Numerical evaluation of internal femur osteosynthesis based on a biomechanical model of the loading in the proximal equine hindlimb.

Femoral fractures are often considered lethal for adult horses because femur osteosynthesis is still a surgical challenge. For equine femur osteosynthesis, primary stability is essential, but the detailed physiological forces occurring in the hindlimb are largely unknown. The objective of this study was to create a numerical testing environment to evaluate equine femur osteosynthesis based on physiological conditions. The study was designed as a finite element analysis (FEA) of the femur using a musculoskeletal model of the loading situation in stance. Relevant forces were determined in the musculoskeletal model via optimization. The treatment of four different fracture types with an intramedullary nail was investigated in FEA with loading conditions derived from the model. The analyzed diaphyseal fracture types were a transverse (TR) fracture, two oblique fractures in different orientations (OB-ML: medial-lateral and OB-AP: anterior-posterior) and a "gap" fracture (GAP) without contact between the fragments. For the native femur, the most relevant areas of increased stress were located distally to the femoral head and proximally to the caudal side of the condyles. For all fracture types, the highest stresses in the implant material were present in the fracture-adjacent screws. Maximum compressive (-348 MPa) and tensile stress (197 MPa) were found for the GAP fracture, but material strength was not exceeded. The mathematical model was able to predict a load distribution in the femur of the standing horse and was used to assess the performance of internal fixation devices via FEA. The analyzed intramedullary nail and screws showed sufficient stability for all fracture types.

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.

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.

Early Clinical Experience with a Newly Designed Interlocking Nail System-Targon(®) Vet.

OBJECTIVE: To describe early clinical experience with a newly designed interlocking nail system (Targon(®) Vet) in diaphyseal fractures in cats and small dogs. STUDY DESIGN: Retrospective case series. ANIMALS: Client-owned cats (n=49) and dogs (n=8). METHODS: Fifty-seven consecutive cases (49 cats, 8 dogs) with 60 long bone fractures were included in the study. Follow-up radiographs were scheduled at 4 and 8 weeks and again 6 months postoperatively. The end point for each case was determined radiographically by a healed fracture. Complications were defined as minor or major. Clinical outcome was subjectively assessed by a full orthopedic examination and follow-up radiographs. Descriptive data are reported. RESULTS: Median age of cats was 18 months (range, 3-220 months) and of dogs was 28 months (range, 7-115 months). Median body weight was 3.7 kg (range, 1.67-8.41 kg) for cats and 8.15 kg (range, 2.68-13.6 kg) for dogs. Median radiographic follow-up was 16 weeks. All fractures with follow-up radiographs available (n=46) were healed with no infections reported. A total of 12 postoperative complications occurred: 3 minor (slippage of the locking screws) and 9 major (5 femoral-irritation of the sciatic nerve, stress protection, fracture because of a missed fissure, femoral neck fracture, intra-operative revision with a rod and plate; 4 tibial-3 with protrusion of the distal locking screw through the skin and 1 with in-growth of the intramedullary nail). CONCLUSION: Implantation of the Targon(®) Vet System was feasible in all cases. It provides an alternative system for diaphyseal fracture repair in cats and small dogs.

Pin Size Selection for Normograde Intramedullary Pinning of Distal Humeral Fractures in the Dog.

