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Biomedical subjects

T Pohjonen

Publications and source records attributed to T Pohjonen.

At least 37 records · Page 2Linked to original sources
PubMed1999

Comparison of self-reinforced poly-L-lactide and steel wire in fixation of sternotomy in rabbits.

BACKGROUND AND AIMS: To investigate the healing of sternotomies fixed with biodegradable self-reinforced poly-L-lactide (SR-PLLA) wire and comparing it with steel wire fixation. MATERIAL AND METHODS: Sixteen rabbits (15 Chinchilla and one New Zealand White rabbit) were operated on. Two parallel holes of 1.5 mm in diameter were drilled in the sternum at the level of the second and third rib and similar holes of 0.8 mm were drilled at the level of the third and fourth rib. A transverse sternotomy was created between both drill hole pairs. The sternotomy with larger drill holes was fixed with 1.1-mm thick SR-PLLA wire. The sternotomy between the smaller drill holes was fixed using 2.0 steel wire. The animals were sacrificed at 2, 7, 26 and 52 weeks postoperatively and specimens were taken, radiographed and studied by both light and scanning electron microscopy. RESULTS: One rabbit died at four months postoperatively as a result of gastrointestinal problems. No other complications were seen. The SR-PLLA wire was slowly degraded. There was no disturbance of bone healing. The implants were surrounded by a fibrous tissue capsule, which also contained chronic inflammatory cells. Both SR-PLLA and steel wires provided sufficient fixation security. No differences in the healing of the sternotomies were observed between SR-PLLA and steel wire fixation. CONCLUSIONS: SR-PLLA wires are biocompatible and useful for sternotomy fixation. They may be suitable for use in clinical applications.

Absorbable Implants↗
PubMed1998

Initial stability of femoral neck osteosynthesis with absorbable self-reinforced poly-L-lactide (SR-PLLA) and metallic screws: a comparative study on 21 cadavers.

The initial stability of femoral neck osteosynthesis provided by three self-reinforced poly-L-lactide (SR-PLLA) or three metallic cannulated screws was compared. A standard transverse subcapital osteotomy was created with a hand saw in 19 pairs of human cadaver femora. Two fixation methods were randomly used in each pair. Fixations were exposed to a progressive cyclic loading test to determine the deflection curves, the ultimate load-carrying capacity, and the total amount of load absorbed. One pair served as a pilot and two nonoperated pairs served as controls. The positioning of the three fixation screws, whether one screw proximally and two screws distally or vice versa, provided equal stability. Metallic fixation proved to be more stable than SR-PLLA fixation as the average maximum load-carrying capacity was 3400N for the metallic and 2600N for the SR-PLLA fixation. However, SR-PLLA screws showed sufficient fixation properties for considering clinical trials in Garden I-II femoral neck fractures in well cooperative patients.

Absorption↗
PubMed1998

Mechanical properties and strength retention of carbon fibre-reinforced liquid crystalline polymer (LCP/CF) composite: an experimental study on rabbits.

A novel composite material with ultra-high flexural strength and cortical-bone-matched elastic modulus made of liquid crystalline polymer reinforced with carbon fibres (LCP/CF) is described. Cylindrical rods of 3.2 mm diameter and 50 mm length were fabricated by a preimpregnation/pultrusion method. The initial mechanical properties of the LCP/CF rods were as follows: flexural strength 448 MPa, flexural modulus 43 GPa, shear strength 164 MPa, and interlaminar shear strength 15.3 MPa. In the in vitro study the LCP/CF rods were immersed in phosphate-buffered saline of 37 degrees C for 12, 24, and 52 weeks. In the in vivo study the LCP/CF rods were implanted into the medullary cavity of both femora and subcutaneous tissue of the New Zealand White rabbits for 12, 24, and 52 weeks. The flexural strength of the LCP/CF rods at 52 weeks was 463 MPa in saline, 467 MPa in the subcutaneous tissue and 466 MPa in the medullary cavity of the femur. The flexural modulus was 44.6, 48.9 and 46.2 GPa, respectively. The corresponding shear strength values were 160, 178 and 181 MPa. We conclude that the LCP/CF is a promising material for high-load applications and the LCP/CF rods retain their initial mechanical properties in one-year follow-up in vivo and in vitro.

