Lipoma Arborescens After a Chronic ACL Tear: A Case Report

Case Diagnosis: A 51-year-old active female with recurrent knee effusions and pain was found to have lipoma arborescens in the setting of a chronic ACL tear.

Case Description or Program Description: An active 51-year-old female presented with worsening right knee pain over the past year. She had a history of a hyperextension injury in 2010 without formal evaluation, and afterwards felt her knee was “never the same”. Pain localized laterally, with associated swelling, stiffness, and mild buckling. On exam, a large effusion was present with restricted range of motion 5°-130° and no laxity on special tests. Radiographs, physical therapy, and a corticosteroid injection were prescribed at first visit.

Setting: Outpatient Sports Medicine Clinic

Assessment/Results: At 4 weeks, the patient returned to clinic reporting temporary symptom relief for two weeks but now with full recurrence of effusion and pain. An MRI was ordered and revealed tricompartmental osteoarthritis, a chronic full-thickness tear of the ACL, and a large joint effusion with lipoma arborescens. Patient was scheduled for an ultrasound guided joint aspiration and repeat corticosteroid injection. Further developments will be discussed.

Discussion (relevance): Lipoma arborescens is a rare, benign phenomena which was first described in 1904 as “post-traumatic adipose tissue proliferation.” The exact pathophysiology of the disease is unknown but both a primary (idiopathic) form and a post-traumatic form have been described. MRI can confirm the diagnosis with a frond-like pattern of fatty tissue seen in the suprapatellar recess. In both forms, early detection and treatment with arthroscopic synovectomy has shown to reduce rates of arthritis formation.

Conclusions: Lipoma arborescens, while a rare cause of joint effusion, is an important condition to be aware of since early detection and intervention may result in arthritis development risk reduction.