In vitro evaluation of screws and suture anchors in metaphyseal bone of the canine tibia

OBJECTIVE: To compare ease of insertion, load to failure, and mode of failure of cortical and cancellous screws, BoneBiter, IMEX, and TwinFix suture anchors in canine metaphyseal tibial bone. STUDY DESIGN: Experimental biomechanical study. ANIMALS: Canine cadaveric tibias. METHODS: One investigator inserted all anchors and subjectively evaluated ease of placement. Anchor systems were loaded to failure along axis of insertion with audio-video recording to determine failure mode. RESULTS: BoneBiter was the most difficult anchor to insert successfully. Mean+/-SD loads to failure were cancellous screw (711+/-193 N), IMEX 4.7 mm 18 g wire (661+/-163 N), IMEX 4.0 mm 18 g wire (661+/-165 N), cortical screw (635+/-184 N), BoneBiter #5 Kevlar suture (393+/- 109 N), and TwinFix 5.0 mm #2 polyester (267+/-73 N). No significant differences were noted among the cortical screw, cancellous screw, IMEX 4.7 and 4.0 mm, all of which were significantly (P<.001) greater than BoneBiter and TwinFix . Failure modes were pullout of bone, suture-wire breakage, eyelet breakage, or no failure to 1000 N: screws (18,0,0,2), IMEX (18,1,1,0), BoneBiter (2,8,0,0), and TwinFix (0,10,0,0). CONCLUSIONS: Fixation devices were user friendly, with the exception of BoneBiter. Mode of failure is dependent on suture material and anchor design. Cortical and cancellous screws, and IMEX anchors with 18 g wire have significantly greater load to failure compared with BoneBiter and TwinFix suture anchors. CLINICAL RELEVANCE: Based on load to failure, ease of use, design characteristics, and cost, IMEX anchors may have advantages over other comparable soft tissue fixation devices.     

Biomechanical analysis of suture anchors and suture materials in the canine femur

Objective— Biomechanical analysis of acute load to failure (ALF) of 3 veterinary and 1 human suture anchor and cyclic load to failure with two suture material/suture anchor constructs in canine femoral condyles.
Study Design— Biomechanical in vitro study.
Sample Population— Cadaveric femora from 20–30 kg dogs.
Methods— Three veterinary and 1 human suture anchor were placed in the cranial and caudal aspects of the femoral condyle and subjected to 0° ALF. Anchors were loaded with 5 USP Fiberwire or 27 kg test nylon leader line (NLL) and subjected to 90° cyclic testing for 10,000 cycles followed by ALF at 90°.
Results— No significant difference in ALF for any anchor type was detected in the cranial aspect of the femoral condyle; however all veterinary anchors had higher ALF in the caudal aspect of the femoral condyle. In cyclic testing, the constructs in descending order (most cycles to least) were: (1) FlexiTwist/NLL, (2) Securos/Fiberwire, Securos/NLL, (3) IMEX/Fiberwire, IMEX/NLL, and (4) FlexiTwist/Fiberwire, Fastin/Fiberwire. Fiberwire was significantly stronger than NLL in post-cycling ALF testing.
Conclusions— Veterinary anchors had higher ALF in the caudal versus cranial aspect of the femoral condyle. Except for the FlexiTwist in which NLL performed better, Fiberwire and NLL both had similar cyclic performance with each veterinary anchor type. The veterinary anchors exceeded the human anchor in ALF and cycles to failure.
Clinical Relevance— The tested veterinary suture anchors with Fiberwire or NLL may be used in the femoral condyle, preferably in the caudal aspect, and should withstand estimated loading conditions in appropriately confined postoperative canine patients.     

Effect of bone diameter and eccentric loading on fatigue life of cortical screws used with interlocking nails

