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PubMed2007

Comparison of the stability of various internal fixators used in the treatment of osteochondritis dissecans--a mechanical model.

The purpose of this study was to determine what characteristics of fixation devices used in the treatment of osteochondritis dissecans (OCD) contribute to improved stability to resist shear loading. An OCD model was designed using rigid polyurethane foam. Each specimen consisted of two components, an osteochondral fragment and a corresponding defect. A total of 40 specimens were prepared and assigned to one of four groups: control (no extrinsic stabilizer); two 2-mm-diameter Kirschner wires (K-wires), 40 mm in length; one threaded washer and a 28-mm screw; and one threaded washer and a 38 mm screw. Each specimen was mounted onto an Iosipescu shear test fixture and subjected to shear loads at a pseudo-static displacement rate of 0.075 mm/s. All groups demonstrated some stability; controls were significantly less stable than all other groups. The group with the threaded washer and 38-mm screw demonstrated the greatest stability (p < 0.001), and no difference was noted between the K-wire and 28-mm screw groups. These results suggest that, in this OCD model, friction conferred some intrinsic stability to resist loads in shear. However, stability was improved with the use of long implants that compressed the fragments together.

Arthroplasty, Replacement↗
PubMed2005

[Internal fixation of sacroiliac joint disruption].

OBJECTIVE: Stabilization of the completely disrupted sacroiliac (SI) joint with two three-hole DC plates. INDICATIONS: Definitive treatment of the posterior pelvic ring in type C injuries (AO classification) with complete SI joint disruption, transiliac or transsacral fracture-dislocation of the SI joint with an insignificant, small fragment. Emergency stabilization of the SI joint following a laparotomy. CONTRAINDICATIONS: Poor general health of patient. Local soft-tissue damage. Rotationally unstable type B pelvic injuries. SURGICAL TECHNIQUE: Supine. Anterolateral approach to the iliac crest. Subperiosteal detachment of the iliac muscle. Debridement of the SI joint and reduction under direct vision. Stabilization of the SI joint with two three-hole DC plates inserted at an angle of 70-90 degrees. POSTOPERATIVE MANAGEMENT: Partial weight bearing on the injured side at 15 kg for 8-12 weeks with two forearm crutches. Implant removal 6-12 months after injury provided ankylosis has not occurred. RESULTS: In 27 patients with disruption of the SI joint consistent with a type C injury, the average displacement of the affected SI joint was 16 mm (8-30 mm). Complications relating to the osteosynthesis occurred as a deep infection in one patient, originating from a concomitant acetabular osteosynthesis. Iatrogenic nerve damage (lateral femoral cutaneous nerve) was present in two patients. 16 patients were followed up using radiologic techniques (pelvic, possibly inlet and outlet views, computed tomography). 13 SI joints healed in anatomic position. The malalignments observed were relatively slight (2-4 mm). There was no secondary implant failure. Almost all patients (n = 14) showed posttraumatic changes of the SI joint (osteophytes, arthrosis, ankylosis).

Adolescent↗
PubMed1994

Effect of surface plasma treatment on the chemical, physical, morphological, and mechanical properties of totally absorbable bone internal fixation devices.

The purpose of this work was threefold: to enhance the adhesion between the reinforced absorbable calcium phosphate (CaP) fibers and the absorbable polyglycolide acid (PGA) matrix, to improve the hydrolytic degradation of the CaP fibers, and preliminarily to evaluate the cytotoxicity of the plasma treated surface of CaP fibers. A CH4 plasma treatment was used to achieve these goals. The microbond method was used to evaluate the effects of the plasma treatment on the interfacial shear strength between the PGA matrix and CaP fibers. The treatment increased the mean interfacial shear strength of the CaP/PGA composite system by 30%. AFM data showed that CH4-treated CaP fibers had considerable microscopic surface roughness, which facilitated mechanical interlocking between the reinforced CaP fibers and PGA matrix. The untreated and plasma-treated fibers were also subjected to in vitro hydrolytic degradation in a phosphate buffer solution of pH 7.44 at 37 degrees C for up to 15 h. CH4 plasma treatment resulted in a considerable lower polar term of the surface energy and a significantly higher disperse term in water media. This change in the proportion of surface energy terms may reduce the capillary wicking phenomena of water through the CaP fiber/PGA matrix interface. The CaP fiber dissolution studies revealed that both CH4 and Parylene plasma polymer coatings appeared to reduce the solubility of CaP fibers, and that the magnitude of reduction was higher in an acidic than a physiologic pH environment. A preliminary cytotoxicity test revealed that both CH4 and Parylene plasma-treated CaP fibers were noncytotoxic. Additional research should be done to determine the optimum plasma conditions and the possible use of other plasma gases to improve the interfacial shear stress of the composite and the dissolution properties of CaP fibers.

