Robert J. Esther
Osteoarthritis or the inflammatory arthropathies cause the vast majority of knee degeneration. A handful of other conditions, however, can lead to significant morbidity. It is important for the physician to be familiar with these less common entities to avoid diagnostic pitfalls and to provide appropriate care. Although this review stresses the orthopedic issues in caring for these patients, treating these conditions often is best accomplished with coordinated input from different specialties. These conditions (Table 21-1) are a heterogeneous group with various causes. Although they are uncommon, it is useful to be aware of the key features of these conditions when evaluating a patient with knee complaints.
Pathogenesis
Osteonecrosis
Osteonecrosis of the knee comprises an array of entities. The exact mechanism for development of this condition remains elusive. An area of the involved bone sustains an ischemic insult that initiates a process of remodeling and collapse. Depending on the location and extent of this collapse, articular surface incongruity leads to joint degeneration. Spontaneous osteonecrosis usually develops in older patients (sixth or seventh decade) without any antecedent trauma or other known risk factor. Younger patients also may develop knee osteonecrosis, usually in association with trauma or other known risk factors such as alcohol consumption or corticosteroid use.
Synovial Chondromatosis
Synovial chondromatosis is an idiopathic process in which articular (hyaline) cartilage is produced in the soft tissues around joints. These cartilaginous areas can then break free and become loose bodies. Patients develop locking, catching, and other mechanical symptoms based on the size and number of these cartilaginous lesions. As a consequence of intra-articular loose bodies, patients develop secondary degenerative changes. Most cases are monoarticular, with the knee joint involved most commonly. Men are approximately two times more likely than women to develop this disorder.
Secondary chondrosarcoma arising in synovial chondromatosis is an exceedingly rare phenomenon. If imaging or clinical findings raise even the possibility of malignancy, it is appropriate to refer the patient to an orthopedic oncologist for further management.
Hemophilic Arthropathy
Hemophilic arthropathy occurs as a consequence of recurrent intra-articular hemorrhages in patients with clotting factor deficiencies. Hemophiliac arthropathy therefore begins with intra-articular bleeding. Reaction to intra-articular blood leads to varying degrees of synovitis. This inflamed synovium is then more susceptible to further intra-articular bleeds, setting up a potential cycle in which patients have recurrent hemarthroses. The extensive chronic synovitis that ensues eventually leads to joint erosions and, over time, end-stage arthropathy.
Pigmented Villonodular Synovitis
Pigmented villonodular synovitis (PVNS) is an idiopathic proliferative condition of synovium in which there is an accumulation of giant cells and hemosiderin. PVNS does not have malignant potential but can be locally aggressive, leading to considerable synovitis that produces erosions and secondary degenerative changes. The knee joint is most commonly involved and, as in synovial chondromatosis, most cases are monoarticular. PVNS is a synovial disease but also can involve periarticular sites such as tendon sheaths and bursae.
Gout and Pseudogout
Patients with pseudogout and gout can develop intra-articular reactions to the characteristic crystals of the two conditions. The body mounts an inflammatory response to the crystals, thereby leading to secondary joint inflammation and eventually degeneration. Patients with calcium pyrophosphate deposition disease (CPPD), or pseudogout, may have a spectrum of findings from acute synovitis to a long-standing arthropathy with secondary degenerative changes. These patients also can develop deposits in hyaline
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and meniscal cartilage. Gout is caused by symptomatic elevation of uric acid, also leading to an inflammatory response to crystals. A combination of dietary factors and medicines—especially thiazide diuretics—can precipitate gouty flares.
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TABLE 21-1 Less Common Causes of Knee Degenerative Joint Disease |
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Diagnosis
Physical Examination and History
As with any medical condition, the evaluation of these patients begins with a careful history. The orthopedist should inquire about onset and duration of symptoms, any antecedent of inciting events, other joints involved, and systemic conditions for which the patient requires medical treatment. Patients with hemophilia should be asked about the number of prior intra-articular bleeds.
As discussed in prior chapters, physical examination should include surface appearance, limb alignment, range of motion, tenderness, instability, presence of effusion, and a thorough neurovascular exam.
For patients with an effusion, an aspiration may be diagnostically useful and give considerable, albeit temporary, symptomatic relief. Synovial fluid in gout and pseudogout will show characteristic crystals under the microscope: Uric acid crystals will be negatively birefringent, and calcium pyrophosphate crystals will be positively birefringent. As some laboratories do not routinely examine body fluid for crystals, it is important to specify this request on the order. Synovial fluid may be bloody in patients with PVNS, but a nonbloody tap does not necessarily exclude this diagnosis. Synovial fluid should also be sent for further laboratory investigations including cell count and, when warranted, Gram stain and culture.
