BRIDGE IN SLOT SURGICAL TECHNIQUE

A 2 to 3 cm mini-arthrotomy is performed in line with the anterior and posterior horn insertion sites of the lateral meniscus. This allows correct orientation of the slot and introduction of the graft. This arthrotomy should be performed directly adjacent to the patellar tendon. A posterolateral incision is also necessary for suture passage during the meniscal repair portion of the procedure. The incision should extend approximately one third above and two thirds below the joint line and allow adequate exposure to protect neurovascular structures during passage of the inside-out sutures. The short head of the biceps musculature is stripped from the posterior capsule and a spoon is placed to protect the peroneal nerve. By staying above the tendon of the long head of the biceps, the peroneal nerve is always safe. An additional incision is made through the iliotibial band inline with its fibers and spread with a self-retainer. This is in order to ensure that the sutures are tied beneath these structures to minimize the chances of capturing the knee due to soft tissue tethering.

Slot orientation follows the normal anatomy of the meniscus attachment sites. A line is made with a 4-mm burr to make a reference slot in the tibial plateau. Its height and width will equal the dimensions of the bur, and its alignment in the sagittal plane should parallel the slope of the tibial plateau (Fig. 25.4). Slot dimensions should be confirmed by placement of a depth gauge in the reference slot, which also measures the anteroposterior length of the tibial plateau (Fig. 25.5). With use of a drill guide, a guide pin is placed just distal and parallel to the reference slot and advanced to but not through the posterior cortex (Fig. 25.6). This is a critical step in ensuring that the graft is placed in an anatomic location. The pin is subsequently overreamed with an 8-mm cannulated drill bit, again with care not to breach the posterior cortex (Fig. 25.7). The trough can then be unroofed with the aid of a pituitary. A box cutter is then used to make a slot 7 to 8 mm wide by 10 mm deep, which is smoothed and refined with a 7 to 8 mm rasp to ensure that the bone bridge will slide smoothly into the slot (Fig. 25.8).

The allograft arrives from the tissue bank as a hemiplateau with the meniscus attached. All nonmeniscal tissue is removed and the exact locations of the anterior and posterior horn anchors are identified. Using a cutting guide, the bridge is then cut to a width of 7 or 8 mm and a depth of 10 mm (Fig. 25.9). The bone bridge should intentionally be undersized by 1 mm to facilitate graft passage and to reduce the risk of inadvertent bridge fracture during insertion. The prepared bridge is then tested for ease of passage through calibrated troughs on the back table. The posterior wall of the bridge should be flush or slanted slightly anterior to the fibers of the posterior horn attachment to allow for insertion at the most posterior edge of the prepared slot. Bone anterior to the anterior horn should be left in place to allow for safer graft manipulation during insertion. A vertical mattress traction suture of 0 polydioxanone (PDS) is placed at the junction of the posterior and middle thirds of the meniscus to assist with graft insertion (Fig. 25.10).

On occasion, the anterior horn attachment can be larger, up to 9 mm wide. If the anterior horn attachment site is wider than the intended width of the bone bridge, the attachment should be left intact, and the width of the

FIGURE 25.4

A 4-mm burr is used to make a reference slot in line with the anterior and posterior horns, parallel to the sagittal slope of the tibial plateau and a width no greater than the burr. (Courtesy of Stryker Endoscopy, San Jose, CA.)


FIGURE 25.5

Stryker guide placed within the reference slot and hooked onto the posterior tibial plateau. The drill guide is in place to measure length of the tibial slot. (Courtesy of Stryker Endoscopy, San Jose, CA.)



FIGURE 25.6

Guide pin placed through the guide handle, care to drill to the posterior tibial cortex but not through it. (Courtesy of Stryker Endoscopy, San Jose, CA.)

FIGURE 25.7

An 8-mm cannulated reamer is advanced over the guide to the measure depth. (Courtesy of Stryker Endoscopy, San Jose, CA.)




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FIGURE 25.8

A: Box cutter is used to convert the rounded slot to a box-shape.

B: Arthroscopic view of the box cutter in place. C: Rasp is used to smooth the edges of the slot.

D: Arthroscopic view of 8 mm rasps in the bone trough. (Courtesy of Stryker Endoscopy, San Jose, CA.)

Bone bridge should be increased accordingly in the area of the anterior horn insertion only. The remainder of the bone bridge should be trimmed to 7 mm as intended. To accommodate the increased width, the corresponding area of the recipient slot should be widened accordingly.

A single barrel, zone-specific meniscal repair cannula placed through the anteromedial portal with the scope in the anterolateral portal is directed toward the capsular attachment of the posterior and middle thirds of the meniscus. A long, flexible nitinol suture passing-pin is placed through the capsule, just anterior to the popliteus tendon, to exit the accessory posterolateral incision. The proximal end of the nitinol pin is then withdrawn from the anterior arthrotomy site, the allograft traction sutures are passed through the loop of the nitinol pin, and the pin and sutures are withdrawn through the posterolateral incision. With the aid of traction sutures, the menis-cal allograft is pulled into the joint through the anterior arthrotomy while the bone bridge is advanced into the tibial slot, and the meniscus is manually reduced under the condyle with a finger placed through the arthrotomy. Appropriate varus stress to open the lateral compartment aids in graft introduction and reduction (Fig. 25.11). Once the meniscus is reduced, the knee is cycled to ensure proper anatomic placement and capturing by the tibiofemoral articulation. Once again, it is critical that the trough is posterior enough. If there is any question at this time, x-ray may be brought in to confirm trough position. The graft is then attached to the capsule with standard inside-out vertical mattress sutures placed from posterior to anterior, equally on the dorsal and ventral meniscal surfaces (Fig. 25.12). This fixation can be supplemented with appropriate all-inside fixation devices placed in the most posterior aspect of the meniscus to minimize the risk of neurovascular injury if one desires. In regards to the bone bridge fixation, there are a variety of ways to ensure fixation. Some advocate leaving the bone bridge without supplemental fixation. Others use an interference screw to add additional compression to the bone bridge within the slot. Still others supplement fixation with sutures tied over a bone bridge. Standard closure of the arthrotomies and accessory incisions is then performed.

FIGURE 25.10

Lateral meniscal allograft with bone bridge cut to size and traction suture placed at the junction of the posterior and middle thirds.


FIGURE 25.9

A diagram showing the allograft bone block being cut to appropriate size. (Courtesy of Stryker Endoscopy, San Jose, CA.)


FIGURE 25.11

Diagrammatic representation of meniscus insertion. (Courtesy of Stryker Endoscopy, San Jose, CA.)



FIGURE 25.12

View of the meniscal allograft in place, secured with inside/out sutures.

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