Total knee arthroplasty (TKA) is a highly successful procedure that replaces the damaged surfaces of the knee joint with artificial components, restoring mobility and alleviating chronic pain. The implant, made of metal and specialized medical-grade plastic, is engineered for durability, often functioning well for 15 to 20 years. While robust, knee replacements are susceptible to compromise from external forces, excessive mechanical stress, or biological failure. Understanding how these components can be injured is paramount for preserving the device’s longevity.
Direct Traumatic Events
Acute, sudden forces can cause immediate structural damage to the knee replacement and surrounding bone tissue. The most common cause of acute failure is a forceful fall or a direct blunt impact, such as a motor vehicle accident, which overwhelms the joint’s integrity. These events result in a periprosthetic fracture, meaning the bone around the implanted components breaks. Fractures may occur in the femur, tibia, or patella, often requiring complex revision surgery to repair the bone and stabilize the implant.
A severe traumatic impact can also lead to acute instability or dislocation of the prosthetic components, causing the metal and plastic pieces to move out of alignment. Patients with underlying conditions like osteoporosis are at a higher risk of sustaining a periprosthetic fracture from a less severe fall. Implementing fall prevention strategies, such as using assistive devices and eliminating tripping hazards, is a necessary long-term precaution for protecting the joint.
High-Risk Activities and Movements
Mechanical injury can occur gradually through repetitive high-stress activities, not just sudden events. These activities accelerate wear, leading to aseptic loosening, where the implant detaches from the bone without infection. The polyethylene liner, the plastic spacer between the metal components, is vulnerable to wear from repeated high-impact loading. When this liner wears excessively, microscopic debris is generated, which triggers a biological response that causes the bone around the implant to slowly erode.
Activities involving jumping, running, or high-impact sports like basketball and football are discouraged because they subject the joint to forces many times a person’s body weight. This intense, repetitive impact shortens the lifespan of the liner, risking premature implant failure. Movements requiring deep knee flexion, such as deep squatting or excessive kneeling, also strain the joint, potentially stressing the fixation of the components to the bone. Patients should favor low-impact alternatives like walking, stationary cycling, or swimming, which allow for mobility and strength building without compromising mechanical integrity. Avoiding activities that involve twisting, pivoting, or heavy weightlifting helps ensure the replacement lasts for its intended duration.
The Danger of Post-Surgical Infection
Periprosthetic joint infection (PJI) is a biological complication distinct from mechanical injury, where bacteria colonize the implant. Infection compromises the bond between the artificial joint and the bone, often requiring prolonged antibiotic treatment and complex surgical intervention. Bacteria, such as Staphylococcus aureus, can be introduced during the initial surgery or spread years later through the bloodstream from an infection elsewhere in the body. This delayed infection, known as hematogenous spread, can originate from minor issues like skin infections, urinary tract infections, or dental abscesses.
Once bacteria adhere to the implant’s surface, they form a protective layer called a biofilm, making them highly resistant to the immune system and standard antibiotics. To prevent this complication, patients are advised to practice meticulous wound care after surgery and maintain excellent oral hygiene. Precautionary antibiotics, or prophylactic treatment, are frequently recommended before any invasive procedure, especially dental work, to minimize the risk of bacteria traveling to the implant site. This proactive medical management defends against a failure mode that is often more challenging to treat than a mechanical injury.
Warning Signs of Complication
Recognizing the early indicators of a problem, whether mechanical or infectious, is crucial for a successful outcome. A sudden onset of severe pain, especially pain that occurs while resting or is significantly worse than post-surgical discomfort, can signal a complication like loosening or an acute fracture. Patients may also experience the knee “giving way” or instability while bearing weight, suggesting component misalignment or failure of the surrounding soft tissues.
Signs pointing toward a possible infection include systemic symptoms like fever and chills, indicating the body is fighting a spreading pathogen. Locally, persistent swelling, increasing redness, or warmth around the knee joint are localized signs of inflammation. Any new drainage from the surgical incision, particularly if it is thick, foul-smelling, or lasts longer than a few days post-surgery, warrants immediate medical attention. If any of these warning signs appear, contact the orthopedic surgeon without delay to ensure prompt diagnosis and treatment.