Chinese patients' knees smaller, different from those of Western patients

One Hong Kong surgeon reports that these physiological differences could impact how orthopedists perform TKA on Asian patients.

SEOUL — Researchers recently reported that Asian patients undergoing total knee arthroplasty require smaller components than their Western counterparts, but a renowned Hong Kong surgeon said there are also morphological differences between the two patient populations.

Peter K.Y. Chiu, MD, of the University of Hong Kong, and colleagues conducted several investigations to identify physiological differences between Chinese and Western knees. He reported on some of their findings at the 15th Triennial Congress of the Asia Pacific Orthopaedic Association, here.

The investigators studied the axial alignment during weight-bearing on radiographs of the entire lower limb for 50 young, healthy Chinese subjects. They reported an average 2.2° of varus alignment, which was greater than what has been reported for Caucasians.

They also found that Chinese patients had a more oblique joint line, which averaged 5°. This finding suggests that the femoral component needs to be externally rotated by 5° in Chinese patients, rather than by the 3° in Caucasians if the tibial cut was made perpendicular to the long axis, Chiu said.

They also studied the rotational alignment using 25 pairs of Chinese cadaveric femurs. "We saw that the posterior condylar line formed an angle of more than 5°, rather than the reported 3° with the transepicondylar axis," he said.

In a third study, the investigators evaluated the posterior slope in 25 pairs of Chinese cadaveric tibiae. Using the intramedullary axis as the reference point, the posterior slope ranged from 11° to 15°. Western subjects reportedly have a 5° to 10° slope, according to medical literature, Chiu said.

In a fourth investigation, Chiu and colleagues measured sagittal bowing of the distal femur in 85 Chinese patients admitted for total knee arthroplasty. They found that the distal one-third of the femur was significantly more bowed that the other femoral areas. Also, the distal bow in the Chinese patients, which averaged 715 mm, "is more than what we have seen in Caucasian patients in the literature," he said.

This exaggerated sagittal bowing in the Chinese femur can affect the femoral component's final sagittal position, Chiu said. "This can ultimately have implications for the choice of implant design we should use with [Chinese] patients."

For more information:
Chiu PKY. Asian knees — Not just smaller but different. ICL001-3. Presented at the 15th Triennial Congress of the Asia Pacific Orthopaedic Association. Sept. 9-13, 2007. Seoul.