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At least 271 records · Page 15Linked to original sources
PubMed1993

Quantitative analysis of bone reactions to relative motions at implant-bone interfaces.

Connective soft tissues at the interface between implants and bone, such as in human joint replacements, can endanger the stability of the implant fixation. The potential of an implant to generate interface bone resorption and form soft tissue depends on many variables, including mechanical ones. These mechanical factors can be expressed in terms of relative motions between bone and implant at the interface or deformation of the interfacial material. The purpose of this investigation was to determine if interface debonding and subsequent relative interface motions can be responsible for interface degradation and soft tissue interposition as seen in experiments and clinical results. A finite element computer program was augmented with a mathematical description of interface debonding, dependent on interface stress criteria, and soft tissue interface interposition, dependent on relative interface motions. Three simplified models of orthopaedic implants were constructed: a cortical bone screw for fracture fixation plates, a femoral resurfacing prosthesis and a straight stem model, cemented in a bone. The predicted computer configurations were compared with clinical observations. The computer results showed how interface disruption and fibrous tissue interposition interrelate and possibly enhance each other, whereby a progressive development of the soft tissue layer can occur. Around the cortical bone screw, the predicted resorption patterns were relatively large directly under the screw head and showed a pivot point in the opposite cortex. The resurfacing cup model predicted some fibrous tissue formation under the medial and lateral cup rim, whereby the medial layer developed first because of higher initial interface stresses. The straight stem model predicted initial interface failure at the proximal parts. After proximal resorption and fibrous tissue interposition, the medial interface was completely disrupted and developed an interface layer. The distal and mid lateral side maintained within the strength criterion. Although the applied models were relatively simple, the results showed reasonable qualitative agreement with resorption patterns found in clinical studies concerning bone screws and the resurfacing cup. The hypothesis that interface debonding and subsequent relative (micro)motions could be responsible for bone resorption and fibrous tissue propagation is thereby sustained by the results.

Biomechanical Phenomena↗
PubMed1995

High-impact poly(L/D-lactide) for fracture fixation: in vitro degradation and animal pilot study.

The impact strength of amorphous lactide copolymers can be significantly improved by blending with biodegradable rubbers. Rubber toughening of amorphous poly(85L/15D -lactide) with the copolymer poly (50/50-trimethylenecarbonate-co-epsilon-caprolactone) results in a high-impact polymer (PDLLA/P(TMC-CL)). In vitro, the PDLLA/P(TMC-CL) blend retained its tensile and impact strength for a long period of time. Up to 45 weeks, the amount of water absorbed by the blend remained very low and no significant mass loss was observed. To test the suitability for fracture fixation, in a dog study mandibular fractures were fixated with PDLLA/P(TMC-CL) bone plates and screws. Bone healing was uneventful without premature failure of the implants. Although long-term degradation studies have to be carried out, PDLLA/P(TMC-CL) seems to be promising for application in fracture fixation.

Animals↗
PubMed1992

Translamino-pedicular screw fixation with bone grafting for symptomatic isthmic lumbar spondylolysis.

Anterior or posterolateral spondylodesis has been reported and used widely as a surgical treatment for lumbar spondylolysis or spondylolisthesis. Although spinal fusion is necessary when there is extensive vertebral slippage or spinal instability, the direct repair of the defect is thought to be anatomical, logical, and less invasive as a surgical treatment for symptomatic lumbar spondylolysis or a minimal degree of spondylolisthesis. This operation, with a few modifications, has been performed since 1985 in our clinic. The results, using Henderson's criteria, were excellent in 64.5% and good in 25.8% of the patients thus treated. For younger patients with symptomatic lumbar spondylolysis, direct repair of the defect using translamino-pedicular instrumentation with bone grafting is recommended, as degenerative changes have not usually occurred in the vertebral discs.

Adolescent↗
PubMed2003

Axial compression generated by cortical and cancellous lag screws in the equine distal phalanx.

