A Biomechanical Evaluation and Assessment of the Accuracy of Reduction of Two Methods of Acetabular Osteotomy Fixation in Dogs

Objective—To compare the accuracy of reduction, biomechanical characteristics, and mode of failure of two methods of acetabular osteotomy repair. Study Design—Acetabular osteotomies were created in 16 paired hemipelves and stabilized with a screw/wire/polymethylmethacrylate composite fixation technique (SWP) or a 2-mm veterinary acetabular plate (VAP). Eight intact hemipelves were used as controls. Sample Population—Twelve canine cadavers. Methods—Accuracy of osteotomy reduction was evaluated grossly and by measurement of articular incongruencies formed in polyvinylsiloxane impression casts. Acetabula were loaded in modified bending until failure using a universal testing machine. Data from load-deformation curves were used to determine the biomechanical characteristics of the repaired and intact acetabula. Mode of failure was evaluated grossly and radiographically. Results—Osteotomy reduction was superior in acetabula stabilized with SWP. Mean values ± standard deviation for load at failure and stiffness of the intact acetabula were 2,796 ± 152.9 N and 267.5 ±61.9 N/mm. Corresponding values for SWP and VAP were 1,192 ± 202.7 N and 136.3 ± 76.5 N/mm, and 1,100.5 ± 331.6 N and 110.0 ± 51.3 N/mm, respectively. The mean load at failure and stiffness of intact acetabula was significantly greater than acetabula stabilized with SWP or VAP. There was no significant difference between SWP and VAP for load at failure or stiffness. Failure of acetabula stabilized with SWP occurred by fracture of the polymethylmethacrylate and ventrolateral bending of the wires. Acetabula stabilized with VAP failed by ventrolateral twisting of the plate and bending of the caudal screws. Conclusions—SWP and VAP provide comparable rigidity, however, the SWP facilitates more accurate osteotomy reduction. Clinical Relevance—These findings support the use of the SWP technique as an alternative method of acetabular fracture repair.     

Ex Vivo Biomechanical Comparison of the 2.4 mm UniLOCK® Reconstruction Plate Using 2.4 mm Locking Versus Standard Screws for Fixation of Acetabular Osteotomy in Dogs

Objective— To compare the accuracy of reduction and the biomechanical characteristics of canine acetabular osteotomies stabilized with locking versus standard screws in a locking plate. Study Design— Ex vivo biomechanical study. Sample Population— Cadaveric canine hemipelves and corresponding femurs (n=10 paired). Methods— Transverse acetabular osteotomies stabilized with 5‐hole 2.4 mm uniLOCK^® reconstruction plates using either 2.4 mm locking monocortical or standard bicortical screw fixation (Synthes^® Maxillofacial). Fracture reduction was assessed directly (craniocaudal acetabular width measurements and gross observation) and indirectly (impression casts). All constructs were fatigue‐tested, followed by acute destructive testing. All outcome measures (mean±SD) were evaluated for significance (P<.05) using paired t‐tests. Results— Craniocaudal acetabular diameters before and after fixation were not significantly different (21.9±1.2 and 21.5±1.2 mm; P=.45). No significant differences were observed in acetabular width differences between pre‐ and postoperative fixation between groups (locking ?0.4±0.4 mm; standard ?0.4±0.3 mm; P=.76). Grossly, there was no significant difference in the repairs and impression casts did not reveal a significant (P=.75) difference in congruency between the groups. No significant differences were found in fracture gap between groups either dorsally (locking 0.38±0.23 mm versus standard 0.22±0.05 mm; P=.30) or ventrally (locking 0.80±0.79 mm versus standard 0.35±0.13 mm; P=.23), and maximum change in amplitude dorsally (locking 0.96±2.15 mm versus standard 0.92±0.89 mm; P=.96) or ventrally (locking 2.02±2.93 mm versus standard 0.15±0.81 mm; P=.25). There were no significant differences in stiffness (locking 241±46 N/mm versus standard 283±209 N/mm; P=.64) or load to failure (locking 1077±950 N versus standard 811±248 N; P=.49). Conclusion— No significant differences were found between pelves stabilized with locking monocortical screw fixation or standard bicortical screw fixation with respect to joint congruity, displacement of fracture gap after cyclic loading, construct stiffness, or ultimate load to failure. Clinical Relevance— There is no apparent advantage of locking plate fixation over standard plate fixation of 2‐piece ex vivo acetabular fractures using the 2.4 mm uniLOCK^® reconstruction plate.     

