Alan R. Cross

Proposed Definitions and Criteria for Reporting Time Frame, Outcome, and Complications For Clinical Orthopedic Studies in Veterinary Medicine

Outcome, and Complications For Clinical Orthopedic Studies in Veterinary Medicine James L. Cook, DVM, PhD, Diplomate ACVS, Richard Evans, PhD, Michael G. Conzemius, DVM, PhD, Diplomate ACVS, B. Duncan X. Lascelles, BVSc, PhD, Diplomate ECVS, Diplomate ACVS, C. Wayne McIlwraith, BVSc, PhD, Diplomate ACVS, Antonio Pozzi, DMV, MS, Diplomate ACVS, Peter Clegg, MA, VetMB, PhD, Diplomate ECVS, MRCVS, John Innes, BVSc, PhD, DSAS (Orth), MRCVS, Kurt Schulz, DVM, Diplomate ACVS, John Houlton, MA, VetMB, DVR, DSAO, MRCVS, Diplomate ECVS, Lisa Fortier, DVM, PhD, Diplomate ACVS, Alan R. Cross, DVM, Diplomate ACVS, Kei Hayashi, DVM, PhD, Diplomate ACVS, Amy Kapatkin, DVM, MS, Diplomate ACVS, Dorothy Cimino Brown, DVM, MSCE, Diplomate ACVS, and Allison Stewart, DVM, MS, Diplomate ACVS Comparative Orthopaedic Laboratory, University of Missouri, Columbia, MO, College of Veterinary Medicine, University of Illinois, Urbana, IL, College of Veterinary Medicine, University of Minnesota, St. Paul, MN, Comparative Pain Research Laboratory, North Carolina State University,

Circular External Skeletal Fixation Stabilization of Antebrachial and Crural Fractures in 25 Dogs

Fracture stabilization using circular external skeletal fixation was evaluated in 14 dogs with antebrachial fractures and 11 dogs with crural fractures. Most dogs were consistently weight bearing on the stabilized limb by 3 days following surgery. Although all dogs developed minor wire/pin tract inflammation and eight dogs developed major wire/pin tract inflammation, postoperative lameness was not consistently associated with wire/pin tract complications. Fractures in 23 dogs achieved radiographic union (mean +/- standard deviation [SD], 61 +/- 21 days; median, 57 days) without additional surgery; two dogs required restabilization of their fractures with linear fixators. Twenty of the 21 owners that could be contacted felt their dog had no (n=15) or only a mild (n=5) intermittent lameness at the time of final, long-term (mean +/- SD, 37 +/- 17 months; median, 42 months) assessment.

Understanding stress concentration about a nutrient foramen

We investigated the microstructural basis of a reduced stress concentration around the primary nutrient foramen of the equine third metacarpus. We quantified the spatial variations of compositional parameters (mineral content, volume fraction, histological architecture, and osteonal trajectories) from microradiographs and polarizing microscopic images of thin sections. These variations in composition and organization in turn cause variations in mechanical properties of cortical bone. We modeled the spatially inhomogeneous anisotropic elastic properties based on the measured compositional parameters and used the properties as inputs to a finite element model of the bone containing the foramen. This model, spatially constructed solely from the microscopic images, was subsequently validated by our mechanical test results. We found that: (1) a primary mechanism for stress concentration reduction appears to be due to an increased compliance near the foramen: the sharp discontinuity represented by the hole is softened by embedding it in a compliant region; (2) a reinforcing ring of increased stiffness exists at some distance from the foramen; and (3) a ring of lamellar bone exists along the foramen inside edge, which might serve to reduce the chance of cracks forming there. Our work is allowing us to design biomimetic structures with holes by mimicking the microstructure near the nutrient foramen.

Use of IMEX SK-circular external fixator hybrid constructs for fracture stabilization in dogs and cats.

Complex long-bone fractures with short juxta-articular fracture segments can be difficult to manage. Recently, IMEX Veterinary, Inc., began producing titanium hybrid rods that can be secured to ring components of the IMEX circular external skeletal fixation system to create SK-circular hybrids. In this case series, SK-circular hybrids were used to stabilize long-bone fractures (two femoral, one humeral, and three tibial fractures) with short distal bone segments in three dogs and three cats with body weights ranging from 1.9 to 15 kg (mean, 6.7 kg; median, 5.4 kg). Although three cases required surgical revision, animals ambulated well and all fractures obtained union. Time to radiographic union ranged from 62 to 137 days (mean, 90 days; median, 84 days). The functional outcome was considered excellent in all six cases.

