Mechanical evaluation of a threaded interference interlocking mechanism for angle-stable intramedullary nailing.

OBJECTIVE: To assess the fatigue and load-to-failure mechanical characteristics of an intramedullary nail with a threaded interference design (TID) in comparison to a commercially available veterinary angle-stable nail with a Morse taper bolt design (I-Loc) of an equivalent size. METHODS: 10 single interlocking screw/bolt constructs of TID and I-Loc implants were assembled using steel pipe segments and placed through 50,000 cycles of simulated, physiologic axial or torsional loading. Entry torque, postfatigue extraction torque, and 10th, 25,000th, and 50,000th cycle torsional toggle were assessed. Each construct was then loaded to failure in the same respective direction as fatigue testing. Four complete constructs of each design were then assessed using a synthetic bone analog with a 50-mm central defect via nondestructive torsional and axial loading followed by axial load to failure. RESULTS: All constructs were angle stable at all time points and withstood fatigue loading. Median insertional torque, extraction torque-to-insertion torque ratio, and torsional yield load were 33%, 33%, and 72.5% lower, respectively, for the TID interlocking screws. No differences in torsional peak load, torsional stiffness, axial yield load, axial stiffness, or axial peak load were identified. No differences in complete construct angle stability, torsional stiffness, axial peak load, axial stiffness, or axial yield load were identified. CLINICAL RELEVANCE: The TID had an inferior torsional yield load when compared to I-Loc implants but generated angle stability and sustained simulated physiologic fatigue loading. The TID may be a suitable mechanism for generating angle stability in interlocking nails.

Outcomes of 15 dogs and two cats with metabone fractures treated with fluoroscopically guided normograde metabone pinning.

OBJECTIVE: To report the outcomes of 15 dogs and two cats with metabone fractures treated with fluoroscopically guided normograde metabone pinning (FGNMP). STUDY DESIGN: Retrospective case series. ANIMALS: A total of 15 client owned dogs and two cats with 57 metabone fractures. METHODS: Description of FGNMP and reporting of the following data: signalment, pre- and postoperative radiographs, intramedullary pin diameter used, anesthesia, surgery and coaptation times, duration to normal weightbearing and bone union, postoperative care and complications. RESULTS: Median surgery time was 54 min (range: 26-99), median duration of coaptation was 14 days (range: 1-5 weeks), median time to normal weightbearing was 16 days (range: 2-45) and median time to bone union was 6 weeks (range: 4-12). All cases had at least 12 months of post-surgical follow-up with a median follow-up of 18 months (range: 12-70). No major complications occurred. Mild radiographic changes associated with subchondral bone sclerosis were noted on follow-up radiographs in 13/57 fractures. All cases returned to normal gait and full (15) or acceptable (2) function. CONCLUSION: In this study, FGNMP was an effective and safe technique for metabone fracture repair, requiring only short-term external coaptation in most patients. Time to bone union and return to normal function compared favorably to previously reported techniques. CLINICAL RELEVANCE: Fluoroscopically guided normograde metabone pinning provides an alternative technique for treatment of metabone fractures.

In vivo evaluation of a polyester and fiberglass composite intramedullary nail for femoral osteosynthesis in calves.

The objective of this study was to test a composite of polyester resin and fiberglass in the form of an intramedullary nail for osteosynthesis of femoral fractures in calves. The methodology was established based on a previous study that used a bovine femur finite element model to simulate fractures, which were then stabilized by the same nails as proposed in this study. General anesthesia was induced in six calves followed by fracture creation via an oblique incision in the middle third of the femoral diaphysis, and osteosynthesis was immediately performed by retrograde insertion of the composite nail. Locking was achieved by drilling the bone and nail without using a jig and introducing two stainless steel screws proximal and two distal to the fracture line. Five of the six calves achieved complete fracture healing after 60 days. No signs of incompatibility or toxicity of the composite were observed. However, limitations were observed during the surgery, such as difficulty in drilling the nail and trimming the remainder portion of the nail that extended beyond the length of the bone. Small fragments produced by these maneuvers were considered irritating to soft tissues during the postoperative period. It was also found that small cracks in the nail tended to propagate in the form of longitudinal fractures. In conclusion, an intramedullary nail made of polyester resin and fiberglass (a low-cost and easy-to-acquire material) was considered biocompatible and capable of allowing bone healing of femoral fractures in young cattle. However, the development of solutions for the reported limitations is crucial prior to recommending the proposed composite for clinical use.

