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Abstracts & Commentary
Synopsis: Two studies examining the issue in different ways confirmed that suspensory fixation yields more tunnel widening than outlet fixation.
Sources: Klein JP, et al. The incidence and significance of femoral tunnel widening after quadrupled hamstring ACL reconstruction using femoral cross pin fixation. Arthroscopy. 2003;19(5):470-476; Barber FA, et al. The effect of outlet fixation on tunnel widening. Arthroscopy. 2003;19(5):485-492.
Tunnel widening following ACL reconstruction has been reported with all types of grafts and fixation methods. Although the amount of widening can be rather dramatic in some cases, the clinical importance outside of difficulty encountered at potential revision surgery remains unclear. Nevertheless, avoiding large bone cavities with possible graft attachment compromise seems desirable. The present 2 papers in the same issue of Arthroscopy examine this issue in different ways.
Klein and colleagues measured femoral tunnel widening following metal cross pin fixation (Slingshot, Mitek, Norwood, Mass) of quadruple hamstring grafts. Tibial fixation was with the Intrafix device (Mitek). Approximately half of the eligible 57 patients were evaluated after at least 1 year (mean, 18 months) with standardized x-rays, clinical exams, KT testing, and IKDC and Lysholm scores. Every single patient had at least 10% tunnel widening, and all but one had 20%. The mean widening was 65.5% at the greatest diameter, or 5.4 mm. There was no correlation between the amount of tunnel widening and knee stability or clinical outcome.
Barber and colleagues studied tibial outlet fixation of bone-patella tendon-bone grafts with an absorbable interference screw (BioScrew, Linvatec, Largo, Fla). If the tendonous length of the graft was greater than 45 mm, they folded over the bone plug onto the tendon to shorten the construct. Thus, the graft was fixed as close as possible to the tibial tunnel outlet in the joint. Using basically the same evaluation tools at a mean of 30 months, they found 90% of the full-length (unfolded) grafts had at least 2 mm of tunnel widening, while none of the flipped grafts had any widening. In fact, the flipped-graft group, which effectively had fixation right at the articular tunnel outlet, had shrinkage of the tunnel to obliteration in almost half of the knees. Once again, no effect on clinical scores or laxity was demonstrated.
Comment by David R. Diduch, MS, MD
You can argue if you want about tunnel widening not appearing to matter based on clinical scores, etc. Revise just one of these and you’ll know this can be a big deal. How can it possibly be good to have large cystic cavities within the knee, for graft healing and for the future?
These 2 studies look at a common problem in different ways, which is fine since the problem is affected by several factors. We know from several studies that the worst combination appears to be allograft, soft-tissue grafts, distal or suspensory fixation, and ethylene oxide sterilization. The first paper demonstrates suspensory fixation with a metal cross pin. While initial fixation strength is ideal, graft motion (windshield wiper) and stretch (bungee cord) can potentially erode bone and diminish healing. The motion can also create a pumping action for joint fluid up into the tunnel. Joint fluid prevents clotting, which is the first step in fracture healing within the tunnel. I personally think that joint fluid is one of the main culprits, and I strive for the tightest fit possible with my hamstring grafts. I also use autograft tissues, as subtle immune rejection has been implicated in this process. Most suspensory cross pin fixation systems require a somewhat loose fit in order to pull the graft up and over the pin. The absorbable Rigid-Fix (Mitek) is the exception, which skewers the graft in the tunnel with 2 pins much closer to the joint.
Aperture or outlet fixation eliminates graft motion, increases stiffness, and shortens the construct. Interference screws may not always seal the tunnel opening to joint fluid, however. This may not matter with bone plugs as they are in direct contact with the tunnel wall and heal quickly. Barber et al nicely describe their procedure to flip the graft when the tendon is long. This achieves a graft fixed close to the joint line and avoids problems with graft-tunnel length mismatch.
Surgeons can make several decisions regarding graft choice and fixation methods, each of which will affect potential tunnel widening and future problems. The general principles we can learn from these 2 studies and others are as follows: Keep the working length of the graft as short as possible, with rigid fixation close to the joint line. Achieve a tight fit with a barrier to joint fluid within the tunnels. Use autograft tissues or avoid any graft sterilized with ethylene oxide.
Dr. Diduch, Associate Professor, Department of Orthopaedic Surgery, University of Virginia School of Medicine, Charlottesville, VA, is Editor of Sports Medicine Reports.