Biomedical subjects

Hansen A Yuan

Publications and source records attributed to Hansen A Yuan.

8 recordsLinked to original sources

PubMed2004

Preclinical evaluation of a poly (vinyl alcohol) hydrogel implant as a replacement for the nucleus pulposus.

STUDY DESIGN: An in vivo investigation into the safety of a novel hydrogel implant designed to replace the diseased nucleus pulposus. OBJECTIVES: To determine the local and systemic safety of this new implant in a nonhuman primate model. SUMMARY OF BACKGROUND DATA: A poly (vinyl alcohol) (PVA) hydrogel has been developed as a prosthetic replacement for the diseased nucleus pulposus. METHODS: PVA implants were inserted into discectomy defects created in the L3-L4 or L4-L5 intervertebral disc in 20 male baboons. Empty discectomy defects served as a surgical control in 8 additional animals. Routine follow-up evaluations included radiography, magnetic resonance imaging, gross pathology, and histopathology of both local and remote tissues. RESULTS: Insertion of the PVA hydrogel from an anterior direction produced extrusions in 5 animals from the first series of 15 surgeries (33%). A modified surgical technique, involving an anterolateral rather than anterior approach, was used in 5 animals, but the extrusion rate remained high (20%). Despite these surgical complications, the PVA implants were well tolerated over 24 months in vivo, with no evidence of device-related pathology in the adjacent disc tissue, spinal cord, or remote tissues. CONCLUSION: Implantation of the PVA implant for periods of up to 24 months produced no evidence of local or systemic toxicity. Additional studies are now needed to determine the efficacy of the device in its intended application.

Animals↗

PubMed2004

Osteoporotic spinal deformity: a biomechanical rationale for the clinical consequences and treatment of vertebral body compression fractures.

This review article develops a biomechanical rationale for the clinical consequences and treatment of osteoporotic vertebral body compression fracture. In patients with osteoporotic vertebral fractures and spinal deformity, altered spinal biomechanics and global spinal imbalance are important factors in the increased morbidity and mortality reported in this population. Severe spinal deformity impairs physical functioning, health, and quality of life. The spinal deformity itself, independent of pain, is a significant cause of disability. Spinal deformity is also an independent risk factor for hip fracture. Treatments directed at osteoporotic vertebral compression fractures should ideally address spinal deformity as well as pain. Balloon kyphoplasty, the minimally invasive technique of reduction and internal fixation of osteopenic vertebral body compression fractures that addresses pain and spinal deformity, is discussed.

Biomechanical Phenomena↗

PubMed2003

Nuclear replacement strategies.

Although still a technology in its infancy, nuclear replacement promises a potential alternative to arthrodesis for patients with discogenic back pain. It is ideally suited to those patients presenting early in the degenerative cascade with minimal to no arthritic changes or disc collapse. The physical nature of the implants seeks to restore the visco-elastic, biomechanical, and fluid characteristics of the natural disc, thus reducing pain while maintaining motion and function.

Arthroplasty, Replacement↗

PubMed2002

New technologies in spine: nucleus replacement.

Nucleus replacement offers several benefits over other surgical options. Several design criteria need to be met. Nucleus prostheses can be either preformed or formed in situ. Preclinical evaluations should include biomechanical testing, biocompatibility testing, and surgical technique evaluation. Indications and contraindications of nucleus prosthesis are largely determined by the benefit-to-risk ratio and benefit-to-cost ratio.

Animals↗

PubMed2002

Prosthetic disc replacement: the future?

Since it first was introduced more than 90 years ago, disc arthrodesis remains the main surgical method for the treatment of degenerative disc disease. Although this procedure does relatively well in stabilizing the anterior column and relieving low back pain by eliminating motion, it is not physiologic and it alters the stress distribution on the adjacent segments. Although the issue of whether this stress alteration leads to symptomatic degeneration remains debatable, it probably is agreed that disc arthrodesis is not the best choice for correcting or preventing anterior column instability caused by degenerative disc disease. The ultimate solution for reestablishing anterior column stability is to restore not only the anatomy but also the normal mechanical function by using a more functional device, prosthetic disc replacement. During the past 401 years, many different designs have been attempted for prosthetic disc replacement. Many biomechanical studies have shown that normal mechanical functions of a disc can be restored by a disc prosthesis. Some early clinical studies have shown promising results. Although it might take more effort to optimize the design and reduce costs and risks, prosthetic disc replacement will be the future of spine care.

Female↗

PubMedDate not supplied

Anterior cervical corpectomy and strut graft fusion using a different method.

BACKGROUND CONTEXT: Strut graft fusion after corpectomy is frequently indicated for certain pathologies in the cervical spine. The "key-hole" technique and "dove-tail" technique are the popular methods used to insert the strut graft at present. Segmental collapse secondary to seating of the graft on cancellous bone and cord injury from placement or dislodgement the graft are our concerns. Our method was designed to solve these possible problems without affecting the arthrodesis. PURPOSE: To evaluate the results of this method that allows the graft to seat on both the hard end plate and cancellous bone of the upper and lower contacting vertebrae in a easy and safe way after varying levels of corpectomy in the cervical spine. STUDY DESIGN: A retrospective clinical and radiographic study conducted by an independent observer was performed on 23 patients treated with this different strut grafting method after cervical corpectomy, with at least 2 years of follow-up. PATIENT SAMPLE: A total of 23 patients from 1983 to 1994 underwent fusion using our strut grafting method with fibular allograft packed with autogenous bone. No augmented internal instrumentation was used in all these patients. The patients with an incomplete record or less than 2 years of follow-up were excluded beforehand. OUTCOME MEASURES: Clinical outcome was assessed by a score based on three factors: neck pain, dependence on medicine and ability to return to work. The total score of these factors was seven. A score from 0 to 3 was defined as satisfactory, and a score from 4 to 7 was defined as unsatisfactory. The result of graft fusion, collapse of interbody height and loss of lordotic angle corrected by the graft were evaluated through the radiographic studies. METHODS: The operative technique creates a notch in the anterior cortex and end plate of the respective superior and inferior vertebraes. Cylinder allograft filled with autogenous cancellous bone was used as bone graft for all patients. The bone graft is cut with corresponding pegs at both ends. The graft is inserted into the corpectomy space with the pegs inserted into the notches and the remainder of the graft placed onto the preserved superior and inferior bony end plates. RESULTS: Twenty patients achieved successful fusion (87%). On average, the loss of anterior and posterior interbody height was 2.79 mm and 2.93 mm, respectively. The average loss of lordotic correction was 2.83 degrees. Eighty-three percent achieved satisfactory clinical outcomes. There were no neurologic injuries encountered during the operation. Partial graft dislodgment occurred in two patients (8.7%). CONCLUSIONS: This different method of strut grafting after cervical corpectomy has proven its safety and efficacy in its fusion and clinical results.

Adolescent↗

PubMedDate not supplied

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.

Animals↗

PubMedDate not supplied

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.

Animals↗