Malcolm Graham Ness

Fracture of the Patella after TPLO in 6 Dogs

OBJECTIVE To describe the clinical findings of dogs that sustained patellar fractures after tibial plateau leveling osteotomy (TPLO). STUDY DESIGN Retrospective case series. ANIMALS Dogs with patellar fractures that occurred after TPLO surgery (n = 6). METHODS Medical records (November 1, 2008-October 31, 2010) were reviewed to identify dogs with patellar fracture occurring after TPLO. RESULTS Six of 305 (2%) dogs had a patellar fracture after TPLO; 5 dogs were clinically lame when the fracture was diagnosed and all had radiographic evidence of patellar tendon thickening. All dogs were treated nonsurgically. In 2 dogs where follow-up radiographs were available there was no evidence of fracture union. No dog had a persistent lameness. CONCLUSION Fracture of the patella is an uncommon complication of TPLO surgery. Nonsurgical management can provide a satisfactory functional outcome.

Failure Mode of Transcondylar Screws Used for Treatment of Incomplete Ossification of the Humeral Condyle in 5 Dogs

OBJECTIVE To investigate the mode of failure of transcondylar screws retrieved from dogs previously treated for incomplete ossification of the humeral condyle (IOHC). STUDY DESIGN Metallurgical study. SAMPLE POPULATION Broken screws (n=5) from dogs with IOHC. METHODS Broken transcondylar bone screws were retrieved from dogs that had apparently successful surgery for IOHC. Screws were measured and examined using scanning electron microscopy (SEM) and energy-dispersive analysis by X-rays (EDX). RESULTS EDX confirmed that screws were made from 316L stainless steel and there was no evidence of significant corrosion or manufacturing faults that might have contributed to implant failure. SEM of the fractured surface of screws revealed a similar and complex pattern of fatigue failure characterized by multidirectional fatigue cracks and the presence of several initiation sites. All screws had signs of fatigue failure because of multidirectional forces of variable magnitude. CONCLUSIONS Intercondylar instability is a feature of IOHC that persists despite placement of a transcondylar screw. CLINICAL RELEVANCE The pathogenesis of IOHC involves chronic intercondylar instability and its treatment using even relatively large transcondylar screws has a risk of late implant failure.

Effect of Screw Type and Distribution on the Torsional Stability of 3.5 mm String of Pearls Locking Plate Constructs

OBJECTIVE To evaluate the effects of screw type (mono- [M] versus bicortical [B]), number, and position on torsional stability of String of Pearls (SOP) locking plate constructs. STUDY DESIGN In vitro mechanical study. METHODS SOP plates (n = 32) were applied to bone models and divided into 8 groups named according to screw type (M or B) and position in each fragment relative to the fracture gap starting at the outermost plate hole. Positive and negative controls were MMM and BBB, respectively. Specimens were non-destructively tested in torsion. Compliance and angular deformation were statistically compared (P < .002). RESULTS The MMM construct was most compliant (P < .001). Compliance decreased in groups with a single bicortical screw (P < .001). Compared to the MMM group, torsional compliance decreased in constructs where a single monocortical screw was replaced with a bicortical screw (P < .001). Compared with a centrally positioned bicortical screw, constructs with a bicortical screw in either outer- or innermost position were 15% and 23% less compliant, respectively (P < .001). Addition of a second bicortical screw/fragment further decreased compliance (P < .001). No significant difference was found between groups with 2 bicortical screws. The BBB construct was least compliant (P < .001). Group responses for angular deformation followed the same pattern of significance recorded for compliance. CONCLUSIONS A minimum of 1 bicortical screw/fragment should be used to increase torsional stability of 3.5 mm SOP constructs. Positioning this screw at the inner- or outermost positions relative to the fracture is preferred, with the innermost position providing the greatest improvement in stability. Should further torsional stability be desired, increasing the number of bicortical screws is recommended. Clinically, these results may assist with preoperative planning of various fracture patterns.

