Arthroscopy of the osteoarthritic knee is a common and costly practice with limited and specific indications. The extent of osteoarthritis (OA) is determined by joint space narrowing, which is best measured on a weight-bearing radiograph of the knee in 30° or 45° of flexion. The patient older than 40 years with a normal joint space should have a magnetic resonance image taken to rule out focal cartilage wear and avascular necrosis before undergoing arthroscopy. Randomized controlled trials of patients with joint space narrowing have shown that outcomes after arthroscopic lavage or debridement are no better than those after a sham procedure (placebo effect), and that arthroscopic surgery provides no additional benefit to physical and medical therapy. The American Academy of Orthopedic Surgeons guideline on the Treatment of Osteoarthritis of the Knee (2008) recommended against performing arthroscopy with a primary diagnosis of OA of the knee, with the caveat that partial meniscectomy or loose body removal is an option in patients with OA that have primary mechanical signs and symptoms of a torn meniscus and/or loose body. There is no evidence that removal of loose debris, cartilage flaps, torn meniscal fragments, and inflammatory enzymes have any pain relief or functional benefit in patients that have joint space narrowing on standing radiographs. Many patients with joint space narrowing are older with multiple medical comorbidities. Consider the complications and consequences when recommending arthroscopy to treat the painful osteoarthritic knee without mechanical symptoms, as there is no proven clinical benefit.
This article presenting a case of a patient with a recent insidious onset of knee pain due to osteoarthritis (OA) is used to illustrate the invaluable information gained from the use of weight-bearing radiographs and magnetic resonance imaging (MRI) of the knee. The use of standing radiographs in 30° or 45° of flexion to rule out joint space narrowing, and the use of MRI in the knee without radiographic evidence of joint space narrowing to look for wear of the articular cartilage and avascular necrosis before recommending arthroscopy is stressed. Two level 1 studies and the American Academy of Orthopedic Surgeons (AAOS) 2008 treatment guidelines are used to review the contraindications and indications of arthroscopic treatment. Three relative indications for treating the painful knee with mild OA and mechanical symptoms from a loose body, meniscus tear, and anvil osteophyte with arthroscopy are discussed.
A 60 year-old man who has struggled with his weight for years presented with 3 months of medial knee pain that prevented him from walking his customary 2 miles a day and has caused him to gain weight. The onset of his pain gradually increased without trauma. The medial area of the knee became sorer the more he walked. He reported occasional night pain that interfered with sleep. He had full motion, a trace effusion, but no mechanical symptoms. His primary care physician treated him with nonsteroidal anti-inflammatory medication, a trial of physical therapy, and a cortisone injection without lasting pain relief. A weight-bearing radiograph of the knee in full extension showed marginal osteophytes but no joint space narrowing, and the radiologist’s MRI report, which the patient had read, identified a degenerative tear of the medial meniscus with cartilage thinning on the medial tibia and femoral condyle (Figure 1). He is impatient, frustrated, convinced that the torn meniscus is causing his pain, and that to resume walking and shed his recent weight gain imposed by inactivity he needs arthroscopic surgery.
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|Figure 1: Weight-bearing radiograph of the knee in full extension (A), MRI of the medial hemijoint (B), and an intraoperative photograph of the cartilage wear at time of TKA (C). The weight-bearing radiograph in full extension shows no medial joint space narrowing and underestimates the cartilage wear shown in the MRI (arrow) and intraoperative photograph (arrow). The reading of the MRI indicated a degenerative medial meniscal tear, however the patient’s pain was more attributable to the lack of articular cartilage on the femur and tibia (arrow) than the incidental finding of the torn meniscus. This patient should have had a weight-bearing radiograph of the knee in 30° to 45° of knee flexion to detect joint space narrowing, which would have eliminated the need for the MRI and any consideration of arthroscopic treatment. |
Should additional standing radiographs in flexion be obtained to determine the level of arthritis before recommending arthroscopic treatment? How can the orthopedist use the weight-bearing radiograph and MRI to counsel the patient as to the cause of the pain and treatment alternatives? Is there evidence from Level 1 studies to support arthroscopic treatment of his knee?
