Short- and medium-term results of the thrust plate prosthesis in patients with polyarthritis.

The thrust plate prosthesis is an implant with metaphyseal fixation to the proximal femur, which leaves the diaphyseal bone untouched. Therefore, this implant is preferred in younger patients. It is dependent on good bone quality in the proximal femur. Because the bone quality is reduced in patients with polyarthritis, this kind of endoprosthesis may have a higher failure rate than conventional stemmed endoprostheses in these patients. Therefore, in patients with polyarthritis, even short- and medium-term results of the thrust plate prosthesis should be analyzed. In all, 47 thrust plate prostheses were implanted in 42 patients with polyarthritis (29 with rheumatoid arthritis, 6 with juvenile chronic arthritis, and 7 with spondylarthritis) and followed prospectively. The average age at operation was 40.8+/-10.7 years. Each patient was clinically and radiologically examined preoperatively, 3 and 6 months after the operation, and at the end of each postoperative year. The mean follow-up was 26.1+/-10.7 months. The clinical findings were evaluated using the Harris hip score. Radiologically, 8 different zones of the thrust plate prosthesis were analyzed for radiolucencies. During the 1st year, the Harris hip score rose continuously from the preoperative average of 42.4+/-6.5 points to 78.8+/-10.3 points 3 months postoperatively, 82.3+/-9.8 points 6 months postoperatively, and 86.8+/-10.1 points 1 year after the operation. The subsequent examinations showed Harris hip score remained at the same level. Five patients (5 joints, 10.6%) had to undergo a revision of the thrust plate prosthesis due to aseptic loosening in 3 and septic loosening in 2. Six prostheses (12.6%) showed radiolucencies, mostly below the thrust plate in zones 1 and 2. Two of them were certainly radiologically loose, which raised the failure rate to 7 of 47 (14.8%). The thrust plate prosthesis improves function and alleviates pain in patients with polyarthritis to a satisfactory degree. Concerning the failure rate, this type seems to yield slightly worse results than cementless stemmed endoprostheses in the same patient group. Due to the preservation of the diaphyseal bone of the femur and the possibility of an unproblematic change to a stemmed endoprosthesis, the thrust plate prosthesis can be recommended for younger patients with polyarthritis.

Electromyographically evident changes in skeletal muscles during tibial lengthening in dogs using the Ilizarov method.

Twenty-four beagle dogs underwent a lower leg lengthening on the right side of 2.5 cm at a distraction rate of 2 times 0.5 mm per day using a circular fixator system. After a latency phase of 5 days and a distraction phase of 25 days, 12 dogs (30-day dogs) underwent electromyography (EMG) of the gastrocnemius muscle on the lengthened and on the control side. The remaining half of the dogs underwent EMG after a consolidation phase of 25 days following the end of distraction (55-day dogs). During every EMG, at least 20 different muscle potentials were analyzed, and the duration, amplitude, and number of phases were determined of each individual potential. The 30-day dogs had significantly longer potential phases on the lengthened side and insignificantly smaller amplitudes compared with the control side. Furthermore, we observed a slightly larger number of polyphasic potentials on the distraction side. In the 55-day dogs, no significant differences were observed in the various parameters between the lengthened and the control side. Comparing 30- and 55-day dogs, the duration of the potentials on the distraction side was not significantly shorter in the 55-day dogs, and the amplitude significantly higher. These findings could indicate combined neurogenous and myopathic alterations of the muscles during the early distraction phase which will be compensated during the later distraction period and the consolidation phase by reparative and reinnervation processes, leaving no lasting functional damage.

Behavior of blood vessels during lower-leg lengthening using the Ilizarov method.

Using a ring fixator, lengthening of the right lower leg by 2.5 cm at a distraction rate of 2 x 0.5 mm per day was performed in 24 beagle dogs. After a postoperative latency period of 5 days and a distraction phase of 25 days, half the dogs were killed (30-day group). The remaining half were killed after a second interval of 25 days (55-day group). After the experiment, the anterior tibialis artery and vein with their supporting vessels, as well as the lesser saphenous vein of both the lengthened right side and the control side were excised and examined histologically, histomorphometrically, and electron microcopically. No morphologic changes of the vascular walls and no increase of collagenous or elastic fibers could be found. The histomorphometric evaluations showed a significant increase in the number of vasa vasorum in the dogs of both the 30- and 55-day groups. No significant difference in thickness of the vascular wall, tunica media, and adventitia could be observed between the lengthened and the control side in both dog groups. It seems that blood vessels can adapt to continuous tension during callus distraction without suffering structural damage and are the least limiting factor concerning distraction speed, distraction rhythm, and distraction length during callus distraction.

Biomechanical properties of tendons during lower-leg lengthening in dogs using the Ilizarov method.

Ten dogs were provided with a circular fixator. Segment resection of the fibula and tibial osteotomy in the right lower leg was performed. 5 days after surgery, a lengthening of the right lower leg by 2.5 cm was performed on 6 dogs using a distraction rate of 0.5 mm, twice per day. 3 dogs with leg lengthening and 2 dogs of the control group without leg lengthening were sacrificed at the end of the distraction phase of 25 days and the remaining dogs after another 25 days. Postmortally the tendons of the tibialis anterior, extensor digitorum longus, peroneus longus and the achilles tendon were taken from the operated right side and the left non-operated control side and were examined biomechanically in cyclic tests. The control group without lengthening showed no changes in the biomechanical properties in the tendons of either side nor in those of the unlengthened left side of the operated dogs. In contrast the biomechanical tests revealed a marked decrease of the elastic modulus, an increase of distraction length and an increase of modulus reduction on the lengthened side compared to the non-operated left side.

Behavior of tendons during lower-leg lengthening in dogs using the Ilizarov method.

Twenty-two dogs were provided with a circular fixator. Lengthening of the right lower leg by 2.5 cm was performed on 18 dogs 5 days after tibial osteotomy using a distraction rate of 0.5 mm, twice per day. Nine dogs with leg lengthening and two dogs of the control group without leg lengthening were sacrificed at the end of the distraction phase of 25 days and the remaining dogs after another 25 days. Post mortem, the tendons of the tibialis anterior, extensor digitorum longus, peroneus longus, and the Achilles tendon were taken from the operated-on right side and the left nonoperated-on control side and were analyzed histologically. The control group showed no histologic changes in the tendons of either side nor in those of the unlengthened left side of the operated-on dogs. Thirty-three tendons (41%) of dogs with leg lengthening were seen to have undergone histomorphological changes. An increase of the peritendinous connective tissue was seen, combined with chronic inflammatory cell infiltration in the tendons and/or the epitendinous tissues, edema, tendon fragmentation, necrosis, scarring of the tendons with dystrophic calcification and/or ossification, and broadening of the tenosynovial sheath. Furthermore, signs of histoneogenesis with growth in the tendons were found. Degenerative changes occurred far more often in the tendons of the ventral side of the lower leg and a slight pes equinus was regularly observed in the lengthened extremity. Therefore, pes equinus prevention and physiotherapy are important in the therapeutic use of lower-leg lengthening to minimize possible stress-induced damage of the ventral tendons.

Holmium: YAG laser-induced aseptic bone necroses of the femoral condyle.

In laser-controlled cartilage-ablation arthroplasties, the attention focuses more and more on the depth effects of the various lasers, especially as heat necroses of the cartilage and even in places of the bone were found in animal experiments. For the first time, two cases of holmium: YAG laser-induced aseptic bone necrosis of the femoral condyles after cartilage ablation are described.