Effect of contouring on bending structural stiffness and bending strength of the 3.5 titanium SOP implant.

OBJECTIVE To compare the bending structural stiffness (BSS) and bending strength (BS) of the 3.5 titanium (Ti) string of pearls (SOP) plate and the 3.5 316LVM stainless steel SOP plate; and the effect of contouring on the BSS and BS of the 3.5 Ti SOP plate. STUDY DESIGN In vitro experimental static 4-point bending materials testing. SAMPLE POPULATION Twenty-five 3.5 mm Ti and five 3.5 mm 316LVM stainless steel SOP locking bone plates. METHODS Each plate was tested in 4-point bending until 10 mm of displacement was achieved. BSS and BS were then calculated for each plate. A 2-sample t-test was used to compare the mean BSS and BS of the different groups. RESULTS The 3.5 Ti SOP plate had lower mean BSS (0.00263 Nm(2) ) but similar mean BS (12.8 Nm) when compared to the 3.5 316LVM SOP (0.00402 Nm(2) , 13.0 Nm). Prebending the 3.5 Ti SOP diminished its mean BSS (0.00224 Nm(2) ) and mean BS (9.4 Nm) when compared to the Ti control. Pretwisting the 3.5 Ti SOP increased its mean BSS (0.00273 Nm(2) ) but decreased its mean BS (12.4 Nm) when compared to the Ti control. CONCLUSION The 3.5 Ti SOP is less stiff but of similar strength to the 3.5 316LVM stainless steel SOP. Prebending the Ti SOP significantly lowers its stiffness and strength. Pretwisting the SOP actually increases its stiffness but slightly lowers its strength.Objective To compare the bending structural stiffness (BSS) and bending strength (BS) of the 3.5 titanium (Ti) string of pearls (SOP) plate and the 3.5 316LVM stainless steel SOP plate; and the effect of contouring on the BSS and BS of the 3.5 Ti SOP plate. Study Design In vitro experimental static 4-point bending materials testing. Sample Population Twenty-five 3.5 mm Ti and five 3.5 mm 316LVM stainless steel SOP locking bone plates. Methods Each plate was tested in 4-point bending until 10 mm of displacement was achieved. BSS and BS were then calculated for each plate. A 2-sample t-test was used to compare the mean BSS and BS of the different groups. Results The 3.5 Ti SOP plate had lower mean BSS (0.00263 Nm2) but similar mean BS (12.8 Nm) when compared to the 3.5 316LVM SOP (0.00402 Nm2, 13.0 Nm). Prebending the 3.5 Ti SOP diminished its mean BSS (0.00224 Nm2) and mean BS (9.4 Nm) when compared to the Ti control. Pretwisting the 3.5 Ti SOP increased its mean BSS (0.00273 Nm2) but decreased its mean BS (12.4 Nm) when compared to the Ti control. Conclusion The 3.5 Ti SOP is less stiff but of similar strength to the 3.5 316LVM stainless steel SOP. Prebending the Ti SOP significantly lowers its stiffness and strength. Pretwisting the SOP actually increases its stiffness but slightly lowers its strength.

Effect of bending direction on the mechanical behaviour of 3.5 mm String-of-Pearls and Limited Contact Dynamic Compression Plate constructs

