TMT Fusion: What It Is, Procedure, Recovery, and Risks

What is a TMT fusion?

A TMT fusion, also known as tarsometatarsal arthrodesis, is a surgical procedure that permanently joins one or more bones of the midfoot's tarsometatarsal joints, typically performed to alleviate pain, correct deformity, or stabilize the foot due to severe arthritis, instability, or complex injuries.

Understanding the Tarsometatarsal (TMT) Joint

The tarsometatarsal (TMT) joints, often referred to as Lisfranc joints, are a group of five joints located in the midfoot where the cuneiform and cuboid bones (tarsals) articulate with the bases of the five metatarsal bones. These joints are crucial for the foot's complex biomechanical function.

• Anatomy of the TMT Joints:

  • First TMT Joint: Connects the medial cuneiform to the first metatarsal.
  • Second TMT Joint: Connects the intermediate cuneiform to the second metatarsal. This joint is often considered the "keystone" of the midfoot arch due to its recessed position and strong ligamentous attachments.
  • Third TMT Joint: Connects the lateral cuneiform to the third metatarsal.
  • Fourth and Fifth TMT Joints: Connect the cuboid bone to the fourth and fifth metatarsals, respectively.
  • These joints are reinforced by a complex network of ligaments, providing stability while allowing for subtle movements.

• Function of the TMT Joints:

  • While individual TMT joints have limited motion, their collective movement allows the midfoot to adapt to uneven surfaces, absorb shock, and contribute to the foot's ability to transition from a flexible structure during initial ground contact to a rigid lever for propulsion during toe-off.
  • They play a vital role in maintaining the longitudinal and transverse arches of the foot, distributing weight, and facilitating efficient gait mechanics.

What is a TMT Fusion?

A TMT fusion, or tarsometatarsal arthrodesis, is a surgical procedure designed to eliminate motion at one or more of the TMT joints by permanently joining the bones together.

• Definition of Fusion (Arthrodesis): Arthrodesis is a surgical technique that involves removing the cartilage from the ends of the bones in a joint and then using plates, screws, or other hardware to hold the bones together until they grow and fuse into a single, solid bone. This eliminates pain caused by joint motion but also removes all movement from that specific joint.

• Purpose of TMT Fusion: The primary goal of a TMT fusion is to:

  • Alleviate Pain: By eliminating motion in an arthritic or unstable joint, the pain associated with movement and degeneration is resolved.
  • Correct Deformity: It can correct severe midfoot deformities, such as those seen in advanced flatfoot or Charcot neuroarthropathy, restoring proper foot alignment.
  • Stabilize the Foot: In cases of severe instability or complex fracture-dislocations (Lisfranc injuries), fusion provides a stable, rigid platform for weight-bearing.

• Conditions Leading to TMT Fusion:

  • Severe TMT Joint Arthritis: Often caused by trauma (e.g., Lisfranc injury), inflammatory conditions (e.g., rheumatoid arthritis), or osteoarthritis.
  • Lisfranc Injury: A severe injury to the TMT joints, involving fracture and/or dislocation, especially if chronic instability or arthritis develops post-injury.
  • Charcot Neuroarthropathy: A progressive degenerative joint disease affecting individuals with neuropathy (e.g., diabetes), leading to severe foot deformity and instability.
  • Midfoot Deformities: Conditions like adult acquired flatfoot deformity (pes planovalgus) where non-surgical treatments or less invasive procedures have failed.

The Surgical Procedure

A TMT fusion is typically performed by an orthopedic foot and ankle surgeon.

• Pre-operative Considerations: Patients undergo thorough evaluations, including X-rays, CT scans, or MRI, to assess the extent of joint damage and plan the precise fusion sites. Medical clearance is also obtained.
• Steps of the Surgery:
  1. Incision: One or more incisions are made on the top (dorsal) aspect of the midfoot, over the affected TMT joints.
  2. Joint Preparation: The surgeon carefully exposes the target TMT joints. All remaining articular cartilage is meticulously removed from the bone surfaces to promote direct bone-to-bone healing.
  3. Bone Grafting: In many cases, a bone graft (autograft from the patient or allograft from a donor) is packed into the joint space to enhance fusion and promote faster healing.
  4. Fixation: The bones are then held rigidly in place using internal fixation devices, most commonly screws, plates, or a combination of both. This hardware provides stability until the bones naturally fuse.
  5. Closure: The incisions are closed in layers, and a sterile dressing and splint or cast are applied.
• Anesthesia: The procedure is typically performed under general anesthesia, often combined with a regional nerve block for post-operative pain control.

