What are the recommended next steps for managing increasing prominence of left protrusio acetabuli on X-ray?

Management of Increasing Prominence of Left Protrusio Acetabuli on X-ray

Refer immediately to an orthopedic surgeon for evaluation and consideration of joint-preserving surgery, as progressive protrusio acetabuli represents a structural hip deformity that requires specialized assessment to prevent irreversible cartilage damage and determine optimal timing for intervention.

Understanding Protrusio Acetabuli

Protrusio acetabuli is a hip joint deformity where the medial acetabular wall invades into the pelvic cavity with associated medial displacement of the femoral head 1. The condition is definitively diagnosed on anteroposterior (AP) pelvic radiographs when the acetabular line projects medial to the ilioischial line 2.

Key radiographic criteria for diagnosis include:

• Center-edge angle of Wiberg >50 degrees 3
• Acetabular-ilioischial distance ≥3 mm in males or ≥6 mm in females 3
• Acetabular line medial to the ilioischial line on AP pelvis radiographs 4, 2

Immediate Diagnostic Workup

Obtain the following imaging and measurements:

• High-quality AP pelvis radiograph with hips in neutral position to accurately assess acetabular depth and femoral head position 5, 2
• Measure center-edge angle of Wiberg and acetabular-ilioischial distance to quantify severity 3
• Evaluate for negative acetabular roof angle and enlarged acetabular fossa, which suggest posteroinferior joint destruction from pincer impingement rather than excessive medial forces 2

Determine Underlying Etiology

The increasing prominence demands investigation for secondary causes, as protrusio can result from:

• Primary idiopathic causes 1
• Inflammatory arthropathies (rheumatoid arthritis, ankylosing spondylitis) 4
• Metabolic disorders (osteomalacia, Paget's disease) 1
• Genetic conditions (Marfan syndrome, where prevalence reaches 27% by age 20) 3
• Neoplastic, infectious, or traumatic processes 1
• Osteopenic bone states predisposing to progressive deformity 6

Clinical Assessment Priorities

Evaluate hip function systematically:

• Calculate Iowa hip score to quantify functional impairment 3
• Measure range of motion in all planes, as protrusio correlates with decreased hip mobility 3
• Assess pain severity and its impact on activities of daily living 3
• Document any mechanical symptoms suggesting cartilage damage or impingement 2

Critical finding: In Marfan syndrome patients over 40 years old, protrusio generally does not cause severely problematic hip function, though it associates with slightly decreased range of motion 3. However, progressive protrusio in other contexts warrants more aggressive intervention.

Treatment Algorithm Based on Age and Cartilage Status

For younger patients with preserved cartilage:

• Modern decision-making relies on advanced cartilage evaluation, not just AP radiographs and patient age 2
• Joint-preserving surgery must be tailored to individual hip morphology 2
• Consider valgus femoral osteotomy as the primary joint-preservation technique, though this must be individualized based on the specific deformity pattern 2
• Recognize that destruction in protrusio hips begins less in the medial joint area and more in the posteroinferior joint, driven by pincer impingement rather than excessive medially directed forces 2

For patients with advanced cartilage loss:

• Total hip arthroplasty becomes necessary when joint preservation is no longer feasible 6
• Surgical planning must address reestablishment of anatomic acetabular position and construction of medial prosthetic or biologic buttress 6
• Severe cases may require bulk, chipped, or pulverized allograft/autograft bone for medial wall reconstruction 6
• In extreme intrapelvic protrusion, resection arthroplasty may be the only alternative 6

Monitoring Strategy

For patients not immediately requiring surgery:

• Serial AP pelvis radiographs to document progression rate 3
• Repeat Iowa hip scores and range of motion measurements to track functional decline 3
• Reassess cartilage status if symptoms worsen or radiographic progression accelerates 2

Critical Pitfalls to Avoid

Do not delay orthopedic referral: The window for joint-preserving surgery closes once cartilage destruction becomes advanced 2. Early specialist evaluation allows for optimal timing of intervention.

Do not assume benign course: While protrusio in Marfan syndrome may remain relatively asymptomatic 3, progressive protrusio from other causes can lead to irreversible joint damage requiring complex reconstructive surgery 6.

Do not rely solely on AP radiographs: Modern surgical decision-making requires advanced cartilage evaluation and understanding of the specific morphologic pattern driving the deformity 2.