Introduction: Total hip and knee arthroplasty (THA/TKA) are surgical procedures with proven benefits. Although the literature reports outcomes of fusion of the lumbar spine comparable to those of THA/TKA in general health-related quality-of-life (HRQoL) questionnaires, functional assessment is nevertheless needed for these results to be of use in clinical practice and management. Aim of our study was to prove that lumbar spinal fusion has similar if not better outcomes than THA/TKA using intervention-specific HRQoL questionnaires and functional assessment questionnaires. Materials and methods: Observational, ambispective, multicentre study of three cohorts undergoing lumbar spinal fusion (n = 115), THA (n = 119) and TKA (n = 253). Patients were evaluated using the Short-Form-12 (SF-12), Harris–Hip-Score, Hospital for Special Surgery Scale (HSS) and Oswestry Low Back Pain Disability questionnaires. A minimum follow-up of two years was conducted. Results: The SF-12 showed significant improvement in all groups. The SF-12 physical component summary score indicated a more severe pre-operative status (p = 0.031) in the THA cohort. The mental component summary score indicated a less severe pre-operative status in the TKA cohort (p = 0.008) and greater post-operative improvement in the TKA and THA cohorts across follow-up (six months p = 0.021; one year p = 0.012; two years p = 0.042). Functional assessment indicated greater pre-operative disability in the THA group. At two years of follow-up, functional improvement according to the Harris, HSS and Oswestry questionnaires were 152.01%, 50.07% and 41.14% respectively. Conclusions: This study demonstrates that lumbar spinal fusion and total knee and hip arthroplasty are comparable in terms of functional improvement when thoroughly studied with health, quality-of-life and functional assessment questionnaires.