Use of veterinary interlocking nails for diaphyseal fractures in dogs and cats: 121 cases

Three-dimensionally printed osteotomy and reaming guides for correction of a multiplanar femoral deformity stabilized with an interlocking nail in a dog

OBJECTIVE

To describe the use of virtual surgical planning (VSP) and three-dimensionally (3D) printed surgical guides for corrective osteotomies stabilized with an interlocking nail in a dog with a multiplanar femoral deformity.

STUDY DESIGN

Case report.

ANIMALS

An 8-year-old male neutered mixed breed dog weighing 44 kg.

METHODS

A dog was presented for a right grade 3 lateral patellar luxation secondary to a multiplanar femoral deformity due to a suspected femoral malunion. A computed tomography (CT) scan was obtained to create virtual femoral models. Corrective osteotomies were simulated with VSP. Custom osteotomy guides and reaming guides were designed to facilitate the correction and the placement of an interlocking nail. The preoperative femoral model, virtually aligned femoral model, custom osteotomy guides, and reaming guides were 3D printed, sterilized, and utilized intraoperatively. A CT scan was performed postoperatively to assess femoral length and alignment.

RESULTS

Custom osteotomy and reaming guides were used as intended by the VSP. Postoperative femoral length as well as frontal, sagittal, and axial plane alignment were within 0.7 mm, 2.2°, 0.5°, and 1.6°, respectively, of the virtually planned femoral model. Two months postoperatively, the dog was sound on visual gait examination, and the patella tracked in the trochlear groove throughout stifle range of motion and was unable to be manually luxated. Radiographs obtained 2 months postoperatively revealed static femoral alignment and implants. Both osteotomies were discernable with callus bridging.

CONCLUSION

Virtual surgical planning and custom osteotomy and reaming guides facilitated complex femoral corrective osteotomies and interlocking nail placement.

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.

Analysis of feline humeral fracture morphology and a comparison of fracture repair stabilisation methods: 101 cases (2009-2020)

OBJECTIVES

The aims of this study were to describe the type, presentation and prognostic factors of feline humeral fractures over a 10-year period and to compare three stabilisation systems for feline humeral diaphyseal fractures.

METHODS

In total, 101 cats with humeral fractures presenting to seven UK referral centres between 2009 and 2020 were reviewed. Data collected included signalment, weight at the time of surgery, fracture aetiology, preoperative presentation, fixation method, surgical details, perioperative management and follow-up examinations. Of these cases, 57 cats with humeral diaphyseal fractures stabilised using three different fixation methods were compared, with outcome parameters including the time to radiographic healing, time to function and complication rate.

RESULTS

The majority of the fractures were diaphyseal (71%), with only 10% condylar. Of the known causes of fracture, road traffic accidents (RTAs) were the most common. Neutered males were over-represented in having a fracture caused by an RTA (P = 0.001) and diaphyseal fractures were significantly more likely to result from an RTA (P = 0.01). Body weight had a positive correlation (r = 0.398) with time to radiographic healing and time to acceptable function (r = 0.315), and was significant (P = 0.014 and P = 0.037, respectively). Of the 57 humeral diaphyseal fractures; 16 (28%) were stabilised using a plate-rod construct, 31 (54%) using external skeletal fixation and 10 (18%) using bone plating and screws only. Open diaphyseal fractures were associated with more minor complications (P = 0.048). There was a significant difference between fixation groups in terms of overall complication rate between groups (P = 0.012). There was no significant difference between fixation groups in time to radiographic union (P = 0.145) or time to acceptable function (P = 0.306).

CONCLUSIONS AND RELEVANCE

All three fixation systems were successful in healing a wide variety of humeral diaphyseal fractures. There was a significantly higher overall complication rate with external skeletal fixators compared with bone plating; however, the clinical impact of these is likely low.

Feline Femoral Fracture Fixation: What are the options?

PRACTICAL RELEVANCE

The femur is the most commonly fractured bone in cats. Femoral fractures usually result from high-velocity trauma such as a road traffic accident or fall from a height and, as such, are associated with a wide variety of concurrent injuries. The initial focus of treatment should always be on assessment and stabilisation of the major body systems. Once any concurrent injuries have been addressed, all femoral fractures need surgical stabilisation, with the notable exception of greenstick fractures in very young cats, which can heal with cage rest alone. A number of different surgical options are available depending on the fracture type, location, equipment, surgeon experience and owner finances.

