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Synovial Diseases of the Hip
Key Points
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Synovial chondromatosis and pigmented villonodular synovitis (PVNS) are the most common primary disorders of the hip synovium.
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Early diagnosis of synovial disorders is important to optimize treatment results and minimize secondary degenerative disease of the hip.
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Surgical techniques of tumor excision include open procedures and arthroscopy depending on the disease pattern.
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Radiation therapy has a role in the treatment of PVNS, usually in the face of recurrent or high-risk disease.
Introduction
The hip is a synovial joint that functions as the primary link between the trunk and lower limbs, providing bodily support and mobility in the upright position. Synovial joints are differentiated from cartilaginous and fibrous joints by the existence of capsules surrounding the articulating surfaces of the joint and the presence of lubricating synovial fluid within the capsule. The synovium is a thin, specialized tissue that lines noncartilaginous spaces within the joints (e.g., hips, knees, elbows). This tissue is a few cell layers thick and plays a major role in regulating the fluid and cellular environment within the joint. A highly vascular capillary system within the synovium provides joint-lubricating fluid containing hyaluronan and lubricin. The synovium mediates molecular and cellular changes within the joint and protects the joint from physiologic and biomechanical stresses. Additionally, the synovium provides macrophage access to the joint. Activated macrophages perform several immunologic functions within the joint space and are important mediators of both joint homeostasis and certain disease states.
Primary disorders of hip synovium are relatively rare, even in a high-volume hip practice. The most common disorders include synovial chondromatosis and pigmented villonodular synovitis (PVNS). Both of these conditions are benign tumors of synovial origin. Successful orthopedic management of these conditions is dependent on a timely diagnosis and successful removal of the primary tumor. Failed treatment and recurrent disease can be associated with articular cartilage degeneration and secondary osteoarthritis. This chapter will review the important concepts associated with diagnosing and treating these benign synovial disorders.
Synovial Chondromatosis
Overview
Synovial chondromatosis is a benign, monoarticular arthropathy that infrequently involves the hip. In fact, hips account for only 10% of diagnosed cases. Disease involving knees (50%–65% of cases) and elbows (20%–25%) is far more common. Males are affected twice as often as females. The disease process begins with metaplastic differentiation of mesenchymal cells in the synovial membrane of the joint. These cells mature into chondroblasts and form small nodules of cartilage in intimal layers of the synovial membrane. These nodules subsequently enlarge and detach to lie within the joint space, resulting in the formation of multiple intracapsular and extracapsular loose bodies. These loose bodies continue to grow in diameter via multiplying chondrocytes and may calcify in their central zones, leading to the term osteochondromatosis ( Fig. 34.1 ).
Villacin et al. described 2 forms of synovial chondromatosis. The primary form of synovial chondromatosis is characterized by numerous small, round loose bodies that are uniform in size. It is not precipitated by any identifiable joint pathology and likely occurs secondary to metaplasia. Lesions are often aggressive and are associated with a high incidence of recurrence. Conversely, the secondary form is characterized by fewer, larger, more variably sized cartilaginous masses. This form is more likely to occur in the setting of preexistent osteoarthritis, rheumatoid arthritis, osteonecrosis, osteochondritis dissecans, neuropathic osteoarthropathy, tuberculosis, or osteochondral fracture. The underlying disease process generates chondral fragments that implant into synovium, inducing metaplastic cartilage formation.
Milgram further described synovial chondromatosis as a self-limited intrasynovial process that occurs in 3 phases: early, transitional, and late. In the early phase, only active intrasynovial disease is present, with no loose bodies. The transitional phase includes both active intrasynovial proliferation and free loose bodies. The late phase shows multiple free osteochondral bodies extruded in the joint space but no demonstrable intrasynovial disease. These phases become important in clinical decision making in determining the necessity of performing synovectomy to treat symptoms and prevent disease recurrence.
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