Biomedical subjects

S Tim Yoon

Publications and source records attributed to S Tim Yoon.

21 records · Page 2Linked to original sources

PubMedDate not supplied

Molecular therapy of the intervertebral disc.

BACKGROUND CONTEXT: Currently, no biologic treatment is available for disc degeneration. However, many different molecules of potential therapeutic benefit are being investigated. PURPOSE: Review and categorize the molecules under investigation for potential therapy in preventing or reversing disc degeneration. STUDY DESIGN: Review article. METHODS: Review of published articles on molecules that may be useful in biologic therapy of the intervertebral disc. RESULTS: The list of molecules under investigation for potential benefit in biologic therapy of the intervertebral disc repair continues to grow. These molecules are so diverse that they no longer all fall into the classic terminology of "growth factor." Some of these molecules are not growth factors at all and some are not even cytokines. At least four different classes of molecules may be effective in disc repair. These include anticatabolics (eg, tissue inhibitors of metalloproteinase [TIMPs]), mitogens (eg, insulin-like growth factor-1 [IGF-1], platelet-derived growth factor [PDGF]), chondrogenic morphogens (transforming growth factor beta [TGF-beta] and bone morphogenetic proteins [BMPs]), and intracellular regulators (LIM mineralization protein-1 [LMP-1] and Sox9). Although some in vitro data are available on all of these molecules, few of these molecules have been tested in vivo with an animal model of disc degeneration. CONCLUSIONS: As the current screening experiments are concluded, more definitive in vivo systems involving a more realistic degeneration model will be a necessary step before attempting human studies.

Biological Products↗

PubMedDate not supplied

Congenital lumbar spinal stenosis: a prospective, control-matched, cohort radiographic analysis.

BACKGROUND CONTEXT: Degenerative lumbar spinal stenosis manifests primarily after the sixth decade of life as a result of facet hypertrophy and degenerative disc disease. Congenital stenosis, on the other hand, presents earlier in age with similar clinical findings but with multilevel involvement and fewer degenerative changes. These patients may have subtle anatomic variations of the lumbar spine that may increase the likelihood of thecal sac compression. However, to the authors' knowledge, no quantitative studies have addressed various radiographic parameters of symptomatic, congenitally stenotic individuals to normal subjects. PURPOSE: To radiographically quantify and compare the anatomy of the lumbar spine in symptomatic, congenitally stenotic individuals to age- and sex-matched, asymptomatic, nonstenotic controlled individuals. STUDY DESIGN/SETTING: A prospective, control-matched, cohort radiographic analysis. PATIENT SAMPLE: Axial and sagittal magnetic resonance imaging (MRI) and lateral, lumbar, plain radiographs of 20 surgically treated patients who were given a clinical diagnosis of congenital lumbar stenosis by the senior author were randomized with images of 20, asymptomatic age- and sex-matched subjects. OUTCOME MEASURES: MRIs and lateral, lumbar, plain radiographs were independently quantitatively assessed by two individuals. Measurements obtained from the axial MRIs included: midline anterior-posterior (AP) vertebral body diameter, vertebral body width, midline AP canal diameter, canal width, spinal canal cross-sectional area, pedicle length, and pedicle width. From the sagittal MRIs, the following measurements were calculated: AP vertebral body diameter, vertebral body height, and AP canal diameter at the mid-vertebral level. On the lateral, lumbar, plain radiograph (L3 level), the AP diameters of the vertebral body spinal canal were measured. METHODS: The images of these 40 individuals were then randomized and distributed in a blinded fashion to five separate spine surgeons who graded the presence and severity of congenital stenosis utilizing a five-tier scale. Images consisting of 15 symptomatic individuals, graded definitely congenitally stenotic (mean age, 51.7 years; range, 43-65 years), and 15 asymptomatic individuals, graded definitely not stenotic (mean age, 50.7 years; range, 41-55 years), were age- and sex-matched and included for further review. From these 30 patients, a lateral, lumbar, plain radiograph and axial and sagittal MRIs (T1/T2 weighted) from L2-L5 were quantitatively analyzed. Rater reliability was assessed by Kappa coefficient testing. RESULTS: The cross-sectional area of the canal was significantly smaller in the congenitally stenotic patients at all lumbar levels measured (L2: 176 mm(2) vs. 259 mm(2), L3: 177 mm(2) vs. 275 mm(2), L4: 183 mm(2) vs. 283 mm(2), L5: 213 mm(2) vs. 323 mm(2), p<.05). Pedicle length was markedly shorter in the stenosis group at each lumbar level (L2: 5.9 mm vs. 8.9 mm, L3: 6.0 mm vs. 8.8 mm, L4: 6.5 mm vs. 9.2 mm, L5: 5.8 mm vs. 9.1 mm, p<.05). Furthermore, midline, axial AP canal diameter, vertebral body width, and sagittal AP canal diameter were all significantly smaller than the control patients (p<.05). A ratio of the AP diameter of the pedicle length to the vertebral body was also noted to be statistically significant on both the lateral plain radiographs (L3: 0.426 vs. 0.704) and sagittal MRI (L2: 0.343 vs. 0.461, L3: 0.361 vs. 0.461, L4: 0.362 vs. 0.481, L5: 0.354 vs. 0.452, p<.05). No difference was noted comparing the AP diameter of the vertebral body (axial and sagittal images), vertebral body height, canal width, and pedicle width. Kappa testing coefficient indicated a strong rater reliability (k=0.81, 95% confidence interval: 0.62-0.94). CONCLUSIONS: Congenital lumbar stenosis has not been clearly defined radiographically. Clinically, congenitally stenotic patients present at a younger age with fewer degenerative changes and multiple levels of involvement. Radiographically, these patients have a shorter pedicular length and as a result a smaller cross-sectional spinal canal area (mean critical values of 6.5 mm and 213 mm(2) were observed, respectively). The mean critical ratios were 0.43 (2:1 AP vertebral body: pedicle length) on the lateral lumbar radiograph and 0.36 on the sagittal MRI. The altered canal anatomy resulting from a decreased pedicle length may anatomically predispose these patients to earlier complaints of symptomatic neurogenic claudication. Identification of the presence of congenital stenosis should increase the treating surgeon's awareness of the potential need for multilevel treatment.