OBJECTIVE: To test the effects of bone diameter and eccentric loading on fatigue life of 2.7-mm-diameter cortical bone screws used for locking a 6-mm-diameter interlocking nail. SAMPLE POPULATION: Eighteen 2.7-mm-diameter cortical bone screws. PROCEDURE: A simulated bone model with aluminum tubing and a 6-mm-diameter interlocking nail was used to load screws in cyclic 3-point bending. Group 1 included 6 screws that were centrally loaded within 19-mm-diameter aluminum tubing. Group 2 included 6 screws that were centrally loaded within 31.8-mm-diameter aluminum tubing. Group 3 included 6 screws that were eccentrically loaded (5.5 mm from center) within 31.8-mm-diameter aluminum tubing. The number of cycles until screw failure and the mode of failure were recorded. RESULTS: An increase in the diameter of the aluminum tubing from 19 to 31.8 mm resulted in a significant decrease in the number of cycles to failure (mean +/- SD, 761,215 +/- 239,853 to 16,941 +/- 2,829 cycles, respectively). Within 31.8-mm tubing, the number of cycles of failure of eccentrically loaded screws (43,068 +/- 14,073 cycles) was significantly greater than that of centrally loaded screws (16,941 +/- 2,829 cycles). CONCLUSIONS AND CLINICAL RELEVANCE: Within a bone, locking screws are subjected to different loading conditions depending on location (diaphyseal vs metaphyseal). The fatigue life of a locking screw centrally loaded in the metaphyseal region of bone may be shorter than in the diaphysis. Eccentric loading of the locking screw in the metaphysis may help to improve its fatigue life.     

Analysis of suture anchor eyelet position on suture failure load

Objective: To compare mechanical performance of 2 orientations of the 5 mm Corkscrew^® suture anchor with #5 Fiberwire^®. Study Design: In vitro biomechanical study. Sample Population: Suture anchor–suture constructs (n=40). Methods: Acute and cyclic tensile loads were applied to suture threaded through eyelets of 40 anchors perpendicular to the long axis of the anchor. Eyelets were positioned so that the suture pull was in line with (anchor rotation angle of 0° [ARA 0]) or 90° (ARA 90) to the eyelet plane. Load at failure, stiffness, and cycles to failure were determined. Results: All constructs failed by suture breakage at the eyelet. Mean load at failure was significantly higher in the ARA 90 group (634±93 N) compared with the ARA 0 group (495±52 N; P=.0015). No significant difference was found between groups for mean number of cycles to failure (270±177 versus 178±109; P=.2166) and stiffness (50±4 versus 48±5 N/mm; P=.3141). Conclusions: The Corkscrew^® 5 mm suture anchor with Fiberwire^® suture fails via suture breakage at the eyelet under higher acute loads if the suture is loaded at an angle of 90° compared with 0° with respect to the plane of the eyelet.     

Microcrack density and length in the proximal and distal metaphyses of the humerus and radius in dogs

OBJECTIVE: To compare microcrack density and length in the proximal and distal metaphyses of the humerus and radius in dogs. SAMPLE POPULATION: Left humerus and radius from each of 10 dogs of medium to large size. PROCEDURE: Metaphyseal specimens were bulk stained in 1% basic fuchsin in graded alcohols and embedded in methylmethacrylate. For quantification of fatigue-induced microscopic damage, transverse sections were prepared from proximal and distal metaphyseal regions, and length and density of microcracks were determined, using light microscopy. RESULTS: Bone region, age, and body weight were not significantly associated with microcrack density or length. CONCLUSIONS AND CLINICAL RELEVANCE: The hypothesis that fatigue-induced injury (increased microcrack density and length) caused by cyclic loading associated with daily activity is greater in bone regions prone to development of osteosarcoma was not supported by data from this study.     

In Vitro Pullout Strength of Screws Inserted in Adult Equine Third Metacarpal Bone After Overdrilling a 4.5-mm Threaded Insertion Hole

