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.

Validation of a finite element model of the Kirschner-Ehmer external skeletal fixation system.

OBJECTIVE: To determine the validity of finite element analysis (FEA) as a means of examining biomechanical properties of the Kirschner-Ehmer external skeletal fixation system. SAMPLE POPULATION: 10 paired tibiae harvested from skeletally mature dogs weighing between 30 and 38 kg immediately following euthanasia for reasons unrelated to musculoskeletal disease. PROCEDURE: A gap fracture was created in each bone; fragments were stabilized with 3 frame configurations (type I, type II, and type III), using enhanced-profile threaded pins. Each bone-frame construct was tested, using a materials testing machine in 3 modes of testing: axial compression (AC), mediolateral (ML) bending, and craniocaudal (CC) bending, for a total of 9 tests/bone. The elastic limit of the constructs was not exceeded during testing. Mean stiffness values were determined from load-displacement curves. A finite element model of each construct was created, using three-dimensional elastic beam elements, and stiffness values were calculated, using FEA. Correlations between experimental and FEA data then were determined. RESULTS: Significant differences in stiffness were seen among all 3 constructs in CC bending and AC, with stiffness increasing with construct complexity. No significant difference in ML bending stiffness was seen between type-II and type-III constructs; however, both were significantly stiffer than the type-I constructs. The experimental and FEA stiffness data were strongly correlated (AC, r = 0.994; ML bending, r = 0.998; CC bending, r = 0.985). CONCLUSIONS AND CLINICAL RELEVANCE: Strong correlations among experimental and FEA data indicate that FEA is a valid method of comparing stiffness of Kirschner-Ehmer external skeletal fixation constructs.

Histomorphometric and angiographic analysis of the humerus in pigeons.

OBJECTIVE: To identify the vascular supply and resorption/formation activity of the humerus of pigeons. DESIGN: Pigeons were injected with the fluorochrome label oxytetracycline and, 5 days later, with the label calcein. 5 days after administration of the second fluorochrome, a wing from each bird was infused with a microparticle barium solution immediately after euthanasia and the chosen humerus was prepared for angiography while the opposite was prepared for histomorphometry. ANIMALS: 17 nine-month-old pigeons, consisting of 9 male and 8 female birds. PROCEDURE: At euthanasia, 1 wing was chosen for infusion and the barium solution was injected through a catheter in the brachiocephalic artery. Both humeruses were harvested. The infused humerus was decalcified, radiographed, and sectioned for H&E staining. The opposite humerus was sectioned and measured by use of a morphometric analyzing system to determine cross-sectional area, endosteal and periosteal perimeters, and percentage of perimeter containing a single and/or double label. RESULTS: All pigeons had an intramedullary arterial supply. The bones had a quiescent appearance histologically, consisting principally of lamellar bone with few osteospecialized cells, resorption surfaces, or osteons. Less than 10% of either the periosteal or endosteal surface acquired a fluorochrome label. CONCLUSIONS: The intramedullary vascular supply of the humerus is similar in structure to the vascular supply to mammalian bones. The humerus is, however, a quiescent bone in the sexually mature pigeon, with little remodeling activity present. CLINICAL RELEVANCE: The intramedullary blood supply may have an important role in the healing of humeral fractures in avian species.

Histomorphometric and angiographic analysis of bone healing in the humerus of pigeons.

