Fixation Choice

Although there are a variety of fixation methods available, Dr Prodromos uses cortical fixation for both ends of the ACL graft, an EndoButton™ on the femoral side and cortical screw on the tibial side.

Our meta-analysis [1], published in 2005 looked at the stability of ACL reconstruction by fixation type and by graft type. Meta-analysis showed that the 4 strand hamstring grafts (4HS) had the greatest stability. Of the 64 studies looked at in the analysis, 24 used 4HS. These were further broken down by fixation types as follows:

  1. EndoButton™ on the femur and "second-generation" fixation methods, not buttons or simple stables on the tibia.(7 series)
  2. Other cortical fixation methods than those in group 1, including 3 sub-groups (11 series)
    1. Those using cross-pin femoral fixation (4 series)
    2. Those using cortical screws on both the femur and tibia. (3 series)
    3. Those using simple buttons for at least one fixation point (4 series)
  3. Interference screw group which was subdivided into 2 sub-groups (6 series)
    1. Those using interference screw fixation on both the tibia and femur (5 series)
    2. Those using augmented interference screws. (1 series)

When these fixation groups were analyzed for stability, group 1 - the EndoButton™ cortical fixation group, performed much better than any other group. The results for this group showed 80% with normal stability and only 1.7% with abnormal stability. By comparison, group 2 had a normal stability of 74% (5.4% abnormal) and group 3 had a normal stability of 77% (6.7% abnormal).

Therefore, this meta-analysis indicated that cortical fixation, specifically with an EndoButton™ resulted in significantly more stable results.

A follow-up study [2] of up to 8 years of our patients who have had ACLR with EndoButton™ femoral fixation and whipstitch post tibial fixation demonstrated one of the highest stability rates reported in the literature.

Bungee Effect

Some researchers argue that cortical fixation, which locates the fixation point far from the anatomic insertion site of the native ACL results in less stiffness, more graft-tunnel movement and tunnel widening, the so-called bungee effect. This argument seems to first have been presented by Höher et al [3] in 1998. Although he presented a logical argument that the bungee effect was one of several factors that could cause the increased tunnel widening that is seen with hamstring grafts over patellar grafts in some studies, he offered no data to back up this theory. Additionally, he noted that bone tunnel widening may be irrelevant since it did not seem to correlate with clinical outcomes.

Paessler et al [4] repeated this argument and used it to support their technique of press-fit graft fixation of hamstring grafts close to the anatomic ACL insertion point. Their results showed no widening of the femoral tunnels and little widening of the tibial tunnels. However, since they compared these results to a BTB technique instead of a cortical fixated hamstring graft, it is difficult to tell how the fixation method impacted the tunnel widening and final stability of the knee.

Clatworthy, et al [5] looked at tunnel widening in hamstring and patellar grafts. Although they found significantly greater tunnel widening in the hamstring group over the patellar group, there were no significant differences in stability, effusion, range of motion, and muscle strength in the 2 groups at one year. Although there were differences between the groups, they were unable to demonstrate a correlation between a longer tunnel and increased tunnel widening. They therefore concluded that the "bungy" effect is not a primary cause of tunnel widening.

Brown, et al [6] examined graft-bone motion and tensile properties of hamstring and patellar grafts using a variety of fixation methods. They found that there is no significant difference in graft-bone motion between aperture and suspensory femoral fixation methods when the stiffness of the femur-ACL graft fixation-ACL graft complex was similar. They found that hamstring tendon grafts fixed using the EndoButton CL™ was one of the fixation methods with the least amount of graft-bone displacement after 1,000 cycles. This group also showed superior fixation strength compared with all other hamstring and PT fixation methods. They concluded that their study does not support the idea of a bungee effect. This data seems to be similar to our findings in the meta-analysis discussed above.

The combined results of these studies suggest that the bungee effect either does not exist at all or has minimal effects. It is possible that it may have some contribution to tunnel widening. However, tunnel widening does not seem to have any significant effects on ultimate stability, which is the most important concern in the outcome of any ACL surgery.

Whipstitch Post Video

This page offers a surgical video that demonstrates the preparation of a 4 strand hamstring semi-tendinosus/gracilis (4ST/Gr) graft using whipstitch and attachment and tensioning of this graft on the tibial end with a cortical screw.

EndoButton™ Video

This page offers a surgical video that demonstrates the attachment of a 4ST/Gr graft to an EndoButton™, insertion of the graft into the drilled tunnels and fixation of the EndoButton™

For full copies of Dr. Prodromos' articles or DVDs, please contact us at 847-699-6810 x207 or