Objective—To determine and compare the in vitro pullout strength of 5.5-mm cortical versus 6.5-mm cancellous bone screws inserted in the diaphysis and metaphysis of adult equine third metacarpal (MCIII) bones, in threaded 4.5-mm cortical bone screw insertion holes that were then overdrilled with a 4.5-mm drill bit to provide information relevant to the selection of a replacement screw if a 4.5-mm cortical screw is stripped. Study Design—In vitro pullout tests of 5.5-mm cortical and 6.5-mm cancellous screws in equine MCIII bones. Sample Population—Two independent cadaver studies each consisting of 14 adult equine MCIII bones. Methods—Two 4.5-mm cortical screws were placed either in the middiaphysis (study 1) or distal metaphysis (study 2) of MCIII bones. The holes were then overdrilled with a 4.5-mm drill bit and had either a 5.5-mm cortical or a 6.5-mm cancellous screw inserted; screw pullout tests were performed at a rate of 0.04 mm/second until screw or bone failure occurred. Results—In diaphyseal bone, the screws failed in all tests. Tensile breaking strength for 5.5-mm cortical screws (997.5 ± 49.3 kg) and 6.5-mm cancellous screws (931.6 ± 19.5 kg) was not significantly different. In metaphyseal bone, the bone failed in all tests. The holding power for 6.5-mm cancellous screws (39.1 ± 4.9 kg/mm) was significantly greater than 5.5-mm cortical screws (23.5 ± 3.5 kg/mm) in the metaphysis. There was no difference in the tensile breaking strength of screws in the diaphysis between proximal and distal screw holes; however, the holding power was significantly greater in the distal, compared with the proximal, metaphyseal holes. Conclusions—Although tensile breaking strength was not different between 5.5-mm cortical and 6.5-mm cancellous screws in middiaphyseal cortical bone, holding power of 6.5-mm cancellous screws was greater than 5.5-mm cortical screws in metaphyseal bone of adult horses. Clinical Relevance—If a 4.5-mm cortical bone screw strips in MCIII diaphyseal bone of adult horses, either a 5.5-mm cortical or 6.5-mm cancellous screw, however, would have equivalent pullout strengths. A 6.5-mm cancellous screw, however, would provide greater holding power than a 5.5-mm cortical screw in metaphyseal bone.     

An in vitro biomechanical comparison of the insertion variables and pullout mechanical properties of ao 6.5-mm standard cancellous and 7.3-mm self-tapping, cannulated bone screws in foal femoral bone

OBJECTIVE: To compare screw insertion variables and pullout mechanical properties between AO 6.5-mm cancellous and 7.3-mm cannulated bone screws in foal femoral bone. STUDY DESIGN: A paired, in vitro mechanical study. SAMPLE POPULATION: Seven pairs of femora from immature (1-7 months) foals. METHODS: The 6.5 cancellous and 7.3-mm cannulated screws were inserted at standardized proximal and distal metaphyseal, and mid-diaphyseal locations. Insertion torque, force, and time to drill, tap (6.5-mm cancellous), guide wire insertion (7.3-mm cannulated), and screw insertion were measured. Screw pullout properties (yield and failure load, displacement, and energy, and stiffness) were determined from mechanical tests. The effects of screw type and location on insertion variables and pullout properties were assessed with repeated measures ANOVA. Pairwise comparisons were examined with post hoc contrasts. Significance was set at P<.05 for all comparisons. RESULTS: Insertion torques for the 7.3-mm cannulated screws were significantly greater than for the 6.5-mm tap, but significantly lower than for the 6.5-mm cancellous screws. Total screw insertion times were similar. Pullout properties of both screws were similar at each femoral location. The holding power of both screws was significantly greater in the mid-diaphysis than in either metaphyseal location. Pullout failure occurred by bone shearing at the bone-screw interface in all specimens. CONCLUSIONS: The 6.5-mm cancellous and 7.3-mm cannulated screws vary in insertion properties, but have similar pullout properties in the mid-diaphysis, proximal, and distal metaphysis of foal femora. Both screw types have greater holding power at the mid-diaphyseal location compared with metaphyseal locations. Based on overall similar holding powers of 6.5-mm cancellous and 7.3-mm cannulated screws, it is unlikely that increasing the screw diameter beyond 6.5 mm will provide increased holding power in foal femoral bone. CLINICAL RELEVANCE: Use of the 7.3-mm cannulated screw should be considered for foal femoral fracture repair when greater accuracy is needed, or when bone threads for the 6.5-mm cancellous screw have been stripped.     

Comparison of Holding Power of Three Different Pin Designs for External Skeletal Fixation in Avian Bone: A Study in Common Buzzard (Buteo buteo)

