Canine Humeri Research Articles

Accuracy of anatomic 3-dimensionally printed canine humeral models.

To evaluate the accuracy of various three-dimensional print (3DP) technologies using morphometric measurements. Experimental. Cadaveric canine humeri and size-matched 3DP models. Fiduciary radiopaque markers were affixed to canine humeri of three different sizes (4, 13, 29 kg) at predetermined anatomical landmarks. 3DP models were created using one of three printers; desktop printers Form 3L and Ultimaker 5S, and industrial printer Objet Connex (n=5/group/printer). Marker based morphometric dimensions between cadavers and 3DP models were statistically compared using 2-factor repeated measures ANOVA followed by Tukey's post-hoc test (p < .05). Bone size and printer type both significantly affected 3DP accuracy, with size having the larger effect (p < .0001 and p < .02, respectively). Regardless of printing technology, model size was smaller than native bone in most cases. At the humeral condylar level, the best accuracy was seen in the medium-sized humerus with the Ultimaker printer ([0.09 mm], p < .03). Accuracy was reduced in the proximal humerus in all groups. Desktop printers were overall more accurate than the industrial printer. Although significant differences were identified between models of different sizes, the submillimetric magnitude of these differences is unlikely to be clinically relevant. While preoperative planning using 3DP models is becoming mainstream, accurate representation of the actual bone is critical. This study demonstrates that common desktop printers are suitable for this purpose.

Effect of orthopedic implants on canine long bone compression stiffness: a combined experimental and computational approach.

Osteosynthesis for canine long bones is a complex process requiring knowledge of biology, surgical techniques and (bio)mechanical principles. Subject-specific finite element analysis constitutes a promising tool to evaluate the effect of surgical intervention on the global properties of a bone-implant construct, but suffers from a lack of validation. In this study, the biomechanical behavior of 10 canine humeri was compared before and after creation of a 10 mm bone defect stabilized with an eight-hole locking compression plate (Synthes®) and two locking screws on each fragment. The response under compression of both intact and plated samples was measured experimentally and reproduced with a finite element model. The experimental stiffness ratio between plated and intact bone was equal to 0.39 ± 0.06. A subject-specific finite element analysis including density-dependent elasto-plastic material properties for canine bone and automatic generation of orthopedic implants was then conducted to recover these experimental results. The stiffness of intact and plated samples could be predicted, with no significant differences with experimental data. The simulated stiffness ratio between plated and intact canine bone was equal to 0.43 ± 0.03. This study constitutes a first step toward the building of a virtual database of pre-computed cases, aiming at helping the veterinary surgeons to make decisions regarding the most suited orthopedic solution for a given dog and a given fracture.

A canine liver fibrosis model to develop a therapy for liver cirrhosis using cultured bone marrow-derived cells.

We have been developing a therapy for liver cirrhosis using cultured autologous bone marrow–derived mesenchymal stem cells (BMSCs). Before human clinical trials can be considered, the safety and efficacy of BMSC infusion in medium to large animals must be confirmed; thus, we developed a canine liver fibrosis model. A small amount of bone marrow fluid was aspirated from the canine humerus to assess the characteristics of BMSCs. We implanted a venous catheter in the stomach and a subcutaneous infusion port in the back of the neck of each canine. Repeated injection of CCl4 through the catheter was performed to induce liver cirrhosis. After 10 weeks of CCl4 injection, eight canines were equally divided into two groups: no cell infusion (control group) and autologous BMSC infusion through the peripheral vein (BMSC group). A variety of assays were carried out before and 4 weeks after the infusion. The area of liver fibrosis stained with sirius red was significantly reduced in the BMSC group 4 weeks after BMSC infusion, consistent with a significantly shortened half‐life of indocyanine green and improved liver function. Conclusion: We established a useful canine liver fibrosis model and confirmed that cultured autologous BMSC infusion improved liver fibrosis without adverse effects. (Hepatology Communications 2017;1:691–703)

Pullout strength of monocortical and bicortical screws in metaphyseal and diaphyseal regions of the canine humerus.

