Lower-Limb Axes, Gap Balancing and Component Alignment in Total Knee Arthroplasty
DNB Orthopaedics • October 2023 • Paper I • Question 7 • 10 Marks [3+3+4]
Introduction
Restoration of lower-limb alignment is a fundamental objective of Total Knee Arthroplasty (TKA). Successful knee replacement requires understanding of the mechanical and anatomical axes of the femur and tibia, restoration of appropriate coronal and sagittal alignment, and creation of stable, balanced flexion and extension gaps.
Historically, mechanical alignment has been the conventional reference in TKA, although contemporary concepts such as anatomical, kinematic and functional alignment modify component positioning in selected patients.
Exam framework: Axes → Bone cuts → Balanced gaps → Correct component rotation → Stable knee through full ROM.
A. Various Axes of the Lower Limb [3 Marks]
1. Mechanical Axis of the Lower Limb
The overall mechanical axis of the lower limb is the line joining:
CENTER OF FEMORAL HEAD
↓
CENTER OF KNEE
↓
CENTER OF ANKLE
In a neutrally aligned limb this line passes approximately through the center of the knee.
2. Femoral Axes
Mechanical Axis of Femur
A line joining the center of the femoral head to the center of the knee.