From Intradiscal Pressure to Multimodal Estimation of Lumbar Spinal Loads.

BACKGROUND: Estimation of lumbar spinal loads is important for understanding low back pain, guiding ergonomic interventions, and informing surgical and rehabilitation planning. Historically, intradiscal pressure (IDP) provided one of the few internal in vivo measures of disc loading; more recently, telemetry, musculoskeletal (MS) modeling, finite element (FE) analysis, hybrid MS-FE approaches, displacement/control-based methods, and AI surrogates have expanded the toolbox for estimating spinal loads. MATERIAL AND METHODS: We present a narrative perspective review based on a literature search in PubMed, Scopus, and Web of Science using terms related to spinal loads, IDP, telemeterized implants, MS modeling, FE analysis, hybrid MS-FE coupling, displacement/control-based methods, wearable/EMG-based approaches, and AI/machine learning surrogates. Human lumbar studies and methodological contributions relevant to load estimation or validation were included; animal models were excluded. RESULTS: Invasive approaches (needle-based IDP, discography, intra-abdominal pressure, and telemeterized implants) provide task-dependent internal pressures or forces in small, selected cohorts and now primarily serve as benchmarks for model validation. MS models estimate segmental compression, shear, and net moments from motion and EMG, with typical L4-L5 compressive forces of ∼1-2 kN in relaxed standing and ∼3-5 kN during common lifting tasks. FE and hybrid MS-FE simulations resolve how these loads are distributed across discs, facets, and ligaments and relate segmental forces to internal stresses. Displacement-driven/control-based models and emerging AI/wearable-based surrogates provide additional non-invasive pathways for task-specific lumbar load estimation. CONCLUSIONS: This methods-focused synthesis outlines how invasive data support MS, FE, hybrid, and AI-based approaches and highlights recurring challenges in muscle redundancy, constitutive and parameter uncertainty, limited in vivo benchmarks, and heterogeneous model reporting. Within this framework, IDP is best regarded as an internal benchmark rather than a stand-alone metric of "spinal load" which is more fully described by compression, shear, moments, and internal stresses.