Use of Radiographs and MRI Before Recommending Arthroscopy
The patient’s age, extra weight, lack of trauma, and no mechanical symptoms suggest this patient has a flare up of preexisting, unrecognized degenerative arthritis of the knee and weight-bearing radiographs of both knees were indicated. Weight-bearing posteroanterior radiographs of the knee in 30° or 45° of flexion should be ordered as the view of the knee in flexion is more sensitive in detecting and showing more joint space narrowing than the conventional anteroposterior radiograph in full extension that was described by Ahlbäck in 1968 (Figure 2).1-3
|Figure 2: Weight-bearing radiograph of a right knee showing the effect that imaging the knee in full extension (left) and 45° of flexion (right) has on detecting the amount of joint space narrowing. The weight-bearing view of the knee in 45° of flexion shows no lateral joint space, while the view in full extension shows 2 mm of joint space. The best view for detecting joint space narrowing is the weight-bearing 30° and 45° knee flexion view (right). Arthroscopic treatment is rarely indicated when the weight-bearing 30° and 45° knee flexion view shows joint space narrowing. |
Joint space narrowing of >2 mm on any weight-bearing radiographs was correlated at the time of arthroscopy with ulceration involving the deep zones of the articular cartilage (grade III) and exposure of subchondral bone (Grade IV).2 The orthopedist can counsel the patient by showing the joint space narrowing on the weight-bearing radiograph of the knee and explaining that there is a direct correlation between joint space narrowing and the arthroscopic findings. With this explanation, the patient can better understand and accept that the insidious pain is more attributable to preexisting underlying OA and not the torn meniscus.
A patient older than 40 years with knee pain and weight-bearing radiographs in flexion and extension that show no joint space narrowing should have an MRI of the knee to rule-out cartilage wear and avascular necrosis before recommending arthroscopy (Figure 3). In the older patient, MRI often detects extensive areas of cartilage loss when the joint space appears normal on standing radiographs. Showing the cartilage wear on the MRI to the patient can help convince them their pain is more likely attributable to OA and that arthroscopic removal of a degenerative meniscus tear is unlikely to provide benefit and improve function. Further explanation that the prevalence of meniscus tears increases with increasing age, and that asymptomatic meniscal tears on MRI of the knee are common in the general population with no knee pain, aching, or stiffness may be needed.4
|Figure 3: MRI of the medial hemijoint of a knee showing a degenerative meniscal tear, mild cartilage loss, and subchondral fracture in the proximal tibia due to avascular necrosis. The patient read the radiologist’s description of the study and falsely concluded that the meniscal tear caused his symptoms and insisted on arthroscopic treatment. The patient was convinced after seeing the subchondral fracture and the mild cartilage loss that arthroscopic treatment would not be helpful. The MRI can change treatment recommendations when weight-bearing radiographs do not show joint space narrowing. |
Contraindications for Treating the OA Knee With Arthroscopy
Many patients report symptomatic relief after undergoing arthroscopy of the knee for OA, however it has been unclear how the procedure achieves this result.5 A randomized clinical trial in a single center by a single surgeon in predominantly male patients with moderate and severe joint space narrowing (Kellgren-Lawrence grade 3 and 4)6 showed that outcomes after arthroscopic lavage or arthroscopic debridement were no better than those after a sham procedure (placebo effect).7 A randomized clinical trial in a single center by multiple surgeons in a population consisting of 60% women with mild to severe joint space narrowing (Kellgren-Lawrence grade 2 to 4) showed that arthroscopic surgery for OA of the knee provided no additional benefit to physical therapy (1 session per week for 12 weeks followed by an unsupervised program at home), patient education, and the stepwise use of acetaminophen, nonsteroidal anti-inflammatory drugs, glucosamine, and the injection of hyaluronic acid.5,8 Accordingly, the American Academy recommended against performing arthroscopy with debridement or lavage in patients with primary diagnosis of symptomatic OA of the knee (Guideline 18); however, they recommended considering partial meniscectomy or loose body removal in patients with symptomatic OA of the knee who also have primary signs and symptoms of a torn meniscus and/or a loose body (Guideline 19).9
