What could be the cause of a 64-year-old female's right-sided hip pain, radiating to the groin area, with a 1-week history, following antibiotic treatment for a tooth infection, and with a past medical history of renal cysts, high cholesterol, and high blood pressure?

Right Lateral Hip Pain Radiating to Groin in 64-Year-Old Woman

You should obtain plain radiographs immediately (AP pelvis and lateral hip views) to evaluate for hip osteoarthritis, femoroacetabular impingement, or greater trochanteric pain syndrome, as this lateral hip pain with groin radiation most likely represents musculoskeletal hip pathology rather than renal disease. 1, 2

Why This Is Not Kidney-Related

• The pain location (lateral hip radiating to groin, not in the loin area), absence of fever, normal urination, and lack of flank tenderness make renal pathology extremely unlikely, despite her history of renal cysts 3, 4
• Renal pain typically presents in the costovertebral angle (loin) and radiates anteriorly to the lower abdomen, not laterally to the hip 3
• Her renal cysts are likely incidental findings unrelated to this presentation 3

Most Likely Diagnoses Based on Pain Location

Lateral Hip Pain with Groin Radiation Suggests:

Greater Trochanteric Pain Syndrome (most common):

• This is the most common cause of lateral hip pain in adults, involving gluteus medius tendinopathy, bursitis, or iliotibial band friction 3, 4
• Pain worsens with movement and weight-bearing, exactly matching her presentation 3
• Often presents in women over 40 years old 3

Hip Osteoarthritis (strong consideration given age >50):

• Classic presentation includes groin pain, but can radiate to the lateral hip and buttock 1, 3
• Pain with movement and internal rotation are typical features 1
• Age 64 makes this a primary consideration despite the lateral pain location 1, 5

Iliopsoas Tendinitis/Bursitis:

• Presents with anterior groin pain along the iliopsoas that can radiate laterally 2
• Worsens with hip flexion activities 2

Diagnostic Algorithm

Step 1: Obtain Plain Radiographs First

• Order AP pelvis and lateral femoral head-neck views bilaterally to rapidly identify hip osteoarthritis, FAI morphology, and structural abnormalities 1, 2, 3, 4
• This is the mandatory first imaging step per American College of Radiology and American Academy of Orthopaedic Surgeons guidelines 6, 1, 2

Step 2: If Radiographs Are Negative or Equivocal

• Obtain MRI of the hip without contrast to detect labral tears, early cartilage damage, bone marrow edema, soft tissue pathology, and iliopsoas bursitis 6, 1, 2
• Alternatively, ultrasound can evaluate the iliopsoas tendon dynamically and assess for greater trochanteric bursitis 6, 2

Step 3: Consider Diagnostic Injection

• Ultrasound-guided corticosteroid injection into the trochanteric bursa or iliopsoas bursa provides both diagnostic confirmation and therapeutic benefit 6, 2
• This can differentiate between intra-articular and extra-articular pain sources 2

Immediate Management While Awaiting Imaging

Initiate NSAIDs immediately:

• Strong recommendation for suspected hip osteoarthritis, greater trochanteric pain syndrome, or iliopsoas pathology 1, 2
• Provides both pain control and anti-inflammatory effect 2

Activity modification:

• Reduce weight-bearing activities that exacerbate pain 2
• Avoid prolonged standing or walking until diagnosis is confirmed 2

Physical therapy referral:

• Target hip muscle strengthening, particularly hip abductors, adductors, flexors, and rotators 1
• Include iliopsoas stretching if iliopsoas pathology is suspected 2

Critical Pitfalls to Avoid

Do not assume renal pathology without loin tenderness or urinary symptoms:

• The absence of costovertebral angle tenderness, fever, and urinary symptoms makes kidney disease extremely unlikely 3, 4
• Lateral hip pain does not represent typical renal pain distribution 3

Do not proceed to advanced imaging without plain radiographs first:

• This violates consensus guidelines and may miss important bony pathology 1, 2

Do not miss referred pain from lumbar spine:

• Examine the spine and consider spine imaging if hip examination findings are inconsistent with the pain pattern 1, 2, 4
• Lumbar radiculopathy can present with posterior or lateral hip pain 3, 4

Avoid opioids for chronic hip pain:

• Consensus recommendation against opioid use for this indication 1

Antibiotic Timing Consideration

• The temporal relationship with antibiotic treatment for tooth infection one week ago is likely coincidental rather than causative 3
• Fluoroquinolone antibiotics can rarely cause tendinopathy, but this would typically affect the Achilles tendon, not the hip region 2
• The lateral hip location and movement-related pain pattern strongly suggest primary musculoskeletal hip pathology rather than drug-induced tendinopathy 3, 4