Whoan Jeang Kim

Biomechanical Evaluation of an Injectable Calcium Phosphate Cement for Vertebroplasty

Study Design. Destructive biomechanical tests using fresh cadaveric thoracolumbar vertebral bodies. Objectives. To evaluate the compression strength of human vertebral bodies injected with a new calcium phosphate (CaP) cement with improved infiltration properties for augmentation of the vertebral bodies before compression fracture and also for vertebroplasty in comparison with polymethylmethacrylate (PMMA) injection. Summary of Background Data. Vertebroplasty is the percutaneous injection of PMMA cement into the vertebral body. While PMMA has high mechanical strength, it cures fast and thus allows only a short handling time. Other potential problems of using PMMA injection may include damage to surrounding tissues by a high polymerization temperature or by the unreacted toxic monomer, and the lack of long-term biocompatibility. Bone mineral cements, such as calcium carbonate and CaP cements, have longer working time and low thermal effect. They are also biodegradable while having a good mechanical strength. However, the viscosity of injectable mineral cements is high, and the infiltration of these cements into vertebral body has been questioned. Recently, the infiltration properties of a CaP cement have been significantly improved, which is ideal for the transpedicular injection to the vertebral bodies for vertebroplasty or augmentation of osteoporotic vertebral body strength. Methods. The bone mineral densities of 30 vertebral bodies (T2–L1) were measured using dual-energy x-ray absorptiometry. Ten control specimens were compressed at a loading rate of 15 mm/min to 50% of their original height. The other specimens had 6 mL of PMMA (n = 10) or the new CaP (n = 10) cement injected through the bilateral pedicle approach before being loaded in compression. Additionally, after the control specimens had been compressed, they were injected with either CaP (n = 5) or PMMA (n = 5) cement using the same technique, to simulate vertebroplasty. Loading experiments were repeated with the displacement control of 50% vertebral height. Load to failure was compared among groups and analyzed using analysis of variance. Results. Mean bone mineral densities of all five groups were similar and ranged from 0.56 to 0.89 g/cm2. The size of the vertebral body and the amount of cement injected were similar in all groups. Load to failure values for PMMA, the new CaP, and vertebroplasty PMMA were significantly greater than that of control. Load to failure of the vertebroplasty CaP group was higher than control but not statistically significant. The mean stiffness of the vertebroplasty CaP group was significantly smaller than control, PMMA, and the new CaP groups. The mean height gains after injection of the new CaP and PMMA cements for vertebroplasty were minimal (3.56% and 2.01%, respectively). Conclusion. Results of this study demonstrated that the new CaP cement can be injected and infiltrates easily into the vertebral body. It was also found that injection of the new CaP cement can improve the strength of a fractured vertebral body to at least the level of its intact strength. Thus, the new CaP cement may be a good alternative to PMMA cement for vertebroplasty, although further in vivo animal and clinical studies should be done. Furthermore, the new CaP may be more effective in augmenting the strength of osteoporotic vertebral bodies for preventing compression fractures considering our biomechanical testing data and the known potential for biodegradability of the new CaP cement.

Augmentation of Pedicle Screw Fixation Strength Using an Injectable Calcium Phosphate Cement as a Function of Injection Timing and Method

