In vivo axial dynamization of canine tibial fractures using the Securos external skeletal fixation system.

Bilateral transverse mid-shaft tibial osteotomies, with a 4-mm gap, were performed in purpose-bred research dogs and stabilized using a Securos Type 2 external skeletal fixotor (ESF). Full (100%) axial dynamization of one randomly selected ESF in each dog was performed at 31 days postoperatively. Caudo-cranial radiographs were obtained at weekly intervals, which were qualitatively and quantitatively evaluated (densitometry and ImageJ analysis). The dogs were euthanatized 13 weeks postoperatively, at which time dual energy x-ray absorptiometry (DEXA), peripheral quantitative computed tomography (pQCT), mechanical testing in torsion, and qualitative histological analysis were performed. A two-tailed paired Student's t-test was performed for statistical analysis of all parameters of interest, with significance set at p < 0.05. Three of five dynamized bones bridged quicker, and four of five dynamized bones appeared to have greater callus formation, however, statistically significant differences could not be definitively determined. Statistically significant differences were not found with densitometry (any time frame), DEXA, pQCT, torsional stiffness or maximum torque. Despite the lack of statistically relevant data, trends were observed with larger callus size and density in the dynamized tibiae. The dynamized tibiae appeared to fracture more consistently outside of the area of the healing callus as compared to the control tibiae. Histological evaluation showed greater remodelling in four of five control limbs when compared to the dynamized limb. Dynamization at 31 days post-operatively may delay bone remodelling, despite a trend towards a larger callus size. The results of this study failed to show a definitive role for early full axial dynamization.

Critically sized osteo-periosteal femoral defects: a dog model.

A 21-mm defect was created in 1 femoral diaphysis each of 15 dogs. Periosteum as well as a cylinder of bone was removed, and the defect was stabilized with a bone plate. Twelve of the defects were filled with an equal volume of autogenous cancellous bone harvested from the ipsilateral ilium. Three defects were left untreated. Cranial to caudal radiographs were taken postoperatively and every 4 weeks for 16 weeks. The radiographs were evaluated for healing using two ordinal scales. At 16 weeks, the dogs were euthanized and the femurs harvested for biomechanical testing and histologic evaluation. Both operated and contralateral not operated femurs were mechanically tested to failure in torsion, and load at failure and stiffness were calculated. All dogs tolerated the procedure well, and were using the operated limb within 1 or 2 days postoperatively. There were no complications noted during the 16 weeks of the study. Unfilled defects did not heal and became atrophic nonunions. The defects filled with autogenous cancellous bone healed in a consistent pattern of consolidation, incorporation, and remodeling, with uniform increases of both ordinal scales used. The femoral cortex opposite the bone plate demonstrated most mature remodeling, evident both radiographically as well as histologically. Unoperated femurs failed at 13.61 +/- 3.88 N-m and grafted femurs failed at 2.96 +/- 1.3 N-m, which was 23% of the measurement of the unoperated femur. Relative stiffness of the unoperated femurs was 5974 +/- 4316 N-m2/radian, and grafted femurs had a relative stiffness of 642 +/- 561 N-m2/radian, which was 10.4% of the measurement of unoperated femur. This model proved to be a critically sized defect, which when left unfilled resulted in an atrophic nonunion, and when filled with cancellous bone resulted in a consistent healing pattern.

The effect of implants loaded with autologous mesenchymal stem cells on the healing of canine segmental bone defects.

