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.     

A mechanical comparison of equine proximal interphalangeal joint arthrodesis techniques: an axial locking compression plate and two abaxial transarticular cortical screws versus an axial dynamic compression plate and two abaxial transarticular cortical screws

Objectives: To compare in vitro monotonic biomechanical properties of an axial 3‐hole, 4.5 mm narrow locking compression plate (ELCP) using 5.0 mm locking screws and 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws inserted in lag fashion (ELCP–TLS) 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 inserted in lag fashion (DCP–TLS) for equine proximal interphalangeal (PIP) joint arthrodesis. Design: Experimental. Animal Population: Cadaveric adult equine forelimbs (n=18 pairs). Methods: For each forelimb pair, 1 PIP joint was stabilized with an axial ELCP using 5.0 mm locking screws and 5.5 mm cortical screws in conjunction with 2 abaxial transarticular 5.5 mm cortical screws inserted in lag fashion and 1 PIP joint 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, 6 construct pairs were tested for cyclic fatigue under axial compression, and 6 construct pairs were tested in single cycle to failure under torsional loading. 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 under axial compression, single cycle to failure, of the DCP–TLS fixation were significantly greater than those of the LCP–TLS fixation. There was no significant difference between the mean number of cycles to failure in axial compression of the LCP–TLS and the DCP–TLS fixations. Mean yield load, yield stiffness, and failure load under torsion, single cycle to failure, of the LCP–TLS fixation were significantly greater than those of the DCP–TLS fixation. Conclusion: The DCP–TLS construct provided significantly greater stability under axial compression in single cycle to failure than the ELCP–TLS construct, the ELCP–TLS construct provided significantly greater stability under torsional loading in single cycle to failure than the DCP–TLS construct, and there was no significant difference in stability between the 2 constructs for cyclic loading under axial compression.     

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

Objectives: To compare number of cycles to failure for palmarodorsal 4‐point bending of a modified 5.5 mm broad locking compression plate (M5.5‐LCP) fixation with a 5.5 mm broad LCP (5.5‐LCP) fixation used to repair osteotomized equine third metacarpal (MC3) bones. Study Design: In vitro biomechanical testing. Animal Population: Adult equine cadaveric MC3 bones (n=6 pairs). Methods: An 8‐hole, M5.5‐LCP, obtained by having a 1.0 mm thickness removed from the bone contact portion of the 5.5‐LCP, was applied to the dorsal surface of 1 randomly selected MC3 from each pair, and an 8‐hole, 5.5‐LCP was applied dorsally to the contralateral bone from each pair using a combination of cortical and locking screws. Plates and screws were applied using standard ASIF techniques to MC3 bones with a mid‐diaphyseal osteotomy. MC3 constructs had palmarodorsal 4‐point bending cyclic fatigue testing. Mean cycles to failure for each method were compared using a paired t‐test within each group. Significance was set at P<.05. Results: Mean±SD cycles to failure of the M5.5‐LCP fixation (188,641±17,971) was significantly greater than that of the 5.5‐LCP fixation (166,497±15,539). Conclusion: M5.5‐LCP fixation was superior to 5.5‐LCP fixation of osteotomized equine MC3 bones in resisting cyclic fatigue under palmarodorsal 4‐point bending. Clinical Relevance: This suggests that biological plate fixation is not the ideal choice for osteotomized equine MC3 bones.     

An In Vitro Biomechanical Comparison of Equine Proximal Interphalangeal Joint Arthrodesis Techniques: An Axial Positioned Dynamic Compression Plate and Two Abaxial Transarticular Cortical Screws Inserted in Lag Fashion Versus Three Parallel Transarticular Cortical Screws Inserted in Lag Fashion

Objectives— To compare in vitro monotonic biomechanical properties of 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 inserted in lag fashion (DCP‐TLS) with 3 parallel transarticular 5.5 mm cortical screws inserted in lag fashion (3‐TLS) for the equine proximal interphalangeal (PIP) joint arthrodesis. Study Design— Paired in vitro biomechanical testing of 2 methods of stabilizing cadaveric adult equine forelimb PIP joints. Sample Population— Cadaveric adult equine forelimbs (n=15 pairs). Methods— For each forelimb pair, 1 PIP joint was stabilized 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 and 1 with 3 parallel transarticular 5.5 mm cortical screws inserted in lag fashion. Five matching pairs of constructs were tested in single cycle to failure under axial compression, 5 construct pairs were tested for cyclic fatigue under axial compression, and 5 construct pairs were tested in single cycle to failure under torsional loading. 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 under axial compression and torsion, single cycle to failure, of the DCP‐TLS fixation were significantly greater than those of the 3‐TLS fixation. Mean cycles to failure in axial compression of the DCP‐TLS fixation was significantly greater than that of the 3‐TLS fixation. Conclusion— The DCP‐TLS was superior to the 3‐TLS in resisting the static overload forces and in resisting cyclic fatigue. Clinical Relevance— The results of this in vitro study may provide information to aid in the selection of a treatment modality for arthrodesis of the equine PIP joint.     