Adjunctive fixation of the humeral epicondyle in a lateral condylar fracture model: Ex vivo comparison of pins and plates with a novel composite (AdhFix).

OBJECTIVE: To compare the biomechanical properties of using a novel composite construct (AdhFix) to an interfragmentary Kirschner wire or a reconstruction plate as adjunctive epicondylar stabilization in simulated lateral unicondylar humeral fractures. STUDY DESIGN: Cadaveric biomechanical assessment. SAMPLE POPULATION: Paired humeri harvested from skeletally mature dogs (14-41 kg), nine cadavers per group. METHODS: Simulated lateral unicondylar humeral fractures were stabilized with a transcondylar 4.5 mm cortical screw placed in lag fashion. Adjunct fixations consisting of a novel composite incorporating 2.7 mm cortical screws on one side, and either a 2.7 mm reconstruction plate or a 1.6 mm Kirschner wire on the contralateral side, were tested within paired humeri. Repaired humeri were axially loaded to failure and construct stiffness, yield load, and ultimate load were obtained from the load-deformation curves. RESULTS: In pairwise comparison, yield load was significantly higher for AdhFix group compared to the pin group, p = .016. No statistical significance was seen in the comparison between AdhFix group and the plate group, p = .25. CONCLUSION: Adhfix was mechanically superior to K-wires, and comparable to plate fixation, for adjunctive fixation in a lateral humeral condylar model. Our results support further investigation of the novel composite for adjunct fracture fixation in lateral humeral condylar fractures. CLINICAL SIGNIFICANCE: The novel composite tested may be a viable alternative for adjunct fixation of humeral condylar fractures, a technique that circumvents plate contouring.

Repair of femoral fractures in calves via external skeletal fixator with intramedullary pin tie-in.

OBJECTIVE: To describe the success rate and associated complications of external skeletal fixator/intramedullary pin tie-in for calf femoral fracture fixation. STUDY DESIGN: Clinical retrospective. ANIMALS: Ten calves, less than 30 days old, with diaphyseal/metaphyseal femoral fractures. METHODS: Medical records were reviewed from the University of Wisconsin from 2000 to 2020. Fractures were repaired using open reduction and fixation. An intramedullary Steinman pin was placed, exiting near the greater trochanter, and utilized for fracture reduction. Bicortical transfixation pins were placed distal and proximal to the fracture site. Poly(methyl methacrylate) (PMMA)-filled tubing connected the transfixation pins and proximal intramedullary pin, creating a Type 1a external skeletal fixator (ESF) tie-in. Follow up was obtained via medical records and phone interviews. RESULTS: Short-term survival rate was 7/10 (70%). Postanesthetic death occurred once. Postoperative complications occurred in all remaining cases. The most common findings were transfixation pin tract lucency and lameness (6/9 cases), implant dysfunction (5/9 cases), and infection (4/9 cases). Three of five cases with long-term follow up survived; all went on to productive careers. CONCLUSION: Although patients were prone to postoperative complications, short-term survival was comparable to previous reports. CLINICAL SIGNIFICANCE: The external skeletal fixator/intramedullary (ESF/IM) pin tie-in is less expensive and offers comparable success rates to other methods, providing a lower cost option for calf femoral fracture repair.

Accuracy of pin placement in the canine thoracolumbar spine using a free-hand probing technique versus 3D-printed patient-specific drill guides: An ex-vivo study.

