Acetabular protrusio is an intrapelvic displacement of both the acetabular fossa and femoral head so that the femoral head projects medial to the ilioischial line (i.e., Kohler line) (Figure 17.1A-C).

In contrast, in coxa profunda, only the acetabular fossa is medial to the ilioischial line (and often considered a “deep acetabular socket”).

The etiology of acetabular protrusio can be primary (e.g., osteoarthritis in middle-aged women) or secondary in nature (e.g., Paget disease, psoriatic arthritis, rheumatoid arthritis, osteogenesis imperfecta, trauma, ankylosing spondylitis).

Good exposure is key to completing an optimal total hip arthroplasty (THA) in such patients, with many THAs requiring an in situ femoral neck cut for safe exposure.

The patient’s femoral head should be kept and used for autogenous acetabular bone graft.

The patient’s acetabulum should be sequentially reamed at the introitus, gradually increasing the reamer diameter until there is a rim fit with punctate bleeding bone.

The urge to medialize the acetabular reamer, as during routine primary THAs, should be strongly resisted.

Cancellous autogenous bone graft obtained from the patient’s femoral head should then be reverse reamed in the acetabulum to fill the defect between the medial wall and trial acetabular component at the introitus of the acetabular fossa.

One may freshen the unreamed surfaces of the sclerotic medial wall with a small reamer or a burr or use a 3.5-mm drill to create punctate bleeding. Avoid weakening the already thin medial wall.

Intraoperative imaging is helpful with a trial acetabular component in place to determine restoration of the hip center of rotation, as well as acetabular component inclination and version.

Lateral decubitus position or supine at the surgeon’s discretion

The author prefers a posterior approach, as it allows for an in situ femoral neck cut, as well as excellent acetabular exposure.

Other operative approaches also are acceptable.

Utilize an anteroposterior radiograph of the hip with magnification correction to determine the appropriate hip center of rotation based on where the ilioischial line should be if acetabular protrusio were not present. Also determine the estimated acetabular component diameter (Figure 17.2). In protrusio cases the cup diameter is often a few millimeters larger than in routine primary cases in the same size patient, because this allows a “rim” fit of the cup, which avoids medial cup placement or subsequent medial migration.

Evaluate the cross-table lateral radiograph for safe placement of acetabular screws (Figure 17.1C).