John Runciman

The effect of the combination of locking screws and non-locking screws on the torsional properties of a locking-plate construct.

Little is known about the torsional properties of bone-plate constructs when a combination of locking and non-locking screws have been used. Sixty cadaveric canine femurs were divided into three groups. In the first group, the plate was affixed using three non-locking screws. In the second group, only locking screws were used while a combination of one locking and two non-locking screws were used in the third group. All constructs were subjected to torsion until failure. Torque, angle of torsion, and work were all calculated at the maximum failure point, as well as at five degrees of plastic deformation, which was thought to be more representative of clinical failure. At the maximum failure point, the locking group had significantly higher torque, angle, and work values than the non-locking group. The combination group was intermediate to the two other groups, and significantly differed from the non-locking group in torque, and from the locking group in work. At five degrees of plastic deformation, the locking group required significantly higher torque and work than the non-locking group. The combination group required a significantly higher torque than the non-locking group. This study suggests that a construct composed of all locking screws will fail at a greater torque value, and sustain greater work to failure in torsion compared to a construct composed of all non-locking screws. The addition of a single locking screw to an otherwise non-locking construct will increase the torque at the offset failure point and may be of clinical value in constructs subjected to high torsional loads.

Evaluation of a laparoscopic technique for collection of serial full-thickness small intestinal biopsy specimens in standing sedated horses

OBJECTIVE To assess a technique for laparoscopic collection of serial full-thickness small intestinal biopsy specimens in horses. ANIMALS 13 healthy adult horses. PROCEDURES In the ex vivo portion of the study, sections of duodenum and jejunum obtained from 6 horses immediately after euthanasia were divided into 3 segments. Each segment was randomly assigned to the control group, the double-layer hand-sewn closure group, or the endoscopic linear stapler (ELS) group. Bursting strength and bursting wall tension were measured and compared among groups; luminal diameter reduction at the biopsy site was compared between the biopsy groups. In the in vivo portion of the study, serial full-thickness small intestinal biopsy specimens were laparoscopically collected with an ELS from the descending duodenum and distal portion of the jejunum at monthly intervals in 7 sedated, standing horses. Biopsy specimens were evaluated for suitability for histologic examination. RESULTS Mean bursting strength and bursting wall tension were significantly lower in the ELS group than in the hand-sewn and control groups in both the duodenal and jejunal segments. Use of the hand-sewn closure technique at the biopsy site reduced luminal diameter significantly more than use of the stapling technique. In the in vivo part of the study, all 52 biopsy specimens collected during 26 laparoscopic procedures were suitable for histologic examination and no clinically important perioperative complications developed. CONCLUSIONS AND CLINICAL RELEVANCE Laparoscopic collection of serial full-thickness small intestinal biopsy specimens with a 45-mm ELS may be an effective and safe technique for use in healthy adult experimental horses.

Computed Tomographic Analysis of Ventral Atlantoaxial Optimal Safe Implantation Corridors in 27 Dogs

Objectives Ventral atlantoaxial stabilization techniques are challenging surgical procedures in dogs. Available surgical guidelines are based upon subjective anatomical landmarks, and limited radiographic and computed tomographic data. The aims of this study were (1) to provide detailed anatomical descriptions of atlantoaxial optimal safe implantation corridors to generate objective recommendations for optimal implant placements and (2) to compare anatomical data obtained in non-affected Toy breed dogs, affected Toy breed dogs suffering from atlantoaxial instability and non-affected Beagle dogs. Methods Anatomical data were collected from a prospectively recruited population of 27 dogs using a previously validated method of optimal safe implantation corridor analysis using computed tomographic images. Results Optimal implant positions and three-dimensional numerical data were generated successfully in all cases. Anatomical landmarks could be used to generate objective definitions of optimal insertion points which were applicable across all three groups. Overall the geometrical distribution of all implant sites was similar in all three groups with a few exceptions. Clinical Significance This study provides extensive anatomical data available to facilitate surgical planning of implant placement for atlantoaxial stabilization. Our data suggest that non-affected Toy breed dogs and non-affected Beagle dogs constitute reasonable research models to study atlantoaxial stabilization constructs.

EX VIVO EQUINE HEART AND LUNG PERFUSION SYSTEM

An ex vivo heart lung perfusion system (EVHLPS) was designed and constructed in order to facilitate the study of hemodynamic and mechanical phenomena associated with the equine pulmonary vascular system. Fresh en bloc heart and lung preparations collected from adult horses were placed in an enclosed chamber in normal anatomic orientation and perfused with isotonic phosphate buffered saline (PBS) via a closed loop, pulsatile perfusion system. Pulmonary artery (PA) pressure, left atrial pressure and perfusate temperature were regulated. Lungs were ventilated by static lung inflation and dynamic positive pressure ventilation (PPV). Instrumentation was introduced into the pulmonary arterial system via an instrument chamber incorporated in the perfusate flow piping upstream from the cranial vena cava. Key physiologic parameters (mean [SD]); PA flow (1.57 [0.61] L/min); systolic pressure (SAP) (42.5 [6.83] mmHg); diastolic pressure (DAP) (30.3 [3.86] mmHg); and perfusate temperature (37.1 [0.46]°C) were observed with en bloc heart and lung preparations (n = 5). PA pulse wave velocity (PWV) was found to vary from 1.72 to 12.50 m/s (n = 2) and appeared to have directly proportional relationships with mean arterial pressure (MAP) and distance within the PA.

