A large-deformation, finite-element study of chondrodiatasis in the canine distal femoral epiphyseal plate.

A large-deformation, finite-element analysis was conducted to model stress fields around the developing growth plate as a first approach to comprehend the clinical application of traction for limb lengthening procedures. The model chosen was a cross section through the distal femoral growth plate of a 14-week-old dog. The chosen section passed through two of the conformational bends (mammillary processes) formed by the natural convolutions of the physis. Three different loading conditions were applied to the distal femoral epiphyseal model. The model also examined the effects of different values of Young's modulus of the growth-plate cartilage. The cortical bone in all cases, experienced the highest stresses. In the growth plate, the highest principal stresses occurred where the physis intersects cortical bone. There were localized stresses that were higher than those that caused fracture in a rabbit model [Guse et al., J. Orthop. Res. 7, 667-673 (1989)]. Results also indicated the following: a small tilt of 0.1 degree in loading application increases the maximum principal stresses and the von Mises stresses in certain regions of the growth plate by about 8%; the shearing stresses in the growth plate are sensitive to Young's modulus of the growth plate; and traction pins that do not grip the cancellous bone in the epiphysis will increase the regions of high principal stress in the growth plate.

Comparison of the Nebraska collar, a new prototype cervical immobilization collar, with three standard models.

OBJECTIVES: To determine whether a novel immobilization collar called the Nebraska collar would restrict motion of the cervical spine better than three traditional designs: the Philadelphia collar, the sterno occipital mandibular immobilizer (S.O.M.I.), and the Lehrman-Minerva cervical orthosis. DESIGN: Cervical spine radiographs and a compass were used to assess motion allowed by four separate cervical collars placed on volunteers. SETTING: University-affiliated level one trauma center. PATIENTS/PARTICIPANTS: Fourteen paid volunteers (six females and eight males) between the ages of twenty and thirty-five years (mean twenty-five years) were recruited. MAIN OUTCOME MEASUREMENTS: The maximum amount of flexion, extension, and lateral bending permitted by each collar was assessed by cervical radiographs taken of the volunteers while wearing each of the four collars. Maximum rotation was measured with a compass positioned on the top of the head of the volunteers and oriented in the horizontal plane. RESULTS: The Nebraska collar restricted rotation (p < 0.0001) and lateral bending (p < 0.0001) significantly more than did the other three orthoses. In total maximum extension from occiput to C7, the Nebraska collar was found to be more restrictive than the Philadelphia collar (p < 0.05) and the S.O.M.I. (p < 0.05). In total maximum flexion, there was no statistically significant difference among the four collars. When the total maximum flexion-to-extension motion was measured, both the Nebraska and Lehrman-Minerva cervical collars were found to be more restrictive than the Philadelphia collar (p < 0.05). CONCLUSION: The new Nebraska collar provides stabilization that is significantly more rigid than the other models tested, with no difference in patient comfort.

Effects of periosteal activation agent on bone repair and ingrowth.

A substance that activates the resting periosteum (PAA) was applied to the periosteal surface in two different healing models using the femurs of 2-kg male rabbits. The activation agent was applied to the periosteal surface over the sites of circular defects drilled through the lateral cortex in one model and over the sites of porous polyethylene implants placed in the lateral cortex and the medullary canal in the other model. Results failed to show that the agent either enhanced bone ingrowth into the porous implants or accelerated bony filling of the circular defects. However, there was indication of enhanced mineralization and periosteal callus formation as early as 24 h after application.