OBJECTIVE: To evaluate the vascular supply and quantitatively compare the periosteal and endosteal callus formed during fracture healing. DESIGN: 36 pigeons were allotted to 2 groups. In each bird, 1 humerus was surgically osteotomized. The wing with the fractured humerus in birds of the first group was infused with a microparticle barium solution, and the humerus was harvested for angiography. Pigeons of the second group were injected with the labels oxytetracycline and calcein. The fractured humerus in each of these birds was harvested for histomorphometry. ANIMALS: 36 nine-month-old pigeons, consisting of 19 male and 17 female birds. PROCEDURE: 1 humerus from each of the 36 pigeons was osteotomized in the center of the bone by use of an obstetrical wire. All fractured wings were placed in a figure-of-8 bandage after surgery. The specimens harvested for angiography were decalcified, radiographed, and sectioned for H&E-stained tissue slides. Humeruses harvested for histomorphometry were cross-sectioned for tissue slides, which were measured, using a morphometric analyzing system for original and new bone areas. RESULTS: A continuous intramedullary circulation was not present at any point in the healing process, although 2 of the 42-day-old fractures had a bridging callus. Quantitatively, the periosteal surface formed the largest amount of callus, though the endosteal surface was also active. CONCLUSIONS: Reformation of the intramedullary circulation may not be imperative for osseous union of the pigeon humerus. Fluorochrome labels cannot be accurately measured at the fracture site. However, subjective evaluation of the endosteal surface indicates it is active during the fracture-healing process even though the periosteal surface provides the largest amount of callus formation. CLINICAL RELEVANCE: Figure-of-8 coaptation is contra-indicated for humeral fractures. The endosteal surface's contribution to the healing process should be considered when avian humeral fractures are stabilized.

Observation of a secondary compressive lesion after treatment of caudal cervical spondylomyelopathy in a dog.

In a 7-year-old Doberman Pinscher with an atactic gait, neurologic examination revealed tetraparesis, conscious proprioceptive deficits, and rigid ventral flexion of the neck. Radiography and myelography revealed a ventral, extradural, dynamic compressive lesion between C6 and C7. Distraction decompression was performed, using cancellous bone screws and methylmethacrylate. After initial improvement, clinical signs recurred 2 weeks after surgery and progressed until the dog was euthanatized 6 weeks after surgery. Postmortem myelography revealed an extradural compressive lesion adjacent to the implant, between C5 and C6. Secondary compressive lesions induced by surgical or biomechanical alterations of the cervical portion of the spine may be complications of treatment of caudal cervical spondylomyelopathy.

The effect of trans-stifle external skeletal fixation and hyaluronic acid therapy on articular cartilage in the dog.

Transarticular external skeletal (TES) fixators were applied unilaterally to the stifle joints of 10 young adult dogs. After 4 weeks, the fixators were removed from all dogs. Two dogs were not allowed a remobilization period, whereas 8 dogs were provided with 4 additional weeks of weight-bearing activity in a kennel run. Four dogs were given high-molecular weight hyaluronic acid by intra-articular injection weekly during the remobilization period. Clinical gait evaluations and range of motion were determined during the remobilization period. Articular cartilage samples from both stifle joints of all dogs were evaluated histologically and histochemically. No significant differences in gait scores or range of motion were noted between treated and untreated dogs. Articular cartilage proteoglycan content was reduced after 4 weeks of trans-stifle external skeletal fixation as determined by loss of alcian blue (AB) histochemical staining. Improved homogeneity of histochemical staining was observed after remobilization. However, remobilization was associated with histological damage to the surface and tangential layers of articular cartilage. Remobilization combined with hyaluronic acid (HA) therapy improved histochemical staining and reduced structural damage to articular cartilage when compared with remobilization alone.

Rapid tissue expansion for the development of rotational skin flaps in the distal portion of the hindlimb of dogs: an experimental study.

In phase I, tissue expanders were implanted subcutaneously over the lateral crural region of four dogs. The expanders were inflated daily to maintain a constant intraluminal pressure for 7 days. All animals tolerated the pressurized expanders well. Some animal patient discomfort was associated with repeated injections into the subcutaneous filling port. One dog developed a limited area of tissue loss and exposure of the expander. Tissue response to the expanders included epidermal hyperplasia, dermal collagen compression with early fibroplasia, and subcutaneous granulation tissue formation adjacent to the expander pocket. In phase II, a second group of four dogs underwent rapid skin expansion over 7 days. The pressure applied to the expanding skin was determined daily and adjusted to approximate the value reported for capillary pressure in the dog. Tissue discoloration occurred in two dogs, suggestive of impaired circulation. Skin flaps were developed from expanded skin and rotated over the talocrural region. Wound dehiscence occurred along the distal flap margin in three phase II dogs. These wounds healed by second intention. Branches of the caudal saphenous artery were identified, using angiography, as the primary blood supply to the skin flaps.

