Lumbar sagittal alignment after fusion with a threaded interbody cage.

STUDY DESIGN: Records of 111 patients randomly selected from a population who received an interbody fusion cage during a clinical Investigation Device Exemption trial (BAK/L) yielded 126 operative levels and were retrospectively assessed. OBJECTIVES: This study examined lumbar spine sagittal alignment and clinical outcomes before and 2 years after fusion surgery. SUMMARY OF BACKGROUND DATA: Lumbar lordosis is important in spinal sagittal alignment and balance, especially the L4-S1 area. Perceived consensus is that anatomically correct lumbar lordosis is desired and that a loss of lumbar lordosis may lead to spine pathology. There is little information on lumbar lordosis after interbody fusion. METHODS: A random sample of 111 patients who received a cylindrical cage implant (total pool of 947 patients) yielded 126 operative lumbar segments. There were 52 posterior approaches and 59 anterior approaches, and all cages were placed in the L4-L5 or L5-S1 levels. Preoperative and 2-year follow-up lateral radiographs were measured for segmental lordosis. Cage position was measured relative to the posterior longitudinal ligament. Segmental lordotic change was correlated to clinical outcome at the 2-year follow-up. RESULTS: Preoperative lordosis was different as a function of surgical approach. There was a significant 2-year decrease in lordosis with the posterior approach group; however, all intervertebral angles were within typical ranges. Clinical outcomes were significantly improved 2 years postsurgery. There was no correlation between changes in lordosis and clinical outcomes. CONCLUSIONS: Interbody lumbar fusion with a threaded cylindrical cage does not appear to have any clinically relevant effects on segmental lordosis, which is maintained within anatomically normal levels. Clinical outcome measures show significant postsurgery improvement, and changes in lordotic angles are not predictive of clinical outcome.

A prospective randomized multicenter clinical evaluation of an anterior cervical fusion cage.

STUDY DESIGN: A prospective, concurrently controlled, randomized, multicenter trial of an anterior Bagby and Kuslich cervical fusion cage (BAK/C; Sulzer Spine-Tech, Minneapolis, MN) for treatment of degenerative disc disease of the cervical spine. OBJECTIVES: To report clinical results with maximum 24-month follow-up of fusions performed with the BAK/C fusion cage. SUMMARY OF BACKGROUND DATA: Threaded lumbar cages have been used during the past decade as a safe and effective surgical solution for chronic disabling low back pain. Threaded cages have now been developed for use in anterior cervical interbody fusions to obviate the need for allografts or autogenous bone grafting procedures while providing initial stability during the fusion process. METHODS: Patients with symptomatic cervical discogenic radiculopathy were treated with either anterior cervical discectomy with uninstrumented bone-only fusion (ACDF) or BAK/C fusion cage(s). Independent radiographic assessment of fusion was made and patient-based outcome was assessed by visual analog pain scale and a Short Form (SF)-36 Health Status Questionnaire. RESULTS: Data analysis included 344 patients at 1 year and 180 at 2 years. When the two cage groups (hydroxya, patite-coated or noncoated) were compared with the ACDF group, similar outcomes were noted for duration of surgery, hospital stay, improvements in neck pain and radicular pain in the affected limb, improvements in the SF-36 Physical Component subscale and Mental Component subscale, and the patients' perception of overall surgical outcome. Symptom improvements were maintained at 2 years. A greater percentage of patients with ACDF needed an iliac crest bone harvest than did BAK/C patients (67% vs.- 3%). Successful fusion for one-level procedures at 12 months was 97.9% for the BAK/C groups and 89.7% for the ACDF group (P < 0.05). The complication rate for the ACDF group was 20.4% compared with an overall complication rate of 11.8% with BAK/C. There was no difference in complications that necessitated a second operative procedure. CONCLUSIONS: These results demonstrate that outcomes after a cervical fusion procedure with a threaded cage are the same as those of a conventional uninstrumented bone-only anterior discectomy and fusion with a low risk of complications and rare need for autogenous bone graft harvest.

Four-year follow-up results of lumbar spine arthrodesis using the Bagby and Kuslich lumbar fusion cage.

