Introduction of the angle of shoulder slope in a South African population

BACKGROUND: The angle of shoulder slope has been reported in accordance with the specific occupational activities of the aviation and textile industries. However, as no accurate definition nor standardised anatomical landmarks exist within the medical field, this study aimed to devise an appropriate definition with preplaced reference landmarks. In addition, the vertebral level of the acromial tip was also determined. METHODS: The sample series comprised 260 posterior radiographs of the shoulder, of which 127 were males and 133 females. The ethnic distribution included ten black, 13 coloured, 49 Indian and 188 white individuals. In accordance with the trapezial line, the angle of shoulder slope was defined and measured as the angle between the line from the spinous process of C7 to the acromial tip and the line from the acromial tip directly across to the median plane of the vertebral column. RESULTS: The standard mean angle of shoulder slope was approximately 13.56±3.70°. Left and right sides appeared to have mean angles of 13.81±3.41° and 13.33±3.95°, respectively. Mean angular values were also calculated in accordance with the demographic representation - sex: male 13.64±3.71°, female 13.48±3.71°; ethnic groups: black: 13.81±3.81°, coloured: 12.18±3.82°, Indian: 12.97±3.09°, white: 13.64±3.96°. Although the acromial tip was commonly aligned to the level of the spinous process of T3, the incidence of the vertebral level of the acromion was categorised into seven groups, viz. i) intervertebral disc between T1 and T2; ii) intervertebral disc between T2 and T3; iii) intervertebral disc between T3 and T4; iv) spinous process of T1; v) spinous process of T2; vi) spinous process of T3; vii) spinous process of T4. CONCLUSION: Since a statistically significant P value was recorded for the comparison between the angle of shoulder slope and the acromial vertebral level, it was postulated that the magnitude of the angle may determine the acromial vertebral level. As the present study incorporated standard osteological landmarks into the definition and calculation of the angle of shoulder slope, it may provide reference data regarding the position of the acromion which may be indicative of shoulder asymmetry and distorted shoulder setting. Level of evidence: Level 3.