What could be the cause of a depression in the gluteal (buttock) region that developed after a bout of pain, with no current pain?

Gluteal Depression Following Pain: Post-Injection Muscle Atrophy

The most likely cause of a gluteal depression that developed after a bout of pain is post-injection gluteal muscle atrophy, typically resulting from intramuscular injection (particularly corticosteroids or other medications) that caused localized muscle damage and subsequent fat atrophy at the injection site.

Primary Differential Diagnosis

Post-Injection Atrophy (Most Likely)

• Intramuscular injections in the gluteal region can cause localized tissue damage, leading to subcutaneous fat atrophy and muscle atrophy that manifests as a visible depression 1
• The initial pain represents the acute inflammatory response to injection trauma, followed by tissue resorption and depression formation as the inflammatory process resolves 1
• This is particularly common with corticosteroid injections but can occur with any intramuscular medication 2
• The depression is typically permanent or very slow to resolve, representing structural tissue loss rather than functional impairment 1

Gluteal Tendon Tear or Tendinopathy

• Gluteal tendinopathy (affecting gluteus medius or minimus tendons) presents with lateral hip pain and can cause localized muscle atrophy over time, though this typically manifests more laterally over the greater trochanter rather than in the central gluteal region 1, 3
• This condition is more common in middle-aged females and interferes with side-lying and weight-bearing activities 1
• The depression would develop gradually over months as the muscle undergoes disuse atrophy secondary to pain-related inhibition 1
• Physical examination would typically reveal tenderness over the greater trochanter and positive provocative tests (single-leg stance for 30 seconds, resisted external rotation) 3

Deep Gluteal Syndrome (Less Likely for Isolated Depression)

• Deep gluteal syndrome involves sciatic nerve entrapment in the subgluteal space, causing buttock pain and radicular symptoms, but does not typically present with isolated surface depression 4, 5, 6
• Key features include posterior hip pain, radicular pain down the leg, difficulty sitting for more than 30 minutes, and tenderness in the deep gluteal space 6
• This would not explain an isolated depression without ongoing neurological symptoms 4, 5

Clinical Evaluation Approach

History Details to Elicit

• Specifically ask about any recent injections in the gluteal region (medications, trigger point injections, corticosteroid injections) within weeks to months before pain onset 2, 1
• Determine if the initial pain was sharp and localized (suggesting injection trauma) versus gradual and activity-related (suggesting tendinopathy) 1, 3
• Assess for any ongoing functional limitations with walking, climbing stairs, or side-lying (which would suggest gluteal tendinopathy rather than simple post-injection atrophy) 1
• Ask about radicular symptoms down the leg or difficulty sitting, which would suggest deep gluteal syndrome 6

Physical Examination Findings

• Palpate the depression to determine if it involves only subcutaneous tissue/fat or extends to muscle belly 1
• Assess for tenderness over the greater trochanter (suggests gluteal tendinopathy) versus no tenderness (suggests post-injection atrophy) 3
• Perform single-leg stance test for 30 seconds—reproduction of lateral hip pain indicates gluteal tendinopathy with 100% sensitivity 3
• Test resisted hip external rotation in supine position (hip flexed 90°)—pain reproduction indicates gluteal tendinopathy with 88% sensitivity 3
• Examine for weakness in hip abduction, which would indicate significant gluteal muscle pathology 1

Diagnostic Imaging Recommendations

Initial Approach

• Plain radiographs of the pelvis and hip are reasonable first-line imaging to exclude bony pathology, though they will not demonstrate soft tissue depression 2
• If post-injection atrophy is suspected based on history and the depression is purely cosmetic without functional impairment, no further imaging may be necessary 2

Advanced Imaging When Indicated

• MRI of the pelvis/hip is the diagnostic modality of choice if gluteal tendinopathy or muscle pathology is suspected, as it can comprehensively assess the gluteus medius and minimus muscles, their tendons, and the trochanteric bursa 2, 1, 3
• MRI will show tendon tears, tendinosis, muscle atrophy, and associated bursitis with high sensitivity 3
• Ultrasound can detect trochanteric bursitis and tendinopathy but may have difficulty distinguishing between these conditions 2

Management Considerations

For Post-Injection Atrophy

• Reassure the patient that post-injection atrophy is typically a cosmetic issue without functional impairment 1
• The depression is usually permanent, though some gradual improvement may occur over 12-24 months 1
• No specific treatment reverses established fat/muscle atrophy from injection trauma 1

For Gluteal Tendinopathy (If Diagnosed)

• Management focuses on load modification through exercise and education about underlying pathomechanics 1
• Avoid excessive hip adduction positions that compress the gluteal tendons 1
• Corticosteroid injection into the trochanteric bursa can provide symptom relief, though this should be used cautiously given the risk of further tissue atrophy 2, 1
• Shock wave therapy and structured exercise programs are alternative treatments 1

Critical Pitfalls to Avoid

• Do not assume all gluteal depressions are benign—always exclude underlying tumor or abscess if there are any red flags (fever, weight loss, progressive symptoms, night pain) 4
• Distinguish between purely cosmetic post-injection atrophy (no treatment needed) versus functional gluteal tendinopathy (requires active management) 1, 3
• If corticosteroid injection is being considered for pain relief, recognize that it may worsen existing atrophy or create new depression 2, 1
• Do not miss deep gluteal syndrome if the patient has radicular symptoms—this requires different management including possible surgical decompression for refractory cases 4, 5, 6