Research on Variable-Stiffness Mechanisms of Robot Wrists for Compliant Assembling-Clamping

The stiffness requirements of robot wrists vary with processes during automatic assembling-clamping of robots. The precision of robots moving workpieces to operating positions in the process of rigid localization is achieved if robot wrists equip with a large stiffness. The pose errors of workpieces in the process of compliant assembling-clamping can easily be compensated if robot wrists with a low stiffness is utilized. The present compliant wrist can not meet the stiffness requirements of different processes. A robot wrist with a large stiffness variation is proposed and its mechanisms of rigid localization and compliant assembling-clamping are studied. The pose models of wrists caused by deformations are established. The influences of wrist stiffness on the deformation of itself are researched. The mechanism of modulating wrist stiffness during compliant assembling-clamping is revealed. A structure of 3-DOF (degrees of freedom) robot wrist with a stiffness variation is proposed. The wrist stiffness is changed by modulating the pretension. The influences of pretensions and geometrical parameters on the variable-stiffness characteristics and the stiffness distribution of a wrist are researched. Finally, the experiments are carried out to verify the feasibility of the wrists finishing assembling-clamping operations by modulating the stiffness.

Wrist Arthrolysis: A Systematic Review of Open and Arthroscopic Techniques

Background Wrist arthrolysis is a viable option in wrist stiffness and can be performed via open or arthroscopic techniques. Purpose The aim of the study is to describe and evaluate the available techniques of open and arthroscopic arthrolysis of the radiocarpal joint and the distal radio ulnar joint (DRUJ) in posttraumatic wrist stiffness. Methods A systematic literature search was performed in PubMed to identify studies reporting on open and arthroscopic wrist arthrolysis. Key words included “open wrist arthrolysis,” “arthroscopic wrist arthrolysis,” “post-traumatic wrist stiffness,” and “DRUJ arthrolysis.” Data were extracted independently by a pair of reviewers. Results Overall, 637 studies were identified; 13 additional articles were found through previous publications (total 650 articles). A total of 612 records resulted after duplicates was removed. Fourteen studies were selected and only eight respected the inclusions criteria. One study focused on volar open arthrolysis and four studies on arthroscopic arthrolysis of the radiocarpal joint; two studies reported on open arthrolysis and two studies on arthroscopic DRUJ arthrolysis. Range of motion following open and arthroscopic wrist arthrolysis improved in all studies. Conclusion Both arthroscopic and open arthrolysis can lead to similar and satisfactory results in radiocarpal joint and DRUJ stiffness.. Level of Evidence This is a level 3a study.

Surgical fixation of fractures of the distal radius within 2 weeks reduces postoperative finger stiffness

Locked anterior plating remains the most common form of surgical fixation for displaced fractures of the distal radius. We hypothesized that delayed surgical fixation later than 2 weeks after injury contributes to poorer patient outcomes for patients with displaced or intra-articular fractures of the distal radius. We conducted a retrospective cohort study of 158 patients who underwent locked anterior plating for an intra-articular or displaced fracture of the distal radius using multiple regression analysis to identify any relationship between patient, injury or treatment factors with the patient-rated wrist and hand evaluation score or finger and wrist stiffness. There was no significant correlation between timing of surgery and functional scores. A delay in time to surgery of more than 2 weeks did correlate significantly with increased finger and thumb stiffness. However, this relationship was not seen for wrist stiffness. Our study supports the consensus that early recovery and function is facilitated by surgical fixation within 2 weeks and that delayed fixation beyond this may contribute to protracted finger stiffness. Level of evidence: IV

Smoking Increases Postoperative Complications After Distal Radius Fracture Fixation: A Review of 417 Patients From a Level 1 Trauma Center

Background: Unstable distal radius fractures that undergo surgical stabilization have varying complication rates in the literature. Smoking is known to affect bone healing and implant fixation rates but has never been definitively shown to affect postoperative outcomes of surgically managed distal radius fractures. Methods: A retrospective review was performed of patients with surgically treated distal radius fractures at a Level 1 Trauma Center who had at least 6 weeks of follow-up over a 5-year period. Charts were reviewed for basic demographic information, comorbidities, details about the operative procedure, and early complications. Notable physical examination findings were noted, such as wrist stiffness and distal radius tenderness to palpation. Statistical analysis was performed to compare the smoking and nonsmoking groups. To control for confounding differences, a hierarchical multivariable regression analysis was performed. Results: Four hundred seventeen patients were included in the study, and 24.6% were current smokers at the time of surgery. The overall complication rate for smokers was 9.8% compared with 5.6% in nonsmokers. The smoking cohort showed significantly higher rates of hardware removal, nonunion, revision procedures, wrist stiffness, and distal radius tenderness. When controlling for the confounding variables of diabetes and obesity, smokers still had significantly higher rates of the same complications. Conclusion: Patients who smoke have a statistically significant higher rate of postoperative distal radius tenderness, wrist stiffness, nonunion, hardware removal, and revision procedures compared with those who do not smoke in a review of 417 total patients undergoing surgical fixation for distal radius fractures.

The Impact of Aging and Hand Dominance on the Passive Wrist Stiffness of Squash Players: Pilot Study (Preprint)

BACKGROUND Passive joint stiffness can influence the risk of injury and the ability to participate in sports and activities of daily living. However, little is known about how passive joint stiffness changes over time with intensive repetitive exercise, particularly when performing unilateral activities using the dominant upper limb. OBJECTIVE This study aimed to investigate the difference in passive wrist quasi-stiffness between the dominant and nondominant upper limb of competitive squash players, compare these results with a previous study on young unskilled subjects, and explore the impact of aging on wrist stiffness. METHODS A total of 7 healthy, right-side dominant male competitive squash players were recruited and examined using the Massachusetts Institute of Technology Wrist-Robot. Subjects were aged between 24 and 72 years (mean 43.7, SD 16.57) and had a mean of 20.6 years of squash playing experience (range 10-53 years, SD 13.85). Torque and displacement data were processed and applied to 2 different estimation methods, the fitting ellipse and the multiple regression method, to obtain wrist stiffness magnitude and orientation. RESULTS Young squash players (mean 30.75, SD 8.06 years) demonstrated a stiffer dominant wrist, with an average ratio of 1.51, compared with an average ratio of 1.18 in young unskilled subjects. The older squash players (mean 64.67, SD 6.35 years) revealed an average ratio of 0.86 (ie, the nondominant wrist was stiffer than the dominant wrist). There was a statistically significant difference between the magnitude of passive quasi-stiffness between the dominant and nondominant wrist of the young and older squash player groups (P=.004). CONCLUSIONS Findings from this pilot study are novel and contribute to our understanding of the likely long-term effect of highly intensive, unilateral sports on wrist quasi-stiffness and the aging process: adults who participate in repetitive sporting exercise may experience greater joint quasi-stiffness when they are younger than 45 years and more flexibility when they are older than 60 years.