Review Question - QID 5486

On the left, Figure A shows a metal-on-metal (MOM) bearing hip resurfacing. On the right, Figure A shows a large head, uncemented metal-on-polyethylene (MOP) total hip replacement. In this setting, the most appropriate treatment option would be revision arthroplasty with constrained polyethylene liner.

Constrained liners should be reserved for patients demonstrating recurrent instability despite treatment with a large femoral head. Other indications include elderly patients who do not require implant longevity or have a low functional demand, as well as patients with deficient or non-repairable abductor mechanisms.

Sikes et al. report on the results of a series of 41 patients (52 hips) with recurrent dislocations. They recommend that large femoral heads (LFH) be used as a first-line treatment in high-risk patients (patients of any age with dementia, neuromuscular disability, and inability to comply with precautions). Constrained liners should be reserved for patients demonstrating recurrent instability despite treatment with an LFH.

Kilampali et al. reviewed late instability of bilateral metal on metal hip resurfacings. They suggest that late instability of hip resurfacing should raise concerns relating to possible local tissue reaction and muscle damage. Concerning features include steeply-inclined acetabular components a large abduction angle of more than 55 degrees along with a combination of small size component.

Figure A shows an image of a revised socket which was performed to convert the MOM THA to a MOP THA. Figure B shows normal parameters of THA components. The recommendation for acetabular position is anteversion 20° ± 10° and abduction 45° ± 10°. For the femur, recommendations are 10°- 15° of anteversion and 41mm - 45mm of offset.

Incorrect Answers:
Answer 1: Conservative treatment would be indicated in patients not suitable for operative intervention.
Answer 2: Medializing the cup would likely increase the potential for dislocation.
Answer 4: Revision arthroplasty to a femoral component with extended offset would help to decrease joint reaction forces. However, this patient has deficient abductors, which is likely related to local tissue reaction and muscle damage from the metal on metal implant.
Answer 5: A large ceramic femoral head and offset polyethylene cup would not help to restore stability.