Hemiarthroplasty Versus Total Hip Arthroplasty for Femoral Neck Fracture in Elderly Patients: Twelve-Month Risk of Revision and Dislocation in an Instrumental Variable Analysis of Medicare Data.

The recomputed first-stage F statistic, in which total facility volume was treated as a covariate rather than an instrumental variable, indicated that the 2 remaining instruments were highly significant (F = 13.7; p < 0.01), demonstrating their validity as instrumental variables 31 - 33 .

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Recently, a large, international randomized trial demonstrated no significant differences between THA and HA in the rates of secondary hip procedures at 2 years, although a nonsignificant trend toward higher rates of early revision surgery was identified in the THA group 16 .

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