Bone mineral density in fractures treated with absorbable or metallic implants.

Absorbable fixation devices have been clinically used in the fracture treatment for over ten years. No studies have been published where bone mineral density has been measured after bone consolidation comparing absorbable and metallic fixation. In this study the bone mineral density was measured after operative ankle fracture treatment with absorbable self-reinforced polyglycolic acid (SR-PGA) screws (14 patients) or with absorbable self-reinforced polylactic acid (SR-PLLA) screws (eight patients) compared with metallic fixation (17 patients). The overall results were radiologically good in every group. A statistically significant difference in the bone mineral density (BMD) was found only in the distal tibial metaphysis between SR-PGA screw and metallic fixation. The BMD increased in the distal tibia after SR-PGA screw fixation by an average 18.3%. The average change of BMD in the distal tibia after SR-PLLA screw fixation decreased by 6.4% while after metallic fixation the average change of MBD decreased by 18.6%. Bone mineral density measurements in the present study may indicate osteogenetic capacity of polyglycolide implants in the bone after fracture or osteotomy fixation. On the other hand, metallic implants showed negative effects to the bone.

Absorbable polylactide pins versus metallic Kirschner wires in the fixation of cancellous bone osteotomies in rats.

A transverse transcondylar osteotomy of the distal femur was fixed with biodegradable self-reinforced polylevolactide (SR-PLLA) pin in 42 rats and with metallic Kirschner wire in 42 rats. Consolidation of the osteotomy and periosteal callus formation was examined within standardised sample fields histologically, histomorphometrically and microradiographically one week, 3, 6, 12, 24, 36 and 48 weeks postoperatively. The intact contralateral femur served as control. From 3-week to 48-week follow-up time the total trabecular bone area of the SR-PLLA group at the osteotomy site was significantly larger in the operated femora than in the intact control femora at the corresponding site. The specimens of the Kirschner wire group showed significantly larger total bone area only at 12 weeks postoperatively as compared with the nonoperated femora. In the SR-PLLA group 28 and in the metallic group 31 osteotomies showed solid bony union. In both experimental groups the osteotomies with solid bony union showed only scantly periosteal callus formation. More abundant callus formation in both experimental groups was related to incomplete union of the osteotomy. No signs of degradation of the SR-PLLA implant could be noticed within the follow-up times of this study. Only mild foreign body reaction to both SR-PLLA pins and metallic Kirschner wires was observed during the observation period. The fixation properties of both SR-PLLA pins and metallic Kirschner wires seem to be sufficient for the fixation of small cancellous bone fragments, but by using SR-PLLA pins instead of Kirschner wires subsequent second operation for removal of the implants can be avoided.

Bone changes after experimental osteotomies fixed with absorbable self-reinforced poly-L-lactide screws or metallic screws studied by plain radiographs, quantitative computed tomography and magnetic resonance imaging.

The healing of the distal femoral osteotomy fixed with self-reinforced poly-L-lactide (SR-PLLA) or metallic screws in 16 rabbits was evaluated with plain radiographs, quantitative computed tomography and magnetic resonance imaging (MRI). At 36 weeks in the metallic fixation there was significantly more external callus than in the SR-PLLA fixation. On the metallic fixation side the cortical bone mineral density was significantly lower than on the non-operated side at 6 weeks as well as at 36 weeks. This decrease was not found in the SR-PLLA fixation. On the MRI on T1-weighted images a dark zone (signal void), and on the T2-weighted images a bright zone (increased signal intensity), was seen surrounding the screws, indicating oedema. At 36 weeks these oedematous zones were significantly smaller in the SR-PLLA fixation group than in the metallic one. The results give indirect evidence towards a more rapid and better osteotomy healing with the more physiologically elastic SR-PLLA screws than with the metallic screws. Fixation with SR-PLLA screws may prevent stress-protection atrophy and weakening of the fixed bone usually caused by the rigid metallic fixation.

Intraosseous cellular response to biodegradable fracture fixation screws made of polyglycolide or polylactide.