Animals↗
PubMed1998

A 5-year in vitro and in vivo study of the biodegradation of polylactide plates.

PURPOSE: The purpose of this study was to investigate the long-term tissue response and duration of degradation of self-reinforced poly-L-lactide (SR-PLLA) multilayer plates in vivo. MATERIALS AND METHODS: Mandibular osteotomies in sheep were fixed with SR-PLLA multilayer plates. The animals were followed for 1, 2, 3, 4, and 5 years, after which histologic studies were performed. RESULTS: The foreign-body reaction was mainly mild, and the osteotomies were well united. After 5 years in vivo, the material was almost completely resorbed, but small particles of polymer could still be detected at the implantation site. SR-PLLA plates were also incubated in vitro for 5 years. The material degraded considerably faster in vivo than in vitro. Molecular weight, melting temperature, and crystallinity of the plates remained at a constant level after 2 years in vitro, indicating very slow degradation of the oligomeric (molecular weight [Mw], 3500 daltons), highly crystalline (heat of fusion, 70 J/g), PLLA residue solely as a result of hydrolysis. Although the plates became increasingly fragile as they degraded, they retained their macroscopic form until the end of the 5-year follow-up. Loss of mass of the plates was 52%+/-8% after 5 years of incubation in vitro. CONCLUSIONS: Although the long degradation period may seem to be a minor drawback to the use of such plates, it does not appear to affect the healing process.

Absorption↗
PubMed1998

Polylactide pin with transforming growth factor beta 1 in delayed osteotomy fixation.

The effect of an absorbable pin containing transforming growth factor beta 1 on fracture healing was studied in a rat model of delayed osteotomy fixation. Transforming growth factor beta 1 was mixed into a blend of L-lactide oligomer and a copolymer of epsilon-caprolactone and DL-lactide that was placed in the grooves of a self reinforced fracture fixation pin made of poly-LD-lactic acid copolymer. A distal femoral osteotomy was made in 54 rats and left untreated. A week later surgery was performed to fix the osteotomy with a fracture fixation pin in 48 rats. In the remaining six rats no fixation was performed. The pin that was used in the study group contained either 5 micrograms (15 rats) or 50 micrograms (15 rats) of the growth factor, while in the control group of 18 rats, an identical pin without growth factor was used. The femurs were examined radiographically, histologically, histomorphometrically, and microradiographically. Tetracycline labeling studies were used after a followup of 1, 3, and 6 weeks. Faster callus formation in the transforming growth factor beta 1 treated animals but no acceleration in the healing of the osteotomy is reported. The addition of bone growth factors to bioabsorbable fracture fixation materials may enhance bone healing.

Animals↗
PubMed1998

Consolidation of craniotomy lines after resorbable polylactide and titanium plating: a comparative experimental study in sheep.

