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Subcortical Backup Fixation in ACL Reconstruction

Shawn M. Gee, M.D., Liang Zhou, M.D., Michael A. Donohue, M.D., and

Matthew A. Posner, M.D.

Abstract: Anterior cruciate ligament (ACL) injuries result in knee instability in a majority of patients. Repair andreconstruction techniques have continually evolved over the past several decades. ACL reconstruction outcomes aredirectly impacted by physical therapy with early range of motion, weightbearing, and progressive strengthening.Therefore, the fixation must be sufficient to withstand the tensile and shear stresses across the graft construct during thebiological healing phase. Occasionally, the primary fixation device is not strong enough to withstand these stresses. Inturn, supplementary fixation devices, which are important especially in cases of revision ACL reconstruction, areimperfect. They occasionally become symptomatic, requiring hardware removal. Posts and washers require bicorticalfixation, with moderate-sized holes in the tibia. Biocomposite screws rely on friction in the boneescrew interface, makingthem susceptible to failure. Tensioning can be problematic with the use of a post-and-washer construct. Subcorticalfixation, which has not previously been described as a backup fixation method, provides several advantages. It requires asmaller, unicortical hole and provides fixation with a much lower profile than post-and-washer and interference-screwconstructs. This is the first description of subcortical backup fixation in ACL reconstruction.

he optimal method of graft fixation in anterior

Table 1. Quick reference

SuppliesOne #2 FiberLoop or FiberWire(optional) One #2 TigerLoop or TigerWireOne Arthrex 3.2-mm drill pinOne Arthrex BicepsButton

Preparation

Tcruciate ligament (ACL) reconstruction remains acontroversial topic in orthopaedics. With the evolutionof aggressive rehabilitation protocols and increasingpressure for athletes to return to sport in shorter timeintervals, adequate graft fixation is a growing concernfor surgeons. In particular, tibial-sided fixation hasgenerated scientific interest, as it has been reported tobe the weakest point in ACL reconstructions.1 Single-and dual-fixation methods are available; however,concerns pertaining to bone density, thread geometry,and insertional torque in primary fixation methodshave led many surgeons to consider supplementaltechniques.2 A recent systematic review of 21 studiesdemonstrated stronger initial fixation strength and less

Fort Belvoir Community Hospital, Fort Belvoir, Virginia, U.S.A.John A. Feagin, Jr Orthopaedic Sports Medicine Fellowship,ew York, U.S.A. (S.M.G., L.Z., M.A.D., M.A.P.); and the Tripleral Center, Honolulu, Hawaii, U.S.A. (L.Z.).rs report that they have no conflicts of interest in the authorshiption of this article. Full ICMJE author disclosure forms arethis article online, as supplementary material.ugust 14, 2021; accepted October 8, 2021.rrespondence to Shawn M. Gee, M.D., 9300 DeWitt Loop, Fort22060, U.S.A. E-mail: shawn.m.gee@gmail.comby Elsevier Inc. on behalf of the Arthroscopy Association of Northis is an open access article under the CC BY-NC-ND licensevecommons.org/licenses/by-nc-nd/4.0/)./211178.org/10.1016/j.eats.2021.10.006

Arthroscopy Techniques, Vol 11, No 2

side-to-side laxity in hybrid tibial-sided graft fixationmethods compared with single modes of fixation,owing to the load-sharing nature of the construct.3

A wide variety of backup fixation options are avail-able. Two commonly used methods include the postand washer and the biocomposite screw. Although

Thread 1 limb of each suture through 1 side of the button and backthrough the opposite side. Thread the other limb through thebutton in the same manner, starting on the opposite side. SeeFigs. 1e4.

DrillingUsing the 3.2-mm drill pin, drill a 3.2-mm unicortical hole 2 to3 cm below the inferior aperture of the tibial tunnel. Ensure thatthe hole is drilled centered on the medial face of the tibia(between the tubercle and posteromedial cortex) directed towardthe fibula. See Fig. 6.

InsertionMaintain tension on the sutures and insert the button through thecortex. Pull on the free suture limbs to seat the button against thetibia. See Figs. 7 and 8.

Tensioning and knot tyingTension each suture limb pair. Once they are tensioned, tie a knotwith opposing suture limbs. One knot using the 4 limbs isrecommended. See Fig. 9.

(February), 2022: pp e171-e176 e171

Fig 1. The cortical button can be attached during graft prep-aration with the BicepsButton and inserter. This figure showsan allograft with 4 trailing #2 sutures, a FiberWire, and aTigerWire.