1-Propanol↗
PubMed1996

Sterility, mechanical properties, and molecular stability of polylactide internal-fixation devices treated with low-temperature plasmas.

The effect of low-temperature plasma on sterility, molecular, mechanical, and crystalline properties of poly (L-lactide), poly (L/D-lactide) and poly (L/DL-lactide) was investigated. Polymers were treated for 15 and 30 min at 100 W with nitrogen, argon, oxygen, and carbon dioxide plasma. All polymers treated with oxygen or carbon dioxide plasma were rendered sterile after 15 min of treatment. Only 70% of the samples treated under similar conditions with nitrogen or argon plasma were sterile. Extension of the exposure time to 30 min and increasing power to 200 W did not improve sterilization efficiency. Plasma sterilization, under the conditions used, caused no significant decrease or increase in overall molecular weight or polydispersity of the polylactides used. In most instances the effect of plasma sterilization was to slightly increase the overall molecular weight of the polymers studied. Treatment with argon plasma led to a more consistent increase in molecular weight than did treatment with nitrogen, oxygen, or carbon dioxide. Analysis of the surface (skin) of a poly(L-lactide) injection-molded rod following plasma sterilization indicated an increase in molecular weight as related to the interior (core) of the rod. Comparison of Mark-Houwink plots for the surface and interior of poly(L-lactide) injection-molded rods following plasma sterilization indicated an increase in chain branching for the surface relative to the interior of the rod. Generally the highly crystalline poly(L-lactide) was less susceptible to change upon plasma treatment than was the less crystalline poly(L/D-lactide) and poly(L/DL-lactide). The mechanical properties (shear strength, bending strength, and moduli) of the polylactides were not affected by plasma treatment. The overall melting temperature and the heat of melting of polylactides studied were not affected by plasma treatment. The melting temperature of the skin of the samples was about 1 degree C higher than the melting temperature of the core due to the chain orientation upon injection-molding. Plasma treatment of the polylactides reduced the melting temperature of the skin by 3 degrees C to 5 degrees C due to the crosslinking or branching at the surface layer.

Analysis of Variance↗
PubMed2003

Finite element analysis of the initial stability of ankle arthrodesis with internal fixation: flat cut versus intact joint contours.

OBJECTIVE: Qualitative comparison of the initial stability provided by two joint preparation techniques and various screw configurations in ankle arthrodesis, using the finite element method.Design. A three-dimensional model of a healthy ankle was developed from computed tomography images. Two groups of models were built, one with the joint contours resected to produce flat surfaces, and the second with the joint contours preserved. In each case, a variety of screw orientations were examined. BACKGROUND: Despite the improved results of ankle arthrodesis, failure rates due to non-union are still reported. The initial stability of the arthrodesis construct seems important in the final outcome of the fusion. METHODS: Non-linear contact finite element analyses were performed in the arthrodesis constructs subjected to internal/external torsion and dorsiflexion. Micromotions at the bone-to-bone interface were calculated for frictionless and Coulomb friction contact, and compared for the two joint preparation techniques and screw configurations. RESULTS: Overall lower peak micromotions were predicted when preserving the joint contours both in torsion and dorsiflexion. For both preparation techniques, the lowest micromotions tended to occur with the screws inserted at 30 degrees with respect to the long axis of the tibia, crossing above the fusion site. Inclusion of friction in the models caused a general decrease on the magnitude of the micromotions as compared to the frictionless case, but did not affect the ranking of the models. CONCLUSIONS: The finite element method can be used as a qualitative tool to study the initial stability of ankle arthrodesis, overcoming the difficulties of measuring bone-to-bone interface micromotions experimentally. Better initial stability was predicted for ankle arthrodesis when the joint contours were preserved rather than resected. Crossing the screws above the fusion site at a steeper angle also tended to increase the stability at the fusion site. RELEVANCE: Finite element analyses can help during the pre-operative planning of ankle arthrodesis. When bone density is not compromised, preserving the joint contour and inserting the screws at less than 45 degrees to the long axis of the tibia, crossing over the arthrodesis site, may offer better initial stability.

Ankle Joint↗
PubMed2000

Response of articular cartilage and subchondral bone to internal fixation devices made of poly-L-lactide: a histomorphometric and microradiographic study on rabbits.