Biomechanical Comparison of Two Alternative Tibial Plateau Leveling Osteotomy Plates with the Original Standard in an Axially Loaded Gap Model: An In Vitro Study

Objective— To compare the axial compression stiffness of osteotomized canine tibiae stabilized with Slocum, Securos, or Synthes plates after a tibial plateau leveling osteotomy (TPLO) procedure. Study Design— In vitro, paired comparison of cadaveric tibial constructs subjected to mechanical testing under an axial load. Sample Population— Canine tibiae (n=16 pairs) from skeletally mature male and female dogs of various breeds (18–55 kg). Methods— Tibial pairs (n=16) were randomly assigned to 1 of 2 study cohorts (n=8 pairs/cohort): cohort 1, tibial osteotomy stabilization with a Slocum or a Securos plate, or cohort 2, tibial osteotomy stabilization with a Slocum or a Synthes plate. One tibia from each pair was stabilized with 1 of each plate design assigned to the cohort after TPLO. A 3.2 mm osteotomy gap was maintained during plate application in all constructs. Load and axial displacement were recorded while constructs were loaded to 2000 N in axial compression. Failure loads were not reported because no distinct yield point or failure point was evident within the load range for many specimens. Failure modes were recorded for each construct, and photographs of typical failures were obtained. Stiffness (N/mm) was calculated from load–displacement curves. Paired comparisons of mean stiffness were performed within study groups using a paired t‐test. Significance was set at P<.05. Results— The mean construct stiffnesses for the Slocum (383±183 N/mm) and Securos (258±64.1 N/mm) constructs were not significantly different (P=.164; power=0.566). The mean construct stiffness for the Synthes constructs (486±91.0 N/mm) was significantly greater than that of the Slocum constructs (400±117 N/mm); P=.0468. Modes of failure for the Slocum (16/16) and Securos (8/8) constructs included plastic deformation of the implant with valgus deformity combined with fibular luxation (2/16 Slocum; 1/8 Securos) or fibular fracture (2/16 Slocum; 4/8 Securos). Most Synthes constructs underwent elastic deformation (7/8). One Synthes construct fractured in the saggital plane through the tibial plateau depression at the point of load application. Conclusions— The Slocum and Securos plate/tibia construct have similar stiffness, whereas the Synthes/tibia constructs are significantly stiffer than the Slocum/tibia constructs. Modes of fixation failure observed in this model were consistent with TPLO fixation failures observed clinically. Clinical relevance— Construct stiffness in axial load varies with implant type. Implants that confer higher stiffness to the construct may result in greater fixation stability in tibial metaphyseal osteotomies.     

Evaluation of four interfragmentary Kirschner wire configurations as a component of screw/wire/polymethylmethacrylate fixation for acetabular fractures in dogs

The biomechanical contribution of the interfragmentary Kirschner wire as a component of composite fixation for acetabular fracture repair was subjectively and objectively evaluated. Acetabular osteotomies were repaired using the screw/wire/polymethylmethacrylate (SWP) composite fixation with or without one of three configurations of Kirschner wire in 32 hemipelves obtained from 16 dogs. Reduction, assessed objectively and subjectively, was unaffected by Kirschner wire placement. Hemipelves repaired with Kirschner wire(s) were subjectively more stable prior to application of polymethylmethacrylate when manually assessed in multiple planes. Consistent incremental increases in stiffness, yield load, and maximum load sustained that were observed during biomechanical testing were not significant, with the exception that hemipelves repaired with two Kirschner wires had significantly greater yield loads than hemipelves repaired without Kirschner wires. The subjective results of this study support the use of at least one interfragmentary Kirschner wire to maintain reduction prior to polymethylmethacrylate application; however, fracture configuration and location may dictate the number and pattern of interfragmentary Kirschner wires used to maintain reduction prior to application of the polymethylmethacrylate. The objective results and observations made during biomechanical testing suggest that use of one or more interfragmentary Kirschner wires may enhance stability after polymethylmethacrylate application.     

An In Vitro Biomechanical Comparison of a 5.5 mm Locking Compression Plate Fixation with a 4.5 mm Locking Compression Plate Fixation of Osteotomized Equine Third Metacarpal Bones

