The Buckling Knee

Having a sense of the knee ‘giving way’ or ‘locking’ is a fairly common complaint by athletes who have twisted their knees in sports like basketball, netball, soccer or badminton. The sensation of ‘giving way’ is an indication that you might have torn your Anterior Cruciate Ligament (ACL) while the ‘locking’ sensation is an indication of a possible meniscus tear.

ACL Injury

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The ACL is a fairly strong ligament found between the knee-joint. Its main role is to limit the forward movement (anterior translation) of the leg bone (tibia) on the thigh bone (femur).

When athletes change direction quickly during their games, they twist their knee inwards. This increases the strain on the ACL and places the ligament at risk of tearing. The ACL tears when the knee is force downwards and inwards beyond the ligament’s ability to hold. Athletes who tear their ACL often report hearing a ‘pop’ on injury.

Unfortunately, the ACL is very rarely the only ligament involved in this kind of injury. It is normally accompanied with a slight tear in the Medial Collateral Ligament (MCL) and either a medial or lateral meniscus (cartilage) tear. These three tears are commonly known as the ‘Unhappy Triad’ or ‘Terrible Triad’.

Meniscal Injury

The meniscus, which is a crescent shaped cartilage between the knee, acts as a cushion to absorb the impact between the leg and thigh bone. The meniscus is better at the handling stress from an up and down motion. It doesn’t do as well under a twisting motion especially when compressed. This motion can cause a tear in the meniscus. The knee feels ‘locked’ when the torn part of the meniscus blocks the movement of the knee.
Immediate swelling and severe pain in the knee are common signs of this Triad injury. However, there are occasions where there will be a delay in the onset of swelling or even no swelling at all. Remember how you injured the knee. It helps your Doctor or Physiotherapist in diagnosing this problem.

Solving the Problem

Sadly, the ACL doesn’t heal on its own due to the poor blood supply to the ligament. It would need to be reconstructed surgically by using either your hamstring tendon or patella tendon. Rehabilitation after surgery normally takes about 6-9 months before the athlete is able to go back to full training.
Nevertheless, there are about 20% of people with ACL tears who are able to go about their day-to-day activities without having their ACL reconstructed.  To cope without surgery, the following muscles need to have good strength and control:

  • Hamstrings
  • Quadriceps (thigh)
  • Gluteus Medius
  • Gastrocneumius (calf)

Besides doing strengthening exercises, slowly getting back into sports specific training is essential. This is so that your muscles can develop an anticipatory reaction (feed-forward mechanism) to prevent injury.

Sports taping of the knee to support the ACL and MCL can also be done as a temporary measure for the athlete to cope with the injury until the end of the season.

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  • Daniel

    Nice article. The brief description of the problem and solution provided is too good.

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  • Rick lambert

    I like this answer but it misses one huge and very common reason for ‘buckling knee’. The muscle strength and coordination of the knee is dominated by L4 nerve root supply. Any irritation or inflammation around this root level (facet joint syndrome) or irritant along the course of this nerve to affect its proper function will lead to patients complaining of knee weakness and buckling without back pain.nnI should know, I must have treated this so many times. Treatments I gave would not have been successful if my observations were an error! So please include this concept in your otherwise excellent article. Thanks.nn

  • vicki

    I have L4 issues and a torn meniscus. Surgery 9/15/11. Knee is buckling and locking and I thought for years it was my spinal issues. I am hopeful this tear when it’s repaired will help my gait,balance,ability to straighten the leg out and stop the buckling/locking. I am afraid. It would be a miracle for me to regain my walking, going down stairs and restore my strength. Spinal fusion L5S1/ L4/5 fusion for cyst/ L3 kyphoplasty. Thanks Rick for being so knowledgeable. I pray I’ll be lucky and be able once again. 

  • tennis bum

    Excellent article. I recently experienced knee buckling playing tennis. Prior to that, had some pain behind the knee, medial side, but not bad (2/10). So I think it couldn’t be the “terrible triad” and more likely L4 nerve root, per Rick Lambert’s comment. Could I get by with a special knee brace? Any other suggestion?

  • Roger Dodger

    I have begun having buckling issues with my right knee “recently”, but I have enough chronic joint problems I can’t actually remember if I’ve ever had this problem for so long (except for when I initially tore my meniscus). I have since had chronic though minor episodes of apparent minor injury or aggravation of the right knee ligaments. However, I also began having back problems one year ago. I have sciatica on the right side and lower back pain. Diagnostic images show a mild L4/L5 spondylolisthesis as well as spondylosis. Is there a way to determine if the buckling and spondylolisthesis are related PRIOR to treatment for an L4 nerve root supply issue (especially because my insurance coverage max on my chiro visits)?