Keywords rotator cuff - shoulder joint - radiography - magnetic resonance imaging - reproducibility
of results
Introduction
The etiology of rotator cuff tendinopathy is not yet fully known, but mechanical overload
is one of the most suggested causes for tendon degeneration, and it may be influenced
by the constitutional factors of the affected individuals.[1 ]
[2 ]
[3 ] The critical shoulder angle (CSA), which is obtained through radiographic evaluations,
has been considered an important predictive factor for mechanical overload.[4 ]
[5 ] A biomechanical assay analysis has also corroborated the establishment of this correlation.[6 ]
The CSA is criticized by some authors, who did not find this same correlation; however,
inadequate positioning on the radiographs may have been a limiting factor in these
studies.[7 ] Based on the possible source of patient positioning bias, tests showing images with
better quality would be the logical way to improve the reproducibility in the evaluation
of the CSA.
Some authors suggested the use of computed tomography, and found a high degree of
agreement with the radiographic study.[8 ] However, tomography exposes the patient to higher doses of radiation than radiography,
and its indication should be more carefully evaluated.[9 ] The use of nuclear magnetic resonance (NMR) does not use ionizing radiation, being
widely requested for the evaluation of various orthopedic conditions, and it also
has less dependence on positional factors that may skew the traditionally used radiographic
image.
In a recent CSA study using magnetic resonance imaging (MRI), it was suggested that
there was higher data variability of the MRI when compared to radiography, which was
more evident in patients with osteoarthritis, and that the method would not be adequate.[10 ]
The present study aims to evaluate the viability of the MRI to obtain the CSA, and
the correlation between the results obtained in radiographic and MR images by a new
MR evaluation methodology.
Materials and Methods
The present prospective, randomized, double-blinded comparative study for radiographic
and MRI evaluation of the CSA was approved by the institutional ethics committee under
number 2.706.960, CAAE: 87182318.2.0000.8054.
The examinations of 15 patients were randomly evaluated and blinded to the evaluator.
Only examinations of patients who were to undergo both radiography and MRI on the
same day, and with positioning standardization, were used.
Inclusion Criteria
Patients over 18 years of age of both sexes who agreed to participate in the study
and had any of the following symptoms: shoulder strength loss, instability, range
of motion limitation, and pain.
Exclusion Criteria
Patients with shoulder deformities, with shoulder fracture sequelae, previous shoulder
surgeries, radiographic positioning error, and indigenous individuals, those mentally
handicapped, or those from other populations who have any ethical conflict.
An Espree 1.5 tesla (Siemens, Munich, Germany) MRI machine was used, as well as an
MS–18S® (General Electric, Boston MA, US) digital radiography equipment.
The pattern of analysis for the position of the radiograph was true anteroposterior,
with the patient in the orthostatic position, and rays penetrating at 90° in the glenoid
joint. The MRI was performed with the patient in supine position.
The coronal MRI was established and standardized during the study, and we evaluated
the best visualization of the target structures, and compared it with the radiographic
results.
The CSA was calculated with the help of the Carestream (Carestream Health, Onex Corporation,
Toronto, Ontario, Canada) software. After standardization, the values obtained were
analyzed using the STATA (StataCorp, College Station, TX, US) software, version 15.0.
The MRI measurements used T1-weighted images for better bone visualization in the
axial and coronal planes ([Figure 1 ]).
Fig. 1 (A) Marking of the most lateral point of the acromion;T2 image, axial plane. (B)
Marking of the most lateral point of the acromion; T1 image, coronal plane. (C) Marking
of the center of the glenoid; T2 image, axial plane. (D) Critical shoulder angle (CSA)
measurement; coronal image at the central section of the glenoid. Line between the
glenoid border and the projection for this section of the most lateral point of the
acromion, obtained in sections A and B.
In the axial plane, the section with the largest lateral projection of the acromion
was identified and marked as the lateral point.
The central point of the glenoid cavity was also found in the axial plane, and marked
in the software to use this point to establish the most central section in the coronal
plane.
The lateral point was superimposed on all coronal plane images; the most central section
of this plane was used to mark the line of the superoinferior axis of the glenoid
cavity, and the line between the lowest point of the glenoid and the lateral point
was artificially inserted into the image by the software. The angle between these
two straight lines was considered the CSA measured by MRI.
The measurement of the angle on the radiographs followed the patterns described by
Moor et al[4 ] ([Figure 2 ]).
Fig. 2 Measurement of the CSA by radiography.
The data were blindly and randomly evaluated by three evaluators, one fellow in shoulder
surgery, a shoulder specialist with three years of experience, and a musculoskeletal
radiology specialist with three years of experience, to establish a learning curve.
