Assessing changes in wrist biomechanics during ageing and optimal design of total wrist arthroplasty and assistive rehabilitation devices

手腕是一个高度复杂的解剖关节，包括桡骨、腕骨和掌骨的相对运动。腕关节炎和损伤可以通过关节融合术（融合术）进行手术治疗，这可以缓解疼痛，但限制或消除关节的运动。因此，越来越多地尝试保留运动的手术，例如全腕关节成形术（TWA），以维持患者的关节功能。Motec腕关节是一种球窝式TWA假体，可替代腕关节的所有解剖关节。虽然Motec患者的随访研究结果是积极的，但尚未对术后活动度（ROM）和效率进行详细评估。特别是那些研究回旋和功能重要的飞镖投掷运动（DTM）。因此，该项目有以下目标。第一次比较TWA前后腕关节的功能ROM和运动效率。其次，研究Motec旋转中心（COR）在腕关节空间内的最佳位置。第三，比较手术前后穿过关节的肌肉的力矩臂。由于手术和实验技术的侵入性，我们采用尸体入路。设计了一种主动式腕关节运动模拟器，通过驱动五个激动肌腱来移动尸体腕关节。通过施加相同的肌腱位移实现不同手术条件之间的控制，并记录肌腱力作为运动效率的测量。在模拟器的评估中，使用双平面X射线视频放射成像（BPVR）和运动形态X射线重建（XROMM）来测量Motec手术前后6具尸体手腕的整体腕关节运动。在这两种情况下，成功地模拟了肘关节/伸展、桡尺偏斜、DTM和回旋。此外，模拟腕关节角度和肌腱力在单个样本内可重复，但在不同样本之间不可重复。评价表明，可以在手术条件之间比较模拟腕关节运动，以确定手术的潜在机械效应。使用尸体模拟器进行了两组实验，在此期间，腕关节角度和肌腱力记录在整个七个运动模式。第一组研究了TWA前后的腕关节（n = 14）。第二组研究了具有六种不同COR位置以及TWA前条件的Motec手腕（n = 6）。这两组实验测量肌腱力作为手腕运动效率的指标，使用BPVR捕获模拟运动，并使用XROMM动画测量手腕角度。在项目的最后阶段，将创建生物力学腕关节模型，以估计解剖和Motec手腕的肌肉力矩臂。虽然这项工作尚未完成，但TWA前后的比较显示，屈曲、伸展和桡尺偏斜的范围以及回旋区没有显著差异。重要的是，Motec手腕能够产生DTM。峰值屈肌腱的力量显着降低Motec手腕在屈曲，并没有其他不同于前TWA条件。除了在伸展过程中TWA后尺侧腕伸肌力下降外，峰值伸肌肌腱力没有显著差异。第二组实验期间收集的数据尚未得到充分处理。我们的目标是确定是否有一个Motec COR位置，在其中实现最佳的ROM和运动效率。还将比较Motec COR的位置与解剖腕部COR的最佳匹配位置。迄今为止的结果表明，Motec TWAs有可能以与术前状态相似的效率重建功能性腕关节运动。需要进一步的研究来确定这些结论是否在体内得到支持。

The wrist is a highly complex anatomical joint comprising relative motion of the radius, carpals and metacarpals. Wrist arthritis and injury can be treated surgically with arthrodesis (fusion), which relieves pain but restricts or eliminates motion at the joint. Therefore, motion preserving procedures, e.g. total wrist arthroplasty (TWA), are increasingly being attempted to maintain patients' joint function. The Motec wrist is a ball and socket style TWA prosthesis which replaces all anatomical articulations at the wrist. While follow-up studies of Motec patients have been positive, detailed assessments of post-operative range of motion (ROM) and efficiency are yet to be performed. Particularly those investigating circumduction and the functionally important Dart Thrower's Motion (DTM). Hence, this project has the following objectives. First to compare functional ROM and efficiency of motion in pre- and post- TWA wrists. Second to investigate optimal placement of the Motec centre of rotation (COR) within the wrist joint space. Third to compare pre- and post- operative moment arms of muscles crossing the joint.Due to invasive surgical and experimental techniques, a cadaveric approach was taken. An active wrist motion simulator was designed to move cadaveric wrists by actuating five agonist tendons. Control between different surgical conditions was achieved by applying identical tendon displacements, and tendon forces were recorded as a measure of motion efficiency. In an evaluation of the simulator, biplanar X-ray videoradiography (BPVR) and X-ray reconstruction of moving morphology (XROMM) were used to measure the overall wrist motions of six cadaveric wrists before and after a Motec surgery. Flexion/extension, radioulnar deviation, DTM and circumduction were successfully simulated in both conditions. Additionally, simulated wrist angles and tendon forces were repeatable within single specimens but not between different specimens. The evaluation suggested that simulated wrist motions could be compared between surgical conditions to determine potential mechanical effects of the surgery. Two sets of experiments were performed using the cadaveric simulator, during which wrist angles and tendon forces were recorded throughout seven motion patterns. The first set studied pre- and post-TWA wrists (n = 14). The second set studied the Motec wrist with six different COR positions as well as a pre-TWA condition (n = 6). Both sets of experiments measured tendon forces as an indicator of wrist motion efficiency, captured simulated motions using BPVR and measured wrist angles using XROMM animations. In the final stage of the project, biomechanical wrist joint models will be created to estimate muscle moment arms in anatomical and Motec wrists. Although this work is yet to be completed.Pre/post-TWA comparison revealed no significant differences in ranges of flexion, extension and radioulnar deviation, or in the area of circumduction. Importantly, the Motec wrist was able to produce DTM. Peak flexor tendon forces were significantly lower in Motec wrists during flexion and did not otherwise differ from the pre-TWA condition. Peak extensor tendon forces did not significantly differ apart from a post-TWA decrease in extensor carpi ulnaris force during extension. Data collected during the second set of experiments is yet to be fully processed. We are aiming to determine whether there is a Motec COR position in which the most optimal ROM and efficiency of motion are achieved. Position of the Motec COR will also be compared with the best-fit location of the anatomical wrist COR. Results thus far suggest that Motec TWAs have the potential to recreate functional wrist motion with similar efficiency to the pre-surgical state. Further studies are required to determine whether these conclusions are supported in vivo.