David Skrade

Effect of the syndesmotic screw on ankle motion.

The purpose of this study was to determine the effect of syndesmotic screw fixation on ankle motion. Eight unpaired osteoligamentous cadaver ankles were tested. The study quantified ankle flexion, talar tilt, ankle drawer, and tibiotalar rotation for each specimen using an MTS biomechanical testing system. Each specimen was tested under a 15-kg and a 70-kg axial load. The testing was repeated after the placement of a syndesmotic screw, a 4.5-mm cortical screw, in accordance with AO technique. There was a statistically significant decrease (P < .05) in tibiotalar external rotation. There was no statistical difference in ankle flexion. There was a significant decrease in the anterior and the posterior drawer tests with the foot in plantar flexion. These were the most significant results. Syndesmotic screw fixation is used for the internal fixation of certain unstable ankle fractures. Opinions differ as to whether the screw should be removed at 6 weeks (prior to weightbearing) or left in place indefinitely. It was concluded that the syndesmotic screw should be removed prior to the return to full activity. Leaving it in place will contribute to abnormal ankle motion; this may result in local discomfort and a possible fatigue fracture of the screw.

Mechanical stability of porous-coated acetabular components in total hip arthroplasty

Five different porous-coated acetabular prosthetic configurations underwent in vitro testing to assess mechanical stability in embalmed cadaver hemipelves: Harris Galante II cup with three cancellous screws, Biomet Universal cup, Whiteside cup with peripheral pegs, Whiteside cup with two cancellous screws, and plain Whiteside cup. Following implantation in a neutral frame, cyclic load testing was done using 33 specimens at 100-kg load for 100,000 cycles using an MTS machine (MTS Systems Corp., Minneapolis, MN). Subsequently, static load-to-failure testing was done in all specimens. Subsidence and micromovement were determined for each specimen using linear variable differential transformers. With cyclic testing, overall cup subsidence revealed a significant increase, from 500 to 100,000 cycles. Overall cup micromovement revealed a significant decrease, and all cup groups demonstrated less than 125 microns (.125 mm) of average mean micromotion at the completion of cyclic testing. The best cup configuration was a 1-mm, oversized, press-fit cup using two 6.5 cancellous screws for additional fixation, which revealed an average mean of 60 microns (.06 mm) of micromovement. Static load testing revealed unacceptable micromovement over 150 microns (.150 mm) in most cups with 300-kg loads.

Thoracic Deformation Contours in a Frontal Impact

The objective of the study was to document the thoracic deformation contours in a simulated frontal impact. Unembalmed human cadavers and the Hybrid III anthropomorphic manikins were tested. Data from the newly developed External Peripheral Instrument for Deformation Measurement (EPIDM) was used to derive deformation patterns at upper and lower thoracic levels. Deceleration sled tests were conducted on three-point belt restrained surrogates positioned in the drivers seat (no steering assembly) using a horizontal impact test sled at velocities of approximately 14.0 m/s. Lap and shoulder belt forces were recorded with seat belt transducers. The experimental protocol included a Hybrid III manikin experiment followed by the human cadaver test. Both surrogates were studied under similar input and instrumentation conditions, and identical data acquisition and analysis procedures were used. For the covering abstract see IRRD 864472.

Experimentally produced ankle fractures in autopsy specimens

Twenty-six unembalmed lower-leg specimens were mounted in an experimental test device with the foot placed at a fixed degree of pronation/supination, dorsiflexion/plantar flexion, or both. Torque versus rotation curves were determined as each foot was externally rotated to failure. Torsional stiffness was determined for the first 20 degrees of external rotation, and energy to failure was noted at the point of initial failure. Anatomic dissection and roentgenographs delineated the degree of injury in all specimens. Gender had the greatest effect on both torque and energy parameters, and the injury pattern. In males, 67% of specimens had an oblique fibular fracture, torn anterior tibiofibular ligament, and torn deltoid ligament (SER2). In females, 45% had a transverse fibular fracture without syndesmotic or deltoid injury. Forty percent of females had the SER2 injury. Angle of supination/pronation did not correlate with a specific injury pattern. Peak axial load had a significant effect on stiffness, but increasing the load by more than three times body weight did not increase injury severity.

Thoracic Deformation and Velocity Analysis in Frontal Impact

The objective of the present study was to measure dynamic chest deformations and compute chest velocity and viscous criterion during real world frontal impacts conducted on a horizontal sled. Four unembalmed human cadavers were restrained using a three-point belt restraint in the driver seat of a sled buck. Two chest bands (each with a 24 gauge capability) were placed on the thorax to record the temporal deformation patterns during impact. All tests were conducted at a velocity of approximately 50 kph. Biomechanical data were gathered digitally at a sampling rate of 12,500 Hz. Multiple rib fractures were identified in all specimens at autopsy. Analysis of approximately 800 temporal deformation contours of the thorax demonstrated regional differences. The overall mean maximum normalized chest deflections, maximum chest compression velocities, and peak viscous response variables ranged from 0.15 to 0.51, 1.79 to 4.87 m/s, and 0.15 to 1.95 m/s, respectively. These findings clearly illustrate the potential use of the chest band output to correlate injury with biomechanical variables and establish thoracic impact tolerance.

The Effect Of Axial Load And Ankle Position On Ankle Stability

Summary The range of motion of 10 fresh cadaveric ankle specimens was measured for flexion, anterior-posterior drawer, inversion-eversion, and internal-external rotation under conditions that simulated normal weight-bearing. At a 70 kg load, range of motion significantly diminished in all directions (p < 0.005). Plantar flexion was diminished to a greater degree than dorsiflexion. For anterior-posterior drawer in the loaded state, ankle flexion did not play a significant role in determining stability. Factors such as ligamentous attachments may be more critical than mortise geometry in determining anterior-posterior translation. For torsion and version, stability was greatest in dorsiflexion. That ankle stability is related to articular congruity with increased load-bearing emphasizes the importance of anatomical restoration of the ankle mortise in the injury state.