Material and knot properties of braided polyester (Ticron) and bioabsorbable poly-L/D-lactide (PLDLA) 96/4 sutures.

The purpose of the present study was to investigate in vitro the biomechanical material and knot properties and histomorphometrical knot properties of 3-0 braided polyester suture (Ticron) and bioabsorbable poly-L/D-lactide (PLDLA) 96/4 suture. In Ticron five throws are needed to form a secure knot, and the 1 = 1 = 1 = 1 = 1 and the 2 = 1 = 1 = 1 configurations are recommended. For PLDLA several granny and square knots formed a secure knot, but the 1 = 1 and 1 = 1 = 1 knots were the best. These PLDLA knots had lower yield force and strain at yield point, but higher stiffness than the recommended Ticron knots. The ultimate force values did not differ, but PLDLA knots had significantly higher strain at ultimate point. In the histomorphometrical analysis of the recommended knots, the PLDLA knots had a significantly smaller knot surface area than the Ticron knots. According to these results, PLDLA suture proved to be suitable for flexor tendon repair.

No long-term effects of ultrasound therapy on bioabsorbable screw-fixed lateral malleolar fracture.

BACKGROUND AND AIMS: The present study was initiated to evaluate the long-term effects of low-intensity ultrasound therapy on bioabsorbable screw-fixed lateral malleolar fractures, which has not been studied earlier. PATIENTS AND METHODS: The study design was prospective, randomized, double-blinded, and placebo-controlled. Sixteen dislocated lateral malleolar fractures were fixed with one bioabsorbable self-reinforced poly-L-lactide screw. The patients used an ultrasound device 20 minutes daily for six weeks without knowing it was active (eight patients) or inactive (eight patients). The follow-up time was 18 months. The radiological bone morphology was assessed by multidetector computed tomography (MDCT) scans, the bone mineral density by dual-energy X-ray absorptiometry scans, and the clinical outcome by Olerud-Molander scoring and clinical examination of the ankle. RESULTS: The MDCT scans revealed that all fractures were fully healed, and no differences were observed in radiological bone morphology at the fracture site. The bone mineral density of the fractured lateral malleolus tended to increase slightly during the 18-month follow-up, the increase being symmetrical in both groups. No differences were observed in the clinical outcome or Olerud-Molander scores. CONCLUSIONS: The six-week low-intensity ultrasound therapy had no effect on radiological bone morphology, bone mineral density or clinical outcome in bioabsorbable screw-fixed lateral malleolar fractures 18 months after the injury.

Coralline hydroxyapatite reinforced with polylactide fibres in lumbar interbody implantation.

Porous hydroxyapatite HA blocks reinforced with poly-l/dl-lactide fibres were used to maintain the lumbar disc space and to start to create intercorporeal fusion in 23 growing pigs. In four pigs two emptied non adjacent disc spaces were left open. After 3, 6, 12 and 16 weeks the implanted disc blocks were studied radiologically, histologically, histomorphometrically, microradiographically, and with oxytetracycline fluorescence. In plain films slight to moderate ossification of the implanted disc spaces was detected at 12 and 16 weeks. Resorption of the implants was seen radiologically from 3 weeks and fragmentation from 12 weeks onwards. In microradiographs disintegration of the coralline inner structure started at 3 weeks. Histologically, connective tissue ingrowth was seen inside the porous structure from three weeks onwards. Small amounts of new bone were visible and connective tissue inside the implant increased from a mean of 65.6% at 3 weeks to a mean of 79.4% at 16 weeks histomorphometrically. The bone ingrowth varied from 0.7 to 1.7%. A loss of height in the implanted disc spaces was seen (p < 0.05, linear regression analysis). In control pigs the emptied disc spaces lost their height similarly. The implants used were not strong enough to maintain the lumbar disc height.

A comparative analysis of the biomechanical behaviour of five flexor tendon core sutures.

Five core suture techniques were compared by static tensile testing in vitro. Fifty porcine tendons were used. The core sutures were performed with 3-0 or 4-0 braided polyester suture (Ticron) and the over-and-over running peripheral sutures with 6-0 monofilament polypropylene (Prolene). The core sutures were: (1) Pennington modified Kessler (3-0), (2) Double Pennington modified Kessler (3-0), (3) 4-strand Savage (3-0), (4) 4-strand Savage (4-0), and (5) 6-strand Savage (4-0). Repairs were compared as paired in regard to one variable: the number of core suture strands, the suture calibre, or the suture configuration. Biomechanical differences between the repair groups started during the linear region, with the yield force and stiffness increasing along with the number of core suture strands. All three variables influenced the strain at the yield point. Thus, the strength of the intact repair can be improved by modifying the core suture. In all repairs gap formation started near the yield point after failure of the peripheral suture. The yield force represents the strength of the intact repair composite and should be considered the strength of the tendon repair.