CLINICAL CHALLENGES

Femoral fractures can vary hugely in complexity and the small size of feline bones can limit the choice of implants. Furthermore, cats can present unique challenges in the postoperative period due to their active nature and the limited means to control their exercise level.

AUDIENCE

This review is aimed at general and feline-specific practitioners who have some experience of feline orthopaedics, as well as those simply wishing to expand their knowledge.

AIMS

The aim of this review is to help clinicians assess, plan and manage feline femoral fractures. It provides an overview of diagnostic imaging and a discussion of a range of suitable surgical options, including the principles of different types of fixation. It also highlights cat-specific issues, approaches and implants pertinent to the management of these cases.

EVIDENCE BASE

A number of original articles and textbook chapters covering many aspects of femoral fractures in cats and dogs have been published. Where possible, this review draws on information from key feline research and, where necessary, extrapolates from relevant canine literature. The authors also offer practical guidance based on their own clinical experience.

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.

Evaluation of a Feline Bone Surrogate and In Vitro Mechanical Comparison of Small Interlocking Nail Systems in Mediolateral Bending

OBJECTIVE

 The aim of this study was to (1) evaluate bending structural properties of a machined short fibre epoxy (SFE) feline bone surrogate (FBS), (2) compare the bending behaviour of small angle-stable interlocking nails (I-Loc; Targon) and locking compression plates (LCP) and (3) evaluate the effect of implant removal on FBS bending strength.

METHODS

 Part 1: Feline cadaveric femurs (n = 10) and FBS (n = 4) underwent cyclic four-point bending and load to failure. Part 2: Fracture gap FBS constructs (n = 4/group) were stabilized in a bridging fashion with either I-Loc 3 and 4, Targon 2.5 and 3.0, LCP 2.0 and 2.4, then cyclically bent. Part 3: Intact FBS with pilot holes, simulating explantation, (n = 4/group) underwent destructive bending tests. Bending compliance, angular deformation and failure moment (F_M) were statistically compared (p < 0.05).

RESULTS

 Native bone and FBS were similar for all outcome measures (p > 0.05). The smallest and largest bending compliance and angular deformation were seen in the I-Loc 4 and LCP 2.0 respectively (p < 0.05). While explanted Targon FBS had the lowest F_M (p < 0.05), I-Loc and LCP constructs F_M were not different (p > 0.05).

CONCLUSION

 The similar bending properties of short fibre epoxy made FBS and native feline femurs suggest that this model could be used for mechanical testing of implants designed for feline long bone osteosynthesis. The I-Loc constructs smaller angular deformation which also suggests that these implants represent a valid alternative to size-matched Targon and LCP for feline fracture osteosynthesis. The significantly lower F_M of explanted Targon may increase the risk of secondary fracture following implant removal.

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.

Mechanical comparison of two small interlocking nails in torsion using a feline bone surrogate

OBJECTIVE

To compare the torsional behavior of two small angle-stable interlocking nails (I-Loc and Targon) with that of locking compression plates (LCP). To evaluate the effect of implant removal on the torsional strength of feline bone surrogates.

STUDY DESIGN

Experimental.

SAMPLE POPULATION

Fracture gap constructs and intact explanted bone surrogates.

METHODS

Fracture gap constructs were stabilized with one of six implants (I-Loc 3 and 4, Targon 2.5 and 3.0, LCP 2.0 and 2.4) and then cyclically tested in torsion (n = 4/group). To simulate implant removal, intact surrogates with implant-specific pilot holes were then twisted to failure (n = 4/group). Torsional compliance (TC; °/Nm), angular deformation (AD; °), and failure torque (F_T ; Nm) were statistically compared (P < .05).

RESULTS

The I-Loc 4 had the smallest TC and AD of all constructs (P < .05). The largest TC (P < .05) was seen with the LCP 2.0. The Targon 2.5 had the largest AD (P < .05) secondary to locking interface slippage. Targon surrogates F_T were the lowest of all groups (P < .05). Conversely, there was no difference between the F_T of the I-Loc, LCP, and intact surrogates (P > .05).

CONCLUSION

We showed that I-Loc nails provided greater torsional stability than size-matched Targon nails and LCPs. Conversely, Targon 2.5 locking interface slippage may jeopardize that construct's stability. Furthermore, the significantly reduced bone surrogate torsional strength provided evidence that the large Targon bolt holes increased the risk of postexplantation iatrogenic fracture.

