Response to letter to the editor

We appreciate Lander et al.’s1 thoughtful letter to the editor and their very positive attention to our study,2 especially noting that our “landmark study” with prompt mobilization after hip fracture is key to functional recovery and patient survival. We agree with Lander et al.1 that measuring time to mobilization from the end of surgery or upon arrival in the recovery room, rather than from the start of surgery, would provide a more accurate estimate. Ideally, this approach should be applied when such data are available; however, this was not possible in the Danish Multidisciplinary Hip Fracture Registry, introducing a potential risk of misclassification. Nevertheless, we believe this limitation has minimal impact on our study, as we adjust for fracture type (cervical femoral vs trochanteric), which partly accounts for the potential impact of duration of surgery on definition and categorization of early mobilization. Research based on population-level registries allows the use and integration of large datasets (in our study, four different registries), enabling adjustment for numerous factors that may influence outcomes, such as mortality. However, as noted by Lander et al.,1 a limitation of our study is the absence of data on factors such as hospital staffing and pain management protocols. These variables could act as confounders for mobilization timing (day 0-2) or as mediators of the association between mobilization and mortality (days 2-30).