Professional Pitchers with GIRD Display Greater Dominant Humeral Retrotorsion than Pitchers with Normal ROM

OBJECTIVES: Glenohumeral internal rotation deficit (GIRD) in the dominant shoulder of a throwing athlete is a previously recognized phenomenon which has been associated with upper extremity injury. The relationship between GIRD and humeral torsion has not clearly been elucidated. The purpose of this study was to compare humeral torsion between professional pitchers presenting with GIRD and those with normal ROM. METHODS: Humeral torsion and shoulder range of motion (ROM) was measured in 128 professional pitchers prior to spring training from 2009-2012. Shoulder external (ER) and internal (IR) ROM was assessed in 90º of abduction with the scapula stabilized. Humeral torsion was measured via ultrasound using previously described and validated methods. GIRD was defined as the loss of internal rotation > 15º with a concomitant loss of 10º total arc of motion. The side-to-side difference in HT was calculated by subtracting the dominant arm (D) HT from the non-dominant (ND) HT. A mixed model ANOVA(side X GIRD) were used to compare pitchers dominant and non-dominant HT between pitchers with GIRD to those without GIRD. Independent t-tests were used to compare the side to side difference in HT between pitchers with GIRD and those without (α=0.05). RESULTS: Pitchers with GIRD displayed alterations in ROM (ER=131.8±14.3, IR= 29.1±10.1, Total Arc=160.9±15.5 ) compared with those with normal ROM (ER=132.0±14.2 , IR= 40.5±11.3 , Total Arc= 172.5 ±16.2 ). Pitchers with GIRD displayed significantly less humeral torsion (i.e. greater retro torsion) in their dominant arm compared to those without (GIRD=4.4±12.0º, Normal=10.4±11.6º, P=0.002). Pitchers with GIRD also displayed a greater side to side difference in humeral retro torsion (GIRD=19.5±11.9 compared with 12.4±12.4º, P=0.001). There was no difference in non-dominant humeral torsion in pitchers with and without GIRD (P>0.05). CONCLUSION: Professional pitchers who display deficits in total arc of motion on the internal rotation side greater than 15º tend to also have greater dominant humeral retro torsion and greater side to side differences. An adaptive increase in humeral retro torsion in the dominant arm due to repetitive throwing may limit internal rotation in the follow through phase of the throwing motion. This, in turn, may increases forces on the posterior soft tissues of the glenohumeral joint leading to the development of GIRD. Given that deficits in total arc of motion and internal rotation are associated with increased arm injury risk future studies should examine the amount of humeral torsion that predisposes a shoulder to develop GIRD.