Table 3.

Types of failure

	Imaging	Surgical	Hazards	Surgical plan
Type I:
Conventional failure modes	Normal or small fluid-filled ‘pseudotumor’ on MRI	Variable	Misdiagnosis, Recurrent infection
Type II:
Synovitis with negative investigations	Normal or small fluid-filled ‘pseudotumor’ on MRI	Varying degrees of synovitis	Misdiagnosis	Need to exclude other causes e.g. infection, mechanical causes. Consider further imaging for psoas, frozen section during revision
Type III:
Soft tissue disruption	MRI shows fluid or solid mass with variable soft tissue and muscle destruction (Figures 2 and 3)	Abductors may be atrophic or avulsed/absent	Instability after revision	Plan for possibility of muscle loss, including need for musle reconstruction (e.g. graft jacket) or captive cup. Like type V, may need pelvic surgeon for full excision of intrapelvic mass
Type IV:
Bone destruction	Osteolysis on CT/plain films. MRI as type I (Figure 4)	Loose cup. Soft tissue reaction varies	Loss of bone stock and need for extensive reconstruction	May need extensive reconstruction. CT and pelvic surgeon may be helpful. Early surgery indicated to prevent fracture
Type V:
Solid pseudotumor	MRI shows large mass. Mass may extend to pelvis (Figure 5)	Massive soft tissue reaction but musculature may be intact	Secondary infection if incompletely excised	Complete excision required. May need pelvic exploration