A Total Knee Replacement (TKR) alleviates chronic joint pain and restores mobility by replacing damaged bone and cartilage with prosthetic components. Swelling is an expected consequence of this major surgery, representing the body’s natural inflammatory response to tissue trauma. While immediate postoperative swelling is normal, its persistence six months after the operation is less common. Persistent swelling suggests the underlying cause of inflammation has not fully resolved and requires investigation to distinguish between lingering recovery factors and more serious medical issues.
The Normal Healing Timeline After Total Knee Replacement
Recovery following TKR is a gradual process, with swelling resolving in a predictable pattern. The acute phase spans the first few weeks, where the knee is maximally swollen and warm due to surgical trauma and internal bleeding. This is when the body’s inflammatory response peaks.
By the subacute phase, spanning one to three months post-surgery, most significant swelling should have subsided substantially. A notable reduction in puffiness and warmth indicates successful initial wound healing. Although tissues are still remodeling, the intense inflammatory reaction has largely passed.
At the six-month mark, recovery is well into the resolution phase, and most patients experience only minimal, intermittent swelling. This residual puffiness is typically mild and occurs only after heavy activity, prolonged standing, or strenuous physical therapy. Persistent, noticeable swelling that occurs daily or is accompanied by other symptoms at six months deviates from the expected timeline and requires clinical attention.
Common Non-Infectious Contributors to Persistent Swelling
Chronic swelling at six months is often related to manageable factors rather than severe complications. A frequent cause is chronic overexertion, where an enthusiastic return to activity or pushing too hard in physical therapy re-irritates the joint. Excessive microtrauma can restart the inflammatory cycle, leading to persistent fluid accumulation.
Another significant factor is the disruption of the body’s natural fluid drainage pathways during surgery. Lymphatic and venous drainage issues can cause chronic fluid retention (edema) in the lower leg. Because muscle pump action is reduced post-surgery, fluid often collects in the lower extremities due to gravity. Swelling is frequently noticed more in the ankle and foot than the knee itself, especially by the end of the day.
The internal formation of scar tissue, known as arthrofibrosis, also contributes to chronic localized inflammation. This excessive scarring stiffens the joint and irritates surrounding soft tissues, causing persistent swelling that is distinctly different from simple fluid buildup. This soft tissue swelling is often accompanied by a noticeable restriction in the knee’s range of motion. Systemic factors, such as high sodium intake or being overweight, can predispose the body to generalized fluid retention and make localized knee swelling difficult to resolve.
Identifying Serious Medical Causes
While many cases of persistent swelling relate to activity levels or fluid dynamics, serious medical conditions must be ruled out. The most concerning is a Periprosthetic Joint Infection (PJI), which can manifest as a delayed or low-grade infection months after surgery. A low-grade PJI may present with chronic pain, warmth, and persistent swelling that fails to improve with conservative measures, rather than obvious fever or pus.
Late-onset PJI is suggested by increasing pain or a return of warmth to the joint, requiring immediate diagnostic testing. Mechanical issues with the prosthetic components also cause chronic irritation and inflammation. Problems like implant loosening or malalignment can cause friction and wear debris that perpetually inflames the joint lining.
A Deep Vein Thrombosis (DVT), a blood clot in the deep veins of the leg, is a risk following surgery and can cause persistent lower leg edema at six months. DVT typically presents with swelling in the calf or ankle, accompanied by pain or tenderness, and requires immediate medical attention due to the risk of the clot traveling to the lungs. Complex Regional Pain Syndrome (CRPS) is a rare nerve-related condition characterized by disproportionate, burning pain, extreme sensitivity to touch, and severe, persistent edema that may involve the foot and ankle.
Steps for Diagnosis and Treatment
Diagnosis begins with a physical examination and a review of symptoms to identify red flags like increasing pain or warmth. The initial workup includes standard X-rays to check for signs of implant loosening or malalignment, such as radiolucent lines around the components. If infection is suspected, blood tests measure inflammatory markers, specifically C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR).
Persistent elevation of CRP and ESR signals an ongoing inflammatory process. The standard for diagnosing a low-grade PJI is joint aspiration (arthrocentesis), where fluid is withdrawn from the knee for cell count and culture analysis. This analysis identifies bacteria or high levels of inflammatory cells, providing a definitive diagnosis.
Treatment is determined by the underlying cause, starting with conservative management for non-infectious issues. This includes consistent application of the R.I.C.E. principles to manage residual inflammation and fluid retention:
- Rest.
- Ice.
- Compression.
- Elevation.
Targeted physical therapy may be adjusted to avoid overexertion while improving muscle strength. If the diagnosis points toward mechanical failure or confirmed PJI, surgical intervention is necessary. This may involve an arthroscopic procedure to remove irritating scar tissue, or a revision surgery to replace implant components in cases of confirmed infection or catastrophic loosening.