Objective— (1) To evaluate resistance to axial extraction of 3 pin designs in avian humerus and tibiotarsus; (2) to assess the effect of pin location within the bone on holding power; and (3) to assess the influence of thread pitch on holding power. Study Design— Resistance of pins to axial extraction was measured immediately after insertion. Animals— Adult common buzzards (Buteo buteo; n=9). Methods— Different pin designs (1 smooth; 2 threaded pins, differing in pitch) were inserted into the proximal and distal metaphysis and the proximal, middle, and distal diaphysis of the humerus and tibiotarsus. Maximum force required for axial extraction of pins was recorded. Results— Smooth pins had the lowest extraction force (P<.05). Pins inserted into the diaphysis (proximal, middle and distal) of the humerus and the distal metaphysis of the tibiotarsus had a greater pullout strength than pins in other locations. Pins with a smaller pitch inserted into the proximal diaphysis and distal metaphysis of the humerus, and the proximal metaphysis of the tibiotarsus had significantly greater holding power than pins with a larger pitch (P<.05). Conclusions— Pins inserted into the diaphysis of humerus and the distal metaphysis of the tibiotarsus are better at resisting extraction. Pins with a smaller pitch possess greater holding power than pins with a larger pitch in avian humerus and tibiotarsus. Clinical Relevance— Consideration should be given to pin location and thread pitch, when choosing external skeletal fixation to repair an avian humeral or tibiotarsal fracture.     

Evaluation of a technique for collection of cancellous bone graft from the proximal humerus in horses

OBJECTIVES: To describe a technique for collecting cancellous bone graft from the proximal humerus in horses. STUDY DESIGN: Prospective evaluation of an experimental bone graft collection technique. ANIMAL POPULATION: Eight horses, 3-15 years, weighing 495-605 kg. METHODS: Horses were anesthetized and positioned in lateral recumbency. The lateral aspect of the proximal humerus was exposed by a 7-10-cm incision extending distally from the greater humeral tubercle, followed by sharp dissection through the omotransversarius muscle and between the infraspinatus and deltoideus muscles. A 12-mm cortical defect was incrementally created in the lateral proximal humerus. Human bone graft harvesting equipment (Acumed, Beaverton, OR) was drilled through this defect to collect a core of cancellous bone. In five horses additional cancellous bone was then collected with conventional instruments. Bone samples were weighed and histologically examined. Horses were monitored and graded for quality of anesthetic recovery, incisional complications, and postoperative lameness. RESULTS: Total mean (+/-SD) surgical time for harvesting bone with the Acumed system and traditional techniques (n=5) was 38+/-6 minutes (range, 32-47 minutes). Mean cancellous bone weight collected with the Acumed system was 3.6+/-0.8 g (range, 2.0-4.6 g), and cancellous bone collected conventionally was 25.6+/-7.5 g (range, 16.8-34.2 g). Minimal incisional complications or postoperative lameness were observed. Mortality was 12.5%; one horse fractured the operated humerus during anesthetic recovery. CONCLUSION: The Acumed system provided limited cancellous bone when used with the technique described. However, the quantity of cancellous bone collected with traditional harvesting instruments was comparable to other sites used in horses. The procedure was associated with minimal postoperative incisional complications or lameness, but because one horse suffered a catastrophic humeral fracture further research is required to assess the effects of this procedure on humeral breaking strength. CLINICAL RELEVANCE: Based on the risk of catastrophic fracture, this technique cannot be recommended for use in clinical cases, especially if an unassisted recovery from general anesthesia is planned.     

Pathophysiology of humeral fractures in a sample of dairy heifers

AIMS: To investigate the pathophysiology of humeral fractures in first-lactation dairy heifers in the North Island of New Zealand.

METHODS: Ten 2-year-old dairy heifers with humeral fractures were subject to euthanasia and the fractured and non-fractured contralateral humeri were collected. Humeri were also collected from 10 unaffected 2-year-old dairy heifers sent for slaughter. Humeri from heifers with and without fractures were examined using computed tomography (CT), and four slices of the diaphysis and lower metaphysis (D1–4) were analysed using the Bone J plug-in for Image J. The humeri were sectioned sagittally and 5?mm bone slabs were processed for histopathology.

RESULTS: There were no differences in bone length between the humeri from heifers with or without fractures (p=0.31). Median cortical bone mineral density at D1 was increased in humeri from affected compared with unaffected heifers (810 vs. 783?mg/cm³; p=0.03), cortical area at D1 was reduced (816 vs. 1,037?mm²; p=0.04), the median stress strain index, a calculated theoretical measure of bone strength, at D1 was decreased (7,288 vs. 9,072?mm³; p<0.01), and the median ratio of overall bone volume (BV) to total volume (TV) was decreased (0.32 vs. 0.38; p<0.01). The median periosteal circumference at D1 was also reduced in humeri from affected compared with unaffected heifers (151 vs. 173?mm; p<0.01). Using a binary logistic regression model, BV/TV was the only variable associated with humeral fractures (p=0.03).In nine of 10 fractured humeri the fracture appeared to have started just distal to the head of the humerus and spiralled distally down the diaphysis to end just above the humeral condyles. Histopathological findings included a reduction in the number, and thickness, of trabeculae in the metaphysis; metaphyseal growth arrest lines, and osteoclastic resorption in fractured humeri. Concentrations of copper in serum from four of five animals with fractures were within, and one was below, normal reference ranges, while concentration of copper in the livers of three heifers with fractures were below adequate ranges.