OBJECTIVE: To compare pin placement accuracy, intraoperative technique deviations, and duration of pin placement for pins placed by free-hand probing (FHP) or 3D-printed drill guide (3DPG) technique. SAMPLE POPULATION: Four greyhound cadavers. METHODS: Computed tomography (CT) examinations from T6-sacrum were obtained for determination of optimal pin placement and 3DPG creation. Two 3.2/2.4-mm positive profile pins were inserted per vertebra, one left and one right from T7-L7 (FHP [n = 56]; 3DPG [n = 56]) by one surgeon and removed for repeat CT. Duration of pin placement and intraoperative deviations (unanticipated deviations from planned technique) were recorded. Pin tracts were graded by two blinded observers using modified Zdichavsky classification. Descriptive statistics were used. RESULTS: A total of 54/56 pins placed with 3DPGs were assigned grade I (optimal placement) compared with 49/56 pins using the FHP technique. A total of 2/56 pins placed with 3DPGs and 3/56 pins using the FHP technique were assigned grade IIa (partial medial violation). A total of 4/56 pins placed using the FHP technique were assigned grade IIIa (partial lateral violation). No pins were assigned grade IIb (full medial violation). Intraoperative technique deviations occurred with 6/56 pins placed using the FHP technique and no pins with 3DPGs. Overall, pins were placed faster (mean ± SD 2.6 [1.3] vs. 4.5 [1.8] min) with 3DPGs. CONCLUSIONS: Both techniques were accurate for placement of spinal fixation pins. The 3DPG technique may decrease intraoperative deviations and duration of pin placement. CLINICAL RELEVANCE: Both techniques allow accurate pin placement in the canine thoracolumbar spine. The FHP technique requires specific training and has learning curve, whereas 3DPG technique requires specific software and 3D printers.

Biomechanical comparison of one pin versus two pin fixation in a canine tibial tuberosity avulsion fracture model.

OBJECTIVE: To determine whether one larger or two smaller diameter pins used for tibial tuberosity avulsion fracture (TTAF) stabilization provides greater axial tensile strength and stiffness when subjected to monotonic mechanical load to failure in normal skeletally mature canine cadavers. STUDY DESIGN: Paired ex vivo biomechanical study. SAMPLE POPULATION: Eleven pairs of adult cadaveric dog tibias. METHODS: Twenty-two tibias from 11 dogs were collected to model a TTAF. Each limb of a pair was randomly assigned a one or two-pin fixation. Tibias were subjected to monotonic, axial load to failure. Fixation stiffness, strength, and pin insertion angles were analyzed with parametric testing. Significance was set at p < .05. RESULTS: The mean strength of the single-pin fixation was 426.2 ± 50.5 N compared to two-pin fixation at 639.2 ± 173.5 N (p = .003). The mean stiffness of the single-pin fixation was 57.3 ± 18.7 N/mm and the two-pin fixation was 71.7 ± 20.5 N/mm (p = .029). The normalized ratio between one and two-pin fixation had a mean stiffness of 68% ± 25.8% and strength of 82.8% ± 24.6%. CONCLUSIONS: In an ex vivo cadaveric TTAF model, vertically aligned two-pin fixation offers greater strength and stiffness when compared to a single-pin fixation. CLINICAL SIGNIFICANCE: When repairing TTAF, surgeons should aim to apply two vertically aligned pins rather than a single pin for greater strength and stiffness.

Surgical stabilisation of distal femoral fractures in calves using a triple pin technique: Twenty-five cases.

BACKGROUND: The goal of this study was to develop a safe fixation technique for the effective treatment of supracondylar and distal diaphyseal femoral fractures in newborn calves. METHODS: This study included a total of 25 newborn calves diagnosed with supracondylar or distal diaphyseal femoral fractures based on anamnesis and clinical and radiographic examination findings. Operations were performed under intrathecal anaesthesia. During the operation, the fracture line was found, and fixation was achieved by placing two Steinmann and Schanz pins. RESULTS: No abnormal findings were seen in the radiographs performed 28 days after surgery, and it was determined that a hard callus had started to form. It was observed that the patients who had lightly stepped on the ground for the first 3 days after the operation were able to walk without any problems on day 28. LIMITATIONS: As this study involved neonatal calves aged 1-14 days, the operation could only be performed under spinal anaesthesia with no sedation. However, sedation is likely to be applied in addition to spinal anaesthesia in older calves. CONCLUSION: It was concluded that the triple pin technique can be safely used in the treatment of supracondylar and distal diaphyseal femoral fractures.

Management of Feline Femoral, Tibial and Humeral Fractures Using a 3.5 mm Titanium Interlocking Nail.

