ACL Injury or Menicus Tear – The Buckling Knee

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Having a sense of the knee ‘giving way’ or ‘locking’ is a fairly common complaint by athletes. This is especially those 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 an Anterior Cruciate Ligament Tear or ACL injury tear, while the ‘locking’ sensation is an indication of a possible meniscus tear.

ACL Injury


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 knees inwards. This increases the strain on the ACL and places the ligament at risk of tearing. The ACL injury tears when the knee forced downwards and inwards beyond the ligament’s ability to hold. Athletes who tear their ACL often report hearing a ‘pop’ on an injury.

Unfortunately, the ACL is very rarely the only ligament involved in this kind of injury. It is normally accompanied by 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 the 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 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.

The role of the meniscus: Redistributing Weight And Shock

You have two C-shaped menisci at each knee. Placed on each side of the knee, they face each other to form a circle of sorts. The outer meniscus on the outer part of your knee is called the lateral meniscus. The inner one is called the medial meniscus.

The function of the meniscus is to distribute the weight or forces at the knee, between your thigh (femur) and shin (tibia) bones more evenly. The meniscus is also very smooth and helps reduce friction during movement. Without the menisci, your thigh and shin bones were be rubbing against each other on their ends. This would be extremely painful and your leg movements will not be smooth.

meniscal tear

The meniscus is a fibrocartilaginous band that is quite tough; designed to bear the brunt of forces acting on it daily. However, twisting the knee or applying direct force in direct contact sports can damaged or tear the meniscus. Because the meniscus has, relatively, poor blood supply, the tears do not heal on their own and may require surgery.

A meniscal tear that catches, locks-the-knee, or produces swelling on a frequent or chronic basis should be removed or repaired before it damages the articular (gliding) cartilage in the knee.

Solving the Problem

Sadly, the ACL doesn’t heal on its own due to the poor blood supply to the ligament. It needs reconstruction surgically by using either the hamstring tendon or the 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 ACL reconstructed.  To cope without surgery, the following muscles need to have good strength and control:

  • Hamstrings
  • Quadriceps (thigh)
  • Gluteus Medius
  • Gastrocnemius (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 (a 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.

Experiencing knee pain? Click here to find out more about physiotherapy for knee pain relief and how Core Concepts can help