What should I do for a knot under the skin after an Intramuscular (IM) injection?

Management of Post-IM Injection Subcutaneous Nodule

A knot under the skin after an IM injection is typically a benign, self-limited complication that requires conservative management with warm compresses, gentle massage, and observation—most resolve spontaneously within days to weeks without intervention.

Immediate Assessment

First, determine the nature and severity of the nodule:

• Assess for concerning features that suggest vascular compromise: skin blanching, livedo reticularis, slow capillary refill, dusky blue-red discoloration, or severe immediate pain 1, 2
• Check for signs of infection: increasing warmth, expanding erythema, purulent drainage, fever, or systemic symptoms
• Evaluate the nodule characteristics: size, tenderness, mobility, and whether it's firm or fluctuant

Conservative Management (First-Line)

For uncomplicated subcutaneous nodules without concerning features:

• Apply warm compresses to the affected area 3-4 times daily for 15-20 minutes to promote absorption and reduce inflammation 1
• Perform gentle massage of the area to help disperse the medication and reduce nodule formation 1
• Avoid further injections at the same site and rotate injection sites systematically to prevent recurrence 3, 4
• Monitor for resolution over 1-2 weeks, as most nodules resolve spontaneously with conservative measures

When to Escalate Care

Seek immediate medical attention if any of the following develop:

• Vascular compromise signs: Progressive skin discoloration, blanching, or tissue necrosis suggesting inadvertent intra-arterial injection—this represents a medical emergency requiring immediate intervention 1, 2
• Severe pain that is disproportionate to examination findings or worsening despite conservative measures 2
• Signs of infection: Fever, expanding erythema, purulent drainage, or systemic symptoms
• Persistent nodule beyond 2-4 weeks that is enlarging or becoming increasingly symptomatic 5

Prevention Strategies

To minimize future nodule formation:

• Use proper injection technique: Insert needle at 90-degree angle into appropriate muscle (deltoid, anterolateral thigh, or ventrogluteal area) 3
• Select appropriate needle length: Use 1-1½ inch needle for adults to ensure proper muscle penetration and avoid subcutaneous deposition 3
• Rotate injection sites systematically: Inject at least 1 cm from previous sites and use different anatomical areas 3, 4
• Inject slowly with steady pressure to minimize tissue trauma 6
• Allow medication to reach room temperature before injection to reduce tissue irritation 4

Common Pitfalls to Avoid

• Do not apply ice initially, as this may worsen tissue injury and delay absorption
• Avoid needle reuse, which increases tissue trauma and nodule formation risk 6
• Do not inject into areas with existing lipohypertrophy or previous nodules, as this impairs absorption and increases complications 4
• Never assume all nodules are benign—always assess for vascular compromise, which requires emergency treatment 1, 2

Special Considerations

The nodule may represent:

• Subcutaneous medication deposition from inadequate needle length or improper technique (most common)
• Local inflammatory reaction to the injected substance 7
• Hematoma formation from vessel trauma during injection
• Rare but serious vascular injury if associated with pain and skin changes 1, 2

Most post-injection nodules are benign injection site reactions that resolve with conservative management within 1-2 weeks 7. However, maintaining vigilance for signs of vascular compromise or infection is essential, as these require urgent intervention to prevent significant morbidity 1, 2.