Lag screw fixation using single 4.5 mm cortical bone screws is a recommended technique for repair of mid-sagittal plane fractures of the distal phalanx in adult horses. However, implant infection and technical difficulties in obtaining adequate interfragmentary compression have made this surgical procedure somewhat controversial. We hypothesized that use of larger diameter screws would result in increased axial compression and improved stability of this fracture. Paired distal phalanges from the forelimbs of 10 adult horses were collected at necropsy and divided in half in the midsagittal plane. Using a randomized block study design, four types of bone screws (4.5 mm cortical, 5.5 mm cortical, 6.5 mm cancellous pre-tapped, and 6.5 mm cancellous non-tapped) were inserted to a depth of 15 mm. During screw insertion, the axial force generated under the screw head was measured with a load washer containing a piezoelectric force transducer, while torque of insertion was recorded with a torsional testing machine. The 6.5mm screw inserted after pre-tapping generated significantly greater axial force (2781 N) than the 4.5 mm (1522 N), 5.5 mm (2073 N) or 6.5 mm non-tapped (2295 N) screws. The relationship between maximal applied torque and axial force generated was linear for each screw type. Each unit of torque applied during insertion of cortical screws resulted in a greater increase in axial compression, as compared to cancellous screws. These data suggest that use of larger diameter screws would result in improved interfragmentary compression of distal phalangeal fractures.

Animals↗
PubMed1975

[Torque load and types of fractures of threaded holes in cortical bone by lag screw. Mechanic and histological studies (author's transl)].

For the better understanding of fracture fixation by means of screws the torque load and types of fractures from threaded screw holes in cortical bone were studied. The experiments were performed on sheep tibia and femora in vitro and in vivo. We applied the 4.5 mm cortical bone screw (AISF) as lag screw. The screw was threaded in until total destruction of the thread occurred. The process of torque load was registered as a torque-angle of twist curve with 4 typical parts. Histologically in most cases shear fractures with different geometry occurred. In some cases we found conical geometric, and in others cylindrical geometric fragments in the threaded screw holes. The value of the torque at which destruction of a threaded hole occurs is a linear function of the thickness of the cortical bone. The gradient of this linear function is 6.6 kpcm/mm. In practical case, the insertional torque may be estimated by multiplying the cortical bone thickness in mm (if known) by a factor 4.

Animals↗
PubMed2004

Graft healing in a bone tunnel: bone-attached graft with screw fixation versus bone-free graft with extra-articular suture fixation.

The purpose of this study was to clarify differences in tendon graft-to-bone tunnel healing between bone-attached tendon grafts with interference-screw fixation and bone-free tendon grafts with extra-articular suture fixation. In 42 Japanese White rabbits, anterior half replacement of the medial collateral ligament was performed using half of the ipsilateral patellar tendon. At the femoral attachment, the bone-plug-attached graft was fixed with an interference screw (group A). The bone-plug-free graft was fixed by the extra-articular suture fixation technique with sutures tied over a button (group B). Biomechanical and histological evaluations were performed at 2, 4 and 8 weeks postoperatively. In biomechanical evaluation, at 2 or 4 weeks 27 of 28 specimens (96%) were pulled out from the femoral tunnel, while one 4-week specimen and all four 8-week specimens failed at the graft's mid-substance. At 2 weeks, the maximum failure load was 25+/-10 N and 24+/-6 N for group A and group B respectively (mean+/-SD). At 4 weeks, the maximum failure load was 42+/-17 N and 35+/-15 N respectively. There were no significant differences in maximum pullout failure load between the groups at 2 or 4 weeks postoperatively. (P=0.887 at 2 weeks and P=0.339 at 4 weeks using ANOVA measurement). Histologically, the bone-attached grafts showed partial bone-to-bone union at the graft-bone tunnel interface at 4 weeks, and complete bony union at 8 weeks. The bone-free grafts exhibited newly formed Sharpey-like collagen fibers at 4 weeks, and strong connection by mature granulation tissue at 8 weeks. Graft-to-bone tunnel healing of bone-attached graft with screw fixation and bone-free graft with extra-articular suture fixation are comparable in terms of biomechanical evaluation during the early postoperative periods.

Animals↗
PubMed1988

Regional alterations in long bone produced by internal fixation devices. Part I. 85Sr clearance.

We examined the effect of rigid plate application on the radiostrontium clearance of the intact canine femur at 6 months. We examined each of the component surgical steps. We calculated the clearance both for the whole bone and for each of the five transverse sections of the whole bone. Screw application, but not drilling, increased the clearance in the segment about the screw holes. Plate application produced an increase in the segment beneath the plate as well as around the screws and in the whole bone. These changes are accomplished not only by an absolute increase in clearance to the middle three segments, but by a relative diminution in clearance by the most proximal and distal segments. The histomorphometric changes in long bones following rigid plating may be accompanied by regional increases in bone blood flow.