STUDY DESIGN: This was a prospective multicenter clinical trial of a lumbar interbody fusion cage with a minimum of 4 years' follow-up. OBJECTIVES: To determine whether the early positive clinical results in fusions with lumbar cages, such as the Bagby and Kuslich (BAK) cage, are maintained beyond 2 years. SUMMARY OF BACKGROUND DATA: Threaded cages have been used increasingly for the treatment of symptomatic degenerative intervertebral disc disease. Concerns about the long-term clinical outcomes of this procedure have been posed, particularly regarding bony fusion viability, revision rates, potential adjacent level disease, and late complications. METHODS: The study cohort was a 196-patient subset from a prospective investigational device exemption. In addition to early postoperative examinations, these patients were examined biannually with a minimum of 4 years' follow-up. Patient outcome was assessed by a 6-point scale that evaluated pain relief, and functional improvement was determined by changes in activities of daily living. Fusion rates and return to work were determined. Complications and secondary operations were reported and categorized as non-device related or device related. RESULTS: The patient cohort with 4-year follow-up represented 25.6% of the original study population eligible at that time. Overall, the largest percentage of pain relief and functional improvements occurred by 3 months, and these improvements were maintained at each follow-up. Overall fusion rate was 91.7% and 95. 1% at 2 and 4 years, respectively. In this cohort, 39.5% of patients were working or were able to work within 3 months of surgery. After 4 years, 62.7% of patients were gainfully employed or able to work. The late-occurring complication rate in this cohort was 13.8% (27/196). Complications necessitating a second operation occurred in 8.7% (17/196), whereas reoperations that were deemed device related were performed in 3.1% (6/196). CONCLUSIONS: This study indicates that the early positive benefits of interbody fusion cage procedures are maintained through 4 years with acceptably low morbidity.

Revision strategies for salvaging or improving failed cylindrical cages.

STUDY DESIGN: This is a review of 20 patients who experienced failure of threaded interbody fusion cages and underwent surgical correction. OBJECTIVE: To review the causes and possible treatment strategies for failed cylindrical cages. SUMMARY OF BACKGROUND DATA: Intraoperative complications have been described in the past; however, management of the postoperative patient with failure of interbody fusion devices has not been described. METHODS: In 20 patients with failed threaded titanium fusion cages (18 Bagby and Kuslich Devices [BAK; Sulzer-Spine Tech, Minneapolis, MN], 2 Ray Threaded Fusion Cages [Ray TFC; Surgical Dynamics, Norwalk, CT) who underwent revision surgery, all had failure before successful arthrodesis was achieved. Eight of the original titanium cages had been inserted anteriorly (7 laparoscopically), and 12 had been inserted for posterior interbody lumbar fusion. Before the revision surgery, five of the implants were thought to be solid by the referring surgeon, but pseudarthrosis was clearly present in all. In addition, 14 other explanted BAK devices were subjected to undecalcified histologic preparation, quantitative histomorphometry, and histopathologic analysis. RESULTS: The average length of time before revision surgery (implant duration) was 31.8 weeks (range, 1-156 weeks). The most common revision procedure was posterior exploration of the symptomatic nerve root with foraminotomy for unrecognized lateral recess stenosis (11 cases) or excision of iatrogenically herniated intervertebral disc fragments (4 cases). However, four cages inserted through posterior exposure during an interbody lumbar fusion procedure had to be removed because of migration into the spinal canal. In nine cases posterior pedicle screw instrumentation was necessary in addition to posterolateral fusion using iliac crest bone grafting. CONCLUSIONS: All 20 cages failed because of surgical technique rather than an intrinsic defect in fusion cage technology. The factors associated with failure of the original insertion procedure were failure to achieve adequate distraction of the anulus fibrosis; undersized cages, especially when placed through the posterior interbody lumbar fusion approach; cerebrospinal fluid leakage or pseudomeningocele; Type 2 diabetes mellitus; the use of local bone graft rather than iliac crest inside the cage; anterior insertion in an excessively lateral position resulting in symptoms of a far lateral disc herniation; and failure to identify the spinal midline during an anterior approach.

The Bagby and Kuslich method of lumbar interbody fusion. History, techniques, and 2-year follow-up results of a United States prospective, multicenter trial.

STUDY DESIGN: A prospective, multicenter trial of the Bagby and Kuslich method of lumbar interbody stabilization for chronic discogenic low back pain, with follow-up evaluation at 3 months, 6 months, and yearly thereafter, with independent radiographic analysis. OBJECTIVES: To report the history of development, the surgical techniques, and results of the Bagby and Kuslich method when used to manage discogenic pain of the lumbar spine in humans. SUMMARY OF BACKGROUND DATA: Disabling chronic low back pain frequently is resistant to conservative management. The "Bagby Basket" effectively has fused the equine and baboon spine. The results of biomechanical and animal studies performed over the last 20 years have suggested that a similar but improved design--the Bagby and Kuslich device--would be useful in stabilizing the human spine. METHODS: From 1992 to 1995, 947 patients with chronic discogenic low back pain were treated by Bagby and Kuslich interbody fusion in a strict, multicenter, prospective clinical trial by using either the open anterior or open posterior approach. The study involved 42 surgeons at 19 medical centers. The authors of the current report analyzed the fusion rates, pain relief, functional status, and complications occurring in patients who underwent long-term follow-up observation. RESULTS: The Bagby and Kuslich method is safe and effective when compared with methods described in previous reports of posterior and anterior lumbar interbody arthrodesis performed by using bone graft alone. Fusion occurred in 91% of patients at 24 months after surgery, and pain was eliminated or reduced in 84%. Function was improved in 91%. There were no device-related deaths, cases of major paralyses, device failures, or deep infections. CONCLUSIONS: Carefully selected middle-aged patients with chronic low back pain secondary to degenerative disc disease can be treated effectively and safely by skilled surgeons using the Bagby and Kuslich device for one- and two-level interbody fusion.

