Protrusio acetabuli: new insights and experience with joint preservation

Abstract

Protrusio acetabuli is identified on anteroposterior (AP) radiographs of the pelvis with an acetabular line projecting medial to the ilioischial line. We documented this radiographic sign and additional radiographic parameters in 19 patients (29 hips) with protrusio and compared the parameters to those of 29 older patients (29 hips) with advanced primary osteoarthritis (OA) but no protrusio and 12 younger patients (22 hips) with protrusio but no advanced OA. A negative acetabular roof angle and particularly large acetabular fossa were more apparent in younger patients; these hips suggest the destruction of a protrusio hip begins less in the medial joint area and more in the posteroinferior joint, and the mechanism is driven less by excessive medially directed forces but by a pincer impingement. While the indication for joint-preserving surgery currently consists primarily of a valgus femoral osteotomy based on AP radiographs and patient age, modern decision making also relies on cartilage evaluation and requires advanced surgical techniques. We conclude joint-preservation surgery must be tailored to the individual hip morphology.

Fig. 1

(A) In a normal hip, the acetabulum sufficiently covers the femoral head. (B) In coxa profunda, the head is more medial with the acetabular fossa being at or medial to the ilioischial line. (C) In protrusio, the femoral head is close, at or medial to the ilioischial line and the acetabular roof is negatively tilted with the center of the femoral head being medial to the anterior and posterior acetabular walls. (Reprinted with permission from Leunig, M., Huff, T., Ganz, R. Femoroacetabular impingement: Treatment of the acetabular side. In: Azar FM, O’Connor MI (eds). Instructional Course Lectures 58. Rosemont, IL: American Academy of Orthopaedic Surgeons; 2009:223–229.)

Fig. 2

A 23-year old female patient with bilateral protrusio acetabuli had severe bilateral hip pain and globally restricted ROM since childhood. Protrusio acetabulum with acetabular line (dashed line) crossing the ilioischial line (solid line) by 6 mm in females and 3 mm in males.

Fig. 3A–B

(A) A 22-year old female patient with bilateral borderline protrusio with severe negative inclination of the acetabular roof complained of global limitations in ROM and bilateral hip pain (left worse than right). (B) Coronal cut of an MR arthrography demonstrates that the acetabular fossa extends far into the weight-bearing zone of the roof, and therefore, rim trimming in such a morphological constellation would further reduce the cartilaginous weight-bearing zone to a critical range.

Fig. 4A–B

(A) The false profile view of the left hip of a 37-year old female patient with bilateral protrusion who complained of worsening symptoms and loss of extension on the left side is shown. While the superior joint space is preserved, there is marked joint space narrowing in the posteroinferior aspect of the joint. A prominent ossification of the inferior rim is visible, indicating posteroinferior impingement. (B) Computer tomography revealed that the area of cartilage destruction and subchondral cyst formation in the posteroinferior joint is even more extensive than on the false profile view. A large bone apposition of the inferior rim can be seen, explaining the impingement and loss of extension.

Fig. 5

An intraoperative image of a surgically dislocated femoral head of a protrusion hip shows severe cartilage abrasions of the posterior contour of the head with a corresponding acetabular cartilage lesion (not shown). With head relocation, the impingement mechanism can be reproduced, and the mode of origin of the “contre coup lesion” [30] can be observed.

Fig. 6A–B

(A) Shown is a 24-year old female patient with post-traumatic protrusio acetabuli after nonoperative treatment of a complex acetabular fracture. (B) An ilioinguinal approach was utilized, and the periacetabular osteotomy allowed manipulation of the acetabular fragment such that the acetabulum was lateralized with anatomic correction of the pubic ramus with a 16-hole pelvic reconstruction plate.

Fig. 7A–B

(A) Bilateral protrusio acetabuli in a 25-year old female patient with an underlying diagnosis of osteogenesis imperfecta with complaints of limited ROM until a fatigue fracture of the acetabular fossa. MR arthrography revealed mild cartilage injury around the medial contour of the head. (B) Three-year postoperative radiographs demonstrated a lateralized acetabulum with a horizontal roof and healing of the fatigue fracture; however, the craniomedial joint space remained narrow.

Fig. 8A–B

(A) A radiograph of a 16-year old male with bilateral protrusio acetabuli and coxa vara with right-sided medial joint space narrowing is shown. The preoperative radiographs demonstrated a pincer acetabulum with a horizontal roof, and therefore, an acetabular reorientation would not address the underlying pathomorphology. (B) Radiographs at 2 years after surgery on the right side and 1.5 years on the left side demonstrated rim trimming with circumferential bone anchors after labral refixation. The right hip revealed a slight increase in medial joint space. The 30° valgus osteotomy improved the joint clearance substantially resulting in markedly improved ROM.

Fig. 9

The treatment algorithm for protrusio joint preservation surgery is shown. We used MRA with radial sequences to determine the status of the articular cartilage. In cases without cartilage degeneration, open surgical dislocation with osteochondroplasty of the acetabular rim and femoral neck is recommended. Valgus ITO may be indicated in cases with inadequate femoroacetabular clearance. In cases with early cartilage degeneration on MRA, the osteochondroplasty is not sufficient and osteotomy of the pelvis, femur, or both depends on the individual morphology. MRA, magnetic resonance arthrography; ITO, intertrochanteric osteotomy; FA, femoroacetabular; WB, weight bearing.