Lower Limb Stability with ACL Impairment
Lower Limb Stability with ACL Impairment
Abstract & commentary
Synopsis: The vertical force parameter during the hop test cannot be easily used to identify knee dysfunction.
Source: Colby SM, et al. Lower limb stability with ACL impairment. J Orthop Sports Phys Ther 1999;29:444-454.
Historically, measures of variables such as strength (torque production) and endurance have provided data with which to judge function and contributed to the decision-making process regarding an injured athlete. Decisions such as when the athlete should be allowed to return to play have been affected by these measures. However, the measures were not valid criteria because they did not actually test function. More recently, such measures as single leg hop and single leg stance have provided the clinician with information more specific to the function of the lower limb of an athlete.
The current study was an attempt to determine if there was, indeed, a difference in these measures among three different athlete populations: ACL deficient (ACLd), ACL reconstructed (ACLr), and normal. The ACLd group had greater than 3 mm of difference between involved and uninvolved knees on a KT1000 test (a device that measures anterior tibial translation). These subjects actually could have a partial ACL, no ACL, a reconstructed but loose ACL, or a loose but intact ACL. ACLr subjects were post-ACL reconstruction with bone-patellar tendon-bone graft, all performed by the same surgeon. All of these subjects had a less than 3 mm side-to-side difference on KT1000 testing. The time postsurgery was a mean of 158 days. Nonimpaired subjects had no history of knee injury. In this study, the ACLd group had five males and eight females with a mean age of 40.4 years; the ACLr group had nine males and two females with a mean age of 26.3 years; and the normal or nonimpaired group included 14 males and 11 females with a mean age of 31.2 years.
Study measures were taken by having the subjects perform activities on a force plate. Measures included vertical, medial-lateral, and anterior-posterior movement of the ground reaction force during the single leg hop (onto the force place) and a step down (onto the force plate). Stability was defined as "the ability to transfer the vertical projection of the center of gravity to the supporting base and keep the knee still."
Twelve normal subjects were tested three times to determine the reliability of the force plate measures. Eleven parameters were calculated, and only those with a correlation of 0.8 or above were used. There was a difference in stabilization time in the healthy subjects between limbs; therefore, this variable was not used to compare the three groups. In addition, the step-down test demonstrated a difference between involved and uninvolved limbs in the ACLr group. Colby and associates conclude from the hop test that it is "difficult to conclude that the vertical force parameter during the hop test can be used to identify dysfunction."
Comment by Clayton F. Holmes, EdD, PT, ATC
This study is an excellent attempt to identify differences among patient populations with respect to some common functional tests. The use of the force platform in this type of research is an essential next step in evaluation of functional measures. Perhaps the most important finding of this study is that many of the measures on the force platform were reliable. However, Colby et al failed to show any major differences between the three groups with respect to these measures. In other words, while these measures are reliable, they did not distinguish between the three groups. However, this should not diminish the need for these tests because they do mimic function and provide some information regarding knee function. They are not all inclusive, but then, no test is. Perhaps this study should be repeated with a longitudinal design. ACLr patients could be followed throughout their rehabilitation in order to determine if these measures change. These patients could be compared to a control group of normals measured at the same time. Doing this would answer the question regarding functional testing and return to play. Colby et al indicate broad external validity when they say that these data may provide "normal standards" with which to compare your patients. Obviously, 49 total subjects do not provide a normative measure, and care should be taken in making comparisons to these results. Overall, this study definitely adds to the body of knowledge regarding functional tests.
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