How Should We Approach Superior Glenoid Wear?

Kevin Famer, MD

Read complete study: Reverse total shoulder glenoid baseplate stability with superior glenoid bone loss

In the article “Reverse total shoulder glenoid baseplate stability with superior glenoid bone loss” by Martin et al, the authors looked to quantify glenoid baseplate stability with worsening superior glenoid bone loss.  The authors utilized a polyurethane bone model, and created superior glenoid bone loss defects such that the attached baseplates had 100% support, 90% support, 75% support, and 50% support.  The authors found the 50% support group had significantly greater micromotion than the other defects and the native state.  The majority of micromotion occurred at the beginning of testing, indicating that some settling may occur with time.  Interestingly, micromotion in the 50% support group exceeded 150 µm, which has been shown in animal models to be the maximum amount of micromotion that allows bony ingrowth.

The authors spend a lot of time describing their testing methods, compared to other published manuscripts.  The authors applied cyclic loading at a fixed 60º glenohumeral angle, which mimics the superiorly directed force during the initiation of abduction, as opposed to other studies that apply force to the baseplate that mimics the force during the range of abduction.  The benefits of the study design of this current study is that it allows real time assessment of micromotion during the course of the analysis, as well as pre and post testing, potentially allowing a better assessment of micromotion early in the loading process.

The information presented in this study is valuable in the sense that using real time of assessment of micromotion, the authors find that increasing superior glenoid wear leads to increasing superior micromotion early in the loading process.  There also appears to be some settling over time, but the issue failure of early bony integration, and its association to loosening over time, is a concern.  Surgeons should be aware of results of this study, and the potential risk of glenoid loosening with uncorrected superior glenoid wear.

When approaching superior glenoid wear, surgeons have three main options.

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How Can We Improve Accuracy in TSA?

Ian Byram, MD

Read complete study: Comparison of patient-specific instruments with standard surgical instruments in determining glenoid component position: a randomized prospective clinical trial

The authors of this randomized clinical study compared 15 anatomic total shoulder arthroplasties performed with patient-specific instrumentation to 16 aTSA cases performed with standard surgical instrumentation.  Preoperative three-dimensional CT scan images were utilized in both groups to plan the desired implant position, then postoperative CT scans were performed to measure the differences between the intended and actual glenoid implant position.  The authors reported improved accuracy of the PSI group with statistically significant decreases in mean deviation of inclination and medial-lateral offset as compared to the standard group. Mean deviation in version was 4.3° ± 4.5° for the PSI group as compared to 6.9° ± 4.4° in the standard surgical group (p=0.11), with significant improvement in version accuracy in patients with preoperative retroversion in excess of 16°. The authors conclude that surgical accuracy is improved by patient specific instrumentation when compared to standard surgical instrumentation, with greatest benefit occurring in patients with severe glenoid deformity.

As technology continues to progress, we will have increased opportunities to improve surgical accuracy in shoulder arthroplasty implant positioning.  These are exciting times, but it is our duty to balance cost and utility with progress.  The current study brings up several interesting points that impact my practice:

  1. Preoperative planning with three-dimensional imaging has greatly improved our knowledge and performance in glenoid implant positioning
  2. Intraoperative instrumentation and/or guidance does improve accuracy
  3. The desired correction of retroversion remains undetermined

By preoperatively templating, I can more reliably enact a surgical plan to meet the needs of my patients, and this should be considered standard of care in shoulder arthroplasty.

Regarding preoperative planning, I routinely obtain preoperative CT scans with three dimensional reconstructions on nearly all shoulder arthroplasty candidates.  The arthritic glenoid does not wear in two dimensions but often with subtle variations that may not be obvious on axillary radiographs or even axial CT cuts alone.  By preoperatively templating, I can more reliably enact a surgical plan to meet the needs of my patients, and this should be considered standard of care in shoulder arthroplasty. In patients with a central wear pattern that have already obtained an MRI to assess the integrity of the rotator cuff I will consider planning based on this study alone, but this is generally only for cost purposes or patient convenience.

With regard to the second point, this study shows how intraoperative guidance can improve accuracy in glenoid positioning, with the greatest benefit seen in patients with severe deformity.  It has been shown numerous times that anatomic placement of implants leads to improved clinical outcomes in shoulder arthroplasty. Intraoperative guidance can be in the form of PSI (as seen in this study), custom implants, or computer guided intraoperative navigation.  In my practice, I have begun to implement CT guided navigation for glenoid implantation.  PSI and computer navigation both offer the ability to improve accuracy, but PSI does not allow for intraoperative corrections such as conversion to reverse arthroplasty or difficulty applying the PSI guide due to anatomical constraints.  In this study, 3 of the 44 patients initially enrolled for anatomic TSA underwent reverse TSA, eliminating them as candidates for PSI.

As an example, the following case is a 67 year old male with a retroverted glenoid and intact rotator cuff based on exam and preoperative imaging.

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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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