ACL Avulsion Fracture

Knee injuries are common in active individuals, athletes and children playing sports. Among the four major ligaments of the knee joint, Anterior Cruciate Ligament (ACL) is the most common to get injured. You must have frequently heard about a tear in the ACL, but another less frequent but debilitating injury is the avulsion fracture of the ACL.

Unlike an ACL tear which can be managed stage-wise and electively, ACL avulsion needs early diagnosis and appropriate treatment to prevent long-term complications. Let’s understand some details herein.

What is an ACL avulsion fracture?

ACL is a key stabilising ligament of the knee that prevents excessive forward movement and inward rotation of the shin bone (tibia).

In an ACL avulsion fracture, the ligament itself remains intact, but it pulls off a fragment of bone from its attachment site, usually from the shin bone (tibia). This injury is different from a mid-substance ACL tear, where the ligament fibres rupture but the attachment to bone is intact.

ACL avulsion fractures are more commonly seen in children and adolescents, as their bones are relatively weaker than ligaments. However, they can also occur in adults, especially after high-energy trauma.

How does it happen?

ACL avulsion fractures typically occur due to sudden forceful stress on the knee, similar to the mechanism of an ACL tear. Common causes include:

• Sports injuries involving sudden twisting or pivoting movements

• Falls from height

• Road traffic accidents

• Hyperextension of the knee

• Direct impact to the knee during contact sports

In children, even relatively low-energy trauma can lead to avulsion fractures due to open growth plates and softer bones.

Who is at risk?

Certain groups are more prone to ACL avulsion fractures:

• Children and adolescents (8 to 16 years age)

• Young athletes involved in football, cricket, basketball, skiing, or gymnastics

• Individuals involved in high-impact or contact sports

• Patients with pre-existing knee instability

Understanding risk factors helps in early suspicion and timely treatment.

What are the symptoms?

The symptoms are similar to other ACL injuries but may vary in intensity. Common symptoms include:

• Sudden onset pain in the knee at the time of injury

• Rapid swelling over the joint (due to bleeding inside the joint)

• Difficulty in bearing weight over the leg

• Feeling of knee instability or ‘giving way’

• Restricted movements of knee joint

In children, symptoms may sometimes be subtle, leading to delayed diagnosis.

How are these injuries classified?

ACL avulsion fractures are commonly classified using the Meyers and McKeever classification, which helps guide treatment:

• Type I: Minimally displaced fragment

• Type II: Partially displaced with intact posterior hinge

• Type III: Completely displaced fragment

• Type IV: Completely displaced and comminuted (multiple small fragments)

  

How to confirm the diagnosis?

A) Clinical Examination

Includes assessment by an orthopaedic surgeon for the knee swelling, tenderness, range of movements and joint stability. Standard ACL tear tests are painful in this scenario and should not be performed.

B) Radiology

• X-ray: Often sufficient to make the primary diagnosis. Type I injuries can be missed out if not looked for carefully.

• MRI: gives further information about:

  • Extent and position of the avulsed fragment

  • Integrity of the ACL

  • Associated injuries like meniscus tears, cartilage damage or injury to other ligaments

Early and accurate imaging plays a key role in treatment planning.

What are the treatment options?

Treatment depends on the age of the patient, displacement of the fractured fragment and functional demands.

A) Non-Surgical Treatment:

It is considered for completely undisplaced (Type I) fractures

Conservative treatment includes:

• Knee immobilisation in a long leg knee brace

• No weight bearing on the leg, by walking with a walker/crutch support.

• Gradual knee bending after 6 weeks

However, weekly follow-up is essential to ensure anatomical healing and avoid residual laxity.

B) Surgical Treatment:

Surgery is recommended for:

• Type II, III, IV (displaced) fractures

• Type I fracture with persistent knee instability or delayed displacement during non-operative management

• High-demand athletes

Arthroscopic Fixation:

Arthroscopy has revolutionised the surgical management of avulsion fractures inside the joint. With this technique, the fracture is visualised with a telescope inserted into the joint through a key-hole incision and fixation is carried out using another key-hole incision.

Arthroscopy offers following advantages over conventional open surgery:

• Key-hole incisions, hence less pain after surgery

• Faster recovery

• Less chances of infection

• Simultaneous visualisation and treatment of other problems in the joint

• Minimal disruption of bone growth in children

Fixation methods include:

• Sutures

• Screws

• Anchors

• Buttons

Whatever the fixation modality is, the goal is to restore avulsed fragment to its anatomical position, thereby restoring normal ACL function.

How is the post-operative recovery?

Rehabilitation under guidance is crucial for a successful outcome. A structured physiotherapy program includes following steps:

• Initial period of non-weight bearing walking with walker/crutches and bracing

• Early range-of-motion exercises

• Gradual strengthening of muscles

• Proprioception and balance training

• Sport-specific training in later stages

Most patients return to daily activities within 6 to 8 weeks and sports within 4 to 6 months, depending on healing and rehabilitation progress.

What are the possible complications of this fracture?

If not treated appropriately, ACL avulsion fractures may lead to:

• Chronic knee instability - feeling of giving way, buckling

• Limited knee movements - stiffness

• Persistent residual pain

• Early onset osteoarthritis

• Need for delayed ACL reconstruction altogether

Early intervention significantly reduces the risk of these complications.

How is the prognosis?

When diagnosed early and treated appropriately, outcomes of ACL avulsion fractures are excellent, especially in children and young athletes. Surgical fixation restores knee stability and allows most patients to return to pre-injury activity levels.

How to prevent it?

While not all injuries can be prevented, the following measures help reduce the risk:

• Proper warm-up and stretching before sports

• Strengthening hip, knee and core muscles

• Learning correct jumping and landing techniques

• Using appropriate footwear

• Avoiding overtraining

To summarise..

ACL avulsion fracture is a distinct knee injury that requires timely diagnosis and individualised treatment.

With advances in arthroscopic techniques and structured rehabilitation, patients can expect excellent recovery and return to an active lifestyle or sports.

If there is knee pain, swelling or instability after an injury, especially in children and adolescents, early consultation with an orthopaedic surgeon is a must.

If you have sustained an injury recently or are suffering from long term joint problems after an injury, consult Dr. Ajinkya Achalare at ArthroSports Clinic, Dadar, Mumbai. With special expertise in arthroscopy and sports injuries, he will help you achieve a complete recovery.

Book a consulatation to know more!