Radiologic Features
Although in some instances a patient may be referred having already had an MRI or other advanced cross-sectional imaging, the accepted first step in radiographic evaluation should be orthogonal plain x-ray films. In addition to these films, additional radiographs may be useful. A standing anteroposterior (AP) view of both knees affords the opportunity to evaluate the contralateral joint. A patellar view is useful for evaluating the patellofemoral articulation. In addition to the usual radiographic stigmata of joint degeneration, films should be scrutinized for loose bodies, radiolucent bony changes, effusions, and changes in the soft tissues. As noted in other chapters, concerns about limb alignment should be addressed by long-leg films that include the hip and ankle.
Although most orthopedists are comfortable with the radiographic manifestations of knee degeneration, the conditions in this chapter often require ancillary studies such as bone scan or magnetic resonance imaging (MRI). As with all medical tests, advanced imaging should be ordered to answer a specific question that will guide diagnosis or treatment. MRI is also useful in the face of unusual or unexpected findings on plain films, such as radiolucent changes on both the tibial and femoral sides of the knee joint. Magnetic resonance imaging is clearly superior to plain films for evaluating soft tissues, bone marrow, and articular cartilage. Computed tomography (CT) scanning is not usually indicated or helpful in the conditions outlined here. Although orthopedists are increasingly comfortable with different imaging modalities, a radiologist with specialized musculoskeletal training is invaluable in choosing which imaging studies are most appropriate and also in the subsequent interpretation of these studies.
Radiographic diagnosis of knee osteonecrosis may be difficult, especially in early stages. Plain films may be negative initially. Traditionally, bone scans have been used for diagnosis. More recent reports show a high sensitivity for MRI. Moreover, MRI is useful in characterizing the exact location and extent of bony and cartilaginous involvement. The classic location of knee osteonecrosis is the medial femoral condyle, but the lateral condyle and proximal tibia also may be involved.
Radiographic manifestations of synovial chondromatosis include intra-articular and periarticular cartilaginous bodies (Fig. 21-1). As these bodies contain varying amounts of mineral, not all will necessarily show up on plain films. MRI is useful in these cases to see the extent and number of loose bodies. As with PVNS, the location and extent of disease as characterized on MRI helps the surgeon plan the appropriate operative treatment.
The radiographic manifestations of PVNS may be subtle, including joint erosions that may appear on both sides of a joint. Occasionally, one may appreciate a soft tissue mass or large effusion on plain film (Fig. 21-2). Because PVNS is a soft tissue process, MRI is the best imaging method to gauge the extent of disease (Fig. 21-3). MRI is extremely useful in preparing an appropriate treatment plan for PVNS of the knee.
Calcium pyrophosphate deposition has a typical radiographic appearance termed chondrocalcinosis. Radiographic manifestations include calcifications of the articular cartilage and the meniscus. Unless one suspects a superimposed meniscal tear or other intra-articular pathology, MRI is not indicated as part of the workup of CPPD.
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Figure 21-1 Anteroposterior (A) and lateral (B) knee x-ray views showing mineralized cartilaginous areas consistent with synovial chondromatosis. |
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Figure 21-2 Lateral knee radiograph in a patient with pigmented villonodular synovitis. Note the considerable soft tissue mass posteriorly and the absence of significant osseous abnormalities. |
Treatment
Nonoperative Management
As with many musculoskeletal disorders, the first line of treatment in many of these conditions is symptomatic care
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including symptom modification and anti-inflammatory medication. Surgical management is indicated when nonoperative methods no longer benefit the patient.
Appropriate medical management is important in treating patients with hemophilia. Avoiding trauma and closely following clotting factor levels are two straightforward ways to minimize the number of intra-articular bleeds. Patients with recent bleeds also may benefit from a brief period of joint immobilization to allow time for soft tissues to recover. Because patients with hemophilic arthropathy tend to develop soft tissue contractures, however, immobilization should be used judiciously.
Patients with hemophilia should be treated at medical centers where the surgeon is supported by an active medical hemophilia program. Hemophiliacs undergoing invasive procedures should be screened for clotting factor inhibitors.
In hemophiliacs, operative intervention not only is potentially dangerous, but also consumes considerable resources, including the time and energy of consulting services and laboratory surveillance of factor and inhibitor levels. For this reason, P-32 radiation synovectomy is attracting increasing interest in the treatment of early arthropathy. Radiation synovectomy is especially appropriate in patients without significant joint degeneration. Although it obviously cannot reverse existing articular damage, the procedure can help break the vicious and destructive cycle of synovial irritation and intra-articular hemorrhage.
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Figure 21-3 Proton density (A) and T2 (B) magnetic resonance images of the same knee as Figure 21-2 showing extensive pigmented villonodular synovitis (PVNS). |
Management of gout is primarily symptomatic. Anti-inflammatory medicines and colchicine are useful in acute flares. For long-term control of high blood uric acid levels, patients should be managed in conjunction with colleagues
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in internal medicine. Pharmacologic treatment (allopurinol) in combination with dietary modifications is recommended.
Osteonecrosis typically is managed nonoperatively at first. However, symptoms frequently persist and operative treatment, usually with arthroplasty, commonly is needed.