A mechanical comparison of 4.5 mm narrow and 3.5 mm broad plating systems for stabilization of gapped fracture models

OBJECTIVE: To evaluate and compare the mechanical properties of 4.5 narrow and 3.5 broad plating systems using their respective cortical and cancellous screws in unstable, central, and eccentric gap fracture models. STUDY DESIGN: Mechanical evaluation and comparison of 2 dynamic compression plate (DCP) systems. SAMPLE POPULATION: Eighteen cortical and 30 cancellous gapped fracture models. METHODS: DCP (4.5 mm narrow, 3.5 mm broad) with their respective cortical screws were applied to cortical bone density polyurethane foam blocks to construct center gap cortical fracture models that were tested in gap closing monotonic 4-point bending. DCP (4.5 mm narrow, 3.5 mm broad) with their respective cancellous screws were applied to cancellous bone density polyurethane foam blocks to construct eccentric gap cancellous fracture models. The cancellous constructs were tested in monotonic gap opening and gap closing cantilever bending and in cyclic axial loading. Univariate and multivariate repeated measures ANOVA were used to compare the maximum loads at failure of the 4.5 mm constructs and 3.5 mm constructs. RESULTS: The 4.5 mm narrow plating system withstood significantly higher loads at failure than the 3.5 mm broad plating system in 4-point bending (P<.0001) and gap opening cantilever bending (P<.0001). The 4.5 mm system failed in gap closing cantilever bending by plastic deformation of the plate, whereas the 3.5 mm system failed by screw pullout. There was no difference between the 2 systems in cyclic axial loading. CONCLUSION: Results indicate that the 4.5 mm narrow plating system has a mechanical advantage over the 3.5 mm broad plating system for stabilization of gapped fracture models. CLINICAL RELEVANCE: The 4.5 mm narrow plating system may be mechanically advantageous compared with the 3.5 mm broad plating system for stabilizing unreconstructed comminuted long bone fractures in large dogs.     

Comparison of a 3-hole 4.5-mm Dynamic Compression Plate and a 7-hole 5.5-mm Y Locking Compression Plate for Arthrodesis of the Proximal Interphalangeal Joint in Horses—an Ex Vivo Biomechanical Study

The objective of this study was to compare the biomechanical properties in a single cycle axial loading test and the types of failures in two constructs (a 3-hole 4.5-mm dynamic compression plate (DCP) and 7-hole 5.5-mm Y locking compression plate (Y-LCP)) in equine proximal interphalangeal joint (PIJ) arthrodesis. One limb in each pair was randomly assigned to PIJ arthrodesis using a 3-hole 4.5-mm DCP combined with two transarticular 5.5-mm cortical screws, whereas the contralateral limb was submitted to PIJ arthrodesis using a 7-hole Y-shaped 5.0-mm LCP in conjunction with one transarticular 4.5-mm cortical screw inserted through the central plate hole. Cortical screws were inserted in lag fashion. Constructs were submitted to a single axial load cycle to failure. Construct stiffness, load, and deformation were analyzed. Dynamic compression plate and Y-LCP arthrodesis constructs did not differ significantly and were equally resistant to axial loading under the conditions studied (DCP and Y-LCP group stiffness, 5685.22 N/mm and 6591.10 N/mm, respectively). Arthrodesis of the PIJ using a DCP and two transarticular 5.5-mm cortical screws or a Y-LCP yielded biomechanically equivalent outcomes under the test conditions considered. However, Y-LCP provides less impact in the palmar/plantar bone. Application of Y-LCP with unicortical screws has equivalent biomechanical characteristics of DCP and may be a safe option for PIJ arthrodesis, where potential trauma secondary to applying bicortical screws in the palmar/plantar aspect of the pastern can be avoided.     

