Knee Injuries

Patient Information


The knee is the largest joint in the body consisting of four bones, multiple ligaments and muscles, which act as shock absorbers during movement. Several large fibrous bands of tissue (ligaments) support the knee on all sides. They provide strength and stability to the joint similar to four legs on a table. The four ligaments that connect the thighbone (femur) and shinbone (tibia) are the anterior cruciate ligament (ACL), posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL). The ACL and PCL limit tibial movement forward and backward and also limit flexion and extension of the knee. The MCL and LCL provide stability to the inside and outside of the knee.


Meniscus tissue is important in protecting the surface of the thigh and leg bones, and transmit forces from the thigh to the leg. They function very much like the break pads of the knee. Meniscus tears are very common injuries and occur in young and older patients alike.

Anterior Cruciate Ligament (ACL) Injury

Injured Knee

An ACL tear is common and occurs during high-impact sporting events or when there is a large amount of turning and twisting. A torn ACL usually occurs when a force is applied to the knee while the foot is firmly planted on the ground or upon landing.

A torn ACL can be painful and swelling of the knee will usually begin immediately after injury or within 24 hours. An ACL may cause a loud popping or cracking sound at the time of the injury. There may be some pain at the time of the impact, which over time may be felt in the calf region. The patient may feel some instability of the joint, perhaps creating the feeling of the knee "giving way."

Not all ACL tears need to be repaired. Patients who are young and/or patients who participate in cutting, jumping, or pivoting sports should consider surgery. The ACL protects the knee from further injury to other structures and prevents the development of early arthritis.

Medial Collateral Ligament (MCL)/Lateral Collateral Ligament (LCL) Injury

MCL Tear

The MCL connects the femur and tibia on the inner side (between the knees) and resists forces acting on the outer side of the knee, and the LCL connects the femur and tibia on the outside of the knee and resists forces acting on the inner side of the knee. The two ligaments provide support and stability to the knee. The MCL is more often injured than the LCL as injuries are often caused by a blow to the outer side of the knee (as seen in contact sports) that stretches and tears the ligaments on the inner side of the knee.

Initial symptoms of MCL and LCL tears include pain, stiffness, swelling and tenderness along the inner side or outside of the knee. In addition, the knee may feel unsteady or it may lock or catch. Isolated MCL tears are very common and usually treated conservatively. LCL injuries are more commonly associated with other ligament injuries and often need repair.

Meniscus Tear

Meniscus Tear

A torn meniscus occurs usually during movements that forcefully rotate the knee while bearing weight. A partial or complete tear of a meniscus sometimes occurs if an athlete quickly twists or rotates the upper leg while the foot is firmly planted. This often occurs in field sports such as soccer and football.

An injured or torn meniscus causes mild to severe pain (particularly when the knee is hyperflexed or during squatting). Severe pain is common when a torn meniscus fragment catches between the femur and tibia. Swelling is less common at the time of injury, but can develop much later. Occasionally, an injury to the meniscus causes an audible click or pop, or the knee may lock, or feel weak. If the meniscus injury is small, these symptoms may resolve over time without treatment, but some meniscus injuries may benefit from surgical treatment.

Surgical options include debridement or repair. Only certain types of meniscus tears can be repaired and generally are reserved for patients younger than 30. Meniscus debridement is a simple procedure with generally quick recovery times.

Cartilage Surgery

Cartilage is a tough, flexible tissue that is found throughout the body. Cartilage acts as a shock absorber as it covers the surface of joints, allowing bones to slide over one another while reducing friction and preventing damage. Cartilage, unlike most other types of tissue, does not have a blood supply. Therefore, damaged cartilage does not heal and can be the first stage in osteoarthritis. Symptoms of articular cartilage damage include swelling, joint pain, stiffness, decreased range of movement in the affected joint and joints that lock or catch. The pain may prevent involvement in normal activities.

Cartilage Cartilage

This is an exciting time in cartilage treatment. Multiple procedures are available and vary in recovery time and technical difficulty. COSM surgeons are training the next generation surgeons in these techniques. The specific surgery is dependent on the cartilage injuries size, location, chronicity, and associated injuries.



Microfracture is the simplest of cartilage procedures and has a good track record in professional athletes. A small tool is used to place defects through the bone underlying an area of complete cartilage loss. This allows for regress of bone marrow into the defect creating a healing response with cartilage like properties.

Patients generally avoid weight bearing for two to four weeks but are encouraged to work on muscle strength and range-of-motion exercises. Total recovery can take four to six months depending on the desired degree of activity.

OATS (Osteochondroal Autolograft Transplant)


OATS is a technique which takes a plug of cartilage and bone from a non weight-bearing region of the knee and replaces a full thickness injury in a symptomatic cartilage injury. The technique works best in lesions less than 1 cm in diameter and provides normal cartilage to the area of injury.

The surgery is more involved than microfracture surgery and the recovery time can take six to nine months before returning to full activity. There are only certain lesions that are amenable to OATS surgery.

Autologous Chondrocyte Implantation (ACI)


ACI surgery is a staged procedure where a known (or highly suspected) cartilage injury is found at the time of surgery and cartilage cells are biopsied. Those cells are cultured to increase the number and re-implanted at a later date. For that reason, ACI surgery requires two procedures. Recovery time is nine to twelve months. ACI surgery is good for harder to repair locations such as under the knee cap (patella).

Allograft OATS Procedure

Allograft OATS surgery is used for lesions larger than one to two centimeters in diameter and often involve not only cartilage but bone defects. The defect is mapped using MRI and a cadaveric donor is found which matches the anatomy. The timing of the OATS surgery is very important to preserve cartilage viability. The recovery can last nine to twelve months.

Allograft OATS Procedure Allograft OATS Procedure