Nonlinear stiffness profiles of external fixators constructed with composite rods

OBJECTIVE: To determine if composite connecting rods confer nonlinear stiffness characteristics on unilateral and bilateral external skeletal fixators (ESF) in cranial-caudal bending and axial loading. STUDY DESIGN: Mechanical testing performed on models. SAMPLE POPULATION: Six models of 6-pin ESF constructs composed of birch dowels, a commercial ESF system, and composite connecting rods. METHODS: Unilateral and bilateral ESF configurations were assembled using either specially designed composite titanium and silicone (composite group) or solid titanium (solid group) connecting rods. Mechanical testing was performed in axial loading and 4-point cranial-caudal bending. Stiffness was determined at a low and high-load range, and was considered increasing and nonlinear if the stiffness at high loads was greater than at low loads. RESULTS: The stiffness of the solid group was linear in all testing modes and configurations. Bilateral composite fixators had a nonlinear increasing stiffness in axial loading and cranial-caudal bending. Unilateral composite fixators had a nonlinear increasing stiffness in axial loading, but not cranial-caudal bending. Solid connecting rods conferred a higher stiffness in all testing modes and configurations. CONCLUSIONS: Composite connecting rods resulted in nonlinear increasing axial and bending stiffness in bilateral fixators, and in axial load in unilateral fixators. CLINICAL RELEVANCE: Conventional ESF can be constructed so that the stiffness increases as load increases. This provides the surgeon with additional options to control the local mechanical environment of a healing fracture, which may be used to enhance fracture healing.     

Transarticular application of external skeletal fixation.

External skeletal fixators provide a useful alternative to external coaptation techniques for immobilization of joints in selected patients. This is especially true when the orthopedic injury involves an open wound requiring daily treatment. Devices such as the K-E splint, the Rudy external fixator boot, and acrylic frame fixators are economical and effective for transarticular fixation in small animal patients. Clinical indications for these techniques have included fixation of tibial or radial fractures with a short distal fragment; arthrodesis of the elbow, carpus, stifle, or tarsus; protection of Achilles tendon repairs; protection of collateral ligament repairs of the tarsocrural joint; and protection when multiple ligaments of the stifle joint have been reconstructed. Use of contoured rods has facilitated transarticular application of type II Kirschner-Ehmer splints. Use of acrylic frames and the Rudy boot technique have extended safe use of transarticular external fixation to extremely small patients not accommodated by the Kirschner system alone. An understanding of the advantages and disadvantages inherent in each of these techniques is critical to proper selection of the best method for a given patient. Attention to the basic principles of pin selection, pin insertion, and frame design are needed for successful execution of the chosen technique.     

Are Circular External Fixators Weakened by the use of Hemispheric Washers?

OBJECTIVES: To compare the axial mechanical stability of 3 circular external fixators systems with and without hemispheric washers. STUDY DESIGN: Experimental study. METHODS: The axial stiffness and load necessary to produce 0.5 and 1 mm of displacement of 10 circular external fixator constructs from 3 manufacturers were tested on a materials testing machine. The constructs tested included the Small Bone fixator (SBF; Hofmann S.a.S., Monza, Italy), the IMEX ring fixator (IMEX Inc., Longview, TX), and the Multiplanar C-Fix (MCF; PanVet Distribuzione, Seriate, Italy). Five configurations were tested for each construct: (1) conventional nut fixation, (2) hemispheric washer fixation with connecting rods offset by 0, (3) 1, and (4) 2 holes, and (5) with a ring placed at maximum angulation. RESULTS: The loads resisted at 0.5 and 1 mm of displacement did not differ when frame configurations were compared (P =.25733 and.33769, respectively). The linear stiffness of the following configurations were decreasingly stiff: standard constructs, hemispheric washers with connecting rods perpendicular to rings, hemispheric washers with connecting rods offset by 1 hole, hemispheric washers with connecting rods offset by 2 holes, and ring offset in relation to bone model. The SBF constructs tested were 34% and 41% more rigid than the IMEX and MCF constructs tested despite the larger diameter of the connecting rods for the IMEX frames (6 mm) compared with the SBF frames (5 mm). The IMEX constructs tested were 6% more rigid than the MCF constructs tested. CONCLUSIONS: Adding hemispheric washers and angling connecting rods in relation to rings did not influence the loads resisted at 0.5 and 1 mm displacement but decreased construct stiffness. CLINICAL RELEVANCE: The use of hemispheric washers had minor effects on the biomechanical performance of fixator frames tested in this study when used to angle a ring in relation to connecting rods for circular external fixators.     