The statistical evaluation was performed respecting the nature of the data. The results
were presented in the format of mean ± standard error (standard deviation, SD). Data
were considered significant with p < 0.05 in a two-tailed curve. The patient examinations were blindly and randomly
evaluated. In the parametric data, comparisons were made using paired t tests, analysis of variance (ANOVA) and the Tukey test.
A comparison was also made between the means obtained by the evaluators and the linear
regression in order to establish the differences in the learning curves of the evaluation
of the radiographs and the MRI between the fellow in shoulder surgery and the specialist
with 3 years of experience in shoulder surgery.
Results
The mean of the angles measured by the radiographs was of 34.61 ± 0.67(SD: 4.54) and
the mean of the MRI exams was of 33.85 ± 0.53 (SD: 3.54); p = 0.29. The mean difference between the radiographic and MRI angles was of 0.76° ± 0.72(SD:
4.81).
Separate data and comparisons in the subgroups fellow in shoulder surgery, shoulder
specialist, and radiologist are summarized in [Table 1 ]. The comparisons between groups by the Tukey method are summarized in the [Table 2 ].
Table 1
X-Ray
Magnetic resonance imaging (MRI)
Mean difference (X-Ray versus MRI)
p -value (X-Ray versus MRI)
Fellow in shoulder surgery
35.21° ± 1.32
33.19° ± 0.87
2.02°
0.15
Shoulderspecialist
34.43° ± 1.09
33.86° ± 0.92
0.57°
0.57
Radiologist
34.19° ± 1.15
34.49° ± 0.98
0.30°
0.84
Analysis of variance among groups
0.82
0.62
0.42
Table 2
Tukey
p -value of the X-Ray among groups
p -value of the magnetic resonance imaging (MRI) among groups
Difference in p -value (X-Ray versus MRI) among groups
Radiologist versus fellow in shoulder surgery
0.82
0.59
0.40
Fellow in shoulder surgery versus specialist
0.89
0.87
0.69
Radiologist versus specialist
0.99
0.88
0.87
In the linear regression, the difference in degrees of the evaluation between radiographs
and the MRI showed a constant of 3.07° with coefficient of -1.15°, which is multiplied
by 1 for the fellow group, by 2 for the specialist group, and by 3 for the radiologist
group.
Discussion
The CSA has been used to evaluate patients with various degenerative and inflammatory
processes of the shoulder. Its data provide an expectation that relates this angle
to some types of injuries.[4 ]
This angular evaluation, however, does not take into account the forces of other muscles
such as the pectoralis major, the latissimus dorsi and the biceps, which may also
contribute to a more accurate predictability of mechanical shoulder overloads,[4 ]
[5 ]
[6 ]
[11 ]
[12 ] since muscle recruitment simplifications are used even in its theorizing.[11 ]
[12 ]
[13 ] Passive structures are also not taken into account this evaluation, as in the current
models only at the extremes of movement they would have some influence on the forces
acting on the shoulder.[14 ]
The assessment of the critical shoulder angle is made by radiographic examination;
however, in patients already undergoing MRI, the use of this ionizing radiation may
be unnecessary. The present study shows a tendency adverse to that of the literature
to compare CSA evaluations by radiography and MRI.[10 ] This divergence may have its origin in the following methodological errors of the
literature: the most lateral point of the clavicle did not have a properly standardized
marking, the sample was insufficient, it was not validated in internal validation
tests, and the MRI and radiography tests were not performed at the same time.
The radiographic examination may present greater difficulty in standardization, being
more dependent on human variables to be performed. This fact becomes clear when we
evaluate the differences between dispersion data in all groups: data dispersion was
greater in the radiographic evaluation groups than in the MRI groups, regardless of
the type of evaluator.
There was greater agreement and proximity of data among more experienced examiners,
with the musculoskeletal radiology specialist presenting the closest data, demonstrating
that there is a clear learning curve, which is more important in the MRI assessment.
In the ANOVA, there is greater agreement in the radiographic evaluation among the
groups and, considering the results demonstrated by the Tukey technique, data dispersion
and linear regression, there is a clear learning curve, possibly linked to the greater
familiarity with imaging tests, especially the MRI.
The learning curve of the MRI assessment seems to be more dependent on specific training
than the radiographic assessment curve. However, this fact may also be related to
the higher exposure of the fellow in shoulder surgery to the radiographic exam during
his training in general orthopedics, so this professional was more familiarized with
radiographic evaluations than MRI images.
These mechanical effects do not seem to influence image extraction.
Conclusion
There were no statistically significant differences in MRI data and CSA radiographs,
with a mean divergence between the methods of only 0.76°.
The MRI seems to have its efficiency associated with more experienced evaluators.
Regardless of the evaluator's experience, data variability was lower in the MRI assessments.