OBJECTIVE: Our objectives were to report complications associated with stabilization of long-bone fractures in cats using a 3.5-mm titanium interlocking nail and to examine the influences of signalment, fracture type and fixation evaluations on the occurrence of complications. STUDY DESIGN: Retrospective clinical study. MATERIAL AND METHODS: Medical and radiographic records of cats with long-bone fractures treated with an interlocking nail were reviewed. Data included age, sex, weight, cause of the fracture, fractured bone(s) and fracture type. Complications were classified as minor and major complications. Fisher's exact tests and logistic regression analysis were used to test whether certain variables of signalment and interlocking nail configuration had an effect on the occurrence of complications. RESULTS: Sixty-seven fractures of 67 cats were examined in this study. Forty-eight femora, sixteen tibiae and three humeri were included. Complications occurred in 11/67 fractures. Major complications occurred in 8/67 fractures and included screw breakage (n = 3), nail breakage (n = 2), nail bending (n = 1), screw loosening (n = 1), non-union (n = 1). Statistical analysis showed a significant difference between fracture types and the occurrence of major complications (p = 0.02). CONCLUSION: In conclusion, use of this commercially available standard 3.5-mm titanium interlocking nail for stabilization of comminuted and oblique humeral, femoral and tibial fractures in cats is feasible.

Mechanical evaluation of a novel angle-stable interlocking nail in a gap fracture model.

OBJECTIVE: To describe the mechanical characteristics of a novel angle-stable interlocking nail (NAS-ILN) and compare them to those of a locking compression plate (LCP) by using a gap-fracture model. STUDY DESIGN: Experimental study. SAMPLE POPULATION: Synthetic bone models. METHODS: Synthetic bone models simulating a 50 mm diaphyseal comminuted canine tibial fracture were treated with either a novel angle-stable interlocking nail (NAS-ILN) or a locking compression plate (LCP). Maximal axial deformation and load to failure in compression and 4-point bending, as well as maximal angular deformation, slack, and torque to failure in torsion, were statistically compared (P < .05). RESULTS: In compression, the maximal axial deformation was lower for NAS-ILN (0.11 mm ± 0.03) than for LCP (1.10 mm ± 0.22) (P < .0001). The ultimate load to failure was higher for NAS-ILN (803.58 N ± 29.52) than for LCP (328.40 N ± 11.01) (P < .0001). In torsion, the maximal angular deformation did not differ between NAS-ILN (22.79° ± 1.48) and LCP (24.36° ± 1.45) (P = .09). The ultimate torque to failure was higher for NAS-ILN (22.45 Nm ± 0.24) than for LCP (19.10 Nm ± 1.36) (P = .001). No slack was observed with NAS-ILN. In 4-point bending, the maximal axial deformation was lower for NAS-ILN (3.19 mm ± 0.49) than for LCP (4.17 mm ± 0.34) (P = .003). The ultimate bending moment was higher for NAS-ILN (25.73 Nm, IQR [23.54-26.86] Nm) than for LCP (16.29 Nm, IQR [15.66-16.47] Nm) (P = .002). CONCLUSION: The NAS-ILN showed greater stiffness in compression and 4-point bending, and a greater resistance to failure in compression, torsion, and 4-point bending, than LCP. CLINICAL IMPACT: Based on these results, NAS-ILNs could be considered as alternative implants for the stabilization of comminuted fractures.

Comparison of Cervical Stabilization with Transpedicular Pins and Polymethylmethacrylate versus Transvertebral Body Polyaxial Screws with or without an Interbody Distractor in Dogs.

OBJECTIVE: The main aim of this study was to compare the biomechanical properties of caudal cervical vertebral stabilization using bicortical transpedicular pins with polymethylmethacrylate (PMMA) versus transvertebral body polyaxial screws and connecting rods with or without an interbody distractor. STUDY DESIGN: Ten canine cervical vertebral columns (C2-T3) were used. Four models (intact, transvertebral body polyaxial screw with interbody distractor [polyaxial + distractor], transvertebral body polyaxial screw without interbody distractor [polyaxial - distractor] and bicortical transpedicular pins/polymethylmethacrylate [pin-PMMA]) were applied to C6-7 sequentially on the same specimens. Angular range of motion (AROM) in the form of flexion and extension was measured at C4-5, C5-6 and C6-7 in all groups. RESULTS: Treated vertebral specimens had significantly less AROM than unaltered specimens. There was no significant difference in AROM between the experimental groups at C6 and C7. Angular range of motion ratio in flexion-extension was 80.8, 72.7 and 78.3% for polyaxial + distractor, polyaxial - distractor and pin-PMMA groups, respectively, which were less than the intact group. There was no significant increase in the range of motion of the adjacent vertebrae after stabilization. CONCLUSION: Stabilization obtained with transvertebral body polyaxial screws was comparable to that from the well-established bicortical pins/PMMA construct. Association of an intervertebral distractor did not change AROM of the polyaxial screw constructs.