Monocortical screws are commonly employed in locking plate fixation, but specific recommendations for their placement are lacking and use of short monocortical screws in metaphyseal bone may be contraindicated. Objectives of this study were to evaluate axial pullout strength of two different lengths of monocortical screws placed in various regions of the canine humerus compared to bicortical screws, and to derive cortical thickness and bone density values for those regions using quantitative computed tomography analysis (QCT). The QCT analysis was performed on 36 cadaveric canine humeri for six regions of interest (ROI). A bicortical, short monocortical, or 50% transcortical 3.5 mm screw was implanted in each ROI and axial pullout testing was performed. Bicortical screws were stronger than monocortical screws in all ROI except the lateral epicondylar crest. Short monocortical metaphyseal screws were weaker than those placed in other regions. The 50% transcortical screws were stronger than the short monocortical screws in the condyle. A linear relationship between screw length and pullout strength was observed. Cortical thickness and bone density measurements were obtained from multiple regions of the canine humerus using QCT. Use of short monocortical screws may contribute to failure of locking plate fixation of humeral fractures, especially when placed in the condyle. When bicortical screw placement is not possible, maximizing monocortical screw length may optimize fixation stability for distal humeral fractures.

Distal Normograde Intramedullary Pin and Locking Plate Placement in the Canine Humerus: A Cadaveric Study.

To identify a repeatable anatomic landmark for pin insertion and to describe the technique for placement of a distal normograde intramedullary (IM) pin of approximately 35% of the IM diameter using this approach combined with a locking compression plate (LCP) on the medial aspect of the canine humerus. Ex vivo anatomic study. Canine cadavers (n=10 Greyhounds). An anatomic landmark for pin insertion was identified based on three-dimensional reconstructions of previous elbow computed tomography studies and cadaveric dissection of the medial aspect of the humeral condyle. Bilateral distal normograde IM pin and LCP placement were performed and confirmed radiographically and by disarticulation and sagittal sectioning. The anatomic landmark for pin insertion was consistently identified in each specimen using the technique described. Distal normograde insertion of a 3.5 mm IM pin was possible in Greyhound cadaveric humeri at the described location in conjunction with a 3.5 mm LCP with fixed angle, locked screws. A monocortical locking screw was required to avoid interference with the IM pin in 28 of 60 of the 3 proximal screw holes. No pin interference was encountered in any of the distal screw holes. The anatomic landmark and technique described in our study enabled repeatable successful placement of a distal normograde IM pin of approximately 35% of the IM diameter combined with an LCP on the medial aspect of the canine humerus. This technique may be useful for locking plate-rod fixation of distal humeral diaphyseal fractures.

The effect of different implant biomaterials on the behavior of canine bone marrow stromal cells during their differentiation into osteoblasts

We investigated the effects of different implant biomaterials on cultured canine bone marrow stromal cells (BMSC) undergoing differentiation into osteoblasts (dBMSC). BMSC were isolated from canine humerus by marrow aspiration, cultured and differentiated on calcium phosphate scaffold (CPS), hydroxyapatite, hydroxyapatite in gel form and titanium mesh. We used the MTT method to determine the effects of osteogenic media on proliferation. The characteristics of dBMSC were assessed using alizarin red (AR), immunocytochemistry and osteoblastic markers including alkaline phosphatase/von Kossa (ALP/VK), osteocalcin (OC) and osteonectin (ON), and ELISA. The morphology of dBMSC on the biomaterials was investigated using inverted phase contrast microscopy and scanning electron microscopy. We detected expression of ALP/VK, AR, OC and ON by day 7 of culture; expression increased from day 14 until day 21. CPS supported the best adhesion, cell spreading, proliferation and differentiation of BMSCs. The effects of the biomaterials depended on their surface properties. Expression of osteoblastic markers showed that canine dBMSCs became functional osteoblasts. Tissue engineered stem cells can be useful clinically for autologous implants for treating bone wounds.

Influence of chondrodystrophy and brachycephaly on geometry of the humerus in dogs.

