9 High-tibial open-wedge valgization osteotomy with plate fixator
1 Surgical principles
The purpose of valgization osteotomy of the proximal tibia is treatment of medial unicompartmental osteoarthritis with varus deformity [1, 2] by shifting the mechanical weight-bearing axis (Mikulicz line) laterally to relieve the medial compartment. High-tibial osteotomy may delay the need for arthroplasty in young and physically active patients. It is regarded as an established procedure for medial osteoarthritis, showing good results . The operation is frequently performed in so-called closed-wedge technique from a lateral approach by removal of a bone wedge as described by Coventry  and Maquet  ( Fig 9-1 ).
The lateral approach necessitates fibular osteotomy or release of the proximal tibiofibular joint and internal fixation of the tibial head laterally. The need to detach the extensor muscles at the lateral aspect of the tibial head is associated with the risk of damage to the peroneal nerve, which has been reported in the literature at between 3.3% and 11.9% for closed-wedge procedures . Electromyographic data even indicate a nerve lesion in 27% of cases .
In contrast to the lateral closed-wedge method, the medial open-wedge technique offers certain advantages:
Only one osteotomy is required.
Fibular osteotomy, dissection of the peroneal nerve, and detachment of the extensor muscles can be avoided.
No shortening of the lower extremity.
The correction of the mechanical axis can be adjusted intraoperatively by gradual opening of the osteotomy gap (“fine- tuning”), whereby ligament instabilities can be treated at the same time by alteration of the caudal inclination of the tibial plateau in the sagittal plane (tibial slope) (see chapter 11 “Osteotomy and ligament instability: tibial slope corrections and combined procedures around the knee joint”). Incomplete osteotomy, leaving a 10 mm bone bridge laterally and a biplanar cutting technique (see below), will increase postoperative stability. The application of a specially designed plate fixator (eg, TomoFix) allows opening of the osteotomy gaps of up to 13 mm without the need for autograft .
Medial open-wedge valgization osteotomy of the proximal tibia is performed as a biplanar osteotomy: horizontal osteotomy of the posterior 2/3 of the tibia leaving a lateral bone bridge of 10 mm as a hinge; anterior ascending complete osteotomy behind the tibial tuberosity at an angle of 110°. The osteotomy is opened slowly, ensuring that the lateral hinge remains intact. Stabilization of the correction with an angular locking system (eg, TomoFix). An osteotomy gap of 13 mm or more should be filled with autogenous cancellous bone graft. This method avoids fibular osteotomy, dissection of the peroneal nerve, release of the extensor muscles, and shortening of the lower extremity.
2 Implant design of the angular locking plate fixator TomoFix
The presented plate fixator (TomoFix) is a specially modified T-shaped locking compression plate (LCP) that has locking holes in the proximal part and combination holes in the longitudinal shaft of the plate ( Fig 9-2a ). The proximal locking holes are adapted to the anatomy of the proximal tibia. An LCP guide sleeve is utilized for drilling the screw holes and ensures correct screw alignment. The locking screws are locked at a fixed angle in the conical threaded plate holes with the torque screwdriver. Self-drilling and self-tapping screws are available that can be inserted mono- or bicortically ( Fig 9-2b-c ). Since angular locking screws do not have a compressive effect, there is no risk of secondary loss of correction after locking the screws. The TomoFix plate guarantees a rigid fixation even in osteoporotic bone. The temporary insertion of 3 mm distances holders preserves the periosteal blood supply and prevents irritation of tendons and ligaments ( Fig 9-2d-e ).
