Using anatomical landmarks to calculate the normal joint line position in Chinese people: an observational study.

BACKGROUND: Restoring the normal joint line (JL) is an important goal to achieve in total knee arthroplasty (TKA). We intended to study the veracity of several landmarks used to level the normal JL in Chinese people.

METHODS: Two hundred fifteen standard CT scans of knee joint were included to measure the distances from landmarks to distal JL (DJL) and posterior JL (PJL), along with femoral width (FW) in order to calculate the ratios. Landmarks included adductor tubercle (AT), medial epicondyle (ME), lateral epicondyle (LE), tibial tubercle (TT), fibular head (FH) and the inferior pole of the patella (IPP). Ratios were calculated between distances and FW (e.g. FHDJL/FW). Linear regression analysis and t test were used to determine the accuracy and the differences amongst sides of the leg, genders and races.

RESULTS: The average of IPPDJL/FW, TTDJL/FW, FHDJL/FW, LEDJL/FW, LEPJL/FW, MEDJL/FW, MEPJL/FW, ATDJL/FW and ATPJL/FW were 0.165, 0.295, 0.232, 0.297, 0.281, 0.327, 0.3PJL, 0.558 and 0.313, respectively. No significant difference had been found between the left and right leg. A gender difference was only found statistically on the ratio of IPP, and also, no linear correlation was observed only between IPP and FW. Most of the difference values lain in a 4-mm threshold for MEDJL (95.81%), LEDJL (94.88%), MEPJL (97.21%), LEPJL (94.88%), ATPJL (93.49%) and ATDJL (100%). Significant differences were observed amongst different races.

CONCLUSIONS: AT, ME and LE can be used as reliable landmarks to locate the normal JL in Chinese population intraoperatively. It is meaningful to come up with a set of ratios to different races.