Abstract
Objectives:
Lateral Extra-Articular Tenodesis (LET) is a surgical technique to control anterolateral rotatory laxity of the knee. During LET, a strip of iliotibial band tissue is harvested, with its attachment at Gerdy’s tubercle preserved. The tissue is passed deep to the fibular collateral ligament and secured to the distal femur. The tenodesis location is technique dependent. The goal of this study is to analyze the tissue isometry in four LET techniques: Lemaire, Classic MacIntosh, Modified MacIntosh, and Mid-metaphyseal techniques.
Methods:
Three-Dimensional (3D) computerized tomography (CT) knee models were obtained from ten fresh-frozen, unpaired, cadaveric human knees, ranging from 0° to 130° of knee flexion in 10° increments. On each knee, the senior surgeon marked the Gerdy’s tubercle and the tenodesis location of the 4 techniques. The marked locations were projected to the respective knee models at all flexion angles using a 3D-3D registration technique. Graft length between Gerdy’s tubercle and the femur tenodesis location was calculated with a 3D wrap-around algorithm, simulating the graft conforming to the osseous contour. Isometry at a given knee flexion angle was calculated by the percent change in length, with respect to the length at 30° of knee flexion. The graft length differences between each LET techniques at each flexion angle was compared with ANOVA. Tukey’s Honestly Significant Difference test was employed for pairwise comparison between techniques at each angle and between angles within each technique.
Results:
The mean graft strain (i.e. percent change in graft length) at each knee flexion angles is shown in Figure 1. In the Lemaire technique, mean graft strain remained within ± 3.6% and no significant difference in graft strain was found in pairwise comparison (p>0.18). In the Classic MacIntosh technique, mean graft strain decreased as the knee was flexed, reaching a minimum strain of -15.7% at 130°, with graft strain from 110° to 130° of flexion being significantly different compared to a more extended knee (p<0.044). In the Modified MacIntosh technique and Mid-metaphyseal technique, mean graft strain increased as the knee is flexed, reaching a maximum strain of 14.7% at 110° for Modified MacIntosh and 10.7% at 110° for Mid-metaphyseal. For both techniques, mean graft strain values between 0° and 30° of flexion was significantly different from mean graft strain values between 90° and 130° of flexion (p<0.006).
One way ANOVA revealed statistically significant differences in mean graft strain between LET techniques at knee angles 80° to 130° (p<0.027). Pairwise comparison showed no significant difference in graft strain between Modified MacIntosh and Mid-metaphyseal Techniques (p>0.44), and between Lemaire and Classic MacIntosh Techniques(p>0.056). Significant difference was found in all other pairwise comparison beyond 80° (p<0.042). These pairwise comparisons can be found in Table 2.
Conclusions:
The graft’s percent change in length from 0° to 70° of knee flexion did not differ between techniques. Both Modified MacIntosh and Mid-metaphyseal had significant graft stretching beyond 70° of knee flexion, and the graft strain did not differ significantly between these two techniques. Mid-metaphyseal technique’s tunnel is located more proximal and anterior on the femur, which may help avoid tunnel convergence with ACL reconstruction. Classic MacIntosh demonstrated significant decrease in graft length between 110° to 130° of knee flexion, which may translate to graft laxity and poor control of rotational instability at high angles of flexion. Lemaire is the most isometric technique with no significant difference in graft strain throughout the knee’s full range of motion. It has previously been described that a ligament length changes greater than 10% subjects the graft to increased strain, deformation, and risk of failure. The rotational control effectiveness of a fully isometric construct versus one that tensions slightly on flexion remains to be investigated.