Bone marrow has been shown to contain a population of rare mesenchymal stem cells that are capable of forming bone, cartilage, and other connective tissues. We examined the effect of cultured autologous mesenchymal stem cells on the healing of critical-sized (twenty-one-millimeter-long) segmental defects in the femora of adult female dogs. Autologous mesenchymal stem cells were isolated from bone marrow, grown in culture, and loaded onto porous ceramic cylinders consisting of hydroxyapatite (65 per cent) and beta-tricalcium phosphate ceramic (35 per cent). The animals were randomly assigned to one of three groups. In Group A (six dogs), a porous ceramic cylinder that had been loaded with autologous mesenchymal stem cells was implanted in the defect. In Group B (six dogs), a ceramic cylinder that had not been loaded with cells was placed in the defect. In Group C (three dogs), the defect was left untreated (no ceramic cylinder was implanted). Radiographs were made immediately after the operation and at four-week intervals. At sixteen weeks, the animals were killed, the involved femora were removed, and undecalcified histological sections from the defects and adjacent bone were prepared. Histological and histomorphometric studies were carried out to examine the healing of the defects and the formation of bone in and around the ceramic implants. Atrophic non-union occurred in all of the femora that had untreated defects, and only a small amount of trabecular bone formed at the cut ends of the cortex of the host bone in this group. In contrast, radiographic union was established rapidly at the interface between the host bone and the implants that had been loaded with mesenchymal stem cells. Numerous fractures, which became more pronounced with time, developed in the implants that had not been loaded with cells. Histological and morphometric analyses demonstrated that both woven and lamellar bone had filled the pores of the implants that had been loaded with mesenchymal stem cells; the amount of bone was significantly greater (p < 0.05) than that found in the pores of the implants that had not been loaded with cells. In addition, a large collar of bone (mean maximum thickness, 3.14 millimeters) formed around the implants that had been loaded with cells; this collar became integrated and contiguous with callus that formed in the region of the periosteum of the host bone. The collar of bone remodeled during the sixteen-week period of study, resulting in a size and shape that were comparable with those of the segment of bone that had been resected. Callus did not develop around the cortex of the host bone or around the defect in any of the specimens in the other two groups.

Type-II external fixation, using new clamps and positive-profile threaded pins, for treatment of fractures of the radius and tibia in dogs.

A new external fixation system for repair of fractures of the radius and tibia was developed that uses positive-profile threaded pins. This system allows for addition of a fixation clamp between 2 installed clamps, predrilling of pin holes through a drill sleeve, use of positive-profile threaded pins in all locations, and easier application of full pins. Type-II external fixators were applied, using this system, to fractures in 10 client-owned dogs, and outcome was evaluated. All fractures healed without complications. Duration of surgery, mean time until radiographic evidence of a bridging callus, and mean time until removal of the external fixator were shorter, and frequency of pin loosening were less than with other techniques. Pin loosening was uncommon. This system provides an important improvement in external skeletal fixation.

Mechanical comparison of two external fixator clamp designs.

OBJECTIVE: To compare two external fixation clamp designs for their ability to resist movement of a fixation pin in relation to the connecting rod. STUDY DESIGN: Two designs of external fixator clamps were attached to connecting rods mounted on a jig for mechanical testing. Fixator pins were placed perpendicular to the connecting rod. A mechanical testing machine was used to deflect each 3.2-mm pin at a distance that was 25 mm from the center of the clamp bolt. Both clamp designs were tightened to 4.4, 6.1, and 7.8 newton-meters (N x m) torque, and loads were applied in a position ramp through 4 mm and resisting loads were measured. Two clamp orientations were used during load application, such that the deflection of the pin tended to tighten the clamp bolt or tended to loosen the clamp bolt. The tests were videotaped to determine mode of failure. Comparisons of the load/displacement curves for the two external fixator clamp designs were made using nonlinear equational curve fitting methods. The resultant plateau and rise coefficients were compared using analysis of variance. RESULTS: Slippage of the pin in relation to the clamp occurred with the Kirschner-Ehmer clamp tightened to 4.4, 6.1, and 7.8 N x m, and slipping of the pin in relation to the clamp occurred with the experimental clamp design tightened to 4.4 and 6.1 N x m but not to 7.8 N m. At 7.8 N x m, the 3.2-mm pin deformed plastically with the experimental clamp design. Increasing the torque of the clamp bolt resulted in superior plateau coefficients for both clamp designs. At each level of tightness and in each clamp orientation to applied pin load, the experimental clamp design provided greater plateau coefficients than did the Kirschner-Ehmer clamp design. At 7.8 N x m of tightness, the Kirschner-Ehmer clamp and bolt bent, whereas only slight plastic deformation of the experimental clamp design occurred. CONCLUSIONS: The experimental external fixator clamp was more secure in resisting fixator pin movement at all levels of tightening compared with the Kirschner-Ehmer-type external fixator clamp. At 7.8 N x m of tightening, the new clamp design did not allow slippage of the pin within the clamp. CLINICAL SIGNIFICANCE: The experimental external fixator clamp should result in greater rigidity of fixator configurations, in addition to providing design features that allow addition of a clamp between two installed clamps, sleeved predrilling of pilot holes for all pins, measurement of pin depth, and placement of positive profile pins at all sites.

