Knee osteoarthritis (OA) is one of the most prevalent joint diseases worldwide, and mechanical loading plays an important role in its development and progression. Accurate knee joint kinematics are essential for computational models that estimate biomechanical parameters such as joint contact forces. Fluoroscopy enables accurate measurement of joint kinematics and may help overcome some limitations of conventional approaches, including soft tissue artefacts associated with optical motion capture and simplified model assumptions about knee joint motion.
This study aimed to develop and evaluate a modelling framework integrating fluoroscopy-derived knee kinematics into an existing musculoskeletal (MSK) model to assess whether this improves the prediction of tibiofemoral (TF) forces and medial-lateral load distribution, and how these outcomes are affected by different modelling choices.
Simulations were conducted using a generic MSK model and walking and squatting data from two subjects from the CAMS-knee dataset. TF flexion–extension (FE) rotations and anterior–posterior (AP) and superior–inferior (SI) translations were derived from fluoroscopy. FE rotation was prescribed during inverse kinematics (IK), while AP and SI translations were implemented as functions of FE rotation by replacing the model’s original coordinate-coupling functions. Subject-specific mean kinematic relationships were also constructed for each activity. Different kinematic prescription configurations were evaluated. Joint loading was estimated using the rapid muscle redundancy (RMR) solver. Total TF forces, as well as medial and lateral compartment forces, medial force peaks, impulse, and medial load ratio (MLR), were evaluated against in vivo measurements.
Fluoroscopy-derived kinematics showed larger excursions and distinct absolute magnitudes than the original model parametrisations. Their prescription led to changes in predicted TF forces and compartmental load distribution. For walking, the kinematic prescription had a limited influence on TF force predictions overall, although the FE-SI configuration showed the poorest agreement with in vivo data. For squatting, all configurations overestimated TF forces, but the FE-AP and FE-AP-SI configurations improved agreement with in vivo measurements. The FE-AP-SI configuration yielded the smallest total TF impulse differences relative to the in vivo reference in both subjects (1.663 BW$\cdot$s and 0.377 BW$\cdot$s), whereas FE and FE-SI produced the largest deviations. Lateral TF forces were predicted more accurately than total or medial forces. Subject-specific mean prescriptions yielded results nearly identical to trial-specific prescriptions.
The effect of prescribing fluoroscopy-derived knee kinematics in a generic MSK model depended on the activity and prescription configuration. No consistent improvements in walking were observed, whereas the FE-AP and FE-AP-SI configurations improved TF force predictions during squatting. Subject-specific mean prescriptions had a negligible effect on predicted forces, supporting a simplified implementation of the framework. Overall, this approach may improve the biomechanical fidelity of MSK models and advance understanding of knee joint loading.