Summary

Arthritis of the Tarsometatarsal (TMT) joints, also known as Midfoot Arthritis, is a common cause of dorsal foot pain and difficulty wearing shoes. It primarily affects the 2nd and 3rd TMT joints (the rigid "Keystone" of the foot), often as a sequela of old Lisfranc injuries or simply primary degeneration. A hallmark sign is the formation of a large dorsal osteophyte known as the "100 Dollar Bump" (or "Saddle Bone"), which rubs against laces. Treatment emphasizes stiff-soled shoes to minimize midfoot stress. Surgery involves fusion (Arthrodesis) of the Medial and Middle columns, while the Lateral column (4th/5th) is usually preserved to maintain foot accommodation. [1,2,3]

Key Facts

• The Column Theory:
  • Medial Column (1st Ray): Mobile. Essential for shock absorption.
  • Middle Column (2nd/3rd Rays): Extremely rigid. The "Keystone". Most Prone to Primary OA.
  • Lateral Column (4th/5th Rays): Mobile. Essential for uneven ground.
• The "100 Dollar Bump": midfoot bossing (osteophytes) creates a prominence. It's called the $100 bump because you can't wear cheap shoes anymore; you need expensive, custom-fit footwear.
• Fusion Rule: You can fuse the 1st, 2nd, and 3rd TMT joints with impunity (they don't move much anyway). NEVER fuse the 4th and 5th if possible—it leads to a stiff, painful lateral foot and stress fractures.

Clinical Pearls

"Lace Pain": The most specific historical clue. "My foot hurts right where I tie my shoelaces."

"Piano Key Test": Provocative maneuver. Hold the hindfoot and stress individual metatarsals up and down. Pain localizes the specific arthritic joint.

"Charcot Mimic": In a diabetic patient with new midfoot swelling/pain, this is Charcot Neuroarthropathy (active phase) until proven otherwise. Do not inject steroids!

                 MIDFOOT PAIN
                       ↓
             X-RAY: TMT ARTHRITIS
            ┌──────────┴──────────┐
        COLUMN 1/2/3            COLUMN 4/5
             ↓                       ↓
       CONSERVATIVE            CONSERVATIVE
   (Stiff Sole / NSAID)        (Wide Shoe)
             ↓                       ↓
          FAILED?                 FAILED?
             ↓                       ↓
          FUSION               RESECTION
      (Arthrodesis)           (Arthroplasty)

Protocol

• Stiff Soles: Carbon fiber insert or Hiking boots. The goal is to stop the midfoot from bending (acting as a lever) during pushoff.
• Rocker Bottom: Rolls the foot forward, bypassing the hinge.
• Lacing Technique: "Skip lacing" (skipping the eyelets over the bump) to reduce direct pressure.
• Injections: Fluoroscopic guided steroid injections. Diagnostic and therapeutic (3-6 months relief).

1. Arthrodesis (Fusion)

• Indication: Painful arthritis of Medial/Middle columns (1st, 2nd, 3rd) failing conservative care.
• Technique:
  • Dorsal incisions. Avoid NV bundle (DP artery/Deep Peroneal Nerve).
  • Remove cartilage + Osteophytes.
  • Correct deformity (restore arch height).
  • Fixation: Plates (dorsal) or Screws (compression).
  • Bone Graft: Often needed (Autograft from Calcaneus or Tibia).
• Outcome: 90% fusion rate. Good pain relief. Foot feels "solid".

2. Exostectomy (Bump Removal)

• Indication: Pain is largely from shoe pressure on the osteophyte, with minimal deep joint pain.
• Procedure: Simple shaving of the dorsal boss.
• Risk: Does not treat the underlying arthritis.

3. Interposition Arthroplasty

• Indication: 4th and 5th TMT joints.
• Rationale: Fusing these joints causes stiffness and stress fractures. Instead, removing the joint surfaces and putting a spacer (tendon/capsule) maintains motion and relieves pain.

To Plate or to Screw?

• IOF Study: Compression screws offer higher compressive forces, but Dorsal Plates offer more stiffness/stability. A "Hybrid" construct (Screw + Plate) is currently considered the strongest.

4th and 5th Joint

• Shawen et al: Confirmed that fusion of the lateral column leads to poor patient satisfaction due to stiffness and lateral foot pain. Resection arthroplasty is superior.

The Condition

The "bridge" of your foot has stiffened and worn out. A bone spur has grown on top, which is why your laces hurt.

The Fix (Fusion)

We will weld the worn-out bones together.

• "Will my foot be stiff?" It is already stiff from the arthritis. Fusing it won't make it much stiffer, but it will stop the pain.
• "Can I wear heels?" No. Flat, comfortable shoes mainly.
• "Recovery?" 6-12 weeks in a cast/boot. It is a slow healer.

Q1: Why do we avoid fusing the 4th and 5th TMT joints? A: The lateral column requires mobility (approx 10mm sagittal motion) to accommodate uneven ground and allow physiological foot twist. Fusing it creates a rigid lateral lever, leading to pain and stress fractures of the metatarsals.

Q2: Which nerve is most at risk during the approach to the 1st/2nd TMT joint? A: Deep Peroneal Nerve and the accompanying Dorsalis Pedis Artery. They run in the interval between the EHL and EDL tendons, directly over the joints.

Q3: What is the "Beam Effect" in midfoot fusion? A: Placing a long axial screw from the metatarsal head up into the cuneiforms/tarsus. It acts like an intramedullary nail ("Beam"), providing superior resistance to bending forces compared to dorsal plates alone.

(End of Topic)