| | | Volume 3, Issue 9 | September 2005 | | Janet Cochrane Miller, D.Phil., Author | Susanna I. Lee, M.D., Ph.D., Editor |
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| | Archived Issues of Radiology Rounds
MGH Department of Radiology Website
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| Imaging Evaluation of Knee Pain
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| - Knee pain evaluation differs depending on whether the etiology was traumatic or atraumatic
- If imaging is required, an initial radiographic (X-ray) examination should be ordered
- MRI is only indicated for evaluation of pain without mechanical symptoms if unexplained pain persists for 3-6 weeks
- Injuries
that are complex or indicative of tears in multiple ligaments should
have urgent referral to the emergency department or to an orthopedist
- Questions of acute septic joint will require aspiration. Plain film imaging may be helpful but is not diagnostic
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Knee
pain is categorized as traumatic or atraumatic, and as acute or non
acute. In each category, the presence of swelling, fever, and
pain severity should be assessed. Mechanical symptoms such as locking
or catching, and instability due to buckling, catching, or weakness
help determine the likely utility of imaging. Because the plain
film imaging study of knee pain differs on whether the cause is
traumatic or atraumatic, this aspect of the history should be provided
when the patient is referred for imaging.
Traumatic Knee Pain
The
injuries from trauma that need emergent treatment are fracture and
femoral-tibial dislocation. Symptoms that are indicative of severe
injury include extreme global pain that increases with weight bearing
or motion, and persists at rest. Joint swelling is generally rapid in
onset and accompanied by severe restriction of the range of motion
(usually only 20° arc). There may be a feeling of knee instability
(buckling, weakness with weight bearing, or a feeling of insecurity).
Symptoms
that indicate a possible fracture are localized point tenderness,
inability to flex the knee to 90°, age ≥ 55 yrs, or inability to bear
weight both immediately after the injury and in the emergency
department. These indicators have a sensitivity of 100% with a
specificity of 46-52%. Anterior-posterior and lateral plain film
examination for a fracture has a slightly lower sensitivity of 85-100%.
Hence, if the sympoms persist but radiography results are negative, a
follow up radiographic examination is appropriate.
| | Most Common Diagnoses for Acute Knee Pain in Adult Primary Care Setting | Sprain or strain | 42% | | Osteoarthritis | 34% | | Ligamentous injury | 11% | | Mensical injury | 9% | | Gout | 2% | | Fracture | 1.2% | | Rheumatoid arthritis | 0.5% | | Infectious arthritis | 0.3% | | Pseudogout | 0.2% |
If
there is evidence of femoral-tibial dislocation, which can occur as a
result of an automobile accident or high-speed impact, there is a
possibility of damage to the popliteal artery or nerve. These patients
should have evaluation in the emergency department, where specialists
may order MR angiography to evaluate for this possibility. Fractures
and injuries that result in tears in multiple ligaments or are
otherwise complex should have urgent referral to the emergency
department or to an orthopedist. For these presentations with clinical
signs of complex injuries, MRI imaging is usually not indicated prior
to subspecialist evaluation. If uncertain of the severity of the
injury, a referral to orthopedics is appropriate. In
cases where the injury is less severe, there is a strong likelihood
that the injury will not require surgery and that the pain will resolve
in 3-6 weeks. Therefore, if the plain films are negative, there is no
previous history of knee problems, no clinical evidence of instability
or giving way, and the pain is moderate, conservative treatment is
indicated (rest, NSAIDS, ice, compression, elevation, activity
modification, physical therapy, crutches). MRI may be indicated in
these patients if clinical re-evaluation 3-6 weeks after the injury
reveals persistent symptoms. In these cases, MRI may be ordered prior
to an orthopedic consultation. |
Plain
film radiographs of the right knee in a 49 year-old with knee pain.
Lateral (A) and anteroposterior (B) views demonstrate medial
compartment narrowing and small osteophytes (arrow) are consistent with
chronic degenerative changes. No fractures or joint effusion is
identified.