Fig 2. Each limb is threaded through 1 side of the button andback through the opposite side. The other limb is threadedthrough the button in the same manner, starting on theopposite side. Two different limbs can be passed at 1 time.

e172 S. M. GEE ET AL.

bicortical fixation in the former construct is appealing,hardware prominence is a concern in some patients. Inturn, biocomposite screws provide a low-profileconstruct, but pull-out concerns arise from the reli-ance on a unicortical boneescrew interface. A biome-chanical study comparing 3 methods of tibial-sidedbackup fixation demonstrated no statistical differencein ultimate load-to-failure of a 4.5-mm post and washercompared with a 4.75-mm biocomposite screw (1148vs. 1007 N; P ¼ .100).4

The use of suspensory fixation is commonly used asthe primary fixation technique among reconstructive

Fig 3. (A) Diagram illustrating proper passage of the first suturemanner as the first. Note that both sutures can also be passed simsuture strands. Note the 3.2-mm drill hole for passage of the but

procedures in orthopaedic sports medicine. Fixed andadjustable-loop constructs rely on a cortical button,seated on the periosteum, for fixation during ACLreconstruction.5 Similarly, cortical button fixation hasbeen described for tenodesis of the long head of thebiceps tendon to the humerus (albeit placement iswithin the intramedullary canal). In a matched-cadaverstudy, no differences in load-to-failure were identifiedbetween button and interference screw fixation (218.8vs. 212 N; P ¼ .625).6 Sutureetendon interface failurehas been reported as the most commonly observedmode of failure with the button technique.7

To date, no study has evaluated the utility ofsubcortical fixation as a backup fixation method in ACLreconstruction. The purpose of this study was todemonstrate use of the unicortical button for subcor-tical backup fixation. Future studies will demonstratethe biomechanics of this backup fixation method.

through the button. The second suture is passed in the sameultaneously. (B) Subcortical placement of the button with 4

ton.

Fig 4. Once the sutures are passed, the inserter can beunthreaded from the button to facilitate pretensioning andgraft passage.

Fig 6. The button is threaded back onto the inserter after graftpassage and primary fixation.

SUBCORTICAL BACKUP FIXATION IN ACLR e173

Surgical Technique

IndicationsSubcortical backup fixation using the unicortical

button (BicepsButton; Arthrex, Naples, FL) can beused in primary and revision ACL reconstructions withquadriceps autograft, bone-to-bone autograft,hamstring autograft, and allograft. It can be used inmost standard ACL reconstruction techniques. For all-inside ACL reconstruction, it can be used for suturesthat are not tied around the Attachable Button System(ABS; Arthrex). During graft preparation, 2 to 4 trail-ing sutures should be placed on the tibial (trailing) sideof the graft. Our technique is shown in the Video 1. Asummary of our technique is given in Table 1.

Fig 5. Quadriceps autograftprepped with a corticalbutton for backup fixation.

SuppliesThe following supplies are recommended: one #2

FiberLoop or FiberWire (Arthrex), one #2 TigerLoop orTigerWire (Arthrex), one 3.2-mm drill pin (Arthrex),and 1 BicepsButton (Arthrex). Alternatively, the drillpin and BicepsButton can be found in the BicepsButtonkit (Arthrex) (Fig. 1).

PreparationDuring graft preparation, use 2 different colored su-

tures (FiberLoop/FiberWire and TiberLoop/TigerWire)and place Krackow stitches in the tibial (trailing) side ofthe graft, creating 4 trailing suture limbs. If usingFiberLoop, ensure that the bulky suture is cut from the

Fig 7. A 3.2-mm drill pin is used to drill a unicortical hole 2 to3 cm below the inferior aperture of the tibial tunnel. The holeis centered on the medial face of the tibia (between the tu-bercle and posteromedial cortex) to ensure that the buttonwill flip.

Fig 9. The button is inserted using the BicepsButton inserter.After insertion, the inserter is unthreaded, and the sutures aretoggled to flip the button. The sutures are tensioned.

e174 S. M. GEE ET AL.

suture tails to facilitate passage through the button. Foradded efficiency, we recommend placing the buttonduring graft preparation. Thread 1 limb of each suturethrough 1 side of the BicepsButton and back throughthe opposite side. Thread the other limb through thebutton in the same manner, starting on the oppositeside (Figs. 2 and 3). Unscrew the BicepsButton inserterand tension the graft (Fig. 4). The BicepsButton canremain in place during graft passage, tensioning, andfixation (Fig. 5).

DrillingAfter the graft has been passed and tensioned and

primary fixation has been performed, thread theBicepsButton inserter onto the button (Fig. 6). Using a

Fig 8. A probe is inserted to clear the cancellous bonebeneath the cortical surface.

3.2-mmdrill pin, drill a 3.2-mmunicortical hole 2 to 3 cmbelow the inferior aperture of the tibial tunnel (Fig. 7).Ensure that the hole is drilled Centered on the medialface of the tibia (between the tubercle and posteromedialcortex) directed toward the fibula. If the hole is too closeto the tibial tubercle or posteromedial cortex of the tibia,the buttonmay not flip.We recommend using a probe toremove the cancellous bone beneath the cortex to facil-itate flipping of the button (Fig. 8).

