Evaluation of teres minor muscle in patients with rotator cuff tear Download

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Evaluation of teres minor muscle in patients with rotator cuff tear using magnetic resonance imaging
+1Sugimori K, 2Sugaya H, 2Takahashi N, 2Hagiwara Y, 2Kawai N, 2Moriishi J, 1Kimura T
+1University of Toyama, 2Funabashi Orthopaedic Sports Medicine Center
[email protected]
INTRODUCTION
We have encountered several patients with rotator cuff (RC) tear
involving supraspinatus (SSP) who experienced postoperative loss of
muscle strength for external rotation. Although infraspinatus (ISP) is a
muscle that may be associated with such loss of muscle strength, teres
minor (TM) should also play a role in the postoperative disturbance of
external rotaion. However, few reports have evaluated the role of TM in
patients with RC tear. Accurate evaluation of the RC is essential for
good shoulder joint reconstruction and magnetic resonance imaging
(MRI) has been reported to be useful for assessing muscle volume and
quality and RC tear size1-3). The purpose of this study was to measure the
volume of TM using MRI to obtain baseline data that we can use to
evaluate the influence of TM in the postoperative results of RC tear.
METHODS
Seventy-four shoulders (45 males and 29 females, average age
61.2±9.9 years old) which have small RC tear without TM tear were
studied. We measured the cross-sectional area (CSA) of the RC muscle
on the most lateral slice on which the scapular spine was in contact with
the scapular body using the oblique sagittal MRI taken before surgery
(Fig. 1). SSP, ISP, TM, and subscapularis (SSC) were measured. Fatty
degeneration in the muscle was evaluated according to Goutallier’s
classification method and divided into two groups: muscles in Goutallier
stages 0 and 1 were defined as the non-denatured group and muscles in
stages 2, 3, and 4 were defined as the denatured group. Statistical
analyses were performed using Mann-Whitney test. Statistical
significance was set at p<0.05.
1
female
male
0.8
0.6
0.4
0.2
0
TM/SSP
TM/ISP
TM/SSC
Figure 3. Adjustment of the CSA of the TM by the CSA of other RC
muscle.
As for the fatty degeneration of RC muscles in the denatured group,
SSP (45 shoulders, 60.8%) and ISP (31 shoulders, 41.9%) were most
frequently involved, whereas such degeneration was rare in TM (1
shoulder, 1.4%) and SSC (5 shoulders, 6.8%). We divided the CSA of
the TM with that of SSP, ISP and SSC muscles and compared the
differences between the non-denatured and denatured groups. There
were significant differences in the ratio of TM/SSC between the nondenatured and denatured groups (Fig. 4). Between group difference was
not apparent in TM/SSP or TM/ISP.
non-denatured
denatured
1
0.8
N.S.
N.S.
N.S.
0.6
0.6
0.4
0.4
0.2
0.2
0
non-denatured
denatured
1
0.8
N.S.
N.S.
N.S.
0.6
female
male
P<0.05
P<0.05
P<0.05
0.4
0.2
0
total
non-denatured
denatured
1
0.8
0
total
female
male
total
female
male
Figure 4. Comparison of the CSA ratio of TM / other RC muscle
between the non-denatured and denatured groups. TM/SSP (left panel),
TM/ISP (middle panel) and TM/SSC (right panel).
.
Figure 1. MRI of the left shoulder. Each muscle has been contoured and
the cross-sectional area was measured using image analysis software.
RESULTS
Seventy-four shoulders consisted of small SSP or ISP tear including
8 SSC tear and there was no apparent TM tear. The CSAs of the RC
muscles (SSP, ISP, TM, and SSC) were 648.6, 908.2, 385.6 and 1760.0
mm2, respectively. The CSAs in male patients were larger than that of
female patients (Fig. 2). To minimize the differences in CSAs between
sexes, we first attempted to divide the CSA of the TM by the patient’s
height or weight. However, this method was not successful. Next, we
divided the CSA of TM by that of other RC muscle. The sex difference
was standardized when the CSA of TM was divided by that of the SSC
(Fig. 3).
mm2
3000
female
male
2500
2000
1500
DISCUSSION
There were significant differences between male and female patients
in terms of RC muscle volume assessed by CSA. Such difference could
not be standardized by height or weight. Kanehisa et al reported that the
muscles of the lower extremity can be adjusted by height, but those of
upper extremity cannot4). They suggested that there might be a
difference in growth balance between the upper and lower extremities.
Our next attempt to adjust the CSA of TM by other parameters viewed
on the same MRI slice indicated that the CSA of TM could be adjusted
by dividing it by the CSA of SSC. Because fatty degeneration was
uncommon in SSC and TM, we suggest that we can adjust the sex
differences by the CSA of SSC. On the other hand, when we adjusted
the CSA of TM with denatured RC muscles, we obtained variable data
because the denatured RC muscles exhibited fat accumulation and
atrophy.
In this study, we have no TM tear with only one fatty degeneration
in all small RC tear patients. These data indicated that CSA of the TM
could be one of the baseline references for the assessment of muscle
volume and quality in RC tear. TM is involved in external rotation of the
shoulder joint and centripetal positioning of the humeral head at the
glenoid. Future analysis of possible functional changes in apparently
intact TM in patients with large or massive RC tears should also be
necessary.
CONCLUSION:
Muscle volume analysis of TM should be important in RC tear and CSA
of TM could be adjusted by dividing it by other RC muscle without fatty
degeneration.
1000
500
0
SSP
ISP
TM
SSC
Figure 2. Comparison of the CSA of the RC muscles.
REFERENCES:
1) Zanetti M et al. Invest. Radiol. 1998; 33:163-170.
2) Tingart MJ et al. Clin. Orthop. Relat. Res. 2003; 415:104-110.
3) Shimizu T, et al. Acta Orthop. Scand. 2002; 73: 40-43.
4) Kanehisa H, et al. Jpn. J. Sports Biomech. Exere. 1997; 1: 148-163.
Poster No. 1797 • 56th Annual Meeting of the Orthopaedic Research Society