PVNS and synovial chondromatosis typically are not amenable to nonsurgical treatment. The natural history of PVNS, especially the diffuse form, is progressive joint erosions and arthropathy. As with hemophiliac arthropathy, there is some interest in using radioactive synovectomy in these patients. Although synovial chondromatosis typically is considered to be less aggressive and self-limiting, the loose bodies of this condition often cause pain, loss of function, and eventually secondary joint degeneration.
Surgical Indications and Outcomes
Patients with hemophilic arthropathy were traditionally managed with open synovectomies. Current trends favor the use of arthroscopic treatment. These procedures require less clotting factor support and are less morbid than open surgical approaches.
Management of end-stage hemophilic arthropathy depends on several issues, including the amount of pain and desired level of function and activity. These patients can have compromised bone stock, distorted osseous architecture, and severe soft tissue contractures from superimposed arthrofibrosis. In spite of these potential difficulties, outcomes of knee replacements in this population may be favorable, but are associated with a higher rate of infection.
Arthroscopic or open synovectomy is the treatment of choice for synovial chondromatosis. When possible, arthroscopic procedures allow the surgeon to remove synovium and loose bodies while avoiding the morbidity of an open approach. Occasionally, extensive disease and difficult location require open synovectomy and debridement. Because patients with these conditions often begin with decreased range of motion, an early and closely supervised physical therapy program is essential postoperatively.
The outcome of treatment of synovial chondromatosis usually is favorable. Some patients develop recurrent disease, but the natural history commonly involves regression of disease. Patients may develop secondary arthritis from loose bodies and may require joint replacement.
Treatment of osteonecrosis ranges from symptomatic, nonoperative care to osteotomies, condylar allografts, and joint replacement. Core decompression and arthroscopic debridement also have been recommended with varying rates of success. The main determinants of treatment choice include the location of the lesion, the amount of joint involvement, the extent of secondary degenerative changes, overall limb alignment, and patient age. Historically, outcomes of knee replacement in osteonecrosis have not been as successful as in other conditions. More recent reports have been more encouraging, however.
Although synovial chondromatosis usually follows a self-limiting course over time, diffuse PVNS is locally aggressive. Inadequate removal of involved synovium can lead to recurrent disease; local recurrence rates are reported as high as 50% in the literature. Localized nodular forms of PVNS may be amenable to arthroscopic removal, but diffuse PVNS should be treated with an open total synovectomy. For patients with advanced degenerative changes, treatment options are nonoperative management versus total joint replacement. Knee fusion has fallen out of favor and should be considered a salvage procedure.
Treatment of crystalline arthropathies is symptomatic. In patients with long-standing disease and extensive surface damage, total knee arthroplasty may be indicated with an expectation of success equal to that for osteoarthritis.
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Patients with gout should continue their preoperative medical regimen to prevent flares in other joints.
Postoperative Management
Management of patients with these conditions includes the principles of postoperative care outlined in previous chapters. Coordinated multispecialty input often is in the patient's best interest. Patients with long-standing adrenal suppression from oral corticosteroids may need perioperative stress dosing. Hemophiliacs obviously must have appropriately titrated clotting factor levels and perioperative input from a hematology service. These patients need clotting factor support for several weeks following the procedure as they embark on a therapy program. Again, close collaboration with colleagues in internal medicine is essential for appropriate perioperative care.
Especially for those patients undergoing open synovectomies, early institution of a physical therapy program is critical. Patients with synovial chondromatosis and PVNS can be affected by a vicious cycle of decreased motion that is further compromised by open and extensive surgery around the involved joint. These patients should receive particularly close attention from therapists and begin working on range of motion as soon as the periarticular soft tissues allow. Hemophiliacs often have considerable preoperative flexion contractures and they, also, should have especially close follow-up with therapy.
Conclusion
Although less common than other knee disorders, the diagnoses discussed above can be treated with reasonable expectations of success if one is aware of the potential difficulties in diagnosis and treatment. Multispecialty care is important and can minimize morbidity and perioperative complications.
Suggested Readings
Flandry FC, Jacobsen KE, Hughston JC, et al. Surgical treatment of diffuse pigmented villonodular synovitis of the knee. Clin Orthop. 1994;300:183–192.
Luck JV, Silva M, Rodriguez-Merchan EC, et al. Hemophilic arthropathy. J Am Acad Ortho Surg. 2004;12:234–245.
Mont MA, Rifai A, Baumgarten KM, et al. Total knee arthroplasty in osteonecrosis. J Bone Joint Surg Am. 2002;84:599–603.
Siegel HJ, Luck JV, Siegel ME. Advances in radionuclide therapeutics in orthopaedics. J Am Acad Ortho Surg. 2004;12:55–64.
Wold LE, Adler CP, Sim FH, et al. Atlas of Orthopedic Pathology. Philadelphia: WB Saunders; 2003.