Can the patellar tendon moment arm be predicted from anthropometric measurements?

The purpose of this study was to examine the relations between patellar tendon moment arm length and several relevant anthropometric characteristics of 22 healthy men. The patellar tendon moment arm length was measured using magnetic resonance imaging with two different methods: (1) measurement of patellar tendon moment arm length (d(PT)) with respect to the tibiofemoral contact point (d(PTCP)) and (2) measurement of d(PT) with respect to the intersection point of the anterior and posterior cruciate ligament (d(PTIP)). Pearson correlation coefficients and a stepwise linear regression analysis were used to examine the relationships between the d(PT) and anthropometric measurements taken. Furthermore, a Student's t-test was used to determine differences between the d(PTCP) and d(PTIP) values. Only knee circumference was a significant d(PTCP) predictor (P < 0.05) but with a very low R2 (0.139). None of the anthropometric parameters examined was found to be a significant d(PTIP) predictor. The correlation coefficients ranged from -0.04 to 0.42. The d(PTIP) values were significantly higher (by 0.84-1.89 cm) than the d(PTCP) values (P < 0.05). These results are in disagreement with previous in vitro findings that d(PT) variance may be explained by knee joint size differences. Hence, existing imaging-based methodologies remain necessary for accurate quantification of the patellar tendon moment arm.