Early dislocation in primary total hip arthroplasty: Evaluation of treatment options following closed reduction

Table 1 Classification of instability after total hip arthroplasty according to Wera et al[11] (modified)

Type	Etiology	Diagnosis	Treatment
I	Acetabular component malposition	Anteroposterior pelvic radiograph: Calculate acetabular version by arcsin (1); pelvic CT: Calculate version	Revision of the acetabular component
II	Femoral component malposition	Pelvic and knee CT performed in same sequence: Measure version	Revision of the femoral component
III	Abductor insufficiency	MARS-MRI: Evaluate abductor soft tissue; gait test: Evaluate for Trendelenburg limp	Constrained liner; some authors have had success with dual mobility components
IV	Impingement	Intraoperative detection: Evaluate for subtle signs of wear on the femoral neck and acetabular metal rim; when performing a full range of motion, check for impingement in all degrees of motion	Remove offending impingement structures
V	Late wear	Anteroposterior pelvic radiograph: Migration of the femoral head superiorly and laterally	Liner exchange; curettage and bone-grafting of the osteolysis for contained defects
VI	Unknown etiology	Unable to be determined based on plain radiograph and advanced imaging	Constrained liner
VII	Spinopelvic imbalance	Sitting and standing lateral radiographs: Evaluate sacral tilt; determine pelvic motion as normal, hypermobile or stiff; and then evaluate cup position and determine anteversion and inclination	Anterversion and inclination of the cup varies based on the position of the acetabular component

CT: Computed tomography; MARS-MRI: Magnetic resonance angiography with susceptibility weighting.