Intramedullary fixation of femoral cortical osteotomies with interlocked biodegradable self-reinforced poly-96L/4D-lactide (SR-PLA96) nails.

Femoral diaphyseal osteotomies of adult sheep were fixed with intramedullary (i.m.) biodegradable self-reinforced poly-96L/4D-lactide (SR-PLA96) nails (Phi 10.66-10.78 mmx195-199 mm) that were interlocked with four Phi 1.5 mm metallic Kirschner (K) wires. Hollow i.m. nails used in the pilot study resulted in implant failure and only two of these sheep were followed long term (18 months and 3 years). In the main study, solid nails were used and this resulted in consolidation in 5/6 cases and in one non-union due to failure of both proximal K wires at 3 weeks. Sheep in the main study were followed for 6 and 12 months. Femurs were studied radiographically, microradiographically, histologically and by oxytetracycline labelling. Good bone healing was achieved and histology showed only a mild tissue reaction to the implant at 6-18 months. At 3 years, the implant had almost degraded and numerous foamy macrophages were ingesting the disintegrated material. No accumulations of lymphocytes implying an immunological inflammatory reaction were seen. This investigation demonstrated that absorbable SR-PLA96 i.m. nails can be used together with interlocking metallic K wires in fixation of simple cortical osteotomies in large animals weighing up to 63 kg. The long-term biocompatibility should be studied in a larger population.

Arthrodesis of the wrist with bioabsorbable fixation in patients with rheumatoid arthritis.

Twenty-four wrist arthrodeses were performed on 18 patients with rheumatoid arthritis using a bioabsorbable self-reinforced poly-L-lactide rod as the fixation device. There was one nonunion which required a re-operation and two nonunions which did not need further treatment. The position of the arthrodesis was ulnar deviation and extension in most patients, and there was high patient satisfaction with 21 of the 24 wrists and satisfactory pain relief in 22 of the 24 wrists. This method for fusing the wrist in patients with rheumatoid arthritis appears reliable and simple to perform.

Complications in the first 1,043 operations where self-reinforced poly-L-lactide implants were used solely for tissue fixation in orthopaedics and traumatology.

This is an analysis from one hospital of the first 1043 operations where pure self-reinforced poly-L-lactide (SR-PLLA) implants have been used alone. The operations were performed between 1988 and 1999 and included 407 orthopaedic patients and 636 trauma patients. There was a total of 107 complications. There were 21 infections but no sinus formation. Failure of fixation was seen in 46 patients. In 936 operations the healing was uneventful.

Biodegradation and strength retention of poly-L-lactide screws in vivo. An experimental long-term study in sheep.

BACKGROUND AND AIMS: Poly-L-lactide implants have gained popularity in the fixation of fractures and osteotomies in the past decade. The aim of the present experimental long-term study was to examine the degradation and strength retention of self-reinforced poly-L-lactide (SR-PLLA) lag-screws and the bone tissue response. MATERIAL AND METHODS: A total of 27 young adult sheep were used. Self-reinforced poly-L-lactide (SR-PLLA) lag-screws of 6.3 mm were implanted in the left proximal femur of nine sheep. At two, three and five years three of the sheep were sacrificed and the degradation was studied radiologically, microradiographically and histologically. For the strength retention measurements five SR-PLLA lag-screws of 6.3 mm and five lag-screws of 4.5 mm were implanted in the subcutaneous tissue of the five sheep and lag-screws of 6.3 mm for the pull-out test in the left proximal femur of 20 sheep. At 0, 12, 18, 24, 32, and 36 weeks bending and shear strength, molecular weight and pull-out measurements were performed. RESULTS: At five years no SR-PLLA material could be seen. The implant area was surrounded by high density bone with bone ingrowth in the screw area. At 36 weeks the bending strength of the 6.3 mm screws had decreased from 257.9 MPa to 36.4 MPa and the shear strength from 131.8 MPa to 19.8 MPa. The pull-out strength of the lag-screws of 6.3 mm in diameter decreased from 1507 N to 331 N in 24 weeks. CONCLUSIONS: SR-PLLA lag-screws showed high initial values, a controlled strength retention and gradual degradation process making the use of them safe also in demanding fixations.

Long-term results of ankle and triple arthrodeses fixed with self-reinforced polylevolactic acid implants in patients with rheumatoid arthritis.