Objectives: To compare the monotonic biomechanical properties and fatigue life of a 5.5‐mm‐broad locking compression plate (5.5 LCP) fixation with a 4.5‐mm‐broad locking compression plate (4.5 LCP) fixation to repair osteotomized equine 3rd metacarpal (MC3) bones. Study Design: In vitro biomechanical testing of paired cadaveric equine MC3 with a middiaphyseal osteotomy, stabilized by 1 of 2 methods for fracture fixation. Animal Population: Fifteen pairs of adult equine cadaveric MC3 bones. Methods: Fifteen pairs of equine MC3 were divided into 3 test groups (5 pairs each) for (1) 4‐point bending single cycle to failure testing, (2) 4‐point bending cyclic fatigue testing, and (3) torsional single cycle to failure testing. An 8‐hole, 5.5 LCP was applied to the dorsal surface of 1 randomly selected bone from each pair and an 8‐hole, 4.5 LCP was applied dorsally to the contralateral bone from each pair using a combination of cortical and locking screws. All plates and screws were applied using standard ASIF techniques. All MC3 bones had middiaphyseal osteotomies. Mean test variable values for each method were compared using a paired t‐test within each group with significance set at P<.05. Results: Mean yield load, yield bending moment, composite rigidity, failure load, and failure bending moment, under 4‐point bending, single cycle to failure, of the 5.5 LCP fixation were significantly greater than those of the 4.5 LCP fixation. Mean cycles to failure in 4‐point bending of the 5.5 LCP fixation (170,535±19,166) was significantly greater than that of the 4.5 LCP fixation (129,629±14,054). Mean yield load, mean composite rigidity, and mean failure load under torsional testing, single cycle to failure was significantly greater for the broad 5.5 LCP fixation compared with the 4.5 LCP fixation. In single cycle to failure under torsion, the mean±SD values for the 5.5 LCP and the 4.5 LCP fixation techniques, respectively, were: yield load, 151.4±19.6 and 97.6±12.1 N m; composite rigidity, 790.3±58.1 and 412.3±28.1 N m/rad; and failure load: 162.1±20.2 and 117.9±14.6 N m. Conclusion: The 5.5 LCP was superior to the 4.5 LCP in resisting static overload forces (palmarodorsal 4‐point bending and torsional) and in resisting cyclic fatigue under palmarodorsal 4‐point bending. Clinical Relevance: These in vitro study results may provide information to aid in selection of an LCP for repair of equine long bone fractures.     

In vitro biomechanical comparison of equine proximal interphalangeal joint arthrodesis techniques: prototype equine spoon plate versus axially positioned dynamic compression plate and two abaxial transarticular cortical screws inserted in lag fashion

Objectives— To compare in vitro monotonic biomechanical properties of an equine spoon plate (ESP) with an axial 3‐hole, 4.5 mm narrow dynamic compression plate (DCP) using 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws (DCP‐TLS) inserted in lag fashion for equine proximal interphalangeal (PIP) joint arthrodesis. Study Design— Paired in vitro biomechanical testing of 2 methods of stabilizing cadaveric adult equine forelimb PIP joints. Animal Population— Cadaveric adult equine forelimbs (n=18 pairs). Methods— For each forelimb pair, 1 PIP joint was stabilized with an ESP (8 hole, 4.5 mm) and 1 with an axial 3‐hole narrow DCP (4.5 mm) using 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws inserted in lag fashion. Six matching pairs of constructs were tested in single cycle to failure under axial compression with load applied under displacement control at a constant rate of 5 cm/s. Six construct pairs were tested for cyclic fatigue under axial compression with cyclic load (0–7.5 kN) applied at 6 Hz; cycles to failure were recorded. Six construct pairs were tested in single cycle to failure under torsional loading applied at a constant displacement rate (0.17 radians/s) until rotation of 0.87 radians occurred. Mean values for each fixation method were compared using a paired t‐test within each group with statistical significance set at P<.05. Results— Mean yield load, yield stiffness, and failure load for ESP fixation were significantly greater (for axial compression and torsion) than for DCP‐TLS fixation. Mean (± SD) values for the ESP and DCP‐TLS fixation techniques, respectively, in single cycle to failure under axial compression were: yield load 123.9 ± 8.96 and 28.5 ± 3.32 kN; stiffness, 13.11 ± 0.242 and 2.60 ± 0.17 kN/cm; and failure load, 144.4 ± 13.6 and 31.4 ± 3.8 kN. In single cycle to failure under torsion, mean (± SD) values for ESP and DCP‐TLS, respectively, were: stiffness 2,022 ± 26.2 and 107.9 ± 11.1 N m/rad; and failure load: 256.4 ± 39.2 and 87.1 ± 11.5 N m. Mean cycles to failure in axial compression of ESP fixation (622,529 ± 65,468) was significantly greater than DCP‐TLS (95,418 ± 11,037). Conclusion— ESP was superior to an axial 3‐hole narrow DCP with 2 abaxial transarticular screws inserted in lag fashion in resisting static overload forces and cyclic fatigue. Clinical Relevance— In vitro results support further evaluation of ESP for PIP joint arthrodesis in horses. Its specific design may provide increased stability without need for external coaptation support.     

