The rheumatoid metacarpophalangeal joint

[Arthroplasty of the hand and wrist]

Arthrosis and autoimmune arthritis frequently lead to major impairment of hand function. Primary therapy consists of well- tried conservative treatments and joint preserving surgical options for special indications. In advanced stages silicon spacers remain the gold standard surgical option for replacement of proximal interphalangeal and metacarpophalgeal joints of the fingers. Alternatively, surface replacement prostheses can restore the biomechanical properties of these joints more porperly. In case of the carpometacarpal (CMC) joint of the thumb, arthroplasty is gaining popularity as modern implants show excellent mid-term outcome. Although current forth generation implants for wrist replacement are promising, total wrist arthroplasty is currently reserved for exceptional indications.

Mechanical properties evaluation of metacarpophalangeal joint prosthesis with new titanium-nickel memory alloy: a cadaver study

OBJECTIVE

Ni-Ti memory alloys are unusual materials for hard-tissue replacement because of their unique superelasticity, good biocompatibility, high strength, low specific gravity, low magnetism, wear resistance, corrosion resistance and fatigue resistance. The current study aims to evaluate its mechanical properties and provide biomechanical basis for the clinical application of the prosthesis.

METHODS

Ten adult metacarpophalangeal joint specimens were randomly divided into a prosthesis group (n = 5, underwent metacarpophalangeal joint prosthesis) and a control group (n = 5, underwent sham operation). Firstly, the axial compression strength was tested with BOSE material testing machine to evaluate its biomechanical strength. Secondly, these specimens were tested for strain changes using BOSE material testing machine and GOM non-contact optical strain measurement system to evaluate the stress changes. Thirdly, fatigue test was performed between groups. Lastly, the mechanical wear of the metacarpophalangeal joint prosthesis was tested with ETK5510 material testing machine to study its mechanical properties.

RESULTS

Axial compression stiffness in the prosthesis group was greater than that in the control group in terms of 30 ° and 60 ° flexion positions (P < 0.05). There was no statistically significant difference between two groups with regards to axial compression stiffness and stress change test (P > 0.05). In the fatigue wear test, the mean mass loss in the prosthesis group's prosthesis was 17.2 mg and 17.619 mm3, respectively. The mean volume wear rate was 0.12%. There was no statistically significant difference in the maximum pull-out force of the metacarpal, phalangeal, and polymer polyethylene pads between the prosthesis group and the control group specimens.

CONCLUSIONS

Ni-Ti memory alloy metacarpophalangeal joint prosthesis conforms to the biomechanical characteristics of metacarpophalangeal joints without implants, and the fatigue strength can fully meet the needs of metacarpophalangeal joint activities after joint replacement.

[Metacarpophalangeal joint replacement]

BACKGROUND

Arthroplasty of metacarpophalangeal (MCP) joints is crucial for patients with rheumatoid arthritis. Motion preserving therapies are mandatory for this joint, since loss of function of the MCP joint is detrimental. Many protheses or spacers have been introduced over the last 80 years, but most of them have been dismissed due to major complications.

CURRENT PROCEDURES

Since the 1960s the Swanson spacer has been established as the reference standard for motion preserving procedures of the finger MCP joints. High fracture rates of the spacer do not seem to limit function and patient satisfaction after all. Current long-term studies show at least promising results for pyrolytic carbon protheses with respect to range of motion, survival, and revision rates in comparison to the Swanson spacer.

Applying evidence in the care of patients with rheumatoid hand and wrist deformities

The traditional approach in managing rheumatoid hand deformities is based on the individual surgeon's experiences. In the current era of evidence-based medicine, formulating treatment for the rheumatoid hand fits perfectly within the framework of evidence-based medicine by leveraging the best evidence from the literature, incorporating surgeons' experience and considering patients' preferences. In this Special Topic article, we use a case example to illustrate how evidence-based medicine can be practiced within the framework of treating rheumatoid hand deformities by distilling the best evidence from the literature to guide surgeons in a rational approach for treating this common condition.