This week, we will continue this discussion by looking at how quadriceps function impacts both movement and kinesiophobia. Anyone that has dealt with an ACL reconstructed athlete over they years knows that pushing quadriceps strength is vital, something you start very early and can sometimes be something that is very difficult to get. This is going to be the area of focus for us this week as we look at a couple of studies that tie quadriceps strength and symmetry to both biomechanical function in single limb performance, injury risk and kinesiophobia.
In a study by Smith et al Am J Sport Med 2015, the authors looked at 75 athletes following ACLR who were cleared for return to sport (RTSport). Each athlete filled out an IKDC (international knee documentation committee form), performed a biodex test for quadriceps strength and had their lower extremity biomechanics measured during a single legged hopping task. What the study showed was that patients who demonstrated the greatest quadriceps deficit at the time of testing also scored poorly on the IKDC and demonstrated movement asymmetries and decreased functional performance on hop testing.
IKDC asks a series of questions related to pain, function, ect and is the patient's perspective of their functional status of their knee during performance of these tasks. Poor performance on this test has been shown in the research to be highly correlated to the actual functional status of the patient's knee. The results of this study would suggest that a decrease in quadriceps strength post ACLR would be associated with a decrease in functional ability in daily activities as well as sporting activities.
This study also evaluated lower kinetic chain biomechanics during performance of single leg hopping tasks. The results showed a strong correlation (P value <.05) between quadriceps weakness and altered lower kinetic chain biomechanics during single leg hopping. These biomechanical differences noted with quadriceps weakness are also associated with an increased risk for non-contact lower kinetic chain injuries.
This can give us some guidance, not only from an assessments standpoint but also from a treatment standpoint. Obviously lower chain kinematics are altered when the athlete experiences quadriceps weakness, so one could assume that assessing single limb movements (like a single leg squat) would be one way we could functionally identify this and could use this further as a training method.
Ho et al J Physio 2015 to investigate this. In this study the authors tested 100 athletes post ACL reconstruction who were cleared for RTSport and wanted to see the correlation between quadriceps function, kinesiophobia and quadriceps strength.
This study showed a weak correlation to strength and kinesiophobia but a strong correlation to strength and altered biomechanics during single limb exercises. In looking at this study, it is difficult to really determine the full depth of the methods and how they were carried out. However, the results are somewhat similar to what Wilk et al J Ortho Sport Phy Ther 1994 showed in this much earlier study. It this study, the authors showed a correlation to quad strength, results on an IKDC and performance of single limb testing. So if quadriceps strength was poor, both IKDC went down as well as symmetry in performance in the single limb testing. However, one thing to keep in mind, for the single limb testing performed in the Wilk study, there was not a measure of biomechanics during performance of the task but rather simply the ability to perform the task. As we know and as pictured above, you can be symmetrical and still be at risk.
Before we close out this discussion on quadriceps strength, one thing that often comes up is how do you test that. I don't have a $30K or $60K Biodex machine in my clinic to test. Is manual muscle testing alone good enough. Before I answer that, I would refer back to several earlier studies by Wilk et al and Ellenbecker et al Isokin Exer Sci 1996. In the Ellenbecker study, they compared isokinetic testing to standard manual muscle testing. What the study showed is that there is sometimes up to a 28% strength deficit or variance in right to left strength before a "experienced" clinician can pick that up in traditional MMT. So how can we possible test and be reliable?
With the advent of technology, there are numerous products on the market to help. Hand held computerized dynamoters have come down dramatically in price and you can now get them for under $1000. This is a great alternative to the expensive isokinetic machines and will aid in giving more reliable data. Now all of this was great information to have but the question should be, what do I do with it.
Next week we will begin to discuss why these deficits continue to remain through rehab and how we can address. Stay tuned as I am super excited to share with you. Have you followed my instragram @bjjpt_acl_guy lately? If not, you are missing out. I am constantly posting the latest research in injury prevention and sports medicine. Don't miss out and please share with your colleagues, athletes and training partners and please be sure to follow us on instagrm @ bjjpt_acl_guy and twitter @acl_prevention. Train hard and stay well. #ViPerformAMI #ACLPlayItSafe