Animals↗
PubMedDate not supplied

Rigid internal fixation of the Austin/Chevron osteotomy with Herbert screw fixation: a retrospective study.

One of the adaptations of the Herbert bone screw (Zimmer Corp., Warsaw, Indiana) in podiatric surgery has been in the fixation of the Austin type osteotomy of the first metatarsal, to obtain rigid internal fixation. Technical difficulties in performing the procedure and complications have resulted in the development of several modifications of the original technique to better facilitate application of the Herbert screw. A brief review of the literature including history of distal metaphyseal osteotomies, and the uses of the Herbert screw is included. The purpose of this manuscript is to present utilization of the Herbert bone screw and modified jig in a modified Austin osteotomy, and to produce rigid internal fixation without the disadvantages of other internal fixation techniques.

Bone Screws↗
PubMed2000

Titanium-alloy enhances bone-pedicle screw fixation: mechanical and histomorphometrical results of titanium-alloy versus stainless steel.

Several types of pedicle screw systems have been utilized to augment lumbar spine fusion. The majority of these systems are made of stainless steel (Ss), but titanium-alloy (Ti-alloy) devices have recently been available on the market. Ti-alloy implants have several potential advantages over Ss ones. High bioactivity and more flexibility may improve bone ingrowth and mechanical fixation, and the material also offers superior magnetic resonance imaging (MRI) and computed tomography (CT) resolution and significantly less signal interference. However, no data are available from loaded spinal constructs regarding bony ingrowth and mechanical fixation. The aim of this study was to analyse the effect of Ti-alloy versus Ss pedicle screws on mechanical fixation and bone ingrowth in a loaded mini-pig model. Eighteen adult mini-pigs underwent total laminectomy and posterolateral spinal fusion at L3-L4, and were randomly selected to receive either Ss (n = 9) or Ti (n = 9) pedicle screw devices. In both groups, the device used was compact Cotrel-Dubousset instrumentation (Sofamore Danek) of an identical size and shape. The postoperative observation time was 3 months. Screws from L3 were used for histomorphometric studies. Mechanical testing (torsional tests and pull-out tests) was performed on the screws from L4. The Ti screws had a higher maximum torque (P < 0.05) and angular stiffness (P < 0.07), measured by torsional testing. In the pull-out tests, no differences were found between the two groups with respect to the maximum load, stiffness and energy to failure. No correlation between removal torque and the pull-out strength was found (r = 0.1). Bone ongrowth on Ti was increased by 33% compared with Ss (P < 0.04), whereas no differences in bone volume around the screws were shown. Mechanical binding at the bone-screw interface was significantly greater for Ti pedicle screws than for Ss, which was explained by the fact that Ti screws had a superior bone ongrowth. There was no correlation between the screw removal torque and the pull-out strength, which indicates that the peripheral bone structure around the screw was unaffected by the choice of metal.

Animals↗
PubMed2003

Tibial fixation comparison of semitendinosus-bone composite allografts fixed with bioabsorbable screws and bone-patella tendon-bone grafts fixed with titanium screws.

