Moving On: Objective Functional Assessment in Spine Surgery

This thesis aims to assess the validity of the 5R-STS as an objective outcome measure of functionality in patients with LDD. The expression “Moving On” refers not only to the field of movement sciences but also to the actual movement required to perform the 5R-STS. Additionally, it signifies a transition from the sole use of PROMs as subjective outcome measures in spine surgery to the adjuvant use of objective outcome measures to better capture patient’s functionality. First, the literature was systematically reviewed using COSMIN guidelines to summarize current evidence on the measurement properties of the 5R-STS in patients with LDD and identify research gaps in the available body of knowledge. This was described in Chapter 2. In order to improve the clinical interpretability of the 5R-STS in patients with LDD, in Chapter 3, the concurrent validity of a previously proposed 5R-STS BSS of OFI was evaluated against the most common PROMs. In order to determine what 5R-STS time constitutes a pathological performance, in Chapter 4, normative reference values and factors independently associated with 5R-STS performance in healthy individuals were identified. Similarly, such factors independently associated with 5R-STS performance and OFI were established for patients with LDD in Chapter 5. Since the 5R-STS aims to reflect functional impairment but objectively, adding a new data point during the preoperative assessment, Chapter 6 determined whether the presence of preoperative OFI measured by the 5R-STS can predict outcomes at 12-months post-discectomy in patients with LDH. Ultimately, for any outcome measurement instrument to be adequately implemented in clinical research, a change in the score considered clinically meaningful by the patient needs to be established. This concept, known as MCID, aims to identify a threshold that is mere than just statistical significance.13 Given the complexity of MCID calculations that can be implemented in spine surgery studies, key considerations were outlined, and a step-by-step calculation guide of different MCID values was described in Chapter 7. Finally, with an increased understanding of clinically meaningful threshold calculations, the MCID for improvement of the 5R-STS in patients with LDH using distribution- and anchor-based methods was estimated in Chapter 8. The main findings of this thesis, along with considerations for future research in this area, are discussed in Chapter 9, while Chapters 10 and 11 include the summary of this thesis in English and Dutch.