Development of artificial cartilage has been one of the future goals in the field of orthopaedic surgery. A few investigators have applied polyvinyl-alcohol hydrogel (single-network) to develop the artificial cartilage. However, it could not be applicable for clinical use due to insufficiency of the strength, the toughness, and the friction properties. The authors have conducted a fundamental study to apply a novel double-network (DN) hydrogel to develop the artificial cartilage. This hydrogel is composed of two independently crosslinked hydrophilic networks of poly-2-acrylamido-2-methyl-propanesulfonic acid (PAMPS) and poly-N,N′-Dimetyl acrylamide (PDMAAm) that are physically entangled with each other. This study evaluated the in vivo influence of a PAMPS/PDMAAm DN hydrogel on counterface cartilage in rabbit knee joints and its ex-vivo frictional properties on normal cartilage.

In the first experiment, the DN gel was implanted in a surgically created defect in the femoral trochlea of rabbit knee joints and the left knee was used as the control.

Evaluations using a confocal laser scanning microscopy demonstrated that the DN gel did not affect the surface microstructure (surface roughness, the number of small pits) of the counterface cartilage in vivo at 4 and 12 weeks. The histology also showed the DN gel had no pathological damage on the cartilage matrices and cells at 4 weeks.

However, 2 of the 5 DN gel-implanted knees showed mild irregularity on the counterface cartilage surface at 12 weeks. In the second experiment, the friction property between the normal and artificial cartilage was determined using a joint simulator apparatus. The ex-vivo mean friction coefficient of the DN gel to normal cartilage was 0.029, while that of the normal-to-normal cartilage articulation was 0.188. The coefficient of the DN gel-to-normal cartilage articulation was significantly lower that of the normal-to-normal cartilage articulation (p< 0.0001). This study suggested that the PAMPS/PDMAAm DN gel has very low friction coefficient on normal cartilage and has no significant detrimental effects on counterface cartilage in vivo, and can be a promising material to develop the artificial cartilage.

Side shift exercise was originally described by Mehta. Since 1986, we adopted it for the treatment of idiopathic scoliosis. Outcome of the side shift exercise for the patients with idiopathic scoliosis after skeletal maturity was evaluated retrospectively. Fifty-three patients with idiopathic scoliosis whose curve was greater than 20 degrees by the Cobb’s method were included in the study. All the patients were treated only by the side shift exercise and their treatment was started after skeletal maturity. Skeletal maturity was diagnosed by Risser’s method as either grade IV or grade V. The study comprised five men and forty-eight women. Twenty-six patients had thoracic curve, eight had thoracolumbar curve, and nineteen had double major curve. Patients were instructed to shift their trunk to the concavity of the curve repetitively while they were standing and to maintain the side shift position while they were sitting. In double major curve, larger curve was the subject of the treatment. The average age at the beginning of the treatment was 16.3 years (range, 13 to 27 years), and the average age at final follow-up was 19.8 years (range, 14 to 33 years). The average follow-up period was 3.5 years (range, one to 11 years). The average Cobb angle at the beginning of the treatment was 33.3 degrees (range, 20 to 74 degrees), and the average Cobb angle at final follow-up was 32.2 degrees (range, 10 to 73 degrees). Curves of four patients decreased 10 degrees or more. Most of long term follow-up studies reported that untreated idiopathic scoliosis progressed even after skeletal maturity. Although the follow-up period was much shorter, results of the present study suggested that the side shift exercise was a useful treatment option for the management of idiopathic scoliosis after skeletal maturity.

Pin clamp motion was continuously monitored using a displacement sensor as patients walked with a dynamic fixator applied. Patients with a shaft fracture, nonunion or lengthening of the tibia were monitored, all of whom were in the stage of dynamization. The Hifixator equipped with a ball bearing mechanism on the inner surface of its dynamic pin clamp was used as a dynamic external fixator. The aim of this study was to estimate the magnitude of movement and the type of deformation occurring at the fracture site or callus generated after distraction osteogenesis. The actual motion of the bone fragment has components with six degrees of freedom, which are transferred to the pin clamp. The magnitude of the displacement of the pin clamp along the shaft is expressed by an equation involving these six components. If the pin clamp has a sufficiently smooth sliding surface and a small clearance between it and the shaft, and the pin clusters are sufficiently rigid during walking, the amount of the displacement can be expressed by the linear combination of these components.

Accuracy of the measurement was evaluated using a bone model fixed with a Hifixator mounted with a displacement sensor, by performing dynamic loading tests with axial, bending and torsional forces The measured values agreed well with the theoretical values when the rigidity of the bone model was high. The displacement was recorded versus time during more than twenty cycles of walking with weight bearing of the patients. The rhythm of walking was controlled with a metronome set at 0.5 Hz. The displacement curve had an oscillatory component synchronized with a heel strike and a toe off, a time dependent component expressed by shifting of the baseline, and an irreversible component during a non-weight bearing period after walking. The three components were analyzed with a simple Voigt model.

In all patients, both the amplitude of the oscillatory component and the time dependent component expressed as retardation time decreased as healing proceeded, and by the time of fixator removal the irreversible component had disappeared. This method was useful for quantitatively evaluation the viscoelastoplascity of the healing site.