The Effect of Plate Luting on Reduction Accuracy and Biomechanics of Acetabular Osteotomies Stabilized With 2.7-mm Reconstruction Plates

OBJECTIVE: To compare the accuracy of reduction and biomechanical characteristics of acetabular osteotomies repaired with luted and nonluted reconstruction plates. STUDY DESIGN: In vitro study. ANIMALS: Pelves removed from 12 adult greyhounds. METHODS: Acetabular osteotomies were created and repaired with a 6-hole, 2.7-mm reconstruction plates in 24 cadaver hemipelves. Ten hemipelves each were assigned to group I and group II. An impression cast of each acetabulum in group I was made before luting (preluting cast). Group I plates were then elevated, luted, and replaced. A second cast of each acetabulum in group I was then made (postluting cast). Step, gap, and total areas of articular osteotomy incongruence were determined from the casts. Group I (luted plate repairs) and group II (nonluted plate repairs) hemipelves were loaded ventral-to-dorsal using a materials-testing machine. Stiffness, yield load, and maximal load sustained were determined. RESULTS: Mean gap and total area of articular osteotomy incongruence for group I preluted plate repairs (7.1 mm(2) and 8.6 mm(2), respectively) were significantly greater than for group I postluted plate repairs (4.1 mm(2) and 5.1 mm(2), respectively). Mean stiffness and maximal load for group I (681 N/mm and 2,555 N, respectively) were significantly greater than for group II (360 N/mm and 1,730 N, respectively). Mean step area and mean load at yield values were not significantly different between groups. CONCLUSIONS: Luted plate repairs of osteotomized acetabulae result in improved reduction and are stiffer and stronger than nonluted plate repairs. CLINICAL SIGNIFICANCE: Plate luting may improve the accuracy of reduction of acetabular fractures where anatomic reduction is required. Plate luting may also increase the stiffness and strength of fracture repairs and arthrodeses.     

A biomechanical comparison of external skeletal fixation and plating for the stabilization of ilial osteotomies in dogs

This in vitro study compares the biomechanical properties of two methods of ilial fracture repair in dogs. Ten pelves were harvested from skeletally mature mixed breed dogs weighing 20-27 kg and bilateral oblique ilial body osteotomies were created. One hemipelvis from each dog was stabilized with a 2.7 mm plate and screws and the contralateral hemipelvis was stabilized with a five pin linear external fixator construct. Each hemipelvis was mounted at an angle of 30 degrees to an actuator platform, such that the acetabulum was centrally loaded by a steel sphere attached to the load cell of a servohydraulic materials testing machine. The construct was loaded at a constant rate of 20 mm/min. A load/displacement curve was generated for each hemipelvis by plotting the sustained load against the actuator movement. The stiffness, yield load and failure load for each hemipelvis were determined from the load/displacement curve. Bending stiffness was defined as the slope of the load/displacement curve from 100 N to yield load. The mode of failure was determined by observations made during testing and gross inspection of each specimen. The mean construct stiffness, yield load and failure load were compared between stabilization groups using a Student's paired t-test with statistical significance set at p<0.05. Nine out of 10 of the hemipelves that were stabilized by plates and screws failed catastrophically by fracture through the caudal screw holes and nine out of 10 of the hemipelves that were stabilized using an external fixator failed by fracture of the ischium in the region supported by the mounting roller, propagating through the most caudal ischial pin. There was not any significant difference (P=0.22) in bending stiffness between stabilization techniques, but yield (1467 N vs 2620 N; P=0.04) and failure (1918 N vs 2687 N; P=0.002) loads were significantly greater for hemipelves stabilized with external fixators.     

Biomechanical Comparison of Two Plating Techniques for Fixation of Acetabular Osteotomies in Dogs

OBJECTIVE: To compare the failure properties of a 5-hole, 2.7-mm curved acetabular plate (AP) to a 5-hole, 3.5-mm reconstruction plate (RP) when applied to acetabular osteotomies. STUDY DESIGN: Cadaver study. ANIMALS OR SAMPLE POPULATION: Pelves of 8 mature, large-breed dogs. METHODS: A 5-hole, 2.7-mm AP and a 5-hole, 3.5-mm RP were contoured and applied to the dorsal acetabulum of each pelvis. A central acetabular fracture was simulated after plate application by a transverse osteotomy with a fine saw. Each acetabulum was loaded in a weight-bearing direction. A load-deformation curve was produced for each construct, and biomechanical properties of the AP and RP were compared with the Student's paired t-test. A P value of < .05 was considered significant. RESULTS: For the AP and RP composite respectively, the mean +/- SD maximum load to failure was 2,721 +/- 632 N and 2,488 +/- 800 N, the stiffness was 4.8 +/- 1.8 N/m and 5.3 +/- 1.9 N/m, and the energy absorbed was 15.1 +/- 5.2 Nm and 16.3 +/- 8.3 Nm. None of these differences was statistically significant. CONCLUSIONS: Both fixation techniques provided comparable strength, stiffness, and energy absorbed under the loading conditions of this study. CLINICAL RELEVANCE: Because of the relative ease of application, the 2.7-mm curved AP may be the practical choice for acetabular fracture repair in large dogs.     