Effects of the number and the position of transfixation pins in acrylic connecting bars.

Acrylic columns are commonly used in external skeletal fixators, especially for fracture management or trans-articular fixations. To the authors' knowledge, there are no studies demonstrating if the number or position of the transfixation pins influence the ultimate strength and stiffness of the acrylic column. The objective of this study was to evaluate the effects of the number and position of transfixation pins (concentric versus eccentric) on the strength and stiffness of acrylic columns placed in axial compression. We hypothesized that strength and stiffness of acrylic columns under axial compression would not be affected by the number or position of the transfixation pins through the column. Three different groups of 12 acrylic columns were constructed with 4, 6, and 8 pins. In each group, 6 columns were constructed with the pins placed concentrically and the remaining 6 columns with the pins placed eccentrically. Each column was then placed under axial compression using a biomechanical testing machine. No significant differences were observed in ultimate strength regarding the number or position of transfixation pins (P = 0.83 and P = 0.27, respectively). However, stiffness was significantly decreased for columns with 4 eccentric pins compared with columns with 6 and 8 eccentric pins (P < 0.01) and with columns with 4 concentric pins (P < 0.001). Although the effects of transfixation pins on the rigidity of acrylic columns do not appear to be clinically significant, these tests were performed only in compression and results might differ if complete external fixator systems are used with different models of testing. Future studies are recommended.

Les colonnes d'acrylique sont couramment utilisées dans les fixateurs externes, notamment pour la gestion des fractures ou les fixations transarticulaires. Selon les auteurs, aucune étude ne démontre si le nombre ou le positionnement des broches de transfixation influence la résistance ultime et la rigidité de la colonne d'acrylique. Les objectifs de cette étude étaient d'évaluer l'effet du nombre et du positionnement des broches de transfixation (concentriques versus excentriques) sur la résistance et la rigidité des colonnes d'acryliques placées en compression axiale. Nous avons émis l'hypothèse que la résistance et la rigidité des colonnes d'acryliques en compression axiale ne seraient pas affectées par le nombre ou le positionnement des broches de transfixation à travers la colonne. Trois groupes différents de douze colonnes acryliques ont été construits avec quatre, six, et huit broches. Dans chaque groupe, six colonnes ont été construites avec les broches placées concentriquement et les six colonnes restantes avec les broches placées de manière excentrique. Chaque colonne a ensuite été placée sous compression axiale à l'aide d'une machine de tests biomécaniques. Aucune différence significative n'a été observée pour la résistance ultime selon le nombre ou le positionnement des broches de transfixation (P = 0,83 et P = 0,27, respectivement). Cependant, la rigidité a été significativement diminuée pour les colonnes avec quatre broches excentriques par rapport aux colonnes avec six et huit broches excentriques (P < 0,01) et avec les colonnes avec quatre broches concentriques (P < 0,001). Bien que les effets des broches de transfixation sur la rigidité des colonnes acryliques ne semblent pas être cliniquement significatifs, ces tests ont été effectués uniquement en compression et les résultats pourraient différer si des systèmes complets de fixateurs externes sont utilisés avec différents modèles de test. De futures études sont recommandées.(Traduit par les auteurs).

Safe corridors for external skeletal fixator pin placement in feline long bones.

