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Protrusio Acetabuli


Key Points

  • The clinical signs of protrusio acetabuli are groin pain, limited hip abduction and, often, a hip flexion contracture. Deepening of the acetabulum leads to painful limitation of abduction as the femoral neck impinges on the superior acetabular margin. Further progression may lead to adductor spasm, and fixed flexion deformities develop. There is often hyperlordosis of the lumbar spine, which compensates for the fixed flexion deformities at the hips. Untreated, the patient may ultimately develop ankylosis of the affected hip.

  • The cardinal radiographic findings of the femoral head medial to the ilioischial line confirm the diagnosis of protrusio acetabuli.

  • Preoperative planning for total hip replacement in protrusion should focus on restoration of the normal center of rotation on the acetabular side. The key is to recognize that the anticipated socket will not lie in contact with the protruded acetabular fossa but rather will be lateralized to a more normal position and will need to rest on the rim rather than the floor of the socket.

  • In exposing the hip with protrusio acetabuli, remember that forceful attempts at dislocation can result in fracture. Wide capsular exposure should help identify the proximal aspect of the femur. To facilitate dislocation, it is recommended to use bone hooks, providing lateral traction to the femur. If dislocation is not possible, then in situ femoral neck osteotomy is indicated.

  • Most complications that occur during exposure can be prevented by avoiding forceful manipulation of the femur. Anticipated use of either in situ neck osteotomy or trochanteric osteotomy is much safer and predictable.

  • The primary bone defect encountered in protrusion is a medial acetabular defect. This can be successfully managed by using the resected femoral head as autograft. The autograft bone should be denuded of cartilage remnants and morselized into 3- to 5-mm bits of graft that can be compacted into the medial defect with either a circular-shaped impactor or using reamers in the reverse mode.

Introduction

Total hip arthroplasty (THA) has clearly been demonstrated to be a successful intervention in the alleviation of pain and improvement in overall function. Much of the functional improvement after total hip replacement can be attributed to an increase in range of motion (ROM). Determinants of ROM are dependent on many factors, including implant position, intrinsic properties of the patient's soft tissues, and bony anatomy. Other chapters in this section have dealt with THA in the setting of insufficient bone coverage as encountered in developmental dysplasia and after fracture. The purpose of this chapter is to discuss the evaluation and treatment of patients with protrusio acetabuli in whom bony overcoverage is the prime problem.

Protrusio acetabuli was first described by the German pathologist Otto in 1824 as Otto pelvis (arthrokatadysis) and later excerpted by Pomeranz. A translation of Otto's original description is as follows:

“The right acetabulum protrudes into the pelvis like half an orange…at the crest corresponding to the center of the acetabular fossa, is an irregular circular defect, measuring one and one-half inches…supplying communication between the acetabulum and abdominal cavity…both the inner aspect of the acetabulum and the head of the femur are devoid of cartilaginous covering, and have the abraded and polished appearance of some gouty joints.”

The etiology of protrusio acetabuli has not been clearly elucidated. There are two main categories of the condition: primary and secondary. McBride and associates nicely described the primary and secondary causes of protrusio acetabuli. Primary protrusio acetabuli is considered by some to be an acquired condition due to incomplete or delayed fusion of the triradiate cartilage. The chondrodystrophy leads to abnormal development of the medial wall of the acetabulum, resulting in protrusion. Other authors believe that primary protrusio acetabuli is idiopathic and by nature a diagnosis of exclusion. Secondary protrusio acetabuli is diagnosed in those cases in which underlying pathology is identified and are well documented. Causes include infectious, neoplastic, inflammatory, metabolic, traumatic, and genetic etiologies ( Box 84.1 ). In addition, iatrogenic protrusio resulting from primary THA has been observed ( Fig. 84.1 ).

Box 84.1
Etiologies of Secondary Protrusio Acetabuli

Infectious

  • Gonococcus

  • Echinococcus

  • Staphylococcus

  • Streptococcus

  • Mycobacterium tuberculosis

Neoplastic

  • Hemangioma

  • Metastatic carcinoma (breast and prostate most common)

  • Neurofibromatosis

  • Radiation-induced osteonecrosis

Inflammatory

  • Rheumatoid arthritis

  • Ankylosing spondylitis

  • Juvenile rheumatoid arthritis

  • Psoriatic arthritis

  • Acute idiopathic chondrolysis

  • Reiter syndrome

  • Osteolysis after hip replacement

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