CLINICAL SIGNIFICANCE

Our results provide evidence to conclude that the small I-Loc nails may be valid alternatives to other osteosynthesis options for feline fracture repair.

Interlocking Nails and Minimally Invasive Osteosynthesis

Reviews of clinical outcomes led to the foundation of a new approach in fracture management known as biological osteosynthesis. As intramedullary rods featuring cannulations and locking devices at both extremities, interlocking nails are well suited for bridging osteosynthesis. Unique biological and mechanical benefits make them ideal for minimally invasive nail osteosynthesis and an attractive, effective alternative to plating, particularly in revisions of failed plate osteosynthesis. Thanks to a new angle-stable locking design, interlocking nailing indications have been expanded to osteosynthesis of epi-metaphyseal fractures, including those with articular involvement and angular deformities such as distal femoral varus and associated patellar luxations.

Tibial fracture repair with angle-stable interlocking nailing in 2 calves

OBJECTIVE

To report tibial fracture repairs with I-Loc angle-stable interlocking nails (AS-ILN) in 2 calves.

STUDY DESIGN

Clinical case reports.

ANIMALS

One 5-day-old Holstein calf and one 3-month-old beefalo calf.

METHODS

In a 50-kg Holstein calf, a proximal juxtametaphyseal comminuted tibial fracture with tibial tuberosity slab fracture was repaired with an 8-160-mm I-Loc nail and 2 cortical lag screws. In an 89-kg beefalo calf, a long oblique middiaphyseal tibial fracture was repaired with an 8-185-mm I-Loc nail and 5 double loop cerclage wires. In each case, an I-Loc AS-ILN was selected because unique biomechanical challenges precluded treatment with traditional osteosynthesis methods, such as external coaptation or plate fixation.

RESULTS

No complications were diagnosed, and clinical union was documented 4 weeks after surgery in both cases. Axial growth continued in both calves, with no evidence of angular limb deformity at 7- and 6-month follow-up.

CONCLUSION

This is the first report describing the use of the I-Loc nail in a bovine species. This application led to uncomplicated healing of tibial fractures and continued growth in both young calves described here.

CLINICAL SIGNIFICANCE

Interlocking nailing may provide an effective and safe alternative for osteosynthesis of tibial fractures in young calves. Insertion of the AS-ILN across the center of the proximal tibial physis of a rapidly growing calf does not seem to alter its growth potential.

Experiences using the Fixin locking plate system for the stabilization of appendicular fractures in dogs

Objectives: To retrospectively evaluate the stabilization of appendicular fractures in dogs using the Fixin locking plate system.

Materials and methods: Medical records and radiographs of dogs with fractures stabilized with the Fixin system in the period from May 2005 to September 2010 were reviewed. For each patient, data pertaining to signalment, the nature of the fracture, implants used, and evidence of fracture healing were recorded. The outcome and complications were determined from clinical and radiographic follow-up examinations. Limb function was evaluated between 40 days and 90 days postoperatively. Owners of pets with complications were contacted by phone for long-term follow-up.

Results: Eighty-two fractures in seventy-five dogs met the inclusion criteria for the study. Radiographic re-examinations were carried out between eight days to two years (median 60 days) following surgery. Seventy-three out of 82 fractures (89%) reached union without complications. Major complications were seen in six dogs (7%). Limb function was graded as ‘normal’ in 73/75 (97%) dogs and ‘mild lameness’ in 2/75 (3%) cases.

Clinical significance: Despite a modest complication rate, the Fixin locking bone plating system appears to be an acceptable choice of implant for the stabilization of appendicular fractures in dogs.

An in vitro biomechanical investigation of an interlocking nail system developed for buffalo tibia

Objectives: The objectives of the study were to determine the mechanical properties of a customized buffalo interlocking nail (BIN), intact buffalo tibia, and ostectomized tibia stabilized with BIN in different configurations, as well as to assess the convenience of interlocking nailing in buffalo tibia.

Methods: The BIN (316L stainless steel, 12 mm diameter, 250 mm long, nine-hole solid nails with 10° proximal bend) alone was loaded in compression and three-point bending (n = 4 each); intact tibiae and ostectomized tibiae (of buffaloes aged 5–8 years, weighing 300–350 kg) stabilized with BIN using 4.9 mm standard or modified locking bolts (4 or 8) in different configurations were subjected to axial compression, cranio-caudal three-point bending and torsion (n = 4 each) using a universal testing machine. Mechanical parameters were determined from load-displacement curves and compared using Kruskal-Wallis test (p <0.05).

