Does grip strength correlate with rotator cuff strength in patients with atraumatic shoulder instability?

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RUQAYYAH YAHYA ALI TURABI
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Background and Aim: Strength deficits within the rotator cuff are recognised cause for the symptoms in atraumatic shoulder instability patients. However, in clinical practice, the strength of these muscles is not always objectively measured for some reasons such as time constraints, patient’s limitation or unavailability of equipment. Some studies reported the correlation between grip strength and rotator cuff strength and suggested using grip strength as an indicator of rotator cuff strength. However, these studies were limited to healthy active population and athletes with asymptomatic shoulders, and the relationship has not been investigated in pathological shoulders, especially atraumatic unstable shoulders. Therefore, this study was proposed to investigate if there is a correlation between grip strength and rotator cuff in atraumatic shoulder instability patients and to determine if testing grip strength can be incorporated in clinical practice as a diagnostic test for rotator cuff strength in these patients. Methods: This cohort study involved twenty patients with atraumatic shoulder instability (13 femaleand7male)withameanage±SD of30± 9.392 years old. Out of the twenty subjects, eight patients presented with bilateral instability, which constituted a total of twenty-eight atraumatic unstable shoulders (N=28). From sitting, grip strength was measured in kilograms using a Jamar hydraulic hand dynamometer. From crook-lying and 90° shoulder abduction (or where tolerated), active range of motion (ROM) of the external rotation (ER) and internal rotation (IR) were measured in degrees with a universal goniometer followed by isometric ER and IR strength in the inner and outer range (measured in kilograms) using a hand-held dynamometer (HHD). Pearson’s correlation test was computed to investigate if there is a correlation between grip strength and rotator cuff strength in different ranges (inner- range IR, inner-range ER, outer-range IR, and outer-range ER). Multiple linear regression was conducted to predict grip strength based on rotator cuff strength. Results: Significant and strong positive correlations were found between grip strength and inner-range IR (r = 0.764, P< 0.001), inner-range ER (r = 0.611, P= 0.001), outer-range IR (r = 0.817, P< 0.001) and outer-range ER (r = 0.736, P< 0.001). A significant regression equation was found (F (4, 23) = 13.254, P < 0.001), with an R2 of 0.697 indicating that the rotator cuff strength explained 69.7% of the variance in the grip strength. Summary and Conclusions: The results support the hypothesis showing that grip strength is strongly associated with rotator cuff strength in atraumatic instability patients. The simplicity of handgrip testing allows it to be used in the clinical scenarios where sophisticated assessment tools are not available. It could be used as a diagnostic test to estimate the strength of the rotator cuff or to monitor the patient’s progression during shoulder rehabilitation programs. Future studies are required to correlate between the strength of hand grip and rotator cuff strength before and after shoulder rehabilitation in this cohort.
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