Knee extensor mechanism disruption is an unusual but serious emergency presentation. Rarely disruption can occur within the patellar tendon which is often associated with systemic diseases such as rheumatoid arthritis and systemic lupus erythematosus. Surgical management is required to repair the patellar tendon after clinical assessment and diagnosis. We describe the case of a 75-year-old man without any known predisposing systemic disease presenting on several occasions before accurate diagnosis and treatment. We include a literature review of similar cases and discuss the importance of missed diagnosis and underlying causes. A treatment algorithm to avoid missing similar injuries is also proposed.