Knee Pop, Swelling and Instability: Could It Be an ACL Tear?

Dr. Horner becomes particularly concerned about an ACL tear when a patient describes:

ACL tears can occur during contact injuries, such as a collision, or without contact. Noncontact injuries are somewhat more common and may occur during cutting, pivoting, landing, or suddenly changing direction.

No single symptom confirms an ACL tear. The history of the injury, physical examination, and appropriate imaging are considered together when making the diagnosis.

Patients with a sudden knee injury followed by a pop, early swelling, difficulty bearing weight, or instability should ideally be evaluated as soon as possible.

Early evaluation allows the knee to be examined for an ACL tear and other possible injuries involving the meniscus, cartilage, or additional ligaments. It does not mean that immediate surgery will necessarily be recommended. Initial treatment may focus on controlling swelling, restoring motion, improving walking, and determining the full extent of the injury.

The decision between ACL reconstruction and nonsurgical management is made later based on the patient's age, activity goals, knee stability, associated injuries, and progress with rehabilitation.

An initial evaluation generally includes:

X-rays do not show the ACL directly. However, they provide important information about other causes of pain and injuries that may have occurred at the same time.

If the history and examination create a high clinical suspicion for an ACL tear, Dr. Horner will generally order an MRI at the first appointment. MRI can evaluate the ACL and identify associated injuries involving the meniscus, cartilage, and other knee structures.

Some patients cannot fully straighten or bend their knee after an injury. Pain and swelling can temporarily restrict motion, but a knee that remains mechanically locked despite gentle stretching and a period of observation can be concerning for a displaced meniscus tear, including a bucket-handle tear.

A displaced meniscus tear may require more urgent evaluation and, in selected cases, surgical treatment. The goal is to preserve and repair the meniscus whenever possible rather than remove the damaged portion.

The meniscus is an important shock absorber that distributes forces across the knee. Preserving functional meniscal tissue may help protect the joint over time, although whether a particular tear can be repaired depends on its pattern, location, tissue quality, and other patient-specific factors.

No. Some patients can be treated with physical therapy, activity modification, and occasionally bracing, particularly when they do not experience recurrent instability and do not plan to return to activities that require frequent cutting or pivoting. The decision guide on ACL surgery versus physical therapy reviews these situations in more detail.

ACL reconstruction is more commonly considered for younger or active patients who want to return to pivoting sports, physically demanding work, or other ACL-dependent activities. Surgery may also be recommended when the ACL tear occurs with certain associated injuries, such as an unstable meniscus tear.

Treatment is individualized according to the patient's goals, examination, imaging, and response to rehabilitation.

If you experienced a sudden pop, rapid swelling, difficulty bearing weight, or a shifting sensation during a knee injury, an orthopedic evaluation can help determine whether the ACL or another structure has been injured.

A knee that remains locked and cannot straighten or bend should be evaluated promptly because a displaced meniscus tear may be present.

Dr. Nolan Horner evaluates knee and sports injuries at his Oak Brook, St. Charles, and Little Village offices.