CMC Arthroplasty: Understanding the Trapezium Removal and Recovery

What bone is removed in CMC arthroplasty?

In carpometacarpal (CMC) arthroplasty, specifically for the thumb, the trapezium bone is typically removed. This procedure, known as a trapeziectomy, aims to alleviate pain and restore function in individuals suffering from severe arthritis at the base of the thumb.

Understanding CMC Arthroplasty

Carpometacarpal (CMC) arthroplasty is a surgical procedure primarily performed to treat advanced osteoarthritis of the thumb CMC joint, also known as the basal joint of the thumb. This joint, formed by the trapezium carpal bone and the first metacarpal bone of the thumb, is crucial for the thumb's wide range of motion, allowing for pinching, grasping, and opposition. Over time, wear and tear can lead to cartilage degradation, causing pain, stiffness, weakness, and loss of function. CMC arthroplasty aims to reconstruct or replace the diseased joint to alleviate these symptoms.

The Specific Bone Removed: The Trapezium

The cornerstone of most thumb CMC arthroplasty procedures is the removal of the trapezium bone.

• Anatomical Location: The trapezium is one of the eight carpal bones located in the wrist. It sits at the base of the thumb, articulating with the first metacarpal bone to form the CMC joint, and also with the scaphoid and trapezoid bones.
• Role in Joint Function: The unique saddle shape of the trapezium's articulation with the first metacarpal allows for the extensive mobility of the thumb, including flexion, extension, abduction, adduction, and opposition.
• Why it's Removed: In severe thumb CMC arthritis, the articular cartilage on the surface of the trapezium (and the first metacarpal) erodes, leading to painful bone-on-bone grinding. Removing the trapezium eliminates this painful contact, creating a space that can then be filled or supported to allow for pain-free motion.

Why is the Trapezium Removed?

The rationale behind removing the trapezium is directly tied to the pathology of thumb CMC joint arthritis:

• Elimination of Painful Bone-on-Bone Contact: The primary goal is to remove the arthritic surfaces that are causing debilitating pain and inflammation. By excising the trapezium, the source of friction and degeneration is removed.
• Creation of a Space: Removing the bone creates a void that prevents the first metacarpal from directly grinding against the adjacent carpal bones (scaphoid or trapezoid). This space can then be managed in various ways to support the thumb's movement without pain.
• Restoration of Mobility and Stability: While the joint is "removed," the subsequent steps of the arthroplasty (often involving tendon interposition or suspension) aim to stabilize the first metacarpal and allow for improved, pain-free range of motion.

Surgical Techniques for Trapezium Excision

While the removal of the trapezium (trapeziectomy) is common, the specific techniques used to manage the resulting void can vary:

• Simple Trapeziectomy: In some cases, particularly in less active individuals, the trapezium is simply removed, and the space is allowed to fill with scar tissue. However, this can sometimes lead to shortening of the thumb or persistent instability.
• Interposition Arthroplasty: This is a very common approach where, after the trapezium is removed, a soft tissue "spacer" is placed into the void. This spacer is typically fashioned from a piece of the patient's own tendon (e.g., a portion of the flexor carpi radialis or abductor pollicis longus tendon) or, less commonly, an artificial implant. The purpose is to prevent bone-on-bone contact and provide a cushion.
• Suspensionplasty: Often performed in conjunction with interposition, this technique uses a portion of a local tendon (like the flexor carpi radialis or abductor pollicis longus) to create a sling or suspension to support the base of the first metacarpal and prevent it from collapsing into the void. This helps maintain thumb length and stability.
• Trapeziectomy with Ligament Reconstruction and Tendon Interposition (LRTI): This is a widely adopted technique that combines the removal of the trapezium with the reconstruction of ligaments and the interposition of a tendon graft.

Post-Operative Recovery and Rehabilitation

Recovery after CMC arthroplasty typically involves several stages to ensure optimal outcomes:

• Immobilization: The hand and thumb are usually immobilized in a cast or splint for several weeks (e.g., 4-6 weeks) to allow initial healing and stabilization of the new joint space.
• Physical or Occupational Therapy: Following immobilization, a structured rehabilitation program is crucial. This typically involves:
  • Early Range of Motion: Gentle exercises to restore movement without stressing the healing tissues.
  • Strengthening: Progressive exercises to rebuild grip and pinch strength.
  • Functional Training: Activities that mimic daily tasks to improve practical use of the hand and thumb.
• Gradual Return to Activity: Patients are guided through a progressive return to normal activities, with full recovery often taking several months.

Potential Outcomes and Considerations

The goal of CMC arthroplasty is significant pain relief and improved thumb function.

• Pain Relief: Most patients experience substantial reduction or elimination of the pain associated with thumb CMC arthritis.
• Improved Function: Enhanced ability to perform daily activities, grip, and pinch without discomfort.
• Strength: While initial strength may be reduced, it typically improves over time with rehabilitation, though it may not always return to pre-arthritis levels.
• Thumb Length: There can be some shortening of the thumb after a trapeziectomy, though suspensionplasty techniques aim to minimize this.
• Complications: As with any surgery, potential risks include infection, nerve injury, persistent pain, or instability, though these are relatively uncommon.

Conclusion

In summary, the removal of the trapezium bone is the defining feature of most CMC arthroplasty procedures for severe thumb arthritis. By excising this degenerated carpal bone, surgeons effectively eliminate the source of pain and create a functional space that, through various reconstructive techniques, allows for the restoration of a pain-free and mobile thumb. For individuals experiencing debilitating pain and loss of function due to thumb CMC arthritis, this surgical intervention offers a highly effective pathway to improved quality of life. Consultation with a qualified hand surgeon is essential to determine the most appropriate course of treatment.