Adult↗

PubMedDate not supplied

Comparison of allograft to autograft in multilevel anterior cervical discectomy and fusion with rigid plate fixation.

BACKGROUND CONTEXT: A relatively high pseudarthrosis rate is associated with multilevel anterior cervical discectomy and fusion (ACDF). Anterior plate fixation increases fusion rate in multilevel ACDF. A debate still exists between the effectiveness of allograft versus autograft in plated multilevel ACDF. PURPOSE: To determine the efficacy of allograft versus autograft in fusion rate and clinical outcome in patients undergoing two- and three-level ACDFs with rigid anterior plate fixation. STUDY DESIGN: A retrospective radiographic and clinical review to assess fusion, risk factors and clinical outcome of 80 consecutive patients who underwent ACDF with rigid anterior plate fixation involving two and three levels with either allograft or autograft. PATIENT SAMPLE: There were 45 patients (56%) who had autogenous iliac crest tricortical grafts and 35 patients (44%) who received tricortical allograft with an average age of 49 years who were treated by multilevel ACDF with rigid anterior plate fixation at a single institution. Thirty-three Peak polyaxial (Depuy-Acromed, Rayham, MA), 26 Orion (Sofamor-Danek, Memphis, TN), 16 Atlantis (Sofamor-Danek, Memphis, TN) and 5 Synthes (Paoli, PA) anterior cervical plating systems were used. All patients underwent ACDF (61 two-level, 19 three-level) by a Smith Robinson technique. All patients had burring of the end plates, 2-mm distraction of the motion segment and graft countersunk 2 mm from the anterior vertebral border. Anterior cervical plate with unicortical screw purchase was used in all cases. Segmental screw fixation was performed in 46 patients. Soft collars were worn postoperatively for 3 to 4 weeks. OUTCOME MEASURES: Follow-up lateral neutral, flexion and extension radiographs were used to assess fusion. The radiographs were reviewed by an independent blinded observer in assessing fusion grades between autograft versus allograft. Clinical outcomes were rated excellent, good, fair and poor based on Odom's criteria. METHODS: Fusion rate and postoperative clinical outcome were assessed in 80 patients who underwent two- or three-level ACDF with rigid anterior plate fixation. Additional risk factors were also analyzed. RESULTS: Radiographic fusion was assessed in all patients (mean, 16 months). Seventy-eight patients (97.5%) achieved solid arthrodesis. Pseudarthrosis occurred in two patients who had allograft for two-level and three-level fusions. Nonsegmental screws were used in the two-level nonunion case. Postoperative dysphagia developed in one two-level nonunion patient, and revision surgery was performed in the other nonunion three-level patient. Twenty-three patients were smokers, and 26 patients had work-related injuries. Clinical outcome (mean, 20 months) was excellent in 23, good in 48 and fair in 9 patients. No statistical significance was noted between demographics, history of tobacco use, graft-type, end plate preparation technique, intermediate segmental screws, plate-type, clinical outcome of fused and nonfused patients and presence of work-related injuries (p>.05). CONCLUSIONS: A high fusion rate of 97.5% was obtained for multilevel ACDF with rigid plating with either autograft or allograft. In this study, nonunion occurred in patients with allograft but this difference was not statistically significant. Fusion was obtained in 97.8% of patients with segmental screw fixation and 97.1% with nonsegmental screw fixation. Nonsegmental screw fixation may contribute to less than adequate stability and contribute to a higher rate of nonunion, but such effects could not be discerned from this study. Excellent and good clinical outcome was noted in 88.8% of the patients. Proper patient selection and meticulous operative technique is essential to obtain high fusion rates and optimal clinical outcome, which is more important than graft type.

Adult↗