Total Knee Arthroplasty (TKA), commonly known as total knee replacement, is a frequent orthopedic procedure performed to alleviate pain and restore mobility. While the surgery is highly successful, it is an invasive process that involves expected blood loss. A hematoma is a complication where bleeding exceeds the body’s ability to stop it, resulting in a localized collection of clotted blood outside a blood vessel in the soft tissues surrounding the joint. A large or expanding collection of blood can cause severe pain, nerve compression, and may increase the risk of infection.
Immediate Bleeding from Surgical Trauma
The fundamental cause of bleeding after a knee replacement is the mechanical trauma inherent to the surgical procedure itself. Total knee arthroplasty requires extensive bone cuts, soft tissue releases, and violation of the intramedullary canal of the femur and tibia to fit the prosthetic components. This process severs numerous small blood vessels, which continue to ooze blood into the surgical site even after the procedure is complete.
The use of a tourniquet during the operation also contributes to post-operative bleeding. While the tourniquet creates a bloodless field for the surgeon to work, its subsequent release causes a phenomenon known as reactive hyperemia. This is a surge of blood flow and pressure into the limb following a period of ischemia, causing sustained local bleeding from vessels that were previously constricted.
This residual bleeding accumulates in the space created by the implantation of the metal and plastic components. The total amount of blood loss, often termed “hidden blood loss,” can range from 300 to over 1000 milliliters in the immediate post-operative period. When this blood extravasates into the surrounding muscle and subcutaneous tissues, it forms a hematoma, which often appears hours or days after the wound has been closed.
Pre-Existing Patient Risk Factors
Pre-operative conditions significantly influence the propensity for hematoma formation, especially those that impair the body’s natural clotting mechanisms. A patient with a pre-existing bleeding disorder, such as hemophilia or von Willebrand disease, has an increased risk of developing a post-operative hematoma.
Chronic diseases can also compromise the body’s ability to clot blood effectively. Chronic liver disease, for instance, impairs the production of clotting factors. Likewise, severe chronic kidney disease is associated with general bleeding issues because uremia, a build-up of waste products, can interfere with normal platelet function.
Pre-operative use of certain over-the-counter medications and supplements is a significant risk factor. Patients are routinely advised to discontinue non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen, naproxen, and high-dose aspirin before surgery. These medications interfere with platelet function, hindering the initial stages of blood clot formation. Similarly, supplements such as fish oil and high-dose Vitamin E have anti-platelet properties and must be stopped at least a week before the procedure to allow normal clotting function to resume.
The Necessary Role of Post-Operative Blood Thinners
The necessary use of post-operative blood thinners is a primary cause of hematoma. Total knee arthroplasty patients face a high risk of developing dangerous blood clots due to surgical trauma, immobilization, and underlying patient risk factors. To prevent these potentially fatal complications, anticoagulant medication is prescribed immediately following surgery.
The medication needed to prevent a blood clot directly increases the risk of local bleeding and hematoma formation. Common anticoagulants used include low-molecular-weight heparin, warfarin, and newer direct oral anticoagulants. Each drug inhibits the clotting cascade, making it harder for the body to seal off the small, damaged vessels in the knee joint.
The dosage and timing of the anticoagulant are highly sensitive. If the dose is too low, the patient remains at risk for developing a blood clot; if the dose is too high, the patient is at risk for an excessive bleed and a significant hematoma. For patients on warfarin, monitoring is required, and levels above the target range indicate an increased risk of bleeding.
The timing of the initial dose can be a direct factor in hematoma size and persistence. For patients with high bleeding risk, a strategy of delayed anticoagulation may be employed. By delaying the start of the blood thinner by one or two days, surgeons allow initial hemostasis to occur, reducing post-operative bleeding without significantly increasing the risk of early blood clot formation.