Evaluation of two dynamic axial fixators for large ruminants

OBJECTIVES: To evaluate healing of a radial osteotomy repaired by application of dynamic axial fixation devices (DAF) in large ruminants. STUDY DESIGN: In vivo study of bone healing after application of 2 DAF types. Model I had 2 sidebars, each with a central cylindrical cuff (internally threaded) with 2 detachable connecting rods telescoping within the cuff. Model II had 2 side bars with 2 moveable clamps with multiple holes. SAMPLE POPULATION: Bull calves (n=8; aged, 1.5-2.0 years; weighing, 175-250 kg). METHODS: A mid-diaphyseal radial osteotomy was repaired by use of a model I (n=4) or model II (n=4) DAF. Calves were monitored for weight bearing, stability of fixation, and radiographically for fracture reduction, alignment and healing at intervals for 6 months. Fixators were removed when there was radiographic evidence of healing. RESULTS: Both the fixators were well tolerated with free movement of adjacent joints. Fragment fixation was maintained until healing in all but 1 model I calf where failure occurred within 7 days. Model II DAF provided more rigid fixation as indicated by early full weight bearing and fracture healing with less callus formation. Functional recovery of repaired limbs occurred within 60 days in surviving calves. CONCLUSIONS: Both bilateral DAFs were easy to apply; however, the model II DAF provided better fixation. CLINICAL RELEVANCE: The model II DAF made of low carbon steel was economical and may be useful for treating long bone fractures in large ruminants.     

Mechanical Evaluation of Half-Pin (Type 1) External Skeletal Fixation in Combination with a Single Intramedullary Pin

Half-pin (type 1) external skeletal fixators with four, three, and two fixation pins and an intramedullary pin, and four-pin external skeletal fixators without an intramedullary pin were applied to prepared canine femurs. Load to failure, load to yield, safe load, and stiffness under compressive and torsional loads were calculated. When tested in compression, all measurements for the four-pin fixators with an intramedullary pin were significantly higher than for the two-pin fixators with an intramedullary pin. The values for all parameters except load to yield were significantly higher for the four-pin fixators with an intramedullary pin than for the four-pin fixators without an intramedullary pin. When tested in torsion, all measurements for the four-pin fixators with an intramedullary pin were significantly higher than for the two or three-pin fixators with an intramedullary pin.     

Finite element method evaluation: articulations and diagonals in an 8-pin type 1B external skeletal fixator

OBJECTIVE: To determine the mechanical properties of articulations and diagonals in an 8-pin type 1b external skeletal fixator (ESF). STUDY DESIGN: Finite element method-computer simulation. METHODS: The control type 1b ESF was supplemented with different articulations and diagonals. The parameters of frame angle, articulation diameter, and pin- or connector-based fastening were altered. The configurations were loaded for axial compression, torsion, and craniocaudal and mediolateral bending as single loads and as a combination. Three-dimensional linear and rotational gap strain and Von Mises stress maxima were determined. RESULTS: For 90 degrees , 60 degrees , and 30 degrees frame angles and 0.48-cm-diameter articulations and diagonals, the best configurations, based on lower gap strain combined with decreased or minimally increased stress maxima for the combined load, were single or double diagonals or four horizontal articulations. Combining double diagonals with double wide horizontal articulations further lowered gap strain. For a 90 degrees frame angle and 0.32-cm-diameter articulations and diagonals, the superior configurations, showing the lowest gap strain combined with decreased or minimally increased stress maxima for the combined load, were double diagonals, four horizontal, or wide double horizontal articulations. The 0.48-cm articulations and diagonals provided lower or similar gap strain than 0.32-cm articulations and diagonals. The connector-to-connector version of these superior configurations provided slightly lower or similar gap strain and stress maxima than the pin-to-pin version. Only pin-to-pin-fastened double diagonals provided better stress maxima than the corresponding connector-to-connector version. CONCLUSIONS: Supplementing a type 1b ESF with double diagonals and wide double articulations results in the greatest increase in stability at the fracture gap for complex fractures or in the initial phase of bone healing.     

Fractures of the mandible and maxilla.