Assessment of stiffness and strength of 4 different implants available for equine fracture treatment: a study on a 20 degrees oblique long-bone fracture model using a bone substitute

OBJECTIVE: To compare the mechanical properties of 4 stabilization methods for equine long-bone fractures: dynamic compression plate (DCP), limited contact-DCPlate (LC-DCP), locking compression plate (LCP), and the clamp-rod internal fixator (CRIF--formerly VetFix). STUDY DESIGN: In vitro mechanical study. SAMPLE POPULATION: Bone substitute material (24 tubes) was cut at 20 degrees to the long axis of the tube to simulate an oblique mid-shaft fracture. METHODS: Tubes were divided into 4 groups (n=6) and double plated in an orthogonal configuration, with 1 screw of 1 implant being inserted in lag fashion through the "fracture". Thus, the groups were: (1) 2 DCP implants (4.5, broad, 10 holes); (2) 2 LC-DCP implants (5.5, broad, 10 holes); (3) 2 LCP implants (4.5/5.0, broad, 10 holes) and 4 head locking screws/plate; and (4) 2 CRIF (4.5/5.0) and 10 clamps in alternating position left and right of the rod. All constructs were tested in 4-point bending with a quasi-static load until failure. The implant with the interfragmentary screw was always positioned on the tension side of the construct. Force, displacement, and angular displacement at the "fracture" line were determined. Construct stiffness under low and high loads, yield strength, ultimate strength, and maximum angular displacement were determined. RESULTS: None of the implants failed; the strength of the bone substitute was the limiting factor. At low loads, no differences in stiffness were found among groups, but LCP constructs were stiffer than other constructs under high loads (P=.004). Ultimate strength was lowest in the LCP group (P=.01), whereas yield strength was highest for LCP constructs (409 N m, P=.004). CRIF had the lowest yield strength (117 N m, P=.004); no differences in yield strength (250 N m) were found between DCP and LC-DCP constructs. Differences were found for maximum angular displacement at the "fracture" line, between groups: LPC相似文献   

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.     

Arthrodesis of the equine proximal interphalangeal joint: a biomechanical comparison of 3-hole 4.5 mm locking compression plate and 3-hole 4.5 mm narrow dynamic compression plate, with two transarticular 5.5 mm cortex screws

Objectives: To compare the biomechanical characteristics of 2 arthrodesis techniques for the equine proximal interphalangeal joint (PIP) using either a 3‐hole 4.5 mm locking compression plate (LCP) or 3‐hole 4.5 mm narrow dynamic compression plate (DCP), both with 2 transarticular 5.5 mm cortex screws. Study Design: Experimental. Sample Population: Cadaveric adult equine forelimbs (^*n=6 pairs). Methods: For each forelimb pair, 1 limb was randomly assigned to 1 of 2 treatment groups and the contralateral limb by default to the other treatment group. Construct stiffness, gap formation across the PIP joint, and rotation about the PIP joint were determined for each construct before cyclic axial loading and after each of four, 5000 cycle loading regimens. After the 20,000 cycle axial loading regimen, each construct was loaded to failure. Results: There were no significant differences in construct stiffness, gap formation, or sagittal plane rotation between the LCP and DCP treatment groups at any of the measured time points. Conclusion: Biomechanically, fixation of the equine PIP joint with a 3‐hole 4.5 mm LCP is equivalent to fixation with a 3‐hole 4.5 mm narrow DCP under the test conditions used.     

In Vitro Mechanical Comparison of 2.0 and 2.4 Limited‐Contact Dynamic Compression Plates and 2.0 Dynamic Compression Plates of Different Thicknesses

Objective: To compare the bending structural stiffness and bending strength of thick and thin 2.4 mm limited contact dynamic compression plates (2.4 LC‐DCP), 2.0 mm LC‐DCP (2.0 LC‐DCP), and 2.0 dynamic compression plates (2.0 DCP). Study Design: In vitro mechanical study. Methods: Two thicknesses of 2.4 LC‐DCP, 2.0 LC‐DCP, and 2.0 DCP stainless‐steel plates were tested in 4‐point bending. Data were collected during bending until implants plastically deformed. Bending structural stiffness and bending strength were determined from load displacement curves. Mechanical properties were compared between plates and the effects of plate type, size, and thickness on stiffness and strength were assessed using ANOVA. Results: The thick 2.4 LC‐DCP implant was the stiffest and strongest; the thin 2.0 DCP implant was most compliant and weakest. Larger sized plates, thicker plates, and limited contact design of plates enhanced stiffness and strength. For the plates studied, plate size had a larger effect than plate type or thickness on stiffness and strength. Conclusion: Increasing the size (width) and thickness of plates increases both the bending structural stiffness and strength. For the plates studied, LC‐DCP implants were stiffer and stronger than DCP implants. Clinical Relevance: Plate bending structural stiffness and strength can be most effectively enhanced by using a larger sized plate, but gains can also be achieved by using a thicker plate and/or an LC‐DCP instead of a DCP implant when possible.     

