Reverse Total Wrist Arthroplasty: New Design and Biomechanical Advantages.

PURPOSE: Although fourth generation total wrist arthroplasties (TWAs) have improved implant longevity compared to earlier generations, high failure rates persist. This study aimed to assess how a shift in the center of rotation will affect kinematic outcomes of the joint. This has been accomplished through a TWA redesign, known as the reverse total wrist arthroplasty (RTWA).

METHODS: Eight cadaveric specimens (75.1 ± 10.9 years, 8 men) were implanted with both a custom load sensing TWA and a novel redesigned RTWA. For both reconstructed states, the specimens were mounted and actuated through flexion-extension (FE) and radial-ulnar deviation (RUD) using an active motion simulator. Muscle forces and articular loading patterns were recorded in both states for comparison of the implant designs. Statistical analysis completed showed RUD motion was underpowered and are therefore presented as exploratory and descriptive because of limited power.

RESULTS: In general, during both FE and RUD the RTWA required a lower magnitude of force from the muscles compared to the TWA state. Throughout FE, four of the five muscles examined required less force after RTWA implantation. Through RUD, three of five required less force. In addition, through both ranges of motion the carpal component joint loading was decreased in all wrist positions (41.6 ± 8.6% and 38.1 ± 7.1% for extension and flexion motion, respectively) after implantation of the RTWA compared to the TWA.

CONCLUSIONS: The redesigned RTWA performed well compared to a standard TWA implant and there was a noted decrease in both the muscle forces and joint loading following RTWA implantation.

CLINICAL RELEVANCE: The new RTWA design may have the potential to reduce the magnitude of force required by muscles to actuate the joint and reduce the high loading patterns within the distal carpal component that are noted after implantation of TWA implants.