Abstract
Problem:
The torsion of the humerus is defined as the angle between the axis of the humeral head and the axis of the trochlea humeri relative to the long axis of the humerus. In performimg shoulder arthroplasty it is an essential part of the procedure to restore the individual torsion. In some cases it might be difficult to detect the orignal border of the joint surface and thus the torsion. This situation occurs in severely destructed humeral heads as well as in fracture cases.
In the literature an average retrotorsion is given between 20–30 degrees, with a high standard deviation.
The aim of the following study was a critical analysis, if the sulcus intertubercularis can serve as an anatomical landmark for the orientation of humeral torsion in shoulder arthroplasty.
Method:
First, we defined the indivdual humeral torsion ( n = 40 ) by two independent anthropometric methods ( method according to Martin, method according to Knußmann).
Afterwards, the results of the measurements were compared to CT- scans taken by the same bones. The CT- measurements were performed by the method of Dähnert and Bernd, who used the midpoint of the humeral joint surface and the sulcus intertubercularis defining the proximal axis of retrotorsion.
Statitstical analysis was performed with varianz analysis, U-test according to Wilcoxon and Smirnov –Komolgorow test.
Results:
The anthropometric measurements according to Martin revealed an average retrotorsion of 23° degrees (+/− 9, 15 °). Comparing these data with the second anthropometric method ( according to Knuβmann) the measurements demonstrated a highly significant relationship( p < 0, 005).
The CT- measurements according to Dähnert showed an average of 53, 8° degrees ( +/− 8, 91°).
The different results were easy to explain because both methods used different bony landmarks.
Performing a varianz analysis the data showed a significant relationship ( p < 0, 05 ).
The average difference between the anthropometric – and the CT-measurements was 31 ° +/− 5, 93 ° degrees ( Minimum 14 °, Maximum 50°)
Conclusion:
In severely destroyed shoulder joints it is sometimes difficult to identify the original anatomic borders of the joint surface. The reconstruction of the anatomical neck is the precondition to detect the individual retrotorsion performing a shoulder arthroplasty.
There are two options if that fails.
You may use an average retrotorsion of about 23 degrees or you may use the sulcus intertubercularis as an anatomical landmark. It only makes sense to use the Sulcus as an anatomical landmark, if there is a constant relationship between the orientation of the sulcus and the retrotorsion of the proximal humerus.
With our measurements we could demonstrate a close relationship between the sulcus and the orientation of the humeral joint surface, relative to the long axis of the humerus ( p< 0, 005 ).
The average difference between the anthropometric – and the CT-measurements was 31 ° +/− 5, 93 ° degrees ( Minimum 14 °, Maximum 50°). Using a standard head of 48 mm and adding the distance to the greater tubercle one should go about 10 mm lateral to the center of the sulcus intertubercularis. The distance varies with the head size.
The probability to match the individual torsion is higher using the sulcus intertubercularis as an anatomical landmark compared to the average retrotorsion.
