Masaaki Chazono

Bone formation and resorption in patients after implantation of β-tricalcium phosphate blocks with 60% and 75% porosity in opening-wedge high tibial osteotomy

Most of the implanted porous beta-tricalcium phosphate (beta-TCP) can be resorbed. However, beta-TCP block with 75% porosity is inadequate for weight-bearing sites until bone incorporation occurs. Thus, the authors have recently developed beta-TCP block with 60% porosity, which is approximately sevenfold greater in terms of compressive strength than that of beta-TCP with 75% porosity. The authors investigated bone formation and resorption of beta-TCP after implantation in patients of beta-TCP blocks with two different porosities. From May 2003 to November 2004, medial opening high tibial osteotomy was performed in 25 patients with a mean age of 66 years. The opened defect was fixed with a Puddu plate. Then 6-8 cm(3) of beta-TCP block with 75% porosity was used to fill the cancellous bone defect, except on the medial side where 2.83-3.18 cm(3) of wedge-shaped beta-TCP block with 60% porosity was implanted. At least 2 years after surgery, the 25 patients had no correction loss, and bone formation was noted in all cases. Complete or nearly complete resorption of beta-TCP with 60 and 75% porosity was obtained within 3.5 years. Thirteen biopsy samples obtained from the 60% porosity implantation sites showed good lamellar bone formation, and the percentage of beta-TCP remaining relative to the newly formed bone plus beta-TCP ranged from 0.3 to 14.5%, with a mean of 6.7%. The authors suspect that mechanical stress loading to the medial side of the tibia facilitated bone formation and resorption of beta-TCP with 60% porosity.

Electron microscopic study on bone formation and bioresorption after implantation of β-tricalcium phosphate in rabbit models

BackgroundThe role of bone formation and bioresorption in an early stage after implantation of β-tricalcium phosphate (β-TCP) was investigated using scanning and transmission electron microscopy (SEM, TEM).MethodsThe ceramic β-TCP cylinders were implanted into cavities drilled in the femoral condyles of eight NZW rabbits. Four of the rabbits were sacrificed at 2 weeks and four at 4 weeks after implantation, respectively. The femoral condyles were excised to prepare the specimens for SEM and TEM.ResultsSEM showed giant cells of more than 20 μm in diameter were observed on the surface of β-TCP at 2 weeks after implantation. TEM demonstrated that collagen fibrils secreted from the monocytic cells invaded β-TCP micropores at 2 weeks. Multinucleated giant cells (MNGCs) were in contact with the surface of β-TCP at 2 weeks. Some of them had a ruffled border (RB) at the cell-substrate interface, characteristic of osteoclasts.ConclusionsThese findings suggest that cell-mediated disintegration by osteoclasts played a role in the bioresorption of β-TCP at an early stage after implantation. In addition, the micropores of β-TCP ceramic may provide an environment for collagen formation, leading to the deposition of apatite crystals. Therefore, the micropores facilitate bone ingrowth as well as ceramic resorption.

Dumbbell-shaped osteochondroma of the fifth rib causing spinal cord compression

Osteochondromas are the most common benign bone tumor, representing 45% of all benign bone tumors. Most occur in the metaphyseal region of long bones such as the femur and tibia. Osteochondromas can also arise from fl at bones and the spine. Costal osteochondromas make up only 1.5% of all osteochondromas, and compressive myelopathy due to a tumor arising from the rib is even rarer. We present an unusual case of a dumbbell-shaped osteochondroma causing spinal cord compression, and we review the literature concerning costal osteochondromas.

Effects of alendronate on bone formation and osteoclastic resorption after implantation of beta-tricalcium phosphate.

The aim of this study was to determine the effects of alendronate (ALN) on osteoclastic resorption of beta-tricalcium phosphate (beta-TCP) and bone formation. beta-TCP blocks of 75% porosity, with or without ALN treatment, were implanted into cavities drilled in rabbit femoral condyles. New bone formation, residual amount of beta-TCP, and the number of tartrate-resistant acid phosphatase-positive cells were evaluated 2 weeks after surgery. The results show that local application of ALN at a concentration of 10(-2) to 10(-6)M reduced the number of osteoclasts on the surface of beta-TCP. New bone formation was also inhibited by ALN in a dose-dependent manner. Thus, inhibition of osteoclast formation resulted in reduced beta-TCP resorption and bone formation. These results suggest that osteoclast-mediated resorption plays an important role in bone formation and a coupling-like phenomenon could occur in beta-TCP-filled bone defects.

Continuous skull traction followed by closed reduction in chronic pediatric atlantoaxial rotatory fixation

