A person can live without a kneecap, though the knee’s function will be permanently changed. The kneecap, medically known as the patella, is a small, flat bone at the front of the knee joint. Its surgical removal, called a patellectomy, is reserved as a last option when the bone is too severely damaged to be repaired or when chronic disease causes debilitating pain. While the body adapts, the leg’s biomechanics are fundamentally altered, requiring significant rehabilitation and adjustment.
The Patella’s Essential Role
The patella is the largest sesamoid bone in the body, embedded directly within the quadriceps tendon. It functions like a pulley, displacing the quadriceps tendon away from the knee’s axis of rotation. This displacement increases the leverage, or mechanical advantage, of the powerful quadriceps muscles. By increasing this lever arm, the patella allows the quadriceps to exert a greater force on the lower leg with less effort, making movements like standing and jumping more efficient. It also serves as a bony shield, protecting the underlying cartilage and the distal end of the femur from direct trauma.
Indications for Removal
Patellectomy is considered only when attempts to preserve the bone have failed. The most common indication is a severely comminuted fracture, where the patella is shattered into multiple, irreparable pieces. If the fragments are too numerous or too small to be successfully fixed, removal becomes the only viable option to restore the integrity of the extensor mechanism.
Chronic conditions can also necessitate this procedure, including advanced patellofemoral osteoarthritis or necrosis that causes intractable and debilitating pain. In these cases, the cartilage underneath the kneecap is worn away, leading to bone-on-bone friction not alleviated by less invasive treatments. A patellectomy may also be performed as a salvage procedure after repeated failed surgeries or in cases of chronic infection or tumor within the bone.
Functional Changes After Removal
The most significant consequence of a patellectomy is the permanent loss of the quadriceps muscle’s mechanical advantage. When the patella is removed, the quadriceps tendon must be sutured directly to the patellar tendon, which shortens the effective lever arm of the entire extensor mechanism. This change in biomechanics results in a substantial reduction in the strength and efficiency of leg extension.
Patients often experience weakness, particularly in movements that require maximum quadriceps effort, such as rising from a low chair or climbing stairs. The loss of leverage can reduce quadriceps strength by as much as 30% to 50%, leading to a noticeable “extension lag,” which is the inability to fully straighten the knee actively against gravity. The knee joint may also feel less stable, sometimes leading to a sensation of the knee “giving way” because the loss of the bony structure increases the laxity of the extensor tendons.
Rehabilitation and Long-Term Prognosis
Recovery after a patellectomy is centered on physical therapy (PT) to maximize the remaining function of the extensor mechanism. The initial phase involves protecting the surgically repaired soft tissues while gradually regaining a safe range of motion. Early focus is placed on non-weight-bearing exercises to prevent scar tissue formation and maintain flexibility.
The long-term prognosis depends heavily on the patient’s dedication to a vigorous rehabilitation program, which can last for a year or more. Although full pre-injury strength is rarely achieved, patients can typically return to most activities of daily living with satisfactory results. High-impact sports are usually permanently limited, but strengthening the quadriceps and surrounding muscles allows the knee to adapt to the new biomechanical reality, enabling a functional and relatively pain-free life.