Thumb CMC Arthroplasty: Tendons Used, Procedure, and Recovery

What Tendon Is Used for CMC Arthroplasty?

The primary tendon typically used for Carpometacarpal (CMC) joint arthroplasty, particularly the ligament reconstruction tendon interposition (LRTI) technique, is a portion of the Flexor Carpi Radialis (FCR) tendon.

Understanding CMC Joint Arthroplasty

The carpometacarpal (CMC) joint of the thumb, also known as the basal joint, is a saddle-shaped joint crucial for the thumb's wide range of motion, including opposition, flexion, extension, abduction, and adduction. This mobility, however, comes at the cost of stability, making it highly susceptible to degenerative osteoarthritis (OA), especially in post-menopausal women.

What is CMC Arthroplasty? CMC arthroplasty is a surgical procedure aimed at alleviating pain and restoring function in cases of severe CMC joint osteoarthritis. The goal is to remove the damaged joint surfaces and create a new, stable, and pain-free articulation. While several techniques exist, one of the most common and effective is the Ligament Reconstruction Tendon Interposition (LRTI) arthroplasty.

Why is it Performed? CMC arthroplasty is indicated when conservative treatments, such as splinting, anti-inflammatory medications, physical therapy, and corticosteroid injections, fail to provide adequate relief from pain, stiffness, and weakness caused by advanced CMC joint degeneration. The procedure aims to reduce bone-on-bone grinding, improve thumb strength, and enhance overall hand function.

The Role of the Flexor Carpi Radialis (FCR) Tendon

The Flexor Carpi Radialis (FCR) tendon is the workhorse in most LRTI procedures due to its anatomical location, sufficient length, and expendability.

Anatomy and Function of the FCR The FCR is one of the primary flexors of the wrist, originating from the medial epicondyle of the humerus and inserting into the base of the second and third metacarpals. Its main actions are wrist flexion and radial deviation (moving the hand towards the thumb side). Crucially, a portion of this tendon can be harvested without significantly compromising wrist function, as other wrist flexors (like the Flexor Carpi Ulnaris) and extensors can compensate.

Harvesting the FCR Tendon During an LRTI procedure, a segment of the FCR tendon (typically 10-15 cm) is harvested. This is usually done by making a small incision along the forearm or wrist, identifying the tendon, and detaching a portion while leaving its proximal attachment intact or re-routing it. The remaining FCR tendon continues to function effectively.

The LRTI Procedure Once the FCR tendon segment is harvested, the damaged trapezium bone (one of the carpal bones that articulates with the thumb metacarpal) is removed. The harvested FCR tendon is then used in two key ways:

• Ligament Reconstruction: The tendon is often woven through a drilled hole in the base of the thumb metacarpal and anchored, creating a new "ligament" to stabilize the thumb base and prevent proximal migration of the metacarpal into the space where the trapezium once was.
• Tendon Interposition: The remaining portion of the FCR tendon is then rolled up or folded and placed into the space created by the removal of the trapezium. This acts as a biological "spacer" or cushion, preventing direct bone-on-bone contact between the thumb metacarpal and the scaphoid bone, thus reducing pain and allowing for smooth, pain-free motion. This interposition helps to maintain the height of the thumb column.

Alternative Tendons and Techniques

While the FCR tendon is the most commonly utilized for LRTI, other options exist depending on surgeon preference, patient anatomy, and specific circumstances.

Palmaris Longus The Palmaris Longus tendon, a superficial tendon on the anterior forearm, is another common choice. However, it is congenitally absent in approximately 10-15% of the population. When present, it is often preferred due to its superficial location, ease of harvest, and minimal functional deficit upon removal. If available, it can serve the same reconstructive and interpositional purposes as the FCR.

Abductor Pollicis Longus (APL) Less commonly, a slip of the Abductor Pollicis Longus (APL) tendon, which helps abduct and extend the thumb, may be used. While it is involved in thumb movement, using a portion for interposition is not as common as the FCR or Palmaris Longus for the LRTI technique itself, but variations exist.

Other Surgical Approaches It's important to note that LRTI is just one type of CMC arthroplasty. Other techniques include:

• Simple Trapeziectomy: Removal of the trapezium without tendon interposition or reconstruction.
• Arthrodesis (Fusion): Fusing the joint, which provides stability but eliminates motion.
• Joint Replacement Arthroplasty: Using artificial implants (prostheses) to replace the joint surfaces. This is less common for CMC than for other large joints due to the unique biomechanics of the thumb and potential for implant wear or loosening.

Biomechanical Principles and Outcomes

The success of LRTI using the FCR (or alternative tendons) lies in its adherence to sound biomechanical principles.

Restoring Stability By reconstructing a ligament and interposing a biological spacer, the procedure aims to restore critical stability to the thumb base, preventing the metacarpal from collapsing into the carpus. This maintained "thumb column height" is essential for effective pinch and grip strength.

Pain Relief and Function The primary outcome is significant pain relief by eliminating the painful bone-on-bone grinding. Patients typically experience improved range of motion, enhanced pinch strength, and a greater ability to perform daily activities without discomfort.

Post-Operative Rehabilitation Following CMC arthroplasty, a structured rehabilitation program is crucial. This typically involves immobilization in a cast or splint for several weeks, followed by gradual mobilization exercises, strengthening, and occupational therapy to regain full function. Adherence to this program is vital for optimal long-term outcomes.

Conclusion

The Flexor Carpi Radialis (FCR) tendon is overwhelmingly the tendon of choice for ligament reconstruction tendon interposition (LRTI) arthroplasty of the thumb CMC joint. Its anatomical suitability, functional expendability, and proven efficacy make it an excellent biological material for creating a stable, pain-free, and functional thumb base. While other tendons like the Palmaris Longus can be utilized, the FCR remains the standard for this common and effective surgical solution to advanced thumb basal joint osteoarthritis.