OBJECTIVE: To determine the optimal intramedullary (IM) pin size for open and percutaneous normograde pinning of the distal humerus. STUDY DESIGN: Ex vivo anatomic study. SAMPLE POPULATION: Sixteen canine cadavers. METHODS: Sixteen pairs of forelimbs were harvested from canine cadavers weighing 25-35 kg. The craniocaudal diameter of the humeral medullary canal, at the distal 80th percentile of its length, was measured on a lateral radiograph. Forelimbs within each pair were allocated to percutaneous or open pinning techniques. Cadavers were divided into three groups based on IM pin diameter relative to the medullary canal diameter: Group 25-35%, Group 36-45%, and Group 46-55%. Pins were inserted normograde into the medial epicondyle and advanced until they exited the proximal humerus. Pin tracts were dissected and damage to soft tissue, bony structures, and location of entry and exit points were documented. The humeri were also cut at the thinnest point of the medial epicondyle and damage to the bone was evaluated. RESULTS: There was no difference in any of the outcomes between the open and percutaneous techniques. Cortical damage was more frequent in Group 46-55% and included blanching and or fracture of the cortex of the medial epicondyle, with fracture occurring in 6/10 limbs in this group. Pins in Group 46-55% exited the farthest and most distal from the optimal exit point and were difficult to place in all limbs. CONCLUSION: This study supports a recommendation for open and percutaneous pinning of the humerus with IM pins 36-45% of the medullary canal diameter measured at the distal 80th percentile of humeral length.

Transfixation pinning and casting of a comminuted metacarpal fracture in a 870 kg bull.

OBJECTIVE: To report metacarpal fracture repair in a bull. STUDY DESIGN: Clinical report. ANIMALS: Simmental bull (n = 1; 870 kg). METHODS: A comminuted right metacarpal fracture was repaired using 2 transfixation pins (6 mm diameter) through the distal metaphysis and diaphysis of the radius and a full limb synthetic resin cast. RESULTS: Slight bending of both pins occurred 1 day after surgery. Both pins were loose and removed at 31 days and a full-limb cast reapplied. The cast was changed at approximately -4 week intervals. On day 50, the right carpus had moderate overextension and a valgus deformity. An exercise program was started on day 62, and on day 110, the cast was replaced with a Robert-Jones-bandage. At 130 days there was circumferential callus formation and the bull was discharged. At 6.5 months, overextension of the right carpus had resolved and carpal valgus had improved. The bull returned to at 7.5 months after surgery, and was successfully used for 4 years. CONCLUSION: For highly valuable cattle like this breeding bull, a surgical treatment of such a fracture should be attempted despite a primarily poor prognosis.

Use of a Modified Intramedullary Pinning Technique for Distal Femoral Physeal Salter-Harris Type I and II Fracture Management: A Retrospective Study of 31 Cats.

OBJECTIVE: To report a modified intramedullary pinning technique, and associated outcomes, for distal femoral physeal Salter-Harris type I and II fracture management in cats. STUDY DESIGN: Retrospective study including client-owned cats presented between November 2014 and February 2022 with distal femoral physeal fractures treated with an intramedullary pin and one antirotational pin inserted in the lateral femoral condyle. Collected data included signalment, fracture characteristics according to the Salter-Harris classification, surgical data (intramedullary and antirotational pin sizes), and outcome data (radiographic and functional outcomes and complications). RESULTS: Thirty-one cats were included in this study. Bone healing was radiographically confirmed 6 to 8 weeks postoperatively in all cases. The majority of cats (30/31) were classified as full functional outcomes at mid-term follow-up. The overall mid-term complication rate was 3% (1/31). Implant migration was not observed and implant removal was not needed in any case. CONCLUSION: The modified intramedullary pinning technique for distal femoral Salter-Harris I and II fracture management in cats was associated with an full functional outcome.

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.

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.

A finite element model to simulate femoral fractures in calves: testing different polymers for intramedullary interlocking nails.

OBJECTIVE: To verify if the finite element method can correctly estimate the performance of polyacetal and polyamide 6 intramedullary nails in stabilizing a femoral fracture in calves and to estimate the performance of a polypropylene nail in same conditions. STUDY DESIGN: Computational and experimental study. SAMPLE POPULATION: Finite element models (FEMs). METHODS: Based on a 3-dimensional finite element method (FEM) of the femoral diaphysis, 3 models were constructed to simulate an oblique simple fracture stabilized by an intramedullary nail composed of 1 of 3 distinct polymers. Models were tested under 6 loading conditions that simulated a static calf or a calf in different walking phases. Maximum bone and implant stresses were compared to yield and rupture stresses of specific materials. RESULTS: Under static conditions, all polymers were resistant to critical deformation and rupture because maximum von Mises stresses were lower than the respective yield and rupture stresses. However, during walking, maximum stresses exceeded the yield and rupture limits of the polymers, in agreement with a previous in vivo study, which used polyacetal and polyamide nails. CONCLUSIONS: FEM correctly estimated that polyacetal and polyamide 6 nails would fail to immobilize an oblique femoral diaphyseal fracture in calves that were allowed to walk freely during the early postoperative period. FEM can be useful in the development of new bovine orthopedic devices.

