A study of isokinetic strength and laxity with and without anterior cruciate ligament injury.
Kewwan Kim, Kyoungkyu Jeon, David R Mullineaux and 1 others
PMID 28174432WHAT IT FOUND
In 31 high school athletes with mild past ACL injury, the injured knee had lower knee flexor strength than the other knee.
Extensor strength and muscle balance were not reported as different. Injured-side anterior laxity at 88 N was also lower, not higher.
Key findings
01The injured knee showed significantly lower knee flexor strength than the non-injured knee on isokinetic testing.
02Anterior laxity measured at 88 N was significantly lower on the injured side than on the non-injured side.
03Knee extensor strength and the flexor/extensor ratio were not reported as significantly different between sides.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
The study included only 31 high school athletes with grade 2 or under ACL injury, so it does not describe other injury grades or other groups. It compared the injured and non-injured knee in the same athletes and did not follow them over time, so it cannot show that weakness or laxity causes injury or predicts future problems. The paper reports several strength and laxity comparisons without naming one primary outcome, so significant findings may be mixed across measures. The injured side showed less anterior laxity at 88 N than the non-injured side, and the authors note a previous study did not find a significant laxity difference.
The easy way to misread this
Do not read the significant laxity difference as evidence that the injured knee has more anterior translation. In this study, the injured side had lower anterior laxity at 88 N than the non-injured side, and the study did not test whether strength or laxity changes cause future injury.