External fixation is an effective method for stabilization of many mandibular fractures. Thorough physical examination and patient stabilization should be instituted before attending to the fractures and associated soft tissue trauma. Normal occlusion rather than perfect reduction is the goal of oral fracture repair. Loose teeth or teeth in the fracture should be removed, as should any avascular bone fragments. Soft tissue wounds should be treated as for any contaminated wound. Mucosal wounds are allowed to heal by second intention. Although prophylactic perioperative antibiotics are indicated, they are usually not needed postoperatively. The three basic types of external fixators described include the Kirschner-Ehmer splint, pins or screws and acrylic, and the biphase splint. All three types are relatively easy to apply, and the principles of their application are similar. A minimum of two pins or screws are placed percutaneously in each fragment, avoiding the mandibular canal. The Kirschner-Ehmer splint is more easily adjustable than the biphase splint or the pin-acrylic splint, which use acrylic connecting bars. The advantages of fixators that use acrylic bars are that the pins or screws need not all be in the same plane and that they are more lightweight than the Kirschner-Ehmer splint. The disadvantages of the biphase splint are its increased expense and its use being limited to larger dogs. External fixators are well tolerated by the animals, and postoperative care is minimal. Mandibular fractures are usually healed in 3 to 5 weeks, and the fixators can be removed with the animal under sedation.     

Influence of an interdental full pin on stability of an acrylic external fixator for rostral mandibular fractures in dogs

OBJECTIVE: To determine total stiffness and gap stiffness of an external fixation system in a canine mandibular fracture gap model incorporating a full interdental pin as the only point of rostral fixation in a bilateral type-I external fixator. SAMPLE POPULATION: 10 canine mandibles. PROCEDURE: Bilateral mandibular ostectomies were performed between premolars 3 and 4. A type-I external fixator incorporating a full interdental pin was placed to stabilize a 0.5-cm fracture gap. Four pin configurations (intact mandibular bodies with fixator; ostectomized mandibular bodies and complete fixator; ostectomized mandibular bodies with caudal pins of rostral fragment cut; ostectomized mandibular bodies with all pins of rostral fragment cut) were tested in dorsoventral bending 5 times on each mandible. The full interdental pin remained intact in all configurations. Total stiffness and gap stiffness were determined for each configuration on a materials testing machine. RESULTS: Total stiffness of intact mandibles was significantly greater than that of ostectomized mandibles, regardless of external fixator configuration. However, total stiffness and gap stiffness were not significantly different among different external fixator configurations applied to ostectomized mandibles. CONCLUSION AND CLINICAL RELEVANCE: External fixator configurations with only the full interdental pin engaging the rostral fragment were as stiff as configurations that had 2 or 4 additional pins in the rostral fragment for the applied loads. External fixators for rostral mandibular fractures may be rigidly secured with rostral fragment implants applied extracortically, avoiding iatrogenic trauma to teeth and tooth roots.     

Incidence of and predisposing factors for nonunion of fractures involving the appendicular skeleton in cats: 18 cases (1998-2002)

OBJECTIVE: To identify the most common sites of and possible predisposing factors for nonunions in cats with fractures of the appendicular skeleton. DESIGN: Retrospective study. ANIMALS: 344 cats treated for fractures between 1998 and 2002, 18 of which developed nonunions. PROCEDURES: Information collected from the medical records included signalment; type of trauma; fracture location, orientation, and type; degrees of displacement and comminution; treatment; and outcome. RESULTS: The tibia and proximal portion of the ulna were identified as the most common sites for nonunions. Factors significantly associated with development of a nonunion included age, body weight, affected bone, fracture type, degree of comminution, and fixation type, with older cats, heavier cats, cats with fractures of the tibia or proximal portion of the ulna, cats with open fractures, cats with comminuted fractures, and cats with fractures stabilized with a type II external skeletal fixator being significantly more likely to develop a nonunion. Eleven of the 18 cats with nonunions had a successful outcome following treatment of the nonunion. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that in cats, fractures involving the tibia and proximal portion of the ulna are more likely to develop nonunions than are fractures involving other sites but that many factors may increase the risk of nonunion. Use of excessively large and rigid type II external skeletal fixators may be associated with development of nonunions; however, type II external skeletal fixators were commonly used to stabilize fractures in sites predisposed to nonunion.     