Tibial fixation remains the weak link of ACL reconstruction over the first 8-12 weeks postoperatively. This study compared the biomechanical properties of tibial fixation for a bone-patellar tendon-bone (BPTB) graft and a novel semitendinosus-bone composite (SBC) allograft with mixed cortical-cancellous bone dowels at each end. Seven paired, fresh frozen cadaveric knees (20-45 years) were stripped of all soft tissue attachments and randomly assigned to receive either the BPTB graft or SBC allograft. Grafts were placed into tibial tunnels via a standard protocol and secured with either a 10 mmx28 mm bioabsorbable (SBC) or titanium (BPTB) screw. Grafts were cycled ten times in a servo hydraulic device from 10-50 N prior to pull to failure testing at a rate of 20 mm/min with the force vector aligned with the tibial tunnel ("worst case scenario"). Wilcoxon Signed Rank Tests were used to evaluate biomechanical differences between graft types ( p<0.05). Tibial bone mineral density and interference screw insertion torque were statistically equivalent between graft types. The mode of failure for all constructs was direct screw and graft construct pullout from the tibial tunnel. Significant differences were not observed between graft types for maximum load at failure strength (BPTB=620.8+/-209 N vs. SBC=601.2+/-140 N, p=0.74) or stiffness (BPTB=69.8 N/mm+/-29 N/mm vs SBC=47.1+/-31.6 N/mm, p=0.24). The SBC allograft yielded significantly more displacement prior to failure than the BPTB graft (15.1+/-4.9 mm vs 9.2+/-1.3 mm, p=0.04). Increased construct displacement appeared to be due to fixation failure, with some evidence of graft tissue tearing around the sutures: Bioabsorbable screw (10 x 28 mm) fixation of the SBC allograft produced unacceptable displacement levels during testing. Further study is recommended using a titanium interference screw or a longer bioabsorbable screw for SBC graft fixation under cyclic loading conditions.

Absorbable Implants↗
PubMed1993

[The dynamic hip screw (DHS) in femoral neck fractures].

Out of 224 patients with femoral neck fractures, 40 patients have been treated by ORIF with the dynamic hip screw, whereas 27 have been fixed by large cancellous bone screws and 148 femoral heads were replaced by a prosthesis. The ORIF with dynamic hip screw has been performed as an emergency intervention within 6.2 hours after accident. Good general condition without contraindication against an emergency operation as well as a biological age below 65 years and no pre-existing coxarthrosis are mandatory for the indication for open rigid internal fixation. Personal follow-up of 37 patients with x-ray documentation after at least 18 months (mean 35.4 months) showed complete rehabilitation in 31 patients and 4 femoral head necrosis (10.8%). We conclude that these good results are due to the short interval between accident and operation as well as to the evacuation of the intraarticular hematoma together with stable internal fixation and functional rehabilitation. Due to our good results we prefer long cancellous bone screws for the operative fixation of femoral neck fractures in younger patients, whereas in the older group the dynamic hip screw is preferred.

Adolescent↗
PubMed1997

Repeat screw stabilization with bone grafting after a failed Herbert screw fixation for acute scaphoid fractures and nonunions.

Eight patients with persistent nonunions after failure of a Herbert screw fixation for both acute scaphoid fractures and nonunions underwent repeat screw internal fixation and bone grafting. They were followed for at least 1 year (average, 19 months) after their last surgical procedure. In 6 patients, union was achieved following the second surgery. These patients were pain free and resumed their previous occupations. The average range of wrist mobility was 87% of that of the uninvolved wrist, and grip strength averaged 93% of that of the uninvolved wrist. In 1 of the 2 patients with an unsuccessful outcome after the second procedure, union was achieved after a third procedure was performed that involved an inlay bone graft and internal fixation using a Kirschner wire. The remaining patient had relief of pain following denervation of the wrist joint. These 2 patients did not show marked clinical improvement and required a change of employment of light work. On the basis of study findings, it appears that revision with a repeat Herbert screw fixation and bone grafting is the treatment of choice for patients with persistent scaphoid nonunions following an unsuccessful Herbert screw procedure in which the screw is not correctly placed.

Acute Disease↗
PubMed1984

Holding power of different screws in the femoral head. A study in human cadaver hips.

The holding power of four different bone screws was measured by a pull-out test in 40 cadaver hips from 10 females and 10 males over 70 years of age. Each femoral head was used to test a 6.5 mm cancellous bone screw and a 12.7 mm hip compression screw. The holding power was higher in screws with a long or wide thread. Generally, the holding power in bones from females was about 70 per cent of that in bones from males.

Aged↗
PubMed2006

New rod-plate anterior instrumentation for thoracolumbar/lumbar scoliosis: biomechanical evaluation compared with dual-rod and single-rod with structural interbody support.