3 Indications and contraindications
The indications for open-wedge valgization osteotomy of the proximal tibia (see Table 9-1 ) are unicompartmental medial osteoarthritis and varus deformity of the lower extremity in physically active patients. This operation can be performed simultaneously with other reconstructive procedures at the medial compartment of the knee to correct varus malalignment, eg,
Osteochondral autograft transfer system (OATS)
Autogenous chondrocyte transplantation (ACT)
Matrix-associated chondrocyte implantation (MACI)
Collagen meniscus implant (CMI)
In anterior cruciate ligament (ACL) reconstruction with preexisting varus deformity, a valgization-extension osteotomy of the proximal tibia will lead to axial correction and reduction of anterior tibial shift. A valgization-flexion tibial head osteotomy stabilizes posterolateral knee joint instability in varus deformity (see chapter 11 “Osteotomy and ligament instability: tibial slope corrections and combined procedures around the knee joint”). The preoperative range of motion of the knee should be at least extension/flexion 0-10-120°. Extension deficits up to 10° can be corrected by altering the tibial slope during osteotomy. Patients should not be older than 65-70 years of age.
Contraindications are (see Table 9-2 ):
Loss of lateral meniscus
Degenerative joint disease or third or fourth degree cartilage damage in the lateral compartment according to the Outerbridge classification 
Limited range of motion of the knee joint, especially extension deficits > 20° (see above)
The procedure should not be carried out in patients with poor soft-tissue conditions at the medial proximal tibia or in acute or chronic inflammation.
Unicompartmental medial osteoarthritis
Varus deformity of the lower extremity
Patient less than 65-70 years of age
Patients who are physically very active
As an adjuvant treatment for the correction of varus deformity at the following operations:
Valgization-extension osteotomy for anterior knee instability and varus deformity
Valgization-flexion osteotomy for posterior/posterolateral knee joint instability
4 Preoperative planning
Correction of axial deformity by osteotomy of the proximal tibia requires careful preoperative planning. Any possible complications or risks must be explained fully to the patient.
4.1 Patient information
In addition to general surgical risks such as vessel and nerve injuries, thrombosis/embolism, complications in wound healing, and early and late infections, the patient must also be made aware of the possibility of delayed bone healing. Hematoma of the lower extremity often develops as well as swelling and lymph edema. It should be emphasized that at a gap width of 13 mm or more requires harvesting and transplantation of cancellous bone graft from the iliac crest. There may be minimal lengthening of the affected extremity ( Table 9-3 ).
4.2 Preoperative diagnostics
Physical examination includes evaluation of the range of motion and the stability of the ligaments. The skin and soft tissues must also be inspected.
Radiological diagnostics include x-rays of the knee in three planes and a weight-bearing x-ray of the entire leg. A weightbearing view of the knee in 45° flexion, a so-called Rosenberg view, and MRI may provide information on the extent of damage of the medial compartment, but are not mandatory.
Prior to the planned procedure, diagnostic knee joint arthroscopy is performed under the same anesthesia in standard technique via the anterolateral portal. The lateral compartment and the lateral meniscus must be intact. Cartilage damages in the medial joint are precisely documented, unstable cartilage flaps are debrided, and microfracturing can be performed. In cases of mechanically relevant tears, the medial meniscus is partially resected ( Table 9-4 ).
4.3 Radiological planning
The authors refer the reader to chapter 4 “Basic principles of osteotomies around the knee” where the planning procedure of the desired axial correction is presented in detail.
4.4 Positioning of patient and instruments
For open-wedge valgization osteotomy of the tibial head the patient is placed in supine position under general or spinal anesthesia. A lateral support and foot pad are attached to the operating table so that the leg can be easily positioned in 90° flexion and in full extension. The entire leg including the iliac crest is draped to allow harvesting of cancellous bone and intraoperative assessment of the leg axis. A thigh tourniquet is normally not required, but a sterile tourniquet can be used.
Preoperative systemic single-shot antibiotic prophylaxis is applied. The image intensifier for intraoperative fluoroscopy is placed on the opposite side.
TomoFix plate fixator, mono- and bicortical locking screws
Oscillating saw with a wide saw blade approximately 90 mm long and a narrow saw blade approximately 50 mm long
Several flat chisels (15–20 mm wide)
Spreading chisel (optional)