Biomechanical Evaluation of Acetabular Cup Implantation in Cementless Total Hip Arthroplasty

Objective: To report biomechanical properties of the Biologic Fixation System (BFX) acetabular cup impacted into a normal canine pelvis and to compare the effect of implant positioned to and beyond the medial acetabular wall. Study Design: In vitro cadaveric study. Animals: Hemipelves of mature, large‐breed dogs (n=6). Methods: For each dog, 1 hemipelvis was reamed to the depth of the acetabular wall (group A) and 1 was reamed an additional 6 mm after penetration of the medial cortex of the acetabulum (group B). The hemipelves were implanted with acetabular cups and loaded in compression through a matching femoral prosthetic component until failure. Specimen stiffness, and failure displacement, load, and energy were determined from load and displacement data and results between groups compared with a paired t‐test. Results: Mean failure load was greater in group A (3812 ± 391 N) than group B (2924 ± 316 N; P<.014). No other differences (P>.05) were observed between groups. Bone fracture (n=5) and cup displacement (1) occurred in group A whereas in group B there were 3 fractures and 3 cup displacements. Conclusions: Although medial placement of the BFX cup affected compressive failure loads, failure loads for both groups exceeded normal physiologic loads. Clinical Relevance: Medial positioning of the acetabular cup does not appear to compromise acetabular implant‐pelvic stability under normal physiologic loads. Because arthroplasty candidates often have abnormal acetabular architecture, mechanical properties of the cup placed in acetabula without a dorsal rim should be investigated.     

In vitro biomechanical comparison of locking compression plate fixation and limited-contact dynamic compression plate fixation of osteotomized equine third metacarpal bones

Objective— To compare monotonic biomechanical properties and fatigue life of a broad locking compression plate (LCP) fixation with a broad limited contact dynamic compression plate (LC‐DCP) fixation to repair osteotomized equine third metacarpal (MC3) bones. Study Design— In vitro biomechanical testing of paired cadaveric equine MC3 with a mid‐diaphyseal osteotomy, stabilized by 1 of 2 methods for fracture fixation. Animal Population— Cadaveric adult equine MC3 bones (n=12 pairs). Methods— MC3 were divided into 3 groups (4 pairs each) for: (1) 4‐point bending single cycle to failure testing; (2) 4‐point bending cyclic fatigue testing; and (3) torsional single cycle to failure testing. The 8‐hole, 4.5 mm LCP was applied to the dorsal surface of 1 randomly selected bone from each pair. One 8‐hole, 4.5 mm LC‐DCP) was applied dorsally to the contralateral bone from each pair. All plates and screws were applied using standard ASIF techniques. All MC3 bones had mid‐diaphyseal osteotomies. Mean test variable values for each method were compared using a paired t‐test within each group. Significance was set at P<.05. Results— Mean yield load, yield bending moment, composite rigidity, failure load and failure bending moment, under 4‐point bending, single cycle to failure, of the LCP fixation were significantly greater than those of the LC‐DCP fixation. Mean cycles to failure for 4‐point bending was significantly greater for the LCP fixation compared with LC‐DCP fixation. Mean yield load, mean composite rigidity, and mean failure load under torsional testing, single cycle to failure was significantly greater for the broad LCP fixation compared with the LC‐DCP fixation. Conclusion— The 4.5 mm LCP was superior to the 4.5 mm LC‐DCP in resisting the static overload forces (palmarodorsal 4‐point bending and torsional) and in resisting cyclic fatigue under palmarodorsal 4‐point bending. Clinical Relevance— The results of this in vitro study may provide information to aid in the selection of a biological plate for the repair of equine long bone fractures.     

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.     

An in vitro biomechanical comparison of a 5.5 mm limited-contact dynamic compression plate fixation with a 4.5 mm limited-contact dynamic compression plate fixation of osteotomized equine third metacarpal bones