MRI
of the right knee 7 weeks following the plain radiographs demonstrates
mucoid degeneration of the anterior cruciate ligament. Proton density
images (A) demonstrate a normally-oriented anterior cruciate ligament
(solid arrow) with thickening and increased signal. The posterior
cruciate ligament (dashed arrow) is normal. Inversion recovery images
(B) demonstrate no joint effusion or marrow edema indicating that this
injury is likely subacute or chronic.
Comparison of Imaging and Clinical Examination for Acute Knee Pain | | Injury | Radiological Examination | Physical Examination |
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| Sensitivity | Specificity | Sensitivity | Specificity | | Fracture | Plain Radiography | 85-100% | 88-92% | 100% | 54% | | Meniscal tear | MRI | 79-89% | 80-91% | 86-88% | 72-92% | | Ligamentous tear | MRI | 75-87% | 91-93% | 74-81% | 95% | | Cartilage damage | MRI | 84% | 90% | 51% | 96% |
Results from a meta analyses of data published from 1986 to 1999 (Jackson et al, 2003)
| Atraumatic Knee Pain
Knee
pain that is atraumatic or has gradual onset is commonly due to
degenerative joint disease (osteoarthritis) but may also be due to
tendonitis, bursitis, inflammatory joint disease, chondromalacia,
osteochondritis dessicans, septic knee, or tumor. Patients presenting
with atraumatic knee pain should first be evaluated with plain film
radiographs. An anterior-posterior view in full extension will show
knee alignment, a posterior-anterior view while standing with 45°
inflexion is best for showing joint-space narrowing.
An
MRI examination may be indicated if the patient has not responded to a
trial of conservative treatment for 3-6 weeks. However, MRI alone has
little to offer for patients with non-traumatic knee pain, no
mechanical symptoms, and findings of degenerative arthritis on plain
films. Because the incidence of abnormal findings such as
meniscal tears is high in asymptomatic patients, any MRI finding must
be carefully correlated with clinical signs and symptoms.
Patients with persistent or recurrent unexplained pain after 3-6 weeks
of conservative treatment may require MRI and may require referral to
an orthopedist as a next step in the evaluation. However, it
should be noted that some orthopedic surgeons do not consider an MRI to
be necessary before arthroscopic surgery or total knee replacement.
Septic Knee
Symptoms
of warmth, marked pain with even a small range of knee motion,
exquisite tenderness, and painful effusion are consistent with septic
knee. In these cases, a routine X-ray may be helpful since an
underlying bone infection can break out into the joint and cause a
secondary infection. In addition, arthrocentesis and laboratory
analysis should be performed to evaluate for infection.
| | MGPO Guidelines for Knee Pain
Managed
care contracts at MGH require management of high cost imaging
utilization. In response, an MGH team, involving orthopedics,
radiology, primary care, and others has been working to develop
guidelines for the optimal management of knee pain. These
guidelines are scheduled to be distributed in the next few months.
Scheduling
Appointments
for knee imaging at all sites can be scheduled through the Radiology
Order Entry system, http://mghroe
or by calling 617-724-9729 (XRAY).
Further Information
For further questions, please contact William Palmer, M.D., Musculoskeletal Radiology, at 617-726-8784.
We
would also like to thank Arthur Boland, M.D., Orthopedic Surgery, and
Jeffrey B. Weilburg, M.D., Associate Medical Director, Massachusetts
General Physicians Organization, for their assistance and advice for
this issue. This article provided useful information about the appropriate use of imaging studies:
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References
| | | Boden, SD, Davis, DO, Dina, TS, Stoller, DW, et al. (1992) A prospective and blinded investigation of magnetic resonance imaging of the knee. Abnormal findings in asymptomatic subjects. Clin Orthop Relat Res 282: 177-85
Calmbach, WL and Hutchens, M. (2003) Evaluation of patients presenting with knee pain: Part I. History, physical examination, radiographs, and laboratory tests. Am Fam Physician 68: 907-12
Jackson, JL, O'Malley, PG and Kroenke, K. (2003) Evaluation of acute knee pain in primary care. Ann Intern Med 139: 575-88 |
©2005 MGH Department of Radiology
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