Greater tuberosity medial malposition: does it affect shoulder abductor moment?

Abstract

The detrimental effect of greater tuberosity malposition on functional scores is well known. Superior or posterior malpositions exceeding five mm lead to excessive loading on the deltoid strength. However, the significance of situations where greater tuberosity becomes medialized due to the compressive effect of the locking plate fixation, especially in fractures with metaphyseal dead space, has not been emphasized. It is hypothesized that this condition may cause shortening of the rotator cuff moment arm and consequently impact functional scores. Between 2012 and 2018, 52 patients, aged 65,28 (ranging 40-85) proximal humerus fractures treated with locking plate fixation were included in the study. Cephalodiaphyseal angle, greater tuberosity displacement , patients reported outcome and Constant-Murley scores were evaluated. The mean Constant Murley score was determined to be 78.76 (ranging from 38 to 100). According to the patients reported outcome 39 excellent , five good , two fair, six poor results were observed. Avascular necrosis with screw migration was detected in five cases, while one patient experienced implant insufficiency along with varus deformity. Greater tuberosity was found to be positioned between 6 mm posterior-superior and -13 mm medial. Significant medial malposition was observed in three patients, with -9, -12, and -13 mm of medialization, respectively. Cephalodiaphysial angle was determined as 139.30 degrees (ranging from 120 to 150 degrees) and showed weak correlation with the functional score. Greater tuberosity medialization also showed weak correlation with the Constant-Murley score. The values exhibiting deviation were associated with low patient-reported outcome results and functional scores. In the examination of greater tuberosity displacement values, it was observed that Neer type 3 and 4 fractures differed significantly from Neer type 2 fractures regarding to Kruskal-Wallis test. Medial impaction of greater tuberosity may be the reason of decreased functional scores, similar to superior or posterior malposition. The medialization of greater tuberosity should be considered as a potential factor leading to the shortening of the rotator cuff's abductor moment.