To assess the geometry of canine humeri as seen on radiographs in chondrodystrophic dogs (CD) and brachycephalic dogs (BD) compared to non-chondrodystrophic dogs (NCD). Mediolateral (ML) and craniocaudal (CC) radiographs of skeletally mature humeri were used (CD [n = 5], BD [n = 9], NCD [n = 48]) to evaluate general dimensions (length, width, canal flare, cortical thickness), curvature (shaft, humeral head, and glenoid), and angulation (humeral head and condyle). Measurements from CD, BD, and NCD were compared. Mean humeral length was shorter in CD (108 mm) compared to BD (184 mm, p = 0.001) and NCD (183 mm, p <0.001). Craniocaudal cortical thickness at 70% of humeral length and ML cortical thickness at 30%, 50%, and 70% of humeral length were less in CD compared to BD and NCD. Humeral shaft curvature was greater in CD (9.9°) compared to BD (6.7°, p = 0.023). The ratio of glenoid radius of curvature / humeral length was greater for CD (11.1%) compared to NCD (9.7%, p = 0.013). The ratio of humeral width / humeral length was greater for BD (29.4%) compared to NCD (26.2%, p = 0.043). The ratio of glenoid length / humeral length was greater in CD (18.0%) than BD (16.4%, p = 0.048) and NCD (15.6%, p <0.001). Bone proportions and curvature in CD differ from BD and NCD. Differences are minor and unlikely to have clinical significance.

Prediction of the mechanical response of canine humerus to three-point bending using subject-specific finite element modelling.

Subject-specific finite element models could improve decision making in canine long-bone fracture repair. However, it preliminary requires that finite element models predicting the mechanical response of canine long bone are proposed and validated. We present here a combined experimental-numerical approach to test the ability of subject-specific finite element models to predict the bending response of seven pairs of canine humeri directly from medical images. Our results show that bending stiffness and yield load are predicted with a mean absolute error of 10.1% (±5.2%) for the 14 samples. This study constitutes a basis for the forthcoming optimization of canine long-bone fracture repair.

Elastic large muscular vessel wall engineered with bone marrow‑derived cells under pulsatile stimulation in a bioreactor.

Bone marrow‑derived cells (BMCs) have demonstrated their ability to differentiate into multiple cell lineages and may be a promising cell source for vascular tissue engineering. Although much progress has been made in the engineering of small blood vessels (<6 mm in diameter) with biodegradable materials such as polyglycolic acid (PGA), it remains a challenge to engineer large vessels (>6 mm in diameter) due to unsatisfactory biomechanical properties. The present study was to engineered an elastic large vessel wall (6 mm in diameter) using a PGA unwoven fibre scaffold covered with BMCs from canine humeri. The cell‑PGA sheet was then loaded into a bioreactor designed for the present study, with dynamic pulsatile culture conditions to mimic the physiological vessel environment. After four weeks of the pulsatile stimuli culture, an elastic vessel wall was formed. Histological analyses demonstrated that layers of smooth muscle‑like cells and well‑oriented collagenous fibres were evenly oriented in the dynamic group. By contrast, disorganised cells and randomly collagenous fibres were apparent in the static group. Furthermore, the engineered vessel wall in the dynamic group exhibited significantly improved biomechanical properties compared with those in static culture group. The approach developed in the present study was demonstrated to have promising potential to be used for the engineering of large vessel as well as other smooth muscle cell‑containing tissues, including bladder, urethral and intestinal tissues.

