## 4 Screening for Secondary Osteoporosis  
The goal of screening is to identify patients with a high risk for secondary osteoporosis in order to initiate bone protection therapy in a timely fashion. This has led to screening for early rather than late signs of vertebral fractures, as well as reductions in BMD following appropriate size corrections. This aligns with a secondary prevention approach, which seeks to mitigate the progression of low BMD and bone fragility following identification in an earlier stage [39]. High-risk patients belong to one of the earlier-mentioned groups, especially those with immobilization with or without additional risk factors and those treated with daily or IV glucocorticoids for more than three months. Recently, two observations have demonstrated the limitations of a \"BMD-focused approach\" instead of implementing a \"fracture- and function-focused approach.\" First, the use of a BMD z-score threshold of \(-2\) or worse to identify a child as having osteoporosis is problematic due to variability in the z-scores arising from the reference databases [41], and secondly, asymptomatic VF can occur at lumbar spine BMD z-scores \(>\)\(-2\), thereby requiring spine imaging for vertebral fractures, especially in children using daily oral or IV glucocorticoids for more than three months where the risk of vertebral fractures is even higher [39]. Other functional outcomes that should also be considered in osteoporosis screening include a history of long bone fractures, growth, pain (especially indicative for vertebral fractures), degree of mobility, muscle strength, and the potential for spontaneous, medication-unassisted recovery (the latter, which is influenced by pubertal stage and residual growth potential). Screening of BMD (by DXA or digital X-ray radiogrammetry) is an adjuvant component of bone health monitoring, as it provides insight into the child's overall bone health trajectory; to this end, BMD is most useful when implemented as a longitudinal monitoring tool, much like linear growth is tracked children as a barometer of overall well-being. The exact timing and frequency of screening BMD depends on the risk of secondary osteoporosis and, consequently, differs between patient groups and the individual patient. In general, the following guidelines can be followed:  
1. Patients that will be treated with daily oral or IV glucocorticoids for more than three months should be considered for a baseline spine radiograph or DXA-based vertebral fracture assessment. This is recommended since the earliest reported vertebral fracture in children treated with glucocorticoids is at 4 months after the start of glucocorticoids [42]. These children should also undergo a follow-up radiograph at 12 months if risk factors are persistent since this is the time point with the highest incidence of vertebral fractures [42, 43]. Annual to biennial imaging for VF is advised afterward for patients still treated with glucocorticoids; VF imaging beyond this critical high-risk period is then customized to the magnitude of risk factors thereafter. For further information on the follow-up frequency, see [PERSON] et al. [39];
2. The same principles apply to children with other risk factors for bone fragility. In children with immobilization, especially in combination with drugs that can cause secondary osteoporosis, screening should start at the latest by 6-8 years of age and then at intervals of about two years thereafter until the end of growth or earlier in case of suffering from back pain or fragility fractures [27, 44]. Monitoring is recommended to start by this time to plan to start with treatment. Treatment should be initiated before there is not enough residual growth potential to reshape vertebral bodies following VFs.