Dear Editor, Atlantoaxial rotatory fixation (AARF) is a disorder of childhood commonly encountered in clinical practice. We report a successful case of conservative management with continuous halo-skull traction followed by closed reduction in a patient with chronic pediatric AARF whose parents refuse surgical treatment. A 7-year-old girl with a history of upper respiratory tract infection developed right-sided neck pain occurring since December 2007. Due to persistent pain whose etiology could not be identified by a pediatrician, she was referred to our department in August of 2008. Three-dimensional computed tomography (3D-CT) clearly showed a lateral inclination of 21 degrees in the AP view (Fig. 1a). Magnetic resonance imaging (MRI) identified a synovial effusion within the anterior atlantoaxial joint space characterized by low signal intensity on T1-weighted images and high signal intensity on T2-weighted images (Fig. 1b). Although spinal cord impingement was observed between the dens and the posterior arch of C1, the patient was neurologically intact. The clinical and radiological findings were considered definitive for chronic AARF. After admission in October of 2008, the patient’s head was immobilized with the halo-ring under general anesthesia. An initial attempt at closed reduction was unsuccessful. Therefore, the patient was in bed in “supine” skull traction at night and seated in a wheelchair during daytime hours under “sitting” skull traction from 2.5–6 kg for 2 months. Lateral plain x-rays showed a little change in the atlantoaxial angle. No neurological deficits were identified during skull traction. We recommended surgical intervention to her parents in order to treat the chronic AARF, but they rejected the offer and requested the continuous conservative management. In December of 2008, a second closed reduction maneuver was performed. Holding the halo-ring firmly attached to the patient’s head and applying her head with the longitudinal and right-sided rotational force, we successfully elevated the atlas and reduced it with crepitation. A coronal reconstruction image of MPR-CT showed a reduction of C1/C2. The patient was immediately put into a halo-vest for 3 months. Three months after removal of the halo-vest, a coronal reconstruction image of MPR-CT revealed spontaneous bony fusion at the right-sided facet joint of C1/2 (Fig. 1c). In contrast, MRI demonstrated a remarkable shrinkage of the synovial effusion within the anterior atlantoaxial joint space, which was swollen before treatment, resulting in an indirect decompression of the spinal cord (Fig. 1d). At the final follow-up, limited range of rotation on her neck was seen, but the patient had no symptoms such as neck pain or neurologic involvement, no torticollis. Multiplanar reconstruction CT and 3D-CT studies are valuable for the diagnosis and evaluation of AARF, including determination of the type and degree of articulating facet displacement of the atlantoaxial subluxation. 3D-CT in particular shows the spatial relations of the atlantoaxial joint with particular clarity, thereby aiding in arriving at a correct diagnosis. Ishii et al. demonstrated that both facet joint deformity and lateral inclination of the atlas M. Chazono (*) Department of Orthopaedic Surgery, NHO Utsunomiya National Hospital, 2160, Shimo-okamoto, Utsunomiya, Tochigi 329–1193, Japan e-mail: chazono@pop02.odn.ne.jp

Basic research and clinical application of beta-tricalcium phosphate (β-TCP)

The mechanism of bone substitute resorption involves two processes: solution-mediated and cell-mediated disintegration. In our previous animal studies, the main resorption process of beta-tricalcium phosphate (β-TCP) was considered to be cell-mediated disintegration by TRAP-positive cells. Thus, osteoclast-mediated resorption of β-TCP is important for enabling bone formation. We also report the results of treatment with β-TCP graft in patients since 1989. Two to three weeks after implantation, resorption of β-TCP occurred from the periphery, and then continued toward the center over time. Complete or nearly complete bone healing was achieved in most cases within a few years and was dependent upon the amount of implanted material, the patients age, and the type of bone (cortical or cancellous). We have previously reported that an injectable complex of β-TCP granules and collagen supplemented with rhFGF-2 enabled cortical bone regeneration of rabbit tibiae. Based on the experimental results, we applied this technique to the patients with femoral and humeral fractures in elderly patients, and obtained bone union.

Significance of peak height velocity as a predictive factor for curve progression in patients with idiopathic scoliosis

BackgroundMuch attention has been paid to peak height velocity (PHV) as a possible predictor of curve progression in patients with idiopathic scoliosis (IS). The aim of this study was to analyze the relationship between the magnitude of the Cobb angle at PHV and scoliosis progression, defined as having surgery prior to skeletal maturity in female patients with IS.MethodsA retrospective review identified 56 skeletally immature female IS patients who were followed until maturity. The mean age and the mean pubertal status at the initial visit were 10 years and 24 months before menarche respectively, with a follow-up period of 5 years. They were divided into two groups: non-surgery group (NS) and surgery group (S), depending on their treatment method in use at the final follow-up visit. Surgery group was defined as an ultimately having surgery due to Cobb angle greater than 45 degrees prior to skeletal maturity regardless of conservative management. Height measurements were recorded at each visit; height velocity was calculated as the height change, in cm, divided by the time interval, in years. The PHV, chronological age at PHV (APHV), height at PHV (HPHV), and final height (FH) were determined for each group. In patients with Cobb angle greater than 30 degrees, the corrected height was calculated by Kono formula and corrected height velocity values were provided. The sensitivity, specificity, and area under the curve (AUC) of the receiver-operating -characteristic (ROC) analysis were calculated to predict spinal curve progression for various Cobb-angle cutoff values at PHV.ResultsThe corrected PHV had a mean value of 8.5 and 8.9 cm/year in the NS-group and S-group, respectively. The APHV was 11.9 and 11 years, the corrected HPHV was 152.9, and 149.3 cm, and the corrected FH was 159.9 and 159.3 cm, respectively. When a Cobb angle of 31.5 degrees was at PHV, ROC analysis revealed 78% sensitivity, 82% specificity, and an AUC of 0.93, acceptable values for curve progression in patients with IS.ConclusionsThese findings indicate that 31.5 degrees of spinal curvature when patients are at PHV is a significant predictive indicator for progression of the curve to a magnitude requiring surgery. We suggest that the curve-progression risk assessment in patients with IS should include PHV, along with measures of skeletal and non-skeletal maturities.