Justin Strickland
Diane L. Dahm
Knee arthroscopy is the most common operative orthopaedic procedure performed in the United States. It is usually performed as an outpatient procedure and is associated with low morbidity and quick recovery. In addition, multiple types of pathology can be addressed at a single operation. Though the natural history of osteoarthritis is unchanged by arthroscopy, symptomatic relief can be achieved with this modality depending on the pathology found at the time of surgery. Recently, the efficacy of arthroscopy in the treatment of osteoarthritis has been questioned. Patient education and surgical indications are important in the discussion regarding the expectations following arthroscopy in the setting of osteoarthritis.
Preoperative Evaluation
Indications
The preoperative evaluation of patients with osteoarthritis is paramount in determining the outcome and expectations following arthroscopy. The following factors suggest higher likelihood of favorable response to arthroscopy:
Clinical Evaluation
When obtaining a history of knee pain from a patient, it is important to note the onset of symptoms and any recent change in symptoms. These patients frequently have a history of chronic knee pain; however, an acute exacerbation or change in the nature of the symptoms may indicate new pathology that may be amenable to arthroscopic treatment. If mechanical symptoms such as catching and locking are present, this may represent meniscal pathology, loose body formation, or an unstable articular cartilage fragment. Localization of pain is also an important factor. Isolated medial or lateral tenderness may indicate a focal articular lesion or symptomatic meniscal pathology. On physical exam, one should note any excessive varus or valgus malalignment or flexion/extension lags. A patient with malalignment in the coronal plane may be a candidate for osteotomy. Finally, patients should be given a trial of nonoperative measures before any operative procedure is undertaken. This might include shoe/heel wedges, use of braces, nonsteroidal anti-inflammatory drugs (NSAIDs) or other medications, injections (steroid and viscosupplementation) and physical therapy. Low-impact exercise and weight loss are also often effective for symptomatic relief in patients with osteoarthritis of the knee.
Radiographic Evaluation
Standing anteroposterior (AP), lateral, posteroanterior (PA) flexion, and sunrise views of the knee should be obtained. One may consider standing full-length hip to ankle films to evaluate alignment. Severe degenerative disease on plain films is a contraindication for arthroscopic treatment of osteoarthritis. Magnetic resonance imaging can be helpful to evaluate for focal cartilage defects. New techniques are now available that may differentiate articular cartilage from synovial fluid and subchondral bone, which makes it easier to identify these sometimes discrete lesions. One should interpret MRI findings in patients older than 65 years of age with osteoarthritis cautiously because a very high percentage of these patients will have a degenerative meniscus tear. As always, the radiographic findings should be correlated with the history and physical examination.
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Figure 22-1 Algorithm for treatment of knee osteoarthritis. TKA, total knee arthroplasty. |
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Figure 22-2 A: Arthroscopic technique of microfracture for a focal articular cartilage defect. B: Confirmation of bleeding subchondral bone in lesion bed. |
Diagnostic Workup Algorithm
An algorithm for evaluation of knee pain for arthroscopic intervention is presented in Figure 22-1.
Treatment
Options
The following options are available when performing arthroscopy in the setting of osteoarthritis:
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Multiple goals may be met when a patient with osteoarthritis undergoes an arthroscopic debridement. The degenerative knee has many potential mechanical irritants that may exacerbate a patient's symptoms. These include meniscal tears, unstable flaps of cartilage, and loose bodies. All pathology should be addressed at the time of surgery. It is recommended that chondroplasty and synovectomy be limited to areas that are symptomatic or have the potential to become problematic. Lavage of the joint may be beneficial as this will dilute the degradative enzymes present in the arthritic knee. Osteophytes may also be removed if found to be causing obvious impingement. The advantages of this approach include low morbidity, quick recovery, and the ability to perform a direct assessment of the articular cartilage. It is important to document the findings at the time of arthroscopy as this may influence future reconstructive options such as unicompartmental versus total knee arthroplasty. Even though arthroscopy is a relatively low morbidity, outpatient procedure, the surgeon and patient must remember that no surgical procedure is without risk. Complications such as infection, hematoma, and postoperative stiffness can rarely occur, and patients should be counseled about this possibility before the procedure.
