Twenty studies met the inclusion criteria (7,569 participants, range 41 to 1,684). Fourteen studies were prospective, two were retrospective and the direction of data collection was not reported in four studies. All 20 studies clearly described their inclusion criteria, used an appropriate reference standard and adequately described the index and reference standard tests. Seventeen studies avoided partial verification bias, 15 avoided differential verification bias and 19 avoided incorporation bias. Thirteen studies blinded interpreters of the index test and six blinded interpreters of the reference standard.
For ultrasonography (15 studies), overall sensitivity was 88% (95% CI 85% to 91%; Ι²=91%), specificity was 99% (95% CI 98% to 99%; Ι² 75%) and DOR was 993.1 (95% CI 333.5 to 2,937.4; Ι² 70%).
For X-ray (19 studies), overall sensitivity was 52% (95% CI 49% to 55%; Ι²=91%), specificity was 100% (95% CI 100% to 100%; Ι²=51%) and DOR was 304.8 (95% CI 121.9 to 761.9; Ι²=55%).
Of the covariates included in a meta-regression, the ultrasonography operator was strongly associated with accuracy. When the analysis was restricted to clinicians other than radiologists, sensitivity was 90% (95% CI 87% to 93%) and specificity was 99% (95% CI 98% to 99%); both analyses had significant heterogeneity.