Self-reinforcing polylevolactic acid (SR-PLLA) implants have been used in arthrodeses of patients with rheumatoid arthritis. No long-term evaluation has been published so far. Two patients (three ankles) with destruction of the ankle joint and seven with destruction of the subtalar joint received ten arthrodeses. One out of three ankle arthrodeses healed and nonunion developed in two. Five out of seven triple arthrodeses attained bony union. Two patients with malunion of the subtalar and talonavicular joints are free of symptoms and need no reoperation. One superficial wound infection healed by oral antibiotics. In one patient, an ankle arthrodesis was performed 6 years after the triple arthrodesis of the left foot. SR-PLLA implants can be used in triple arthrodesis in rheumatoid arthritic patients with good results comparable to those of other studies. The problems with nonunion of ankle arthrodeses noticed in former studies are also attributable to this fixation method.

Comparison of absorbable poly-L-lactide and metallic intramedullary rods in the fixation of femoral shaft osteotomies: an experimental study in rabbits.

An osteotomy of the distal femoral diaphysis was fixed with an intramedullary self-reinforced poly-L-lactide (SR-PLLA) rod in 22 and with a metallic rod in 38 skeletally mature rabbits. Histomorphometric and quantitative computed tomography (QCT) were performed to assess time-related changes in the consolidation process of the osteotomy of cortical bone and development of the external callus. The follow-up times were 8, 16, 24, and 48 weeks for radiologic and 16, 24, and 48 weeks for histologic studies; 19/22 of the SR-PLLA and 34/38 of the metallic fixed osteotomies healed during the observation periods. On microscopic evaluation, no difference was found in histologic parameters such as external callus area and fraction, and endosteal callus area and fraction between SR-PLLA and metallic fixed osteotomies. The total external callus area increased up to 16 weeks and subsequently decreased linearly over time in both experimental groups. However, the mean endosteal bone area and fraction decreased after 16 weeks in metallic fixated femora, while in the SR-PLLA fixated femora, both these values increased, being greater in the SR-PLLA group. The mean external callus QCT density decreased after 8 weeks in both experimental groups, the decrease being greater in the SR-PLLA group. Nevertheless, no significant difference was detected between SR-PLLA and metallic fixed femora in any of the follow-ups. These results suggest that both SR-PLLA and metallic rods are suitable in the fixation of femoral shaft osteotomies in rabbits. Furthermore, SR-PLLA rod fixation seems to have a minor stress-shielding effect.

Shear-load carrying capacity of cancellous bone after implantation of self-reinforced polyglycolic acid and poly-L-lactic acid pins: experimental study on rats.

Both distal femora of 40 rats were implanted with a self-reinforced polyglycolic acid (SR-PGA) pin in the right femur and with a self-reinforced poly-L-lactic acid (SR-PLLA) pin in the left femur. The intact femora of 20 rats served as controls. The follow-up times were 1, 3, 6, 12, 24, 36, 48, and 52 weeks. After killing all operated and control femora were examined macroscopically and radiographically. The shear-load carrying capacities of all the femurs were investigated, and the SR-PGA and SR-PLLA fixed specimens were compared with each other and with the control specimens. The shear-load carrying capacities reached their highest values at 36 weeks in the SR-PGA and SR-PLLA fixed and control specimens. Thereafter they gradually decreased. At 52 weeks both the SR-PGA fixed specimens and the control specimens had statistically significantly (p < 0.001) higher values than the SR-PLLA fixed specimens, when the influence of the pins had ceased. Otherwise, the shear-load capacities showed higher values in the SR-PLLA fixed specimens, as the pins carried the load. During the whole follow-up period the mean shear-load carrying capacity of the SR-PGA fixed specimens was 171.2 N and that of the SR-PLLA fixed specimens 180.9 N, the corresponding value of the control specimens was 148.2 N.

Long-term results of wrist arthrodeses fixed with self-reinforced polylevolactic acid implants in patients with rheumatoid arthritis.

OBJECTIVE: Implants made of self-reinforcing polylevolactic acid (SR-PLLA) have been successfully used in arthrodeses of patients with rheumatoid arthritis. No lone-term evaluation on bioabsorbable fixation in patients with rheumatoid arthritis has been published so far. METHODS: In this study 21 wrist fusions were performed on 18 patients with rheumatoid arthritis by using SR-PLLA rods as fixation devices. The follow-up time was 3-8 years (mean 5.4 years). RESULTS: The results showed one non-union but no infections or problems associated with the bioabsorbable implants used. CONCLUSION: According to this study, fixation of wrist arthrodesis in patients with rheumatoid arthritis can be performed by using SR-PLLA implants with favourable results. The benefit of this method is the avoidance of the removal operation of fixation devices.