Mesenchymal stem cells in osteobiology and applied bone regeneration.

Bone marrow contains a population of rare progenitor cells capable of differentiating into bone, cartilage, muscle, tendon, and other connective tissues. These cells, referred to as MSCs, can be purified and culture expanded from animals and humans. This review summarizes recent experimentation focused on characterizing the cellular aspects of osteogenic differentiation, and exploration of the potential for using autologous stem cell therapy to augment bone repair and regeneration. The authors have completed an array of preclinical studies showing the feasibility and efficacy of MSC based implants to heal large osseous defects. After confirming that syngeneic rat MSCs could heal a critical size segmental defect in the femur, it was established that human MSCs form bone of considerable mechanical integrity when implanted in an osseous defect in an immunocompromised animal. Furthermore, bone repair studies in dogs verify that the technology is transferable to large animals, and that the application of this technology to patients at geographically remote sites is feasible. These studies suggest that by combining MSCs with an appropriate delivery vehicle, it may be possible to offer patients new therapeutic options.

Effect of combined administration of insulin-like growth factor and platelet-derived growth factor on the regeneration of transected and anastomosed sciatic nerve in rats.

OBJECTIVE: To evaluate the efficacy of combined administration of platelet-derived growth factor (PDGF) and insulin-like growth factor (IGF-I) on the regeneration of transected and anastomosed sciatic nerves. ANIMALS: 25 male Lewis rats. PROCEDURE: Transection and anastomosis was performed of the left sciatic nerve of all rats. At the time of surgery, treatment group rats received a combination of PDGF (0.75 microgram) and IGF-I (1.5 micrograms) along with vehicle (2% methyl cellulose gel) at the anastomosis site. Control rats received vehicle alone. Evaluation consisted of motor evoked potentials and nerve conduction velocity, quantitative histologic examination, sciatic functional index, and visual assessment of repair organization (lesion scores). RESULTS: Significant differences in motor evoked potential latency, nerve conduction velocity, axon number, sciatic functional index, or lesion scores were not found between groups. CONCLUSIONS: Combined administration of PDGF and IGF-I did not enhance peripheral nerve regeneration in a transection and anastomosis model as determined 6 weeks after surgery. CLINICAL RELEVANCE: These findings support the assumption that mechanical, versus trophic, effects predominate when nerve ends are closely apposed.

Partial regeneration of the sciatic nerve in rats enhances motor excitability to magnetic stimulation.

Motor-evoked potentials elicited from transcranial magnetic stimulation were recorded from both cranial tibial muscles of 10 Lewis rats. One sciatic nerve was then transected and surgically reanastomosed and allowed to regenerate for 6 weeks. Walking function was tested weekly using a footprint test giving a functional sciatic nerve index. At the end of the study motor-evoked potentials were again performed, as were nerve conduction velocities and supramaximal stimulation of operated and unoperated sciatic nerves. The nerve was evaluated for myelinated axon numbers. Functional sciatic index, numbers of myelinated axons, nerve conduction velocities, and supramaximal stimulation demonstrated the regenerated nerve to be functional, but to a lesser extent than the unoperated nerve. In all cases the amplitude of the compound muscle action potential evoked from transcranial magnetic stimulation of the motor cortex was greater in the operated motor pathway. This finding demonstrates hyperexcitability of the motor pathway to magnetic stimulation during peripheral nerve regeneration.

The pathophysiology of spinal cord injury and its clinical implications.

The pathophysiology of spinal cord injury can be categorized as acute impact or compression. Acute impact injury is a concussion of the spinal cord. This type of injury initiates a cascade of events focused in the gray matter, and results in hemorrhagic necrosis. The initiating event is a hypoperfusion of the gray matter. Increases in intracellular calcium and reperfusion injury play key roles in cellular injury, and occur early after injury. The extent of necrosis is contingent on the amount of initial force of trauma, but also involves concomitant compression, perfusion pressures and blood flow, and administration of pharmacological agents. Preventing or quelling this cascade of events must involve mechanisms occurring in the initial stages. Spinal cord compression occurs when a mass impinges on the spinal cord causing increased parenchymal pressure. The tissue response is gliosis, demyelination, and axonal loss. This occurs in the white matter, whereas gray matter structures are preserved. Rapid or a critical degree of compression will result in collapse of the venous side of the microvasculature, resulting in vasogenic edema. Vasogenic edema exacerbates parenchymal pressure, and may lead to rapid progression of disfunction. Treatment of compression should focus on removal of the offending mass.

