Alignment evaluation using different distal reference points after total knee arthroplasty.

Area of Science:

• Orthopedic Surgery
• Biomechanics
• Medical Imaging

Background:

• Traditional total knee arthroplasty (TKA) alignment assessment uses the ankle's center as the distal tibial reference.
• The true load-bearing mechanical axis for TKA should extend from the femoral head center to the calcaneus's lowest point.
• Discrepancies exist between ankle-based and calcaneal-based alignment measurements in TKA.

Purpose of the Study:

• To compare alignment differences in total knee arthroplasty (TKA) using ankle center versus calcaneal contact reference points.
• To evaluate the impact of different reference points on load-bearing axis displacement and angular measurements at the knee.

Main Methods:

• Recruited patients with medial osteoarthritis undergoing primary total knee arthroplasty.
• Assessed alignment using two reference points: center of the ankle (Group A) and calcaneal contact point (Group C).
• Compared the incidence of calcaneal contact point lateralization, load-bearing axis displacement, anatomical axis angle, mechanical axis angle, and tibial component angle.

Main Results:

• In 88.3% of cases, the calcaneal contact reference point was lateral to the ankle's center.
• Calcaneal reference points showed significantly greater load-bearing axis displacement at the knee (38.7% vs. 34.0%, p < 0.0001).
• Calcaneal references indicated significantly more valgus alignment compared to ankle references (e.g., anatomical axis: 5.6° vs. 4.8°, p < 0.0001).

Conclusions:

• Ankle reference methods may underestimate valgus alignment, potentially leading to varus measurements that differ from neutral alignment.
• The calcaneal reference method reveals significant valgus alignment not captured by traditional ankle references.
• Accurate preoperative planning, intraoperative execution, and postoperative evaluation in TKA require consideration of calcaneal-based alignment.