Technical Note

Avoiding Graft-Tunnel Mismatch in Endoscopic AnteriorCruciate Ligament Reconstruction: A New Technique

Gregg P. Hartman, M.D., and Domenick J. Sisto, M.D.

Summary: A common problem encountered in endoscopic anterior cruciateligament reconstruction is graft-tunnel mismatch. A technique not previouslydescribed in the literature is illustrated. This technique provides direct measure-ment of the tibial tunnel length plus the intra-articular distance. This allows directcalculation of the length of the femoral tunnel necessary to avoid a graft-tunnelmismatch. This technique has been used very effectively in our institution withexcellent, reproducible results.Key Words: ACL reconstruction—Graft mis-match.

Bone–patella tendon–bone autografts and allograftsare used in anterior cruciate ligament (ACL)

reconstructions. A concern when using these graftswith the endoscopic technique is the possibility ofgraft-tunnel mismatch. When there is a significantgraft-tunnel mismatch, interference screw fixation isdifficult and other fixation techniques must be used.This article describes a simple technique that allowsthe surgeon to directly measure the tibial tunnel lengthplus the intra-articular distance. This allows the sur-geon to calculate exactly how deep the femoral tunnelneeds to be drilled in order to avoid any mismatch.

OPERATIVE TECHNIQUE

Arthroscopic examination of the knee is performedin the usual fashion and associated intra-articularpathology is addressed in an appropriate manner. Thediagnosis of a significant ACL tear is confirmed. Thetorn ACL stump is debrided and an adequate notch-

plasty is performed. If an autograft is being used,attention is then directed toward harvesting the middlethird of the patella tendon to procure 25-mm boneplugs. If an allograft is being used, a similar size graftis harvested. The graft is taken to the back table to beprepared.

Graft preparation involves sizing the bone blocks to10 mm in diameter. Drill holes are then placed in thebone blocks. Two No. 2 Ethibond sutures are passedthrough the femoral bone plug (Ethicon, Somerville,NJ). One No. 2 Ethibond suture and one 25-gauge wireare passed through the tibial bone plug. The total graftlength (TGL) is measured. The femoral bone blocklength (FBBL) is also recorded. The graft is thenplaced is a moist laperotomy sponge in a safe place.

Attention is then turned back to the patient’s knee.The tibial tunnel guide is set to 60° is most cases. Theguide is placed on the posterior third of the ACL stumpand the guide pin is placed. The guide pin is theoverdrilled with the 10-mm drill. The 7-mm over-the-top guide is then used to place the femoral guide pin.The endoscopic drill bit is then placed over the guidepin and firmly pressed into the medial aspect of thelateral femoral condyle. This drill bit is calibrated toallow the femoral tunnel to be drilled to the desiredlength. Before drilling the femoral tunnel, the cali-brated markings are read at the entrance to the tibial

From the Los Angeles Orthopaedic Institute, Sherman Oaks,California, U.S.A.

Address correspondence and reprint requests to Domenick J.Sisto, M.D., Los Angeles Orthopaedic Institute, 4955 Van NuysBlvd, Suite 615, Sherman Oaks, CA 91403, U.S.A.

r 1999 by the Arthroscopy Association of North America0749-8063/99/1503-2045$3.00/0

338 Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 15, No 3 (April), 1999: pp 338–340

tunnel on the anterior aspect of the tibia (Fig 1). Thelength read here is the combined length of the tibialtunnel length plus the intra-articular distance(TTL1IAD). A simple formula can then be used todetermine the femoral tunnel length (FTL) needed toavoid any graft-tunnel mismatch. The formula isTGL 2 (TTL1IAD) 5 FTL.

The femoral tunnel is then drilled to the appropriatelength. The graft is pulled into position. Interferencescrews are then used for fixation of the bone blocks inboth the femur and the tibia.

DISCUSSION

Biomechanical studies have recently shown thatfixing the tibial bone block with either staples or aninterference screw provides adequate strength,1 but if asurgeon plans on using an interference screw in boththe femoral and tibial tunnels, graft-tunnel mismatchcan be a major concern. There have been a number ofarticles in the past that have addressed this issue.Kenna et al.2 suggested using a calibrated guide to varythe length of the tibial tunnel. They suggested that byknowing the total length of the graft and subtracting 50(the femoral tunnel length plus the average intra-articular distance), one could determine the length ofthe tibial tunnel necessary to avoid mismatch. Thistechnique is effective, but is not always accurate.

