Keun Su Kim

Adjacent segment motion after a simulated lumbar fusion in different sagittal alignments: a biomechanical analysis.

Study Design. An in vitro biomechanical study of adjacent segment motion (at L3–L4 and L5–S1) after a simulated lumbar interbody fusion of L4–L5 in different sagittal alignments was carried out. Objectives. To test the hypothesis that an L4–L5 fixation in different sagittal alignments causes increased angular motion at the adjacent levels (L3–L4 and L5–S1) in comparison with the intact spine. Summary of Background Data. Clinical experience has suggested that lumbar fusion in a nonanatomic sagittal alignment can increase degeneration of the adjacent levels. It has been hypothesized that this is the result of increased motion at these levels; however, to the authors’ knowledge no mechanical studies have demonstrated this. Methods. Eight fresh human cadaveric lumbar spines (L3–S1) were biomechanically tested. Total angular motion at L3–L4 and L5–S1 under flexion-extension load conditions (7-Nm flexion and 7-Nm extension) was measured. Each specimen was tested intact, and then again after each of three different sagittal fixation angles (at L4–L5): (1) in situ (21°lordosis), (2) hyperlordotic (31°lordosis), and (3) hypolordotic (7°lordosis). The simulated anterior/posterior fusion was performed at L4–L5 with pedicle screws posteriorly, vertebral body screws anteriorly, and an interbody dowel. Results. The averaged values for flexion-extension motion at L3–L4 were as follows: intact specimen 2.0°, in situ fixation 4.0°, hyperlordotic fixation 1.7°, hypolordotic fixation 6.5°. The averaged values for flexion-extension motions at L5–S1 were as follows: intact specimen 2.3°, in situ fixation 2.6°, hyperlordotic fixation 3.6°, hypolordotic fixation 2.9°. Conclusion. Hypolordotic alignment at L4–L5 caused the greatest amount of flexion-extension motion at L3–L4, and the differences were statistically significant in comparison with intact specimen, in situ fixation, and hyperlordotic fixation. Hyperlordotic alignment at L4–L5 caused the greatest amount of flexion-extension motion at L5–S1, and the difference was statistically significant in comparison with intact specimen but not in situ fixation or hypolordotic fixation.

The Effect of Bone Morphogenetic Protein-2 on Rat Intervertebral Disc Cells in Vitro

Study Design. An in vitro experiment to determine the molecular and cellular effect of recombinant human bone morphogenetic protein-2 on cultured rat intervertebral disc cells was performed. Objectives. To determine the effect of recombinant human bone morphogenetic protein-2 on cell proliferation, production of sulfated-glycosaminoglycan, and the expression of genes specific for chondrocytes (Type II collagen, aggrecan, and Sox9) in cultured rat intervertebral disc cells. Summary of Background Data. Intervertebral disc degeneration is associated with cellular and biochemical changes, which include decreased synthesis of cartilage specific gene products such as Type II collagen and aggrecan. Although bone morphogenetic protein-2 is known to induce chondrogenesis during new bone formation, the effects on intervertebral disc cells have not been characterized. Method. Cells were isolated from the anulus fibrosus and transition zones of lumbar discs from Sprague-Dawley rats. The cells were grown in monolayer and treated with recombinant human bone morphogenetic protein-2 (0, 10, 100, 1000 ng/mL) in Dulbecco’s Modified Eagle Medium/F-12 with 1% fetal bovine serum (day 0). On days 2, 4, and 7 after recombinant human bone morphogenetic protein-2 treatment, sulfated-glycosaminoglycan content in the media was quantified using 1,9-dimethylmethylene blue staining. The results were normalized according to culture duration and cell number. On day 7, mRNA was extracted for reverse transcriptase-polymerase chain reaction and real-time polymerase chain reaction to quantitate mRNAs of Type I collagen, Type II collagen, aggrecan, Sox9, osteocalcin, and glyceraldehyde phosphate dehydrogenase. Cell number was determined with a hemocytometer. Results. Recombinant human bone morphogenetic protein-2 at 100 and 1000 ng/mL yielded a 17% and 42% increase in cell number on day 4, and a 59% and 79% on day 7, respectively. Recombinant human bone morphogenetic protein-2 at 10 ng/mL had no effect on cell number. Sulfated-glycosaminoglycan increase was greatest at day 7, increasing by 1.3-, 2.1-, and 3.6-fold with recombinant human bone morphogenetic protein-2 treatments of 10, 100, and 1000 ng/mL, respectively. Increases in mRNA levels of Type II collagen, aggrecan, Sox9, and osteocalcin were observed with recombinant human bone morphogenetic protein-2 concentrations of 100 and 1000 ng/mL on day 7 as determined by reverse transcriptase-polymerase chain reaction. No detectable increase in mRNA level of Type I collagen was observed with any levels of recombinant human bone morphogenetic protein-2. Real-time polymerase chain reaction showed the greatest effect at 1000 ng/mL recombinant human bone morphogenetic protein-2, leading to an 11.5-fold increase in aggrecan, a 4.6-fold increase in Type II collagen, a 5.3-fold increase in Sox9, and a 1.9-fold increase in osteocalcin mRNA above untreated controls at day 7. Conclusion. The results of this study show that recombinant human bone morphogenetic protein-2 enhances disc matrix production and chondrocytic phenotype of intervertebral disc cells. Recombinant human bone morphogenetic protein-2 increases cell proliferation and sulfated-glycosaminoglycan (proteoglycan) synthesis. It increases mRNA of Type II collagen, aggrecan, and Sox9 genes (chondrocyte specific genes), and osteocalcin, but not Type I collagen or glyceraldehyde phosphate dehydrogenase.

