Summary:
Researchers in the Mechanical Engineering Department at UCLA have developed a compliant wrist implant as an alternative to current wrist arthroplasty devices.
Background:
Conventional wrist replacements often lack the longevity and stability required to make total wrist arthroplasty (TWA) the preferred treatment for active patients with pan-carpal or distal radio-ulnar joint pathologies requiring surgical intervention. The complex structure of the wrist poses significant hurdles for arthroplasty. During a TWA procedure, the ligaments of the wrist are excised along with portions of the proximal and distal carpal rows. This loss of ligamentous support leaves unrestrained wrist implants highly prone to subluxation, or partial dislocation, under load-bearing conditions. This can consequently leads to painful injuries, accelerated implant wear, and abnormal load distribution on the radial and carpal/metacarpal anchoring bones. Conversely, constrained wrist implants fail to replicate the wrist's intricate biomechanics. Their rigidity introduces additional load-bearing disadvantages, often resulting in loosening at the metacarpal attachment over time. These constraints also impose challenges in distributing mechanical stresses, further compromising implant stability and functionality. Successful integration of wrist replacements requires sufficient viable bone stock. In its absence, wrist fusion remains the only viable alternative, as the risks of unstable anchoring and subsidence outweigh the potential benefits of arthroplasty. To address the current shortcomings of TWA procedures, there is a critical need for innovative designs that address these biomechanical and structural challenges.
Innovation:
UCLA researchers in the department of Mechanical Engineering have developed an orthopedic wrist implant that incorporates two compliant mechanisms arranged in a series configuration to closely replicate the biological range of wrist motion, including the characteristic circumduction motion. Unlike conventional wrist implants, which typically utilize condyloid or ball-and-socket mechanisms—either constrained or unconstrained—this design introduces two primary compliant mechanical structures (flexures). The first flexure replicates the natural flexion/extension motion of the wrist, while the second, aligned in series with the first, facilitates radio-ulnar deviation. By aligning the rotational axes of the two flexure systems, the design achieves coupled degrees of freedom, enabling smooth and coordinated actuation of circumduction and dart-thrower motions. This advanced design represents a significant step forward in providing more natural, functional, and reliable wrist implant solutions.
Potential Applications:
• Wrist arthroplasty procedures and revision cases
• Trauma and injury reconstruction
• Congenital deformities
• Severe joint degradation for patients with rheumatoid or osteoarthritis
• Patient-specific implants
Advantages:
• Increase stability and reduced risk of dislocation or mechanical instability
• Enhanced structural support for accommodating loading
• Improved durability and performance overtime
• Maintenance of 2 degrees of freedom
• Limited rubbing and wear formation
State of Development:
This invention was first conceived in conversations beginning in Summer 2022. The invention was first reduced to practice in a dissection session and subsequent discussion on 11/11/2022.
Publications:
1. Huxman, C., and Butler, J. (September 10, 2021). "A Systematic Review of Compliant Mechanisms as Orthopedic Implants." ASME. J. Med. Devices. December 2021; 15(4): 040802. https://doi.org/10.1115/1.4052011
2. Bilancia, P., Baggetta, M., Berselli, G., Bruzzone, L., & Fanghella, P. (2021). "Design of a bio-inspired contact-aided compliant wrist". Robotics and Computer-Integrated Manufacturing, 67, 102028. https://doi.org/10.1016/j.rcim.2020.102028
3. Davis, R. F., Weiland, A. J., & Dowling, S. V. (1982). "Swanson implant arthroplasty of the wrist in rheumatoid patients." Clinical Orthopaedics and Related Research, 166. https://doi.org/10.1097/00003086-198206000-00022
Reference:
UCLA Case No. 2023-261
Lead Inventor:
Tyler Clites, UCLA Professors of Mechanical and Aerospace Engineering