CONCLUSIONS: The CT and histological findings were consistent with a diagnosis of osteoporosis. We propose that humeral fractures in dairy heifers are associated with osteoporosis, possibly as a result of insufficient deposition of bone during growth because of protein-calorie malnutrition. Increased osteoclastic resorption of bone associated with calcium mobilisation for lactation, and periods of copper deficiency may contribute to bone weakening.     

In Vitro Comparison of a Novel External Fixator and Traditional Full‐Limb Transfixation Pin Cast in Horses

Objective: To compare the mechanical properties and failure modes of a standardized short oblique distal radial metaphyseal osteotomy stabilized using either a transfixation pin cast (TPC), a modular‐sidebar external skeletal fixator (ESF), or a solid‐sidebar ESF (modular‐ or solid‐ESF, respectively) using static or cyclic axial loading to failure. Study Design: In vitro study. Animals: Equine cadaver forelimbs. Methods: A 30° oblique distal radial osteotomy was created and stabilized using 1 of the 3 fixation methods: (1) TPC, (2) modular‐ESF, or (3) solid‐ESF. Limbs were tested using static (TPC, modular‐ESF, and solid‐ESF) or cyclic (TPC and solid‐ESF) axial loading to failure. The stiffness, yield load, yield displacement, failure load, and failure displacement for static loading and the cycles to failure for cyclic loading at 75% failure load were obtained. Data were analyzed using a Kruskal–Wallis test. Level of significance was P<.05. Results: The solid‐ESF had a greater stiffness, higher yield and failure load and a lower yield and failure displacement than the TPC (P=.01) and the modular‐ESF (P=.02). TPC had a higher yield load, failure load, and yield displacement than the modular‐ESF (P=.01). Mean cycles to failure for TPC was 2996±657 at a load of 16,000 N and for solid‐ESF 6560±90 cycles at a load of 25,000 N. Conclusions: The solid‐ESF was stiffer and stronger than the TPC and modular‐ESF and failed at a greater number of cycles in axial loading compared with the TPC. Clinical Relevance: This study is an initial step in evaluating the solid‐ESF. Further testing needs to be performed, but this fixation may offer a viable alternative to the traditional TPC for stabilization of long bone fractures in adult horses.     

Holding Power of Different Pin Designs and Pin Insertion Methods in Avian Cortical Bone

Objective —To measure pullout strength of four pin types in avian humeri and tibiotarsi bones and to compare slow-speed power and hand insertion methods.
Study Design —Axial pin extraction was measured in vitro in avian bones.
Animal Population —Four cadaver red-tailed hawks and 12 live red-tailed hawks.
Methods —The pullout strength of four fixator pin designs was measured: smooth, negative profile threaded pins engaging one or two cortices and positive profile threaded pins. Part 1: Pins were placed in humeri and tibiotarsi after soft tissue removal. Part 2: Pins were placed in tibiotarsi in anesthetized hawks using slow-speed power or hand insertion.
Results —All threaded pins, regardless of pin design, had greater pullout strength than smooth pins in all parts of the study ( P < .0001). The cortices of tibiotarsi were thicker than the cortices of humeri ( P < .0001). There were few differences in pin pullout strengths between threaded pin types within or between bone groups. There were no differences between the pullout strength of pins placed by slow-speed power or by hand.
Conclusions —There is little advantage of one threaded pin type over another in avian humeri and tibiotarsi using currently available pin designs. There were few differences in pin pullout strengths between humeri and tibiotarsi bones. It is possible that the ease of hand insertion in thin cortices minimizes the potential for wobbling and therefore minimizes the difference between slow-speed drill and hand insertion methods.
Clinical Relevance —Threaded pins have superior bone holding strength in avian cortices and may be beneficial for use with external fixation devices in birds.     

