MZ twinsa (N = 30b)
DZ twinsa (N = 28c)
p value
Age (year)
63.66 ± 4.32 (53–72)
63.78 ± 1.96 (60–66)
Female
62.40 ± 6.3 (53–72)
63.77 ± 2.03 (60–66)
0.264
Male
64.30 ± 2.86 (61–71)
63.80 ± 1.83 (61–66)
0.978
Acromiohumeral distance (mm)
10.13 ± 1.70
9.69 ± 1.74
0.197
Table 2
Summary of acromiohumeral distance heritability analysis
MZ twins | DZ twins | |||||||
---|---|---|---|---|---|---|---|---|
p value of mean squares | p value of mean squares | |||||||
Mean difference (mm) | Within pairs | Among pairs | ICC | Mean difference (mm) | Within pairs | Among pairs | ICC | Heritability |
−0.13 | <0.001 | 0.450 | 0.91 | 0.10 | <0.001 | 0.849 | 0.50 | 0.82 |
Table 3
Acromiohumeral distance (AHD) differences according to occupation
Monozygotic twins | Dizygotic twins | |||
---|---|---|---|---|
Occupation | AHDa (mm) | p value | AHDa (mm) | p value |
HMW | 10.25 ± 1.88 | 0.842 vs. ASW | 9.55 ± 1.89 | 1.00 vs. ASW |
ASW | 9.88 ± 2.30 | 1.00 vs. PW | 9.60 ± 0.80 | 1.00 vs. PW |
PW | 10.60 ± 1.31 | 1.00 vs. HMW | 9.80 ± 1.79 | 1.00 vs. HMW |
The resulting heritability index showed genetic factors to be the main cause of the variability of the acromiohumeral distance, with shared and unique environmental factors contributing only slightly to the variability.
The role of genetic factors is also supported by the results of the acromiohumeral distance comparisons of the three groups of workers. No significant differences were found among groups who performed or had performed different types of labor. This was confirmed both in the whole study cohort and within the monozygotic and dizygotic subjects. These data appear to be partially in contrast to those of Frost and Andersen [51], who observed that shoulder-intensive work was a risk factor for impingement syndrome. Analogously, van Rijn et al. [52] noted that highly repetitive work was associated with the occurrence of subacromial impingement, and Roquelaure et al. [53] observed that skilled blue-collar workers were more likely to develop subacromial impingement, especially if forced to abduct the arm repeatedly. Finally, in a longitudinal study, Svendsen et al. [54] showed that forceful work, work with elevated arms, and repetitive work each doubled the risk of surgery for subacromial impingement.
Our study suggests that the anatomical features that influence the width of the subacromial space are mainly genetically determined. However, if the subacromial space is already constitutionally narrow, external factors would strongly contribute to further reduction of the space, making it too tight. This might occur as a consequence of the ossification of the acromial insertion of the coracoacromial ligament [9]; of contracture of the posterior capsule of the glenohumeral joint, which would lead to upward migration of the humeral head [55–57]; or of scapular muscle performance deficits [58].
Rotator Cuff Integrity in Patients with Antique Unilateral Upper-Limb Amputation
In order to test the role of the extrinsic factors in the genesis of the rotator cuff tear, we evaluated by an MRI exam, both shoulders of 25 patients with antique unilateral upper-limb amputation (Fig. 1a, b).
Fig. 1
Evaluation of active shoulder flexion (a) and abduction (b) in a 72 years old male with a right upper-limb amputation
Rotator Cuff Tendon Status (Structural and Qualitative Condition) According to Sugaya Classification [59] and Rotator Cuff Muscle Tropism According to Fuchs Classification [60]
Oblique coronal, oblique sagittal, and axial T2-weighted spin-echo MRI images were obtained in all subjects. Coronal oblique shoulder images were in plane parallel to the supraspinatus tendon. The patients were examined in the supine position with the arm at the side, the palm facing up, and the hand under the hip in order to keep the shoulder motionless. The acromiohumeral distance (AHD) of both shoulders was also measured in the participants with full thickness cuff tear. The AHD was calculated in coronal oblique projection as the distance between the most caudal point of acromion lower surface and the most cranial point of proximal humerus.
The results are summarized in Tables 4 and 5 Gumina S, 2015. Table 4 shows the healthy status of rotator cuffs in the studied group according to Sugaya classification. The general tendency showed not significant repartitions between the amputated and the healthy side (p = 0.18). When each shoulder was separately evaluated, a significant prevalence of Sugaya type II category in the amputated side (χ 2 = 12.5, p = 0.02) and of Sugaya type I category in healthy side (χ 2 = 25.5, p < 0.001) was found. Considering only the 19 participants with no rotator cuff tear, the mean values of the AHD of the amputated and healthy side were 0.81 cm (SD: 0.11) and 0.87 cm (SD: 0.13), respectively; thus, a significant difference was found (p = 0.02).
Table 4
Distribution of the sample according to Sugaya classification
Amputated side | Healthy side | |
---|---|---|
Type I | 7 (28 %) | 13 (52 %) |
Type II | 10 (40 %) | 7 (28 %) |
Type III | 4 (16 %) | 2 (8 %) |
Type IV | 1 (4 %) | 1 (4 %) |
Type V | 3 (12 %) | 2 (8 %) |
χ 2 = 12.5, p = 0.02 | χ 2 = 25.5, p < 0.001 |
Table 5
Distribution of the sample according to Fuchs’ classification
Amputated side | Healthy side | p-valuea | |
---|---|---|---|
Type 0 | – | 1(4 %) | 0.033 |
Type I | 8 (32 %) | 13 (52 %) | |
Type II | 7 (28 %) | 8 (32 %) | |
Type III | 5 (20 %) | 1(4 %) | |
Type IV
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