Reliability, responsiveness, and validity of handheld dynamometry for assessing quadriceps strength in total knee arthroplasty.
Andrew J Kittelson, Jesse C Christensen, Brian J Loyd and 3 others
PMID 32142620WHAT IT FOUND
Handheld dynamometry is a reliable and responsive way to track quadriceps strength in total knee replacement patients, but its readings are not interchangeable with lab equipment.
Use it to monitor progress over time, not to compare scores against electromechanical dynamometry results.
Key findings
01Handheld dynamometry showed excellent within-session reliability (ICC 0.91-0.94) and high responsiveness, with standardized response means greater than 1.2 for detecting strength changes after surgery.
02While handheld and electromechanical dynamometry scores correlated moderately to strongly (r=0.60 to 0.84), there was systematic disagreement in actual force values, with handheld measures underestimating strength, especially at higher forces.
03The bias between the two methods was most pronounced before surgery (mean difference 129.5 Newtons) and reduced but persisted at 2 weeks (45.9 Newtons) and 6 weeks (94.8 Newtons) post-surgery.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTsWhat it means for SLPs
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What it does not show
Reliability was tested only within a single session (a few minutes apart), so it does not account for day-to-day variability or changes in patient condition between visits. Follow-up stopped at 6 weeks, missing the longer recovery period where strength continues to change for months. The study was a secondary analysis of existing data, not designed specifically for this comparison. Participants received standard care and outpatient physical therapy, which varied by patient and was not controlled, so strength changes reflect natural recovery plus uncontrolled rehab.
Declared interests
Funded by the National Institutes of Health (Extramural). No other conflicts declared in the provided text.
The easy way to misread this
Do not assume that a handheld dynamometry score can replace an electromechanical dynamometry score in your records. The handheld device systematically underestimates force, with differences ranging from 45.9 to 129.5 Newtons, so the two methods are not interchangeable.