CT-Based Intraoperative Navigation for Glenoid Placement in TSA

Moby Parsons, MD

3D imaging technology has led to a much better understanding of glenoid morphology and how it is affected by the wear process in shoulder arthritis. The pathologic triad as described by Matsen1 (1. posterior humeral subluxation; 2. increased glenoid retroversion; 3. biconcave glenoid) is encountered in many arthritic shoulders. Other wear patterns like superior erosion may also commonly occur in certain conditions like cuff tear arthropathy. One of the principle goals of shoulder replacement, whether anatomic or reverse, is to recognize and correct pathologic glenoid deformity as failure to do so may risk premature loosening of the glenoid implant due to abnormal loading mechanics.

Unfortunately, even experienced shoulder surgeons do a poor job in correcting glenoid erosion. A meta-analysis by Sadoghi et al demonstrated an average error in glenoid correction of +/- 11 degrees2. Other research by Iannotti et al showed an angular variability of 10 degrees in pin placement using a free-hand technique3.

Advanced CT imaging has allowed surgeons to preoperatively plan the placement of the glenoid component with the goal of correcting pathologic version, minimizing bone loss and preventing penetration of the glenoid vault.

This lack of precision is no longer acceptable given today’s technology. Advanced CT imaging has allowed surgeons to preoperatively plan the placement of the glenoid component with the goal of correcting the pathologic version, minimizing bone loss and preventing penetration of the glenoid vault. As many systems now offer augmented glenoid implants, such systems also allow selection of the optimal implant for each given case. Research looking at the ability of surgeons to recreate a preoperative plan using conventional, free-hand instruments compared to surgical navigation has been performed. The results demonstrate that even with planning, a surgeon’s ability to execute that plan remains very inaccurate. The scatter plot above shows the range of implantation variability without navigation in blue compared to with navigation in orange. These results clearly show that eye-balling it in the operating room is no longer acceptable with today’s technology.

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My Experience with Trabecular Metal-Backed Glenoids

Ian Byram, MD

Read complete study: Outcomes of Trabecular Metal-backed glenoid components in anatomic total shoulder arthroplasty.

The authors of this study present a series of 47 total shoulder arthroplasties performed with trabecular metal-backed glenoid components, reporting radiographic and clinical outcomes at an average follow-up of 41 months.  The operative technique described involved placement of a trabecular metal peg-keel construct, with the vast majority placed in an uncemented, press-fit fashion.  The authors noted that this method of implantation is not approved by the FDA, but this technique is “acceptable practice.”  Patients were placed into a sling for four weeks and external rotation was limited for six weeks.

Five of the 47 patients (11%) underwent revision to reverse TSA for rotator cuff failure at an average of 12 months postoperative and were not included in the radiographic analysis.  Despite excluding these patients, the authors still report an alarming rate of metal debris and osteolysis (25%) with one catastrophic failure at a minimum of two years follow-up.  Notably, the majority of patients with radiographic changes were asymptomatic.  For all revisions in this series, the authors note the “substantial central bone loss” in the glenoid vault, requiring bone grafting for reverse baseplate implantation.  As a result of the high rate of metallic debris and osteolysis, the authors have discontinued the use of the trabecular metal glenoid.

“The authors still report an alarming rate of metal debris and osteolysis (25%) with one catastrophic failure at a minimum of two years follow-up.

For a short period of time in my practice, I utilized this same trabecular metal backed glenoid.  Preparation for this implant requires perpendicular glenoid exposure and removal of bone from the central glenoid vault in a cross shape with a series of drill holes and punches.  In my experience revising this implant, I also have noted severe central bone loss requiring bone grafting and occasional staged reconstruction.

Similar to the authors of this study, I had one catastrophic failure in a 50 year old male with normal bone density and no comorbidities.  Continue reading

How Do I Manage Glenoid Bone Loss?

Read complete study: Bone Graft Augmentation for Severe Glenoid Bone Loss in Primary Reverse Total Shoulder Arthroplasty

Kaveh R. Sajadi, MD

Following the legacy of hip and knee replacements in relieving pain and improving function for patients with arthritis, shoulder replacements are now the fastest growing joint replacement. Shoulder replacements reliably improve the quality of life for most patients and approximately 85% are still in place 15 years later. The leading cause of failure is loosening of the component on the glenoid side of the shoulder. Minimizing this improves longevity and outcomes.

Shoulder arthritis is often characterized by significant glenoid bone loss. Classically, primary arthritis is associated with posterior glenoid wear, while rotator cuff tear arthropathy leads to superior glenoid wear. To minimize the risk of glenoid loosening, it is important to restore glenoid alignment and version and obtain secure fixation. The surgeon may be faced with managing diminished bone stock or significant deformity to achieve these goals. The primary options for managing bone loss on the glenoid side are eccentric reaming, bone grafting, and augmented glenoid implants.

In “Bone Graft Augmentation for Severe Glenoid Bone Loss in Primary Reverse Total Shoulder Arthroplasty,” Dr. Lorenzetti and his coauthors have reported their outcomes with one of these approaches, bone grafting, in conjunction with reverse shoulder arthroplasty.  The authors had two goals: first, to determine the outcome of reverse arthroplasty when bone grafting was performed as part of a primary procedure; second, to correlate outcomes with the amount of native bone support at implantation. They conducted a retrospective of 57 patients with minimum 2-year follow up who had this procedure done.

