Yupeng Ren

Ultrasonic evaluations of Achilles tendon mechanical properties poststroke

Spasticity, contracture, and muscle weakness are commonly observed poststroke in muscles crossing the ankle. However, it is not clear how biomechanical properties of the Achilles tendon change poststroke, which may affect functions of the impaired muscles directly. Biomechanical properties of the Achilles tendon, including the length and cross-sectional area, in the impaired and unimpaired sides of 10 hemiparetic stroke survivors were evaluated using ultrasonography. Elongation of the Achilles tendon during controlled isometric ramp-and-hold and ramping up then down contractions was determined using a block-matching method. Biomechanical changes in stiffness, Youngs modulus, and hysteresis of the Achilles tendon poststroke were investigated by comparing the impaired and unimpaired sides of the 10 patients. The impaired side showed increased tendon length (6%; P = 0.04), decreased stiffness (43%; P < 0.001), decreased Youngs modulus (38%; P = 0.005), and increased mechanical hysteresis (1.9 times higher; P < 0.001) compared with the unimpaired side, suggesting Achilles tendon adaptations to muscle spasticity, contracture, and/or disuse poststroke. In vivo quantitative characterizations of the tendon biomechanical properties may help us better understand changes of the calf muscle-tendon unit as a whole and facilitate development of more effective treatments.

Combined Passive Stretching and Active Movement Rehabilitation of Lower-Limb Impairments in Children With Cerebral Palsy Using a Portable Robot

Background. Ankle impairments are closely associated with functional limitations in children with cerebral palsy (CP). Passive stretching is often used to increase the range of motion (ROM) of the impaired ankle. Improving motor control is also a focus of physical therapy. However, convenient and effective ways to control passive stretching and motivate active movement training with quantitative outcomes are lacking. Objective. To investigate the efficacy of combined passive stretching and active movement training with motivating games using a portable rehabilitation robot. Methods. Twelve children with mild to moderate spastic CP participated in robotic rehabilitation 3 times per week for 6 weeks. Each session consisted of 20 minutes of passive stretching followed by 30 minutes of active movement training and ended with 10 minutes of passive stretching. Passive ROM (PROM), active ROM (AROM), dorsiflexor and plantarflexor muscle strength, Selective Control Assessment of the Lower Extremity, and functional outcome measures (Pediatric Balance Scale, 6-minute walk, and Timed Up-and-Go) were evaluated before and after the 6-week intervention. Results. Significant increases were observed in dorsiflexion PROM (P = .002), AROM (P = .02), and dorsiflexor muscle strength (P = .001). Spasticity of the ankle musculature was significantly reduced (P = .01). Selective motor control improved significantly (P = .005). Functionally, participants showed significantly improved balance (P = .0025) and increased walking distance within 6 minutes (P = .025). Conclusions. Passive stretching combined with engaging in active movement training was of benefit in this pilot study for children with CP. They demonstrated improvements in joint biomechanical properties, motor control performance, and functional capability in balance and mobility.

Changes of calf muscle-tendon biomechanical properties induced by passive-stretching and active-movement training in children with cerebral palsy

Biomechanical properties of calf muscles and Achilles tendon may be altered considerably in children with cerebral palsy (CP), contributing to childhood disability. It is unclear how muscle fascicles and tendon respond to rehabilitation and contribute to improvement of ankle-joint properties. Biomechanical properties of the calf muscle fascicles of both gastrocnemius medialis (GM) and soleus (SOL), including the fascicle length and pennation angle in seven children with CP, were evaluated using ultrasonography combined with biomechanical measurements before and after a 6-wk treatment of passive-stretching and active-movement training. The passive force contributions from the GM and SOL muscles were separated using flexed and extended knee positions, and fascicular stiffness was calculated based on the fascicular force-length relation. Biomechanical properties of the Achilles tendon, including resting length, cross-sectional area, and stiffness, were also evaluated. The 6-wk training induced elongation of muscle fascicles (SOL: 8%, P = 0.018; GM: 3%, P = 0.018), reduced pennation angle (SOL: 10%, P = 0.028; GM: 5%, P = 0.028), reduced fascicular stiffness (SOL: 17%, P = 0.128; GM: 21%, P = 0.018), decreased tendon length (6%, P = 0.018), increased Achilles tendon stiffness (32%, P = 0.018), and increased Youngs modulus (20%, P = 0.018). In vivo characterizations of calf muscles and Achilles tendon mechanical properties help us better understand treatment-induced changes of calf muscle-tendon and facilitate development of more effective treatments.

Effects of repeated ankle stretching on calf muscle-tendon and ankle biomechanical properties in stroke survivors.

