Mechanical comparison of 3 different clamp and 2 different rod types of a new veterinary internal fixation system, 4.5/5.5-mm VetFix

Mechanical Testing of Sliding on Pivot-Locking Clamp (SOP-LC) Fracture Repair System in Four-Point Bending and Torsion

OBJECTIVES

 The first objective of this study was to compare the mechanical performance of a straight and contoured rod for the sliding on pivot-locking clamp (SOP-LC) system. The second objective was to compare single-cycle bending and torsion of the SOP-LC rod-bone constructs to a bone gap model between two clamp configurations.

STUDY DESIGN

 First experiment, 5 mm diameter rods from the 3.5 mm SOP-LC system, 4 straight and 4 bent rods were mechanically compared in four-point bending. The second experiment, 8 constructs with clamps on a single side of the rod and 8 constructs with clamps on alternating sides were compared in four-point bending and torsion. A torque limiting screwdriver at 2.5N was used for all constructs.

RESULTS

 There were not significant differences between the noncontoured versus contoured rods. Constructs with clamps on a single side had a significantly higher yield load, yield displacement and bending strength, but the constructs with alternating clamps had a significantly higher initial torsional stiffness. There were no other significant differences. Mild clamp slippage and mild screw bending were noted in all the torsion tested constructs graphically with multiple stiffness slopes and visually on the post-tested constructs.

CONCLUSION

 Torque applied to initial screw placement may play a role in reducing clamp slippage. Although bending yield load, bending yield displacement, bending strength and torsional stiffness were improved by different clamp placement, clinically this will depend on fracture type. Further studies are needed for clinical significance.

Influence of screw head diameter on ex vivo fixation of equine lateral condylar fractures with 5.5 mm cortical screws

OBJECTIVE

To determine the influence of screw head diameter on equine condylar fracture fixation with 5.5 mm cortical screws.

STUDY DESIGN

Ex vivo, biomechanical study, blinded, matched-pair design.

SAMPLE POPULATION

Fifteen pairs of equine third metacarpal (MC3) bones.

METHODS

Lateral condylar fractures were simulated by parasagittal osteotomies and repaired pairwise by 2 × 5.5 mm cortical screws of 8 mm (standard) or 10 mm (modified) head diameter. Interfragmentary compression at maximum screw insertion torque was measured. The instrumented specimens were pairwise stratified for biomechanical testing under the following modalities (n = 5): (1) screw insertion torque to failure, (2) quasi-static axial load to failure, and (3) cyclic axial load to 2 mm displacement followed by failure. Tests (1) and (2) were analyzed for yield, maximum, and failure torque/angle and load/displacement, respectively. Number of cycles to 2 mm displacement and failure was assessed from test (3).

RESULTS

Maximum insertion torque was greater, and failure angle smaller, when constructs repaired with modified screws were tested (8.1 ± 0.5 vs. 7.4 ± 0.5 Nm; P = .0047 and 550 ± 104 vs. 1130 ± 230; P = .008). Axial yield (7118 ± 707 vs. 5740 ± 2267 N; P = .043) and failure load (12 347 ± 3359 vs. 8695 ± 2277 N; P = .043) were greater for specimens repaired with modified screws. No difference was detected between constructs in the number of cycles to 2 mm displacement.

CONCLUSION

Condylar MC3 osteotomies repaired with modified 5.5 mm cortical screws sustained greater maximal hand torque insertion, smaller insertion failure angle and 1.4 fold greater quasi-static failure forces than constructs repaired with standard 5.5 mm screws.

CLINICAL SIGNIFICANCE

Use of modified screws with larger heads may improve the fixation of condylar fractures in horses. These results provide evidence to justify clinical evaluation in horses undergoing fracture repair.

An In Vitro Biomechanical Comparison Between Prototype Tapered Shaft Cortical Bone Screws and AO Cortical Bone Screws for an Equine Metacarpal Dynamic Compression Plate Fixation of Osteotomized Equine Third Metacarpal Bones

OBJECTIVES

To compare biomechanical properties of a prototype 5.5 mm tapered shaft cortical screw (TSS) and 5.5 mm AO cortical screw for an equine third metacarpal dynamic compression plate (EM-DCP) fixation to repair osteotomized equine third metacarpal (MC3) bones.

STUDY DESIGN

Paired in vitro biomechanical testing of cadaveric equine MC3 with a mid-diaphyseal osteotomy, stabilized by 1 of 2 methods for fracture fixation.

ANIMAL POPULATION

Adult equine cadaveric MC3 bones (n=12 pairs).

