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Title
Imaging for Knee and Shoulder Problems
Authors
William Hollingworth, PhD
Department of Radiology, University of Washington, USA
Adrian K Dixon, MD, FRCR, FRCP
Department of Radiology, University of Cambridge, UK
John R Jenner, MD, FRCP
Rheumatology, Addenbrooke’s NHS Trust, Cambridge, UK
KEY POINTS
Issues
i.
Imaging of the knee:
1. What is the role of radiography in patients with an acute knee injury
and possible fracture?
2. When should MRI be used for patients with suspected meniscal or
ligamentous knee injuries?
3. Is radiography useful in evaluating the osteoarthritic knee?
Special case: Imaging of the painful prosthesis
ii.
Imaging of the shoulder:
1. When is radiography indicated for patients with acute shoulder pain?
2. Which imaging modalities should be used in the diagnosis of soft
tissue disorders of the shoulder?
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Key points
•
Knee radiographs of the acutely injured knee in the emergency department are rarely
useful for determining therapy except in patients: aged 55 or older; or with isolated
tenderness of patella; or with tenderness at head of fibula; or inability to flex 90 degrees;
or inability to weight bear both immediately and in the emergency department for 4 steps
(Strong evidence).
•
MRI is an accurate and valuable diagnostic tool for confirming or excluding the presence
of meniscal and cruciate ligamentous knee injuries (Moderate evidence). If used in
selected patients, in whom arthroscopy is probable but not inevitable, MRI can reduce the
overall arthroscopy rate and the number of purely diagnostic arthroscopies (Moderate
evidence).
•
There is currently insufficient evidence to demonstrate that the routine use of radiography
in patients with suspected chronic osteoarthritic knee pain will alter management or the
outcome of patients. However radiography is required before decisions regarding knee
replacement surgery.
•
The use of radiography to evaluate patients with suspected recurrent atraumatic shoulder
dislocation is unnecessary in most cases (Limited evidence). Furthermore, selective
imaging strategies may be able to rationalize the number of pre-reduction and/or postreduction radiographs required in suspected first-time or traumatic shoulder dislocations
(Limited evidence).
•
Ultrasound, MRI and MR arthrography all have high specificity in the diagnosis of full
thickness rotator cuff tears. Therefore in populations with a moderate prevalence of
rotator cuff tears, a positive result on any one of these tests can confirm the diagnosis
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with a high degree of certainty (Moderate evidence). Until further data are available, the
choice between these tests will be largely dependent on physician preference and
available resources.
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i.
Imaging of the knee
Issue 1 – What is the role of radiography in patients with an acute knee injury and possible
fracture?
Summary
Acute knee trauma provides a common diagnostic quandary in accident and emergency
departments. Fractures are present in 4 to 12% of patients presenting with knee injuries, and yet
radiography may be requested in excess of 70% of cases. Several guidelines are available to
help clinicians target imaging at high-risk patients. There is strong evidence (Level 1) to suggest
that the five criteria of the Ottawa Knee Rule (OKR) are highly sensitive at predicting fractures
in adults and moderate evidence (Level 2) that this rule can be generalized to children older than
5 years of age. Further work is needed to evaluate the impact of the OKR on the costeffectiveness of medical care.
Issue 2 – When should MRI be used for patients with suspected meniscal and ligamentous
knee injuries?
Summary
Empirical work demonstrates that the utilization of knee MRI among Medicare and Medicaid
enrollees increased rapidly by 140% in the early 1990s. There is limited evidence (Level 3) to
support the theory that, for some patients, a composite clinical examination performed by an
experienced musculoskeletal specialist can bypass the need for MR imaging by directly
identifying patients with cruciate or meniscal injuries amenable to arthroscopic repair. However,
there is also moderate evidence (Level 2) that MRI is a highly accurate method of diagnosing
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soft tissue knee injuries in patients where the clinical picture is not clear. If MRI is used in
patients likely to undergo arthroscopy, there is moderate evidence (Level 2) indicating that it can
substantially reduce the overall arthroscopy rate and limit the number of purely diagnostic
arthroscopies without detriment to patient quality of life.
