The uncommon causes of anterior knee pain should always be considered in the differential diagnosis of a painful knee when treatment of common origins become ineffective. A case is presented in which the revised diagnosis of infrapatellar contracture syndrome was made after noting delayed progress in the rehabilitation of an active female patient with a presumed anterior horn medial meniscus tear and a contracted patellar tendon. The patient improved after the treatment program was augmented with closed manipulation under arthroscopy and infrapatellar injection of both corticosteroids and a local anesthetic. Infrapatellar contraction syndrome and other uncommon sources of anterior knee pain, including arthrofibrosis, Hoffa's syndrome, tibial collateral ligament bursitis, saphenous nerve palsy, isolated ganglions of the anterior cruciate ligament, slipped capital femoral epiphysis, and knee tumors, are subsequently discussed. Delayed functional advancement in a rehabilitation program requires full reassessment of the patient's diagnosis and treatment plan. Alternative diagnoses of knee pain are not always of common origins. Ample knowledge of uncommon causes of anterior knee pain is necessary to form a full differential diagnosis in patients with challenging presentations.