Chapter 24 Arthroscopic Thumb Carpometacarpal Interposition Arthroplasty

10.1055/b-0035-121134

Chapter 24 Arthroscopic Thumb Carpometacarpal Interposition Arthroplasty

Introduction

Osteoarthritis in the thumb carpometacarpal (CMC) joint is a common condition, especially in women over 60 years of age. Various treatment approaches are currently being used, including fusion, prosthesis, and trapeziectomy, with or without ligament reconstruction. The outcomes are generally good with these methods, but problems persist. In the early stages of moderate osteoarthritis and normal alignment, arthroscopic interposition arthroplasty makes sense. It is straightforward for the patient and does not burn any bridges if another procedure is needed later on.

Operative Technique

Patient Preparation and Positioning

The procedure is performed under regional anesthesia. The patient’s arm is secured to the arm board. Traction is placed on the thumb using a finger trap. Only 2 to 3 kg of counterweight is needed.

Exploration of the Thumb Carpometacarpal Joint

A needle is used to locate the 1 palmar (1P) portal, which is in front of the first compartment (abductor pollicis longus and extensor pollicis brevis). This portal is located at the palmar–dorsal skin junction of the hand, or even slightly in front on the volar side ( Fig. 24.1 ). The terminal branches of the radial nerve are not a concern at this level. This portal can be enlarged as needed to accommodate the implant. The joint is identified with hemostats, and the sheath and arthroscope are inserted. Direct entry is possible because this joint is not concave as is the wrist joint. A standard 2.4 mm scope is used, although some prefer to use a smaller (1.9 mm) scope. Based on our experience, this smaller, more fragile scope is not necessary. The second portal (1 dorsal [1D]) is located using a needle and the scope’s transillumination feature; this portal is positioned behind the first compartment ( Fig. 24.2a, b ). The shaver is inserted through this portal.

**Fig. 24.1** Intraoperative view of a needle being used to locate the 1 palmar (1P) portal in front of the first compartment.

Debridement of the Thumb Carpometacarpal Joint

The thumb CMC joint is usually filled with inflamed syno-vial tissue. As a consequence, the first step is a synovectomy with the shaver ( Fig. 24.3a–c ). The shaver and scope positions can be reversed to finish the synovectomy. In some patients, the joint will contain foreign bodies that are free-floating or partially attached to the capsule. These must be completely removed ( Fig. 24.4 ).

Osteophyte Resection

Regardless of implant type, every single trapezium osteophyte must be resected. The medial osteophyte is removed first with the scope in 1D and the bur in 1P ( Figs. 24.5a–c and 24.6a–c ). The bur and scope positions are reversed to resect a lateral osteophyte ( Fig. 24.7a, b ). A pyrocarbon implant may require resection of the volar and dorsal osteophytes at the base of the first metacarpal as well.