Biomechanical comparison of anterior instrumentation for the cervical spine.

Metal fixation has been advocated to achieve immediate local stabilization during anterior cervical fusion surgery. Screw loosening, screw backout, and breakage of screws or plates remain clinical complications that warrant concern. This study examined the biomechanical characteristics of a prototype anterior cervical plating system with unique screw and plate geometries in comparison to a fixation system currently used clinically. Compared with a standard screw design, a taper screw design resulted in increased ultimate strength and fatigue life. The addition of a locking pin hole in the tapered screw made the screw's fatigue life comparable to the standard design. Pullout strength was comparable in all screw designs. The prototype fixation system had higher strength in pure compression and compression with bending than the comparative system, while also demonstrating improved fatigue characteristics. The tensile bending stiffness of the prototype was double that of the comparative system and within the anatomical range of cervical vertebrae, the bending moment was greater. Torsional yield strength was greater than the reported breaking strength of cervical disc in situ for both systems. The unique designs of the screw and plate geometry resulted in an anterior cervical plate fixation system that is stronger with decreased risk of fatigue failure than a currently used system. Clinical evaluation in patients requiring immediate stabilization is warranted.

Intradiscal pressure measurements above an instrumented fusion. A cadaveric study.

STUDY DESIGN: An in vitro study to determine the intradiscal pressure changes during flexion in levels above a simulated fusion was performed. OBJECTIVES: To determine if intradiscal pressure increases more during flexion in discs above an instrumented spinal segment compared to an uninstrumented segment. SUMMARY OF BACKGROUND DATA: The progressive degeneration of intervertebral discs adjacent to a fused or fixed segment is a phenomenon that is noted but poorly understood. Intuitively, the degeneration appears to be a function of altered biomechanics of the motion segments in the spine. METHODS: Two intervertebral disc levels were evaluated, L3-L4 and L4-L5 from each of six fresh frozen cadaver spines. Pressure measurements were taken with the spine uninstrumented, with bilateral pedicle screw-rod instrumentation from L5 to S1, and with bilateral pedicle screw-rod instrumentation from L4 to S1. Pressure measurements were accomplished with Millar Mikro-Tip pressure transducers. The transducers were placed within the nucleus pulposus of L3-L4 and L4-L5 intervertebral discs. Pressure data were recorded by computer data acquisition. The pressure data were compared by intervertebral level and by the effects of added instrumentation. RESULTS: In general, the addition of instrumentation significantly affected the intradiscal pressure in the levels above a simulated fusion. The intradiscal pressure increased as the amount of levels involved in the simulated fusion increased. The intradiscal pressure increased as flexion motion increased. A greater increase was seen at the L4-L5 level than the L3-L4 level. When L5-S1 fixation was added, the intradiscal pressure increased. When L4-S1 fixation was added, the intradiscal pressure further increased. CONCLUSION: This study demonstrated increasing intradiscal pressures during flexion.

Contractility and myosin heavy chain isoform patterns in developing tracheal muscle.

Changes in airway smooth muscle reactivity with development may be caused by either modification of the excitation-contraction coupling system or alteration of the contractile apparatus. The mechanism responsible for the reported changes in reactivity was addressed in this study by examining airway smooth muscle contractility and myosin heavy chain isoform patterns as a function of post-neonatal development. Changes in length and force, in response to supramaximal electrical stimulation, were recorded simultaneously as functions of time for tracheal smooth muscle (TSM) strips from 8-week-old and 25-week-old male rabbits. Both the passive and active length-tension (L-T) curves as well as the force-velocity (F-V) curves for the two age groups of rabbit TSM were not significantly different indicating no changes in contractility during post-neonatal development in rabbits. This conclusion is surprising in light of reports of myosin heavy chain (MHC) isoform shifts in porcine trachealis during comparable periods of development. Therefore, MHC isoform ratios were compared by sodium dodecyl sulfate-polyacrylimide gel electrophoresis for tracheal smooth muscle from male rabbits of 8 and 25 weeks of age. Unlike the reported MHC isoform shifts in the pig tracheal muscle, the rabbit trachealis showed no difference in MHC isoform ratios between the two age groups compared in this study. In conclusion, no changes occur in contractility or MHC isoform patterns during post-neonatal development of rabbit tracheal smooth muscle. Therefore, reported changes in airway muscle reactivity are likely due to changes in receptors or in second messenger systems rather than to changes in the contractile apparatus.