BACKGROUND The objective of this study was to investigate changes in active and passive biomechanical properties of the calf muscle-tendon unit induced by controlled ankle stretching in stroke survivors. METHODS Ten stroke survivors with ankle spasticity/contracture and ten healthy control subjects received intervention of 60-min ankle stretching. Joint biomechanical properties including resistance torque, stiffness and index of hysteresis were evaluated pre- and post-intervention. Achilles tendon length was measured using ultrasonography. The force output of the triceps surae muscles was characterized via the torque-angle relationship, by stimulating the calf muscles at a controlled intensity across different ankle positions. FINDINGS Compared to healthy controls, the ankle position corresponding to the peak torque of the stroke survivors was shifted towards plantar flexion (P<0.001). Stroke survivors showed significantly higher resistance torques and joint stiffness (P<0.05), and these higher resistances were reduced significantly after the stretching intervention, especially in dorsiflexion (P=0.013). Stretching significantly improved the force output of the impaired calf muscles in stroke survivors under matched stimulations (P<0.05). Ankle range of motion was also increased by stretching (P<0.001). INTERPRETATION At the joint level, repeated stretching loosened the ankle joint with increased passive joint range of motion and decreased joint stiffness. At the muscle-tendon level, repeated stretching improved calf muscle force output, which might be associated with decreased muscle fascicle stiffness, increased fascicle length and shortening of the Achilles tendon. The study provided evidence of improvement in muscle tendon properties through stretching intervention.

Developing a Multi-Joint Upper Limb Exoskeleton Robot for Diagnosis, Therapy, and Outcome Evaluation in Neurorehabilitation

Arm impairments in patients post stroke involve the shoulder, elbow and wrist simultaneously. It is not very clear how patients develop spasticity and reduced range of motion (ROM) at the multiple joints and the abnormal couplings among the multiple joints and the multiple degrees-of-freedom (DOF) during passive movement. It is also not clear how they lose independent control of individual joints/DOFs and coordination among the joints/DOFs during voluntary movement. An upper limb exoskeleton robot, the IntelliArm, which can control the shoulder, elbow, and wrist, was developed, aiming to support clinicians and patients with the following integrated capabilities: 1) quantitative, objective, and comprehensive multi-joint neuromechanical pre-evaluation capabilities aiding multi-joint/DOF diagnosis for individual patients; 2) strenuous and safe passive stretching of hypertonic/deformed arm for loosening up muscles/joints based on the robot-aided diagnosis; 3) (assistive/resistive) active reaching training after passive stretching for regaining/improving motor control ability; and 4) quantitative, objective, and comprehensive neuromechanical outcome evaluation at the level of individual joints/DOFs, multiple joints, and whole arm. Feasibility of the integrated capabilities was demonstrated through experiments with stroke survivors and healthy subjects.

IntelliArm: An exoskeleton for diagnosis and treatment of patients with neurological impairments

This paper presents a novel 7 (active) +2 (passive) degrees of freedom (DOF) exoskeleton to achieve effective rehabilitation of upper limbs with neurological impairment. The 7+2 DOF robot was designed for allowing anatomically correct motions in the upper extremity, and for measuring 18 axis forces/torques and 9 DOF positions. A novel four-step integrated rehabilitation approach was developed and tested including (1) accurate and quantitative diagnosis which is not practical to do during manual clinical examinations or with existing robotic devices; (2) strenuous stretching of spastic joints based on the diagnosis and with intelligent control to adjust the stretching velocity constantly according to the joint conditions; (3) voluntary movement exercise to perform realistic functional tasks based on the patient-specific diagnosis, and (4) outcome evaluations which assessed the treatment outcome quantitatively with multiple physiological measures.

