L. Novejosserand et al., FACTORS INFLUENCING THE ACROMIO-HUMERAL H EIGHT, Revue de chirurgie orthopedique et reparatrice de l'appareil moteur, 82(5), 1996, pp. 379-385
Purpose of the study The narrowing of the Acromio Humeral Interval (AH
I) under 6-7 mm, lower limit reported in normal shoulder, has been con
sidered to be a specific indicator for full-thickness cuff tears. The
purpose of this study was to analyse the factors influencing the AHI.
Methods 264 shoulders were operated on between 1984 and 1994 for full
thickness tear of the supraspinatus and infraspinatus associated or no
t with an anterior cuff lesion. All patients had X-ray with A.P. view
of the shoulder in neutral rotation. The AHI was defined as the shorte
st distance measured between the inferior cortex (dense line) of the a
cromion and the humerus. CT arthrogram was performed in 84 patients to
analyse cuff muscular fatty degeneration. A full thickness tear was c
onfirmed and measured by surgical approach in all cases. Results There
was a moderate significant relationship (p < 0.05) between AHI and sy
mptoms duration. There was a significant relationship between AHI and
tear size (p < 0.05), When the supraspinatus tendon was only torn, the
mean AHI was 9.5 +/- 0.17 mm (4.5 per cent of narrowing AHI). When su
pra and infraspinatus tendon were torn, the mean AHI was 7.5 +/- 0.4 m
m (28 per cent of narrow AHI) and when an anterior lesion was associat
ed, the mean AHI decreased to 5.4 +/- 0.5 mm and the percentage of nar
row AHI increased to 63 per cent. The AHI was not influenced by the bi
ceps rupture with a similar symptoms duration, the mean AHI was 9 +/-
0.5 mm with biceps tear versus 9.2 +/- 2 mm when the biceps was normal
. However, the mean AHI decreased to 5.5 +/- 0.6 mm when the long head
of the biceps was dislocated and the AHI was less than 7 mm in 61 per
cent of the cases. A highly significant relationship was found betwee
n the AHI and the infraspinatus muscle degeneration. We have found 100
per cent incidence of AHI narrowing when the infraspinatus was degene
rated (mean AHI 2.2 +/- 1.1 mm). A moderate similar relationship was f
ound concerning the supraspinatus muscle (p < 0.05) and no relationshi
p was found with the subscapularis degeneration. Discussion The infras
pinatus, external rotator of the humerus, seems to be the major active
depressor of the humeral head. The biceps tendon, which is a passive
depressor of the humerus, has no influence on the AHI whatever it is r
uptured or not. However biceps dislocation is associated with signific
ant humeral head superior migration. Symptoms duration and cuff tear s
ize seem to be only secondary factors affecting the AHI. Conclusion AH
I narrowing should evocate a severe cuff tear with biceps dislocation
or muscular degeneration. In these cases, surgical repair might be que
stionable. AHI value is more prognostic than diagnostic.