Three Indications for Treating the OA Knee With Arthroscopy
One indication for treating the knee with mild to severe OA with arthroscopy is the complaint of mechanical symptoms from a loose body and (Figure 4). For the loose body to be mobile and cause locking, it should reside anterior to the knee in the suprapatellar pouch on the radiograph. A posterior loose body typically is not mobile and does not cause locking because it is trapped inside the walls of a Baker’s cyst. A second indication is arthroscopic removal of a meniscal tear when the presenting symptoms are mechanical with pain localized on the joint line in the knee with mild joint space narrowing (Kellegren-Lawrence grade 1). A meniscal tear is rarely the primary cause of pain in the knee with radiographic moderate to severe OA (Kellegren-lawrence grade 3 and 4). The third indication is arthroscopic excision of an anterior anvil osteophyte to improve extension in the knee with mild OA and a flexion contracture (Figure 5).10
|Figure 4: Lateral radiographs of 2 knees showing the typical location of symptomatic (left) and asymptomatic (right) loose bodies in the osteoarthritic knee. Symptomatic loose bodies are anterior to the knee in the suprapatellar pouch and are mobile. Asymptomatic loose bodies are posterior to the knee and because they are trapped in a Baker’s cyst they are not mobile and do not cause mechanical symptoms of locking. |
|Figure 5: Lateral radiograph shows an anvil osteophyte (outlined by dots) in a knee with a flexion contracture and mild osteoarthritis. Arthroscopic excision of the anvil osteophyte can remove the mechanical block between the anvil osteophyte and the intercondylar notch and restore extension. |
A patient should not be treated with arthroscopy when the weight-bearing radiographs in either 0° and 45° of knee flexion show joint space narrowing, the MRI shows substantial cartilage wear indicating OA, and there are no mechanical symptoms of a loose body, meniscal tear, or an extension loss from an anvil osteophyte. Counsel the patient that the prevalence of coexisting meniscal tears and OA in middle-aged and elderly patients is high4,8 and that arthroscopic debridement of the osteoarthritic knee is no more effective than sham surgery and physical and medical therapy. 5,7
- Davies AP, Calder DA, Marshall T, Glasgow MM. Plain radiography in the degenerate knee. A case for change. J Bone Joint Surg Br. 1999; 81(4):632-635.
- Rosenberg TD, Paulos LE, Parker RD, Coward DB, Scott SM. The forty-five-degree posteroanterior flexion weight-bearing radiograph of the knee. J Bone Joint Surg Am. 1988; 70(10):1479-1483.
- Ahlback S. Osteoarthrosis of the knee. A radiographic investigation. Acta Radiol Diagn (Stockh). 1968; (Suppl 277):7-72.
- Englund M, Guermazi A, Gale D, et al. Incidental meniscal findings on knee MRI in middle-aged and elderly persons. N Engl J Med. 2008; 359(11):1108-1115.
- Kirkley A, Birmingham TB, Litchfield RB, et al. A randomized trial of arthroscopic surgery for osteoarthritis of the knee. N Engl J Med. 2008; 359(11):1097-1107.
- Kellgren JH, Lawrence JS. Radiological assessment of osteo-arthrosis. Ann Rheum Dis. 1957; 16(4):494-502.
- Moseley JB, O’Malley K, Petersen NJ, et al. A controlled trial of arthroscopic surgery for osteoarthritis of the knee. N Engl J Med. 2002; 347(2):81-88.
- Marx RG. Arthroscopic surgery for osteoarthritis of the knee? N Engl J Med. 2008; 359(11):1169-1170.
- AAOS Guidelines. Treatment of osteoarthritis of the knee (non-arthroplasty). http://www.aaos.org/research/guidelines/guide.asp. Accessed June 24, 2009.
- Lakdawala A, Ireland J. The ‘anvil’ osteophyte-a primary cause of fixed flexion of the knee? Knee. 2005; 12(3):191-193.
Dr Howell is from the Department of Mechanical Engineering, University of California Davis, Sacramento, California.
Dr Howell is a consultant for Biomet Sports Medicine and Stryker Orthopaedics.
Presented at Current Concepts in Joint Replacement 2009 Winter Meeting; December 9-12, 2009; Orlando, Florida.
Correspondence should be addressed to: Stephen M. Howell, MD, University of California Davis, 8100 Timberlake Way, Ste F, Sacramento, CA 95823 (email@example.com).