Identification and management of brain tumors.

Brain tumors occur commonly in small animals. The clinical history and physical examination findings can strongly suggest their presence. Specifically, an older dog with onset of seizures and behavioral changes, or an older cat with behavioural changes and weakness, should be further evaluated for the presence of a brain tumor. A thorough neurological examination should be performed to localize the lesion(s). Groups of neurological signs will suggest the tumor to be cerebral, cerebellar, or brainstem. Cerebral tumors without brainstem signs carry the best prognosis, especially for cats. Patients suspected of having brain tumors should be imaged with computed tomography, or magnetic resonance imaging. Initial medical therapy includes anticonvulsants and glucocorticosteroids. Cerebral tumors not located on the floor of the calvarium can be successfully excised. These and other tumors can also be treated with radiation therapy.

Modified distraction-stabilization technique using an interbody polymethyl methacrylate plug in dogs with caudal cervical spondylomyelopathy.

A modified technique for distraction-stabilization that used an interbody polymethyl methacrylate plug was performed in 22 dogs with confirmed caudal cervical spondylomyelopathy. Myelographically, all compressive lesions were dynamic and predominantly located ventral to the spinal cord. Nineteen of 21 (90%) dogs for which success/failure could be determined had a successful outcome, and 11 of 22 (50%) dogs attained normal neurologic status. The 2 cases that were considered failures involved dogs that were nonambulatory tetraparetic prior to surgery and failed to improve to a functional status. Complications were self-limiting and included ventral displacement of the cement without loss of distraction in 1 dog and diskosponsylitis at an adjacent disk space in another dog. Evidence of fusion of the affected vertebrae, in the distracted position, was radiographically evident in all dogs. Use of the interbody polymethyl methacrylate plug appears to be a viable surgical treatment of caudal cervical spondylomyelopathy in dogs.

Partial scapulectomy for management of sarcomas in three dogs and two cats.

Three dogs and 2 cats were treated by partial scapulectomy for management of sarcomas of the proximal aspect of the scapula. Surgical margins were considered complete in all cases. In 3 animals, limb function was excellent for 8, 18, and 24 months, respectively, after surgery. Poor limb function persisted in 1 dog that developed local metastatic disease to the affected forelimb. One dog had good limb function for 3 months after surgery and underwent force-plate analysis, which determined a reduction in peak vertical force, decelerating force, and stride time for the affected limb, compared with that for the forelimb that was not subjected to surgery. Tumor recurrence associated with fibrosarcomas was detected in 2 animals. In selected cases, partial scapulectomy can preserve limb function and may be considered a viable alternative to limb amputation.

Comparative viability of peninsular and island axial pattern flaps incorporating the cranial superficial epigastric artery in dogs.

Experimental island and peninsular axial pattern flaps that incorporated the cranial superficial epigastric artery and vein were developed in 6 Beagles. Mean percentage of flap area that survived, for both flaps, was 87%, and percentage of surviving flap area was not significantly different for island versus peninsular flaps. In 1 dog, ligation of an aberrant, perforating branch of the cranial epigastric artery resulted in necrosis of 53% of the flap area. The cranial superficial epigastric axial pattern flaps have potential application for closure of skin defects within their arc of rotation and may be particularly useful for closure of large defects on the ventral aspect of the thorax. A peninsular flap was used to close a defect of the ventral portion of the thoracic wall in a clinical case.

Vascular supply of the tendon of the equine deep digital flexor muscle within the digital sheath.

The vascular and microvascular anatomy of the equine deep digital flexor tendon (DDFT) within the digital sheath was studied by injecting the vasculature with either colored latex or barium sulphate for radiographic, microangiographic, histologic, and computed tomographic (CT) evaluation. Consecutive 4-mm thick two-dimensional CT slice data were reconstructed to 3-dimensional volumetric images to enhance spatial evaluation of the blood supply. Gross dissection and angiographic studies identified three major vascular sources. Above the fetlock, the DDFT was supplied by either a branch of the medial palmar artery (Arteriae digitalis palmaris communis II) or a branch of the medial palmar digital artery (A. digitalis [palmaris propria III] medialis). Below the fetlock, the DDFT was supplied by branches from the lateral and medial palmar branches to the proximal phalanx (Ramus palmaris phalangis proximalis). The most distal aspect of the tendon received small branches from the medial and lateral palmar digital arteries. Using histology and microangigraphy we observed an extensive and uniform intratendinous vascular network above and below the fetlock, with a relatively avascular region of tendon palmar to the fetlock. The most distal 2.0 to 2.5 cm of the tendon within the sheath was heavily infiltrated with fibrocartilage along its dorsal aspect.

