Evidence before this study: Acute appendicitis is the most common general surgical emergency in children. Its diagnosis remains challenging and children presenting with acute right iliac fossa (RIF) pain may be admitted for clinical observation or undergo normal appendicectomy (removal of a histologically normal appendix). A search for external validation studies of risk prediction models for acute appendicitis in children was performed on MEDLINE and Web of Science on 12 January 2017 using the search terms ["appendicitis" OR "appendectomy" OR "appendicectomy"] AND ["score" OR "model" OR "nomogram" OR "scoring"]. Studies validating prediction models aimed at differentiating acute appendicitis from all other causes of RIF pain were included. No date restrictions were applied. Validation studies were most commonly performed for the Alvarado, Appendicitis Inflammatory Response Score (AIRS), and Paediatric Appendicitis Score (PAS) models. Most validation studies were based on retrospective, single centre, or small cohorts, and findings regarding model performance were inconsistent. There was no high quality evidence to guide selection of the optimum model and threshold cutoff for identification of low-risk children in the UK and Ireland. Added value of this study: Most children admitted to hospital with RIF pain do not undergo surgery. When children do undergo appendicectomy, removal of a normal appendix (normal appendicectomy) is common, occurring in around 1 in 6 children. The Shera score is able to identify a large low-risk group of children who present with acute RIF pain but do not have acute appendicitis (specificity 44%). This low-risk group has an overall 1 in 30 risk of acute appendicitis and a 1 in 270 risk of perforated appendicitis. The Shera score is unable to achieve a sufficiently high positive predictive value to select a high-risk group who should proceed directly to surgery. Current diagnostic performance of ultrasound is also too poor to select children for surgery. Implications of all the available evidence: Routine pre-operative risk scoring could inform shared decision making by doctors, children, and parents by supporting safe selection of lowrisk patients for ambulatory management, reducing unnecessary admissions and normal appendicectomy. Hospitals should ensure seven-day-a-week availability of ultrasound for medium and high-risk patients. Ultrasound should be performed by operators trained to assess for acute appendicitis in children. For children in whom diagnostic uncertainty remains following ultrasound, magnetic resonance imaging (MRI) or low-dose computed tomography (CT) are second-line investigations.

The global incidence of tuberculosis (TB) infection was estimated by the WHO to be 10 million cases in 2018, 85% of whom had pulmonary TB (pTB) infection (WHO 2019). In Europe, the extrapulmonary TB (EPTB) incidence is increasing, accounting for 22.6% of new cases reported in 2017 (ECDC 2019). Furthermore, the incidence of articular TB infections has risen in Europe (Jutte 2004, Lesic 2010. This is reflected in UK surveillance data, where in 2017, 2.2% of new TB cases presented with non-spinal bone infections (Kruijshaar 2009, PHE 2018. Globally, this rise in EPTB infections has largely been ascribed to a growing population of immunosuppressed patients including those on long-term steroids and biologic therapies, as well as to an ageing population (Pigrau-Serrallach 2013, Byng-Maddick 2016). However, in low-incidence countries in Europe the rise in articular TB infections has also been attributed to increasing rates of migration (Jutte 2004, Krujishaar 2009. EPTB infection is thought to occur through haematogenous, contiguous or lymphatic spread in the primary infection stage, when mycobacteria can spread to any organ or tissue and remain dormant for years. Articular infection most commonly affects weight-bearing large joints such as the spine, knees and hips. Infection is often slowly progressing with joint effusions and pain, progressing to the formation of sinus tracts and eventually to complete joint destruction (Hogan 2017). Initial symptoms are vague and may mimic other conditions such as bacterial osteoarticular infection. This can result in significant diagnostic delay, especially in settings where TB is non-endemic and clinical suspicion is low (Erdem 2005, Broderick 2018). Most studies describing osteoarticular TB have focused on paediatric populations or on spinal TB with only a few published case series of extra-