Intrapelvic cup migration is a serious complication after total hip arthroplasty, in which the prosthetic acetabular cup migrates or drifts into the pelvic inlet.
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Epidemiology
Fortunately, this complication is very rare. There seems to be a female predisposition 1-3.
Risk factors
Factors increasing the likelihood of developing intrapelvic cup migration include 1-3:
- osteopenia / osteoporosis
- overactivity and uncontrolled weight-bearing in the immediate postoperative period
Associations
Clinical presentation
Intrapelvic cup migration might present with hip pain and the inability to bear weight together with other variable symptoms for example pelvic or lower abdominal pain, hematuria fever or even shock.
Complications
Intrapelvic cup migration can lead to potentially life-threatening conditions 1:
- neurovascular injury
- laceration
- thrombosis
- pseudoaneurysm
- arteriovenous fistula
- involvement of the pelvic organs
- viscus perforation
Pathology
Etiology
Intrapelvic cup migration can arise from the following conditions 1:
- aseptic loosening
- infection of hip prosthesis
- cup malpositioning
- acetabular fractures
- reaction to metal
Radiographic features
Intrapelvic cup migration is defined as the migration of the cup or parts of it into the pelvic inlet and can be depicted on the anteroposterior view of the pelvis. Regarding the potential associated complications, the condition should be further investigated with CT angiography of the pelvis.
Plain radiograph
An anteroposterior view of the pelvis and lateral hip images are a good initial examination to confirm the intrapelvic cup migration beyond the ilioischial line 1,2.
CT
CT angiography is the mainstay in the preoperative vascular workup, which includes the localization of the migrated cup, screws and debris and the relation to the pelvic organs in particular to the neurovascular structures and the lower urogenital tract as well as the evaluation of acetabular bone deficiency and fracture lines and the integrity of the iliopsoas muscle.
It should ideally comprise an arterial a venous phase and CT urography 1,2.
MRI
Due to artifacts and the potential induction of further migration of implant parts and timing issues in an emergency MRI has no significant role in the workup 1.
Radiology report
The radiological report should include a description of the following 1:
- location of the intrapelvic cup with relation to the pelvic organs and neurovascular structures
- the integrity of the iliopsoas muscle
- complications as hemorrhage or perforation, fistula formation
- potential variant anatomy
- potential causes (acetabular fractures, signs of infection of hip prosthesis)
Treatment and prognosis
Treatment is surgical and often involves a two-step approach including the removal of the migrated intrapelvic cup, associated implants and fragments as well as the surgical inspection and repair of injured neurovascular structures and other pelvic organs on one hand and finally acetabular reconstruction and cup revision on the other 1,2.
The intrapelvic cup removal might include a classic extraperitoneal approach, a transabdominal approach or both, depending on the situation. It has been suggested that a subperitoneal approach is sufficient if the iliopsoas muscle is intact 1,5.
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