Study Design. Axial pullout tests using fresh cadaveric thoracolumbar vertebral bodies. Objectives. To evaluate the effect of a new injectable calcium phosphate cement on the axial pullout strength of both revised and augmented pedicle screws in comparison with polymethyl methacrylate and in terms of injection method. Summary of Background Data. Failure of pedicle screws by loosening and back out remains a significant clinical problem and is of particular concern for patients with low bone quality. Polymethyl methacrylate was shown to significantly improve the screw pullout strength. However, polymethyl methacrylate is known to have a high polymerization temperature, which may damage surrounding tissues, and a short handling time, and it lacks long-term biocompatibility. Bone mineral cements such as calcium phosphate have a longer working time, very low thermal effect, and are biodegradable as well as having good mechanical strength. Recently, new calcium phosphate cement with improved infiltration properties for better injectability has been introduced, but its performance in augmenting the pedicle screw fixation has not been tested yet. Methods. The bone mineral densities of 52 vertebral bodies (T11–L5) were measured using dual-energy x-ray absorptiometry. In each vertebral body, a 6.5-mm-diameter and 45 ± 5-mm-long pedicle screw was inserted into either the right or left pedicle, representing an initial intact implantation. These intact screws were pulled axially until failure at 10 mm/min. Following failure of the intact pedicle, 3.0 cc of cement was injected into the failed screw hole, representing a revision case, and the prepared screw hole in the contralateral intact pedicle representing an augmentation case. The cement was injected either to the distal tip of the screw hole (calcium phosphate-1 group, n = 19) or along the entire length of the screw hole (calcium phosphate-2 group, n = 20), and the screws were inserted. The cement was then allowed to cure for 24 hours at room temperature before both screws were pulled to failure. In 13 specimens, polymethyl methacrylate was injected along the entire length of the screw hole (polymethyl methacrylate group). Kruskal-Wallis and Mann-Whitney tests were used to compare the screw pullout strengths for study groups, whereas linear relationships between variables were assessed with scatter plots and Spearman correlation coefficients with a significance level of 0.05. Results. Mean bone mineral densities of all groups were similar. A significant positive correlation was seen between bone mineral density and intact pullout strength. In revision, the pullout strength of calcium phosphate-1 was similar to that of intact, whereas the pullout strength of calcium phosphate-2 and polymethyl methacrylate was significantly greater than that of intact. In augmentation, all 3 injection methods significantly improved the pullout strength over intact. Injection of the calcium phosphate cement along the entire screw length was found to produce significantly higher pullout strengths than injection only at the distal tip of the screw in revision case. Injection of polymethyl methacrylate produced significantly higher pullout strengths than the injection of calcium phosphate by either method in both revision and augmentation. Conclusion. Results of this study demonstrate that the new calcium phosphate cement can improve the axial pullout strength of revised and augmented pedicle screws when injected along the entire length of the screw. This suggests that the injection method may be crucial for revision of failed pedicle screws. Considering inherent properties more favorable for in vivo application, such as nonexothermal polymerization and longer working time, and significant improvement in pullout strength, the new calcium phosphate cement may be a good alternative to polymethyl methacrylate for the augmentation of pedicle screw fixation.

Factors Affecting Clinical Results after Corrective Osteotomy for Lumbar Degenerative Kyphosis

Study Design This study is a prospective, clinical study for lumbar degenerative kyphosis. Purpose To determine the factors affecting postoperative clinical outcomes in patients who undergo corrective osteotomy for lumbar degenerative kyphosis. Overview of Literature Only a small number of studies have reported clinical results for surgery for lumbar degenerative kyphosis. There are almost no studies about prognostic factors that predict postoperative clinical results. Methods This study involved 25 patients who were diagnosed with lumbar degenerative kyphosis and who underwent corrective osteotomy following gait analysis. A pedicle subtraction osteotomy was done at the third lumbar vertebra (L 3). Regarding the fusion level, surgery was done within a range from T10 proximally to S1 distally. Of these, for rigid fixation of a distal part, an iliac screw was used. Pain was evaluated using a 10-point pain scale and a questionnaire about activities. We also evaluated cosmesis and subjective satisfaction using a modified version of the Scoliosis Research Society Outcome-22 (SRS-22) instrument. This assessment was done using a 5-point scale which was designed by us. We assigned patients to group A (good clinical outcomes) if their postoperative pain score was lower than 4 (of 10 points) and if scores indicating activity, cosmesis and subjective satisfaction were higher than 11 (of 15 points). All other patients were assigned to group B (poor clinical outcomes). Results Clinical outcomes were good in 64% of patients (16/25) and poor in 36% (9/25). Regarding cosmesis and subjective satisfaction, there were significant differences between the two groups. There were also significant differences in physical factors of individual patients such as body mass index (BMI): 23.78 ± 2.79 in group A and 26.44 ± 2.75 in group B. On gait analysis, there was a significant difference in the dynamic pelvic tilt: 7.5 ± 3.3° in group A and 11.72 ± 1.89° in group B. Conclusions There is no correlation between preoperative degree of kyphotic deformity and clinical outcomes. The degree of anterior rotation of pelvic tilt does not change significantly; rather, compensatory mechanisms of the pelvis and BMI were found to have more influence. Because neither the degree of satisfaction with clinical outcomes nor the increased activity was relatively higher, a more sincere decision should be made before recommending corrective osteotomy for degenerative lumbar kyphosis.

