Understanding ACL Tears

The anterior cruciate ligament (ACL) is one of the main stabilizing ligaments of the knee joint and has garnered somewhat of an infamous reputation in the health and sports populations. In light of the continued questions from our clients, I thought it might be helpful to demystify it: what it is, what it does, how it becomes injured, and what happens after it’s injured. To understand this clearly it is important to understand the anatomy a bit better as well.

A ligament is a piece of connective tissue that connects two pieces of bone together. It is not a muscle or a tendon. Ligaments strictly go from one piece of bone to another to provide stability. In this case, the ACL is one of four main ligaments that stabilizes the knee joint. The knee joint specifically is where the bottom of your thigh bone (femur) meets the top of your shin bone (tibia). It is a large joint with high demand and thus you have four main ligaments to provide the necessary stability: front-back-left-right.

ACL: Anterior Cruciate Ligament inside of the knee

• prevents the shin bone from moving too far forward relative to the thigh bone

If you can now visualize that the knee itself is supposed to bend and straighten then you can apply the above information and appreciate that the shin bone isn’t supposed to move too far in any direction otherwise you risk severe injury. If it does happen, then the ligaments become stretched to or even beyond capacity. This is where partial or complete tears happen and it is the extent of the tear and location of the tear on the ligament that determines the outcome/options. In the case of the ACL, its specific location is inside of the knee, in the middle, and attaches from the bottom of the thigh bone to the top of the shin bone at a slight angle. 

How does this happen? The ACL usually falls victim to hyperextension, rotary force, or deceleration. Each of these can result in some or all of the fibers being stretched or torn.

Hyperextension: knee straightens excessively or forcefully too far backward

Rotary Force: The foot is planted while there is a rotational movement at the knee

Deceleration: Rapid slowing down while the knee bends often with the hips low

A partial tear can mean only some of the fibers are stretched/torn. If the percentage of these involved fibers is low enough and/or in a location that can heal well then rest, aggressive rehab, and activity modification may be sufficient for full recovery. If, however, there is substantial damage or a complete rupture then the stability of the knee will be compromised because the ligament can no longer be structurally sound and provide protection against forces trying to move the knee.

Once there is suspicion of ACL injury your sports medicine team will perform a series of clinical tests and also refer out for imaging to confirm. This is where the precise extent of the injury can be identified and suggestions for a best scenario for a complete recovery. If that means surgery, then the specific timeline and type of repair will be discussed with your surgeon. It may come as a shock but there are some instances where even a complete rupture may benefit from a non-operative approach. Location of tear, age, and activity level will facilitate this decision (and more to come in a separate blog).

While there are a number of different options for repair, we will save those for separate posts and instead focus on managing expectations for a generic timeline of ACL injury and repair. The timeline for recovery of a non-operative ACL injury can and will vary from person to person. However, a surgically repaired ACL (ACLR: Anterior Cruciate Ligament Reconstruction) will generally take a full nine to twelve months to ensure safe Return to full Participation in Sports (RTP or RTS).

Activities such as walking, jogging, strength training, etc will be introduced well before that in the five to eight-month range. But higher-level activities like contact sports, multi-directional sports, jumping and landing, change of direction, sprinting, etc. will most likely be given the green light no earlier than nine months.

This is because research has shown us that re-injury rates are close to 100% around five months RTP and (assuming continued and effective rehab) that risk drops 50% each month after. So that means months nine-twelve are where that risk drops to the single digits for %.

And time alone isn’t the only thing that determines readiness for RTP/RTS. A proper sports medicine staff will implement performance evaluations or movement/strength tests in the clinic to prove sufficient strength, endurance, and body tolerance to repeated higher-level movements. Specific strength, hopping, jumping, landing, change of direction, and sprinting/stopping drills will be used to create a high level of confidence for an approved RTP/RTS.

And finally, our specific recommendation from your team at Feldman PT & Performance is that you continue this high-level training even after your return to the sport because your risk of injury or re-injury remains elevated for up to two years. We don’t like our clients to abruptly stop their knee-focused work because this can have unintended consequences. Our specific plans include continued clinic care, remote coaching, and proper endurance training to ensure the knee remains at a high strength and neuromuscular performance level.

So at the risk of straying from my purpose, I’ll leave the rest for another day, and another blog. The goal for today was to unpack the ACL and help show what it is, what it does, and what happens when it becomes injured. The nuances will be covered later, and should you have any questions then we would love the chance to answer them.