Objectives— To compare monotonic biomechanical properties and fatigue life of a 5.5 mm broad limited‐contact dynamic compression plate (5.5‐LC‐DCP) fixation with a 4.5 mm broad LC‐DCP (4.5‐LC‐DCP) fixation to repair osteotomized equine third metacarpal (MC3) bones. Study Design— In vitro biomechanical testing of paired cadaveric equine MC3 with a mid‐diaphyseal osteotomy, stabilized by 1 of 2 methods for fracture fixation. Sample Population— Adult equine cadaveric MC3 bones (n=18 pair). Methods— MC3 were divided into 3 test groups (6 pairs each) for: (1) 4‐point bending single cycle to failure testing; (2) 4‐point bending cyclic fatigue testing; and (3) torsional single cycle to failure testing. The 8‐hole, 5.5 mm broad LC‐DCP (5.5‐LC‐DCP) was applied to the dorsal surface of 1 randomly selected bone from each pair. One 8‐hole, 4.5 mm broad LC‐DCP (4.5‐LC‐DCP) was applied dorsally to the contralateral bone from each pair. Plates and screws were applied using standard ASIF techniques. All MC3 bones had mid‐diaphyseal osteotomies. Mean test variable values for each method were compared using a paired t–test within each group. Significance was set at P<.05. Results— Mean yield load, yield bending moment, composite rigidity, failure load and failure bending moment under 4‐point bending, single cycle to failure, of the 5.5‐LC‐DCP fixation were significantly greater (P<.024) than those of the 4.5‐LC‐DCP fixation. Mean cycles to failure for 4‐point bending was significantly (P<.05) greater for the 4.5‐LC‐DCP fixation compared with the 5.5‐LC‐DCP fixation. Mean yield load, mean composite rigidity, and mean failure load in torsion for the 5.5‐LC‐DCP fixation was not significantly different (P>.05) than those with the 4.5‐LC‐DCP fixation. Conclusion— 5.5‐LC‐DCP fixation was superior to 4.5‐LC‐DCP fixation in resisting the static overload forces under palmarodorsal 4‐point bending. There was no significant difference between 5.5‐LC‐DCP fixation and 4.5‐LC‐DCP fixation in resisting static overload forces under torsion; however, the 5.5‐LC‐DCP offers significantly less stability (80% of that of the 4.5‐LC‐DCP) in cyclic fatigue testing. Clinical Relevance— The results of this in vitro study may provide information to aid in the selection of a biological plate for long bone fracture repair in horses.     

Biomechanical comparison of a circular external skeletal fixator construct to pin and tension band wire fixation for the stabilization of olecranon osteotomies in dogs: a cadaveric study

OBJECTIVE: To compare anatomic reduction and the biomechanical properties of a circular external skeletal fixator (CESF) construct to pin and tension band wire (PTBW) fixation for the stabilization of olecranon osteotomies in dogs. STUDY DESIGN: Cadaveric study. ANIMALS: Forelimbs from 12 skeletally mature mixed-breed dogs, weighing 23 to 28 kg. METHODS: An olecranon osteotomy was stabilized with either a CESF construct or PTBW fixation. A single distractive load to failure was applied to each specimen through the triceps tendon. Osteotomy reduction and biomechanical properties were compared between fixation groups. RESULTS: Reduction was not significantly different (gap: P =.171; malalignment: P =.558) between fixation groups. Osteotomies stabilized with the CESF had greater stiffness (P <.0001) and maximum load sustained (P <.0001) compared to PTBW fixation. There was no significant difference for yield load (P =.318) or for load at 1 mm of axial displacement (P =.997) between fixation groups. Failure of fixation occurred by bending of the intramedullary Steinmann pin and the fixation wires in the CESF specimens and by untwisting of the tension band wire knot with pullout and bending of the Kirschner wires in the PTBW specimens. CONCLUSIONS: Specimens stabilized with the CESF construct had similar reduction and yield load, greater stiffness and maximum load sustained, and less elastic deformation than specimens stabilized with PTBW fixation. CLINICAL RELEVANCE: The CESF construct may provide a biomechanically favorable alternative to PTBW fixation for stabilization of olecranon osteotomies in dogs, and its application warrants clinical investigation.     

A Laparoscopic‐Sutured Gastropexy Technique In Dogs: Mechanical and Functional Evaluation

Objective— To describe a laparoscopic‐sutured gastropexy technique in dogs and evaluate the tensile strength of the adhesion and effects on gastric function. Study Design— Experimental study. Animals— Female beagle dogs (n=7). Methods— A laparoscopic‐sutured gastropexy technique was evaluated by ex vivo tensile distraction tests 10 weeks after surgery. The effect of the adhesion on gastric emptying, mucosal permeability, and systemic inflammation were evaluated by monitoring the C‐reactive protein (CRP) and sucrose permeability, and by radiographic evaluation of gastric emptying 2 weeks before and 10 weeks after surgery. Results— Mean (±SD) tensile force to disrupt adhesions was 51.1±16.4 N. There was no significant postoperative increase in CRP concentration or change in sucrose permeability. The area under the curve representing the postprandial decrease in gastric radiographic area increased by 11% after gastropexy. Conclusions— This laparoscopic gastropexy technique had appropriate mechanical and functional characteristics with limited morbidity. Clinical Relevance— This laparoscopic‐sutured gastropexy provides adhesion strength comparable with other gastropexy techniques tested at 10 weeks postoperatively. Only minor changes in gastric emptying were observed 10 weeks after surgery.     