Comparison of the holding power of 3.5-mm cortical versus 4.0-mm cancellous orthopedic screws in the pelvis of immature dogs (cadavers).

A 3.5-mm cortical orthopedic screw was compared with a 4.0-mm cancellous screw for maximal load to failure in the pelvis of immature dogs. The pelvis from young cadavers (7 to 13 months old) was divided into hemipelves and used for testing of the 2 screw types. Two sites in each hemipelvis were used, mid-shaft of the ilium and mid-sacrum, including the wing of the ilium. The screws were extracted, and maximal load to failure and mode of failure were recorded. Maximal load to failure per millimeter of engaged thread was calculated. In either pelvic site, the 4.0-mm cancellous screw required a significantly (P < 0.05) higher pullout force per millimeter of engaged screw threads than did the 3.5-mm cortical bone screw.

Collagen fabrics as biomaterials.

Tissue-engineered implants require appropriate biomaterials to serve the required physical function of the tissue being repaired or replaced while facilitating remodeling of the implant. We report on the development of implantable fabrics manufactured from continuous collagen threads. The collagen threads are formed by extrusion of native, acid-extracted bovine collagen into a buffered solution of polyethylene glycol, followed by rinsing and air drying. The high manufacturing rate of such threads permits the production of collagen fabrics of various configurations. The fiber diameter can be controlled, and threads with dry diameters as low as 25 microm have been produced. Braids and bundles of collagen threads implanted as a replacement of the anterior cruciate ligament in a dog model were completely remodeled into host tissue by 12 weeks. Knitted collagen fabrics implanted in a rat abdominal repair model prevented herniation, and connective tissue ingrowth was observed within the fabric by 12 weeks.

Controlled tissue expansion in the distal extremities of dogs.

Controlled tissue expansion using a 100 cc rectangular silicone elastomer expander was performed in the mid-antebrachium and mid-crus of eight adult mixed-breed dogs. Two expander inflation schedules were followed. Group 1 dogs (n = 4) underwent expander inflation using 10 cc sterile saline every other day, and group 2 dogs (n = 4) underwent expander inflation using 15 cc sterile saline every other day until the nominal volume (100 cc) was attained. Significant mean postexpansion increases in skin surface area of 94.1 cm2 (35.9%) and 108.9 cm2 (37.3%) were measured in the antebrachium and crus, respectively (p < .05). In a second procedure, the expanders were removed and skin flaps were developed from the redundant tissue generated during the expansion process. Single pedicle advancement flaps and transposition flaps were used to cover surgically created defects measuring 5 x 10 cm in the antebrachium and crus. Single pedicle advancement flaps consistently measured 10 x 10 cm and could be advanced to cover defects involving one third of the mid-antebrachial or mid-crural circumference. Transposition flaps were rotated up to 170 degrees and the donor site defects were easily closed under minimal or no tension. Complications included an abscess in one dog and seroma formation in four dogs. Differences in success or complication rates between group 1 dogs and group 2 dogs were not observed; an accelerated inflation schedule using 15 cc sterile saline every other day was recommended.

The use of a cap-shaped coil for transcranial magnetic stimulation of the motor cortex.

A cap-shaped coil is introduced as a superior design for inducing transcranial magnetic motor evoked potentials for spinal cord monitoring. Evaluation of the magnetic characteristics of the cap coil showed higher induced electrical fields at and below the depth of the cortical surface, compared to a 9-cm, butterfly-shaped coil. Twenty normal adults were stimulated with the cap coil and a 9-cm round coil in three positions. Compound muscle action potentials were recorded from the left and right abductor digiti minimi and anterior tibialis muscles. The cap coil induced potentials with higher intensities and lower variability between consecutive stimuli. The cap coil was also more able to simultaneously induce motor evoked potentials from the four muscles studied. This coil design should provide superior means of inducing transcranial magnetic motor evoked potentials in multiple muscles.