Disc degeneration in the rabbit: a biochemical and radiological comparison between four disc injury models.

Study Design. A biochemical and radiologic comparison of 4 disc injury models to produce disc degeneration in the rabbit was carried out in 2 experiments. Objectives. To develop a reliable animal model of intervertebral disc degeneration. Summary of Background Data. In order to study various interventions for retarding or preventing disc degeneration, a reliable animal model of disc degeneration is needed. Methods. First experiment: 7 New Zealand white rabbits (1 year old, 3.5–4.5 kg body weight) were used to test 4 different disc injury models; intradiscal injection of Camptothecin (an apoptotic agent) using a 23-gauge needle at L2–L3, nucleus aspiration using a 21-gauge needle at L3–L4, 3 anulus punctures using a 21-gauge needle at L4–L5, and 1 anulus puncture using a 18-gauge needle at L5–L6. The L1–L2 level was used as a control. Rabbits were killed 12 weeks later. Lumbar spinal magnetic resonance images were assessed using 4 grades of disc degeneration. The water content of the nucleus was measured. Dimethylmethylene blue (DMMB) assay was used to measure the sulfated-glycosaminoglycan content. Second experiment: the 21-gauge 3-puncture and the 18-gauge 1-puncture models, thought most effective in producing disc degeneration in the first experiment, were again used in a second study. Six rabbits were killed 8 weeks later, the water and sulfated-glycosaminoglycan contents being measured as in the first experiment. Results. In the first experiment, the water content in the aspiration and puncture models was significantly decreased. Only the sulfated-glycosaminoglycan content in the aspiration model showed a significant decrease as compared to the control. Disc heights and magnetic resonance grades documented significant degeneration occurring in the aspiration and puncture models. In the second experiment, the water content showed a significant decrease in the 21-gauge 3-puncture model, whereas neither of the results for the sulfated-glycosaminoglycancontent showed a significant difference as compared to the control data. Conclusion. In the first experiment, the 21-gauge 3-puncture and the 18-gauge 1-puncture models produced the most consistent disc degeneration in the rabbit lumbar spine. When these 2 models were again studied in the second experiment, the 21-gauge 3-puncture technique was superior in producing disc degeneration over a shorter period of time.

Two-level Anterior Cervical Discectomy versus One-level Corpectomy in Cervical Spondylotic Myelopathy

Study Design. A retrospective investigation of clinical and radiologic outcomes after surgical treatment for 2-level cervical spondylotic myelopathy (CSM). Objective. The study was undertaken to compare the outcomes of 2 different anterior approach types for 2-level CSM. Specifically, 2-level anterior cervical discectomy and fusion (ACDF) was compared with 1-level anterior cervical corpectomy and fusion (ACCF). Summary of Background Data. The optimal surgical approach for 2-level CSM has not been defined, and thus, the relative merits of 2-level ACDF and 1-level ACCF remain controversial. However, few comparative studies have been conducted on these 2 surgical approaches. Methods. The authors reviewed the case histories of 31 patients that underwent surgical treatment for 2-level CSM from 2002 to 2006. Cases of myelopathy because of cervical ossification of posterior longitudinal ligament were excluded. Thirty-one patients (16 men and 15 women) of mean age 54.45 ± 11.6 years (28 ∼ 77) were included. The average follow-up period was 26.23 ± 15.0 months (12 ∼ 63). The authors compared perioperative parameters (hospital stays, bleeding amounts, operation times, complications), clinical parameters (Japanese Orthopedic Association scores, Visual Analog Scale scores for neck and arm pain), and radiologic parameters (total cervical range of motion, segmental range of motion, segmental height, cervical lordosis, fusion rate). Results. Of these above parameters, operation time (P = 0.001) and bleeding amount (P = 0.001) were significantly greater in the ACCF group, whereas segmental height (P = 0.018) and postoperative cervical lordosis (P = 0.009) were significantly lower in the ACCF group. However, other parameters were not significantly different in the 2 groups. Conclusion. Surgical managements of 2-level CSM using ACDF or ACCF were found to be similar in terms of clinical outcomes. However, 2-level ACDF was found to be superior to 1-level ACCF in terms of operation times, bleeding amounts, and radiologic results.

