**3. Surgical technique**

The indications for both meniscus allograft and scaffold vary by surgeon, but in general, the patient should have previously undergone a total or partial meniscectomy, respectively, and present with discomfort only in the compartment previously operated upon. Maximal osteoarthritis allowed is grade III and a minimum 2 mm joint space. Also, if the knee is clinically unstable, it should be stabilized at the time of the procedure with respect to the anterior cruciate ligament. If operative knee alignment is more than 3–5 degrees different concerning the involved compartment compared to the contralateral knee, an osteotomy should be performed to unload the affected compartment.

For meniscus allograft transplant, the traditional methodology denotes the use of medial side double bone plugs, and a press-fit bone bridge (keyhole) method on the lateral side (**Figure 1**). On the medial side bone plugs are used due to graft size and anterior attachment variability, while on the lateral side bone bridges are used due to horn proximity [13]. In the case of a concomitant ACL and lateral meniscus, the femoral and tibial ACL tunnels are drilled initially and then the lateral meniscus trough is made. The femoral side of the ACL is then secured, followed by placement of the lateral meniscal allograft, and finally the tibial side of the ACL is secured. While a number of papers have investigated all-soft tissue constructs, several basic science studies have demonstrated improved biomechanical function with bony meniscal attachments [23, 24].

For meniscus scaffolds, surgical technique is similar for both devices. This begins with arthroscopic resection of the surrounding damaged tissue and subsequent implantation of a custom-sized scaffold. The sized scaffold is then sutured to the meniscal rim and capsule using standard techniques (**Figure 2**).

#### **Figure 2.** *Custom meniscal scaffold sizing and fixation.*

Initially, a partial meniscectomy is performed, with surgical debridement back to the vascularized zone of the damaged portion of the native meniscus. It is particularly important that the meniscal rim be continuous, especially at the popliteal hiatus of the lateral meniscus. If there is complete loss of the tissue in front of the popliteus tendon, it should be considered a total loss and thus a contraindication for a meniscus scaffold. After debridement, the resulting void is sized along the peripheral edge using the meniscal ruler supplied with the scaffold. The scaffold is then cut to fit, placed into the knee, and finally sutured to the native meniscus. The surgeon can use an all-inside, inside-out, or outside-in suture technique depending on the area to be sutured and their experience and preference [25].
