Mechanics of hip dysplasia reductions in infants using the Pavlik harness: a physics-based computational model.

Biomechanical factors influencing the reduction of dislocated hips with the Pavlik harness in patients of Developmental Dysplasia of the Hip (DDH) were studied using a three-dimensional computer model simulating hip reduction dynamics in (1) subluxated and (2) fully dislocated hip joints. Five hip adductor muscles were identified as key mediators of DDH prognosis, and the non-dimensional force contribution of each in the direction necessary to achieve concentric hip reductions was determined. Results point to the adductor muscles as mediators of subluxated hip reductions, as their mechanical action is a function of the degree of hip dislocation.

Oblique tibial osteotomy revisited.

Purpose: Oblique proximal tibial osteotomy is a useful option for correcting deformity associated with Blount's disease (tibia vara). Safe, adequate correction depends on technical issues that have evolved since the original description of the procedure.

Methods: Retrospective review of surgical experience.

Pathological fracture after migration of cement used to treat distal femur physeal arrest.

Treatment of physeal arrest with bar removal and placement of interposition materials in young patients has been shown to restore physeal growth. Among the various materials that have been used to prevent early reformation of the physeal bar (fat, silastic, cartilage), Peterson recommended the use of Cranioplast, as this material can prevent bar reformation, and it is radiolucent because it does not contain barium. Peterson suggested steps be taken to prevent migration of the Cranioplast, as migration of the interposition material might allow for reformation of the physeal bar.

Shoulder motion description: the ISB and Globe methods are identical.

Background: Three-dimensional shoulder position may be described by rotation sequences such as the proposed ISB standard. Alternative techniques to describe position (the Globe method) seek to simplify this description by eliminating rotation sequences and substituting unambiguous measurements.

Methods: Both methods (ISB and Globe) were applied to an analysis of shoulder positions, and an overall comparison was performed.

Lateral acetabular rotation improves anterior hip subluxation.

Surgical reorientation of the acetabulum is used to improve stability of subluxated or dysplastic hips, but the specific mechanical consequences of reorientation have not been quantified. I used a rigid body spring model of the human hip to study the effects of different acetabular positions on hip stability during single-limb stance. The model predicted subluxation direction and magnitude, and the effective joint contact area, as functions of acetabular position.

Theoretical study of subluxation in early Legg-Calvé-Perthes disease.

The relationship between mechanical subluxation and femoral head necrosis geometry in Legg-Calvé-Perthes disease (LCP) was investigated with a three-dimensional rigid body-spring method hip model. Femoral head models with progressively larger regions of necrosis, corresponding to the four Catterall grades, were placed in a spherical acetabular model and studied in static single-limb stance configuration, with variable mechanical rigidity of the necrotic segment. The degree of subluxation was dependent on the geometric region of involvement, mechanical properties of the segment, and direction of loading force.

Three-dimensional muscle-tendon geometry after rectus femoris tendon transfer.

Background: Rectus femoris tendon transfer is performed in patients with cerebral palsy to improve knee flexion during walking. This procedure involves detachment of the muscle from its insertion into the quadriceps tendon and reattachment to one of the knee flexor muscles. The purpose of the present study was to evaluate the muscle-tendon geometry and to assess the formation of scar tissue between the rectus femoris and adjacent structures.

Alterations in functional movement after axillary burn scar contracture: a motion analysis study.

Children with axillary burns often develop scar contractures that restrict shoulder movement. Objective data on functional movement patterns after contracture formation is sparse. The purpose of this study was to determine how axillary contractures affect shoulder movement during activities of daily living (ADLs).