Results: Intact tibiae were significantly stronger than BIN and bone-BIN constructs in all testing modes. The strength of fixation constructs with eight locking bolts was significantly more than with four bolts. Overall strength of fixation with modified locking bolts was better than standard bolts. Based on technical ease and biomechanical properties, cranio-caudal insertion of bolts into the bone was found better than medio-lateral insertion.

Clinical significance: The eight bolt BINbone constructs could be useful to treat tibial fractures in large ruminants, especially buffaloes.

Use of intramedullary fully-threaded pins in the fixation of feline and canine humeral, femoral and tibial fractures

Intramedullary fully-threaded pins were manufactured from an alloy of titanium, aluminium and vanadium in a fully-threaded style. Pins were produced in various diameters, ranging from 4 mm to 11 mm. Pin lengths varied from 5 cm to 22 cm. The proximal end of the pins was designed to fit into a hexagonal screwdriver, while the distal end was slightly tapered to allow for ease of entry into cancellous bone. Treatment using the fully-threaded intra- medullary pin was carried out in a total of 175 fractures of the humerus, femur, and tibia in 95 cats (bilateral femur in 1 case) and 77 dogs (bilateral femur in 2 cases). Radiographic follow-up for the cases was performed at monthly intervals. Non-union developed in one dog with a femoral fracture in which cerclage wire had also been used. Delayed healing and lameness were observed in two other dogs. Healing with excessive callus formation was observed in 16 dogs. However, there were not any problems noted in these dogs in regards to limb usage. Clinical and radiological results obtained for the remaining cases were found to be very good. Normal, complete fracture healing occurred between four to 14 weeks in dogs, and between four to 12 weeks in cats. Pins were removed upon observation of satisfactory functional and radiographic recovery. Pins could not be removed from 26 cats and 21 dogs as the owners had declined pin removal, or because the owners were lost to follow-up.

Avaliação do uso de haste bloqueada e bloqueio transcortical no reparo de fraturas diafisárias de fêmur em felinos

As hastes bloqueadas além de permitirem estabilização rígida de fraturas, possuem vantagens biomecânicas quando comparadas a outras técnicas de imobilização, por atuar ao longo do eixo mecânico central do osso, além de preservar os conceitos de padrões biológicos de osteossíntese . O uso limitado de hastes bloqueadas em gatos se atribui ao fato da cavidade intramedular ser pequena, limitando o tamanho e diâmetro dos pinos. Relatam-se casos de 10 felinos que apresentavam fraturas fechadas simples ou múltiplas da diáfise femoral. Os animais pesavam entre 3,5 e 5 kg, o que permitiu a utilização de hastes de 4,0mm e 4,7mm de diâmetro. Para inserção da haste, adotou-se a via retrógrada ou a normógrada e foram realizados bloqueios com quatro parafusos de titânio de 2,0 mm de diâmetro. Complicações intra-operatórias não ocorreram, entretanto um animal sofreu fratura de colo femoral e fratura transversa distal ao implante, três dias após o ato cirúrgico, devido a novo trauma. Os animais foram submetidos a exames radiográficos até quatro meses após a intervenção, evidenciando-se formação de calo ósseo secundário e consolidação óssea em período de 61-89 dias. Clinicamente, ocorreu esporadicamente alteração na marcha por leve claudicação de apoio definida por escala de claudicação, entretanto os animais iniciaram o apoio adequado entre três e oito dias após o ato operatório. Complicações pósoperatórias ocorreram referentes ao animal que sofreu novo trauma, entretanto notou-se consolidação do foco primário tratado pelo implante com 61 dias e consolidação da nova fratura num período total de 150 dias do início do tratamento conservativo por penso esparadrapado e tala. Conclui-se que o uso de haste bloqueada em felinos foi adequado uma vez que houve consolidação óssea em todos os casos, com retorno precoce da função do membro, permitindo a deambulação.

In Vitro Mechanical Comparison of Screwed, Bolted, and Novel Interlocking Nail Systems to Buttress Plate Fixation in Torsion and Mediolateral Bending

OBJECTIVE

To compare standard interlocking nails (ILN) with a newly designed ILN featuring an angle-stable locking mechanism (ILNn).