The consolidation process of craniotomy lines in a skeletally immature large mammal was studied. A traditional narrow titanium miniplate was compared with a 0.5-mm-thick, 12-mm-wide absorbable punched self-reinforced poly-L-lactide (SR-PLLA) plate, both fixed with titanium miniscrews over bilateral parietal 2.5-mm-wide stable transosseous craniotomies on nine female sheep (16 to 20 months old). After 6, 12, 20, 52, and 104 weeks, cross-sectional histology, histomorphometry, and oxytetracycline chloride fluorescence studies were done to compare the healing process of the craniotomy lines and to study the biocompatibility and the degradation process of the SR-PLLA plate. The consolidation pattern supported the principle of guided tissue regeneration: under the wide, resorbable plate osseous bridging proceeded evenly throughout the line, whereas titanium plating led to bulky, uneven growth in the bone margins. All SR-PLLA-plated osteotomy lines had healed completely by 20 weeks, whereas none of the titanium-plated lines had consolidated during a follow-up of 1 year. The nonossified gaps were filled with dense connective tissue. Histomorphometric analysis showed that osseous bridging proceeded significantly faster on the resorbable plate side compared with the titanium side (p < 0.001). The osteoid surface fraction over the total trabecular surface was highest at 6 weeks, being 63 percent on the SR-PLLA side and only 36 percent on the titanium side. The oxytetracycline chloride fluorescence studies confirmed these findings. After 52 weeks, there was no osteoid or oxytetracycline chloride fluorescence left as a sign of terminated ossification, even in the nonconsolidated titanium sides. Microscopic cracking of the plate was evident at 12 to 20 weeks, and the first signs of active resorption were present at 52 weeks. After 2 years, the plate had disappeared and tiny polylactide particles were being actively reabsorbed. The biocompatibility of SR-PLLA and titanium was good, and no adverse cellular reactions to these materials were noted, except a clinical foreign body reaction caused by loosened titanium miniscrews. A densely punched, 0.5-mm-thick self-reinforced PLLA plate seems to retain its integrity for a sufficiently long time to complete osseous healing of a 2.5-mm-wide craniotomy line in the sheep calvarial area. A thin, wide fixation plate enables superior healing, especially in osseous defects. The degradation process of the SR-PLLA plate begins within 1 year and is far advanced after 2 years. By using absorbable SR-PLLA fixation plates instead of metallic plates, a subsequent operation for the removal of the implants can be avoided. SR-PLLA devices could thus be a potential additive or even alternative to metallic implants in craniofacial surgery.

Animals↗
PubMed1998

Bioabsorbable polymers: materials technology and surgical applications.

Biostable and bioabsorbable biomaterials are used to manufacture implants for supporting, replacement, augmentation and guiding of growth of tissues. Bioabsorbable implants are a better choice for applications where only the temporary presence of the implant is needed. Because of bioabsorption of such implants, there is no need for a removal operation after healing of the tissue and the risks of implant related, long-term complications are eliminated or strongly reduced. Reinforcing of bioabsorbable materials is necessary in order to develop strong and safe, small implants for fixation of bone fractures and connective tissue damage. Self-reinforced bioabsorbable polymeric implants have been used so far extensively in the treatment of traumas of the musculoskeletal system.

Biocompatible Materials↗
PubMed1998

Intraosseous plating: a new method for biodegradable osteofixation in craniofacial surgery.

Biodegradable miniplates and screws offer special possibilities for surgical techniques because the removal operation is avoided. In areas beneath thin skin, intraosseous plating could be preferable to avoid palpability and transient swelling during resorption. The tissue reaction to a 0.5-mm-thick self-reinforced poly-L-lactide (SR-PLLA) plate fixed with an SR-PLLA miniscrew was studied histologically and histomorphometrically after implantation into the calvarium of six young sheep. After follow-up periods of 6, 20, and 52 weeks, no signs of adverse tissue reaction such as clinically manifest foreign body reaction or histologically manifest osteolysis were noted. By 52 weeks the implants were largely in direct contact with remodeled, dense bone tissue. No signs of fragmentation or resorption were noted in the intraosseous parts of the implants, whereas the screw head had been fragmented and was undergoing resorption at 52 weeks. The screw head is unnecessary in this plating method and could have been removed with a hot wire loop. The excellent biocompatibility of the mechanically strong, resorbable SR-PLLA plate with miniscrew fixation provides a possibility for intraosseous plating in less loaded craniofacial areas, especially in areas with very thin soft-tissue coverage.

Absorption↗
PubMed1997

Comparison of the fixation of subcapital femoral neck osteotomies with absorbable self-reinforced poly-L-lactide lag-screws or metallic screws in sheep.

Seven subcapital femoral osteotomies of adult sheep were each fixed with two absorbable self-reinforced poly-L-lactide lag-screws, and seven other osteotomies were each fixed with two metallic cancellous bone screws. At 3 and 12 weeks, radiographs were taken and callus formation, displacement, and union were evaluated. At 12 weeks, the animals were killed and strength measurements were carried out. According to the radiographs, union was achieved in six of seven osteotomies in both groups, while after 3 weeks one fixation in both the group treated with absorbable screws and the group treated with metallic screws had failed. There were no statistical differences between the groups with respect to callus formation or displacement. Regarding the strength of the osteotomized bones, at 12 weeks there were no statistically significant differences in the load-carrying capacity between the bones fixed with self-reinforced poly-L-lactide screws and those fixed with metallic screws. These results showed that self-reinforced poly-L-lactide screws, which have been used successfully in fractures and osteotomies in cancellous bone, are strong enough to support this more demanding fixation of weight-bearing bones.