Miller and Hinkin3 published on the ‘‘N17 rule’’ fortibial tunnel placement. This was also a method thatprovided the surgeon with a systematic way to vary thetibial tunnel length. The ‘‘N57 rule’’ was recentlytested prospectively by Pagnano et al.4 Pagnano re-ported a 50% success rate using this method. Pagnanosummarized that the ‘‘N17 rule’’ did not reliablyproduce a tibial tunnel length that allowed for interfer-ence screw fixation in the tibia.

Fowler and DiStefano5 proposed a method of deal-ing with graft-tunnel mismatch that would still allowfor interference screw fixation. Their method involvessecuring a cancellous bone plug to the graft. Thiseffectively lengthens the bone block allowing forinterference screw fixation.

Olszewski et al.6 recently published the results of astudy that reviewed these methods. This study alsoevaluated the ‘‘N12 mm Rule’’ for determining opti-mal tibial tunnel length. The conclusion of this studywas that a combination of the ‘‘N17 rule’’ and the‘‘N 12 mm rule’’ provided the most accurate method.If graft-tunnel mismatch does occur, provided that atleast 1 cm of bone remains in the tibial tunnel,adequate interference screw fixation can be obtained.7

We believe that a simple method that eliminates theproblem of graft-tunnel mismatch has not heretoforebeen described. The method described in this articleprovides the surgeon with a systematic way to vary thefemoral tunnel length to avoid graft-tunnel mismatch.Currently, a prospective study is underway that isscientifically analyzing this method.

In summary, by directly measuring the length of thetibial tunnel and the intra-articular distance, and sub-tracting this from the total graft length, one candetermine exactly how deep the femoral tunnel needs

FIGURE 1. The calibrated endoscopic drill is placed over the guidepin and pressed against the medial wall of the lateral femoralcondyle. The drill bit is then read at the anterior aspect of the tibia.In this example, the TTL1 IAD 5 75 mm. If the total graft lengthis 100 mm, the femoral tunnel needs to be drilled 25 mm deep (100mm2 75 mm5 25 mm).

339AVOIDING GRAFT-TUNNEL MISMATCH

to be in order to avoid graft-tunnel mismatch. Thismethod is easy, reproducible, and early data suggestthat it is very effective.

REFERENCES

1. Gerich TG, Cassim A, Lattermann C, Lobenhoffer HP. Pulloutstrength of tibial graft fixation in anterior cruciate ligamentreplacement with a patellar tendon graft: Interference screwsversus staple fixation in human knees.Knee Surg SportsTraumatol Arthrosc1997;5:84-88.

2. Kenna B, Simon TM, Jackson DW, Kurzweil PR. EndoscopicACL reconstruction: A technical note on tunnel length forinterference fixation.Arthroscopy1993;9:228-230.

3. Miller MD, Hinkin DT. The ‘‘N17 Rule’’ for tibial tunnelplacement in endoscopic anterior cruciate ligament reconstruc-tion. Arthroscopy1996;12:124-126.

4. Pagnano MW, Kim C, Hulie G, Scott WN. Difficulties with the‘‘N 57 Rule’’ in endoscopic anterior cruciate ligament reconstruc-tion. Arthroscopy1997;13:597-599.

5. Fowler BL, DiStefano VJ. Tibial tunnel bone grafting: A newtechnique for dealing with graft-tunnel mismatch in endoscopicanterior cruciate ligament reconstruction.Arthroscopy1998;14:224-228.

6. Olszewki AD, Miller MD, Ritchie JR. Ideal tibial tunnel lengthfor endoscopic anterior cruciate ligament reconstruction.Arthros-copy1998;14:9-14.

7. Pomeroy G, Baltz M, Pierz K, Nowak M, Post W, Fulkerson JP.The effects of bone plug length and screw diameter on theholding strength of bone–patellar tendon–bone grafts.Arthros-copy1998;14:148-152.

340 G. P. HARTMAN AND D. J. SISTO