Tuberculosis of the Knee Joint

Tuberculosis (TB) of the knee joint is a form of skeletal tuberculosis, which occurs when the bacteria Mycobacterium tuberculosis spreads from a primary siteusually the lungsto the knee joint. While TB is primarily associated with pulmonary infection, skeletal involvement accounts for approximately 1-3% of all TB cases, with the knee joint being one of the most commonly affected areas in the lower extremities.

Pathophysiology

The infection typically spreads to the knee joint through the bloodstream (hematogenous spread). Once the bacteria reach the synovial membranethe lining of the jointthey trigger an inflammatory response. If left untreated, the infection leads to the formation of granulomas, cartilage destruction, and eventually the involvement of the bone itself. This progressive damage can result in significant deformity and loss of joint function.

Clinical Presentation

Symptoms of knee TB are often insidious, meaning they develop slowly over several months. Key signs include:

• Pain: Chronic, dull aching pain that worsens with activity or weight-bearing.
• Swelling: Persistent swelling of the knee joint due to synovial thickening or fluid accumulation.
• Stiffness: Restricted range of motion, particularly in the morning.
• Limping: Changes in gait as the patient attempts to alleviate pain.
• Systemic symptoms: Low-grade fever, night sweats, fatigue, and unexplained weight loss.

Diagnosis

Early diagnosis is critical to preventing permanent joint destruction. Clinicians utilize a combination of methods:

• Imaging: X-rays may show joint space narrowing or bone erosions. MRI is the gold standard for early detection, as it effectively visualizes soft tissue inflammation and synovial thickening.
• Laboratory Tests: Blood tests such as Erythrocyte Sedimentation Rate (ESR) and C-reactive protein (CRP) are typically elevated.
• Biopsy: The definitive diagnosis is often made through a needle or open biopsy of the synovial tissue, followed by culture or PCR testing to identify the presence of the bacteria.

Treatment Approaches

The management of TB of the knee is primarily medical, supported by surgical intervention when necessary.

Medical Management: The cornerstone of treatment is a prolonged course of anti-tubercular chemotherapy. This typically involves a multi-drug regimen (such as Isoniazid, Rifampicin, Pyrazinamide, and Ethambutol) for a period of 6 to 12 months, depending on the severity and response to treatment.

Surgical Management: Surgery is reserved for cases where there is severe joint destruction, abscess formation, or a lack of response to medical therapy. Procedures may include synovial debridement (cleaning of the joint lining), drainage of abscesses, or, in advanced stages where the joint is destroyed, arthrodesis (joint fusion) or joint replacement (after the infection is fully eradicated).

Prognosis and Rehabilitation

With early intervention, many patients can retain good knee function. Physical therapy plays a vital role during recovery, helping to restore strength and range of motion. Adherence to the full course of medication is the most important factor in preventing relapse and the development of drug-resistant strains of the bacteria.