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1 Department of Radiology, Orthopedic University Hospital, Balgrist, Forchstr.
340, Zurich CH-8008, Switzerland.
2 Department of Orthopedic Surgery, Orthopedic University Hospital, Balgrist,
Zurich CH-8008, Switzerland.
Received November 20, 2002;
accepted after revision February 28, 2003.
Address correspondence to K. Strobel
(klaustro{at}bluewin.ch).
Abstract
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MATERIALS AND METHODS. The acromioclavicular joint of 50 patients (20 women, 30 men; mean age, 51 years; range, 25-75 years) was evaluated on MRIs of the shoulder. Osteophytes, subchondral cysts and irregularities, bone marrow edema, joint effusion, and joint capsule hypertrophy were assessed by two musculoskeletal radiologists in consensus. Local anesthetics were injected into the acromioclavicular joint with fluoroscopic guidance. Patients graded pain relief on a visual analogue scale (0-100%) after 15 min. The relationship between pain relief and MRI findings was assessed with the Mann-Whitney U test. Pain relief equal to or greater than 70% was rated as a positive response to the injection. This cutoff value was used to calculate sensitivity, specificity, accuracy, and predictive values of the various MRI findings in determining which acromioclavicular joints were responsive to joint injections.
RESULTS. Mean pain relief after injection was 38%. Pain relief was significantly related to capsular hypertrophy (p = 0.007) and was equal to or greater than 70% in 11 patients. The sensitivity in diagnosing a successful injection (range, 9-82%) was highest for caudal osteophytes (82%) and capsular hypertrophy (73%). The specificity (range, 51-97%) was highest for subchondral cysts (97%), subchondral bone marrow edema (95%), and joint effusion (92%).
CONCLUSION. Pain relief after intraarticular injection is significantly related to capsular hypertrophy diagnosed on MRI. MRI findings have a reasonable sensitivity and a high specificity in predicting relevant short-term pain relief after intraarticular injection.
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The purpose of this study was to evaluate which MRI findings in the acromioclavicular joint are predictive of pain relief after intraarticular injection.
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The patients were excluded from the study when the time interval between MR arthrography and the acromioclavicular joint injection was longer than 4 months (n = 56), when they had previously undergone shoulder surgery (n = 43), and when they had concurrent injection of the acromioclavicular joint and the subacromial space (n = 53). In five patients, either the MRIs or the fluoroscopic images obtained during the injection were not available for review. This resulted in a study population of 50 patients (20 women, 30 men; mean age, 51 years; age range, 25-75 years).
In these 50 patients, symptomatic acromioclavicular joint osteoarthritis had been suspected before the injection but had to be reconfirmed for therapeutic decisions, which potentially included acromioclavicular joint resection. In 46 of the 50 patients, the details of the clinical decision-making were specifically documented in the patient's charts (either body cross test or pain during local palpation or both). Rheumatoid arthritis and septic arthritis were excluded clinically. None of the patients had major trauma. Extrinsic causes of shoulder pain were excluded by a detailed physical examination of the cervical spine. In equivocal cases (n = 8), MRI of the cervical spine was performed. These MRIs did not show abnormalities relevant for the differential diagnosis of acromioclavicular joint osteoarthritis.
Informed consent was obtained for all examinations. The study was accepted by the hospital's ethics committee.
Acromioclavicular Joint Injection
The injection of the acromioclavicular joint was performed with
fluoroscopic control with a 25-gauge needle introduced either anteriorly or
superiorly with the patient in the supine position. First, 0.3 mL of contrast
material (Iopamiro 300 [iopamidol, 300 mg of iodine per milliliter], Bracco
Diagnostics, Princeton, NJ) was injected. An anteroposterior spot radiograph
was obtained for documentation (Fig.
1). Then, a maximum of 40 mg (1.0 mL) of crystalloid
corticosteroid suspension (Kenacort A 40 [40 mg of triamcinolone],
Bristol-Myers Squibb, New York, NY) and 1 mL of anesthetics (Scandicain 2%
[mepivacain hydrochloride], Astra Zeneca, London) were injected.
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Fifteen minutes after the injection, pain relief was assessed with a visual analog scale [13]. The extremes of the scale were defined as no pain reduction (0%) and complete pain reduction (100%). The patients were instructed to place a mark on the scale corresponding to their subjective assessment of pain reduction. Patients with pain limited to certain shoulder positions or to joint motion were instructed to reproduce the normally painful position or motion. The distance between the left anchor and the patient's mark was measured in millimeters and expressed as a percentage of pain reduction in the original written reports. Pain reduction of 70% or more was considered to be clinically relevant and, therefore, to indicate a successful acromioclavicular joint injection.
