Lower limb apophysitis cause long-term pain, decrease in function, and can reduce or completely hinder participation in sports and physical activity, yet there is little knowledge on the long-term consequences for health. Our objective with this investigation is to capture self-reported health-status for all adults having been diagnosed with lower limb apophysitis in the period of 1977 to 2020 and compared these data with normative values for the background population. We are therefore conducting a national cross-sectional study based on data from the Danish National Patient Registry. In this protocol we describe, as detailed as possible, the planned methods.

Inclusion Criteria:

• All patients aged 18-55 having received diagnostics codes pertaining to lower limb apophysitis (Severs, Sinding-Larsen Johansson, Osgood Schlatter) in the years 1977-2020 in Denmark will be eligible to participate.

Exclusion Criteria:

• Diseased participants will be censored

Sample size will be of convenience with no pre-determined cut-off for smallest or largest sample of interest, rather, the final sample of respondents will be based on however many have been designated the diagnostic codes and responds to the survey.

The full dataset, excluding all personal identifiers, will be posted alongside the pre-print when the results have been disseminated.

After primary publication and for the foreseeable futures thereafter.