Effects of hyperthermia on bone. I. Heating rate patterns induced by microwave irradiation in bone and muscle phantoms.

We describe the initial heating rate patterns generated by microwave irradiation of 915 MHz, with constant power output, in muscle-equivalent phantoms containing a freshly excised bone, and compared with those in phantoms consisting of muscle-equivalent gel only. At 1 cm depth the muscle was cooler in the centre of the field when bone was present underneath. Also, the orientation of the bone in the field had a pronounced effect on the heating rate profiles in the overlying muscle: when the long axis of the bone was parallel to E field, a hot area in the centre of the field was observed; after rotation of the applicator by 90 degrees so that the long axis of the bone was perpendicular to the E field, more homogeneous heating was obtained along most of the field. In contrast, the heating patterns obtained in the cortex of the bone at similar depth (1.3 cm) were not substantially influenced by its orientation in the field. Depending on field location, the heating rate of the cortical bone closest to the applicator was within 50-75% of the SAR in muscle at the same depth. We believe that these data may be useful for the extension of such measurements in vivo, to permit the effective application of hyperthermia, with or without radiation, in the treatment of bone lesions.

Effects of hyperthermia on bone. II. Heating of bone in vivo and stimulation of bone growth.

Previous studies in vitro have shown that it is possible to achieve comparable temperature distribution in bone and the adjacent soft tissues, under appropriate experimental conditions. The objective of the present work was to determine the effects of hyperthermia on bone in vivo. In order to obtain direct temperature measurements in bone, catheters were surgically installed on top of and inside the medullary cavity of the femur of normal rabbits. The thighs were irradiated with 915 MHz microwaves for 45 min, once or twice a week. The temperatures on and inside the bone were maintained between 42.5 and 44.0 degrees C; the resulting temperatures in the muscle were within 1.0 degrees C at depths equidistant from the applicator. After four to six treatments the femora were excised for histopathological examination. New trabecular bone was deposited around the catheters; most bone components including periosteum, osteoid, and fully calcified matrix could be seen. Large numbers of osteoblasts and osteoclasts lined the trabecular surfaces, and numerous cement lines were visible, running in all directions, indicating extensive bone deposition and remodelling. In contrast, control bones (catheters installed--no hyperthermia) showed much less ossification, with many areas of thin incomplete osteoid. Further, bones treated with hyperthermia only (no surgical trauma) showed no such changes. Thus, it appears that following an initial insult, hyperthermia promotes bone deposition.

Subtalar arthrodesis in children with cerebral palsy: results using iliac bone plug.

Twenty-six extra-articular subtalar arthrodeses were performed on 15 patients with flexible planovalgus feet due to cerebral palsy. Following muscle balancing procedures, an iliac bone plug was used to stabilize the sinus tarsi. A review of the results up to 12 years, average 6.8, is presented. Overall satisfactory results were achieved in 88.4% of the patients, unsatisfactory in 11.6%. All children were immobilized in short-leg walking casts for 6 to 8 weeks. The surgical technique is described. The procedure gave good stability to the subtalar joint and was found to be reliable. Graft acquisition was simple and there were no complications.

Pedal polydactyly. A case report.

Polydactyly is a common pedal deformity with great variation in clinical presentation. There is a tendency toward a higher incidence in previously affected families, but the actual occurrence rate of the different forms of polydactyly has not been agreed upon in the literature to date. Most authors agree that the isolated deformity is an expression of an autosomal dominant gene with varied penetrance. Syndromatically associated polydactyly is inherited as an autosomal recessive trait. Surgical intervention should be attempted as early as possible. Correction should be undertaken only after a thorough clinical and radiographic evaluation has been performed. The patient's postoperative goals should always be considered. It is not necessary to remove the supernumerary digit if it does not interfere with the foot's function and comfort. Cosmesis should not be the chief consideration. The surgeon should strive to return the foot to a more normal contour while maintaining or improving foot function.

Three-point fixation walking spica cast: an alternative to early or immediate casting of femoral shaft fractures in children.

A retrospective review of 28 children treated for middle and proximal femoral shaft fractures was undertaken. Following preliminary traction, a modified pantaloon walking spica, utilizing the principle of total contact and three-point fixation molding, was applied, followed by immediate ambulation. The mean anterior bow was 5 degrees varus/valgus, 6.5 degrees angulation, and 1.2 cm shortening. There were no significant differences in the results when age groups or proximal to mid-shaft fractures were compared. No further shortening or angulation occurred with ambulation. The advantages of early ambulation and better control of proximal shaft fractures are discussed.