An in vitro biomechanical study of bone plate and interlocking nail in a canine diaphyseal femoral fracture model

OBJECTIVE: To compare the structural properties and the interfragmentary motion in ostectomized canine femurs stabilized with either an 8-mm interlocking nail system (IN) or a 10-hole dynamic compression broad plate (DCP). ANIMAL OR SAMPLE POPULATION: Ten pairs of adult canine femurs with a 25-mm mid-diaphyseal gap. METHODS: Bone specimens were divided into 2 groups (10 femurs each). Left femurs were stabilized with a DCP and 8 bicortical screws; right femurs were stabilized with an IN and 3 screws. Mechanical tests were performed in eccentric axial loading and in craniocaudal bending. The testing was first conducted nondestructively and then until breakage. Structural properties, ie, stiffness, yield limits, and failure limits, were determined. Interfragmentary motion was measured during nondestructive tests with the use of an optoelectronic device. Axial, transverse, and rotational motions were calculated. Mean values of stiffness, yield and failure limits, and axial and shear motions for each fixation method were compared using a paired t test within each group (P <.05). RESULTS: Mean (+/-SD) values of stiffness and failure limit were significantly higher for IN constructs than for DCP constructs in compression, while there was little difference in the results between each tested group in bending. Mean yield load values were significantly higher for IN than for DCP specimens in compression as well as in bending. The axial-motion analysis revealed significant differences between IN and DCP groups during bending tests only. The highest score of transverse motion at the gap was recorded during bending tests, and was higher for DCP than for IN specimens. There were insignificant differences between the two groups with regard to rotation around the diaphyseal axis. CONCLUSIONS AND CLINICAL RELEVANCE: Structural properties and interfragmentary shear motion analysis demonstrated a much higher rigidity in the IN-bone than in the DCP-bone constructs.     

An In Vitro Biomechanical Comparison of Dynamic Condylar Screw Plate Combined with a Dorsal Plate and Double Plate Fixation of Distal Diaphyseal Radial Osteotomies in Adult Horses

Objective— To compare stiffness and strength of a dynamic condylar screw plate combined with dorsal broad dynamic compression plate (DCS–bDCP) fixation with double broad dynamic compression plate (dbDCP) fixation used to repair oblique distal fractures of adult equine radii. Study Design— Experimental. Sample Population— Adult equine radii (n=10 pair). Methods— An unconstrained three‐dimensional loading–measurement system was used to determine stiffness of a 50 mm long intact, and then DCS–bDCP or dbDCP‐plated osteotomized/ostectomized segment of radii when subjected to a nondestructive sequence of compression, torsion, and lateral‐to‐medial (LM), medial‐to‐lateral (ML), cranial‐to‐caudal (CrCa), and caudal‐to‐cranial (CaCr) bending. Uniform load over the entire length of construct identified its weakest characteristics during torsion and LM and CrCa bending to failure. Results— No difference was observed between osteotomized/ostectomized DCS–bDCP and dbDCP construct stiffness for all 6 loading modes, and strength for all 3 failure loads. Ostectomized DCS–bDCP and dbDCP construct stiffness was significantly lower than osteotomized radii, the latter approaching intact for axial, LM, and CrCa bending. Most frequent failure was bone fracture through exit site of a screw located adjacent to osteotomy/ostectomy. Conclusions— DCS–DCP and dbDCP constructs had comparable strength and stiffness when repairing osteotomies/ostectomies in equine adult radius bone. Fracture reduction increased stiffness that approached intact bone for loads that placed the unplated side in compression. Clinical Relevance— DCS–bDCP and dbDCP constructs are comparable in stiffness and strength when applied to oblique distal diaphyseal osteotomies/ostectomies in equine radius bone. However, the DCS's localized effect on distal epiphyseal structure because of additional bone removal remains to be investigated under in vivo articular loading conditions.     

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.     

