Total Knee Arthroplasty (TKA), or knee replacement surgery, is highly successful in alleviating chronic pain from severe arthritis. While most patients experience significant relief and improved function, a small percentage may report persistent or new pain after recovery. This discomfort often relates to the soft tissues surrounding the new implant rather than the prosthesis itself. This raises the question of whether injections, a common treatment for non-surgical knee pain, can be safely used after the joint has been replaced.
Sources of Pain After Knee Replacement
The pain considered for injection typically does not originate from the implant components, which would suggest failure or loosening. Instead, discomfort frequently stems from irritation or inflammation in the peri-articular structures, meaning the tissues surrounding the joint. This soft tissue involvement includes conditions like bursitis, which is the inflammation of the fluid-filled sacs that cushion the knee.
A common site is the pes anserinus bursa, located on the inner side of the knee below the joint line. Tendonitis, or inflammation of tendons like the quadriceps or patellar tendon, can also cause discomfort. Pain may also be referred from other areas, such as the hip or lower spine, or result from irritation of small nerves around the surgical site. A thorough physical examination and diagnostic imaging are necessary to pinpoint the exact, non-implant related origin of the lingering pain.
Injectable Treatments Used for Post-Surgical Pain
When the pain source is confined to the soft tissues outside the joint, certain injections can provide targeted relief. Corticosteroid injections, often called steroid shots, are a frequent choice for localized inflammation, such as bursitis or tendonitis. These injections deliver a potent anti-inflammatory medication directly to the site of irritation, significantly reducing swelling and pain. They are most effective when applied to structures like the pes anserinus bursa or an inflamed tendon sheath.
Another category is nerve blocks, which target specific nerves transmitting pain signals from the knee area. A genicular nerve block, for instance, involves injecting a local anesthetic, sometimes with a corticosteroid, near the nerves supplying sensation to the knee capsule. These injections are performed outside the joint space and can help manage chronic pain patterns. Injections of hyaluronic acid, used to lubricate arthritic joints, are generally avoided after TKA because the diseased joint surfaces have been removed.
The Danger of Infection
The primary concern with any needle penetration near a prosthetic joint is the risk of introducing bacteria, leading to a Periprosthetic Joint Infection (PJI). PJI is a serious complication that is difficult to treat because bacteria adhere to the implant surfaces, forming a protective biofilm. This biofilm shields the bacteria from the body’s immune system and standard antibiotics.
Injections administered directly into the joint space after TKA carry a significantly increased risk of PJI compared to patients who do not receive an injection. If an infection develops, it almost always requires complex revision surgery to remove the infected implant, clean the joint space, and often replace the components.
To minimize this risk, healthcare providers employ stringent protocols. These include using ultrasound or X-ray guidance to ensure the needle remains outside the joint capsule and is accurately placed in the soft tissue structure. Absolute adherence to sterile technique is practiced, and sometimes prophylactic antibiotics may be administered.
When Injections Are Not Appropriate and Alternatives
Injections are ruled out if the diagnostic workup suggests mechanical issues with the implant, such as aseptic loosening or component malalignment. Similarly, if blood tests show elevated inflammatory markers indicating an active infection, an injection is contraindicated until the infection is investigated and treated. In these scenarios, a comprehensive evaluation, including X-rays, blood work, or specialized metal artifact reduction magnetic resonance imaging (MARS-MRI), must precede any therapeutic decision.
For patients whose pain is not addressable by a localized injection, or who wish to avoid infection risk, several non-invasive alternatives exist. Targeted physical therapy remains a cornerstone of post-operative management, focusing on strengthening muscles and improving range of motion. Activity modification, avoiding high-impact activities that aggravate soft tissues, is also recommended. Simple measures like applying heat or ice and using over-the-counter medications, such as NSAIDs or acetaminophen, can provide sufficient pain relief. The decision to proceed with any injection requires a careful assessment of potential benefits against the risk of infection, made collaboratively with an orthopedic specialist.