Medical background – Rheumatoid arthritis (RA) is the most frequent chronic inflammatory joint disease with a prevalence around 0.5% [1]. RA is a peripheral polyarthritis involving hands and feet: foot function is compromised, with accompanying changes in plantar pressures and gait disturbances. The impact on patients is serious, involving foot pain and limitations in weight-bearing activities, restricting participation and decreasing quality of life [2]. The impact of RA on foot joint can possibly manifest in instability, difficulties in walking and consequently functional limitations that strongly impact daily activities. Foot pain and foot disability can be reduced by customized foot orthoses and therapeutic footwear [1]. Orthotic insoles are commonly used in the treatment of patients with RA with the aim of pain reduction and functional improvement. Although the usage of insoles is usually associated with pain relief, the mechanisms involved within this treatment lack methodological assessment. In particular, insole design and its relation to internal effects such as joint pressure and soft tissue deformations have not been investigated due to the challenging nature of such studies in a clinical context.

Medical question – From a medical point of view, the INORA project aims at understanding the mechanisms of action of shoes and orthotic insoles through patient-specific computational biomechanical models in order to propose a rational approach to their design. On a more fundamental aspect, these models will help in uncovering the mechanical determinants to pain relief, which will enable the long-term well-being of patients.

Hypothesis – Motivated by the numerous studies highlighting erosion and joint space narrowing in RA patients [3], we postulate that a significant contributor to pain is the internal joint loading (cartilage pressure) when the foot is inflamed. This hypothesis dictates the need of a high-fidelity volumetric segmentation for the construction of the patient-specific geometry. It also guides the variables of interests in the exploitation of a finite element (FE) model.

Project objectives – The INORA project aims at providing numerical tools to the scientific, medical and industrial communities to better describe the mechanical loading on diseased distal foot joints of RA patients and propose a patient-specific methodology to design pain-relief insoles.

[1] Guillemin F, Saraux A, Guggenbuhl P, Roux C, Fardellone P, Le Bihan E, et al. (2005) Prevalence of rheumatoid arthritis in France: 2001. Ann Rheum Dis. 64(10): 1427–30
[2] Turner D, Helliwell P, Lohmann Siegel K, Woodburn J (2008) Biomechanics of the foot in rheumatoid arthritis: Identifying abnormal function and the factors associated with localised disease “impact.” Clin Biomech. 23(1): 93–100.
[3] Scott, D. L., Smith, C., & Kingsley, G. (2003) Joint damage and disability in rheumatoid arthritis: an updated systematic review. Clinical and experimental rheumatology, 21(5; SUPP 31): S20-S27.