What is the likely differential diagnosis (DDX) for a patient with a painful bony protrusion on the side of a previous hip fixation with nail placement by an orthopedic (ortho) specialist?

Differential Diagnosis of Painful Bony Protrusion After Hip Nail Fixation

The most likely diagnosis is hardware prominence with nail protrusion over the greater trochanter causing soft tissue irritation, gluteus medius injury, and potential hematoma formation. 1

Primary Differential Diagnoses

Hardware Prominence/Protrusion (Most Likely)

• Nail protrusion over the greater trochanter can cause chronic hip and thigh pain by damaging soft tissues around the gluteus medius, potentially leading to delayed hematoma formation even months after surgery. 1
• This complication occurs when the cephalomedullary nail extends beyond the greater trochanter, creating mechanical irritation of overlying soft tissues 1
• Patients typically present with chronic pain that may suddenly worsen if hematoma develops 1
• Radiographs should be the first imaging modality to assess hardware position and identify protrusion. 2, 3

Heterotopic Ossification (HO)

• HO is a common complication after hip surgery with frequency varying from 15-90%, presenting as painful bony protrusion in soft tissues around the hip. 4
• Risk factors include male gender, hip ankylosis, and previous history of HO 4
• Diagnosis is based on AP radiographs using the Brooker classification (grades I-IV), with bone scan as confirmatory testing. 4
• Radiographs help assess heterotopic ossification as a cause of lateral hip pain 2

Periprosthetic/Hardware-Related Complications

• Greater trochanter fractures or avulsions can occur and are assessed on radiographs, though seemingly isolated fractures frequently have occult intertrochanteric extension requiring advanced imaging. 2, 3
• Periosteal bone reaction visible on CT is a specific finding for complications 2
• Trochanteric surface irregularities >2mm may indicate abductor tendon abnormalities 2

Diagnostic Approach

Initial Imaging

• Obtain AP pelvis and lateral hip radiographs first to evaluate hardware position, heterotopic ossification, periprosthetic fractures, and greater trochanter pathology. 2, 3
• Compare with prior postoperative radiographs to assess for hardware migration or progressive changes 2

Advanced Imaging When Radiographs Are Equivocal

• If radiographs are negative or equivocal but clinical suspicion remains high, obtain MRI for fracture detection, soft tissue evaluation, and hematoma identification. 3
• MRI with metal artifact reduction sequences (MARS-MRI) enables evaluation of soft tissues around the prosthetic hip, particularly the pseudocapsule and tendons 5
• MRI is particularly valuable as occult intertrochanteric extension frequently accompanies seemingly isolated greater trochanter pathology. 3
• CT with metal artifact reduction (MAR) provides detailed assessment of bony structures and hardware position 5
• Ultrasound can assess soft tissues adjacent to hardware without metal artifacts 5

Key Clinical Pitfalls

Avoid Misdiagnosis

• Do not dismiss chronic hip pain after nail fixation as simple bursitis—consider hardware protrusion with soft tissue injury and potential hematoma formation. 1
• The American College of Radiology warns that extracapsular disease could be misinterpreted as trochanteric bursitis 5

Hardware Assessment

• Carefully evaluate whether the nail protrudes beyond the greater trochanter on lateral radiographs, as this is the primary mechanism for soft tissue damage. 1
• Even with radiographic bone healing, hardware prominence can cause persistent symptoms requiring removal 1

Timing Considerations

• Heterotopic ossification typically develops in the early postoperative period but continues to mature over months 4
• Delayed hematoma from hardware irritation can occur suddenly even 1-2 years after surgery without new trauma 1

Management Implications

• If hardware protrusion is confirmed as the cause, nail removal resolves chronic pain without complications such as femoral neck fracture in appropriately healed cases. 1
• For heterotopic ossification causing functional deficit, revision arthroplasty with HO resection is the definitive treatment 4
• Prevention of future cases requires ensuring the nail does not protrude over the greater trochanter during initial fixation 1