Comparison of insertion time and pullout strength between self-tapping and non-self-tapping AO 4.5-mm cortical bone screws in adult equine third metacarpal bone

OBJECTIVE: To compare screw insertion characteristics and pullout mechanical properties between self-tapping (ST) and non-self-tapping (NST) AO 4.5-mm cortical bone screws in adult equine third metacarpal bone (MC3). STUDY DESIGN: In vitro biomechanical experiment. ANIMALS OR SAMPLE POPULATION: Seven pairs of adult equine MC3. METHODS: Bicortical holes were drilled transversely in proximal metaphyseal, diaphyseal, and distal metaphyseal locations of paired MC3. NST screws were inserted in pre-tapped holes in 3 sites of one bone pair, and ST screws were inserted in non-tapped holes of contralateral MC3. Tapping and screw insertion times and maximum torques were measured. Screw pullout mechanical properties were determined. RESULTS: Screw insertion time was longer for ST screws. Total time for tapping and insertion (total insertion time) was over twice as long for NST screws. Statistically significant differences were not observed between screws for any pullout mechanical property. From pullout tests, diaphyseal locations had significantly stiffer and stronger structure than metaphyseal locations. Pullout failure more commonly occurred because of screw breakage than bone failure. Bone failure and bone comminution were more commonly associated with ST screws. Bone failure sites had pullout failure loads that were 90% of screw failure sites. CONCLUSIONS: NST and ST 4.5-mm-diameter cortical bone screws have similar pullout mechanical properties from adult equine MC3. ST screws require less than half the total insertion time of NST screws. CLINICAL RELEVANCE: Use of ST 4.5-mm-diameter cortical bone screws should be considered for repair of adult equine MC3 fractures; however, bone failures at screw sites should be monitored.     

Influence of locking bolt location on the mechanical properties of an interlocking nail in the canine femur

Objective: To determine whether the fatigue properties of an interlocking nail (ILN) construct are influenced by metaphyseal or diaphyseal location of the locking bolt. Study Design: Ex vivo mechanical investigation. Sample Population: Adult canine femora (n=19 pairs). Methods: Femora were implanted with a 6‐mm diameter ILN. In 1 femur, the ILN was locked with a 2.7 mm bolt placed in the diaphysis; the ILN in the contralateral femur was locked with a bolt placed in the metaphysis. Constructs were tested to failure in axial loading (9 pairs) or torsion (10 pairs), with failure defined as displacement>2 mm or a total of 500,000 cycles for axial loading, and rotation>45° for torsional loading. Outcome measures included initial construct stiffness, number of cycles to failure, peak load, and peak torque. After testing, microradiography and histology were used to determine the location and nature of construct failure. Results: Metaphyseal bolts failed at higher axial loads than diaphyseal bolts (P=.03), with bolt failure because of bending at the nail‐bolt interface. All of the metaphyseal bolt constructs survived torsional testing whereas 9 of 10 diaphyseal bolt constructs failed catastrophically because of spiral fracture through the adjacent cortical bone. Conclusions: Placement of a locking bolt in metaphyseal bone extends fatigue life under axial loading and decreases the incidence of catastrophic failure under torsional loading.     

Ex vivo comparison of one versus two distal screws in 8 mm model 11 interlocking nails used to stabilize canine distal femoral fractures

OBJECTIVE: To compare the structural properties of an 8 mm model 11 interlocking nail (IN) with 2 proximal and 2 distal screws (2/2) to 2 proximal and 1 distal screws (2/1) in an unstable canine fracture model. STUDY DESIGN: Ex vivo biomechanical investigation. SAMPLE POPULATION: Eight pairs of adult canine femurs. METHODS: A simple transverse distal metaphyseal femoral fracture with a 1 cm gap was created. The unstable fracture in 1 femur was repaired with a nail with 2 distal and 2 proximal screws and the paired femur with a nail with 1 distal and 2 proximal screws. Cyclic mechanical testing in torsion was performed to assess fatigue life, peak torque, stiffness, and mode of failure. RESULTS: All 2/1 IN-femoral constructs, but only 2 of eight 2/2 constructs, failed before completion of 50,000 loading cycles. The 2/2 constructs had significantly greater peak torque to failure (P = .002) and longer fatigue life (P = .00003) compared with 2/1 constructs. There were no significant differences in stiffness between 2/2 and 2/1 constructs when the non-failed constructs were compared (P > .5). All constructs failed by screw deformation. CONCLUSIONS: An 8 mm model 11 IN used for fixation of unstable canine distal femoral fractures has a longer fatigue life and is stronger under torsional loads when 2 rather than 1 distal screws are placed. CLINICAL RELEVANCE: When repairing unstable canine distal femoral fractures with an IN system, 2 distal screws should be inserted to avoid catastrophic implant failure before bone healing is achieved.     