Grafting of Massive Tibial Subchondral Bone Defects in a Caprine Model Using β-tricalcium Phosphate Versus Autograft

Objective: This study evaluated the ability of β-tricalcium phosphate particles (β-TCP) and autograft (AUTO) to maintain joint surface morphology when used to supplement massive subchondral bone defects in a caprine model. Design: This was a prospective, parallel arm study with 2 experimental arms and a control group. Methods: Unilateral, 11 mm diameter, 25 mm deep cylindrical defects were created in tibial subchondral bone of anesthetized goats (n = 16) and filled with autograft or β-tricalcium phosphate particles. The contralateral limbs served as internal controls. Goats were killed at 3 months and both tibiae harvested. Molds made of the tibial plateau surface were used to create positive casts from which medial and lateral tibial plateau surfaces of both experimental (β-tricalcium phosphate particles, autograft) and control limbs were digitized in 3 dimensions. Mirror images of the medial condyle surface contours from the controls were superimposed onto the experimental surfaces and deviations were compared using a Student t test (α = 0.05). Tibiae were then cut sagittally into medial (biomechanics) and lateral (histology) halves. Compressive modulus within the defect area was assessed by indentation to 2.0 mm at 0.2 mm per second using a 6-mm diameter pin. Specimens from the lateral tibial plateau were processed for undecalcified histology and the area of bone within the defect region measured. The articular surface of 86% of the autograft and 0% of the β-tricalcium phosphate particles group had degenerative changes, with 29% of autograft goats exhibiting large-scale plateau collapse. Mean surface deviation for autograft was significantly greater than for β-tricalcium phosphate particles (2.19 ± 1.49 mm versus 0.78 ± 0.19 mm), as was maximum surface deviation (11.19 ± 8.02 mm versus 4.39 ± 1.33 mm) (P < 0.05). The compressive modulus within the defect area for control animals was significantly higher than the experimental groups (P < 0.05). Significantly more bone was regenerated within β-tricalcium phosphate particle-grafted defects compared to autograft (P < 0.05). These results indicated that β-tricalcium phosphate particles might be a useful graft material for local repair of load bearing skeletal sites such as depressed tibial plateau fractures.

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 Students 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.

The Effect of Shock Wave Therapy on Patellar Ligament Desmitis after Tibial Plateau Leveling Osteotomy

Objective To determine if shock wave therapy (SWT) after tibial plateau leveling osteotomy (TPLO) has a beneficial effect on patellar ligament inflammation assessed by thickening of the ligament and ligament fiber disruption. Study Design Prospective, randomized, controlled clinical trial. Animals Dogs (n = 30). Materials and Methods Dogs that had TPLO (July 1, 2009 to June 1, 2010) were enrolled. The affected stifle was examined by radiographs and ultrasonography preoperatively and 4, 6, and 8 weeks after TPLO. At 4 and 6 weeks, dogs in the treatment group were briefly anesthetized and treated with SWT. Patellar ligament thickness on a lateral radiographic projection was measured at 1/4, 1/2, 3/4 of the distance from origin to insertion. Ultrasound images were evaluated for patellar ligament disruption and periligament edema. Results There was significant difference in thickness (P = .0264) only at the distal point; therefore, only this point was used to measure difference between the control and treatment groups. A significant difference between groups was reached at 6 and 8 weeks (P = .0059 and P = .0095, respectively) postoperatively. No significant ultrasonographic differences were found. Conclusion Based on these results, SWT decreases the radiographic signs of patellar ligament desmitis.OBJECTIVE To determine if shock wave therapy (SWT) after tibial plateau leveling osteotomy (TPLO) has a beneficial effect on patellar ligament inflammation assessed by thickening of the ligament and ligament fiber disruption. STUDY DESIGN Prospective, randomized, controlled clinical trial. ANIMALS Dogs (n = 30). MATERIALS AND METHODS Dogs that had TPLO (July 1, 2009 to June 1, 2010) were enrolled. The affected stifle was examined by radiographs and ultrasonography preoperatively and 4, 6, and 8 weeks after TPLO. At 4 and 6 weeks, dogs in the treatment group were briefly anesthetized and treated with SWT. Patellar ligament thickness on a lateral radiographic projection was measured at 1/4, 1/2, 3/4 of the distance from origin to insertion. Ultrasound images were evaluated for patellar ligament disruption and periligament edema. RESULTS There was significant difference in thickness (P = .0264) only at the distal point; therefore, only this point was used to measure difference between the control and treatment groups. A significant difference between groups was reached at 6 and 8 weeks (P = .0059 and P = .0095, respectively) postoperatively. No significant ultrasonographic differences were found. CONCLUSION Based on these results, SWT decreases the radiographic signs of patellar ligament desmitis.