Replacement of the medial collateral ligament with polypropylene mesh or a polyester suture in dogs.

The medial collateral ligament of one stifle in 20 adult dogs was excised and replaced with polypropylene mesh or a polyester suture. After 26 weeks, the fibrous tissue-prosthesis composites were evaluated clinically, morphologically, and biomechanically. Clinical lameness was not significantly different after 10 days. The polypropylene mesh reconstructions consistently had more fibrous tissue and greater collagenous ingrowth than the polyester suture reconstructions. There were four complications related to fixation of the polypropylene mesh prosthesis and one to the polyester suture. The polypropylene mesh reconstructions had greater stability and were biomechanically more similar to the natural ligaments than the polyester suture reconstructions. Although the results with polypropylene mesh were favorable, more challenging biomechanical testing and alternative anchoring techniques are required before polypropylene mesh can be recommended as a collateral ligament replacement in dogs.

Delayed and nonunion fractures.

Failures in bone healing can result from technical problems, biologic failures, or a combination of the two. Inadequate stabilization of bone fragments against the effects of rotational forces is a common cause of nonunion. Early identification of a pseudoarthrosis can be difficult; the diagnosis is usually delayed, thus the morbidity associated with this disorder is significant. Often, the nonunion is complicated by atrophy of surrounding soft tissues, muscle contracture, and stiff joints. The goals in the treatment of the nonunion are to identify and correct the underlying causes, with the primary objective being the return of function. The type of treatment depends on the classification of the pseudarthrosis, including the condition of the surrounding soft tissues, blood supply, and viability of the nonunion, location, and presence or absence of infection.

Application and postoperative management of external skeletal fixators.

Application of external skeletal fixation involves preoperative assessment of the fracture with regards to healing potential of the bone and stabilizing requirements of the fixator. The fixator can be used alone or with supplemental (IM pin, cerclage, hemicerclage, Kirschner wires, bone screws) fixation to counteract shear, bending, and torsional forces at the fracture site. In addition, cancellous bone grafting can be used to enhance fracture healing. Rigid frames should be based on predrilling pilot holes followed by slow speed or hand insertion of smooth and threaded pins. Precise knowledge of regional anatomy precludes iatrogenic neurovascular or muscular tissue damage, which, subsequently, improves patient morbidity. Postoperative care of the fixator consists of bulky wraps to control pin-skin motion and cleaning of pin tract drainage sites. "Dynamization" or bone loading can be performed during fracture healing to stimulate osteosynthesis. This involves staged disassembly and reduction of frames by removing pins and connecting rods.

Talocalcaneal luxation: An anatomic and clinical study.

Talocalcaneal luxation in dogs was studied by anatomic dissection of the talocalcaneal joint in cadavers and review of five clinical cases. The integrity of the talocalcaneal joint was maintained by two strong ligaments traversing the tarsal sinus between the two bones. The joint was found to be a low motion joint. Luxation in clinical cases was not always apparent on standard radiographic views. Three dogs were treated surgically with a screw inserted in lag fashion from talus to calcaneus. One luxation was treated surgically with figure-of-eight orthopedic wires and one was treated with external coaptation. Four dogs returned to their previous levels of function without clinically detectable lameness.

Ellis pin complications in seven dogs.

Complications developed with the clinical use of Ellis pins in external skeletal fixation in seven dogs weighing 11 to 24 kg. Pins broke at the threaded-nonthreaded shaft junction in six dogs, and there was radiographic evidence of pin loosening six dogs. One pin pulled out causing loss of fixation in one dog. These complications with the recently introduced Ellis pin emphasize a need for further evaluation of its proper use.

