Mechanical and histological characteristics of rheumatoid wrist tendons and ligaments

Replacement arthroplasty for reconstruction of deformed and painful wrist joints due to rheumatoid arthritis has had a high incidence of migration, dislocation, and fracture. I believe that these failures are associated with the insufficiency and maybe the degraded mechanical properties of the rheumatoid tendons and ligaments. Such a hypothesis has not been investigated in the literature. An experimental study was undertaken to characterize the mechanical behaviour of rheumatoid wrist extensor tendons and ligaments in order to comment on the adequacy of the rheumatoid tissues in reconstructive surgery.

An experimental protocol was developed to characterize the tissues including mechanical tensile testing via standard viscoelastic tests and histological evaluation via microscopy. Material properties of non-rheumatoid and rheumatoid tissues from twenty-one patients undergoing wrist arthrodesis were measured, compared, and correlated. Results of the mechanical tests showed that rheumatoid tendons demonstrate decreased properties in terms of stiffness, ability to sustain load upon relaxation, and strength when compared to equivalent non-rheumatoid tendons. Histological slides of rheumatoid tissues showed increased signs of inflammation: invasion of inflammatory cells with neovascularization, fibrin deposition, and edema. The differences in mechanical and histological properties between non-rheumatoid and rheumatoid tissues were found to be statistically significant.

Two additional series of experiments were performed to determine a suitable method to measure the physical parameters of the specimens and determine the preservation method which would the least affect tissue properties. The Vernier calliper was selected to measure gauge length and cross-sectional area of tendons, while freezing at $-$20$\sp\circ$C was chosen to preserve tissue until testing time.

The present research work is a first step in characterizing rheumatoid tendons and ligaments. Histological examination of tissues showed that rheumatoid arthritis invades the tissues surrounding the wrist joint, and affects the structure of the tendons and ligaments. The mechanical properties of the tissues have been altered in such a way that the tendons and ligaments may be less effective in stabilizing the wrist, and are less able to secure a wrist implant. The second step in characterizing rheumatoid tissues could pertain to a biochemical analysis. A better understanding of rheumatoid tissue behaviour will lead to an improved management of wrist instability and deformities. Future work may lie in the development of a bio-inert material to be used in reconstructive surgery with current wrist implants, and the design of a wrist arthroplasty which promotes bony integration while maintaining soft tissue integrity.