Issue 3 – Is radiography useful in evaluating the osteoarthritic knee?
Summary
Radiography is frequently used to assess the extent of disease in the osteoarthritic knee.
However, there is poor correlation between imaging findings and patient symptoms.
Furthermore, there is currently insufficient evidence (Level 4) to support the hypothesis that
routine use of radiography in patients with chronic knee pain will improve patient management
and quality of life.
Special case: Imaging of the painful prosthesis
The potentially infected knee prosthesis is a case where the evidence for the various imaging
investigations is rather weak. The patient presents with pain and perhaps instability some
months/years after a successful knee replacement. Plain radiography of the total extent of the
prosthesis (including the femoral and tibial tips) is performed; interpretation is easier if these
images can be compared with those obtained at the post-operative stage, if available; lucency
around the stem of the prosthesis may be associated with loosening or infection. Despite
software developments to reduce artifacts from the metallic prosthesis, neither CT nor MRI can
offer much here. Skeletal scintigraphy can provide evidence of abnormal osteoblastic activity
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around the prosthesis which should be more intense in relation to infection than loosening; some
centers proceed to white cell scintigraphy which may help in this distinction. Other centers use
arthrography which may provide a microbiological sample if there is a large effusion. In any
event there is a wide range of sensitivities and specificities in these tests. Interpretation is also
complex because the investigations are often spread out over several weeks. Furthermore there is
frequently no gold standard as the ultimate arbiter, the decision to perform revision surgery, is
not undertaken lightly and is ultimately still based on clinical rather than radiological grounds.
At present, there is insufficient evidence (level 4) to recommend any particular imaging
approach.
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ii.
Imaging of the Shoulder
Issue 1 – When is radiography indicated for patients with acute shoulder pain?
Summary
Conventional teaching advocates both pre- and post-reduction radiographs for patients with
clinically suspected shoulder dislocation and survey data confirm that many hospitals follow this
recommendation. However, more recent research has provided limited evidence (Level 3) that
radiographs are not necessary in most patients with recurrent atraumatic dislocation.
Furthermore, there is limited evidence (Level 3) that the pre-reduction radiograph may be
omitted in traumatic joint dislocations provided that the clinician is confident of the diagnosis.
An alternative approach that eliminates the post-reduction radiograph in patients with prereduction radiographs demonstrating dislocation and no fracture is also supported by limited
evidence (Level 3). Limited evidence also suggests that, in patients without obvious shoulder
deformity, radiography should be targeted at those with bruising and/or joint swelling, or with a
history of fall, pain at rest and abnormal range of motion. However, more research is needed to
validate these guidelines and to provide head-to-head comparisons of selective imaging
strategies to demonstrate the relative the feasibility and cost-effectiveness of implementation.
Issue 2 – Which imaging modalities should be used in the diagnosis of soft tissue disorders
of the shoulder?
Summary
There is moderate evidence (Level 2) that both MRI and ultrasound have fairly high sensitivity
(>85%) and specificity (>90%) in the diagnosis of full-thickness rotator cuff (RC) tears and,
therefore, a positive test result is likely to be useful for confirming tears in patients for whom
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surgery is being considered. The results of ultrasound studies were more variable perhaps
reflecting the operator-dependent nature of the technique. The few studies conducted on the
accuracy of MRA suggest that it may be more accurate than either MRI or ultrasound, however
more data are needed to reinforce the limited evidence (Level 3) to date. Until these data are
available, the choice between ultrasound and MR techniques is likely to be primarily based on
physician preference and the availability of imaging equipment and personnel. The sensitivity of
all three of these minimally invasive tests for partial-thickness RC tears is relatively poor. This
may, in part, be due to the poorly defined diagnostic criteria for these more subtle lesions.
Several studies including a randomized trial have provided strong evidence (Level 1) that MRI
can influence the management of patients with shoulder pain. However, there is insufficient
evidence (Level 4) demonstrating an eventual benefit to patient quality of life.
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