Animals↗
PubMed1997

Fixation of osteotomies of the distal femur with absorbable, self-reinforced, poly-L-lactide plates. An experimental study on rabbits.

Osteotomies of the distal femur were fixed with two self-reinforced poly-L-lactic acid (SR-PLLA) plates and metallic screws placed through the plates on each side of the femur in 23 adult rabbits. They were followed-up after 3, 6, 12 and 24 weeks. After killing, radiological, histological, microradiographic and oxytetracycline fluorescence studies were performed. Except for one histologically confirmed fibrotic non-union at 24 weeks, the osteotomies healed, including one involving a rabbit which had suffered an ipsilateral femoral shaft fracture of unknown cause. No malformations were observed, and the macroscopically detected swelling was a normal postoperative reaction. This study showed that SR-PLLA plates implanted on both sides on the bone are suitable for the fixation of weight-bearing cancellous bone osteotomies in rabbits.

Absorption↗
PubMed1997

Mandibular osteotomy fixed with biodegradable plates and screws: an animal study.

The objective of the study was to evaluate the use of a totally biodegradable fixation device in the fixation of mandibular osteotomy in sheep. Mandibular unilateral body osteotomies were fixed with biodegradable self-reinforced poly-L-lactide (SR-PLLA) multi-layer plates and screws in nine sheep. The unoperated sides acted as control. The follow-up times were 6, 12 and 24 weeks, after which radiological, mechanical and histological studies were carried out. An analysis of the implanted material was also carried out. The results showed that the SR-PLLA plates and screws were strong enough to fix the osteotomy and that the osteotomies healed mainly with callus formation. Therefore we conclude that SR-PLLA multi-layer plates and screws can be used together successfully in the fixation of mandibular osteotomies without maxillomandibular fixation. However, before they can be used in humans, the size of the plate and screws should be decreased.

Animals↗
PubMed1997

Strength retention of self-reinforced poly-L-lactide screws. A comparison of compression moulded and machine cut screws.

The effect of the manufacturing method on the strength retention of self-reinforced poly-L-lactide (SR-PLLA) screws was studied in vitro and in vivo from 3 up to at least 15 weeks. SR-PLLA screws were manufactured from axially oriented SR-PLLA billets by the conventional compression moulding process and an in-house developed machine cutting technique. New machined SR-PLLA screws (thread diameters 4.5 mm and 3.5 mm) were significantly stronger than older compression moulded SR-PLLA screws (4.5 mm and 3.5 mm) in bending and torque strength tests but significantly weaker in shear strength tests. In pull out tests there were not significant strength differences between the screws. Mechanical analysis and molecular weight measurements confirmed earlier observations that SR-PLLA degrades faster in vivo than in vitro. These results suggest that the new screws could be suitable for clinical use.

Journal Article↗
PubMed1996

Characteristics of poly(L-)lactic acid suture applied to fascial closure in rats.

A new poly(L-)lactic acid (PLLA) thread was tested by applying it in fascial closures of male Wistar rats. The tissue reactions around the thread and in the fascial union, and the changes on the surface and the mechanical properties of the thread were evaluated at 1, 3, 6, 12, 28, and 52 weeks following surgery. Histologically, the extension of the general inflammatory reaction and the number of the different cell types did not markedly change during the 52-week follow-up period. The surface of the thread was intact up to 28 weeks when examined with the scanning electron microscope. At 52 weeks no thread was found. The breaking force and the stretching of the incubated PLLA thread was reduced about 20% during the first 2 weeks and it remained constant up to 6 weeks. The in vivo testing of the fascial strips closed with the PLLA thread retained their resistance against the breaking force, nearly comparable to that of the intact control fascial strips. It can be concluded that the PLLA thread is a suitable suture for wounds that require healing time of up to 28 weeks and thus need good support from the suture.

