Table 1.

Time-frame of the follow-up questionnaires

Follow-up
Baseline	First intervention injections Physical examination AOFAS PROMs PRODISQ cost-effectivity
6 weeks	Second intervention injection Physical examination AOFAS PROMs
12 weeks	AOFAS PROMs PRODISQ cost-effectivity
26 weeks	AOFAS PROMs PRODISQ cost-effectivity
39 weeks	PRODISQ cost-effectivity
52 weeks	AOFAS PROMs PRODISQ cost-effectivity
5 years	AOFAS PROMs

In addition to the AOFAS score, the following PROMs will be taken: FAOS, AOS, VAS, AAS, SF-36, GAS, EQ-5D-3L. These PROMs will be elaborated on further on. Furthermore, PRODISQ will be used to perform a cost-effectivity analysis. These questionnaires can be found in online supplementary appendix 1.

AAS, Ankle Activity Score; AOFAS, American Orthopaedic Foot and Ankle Society; AOS, Ankle Osteoarthritis Score; EQ-5D-3L, EuroQol-5 dimensions-3 levels; FAOS, Foot and Ankle Outcome Score; GAS, Global Attainment Scaling; PRODISQ, PROductivity and DISease Questionnaire; PROM, patient-reported outcome measures; SF-36, subjective patient satisfaction Short Form Health Survey-36; VAS, Visual Analogue Scale.