Viktor E. Krebs
The hip joint, a diarthrodial or synovial joint, under normal conditions can function under very high loads and stresses for seven to eight decades. The thick, fibrous joint capsule encloses the metabolically active synovial connective tissue in an environment that nourishes and protects the articular cartilage. A highly permeable vascular capillary system invests the synovium and functions to produce synovial fluid, a plasma ultrafiltrate that sustains and lubricates the avascular cartilage. The synovium is also immunologically active and harbors cells capable of phagocytosis for removal of cell degradation products from the joint and joint fluid. The syn-ovium plays a critical role in maintaining the balance between physiological processes and pathological changes, and its proper function is essential for long-term joint durability. When aging or a pathological condition alters the function of the synovial lining, biochemical or biomechanical breakdown of the articular cartilage may occur and result in eventual progressive degeneration. Unfortunately, our knowledge of the early pathologic changes in the hip joint that preclude degeneration and arthritis have not been historically well defined or studied. In comparison to other, more accessible joints, a diagnosis of hip joint synovitis or early degeneration is more difficult because the clinical signs and symptoms are protean and nonspecific, and there are no pathognomonic radiological signs. The majority of patients with synovitis or early degeneration of the hip are not evaluated or diagnosed until the process affecting the joint is well established. Once bony changes within the hip joint have occurred, the process of joint degeneration becomes progressive and, unfortunately, in most cases irreversible.
Although trauma and repetitive impact loading account for a significant percentage of patients with early degenerative hip disease, synovial and intra-articular pathology may prove more contributory as our understanding of these processes evolves. The hallmark of early joint degeneration secondary to synovial pathology is juvenile rheumatoid arthritis. Syn-ovitis in the immature articulation not only causes joint destruction, but also results in hypertrophy of the growth plates, bone hypertrophy, leg length discrepancy, and angular defor mities. Identification and treatment of synovial disorders affecting the hip joint, systemic or local, with or without underlying bony architectural abnormalities, may in the future help curtail early hip joint degeneration. Hip arthroscopy provides us with the minimally invasive technique needed to diagnose, investigate, and treat synovial disorders of the hip at an early stage.
In the hip joint, synovial involvement in the degenerative process has been geographically described as focal or diffuse. Focal synovitis emanates from the covering of the ligamen-tum teres, and results in the inflammatory pulvinar located in the acetabular fossa. The diffuse pattern involves the entire synovial lining of the capsule in addition to the pulvinar. Studies have shown that changes in the synovium are a very early and integral part of osteoarthritis. Light and electron microscopic studies have revealed two distinct types of os-teoarthritic synovitis: an early, proliferative form and a late fibrous form.1 The essential feature of the proliferative syn-ovitis is venous stasis with increased capillary permeability. A progression from proliferative to fibrous synovitis is the result of longstanding chronic venous insufficiency that results in synovial scarring and thickening.2 Rheumatoid synovium shows similar vascular changes, but is also characterized by a severe inflammatory reaction that is moderate or absent in osteoarthritis.2 In both situations the synovial scarring and thickening result in decreased range of motion and altered joint mechanics that may combine with the intra-articular inflammation to create an environment that destroys the articular surface.
Until the advent of reproducible and safe techniques for hip arthroscopy, access to the hip joint required an arthrotomy and its associated morbidity. Hip arthroscopy has provided minimally invasive access to the hip joint, the ability to inspect, biopsy, diagnose and, within the limits of our technology and knowledge, to treat early hip disease. When a patient presents with monoarticular inflammatory arthritis of the hip, synovial tissue biopsies provide tissue for histopathologic diagnosis, which may help guide specific therapy. Arthroscop-ically directed biopsy not only provides tissue, but also si multaneously provides additional information about the extent of synovitis and the state of the articular surfaces. Syn-ovectomy may also complement the medical treatment of selected patients with rheumatoid arthritis and hemophilia.5 Hip joint synovectomy in these systemically based disorders has been effective for pain relief and symptomatic control, but has only curtailed the relentless progression of the degenerative process. In localized conditions, such as pigmented vil-lonodular synovitis and synovial chondromatosis, early syn-ovectomy is the treatment of choice.3-5 Although complete synovectomy cannot be performed with arthroscopic techniques, the perilabral tissue, inferior capsular tissue, and syn-ovium overlying the ligamentum teres can be visualized and removed. Partial synovectomy or debulking often results in remarkable symptomatic improvement in patients with inflammatory conditions.6-10 When a complete synovectomy is advocated, a semiarthroscopic technique has been described that may be advantageous over open synovectomy, which requires dislocation of the femoral head and increases the inherent risk of avascular necrosis in patients who are also frequently dependent on high-dose steroid medications.4
Intra-articular and synovial conditions have been a focus for those who advocate application of the arthroscope to the hip joint. Intervention has been reported in synovial chondromatosis/osteochondromatosis, pigmented villonodu-lar synovitis (PVNS), inflammatory arthropathies including rheumatoid arthritis, and acute septic arthritis. Other conditions that result in acute and chronic synovitis within the hip, such as hemosiderotic synovitis secondary to hemophilia and chondrocalcinosis,11 although not reported in the literature specifically for the hip joint, may in certain situations also benefit from arthroscopic intervention. The remainder of the chapter reviews the intra-articular and synovial conditions that have been diagnosed and treated with hip arthroscopy, provides visual documentation of the conditions, and reviews the current and future directions in the treatment of these disorders of the hip joint.
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