Partial vs Total Knee Replacement

Knee replacement surgeries are safe and effectively manage the pain and disability caused by osteoarthritis. During knee replacement surgery, the ends of the diseased joint are replaced with prosthetic metal and plastic parts.

While in total knee replacement all the compartments of the knee joint are usually replaced, a partial knee replacement only involves the replacement of a single knee compartment.

The knee joint is divided into three compartments or spaces. The joint is formed by the lower end of the thigh bone, the upper part of the shinbone, and the undersurface of the kneecap.

The inner side of the knee is called the medial compartment, and similarly, the outer side of the knee forms the lateral compartment. In front of the knee, the joint formed by the kneecap and the thigh bone forms the patellofemoral compartment.

The bones forming the knee joint are covered with a glistening white tough tissue known as articular cartilage. The articular cartilage helps in the smooth gliding of the joint in motion. Various ligaments, meniscus, and muscles provide additional stability to the knee joint.

Majority of the patients who may need joint replacement surgery suffer from osteoarthritis. Osteoarthritis is a wear and tear disease of the joint that gradually destroys the articular cartilage, the bone ends, and the ligaments secondary to instability. Arthritis may affect all the compartments at the same time or may start in one of the compartments first.

Patients with knee arthritis may complain of pain, stiffness, or deformity. A knee replacement surgery is only offered to the patients when all other nonsurgical treatments have been tried. Nonsurgical treatments include physical therapy, cortisone injections, and pain medications, etc.

Partial knee replacement

In a partial knee replacement, only one of the compartments of the knee is replaced. During a partial knee replacement surgery, the surgeon accesses the joint through a usually smaller incision. The diseased ends of the bones forming the compartment are then cut to be removed. All the ligaments and other soft tissue structures are left intact.

A metal prosthetic component is placed on the cut bony ends and fixed with bone cement. A high-grade plastic part is placed in between the metal parts for the smooth gliding of the metal surfaces. The incision is closed in layers and the patient is able to walk the same day of the surgery.

Not all patients are candidates for partial knee replacement. The partial replacement surgery is only recommended in the following patients:

• Patients with evidence indicating the involvement of only one compartment of the knee joint.
• The knee joint is stable without any damage to the ligaments such as the anterior cruciate ligament, posterior cruciate ligament, or medial and lateral collateral ligaments.
• Patients with no history of meniscus surgery in the other compartment.
• Generally, patients aged 60 or more with less demanding lifestyles who are not obese.
• Patients with no evidence or history of inflammatory arthritis such as rheumatoid arthritis, reactive arthritis, etc.
• Patients with no significant deformity of the knees such as bow legs, knock knees, flexion deformities, or inability to bend the knee more than 90 degrees.

Partial vs Total Knee

Since the partial knee replacement involves the replacement of only one of the knee compartments, the surgery time is significantly less than the total knee replacement. The risk of complications associated with a knee replacement surgery such as blood loss, nerve damage, deep vein thrombosis, infection, etc is also less in the case of a partial knee replacement.

Since less tissue and bone are cut and the ligaments are left intact, a partial knee replacement has a more natural feeling to the knee joint. Comparatively, patients who undergo total knee replacement often complain of feeling unnatural mechanical knees. The unnatural feeling is a result of the removal of the ligaments of the knee that carry nerve sensations to the brain.

Patients undergoing partial knee replacement are able to get back to their daily activities sooner than total knee replacement. As significantly less cutting is involved in a partial knee replacement, the patients experience less postoperative pain and are able to participate in rehabilitation sooner.

Partial knee replacement however is not frequently done even in patients with unicompartmental knee arthritis as:

• In the majority of cases, a partial knee replacement may need revision surgery in the form of a complete knee replacement. Arthritis eventually may involve the other compartments of the knee causing pain and deformity.
• The revision surgery to total knee replacement from a partial joint replacement is often more complicated than a primary total knee replacement surgery.
• A number of patients with knee arthritis have deformities such as knock knees, bow-legs, or inability to completely straighten or bend the knee. The deformity can be easily corrected in a total knee replacement leading to better knee kinematics.
• Any subsequent ligament or meniscus damage in a patient with a partial knee replacement surgery may require a revision into a total knee replacement.
• Inflammatory arthritis usually involves the entire joint instead of a single compartment. Patients with inflammatory arthritis are more effectively managed with a total knee replacement surgery.

Total knee replacement surgery has revolutionized the management of knee arthritis. Patients today prefer an early joint replacement surgery after failure of non-surgical methods due to the drastic improvement in quality of life with regained mobility.

The majority of the patients who may be candidates for a partial knee replacement generally opt for a total knee replacement due to lower revision rates.