Biomechanical Properties of the 1.5 mm Locking Compression Plate: Comparison with the 1.5 and 2.0 mm Straight Plates in Compression and Torsion

OBJECTIVES  The purpose was to compare the biomechanical properties of a 1.5 mm locking compression plate (1.5 LCP) to the 1.5 mm straight plate (1.5 P), 1.5 mm straight plate stacked (1.5 PSt) and 2.0 mm straight plate (2.0 P) in compression and torsion. We hypothesized that biomechanical properties of the 1.5 LCP would be equivalent to properties of the 1.5 P and would represent an alternative for the treatment of radial fractures in miniature breed dogs in which those plates would be used. MATERIALS AND METHODS  A 1 mm fracture gap model was created with a bone surrogate stabilized with a six-hole plate. Sixteen constructs were built for each of the four plate configurations. Eight constructs from each group were tested in compression to failure and eight constructs were tested in torsion to failure. RESULTS  In compression testing, the 1.5 LCP was stiffer than the 1.5 P, and had similar stiffness than the 1.5 PSt and the 2.0 P. The load at yield of the 1.5 LCP was slightly lower than the 1.5 P. In torsion, the 1.5 LCP and 1.5 P had similar stiffness, but 1.5 LCP was slightly stronger than 1.5 P. The 1.5 PSt and 2.0 P were overall superior to the 1.5 LCP but only marginally so for the 1.5 PSt. CLINICAL RELEVANCE  The 1.5 LCP can be considered biomechanically equivalent to the 1.5 P under the present experimental conditions. The use of the 1.5 LCP can be considered as an option for radial fracture repair in dogs in which a 1.5 P would have otherwise been used. The use of a locking plate to improve overall success rate, in these fractures, remains to be confirmed clinically.

Ex vivo torsional properties of a 2.5 mm veterinary interlocking nail system in canine femurs: Comparison with a 2.4 mm limited contact bone plate

OBJECTIVE To evaluate the torsional properties of the Targon® Vet Nail System (TVS) in small canine femurs and to compare these properties to those of the 2.4 mm LC-DCP® plates. METHODS Thirty-six cadaveric femurs were allocated to three groups (n = 12). In all bones, points just distal to the lesser trochanter and just proximal to the fabellae were marked and a midshaft transverse osteotomy was performed. Group 1: bones were fixed with the 2.5 mm TVS with the bolts applied at the pre-identified marks. Group 2: A TVS system with 25% shorter inter-bolt distance was used. Group 3: A 7-hole 2.4 mm LC-DCP® plates were applied. All constructs were tested non-destructively for 10 cycles, followed by an acute torsion to failure. RESULTS Torque at yield was 0.806 ± 0.183 and 0.805 ± 0.093 Nm for groups 1 and 2 and 1.737 ± 0.461 Nm for group 3. Stiffness was 0.05 ± 0.01, 0.05 ± 0.007, and 0.14 ± 0.015 Nm/° for groups 1 to 3 respectively. Maximal angular displacement under cyclic loading was 16.6° ± 2.5°, 15.6° ± 2.1°, and 7.8° ± 1.06° respectively. There was no significant difference for any of the parameters between groups 1 and 2. Both torque at yield and stiffness were significantly greater between group 3 and groups 1 and 2. CLINICAL SIGNIFICANCE The TVS had approximately half the torsional strength and approximately 1/3 of the stiffness of the 2.4 mm bone plate. Slippage of the locking mechanism was probably the cause of the early failure. The system should be considered as a low-strength and low-stiffness system when compared to bone plates.

Development of a technique for determination of pulmonary artery pulse wave velocity in horses

Calcification of the tunica media of the axial pulmonary arteries (PA) has been reported in a large proportion of racehorses. In humans, medial calcification is a significant cause of arterial stiffening and is implicated in the pathogenesis of cardiac, cerebral, and renal microvascular diseases. Pulse wave velocity (PWV) provides a measure of arterial stiffness. This study aimed to develop a technique to determine PA-PWV in horses and, secondarily, to investigate a potential association between PA-PWV and arterial fibro-calcification. A dual-pressure sensor catheter (PSC) was placed in the main PA of 10 sedated horses. The pressure waves were used to determine PWV along the PA, using the statistical phase offset method. Histological analysis of the PA was performed to investigate the presence of fibro-calcified lesions. The mean (±SD) PWV was 2.3 ± 0.7 m/s in the proximal PA trunk and 1.1 ± 0.1 m/s further distal (15 cm) in a main PA branch. The mean (±SD) of mean arterial pressures in the proximal PA trunk was 30.1 ± 5.2 mmHg, and 22.0 ± 6.0 mmHg further distal (15 cm) within the main PA branch. The mean (±SD) pulse pressure in the proximal PA trunk was 15.0 ± 4.7 mmHg, and 13.5 ± 3.3 mmHg further distal (15 cm) within the main PA branch. Moderate to severe lesions of the tunica media of the PAs were observed in seven horses, but a correlation with PWV could not be established yet. Pulmonary artery PWV may be determined in standing horses. The technique described may allow further investigation of the effect of calcification of large PAs in the pathogenesis of equine pulmonary circulatory disorders.NEW & NOTEWORTHY Pulmonary artery pulse wave velocity was determined safely in standing sedated horses. The technique described may allow further investigation of the effect of calcification of large pulmonary arteries in the pathogenesis of pulmonary circulatory disorders in horses.