In vitro comparison of metaphyseal and diaphyseal placement of centrally threaded, positive-profile transfixation pins in the equine third metacarpal bone

OBJECTIVE: To evaluate in vitro holding power and associated microstructural and thermal damage from placement of positive-profile transfixation pins in the diaphysis and metaphysis of the equine third metacarpal bone. SAMPLE POPULATION: Third metacarpal bones from 30 pairs of adult equine cadavers. PROCEDURE: Centrally threaded positive-profile transfixation pins were placed in the diaphysis of 1 metacarpal bone and the metaphysis of the opposite metacarpal bone of 15 pairs of bones. Tensile force at failure for axial extraction was measured with a materials testing system. An additional 15 pairs of metacarpal bones were tested similarly following cyclic loading. Microstructural damage was evaluated via scanning electron microscopy in another 6 pairs of metacarpal bones, 2 pairs in each of the following 3 groups: metacarpal bones with tapped holes and without transfixation pin placement, metacarpal bones following transfixation pin placement, and metacarpal bones following transfixation pin placement and cyclic loading. Temperature of the hardware was measured with a surface thermocouple in 12 additional metacarpal bones warmed to 38 C. RESULTS: The diaphysis provided significantly greater resistance to axial extraction than the metaphysis. There were no significant temperature differences between diaphyseal and metaphyseal placement. Microstructural damage was limited to occasional microfractures seen only in cortical bone of diaphyseal and metaphyseal locations. Microfractures originated during drilling and tapping but did not worsen following transfixation pin placement or cyclic loading. CONCLUSIONS AND CLINICAL RELEVANCE: Centrally threaded, positive-profile transfixation pins have greater resistance to axial extraction in the diaphysis than in the metaphysis of equine third metacarpal bone in vitro. This information may be used to create more stable external skeletal fixation in horses with fractures.     

Pullout strength for three suture patterns used for canine tracheal anastomosis

OBJECTIVE: To compare pullout strength of 3 suture patterns used for canine tracheal anastomosis. STUDY DESIGN: Experimental study. SAMPLE POPULATION: Cadaveric canine tracheae (n = 20). METHOD: Tracheal segments were anastomosed with 1 of 3 suture patterns: simple continuous, simple interrupted, and simple interrupted reinforced with horizontal mattress, each encircling annular cartilage rings adjacent to the transection site. Horizontal mattress sutures encircled the annular rings proximal and distal to the rings closest to the anastomosis. Each construct was distracted (0.5 mm/s) in a materials testing machine to failure. Load-displacement curves were generated and failure load (pullout strength) determined and mode of failure recorded. RESULTS: Tracheal anastomosis with a simple interrupted pattern was significantly weaker (mean+/-SD pullout strength, 102.55+/-30.14 N) than simple continuous (135.53+/-15.47 N) or simple interrupted plus horizontal mattress (132.39+/-21.46 N), which were not different from each other. Mode of failure was consistently by suture tear out. CONCLUSIONS: Both simple continuous and simple interrupted reinforced with horizontal mattress suture patterns have significant biomechanical advantage over a simple interrupted pattern alone in canine cadaveric tracheal anastomosis. The simple continuous pattern had the least variability in pullout strength. CLINICAL RELEVANCE: A simple continuous technique should be considered when selecting a tension-relieving pattern for canine tracheal anastomosis. It offers the same biomechanical advantage as a simple interrupted pattern reinforced with a horizontal mattress pattern and its strength appears to be reliably maintained when tested in canine cadaver tracheae.     

