Correlation of isokinetic and novel hand-held dynamometry measures of knee flexion and extension strength testing

by Simon Mole

As Physiotherapists we are constantly talking to our patients about getting stronger, improving motor control and changing aberrant patterns of movement. Our training gives us a unique skill set that allows us to assess movement abnormalities and this is something that I think we do remarkably well. However, knowledge of what causes these movement abnormalities and even their significance in our patient’s clinical presentation is where I think we need to improve. If you were to have 10 experienced Physiotherapists  looking at the same patient, odds are they would see the same things, but there’d be significant variation in each Physio’s explanation of why the patient moved the way they did. Each Physio’s explanation would fit within their individual paradigm, a combination of their knowledge base and personal experience. As a profession, I think we need to try and bring our paradigms closer and recognise that there are often gaps in our clinical reasoning, things we may not be able to explain completely or alternate explanations for what we see. This can in part be achieved if we are accurate and specific with our assessment, which brings me to assessing strength.

 

Traditional manual muscle testing (Grades 0-5) has huge reliability issues. Grades 4 & 5 are largely subjective and in an orthopaedic or Sports population are meaningless. Dynamometry eliminates any subjectivity and handheld dynamometry has been shown to have similar accuracy to isokinetic testing (Whiteley et al. 

 

Correlation of isokinetic and novel hand-held dynamometry measures of knee flexion and extension strength testing  

Journal of Science and Medicine in Sport, Volume 15, Issue 5, September 2012, Pages 444-450 ), making it a robust and simple clinical tool. It also allows us to quickly and accurately measure strength in specific muscle groups, giving us and our patients a number and as we know, patients love a number. If only I could make money from the question ‘ Is that strong?’ when I test their rotator cuff. I rarely answer one way or the other, but it’s amazing the look of excitement that they have when you find that there is a significant deficit in their effected limb. That’s when they buy into their rehabilitation, wanting to know how to get stronger, how to improve that number.

 

Our epidemiological data doesn’t give us a lot of information about strength, what is normal and what is what is not. In the throwing literature there’s agreement that the ratio of IR to ER strength should be around 1.5 and that if this ratio gets higher that 1.8 the risk of injury increases. This however is only one population group, and although there are similar ratios spoken about in the lower limb (quads/hamstrings, abductors/adductors) there is so much more work to be done. More recently researchers have started to look at strength as a percentage of body weight and this is where our future lies. Boettcher (2013 Sports Physio – APA Publication) recently published data showing that in elite swimmers with no history of shoulder pain, shoulder IR was 30% of body weight while ER was 20% of body weight. This type of data will drive our rehabilitation, giving us direction for our strength programs and for me is where I am watching most closely. This type of knowledge combined with accurate assessment tools makes us better therapists.


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