CAD/CAM transtibial prosthetic sockets from central fabrication facilities: how accurate are they?

This research compares transtibial prosthetic sockets made by central fabrication facilities with their corresponding American Academy of Orthotists and Prosthetists (AAOP) electronic shape files and assesses the central fabrication process. We ordered three different socket shapes from each of 10 manufacturers. Then we digitized the sockets using a very accurate custom mechanical digitizer. Results showed that quality varied considerably among the different manufacturers. Four of the companies consistently made sockets within +/-1.1% volume (approximately 1 sock ply) of the AAOP electronic shape file, while six other companies did not. Six of the companies showed consistent undersizing or oversizing in their sockets, which suggests a consistent calibration or manufacturing error. Other companies showed inconsistent sizing or shape distortion, a difficult problem that represents a most challenging limitation for central fabrication facilities.

Assessment of residual-limb volume change using bioimpedence.

We investigated electrical bioimpedance as a potential measurement modality to assess residual-limb volume change in lower-limb amputees. Four strip electrodes were positioned across the anterior lateral to posterior lateral aspects of the proximal lower leg or residual limb such that the outer pair applied current and the inner pair sensed voltage. A commercial bioimpedance analyzer supplied current at 50 fre quencies between 5 kHz and 1 MHz and then used a well-validated model to determine fluid resistance. From these data, extracellular fluid volume (V(ECF)) could be estimated. Bench test evaluation showed the instrument to have a root-mean-square error of less than 0.014% over a 1 h interval. Tests of subjects who had been transtibial amputees for at least 2 yr showed V(ECF) changes from postural adjustments well outside the instrument error and normal minute-to-minute biological variability. The rate of V(ECF) change while standing with the prosthesis donned was greater for diabetic subjects than for nondiabetic subjects. Bioimpedance analysis may have use in prosthetics research, where comparing residual-limb volume at different time points or under different treatment conditions is of interest.

Disturbed paraspinal reflex following prolonged flexion-relaxation and recovery.

STUDY DESIGN: Repeated measures experimental study of the effect of flexion-relaxation, recovery, and gender on paraspinal reflex dynamics. OBJECTIVE: To determine the effect of prolonged flexion-relaxation and recovery time on reflex behavior in human subjects. SUMMARY OF BACKGROUND DATA: Prolonged spinal flexion has been shown to disturb the paraspinal reflex activity in both animals and human beings. Laxity in passive tissues of the spine from flexion strain may contribute to desensitization of mechanoreceptors. Animal studies indicate that recovery of reflexes may take up to several hours. Little is known about human paraspinal reflex behavior following flexion tasks or the recovery of reflex behavior following the flexion tasks. METHODS: A total of 25 subjects performed static flexion-relaxation tasks. Paraspinal muscle reflexes were recorded before and immediately after flexion-relaxation and after a recovery period. Reflexes were quantified from systems identification analyses of electromyographic response in relation to pseudorandom force disturbances applied to the trunk. RESULTS: Trunk angle measured during flexion-relaxation postures was significantly higher following static flexion-relaxation tasks (P < 0.001), indicating creep deformation of passive supporting structures in the trunk. Reflex response was diminished following flexion-relaxation (P < 0.029) and failed to recover to baseline levels during 16 minutes of recovery. CONCLUSION: Reduced reflex may indicate that the spine is less stable following prolonged flexion-relaxation and, therefore, susceptible to injury. The absence of recovery in reflex after a substantial time indicates that increased low back pain risk from flexion-relaxation may persist after the end of the flexion task.

Active trunk stiffness increases with co-contraction.

Trunk dynamics, including stiffness, mass and damping were quantified during trunk extension exertions with and without voluntary recruitment of antagonistic co-contraction. The objective of this study was to empirically evaluate the influence of co-activation on trunk stiffness. Muscle activity associated with voluntary co-contraction has been shown to increase joint stiffness in the ankle and elbow. Although biomechanical models assume co-active recruitment causes increase trunk stiffness it has never been empirically demonstrated. Small trunk displacements invoked by pseudorandom force disturbances during trunk extension exertions were recorded from 17 subjects at two co-contraction conditions (minimal and maximal voluntary co-contraction recruitment). EMG data were recorded from eight trunk muscles as a baseline measure of co-activation. Increased EMG activity confirms that muscle recruitment patterns were different between the two co-contraction conditions. Trunk stiffness was determined from analyses of impulse response functions (IRFs) of trunk dynamics wherein the kinematics were represented as a second-order behavior. Trunk stiffness increased 37.8% (p < 0.004) from minimal to maximal co-activation. Results support the assumption used in published models of spine biomechanics that recruitment of trunk muscle co-contraction increases trunk stiffness thereby supporting conclusions from those models that co-contraction may contribute to spinal stability.