A multicenter retrospective study of the clinical results of the LINK SB Charité intervertebral prosthesis. The initial European experience.

OBJECTIVE: This study is a multicenter, retrospective review of the initial clinical results of an artificial disc replacement, the LINK SB Charité intervertebral prosthesis. METHODS: Independent analysis by chart review included patient demographics, surgical data, and a comparison of presurgical to follow-up data. Data were analyzed from 93 patients (average age = 43.0 +/- 7.3) in whom a total of 139 Model III prostheses (Waldemar Link GmbH & Co, Hamburg, Germany) were implanted. RESULTS: The predominant diagnostic indication for the disc was degenerative disc disease (52.4%). The L4-L5 and L5-S1 levels comprised 87.1% of all levels implanted. The average follow-up was 11.5 +/- 8.4 months. After disc implantation, a significant proportion of the patient sample experienced pain relief (P < 0.05). Improvements were also noted in pain intensity, walking distance, lumbar mobility, and the percentage of patients showing a positive SLR or neurological weakness. No difference in work status after disc implantation could be detected. Device failure, migration, or dislocation occurred in 6 of 93 (6.5%) patients. CONCLUSIONS: This study represents the largest multicenter case series of any functional artificial disc implantation. Carefully controlled, prospective studies that compare disc implantation and fusion are warranted.

Pulmonary arterial smooth muscle contractility in hypoxia-induced pulmonary hypertension.

The highly compliant low-resistance pulmonary vasculature is markedly altered with chronic hypoxia. Remodeling in response to hypoxia and/or hypertension involves hypertrophy and hyperplasia of smooth muscle and excessive deposition of connective tissue that likely contributes to the maintenance or exasperates the already elevated pulmonary arterial (PA) pressure. The purpose of this study was to investigate the effect of chronic hypoxia on the contractile properties of PA smooth muscle. Isometric and isotonic experiments were performed on excised PA rings from pulmonary hypertensive (induced by 14 days of hypoxia) Sprague-Dawley rats. A doubling of the vessel wall thickness occurred during the development of hypoxia-induced pulmonary hypertension. Functionally, there was a decrease in isometric stress (force to cross-sectional area ratio). No difference was detected in the velocity of shortening or in total shortening ability. This study provides evidence that, in addition to the morphological changes, changes in PA smooth muscle contractility also appear to play a role in the development and/or maintenance of hypoxia-induced pulmonary hypertension.

Extracorporeal liver ablation using sonography-guided high-intensity focused ultrasound.

RATIONALE AND OBJECTIVES: High-intensity focused ultrasound (HIFU) is the only radiation beam that can remotely destroy deep-seated tissue targets without causing damage to the intervening tissues. This study evaluates the ability of sonography-guided HIFU to extracorporeally induce liver ablation in a rabbit model. METHODS: Under sonographic guidance, the HIFU beam was transcutaneously focused at the target tissue in the liver through a subcostal approach. A computer controlled the HIFU exposure and transducer movement to destroy a preselected tissue volume. Simultaneous sonography monitored the tissue response. Ten insonated rabbits were killed from days 0 to 10, and the liver and intervening tissues were examined histologically. RESULTS: A sharply demarcated sonolesion of coagulation necrosis was produced in the liver in 9 of 10 animals. No damage was found in the intervening tissues (n = 6) when adequate acoustic coupling and proper beam path was applied. CONCLUSION: Sonography-guided HIFU might be a potential new modality for extracorporeal inducement of liver cancer ablation without resorting to laparatomy.

Laser and suture anastomosis: passive compliance and active force production.

