CHAPTER 21 Arthroscopic Synovectomy and Treatment of Synovial Disorders

Introduction

The hip is a synovial joint that bears significant loads over a lifetime. There are various conditions that can lead to hip joint dysfunction and result in significant disability. Synovial hip disorders are less common hip conditions and include synovial chondromatosis, pigmented villonodular synovitis (PVNS), septic arthritis, and inflammatory arthropathies.

Much of the literature that addresses the management of hip synovial disorders is based on reports that involve the treatment of other joints. However, these conditions do affect the hip joint proper, and a systematic approach can lead to acceptable outcomes in appropriately selected individuals. This chapter will describe synovial disorders and their typical presentation, physical examination findings, appropriate imaging studies, and hip arthroscopy indications for the management of these less commonly encountered disorders. In addition, a detailed surgical technique for central and peripheral compartment synovectomy is described.

Basic science

Synovial chondromatosis and synovial osteochondromatosis are the result of intrasynovial cartilage metaplasia, and it can cause the formation of multiple intra- and extra-articular loose bodies. These loose bodies may be primarily cartilaginous and associated with very little articular cartilage damage. With time, these loose bodies can ossify to variable degrees and result in progressive erosive changes near the hip joint proper. The cause and pathogenesis of PVNS remain unclear. The condition appears to be the result of a fibrohistiocytic chronic inflammatory or neoplastic response. It is associated with synovial proliferation (either diffuse or focal), joint effusion, and bony erosion with characteristic hemosiderin deposition within the synovial mass. Multiple loose bodies and PVNS of the hip are associated with more erosive and degenerative changes than those seen in the knee as a result of the more constrained nature of the hip joint proper. Rheumatoid arthritis is the most common inflammatory arthropathy that affects the hip joint. The initial pathology involves the inflammation of the synovium, which leads to the eventual destruction of the joint if left untreated. A septic hip results in microorganisms activating an inflammatory response that recruits polymorphonuclear cells. Bacteria, synovial cells, and polymorphonuclear cells release enzymes that facilitate the degradation of glycosaminoglycans and the subsequent loss of collagen; this ultimately results in the gross destruction of articular cartilage and the development of arthritis if untreated early during the course of its development.

History

The typical history is quite variable for patients who present with synovial disorders. Patients with synovial chondromatosis are more commonly males in the third to fifth decade of life. They will typically present with deep groin and deep lateral hip pain that is often mechanical in nature as a result of loose bodies. These patients will frequently report catching and locking that may be quite unpredictable and that can have variable asymptomatic periods. Over time, the symptoms may become more frequent, with associated rest pain that is not related to activity; this may be the result of progressive articular cartilage destruction caused by the mechanical effects of the loose bodies. Pigmented villonodular synovitis typically presents during the third and fourth decades of life, with no gender predilection. It is typically monoarticular with associated aching and rest pain and variable mechanical symptoms. A longer duration of symptoms is associated with progressive degenerative and erosive changes and with a presentation that is similar to that of degenerative arthritis at a relatively young age. Patients will note progressive stiffness and range-of-motion limitations. Septic arthritis of the hip has a similar presentation to septic arthritis elsewhere. There is usually no history of trauma, and there may be a preceding illness. Septic arthritis of the hip is more prevalent among immunocompromised hosts and patients with frequent bacteremic episodes. Patients will often present with fever, chills, rapidly progressive groin pain, and irritability with range of motion. Joint aspiration is usually diagnostic. Inflammatory arthropathies that affect the hip joint can lead to end-stage arthritis. Earlier during the course of the disease, however, patients will occasionally present with hip joint irritability as a result of synovitis that is unresponsive to oral or injectable medication. Occasionally, this may be the first presentation of a patient with an undiagnosed inflammatory arthritis.

Physical examination

The physical examination findings of patients with synovial disorders can be variable. If intermittent mechanical symptoms are the primary complaint, the physical examination can be normal. When synovitis is present, pain is typically experienced with range of motion of the hip, primarily at the end of the range. These patients may have secondary labral tears and chondral pathology. The anterior impingement test (i.e., hip flexion, adduction, internal rotation) is indicative of anterolateral rim pathology, and the posterior impingement test (i.e., hip extension, external rotation) indicates posterolateral rim pathology. A septic hip will often present with a severely antalgic gait and extreme pain with any attempts at range of motion, whereas an active synovitis caused by an inflammatory arthropathy will present with pain at the end of the range of motion with variable, less dramatic pain during early and mid–range-of-motion testing. Global restrictions of range of motion are usually indicative of advanced disease and end-stage hip joint destruction. A complete examination of the lower back, the pelvis, extra-articular hip structures, and, occasionally, the gastrointestinal and genitourinary systems is critical to rule out other causes of pain that can be referred to the hip region.

Imaging and diagnostic studies

When evaluating a patient with symptoms that are consistent with hip joint pathology, plain radiographs should be obtained first. We typically obtain an anteroposterior radiograph of both hips with 2 cm to 4 cm between the pubic symphysis and the sacrococcygeal junction. A frog-leg lateral radiograph and a cross-table lateral radiograph with 15 degrees of internal rotation complete the initial series. Radiographic abnormalities may include arthritis, arthrosis, dysplasia, femoroacetabular impingement, and loose bodies. It has been reported that radiographs fail to diagnose loose bodies up to 50% of the time; this may be a result of the inconsistent calcification of these loose bodies and because they may be obscured by overlying structures. Large and multiple lucencies on plain radiographs are consistent with PVNS (Figure 21-1, A). Magnetic resonance arthrography (MRA) is the gold standard imaging technique for evaluating the hip joint proper. MRA has been shown to be very sensitive for labral tears and less accurate for chondral pathology. Filling defects can indicate loose bodies, as has been seen with synovial chondromatosis. As a result of hemosiderin deposition, pigmented villonodular synovitis is seen as a spotty or extensive low-signal area within proliferative synovial masses on T1 and T2 images; this condition is best seen on fast-field echo-sequence MRA images (see Figure 21-1, B). MRA imaging will typically reveal an effusion and variable degrees of synovitis in the setting of an acute septic hip; an aspiration can also be performed as part of this imaging. Chronic infection with associated osteomyelitis and adjacent abscesses should be ruled out in this setting before arthroscopic hip irrigation and synovial debridement are performed. MRA has important applications for imaging the rheumatoid joint. Bony erosions are visualized with MRA during the early stages of rheumatoid arthritis, and they are frequently detected before they appear on plain radiographs. MRA also detects bone marrow edema, which is another important feature that is associated with inflammatory joint disease and that may be a forerunner of erosion. Synovial membrane inflammation and hypertrophy are detected after contrast enhancement and also with the use of dynamic MRA techniques, which provide a noninvasive method for accurately measuring the inflammatory process.