Two of the most common causes of swelling of the knee after an injury playing sports are tears of the ACL and the important C-shaped cartilages of the knee called the meniscus. While both can cause symptoms of pain, swelling, and ‘giving way’, the treatment of these common injuries can be different and involve different lengths of recovery times.

Seventy percent of acute hemarthosis (bleeding inside the knee resulting in swelling) is a tear to the ACL. Most ACL tears involved a non-contact pivoting injury with an audible or palpable ‘pop’. Usually within one hour the knee is tense and attempts to move it are painful. Attempts to place weight on that leg may be difficult. As the swelling resolves, attempts to pivot on that leg can result in the sensation that the knee is unstable because the ACL is one of the stabilizers of the knee. The pain may get better as the swelling resolves until the knee ‘gives way’ again.

The diagnosis of an ACL tear is from the history and physical exam. If the team physician or athletic trainer can examine the knee prior to the swelling, then a Lachman’s exam will demonstrate the tear. Once the swelling occurs and the hamstrings start to go into spasm, the Lachman’s exam may become too painful. An MRI is a useful adjunct to the diagnosis and can determine if one or both of the menisci were torn also. Approximately 75% of ACL tears involve a tear of a meniscus.

The treatment for an ACL with instability is reconstruction of the ligament in those that want to maintain an active lifestyle with cutting and pivoting activities. The ACL has a poor healing rate with attempts to sew it back together. Therefore, the ligament is reconstructed by taking another ligament such as the hamstrings or middle third of the patellar tendon and rebuilding the ACL with the aid of drill holes in the bone. All this can be done arthroscopically as an outpatient surgery. Rehabilitation involves several months of a structured physical therapy program tailored to the patients needs.

Tears of the meniscus are one of the most common injuries of the knee requiring surgery. The tearing of the meniscus can involve a twisting motion of the knee and the swelling usually takes several hours to develop. The sensation of ‘catching and popping’ with attempts to move the knee are common. Treatment of meniscal tears depends on the location, size and shape of the tear. Unstable tears in the outside of the meniscus in younger patients are often repaired. Other tears of the meniscus are debrided arthroscopically as an outpatient procedure. The recovery time for treatment of isolated meniscal tears is usually quicker than that of an ACL. Studies have shown that no change in the length of rehabilitation time is usually needed if an ACL reconstruction is done at the same time as a meniscal repair.