanted with ethylene oxide-sterilized allograft bone. OBJECTIVES: To determine fusion success, biocompatibility of the carbon polymer material, and possibility of carbon wear debris at intervals after surgical implantation. METHODS: Goats were killed at 6 months, 12 months, and 24 months and full-body autopsies were done. Spine specimens were studied by plain radiography, three-dimensional reformatted computed tomography studies, and histology. RESULTS: At 6 months, one of three allograft implantations showed histologic and radiographic fusion, whereas five of five carbon fiber-reinforced polymer cage fusions showed at least partial fusion. At 12 months, two of three allograft implantations and five of five carbon fiber-reinforced polymer cage fusions were solidly fused. At 24 months, five of five allograft implantations and three of three carbon fiber-reinforced polymer cage implantations were solidly fused. CONCLUSIONS: Interbody fusion using a carbon cage implant packed with autologous bone achieved a quicker and more reliable fusion compared with ethylene oxide-sterilized allograft bone. There were no adverse effects from the implant material.

Pseudarthrosis rate after allograft posterior lumbar interbody fusion with pedicle screw and plate fixation.

STUDY DESIGN: Twenty-five of 26 consecutive patients were studied after posterior lumbar interbody fusion using ethylene oxide-sterilized allograft bone for posterior lumbar interbody fusion and autologous bone for posterolateral fusion with posterior fixation using pedicle screws and variable screw placement plates. OBJECTIVES: Patients were studied at 1 year to determine rate of complications, pseudarthrosis, and re-operations. METHODS: Clinical success was determined by combined five-point analog pain and function scales. Fusion success was determined by plain radiographs. RESULTS: Complications occurred in four of 25 patients (16%). Re-operations were done in nine of 25 patients (36%) with seven re-operations (28%) to treat frank failures of the donor bone. Although some patients subsequently improved with repeat surgery, the result of the donor bone posterior lumbar interbody fusion was excellent in nine patients, good in four, fair in eight, and poor in four. Posterior lumbar interbody fusion success was achieved in 14 of 25 patients (56%). Clinical success was achieved in 15 of 25 patients (60%). CONCLUSIONS: Although the mechanical principles of posterior lumbar interbody fusion were affirmed, the adequacy of ethylene oxide-sterilized allograft bone in meeting the mechanical and biologic needs of posterior lumbar interbody fusion was questioned.

Technique of reduction and internal fixation of thoracolumbar fracture-dislocation using pedicle screws and variable screw placement plates.

Spinal column injuries to the thoracolumbar region are common and leave one fifth of patients with neurological deficit. The authors describe a case of complete fracture-dislocation at lumbar 1-2 level with paraplegia. They detail their surgical technique for reduction, stabilization, and fusion using pedicle screws and plates. Surgical management of such injuries allows rapid rehabilitation of patients with spinal column injuries.

A biomechanical analysis of decompression and reconstruction methods in the cervical spine. Emphasis on a carbon-fiber-composite cage.

Biomechanical analysis of three different patterns of instability--that created by fifth and sixth cervical anterior discectomy, that created by one-level (fifth cervical) anterior corpectomy, and that created by two-level (fourth and fifth cervical) corpectomy--was performed in eighteen calf spines. Three types of anterior reconstruction--anterior iliac strut bone-grafting, use of an anterior carbon-fiber-composite cage packed with cancellous bone graft, as well as use of polymethylmethacrylate anteriorly--were cyclically tested in axial compression, torsion, and flexion-extension. Each of these types of reconstruction was also tested with supplemental posterior wire stabilization (the triple-wire technique of Bohlman). Regardless of the type of anterior instability, the carbon-fiber-reinforced cage packed with cancellous bone graft was more rigid than the iliac bone graft alone. The cage resulted in good stiffness in the axial compression and rotation tests and was the most rigid construct in the flexion-extension tests. The superior aspect of the polymethylmethacrylate constructs loosened at the bone-cement interface in eight of the twelve specimens during flexion-extension testing. The addition of the supplemental posterior wiring to the anterior constructs provided additional rigidity in flexion-extension testing.

A carbon fiber implant to aid interbody lumbar fusion. Two-year clinical results in the first 26 patients.

The success of posterior lumbar interbody fusion (PLIF) has been limited by mechanical and biologic deficiencies of the donor bone. The authors have designed a carbon fiber-reinforced polymer implant that separates the mechanical and biologic functions of PLIF. The cagelike implant provides an actual device designed to meet the mechanical requirements of PLIF and replaces the donor bone with autologous bone, the best possible bone for healing. The authors report 2-year follow-up results for their first 26 consecutive patients, 18 of whom were postsurgical failed backs with a total of 37 previous surgeries. At 2 years, 28 of 28 PLIF cage fusion levels and 6 of 11 (54.5%) allograft levels exhibited radiographic fusion, a statistically significant difference at P = 0.0002. Clinical results were excellent in 11/26, good in 10/26, fair in 3/26, and poor in 2/26. Fair and poor results were attributable to objective identifiable problems unrelated to the carbon cage. The carbon implant achieved successful fusion in 6/6 (100%) of followed patients treated for a failed ETO allograft interbody fusion. A prospective controlled multi-centered study is being initiated.

The variable screw placement spinal fixation system. Report of a prospective study of 250 patients enrolled in Food and Drug Administration clinical trials.