Limb Gait Score of Femur Fracture Fixated by Intramedullary Pinning in Dogs.

Animal posture, limb gait, and body weight-bearing in dogs can be evaluated by limb gait score. In this study, nine adult male dogs of local breed were used to induce a complete transverse femoral mid-shaft fracture fixed internally by intramedullary pining under general anesthesia with the aseptic technique and followed for 60 days postoperative. The data were analyzed, including five degrees that indicate the correlation among animals' posture, limbs, and body weight tolerance per day. The results demonstrated that in grade 5, the animals completely hold the affected limb during standing position 1st-3rd day postoperative. From the 4th-10th day postoperative, in grade 4, the animals supported the body weight on the affected limb in the standing position and hold it during waking. In grade 3, from 11th-21th day postoperative, the operated animals supported body weight on the affected limb in slow waking and hold it in speed waking and running. From the 22nd-28th day postoperative, in grade 2, the animals used the limb in speed walking, from the 29th-35th day postoperative. In grade1, the animals could use the limb in running from the 36th-2nd day postoperative. In grade 0, the animals used the limb normally in walking, running, and jumping until the end of experimental periods (60th day postoperative). The results indicated that limb gait scores in dogs can be used for the evaluation of the relationships among animals' posture, limb gait, and body-weight bearing per day during bone regeneration processing of femur fracture fixed by intramedullary pining.

Prospective evaluation of minimally invasive plate osteosynthesis in 36 nonarticular tibial fractures in dogs and cats.

OBJECTIVE: To evaluate the clinical outcome of minimally invasive plate osteosynthesis (MIPO) for nonarticular tibial fractures stabilized using bone plates with or without an intramedullary rod (IMR). STUDY DESIGN: Prospective study. ANIMALS: Dogs (n=28) and 8 cats. METHODS: After closed reduction, fracture fixation was achieved using an epiperiosteal plate inserted percutaneously through epiphyseal small incisions. In some fractures, an IMR was inserted via medial parapatellar arthrotomy. Radiographs were recommended every 3 weeks until clinical union. Postoperative tibial length and alignment were compared with contralateral measurements (P<.05). Time to clinical union and complications were recorded. RESULTS: An IMR was used in 30.5% of the cases. Repaired tibiae were 1% shorter than contralateral tibiae (P<.05). Frontal and sagittal alignment were similar between repaired and contralateral tibiae (P>.05). Six dogs were lost for follow-up; owners indicated normal function. In 30 cases for which bone healing was documented, mean±SD healing time was 45±20.8 days; however, when considering the 23 cases, which completed preestablished scheduled follow-ups, healing time was 36±11.6 days. Minor complications occurred in 4 cases (11%). One major complication (3%) consisting of a plate fracture was successfully revised using MIPO with a larger plate. CONCLUSIONS: Consistent restoration of alignment was accomplished using MIPO techniques. Furthermore, MIPO appeared to yield faster healing times and lower complication rates than those reported with conventional plate osteosynthesis.

Influence of locking bolt location on the mechanical properties of an interlocking nail in the canine femur.

