TB Knee: Triple Deformity, Stages of Destruction & Rehab MCQs

Tuberculosis of the Knee

The knee is the third most common site for skeletal tuberculosis (after spine and hip). It is usually a Synovial disease primarily, eroding the bone secondarily (unlike the hip/spine where bone involvement is early).

1. Stages of Disease

• Stage I (Synovitis): Synovial hypertrophy and effusion. Joint space is normal or widened. Deformity: Flexion (to accommodate fluid).
• Stage II (Early Arthritis): Marginal erosions and destruction of articular cartilage. Deformity: Flexion + Posterior Subluxation.
• Stage III (Advanced Arthritis): Severe destruction ("Triple Deformity") and fibrous ankylosis.
• Stage IV (Sequelae): Bony ankylosis (fusion) in deformity.

2. The "Triple Deformity"

Classic Sign of Advanced TB Knee:
Due to hamstring spasm and cruciate ligament destruction, the tibia assumes three positions relative to the femur:
1. Flexion
2. Posterior Subluxation (Tibia sags backwards)
3. External Rotation

3. Diagnosis & Treatment

• Biopsy: Synovial biopsy is the gold standard (Granulomas seen).
• X-ray: Phemister's Triad (Osteoporosis, Marginal erosions, Joint space reduction).
• Management:
  • Chemotherapy (ATT): Mainstay for 12-18 months.
  • Surgery: Synovectomy (Stage I/II) or Arthrodesis (Fusion) for painful destroyed joints. Total Knee Replacement (TKR) is controversial and risky.

25 Practice MCQs

Q1. Triple Deformity of the knee consists of:

Answer: A). Caused by the pull of the Biceps Femoris (External rotator) and Hamstrings (Flexors).

Q2. TB Knee primarily affects the:

Answer: A). Unlike the spine (bone first), the knee is a large synovial joint, so synovitis is the primary pathology.

Q3. "Phemister's Triad" on X-ray includes:

Answer: A). Distinct from Pyogenic arthritis (where joint space loss is rapid).

Q4. Which muscle is primarily responsible for the external rotation deformity?

Answer: A). It inserts on the fibula head and pulls the tibia into ER.

Q5. Synovectomy is most effective in:

Answer: A). Removes the diseased load and saves the cartilage.

Q6. Posterior subluxation of the tibia occurs because of:

Answer: A). The tibia slides backward on the femur.

Q7. A "Cold Abscess" in the knee may track to the:

Answer: A). Following tissue planes.

Q8. Arthrodesis (Fusion) is indicated for:

Answer: A). Provides a stable, painless, albeit stiff knee. Ideally 10-15 degrees flexion.

Q9. Total Knee Replacement (TKR) in quiescent TB:

Answer: A). Infection can flare up even years later.

Q10. The diagnosis is confirmed by:

Answer: A). Look for caseating granulomas.

Q11. "Melon seed bodies" (Rice bodies) found in the joint are:

Answer: A). Characteristic finding.

Q12. Initial treatment for active TB knee is:

Answer: A). Rest relieves spasm; drugs kill the bacteria.

Q13. Fibrous ankylosis is characteristic of TB because:

Answer: A). Unlike pyogenic infection (Bony ankylosis), TB often leaves a stiff, painful fibrous joint.

Q14. Muscle wasting in TB knee involves:

Answer: A). Rapid wasting is a consistent sign.

Q15. A "Kissing Sequestrum" involves:

Answer: A). Symmetrical contact lesions.

Q16. Night cries are due to:

Answer: A). Common in children.

Q17. During the active phase, weight bearing is:

Answer: A). Prevents collapse and deformity.

Q18. The "White Swelling" of the knee refers to:

Answer: A). Pale, boggy swelling typical of TB synovitis.

Q19. Differential diagnosis includes:

Answer: A). Can mimic chronic inflammatory conditions.

Q20. What is "Bony Ankylosis"?

Answer: A). Rare in TB unless superadded infection occurs.

Q21. Flexion deformity is corrected by:

Answer: A). Gradual correction.

Q22. Duration of ATT for skeletal TB is:

Answer: B). Bone penetration requires longer duration.

Q23. Inguinal Lymphadenopathy is:

Answer: A). Lymph nodes drain the knee.

Q24. The term "Caries Sicca" refers to:

Answer: B). Granulomatous form without much exudate.

Q25. Rehabilitation focuses on:

Answer: A). Mobilize once pain subsides.