The effect of autologous bone marrow stromal cells differentiated on scaffolds for canine tibial bone reconstruction

Bone marrow contains mesenchymal stem cells that form many tissues. Various scaffolds are available for bone reconstruction by tissue engineering. Osteoblastic differentiated bone marrow stromal cells (BMSC) promote osteogenesis on scaffolds and stimulate bone regeneration. We investigated the use of cultured autologous BMSC on different scaffolds for healing defects in tibias of adult male canines. BMSC were isolated from canine humerus bone marrow, differentiated into osteoblasts in culture and loaded onto porous ceramic scaffolds including hydroxyapatite 1, hydroxyapatite gel and calcium phosphate. Osteoblast differentiation was verified by osteonectine and osteocalcine immunocytochemistry. The scaffolds with stromal cells were implanted in the tibial defect. Scaffolds without stromal cells were used as controls. Sections from the defects were processed for histological, ultrastructural, immunohistochemical and histomorphometric analyses to analyze the healing of the defects. BMSC were spread, allowed to proliferate and differentiate to osteoblasts as shown by alizarin red histochemistry, and osteocalcine and osteonectine immunostaining. Scanning electron microscopy showed that BMSC on the scaffolds were more active and adhesive to the calcium phosphate scaffold compared to the others. Macroscopic bone formation was observed in all groups, but scaffolds with stromal cells produced significantly better results. Bone healing occurred earlier and faster with stromal cells on the calcium phosphate scaffold and produced more callus compared to other scaffolds. Tissue healing and osteoblastic marker expression also were better with stromal cells on the scaffolds. Increased trabecula formation, cell density and decreased fibrosis were observed in the calcium phosphate scaffold with stromal cells. Autologous cultured stromal cells on the scaffolds were useful for healing of canine tibial bone defects. The calcium phosphate scaffold was the best for both cell differentiation in vitro and bone regeneration in vivo. It may be possible to improve healing of bone defects in humans using stem cells from bone marrow.

Determination of the Mechanical Axis and Joint Orientation Lines in the Canine Humerus: A Radiographic Cadaveric Study

To describe a radiographic method for determination of the mechanical axes and joint orientation lines in orthogonal planes for the canine humerus and establish a range of normal joint orientation angles in a population of large breed dogs. Radiographic study. Humeri (n = 50) of skeletally mature, nonchondrodystrophic canine cadavers, weighing 20-40 kg with no evidence of orthopedic disease. Mediolateral and craniocaudal digital radiographs were used to establish anatomic landmarks for determination of the mechanical axis in both frontal and sagittal planes, the joint orientation lines of both shoulder and elbow and measurement of the resulting mechanical lateral distal humeral angle (mLDHA) in the frontal plane, and the mechanical caudal proximal humeral angle (mCaPHA), and mechanical cranial distal humeral angle (mCrDHA) in the sagittal plane. Means (± SD) for the joint orientation angles were: mLDHA, 86.92 ± 1.24°, mCaPHA, 43.28 ± 5.44°, and mCrDHA, 71.86 ± 3.97°. The 95% CI ranges for the joint orientation angles were mLDHA, 86.58-87.86°, mCaPHA, 41.77-44.79°, and mCrDHA, 70.76°-72.96°. A method for measurement of the mechanical axis and associated joint angles of the normal canine humerus in the frontal and sagittal planes was established and reference intervals reported. In the frontal plane, it was determined that the canine humerus is not perpendicular to the elbow joint; therefore, elbow mechanical axis deviation is normal and requires further assessment.

Defining a Safe Corridor for Transcondylar Screw Insertion Across the Canine Humeral Condyle: A Comparison of Medial and Lateral Surgical Approaches

To (1) develop guidelines for the location of drill entry and exit points when inserting a transcondylar screw across the canine humerus; (2) compare the safe corridor for transcondylar screw insertion when drilling medial-to-lateral with drilling lateral-to-medial. Anatomic study. Dogs (n = 43). The optimum position of a transcondylar screw in 84 elbows was determined using CT multiplanar reconstructions. The positions of drill entry and exit points were defined relative to the epicondyles. Differences in elbow size were accounted for by dividing the measurements by the humeral condylar diameter (HCD), to give normalized measurements. Mean values of normalized measurements were used to develop universal guidelines for the location of drill entry and exit points. These guidelines were then applied to the 84 elbow CT reconstructions. The size of the safe corridor around this calculated drill line was determined, and expressed as tolerance angles in the frontal and transverse planes. The size of the safe corridors for medial-to-lateral and lateral-to-medial drilling were compared. The lateral entry/exit point was 0.3 × HCD cranial and 0.3 × HCD distal to the lateral epicondyle. The medial entry/exit point was 0.3 × HCD cranial and 0.2 × HCD distal to the medial epicondyle. Using these guidelines resulted in safe virtual screw placement in all 84 elbows. The tolerance angle in the frontal plane was significantly smaller when drilling medial-to-lateral compared with drilling lateral-to-medial (P < .001). Medial-to-lateral drilling for transcondylar screw placement carries a higher risk of inadvertently penetrating the joint compared with lateral-to-medial drilling.

