Total knee arthroplasty using anatomic alignment can produce mid-flexion laxity.

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Knee Kinematics

Background:

• Total knee arthroplasty (TKA) utilizes either anatomic or mechanical alignment techniques.
• Alignment is determined by bone axes crucial for prosthetic component implantation.
• Understanding axis relationships and soft tissue balance is key in TKA.

Purpose of the Study:

• To examine tibial and femoral axes during simulated knee motion.
• To determine the relationship between these axes and medial-lateral soft tissue balance.
• To evaluate the clinical implications for total knee arthroplasty.

Main Methods:

• Utilized seven fresh-frozen lower limb specimens.
• Intact joint capsule, muscles, tendons, and ligaments were preserved.
• Kneeling simulator jig produced physiologic knee motion to track joint spacing and laxity.

Main Results:

• Statistically significant differences in medial and lateral joint spacing were observed between alignment axes at all flexion angles.
• Anatomic alignment showed mid-flexion lateral opening and late-flexion medial opening.
• Mechanical alignment consistently demonstrated a 2-3 mm larger lateral than medial joint space.

Conclusions:

• Mid-flexion laxity is a significant clinical concern for natural knee replacement feel.
• Mechanical alignment is currently preferable to anatomic alignment due to consistent joint spacing.
• Ligament lengthening or femoral component adjustments can address spacing issues in TKA.