The patient is positioned supine, the lower limb is prepared and draped, and a tourniquet is positioned on the thigh. Arthroscopy should be performed in patients to confirm the indication and evaluate the intra-articular status; after this step the tourniquet is inflated. An anteromedial vertical incision is performed midway between the medial border of the tubercle and the posterior border of the tibia, just below the pes anserinus and 1 cm below the joint line. The sartorial fascia is elevated to visualize the hamstring and the superficial medial collateral ligament (MCL), and a blunt retractor is placed posteriorly to protect both these structures and the neurovascular ones. The patellar tendon is exposed and protected. Under fluoroscopic control, a guide wire is positioned from medial to lateral, at the level of the superior aspect of the tibial tubercle, anteromedially, arriving 1 cm below the joint line (Fig. 10.3a). A cortical osteotomy is performed using and oscillating saw, inferiorly to the guide wire to prevent superior migration and intra-articular fractures, and it is continued with an osteotome under fluoroscopic control. Once the osteotomy is completed, the medial opening is created using an apposite wedge placed to the planned depth (Fig. 10.3b). A wedge placed anteriorly causes an increase of the tibial slope, while, if the wedge is placed posteriorly, a slight decrease of the tibial slope is achieved [41]. Anterior and posterior gaps are then measured in order to calculate the amount of slope modification as described by Noyes et al. [30]: if the anteromedial gap is half of the posteromedial, the tibial slope will not change; otherwise for each 1 mm of increase in the anterior gap, the posterior slope will increase by 2°. Furthermore, if the anterior gap is greater than 1 cm, a tibial tubercle osteotomy is recommended in order to avoid patella infera. The lower limb alignment is checked under fluoroscopic control, and the gap is filled with either autograft, allograft, or synthetic bone. Finally, the osteotomy is stabilized using a contour lock or 4-hole plate (Arthrex, Naples, FL, USA) with 6.5 mm cancellous screws proximally and 4.5 mm cortical screws distally (Fig. 10.4). The final result is checked under fluoroscopic control, the tourniquet is deflated, and the wound is closed in a standard fashion. With small corrections, a 4-hole plate will be satisfactory, but for large corrections and biplanar correction, the contour lock plate is preferred.

Although good long-term results are reported with opening-wedge HTO, it remains a challenging procedure with some intraoperative risks like neurovascular injury, fracture of the lateral cortical hinge or fracture into the lateral tibial plateau and resultant osteotomy instability, loss of correction, and delayed/nonunion of the osteotomy. To make the medial opening-wedge HTO a more reproducible procedure with less risk of complications, the iBalance™ HTO system (Arthrex, Naples, FL) was developed. It includes an instrumentation with a neurovascular blunt retractor, a patellar retractor, an alignment handle, and a new cutting guide. With this system the surgeon is able to reduce the risk of fracture by hinging on a predrilled hole to allow dissipation of forces laterally; besides the alignment handle allows to easily check the correction both on the sagittal and coronal plane. The novel implant is made of polyetheretherketone (PEEK), a new radiolucent and bio-inert material which is already used in different orthopedic implants [43]. In literature this system has been described to be safe and with some advantages like the protection of the neurovascular bundle, a low profile nature of the implant reducing soft tissue irritation, and the ability to maintain the alignment in both the coronal and sagittal planes [44].

The approach is the same we described in the above section. After the detachment of the medial collateral ligament and the exposition of the patellar tendon, the alignment handle with the keyhole guide is positioned with the patellar retractor, and the alignment is checked with the C-arm on both the sagittal and coronal plane. The biplanar alignment bars should be positioned on the joint line on the anteroposterior view, and the two bars should appear as a single one on the lateral view. Once the correct alignment in both planes is obtained, the keyhole guide is fixed with pins and the alignment handle is removed. At this point a keyhole reamer is used to drill two holes to allow dissipation of forces laterally and to accommodate the plate. Now the cutting guide and the neurovascular blunt retractor are assembled to the system. The cut is performed and the system is removed; now the opening jack paddles are inserted into the osteotomy, and the correction is obtained slowly opening the jack by turning the turn key handle. Once the correction is obtained, the iBalance™ PEEK implant can be positioned; the gap is filled with autologous bone graft from the drilled holes and bone substitute can be used. The PEEK plate is fixed with two cancellous anchors (screws) proximally and two cortical anchors distally. Figure 10.5 shows few steps of this technique.

We normally use a circular external fixator (Taylor Spatial Frame™, Smith and Nephew) with gradual correction only if the deformity is large, usually greater than 17.5°. In these cases, the fixator is assembled preoperatively using three rings 4 cm larger than the diameter of the leg. Preoperatively the correction is calculated in each plane and if any length needs to be adjusted, but then this is confirmed after application of the fixator postoperatively. The first ring is positioned at the level of the fibular head and the second below the tibial tubercle, and they are joined by the six correction rods. The third ring is preset approximately 5 cm distal to the second one using four tethered rods. The proximal ring is placed parallel to the tibial articular surface in both the coronal and sagittal planes. The two distal rings are aligned to the tibial shaft, and the deformity to be corrected is between the first and second ring. The apparatus is then sterilized, the lower limb is prepared, and the tourniquet is inflated. A 3-cm incision is made 10 cm below the fibular head posterolaterally, the plane between soleus and peronei is developed, and an oblique fibular osteotomy is performed. The external fixator is then applied to the leg. The first ring is secured using two wires and one half-pin across the tibia, and the second ring is then secured with one wire and one half-pin across the tibia (to avoid the peroneal branches, the pins should be placed more laterally than medially). The third ring is stabilized with two wires passing across the tibia. At this point a 1.5-cm incision is performed anteriorly just distal to the tibial tubercle, the periosteum is elevated, and a tibial osteotomy is performed (Fig. 10.6). Some correction can be performed during the surgery to ensure the osteotomy will correct, and then it can be gradually done beginning 7–10 days postoperatively (callotasis).