PMC4957170_01
Case 1: Initial postoperative right hip radiograph.
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THA with placement of a 54-mm trabecular metal modular acetabular shell (Zimmer, Warsaw, IN), a 3.5-mm lateralized Longevity cross-linked PE liner (Zimmer, Warsaw, IN) with 36-mm inside diameter, a Fitmore press fit stem (Zimmer, Warsaw, IN), B11 12/14 taper with +3.5-mm neck length, and a 36-mm cobalt-chrome femoral head (Fig. 1).
Case 1: Anteroposterior hip radiographs. (a) Dislocation of the right hip. (b) Interval relocation of the femoral head within the acetabular cup. The head is subtly eccentric and proud in comparison to the initial postoperative radiograph.
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The patient's recovery was uncomplicated and he returned to a high level of function until 5 months postoperatively, when he dislocated his right hip after a slip and fall from standing position (Fig. 2a). Postreduction radiographs consistently demonstrated a nonconcentric, incomplete reduction, which was not recognized until the patient was evaluated by members of the orthopaedic team (Fig. 2b).
Case 1: Intraoperative picture during right THA revision showing a posterosuperior defect in the acetabular liner. The fracture fragment has been removed from its position interposed between the head and cup.
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On exploration of the hip joint, a fragment of the posterior lip of the HXLPE liner was found incarcerated between the femoral head and the acetabular cup liner which had been blocking successful reduction (Fig. 3).
Case 1: Postoperative right hip radiograph after revision to a constrained liner.
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The acetabular shell and femoral stem remained in good position and were not exchanged (Fig. 4).
PMC4957170_02
Case 2: Initial postoperative right hip radiograph.
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A 26-year-old woman with rheumatoid arthritis underwent primary right THA with placement of a 50-mm trabecular metal modular acetabular shell (Zimmer, Warsaw, IN), a 3.5-mm lateralized Longevity cross-linked PE liner (Zimmer, Warsaw, IN) with 36-mm inside diameter, a size 12 Trabecular Metal press fit stem (Zimmer, Warsaw, IN) with a +3.5-mm neck length, and 36-mm cobalt-chrome femoral head (Fig. 5).
Case 2: Anteroposterior hip radiographs. (a) Dislocation of the right hip. (b) Interval relocation of the femoral head within the acetabular cup. The head is concentrically reduced but proud of the initial postoperative position.
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At 11 months, the patient suffered a spontaneous dislocation with minimal internal rotation, flexion, and adduction while sitting on a stool (Fig. 6a). Her hip was reduced in the emergency department, but radiograph imaging showed that the femoral head was not completely seated within the acetabular liner (Fig. 6b).
Case 2: Highly cross-linked polyethylene acetabular liner with posterior rim fracture fragment. Intraoperatively, the fragment was found incarcerated between the liner and the femoral head.
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The fracture plane occurred at the contact point between the liner and the edge of the rim of the metal shell (Fig. 7).
Case 2: Postoperative right hip radiograph after acetabular revision with correction of the abduction angle and liner replacement.
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The entire component was revised to a more desirable abduction angle of 45  and 20  of anteversion and secured with 3 dome screws (Fig. 8).