As biodegradable pins and screws have increasingly been used in the internal fixation of fractures, sterile inflammatory reactions have occasionally occurred. The aim of the present experimental study was to assess the cellular response within cancellous bone to biodegradable polyester screws. In 45 rabbis a transverse distal femoral osteotomy was fixed with a 4.5 x 30 mm screw made either of polyglycolide (PGA, in 20 rabbits) or polylactide (PLA, in 25 rabbits). The follow-up times were 3, 6, 12, 36 or 48 weeks. The time-related and spatial characteristics of the cellular response were examined histomorphometrically using standardised sample fields under polarised-light microscopy. Polymorphonuclear granulocytes and mononuclear round cells were scarce in all follow-up groups. The occurrence of phagocytic cells (mononuclear macrophages and foreign-body giant cells) was highest in the PGA-fixed 12-week specimens. The giant cells seemed to adhere to the implant surface at an early stage, whereas the ultimate digestion and clearing of the decomposing polymeric material later on were performed by macrophages invading the implant body. No PGA was left in the 36-week specimens, while the gross geometry of the PLA screws was still intact at 48 weeks. In conclusion, the inflammatory response to these polymers was quite mild. Thus it seems probable that some other additional factors must influence the occurrence of the clinical inflammatory reactions.

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.

Holding power of metallic screws in cancellous bone and metallic plates in cortical bone. An experimental study on rabbits using polymethylmethacrylate and bone graft as supporting material.

The holding power of metallic screws in cancellous bone and metallic plates in cortical bone was tested in sixty rabbits (n = 60). These metallic devices were fixed either without support or with the support of plastic material or autogenous bone graft. The fixation firmness was studied radiographically and by a test of the bonding strength. After six weeks, the mean value of the holding power of screws in cancellous bone without support was 440 N, and that of screws supported by polymethylmethacrylate 674 N and by bone graft 540 N. Corresponding values after twelve weeks were 436 N, 664 N, and 616 N. Fixation with polymethylmethacrylate was better than either fixation without support (P < 0.001, t-test) or fixation with bone graft (P < 0.01), whereas fixation with bone graft was better than fixation without support (P < 0.07). The best fixation was achieved by polymethylmethacrylate according to group mean values. Our investigation of the holding power of plates in cortical bone did not reveal any statistically significant differences between the methods used.

Intramedullary fixation of cortical bone osteotomies with self-reinforced polylactic rods in rabbits.

Osteotomies of the femoral shaft in rabbits were fixed with intramedullary rods made of poly-L-lactic acid (SR-PLLA) and poly-DL/L-lactic acid (SR-PDLLA/PLLA). Follow up was from one week to 2 years. In the PLLA group, in 37 out of 40 osteotomies the fixation was firm and the bone was united. In the PDLLA/PLLA group, the fixation was firm in 30 out of 45, but in 13 of these angular deformity of more than 10 degrees had occurred. The fixation had failed in 15. No inflammatory or foreign body reaction was seen in either group. This study demonstrates that SR-PLLA rods are suitable fixation for cortical osteotomies in rabbits.

Do intramedullary rods of self-reinforced poly-L-lactide or poly-DL/L-lactide cause lactic acid acidosis in rabbits?

Intramedullary rods of self-reinforced poly-DL/L-lactic acid or poly-L-lactic acid were implanted in both femurs of ten rabbits for 60 weeks. Levels of arterial blood L- and D-lactate, pyruvate, pH, pCO2, base excess, standard bicarbonate, pO2 and O2-saturation were determined before implantation and 1, 3, 6, 12, 24, 36, 48 and 60 weeks after implantation. No significant increase in blood L- and D-lactate level was observed at any follow-up. Also, the blood acid-base balance remained normal throughout the study. Further studies on larger implants and on larger animals with follow-ups up to 5 years are recommended.

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.

Absorption, biocompatibility, and fixation properties of polylactic acid in bone tissue: an experimental study in rats.