The variable screw placement (VSP) system uses transpedicular screws and slotted plates to achieve constrained segmental fixation of the spine. A prospective multicenter study of 250 patients was performed under a Food and Drug Administration approved protocol to test the safety and effectiveness of this system. Complete 2-year follow-up data are reported for 169 of 223 (73%) patients who had fixation of three spinal levels or fewer. "Clinical success" was defined as an excellent or good result or improvement of two grades in a 10-point combined pain and function scale. "Fusion success" was defined by presence of continuous trabecular bone bridging the fusion area. For 86 patients with postsurgical failed back syndrome, clinical success was achieved in 69 (80.2%) and fusion success in 76 of 83 (91.6%) patients. These success rates were statistically higher than previous literature reports (P = 0.01 for clinical success and P = 0.02 for fusion success). For spondylolisthesis, clinical success was achieved in 44 of 57 patients (86.3%) and fusion success in 43 of 47 (91.5%) patients. For spinal stenosis, clinical success was achieved in 25 of 32 patients (78.1%) and fusion success in 30 of 31 (96.8%) patients. Overall fusion success was achieved in 186 of 200 (93%) patients with no statistical difference when comparing the numbers of levels fused. There were 21 device-related complications (8.4%) and 16 non-device-related complications (6.4%).

Compression strength of donor bone for posterior lumbar interbody fusion.

Forty-three blocks of allograft bone used clinically for posterior lumbar interbody fusion and twenty-three blocks of xenograft bone from goats and cows were tested in compression and compared with the clinical mechanical requirements of posterior lumbar interbody fusion. Variations in processing methods allowed evaluation of the effects of processing on mechanical strength. Fresh-frozen cancellous bone from Os Bone (Cleveland, OH) failed at an average load of 863 +/- 615 N. Fresh-frozen cancellous bone from the Mid American Tissue Center (Massilon, OH) failed at an average load of 3492 +/- 1720 N. Freeze-dried cancellous bone obtained from the American Red Cross failed at an average load of 1595 +/- 1031 N. Air-dried ethylene oxide sterilized cancellous bone from Os Bone failed at an average load of 1338 +/- 691 N. Air-dried ethylene oxide sterilized cancellous bone from Mid America failed at an average load of 1616 +/- 1157 N. Fresh-frozen tricortical bone from Mid America failed at an average load of 2257 +/- 1081 N. Air-dried ethylene oxide sterilized tricortical bone from Os Bone failed at an average load of 2474 +/- 1928 N. Air-dried ethylene oxide sterilized tricortical bone from Mid America failed at an average load of 2308 +/- 422 N. Bovine Surgibone from Unilab (Hillside, NJ) failed at an average load of 2967 +/- 399 N. Strength of bone in compression was not weakened by freeze drying, air drying, ethylene oxide sterilization, or by incubation at 37 degrees C for 1 week before testing.(ABSTRACT TRUNCATED AT 250 WORDS)

A carbon fiber implant to aid interbody lumbar fusion. Mechanical testing.

A carbon-fiber-reinforced polymer implant has been designed to aid interbody lumbar fusion. The cage-like implant has ridges or teeth to resist pullout or retropulsion, struts to support weight bearing, and a hollow center for packing of autologous bone graft. Because carbon is radiolucent, bony healing can be imaged by standard radiographic techniques. The device has been mechanically tested in cadaver spines and compared with posterior lumbar interbody fusion performed with donor bone. The carbon device required a pullout force of 353 N compared with 126 N for donor bone. In compression testing, posterior lumbar interbody fusion performed with the carbon device bore a load of 5,288 N before failure of the vertebral bone. Posterior lumbar interbody fusion performed with donor bone failed at 4,628 N, and unmodified motion segments failed at 6,043 N. The carbon fiber implant separates the mechanical and biologic functions of posterior lumbar interbody fusion.

Investigation of flow rates of oxygen systems used in general aviation.

Flow rates of two general aviation constant flow oxygen systems were tested at altitude using a Ted Nelson flow meter and using timed flow into a volume bag. Contrary to the manufacturer's claim, the Rajay SK-10 system was not altitude compensated and provided a flow rate of about 2.2 1/min independent of altitude. The Scott system provided the stated 2.5 l/min with the standard connector and 8 l/min with the "green" connector, the significance of the color code being not widely understood. The conclusions of the 1975 report on oxygen mask performance should be revised according to these flow data. The Ted Nelson flow meter performed within its stated accuracy.

Instability of the subtalar joint. Diagnosis by stress tomography in three cases.

Lateral instability in the subtalar joint was documented by a method of stress tomography in three patients. The subtalar inversion angle averaged 38 degrees +/- S.D. 6 degrees in asymptomatic feet and 57 degrees +/- S.D. 5 degrees in those with unstable subtalar joints . Review of the literature suggests that as many as 10 per cent of patients having the Watson-Jones procedure for abnormal talar tilt also have instability in the subtalar joint. It is felt that the subtalar joint should be evaluated in patients seen with the clinical symptom of lateral instability.

Femoral neuropathy complicating anticoagulant therapy.

A twenty-six year old white male on long-term sodium warfarin (Coumadin therapy for recurrent thrombophlebitis had sudden onset of severe groin pain, right iliac hematoma, and a femoral nerve palsy. A review of the twelve previously reported cases of this hemorrhagic complication indicates that immediate surgical decompression may be necessary to prevent residual disability.