Causes of the clinical tissue response to polyglycolide and polylactide implants with an emphasis on the knee.

The causes of a clinical tissue response to self-reinforced polyglycolide (SR-PGA) and self-reinforced polylactide (SR-PLLA) implants were studied in the first 2500 polymeric fixations. The incidence was 8.0% in fixations with implants made of SR-PGA (n = 1879) and 0% in SR-PLLA fixations (n = 621). A small number of fixations per site seemed to increase the incidence of a tissue response. In diagnoses involving over 50 fixations, except for ankle fractures, the incidence was 4.2%. The site of fixation influenced the incidence; the lowest incidence was seen for radial head fracture fixation (1.1%). The aromatic dye which has not been used since 1988 in the SR-PGA implant increased the response. A large total implant volume and a large number of implants increased the incidence of a tissue response. In the knee (n = 131), the incidence of a clinical tissue response was 4.3%, with four fluid accumulations and one synovitis of the knee after fixation with SR-PGA implants.

Inability of transforming growth factor-beta 1, combined with a bioabsorbable polymer paste, to promote healing of bone defects in the rat distal femur.

The ability of transforming growth factor-beta 1 (TGF-beta 1) to promote bone formation suggests that it may have potential as a therapeutic agent in bone defects. However, there still exists a need for an effective method of delivering TGF-beta 1 to the site of an osseous defect. In the present study, TGF-beta 1 was embedded in a bioabsorbable polymer paste (a blend of an L-lactide oligomer and a copolymer of epsilon-caprolactone and DL-lactide). The release of TGF-beta 1 from the polymer paste was examined in vitro with an enzyme-linked immunosorbent assay, which showed sustained release of active TGF-beta 1 over a 7-day period. Further, the polymer paste was used to fill a bone defect in the rat distal femur. The amount of TGF-beta 1 per rat was 50 micrograms, while in a control group we used an identical polymer paste without the growth factor. After a follow-up of 1 week and 3 weeks, the femurs were examined radiographically, histologically, histomorphometrically, microradiographically, and were also used for tetracycline-labeling studies. TGF-beta 1 did not enhance healing of the bone defect. A combination of growth factors would probably be a more potent osteoinductor than TGF-beta 1 alone.

The fixation properties of carbon fiber-reinforced liquid crystalline polymer implant in bone: an experimental study in rabbits.

A novel composite material with ultra-high strength and a low elastic modulus called carbon fiber-reinforced liquid crystalline polymer (LCP/CF) has been developed. We studied the fixation properties of an intramedullary LCP/CF rod in rabbit bone. The medullary canals of both femora were reamed with a drill 3.2 mm in diameter starting from the trochanteric fossa in eleven New Zealand White rabbits weighing on average 4.8 kg. A smooth LCP/CF rod 3.2 mm in diameter and 50 mm in length was introduced into the medullary canal of both femora. The follow-up intervals were 0, 6, 12, and 52 weeks. The upper part of the harvested femora was cut into two pieces, each 25 mm in length. A mechanical push-out test was performed within 48 h to determine bone-implant interface attachment strength in the proximal (cancellous) and distal (cortical) locations. The mean push-out strength values at 0, 6, 12, and 52 weeks were 61, 250, 382, and 612 KPa in the cancellous location and 0, 32, 41, and 68 KPa in the cortical location, respectively. The strength of the bone/implant interface appeared to be quite low, similar to other uncoated or nonporous implants, but it was found to increase with time.

Tissue response to polyglycolide and polylevolactide pins in osteotomized cancellous bone.

A transcondylar osteotomy of the distal femur was fixed with a self-reinforced polyglycolide pin in one hind leg and with a self-reinforced polylevolactide pin in the other hind leg of 49 rats. The intact femurs of eight rats that did not have surgical treatment were used as controls. The tissue reaction to the implant and the consolidation of the osteotomy were examined radiographically, histologically, histomorphometrically, microradiographically, and using oxytetracycline fluorescence studies. The followups were from 1 to 52 weeks. A vigorous osteostimulatory tissue response to self-reinforced polyglycolide pins and self-reinforced polylevolactide pins was observed 1 week after fixation. This reaction reached its highest value 24 weeks after self-reinforced polyglycolide pin fixation and 6 weeks after self-reinforced polylevolactide pin fixation. The highest values of the mean trabecular bone area fraction, 27.9% for self-reinforced polyglycolide pins and 28.1% for self-reinforced polylevolactide pins, were measured at 48 weeks. At 12 weeks there was a peak of phagocytizing macrophages in the specimens with self-reinforced polyglycolide pin fixation. During the followup, total phagocytosis of self-reinforced polyglycolide pins was seen, but only a few signs of degradation of self-reinforced polylevolactide pins were observed. Both polymeric implants seemed to possess osteostimulatory properties, and the biocompatibility and clinical relevance proved to be acceptable.