Guided bone regeneration with beta-tricalcium phosphate and poly L-lactide-co-glycolide-co-epsilon-caprolactone membrane in partial defects of canine humerus

This study was performed to evaluate the effect of beta-tricalcium phosphate and poly L-lactide-co-glycolide-co-epsilon-caprolactone (TCP/PLGC) membrane in the repair of partial bone defects in canine proximal humerus. Three adult mixed-breed dogs were used during the experimental period. The length of the defect was quarter of the full length of humerus, and width of the defect was quarter of middle diameter of the lateral aspect of humerus. The humeri of each dog were divided into treatment (TCP/PLGC) and control groups. The defect was covered with TCP/PLGC membrane in treatment group. To evaluate regeneration of the bone, computerized tomography (CT) and histopathologic examination were performed. The radiopaque lines were appeared at the original defect sites in TCP/PLGC group but below the original site in control at 4th week. Radiopacity and thickness of the defect sites, and radiopaque lines were more increased at 8th week than those of 4th week. Histopathologic findings revealed fibrous connective tissue migration into the defect and the migration inhibited the structure of new cortex to be placed in the original level in control whereas new cortex growth was found in the level of original line in TCP/PLGC group. However, the new cortical bone in the TCP/PLGC group was thinner and less organized than the adjacent intact cortex, and the amount of new cancellous bones were also scanty. The result suggested that TCP/PLGC membrane is a good guided bone regeneration material to restore the original morphology of humerus in partial defect.     

Evaluation of compression generated by self compressing Orthofix bone pins and lag screws in simulated lateral humeral condylar fractures.

A simulated lateral humeral condylar fracture was created in each of the 52 humeri collected from 26 dogs. One humerus from each pair was stabilized with a 2.0 mm cortical bone screw which was inserted in lag fashion. The other humerus from each pair was stabilized with a 2.2 mm threaded diameter Orthofix pin inserted across the condyle. Prior to each repair, an antirotational K-wire was placed and then the Pressurex Sensitive film was inserted in the osteotomy site in order to determine the compressive pressure (MPa), compressive force (KN), and area of compression (cm(2)) achieved during fixation. The maximum insertional torque achieved before stripping was measured for each implant. The mean compression generated by insertion of a 2.0 mm lag screw was 20.36 +/- 1.51 MPa compared to 18.88 +/- 1.76 MPa generated by a 2.2 mm Orthofix pin (p < 0.003). The mean area of compression generated by insertion of a 2.0 mm lag screw was 2.39 +/- 1.29 cm(2), compared to 1.16 +/- 0.84 cm(2) generated by insertion of a 2.2 mm Orthofix pin (p < 0.0001). The mean compressive force (compression x area compressed) generated by insertion of a 2.0 mm lag screw was 4.96 +/- 2.90 Kn, compared to 2.20 +/- 1.65 Kn generated by insertion of a 2.2 mm Orthofix pin (p < 0.0001). The mean insertion torque to failure for the lag screws was 0.49 +/- 0.07 NM, compared to 0.91 NM +/- 0.18 NM generated by the Orthofix pins (P < 0.0001). Both repair methods are likely to be acceptable for the repair of similar fractures in small breed dogs.     

An ex vivo mechanical evaluation of single versus double semitubular plate fixation of a transverse distal-third scapular osteotomy in the dog

OBJECTIVE: To compare single versus double semitubular plate fixation for scapular body fractures. STUDY DESIGN: Ex vivo mechanical study. SAMPLE POPULATION: Eighteen paired cadaveric canine scapulae. METHODS: Transverse scapular body osteotomies were created in the distal third of 18 pairs of scapulae. One scapula of each pair was repaired with a single plate, whereas the contralateral scapula was repaired with 2 plates. Initial strength and stiffness of the constructs were measured in 10 pairs of scapulae. Eight pairs of scapulae underwent cyclic loading and then were subjected to failure testing. RESULTS: Double-plate fixation was significantly stronger (3,899 +/- 632 N) but not stiffer (614 +/- 130 N/mm) than the single-plate fixation (3,238 +/- 935 N and 537 +/- 202 N/mm, respectively). Cyclic loading variables were not significantly different between the 2 methods of fixation. After cyclic loading, double-plate fixation was significantly stronger (2,916 +/- 618 N) than single-plate fixation (2,347 +/- 495 N). There was no significant difference (P =.11) in stiffness between double- versus single-plate fixations: 734 +/- 247 N/mm and 595 +/- 139 N/mm, respectively. CONCLUSIONS: Double-plate fixation was generally stronger and stiffer than single-plate fixation. Because all constructs failed at loads that greatly exceeded those estimated to occur clinically, any difference between the 2 methods of fixation probably is not clinically relevant. CLINICAL RELEVANCE: Single-plate fixation may be of sufficient strength for fixation of scapular body fractures.