Computer-Assisted Opening Wedge High Tibial Osteotomy

Douglas W. Jackson

Blaine Warkentine

After using computer assistance in various knee surgery applications, we found this technology particularly helpful in obtaining the desired alignment in an opening-wedge proximal tibial osteotomy. Prior to its use, intraoperative fluoroscopy, radiographs, and/or visual assessments were the tools to assist in trying to obtain the desired intraoperative alignment. Computer assistance offers real time alignment information related to rotation of the limb as well as the exact sagittal and coronal planes for the osteotomy. This information is obtained with less radiation exposure (to patient, staff, and surgeon) and has enabled us to use smaller incisions as well as decrease our overall operative time. This application of computer-assisted surgery is based on and draws heavily from the contributions and techniques described by Dr. Guancarlo Puddu (see Chapter 30).

INDICATIONS/CONTRAINDICATIONS

Indications

Our current indications for computer-assisted opening wedge proximal osteotomy reflect our practice’s patient profile. This procedure is considered in our physically active patients and in combination with certain other knee procedures:

The patient has pain and limitations primarily related to the knee’s medial compartment.
The patient is “physiologically” younger and wants to continue high-demand activities after surgery.
The varus alignment is less then 12 degrees. In our experience caring for an active patient population, those requiring greater than 12 degrees of correction usually have more than unicompartment disease. In addition, those with larger corrections require significant bone grafting at the opening osteotomy site and run a higher risk of nonunion. In our experience, patients with high degrees of malalignment represent more individualized approaches; and while they may benefit from computer-assisted surgery applications, those techniques used are beyond the scope of this chapter.
The opening wedge osteotomy is in combination with other surgical procedures in the knee where there is the desire to unload the diseased medial compartment of the knee. It is used in attempt to provide a more favorable environment for a desired biologic response or protected healing for another procedure. These include:
- Microfracture
- Chondrocyte transplantation, osteochondral autografts and allografts
- Meniscal allograft transplant
- Helping to reduce loads associated with varus and posterolateral ligament insufficiency and/or reconstructions
- Anterior cruciate ligament (ACL) reconstruction associated with symptomatic arthritic medial compartment

Contraindications

Inflammatory arthritis
Tricompartmental disease
A flexion arc of less the 110 degrees (this and those contraindications below are in our patients whose objective is to remain physically active)
Greater than a 5-degree flexion contracture
Greater than 12 degrees of varus
Tibiofemoral subluxation on standing radiograph
Previous meniscectomy in the contralateral compartment

PREOPERATIVE PLANNING

The history and physical examination establish that the physiologically younger, active patient being evaluated has symptoms primarily related to the knee’s medial compartment. The knee range of motion (ROM) is documented; weight-bearing radiographs allow joint space determinations. If an osteotomy is being considered in those patients with varus alignment that is felt to contribute to their current complaints or is over weighting their medial compartment, we obtain an overall leg alignment on long-standing weight-bearing radiograph. In the group of patients who are also being evaluated for other surgical procedure(s) of the knee, it is part of the initial evaluation. These include any biologic restoration of their cartilage surfaces or a meniscus replacement in the overloaded compartment. It is unlikely that a biologic replacement will survive any better than the native tissues if the abnormal forces continue to be present. In addition, we consider it in varus alignment associated with posterolateral and varus instability (see Chapter 24).

SURGERY

Patient Positioning

The patient is positioned on the operating room table in the supine position with a tourniquet (which we may or may not use for portions or all of the procedure) applied. The entire lower extremity is prepared and draped separately from the groin distally in the usual orthopaedic manner. We use an adhesive wrap on the leg to decrease the bulky surgical stocking, allowing better visualization of the leg alignment.

Technique

An arthroscopic examination is performed and the treatable intra-articular cartilage and meniscal pathology addressed before the osteotomy. It varies among patients, but it is common to remove, debride, and contour a portion of a degenerative medial meniscus and loose or fragmented articular cartilage in the medial compartment. In addition, loose bodies and intra-articular debris and localized chondroplasties may be performed (see Chapter 26). Exposed bone that meets the indications in Chapter 27 may be addressed with microfracture or chondrocyte transplantation (see Chapter 29). Autograft (see Chapter 28) and allograft (see Chapter 33) osteochondral transplantation, meniscal allograft (see Chapters 10 and 11) or ACL reconstruction (see Chapter 12) may be performed in conjunction with the tibial osteotomy (see Chapter 24).

There are several companies that offer computer chosen software to assist in proximal tibial osteotomy, and use different methods for acquiring the position and alignment of the limb. Ideally, newer versions will allow less invasive data acquisition methodology. We currently use a system that requires femur and tibia reference arrays. The distal femur array is placed along the lateral intermuscular septum. For the tibia they are placed percutaneously along the lateral aspect of proximal one-third of the tibia (Fig. 31-1). In addition, the system we currently use has a navigated drill guide (Fig. 31-2), a round tip surface pointer, and a sharp percutaneous pointer.

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