Stifle joint luxation in the cat: treatment using transarticular external skeletal fixation

Extra-articular suturing techniques and transarticular external skeletal fixators were used to repair traumatic luxation of the stifle joint in four cats. Rupture of the cranial cruciate, caudal cruciate and medial collateral ligaments, together with injury to one or both menisci, were the most common injuries observed. The method of stifle repair was successful in all cases, but serious complications occurred when cats with transarticular external fixators were not kept confined indoors. Complications consisted of pin loosening and disruption of the fixator, or fractures through proximal or distal pins. Transarticular external skeletal fixation was considered to be a simple and effective method of maintaining short-term joint stability to allow healing of injured soft tissue structures. The apparatus facilitated early weightbearing and, on removal, allowed for the return of near-normal stifle function. Careful pin insertion and owner compliance in enforcing confinement are essential in minimising complications associated with immobilising the stifle joint using transarticular external skeletal fixation.     

Classification of Involuntary Movements in Dogs: Myoclonus and Myotonia

Myoclonus is a sudden brief, involuntary muscle jerk. Of all the movement disorders, myoclonus is the most difficult to encapsulate into any simple framework. On the one hand, a classification system is required that is clinically useful to aid in guiding diagnosis and treatment. On the other hand, there is need for a system that organizes current knowledge regarding biological mechanisms to guide scientific research. These 2 needs are distinct, making it challenging to develop a robust classification system suitable for all purposes. We attempt to classify myoclonus as “epileptic” and “nonepileptic” based on its association with epileptic seizures. Myotonia in people may be divided into 2 clinically and molecularly defined forms: (1) nondystrophic myotonias and (2) myotonic dystrophies. The former are a group of skeletal muscle channelopathies characterized by delayed skeletal muscle relaxation. Many distinct clinical phenotypes are recognized in people, the majority relating to mutations in skeletal muscle voltage‐gated chloride (CLCN1) and sodium channel (SCN4A) genes. In dogs, myotonia is associated with mutations in CLCN1. The myotonic dystrophies are considered a multisystem clinical syndrome in people encompassing 2 clinically and molecularly defined forms designated myotonic dystrophy types 1 and 2. No mutation has been linked to veterinary muscular dystrophies. We detail veterinary examples of myotonia and attempt classification according to guidelines used in humans. This more precise categorization of myoclonus and myotonia aims to promote the search for molecular markers contributing to the phenotypic spectrum of disease. Our work aimed to assist recognition for these 2 enigmatic conditions.     

Principles of long bone fracture management.

The fixation of fractures in which one of the following primary devices is used: IM pins, bone plates, external skeletal fixators, can benefit from the additional application of any number of secondary devices. The secondary devices include cerclage, hemicerclage, or interfragmentary wires, skewer-pins, screws, and external skeletal fixators. These are indicated to facilitate the repair and eliminate the forces acting on the fracture site. A complete understanding of all the methods of fixation facilitates the selection of the proper implant or combination of implants. This information must be combined with the knowledge of how each device is most appropriately used depending on both the fracture type and fracture location. Taking into consideration all of these factors helps ensure that fracture healing occurs in the shortest possible time with the fewest complications. The ultimate goal of obtaining a full return to function may thereby be achieved.     

The use of a circular external skeletal fixation device for the management of long bone osteotomies in large ruminants: an experimental study