One carotid from each dog underwent a laser anastomosis and the other carotid an interrupted suture repair. One or eight weeks later (n greater than or equal to 4 dogs/time period); four rings (1 mm in length) containing the laser or suture anastomosis or the normal artery (two/dog) were removed. Using a photoelectric force transducer and lever system, the ring was stretched in increments and passive force measured. At each length, the arterial muscle was stimulated and active force measured. The mean laser and control passive length/tension (L/T) curves were not different (P greater than 0.05), but the suture curve was shifted downward (P less than 0.05). The mean laser and suture active L/T curves were similar at 1 week (greater than 0.05) and lower than the control curve (P less than 0.04). At 8 weeks, the laser-repaired vessels produced an active force similar to control muscle (P greater than 0.05) but the suture repairs could not generate this active force (P less than 0.05). These data suggest that the laser repair and normal artery are more mechanically compatible than the suture repair as studied by this method.

Percutaneous pulsed-dye laser lithotripsy of gallbladder stones in swine.

Human gallstones were surgically implanted in the gallbladders of 14 pigs. Nine to 16 days later a sheath was successfully placed percutaneously into the gallbladders of 13 animals using ultrasound and fluoroscopy. Two methods were used to guide laser fragmentation: (1) fluoroscopy and a steerable double lumen catheter (two animals), and (2) a flexible endoscope (11 animals). Laser treatment was done in 12 animals with a flashlamp-pumped pulsed-dye laser. A mean of 3600 pulses/animal were delivered using a wavelength of 504 nm and a maximum energy of 60 mJ/pulse. No fragmentation occurred in two animals, partial fragmentation occurred in six, and complete fragmentation occurred in four. Endoscopic guidance was superior to fluoroscopic guidance. Complications (sheath dislodgment, gallbladder perforation, bleeding) occurred in eight of 14 animals. Pulsed-dye laser fragmentation of gallbladder stones is feasible using endoscopic guidance. The use of this technique through an acute percutaneous tract may be associated with complications.

Experimental gallstone dissolution with methyl-tert-butyl ether (MTBE) and transcutaneous ultrasound energy.

The simultaneous application of ultrasound energy greatly accelerated the rate of cholesterol gallstone dissolution by methyl-tert-butyl ether (MTBE). In vitro experiments using this treatment showed that a 498-mg stone burden could be dissolved in 19.5 minutes, approximately 100% faster than what could be achieved with MTBE alone. Pigs (n = 13) with surgically implanted gallstones were treated with MTBE and transcutaneously applied ultrasound from a prototype system built for clinical studies. The average stone reduction of all pigs was 470.46 mg +/- 60.44 mg; 91.39% of an average implanted burden of 515.08 +/- 18.03 mg. Control group pigs (n = 9), receiving only an MTBE infusion, showed an average stone reduction of 51.77%. Enzymes indicative of hepatocellular injury showed no significant abnormalities after 6 weeks. Gallbladder ablation with a fibrous remnant (ie, no mucosa, no lumen, patent cystic duct) occurred in 10 (70%) of the pigs.

A large animal model (swine) to study the diagnosis and treatment of cholelithiasis.

Human gallstones were surgically placed into the gallbladders of 200 swine. Eight of these swine were used as a prospective series to verify that the placement and presence of human gallstones in their gallbladders caused no significant pathologic changes in the gallbladder and that the gallstones were not spontaneously dissolved. Although limitations exist, the advantages of this procedure demonstrate that the surgically prepared swine is an appropriate model for controlled in vivo experiments in radiologic imaging or interventional treatment. A 4 F pig-tailed catheter designed for Trocar insertion was developed as a companion to this model.

Surface electromagnetic wave coupling efficiencies for several excitation techniques.

The excitation efficiencies for coupling surface electromagnetic waves onto aluminum at a microwave frequency (f = 8.445 GHz, lambda = 3.55 cm) were studied experimentally for several different standard microwave techniques as well as two optical techniques (prism and grating) applied to the microwave frequency region and two new techniques (hump and valley). The peak measured efficiencies found were: for the standard rectangular waveguide, 92%; for the horn antenna, 73%; for the right angle prism properly gapped above the metal, 60%; for the hump of 10-wavelength radius of curvature, 35%; for the thin grating strips on polystyrene coated metal, 30%; for the grating bars gapped (1/2) wavelength above the metal, 26%; and, for the valley of 10-wavelength radius, 12%. The measurement of the excitation efficiencies for prism and grating coupling techniques sometimes required that the prism or grating be in the near field of the antenna. In addition to measuring peak efficiencies, the efficiencies were measured as functions of the gap heights, the angular orientations, the different diffraction modes, the shapes, and the materials of the grating bars. The coupling efficiencies for both prism and grating couplers show a strong dependence on gap height above the metal. Dielectric grating bars were found to be inefficient compared to solid or hollow metallic bars, or thin metallic strips. The distance between the target point of the center line of the microwave horn antenna and the corner of the prism was found to be about 1 wavelength for maximum prism coupling efficiency.