Corticosteroid Injection for Plantar Nerve Lesion and Metatarsalgia
Corticosteroid injection into the 3rd digital interspace is medically indicated for this patient with plantar nerve lesion (likely Morton's neuroma) and metatarsalgia, particularly if initial conservative measures have been attempted or failed. 1
Clinical Justification
The American College of Foot and Ankle Surgeons guidelines explicitly recommend corticosteroid injections as part of the treatment algorithm when initial conservative measures fail to provide adequate relief for conditions like Morton's neuroma. 1 This represents standard-of-care treatment for plantar nerve pathology presenting with forefoot pain.
Diagnostic Considerations
- Morton's neuroma (plantar digital neuritis) is a syndrome caused by neuroma development in a digital nerve just proximal to its bifurcation, causing severe neuralgic pain in the distal sole referred to the corresponding toes. 2
- MRI has 93% sensitivity for Morton's neuroma diagnosis, though clinical diagnosis combined with imaging findings supports treatment decisions. 1
- The 3rd intermetatarsal space is a classic location for Morton's neuroma, making the injection anatomically appropriate. 2
Treatment Algorithm Position
Conservative management should ideally precede injection therapy, including NSAIDs and orthotic devices. 1 However, corticosteroid injection is recognized as both a diagnostic and therapeutic tool that is appropriate when:
- Initial conservative treatment has been attempted
- Pain significantly impacts function
- The patient requires more definitive intervention 1
The British Journal of Dermatology guidelines recommend triamcinolone acetonide as the preferred agent, with injections placed beside the neuroma rather than directly into it. 1
Evidence for Effectiveness
While evidence quality varies across foot conditions, corticosteroid injection combined with local anesthetic has been the standard treatment for Morton's metatarsalgia since at least 1987. 2 The injection serves dual purposes:
- Therapeutic effect from corticosteroid anti-inflammatory action
- Diagnostic confirmation if pain relief occurs with the anesthetic component 2
Safety Considerations and Precautions
Important Caveats
Diabetic patients require special counseling: They should be informed about transient hyperglycemia risk, particularly days 1-3 post-injection, and advised to monitor glucose levels closely during this period. 3, 4
Timing Restrictions
- Avoid injection within 3 months of planned joint replacement surgery if applicable to adjacent joints. 3, 4
- The decision to reinject should consider response to previous injections. 3, 4
Post-Injection Management
- Avoid overuse of the injected area for 24 hours following injection, though prolonged immobilization is discouraged. 3
- Patients should be counseled on expected recovery timeline and when to seek re-evaluation. 1
Potential Complications
While serious adverse events are rare with digital nerve blocks, patients should be informed of:
- Transient post-injection pain (common, managed with ice and analgesia) 5
- Infection risk (very rare, approximately 3 per 699 injections in pooled data) 5
- Fat pad atrophy with repeated injections (theoretical concern) 5
Critical distinction: The plantar fascia rupture risk associated with corticosteroid injection for plantar fasciitis 6 is not applicable to digital nerve blocks in the intermetatarsal space, as the injection site and target tissue are anatomically distinct.
Documentation Requirements
Informed consent should be obtained and documented, explaining:
- Nature of the procedure
- Potential benefits and risks
- Alternative treatment options
- Expected outcomes 3
This injection is medically indicated and represents appropriate, guideline-concordant care for the documented diagnoses. 1