Abstract
Background:
Objective assessment of strength is essential for recovery monitoring and clinical decision-making. However, assessment methods vary greatly among clinicians, particularly in the upper extremity [1]. Hand-held dynamometry (HHD) of the shoulder can vary due to positional differences, clinician strength, and stabilization method [2]. Strength testing with a Biodex dynamometer is considered the gold standard, but agreement with more cost-effective HHD testing remains unclear [2].
Hypothesis:
We hypothesized that shoulder internal rotation (IR) and external rotation (ER) HHD measures captured in a prone testing position would demonstrate the strongest agreement with Biodex measures.
Methods:
Healthy, youth athletes (14-18 years) participating in contact or overhead upper-extremity sports were recruited. HHD strength testing was completed as part of a series of upper extremity functional tests. HHD test positions, including prone (90° shoulder abduction; neutral rotation), supine (90° shoulder abduction; neutral rotation), and seated (90° shoulder abduction; 90° ER), were completed in a randomized order (Figure 1). Biodex testing was completed in a seated position (45° shoulder abduction; neutral rotation) at 60 degrees/second (Figure 2). Strength was captured in Newton-meters (Nm). Intraclass correlation coefficients (ICCs) were computed to determine agreement, and Wilcoxon signed-rank tests (with effect sizes, r) were conducted to identify paired differences.
Results:
128 participants (74M, 16.8±1.0 years) were tested. Agreement between Biodex and HHD positions ranged from moderate to good for IR measures but were consistently poor for ER measures (ICCs=0.16-0.41). Specifically, for IR measures, the strongest agreement with Biodex was found with the prone position (ICC=0.82, 95%CI=0.72-0.88), followed by supine (ICC=0.77, 95%CI=0.69-0.83) and seated (ICC=0.59, 95%CI=0.41-0.72). However, IR strength significantly differed between Biodex and HHD in prone (p<0.001, r=-0.41), supine (p=0.004, r=-0.25), and seated (p<0.001, r=-0.50) positions. Similarly, for ER strength, HHD measures significantly differed from Biodex measures in prone (p<0.001, r=-0.87), supine (p<0.001, r=-0.87), and seated (p<0.001, r=-0.50) positions.
Conclusion:
Shoulder IR and ER HHD measures in all testing positions differed from Biodex values; however, agreement for HHD and Biodex IR strength values was moderate to good. While the statistical differences highlight that Biodex testing remains the gold standard for capturing strength measures, moderate to good agreement with the HHD for IR suggests a viable alternative.
