Hansen A. Yuan

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.

Early Clinical Experience with the Syracuse I-Plate: An Anterior Spinal Fixation Device

Sixteen patients were treated with a new anterior internal fixation device after thoracolumbar or lumbar decompression, and fusion with bone grafting. Ten patients had acute burst fractures, four had metastatic tumors, and two had old, healed fractures with deformity. In the acute fracture group, eight patients had neurologic deficits and seven patients experienced improvement. Six patients had lesions of the conus medullarls, all of which improved. The four patients with metastatic tumors underwent surgery for back and leg pain and all gained significant relief. Two patients had correction of old fracture deformity with satisfactory outcome. Complications were minimal. The new anterior stabilization device provided early stability, allowed early patient mobilization, was easy to insert, and has a low profile. Late collapse, non-union, and kyphotic deformity have not been noted thusfar.

Nucleus Replacement With the DASCOR Disc Arthroplasty Device: Interim Two-Year Efficacy and Safety Results From Two Prospective, Non-Randomized Multicenter European Studies

Study Design. A prospective, nonrandomized multicenter study of lumbar disc nucleus replacement using the DASCOR Disc Arthroplasty Device. An interim analysis of clinical results is presented, obtained from European patients enrolled in 2 studies. Objective. To determine the safety and efficacy of the DASCOR Device for the treatment of symptomatic single-level degenerative disc disease (DDD). Summary of Background Data. Patients suffering from DDD have been limited to a choice between nonoperative therapies or invasive surgical treatments such as total disc replacement or spinal fusion. The DASCOR Device was developed to provide an alternative treatment with a less invasive surgical intervention. Methods. A total of 85 patients from 11 European centers were enrolled in 1 of 2 studies between February 2003 and July 31, 2007. Data were collected before surgery and after surgery at 6 weeks and at 3, 6, 12, and 24 months. The clinical outcome measures were obtained from the Visual Analog Scale (VAS) for back pain, the Oswestry Disability Index (ODI), radiographic assessments, and records of analgesic medication use. Results. Mean VAS and ODI scores improved significantly after 6 weeks and throughout the 2 years. Radiographic results demonstrated, at a minimum, maintenance of disc height with no device expulsion and, despite Modic-Type 1 changes, no subsidence. Fourteen patients had serious adverse events including device explants in 7 patients (7 of 85), in which the main complication was resumed back pain after time. Patients’ rate of analgesic medication decreased dramatically over time, with all patients experiencing significant improvements after 3 months and nearly no analgesic medication or narcotic drug use at 2 years. Conclusion. The interim outcomes showed significant improvements in mean ODI and VAS scores. The results of these European studies suggest that the DASCOR Device may be a safe and effective less-invasive surgical option for patients with DDD.

Characterization of a developing lumbar arthrodesis in a sheep model with quantitative instability

BACKGROUND CONTEXT Mechanical forces have been considered responsible for stress shielding an arthrodesis, but the biology of a developing lumbar fusion has not been well characterized. PURPOSE A large animal model was used to test the hypothesis that mechanical forces modify the biological processes involved in a developing bony fusion. STUDY DESIGN Lumbar fusion was performed in an ovine model using custom instrumentation that permitted a controlled degree of anterior-posterior translation after surgery. Fusion sites were evaluated by radiography, microradiography, histology and histomorphometry at time points that corresponded with predicted early and later stages of bone healing. METHODS Fourteen skeletally mature ewes underwent lumbar spinal fusion under general anesthesia. In the control (stable) group, the spine was rigidly fixed with a cage anteriorly and pedicle screws posteriorly. In the experimental (unstable) group, the spine was destabilized by an annulectomy (with no anterior implant) and custom pedicle screws that allowed 2 mm of anterior-posterior translation. Animals were euthanized 6 and 12 weeks after surgery. RESULTS Radiographs confirmed that the fusion mass had not fully consolidated at either time point. Microradiographs revealed a trend toward increased bone formation at 6 weeks in the stable case as compared with the unstable, but by 12 weeks, this trend had reversed (p=.03). Intramembranous bone formation was the primary mechanism of healing near the transverse process in animals with both stable and unstable fixation. In the area between the two transverse processes, new bone formation occurred primarily through endochondral ossification. At 12 weeks, the stable case had significantly more cartilage formed (p=.023) but less newly formed bone (p=.07) as compared with the quantitatively unstable. CONCLUSIONS This clinically realistic animal model allowed characterization of the biology of the developing arthrodesis before fusion. Under stable or unstable conditions, endochondral ossification was the predominant mechanism of new bone formation within the intertransverse process region. This finding, which contrasts with previous reports from small animal models of spine fusion, may reflect a difference in biology that results from the increased size of the intertransverse space in sheep as compared with small animals. Interestingly, mechanical instability increased the formation of new bone within this region, but not at the transverse process. Endochondral ossification therefore appears to respond to mechanical factors in the fusion site. The ovine model shows promise as an alternative to the rabbit model and may provide a more stringent test for potential new surgical and nonsurgical strategies for spine fusion.

