Optimal Center of Rotation for Ball-And-Socket Thumb Carpometacarpal Arthroplasty Identified Using Three-Dimensional...

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Medical device design

Background:

• Thumb carpometacarpal (CMC) joint arthritis is a common condition requiring surgical intervention.
• Total joint arthroplasty is a viable surgical option for CMC joint arthritis.
• The optimal positioning of the center of rotation (COR) for CMC joint implants remains unquantified.

Purpose of the Study:

• To identify ideal ball-and-socket implants for thumb CMC joint arthroplasty.
• To determine the optimal position of the COR for these implants.
• To restore natural thumb kinematics through precise implant placement.

Main Methods:

• Acquired CT images of ten healthy male right thumbs.
• Created 3D bone models using 3D CAD software.
• Designed and virtually tested ball-and-socket implants with variable neck offset, height, and rotation.
• Identified the COR with minimal positional change across various thumb movements.

Main Results:

• Optimal COR achieved with a 4.5 mm offset.
• Optimal neck rotation angle determined as 130.6° (radial to palmar side of the first metacarpal).
• Optimal implant height set at 43.6 mm from the distal metacarpal end.
• These parameters restored near-normal thumb kinematics.

Conclusions:

• This research provides crucial data for developing improved thumb CMC joint arthroplasty implants.
• Findings can guide surgical techniques for optimal implant placement.
• The study establishes a reference for achieving natural thumb joint function post-surgery.