Which of the following is a typical exam finding after ACL injury related to quadriceps strength?

• A. Decreased quad strength <80%
• B. Increased quad strength
• C. Decreased ROM
• D. Pain only with extension

Answer: (A)

Quadriceps weakness after an ACL injury is a common finding due to arthrogenic inhibition from swelling and altered joint sensory input, which lowers the neural drive to the quadriceps. Clinically, this presents as reduced quadriceps strength on resisted knee extension, typically quantified as less than about 80% of the strength of the opposite leg. This weakness is a hallmark of the injury and a primary focus of rehabilitation to restore knee function. Increased quadriceps strength would not be expected acutely after ACL injury, while decreased range of motion or pain with extension can occur for other reasons but do not specifically reflect quadriceps weakness.