Why do knees loosen after artificial joint replacement?

Knee replacement is a common orthopedic surgery, especially for patients with end-stage knee osteoarthritis. MSc.BSc.CKI Le Nhat Thanh, Department of Orthopedics, Tam Anh General Clinic District 7, said one of the most serious and challenging complications is loosening of the artificial knee joint, accounting for about 20-30% of cases requiring re-operation after knee replacement. This is the consequence of many complex factors, from surgical techniques, implant material characteristics, to the patient’s health status and lifestyle.

Doctors point out some possible causes of loose knee joints after surgery as follows:

Natural wear and tear. Artificial knee joints usually have a lifespan of about 20-30 years. Patients under 60 years old, with high levels of physical activity (jogging, carrying heavy loads, playing high-intensity sports) will create greater load on the joints, faster wear rate and increased risk of early joint loosening.

Obesity is also an independent factor that increases the impact force on the knee joint by 3-5 times the body weight during exercise. This is the most common form of joint loosening, and is not related to infection.

Osteoporosis, advanced age, and long-term history of corticosteroid use increases the risk of periarticular fractures after knee replacement, most commonly in the femoral condyle area, which can directly cause loosening or displacement of artificial joint components. Therefore, older people must be screened and treated for osteoporosis (if any) after joint replacement.

The surgical technique is not good greatly affects the durability of artificial joints. Improper placement of the limb axis, improper ligament balance, or improper joint size selection can all cause uneven force distribution across the joint surface, promoting premature wear and loosening of the joint.

Artificial joint infection is the cause of joint loosening with the most serious consequences. According to Dr. Thanh, this rate fluctuates around 1-2%, bacteria stick to the implant surface and form biofilm, causing chronic inflammation, bone loss and leading to joint loosening. This process can happen early in the first 3 months or late (from 3 months to 2 years) or very late due to bacteria from a distant infection (teeth, urinary tract…) following the bloodstream to the joint.

Risk factors include poorly controlled diabetes, obesity, immunodeficiency, rheumatoid arthritis being treated with biological drugs, or a history of multiple surgical interventions in the knee area.

Dr. Thanh recommends that patients after knee replacement have regular check-ups as scheduled, follow rehabilitation instructions, and control their weight and underlying diseases well. Recognize early and immediately report to the doctor when unusual symptoms appear such as recurring knee pain, feeling of unstable knee, prolonged swelling or limb axis deformity for timely intervention.