STUDY DESIGN

Six experimental groups.

SAMPLE POPULATION

Bone models (n=48) treated with 6 and 8 mm nails locked with screws or bolts (ILN6s, ILN8s, ILN6b, ILN8b, respectively), ILNn, and a 3.5 mm broad-DCP (br-DCP); n=4/testing mode.

METHODS

Specimens were tested in torsion or 4-point bending. Construct compliance, deformation, and slack were statistically compared (P<.05).

RESULTS

Regardless of testing mode, construct compliance was greater with smaller ILN. Screwed constructs were more compliant than bolted ones, with a significant difference between ILN6s and ILN6b in torsion. Plated constructs were significantly more compliant than the ILNn. Angular deformation was consistently greater with smaller ILN. Screwed ILN constructs sustained approximately 2 x the torsional deformation of the bolted ones (approximately 36 degrees [ILN6s] versus approximately 18 degrees [ILN6b]). Comparatively, ILNn constructs had significantly less torsional (approximately 8 degrees) and bending (approximately 4 degrees) deformation than other constructs. Whereas standard ILN constructs had slack in both modes, ILNn and br-DCP construct deformations consistently occurred without slack.

CONCLUSIONS

Use of bolts rather than screws improved ILN mechanical behavior, but neither locking mechanism completely counteracted torsion and bending forces. Conversely, the ILNn angle-stable locking system eliminated torsional and bending slack, resulting in comparable mechanical performances between ILNn and plated constructs.

CLINICAL RELEVANCE

The angle-stable locking mechanism of the new ILN eliminates all slack in the system; thus, interfragmentary motion will likely be reduced compared with standard ILN, which may improve the local environment for fracture healing.

Mechanical Comparison of an Interlocking Nail Locked with Conventional Bolts to Extended Bolts Connected with a Type-Ia External Skeletal Fixator in a Tibial Fracture Model

OBJECTIVE

To compare the structural properties of interlocking nails (ILNs) locked with bolts (ILNb) to ILN locked with extended bolts connected with a type-IA external skeletal fixator (ILN-ESF) in a fracture gap model.

STUDY DESIGN

Experimental study.

SAMPLE POPULATION

Synthetic tibial bone substitutes.

METHODS

Custom-made synthetic tibial bone substitutes were implanted with standard ILNs locked with either bolts or extended bolts connected to an external skeletal fixation (ESF). Constructs were tested in torsion, bending, and axial compression (n=4/testing mode). Data, consisting of construct compliance and associated deformation, were compared using t-tests.

RESULTS

The ILN-ESF construct compliance and deformation were significantly less than those of the ILNb construct in torsion, bending, and compression (P<.001). Slack was present in the ILNb construct under torsion and bending, but not in the ILN-ESF construct, regardless of testing mode.

CONCLUSIONS

Substitution of locking bolts with extended bolts connected to an ESF significantly reduced the construct compliance and overall deformation in torsion, bending, and compression. Furthermore, the inherent slack of the ILNb was eliminated by the use of an ESF in torsion and bending.

CLINICAL RELEVANCE

The improvement in structural properties of the ILN-ESF constructs could diminish interfragmentary motion at the fracture site and potentially improve bone healing.

Ex vivo comparison of one versus two distal screws in 8 mm model 11 interlocking nails used to stabilize canine distal femoral fractures

OBJECTIVE

To compare the structural properties of an 8 mm model 11 interlocking nail (IN) with 2 proximal and 2 distal screws (2/2) to 2 proximal and 1 distal screws (2/1) in an unstable canine fracture model.

STUDY DESIGN

Ex vivo biomechanical investigation.

SAMPLE POPULATION

Eight pairs of adult canine femurs.

METHODS

A simple transverse distal metaphyseal femoral fracture with a 1 cm gap was created. The unstable fracture in 1 femur was repaired with a nail with 2 distal and 2 proximal screws and the paired femur with a nail with 1 distal and 2 proximal screws. Cyclic mechanical testing in torsion was performed to assess fatigue life, peak torque, stiffness, and mode of failure.

RESULTS

All 2/1 IN-femoral constructs, but only 2 of eight 2/2 constructs, failed before completion of 50,000 loading cycles. The 2/2 constructs had significantly greater peak torque to failure (P = .002) and longer fatigue life (P = .00003) compared with 2/1 constructs. There were no significant differences in stiffness between 2/2 and 2/1 constructs when the non-failed constructs were compared (P > .5). All constructs failed by screw deformation.

