Preoperative determination of tibial nail length: An anthropometric study

OBJECTIVE To assess the correlation between five anthropometric parameters and the distance from tibial tuberosity to medial malleolus in 100 volunteers. METHODS Six anthropometric parameters were measured in 50 male and 50 female medical students using a metallic scale: medial knee joint line to ankle joint line (K-A), medial knee joint line to medial malleolus (K-MM), tibial tuberosity to ankle joint (TT-A), tibial tuberosity to medial malleolus (TT- MM), olecranon to 5th metacarpal head (O-MH) and body height (BH). Nail size predicted based upon TT-MM measurement was chosen as ideal nail size. A constant was derived for each of the six anthropometric parameters which was either added or subtracted to each measurement to derive nail size. A regression equation was applied to BH measurements. Nail sizes calculated were compared with that obtained from TT-MM measurement and accuracy was evaluated. Accuracy of O-MH and BH regression equations recommended by other authors were calculated in our data. RESULTS Adding 11 mm to TT-A distance had highest accuracy (81%) and correlation (0.966) in predicting nails correctly. Subtracting 33 mm from K-MM measurement and 25 mm from K-A distance derived accurate sizes in 69% and 76% respectively. Adding 6 mm to O-MH distance had a poor accuracy of 51%. Nail size prediction based upon body height regression equation derived correct nail sizes in only 34% of the cases. Regression equation analysis by other authors based on O-MH and BH distances yielded correct sizes in 11% and 5% of the cases respectively. CONCLUSION TT-A, K-A and K-MM measurements can be used simultaneously to increase accuracy of nail size prediction. This method would be helpful in determining nail size preoperatively especially when one anatomic landmark is difficult to palpate.