OBJECTIVES: External skeletal fixation is an established technique in cats for biological fixation of long bone fractures, stabilisation of the joints, and treatment of shearing injuries and angular deformities. As appropriate and accurate pin insertion is imperative for a successful outcome, knowledge of topographic anatomy and areas that are safe (safe corridors) for pin placement is integral to successful surgery. At present, however, safe corridors have not been determined fully in feline orthopaedics, with surgeons having to rely on knowledge based on canine orthopaedics. This study was performed to determine safe corridors for pin placement in feline long bones. METHODS: The limbs of six feline cadavers were frozen. Only limbs with no history of orthopaedic conditions were used. Transverse sections through the limbs were examined, and anatomical structures were determined in relation to the bone. These structures were compared with those of the contralateral limbs, which were dissected for topographic assessment. Safe corridors were defined as topographic areas where no vital structures, muscles or joints were present. RESULTS: Examination of the humerus revealed safe corridors at its proximal craniolateral aspect and on the medial and lateral humeral condyles. Safe corridors of the antebrachium were identified on the lateral aspect of the olecranon, the distal two-thirds of the medial antebrachium and the distal third of the lateral antebrachium. Safe corridors in the femur consisted of a small area lateral to and just below the major trochanter, and on the medial and lateral femoral condyles. Evaluation of the tibia revealed safe corridors on the medial aspect of the entire tibia, the cranial aspect of the proximal tibia on the tibial crest and the area just proximal to the lateral malleolus. CONCLUSIONS AND RELEVANCE: Safe corridors for pin placement during external skeletal fixation in feline limbs differed from those in canine limbs. Knowledge of canine anatomy may be inapplicable to pin placement in feline limbs undergoing external skeletal fixation.

Effect of Bidirectional Insertion of External Skeletal Fixation Pins on Axial Pullout Strength in Canine Cadaveric Bone.

OBJECTIVE: The aim of this study was to evaluate the effect of bidirectional insertion on axial pullout strength of tapered run out (TRO), traditional negative profile (TNP) and positive profile (PP) pins. STUDY DESIGN: Cadaveric adult canine tibiae were harvested. Tapered run out pins (Group 1) were inserted unidirectionally to the desired position; bidirectionally past the desired position, then withdrawn to the desired position (Group 2); and bidirectionally as described for Group 2, repeated twice (Group 3). Traditional negative profile pins (Group 4-6) and PP pins (Group 9-11) were placed in the same manner. Tapered run out (Group 7), TNP (Group 8) and PP pins (Group 12) were driven unidirectionally such that the shaft of the pin violated the cis-cortex. A servohydraulic testing machine extracted the pins and measured axial peak pullout strength. RESULTS: Positive profile pins had significantly greater pullout strength than TRO and TNP pins placed unidirectionally to the desired position. Method of insertion had no effect on peak pullout strength of TNP pins. TRO and PP pins inserted unidirectionally to the desired position had significantly greater peak pullout strengths than insertion bidirectionally or if the shaft of the pin violated the cis-cortex. CONCLUSION: The authors recommend that pins used for external skeletal fixation should be placed unidirectionally to the desired position with fluoroscopic guidance, intra-operative depth gauge measurements or measurements from preoperative radiographs. Repositioning pins results in loss of peak pullout strength with TRO and PP pins.

Determination of the insertion position of implants for the cross-pin fixation of distal femoral physis fractures.

The cross-pin technique for the treatment of distal femoral physis fractures (specifically, Salter-Harris Type I fractures) was investigated using femurs collected from beagle cadavers. The pin was inserted from the medial surface of the femur at an inclination of approximately 30 to 45° relative to the long axis of the femur in the anteroposterior direction; the pin exit was set proximal to the origin of the long digital extensor tendon. Digital and radiographic images of the femur in the anteroposterior and lateral directions were obtained. In both types of images, the insertion angle of the pin relative to the long axis was measured. Results suggest that when inserting a pin proximal to the fracture line, the ideal position can be achieved by inclining the pin approximately 20° cranially relative to the long axis of the lateral direction of the femur, in addition to the previously described criteria.

La technique des tiges croisées pour le traitement des fractures de la physe fémorale distale (en particulier, les fractures de Salter-Harris de type I) a été étudiée à l'aide de fémurs prélevés sur des cadavres de beagle. La tige a été insérée à partir de la surface médiale du fémur à une inclinaison d'environ 30 à 45° par rapport au grand axe du fémur dans la direction antéropostérieure; la sortie de la tige était localisée en amont de l'origine du tendon extenseur digital long. Des images numériques et radiographiques du fémur dans les directions antéropostérieure et latérale ont été obtenues. Dans les deux types d'images, l'angle d'insertion de la tige par rapport au grand axe a été mesuré. Les résultats suggèrent que lors de l'insertion d'une tige proximale au trait de fracture, la position idéale peut être obtenue en inclinant la tige d'environ 20° crânialement par rapport au grand axe de la direction latérale du fémur, en plus des critères décrits précédemment.(Traduit par Docteur Serge Messier).

