Copyright 2009
Hunt Udall MD, Matthew Diltz MD
Definition
The synovium of the hip is vascularized connective tissue which lacks a basement and lines the inside of the joint capsule.
It is the main lubricating system of the hip, producing the synovial fluid which bathes the hip cartilage and labrum. The synovium mediates the nutrient exchange between blood and synovial fluid. There are two types of cells within the synovium, Type A cells which are important in phagocytosis of foreign bodies, and Type B cells which produce the synovial fluid.
The function of the synovial fluid helps keep the coeffecient of friction low with the gliding surfaces of the femoral head and acetabulum. Synovial fluid is composed of hyaluronic acid and lubricin (a lubricating glycoprotein).
Common diseases include inflammation of the synovium (synovitis) from autoimmune diseases such as rheumatoid arthritis and lupus. Pigmented villonodular synovitis (PVNS) presents with pain and swelling of the hip and unique imaging on MRI. Synovial chondromatosis is a process that results in proliferation and cartilage metaplasia with resulting loose bodies within the hip.
Commonly used diagnostic procedures include MRI to evaluate the synovium and arthroscopy with biopsy if any diagnosis is in question
PVNS is treated with either open or arthroscopic synovectomy, but has a high recurrence rate. Synovial chondromatosis is also treated with open or arthroscopic removal of affected tissue.
References
Mark Miller. Review of Orthopaedics pp 42, 261-262. Saunders Elsevier, Philidelphia, 2