The absorption, biocompatibility, and fixation properties of self-reinforced (SR) poly-L-lactic acid (PLLA) and poly-DL-lactic acid (PDLLA) were investigated in cancellous bone in 56 rats. Osteotomies of the distal femur were operatively fixed with cylindrical implants made of SR-PLLA and SR-PDLLA/PLLA (40 PDLLA:60 PLLA). The follow-up times were one, three, six, 12, 24, 36, and 48 weeks. Roentgenographic, microradiographic, histologic, histomorphometric, and oxytetracycline-labeling studies were done. Histologically, there was no evidence of inflammation or foreign-body reaction in the bony tissues. Histomorphometric analysis showed that absorption in the SR-PDLLA/PLLA implant was faster than in the SR-PLLA implant. Absorption started peripherally in the implants and continued with subsequent replacement by new bone. At 48 weeks the implant was completely surrounded by a layer of new bone. The SR-PLLA and SR-PDLLA/PLLA implants were visible in all specimens during the 48-week follow-up period. Ninety-five percent of the osteotomies were consolidated. Implants made of SR polylactic acid in rats proved to be biocompatible and slowly absorbable, and they possessed sufficient mechanical properties for fixation of osteotomies.

Fixation of experimental osteotomies with absorbable polylactic acid screws.

Absorbable screws made of self-reinforced poly-L-lactic acid (SR-PLLA) and poly-DL/L-lactic acid (SR-PDLLA/PLLA) were used for fixation of cancellous bone osteotomies of the distal femur in rabbits. The initial molecular weight of PLLA was 260.000 and that of PDLLA 100.000. The follow-up times were from one week to 96 weeks. Seventy-two rabbits were operated on, 36 in the PLLA group and 36 in the PDLLA/PLLA group. After sacrifice, radiographic, micro-radiographic, histologic, histo-morphometric, and oxytetracycline-labelling studies were performed. In the PLLA group 34/36 (94%) osteotomies and in the PDLLA/PLLA group 31/36 (86%) osteotomies healed without delay or angular deformity. The present investigation shows that absorbable SR-polylactic acid screws are suitable for fixation of weight loading cancellous bone osteotomies in rabbits. Based on these promising results, a clinical study where cancellous bone fractures are fixed with SR-PLLA screws has been started.

Problems associated with longitudinal fractures of the femoral shaft in adults. A comparison between intramedullary nailing, interlocking intramedullary nailing and plating.

The results of 64 operatively treated patients with longitudinal femoral shaft fracture are presented. Twenty-four fractures were treated with an intramedullary nail, six with an interlocking intramedullary nail and 34 with plating. The functional end results were good and the anatomical result satisfactory in all groups although treatment with plate caused several failures. We conclude that intramedullary nailing is a good and safe method to treat non-comminuted fractures of the femoral shaft.

Incidence of local complications after intramedullary nailing and after plate fixation of femoral shaft fractures.

A consecutive series of 378 patients with 381 acute adult femoral shaft fractures in previously intact femora admitted during a 10-year period was reviewed for the incidence of local complications including malunion. The majority, 282 fractures (74%), were caused by motor vehicle accidents. The median age of the patients was 28 years. The policy of management was internal fixation of the fracture on the day of admission. The method of treatment was intramedullary nailing (Küntscher or interlocking nailing) in 279 and plate fixation in 102 fractures. A local complication occurred in 90 patients (24%). Of these 90 cases 24 had malunion only while in the remaining 66 patients there was mechanical failure of fixation in 27, local infection in 20 (5.3% of the total), delayed union or nonunion in 15, and refracture in four patients. Concurrent injuries in the lower extremities were associated with a significantly increased frequency of delayed union, nonunion, and refracture. In 41 patients (11%) a total of 58 reoperations had to be undertaken because of local complications. There was an over-representation of plated fractures among those patients suffering a local complication classified as severe, 24 out of 37 (chi 2 = 30.3; p less than 0.001). Consequently, we now only exceptionally use plate fixation in the management of femoral shaft fractures.