STUDY DESIGN: A new rod-plate anterior implant was designed to provide plate fixation at the cephalad and caudal-end segments of a 5-level anterior spine construct. Biomechanical testing was performed on calf spines instrumented with 5-segment anterior scoliosis constructs. OBJECTIVES.: To analyze the initial and post-fatigue biomechanical performance of the new implant, and compare it to an anterior dual-rod construct and a single-rod construct with interbody cages. SUMMARY OF BACKGROUND DATA: Using single-rod anterior instrumentation for thoracolumbar and lumbar scoliosis, an unacceptable incidence of loss of correction, segmental kyphosis, and pseudarthrosis has been reported. Inadequate construct stiffness due to early postoperative bone-screw interface failure, especially at cephalad and caudal-end vertebrae, has been implicated as the cause of these complications. METHODS: Thirty calf spines were instrumented over 5 segments with: (1) single-rod augmented with rod-plate implants, (2) dual-rod construct, and (3) single-rod with titanium mesh cages. Stiffness in flexion-extension and lateral bending modes was determined initially and post-cyclical loading by measuring segmental range of motion (ROM). Post-fatigue screw pullout tests were also performed. RESULTS: In lateral bending, the caudal-end segmental ROM for rod-plate construct was 54% less than single-rod with cages construct (P < 0.05), with no difference between rod-plate and dual-rod constructs. In flexion-extension, the rod-plate construct showed 45% to 91% (initial test) and 84% to 90% (post-fatigue) less ROM than the single-rod with cages construct (P < 0.001). Again, there was no difference between rod-plate and dual-rod constructs at the cephalad and caudal-end segments. Post-fatigue screw pullout strengths of the rod-plate construct were significantly greater than those of the dual-rod and single-rod with cages constructs (P < 0.05). CONCLUSIONS: The rod-plate construct was significantly stiffer and provided greater stability of bone-screw interface than the single-rod with cages construct. It achieved similar stiffness and improved bone-screw interface stability compared to dual-rod construct.

Animals↗
PubMed2002

Pubic bone anchoring devices for the surgical treatment of urinary stress incontinence in patients with severe genital prolapse.

The aim of this study was to test a surgical technique for the treatment of stress urinary incontinence associated with genital prolapse through a transvaginal suspension anchored to the pubic bone. Thirty-seven patients with severe genital prolapse and urodynamically proven stress incontinence were operated on with this procedure from February 1998 to May 2000. Preoperatively a detailed history, pelvic examination and urodynamic studies were carried out. The degree of prolapse was assessed pre- and postoperatively in the lithotomy position in accordance with the classification proposed by Baden and Walker [8]. Two titanium bone screws with no. 1 polypropylene sutures attached to them and a battery-operated screw inserter are used to fix the vaginal sutures to the pubic bone bilaterally. The procedure is performed transvaginally with no abdominal or suprapubic incisions. Objective outcomes were assessed by symptom assessment, clinical examination and a full urodynamic evaluation at 6 months postoperatively, and annually by clinical evaluation. Subjective outcomes were assessed by directly interviewing the patients about their postoperative urinary symptoms and asking them to classify their level of satisfaction. An objective cure rate (no objective loss of urine during coughing in the absence of a simultaneous detrusor contraction) at the 6-month postoperative urodynamic evaluation was observed in 23 of 37 patients (62%). Recurrent anterior vaginal wall prolapse (grade 2) had developed in 7 of 37 patients (27%). Subjectively, 73% of the patients expressed satisfaction with the procedure. Early results using two bone screws into the pubis to fix the periurethral and perivesical tissues and vagina to the posterior surface of the pubic bone were disappointing. Based on our results we have abandoned the use of this procedure to correct stress incontinence associated with severe genital prolapse.

Aged↗
PubMedDate not supplied

The effects of screw removal on bone strain in an idealized plated bone model.

An idealized plated bone model was used to test the hypothesis that selected screw removal could alter the bone strain field and be a viable treatment for stress protection osteoporosis. Eighteen bone screw modifications were evaluated for their effects on bone strain. The three variables studied were number, position, and length of screws. Removal of two or four bone screws from an eight hole plate significantly increased the strain per load on the bone model over the values with eight screws in the plate (p less than 0.05). The four screw configurations increased bone strain more than the six screw configurations. It also was shown that the position of screws in the plate could significantly alter the bone strain per load results. Removal of six bone screws from an eight hole plate also increased the bone strain per load, but to excess in some tests. In those configurations, the results were not statistically different from the unplated configuration. Replacement of the full length screws with eight half length screws that engaged only the near cortex significantly reduced bone strain per load as compared with eight bicortical bone screws.

Animals↗