Femoral Tunnel Length in Anterior Cruciate Ligament Reconstruction Using an Accessory Medial Portal (SS-66)

Abstract

Independent femoral tunnel drilling has been described in anterior cruciate ligament (ACL) reconstruction, however there is concern that tunnels will be too short. To counterbalance that and also provide better exposure to the notch, hyperflexion of the knee and the use of an accessory medial portal have been described. (Figure 1) The purpose of this study was to evaluate tunnel length during independent femoral tunnel drilling using an accessory medial portal with the knee in maximal hyperflexion, and then correlate the tunnel length and flexion angle with anthropometric data. During a 9 month period, 83 consecutive patients undergoing primary ACL reconstruction by the three senior authors were included in the study. All patients underwent independent femoral tunnel drilling using an accessory medial portal with maximal knee hyperflexion. Tunnel length and maximal intra-operative knee flexion angles were measured. In addition, height, weight, and body mass index (BMI) were recorded in order to correlate with tunnel length and knee flexion angles. The size of the lateral femoral condyle (LFC), as measured on magnetic resonance imaging (MRI) or plain radiograph, was also correlated with tunnel length and knee flexion angles (available in 67 patients). The average tunnel length was 36.8 +/− 3.3 mm (range 26-45) with all but one tunnel greater than 30 mm. The average knee flexion angle was 134.3 +/− 5.0 degrees (range 122-147). The average BMI was 27.7 +/− 7.9 kg/m2 (range 17.7-63.3), calculated from average height 173.3 +/− 9.1 cm (range 150-195.6) and weight 83.3 +/− 24.8 kg (range 49.7-172.2). Average LFC width was 32.6 +/− 4.8 cm (range 26.1-60.3), and depth was 60.6 +/− 5.0 cm (range 48.1-73.3). Height (r=0.52, P<0.001) and weight (r=0.34, P=0.002), but not BMI, correlated positively with tunnel length. Width (r=0.33, P=0.006) and depth (r=0.34, P=0.005) of the LFC also correlated positively with tunnel length. Knee flexion angle was not correlated with tunnel length (r=-0.08, P=0.45), or width (r=−0.06, P=0.62) and depth (r=−0.14, P=0.28) of the LFC. Knee flexion angle was negatively correlated with weight (r=−0.55, P<0.001) and BMI (r=−0.55, P<0.001). Using an accessory medial portal for independent femoral tunnel drilling with maximal knee hyperflexion in ACL reconstruction produced only one tunnel less than 30mm. This technique, therefore, consistently produces tunnels of adequate length. Tunnel lengths tend to be longer with increasing patient height, mass, and larger LFC dimensions. Maximum knee flexion angle achieved intraoperatively tends to be less for patients with increasing weight and BMI.