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

Turabi R, Horsely I, Birch H, Jaggi A. Does grip strength correlate with rotator cuff strength in patients with atraumatic shoulder instability? Bulletin of Faculty of Physical Therapy. 2022;27(1):1.

Objectively measuring rotator cuff strength (‘peak force’ to be exact, but that’s a post for another day) in the clinic can be challenging in certain patients, when time is an issue, when patient strength exceeds therapist strength and when you don’t have the right equipment and set-up to obtain accurate and repeatable measures.
I’ve been following a thread of articles lately demonstrating very close agreement between measures of rotator cuff strength and grip strength, the latest looking at the relationship between grip strength and internal/external rotation force measures in people with atraumatic instability. Approx. 2/3 of my clinical caseload are young people with atraumatic shoulder instability and regaining rotator cuff function (including strength) is a critical part of rehabilitation. However, some are not able to attain optimal shoulder strength test positions, and unless you have a reasonable amount of time and the right equipment (and set-up to obtain accurate and reliable measures), direct measures of rotator cuff strength can be difficult to obtain.

The simple method of measuring grip strength used in this study produced peak force values that correlated with internal and external rotation peak isometric force values in this patient group (r2 0.70 for the statos out there). Previous studies have produced r2 values up to 0.91 for the correlation between grip strength and external rotation strength (strong correlation).

This means that grip strength may provide a simple, quick, convenient and relatively cheap method of indirectly tracking changes in rotator cuff function (peak force) with the following clinical applications:
▪️ for patients who can’t tolerate typical shoulder strength testing positions (due to pain, stiffness, apprehension or fear)
▪️ can be used by small therapists working with stronger patients
▪️ where space, time or access to equipment are limited
▪️ can be used as a 'field' measure of monitoring rotator cuff function in upper limb sports (e.g throwing, swimming).
 
Full text link: https://link.springer.com/content/pdf/10.1186/s43161-021-00059-3.pdf