Mechanical and Biomechanical Characterization of a Polyurethane Nucleus Replacement Device Injected and Cured In Situ Within a Balloon

Background The DASCOR device has recently been introduced as an innovative nucleus replacement alternative for the treatment of low-back pain caused by degenerative intervertebral disc disease. The purpose of this study was to characterize, through a series of preclinical mechanical bench and biomechanical tests, the effectiveness of this device. Methods A number of samples were created using similar preparation methods in order to characterize the nucleus replacement device in multiple mechanical bench tests, using ASTM-guided protocols, where appropriate. Mechanical bench testing included static testing to characterize the devices compressive, shear properties, and fatigue testing to determine the devices compressive fatigue strength, wear, and durability. Biomechanical testing, using human cadaveric lumbar spines, was also conducted to determine the ability of the device to restore multidirectional segmental flexibility and to determine its resulting endplate contact stress. Results The static compressive and shear moduli of the nucleus replacement device were determined to be between 4.2–5.6 MPa and 1.4–1.9 MPa, respectively. Similarly, the ultimate compressive and shear strength were 12,400 N and 6,993 N, respectively. The maximum axial compressive fatigue strength of the tested device that was able to withstand a runout without failure was determined to be approximately 3 MPa. The wear assessment determined that the device is durable and yielded minimal wear rates of 0.29mg/Mc. Finally, the biomechanical testing demonstrated that the device can restore the multidirectional segmental flexibility to a level seen in the intact condition while concurrently producing a uniform endplate contact stress. Conclusions The results of the present study provided a mechanical justification supporting the clinical use of the nucleus replacement device and also help explain and support the positive clinical results obtained from two European studies and one US pilot study. Clinical Relevance Nucleus replacement devices are rapidly emerging to address specific conditions of degenerative disc disease. Preclinical testing of such devices is paramount in order to potentially ensure successful clinical outcomes post implantation

Gelfoam as a barrier to prevent polymethylmethacrylate-induced thermal injury of the spinal cord: in vitro and in vivo studies in pigs.

Gelatin sponge (Gelfoam; Upjohn, Kalamazoo, MI, U.S.A.) is commonly used as an interpositional barrier to shield the spinal cord from thermal injury during vertebral reconstruction with polymethylmethacrylate bone cement. The aim of this study was to record epidural and intradural temperatures during polymethylmethacrylate reconstruction of vertebral corpectomy defects. Three surgical techniques (subtotal corpectomy, total corpectomy with insertion of a Gelfoam barrier, and total corpectomy with no barrier) were compared in vivo and in vitro in a porcine model. As expected, total corpectomy defects cemented without a Gelfoam barrier produced the highest epidural temperatures in vivo (52.8 degrees C) and in vitro (58 +/- 2 degrees C). The Gelfoam barrier provided some protection against heat transfer, but peak temperatures and absolute temperature increases were significantly higher than in defects with an intact posterior cortex (p < 0.05). These results indicate that an intact posterior cortex provides the best protection against heat transfer, whereas the use of a Gelfoam barrier appears to provide only partial protection against thermal injury.

Assessment of a synthetic anterior cervical ligament in a spinal fusion model in sheep

BACKGROUND CONTEXT The anterior cervical ligament is routinely excised during cervical interbody fusion. Loss of this ligament may predispose to instability at the fusion site. Anterior plating restores stability but leads to a risk of stress shielding. An alternative approach would be to use a less rigid fixation system that would provide anterior support while allowing micromotion that could enhance bone healing within the fusion site. PURPOSE To determine whether augmentation of an interbody fusion with a synthetic ligament enhances fusion. STUDY DESIGN Prospective randomized study in a large animal model of cervical fusion. OUTCOME MEASURES The primary outcome was evidence of interbody fusion, as determined by radiography, computed tomography (CT), histology and biomechanical testing. METHODS Twelve skeletally mature sheep underwent single level (C2-3) anterior discectomy and interbody fusion using fresh frozen allograft. In six animals, the fusion was augmented with a braided polyethylene device rigidly fixed to C2 and C3 with screws. Sheep were euthanized 12 weeks postoperatively. Specimens were radiographed and then examined by CT. Six fusion sites (three control, three augmented) were used for nondestructive biomechanical testing to assess the stability of the fusion site. The remaining specimens were processed for undecalcified histology. RESULTS As determined by radiography, the augmented group had 83% solid union as compared with 67% in the control group (p<.05). There was no difference regarding bone graft dislodgment between the two groups. The extension stiffness of the augmented group was significantly higher (p<.05) than that of controls, but there was no significant difference between the two groups in flexion stiffness. There was no significant difference in bone formation in the two groups as determined by CT and histology, although there was a trend for increased endochondral ossification in the augmented repairs. There was no evidence of significant adverse tissue reactions to the ligament. CONCLUSIONS Use of a synthetic ligament was associated with a moderate increase in fusion rate and a statistically significant increase in fusion site stiffness in extension. The use of an augmentation device, such as this synthetic ligament, may be beneficial in cervical fusion, especially when multilevel surgery is being contemplated.

Treatment of Painful Long-standing Displaced Fracture-Dislocations of the Sacrum: A Case Report

A 19-year-old white man sustained multiple injuries, including a severely displaced Malgaigne fracture. Secondary uncontrollable hemorrhage was treated successfully by arterial embolization. The patient retained a painfully displaced right sacroiliac joint. His multiple injuries resolved symptom free with the exception of the right sacroiliac region. An attempt to reduce the dislocation by an extensive soft tissue release and skeletal traction was unsuccessful. Solid fusion of the L4 and L5 vertebrae to the ilium significantly reduced the patients pain. Painful, long-standing severely displaced Malgaigne fracture can be successfully treated by sacroiliac arthrodesis without reduction.