Marrow stimulating techniques such as abrasion arthroplasty, microfracture, and drilling are options typically used for focal cartilage defects. These are more frequently used in younger, active patients with otherwise absent or mild degenerative changes on x-ray views. The goal of these procedures is to penetrate the subchondral bone overlying the defect to stimulate bleeding and the release of marrow contents. This will allow pluripotential mesenchymal cells to invade the defect and begin the process of fibrous metaplasia. Varying amounts of fibrocartilage will eventually fill the defect. Small amounts of hyaline cartilage may be present. Abrasion arthroplasty uses an arthroscopic burr to perform the technique. Simple drilling can also be performed; however, because of its ease of use and lack of heat generation, the so-called microfracture technique has become more widely used. Microfracture is a relatively simple technique using a specialized awl to penetrate the subchondral bone (Fig. 22-2). A depth of 2 to 4 mm is recommended. A bridge of at least 4 mm should be maintained between holes to sustain the integrity of the subchondral bone. Thermal necrosis is not an issue with microfracture as it may be with
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abrasion arthroplasty, standard drilling, or thermal chondroplasty.
Thermal chondroplasty is a technique that uses a radiofrequency probe to generate heat to denature collagen. This is effective in smoothing and stabilizing articular cartilage defects. However, it has not been proven that this method prevents the propagation of these lesions or that there is a benefit over mechanical chondroplasty. In addition, significant chondrocyte death has been reported with both bipolar and monopolar systems in in vitro studies. This is concerning as it can be difficult to control the temperature of the probe at the cartilage surface. Irreversible damage to articular cartilage occurs at >55°C. Because of these uncertainties, we recommend using this modality with extreme caution and suggest that further studies are needed to justify its routine use to treat cartilage defects.
Results
The clinical results obtained following arthroscopy for osteoarthritis are difficult to interpret. Most published reports are retrospective with variable inclusion criteria, definition of procedures, and outcome measures. These studies have found that arthroscopic debridement yields satisfactory results in 60% to 70% of patients at 2- to 4-year follow-up. There appears to be no clear advantage to subchondral drilling or abrasion arthroplasty in these patients. One prospective study comparing arthroscopic debridement versus placebo surgery found no difference in clinical outcome at 2-year follow-up. In this study, however, patients were not stratified with respect to presence or absence of meniscal pathology, mechanical symptoms/signs, or malalignment. In another prospective outcome study, 44% of patients were found to have improvement in pain at 2-year follow-up. Variables associated with improvement included medial joint line tenderness, a positive Steinman test, and the presence of an unstable meniscus tear at arthroscopy. Older patients (>70 years of age) were more likely to be treated with early total knee arthroplasty following arthroscopic debridement compared with patients younger than 60 years of age. This is consistent with the fact that arthroscopic debridement does not change the natural history of osteoarthritis.
With respect to marrow stimulating techniques, the available data support the use of microfracture for focal cartilage defects. Significant improvements in outcome can be expected in 70% to 80% of patients. Improved results are found in those patients with lower body mass index (<30 kg/m2), relatively short duration of preoperative symptoms, and higher fill grade as measured by postoperative MRI. In addition, microfracture combined with medial opening wedge osteotomy has been shown in one study to decrease pain and improve function in those patients with chondral defects and varus malalignment at a minimum follow-up of 2 years.
In summary, the role of arthroscopy for osteoarthritis of the knee remains controversial. Symptomatic relief can be expected when patients are carefully selected and properly counseled. The best outcomes are found in patients with a short duration of symptoms of which mechanical symptoms are a significant component, those with unstable meniscal tears and mild to moderate changes on x-ray films, and those who are in the early stages of the disease process without significant malalignment (Table 22-1). Despite these findings, one study showed surgeons were only 60% accurate in predicting which patients would have a successful outcome following arthroscopy.
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TABLE 22-1 Results |
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Postoperative Management
Patients may weight-bear as tolerated following simple arthroscopic debridement and lavage for osteoarthritis of the knee. Pain control measures may include intraoperative subcutaneous anesthetic injection, intra-articular anesthetic, corticosteroid or narcotic injection, intra-articular pumps for postoperative local anesthetic delivery, oral pain medications, and edema control. Based on data from experimental and clinical studies, the use of continuous passive motion and protected weight bearing is widely used for 6 weeks following marrow stimulating procedures. There is some evidence to suggest that dynamic compression may facilitate a better-quality repair tissue, which in theory would contain a higher percentage of hyaline cartilage. It is unknown if this protocol affects long-term clinical outcomes following microfracture.
A gradual return to primarily low-impact activities is suggested when pain and swelling have decreased and strength has returned. Return to higher-level impact activities and sports has not been well studied in this population, and recommendations should be individualized based on the patient's goals and clinical outcome.
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Lu Y, Edwards RB, Colby J, et al. Thermal chondroplasty with radiofrequency energy. An in vitro comparison of bipolar and monopolar radiofrequency devices. Am J Sports Med. 2001;29:42–49.
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