Unipolar versus Bipolar
Moderate evidence supports that the outcomes of unipolar and bipolar hemiarthroplasty for unstable (displaced) femoral neck fractures are similar.

One high strength study (Davison et al 49) and seven moderate strength (Raia et al 74, Cornell et al 75, Jeffcote et al 76, Calder et al 60, Calder et al 77, Hedbeck et al 78, Kenzora et al 79) Kenzora studies compared unipolar and bipolar hemiarthroplasty for the treatment of displaced femoral neck fractures.  All of the included studies showed equivalence in functional and radiographic outcomes, suggesting no significant benefit for bipolar articulation over unipolar hemiarthroplasty for displaced femoral neck fracture. A meta-analysis of mortality at six months and one year show no significant differences between unipolar and bipolar hemiarthroplasty.
Risks and Harms of Implementing this Recommendation
The majority of the reviewed studies reported that that unipolar heads were acknowledged as being significantly less expensive than the bipolar heads without any accompanying clinical difference recognized. 
There is no apparent harm associated with implementing this recommendation and cost savings represent a direct economic benefit from the preferential use of unipolar articulations.

Future Research
None needed