Question
A 58 year old woman with rheumatoid arthritis has bilateral groin pain and stiffness, worse on the right.
- What is the radiological diagnosis and how is it defined?
- What are the causes?
- What are the principles of hip arthroplasty here?
Answer
Definition
- Protrusio acetabuli
- Femoral head medial to the ilioischial (Kohler) line by more than 3 mm in men and 6 mm in women
- Centre edge angle over 40 degrees
Causes
- Primary (Otto pelvis)
- Rheumatoid and other inflammatory arthritis
- Paget disease and osteomalacia
- Marfan syndrome and other connective tissue disorders
- Trauma, infection and migrated implants
Arthroplasty principles
- Template to restore the hip centre lateral to the Kohler line
- In situ neck osteotomy if the head cannot be dislocated safely
- Avoid medial reaming
- Impaction grafting of the medial wall with morcellised graft
- Peripheral rim fit uncemented cup, or a cage or ring for large defects
Related pages
Author Contributions
Orthofracs team
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.