Recovery and Rehabilitation

Recovery from a TMT fusion is a lengthy process, often taking several months, and requires significant patient compliance.

• Immediate Post-operative Phase (Non-weight-bearing):
  • For the first 6-12 weeks, the foot is kept immobilized in a cast or boot, and strict non-weight-bearing is enforced to allow the bones to begin fusing. Crutches, a walker, or a knee scooter are necessary.
  • Elevation and ice are crucial to manage swelling.
  • Pain medication will be prescribed.
• Transition to Weight-bearing:
  • Once X-rays confirm early signs of fusion, typically around 6-12 weeks, the surgeon will gradually allow partial weight-bearing in a protective boot.
  • Physical therapy often begins during this phase, focusing on gentle range of motion for non-fused joints and maintaining strength in the rest of the limb.
• Rehabilitation Goals:
  • Restore Gait Mechanics: Re-educating the body to walk with the fused joint, adapting to the altered foot mechanics.
  • Improve Strength and Endurance: Strengthening the muscles of the leg and foot to compensate for the lack of motion in the fused joint.
  • Enhance Balance and Proprioception: Re-training the body's sense of position and balance, which can be affected by changes in foot mechanics.
  • Minimize Compensatory Strain: Addressing any compensatory movements that might put undue stress on adjacent joints or other parts of the kinetic chain.
• Long-term Considerations: Full bone healing can take 6-12 months, and maximum recovery of function may take up to a year or more. Activity levels will gradually increase under guidance from the surgical and rehabilitation team.

Potential Risks and Complications

While generally successful, TMT fusion, like any surgery, carries potential risks.

• Common Surgical Risks:
  • Infection: Risk of bacterial infection at the surgical site.
  • Bleeding: Excessive bleeding during or after surgery.
  • Nerve Damage: Injury to nerves, potentially causing numbness or weakness.
  • Blood Clots: Deep vein thrombosis (DVT) or pulmonary embolism (PE).
• Specific TMT Fusion Risks:
  • Non-union (Pseudoarthrosis): Failure of the bones to fuse properly, requiring further surgery. This is a significant concern and can be influenced by factors like smoking, diabetes, and bone quality.
  • Mal-union: Bones fuse in an improper alignment, leading to persistent pain or functional issues.
  • Hardware Complications: Screws or plates may become painful, break, or loosen, necessitating removal.
  • Adjacent Joint Arthritis: Increased stress on the joints immediately adjacent to the fusion site can lead to accelerated degeneration and pain in those joints over time.
  • Chronic Pain: Despite successful fusion, some patients may experience ongoing discomfort.

Life After TMT Fusion: Functional Implications

A TMT fusion significantly alters the biomechanics of the foot, which has lasting implications for mobility and activity.

• Impact on Gait and Mobility:
  • The fused joint becomes rigid, eliminating the subtle adaptability of the midfoot. This can lead to a stiffer gait and reduced shock absorption through the midfoot.
  • Patients often learn to compensate by increasing motion at the ankle and other foot joints, or by adjusting their stride.
  • While high-impact activities might be limited, most patients can return to daily walking, light exercise, and many recreational activities.
• Activity Modifications:
  • High-impact activities such as running, jumping, and aggressive court sports are often discouraged or significantly modified to protect the fused joint and surrounding structures.
  • Activities like swimming, cycling, and elliptical training are generally well-tolerated and encouraged for cardiovascular fitness.
• Importance of Footwear:
  • Supportive, well-cushioned footwear with a rigid sole is often recommended to help manage forces across the foot and provide stability.
  • Custom orthotics may be prescribed to optimize foot alignment and comfort.

Conclusion

A TMT fusion is a complex and often life-changing surgical procedure aimed at alleviating severe midfoot pain, correcting deformity, and stabilizing the foot. While it eliminates motion in the fused joints, it can significantly improve quality of life for individuals suffering from debilitating conditions like advanced arthritis or severe Lisfranc injuries. Understanding the intricate anatomy of the midfoot, the purpose of the fusion, and the commitment required for rehabilitation is crucial for patients contemplating this procedure and for fitness professionals guiding individuals through their recovery journey. Through diligent rehabilitation and appropriate activity modification, many individuals can regain substantial function and return to a fulfilling, active lifestyle.