A Biomechanical Comparison of 7-Hole 3.5 mm Broad and 5-Hole 4.5 mm Narrow Dynamic Compression Plates

Seven-hole 3.5 mm broad and 5-hole 4.5 mm narrow dynamic compression plates were applied to paired canine cadaveric tibias in a stable fracture model. Paired tibias were tested to acute failure in rotation and four-point bending, and to fatigue failure in four-point bending. Resistance to screw pullout was measured for three 3.5 mm cortical screws and two 4.5 mm cortical screws inserted in the configurations of the bone plates. All plate-bone systems failed by fracture of the bone through a screw hole. The 3.5 mm plate-bone system was stronger in acute failure in rotation and in four-point bending. There was no difference in stiffness, and no difference in the number of cycles to failure in fatigue testing. Three 3.5 mm screws had greater resistance to pullout than two 4.5 mm screws. Results indicate that the 7-hole 3.5 mm broad dynamic compression plate has a biomechanical advantage over the 5-hole 4.5 mm narrow dynamic compression plate.     

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.     

In vitro biomechanical comparison of dynamic compression plates with a rough contact surface and a polished contact surface for fixation of osteotomized equine third metacarpal bones

Objectives: To compare the number of cycles to failure of 4.5 mm broad dynamic compression plates (DCP), 4.5 mm broad limited‐contact dynamic compression plates (4.5‐LC‐DCP), and 5.5 mm broad limited‐contact dynamic compression plates (5.5‐LC‐DCP) having a rough (denoted by a prefix R‐) versus a standard smooth contact surface for the fixation of osteotomized equine 3rd metacarpal (MC3) bones. Study Design: Experimental. 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 comparison of (1) R‐DCP fixation with DCP fixation, (2) R‐4.5‐LC‐DCP fixation with 4.5‐LC‐DCP fixation, and (3) R‐5.5‐LC‐DCP fixation with 5.5‐LC‐DCP fixation to repair osteotomized equine MC3 bones under palmarodorsal 4‐point bending cyclic fatigue testing. For each group an 8‐hole plate with rough contact surface was applied to the dorsal surface of one randomly selected bone from each pair and a corresponding 8‐hole plate with smooth contact surface 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 number of cycles to failure for each method were compared using a paired t‐test within each group. Significance was set at P<.05. Results: Mean cycles to failure ± standard deviation was significantly greater for the R‐DCP fixation (230,025 ± 23,129) compared with the DCP fixation (103,451 ± 14,556), for the R‐4.5‐LC‐DCP fixation (99,237 ± 14,390) compared with the 4.5‐LC‐DCP fixation (46,464 ± 6325) and for the R‐5.5‐LC‐DCP fixation (65,113 ± 7796) compared with the 5.5‐LC‐DCP fixation (34,224 ± 3835). Conclusion: For the fixation of osteotomized MC3 bones, the constructs with plates having rough contact surface were superior to the corresponding constructs with plates having standard smooth contact surfaces in resisting cyclic fatigue under palmarodorsal 4‐point bending.     

Arthrodesis of the Equine Proximal Interphalangeal Joint: A Biomechanical Comparison of Two 7-Hole 3.5-mm Broad and Two 5-hole 4.5-mm Narrow Dynamic Compression Plates