Biomechanical Comparison of 4.0‐mm Short‐Threaded Cannulated Screws and 4.0‐mm Short‐Threaded Cancellous Screws in a Canine Humeral Condylar Fracture Model

To compare biomechanical properties of a humeral condylar fracture model stabilized either with a 4.0-mm short-threaded cancellous screw (CCS) or with a 4.0-mm short-threaded cannulated screw (CNS). In vitro biomechanical study. Bilateral cadaveric canine humeri (n = 20). Fractures of the lateral portion of the humeral condyle were simulated by standardized osteotomies; 10 condyles were each stabilized with CCS and 10 with CNS. Axial compression load was applied to each specimen until failure and force-displacement curves generated. Testing data for each construct were determined and compared using either a Student's paired t-test (quantitative data) or a χ(2) test (qualitative data) with statistical significance set at P < .05. Yield load (elastic limit), ultimate load at failure, and displacements at loads corresponding to walk and trot were determined from each curve. Mean ± SD ultimate load at failure was significantly higher (P = .01) for CCS constructs (1261 ± 261 N) than for CNS constructs (1078 ± 231 N). Yield loads were not significantly different (P = .10) between construct types, and exceeded all expected loads supported by the humeral condyle at walk. The risk of having a yield load below the expected physiologic load at trot was not statistically higher with a CNS construct compared with a CCS construct (P = .26). Humeral condylar fracture repaired either by a 4.0-mm cannulated screw or a 4.0-mm cancellous screw have comparable stability in this condylar fracture model.

The Effect of Environmental Storage Conditions on Bone Marrow Fat Determination in Three Species

Diagnostic laboratories are frequently required to assess the antemortem nutritional condition of deceased animals. The percentage of fat in the bone marrow is used to diagnose starvation because this fat depot is typically the last in the body to be depleted. Diagnosticians rely on measurement of bone marrow adipose content using fat solvent-extraction methods; however, the effects of tissue storage conditions before processing have not been fully assessed. The current study focuses on evaluating the effects of 3 storage conditions (refrigeration [4 °C], freezing [-20 °C], and ambient temperature [9.9-34.4 °C]) on the percentage of fat in the bone marrow from 3 species. Equine, bovine, and canine humeri and femurs were removed within 24 hr of death from adult animals in adequate body condition and then stored as described for a minimum of 30-60 days. Bone marrow was harvested from these tissues at the time of necropsy and after 30-60 days. Percentage of fat was measured using an automated solvent extractor. Mean percentage of fat in the bone marrow in initial equine, bovine, and canine samples was 81.75%, 86.33%, and 59.96%, respectively. The results indicate that bovine and equine percentage of fat in bone marrow does not change after 30-60 days, regardless of the storage condition, whereas the fat content from canine tissues varies when stored at ambient temperatures. Results suggest that postmortem interval and environmental conditions of samples must be considered in the postmortem evaluation of bone marrow fat concentration in at least some species.

