Objectives Opportunistic screening for osteoporosis using computed tomography (CT) examinations that happen to visualise the spine can be used to identify patients with osteoporosis. We sought to verify the diagnostic performance of vertebral Hounsfield unit (HU) measurements on routine CT examinations for diagnosing osteoporosis in a separate, external population. Methods Consecutive patients who underwent a CT examination of the chest or abdomen and had also received a dualenergy X-ray absorptiometry (DXA) test were retrospectively included. CTs were evaluated for vertebral fractures and vertebral attenuation (density) values were measured. Diagnostic performance measures and the area under the receiver operator characteristics curve (AUC) for diagnosing osteoporosis were calculated. Results Three hundred and two patients with a mean age of 57.9 years were included, of which 82 (27 %) had osteoporosis according to DXA and 65 (22 %) had vertebral fractures.The diagnostic performance for vertebral HU measurements was modest, with a maximal AUC of 0.74 (0.68 -0.80). At that optimal threshold the sensitivity was 62 % (51 -72 %) and the specificity was 79 % (74 -84 %). Conclusions We confirmed that simple trabecular vertebral density measurements on routine CT contain diagnostic information related to bone mineral density as measured by DXA, albeit with substantially lower diagnostic accuracy than previously reported. Key Points • We externally validated the value of vertebral trabecular bone attenuation for osteoporosis • These diagnostic performance measures were, however, substantially lower than previously reported • This information might be useful when considering the implementation of opportunistic osteoporosis screening

• Routine CT may gain a role in bone attenuation measurements for osteoporosis • Contrast media injection has substantial influence on CT-derived bone density • Contrast-enhanced CT leads to underestimation of osteoporosis compared to unenhanced CT • Adjusting for contrast injection phase may improve CT screening protocols for osteoporosis.

Purpose To describe the validity and inter- and intra-observer reliability of the lateral femoral notch sign (LFNS) as measured on conventional radiographs for diagnosing acute anterior cruciate ligament (ACL) injury. Methods Patients (≤ 45 years) with a traumatic knee injury who underwent knee arthroscopy and had preoperative radiographs were retrospectively screened for this case–control study. Included patients were assigned to the ACL injury group ( n = 65) or the control group ( n = 53) based on the arthroscopic findings. All radiographs were evaluated for the presence, depth and location of the LFNS by four physicians who were blind to the conditions. To calculate intra-observer reliability, each observer re-assessed 25% of the radiographs at a 4-week interval. Results The depth of the LFNS was significantly greater in ACL-injured patients than in controls [median 0.8 mm (0–3.1 mm) versus 0.0 mm (0–1.4 mm), respectively; p = 0.008]. The inter- and intra-observer reliabilities of the LFNS depth were 0.93 and 0.96, respectively. Secondary knee pathology (i.e., lateral meniscal injury) in ACL-injured patients was correlated with a deeper LFNS [median 1.1 mm (0–2.6 mm) versus 0.6 mm (0–3.1 mm), p = 0.012]. Using a cut-off value of 1 mm for the LFNS depth, a positive predictive value of 96% was found. Conclusion This was the first study to investigate the inter- and intra-observer agreement of the depth and location of the LFNS. The depth of the LFNS had a very high predictive value for ACL-injured patients and could be used in the emergency department without any additional cost. A depth of > 1.0 mm was a good predictor for ACL injury. Measuring the depth of the LFNS is a simple and clinically relevant tool for diagnosing ACL injury in the acute setting and should be used by clinicians in patients with acute knee trauma. Level of evidence Diagnostic study, level II.