To study the tissue response of articular cartilage and subchondral bone to biodegradable fixation devices, pins and rods made of poly-L-lactide with a fibers-in-matrix texture were implanted through the articular surface of the intercondylar portion of the distal rabbit femur. The initial raw material viscosity average molecular weight of the polymer was 660,000. One pin or screw was implanted per animal. The pins were cylindrical and measured 4.5 mm in transverse diameter. The screws had a core diameter of 3.2 mm and an outer diameter of 4.5 mm. At insertion, the implants were cut flush with the articular surface. After follow-up times of 36 and 48 weeks, the specimens were examined histomorphometrically and microradiographically. The intact contralateral femur served as a control for comparison. No signs of erosion or degradation of the polymer could be seen in the specimens. A brim of reparative tissue was formed at the entrance of the implant channel. The width of the reparative tissue from the tissue-implant boundary towards the center of the entrance hole varied greatly between the specimens, from 30 to 950 microm. In most specimens this bridging tissue consisted of undifferentiated mesenchymal tissue. Only two out of 24 specimens showed a near-normal metachromatic toluidine-blue staining of the matrix. Degenerative chondrocyte clustering occurred in the pre-existing cartilage within a 400 microm wide zone from the tissue-implant interface into the recipient tissues. Some new-bone formation was seen to envelop the implant in all specimens, but the fractional osteoid formation surface of the trabeculae showed a value significantly higher than that of the intact control side only in the screw-implanted 36-week specimens. Because of the long degradation time of poly-L-lactide, the restoration process of the articular cartilage was slow, and with regard to the quality and quantity of the reparative tissue, very variable. Large implants made of poly-L-lactide may not be suitable for insertion through intra-articular surfaces.

Animals↗
PubMed1996

Bone growth after osteotomy and internal fixation in young rabbits.

The factors leading to overgrowth following fixation of long-bone fractures in children have never been clearly understood. The amount of trauma and the type of fixation may play a role. A rabbit model was used to investigate the influence of a femoral osteotomy and plate fixation on subsequent growth. Unilateral midshaft femoral osteotomy was performed in 6-week-old rabbits, and the bone was fixed internally with a plate and screws. End-to-end reduction was performed either at full length or with a segment removed. Bone length measurements at the end of growth revealed no significant difference in growth between the control femur and the femur that had undergone osteotomy and plate fixation. Shortened plated femora also showed no tendency to grow longer or faster than full-length fixed femora or controls. Interestingly, in the ipsilateral tibia a small but statistically significant length increase, equivalent to about 2% increase in additional growth, was observed, whereas technetium-99 methylene diphosphonate uptake was reduced in the tibial physes. In the context of the rabbit experimental model chosen, these results suggest that significant femoral over-growth does not occur following femoral osteotomy and plate fixation.

Animals↗
PubMed1997

The unstable iliac fracture: a biomechanical evaluation of internal fixation.

Neither plating nor lag screw fixation of a displaced iliac wing fracture as part of an unstable pelvic ring disruption has been studied biomechanically. The purpose of this study was to compare the stability of various combinations of fixation, specifically contrasting lag screws placed between the tables of the ilium with plating in different locations across the fracture line. Various combinations of these fixation implants were evaluated for an unstable iliac fracture. A longitudinal iliac fracture was created in each of six hemi-pelvic specimens prior to testing. Compressive force, up to 500 N or to the magnitude necessary to displace the fracture 2 mm, was applied to the fracture line through the hemi-pelvis for each of the plate and lag screw combinations tested. There was no statistical difference between any of the implants or combinations tested. A single 3.5-mm reconstruction (cephalad) plate placed along the cephalad internal aspect of the iliac crest provided the least stability allowing 2 mm of displacement with a mean load of 80 N. The two combinations of fixation that required the greatest loads for 2 mm of displacement were a single 3.5-mm lag (cephalad) screw inserted into the iliac crest between the tables of the ilium coupled with either a 3.5-mm reconstruction (brim) plate placed along the internal aspect of the inferior iliac fossa at the pelvic brim (239 N) or a 4.5-mm lag (brim) screw between the inner and outer tables at the inferior aspect of the fracture just above the greater sciatic notch (225 N).

Aged↗
PubMed1988

Early temporary porosis of bone induced by internal fixation implants. A reaction to necrosis, not to stress protection?

Stabilization of the fracture using implants requires contact surfaces between implant and bone. Such contact has been observed to induce bone porosis first seen at one month after surgery. Bone loss in the vicinity of implants has hitherto been explained as being induced by mechanical unloading of the bone (stress protection). Experiments in sheep, dogs, and rabbits combining intravital staining of blood circulation and polychrome fluorescent labeling of bone remodeling leads to the conclusion that early bone porosis in the vicinity of the implants is the result of internal remodeling of cortical bone and is induced by necrosis rather than by unloading. This theory is favored by the evidence that (1) the bone porosis is of a temporary nature, an intermediate stage in internal bone remodeling; (2) the pattern of the remodeling zone is closely related to that of the disturbed circulation, and not to that of unloading; (3) plastic plates may produce more porosis than steel plates; and (4) improved blood circulation using modified plates resulted in reduced porosis. The clinical relevance of these findings is related first to the temporary weakening of the bone, and second to the possibility of sequestration. Sequestration may be the result of intensified remodeling activity in the presence of inflammation or infection.

