Determination of correct length after total trapeziometacarpal arthroplasty

Aandoening(en): Hand

Specialist(en): Prof. Dr. Joris Duerinckx

Introduction
The treatment of trapeziometacarpal (TMC) osteoarthritis aims to restore the function of the thumb and create a pain free, stable, and mobile joint with preserved thumb strength. Various surgical techniques have been described. TMC arthroplasty is a relatively new technique with variable results reported in recent literature. The majority of failures and revisions are due to loosening or dislocation. In an attempt to improve the outcomes, guidelines for correct cup positioning have recently been described (Duerinckx and Caekebeke. Journal of Hand Surgery Eur 2016). Stem position is relatively straightforward. However, no clear guidelines exist concerning neck length and its effect on postoperative thumb length and stability of the construct.

In this study we try to:

1. define a way to determine thumb length intraoperatively
2. determine optimal neck length for optimal stability and motion.
3. offer clear and simple intraoperative guidelines and techniques to achieve previous statements.

Material and methods
We will test 12 fresh-frozen human cadaveric thumbs (6 cadavers). We will thaw the cadavers for 24 hours at 4°C before preparation.
First, a preoperative clinical thumb length evaluation will be performed. Next, a ball-and-socket TMC prosthesis will be implanted. A palmar Moberg-Gedda approach will be used to spare the dorsal and palmar ligamentous stabilizers of the TMC joint. Two parallel K-wires will be placed in the STT-joint. The osteotomy  at the distal articular surface of the trapezium will be made parallel to these K-wires  to achieve a cut that is aligned with the center of rotation of the TMC joint. The osteotomy at the distal articular surface of the trapezium and the base of the 1^st metacarpal will be performed simultaneously using a double cut oscillating saw blade of 5mm (DS ref nr 532.085S). This gap corresponds to the length of a prosthetic construct with a medium length neck. A prosthesis will be implanted and fitted with a neck of medium length (0). Correct position of the prosthesis will be checked on fluoroscopy.

Finally, following assessments will be made:

• Thumb ROM (on testing machine)
• Stability
• Push-pull with 1kg longitudinal traction on the thumb
• Clinical thumb length
• Radiographical thumb length

These assessments will be repeated for incrementally longer neck lengths: L (+2mm), XL (+4mm) and XXL (+6mm).

 

 

 

 

 

 

 

 

 

 

 

 

---