InsertionMaintain tension on the sutures and insert the button

through the cortex (Fig. 9). If the button does not easilypass through the cortex, avoid twisting it, as the tip may

Fig 10. A knot is tied with opposing suture limbs. One knotusing the 4 limbs is recommended.

Fig 11. (A) Postoperative ante-roposterior x-ray showing theunicortical button along themedial face of the tibia. (B) Post-operative lateral x-ray.

SUBCORTICAL BACKUP FIXATION IN ACLR e175

break off of the inserter. Instead, lightly tap the inserter.Unthread the inserter but leave the inserter within thehole. Pull on the free suture limbs to seat the buttonagainst the tibia. Remove the inserter from the hole andpull the sutures to ensure that the button is positionedproperly.

Tensioning and Knot TyingTension each suture limb pair by hand. Once they are

tensioned, tie a knot with opposing suture limbs(Fig. 10). One knot using the 4 limbs is recommended.Postoperative x-rays are shown in Fig. 11.

DiscussionWe describe ACL subcortical backup fixation with a

unicortical button. As the surgical technique is identicalto that used in tenodesis procedures of the long head ofthe biceps tendon, it may be readily reproducible for

Table 2. Advantages and disadvantages

Category Advantages

Size of hole 3.2 mm Smalbic

Type of fixation Unicortical button No reStrength of fixation Undergoing biomechanical testing Mini

biclig

Number of suturestrands supported

Four #2 FiberWire strands (2 pairs) Supprecstr

Hardware prominence Minimal, size of knot Smalmo

surgeons who are familiar with that use. Advantagesand disadvantages are summarized in Table 2. Advan-tages over using a 4.75-mm biocomposite anchorinclude the smaller size of the unicortical hole (3.2 vs.4.0 mm), which theoretically creates a smaller stressriser within the tibia; no reliance on the boneescrewinterface for fixation; and decreased cost of theimplant. Whereas the biocomposite anchor (Swive-Lock) predictably fails at the boneescrew interface, thebutton technique has been shown to fail mostcommonly at the sutureetendon interface.7

Compared with a post-and-washer construct, which ispartially subcutaneous, the subcortical button alleviatesthe concern for hardware prominence. Additionally, thismethod may be used in other surgeries that requiretibial-sided fixation, such as meniscal root repair.A disadvantage of the unicortical button is the

comparative difficulty of hardware removal when

Disadvantages

ler than 4.0-mm hole for SwiveLock and 4.5-mm hole for 6.5-mmortical post; larger than 2.5-mm hole for 4.5-mm bicortical postliance on friction in the boneescrew interface versus SwiveLockmal displacement and excellent strength in proximal subpectoraleps tenodesis; unknown biomechanical strength in anterior cruciateament (ACL) backup fixationorts �4 strands of #2 FiberWire recommended in most ACLonstruction techniques; bicortical post and SwiveLock support >4ands (if needed)ler hardware prominence compared with bicortical post and washer;re prominent than SwiveLock because of overlying knot

Table 3. Pearls and pitfalls

Pearls Pitfalls and Risks

PreparationThe button can be placed during graft preparation. Removethe inserter after preparation, before graft passage.

If the button is placed after graft passage, a few extra minutes may berequired.

Use no more than 4 strands of #2 suture. More strands are unlikely to pass through the button.If using FiberLoop, ensure that the bulky suture is cut fromthe suture tails to facilitate passage through the button.

The bulky FiberLoop tails may not pass through the button if not cut.

When prepping the graft, use 2 different-colored sutures (e.g.,FiberLoop/FiberWire and TigerLoop/TigerWire); passopposing suture ends through each side of the button

If opposing ends are passed through same side of the button, fixationmay be affected. If the sutures are the same color, it will be unclearwhich to tie together.

DrillingEnsure that the hole is centered on the medial face of thetibia.

If the hole is too close to the tibial tubercle or posteromedial cortex, thebutton may not flip.

Consider multiple drill passes. This will allow the button tomore easily slide through the hole.

If cancellous bone is present, the button may not flip.

Consider using a probe to remove the cancellous bonebeneath the cortex after drilling.

InsertionIf the button does not pass, do not twist the inserter. Instead,remove and insert the drill again. You can also lightly tap theinserter.

Twisting the inserter may bend the threaded tip, causing it to breakinside the button.

TensioningTension the graft by pulling opposing suture endsindependently.

If the graft is not tensioned, backup fixation will fail.

Knot tyingConsider tying opposing strands together (i.e., 1 larger knot,rather than 2 smaller knots). A larger knot will be unable toslide through the 3.2-mm hole (less displacement).

e176 S. M. GEE ET AL.

needed, such as in the case of postoperative infection,given the intramedullary placement of the device. Atheoretical concern is migration of the knot stack, whichdirectly overlies the tunnel, and may serve as a point offailure. Pearls and pitfalls are summarized in Table 3.

AcknowledgmentsThe opinions or assertions contained herein are the

private views of the author and are not to be construedas official or as reflecting the views of the Departmentof the Army or the Department of Defense.

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