OBJECTIVE To compare the bending properties of String-of-Pearls® (SOP) and Limited Contact Dynamic Compression Plate® (LC-DCP) constructs in orthogonal bending directions. METHODS 3.5 mm SOP and LC-DCP plates were fixed to a bone model simulating a comminuted tibial fracture. Specimens were non-destructively tested in both mediolateral and craniocaudal bending for 10 cycles. Bending stiffness and total angular deformation were compared using parametric analyses (p <0.05). RESULTS For both constructs, stiffness was significantly less when bending moments were applied against the thickness of the plates (mediolateral bending) than against the width (craniocaudal bending). When compared to the mediolateral plane, bending constructs in the craniocaudal plane resulted in a 49% (SOP group) and 370% (LC-DCP group) increase in stiffness (p <0.001). Mediolateral bending stiffness was significantly greater in the SOP than the LC-DCP constructs. Conversely, in craniocaudal bending, SOP constructs stiffness was significantly less than that of the LC-DCP constructs. The differences between the two constructs in total angular deformation had an identical pattern of significance. CLINICAL SIGNIFICANCE This study found that SOP showed less variability between the orthogonal bending directions than LC-DCP in a comminuted fracture model, and also described the bi-planar bending behaviour of both constructs. Although not exhibiting identical bending properties in both planes, SOP constructs had a more homogenous bending behaviour in orthogonal loading directions. The difference between the SOP with a circular cross sectional shape compared to the rectangular shape of standard plates is probably responsible for this difference.

Effect of Intramedullary Rod Diameter on a String of Pearls Plate‐Rod Construct in Mediolateral Bending: An In Vitro Mechanical Study

OBJECTIVE To evaluate the effect of intramedullary rod (IMR) diameter on the mechanical behavior of string of pearls (SOP) plate-rod constructs. STUDY DESIGN In vitro mechanical study. SAMPLE POPULATION Synthetic bone models (n = 24). METHODS Locking 3.5 mm SOP plates were fixed to a tibial bone model with a 50 mm fracture gap. Four experimental groups (n = 4) were tested: monocortical SOP construct alone and monocortical SOP constructs augmented with a 2.4, 3.2, or 4.0 mm IMR corresponding to 24, 32, or 40% filling of the medullary cavity diameter (SOP-24, SOP-32, SOP-40). Control groups (n = 4) were stabilized with either a bicortical SOP plate (SOP-B) or a 3.5 mm limited contact dynamic compression plate (LC-DCP) with a 4.0 mm IMR filling 40% of the medullary cavity diameter (LC-DCP-40). Specimens were tested in mediolateral bending. Construct compliance (CC) and angular deformation (AD) were compared between construct types (P < .05). RESULTS CC and AD incrementally decreased with increasing IMR diameter (P < .001). There were no statistical differences between SOP-24 and SOP-B (P = .806) or between SOP-32 and LC-DCP-40 (P = .773), which was also the least compliant of all constructs (P < .001). AD followed an identical pattern of significance. CONCLUSIONS Biological osteosynthesis often relies on more compliant bridging constructs to promote beneficial micromotion at the fracture. Our study suggests use of a smaller diameter IMR (SOP-32) is comparable to a conventional plate-rod construct (LC-DCP-40). Should greater compliance be desired, an even smaller diameter IMR (SOP-24) may prove beneficial while as stable as an accepted bicortical construct (SOP-B).Objective To evaluate the effect of intramedullary rod (IMR) diameter on the mechanical behavior of string of pearls (SOP) plate-rod constructs. Study Design In vitro mechanical study. Sample population Synthetic bone models (n = 24). Methods Locking 3.5 mm SOP plates were fixed to a tibial bone model with a 50 mm fracture gap. Four experimental groups (n = 4) were tested: monocortical SOP construct alone and monocortical SOP constructs augmented with a 2.4, 3.2, or 4.0 mm IMR corresponding to 24, 32, or 40% filling of the medullary cavity diameter (SOP-24, SOP-32, SOP-40). Control groups (n = 4) were stabilized with either a bicortical SOP plate (SOP-B) or a 3.5 mm limited contact dynamic compression plate (LC-DCP) with a 4.0 mm IMR filling 40% of the medullary cavity diameter (LC-DCP-40). Specimens were tested in mediolateral bending. Construct compliance (CC) and angular deformation (AD) were compared between construct types (P < .05). Results CC and AD incrementally decreased with increasing IMR diameter (P < .001). There were no statistical differences between SOP-24 and SOP-B (P = .806) or between SOP-32 and LC-DCP-40 (P = .773), which was also the least compliant of all constructs (P < .001). AD followed an identical pattern of significance. Conclusions Biological osteosynthesis often relies on more compliant bridging constructs to promote beneficial micromotion at the fracture. Our study suggests use of a smaller diameter IMR (SOP-32) is comparable to a conventional plate-rod construct (LC-DCP-40). Should greater compliance be desired, an even smaller diameter IMR (SOP-24) may prove beneficial while as stable as an accepted bicortical construct (SOP-B).