A combined tension band and lag screw technique for fixation of olecranon osteotomies.

A combined tension band and lag screw technique for fixation of olecranon osteotomies was used in six canine clinical patients weighing 4.5 to 19 kg. After the proximal part of the ulnar shaft was exposed, a screw hole was drilled and tapped just cranial to the caudal cortex of the olecranon. An osteotomy was performed and the hole in the olecranon fragment was overdrilled to form a gliding hole. For reconstruction, the olecranon was reduced anatomically and compressed with a screw placed in lag fashion. With the trochlear notch exposed, a Kirschner wire was inserted cranial to the screw, using care not to enter the elbow joint. A double-twist figure-eight tension band wire was placed around the Kirschner wire in five dogs and around the screw in one dog. In this dog, a spiked washer was used with the screw because a small olecranon fragment had been produced by incorrect osteotomy position. A painful soft tissue swelling over the prominent washer, which resolved after implant removal, was the only complication attributed to the technique. The combined tension band wire and lag screw technique was a rapid and reliable method for fixation of olecranon osteotomies.

Relationship of femoral intramedullary pins to the sciatic nerve and gluteal muscles after retrograde and normograde insertion.

An anatomic analysis of retrograde and normograde intramedullary (IM) pinning of proximal, midshaft, and distal femoral fractures was performed in 28 canine cadavers. For all fracture locations, normograde pins were significantly more cranial in the middle gluteal muscle than retrograde pins (p less than 0.01). There was no significant difference between pinning techniques in craniocaudal position of the IM pin in the superficial gluteal muscle. In distal fractures, normograde pins were placed significantly more lateral than retrograde pins in the superficial gluteal muscle (p less than 0.01). One of 15 normograde pins and 9 of 13 retrograde pins were located in the medial half of the trochanteric fossa. Normograde pins were significantly more lateral in the trochanteric fossa than were retrograde pins in midshaft fractures (p less than 0.01). Normograde pins were significantly (p less than 0.01) farther from the sciatic nerve than retrograde pins when the hip was positioned at coxofemoral flexion angles of 85 degrees in midshaft and 110 degrees in distal fractures. Seven of 13 retrograde pins, but none of 15 normograde pins, contacted the sciatic nerve. Normograde pinning of the femur may be less likely to induce sciatic nerve injury, particularly in midshaft and distal fractures.

Osteofascial compartment syndrome in the dog.

Experimentally induced osteofascial compartment syndrome (OFCS) has been reported in the craniolateral compartment of the canine crus. In this study, anatomic dissections and contrast radiographs were used to describe three additional osteofascial compartments in canine limbs. Experimental OFCS was produced in four different compartments, and caused muscle and nerve pathology in each. When compartment pressures were evaluated in traumatized animals, moderate elevations in compartment pressures were found. A compartment syndrome that developed in one dog was surgically decompressed, returning elevated pressures to a safe level.

Upper airway obstruction. General principles and selected conditions in the dog and cat.

This article presents an overview of the clinical features of upper airway obstructive disorders. It includes more detailed discussions of certain common conditions such as brachycephalic airway syndrome, laryngeal paralysis, and upper airway obstruction due to trauma, foreign bodies, extraluminal masses, and tumours of the larynx and trachea.

Free chondral fragment involving the lateral trochlear ridge of the talus in a dog.

A saucer-shaped defect involving the lateral trochlear ridge of the talus and a radiopaque joint fragment were evident on radiographs of the left tarsus in a 6-month-old Rottweiler. Surgical treatment involved removal of the joint fragment and debridement of the defect. Histologic interpretation of the specimen was a chondral fragment. It is important to realize the possibility of a lesion in the location described, as this may be an additional site for osteochondrosis dissecans of the canine tarsus.