A Biomechanical Comparison of Three Hybrid Linear-Circular External Fixator Constructs

OBJECTIVE To evaluate the stiffness, displacement, ring deformation and bone model motion of 3 configuations of linear-circular hybrid fixator constructs loaded in axial compression, craniocaudal and mediolateral bending, and torsion. STUDY DESIGN Biomechanical evaluation. SAMPLE POPULATION Three hybrid construct configurations with 8 replicates/configuration. METHODS Construct Ia used a single, 84 mm, incomplete ring and 2 tensioned olive wires to stabilize 1 bone segment and a primary hybrid rod with 3 fixation pins to stabilize the other bone segment. Constructs Ia(d) and Ib were similar to Ia with the addition of a secondary diagonal hybrid rod. Construct Ib had a fixation pin inserted orthogonally from the diagonal rod. Constructs were loaded for 10 cycles in each mode of loading using a materials testing machine. Ring deformation was assessed by obtaining serial ring measurements. Bone model motion at the fracture gap as a result of loading was also calculated. RESULTS Axial compression: constructs Ia(d) and Ib were significantly stiffer than construct Ia. Craniocaudal bending: Construct Ib was significantly stiffer than construct Ia. Mediolateral bending: there were no significant differences between constructs. Torsion: Construct Ib was significantly stiffer than constructs Ia and Ia(d) . Permanent ring deformation did not occur. Bone model translational motion decreased in constructs Ia(d) and Ib compared to construct Ia. CONCLUSIONS Addition of a secondary hybrid rod as well as biplanar fixation pin placement improved construct stiffness in several loading modes.

Axial stiffness and ring deformation of complete and incomplete single ring circular external skeletal fixator constructs

OBJECTIVE To compare the axial stiffness, maximum axial displacement, and ring deformation during axial loading of single complete and incomplete circular (ring) external skeletal fixator constructs. SAMPLE 32 groups of single ring constructs (5 constructs/group). PROCEDURES Single ring constructs assembled with 2 divergent 1.6-mm-diameter Kirschner wires were used to stabilize a 60-mm-long segment of 16-mm-diameter acetyl resin rod. Construct variables included ring type (complete or incomplete), ring diameter (50, 66, 84, or 118 mm), and fixation wire tension (0, 30, 60, or 90 kg). Axial loading was performed with a materials testing system. Construct secant stiffness and maximum displacement were calculated from the load-displacement curves generated for each construct. Ring deformation was calculated by comparing ring diameter during and after construct loading to ring diameter prior to testing. RESULTS Complete ring constructs had greater axial stiffness than did the 66-, 84-, and 118-mm-diameter incomplete ring constructs. As fixation wire tension increased, construct stiffness increased in the 66-, 84-, and 118-mm-diameter incomplete ring constructs. Maximum axial displacement decreased with increasing fixation wire tension, and complete ring constructs allowed less displacement than did incomplete ring constructs. Incomplete rings were deformed by wire tensioning and construct loading. CONCLUSIONS AND CLINICAL RELEVANCE Mechanical performance of the 66-, 84-, and 118-mm-diameter incomplete ring constructs improved when wire tension was applied, but these constructs were not as stiff as and allowed greater displacement than did complete ring constructs of comparable diameter. For clinical practice, tensioning the wires placed on 84- and 118-mm-diameter incomplete rings to 60 kg is recommended.

Closed reduction and fluoroscopic-assisted percutaneous pinning of 42 physeal fractures in 37 dogs and 4 cats†

OBJECTIVE To report complications and clinical outcome of dogs and cats that underwent fluoroscopic-assisted percutaneous pinning (FAPP) of physeal fractures. STUDY DESIGN Retrospective study. ANIMALS Client-owned dogs (n = 37) and cats (n = 4). MATERIALS AND METHODS Records (August 2007-August 2014) of physeal fractures treated with FAPP in 3 hospitals were evaluated. Data collected included signalment, fracture characteristics (etiology, location, duration, Salter-Harris classification, preoperative and postoperative displacement), surgical information (implant size, surgical duration), and outcome assessment information (functional outcome, radiographic outcome, and complications). RESULTS The majority of animals (92%) were classified as full functional outcome. No significant predictors of functional outcome were identified. The overall complication rate was 15% (n = 6). Elective pin removal rate was 41% (n = 17). Goniometry and limb circumference measurements of the affected and contralateral limbs were not significantly different in dogs for which measurements were obtained. Seventeen of 18 animals (16 dogs, 2 cats) measured had bone length changes on follow-up radiographs. CONCLUSION FAPP is associated with an excellent functional outcome in a narrow selection of fracture configurations, specifically those with minimal displacement and for which anatomical alignment can be achieved with closed reduction.