Animals↗
PubMed2000

Histomorphometric study on high-strength hydroxyapatite/poly(L-lactide) composite rods for internal fixation of bone fractures.

The purpose of this study was to investigate the bone-implant interface of high-strength hydroxyapatite (HA)/poly(L-lactide) (PLLA) composite rods. As reinforcing particles, two types of HA particles-calcined HA (c-HA) and uncalcined HA (u-HA)-were applied to allow comparison of their suitability as bioactive fillers. Four types of composites (c-HA30, c-HA40, u-HA30, and u-HA40), which contained 30 or 40% by weight of each HA particle, were used. Unfilled PLLA rods were used as controls. A hole was drilled in the distal femora of 50 rabbits, and a composite or unfilled PLLA rod was implanted in a press-fit manner. Two, 4, 8, and 25 weeks after implantation, the samples were examined histologically by light microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). An image analyzer was used for histomorphometric analysis of the bone-implant interface. An affinity index was calculated for each material; this was the length of bone directly apposed to the rods expressed as a percentage of the total length of the rod surface. In all the composites, histologic examination showed new bone formation at 2 weeks after implantation. The bone gradually grew along the composite surface. SEM showed direct bone contact with the composites without intervening fibrous tissue. During follow-up, the affinity indices of all the composite rods were significantly higher than those of the unfilled PLLA rods (p < 0.01; two-way ANOVA). The maximum affinity index (41%) was attained at 4 weeks in c-HA40 rods. In contrast, little bone contact was seen in unfilled PLLA rods. The only significant difference in affinity indices among the composites was that c-HA40 had a higher affinity index than u-HA40 (p < 0.05 at 4 weeks). No disintegration of rods or polymer debris, which could elicit inflammatory tissue reactions, was observed even at 25 weeks. Our results indicate that osteoconductive bone formation on composites could enhance the stability between bone and implant in fracture repair.

Absorbable Implants↗
PubMed1985

A new type of intramedullary nail for the internal fixation of subtrochanteric fractures of the femur.

The Author has developed a modified intramedullary nail for the stabilisation of fractures in the subtrochanteric and proximal one-third of the femur. Due to its three tapered fins the rod fits well into the funnel-like medullary cavity of the proximal femur preventing varus or rotational displacement of the proximal fragment. This method has been applied in 16 cases. Its particular advantages are the chance to perform the operation closed, a short operating time and period in hospital, early weight bearing and a simple surgical technique without the need for special instrumentation, requiring little radiographic exposure during surgery. The ideal and relative indications for the application of the technique are discussed. Biomechanical tests have confirmed that the finned medullary nail is the most stable method of fixation of the fractures when compared with other alternative devices.

Adult↗
PubMed1975

[Internal fixation with soft-tissue lesions: fracture with nerve damage (author's transl)].

Typical nerve damage after fractures due to the topographical proximity of the nerves to the bones, are shown and therapeutic principles are discussed. Primary traumatic lesions are differentiated from so-called "creeping paralysis". The methods of choice are neurolyses, nerve suture or transplantation, each at the appropriate time. Evaluation of 83 of the 128 Patients undergoing microsurgical operations on the nerves in recent years is presented after re-exmination by independent neurologists. One-third showed definite signs of regeneration, more than one-third had good functional results, and poor results were recarded for 25 percent of the patients.

Fractures, Bone↗
PubMed1999

Rotational acetabular osteotomy using biodegradable internal fixation.

We used biodegradable poly-L-lactide screws in rotational acetabular osteotomy in 41 hips of 41 patients, and studied the complications after an average follow-up of 4.9 years (range 1.0-7.7 years). There were 39 females and 2 males, their average age at the time of the operation was 32 years (range 12-55 years). A small subcutaneous abscess appeared around the non-absorbable sutures in 2 patients after surgery. There was 1 case of thrombophlebitis and 1 of local dermatitis. The small subcutaneous abscess resolved after the removal of the suture material in the 2 cases, and the thrombophlebitis resolved with aspirin. The local dermatitis persisted but was cured by local steroid therapy over 5.8 years. The incidence of local dermatitis after the use of biodegradable implants should be further investigated.

Absorbable Implants↗