Surgical Technique with Bone Patellar Tendon Bone Allograft

Examination of the patient under anesthesia should confirm preoperative diagnosis of graft failure and rule out the presence of a complex instability pattern. The sequence of operative steps is in general the same as that used for primary ACL reconstruction: diagnostic arthroscopy and débridement of failed graft, tibial followed by femoral tunnel preparation, allograft preparation (alternatively, depending on anticipated needs, graft preparation can take place as the initial step or simultaneous to other steps), passage, cycling, and fixation of the graft. Most revision reconstructions can be accomplished via an endoscopic, single-incision technique.

The patient is placed in a supine position with the operative extremity held in standard ring-type leg holder. The nonoperative leg is flexed at both the knee and hip and secured in a padded gynecologic leg holder. The waist of the table is flexed and the foot is dropped, permitting easy access to both medial and lateral aspects of the knee. If the need for extensive bone grafting of widened tunnels is anticipated, then the ipsilateral iliac crest can be prepped and draped into the field. Standard arthroscopic portals are established, and a general diagnostic arthroscopy is performed. Status of the medial, lateral, and patellofemoral compartment articular cartilage as well as the menisci is evaluated and recorded. Residual ACL tissue is débrided, taking particular care to débride the tibial ACL footprint such that the medial tibial spine, the leading edge of the posterior cruciate ligament, and the posterior aspect of the anterior horn of the lateral meniscus can be identified as landmarks for accurate tibial tunnel placement. The exit point of the previous tibial tunnel and the entry point of the previous femoral tunnel are defined carefully with a shaver and arthroscopic elec-trocautery, and a final plan is formulated for revision tunnel preparation.

Removal of previously placed interference screws can be challenging and, if not done carefully, can lead to cortical violation of the tibia and/or femur, including posterior wall blowout. Although not routinely necessary, use of intraoperative image intensification can facilitate removal and permits evaluation of cortical integrity. A number of strategies can aid in the safe removal of a femoral interference screw. A spinal needle should be used to triangulate and establish the proper angle for removal, and at times the screw can be accessed via the tibial tunnel.

Tunnels in acceptable position are redrilled and cleared of all fibrous tissue, and the bone blocks of the allograft sized appropriately to fill the tunnels. Passage of the arthroscope through the tibial and/or femoral tunnel permits confirmation of the adequacy of debridement and maintenance of osseous integrity.

Old tunnels that are malpositioned by more than one diameter can be bypassed, as the new tunnels can be placed in anatomic position without overlap (Fig. 52-6) and may not require hardware removal. However, for cases in which preexisting hardware interferes with new tunnel placement, hardware removal and, where indicated, bone grafting of a subsequent defect should be done prior to drilling the new tibial or femoral tunnel. A clear arthroscopic cannula placed through the standard or an accessory inferomedial portal can be useful for packing allograft chips into the femoral tunnel. A solid block of allograft bone fashioned from the excess that accompanies a standard BPTB allograft can be also be used to fill bony defects in either the femoral or tibial tunnels (Fig. 52-7).

The degree of tunnel enlargement present at the time of reconstruction may require special attention. Tunnel enlargement that compromises attempts at revision graft fixation must be staged. In the first stage, the failed graft is excised, tunnels are debrided of all soft tissue, and allograft chips, autograft (e.g., iliac crest), or a mixture of both is used to fill all bony defects (Fig. 52-8). The patient is then treated with protected weight bearing for 8 to 12 weeks until bone graft incorporation is complete and new tunnels can be prepared through restored bone

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Figure 52-6 Drawing illustrating nonoverlapping tunnels. The anterior position of the existing femoral tunnel (1) allows drilling of the revision tunnel posteriorly (2) as in a primary case. (From Bach BR Jr, Mazzocca A, Fox JA: Revision anterior cruciate ligament surgery. In Grana WA [ed]: Orthopaedic Knowledge Online. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2003.)

Figure 52-7 Series of intraoperative arthroscopic photos demonstrating revision of a malpositioned femoral tunnel. A, Removal of interference screw from original reconstruction. B, Bone grafting of original femoral tunnel. C, Drilling of revision femoral tunnel in isometric position.

Figure 52-7 Series of intraoperative arthroscopic photos demonstrating revision of a malpositioned femoral tunnel. A, Removal of interference screw from original reconstruction. B, Bone grafting of original femoral tunnel. C, Drilling of revision femoral tunnel in isometric position.

Figure 52-8 Drawing illustrating bone grafting of an enlarged tibial tunnel. (From Bach BR Jr, Mazzocca A, Fox JA: Revision anterior cruciate ligament surgery. In Grana WA [ed]: Orthopaedic Knowledge Online. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2003.)

Figure 52-9 Illustration of the "divergent tunnel" concept, in this case demonstrating a revision femoral tunnel (2) drilled from outside in using a two-incision technique. (From Bach BR Jr, Mazzocca A, Fox JA: Revision anterior cruciate ligament surgery. In Grana WA [ed]: Orthopaedic Knowledge Online. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2003.)

stock. For cases of mild tunnel enlargement in which a single interference screw is judged to be inadequate, techniques such as using large bone blocks on the allograft, bone grafting at the time of the reconstruction, or stacking interference screws in which a second screw is placed parallel to and alongside the first screw can enhance fixation strength.

As in index reconstruction, the tibial tunnel is prepared first. An elbow-type aiming guide is typically recommended. The tendinous portion of the graft is measured and the "n + 10" rule used to determine the appropriate guide setting. It can be helpful to leave the tibial-side bone block intentionally long to compensate for possible graft-tunnel mismatch. Excess bone block can later be trimmed as needed.

In some instances, the posterior wall of the femoral tunnel is found to be "blown out" or is violated during attempts to bypass an old anterior femoral tunnel at the time of revision surgery. Interference screw fixation is compromised in these situations because an intact osseous tube is required for interference fit. Cases of posterior wall blow out can be approached using the "divergent tunnel" concept, which refers to the fact that both the femoral and tibial tunnels can have a variety of different orientations without changing the intra-articular orientation of the graft. Arthroscopic two-incision technique permits rigid interference screw fixation through outside-in screw placement in cases in which the posterior cortex is blown out (Fig. 52-9). Alternatively, an EndoButton (Smith & Nephew, Andover, MA) technique can be used, eliminating the need for posterior wall integrity.

Following placement of new tunnels and bone grafting where needed, the graft is passed in standard fashion. Femoral-side fixation is achieved as described; and the graft is cycled in order to pre-tension the graft and evaluate isometry. The graft should translate no more than 1 to 2 mm in the tibial tunnel as the knee comes into full extension if tunnel placement is correct. Tibial-side fixation is then achieved with the knee in full extension and axially loaded. Some surgeons prefer to achieve tibial-side fixation with the knee held in a reverse Lachman position, but this maneuver raises concern about overconstraining the knee. Interference screw fixation can be reinforced using a screw and washer construct or staples if bone is deficient or osteopenic or if fixation is simply judged to be inadequate. Restoration of

Figure 52-9 Illustration of the "divergent tunnel" concept, in this case demonstrating a revision femoral tunnel (2) drilled from outside in using a two-incision technique. (From Bach BR Jr, Mazzocca A, Fox JA: Revision anterior cruciate ligament surgery. In Grana WA [ed]: Orthopaedic Knowledge Online. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2003.)

stability is assessed with Lachman and pivot-shift testing intraoperatively.

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