Abdominal Muscles↗
PubMed1996

Intraosseous plating with absorbable self-reinforced poly-L-lactide plates in the fixation of distal femoral osteotomies on rabbits.

Osteotomies of distal femur were fixed by intraosseous self-reinforced poly-L-lactic acid (SR-PLLA) plates in 29 adult rabbits. The follow-up times were from 3 to 24 weeks. After sacrifice, radiological, histological, microradiographic, and oxytetracycline fluorescence studies were performed. Although radiographically no redisplacements were found, in 12 weeks two fixations were broken and a fibrotic nonunion was observed in one case. At 24 weeks full bone consolidation was seen in all except one osteotomy. No foreign-body reactions were observed. The present article is the first report on successful application of absorbable plates for intraosseous fixation of weight-bearing bone osteotomies. The present investigation demonstrated that the SR-PLLA plates were suitable for the fixation of cancellous bone osteotomies in rabbits.

Animals↗
PubMed1996

Strength of the fixation of patellar tendon bone grafts using a totally absorbable self-reinforced poly-L-lactide expansion plug and screw. An experimental study in a bovine cadaver.

In a bovine cadaver study, bone-tendon-bone graft fixation strength with different graft geometry and fixation devices was measured to evaluate the fixation strength of totally absorbable implants: a 6.0-mm expansion plug and 6.3-mm screw both made of self-reinforced polylactide (SR-PLLA). Comparison was made with 6.5-mm AO cancellous screw. Maximum tensile force to dislodge the bone plug from the bone tunnel was recorded. First, two preliminary tests were performed. In the first test, triangular bone plugs were used (9-mm diameter). The direction of the pull force was parallel to the bone tunnel. The maximum tensile forces were 786 N in femoral insertions and 625 N in tibial insertions, mean. After this, we evaluated the influence of change in the pullout direction. In the second test, a circular bone plug was used with no fixation but the direction of the pull force was parallel to the tibial or femoral axis and the bone plug (10-mm diameter) was in a 30 degrees to 40 degrees angle to the direction of the pull force and it was compressed to the tunnel (9-mm diameter). The maximum tensile forces were 783 N in femoral insertions and 695 N in tibial insertions, mean. In the final third test, we used a curved saw in harvesting the graft. This made a half-circular bone block with a diameter of 12 mm. The maximum tensile force to dislodge the bone plug from the bone tunnel was recorded and the pull force was in a 30 degrees to 40 degrees angle to the tunnel. The results were evaluated with Student's t-test and Mann-Whitney U-test. With the AO screw, the maximum tensile force to dislodge the bone plug from the bone tunnel was 2,113 +/- 407 N (mean +/- standard deviation) and it was better than the fixation strength of the SR-PLLA expansion plug, 1,379 +/- 328 N (P = .009, t-test) and better than the fixation strength of SR-PLLA screw, 1,454 +/- 230 N (P = .007, t-test). However, the maximum tensile force of both SR-PLLA implants in all measurements in the third test were above 1,100 N and it seems that the initial strength of totally absorbable implants is enough for the clinical use.

Animals↗
PubMed1995

Fixation strength of a biodegradable screw in anterior cruciate ligament reconstruction.

We compared the strength of fixation of a biodegradable screw with that of two metal screws in a bone-patellar-tendon-bone (BPTB) graft in the bovine knee. We used 33 fresh BPTB specimens with a circular tibial bone plug of 9 mm in diameter which were anchored in a tibial metaphyseal bone tunnel with either an interference screw (n = 11), an AO cancellous screw (n = 11) or a fibrillated, self-reinforced biodegradable poly-L-lactide screw (n = 11). The mean force to failure (+/- SD) in the three groups was 1358 +/- 348 N, 1081 +/- 331 N and 1211 +/- 362 N, respectively. There was no significant difference in the groups with regard to the linear load or the elastic moduli of the fixation. We conclude that the biodegradable screw is as good as either of the two metal screws in the fixation of a BPTB graft in the bovine knee and can be recommended for ACL reconstruction using this type of graft.

Analysis of Variance↗