Thoracic Ligament Ossification in Patients With Cervical Ossification of the Posterior Longitudinal Ligaments: Tandem Ossification in the Cervical and Thoracic Spine

Study Design. A retrospective investigation of patients who underwent decompressive surgery for cervical ossification of the posterior longitudinal ligament (OPLL). Objective. In this study, we would like to introduce a new terminology for the phenomena of coexisting paraspinal ligament ossification in 2 adjacent spinal regions as “tandem ossification.” The purpose of this study is to evaluate the incidence and features of tandem ossification in patients with cervical OPLL. Summary of Background Data. Sometimes, OPLL and ossification of the ligamentum flavum (OLF) may coexist in the cervical and thoracic spine on the account of similar pathogenesis. However, there has been only a few previous reports concerning about the incidence of concurrent thoracic ligament ossification in the patients with cervical OPLL. Methods. We reviewed the cervicothoracic magnetic resonance imaging (MRI) and computed tomography (CT) images of patients who underwent decompressive surgery for cervical OPLL in our institute during the last 5 years. Total 68 cases of cervical OPLL patients were included. All patients underwent surgical decompression due to cervical myelopathy or myeloradiculopathy. We focus, however, on the presence of thoracic tandem ossification found in 23 of these cases (33.8%); 21 had thoracic OLF, 5 had thoracic OPLL and 3 had both combined. Results. Six of the 23 patients (26.1%) with thoracic tandem ossification had myelopathic symptoms, and required secondary thoracic surgery within 3.3 months (1–7 months) of the original cervical procedures. There were no significant differences in age, sex, cervical OPLL type, or length of cervical OPLL between the patients with and without tandem ossification. Conclusion. Patients having cervical surgery for OPLL should also undergo simultaneous studies of the thoracic spine looking for tandem OPLL and/or OLF. The frequency of tandem lesions in this series was 23 of 68, with 6requiring subsequent surgery for an evolving thoracic myelopathic deficit.

Radiological Changes in the Bone Fusion Site After Posterior Lumbar Interbody Fusion Using Carbon Cages Impacted With Laminar Bone Chips : Follow-Up Study Over More Than 4 Years

Study Design. A retrospective clinical study with a follow-up of more than 4 years was conducted. Objectives. To know the radiologic changes in the interbody bone fusion site in patients who had received posterior lumbar interbody fusion (PLIF) using carbon fiber cages. Summary of Background Data. PLIF using cages is a popular surgical method for treating degenerative lumbar spinal diseases. However, there are few reports on the radiologic changes in the bone fusion site after this procedure. Method. Forty-one patients were observed (male-to-female ratio 12:29; mean age 51 years; 1-level-to-2-level PLIF 37:4) for 56 months (range 48–78). Anteroposterior and lateral radiograph films were taken from all patients immediately after bone fusion, at 6 and 12 months after surgery, and at follow-up. The extent of the bone fusion was classified as: only inside the cage; around the cage; extending to the vertebral cortical margin; and overgrowth beyond the vertebral cortical margin. The extent of bone fusion was observed anterior and posterior to the cages. Results. Of the 45 fusion levels examined in these 41 patients, successful bone fusion was observed in 40 levels of 36 patients (88%). All the successful fusions occurred inside and posterior to the cages. Of the 40 successful fusion levels at 6 and 12 months after surgery, 10% and 35% of the levels showed the fusion mass to be both inside and around the cages, while the remaining 90% and 65% of the levels showed the fusion mass only inside the cages, respectively. More than 4 years after surgery, 82% of the levels showed the fusion mass extending to the posterior cortical margin, and 2 levels (5%) with shallowly inserted cages showed bony overgrowth into the spinal canal. Conclusion. All the intervertebral bone fusion after PLIF occurred inside the cages and in the posterior intervertebral space. We suggest the complete removal of discmaterial and deep insertion of the cages to create sufficient posterior intervertebral space for bone growth. PLIF using cages impacted with laminar bone chips is a useful method when considering the time required for surgery and the morbidity of the autograft donor sites.