MRI
MRI was performed on either a 1.0-T scanner (Impact Expert, Siemens Medical
Systems, Erlangen, Germany) or a 1.5-T scanner (Symphony, Siemens Medical
Solutions). The shoulder was placed in a dedicated receive-only shoulder coil
with the shoulder in a neutral position. All study patients underwent MRI
according to the institution's standard protocol, which includes the
intraarticular injection of gadopentetate (10 mL of 2 mmol/L of gadopentetate
dimeglumine [Magnevist, Berlex, Wayne, NJ]) unless inflammatory or neoplastic
disease was suspected. This fact explains our MRI parameters but is not
relevant for the diagnosis of acromioclavicular joint arthritis and,
therefore, for this article.
On the 1.0-T scanner, we acquired the following sequences: an oblique coronal double-echo turbo spin-echo sequence (TR/TE range, 3500/16-98; section thickness, 3 mm), an oblique coronal T1-weighted fat-saturated spin-echo sequence (TR/TE, 800/20; section thickness, 4 mm), an oblique sagittal T1-weighted turbo spin-echo sequence (700/12; section thickness, 5 mm), and transverse T1-weighted spin-echo images (580/20; section thickness, 4 mm).
The imaging protocol on the 1.5-T scanner included an oblique coronal double-echo fat-saturated turbo spin-echo sequence (TR/TE range, 3300/14-95; section thickness, 4 mm), an oblique coronal T1-weighted fat-saturated turbo spin-echo sequence (TR/TE, 777/12; section thickness, 3 mm), an oblique sagittal T1-weighted spin-echo sequence (600/12; section thickness, 4 mm), and a transverse T1-weighted spin-echo sequence (600/12; section thickness, 3 mm).
Analysis of the MRIs
The MRIs were retrospectively evaluated by two experienced musculoskeletal
radiologists in consensus. They were unaware of clinical data and the results
of the injection. We assessed the following imaging aspects: presence and size
of either cranial or caudal osteophytes or both (maximal length of the
protrusion from the originating bone on oblique coronal and oblique sagittal
images), presence of subchondral cysts (rounded subchondral abnormalities with
fluid-equivalent signal behavior), contour irregularities either of the
acromion or clavicle or both, subchondral bone marrow edema either of the
acromion or clavicle or both (hypointense signal on T1-weighted and
hyperintense signal on T2-weighted images with or without fat saturation),
acromioclavicular joint effusion (fluid-equivalent signal in the
acromioclavicular joint space), and thickness of the acromioclavicular joint
capsule (maximal protrusion from the adjacent bones on oblique sagittal or
oblique coronal images). A capsular thickness equal to or greater than 3 mm
was considered to represent hypertrophy. Measurement of the joint capsule and
osteophytes is illustrated in Figure
2.
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Statistical Analysis
The presence or absence of an MRI finding was compared with the amount of
pain reduction after intraarticular injection using the Mann-Whitney
U test. A p value of less than 0.05 was considered
significant. Sensitivity, specificity, accuracy, and positive and negative
predictive values in predicting a positive response on the visual analog scale
(
70%) were calculated for each MRI finding separately.
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MRI Findings
Cranial osteophytes were found in 14 patients (5/11 patients with 70%
pain relief, 9/39 patients with pain relief < 70%). The mean size of the
cranial osteophytes was 3.4 mm (range, 1-6 mm). Caudal osteophytes were found
in 26 patients (9/11 vs 17/39 patients). The mean size of the caudal
osteophytes was 3.0 mm (1-6 mm) (Fig.
3). Subchondral bone abnormalities were seen in 17 patients.
Subchondral cysts were found in three patients (2/11 vs 1/39); subchondral
irregularities, in 17 patients (2/11 vs 15/39; and bone marrow edema, in three
patients (1/11 vs 2/39) (Figs.
4 and
5). Acromioclavicular joint
effusion was found in five patients (2/11 vs 3/39)
(Fig. 6) and capsular
hypertrophy in 27 patients (8/11 vs 19/39). Mean capsular thickness in 27
patients with capsular hypertrophy was 3.4 mm (range, 3-7 mm) (Figs.
7 and
8). Twenty patients had rotator
cuff lesions (12 partial tears: 1/11 vs 11/39); eight had full-thickness tears
(2/11 vs 6/39).
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Value of MRI Findings for the Diagnosis of a Painful
Acromioclavicular Joint
The amount of pain relief in the presence or absence of the various MRI
findings and the corresponding statistical evaluations are presented in
Table 1. The mean pain relief
(visual analog scale) was significantly different for patients with and
without the MRI diagnosis of capsular hypertrophy (p = 0.007).
Borderline significance was found for the presence of caudal osteophytes
(p = 0.051). For all other MRI parameters, the differences in pain
response were not significant.
