A physiotherapist is involved in the treatment of a person with a 5 year history of a chronically unstable patella. The patient receives unusual treatment (femoral condyle reconstruction), however with successful rehabilitation, they achieve impressive outcomes (gains of 130 degrees knee flexion and independent weight bearing walking after 6 days). The physiotherapist decides this uncommon situation would be worthy of publishing in a journal, which they proceed to do. 

What kind of study design would be used for this report?