[Uncertainty in the radiological evaluation of deformity in proximal humerus fractures]

The accurate measurement of the deformity of proximal humerus fractures is essential for a proper treatment, particularly in the growing bone. Due to the local pain the correct projection in standard X-rays is difficult to achieve and, in contrast to other joints, cannot be verified in the X-ray. Even with the correct projections a mismeasurement can occur when the rotation is 45° to both planes. The aim of this study was to objectify the error sources and reveal starting points for an improvement.

In a three-step study we initially developed a mathemathical formula in cooperation with the faculty of mathematics of the University of Duisburg-Essen. This formula was proved with X-ray imaging of a steel rod which was bent 120°, simulating a 60° deformity. X-ray images with different rotation and tilt were taken and compared with the values calculated with the above-mentioned formula. In the third step X-rays of a healthy shoulder in different rotation and tilt positions were presented to 2 orthopaedic and 3 radiological consultants. The aim was to determine the direction and amount of rotation and tilt.

The first theoretical step resulted in a mathematical formula which describes the optical deformation based on real deformation, tilt and rotation. The evaluation showed a mean difference of 0.5° (0-1.2°) between the calculated and the measured values. In the third step, evaluation of the X-rays of a shoulder showed that two in 50 (4 %) of the values were correct, in additional 28 cases (56 %) the tendency of the direction of the rotation was correct, the extent of the rotation was missed by 19.6° (0-60°). Ante- and retroversion were evaluated correctly in nine cases (18 %), the extent was missed by a mean of 23° (0-50°). In seven cases (18 %) the tendency for rotation and ante-/retroversion was correct, in 11 cases (22 %) one or both aspects could not be evaluated, in additional 8 cases (16 %) the extent could not be estimated.

Our results show that rotation and tilt of the proximal humerus cannot be estimated in shoulder X-rays and therefore a reliable measurement of the deformity of proximal humerus fractures is extremely unsafe. This problem is relevant for clinical practice because of the high likeliness of unaccurate projections in shoulder X-ray imaging after trauma. Especially for the growing bone the problem is evident, so that new ways of determining the deformity are mandatory.