Computer-aided shoulder arthroplasty is safe, useful - Academy News at the 2007 AAOS Annual Meeting

Computer-aided shoulder arthroplasty is safe, useful

By Sally Chapralis

Computer-aided navigation is already effectively being used to improve implant alignment in knee and hip arthroplasties. Yesterday, the authors of scientific paper 040 reported on their successful initial clinical experiences using an image-free navigation system for shoulder arthroplasties.

The team reported that trackers did not impede surgical performance, that the navigation system provided real-time feedback on the humeral resection as it relates to anatomic neck geometry and that the system also provided real-time angulation of the glenoid reamer relative to preoperative glenoid deformity.

“Fortunately, the learning curve for computer-aided shoulder arthroplasty appears to be substantially less than in hip or knee navigation,” reported the authors. “In our earliest experiences, navigation added approximately 20 minutes to 30 minutes to the procedure. We currently use navigation on a routine basis with an additional 10 minutes per procedure.”

(Left) A tracking device attached to the glenoid reamer is used to provide real-time feedback on the change in version and inclination relative to the native glenoid. (Right) A navigated plate is used to record inclination and retroversion of the resected humeral head.

Patient group

The study involved a single surgeon who performed 27 shoulder arthroplasties, from August 2005 through September 2006, using an image-free navigation system. The patients—17 males and 10 females—ranged in age from 39 to 85 years old (mean age: 62.0 years; standard deviation 11.3 years).

An anatomic glenohumeral implant system was used for the 24 patients diagnosed with either primary osteoarthritis, instability, or avascular necrosis. The three patients with cuff-tear arthropathy were treated with a reverse prosthesis.

Surgical approach

Under a standard protocol for shoulder arthroplasty, pre-operative computed tomography (CT) scans were used to evaluate native glenoid morphology, but the images were not input into the navigation system.

Patients were in a modified beach chair position and a standard deltopectoral approach to the shoulder joint was used. Optical trackers were attached to the proximal humerus, a navigated pointer probe was used to create a reference line for humeral version and a navigated canal introducer was inserted into the humeral canal to create a reference axis for humeral inclination. The navigation system was used to measure the anatomic neck axis before resection of the humeral head, and to record inclination and retroversion of the resected plane. Standard techniques were used to implant the humeral stem.

An optical tracking device attached to the coracoid process enabled glenoid navigation. Version and inclination of the native glenoid surface was captured with a navigated glenoid trial component. A navigation tracker, attached to the glenoid reamer, provided real-time feedback on the change in inclination and version relative to the native glenoid during reaming. Finally, the scapular tracking device was removed and the glenoid component implanted using standard techniques.

Results

In all surgeries the trackers “held secure during each procedure, did not impede surgical performance or access to the operative site, and did not damage tissues surrounding and underlying the optical tracking devices,” according to the authors.

The navigation system accurately noted “the anatomic and resected humeral neck orientation, humeral head diameter, and final glenoid reamer orientation in relation to the native glenoid.”

Encouraging initial experience

“Our early experience,” the authors reported, “suggests that the reverse prosthesis is a compelling application for computer-aided shoulder navigation technology.” The navigation system enabled the surgeon to ream the glenoid surface at a specific amount of negative inclination. With “accurate and reproducible methods for establishing appropriate inferior glenoid tilt,” surgeons can improve survivorship of reverse shoulder arthroplasties “by minimizing shear forces across the bone-implant interface and reducing the incidence of scapular notching.”

The authors also noted that navigation technology would be particularly helpful in situations where normal anatomy is distorted, for example, with fractures, revisions or dysplasia. “Where complex anatomy or severe deformity is encountered, navigation may save time compared to existing techniques by streamlining the intra-operative decision-making process.

Computer-aided shoulder navigation would not enable shoulder arthroplasty in patients who already have standard contraindications to the procedure, such as infection or poor overall health. In addition, severe osteopenia could inhibit secure attachment of the tracking devices.

While obesity can compromise registration accuracy and fixation of tracking devices in hip and knee arthroplasties, the authors “do not consider obesity a contraindication to the use of computer-aided shoulder arthroplasty.” More than half of the patients in their study had a body mass index (BMI) greater than 30, “and system functionality was not negatively affected even for the largest patient (BMI = 64.0).”

This clinical study—the first to describe computer-aided navigation techniques for shoulder arthroplasty—demonstrates significant value in this surgery, but “longer-term results are needed to determine the effect of this technology on clinical outcomes.”

Researchers include T. Bradley Edwards, MD and Gary M. Gartsman, MD, both of Houston, Texas, and Vineet K. Sarin, PhD, of Camarillo, Cal. Dr. Edwards is a consultant for Tornier and Kinamed Navigation Systems; Dr. Gartsman is a consultant for Tornier, and Dr. Sarin is a consultant for Kinamed Navigation System.


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