The study was undertaken to evaluate the feasibility of a simple, inexpensive model of circular external fixator (CEF) for use in large ruminants. A simple model of CEF frames consisting of four full rings (13-19 cm diameter, 4 cm wide and 4 mm thick with 18-24 holes) connected by threaded rods (8 mm diameter, 10-15 cm long) and nuts was developed using mild (low carbon) steel and were nickel-plated. In the first phase of the study, three male cow calves were utilized to study the feasibility of application of the fixators in the metatarsus, tibia and radius, in reference of adaptation and tolerance by animals. In the second phase, the fixators were tested in osteotomized bones. Six bull calves of 1.5-2 years of age weighing about 200-250 kg were utilized for this purpose. After preparing the area for aseptic surgery, under xylazine (at 0.1 mg/kg, i.m.)-ketamine (i.v. till effect) general anaesthesia, the test bone (metatarsus, radius and tibia in two animals each) was approached through the medial surface and an osteotomy was created with a saw and chisel at the mid-diaphysis. The pre-constructed 4-ring CEF was mounted on the limb around the test bone in such a way that it formed a cylinder with the axis of the limb at the centre. Each ring was then fixed to the bone with a pair of beaded wires (316 SS) of 3.5 mm diameter. During the post-operative period, the animals were observed for any change in behaviour, tolerance of the fixators, the weight bearing on the test limb, the status of the fixator, and the level of reduction of the osteotomy, alignment and healing at different intervals. The fixation of CEF was easier in the metatarsus and radius than in the tibia. The inner ring diameters found adequate for metatarsus, radius and tibia were 13-15 cm, 15-17 cm and 17-19 cm, respectively. The fixators applied to different bones were well-tolerated, and the animals could lay down, stand and walk freely with the fixator without any problems. All the animals showed good weight bearing in the immediate post-operative period. Weight bearing, however, slightly reduced in the inflammatory period and showed improvement after about 4 weeks. Wire tract infection was seen in all the animals, which was more on proximal wire tracts on lateral aspect of limbs. Circular fixators were well-tolerated by all the animals, and there was no breaking/bending of connecting rods, slotted bolts or the rings at any stage of observation. Slight bowing of some wires was noticed in cases of tibia and radius (in phase II) and bending of some wires was noticed from first week in two animals one each in radius and tibia. Bone fragments were well maintained until healing occurred (appearance of bridging periosteal callus) at 60-70 days. The functional results were good in all but one case of tibia, where a mal-union was recorded. From this study, it can be concluded that CEF are well-tolerated by large ruminants and can be used to treat long bone fractures. The fixator assembly using mild steel is sufficiently strong to maintain fracture fixation and is inexpensive. The simple design of the CEF appears to be sufficient to treat simple diaphyseal fractures of the metatarsus and radius. Improvement in the technique of fixation and design-like coupling of linear and circular fixator components into hybrid constructs may help to provide greater rigidity in treating tibial and open long bone fractures.     

分类、聚类与草原类型

本文阐明分类与聚类在草原分类中同等重要。据此建立的草原综合顺序分类系统(IOCSG)应遵循6项原则,即草原分类要素的完整性原则、草原分类体系内涵的综合性原则、草原分类指标的相对稳定性原则、草原分类同级指标的可比性原则、草原分类特征指标的确限性原则和草原分类体系普适的周延性原则。该分类系统含有类(以地带性水热特征为指标)、亚类(以土地特征为指标)和型(以植被特征为指标)3个基本级别;7个热量级和6个湿润度级。依据本分类系统全球天然草原分为42类,中国有41类。本分类系统在生物种适宜度计算、全球变化对草原类型演替方向的预测、草坪引种等方面进行了论证。该文阐明了草原类型学对草业科学的基础理论意义和实践意义。     

Evolution of the treatment of canine radial and tibial fractures with external fixators

OBJECTIVES: To determine if indications for external fixator treatment of radial and tibial fractures, management of the fractures, or outcomes have changed over three decades. METHODS: Three groups of dogs were identified from discrete time spans within three decades and the medical records and radiographs were evaluated. The groups were compared in order to determine whether indications (signalment, etiology, fracture type and configuration), reduction method, equipment and implants, frame types and pin numbers, numbers of radiographic reevaluations, use of destabilization, frequency of pin track osteolysis, frame removal times and percentage of complications remained the same over the decades. RESULTS: The indications for external fixator treatment of radial and tibial fractures remained consistent over three decades. The equipment and implants changed over the decades. Frame construction changed from the predominately Type II frames constructed in the 1980's and 1990's to a variety of modified Type II, Type Ia, Type Ib and hybrid frames constructed in the 2000's. The frequency of pin track osteolysis decreased significantly over the decades. Frame removal times have not changed significantly over the past three decades. Complications (nonunion, delayed union, osteomyelitis, implant failure and premature frame loss) have decreased over this time. CLINICAL SIGNIFICANCE: Improvements in techniques and equipment have led to decreased complications with external fixators.     

Static Strength Evaluation of Six External Skeletal Fixation Configurations

The relative strength of six different configurations of external skeletal fixation was determined by subjecting them to axial compression, and shear and torsion forces while measuring the load they would sustain before failing. The double clamp, single connecting bar, double connecting bar, quadrilateral frame, full pin splintage and three- dimensional tent configurations were found to be successively stronger in all three of the tests with the exception of the quadrilateral frame being more resistant to shear force than the full pin splintage configuration.