Special Issue Orthopedic and Rehabilitation Engineering II

This is the second of two issues on orthopedic and rehabilitation engineering. Orthopedic engineering and rehabilitation engineering are multidisciplinary fields and include, among others, multiscale studies on the mechanical and neurological functions of the musculoskeletal system under normal and pathological conditions. Pathologies may result from illness or injury which can be caused by trauma and/or poor environmental conditions, workplace risk factors, and extended engagement in unusual physical activities (either extreme, e.g., professional athletes, or altogether lack of activities).

Research studies may combine in vivo or in vitro measurements with novel neuro-biomechanical modelling. Of special interest is the implementation of findings obtained for improved diagnostics, monitoring of functional progress, and indications for therapy. Additional aspects are related to biomechatronics, which deal with intelligent electromechanical systems to support and/or enhance affected functions of the human body.

This issue presents a total of 6 papers (four research papers and two review papers), reflecting a variety of topics, including muscle hardness, skeletal fixation procedure, artificial joint design, gait analysis of lower limb amputees, myoelectric control of finger prostheses and vocation-related neuromusculoskeletal deficiencies in professional musicians.

Ren et al. [1] reported on muscle hardness, defined as a mechanical property that represents transverse muscle stiffness, and exhibits an intrinsic viscoelastic tension. Specifically, they referred to the relationship between muscle hardness and different muscle lengths/positions. They made use of shear wave elastography (SWE) to measure the muscle hardness of several muscles using an ultrasound probe which generated a radiation force followed by tissue deformation, resulting in the propagation of a transient shear wave. This propagation was captured by an ultra-fast ultrasound image to calculate the tissue hardness. Interestingly, the significance of muscle hardness is both at the molecular level (since it has been shown that muscle fiber stiffness is proportional to the number of attached cross-bridges, and changes linearly as the muscle fiber develops the force) and at the macroscopic level.

Surgical plans for syndesmotic fixation following injury at the distal tibiofibular joint was reported by Goh et al. [2]. If this injury is not properly treated, e.g., if the syndesmosis is fixed unstably or in a non-anatomical position, the ankle joint may not function normally and patients may suffer from serious chronic pain and instability, thus causing post-traumatic arthritis. The aim of this study was thus to optimize, by FE analysis, the metal screw fixation technique. The following four parameters were examined: level and diameter of the screw, material of the syndesmotic screw and number of penetrated cortical bones.

A finite element (FE) analysis of the proximal femur for designing femoral stems for total hip replacement was presented by Solórzano et al. [3]. Both cortical and trabecular regions were represented with transverse isotropic properties, and the joint loading used, which included muscle action, was made similar to that of young, active patients. To qualitatively and quantitatively assess the risks of stress shielding, the following FE model parameters were included: stem material, absence of anatomical femoral neck and level of osteotomy.

The gait of persons with unilateral above knee amputations was analyzed by Xu et al. [4] to compare the inter-joint coordination of the amputated and non-amputated limbs to that of able-bodied controls. Smooth gait was assessed by means of the defined continuous relative phase (CRP) and the decomposition index (DI).

A comprehensive overview of myoelectric control regarding finger prosthesis for patients with finger implants following multiple finger loss was presented by Srimaneepong et al. [5]. It argued that the lack of somatosensory feedback and full control robustness, cannot provide sufficient control speed, and patients are incapable of reproducing various hand movements; primarily due to motion artifacts which typically occur in the low-frequency range. However, real-time motion artifact suppression algorithms can be used on an ultra-low-power microcontroller to achieve high robustness.

The sixth and last contribution in this issue is also a review, discussing the vocation-related musculoskeletal disorders (Mizrahi [6]). This situation occurs specifically in orchestra musicians, due to the unusual and non-symmetrical postures required during playing. The long-playing hours expose the neuromusculoskeletal system to overuse conditions, thus making the system more susceptible to fatigue and injury. This review provides a description of the playing-related motor disorders in performing musicians, and of the methodologies used to identify and evaluate these disorders, particularly for violinists and other upper-string players. These include EMG, image analysis, motion capture and analysis, FE methods, forces of impact nature and/or of repetitive patterns leading to trauma and injury.