The Effect of Reducing the Bone to Cast Distance in an Equine Transfixation Pin Cast: An Ex Vivo Biomechanical Study.

OBJECTIVE: The aim of this study was to evaluate the effect of reducing the bone to cast distance on the resistance of the pin to cyclic loading in equine transfixation pin casts. STUDY DESIGN: Eleven pairs of cadaveric equine third metacarpal bones were prepared and one 6.3/8.0 mm transfixation pin was placed in standard fashion 10 mm proximal to the distal physeal scar into each bone. One metacarpus of each pair was tested with a distance of 10 mm (10 mm group) and the contralateral metacarpus with a distance of 20 mm (20 mm group) between the outer cortex of the bone and the fixation of the pin. Eight pairs were tested using a simplified test set-up in which the pins were fastened at both ends to polyoxymethylene-copolymer sleeves. The pins of the remaining three pairs of bones were incorporated into a fibreglass cast. All specimens were tested under cyclic loading until failure of the pin in axial compression. RESULTS: All pins failed uni- or bilaterally at clinically relevant load levels. Pins of the 10 mm group endured significantly (p < 0.05) higher load levels and total number of cycles until failure compared with the pins of the 20 mm group. CONCLUSION: The distance between the bone surface and the cast at the location of pin insertion has a significant effect on resistance of the pins to cyclic loading. Therefore, the amount of padding applied underneath an equine transfixation pin cast can have an influence on the overall stability and durability of the construct.

Accuracy and Safety of Image-Guided Freehand Pin Placement in Canine Cadaveric Vertebrae.

OBJECTIVE: The aim of this study was to validate an imaging technique for evaluation of spinal surgery accuracy and to establish accuracy and safety of freehand technique in the thoracolumbar spine of large breed dogs. STUDY DESIGN: After thoracolumbar spine computed tomography (CT), 26 drilling corridors were planned then drilled to receive 3.2 mm positive profile pins using a freehand technique. After pin removal, CT was repeated. All entry points, exit points and angles of the preoperative planned trajectories were compared with postoperative ones using an image registration and fusion technique by three observers. Corridor coordinates for entry and exit points were evaluated in three dimensions and angles were measured in one plane. Intraclass correlation coefficient (ICC) was used to establish the imaging technique reliability and descriptive statistics were used to report on the freehand technique accuracy. Safety was evaluated using a vertebral cortical breach grading scheme. RESULTS: Intraclass correlation coefficient for the entry points, exit points and angle were 0.79, 0.96 and 0.92 respectively. Mean deviations for the entry points, exit points and angle were 3.1 mm, 6.3 mm and 7.6 degrees respectively. Maximum deviations were 6.3 mm, 11.0 mm and 16.4 degrees. Most deviations were lateral and caudal. All corridors were judged as safe. CONCLUSION: The imaging technique reliability was good to excellent to study spinal surgery accuracy. Implant deviations should be anticipated when planning stabilization surgery in large breed dogs using the freehand-guided technique.

Defining a safe corridor for trans-iliac pin placement in cats.

OBJECTIVE: To identify whether a theoretical predictable safe corridor is available in cats for placement of trans-iliac pins without the use of fluoroscopy. METHODS: Twenty-one cats with straight orthogonal normal pelvic radiographs were included. Two start points were evaluated: a midpoint and a dorsal point. The midpoint was defined as midway between the dorsal lamina of the sacral vertebral canal and the cranial dorsal iliac spine. The dorsal start point was 2 mm ventral to the cranial dorsal iliac spine. The pin was assumed to be driven at 90 degrees to the lateral face of the ilium, and considered surgeon accuracy was ±4 degrees from the perpendicular. The angular range and the distance between the iliac wings from the ventrodorsal radiograph were used to calculate the possible cross-sectional area and pin exit location if driven from one iliac wing to the other. The corridor was then evaluated for repeatability in six randomly selected cats. RESULTS: Vertebral foramina penetration risk was identified in some cats when using a 1.6 and 2 mm-diameter pin using the mid-iliac wing start point. The dorsal start point decreased the available pin placement area but reduced the risk of entering the hazardous zone for all pin sizes up to 2 mm. CONCLUSION AND RELEVANCE: A theoretical defined safe corridor is available for trans-iliac pin placement in cats between 2.0 and 5.5 kg. A 1.2-mm pin is the safest if using the mid-iliac wing start point. A more dorsal start point can accommodate up to a 2.0-mm pin if correctly aligned to the sacrum.

