Biomechanical properties of a biodegradable calcium phosphate hydraulic cement (CPHC) were tested with rabbits. The cement was composed of ␤-tricalcium phosphate (␤-TCP), monocalcium phosphate monohydrate (MCPM), and calcium sulfate hemihydrate (CSH), ␤-TCP-MCPM-CSH cement. Cylinders of 4.7 mm in diameter and 10 mm in length were put into bone cavities created in the distal epiphysis of femurs in rabbits. Cylinders of the same size of porous biphasic calcium phosphate ceramics (BCPC, 75% hydroxyapatite and 25% ␤-TCP) were implanted as references. Two, 4, 12, and 16 weeks after the operation, the rabbits were sacrificed. Histomorphometry showed that the cement was resorbed, leaving only 7.67 ± 1.81% of bone cavity after 12 weeks. Newly formed bone occupied 34.59 ± 4.00% of the cavity. Cylindrical bone-material composites were cut out with a small dental burr. Compressive force was applied to the specimens and compressive strength, elastic modulus, and toughness were calculated. The same tests were performed on cylinders of normal bone from the same site, which served as controls. The compressive strength and the toughness of the cement-bone composite were higher than those of normal bone and porous ceramics 12 weeks after the operation (p < 0.05). At 16 weeks the compressive strength and the toughness returned to the normal bone values. The elastic modulus of the porous ceramicbone composite was higher than the normal bone at 4, 12, and 16 weeks after surgery (p < 0.05). We found that the ␤-TCP-MCPM-CSH cement is replaced by new bone and that the cement-new bone composite has similar or better mechanical properties than normal bone within 16 weeks. This study suggests the usefulness of a particular cement for filling bone defects or for temporary fixation of orthopedic implants.

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Glass plates of the chemical composition: CaO (29.0), SiO 2 (31.0), Fe 2O 3 (40.0), B 2O 3 (3.0), P 2O 5 (3.0) in weight ratio were heated to 1050 degrees C at a rate of 5 degrees C/min and then cooled to laboratory temperature. The resulting glass-ceramic containing magnetite and wollastonite crystals showed high-saturation magnetization. The bonding ability of this new glass-ceramic to bone tissue was evaluated using rabbit tibiae, and compared with glass of the same composition. This glass-ceramic formed a Ca, P-rich layer on its surface and bonded tightly with bone within 8 weeks of implantation. However, the glass did not form this Ca, P-rich layer, nor had it bonded with bone at 25 weeks. The bone-heating ability of this glass-ceramic was investigated by applying a max. 300-Oe, 100-kHz magnetic field. The granules of the glass-ceramic filled in the rabbit tibiae heated the whole surrounding bone to more than 42 degrees C and maintained this temperature for 30 min. Bioactive ceramics reinforce the mechanical strength of bone tissue. Furthermore, this heat-generating bioactive glass-ceramic can be used for hyperthermic treatment of bone tumors.

Object. The authors conducted a study to examine the incidence and causes of postoperative C-5 radiculopathy, and they suggest preventive methods for C-5 palsy after anterior corpectomy and fusion. Methods. The authors included in the study 18 patients with postoperative C-5 radiculopathy from 563 patients who underwent anterior decompression and fusion for cervical myelopathy. There were 10 cases of ossification of the posterior longitudinal ligament (OPLL) and eight cases of cervical spondylotic myelopathy (CSM). All patients received conservative treatment. Posttreatment full recovery was present in eight patients, and Grade 3/5 strength was documented in six in whom some weakness remained. Radiographic evaluation revealed that the C3–4 and C4–5 cord compression was significantly more severe in patients with paralysis than in those without paralysis. The incidence of paralysis was higher in patients with OPLL than in those with CSM (chi-square test, p = 0.03). The incidence of paralysis increased in parallel with the number of fusion levels (correlation coefficient r = 0.94). Multivariate analysis revealed that the final manual muscle testing (MMT) value was closely related to the preoperative MMT value (computed t value 4.17; p < 0.01) and preoperative Japanese Orthopaedic Association (JOA) score for cervical myelopathty (computed t value, 2.75; p < 0.05). Conclusions. Preexisting severe stenosis at C3–4 or C4–5 in patients with OPLL is a risk factor for paralysis. Preoperative muscle weakness and a low JOA score are factors predictive of poor recovery.