OBJECTIVE: To compare the biomechanical characteristics and mode of failure of two different dynamic compression plate (DCP) techniques for proximal interphalangeal joint (PIPJ) arthrodesis in horses. STUDY DESIGN: Randomized block-design blocking on horse (1-5), method of fixation (two 7-hole, 3.5-mm broad DCP vs two 5-hole, 4.5-mm narrow DCP), side (left, right), and end (front, hind). Constructs were loaded to failure in 3-point bending in a dorsal-to-palmar (plantar) direction. SAMPLE POPULATION: Ten paired limbs from 5 equine cadavers. METHODS: Two 7-hole, 3.5-mm broad dynamic compression plates (bDCP) were used in 1 limb of a pair, and two 5-hole 4.5-mm narrow dynamic compression plates (nDCP) were used on the contralateral limb. Plates were positioned abaxially across the dorsomedial and dorsolateral aspect of the PIPJ. Arthrodesis constructs were loaded (19 mm/s) in 3-point bending in a dorsal-to-palmar (plantar) direction using a materials-testing machine. Composite stiffness, yield point, and maximal bending moment at failure were obtained from bending moment-angular deformation curves. Data were analyzed using ANOVA, X(2) analysis, and Fisher's exact tests; the power of the test was calculated when differences were not significant. RESULTS: There were no significant differences in composite stiffness (P >.05; power = 0.8 @ delta = 21.9%), yield point (P >.05; power = 0.8 @ delta = 34.4%), or maximal bending moment (P >.05; power = 0.8 @ delta = 17.8%) between the two fixation techniques. For bDCP constructs, 11% (15 of 140) of the 3.5-mm screws were damaged; 7 of the screw heads pulled through plates where the plates bent, 1 screw head broke off, and 7 screws were bent or pulled out of the phalanx. For nDCP constructs, 8% (8 of 100) of the 4.5-mm screws were damaged; 1 screw head pulled through a plate, 1 screw head broke off, and 6 screws were bent or pulled out of the phalanx. CONCLUSIONS: There were no biomechanical or failure differences between bDCP and nDCP fixation of the PIPJ in horses when evaluated in single-cycle 3-point bending to failure. CLINICAL RELEVANCE: There is no biomechanical advantage to the use of two 7-hole, 3.5-mm bDCP in equine proximal interphalangeal arthrodesis compared with two 5-hole, 4.5-mm nDCP. Two 5-hole, 4.5-mm nDCP may be easier to place, whereas two 7-hole, 3.5-mm bDCP may provide more versatility in fracture repair.     

Intervertebral biomechanics of locking compression plate monocortical fixation of the canine cervical spine

Objective: To evaluate the use of a locking compression plate (LCP) with monocortical screw purchase for stabilization of the canine cervical spine. Study Design: Experimental study. Animals: Cadaveric canine cervical spine specimens (n=7). Methods: Flexion and extension bending moments were applied to canine cadaveric specimens (C3–C6) in 4‐point bending, before and after creation of a ventral slot at C4–C5, and after fixation with a 5 hole, 3.5 mm LCP with monocortical screw placement. Screw placement and penetration into the vertebral canal were determined by radiography. Range of motion, stiffness, and energy for passive physiologic loads were determined for the C3–C4, C4–C5, and C5–C6 vertebral motion units (VMU). Monotonic failure properties were determined for cervical extension. Effects of treatments on biomechanical variables were assessed using repeated measures analysis of variance and least square means (P≤.05). Results: The ventral slot procedure increased range of motion at the treated VMU. Plate fixation decreased range of motion, increased stiffness, and decreased energy at the treated VMU. No changes were observed at adjacent VMUs. None of the screws penetrated the vertebral canal. Mean (± SD) yield bending moment of plate stabilized, slotted spines was 15.6 ± 4.6 N m. Conclusion: LCP fixation with monocortical screws stabilized the canine cervical spine.     

Failure mode and bending moment of canine pancarpal arthrodesis constructs stabilized with two different implant systems

Objective— To compare failure mode and bending moment of a canine pancarpal arthrodesis construct using either a 2.7 mm/3.5 mm hybrid dynamic compression plate (HDCP) or a 3.5 mm dynamic compression plate (DCP).
Study Design— Paired in vitro biomechanical testing of canine pancarpal arthrodesis constructs stabilized with either a 2.7/3.5 HDCP or 3.5 DCP.
Sample Population— Paired cadaveric canine antebrachii (n=5).
Methods— Pancarpal arthrodesis constructs were loaded to failure (point of maximum load) in 4-point bending using a materials-testing machine. Using this point of failure, bending moments were calculated from system variables for each construct and the 2 plating systems compared using a paired t-test. To examine the relationship between metacarpal diameter and screw diameter failure loads, linear regression was used and Pearson' correlation coefficient was calculated. Significance was set at P <.05.
Results— HDCP failed at higher loads than DCP for 9 of 10 constructs. The absolute difference in failure rates between the 2 plates was 0.552±0.182 N m, P =.0144 (95% confidence interval: −0.58 to 1.68). This is an 8.1% mean difference in bending strength. There was a significant linear correlation r=0.74 ( P -slope=.014) and 0.8 ( P -slope=.006) between metacarpal diameter and failure loads for the HDCP and 3.5 DCP, respectively.
Conclusion— There was a small but significant difference between bending moment at failure between 2.7/3.5 HDCP and 3.5 DCP constructs; however, the difference may not be clinically evident in all patients.
Clinical Relevance— The 2.7/3.5 HDCP has physical and mechanical properties making it a more desirable plate for pancarpal arthrodesis.     

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.