Clinical application of the small I-Loc interlocking nail in 30 feline fractures: A prospective study.

OBJECTIVE: To describe medium-term functional outcome after nail osteosynthesis in feline traumatology and report clinically relevant recommendations for I-Loc angle-stable interlocking nail use in cats. STUDY DESIGN: Prospective clinical study. SAMPLE POPULATION: Client-owned cats (n = 29). METHODS: Consecutive cases with femoral, tibial, or humeral fractures were included. Outcome measures included fracture and surgical procedure description, limb alignment, nail size vs body weight (BW), percentage of nail medullary canal (MC) fill, time to limb function at clinical union (CU), and complications. Descriptive statistics were reported and compared with historical data. RESULTS: Bone distribution was 53.3% femora, 30% tibiae, and 16.7% humeri. There were six epimetaphyseal and 24 diaphyseal fractures. Overall, 67% of fractures were comminuted. Open reduction and minimally invasive techniques were used in 73% and 27% of cases, respectively. Seventeen I-Loc 3 (cat mean BW 4.4 ± 2.2 kg) and 13 I-Loc 4 (cat mean BW 5.2 ± 1.2 kg) nails were placed with mean MC fill of ≤50%. Average time to CU was 7.2 weeks. At CU, lameness had resolved or was mild in every cat, and all cats ultimately regained full limb function. No major complications were encountered. CONCLUSION: Because of improved CU times, excellent functional outcomes, and low complication rate, our results provide evidence that I-Loc nails are safe and effective for feline traumatology. CLINICAL SIGNIFICANCE: The I-Loc may be advantageous for fixation of epimetaphyseal fractures. Because of feline bone specific dimensional constraints, I-Loc 3 is likely appropriate for all feline humeri and most tibiae, while I-Loc 4 is well sized for feline femora.

Accuracy of Patient-Specific 3D Printed Drill Guides in the Placement of a Canine Coxofemoral Toggle Pin through a Minimally Invasive Approach.

OBJECTIVE: The aim of this study was to evaluate the accuracy of patient-specific three-dimensional printed drill guides (3D-PDG) for the placement of a coxofemoral toggle via a minimally invasive approach. MATERIALS AND METHODS: Pre-procedure computed tomography (CT) data of 19 canine cadaveric hips were used to design a cadaver-specific 3D-PDG that conformed to the proximal femur. Femoral and acetabular bone tunnels were drilled through the 3D-PDG, and a coxofemoral toggle pin was placed. The accuracy of tunnel placement was evaluated with post-procedure CT and gross dissection. RESULTS: Coxofemoral toggle pins were successfully placed in all dogs. Mean exit point translation at the fovea capitis was 2.5 mm (0.2-7.5) when comparing pre- and post-procedure CT scans. Gross dissection revealed the bone tunnel exited the fovea capitis inside (3/19), partially inside (12/19) and outside of (4/19) the ligament of the head of the femur. Placement of the bone tunnel through the acetabulum was inside (16/19), partially inside (1/19) and outside (2/19) of the acetabular fossa. Small 1 to 2 mm articular cartilage fragments were noted in 10 of 19 specimens. CLINICAL SIGNIFICANCE: Three-dimensional printed drill guide designed for coxofemoral toggle pin application is feasible. Errors are attributed to surgical execution and identification of the borders of the fovea capitis on CT data. Future studies should investigate modifications to 3D-PDG design and methods. Three-dimensional printed drill guide for coxofemoral toggle pin placement warrants consideration for use in select clinical cases of traumatic coxofemoral luxation.