High Tibial Osteotomy

Overview

An osteotomy is a surgical procedure to realign a bone in order to change the biomechanics of a joint, especially to change the force transmission through a joint.

These procedures must be performed accurately, not only to create the desired geometries but also to provide biological environments for rapid and effective healing.

In particular, the high tibial osteotomy (HTO) is a corrective surgical procedure in which the upper part of the tibia is resected so that the lower limb can be realigned. The most common form of HTO is the closing wedge osteotomy, in which the realignment is achieved by removing a lateral wedge of bone from the proximal tibia.

Typical Medial Arthritis of the Knee

Many patients suffering from arthritis of the knee have deterioration of the soft tissues on only one side of the knee. This condition is called unicompartmental arthritis and usually it is the medial or inner compartment of the knee that is affected. HTO is a procedure that attempts to shift the weight-bearing axis of the knee towards the healthy compartment, thus unloading the damaged compartment. The most common surgical alternative to the procedure is a total knee arthroplasty or unicompartmental arthroplasty.

Total knee arthroplasty has a typical survival rate of 90% at 15 years after the procedure, but the polyethylene articulating surfaces generate wear particles that lead to loosening or failure and subsequent revision.

By contrast, HTO preserves the joint's original cartilage and corrects the fundamental mechanical problem of the knee. This advantage of HTO is especially important to the young active patient, for whom an arthroplasty has a greater probability of earlier failure than is likely for an older inactive patient. In North America, the cost of an osteotomy is approximately 1/3 that of an arthroplasty.

We have developed a system that uses a preoperative planning system to perform a "virtual surgery" on a 3D model of the tibia, and an intraoperative guidance system to allow the surgeon to accurately accomplish the plan.

Traditional Planning and Surgery

The HTO is often performed with the modified Coventry technique.

1. The surgeon uses a plain X-ray film to find the preoperative anatomical alignment of the knee. Lines are drawn on the film with a ruler and protractor to estimate the size of the corrective wedge.
   
2. In the operating room a pair of guide wires are drilled from the lateral side to the medial side, ideally forming a perfect triangle.
   
3. A conventional oscillating saw is run along the guide wires, the bulk of the wedge is removed, and the "hinge" of cortical bone is refined by osteoclasis or chiselling.
   
4. The bone fragments are reduced, then fastened with one or more surgical staples. The surgical site is then sutured closed in layers.

Computer Assisted Planning

We have developed preoperative planning software that allows the surgeon to plan and perform a virtual osteotomy on a 3D model of the patient's knee. Our planning system mimics the traditional planning method, but with two crucial differences: the planning is inherently 3D, and we simulate the expected result of the procedure. The first step is to find the tibial axis and plateau on the 3D model.

In the next part of the process, the surgeon plans the procedure by translating a "cutting plane" distally from the plateau; then a wedge size is calculated and displayed. The plan can be reviewed from any angle, providing the surgeon with a full 3D view of the patient's anatomy and of the proposed correction, as illustrated by the two "3-D" images. The system also removes the wedge and reduces the bone fragments, which produces a simulation of the osteotomy. The surgeon can review the expected change in the load axis as well as directly visualize the predicted outcome.

Computer Assisted Intraoperative Guidance

After performing registration of the patient to the CT scan and the plan for the procedure, the surgeon uses a guidance system to implant the guide wires. An optoelectronic system tracks the motion of the tibia and of the surgical drill.

Our guidance system then superimposes a virtual instrument on the images and plans, and calculates the distances and angles to the planes that define the plans. The surgeon can use these image to accurately drill, cut, and realign the bones during the surgical procedure.

References

Further information on our HTO work can be found in the Publications section; please use the links below:

1. R. E. Ellis, C. Y. Tso, J. F. Rudan, and M. M. Harrison. A surgical planning and guidance system for high tibial osteotomy. Journal of Computer Aided Surgery, 4(5):264-274, 1999.
2. R. E. Ellis, J. F. Rudan, and M. M. Harrison. Computer-enhanced orthopaedic surgery: The high tibial osteotomy. In Proceedings of the ASME Bioengineering Conference, BED-Vol. 42, pages 17-18, 1999.
3. C. Y. Tso, R. E. Ellis, J. F. Rudan, and M. M. Harrison. A surgical planning and guidance system for high tibial osteotomies. In Medical Image Computing and Computer-Assisted Intervention - MICCAI'98, pages 39-50. Springer Lecture Notes in Computer Science 1496, 1998.
4. C.Y. Tso. "A planning and guidance system for osteotomies". Master's thesis, Queen's University at Kingston, 1997.