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Synopsis: Tunnel expansion is not a problem peculiar to hamstring ACL reconstructions. Tibial tunnel expansion was seen by CT in patients reconstructed with patellar tendon grafts and followed over a 2-year period.
Source: Fink C, et al. Tibial tunnel enlargement following anterior cruciate ligament reconstruction with patellar tendon autograft. Arthroscopy. 2001;17(2):138-143.
Although its clinical significance is unclear, tibial tunnel enlargement does occur, even with patella tendon autografts. In this paper, 34 patients had sequential CT scans and clinical evaluation following ACL reconstruction with patellar tendon autografts. The diameters of the tibial tunnel were noted to increase more than 30% in the sagittal plane and 16% in the coronal plane within 2 years. The enlargement was largest in the mid-portion of the tunnel, with expansion of almost 50% in the sagittal plane. Sequential studies demonstrated that tunnel enlargement began early in the postoperative period, reaching almost 50% of maximum enlargement within the first few weeks postoperatively. There was no correlation found between tunnel expansion and clinical results.
Comment by Mark D. Miller, MD
Tunnel enlargement following ACL reconstruction is a current focus of much investigation. Although most authorities agree that it is of no known clinical consequence, it certainly has implications for revision surgery. From what I have learned through my own experience, I always use back-up fixation for revision cases.
I discussed this topic in a previous review and concluded that, at least for the femoral side of hamstring ACL reconstructions, more tendon placed in the tunnel and improved fixation might reduce the amount of enlargement.1 Others have suggested that aperture fixation (typically with a bioabsorbable screw) may reduce the incidence of tunnel enlargement. A recent study, however, demonstrated increased enlargement (122%) with this method of fixation vs. other devices.2 In fact, this study reported that the EndoButton had the lowest amount of enlargement (36%) of all the devices studied. Clatworthy and associates concluded that tunnel widening cannot be avoided by fixing the graft closer to the joint or eliminating the bungee cord.
Returning to the present study, it is interesting that this phenomenon also occurs with patellar tendon grafts. According to the authors, it does not occur on the femoral side, presumably because the bone block is fixed immediately adjacent to the intra-articular margin, but perhaps also because of gravity effects. Fink et al also should be commended for using serial CT scans to accurately characterize this phenomenon. Undoubtedly there will be more papers to follow on this topic—stay tuned!
1. Miller M. Tunnel expansion with EndoButton in hamstring ACLs. Sports Medicine Reports. 2001;3(1):2-3.
2. Clatworthy MG, et al. Tunnel widening in hamstring ACL reconstruction: A prospective clinical and radiographic evaluation of four different fixation techniques. In: Program and abstracts of the Annual Meeting of the American Academy of Orthopaedic Surgeons. February 28-March 4, 2001; San Francisco, Calif; Poster PE014 (Abstract) 369-370.