Background Over 85% of rheumatoid arthritis (RA) patients experience feet and ankle problems during the course of the disease. Persistent foot and ankle problems still occur even after clinical remission is reached . In RA, synovitis, effusion, and eventually erosive arthritis are thought to cause clinically recognizable planovalgus or valgus heel . With the intention to stabilize and align the foot, patient-specific foot orthotics (FO) are commonly prescribed to this patient group. A limitation of the previous literature on FO to treat RA and related diseases is that it has focused exclusively on clinical outcomes of FO such as pain and physical function, while overlooking the biomechanical principles on which the rationales for FO is based .
Objectives The aim of this study was to investigate the effect of patient-specific FO on hip loading during gait. This was accomplished by developing patient-specific (PS) musculoskeletal models (MS) capable of estimating joint mechanics with and without the FO.
Methods Four early stage RA patients were recruited for this study. A pair of FO was developed for each patient using a weight bearing casting technique. PS bone geometry was obtained from magnetic resonance imaging (MRI) images and segmented in an image analysis package (Mimics 19, Materialse, Belgium). Motion capture was performed with an eight-camera setup (Qualysis, Sweden) with reflective markers together with three force plates (AMTI, USA) sampling at 100 and 1000 Hz, respectively. The gait trials consisted of two conditions: one with the PS FO and one with a control insole (C). PS MS models of each patient were developed using the AnyBody Modeling System (AnyBody Technology, Denmark), Figure 1A. Muscle attachments were made PS based on the Twente Lower Extremity Model version 2.0 dataset using advanced morphing to customize a generic cadaver-based model with respect to PS morphology acquired from MRI . Accurate joint centers and axes were calculated with analytical surface fits to the segmented MRI bones for the hip, knee and ankle.
Results Peak hip force for medio-lateral (ML) proximo-distal (PD) and antereo-posterior (AP) is presented in Figure 1B for the C and FO with values for each subject.
Conclusions The results of this study indicate that FO can change the load distribution in the hip joint. A reduction or similar values for ML, DP and AP force was found for all but one participant. These changes may potentially contribute to the reduction in pain. Further studies are needed to investigate if there is a relationship between changed loading and pain for RA patients. This knowledge can potential be used for design of better FO and clinical guidelines for use of FO.
Hennessy K. et al, Arthritis Care Res, 64: 311–320, 2012.
Lewinson R. et al., Ann Biomed Eng, 44: 3173–3185, 2016.
Marra M, et al., J Biomech Eng. 137: BIO-14–1490, 2015.
Acknowledgements The study is financially supported by The Danish Rheumatism Association [R142-A4113].
Disclosure of Interest None declared