Mechanical comparison of two suture constructs for extra-capsular stifle stabilization

Objective: Mechanical evaluation of 2 suture constructs for extracapsular stifle stabilization. Study Design: In vitro study. Sample Population: Crimped interlocking loop constructs (ILC) of 45 kg nylon leader line (NLL) and Orthofiber^® (OF). Methods: ILC were tightened to 100 N, then crimp secured. Ramp to failure (n=10/group)—Data were derived from force/displacement plots. Stress–relaxation testing (n=10/group)—ILC's were nondestructively loaded and held at resultant displacement as force data were recorded. Incremental, cyclic loading (n=10/group)—ILC's were loaded (5 cycles/set) starting at 100 N and incrementally increased by 50 N (1 and 3 Hz protocols). Loop tension and elongation were recorded after each set. Results: Ramp to failure—initial loop tension was similar (NLL 75.5 ± 9.5 N; OF 68.7 ± 10.4 N, P=.140). Tested OF constructs were stiffer (NLL 125.7 ± 4.0; OF 234.6 ± 25.0 N/mm, P≤.001), had lower yield load (NLL 193.6 ± 13.8; OF 137.3 ± 94.3 N, P≤.001), lower peak load (NLL 873.7 ± 68.6; OF 653.6 ± 80.2 N, P≤.001), and lower elongation at failure (NLL 19.1 ± 1.4; OF 5.2 ± 1.0 mm, P≤.001) and at yield (NLL 1.52 ± 0.2; OF 0.3 ± 0.6 mm, P=.003) than NLL constructs. Yield in NLL ILC's was variable knot tightening/crimp slippage, but only crimp‐suture slippage in OF. Stress–relaxation testing—OF demonstrated greater relaxation. Incremental, cyclic loading—induced ILC elongation and tension loss in both groups, independent of loading frequency. NLL lost tension at lower rate, but elongated more than OF. Conclusions: NLL construct is mechanically superior to OF construct.     

Acetabular ventroversion with double pelvic osteotomy versus triple pelvic osteotomy: a cadaveric study in dogs

Objective: To determine which of 3 different plate angles (20°, 25°, 30°) used in double pelvic osteotomy (DPO) would result in the most similar acetabular angle (AA) achieved with a 20° triple pelvic osteotomy (TPO) technique in dogs. Study Design: Experimental anatomic study. Animals: Cadaveric canine pelves (n=8). Methods: Transverse plane computed tomographic images of cadaveric pelves with intact sacroiliac joints, mounted in a custom jig, were made (baseline) and again after DPO (20°, 25°, 30°) and TPO (20°) and pelvic angles measured in 6 transverse planes. Pelvic angles of the 3 DPO techniques were compared with TPO using concordance correlation to determine which DPO angle resulted in an acetabular ventroversion angle closest to TPO. Results: Mean ± SD AAs were 32.89 ± 2.23 (baseline), 47.39 ± 4.39 (20° DPO), 51.43 ± 5.06 (25° DPO), 54.75 ± 4.38 (30° DPO), and 50.20 ± 5.76 (20° TPO). Concordance correlations for the AA compared with 20° TPO were 0.027 (baseline), 0.721 (20° DPO), 0.902 (25° DPO), and 0.593 (30° DPO). A concordance correlation of ≥0.8 indicates good correlation. Conclusions: A 25° DPO is most similar in acetabular ventroversion to 20° TPO (concordance correlation, 0.902).     

Mechanical evaluation of pin and tension-band wire factors in an olecranon osteotomy model

OBJECTIVE: To evaluate the effect of altering pin and wire diameter, wire position and configuration, and osteotomy angle on applied load and absorbed strain energy in a pin and tension-band wire (PTBW) fixation model. STUDY DESIGN: In vitro mechanical study. SAMPLE POPULATION: Delrin models (n=96). METHODS: PTBW was applied to Delrin olecranon osteotomy models. A control configuration was defined and then altered, 1 variable (wire diameter, pin diameter, wire-hole position, wire configuration, osteotomy angle) at a time, to create 11 test configurations. Tensile force was applied and displacement at the caudal aspect of the osteotomy was measured. Fixation strength, in terms of tensile load and strain energy, was compared between control and each test configuration at 4 osteotomy displacements. RESULTS: Models with larger wire, pins, or combined figure-of-eight/lateral wires were stronger than control, whereas those with smaller wire, pins, or a solitary lateral wire were weaker. The superior strength of the larger wire was apparent for all assessed osteotomy displacement. CONCLUSIONS: PTBW fixation strength increases as implant diameter is increased, with wire diameter having greatest effect. Lateral wire configuration is weaker than figure-of-eight, but can be added to figure-of-eight configuration to increase strength. Wire-hole position and osteotomy angle have little effect on PTBW strength. CLINICAL RELEVANCE: Wire diameter is the key determinant of PTBW strength, whereas pin diameter is somewhat less critical. Wire passage through an additional hole proximally provides equivalent strength and may avoid soft-tissue entrapment and subsequent loosening.     