Solitary pelvic osteochondroma causing L5 nerve root compression.

Osteochondroma is the most common benign bone tumor, accounting for more than one-third of all benign bone tumors. It usually develops at the metaphysis of the long bones, especially the distal femur and proximal tibia. Approximately 40% of osteochondromas are found around the knee. Osteochondroma commonly presents as a painless mass and is incidentally identified via plain radiographs. Thus, surgical excision is not routinely recommended unless the tumor causes clinical symptoms or cosmetic distress. Osteochondroma located in the pelvis is unusual. Spinal nerve root compressions due to pelvic osteochondroma are also rarely reported. We assessed the solitary pelvic osteochondroma of a 33-year-old man mimicking spinal disease. An exostotic bony projection composed of dense calcification of the cartilaginous cap arose from the iliac crest, which was located just lateral to the right sacroiliac joint in the paravertebral area, L5 level. Magnetic resonance imaging showed an irregular, exophytic outgrowing calcified mass with cartilage cap and exostotic mass compressed to the proximal part of the right L5 nerve root lateral to the nerve root foramen. The L5 nerve root was focally compressed and thinned.En bloc excision, the treatment of choice of symptomatic osteochondroma, was performed. The patient had complete resolution of symptoms postoperatively, and other neurologic symptoms may be expected to improve over time.

Ten trigger fingers in an adult man: a case report.

Trigger finger is a common disease particularly in the middle aged women. A very rare case in which an adult man had 10 trigger fingers was experienced. He was treated with local steroid injections in both thumbs, but trigger finger disease has been aggravated in every digit of both hands. We performed an early operative treatment. Three months after the operation, the patient could perform his work without discomfort in his hands and showed normal range of motion in all fingers.

Eleven levels of spinous process fractures in thoracolumbar spine.

Cases of over 5-level spinous process fractures are extremely rare. Thoracolumbar region of spine is superimposed on ribs; and as such additional studies such as computerized tomography are needed to diagnose fractures in this region. We report a case of 11 contiguous level thoracolumbar spinous process fractures, which has been treated conservatively.

Multilevel Thoracolumbar Spondylolysis with Spondylolisthesis at L4 on L5

A 24-year-old male patient was initially evaluated for persistent back pain. The visual analogue scale (VAS) score was 7 points. Physical examination revealed a decreased range of lumbar spinal motion, which caused pain. Simple X-ray revealed Meyerding grade 1 spondylolisthesis at L4 on L5, with mild dome-shaped superior endplate and consecutive multilevel spondylolysis at T12-L5. Standing anteroposterior and lateral views of the entire spine revealed normal balance of sagittal and coronal alignment. A computed tomography scan revealed bilateral spondylolysis at T12-L4, left unilateral spondylolysis at L5, and spina bifida at L5 to sacral region. Magnetic resonance imaging revealed mild dural ectasia at the lumbar region. Due to the absence of any neurological symptoms, the patient was managed conservatively. He was rested a few weeks with corset brace and physiotherapy. After treatment, his back pain improved, VAS score changed from 7 to 2, and he was able to return to normal activity.