What are the Benefits of CAOS for Shoulder Replacement?

Ari R Youderian, MD

Read complete study: Benefit of intraoperative navigation on glenoid component positioning during total shoulder arthroplasty

I have now performed my first 40 shoulder replacement cases with computer assisted orthopaedic surgery (CAOS).  As an early adopter of this technology, the meta-analysis by Sadoghi et al, “Benefit of intraoperative navigation on glenoid component positioning during total shoulder arthroplasty” was very intriguing to me.  The authors reveal seven cases of comparative studies between CAOS and standard shoulder replacement.  The biggest finding was a combined 6 degree difference in glenoid version, but they found limited data and differences in inclination or other parameters.  The study emphasizes the point that navigation will continue to demonstrate improved accuracy in postoperative position, but we are only scratching the surface with the power of this technology.  As a fairly high volume shoulder surgeon, even I can easily see a difference in glenoid placement, angulation and screw positions as I compare my postoperative radiographs from my navigated cases to my pre-navigation cases.

The good news is that CAOS for shoulder replacement is finally here.  This is not the same as patient specific instrumentation; it’s a step further.  The newest CAOS system allows for robust planning, continuous feedback to the surgeon throughout the case and the ability to deviate from the plan but still always know where you are.  The authors make a great point about the added benefit of both accuracy and reliability.  Not only do these systems allow you to place a glenoid within 1mm and degree of your plan, but they will commonly decrease the margin of error.  This is a common theme of eliminating outliers, seen with the knee CAOS systems, especially for those who perform these cases less often.

During my fellowship, CAOS was not available.  My mentor was finishing up his work on the first patient specific navigation system, and we used a robust 3-D planning tool.  I quickly bridged the gap between the standard radiograph and 2-dimensional planning seen in residency to the eye-opening concepts of 3-D, including planning and implementation of glenoid sizing, seating, use of augmented implants, finding the best bone for fixation and bone graft planning in severe deformity cases.

Preoperative planning software has allowed me to more accurately choose glenoid sizes and augmentation, as well as estimate the patient’s native glenoid position.

Since that time, these concepts have permeated in each case that I carefully planned, but I did not have the tools to translate them to the operating room.  Previous studies have demonstrated that the use of preoperative planning software alone adds to the accuracy of glenoid placement.  Preoperative planning software has allowed me to more accurately choose glenoid sizes and augmentation, as well as estimate the patient’s native glenoid position.  In addition, augmented glenoids are much easier to place with CAOS, as the guessing of how much bone to remove and at what angle to start are removed from the equation.  The majority of my decision making is now performed prior to the start of the surgery, and it is then executed more promptly and efficiently during the surgery.

One important clarification that this study does not address is the difference between cadaver studies, virtual studies and in vivo studies.

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