In addition, they used CT scans preoperatively and plain radiographs postoperatively to measure the degree of bone loss and the amount of native bone support under the glenoid baseplate. Replacements were performed for rotator cuff tear arthropathy, rheumatoid arthritis, osteoarthritis, and chronic dislocations. Due to the diversity of diagnoses, the wear pattern varied.  ASES, Simple Shoulder Test, VAS pain and function scores, and patient satisfaction were assessed at minimum 2-year follow up.

Intraoperative decision making determined that if at least 80% of contact could not be achieved between the baseplate and native glenoid, bone grafting was utilized. When available and of sufficient quality, humeral head autograft was preferentially used. Otherwise, femoral head allograft was chosen. Virtual models of the bone and implant were created based on preoperative CT and postoperative x-rays and used for virtual implantation to determine the baseplate contact with native bone, which was reported as a percentage of total surface area available. A previously performed cadaveric study was used as a validation for this virtual technique.

The authors reported significant improvements in ASES scores, patient satisfaction, simple shoulder test, range of motion, and pain scores. Further, they documented graft incorporation in 98% of patients. The mean contact area percentage of the implant on native bone was 17%. They did not find an association of outcome with bone contact area.

I commend the authors on their technique and outcomes. Their high incorporation rate and low failure rate show that bone grafting for significant glenoid defects is a successful technique. It is important to consider some factors not specifically mentioned though.

First, restoration of normal glenoid alignment is an important goal of reverse arthroplasty, and the authors do not report pre- or postoperative version. Second, graft preparation and sizing should optimize this restoration and shaping the glenoid bone graft can be challenging. Finally, although contact with native bone is measured, the amount of fixation of the implant into native bone is not described. The implant must make significant purchase, generally a centimeter or more, in the native glenoid, often through the graft, to achieve stable fixation. Having a long central post/cage or screw facilitates this.

I have performed this technique with success as well. The pictures below are of a 71-year-old gentleman with a Walch B2 glenoid with approximately 25 ° of posterior glenoid wear. I chose to use humeral head autograft with a long central post implant to insure fixation in native bone. Preoperative and postoperative imaging are included.

Pre-op

Post-op

While this paper describes one particular method, it is important to remember there are other ways to manage glenoid bone loss.  Continue reading

What Is the Best Option for Addressing Difficult Glenoids with Implants?

Curtis Noel, MD

Read complete study: Total shoulder arthroplasty for glenohumeral arthritis associated with posterior glenoid bone loss: results of an all-polyethylene, posteriorly augmented glenoid component

The authors reported on 19 patients with 20 total shoulders with minimum two-year follow-up using an augmented glenoid component. They hypothesized the need for augmented glenoids as a way to save bone and prevent medializing the joint line. The average follow-up was 36 months, and the average pre-op retroversion to be corrected was 23.5⁰. The study showed significant improvements in forward elevation and external rotation, while also showing improvements in the SF36 physical form. The implant used in this study was an all-polyethylene, step-cut glenoid with an “anchor peg” for bone growth, in which 12 of the 19 patients showed osseus integration. The conclusion of the authors was that the short-term results are promising for these augmented glenoids, but further research needs to be completed.

Literature Review:

I agree with these authors, and others, on the need to address retroversion in total shoulder arthroplasty. Treating the retroverted glenoid is challenging. For these B2 and B3 glenoids, surgeons have limited options. We know that implanting the glenoid in retroversion is not a good option as it increases the edge loading and leads to early loosening and failure. Reaming down the high side and placing a ‘standard’ glenoid can medialize the joint line and places the implant on subcortical bone, which is also not ideal. Using an anatomic total shoulder with an augmented glenoid implant is an attractive option, as it allows the placement of the implant on more solid bone and maintains the joint line. A final option is placing a reverse total shoulder, which may be the best option for some patients.

I currently prefer a wedge augmented glenoid component, instead of a step-cut implant. In my hands, the wedge glenoid is easier to implant and is more bone preserving.

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Patient-Specific Guides with a Custom Implant: Is This a Practical Solution?

Joseph Zuckerman, MD

Read complete study: A patient Specific guide for Optimizing custom made glenoid implantation in cases of severe glenoid defects.

These authors studied the ability to implant a custom glenoid component in 10 cadaver glenoids with glenoid defects using patient-specific guides and traditional non-guided techniques. The use of the patient-specific guide reduced angular deviations from the plan and significantly improved the position and length of the screw placements when used to implant the custom made glenoid components.

Literature Review:

The authors have focused on a well-known challenge in shoulder arthroplasty – treatment of the deformed glenoid during anatomic or reverse shoulder arthroplasty. There is no doubt that two approaches canbe developed to address this issue. The first is the use of patient-specific guides (or intraoperative positioning devices) to improve the accuracy of component placement. We all recognize that a properly placed glenoid component will have longer-term survival than a malpositioned component. The second approach is to have non-standard glenoid components available to address the deformity. These can be either custom-made implants specific for the patient being treated or augmented “off the shelf” implants that address the common deformities encountered.

I have found that using non-custom or “off the shelf” augmented glenoid components have addressed many of the bone-loss issues I have encountered.

The authors actually combine both approaches – they use a custom implant with a specimen-specific guide. This could be perceived as the “best of both” but in actuality it is quite impractical from a cost perspective. The incremental cost of a custom implant combined with a CT-generated, patient-specific guide would add significant incremental cost. In 2016, regardless of where the surgery is being performed in the world, it is a surgeon’s responsibility to consider cost, especially in the context of cost vs. potential benefit. In addition, the FDA has been very strict on the use of custom implant components, which leaves us surgeons limited options for this approach. Continue reading