What type of nodule is commonly found on the flexor hallucis longus (FHL) tendon?

Nodules on the Flexor Hallucis Longus Tendon

The most common nodule found on the flexor hallucis longus (FHL) tendon is a stenosing tenosynovitis nodule, which develops as part of an overuse injury that causes tendon thickening and nodule formation within the tendon sheath. 1, 2

Clinical Presentation and Pathophysiology

Nodules on the FHL tendon typically present with:

• Localized pain and tenderness along the course of the FHL tendon
• Crepitus on movement of the great toe, especially with the ankle in plantar flexion 1
• Pain with active flexion of the great toe
• Potential limitation in range of motion

These nodules develop through several mechanisms:

1. Overuse injury: Most commonly seen in ballet dancers and athletes due to repetitive stress 1, 3
2. Post-traumatic: Can develop following ankle sprains or other foot trauma 2
3. Stenosing tenosynovitis: Inflammation of the tendon sheath leading to nodule formation and adhesions 1, 2

Anatomical Considerations

The FHL tendon can develop nodules at various points along its course:

• At the fibro-osseous tunnel behind the ankle (most common location)
• At the knot of Henry (where FHL crosses the flexor digitorum longus)
• Near the insertion at the base of the distal phalanx of the hallux

Diagnostic Approach

Physical Examination

• Palpate for localized tenderness along the FHL tendon course
• Perform passive and active range of motion of the great toe
• Check for crepitus during toe movement with the ankle in plantar flexion 1

Imaging

• Ultrasound: Excellent for detecting tendon nodules, thickening, and surrounding inflammation 4
• MRI: Provides detailed evaluation of soft tissues and can detect associated inflammation and edema 4

Differential Diagnosis

1. Stenosing tenosynovitis nodule: Most common finding, with tendon thickening and nodule formation 1, 2
2. Partial longitudinal tear: Found in 71% of dancers with FHL pathology 3
3. Os interphalangeus: An ossicle located in the joint capsule of the interphalangeal joint that can be mistaken for a nodule 5
4. Tendinosis with mucinoid degeneration: Can present with nodular thickening 6
5. Rheumatoid nodule: Less common, associated with systemic rheumatoid disease 7

Management

Conservative Treatment

• Relative rest and activity modification
• NSAIDs for pain and inflammation 4
• Physical therapy focusing on gentle stretching and mobilization 4

Surgical Management

When conservative treatment fails (typically after 3-6 months):

• Arthroscopic release: Minimally invasive approach to release the tendon sheath and remove nodules 1, 2
  • Approach through standard posterolateral and posteromedial ankle portals
  • Removal of nodules and release of the tendon sheath from the superior border to the entrance of the fibro-osseous tunnel
  • Success rate of approximately 70-80% excellent or good results 2

Prognosis

• With appropriate surgical management, 81% of patients can return to the same level of activity 2
• Dancers may require longer rehabilitation periods compared to non-dancers 3
• Complication rate of approximately 18%, with reoperation rate around 4% 2

Key Points to Remember

• Stenosing tenosynovitis nodules are the most common type of nodule affecting the FHL tendon
• The condition is particularly common in ballet dancers but can occur in any individual following trauma or overuse
• Crepitus and pain on moving the great toe with the ankle in plantar flexion are diagnostic hallmarks
• Arthroscopic release is an effective treatment option with good outcomes when conservative management fails