CONCLUSIONS

An 8 mm model 11 IN used for fixation of unstable canine distal femoral fractures has a longer fatigue life and is stronger under torsional loads when 2 rather than 1 distal screws are placed.

CLINICAL RELEVANCE

When repairing unstable canine distal femoral fractures with an IN system, 2 distal screws should be inserted to avoid catastrophic implant failure before bone healing is achieved.

In vitro mechanical evaluation of torsional loading in simulated canine tibiae for a novel hourglass-shaped interlocking nail with a self-tapping tapered locking design

OBJECTIVE

To describe a novel interlocking nail (ILN) and locking system and compare the torsional properties of constructs implanted with the novel ILN or a standard 8-mm ILN (ILN8) by use of a gap-fracture model.

SAMPLE POPULATION

8 synthetic specimens modeled from canine tibiae.

PROCEDURES

An hourglass-shaped ILN featuring a tapered locking mechanism was designed. A synthetic bone model was custom-made to represent canine tibiae with a 50-mm comminuted diaphyseal fracture. Specimens were repaired by use of a novel ILN or an ILN8 with screws. Specimens were loaded for torsional measurements. Construct compliance and angular deformation were compared.

RESULTS

Compliance of the ILN8 was significantly smaller than that of the novel ILN. Mean +/- SD maximum angular deformation of the ILN8 construct (23.12 +/- 0.65 degrees) was significantly greater, compared with that of the novel ILN construct (9.45 +/- 0.22 degrees). Mean construct slack for the ILN8 group was 15.15 +/- 0.63 degrees, whereas no slack was detected for the novel ILN construct. Mean angular deformation for the ILN8 construct once slack was overcome was significantly less, compared with that of the novel ILN construct.

CONCLUSIONS AND CLINICAL RELEVANCE

Analysis of results of this study suggests that engineering of the locking mechanism enabled the novel hourglass-shaped ILN system to eliminate torsional instability associated with the use of current ILNs. Considering the potential deleterious effect of torsional deformation on bone healing, the novel ILN may represent a biomechanically more effective fixation method, compared with current ILNs, for the treatment of comminuted diaphyseal fractures.

Internal fracture fixation

Over the past decade, many improvements to small animal internal fracture fixation have been developed, including improved fixation techniques and a more diverse selection of implants. The understanding that appropriate fixation selection is based on a plethora of biologic, mechanical, and clinical factors has also emerged. Classically, the methods of internal fracture fixation have used pins, wires, screws, and plates to rigidly stabilize fractures that have been anatomically reduced with significant disruption to the biologic fracture environment. Newer methods attempt to minimize trauma to the soft tissues surrounding a fracture and promote biologic osteosynthesis using such implants as interlocking nails and plate-rod fixations. This review provides an overview of both the traditional and current principles of small animal internal fracture fixation.

Two Techniques for Supplementing Interlocking Nail Repair of Fractures of the Humerus, Femur, and Tibia: Results in 12 Dogs and Cats

OBJECTIVE

To describe 2 devices for improving stabilization of inadequately stabilized interlocking nail (ILN) repairs of the humerus, tibia, and femur in dogs and cats.

STUDY DESIGN

Prospective study.

ANIMALS

Twelve client-owned dogs and cats.

METHODS

Two devices to further stabilize ILN repair of inadequately stabilized diaphyseal fractures were developed. Device 1 was an axial extension for the ILN that was connected to a conventional type I external skeletal fixator (ESF) with a short connecting bar. Device 2 had hybrid ILN bolt/ESF pins that were used to lock the ILN and serve as the pins for a type I ESF. Devices were used at the initial surgery when the stability of ILN repair was considered inadequate based on palpable fracture segment movement, insufficient medullary canal filling of the ILN at the fracture site, or when the ILN was used in a buttress mode. Outcome was obtained by recheck examinations, radiography, and telephone interview.