Intramedullary fixation of cortical bone osteotomies with absorbable self-reinforced fibrillated poly-96L/4D-lactide (SR-PLA96) rods in rabbits.

Osteotomies of the femoral diaphysis were fixed with absorbable self-reinforced fibrillated poly-96L/4D-lactide (SR-PLA96) intramedullary rods (4.5 mm x 50-60 mm) in 43 adult rabbits. Follow-up times varied from 3 weeks to 3 yr. After sacrifice histological, oxytetracycline-fluorescence and microradiographic studies of the bones were performed. Strength characteristics and changes in crystallinity and molecular weight of the rods were also measured. All osteotomies were evaluated radiographically. Thirty-six osteotomies (84%) healed uneventfully. The implant disappeared almost totally within 3 yr and histology showed only a minor foreign body reaction. From 6 weeks on, the bending force needed to break the osteotomy was comparable to the bending force needed to break the control bone. The shear strength of the rods displayed only minor changes for the first 24 weeks. Subsequently, the rods rapidly lost their strength and at 48 weeks there was practically no shear strength left, which is ideal for healing of an osteotomy. The present investigation demonstrated, that absorbable. fibrillated SR-PLA96-rods can be used for the intramedullar fixation of simple cortical bone osteotomies in rabbits. These results have encouraged us to continue our studies with the fixation of experimental cortical bone osteotomies in larger species.

Bioabsorbable fixation in orthopaedic surgery and traumatology.

Bioabsorbable internal fixation devices were introduced clinically in the treatment of fractures and osteotomies of the extremities at the Department of Orthopaedics and Traumatology, Helsinki University, in 1984. Since November 5, 1984, a total of 3200 patients were managed using bone or ligament fixation devices made of self-reinforced (matrix and fibres of the same polymer) bioabsorbable alpha-hydroxy polyesters. The devices used included cylindrical rods, screws, tacks, plugs, arrows, and wires. The most common indication for the use of bioabsorbable implants was the displaced malleolar fracture of the ankle. Transphyseal fixation with small-diameter, mainly polyglycolide pins was used in children. The postoperative clinical course was uneventful in more than 90% of the patients. The complications included bacterial wound infection in 4% and failure of fixation in 4%. In one-fifth of the latter cases, however, re-operation was not necessary. The occurrence of non-infectious foreign-body reactions two to three months postoperatively has been observed in 2% of the patients operated in the last few years with polyglycolide implants but none of the patients managed with polylactide implants. This inflammatory tissue response often required aspiration with a needle but did not influence the functional or radiologic result of the treatment. Owing to the biodegradability of these internal fixation devices, implant removal procedures were avoided. This results in financial benefits and psychological advantages. Bioabsorbable implants can also be used in open fractures and infection operations.

Treatment of subcapital femoral neck fractures with bioabsorbable or metallic screw fixation. A preliminary report.

BACKGROUND AND AIMS: Cancellous bone fractures and arthrodeses have been treated successfully with bioabsorbable polyglycolide and poly-L-lactide implants. In this study bioabsorbable poly-L-lactide lag screws and metallic screws were compared in the fixation of subcapital femoral neck fractures. PATIENTS AND METHODS: Forty patients with femoral neck fractures were treated by internal fixation using three bioabsorbable self-reinforced poly-L-lactide (SR-PLLA) lag screws of 6.3 mm in diameter and 38 patients using three metallic screws of 7 mm in diameter. In addition, one patient was operated on using two and one using four metallic screws. The patients did not differ in age, body weight or primary dislocation of the fracture. There were six males in the lactide group versus 14 in the metallic fixation group. There were two Garden Stage I, 27 Garden Stage II, nine Garden Stage III, and two Garden Stage IV fractures in both groups. RESULTS: In the Garden I and II fractures there were 5/29 redislocations after SR-PLLA fixation and 8/29 after metallic fixation. In the Garden III fractures there were 4/9 and in the Garden IV fractures 2/2 redislocations in both groups. The ability to walk and the range of movement were better after bioabsorbable fixation. CONCLUSION: Self-reinforced poly-L-lactide lag screws can be used safely to fix subcapital femoral neck fractures in Garden Stage I and II fractures and in younger patients in Garden III fractures.