The Influence of the Abduction Joints of Four Fingers to Grasp: Experimental and Simulated Verification

The thumb is the most important finger of the human hand and has a great influence on grasp manipulations. However, the extent to which joints other than the thumb joints affect the grasp, and thus, which joints should be included in a prosthetic hand, remains an open issue. In this paper, we focus on the metacarpophalangeal joints of the four fingers, except the thumb, which can generate flexion/extension and abduction/adduction motions. The contribution of these joints to grasping was evaluated in four aspects: grasp size, grasp force, grasp quality and grasp success rate. Six subjects participated in experiments with respect to the maximum grasp size and grasp force. The results show that possessing abduction mobility of the metacarpophalangeal joints can increase the grasp size by 4.67 ± 1.93 mm and the grasp force by 5.27 ± 4.25 N. Then, the grasping quality and success rate were tested in a simulation platform and using a robotic hand, respectively. The results show that grasp quality was promoted by 76.7% in the simulated environment with abduction mobility compared to without abduction mobility, whereas the grasp success rate was promoted by 68.3%. We believe that the results of this work can benefit the understanding of hand function and prosthetic hand design.

Treatment of Phalangeal Joint Stiffness Related to Proximal Phalangeal Bone Fractures: Therapeutic Effects on the Range of Motion and Finger Pain

Purpose: Proximal phalangeal bone fractures with displacement are treated using operative procedures. These fractures can cause stiffness of the interphalangeal or metacarpophalangeal joints, which can be relieved using various operative and nonoperative techniques. This study analyzed the range of motion (ROM) and pain after a combination therapy to treat finger stiffness following proximal phalangeal fractures.Methods: Fifty-two patients who underwent operative procedures for proximal phalangeal fractures and showed finger stiffness from March 2015 to January 2021 were included in this retrospective study. The patients in group 1 (n=24) performed elastic resistance exercises, while those in group 2 (n=28) underwent conventional exercise. ROM and pain score were measured at 5, 8, and 12 weeks postoperatively. Furthermore, a patient with a swan-neck deformity and intractable stiffness was treated using partial translocation of the extensor apparatus, and the postoperative outcome is presented.Results: Group 1 showed a larger ROM and less pain than group 2 at 12 weeks postoperatively (p<0.05). Patients in both groups exhibited notable improvements with regard to ROM and pain during the study period (p<0.05). In addition, the swan-neck deformity accompanying hyperextension of the proximal interphalangeal joint was significantly relieved.Conclusion: Proximal phalangeal bone fractures can lead to stiffness of the interphalangeal and metacarpophalangeal joints. Joint stiffness was relieved using an elastic resistance exercise protocol in the early postoperative period. Intractable stiffness showing a fixed joint angle can be treated with thorough tenolysis and corrective surgery.

Evidence for the Presence of Synovial Sheaths Surrounding the Extensor Tendons at the Metacarpophalangeal Joints

Background. MRI-detected inflammation around the metacarpophalangeal (MCP-)joints is prevalent in RA and poses a markedly increased risk of RA-development when present in arthralgia patients. Such inflammation is called &lsquo;peritendinitis&rsquo;, since anatomy literature reports no presence of a tenosynovial sheath at these tendons. However, the presence or absence of a synovial sheath at these extensor tendons has never been studied. Methods. A macroscopy and microscopy study of extensor-tendons at the MCP-joints of two embalmed human hands was performed. Routine histology was performed with Haematoxylin-Eosin staining. Results. We found evidence for the presence of synovial lining around extensor-tendons at MCP-joints. A delimited space surrounding the extensor digitorum tendon was observed, which was lined with an epithelium representing fibroblast-like synoviocytes. Conclusion. Contrast-enhancement around extensor tendons at MCP joints observed on MRI in RA represents tenosynovitis and thus inflammation of synovial tissue. Further studies with larger numbers of specimen are warranted to study anatomic variants. In addition, the molecular composition of the tenosynovium remains to be characterized.

Outcomes of Surface Replacement Arthroplasty in Metacarpophalangeal Joints Affected by Noninflammatory Arthritis

Background The purpose of this study was to investigate the outcomes of surface replacement arthroplasty (SRA) for noninflammatory arthritis of the metacarpophalangeal (MCP) joint. Methods Records from 20 SRAs performed between 1995 and 2017 in 17 patients with noninflammatory arthritis affecting the MCP joint were retrospectively reviewed. The mean follow up was 6.6 years. Results Three arthroplasties (15%) underwent 4 revision operations. The 2-, 5-, 10-, and 15-year rates of survival from surface replacement implant revision were 90%, 90%, 79%, and 79%, respectively. Major complications occurring in revised joints included arthrodesis (n = 1) and amputation (n = 1). The overall reoperation rate was 35%. The 2-, 5-, 10-, and 15-year rates of overall reoperation-free survival were 75%, 69%, 60%, and 60%, respectively. Conclusions Pain ratings and MCP arc of motion significantly improved following arthroplasty. Metacarpophalangeal SRA for noninflammatory arthritis can improve arc of motion and pain. Revision is uncommon; however, 1 in 3 joints requires reoperation.

Clinical outcomes after mini-hook plate fixation for small avulsion fractures around the interphalangeal or metacarpophalangeal joints of the hand

Background Mini-hook plate has been described for the treatment of various small avulsion fragments in the hand. This retrospective study aimed to evaluate clinical outcomes after mini-hook plate fixation in patients with an avulsion fracture around the interphalangeal or metacarpophalangeal joints of the hand. Methods Nineteen patients with avulsion fractures around the interphalangeal or metacarpophalangeal joints of the hand were included in this study. Seven patients had a mallet fracture, and 12 patients had other phalangeal avulsion fractures including central slip, collateral ligament, volar plate, and flexor avulsion fractures. The osseous union and functional outcomes, including finger joint motion, joint stability, pinching strength, and the disabilities of the arm, shoulder, and hand score, were evaluated. Results The mean duration of follow-up was 33.8 months. All patients in mallet and other phalangeal avulsion fractures achieved osseous union between the avulsion fragment and phalangeal bone, and there was no joint subluxation. There were no significant differences in the disabilities of the arm, shoulder, and hand scores. However, the patients with mallet fracture have lower mean percentage values of the total active range of motion and pinching strength than other phalangeal avulsion fractures. We abandoned this procedure in mallet fractures because the early results after mini-hook plate fixation in mallet fractures appeared unfavorable. Conclusion These results suggest that the mini-hook plate fixation can provide sufficient stability and good clinical outcomes in those with phalangeal avulsion fractures. However, the outcomes for mallet fractures were not as good as those for other phalangeal avulsion fractures.