OBJECTIVE: To determine whether the fatigue properties of an interlocking nail (ILN) construct are influenced by metaphyseal or diaphyseal location of the locking bolt. STUDY DESIGN: Ex vivo mechanical investigation. SAMPLE POPULATION: Adult canine femora (n = 19 pairs). METHODS: Femora were implanted with a 6-mm diameter ILN. In 1 femur, the ILN was locked with a 2.7 mm bolt placed in the diaphysis; the ILN in the contralateral femur was locked with a bolt placed in the metaphysis. Constructs were tested to failure in axial loading (9 pairs) or torsion (10 pairs), with failure defined as displacement > 2 mm or a total of 500,000 cycles for axial loading, and rotation > 45° for torsional loading. Outcome measures included initial construct stiffness, number of cycles to failure, peak load, and peak torque. After testing, microradiography and histology were used to determine the location and nature of construct failure. RESULTS: Metaphyseal bolts failed at higher axial loads than diaphyseal bolts (P = .03), with bolt failure because of bending at the nail-bolt interface. All of the metaphyseal bolt constructs survived torsional testing whereas 9 of 10 diaphyseal bolt constructs failed catastrophically because of spiral fracture through the adjacent cortical bone. CONCLUSIONS: Placement of a locking bolt in metaphyseal bone extends fatigue life under axial loading and decreases the incidence of catastrophic failure under torsional loading.

Combined intramedullary and external skeletal fixation of metatarsal and metacarpal fractures in 12 dogs and 19 cats.

OBJECTIVE: To report surgical technique, clinical experiences, and long-term outcomes of combined intramedullary/external skeletal fixation of metatarsal (MT) and metacarpal (MC) fractures in dogs and cats. STUDY DESIGN: Case series. ANIMALS: Dogs (n = 12); 19 cats. METHODS: Clinical and radiographic records of animals managed by combined intramedullary/external fixation of MT/MC fractures were reviewed. Signalment, fracture configuration, complications, and subjective clinical findings were recorded. Surgical technique involved retrograde intramedullary pin placement into fractured MT/MC bones, and transverse pin placement in the base of the MT/MCs or tarsal/carpal bones. Contoured pin ends were enshrouded dorsally in epoxy resin and implants maintained until fracture union. Postoperative clinical and radiographic reassessment was performed where possible. RESULTS: Small breed dogs (n = 12) and 19 cats were operated. Fixator removal occurred in < 10 weeks in all cases. Complications included synostosis (n = 2), pin tract discharge (7), excessive postoperative swelling (8), skin abrasions from the frame (2), and paw distortion associated with frame impingement (2). Long-term radiography documented degenerative changes associated with MT-phalangeal or MC-phalangeal joints in 2 dogs; 7 cats, but changes were typically graded mild or moderate and affected only 1 or 2 joints. CONCLUSIONS: Combined intramedullary/external fixation of MT/MC fractures is viable, particularly juxta-articular fractures. Pin penetration of MT-phalangeal or MC-phalangeal joints may cause morbidity and requires further study.

Ulnar interlocking intramedullary nail stabilization of a proximal radio-ulnar fracture in a dog.

OBJECTIVE: To report use of an ulnar interlocking intramedullary nail for repair of an open highly comminuted fracture of the proximal third of the antebrachium in a dog, caused by gunshot. STUDY DESIGN: Case report. ANIMALS: 1.5-year old, 60 kg, neutered male Mastiff. METHODS: An ulnar interlocking intramedullary nail was used to stabilize an open comminuted proximal antebrachial fracture and a cast applied for 4 weeks. RESULTS: Union by secondary bone healing occurred in 8 weeks. At 16 weeks, there was advanced remodeling of the radial and ulnar bony callus and fracture lines were no longer evident. Limb use was normal with normal pain free range of motion of the right elbow. CONCLUSION: Ulnar interlocking nail is a viable alternative treatment for highly comminuted fracture of the proximal third of the antebrachium in dogs.

Biomechanical comparison of a new expandable intramedullary nail and conventional intramedullary nails for femoral osteosynthesis in dogs.

