Question:
Which activity will be difficult to perform for a patient with an anterior cruciate deficient joint?
Which activity will be difficult to perform for a patient with an anterior cruciate deficient joint?
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The ACL resists forward shift of the tibia; activities needing a strong quadriceps pull in a bent knee, like walking downhill, are hardest.
Updated On: Jul 8, 2026
- Walk downhill
- Walk uphill
- Sit cross leg
- Getting up from sitting
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The Correct Option is A
Solution and Explanation
Step 1: Understand what the ACL does.
The anterior cruciate ligament (ACL) stops the tibia (shin bone) from sliding forward under the femur (thigh bone) and also checks excess rotation of the knee. Once it is torn, the knee loses this forward translation control, so any activity that pushes the tibia forward becomes hard to do without the knee giving way.
Step 2: Work out what downhill walking does to the knee.
Walking downhill needs the knee to stay slightly bent while the quadriceps muscle contracts to control the descent, an eccentric contraction. A contracting quadriceps pulls the tibia forward through the patellar tendon. In a normal knee the ACL resists this pull. In an ACL deficient knee there is nothing to resist it, so the tibia shifts forward and the knee feels unstable or gives way. This is why patients with ACL tears specifically struggle with downhill walking, running, and quick deceleration.
Step 3: Check why the other activities are less affected.
(B) Walking uphill: Uphill walking loads the hip more and needs less quadriceps braking, so it does not push the tibia forward the same way. Patients manage this reasonably well.
(C) Sit cross leg: This needs knee flexion and some rotation but no strong quadriceps contraction against gravity, so ACL deficient patients can usually do this.
(D) Getting up from sitting: This does load the quadriceps, but the knee moves from flexion to extension in a controlled, low speed way without the sudden forward shear seen in downhill walking, so it is tolerated better.
Step 4: Final Answer.
The activity that is hardest for an ACL deficient knee is downhill walking, because it combines knee flexion with a strong quadriceps pull that shifts the tibia forward with no ligament to stop it.
\[ \boxed{\text{Walk downhill}} \]
The anterior cruciate ligament (ACL) stops the tibia (shin bone) from sliding forward under the femur (thigh bone) and also checks excess rotation of the knee. Once it is torn, the knee loses this forward translation control, so any activity that pushes the tibia forward becomes hard to do without the knee giving way.
Step 2: Work out what downhill walking does to the knee.
Walking downhill needs the knee to stay slightly bent while the quadriceps muscle contracts to control the descent, an eccentric contraction. A contracting quadriceps pulls the tibia forward through the patellar tendon. In a normal knee the ACL resists this pull. In an ACL deficient knee there is nothing to resist it, so the tibia shifts forward and the knee feels unstable or gives way. This is why patients with ACL tears specifically struggle with downhill walking, running, and quick deceleration.
Step 3: Check why the other activities are less affected.
(B) Walking uphill: Uphill walking loads the hip more and needs less quadriceps braking, so it does not push the tibia forward the same way. Patients manage this reasonably well.
(C) Sit cross leg: This needs knee flexion and some rotation but no strong quadriceps contraction against gravity, so ACL deficient patients can usually do this.
(D) Getting up from sitting: This does load the quadriceps, but the knee moves from flexion to extension in a controlled, low speed way without the sudden forward shear seen in downhill walking, so it is tolerated better.
Step 4: Final Answer.
The activity that is hardest for an ACL deficient knee is downhill walking, because it combines knee flexion with a strong quadriceps pull that shifts the tibia forward with no ligament to stop it.
\[ \boxed{\text{Walk downhill}} \]
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