METHODS

Twelve pairs of equine 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. An EM-DCP (10-hole, 4.5 mm) was applied to the dorsal surface of each, mid-diaphyseal osteotomized, MC3 pair. For each MC3 bone pair, 1 was randomly chosen to have the EM-DCP secured with four 5.5 mm TSS (2 screws proximal and distal to the osteotomy; TSS construct), two 5.5 mm AO cortical screws (most proximal and distal holes in the plate) and four 4.5 mm AO cortical screws in the remaining holes. The control construct (AO construct) had four 5.5 mm AO cortical screws to secure the EM-DCP in the 2 holes proximal and distal to the osteotomy in the contralateral bone from each pair. The remaining holes of the EM-DCP were filled with two 5.5 mm AO cortical screws (most proximal and distal holes in the plate) and four 4.5 mm AO cortical screws. All plates and screws were applied using standard AO/ASIF techniques. 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 4-point bending yield load, yield bending moment, bending composite rigidity, failure load and failure bending moment of the TSS construct were significantly greater (P<.00004 for yield and P<.00001 for failure loads) than those of the AO construct. Mean cycles to failure in 4-point bending of the TSS construct was significantly greater (P<.0002) than that of the AO construct. The mean yield load and composite rigidity in torsion of the TSS construct were significantly greater (P<.0039 and P<.00003, respectively) than that of the AO construct.

CONCLUSION

The TSS construct provides increased stability in both static overload testing and cyclic fatigue testing.

CLINICAL RELEVANCE

The results of this in vitro study support the conclusion that the EM-DCP fixation using the prototype 5.5 mm TSS is biomechanically superior to the EM-DCP fixation using 5.5 mm AO cortical screws for the stabilization of osteotomized equine MC3.

Clinical evaluation of the CRIF 4.5/5.5 system for long-bone fracture repair in cattle

OBJECTIVE

To report clinical evaluation of the clamp rod internal fixator 4.5/5.5 (CRIF 4.5/5.5) in bovine long-bone fracture repair.

STUDY DESIGN

Retrospective study.

ANIMALS

Cattle (n=22) with long-bone fractures.

METHODS

Records for cattle with long-bone fractures repaired between 1999 and 2004 with CRIF 4.5/5.5 were reviewed. Quality of fracture repair, fracture healing, and clinical outcome were investigated by means of clinical examination, medical records, radiographs, and telephone questionnaire.

RESULTS

Successful long-term outcome was achieved in 18 cattle (82%); 4 were euthanatized 2-14 days postoperatively because of fracture breakdowns. Two cattle had movement of clamps on the rod. Moderate to severe callus formation was evident in 11 cattle 6 months postoperatively.

CONCLUSIONS

Movement of clamps on the rod was recognized as implant failure unique to the CRIF. This occurred in cattle with poor fracture stability because of an extensive cortical defect. The CRIF system may not be ideal to treat metacarpal/metatarsal fractures because its voluminous size makes skin closure difficult, thereby increasing the risk of postoperative infections.

CLINICAL RELEVANCE

CRIF cannot be recommended for repair of complicated long-bone fractures in cattle.

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.

An In Vitro Biomechanical Comparison of a Prototype Equine Metacarpal Dynamic Compression Plate Fixation with Double Dynamic Compression Plate Fixation of Osteotomized Equine Third Metacarpal Bones

OBJECTIVES

To compare the monotonic biomechanical properties of a prototype equine third metacarpal dynamic compression plate (EM-DCP) fixation with a double broad dynamic compression plate (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.

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 testing. The EM-DCP (10-hole, 4.5 mm) was applied to the dorsal surface of one randomly selected bone from each pair. Two DCPs, 1 dorsally (10-hole, 4.5 mm broad) and 1 laterally (9-hole, 4.5 mm broad) were applied 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

Mean 4-point bending yield load, yield bending moment, bending composite rigidity, failure load and failure bending moment of the EM-DCP fixation were significantly greater (P<.0001) than those of the double broad DCP fixation. Mean cycles to failure in 4-point bending of the EM-DCP fixation was significantly greater (P<.0008) than that of the double broad DCP fixation. Mean yield load, composite rigidity, and failure load in torsion of the EM-DCP fixation were significantly greater (P<.0035) than that of the double broad DCP fixation.

CONCLUSION

The EM-DCP provides increased stability in both static overload testing and cyclic fatigue testing.

CLINICAL RELEVANCE

Results of this in vitro study support the conclusion that the prototype EM-DCP fixation is biomechanically superior to the double broad DCP fixation for the stabilization of osteotomized equine MC3.