Advanced untreated tuberculosis of the knee may progress to a classical 'triple deformity'. This consists of:

• A Extension deformity, anterior subluxation, and varus angulation
• B Flexion deformity, posterior subluxation, and external rotation ✓
• C Flexion deformity, valgus angulation, and internal rotation
• D Recurvatum deformity, posterior subluxation, and adduction

Explanation

In advanced knee tuberculosis, unopposed hamstring action and patient positioning produce a fixed flexion deformity; relaxation and stretching of the cruciate ligaments allow posterior subluxation of the tibia; and the limb assumes external rotation. This triple deformity signals gross joint destruction and corresponds to the late stages requiring arthrodesis after control of disease. Valgus and recurvatum deformities are not features of tuberculous knee involvement.

Reference: Maheshwari's Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.