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CURRENT CONCEPTS
Femoral Tunnel Placement in
ACL Reconstruction Central Footprint vs. AM bundle (continued)
In a MOON group study in which six surgeons performed 229 autograft transtibial ACLR. These were compared with 209 transportal ACLR’s. There was no difference in the revision rate.
In a recently completed study Clatworthy in a prospective sequential single surgeon study compared the revision rate of 1016 transtibial hamstring ACL reconstructions followed for 6 – 15 years with 464 transportal hamstring ACL reconstructions followed for 2–6 years.
His transtibial technique utilised a short oblique tibial tunnel which enabled the femoral tunnel to sit within the anatomical footprint in a high AM position. Clatworthy changed to a transportal technique to enable a central femoral tunnel. This resulted in a more forward (distal) and lower (posterior) femoral tunnel position.
Sex, age, graft size, time to surgery, meniscal repair and meniscectomy data were collected and evaluated as contributing factors for ACL graft failure to enable a multivariate analysis.
• His transtibial revision rate was 5.1%, 52 revisions from 1016 ACLR’s.
• His transportal revision rate was 6.9%, 32 revisions from 464 ACLR’s
Utilizing a single variate analysis transportal ACLR technique has a hazard ratio which was is 2.4X higher than transtibial. This is significant p=<0.001.
There was no difference in sex, age or lateral meniscal repair rates between the two groups. There were differences in graft size, time to surgery, medial meniscal repair rates & and medial & lateral % meniscus remaining
Adjusting for all these factors the multivariate hazard ratio was 2.3X higher for the transportal technique. This remains significant p=0.001
The transportal ACLR’s had a shorter follow up period thus the revision rate was also determined per 100 graft years to determine the relative risk of failure between the two techniques.
• The transportal revision rate was 0.14 failures per 100 graft years
• The transtibial revision rate was 0.04 failures per 100 graft years
Thus the ACL grafts placed more centrally in the footprint had a 3.5x higher revision rate than the grafts placed in a high AM position per 100 graft years which is significant p=<0.001.
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• 61% of the transportal ACL graft failures occurred in the first year post surgery.
• 27% of the transtibial ACL graft failures occurred in the first year post surgery.
The transportal had a significantly higher earlier failure rate p=<0.001
He concluded that placement of the ACL graft in a more central femoral footprint position has a higher and earlier revision rate than an ACL graft placed in a high femoral AM position. As discussed in this review central footprint ACL reconstruction is less isometric. The resultant higher graft strains from this technique is the likely explanation for the increased revision rate.
In response to the increased failure rate Clatworthy modified his surgical technique. He continued to use the transportal technique but aimed to place the femoral tunnel in the AM bundle center rather than the center of the femoral footprint.
The failure rate data for the three techniques in the first two years is:
• Transtibial AM femur, posterior tibia–3/171–1.8%
• Transportal central femur, centromedial tibia–9/238–3.8%
• Transportal AM femur, centromedial tibia–2/178–1.1%
These early results indicate that the central femoral tunnel position is the reason for the higher failure rate rather than the surgical technique utilized to drill the femoral tunnel and bringing the tibial tunnel more anteriorly has not resulted in an increased failure rate.
In a recently completed study Andy Williams has shown a similar increase in both patella tendon and hamstring failure rate when he moved from a high AM to a central femoral footprint position.
When comparing clinical results it is easy to forget to regard those results in terms of the demographic of that surgeon’s / surgeons’ practice(s). Doing so will not only put the quoted results in context
28 ISAKOS NEWSLETTER 2015: Volume II