RESULTS

Device 1 was applicable to fractures of the humerus and femur, but was not used for fractures of the tibia because the ILN extension would have interfered with the stifle. No gross loosening of the ILN/ESF extension connection to the ILN occurred. Device 2 was easily placed and used in the humerus, femur, and tibia. Device 2 allowed removal of the ILN interlock to one or both main fracture segments non-invasively. Clinically, both devices added stability compared with ILN repair alone. Both devices facilitated controlled destabilization of the fracture repair as healing progressed. Complications of pin tract infection, and premature hybrid bolt/ESF pin loosening resulting in premature ESF removal each occurred in 1 patient. Four of 28 hybrid ILN/ESF pins were grossly loose at 4- or 6-week postoperative recheck examinations. Outcomes were excellent (9), good (1), fair (1), and poor (1).

CONCLUSIONS

Inadequately stabilized ILN repair of fractures can be stabilized by use of either device, both of which also permit controlled destabilization of the repair during healing. Device 2 can be used when non-invasive removal of the ILN interlock is desired during healing.

CLINICAL RELEVANCE

These 2 devices should be considered as alternative methods for stabilization of inadequately stabilized ILN repairs in dogs and cats, or when controlled destabilization of an ILN fracture repair is desired.

Tibial fractures

Tibial fractures are common in small animal practice. As with other appendicular fractures, the patient's age, fracture location, and fracture type must be considered thoroughly. While methods for tibial fracture repair are similar to those used for appendicular fractures elsewhere, there are some unique considerations, both anatomically and functionally, that must be contemplated before repair. The following article will review the incidence of tibial fractures, tibial fracture types, and options for tibial fracture management and treatment. The use of external fixators, orthopedic bone plates, open reduction with internal fixation (ORIF), and external coaptation will be discussed. An emphasis will be placed on the most common types of tibial fractures, as well as those best suited for repair by general practitioners of veterinary medicine. Three case based examples will follow the overview.

Effects of Static Fixation and Dynamization after Interlocking Femoral Nailing Locked with an External Fixator: An Experimental Study in Dogs

OBJECTIVE

To determine bone healing at 20 weeks, after either static fixation (SG) or after dynamization (DG) at 4 weeks in osteotomized canine femurs repaired with an interlocking nail (ILN) secured with a type I external skeletal fixator (ESF).

STUDY DESIGN

Experimental study.

ANIMALS

Ten adult beagle dogs.

METHODS

After mid-diaphyseal femoral osteotomy, femurs in 10 dogs were repaired with an ILN secured with 4 (2 proximal, 2 distal) threaded custom pins (TP; 2.7-mm-diameter cortical screw with a 2-mm shaft attached to the screw head) to which 2 parallel connecting bars were attached in a type I ESF configuration. In 5 dogs, dynamization was performed at 4 weeks by removing the connecting bars and 2 distal screws. Limb function, range of motion of the stifle joint (ROMSJ), radiographic evidence of bone healing, and complications were studied for 20 weeks.

RESULTS

Full limb function was achieved between 8 and 10 weeks in SG dogs, but a decreased ROMSJ was observed from 5 to 8 weeks. In DG dogs, full limb function occurred between 5 and 6 weeks except in 1 dog, and ROMSJ was considered normal in all dogs. Bone healing was not affected by dynamization. Average healing time for SG was 12.8 weeks, and for DG it was 13.6 weeks. Periosteal reaction at TP insertion points, osteolysis around the thread and head of TPs were observed in both groups. A windshield-wiper effect was observed at the tip of 1 ILN.

CONCLUSION

ILN locked with a type I ESF can be used for fixation of mid-shaft femoral fractures. Dynamization at 4 weeks did not affect bone healing but did prevent stifle ankylosis and promoted earlier limb function.

CLINICAL RELEVANCE

ILN locked with a type I ESF is seemingly a feasible method for repair of mid-shaft femoral fractures and may decrease risk of nail failure.

Tibiotarsal fracture repair in a bald eagle (Haliaeetus leucocephalus) using an interlocking nail

A 14-yr-old, 5.13-kg bald eagle (Haliaeetus leucocephalus) was hit by a car and presented to the Michigan State University Small Animal Clinic with an open, grade II, transverse, midshaft, Winquist-Hansen type-II-comminuted left tibiotarsal fracture. The fracture was reduced and fixation established with a 4.7-mm-diameter, 112-mm-long, four-hole veterinary intramedullary interlocking nail maintained in position by single 2-mm transcortical screws placed in the main proximal and distal fragments. The bird was weight bearing on the bandaged limb 48 hr postoperatively. Radiographs obtained 4 wk postoperatively revealed bridging callus over three of four cortices. The bird was released after 5 mo of rehabilitation.