Results of Screw/Wire/Polymethylmethacrylate Composite Fixation for Acetabular Fracture Repair in 14 Dogs

Objective- To assess the clinical results in dogs with acetabular fractures stabilized using a screw-wire-polymethylmethacrylate (SWP) composite fixation.
Study Design- A retrospective study of client-owned dogs with acetabular fractures.
Animals- Fourteen dogs ranging in age from 4 to 95 months (mean, 34 ±25 months; median, 25 months) and body weight from 8 to 39 kg (mean, 25 ±6 kg; median, 27 kg).
Methods- Medical records and radiographs were retrospectively evaluated to determine location of the fracture, presence of preexisting degenerative joint disease, accuracy of fracture reduction and complications associated with surgery. Long-term results were evaluated by subjective assessment of lameness, elicitation of pain and/or crepitus on manipulation of the coxofemoral joint, measurements of pelvic limb circumference, coxofemoral joint goniometric measurements, and radiographic evaluation.
Results- Fracture reduction was considered anatomic in 13 dogs. At the time of the last follow-up evaluation (mean, 347 ±261 days; median, 380 days) 10 dogs were sound on the affected limb, three dogs had a subtle weight-bearing lameness of the affected limb, and the remaining dog had a consistent non-weight-bearing lameness of the affected limb. Mild (n = 10) or moderate (n = 1) degenerative changes of the affected coxofemoral joint attributed to the acetabular fracture and its repair were noted on the follow-up radiographs in 11 dogs. Limb circumference of the affected limb ranged from -8.2% to +10.8% (mean, -0.8 ±4.2%; median, -0.7%) of the contralateral limb.
Conclusions- The SWP composite fixation consistently maintained anatomic reduction, was associated with few complications, and yielded satisfactory clinical results.
Clinical Relevance- The SWP composite fixation technique would seem to be an acceptable means of stabilizing acetabular fractures in dogs.     

An in vitro biomechanical comparison of a limited-contact dynamic compression plate fixation with a dynamic compression plate fixation of osteotomized equine third metacarpal bones

OBJECTIVES: To compare the monotonic biomechanical properties and fatigue life of a broad, limited contact, dynamic compression plate (LC-DCP) fixation with a broad, dynamic compression plate (DCP) fixation to repair osteotomized equine 3rd metacarpal (MC3) bones. STUDY DESIGN: In vitro biomechanical testing of paired cadaveric equine MC3 with a mid-diaphyseal osteotomy, stabilized by 1 of 2 methods for fracture fixation. ANIMAL POPULATION: Twelve pairs of adult equine cadaveric MC3 bones. METHODS: Twelve pairs of equine MC3 were divided into 3 test groups (4 pairs each) for (1) 4-point bending single cycle to failure testing, (2) 4-point bending cyclic fatigue testing, and (3) torsional single cycle to failure testing. An LC-DCP (8-hole, 4.5 mm) was applied to the dorsal surface of 1 randomly selected bone from each pair. One DCP (8-hole, 4.5 mm broad) was applied dorsally to the contralateral bone from each pair. All plates and screws were applied using standard AO/ASIF techniques to MC3 bones that had mid-diaphyseal osteotomies. Mean test variable values for each method were compared using a paired t-test within each group. Significance was set at P<.05. RESULTS: The mean 4-point bending yield load, yield bending moment, composite rigidity, failure load, and failure bending moment of LC-DCP fixation were significantly greater (P<.01) than those of broad DCP fixation. Mean cycles to failure for 4-point bending was significantly (P<.001) greater for broad DCP fixation compared with broad LC-DCP fixation. Mean yield load, mean composite rigidity, and mean failure load in torsion was significantly (P<.02) greater for broad LC-DCP fixation compared with broad DCP fixation. CONCLUSION: Broad LC-DCP offers increased stability in static overload testing, however, it offers significantly less stability in cyclic fatigue testing. CLINICAL RELEVANCE: The clinical relevance of the cyclic fatigue data supports the conclusion that the broad DCP fixation is biomechanically superior to the broad LC-DCP fixation in osteotomized equine MC3 bones despite the results of the static overload testing.