Jarkko Vasenius

Acute dislocation of the patella : a prospective review of operative treatment

We report a prospective study of 55 patients with acute primary patellar dislocation, all treated by operation and followed up for at least two years. Diagnosis was based on the history of a lateral displacement, with medial tenderness and a positive apprehension test; redislocations were excluded. Before operation, the difference in lateral shift on skyline views of the injured and control patellae was highly significant. At operation, rupture of the medial retinaculum of the patella was seen in all but one case. There were medial marginal fractures of the patella in 23 cases. Subjective results of the operation were excellent or good in 44 of the 55 at two years with a redislocation rate of only 9%. Most patients were able to return to the same level of sporting activity as before the injury.

Comparison of absorbable self-reinforced multilayer poly-1-lactide and metallic plates for the fixation of mandibular body osteotomies: An experimental study in sheep

Eighteen unfavorable transverse osteotomies were created in the mandibular body of sheep. Nine were fixed with self-reinforced poly-l-lactide and nine with metallic dynamic compression plates. Both plates were fixed with similar titanium screws. The follow-up times for radiographic, histologic, and microradiographic studies were 6, 12, and 24 weeks. With both methods, bony union with callus formation was accomplished by 6 weeks in all but one osteotomy in the metallic fixation group. There were no signs of plate failure.

The tissue-implant interface during degradation of absorbable polyglycolide fracture fixation screws in the rabbit femur.

A transverse transcondylar osteotomy of the distal femur was fixed with an axially placed absorbable fracture fixation screw made of polyglycolide (PGA) in 25 rabbits. Changes at the tissue-implant interface accompanying degradation of the screw were examined histologically, histomorphometrically, and microradiographically seven, 20, 40, 80, and 250 days after implantation. At seven days postimplantation, a layer of fibroblasts was seen surrounding the implant, and new bone formation was discernible in the host tissues adjacent to this membranous structure. At 20 days postimplantation, the geometry of the screw was still intact and the tissue-implant boundary was distinct. The first signs of invasion of vascular granulation tissue into the implant were observed 40 days after implantation, at which time the osteotomies were united. The apparent walling-off response by formation of new trabecular bone outlining the PGA profile continued, with the greatest mean trabecular bone volume fraction at the interface, 23.9%, measured at 40 days. A significant decrease in the new bone volume occurred between 40 and 80 days postimplantation. The intensity of the foreign-body reaction seen was histologically moderate. The giant cell count was highest at 80 days postimplantation, when the migratory activity of phagocytic cells had transported intracellular particulate polymeric debris 400-800 microns away from the original tissue-implant boundary. At 250 days postimplantation, no birefringent polymeric material could be seen in the specimens. No contraindications for the clinical application of PGA implants emerged in this study.

Comparison of in vitro hydrolysis, subcutaneous and intramedullary implantation to evaluate the strength retention of absorbable osteosynthesis implants

To evaluate the behaviour of mechanical properties of absorbable osteosynthesis implants in vivo, the strength retention of self-reinforced polyglycolide rods in distilled water at 37 degrees C in the subcutis and femoral medullary cavity of the rabbit was investigated. The self-reinforced polyglycolide rods lost their strength significantly faster in vivo than in vitro. The strength loss of the self-reinforced polyglycolide rods was only slightly faster in the medullary cavity than in the subcutis. As the removal of the implants from the medullary cavity became difficult 5-6 wk after implantation, it is suggested that subcutaneous implantation would be a suitable method to evaluate the strength retention of absorbable osteosynthesis implants.

Biodegradable self-reinforced polyglycolide (SR-PGA) composite rods coated with slowly biodegradable polymers for fracture fixation: strength and strength retention in vitro and in vivo

Abstract The strength retention of coated and uncoated self-reinforced polyglycolide (SR-PGA) rods was evaluated after immersion in distilled water at 37°C and after implantation in the subcutis of rabbit. Slowly biodegradable coatings improved only the in-vitro strength retention of SR-PGA osteosynthesis implants. In the in-vivo environment the rods lost their strength in 5–6 weeks, and there was no significant difference in the strength retention between coated and uncoated rods. The SR-PGA rods lost their strength considerably faster in vivo than in vitro.

Comparison of shear strength of osteotomies fixed with absorbable self-reinforced poly-L-lactide and metallic screws

Nine experimental osteotomies on the neck of a sheeps left mandibular condyle were fixed with self-reinforced poly-L-lactide (SR-PLLA) screws. Metallic screws were used in a group of nine sheep for the same fixation of the osteotomy. The right condyle of each sheep acted as a control. Radiographic analysis was carried out at 3 weeks and at sacrifice (6, 12 or 24 weeks) when the shear force needed to break the osteotomy site was measured. No significant differences were detected at 3, 6 or 24 weeks, but at 12 weeks the SR-PLLA-fixed condyles seemed to tolerate shear force somewhat better.The results are very promising and have led us to continue with development of smaller screws and a self-reinforced poly-L-lactide plate.