Intramedullary nailing of diaphyseal femoral fractures is a commonly used treatment method in dogs because of its biological and biomechanical advantages compared to bone plating. To achieve adequate resistance of the intramedullary nail against torsional and axial compressive forces, additional application of transcortical screws is needed. As these interlocking screws represent a frequent cause of post-operative complications, a new expandable intramedullary nail (EXPN) was developed, which was designed to provide adequate fracture stabilisation without the need for transcortical fixation. The evaluation of the biomechanical properties of the new EXPN with regard to torsional, compressive and bending stability as well as direct comparison to the biomechanical properties of conventional Steinmann (STMN)- and interlocking (ILN) nails was carried out with different biomechanical test arrangements. No significant statistical differences regarding the torsional and bending resistance between the EXPN and ILN group were seen, which indicates that rotatory as well as bending stability of the innovative EXPN is similar to the conventional ILN. Nevertheless, the percentage deviation between the attempted and successfully reached physiological compressive forces was significantly higher (p = 0.045) in the EXPN group compared to the ILN group, which indicates that the compressive stability of the innovative EXPN might be weaker compared to the ILN. In summary, the new EXPN represents an interesting alternative to conventional intramedullary nails. However, in direct comparison to conventional interlocking nails, the EXPN has shown weaknesses in the neutralization of axial compressive forces, which indicates that at least biomechanically the interlocking nail seems advantageous. Further in-vitro and in-vivo investigations are required before clinical use can be recommended.

Advances in Exotic Animal Osteosynthesis.

Exotic animal orthopedics has not incorporated the most recent progress made in small animal surgery or human medicine. Although minimally invasive osteosynthesis has been incorporated as a routinely used alternative in small animals, its use in exotic animals is still in its infancy. This article compliments the reviews of orthopedics in small mammals, birds, and reptiles in the previous issue. It reviews relevant recent studies performed in laboratory animals about new orthopedic materials and techniques showing potential to become incorporated into the routine orthopedic treatment of exotic animals in the coming years.

Elbow joint luxation in a 1-month-old foal.

This paper reports on luxation of the elbow joint without concomitant fracture in a 1-month-old foal. Conservative treatment, with closed reduction and full-limb bandaging, including caudal and lateral splints, seemed successful initially, however, failed to provide enough stability and luxation recurred, and open reduction and surgical placement of prosthetic collateral ligaments was required. Luxation of the elbow joint should be considered when acute non-weight bearing forelimb lameness occurs associated with pain and swelling in the area of the elbow in young foals. Closed reduction failed to provide sufficient joint stability.

Effect of stack pins on the stiffness of interlocking nails in an unstable osteotomy model.

Interlocking nails have been shown to be an effective means to stabilise long bone fractures. When used in non-load sharing fracture repairs with minimal medullary canal filling, the authors noted instability of the main fracture fragments. The addition of multiple intramedullary pins in stack pin fashion eliminated the instability. ILN and ILN/SP constructs were loaded in four-point bending using an unstable osteotomy model. The gap between the ILN and ILN/SP groups was compared. Significant changes were seen with the ILN/SP constructs in the cranial to caudal plane.

Surgical Repair of Radial-Ulnar Fracture by Static Intramedullary Interlocking Nailing in a Crossbred Heifer.

OBJECTIVE: Study included surgical management of radius and ulna fracture in a 2-year-old, 220 kg crossbred heifer presented with a 2-day-old history of injury resulting in severe, non-weight bearing lameness of the left forelimb. METHODS: The condition was diagnosed clinically and confirmed radiographically as a middle third oblique comminuted fracture of the left radius and ulna. Static intramedullary interlocking nailing was performed for fracture fixation. An interlocking nail of 12-mm diameter and 26-cm length was introduced in a retrograde manner from the distal aspect of the radius. RESULTS: The animal was able to bear weight on the affected limb within 7 days post surgery. Good callus formation and complete weight bearing were observed by 35th day. Bending of the screws and osteophytic reaction were the major postoperative complications observed radiographically. CLINICAL SIGNIFICANCE: From this case study, it was established that static intramedullary interlocking nailing can be used as an alternative technique for fracture repair of the radius and ulna in cattle where stable fracture fixation by bone plating is questionable.