Neural interfacing architecture enables enhanced motor control and residual limb functionality postamputation

Despite advancements in prosthetic technologies, patients with amputation today suffer great diminution in mobility and quality of life. We have developed a modified below-knee amputation (BKA) procedure that incorporates agonist–antagonist myoneural interfaces (AMIs), which surgically preserve and couple agonist–antagonist muscle pairs for the subtalar and ankle joints. AMIs are designed to restore physiological neuromuscular dynamics, enable bidirectional neural signaling, and offer greater neuroprosthetic controllability compared to traditional amputation techniques. In this prospective, nonrandomized, unmasked study design, 15 subjects with AMI below-knee amputation (AB) were matched with 7 subjects who underwent a traditional below-knee amputation (TB). AB subjects demonstrated significantly greater control of their residual limb musculature, production of more differentiable efferent control signals, and greater precision of movement compared to TB subjects (P < 0.008). This may be due to the presence of greater proprioceptive inputs facilitated by the significantly higher fascicle strains resulting from coordinated muscle excursion in AB subjects (P < 0.05). AB subjects reported significantly greater phantom range of motion postamputation (AB: 12.47 ± 2.41, TB: 10.14 ± 1.45 degrees) when compared to TB subjects (P < 0.05). Furthermore, AB subjects also reported less pain (12.25 ± 5.37) than TB subjects (17.29 ± 10.22) and a significant reduction when compared to their preoperative baseline (P < 0.05). Compared with traditional amputation, the construction of AMIs during amputation confers the benefits of enhanced physiological neuromuscular dynamics, proprioception, and phantom limb perception. Subjects’ activation of the AMIs produces more differentiable electromyography (EMG) for myoelectric prosthesis control and demonstrates more positive clinical outcomes.

Age does not influence muscle fiber length adaptation to increased excursion

Muscle fiber length adaptation to static stretch or shortening depends on age, with sarcomere addition in young muscle being dependent on mobility. Series sarcomere number can also increase in young animals in response to increased muscle excursion, but it is not clear whether adult muscles respond similarly. The ankle flexor retinaculum was transected in neonatal and adult rats to increase tibialis anterior muscle excursion. Sarcomere number in tibialis anterior was determined after 8 wk of adaptation. Muscle moment arm and excursion were increased 30% ( P < 0.01) in both age groups. Muscle cross-sectional area was reduced by 12% ( P < 0.01) in response to the increased mechanical advantage, and this reduction was unaffected by age. Fiber length change was also unaffected by age, with both groups showing a trend ( P < 0.10) for slightly (6%) increased fiber length. Retinaculum transection results in shorter muscle length in all joint configurations, so this trend opposes the fiber length decrease predicted by an adaptation to muscle length and indicates that fiber length is influenced by dynamic mechanical signals in addition to static length.

Passive Ankle Stiffness in Subjects With Diabetes and Peripheral Neuropathy Versus an Age-Matched Comparison Group

Background and Purpose. Patients with diabetes mellitus and peripheral neuropathy (DM and PN) often complain of joint stiffness. Although stiffness may contribute to some of the impairments and functional limitations found in these patients, it has not been quantified in this population. The purpose of this study was to quantify and compare passive ankle stiffness and dorsiflexion (DF) range of motion in subjects with DM and PN versus an age-matched comparison group. Subjects. Thirty-four subjects were tested (17 subjects with DM and PN and 17 subjects in an age-matched comparison group). There were 10 male subjects and 7 female subjects in each group. Methods. A Kin-Com dynamometer was used to measure passive plantar flexor torque as each subject's ankle was moved from plantar flexion into dorsiflexion at 60°/s. The following variables were compared using a Student t test: initial angle (angle of onset of plantar flexor torque), maximal dorsiflexion angle, plantar flexor muscle excursion (difference between initial angle and maximal dorsiflexion angle), slope of the first half of the plantar flexor torque curve (stiffness 1 measurement), and slope of the second half of the plantar flexor torque curve (stiffness 2 measurement). Results. The subjects with DM and PN group had smaller maximal dorsiflexion angles and less plantar flexor muscle excursion than the comparison group. There was no difference in initial angle, stiffness 1 measurement, or stiffness 2 measurement. Conclusion and Discussion. Although the subjects with DM and PN had less dorsiflexion range of motion than did the comparison group, there was no difference in stiffness between the groups. This finding suggests that people with DM and PN have “short” versus “stiff” plantar flexor muscles.

Sarcomere number adaptation after retinaculum transection in adult mice.

Skeletal muscle has been shown to adjust serial sarcomere number in response to chronic static length changes. However, the adaptive responses to alterations in the dynamic environment are less well defined. The adaptations of the adult mouse tibialis anterior (TA) muscle to altered length and excursion were investigated by surgical transection of the flexor retinaculum. TA moment arm and muscle excursion increased by 38&plusmn;7 % (mean &plusmn; s.e.m.) and fully extended (plantarflexed) muscle length was decreased by 8 % after flexor retinaculum transection. In spite of the significant shortening of the muscle in full plantar- and dorsiflexion, serial sarcomere number decreased by 10&plusmn;1 % after 2 weeks of recovery. Gait analysis of these transected animals revealed a 14&plusmn;3 % decrease in dorsiflexion angular velocity after transection. The decrease in angular velocity was less than the increase in moment arm and, as a result, muscle velocity was calculated to increase by 20&plusmn;4 %. These data suggested that the muscle adapted in response to the underlying change in length, irrespective of the altered excursion or velocity.