The effect of high and low pressure pulsatile lavage on soft tissue and cortical blood flow: a canine segmental humerus fracture model

To determine the effect of high pressure pulsatile lavage (HPPL) and low pressure pulsatile lavage (LPPL) on cortical and soft tissue blood flow in a canine humerus segmental fracture model. Midshaft humeral osteotomies to create a 2-cm segment of diaphyseal bone were performed on bilateral canine humeri. Each osteotomy site was irrigated using either high pressure (n = 6) or low pressure (n = 5) pulsatile lavage prior to stabilization with a 5-mm steinman pin. Perfusion of cortical bone, periosteum, and biceps muscle was measured using Laser Doppler Flowmetry during four intraoperative intervals: pre-osteotomy, post-osteotomy, post-lavage, and post-nailing. Following osteotomy, a significant drop occurred in cortical perfusion (HPPL P = 0.049, LPPL P = 0.021) and in periosteal flow (HPPL P = 0.019, LPPL P = 0.012). Following irrigation there was no significant decrease in blood flow in either group for muscle (HPPL P = 0.249, LPPL P = 0.41), periosteum (HPPL P = 0.381, LPPL P = 0.402), or cortex (HPPL P = 0.398, LPPL P = 0.352) measurements. There was no significant difference between irrigation groups in post-lavage perfusion values for muscle (P = 0.326), periosteum (P = 0.452), and cortex (P = 0.464). Cortical perfusion decreased significantly post-nailing (HPPL P = 0.027, LPPL P = 0.047). Measurements did not differ significantly between groups at any other time interval. Although previous work has demonstrated an association between HPPL and detrimental structural changes in bone, this study demonstrates that HPPL does not adversely affect cortical or soft tissue blood flow acutely. Further, LPPL offers no acute benefit to cortical or soft tissue perfusion.

Morphological Changes in Articular Cartilage Due to Static Compression: Polarized Light Microscopy Study

We studied the deformation of the extracellular matrices in articular cartilage using a new compression-preservation method in histology. A Hoffman clamp was used to compress the tissue, which remained throughout the paraffin procedure and was removed from the embedded tissue block just before microtoming. Then 14 cartilage-bone blocks from 2 canine humeri were compressed for various strain levels from 5% to 65%. The histological sections were studied using a polarized light microscope, which generated a pair of two-dimensional maps of the fibril orientation (angle) and fibril organization (retardance) for each section. Results were 3-fold. One there was little change in the angle and retardance profiles of the tissue for strain levels 0–15% and a significant change in these profiles for strain levels 15% and above. Two for higher compression, more fibrils became aligned parallel to the articular surface; and three at ∼30% strain, a second “transitional zone” was formed in the deep part of the tissue. We concluded that this novel compression procedure can be used effectively to study the altered architecture of the collagen matrix in compressed cartilage.YX and GL would like to dedicate this paper to a co-author of this study and our long-time collaborator in cartilage research, Nancy Burton-Wurster (1941–2006).

Guided bone regeneration with beta-tricalcium phosphate and poly L-lactide-co-glycolide-co-epsilon-caprolactone membrane in partial defects of canine humerus

This study was performed to evaluate the effect of beta-tricalcium phosphate and poly L-lactide-co-glycolide-co-epsilon-caprolactone (TCP/PLGC) membrane in the repair of partial bone defects in canine proximal humerus. Three adult mixed-breed dogs were used during the experimental period. The length of the defect was quarter of the full length of humerus, and width of the defect was quarter of middle diameter of the lateral aspect of humerus. The humeri of each dog were divided into treatment (TCP/PLGC) and control groups. The defect was covered with TCP/PLGC membrane in treatment group. To evaluate regeneration of the bone, computerized tomography (CT) and histopathologic examination were performed. The radiopaque lines were appeared at the original defect sites in TCP/PLGC group but below the original site in control at 4th week. Radiopacity and thickness of the defect sites, and radiopaque lines were more increased at 8th week than those of 4th week. Histopathologic findings revealed fibrous connective tissue migration into the defect and the migration inhibited the structure of new cortex to be placed in the original level in control whereas new cortex growth was found in the level of original line in TCP/PLGC group. However, the new cortical bone in the TCP/PLGC group was thinner and less organized than the adjacent intact cortex, and the amount of new cancellous bones were also scanty. The result suggested that TCP/PLGC membrane is a good guided bone regeneration material to restore the original morphology of humerus in partial defect.

