CORR Insights®: Risk of Perforation Is High During Corrective Reaming of Retroverted Glenoids: A Computer Simulation Study

Where Are We Now?

With an aging population, the number of patients undergoing total shoulder arthroplasty is increasing. Whether these procedures will achieve our patients’ surgical goals depends in large measure upon addressing adequately the deformities that occur with osteoarthritis. Walch and colleagues [4] described three glenoid morphologies associated with primary glenohumeral arthritis. In Type A glenoids, the humeral head is centered within the glenoid cavity, which will have either minor (Type A1) or major (Type A2) central glenoid erosions. Type B1 glenoids present with a posteriorly subluxated humeral head, a narrowing of the posterior joint space, subchondral sclerosis, and osteophytes; Type B2 glenoids present with a posterior cupula resulting in a biconcave glenoid shape. Type C glenoids involve more than 25^o of glenoid retroversion and have a dysplastic origin. In Type C glenoids, the humeral head is centered or slightly posteriorly subluxated.

The posterior glenoid erosion seen with Type B glenoids increases with age and leads to an excess of glenoid retroversion and humeral head subluxation. The inability to correct this deformity prior to implantation may result in asymmetric glenoid implant wear, implant loosening, and posterior subluxation of the humeral head.

There are several options available for treating asymmetric glenoid wear, including asymmetric glenoid reaming, posterior bone grafting with internal fixation, specialized glenoid implants (posteriorly augmented glenoid component, custom implants, inset glenoid components), and other strategies (anterior capsular release, posterior capsulorrhaphy, altering humeral retroversion). Reverse shoulder arthroplasty can also be used in less-active patients.

In the current study, Aleem and colleagues [1] found that with anterior asymmetric glenoid reaming, those glenoids with > 25^o of retroversion have a higher risk of glenoid vault perforation by pegged glenoid components. Additionally, the most-severely retroverted glenoids also demonstrated decreased bone density after reaming in this computer-simulation study. With either situation, glenoid vault penetration and decreased bone density, the risk of glenoid loosening is potentially increased.

Where Do We Need To Go?

Most studies evaluating the treatment of the B2 glenoid are retrospective case series, which have shown mixed results concerning total shoulder arthroplasty in terms of functional outcomes and risks of complications [2, 3, 5]. The effect of glenoid vault perforation by the glenoid prosthesis is unclear, nor is it known whether there is a higher incidence of glenoid loosening or worsened clinical outcomes. In addition, the degree of glenoid vault penetration needed to affect clinical outcomes is unknown.

This paper reiterates the need for preoperative CT scans to adequately assess the degree of posterior glenoid wear and glenoid bone loss. These CT scans can aid in the preoperative planning process and may help determine which surgical procedure (asymmetric glenoid reaming vs. posterior glenoid bone grafting) and implant option (posteriorly augmented glenoid vs. in line pegged glenoid) to use for a particular patient. But as with any good study, several questions remain: Do surgeons need to correct the posterior glenoid retroversion, and if so, how much glenoid retroversion should be corrected? Are different implant designs associated with a differential risk of glenoid component loosening? Does glenoid vault perforation and poor bone quality increase the risk of implanted-related complications?

Finally, clinicians should honestly evaluate the implant designs they use. Do the implant’s features (such as in-line pegs, triangularly oriented pegs, keeled glenoids, or other design elements) really make a difference? A critical evaluation of existing systems would help identify the deficiencies of current designs, if any, and thus determine whether there is a need for future designs or modifications.

How Do We Get There?

It would be difficult to perform a randomized trial that addresses treating the B2 glenoid. Potential solutions to evaluate this problem include the use of a joint registry, use of CT scan software packages that evaluate multiple implant designs, and the critical evaluation of current and future glenoid implant designs.

A joint registry, such as the American Joint Replacement Registry, should be able to combine the results from multiple surgical sites, which could fill the gaps in our knowledge that remain. Combining the results from several centers could potentially address the questions raised above. The use of CT scan software packages that allow for templating of glenoid components on CT images, particularly three-dimensional CT images, may help clinicians understand the potential advantages and limitations of a particular implant design.