Osteolytic Changes After Polyglycolide Pin Fixation in Chevron Osteotomy

Absorbable polyglycolide pins were used for fixation of 94 chevron osteotomies in 70 patients at the Department of Orthopaedics and Traumatology, Helsinki University Central Hospital, between 1986 and 1992. Postoperative osteolytic changes around the degrading pin occurred in 21 of 94 (22%) metatarsal heads. In 17 of 21 metatarsal heads, polydioxanone-coated polyglycolide pins were used. This type of pin has not been used since 1988. At follow-up, 16 of 21 osteolytic changes resolved completely and four partially resolved. In the remaining one, the osteolytic area remained visible after 6 years. Cystic changes in the metatarsal head, not attributable to the location of the absorbable implants, occurred in seven (7.4%) metatarsal heads and avascular necrosis of the entire metatarsal head in one (1.1%). Foreign body reaction occurred in six (6.3%) metatarsal heads and wound infection in three (3.2%) metatarsal heads. No association was observed between osteolytic changes and foreign body reaction or infection. Osteolysis in patients receiving polyglycolide implants only require observation, because associated symptoms with the radiographic findings are transient.

Mechanical properties of biodegradable poly-l-lactide ligament augmentation device in experimental anterior cruciate ligament reconstruction

SummaryThe mechanical properties, including maximum load, elongation, and axial rigidity, of the biodegradable poly-l-lactic acid (PLLA) ligament augmentation device were investigated, 6, 12, 24, and 48 weeks after experimental anterior cruciate ligament (ACL) repair in 32 sheep. In 16 sheep the cut ACL was removed and reconstructed with the fascia lata augmented with a braided PLLA implant 3.2 mm in diameter. In 16 sheep the ACL was cut from its midportion, sutured, and then augmented with a PLLA implant. The contralateral knee served as a control. At 6 weeks the maximum loads of the reconstructed ACL in the fascia lata-PLLA and primary suture-PLLA groups were 9% and 6%, respectively, of the contralateral ACL, but they increased with time and at 48 weeks were 21% and 12%, respectively, of the control. In the fascia lata-PLLA group the increase in maximum load was evident (P < 0.05) during the follow-up period. During the first 12 weeks the axial rigidity (expressing the elasticity of the reconstruction) was poor, especially in the high-stress region corresponding to the tensile load close to the maximum load. Thereafter the axial rigidity increased, being 48% of the control in the fascia lata-PLLA group and 29% in the primary suture-PLLA group at 48 weeks. In the low-stress region between 10 N and 100 N the increase in axial rigidity in the fascia lata-PLLA group was apparent (P < 0.05) throughout the follow-up, with values of 72% of the control in the fascia lata-PLLA and 47% in the primary suture-PLLA group at 48 weeks. Fascia lata augmented with PLLA seemed to yield a better result than primary suture augmented with PLLA, although no statistically significant difference was found. Despite modest mechanical properties in the early postoperative period, good functional recovery with minor radiographic changes and acceptable mechanical properties were achieved by the end of the 1-year follow-up period.

Absorbable polyglycolide screws in internal fixation of femoral osteotomies in rabbits

In 20 rabbits, a transverse distal femoral osteotomy was fixed using a 4.5 by 30-mm absorbable screw made of polyglycolide. No postoperative external support was used. The consolidation of the osteotomy was investigated histologically, morphometrically, and microradiographically in groups of 4 to 6 rabbits that were followed for 3, 6, 12, or 36 weeks. Fourteen osteotomies showed solid bony union; and in 3, several bone trabeculae were seen to bridge a still partially ununited osteotomy. In another 3 rabbits, each with a follow-up time of 12 or 36 weeks, no convincing signs of progressing consolidation could be seen. Only 1 of these rabbits showed displacement of the distal fragment.

The effect of osteotomy and osteosynthesis in the mandibular condyle. A radiologic and histologic study in sheep

Eighteen oblique osteotomies in sheep mandibular condylar necks were fixed with self-reinforced poly-L-lactide (SR-PLLA) (n = 9) or stainless steel (n = 9) screws (core diameters 2.4, 2.7, 3.0, or 3.5 mm). No intermaxillary fixation (IMF) was applied. The follow-up periods were 6, 12, and 24 weeks, respectively, after which the sheep were killed, and the status of the condylar head was assessed radiographically and histologically. The results showed that the fixation had been adequate. Bony destruction, osteophytes, and flattening of the condylar head, however, were frequently observed in both groups, as compared with the unoperated contralateral condyle. Histologic studies revealed that the thickness of the condylar head cartilage had increased and that the boundaries of the different cell layers were irregular, as was the junction of cartilage and bone. The diameter of the screw did not seem to have any influence on the occurrence of either radiologic or histologic signs of condylar degeneration. These findings indicate that screw fixation of condylar fractures in the mandible without IMF might result in degenerative joint disease.