Canine Elbow Realignment Osteotomy (CERO): Validation of the Accuracy of Acute Radial Lengthening in a Cadaveric Incongruency Model

OBJECTIVE To verify the ability of a novel Canine Elbow Realignment Osteotomy (CERO) system for acute axial radial or ulnar lengthening to restore normal elbow congruency in a shortened radius cadaver model using assessment by computed tomography (CT). STUDY DESIGN In vitro cadaver study. ANIMALS Five pairs of greyhound forelimbs from animals euthanatized for reasons unrelated to the study. METHODS CT of each elbow was performed (1) pre-operatively (pre-op), (2) after placement of a linear motor IMEX™ external skeletal fixator (ESF) on the radius with diaphyseal ostectomy and radial shorting of 1-5 mm (post-ESF), and (3) after CERO surgery to lengthen the radius proximal to the ostectomy site by an amount equal to the degree of radial shortening (post-CERO). The joint space at 7 loci on dorsal plane and 6 loci on sagittal plane reconstructions was measured to assess changes in joint congruity between pre-op, post-ESF, and post-CERO. Repeated measures ANOVA with post hoc comparisons were performed to compare measurements between the 3 groups. RESULTS Mean joint space measurements at most loci in the dorsal and sagittal planes were significantly different post-ESF compared with pre-op, confirming development of joint incongruency with the model. Post-CERO joint space measurements did not differ significantly compared with pre-op measurements, demonstrating the return to normal joint congruency using the CERO procedure. CONCLUSION CERO surgery restored humeroradioulnar congruency in our cadaver model and may have application for acute correction of axial radial or ulnar incongruency in canine elbows secondary to elbow dysplasia or premature growth plate closure.

Dorsal Slab Fracture of the Fourth Carpal Bone in a Racing Greyhound

OBJECTIVE To report the diagnosis and surgical management of a dorsal slab fracture of the fourth carpal bone in a racing greyhound. STUDY DESIGN Clinical report. ANIMAL Three-year-old, male racing Greyhound. METHODS The fracture was not visible on orthogonal radiographs and the diagnosis was made by computed tomography. Open reduction and internal fixation with 2 countersunk 2.0-mm screws inserted in lag fashion was performed via a dorsal approach. Outcome was analyzed objectively by comparing preinjury and postsurgery racing performances. RESULTS Internal fixation resulted in fracture healing and the dog returned to racing recording times similar to those before injury. CONCLUSION Fractures of the fourth carpal bone may not be visible on standard orthogonal radiographic views and cross-sectional imaging may be required for more accurate identification. Surgical management was successful with the dog returning to preinjury levels of competition.Objective To report the diagnosis and surgical management of a dorsal slab fracture of the fourth carpal bone in a racing greyhound. Study Design Clinical report. Animal Three-year-old, male racing Greyhound. Methods The fracture was not visible on orthogonal radiographs and the diagnosis was made by computed tomography. Open reduction and internal fixation with 2 countersunk 2.0-mm screws inserted in lag fashion was performed via a dorsal approach. Outcome was analyzed objectively by comparing preinjury and postsurgery racing performances. Results Internal fixation resulted in fracture healing and the dog returned to racing recording times similar to those before injury. Conclusion Fractures of the fourth carpal bone may not be visible on standard orthogonal radiographic views and cross-sectional imaging may be required for more accurate identification. Surgical management was successful with the dog returning to preinjury levels of competition.