Biomechanical Comparison of Orthofix Pins and Cortical Bone Screws in a Canine Humeral Condylar Fracture Model

To compare shear stability of simulated humeral lateral condylar fractures reduced with either a self-compressing pin or cortical bone screw. In vitro biomechanical tests. Bilateral cadaveric canine humeri (n=18) without evidence of elbow disease. Lateral condylar fracture was simulated by standardized osteotomy. Bone fragments were stabilized with a self-compressing pin or a cortical bone screw (2.7 or 3.5 mm) inserted in lag fashion. Specimens were mounted in a materials testing system and the condylar fragment displaced in a proximal direction until failure. Mechanical testing variables derived from load-deformation curves were compared between stabilization methods using a Student's paired t-test. There were no statistically significant differences for mechanical testing variables between pin and screw stabilized specimens at expected walk and trot loads. Three yield points subjectively coincided with yield of the interfragmentary interface (Y1), bone at the implant interface (Y2), and implant deformation (Y3). Displacements at Y1 were 48-156% greater for pin than screw stabilized specimens. Y2 and Y3 loads were higher for screw than pin stabilized specimens, but likely supraphysiologic for dogs convalescing after surgical repair. A self-compressing pin or a cortical bone screw inserted in lag fashion both provided adequate strength in applied shear to sustain expected physiologic loads through the repaired canine elbow during postoperative convalescence. Because self-compressing pins were easy to implant and mechanical properties were not significantly different than cortical screws at expected physiologic loads, pins should be considered for the repair of traumatic humeral condylar fractures.

Effects of three intramedullary pinning techniques on pin location and articular damage in the canine humerus

The purpose of this study was to compare the pin location and articular damage for intramedullary (IM) pins inserted into the humerus in a directed retrograde, non-directed retrograde, and normograde fashion. Proximal pin positioning in the humerus was significantly more cranial (p < 0.05) using both retrograde techniques when compared to the normograde technique, although this did not cause significant interference with anatomical structures. The distance to the biceps tendon, transverse humeral ligament, and the distal pin location was similar with all insertion techniques, however two of ten pins passed in a non-directed retrograde fashion penetrated the shoulder joint. The results of this study suggest that although non-directed retrograde pinning cannot be recommended, either normograde or retrograde pins directed craniolaterally provide acceptable techniques for insertion of IM pins during distal humeral fracture repair.

Mechanical Performance of a Screw‐Type Veterinary Suture Anchor Subjected to Single Load to Failure and Cyclic Loads

To characterize the mechanical performance of a veterinary bone anchor under static and cyclic loads. Mechanical testing study. Cadaveric canine humeri. Humeri (6 pairs) were collected from skeletally mature dogs (mean [+/-SD] age, 17.2+/-2.1 months; weight, 20.8+/-1.5 kg). Bone anchors were inserted in the proximal metaphysis using nylon, and were longitudinally extracted. For the opposite humerus, anchors were subjected to longitudinal cyclic load (50% of the load at failure of their pair) for 1200 cycles then longitudinally loaded to failure. Anchors were then installed in a similar and adjacent area of these 2(nd) humeri with nylon and cyclically tested perpendicular to the axis of anchor insertion (100% of the longitudinal holding power of their pair) for 1200 cycles, then perpendicularly loaded to failure. Paired t-tests were used to compare holding power before and after longitudinal cyclic testing. Longitudinal holding power of the screw-type anchor in the proximal humerus was 385+/-30 N. Anchor pullout was the only mode of failure. Anchors in the paired humeri did not fail after 1200 cycles of 50% longitudinal loading, and post-cycle holding strength was not different (335+/-87 N; P=.32). Perpendicularly loaded anchors did not fail after 1200 cycles of 100% of opposite longitudinal holding strength, and had post-cycle perpendicular holding strengths of 514+/-72 N. Suture breakage was the mode of failure. Bone anchor holding strength is dependent on orientation of suture load. Screw-type bone anchor holding strength was not affected by longitudinal cyclic loading, and holding strengths of approximately 385 N can be expected in metaphyseal bone of large-breed mature dogs. Perpendicularly loaded anchors have higher failure loads, and holding strength of approximately 514 N can be expected in metaphyseal bone of the proximal humerus.