Arthur D. Steffee

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.

A morphometric study of human lumbar and selected thoracic vertebrae

The results of a morphometric study of selected human vertebrae undertaken to provide data for implant design are presented in this report. Twenty-seven dimensions were measured from thoracic (T2, T7, T12) and lumbar (L1–L5) vertebrae using prepared spinal columns from 30 skeletons belonging to the Hamann-Todd Osteological Collection. Maximum and minimum pedicle dimensions indicated that the pedicles are less symmetric cephalad than they are caudal. Vertebral body height increases caudally except posteriorly where, after an initial increase, it decreases in the lower lumbar region. Major and minor body diameters and the major spinal canal diameter slightly increase caudally, whereas minor spinal canal diameter exhibits little or no change.

Posterior lumbar interbody fusion and plates.

Posterior lumbar interbody fusion (PLIF) is accepted by many authors as the surgical treatment for herniated discs, degenerative disc conditions, and Grades I and II spondylolistheses. PLIF is now used in conjunction with newly developed segmental spine plates by using transpedicular screw fixation to enhance the osteosynthesis and success rate of interbody fusion. To date, 104 fusions have been performed in 67 patients with no dislocations of any interbody grafts and no indication of absorption, pseudoarthrosis, or infections.

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.

Artificial disc replacement. Preliminary report with a 3-year minimum follow-up.

Artificial disc replacement was performed in six patients with an average age of 55 years and average follow-up of 3.4 years. Four of the six patients had juxtafusion degeneration, one had multilevel disc degeneration, and one patient had isolated disc resorption. The Acroflex disc (Acromed Corporation, Cleveland, OH), which was used in the replacement, is composed of a rubber core vulcanized to two titanium end plates. The latter have superior posts to provide for initial mechanical fixation and porous in-growth surfaces for long-term fixation. Satisfactory results occurred in four of six patients. Poor results occurred in the presence of deformity that resulted in prosthetic failure and isolated disc resorption. There was an average 8 degrees angular and 2.3-mm translational movement and satisfactory in-growth at all interfaces. Design objectives of endurance, biocompatibility, geometry, kinematics, constraint, dynamics, stability, and fail-safe were met; however, this study is preliminary in nature.

Posterior transvertebral osteotomy for adult thoracolumbar kyphosis

Study Design A retrospective case study was performed on the single-stage posterior transvertebral closing-wedge osteotomy for treatment of adult thoracolumbar kyphosis. Summary of Background Data Forty-one consecutive cases in 38 patients available for follow-up, averaging 33 months (range 4–87 months), are included. All patients had severe pain and/or deformity; 51% of cases had previous fractures, and 49% had postlaminectomy failed back syndromes with kyphosis. A preoperative neurologic deficit was present in 34% of the cases including two with cauda equina syndrome. Methods Patient examination and interviews, subjective questionnaire, chart reviews, and radiographic measurements were performed independently. Complications, risks, benefits, results, and biomechanical considerations were evaluated and discussed as compared with other techniques. Results All cases had solid union at follow-up; 93% maintained correction averaging 35° with three requiring revision for failure. Postoperatively, 19.5% of the cases had new neurologic deficits with five (12.2%) temporary or minor and three (7.3%) major, including one with unimproved paraplegia at follow-up. Eight of the 14 preoperative neurologic deficit cases improved postoperatively; 26 additional surgeries were performed on 18 patients most commonly for pain (x11) and additional trauma (x4). The subjective questionnaire results indicated significant patient satisfaction, with 76% stating they would repeat the surgery and 90% recommending it to another. Conclusion This technically demanding high-risk procedure provides an effective and mechanically superior correction for acute angle thoracolumbar kyphosis in selected adult patients, with high subjective satisfaction.

Interbody fusion and instrumentation.

Fusion indications in adult degenerative disk disease of the lumbosacral spine include isolated disk resorption, primary and secondary instability, recurrent disk herniation, and pseudarthrosis. Common to these indications are variable proportions of biomechanical insufficiency of the motion segment, instability, deformity, and spinal stenosis. Apart from favorable psychosocial and work related variables, satisfactory outcome is dependent on treatment by a combination of diskectomy, decompression, and deformity correction, in addition to fusion. Isolated intertransverse or interbody fusions show variable fusion rates that are increased by concurrent instrumentation. Persistent pseudarthrosis rates and instrumentation failures have prompted circumferential fusion techniques. Posterior lumbar interbody fusion (PLIF) and segmental pedicle-based plate fixation overcome earlier problems with PLIF by allowing for wide decompression and increased exposure for disk space preparation, minimizing neural injury. Pedicle fixation restores segmental stability and minimizes graft retropulsion. Restoration of anterior column support prolongs instrumentation life, and increases fusion rates irrespective of the number of levels fused. Disk space distraction, with the use of instrumentation as a working tool, permits safer decompression of the intraforaminal zone, a common area of stenosis, and single or multilevel deformity correction to restore coronal, axial, and sagittal alignment and spinal balance. Even though the surgical technique is demanding, fusion rates up to 96% and clinical success up to 86% are achieved.

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)

Treatment of L5-S1 spondyloptosis by staged L5 resection with reduction and fusion of L4 onto S1 (Gaines procedure).

Study Design and Objectives A retrospective study was performed on the two-stage Gaines procedure for the treatment of spondyloptosis, evaluating indications, techniques, results, and patient satisfaction. Summary of Background Data Sixteen consecutive patients from two institutions were Included. Their average age was 24 years. Average follow-up was 3.9 years, with 11 patients included in follow-up 2 or more years. Ten patients (63%) had a preoperative neurologic deficit-three with cauda equina syndrome, one with foot drop. All patients had severe back or radicular symptoms and significant disability or severe deformity. Methods Patient examinations, interviews, chart review, and radiographic measurements all were performed Independently. A subjective questionnaire was administered to each patient comparing preoperative with postoperative changes in pain, function, and appearance, as well as their overall outcome assessment. Results Postoperatively, 12 patients (75%) had early neurologic deficits, with seven of these having had a preoperative deficit. Four of these seven had a persistent deficit at follow-up, one with a permanent foot drop and three with documented weakness that was still improving at follow-up. The patient with preoperative foot drop remained unchanged, and the remaining seven patients with early deficit all recovered within 1 year. All three patients with preoperative cauda equina syndrome recovered postoperatively. The subjective questionnaire results revealed extremely high patient satisfaction. They reported significant improvement in pain, function, and appearance. Conclusions Despite the relatively high complication rate, with appropriate patient selection, planning, and surgical technique, this procedure appears to be a sound method for treating severe cases of spondyloptosis, yielding very high patient satisfaction.

Reduction and stabilization of grade IV spondylolisthesis.

Virtually any degree of spondylolisthesis can be reduced and held using variable screw placement (VSP) slotted plates and transpedicular screws. All of the soft tissue holding the displaced vertebrae must be stretched prior to pulling the vertebrae back into normal alignment. Complete control of the displaced vertebrae is gained through the transpedicular screws, and fixation is accomplished by bolting the screws to the spine plates that have been bent to achieve the proper lumbar lordosis. Ultimate stability is gained by both a bilateral lateral and interbody fusion.