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Sensitivities, specificities, accuracies, and positive and negative
predictive values for each MRI finding in detecting a positive result of
intraarticular injections (cutoff for positive response, 70% pain relief
on the visual analog scale) are summarized in
Table 2. The sensitivity of the
different MRI findings in detecting painful acromioclavicular joints varied
considerably (range, 9-82%). The highest sensitivities were found for
thickening of the joint capsule (73%) and for caudal osteophytes (82%). The
specificity ranged from 51% to 97% and was highest for joint effusion (92%),
subchondral bone marrow edema (95%), and subchondral cysts (97%).
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Selective injection of the acromioclavicular joint with anesthetics is a valuable diagnostic tool that improves accuracy of the physical examination [20, 21]. In a cadaveric study, acromioclavicular joint injection without imaging guidance was technically successful (purely intraarticular) in only 67% (16/24 joints) [22]. For this reason, we use fluoroscopic guidance to avoid misleading results caused by inadvertent injection of the subacromial-subdeltoid bursa. If combined with steroids, acromioclavicular joint injection may lead to relevant short- and midterm pain relief and functional improvement [12, 22] and may be considered before surgical, preferably endoscopic, acromioclavicular joint resection [23, 24]. Steroids have routinely been injected in our patient population but have not been further evaluated because of the retrospective study design with patients commonly proceeding to surgery or lost to follow-up.
We have evaluated seven different single parameters associated with
osteoarthritis of the acromioclavicular joint: cranial and caudal osteophytes,
subchondral cysts, subchondral irregularities, bone marrow edema in the distal
acromion or clavicle, joint effusion, and capsular hypertrophy. Their
prevalences were highly variable. Subchondral cysts, bone marrow edema, and
joint effusion were rare in our patients (n = 3, 3, and 5,
respectively). They had a high specificity (97%, 95%, and 92%, respectively)
but a low sensitivity (18%, 9%, and 18%, respectively) in predicting a
successful ( 70% effect on the visual analog scale) intraarticular
injection. Because of the low prevalences of these findings, these values may
be distorted, however, and meaningful statistical calculations were not
possible. These findings may still be relevant. Jordan et al.
[19] found high signal in the
distal clavicle in 11% and in the distal acromion in 10% of their symptomatic
patients but never in their asymptomatic patients. This was the only MRI
finding (of a total of 11 parameters evaluated in their study) that was weakly
correlated with clinical findings. In another investigation
[25], subchondral
hyperintensity of the distal clavicle seen on T2-weighted images was more
common than that in our study population (prevalence, 12.5%).
Extensive findings may represent an early manifestation of osteolysis of the distal clavicle, and patients may benefit from surgical resection. The possible relevance of subchondral edema or edemalike abnormalities is also supported by investigations relating to other joints, such as the knee and foot [26, 27]. Schweitzer et al. [28] found acromioclavicular joint effusion in 67% of their patients and 12% of their asymptomatic volunteers, whereas Jordan et al. [19] found effusion in 45% of their patients and in none of their asymptomatic volunteers. They concluded that joint effusion appeared to be an asymptomatic manifestation of osteoarthritis because there was no association between joint fluid and clinical findings.
Jordan et al. [19] reported a high prevalence (65%) of capsular hypertrophy in both their patient group (mean age, 41 years) and the asymptomatic control group (48%; mean age, 28 years) and no significant relationship with clinical findings (local palpation and body cross test). In our study, a patient's capsular hypertrophy was significantly related to the amount of pain relief after injection. Unfortunately, different studies cannot be compared directly because there is no uniform definition of capsular hypertrophy. We have used a cutoff of equal to or greater than 3 mm for the diagnosis of capsular hypertrophy. This is compatible with a sonographic study published by Alasaarela et al. [29], who found a mean capsular thickness of 2.2 mm (SD, ± 0.5 mm) in asymptomatic control subjects 21-32 years old. The joint capsule appears to be a key element for stability of the acromioclavicular joint [30, 31]. Capsular hypertrophy may reflect the increased amount of stress associated with joint incongruity and instability.
To perform MRI solely to detect disorders of the acromioclavicular joint would not be efficient. However, standard MRI sequences of the shoulder regularly include the acromioclavicular joint. If the radiologist knows the importance of the various MRI findings, he or she can add essential information for further therapeutic decisions, which may include acromioclavicular joint resection. In unequivocal cases, diagnostic injections may become unnecessary.
Because of the retrospective study design, it was not possible to evaluate the long-term relief of pain by the corticosteroids injected in all our patients. Many patients underwent shoulder surgery within a short time after the injections, which prevented a long-term follow-up. This aspect has been covered by other publications. Jacob and Sallay [12] reported that 81% of their patients did not have long-term relief from acromioclavicular joint injection with corticosteroids. Most of their patients underwent resection of the distal clavicle.
In conclusion, the amount of pain relief after intraarticular injection is significantly related to capsular hypertrophy diagnosed on MRIs. MRI findings have a reasonable sensitivity and a high specificity in predicting relevant short-term pain relief after intraarticular injection.
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