Deltoid Ligament Reconstruction: A Novel Technique with Biomechanical Analysis

Background: Deltoid ligament insufficiency has been shown to decrease tibiotalar contact area and increase peak pressures within the lateral ankle mortise. This detrimental effect may create an arthritic ankle joint if left unresolved. Reconstructive efforts thus far have been less than satisfactory. We describe a novel technique that reconstructs both main limbs of the deltoid ligament in anatomic orientation while providing secure graft fixation. Materials and Methods: Six pairs of fresh frozen cadaveric lower extremities were utilized. Matched right and left lower limbs (one pair) were allocated either to a deltoid reconstruction group or an intact deltoid group. The anterior tibial tendon was chosen as the graft for ligament reconstruction, and was harvested from the ipsilateral specimen. Tunnels were created in the distal tibia at the deltoid origin, and at the talus (deep) and calcaneus (superficial) deltoid insertions. Following measurement, the graft was cut to the appropriate size and endobuttons weaved into both tendon ends. The graft ends were passed through the talus and calcaneus respectively. The residual graft loop was then routed through the tibial tunnel and secured proximally with a cancellous screw post and spiked washer. Following specimen mounting, a multiaxis testing apparatus with three separate motors allowed three planes (dorsiflexion/plantarflexion; inversion/eversion; and internal/external rotation) of motion. Angular rotations and linear translations of the tibia in the X-Y-Z directions were measured for a given torque in external/internal rotation, dorsiflexion/plantarflexion, or eversion/inversion, under a constant velocity of 2 degrees per second. Testing consisted of a 2 Nm preload for 20 cycles in internal rotation/external rotation and inversion/eversion prior to data collection of 10 cycles at this level of torque. Similarly, a preload of 1 Nm for 20 cycles was used in dorsiflexion/plantarflexion prior to data collection of 10 cycles at this torque level. Data were collected in the control specimens (the matched contralateral extremity) with the deltoid ligament intact, and following complete sectioning of the ligament complex (both bundles). Results: Angular displacement at a 2 Nm level torque was significantly greater in the sectioned group compared to the deltoid reconstruction group in external rotation and eversion (p = 0.006 and p = 0.017 respectively). There was no statistical difference in angular displacement between the deltoid intact and reconstructed group in external rotation and eversion when tested at 2 Nm of torque (p = 0.865 and p = 0.470, respectively). The stiffness of the reconstruction was 136.4 ± 40.2% compared to the intact ligament. Stiffness data were statistically insignificant in both plantar flexion and dorsiflexion between the reconstructed and sectioned groups (p = 0.050 and p = 0.126). Conclusion: The described reconstruction technique under low torque was able to restore eversion and external rotation stability to the talus, which was statistically similar to the intact deltoid ligament. This novel technique developed its strength not only from the anatomic orientation of the reconstructed ligament, but the strength of the components chosen to fix the tendon graft to the bone. Clinical Relevance: This utilitarian reconstruction may be incorporated into total ankle arthroplasty, triple arthrodesis, and sports injuries to re-establish lost medial stability.

Impact of talar component rotation on contact pressure after total ankle arthroplasty: a cadaveric study.

Background: There is limited literature available to assess the impact of talar component rotation on total ankle contact biomechanics. Materials and Methods: Six male cadaveric below-knee specimens were implanted with Agility® total ankles. The sequence of talar rotation for each specimen was randomized between: Neutral, 7.5 degrees internal and 7.5 degrees external rotation. Contact pressure was measured using Tekscan ankle sensors during sequential static axial loadings and 10 simulated dynamic strides under 650 N axial load. Results: The peak pressure (PP) increased for the internally (PPstatic = 7.0 ± 0.27 MPa (mean ± SD), p < 0.001; PPdynamic = 7.8 ± 0.22 MPa, p = 0.001) and externally rotated talar component positions (PPstatic = 6.2 ± 0.22 MPa, p = 0.011; PPdynamic = 7.6 ± 0.29 MPa,p = 0.004) as compared to neutral (PPstatic = 5.5 ± 0.13 MPa; PPdynamic = 6.3 ± 0.11 MPa). The contact area under 650 N load was reduced for both talar component internal (97.38 ± 17.7 mm2, p = 0.001) and external rotation (152.66 ± 16.8 mm2, p = 0.022) as compared to neutral (190.02 ± 13.8 mm2). There was a significant rotational torque for the malrotated talar components as compared to neutral, that increased with axial loading (p = 0.044). Conclusion: Near the extremes of talar malrotation, there was a consistent change from a continuous tibiotalar contact area to a pattern of two-point contact; the orientation of which opposed the direction of talar component malrotation. Talar component malrotation resulted in: increased peak pressure, decreased contact area and increased rotational torque that resisted the malrotation. Clinical Relevance: Talar component malrotation may contribute to premature polyethylene wear as well as potential talar loosening secondary to the rotational torque generated as the geometry of the prosthesis attempts to seek congruency.

Characterization of spasticity in cerebral palsy: dependence of catch angle on velocity

Aim  To evaluate spasticity under controlled velocities and torques in children with cerebral palsy (CP) using a manual spasticity evaluator.

Developing an Intelligent Robotic Arm for Stroke Rehabilitation

Arm impairments in patients post stroke involve the shoulder, elbow and wrist simultaneously. Patients may develop spasticity and reduced range of motion (ROM) at the multiple joints with abnormal couplings between the multiple joints and between the multiple degrees of freedom (DOF). They may lose independent control of individual joints and coordination among the joints. This project is aimed at developing a whole arm intelligent rehabilitation robot capable of controlling the shoulder, elbow, and wrist individually and simultaneously while allowing trunk motions, with the following integrated features: 1) it has unique diagnostic capabilities to determine which joints and which DOFs have significant changes in the neuromechanical properties, which joints lose independent control, what are the abnormal couplings, and whether the problem is due to changes in passive muscle properties or active control capabilities; 2) based on the diagnosis, it stretches the spastic/deformed joints forcefully under intelligent control to loosen up the specific stiff joints/DOFs; 3) with the stiff joints loosened up, the patients practice voluntary functional movements with assistance from the robot to regain/improve their motor control capability; and 4) the outcome is evaluated quantitatively at the levels of individual joints, multiple joints/DOFs, and the whole arm.