A 55-year-old woman with advanced knee osteoarthritis, BMI 31, and well-controlled type 2 diabetes is listed for total knee replacement (TKR). During templating, her hip-knee-ankle axis shows 10° varus malalignment. Which neutral mechanical axis correction is the TARGET of TKR alignment?
- A 3° of anatomical valgus of the tibial cut to match the natural femoral-tibial angle
- B 5° of mechanical valgus to offload the medial compartment
- C 0° of the mechanical axis (anatomical neutral), placing the load through the centre of the knee joint ✓
- D The native limb alignment is preserved; no correction of varus is performed
Explanation
The principal goal of total knee replacement is to restore the neutral mechanical axis — a straight line from the centre of the femoral head through the centre of the knee to the centre of the ankle, i.e., 0° of mechanical alignment. This evenly distributes load across both compartments and reduces implant wear and loosening. The anatomical axis of the femur is in ~6° valgus relative to the mechanical axis, which is why the distal femoral cut is made at 5–7° valgus to the femoral shaft to achieve 0° mechanical alignment. The tibial cut is made at 90° to the tibial mechanical axis (0° or slight posterior slope only).
Reference: Maheshwari Essential Orthopaedics, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.