CA system increases accuracy of distal radius osteotomies

System helps correct radial deformity using computed tomography-based 3-D isosurface models.

Issue: January 2004

PHOENIX — Canadian researchers who used a computed tomography-based computer-assisted surgical system to perform distal radius osteotomies reported that clinical and functional outcomes were comparable to or better than those obtained using conventional techniques.

Objective radiographic measurements with the computer-assisted (CA) technique were improved in all planes compared to traditional corrective distal radius osteotomies (DRO), investigators said.

Less radiation exposure

Other advantages of the system were less radiation exposure due to reduced use of fluoroscopy and less time needed for corrective osteotomy when the system was used for preoperative planning and subsequently in the operating room for image guidance.

This is a technically and clinically useful procedure, according to George G.S. Athwal, MD. “We obtained excellent radiographic correction. Our functional outcomes were consistent with those reported in the literature,” he said.

--- During the surgical portion of performing a computer-assisted distal radius osteotomy, the surgeon drills holes for the plate in locations determined by the computer. A standard dorsal approach is used.
COURTESY OF GEORGE G.S. ATHWAL

Athwal, chief resident, and Dr. Pichora, chairman of orthopedic surgery at Queens University Hospital in Kingston, Ontario, presented results of a single-cohort, in vivo feasibility study during the American Society for Surgery of the Hand 57th Annual Meeting, here. For the study, conducted from 1998 to 2000, the CA DRO system was used to correct post-traumatic deformity of the distal radius following malunion in six patients. Five sustained their original fractures from a low-energy fall onto an outstretched hand. They were primarily treated with closed reduction and casting.

Range of motion (ROM), grip strength, the Disabilities of the Arm, Shoulder and Hand (DASH) score, postoperative radiographic correction and computed tomography (CT) models were used to assess the long-term outcome following a CA DRO. “All osteotomies united at a mean time of nine weeks,” Athwal said. No re-operations were required.

At an average final follow-up of 25 months, investigators assessed the patients’ ROM and grip strength. The average ROM was 87% and average grip strength was 79% of the opposite limb. The average DASH score was 14 (range 3.3 to 53.3).

Correction amount calculated

Investigators measured radial inclination, volar tilt and ulnar variance to assess the system’s ability to obtain anatomical correction. The patients’ malunions had an average radial inclination of 12°. Using calculations made from the normal contralateral wrists, the investigators’ goal for correction was 23°. Inclination correction at final follow-up was 21°. Volar tilt of the treated malunions averaged 30° dorsal and 21° volar; the correction goal was 10° of volar tilt. At final follow-up the correction for this measurement was 9°. Ulnar variance of the malunions measured 7.5 mm. The goal of correction was 1.5 mm and correction at final follow-up was 1.9 mm.

The CA DRO system, developed by Drs. Pichora and Ellis in 1998, is used in a two-step process. The first step is preoperative planning and the second is intraoperative execution of that plan. For the first step, a computer-generated CT-based isosurface model of the malunited radius is created by the user, and a mirror image of the model is made to recreate the normal contralateral radius. This functions as a template.

--- To achieve the anatomic correction, the surgeon fixes the wrist plate in the exact position specified by the system. The defect was filled with autologous iliac crest bone graft.
COURTESY OF GEORGE G.S. ATHWAL

Next, a virtual osteotomy is done and the distal fragment is aligned using the template to recreate the normal anatomy of the distal radius. “The 3-D planning process allows you a perspective not available with plain radiographs,” Athwal said.

A model of a fixation plate is then placed on the radius model to realign the distal radius. The location and orientation of the plate, as well as the screw hole locations, are computer-determined. During surgery, these steps are performed under image guidance.

Image guidance used in OR

During the second step, the preoperative plan is exactly reproduced in the operating room using image guidance and a standard dorsal approach. An optical tracking system is used to register the wrist’s bony landmarks in the computer. The previously marked drill holes are made using an image-guided drill and the osteotomy is completed. The fixation plate is attached to the distal fragment and together the fragment and plate are fixed in the proper system-determined position. Investigators used postoperative isosurface models and standardized radiographs to determine the accuracy of the corrections in the patients they treated with CA DRO.

--- Performing the osteotomy and drilling holes for the plate is done under image guidance. The surgeon is shown viewing a computer monitor in the OR which displays the corrected distal radius model created during the preoperative planning phase.
COURTESY OF GEORGE G.S. ATHWAL

When discussing the manuscript at the meeting, Geoffrey H.F. Johnston, MD, of Saskatoon, Saskatchewan, said, “This CA DRO surgical planner does seem to work as the authors profess and represents an advance in orthopedic technology and a new treatment option.”

In an interview with Orthopedics Today, Athwal said enrollment is underway for 20 to 30 patients who will be treated with the CA DRO system as part of a prospective study. Another application of the same system and software was developed at Athwal’s institution for localization of osteoid osteomas, and it is particularly effective for those that are in difficult-to-access locations, such as the hip he said.

For your information:

Athwal GGS, Pichora DR, Ellis RE, Small CF. Computer assisted distal radius osteotomy: long-term outcomes of a clinical feasibility study. #9A. Presented at the American Society for Surgery of the Hand 57th Annual Meeting. Oct. 3-5, 2002. Phoenix.