Saturday, July 22, 2017

Three Dimension Pre-Operative Planning and Patient Specific Instrumentation for Total Shoulder Arthroplasty

Three Dimension Pre-Operative Planning and Patient Specific Instrumentation for Total Shoulder Arthroplasty

These authors review several different types of patient-specific instruments that have been developed for glenoid placement in total shoulder arthroplasty.  Each of the reviewed approaches require three-dimensional (3D) pre-operative planning.  Patient specific instrumentation can be single use disposables or reusable instruments adjusted using a surrogate model of the glenoid containing the location of the guide-pin or by using an adjustable and reusable base having the location of the guide pin within the base. Each of these types of patient specific instruments have advantages related to use, cost of the technology and speed by which the technology can be delivered to the surgeon. The authors concluded that there has been no difference demonstrated to date related to accuracy of glenoid component placement using these PSI tools.

The authors state that 3D planning significantly improves the accuracy of glenoid bone preparation
and implant placement. All of these technologies still require the expertise of the surgeon to provide proper surgical exposure and clinical judgment. The technology improves the accuracy of glenoid implant placement, but does not solve the question of the best implant to use or the best location of that implant.

Comment: This is a review of some of the available approaches to three dimensional 3-D planning. As the authors point out, the instrumentation cannot determine which implant or what implant location is best for each patient. Such a decision requires the experienced judgment of the surgeon, who needs to incorporate observations on the quantity and quality of available glenoid bone, the amount of glenoid bone that would need to be removed to implement various component designs and positions, the humeral and soft tissue factors that help determine glenohumeral stability, and the specific demands of the patient.

Some key question are relevant:
(1) does changing glenoid version improve the clinical outcomes of shoulder arthroplasty?
(2) if glenoid version is to be changed, how can the surgeon optimize the balance between the amount of version change and the amount of glenoid bone sacrifice necessary to achieve that change?
(3) what is the incremental cost and time spent for 3D scans, 3D planning, and patient specific instrumentation over a set of plain films and conventional instrumentation?
(4) what is the incremental benefit to the patient of these 3D technologies in terms of clinical outcome?
(5) if these technologies are of incremental value (i.e amount of improvement in clinical outcome in comparison to conventional approaches/increase in cost in comparison to conventional approaches), which surgeons should use them for which patients? In other words, what would appropriate use criteria look like for these 3D technologies?
(6) is increased surgical exposure or increased surgical time required for these 3D technologies?
(7) what is the learning curve for these technologies?
(8) what are the complications associated with these technologies?

A recent post is relevant to this discussion:

Does Postoperative Glenoid Retroversion Affect the 2-Year Clinical and Radiographic Outcomes for Total Shoulder Arthroplasty?

While glenoid retroversion and posterior humeral head decentering are common preoperative features of severely arthritic glenohumeral joints, the relationship of postoperative glenoid component retroversion to the clinical results of total shoulder arthroplasty (TSA) is unclear. Studies have indicated concern for inferior outcomes when glenoid components are inserted in 15° or more retroversion.

In a population of patients undergoing TSA in whom no specific efforts were made to change the version of the glenoid, these authors asked whether at 2 years after surgery patients having glenoid components implanted in 15° or greater retroversion had (1) less improvement in the Simple Shoulder Test (SST) score and lower SST scores; (2) higher percentages of central peg lucency, higher Lazarus radiolucency grades, higher mean percentages of posterior decentering, and more frequent central peg perforation; or (3) a greater percentage having revision for glenoid component failure compared with patients with glenoid components implanted in less than 15° retroversion. They examined the records of  201 TSAs performed using a standard all-polyethylene pegged glenoid component

inserted after conservative glenoid reaming without specific attempt to modify preoperative glenoid version.

Of these, 171 (85%) patients had SST scores preoperatively and between 18 and 36 months after surgery. Ninety-three of these patients had preoperative radiographs in the database and immediate postoperative radiographs and postoperative radiographs taken in a range of 18 to 30 months after surgery. Twenty-two patients had radiographs that were inadequate for measurement at the preoperative, immediate postoperative, or latest followup time so that they could not be included. In comparison to those included in the analysis, the excluded patients did not have substantially different mean age, sex distribution, time of followup, distribution of diagnoses, American Society of Anesthesiologists class, alcohol use, smoking history, BMI,  history of prior surgery or preoperative glenoid version. They analyzed the two year outcomes in the remaining 71 TSAs, comparing the 21 in the retroverted group (the glenoid component was implanted in 15° or greater retroversion (mean ± SD, 20.7° ± 5.3°)) with the 50 in the non-retroverted group ( the glenoid component was implanted in less than 15° retroversion (mean ± SD, 5.7° ± 6.9°)). 

The mean (± SD) improvement in the SST (6.7 ± 3.6; from 2.6 ± 2.6 to 9.3 ± 2.9) for the retroverted group was not inferior to that for the nonretroverted group (5.8 ± 3.6; from 3.7 ± 2.5 to 9.4 ± 3.0). The percent of maximal possible improvement (%MPI) for the retroverted glenoids (70% ± 31%) was not inferior to that for the nonretroverted glenoids (67% ± 44%).  The 2-year SST scores for the retroverted (9.3 ± 2.9) and the nonretroverted glenoid groups (9.4 ± 3.0) were similar (mean difference, 0.2; 95% CI, - 1.1 to 1.4; p = 0.697). No patient in either group reported symptoms of subluxation or dislocation. The radiographic results for the retroverted glenoid group were similar to those for the nonretroverted group with respect to central peg lucency (four of 21 [19%] versus six of 50 [12%]; p = 0.436; odds ratio, 1.7; 95% CI, 0.4-6.9), average Lazarus radiolucency scores (0.5 versus 0.7, Mann-Whitney U p value = 0.873; Wilcoxon rank sum test W = 512, p value = 0.836), and the mean percentage of posterior humeral head decentering (3.4% ± 5.5% versus 1.6% ± 6.0%; p = 0.223). The percentage of patients with retroverted glenoids undergoing revision (0 of 21 [0%]) was not inferior to the percentage of those with nonretroverted glenoids (three of 50; [6%]; p = 0.251).

The authors concluded that in this series of TSAs, postoperative glenoid retroversion was not associated with inferior clinical results at 2 years after surgery. 

Comment:  Glenoid retroversion is a relatively common finding in arthritic glenohumeral joints coming to shoulder arthroplasty. Shoulders with preoperative glenoid retroversion tend to have poorer preoperative shoulder comfort and function, posterior decentering, and glenoid biconcavity, all indicating a more severe form of the disease. There is currently great interest in methods for altering this glenoid retroversion that is commonly found in osteoarthritic glenohumeral joints. Methods used include posterior glenoid bone grafts, reaming the anterior aspect of the glenoid, and posteriorly augmented glenoid components. This study reports the two year results of a more conservative approach in which minimal glenoid bone is removed by reaming and specific attempts to alter glenoid version are not used.

Here is the two year radiographic followup on a 55 year old patient from our practice. Preoperative films show a type B2 genoid with retroversion, biconcavity and posterior humeral subluxation.

Here are the 2 year films of this shoulder after conservative shoulder arthroplasty using a standard glenoid component without attempts to modify glenoid version. The humeral head is centered in the prosthetic glenoid. At two years after surgery the patient was able to perform all 12 functions of the Simple Shoulder Test.

Note that sufficient bone stock remains to perform a revision total or a reverse total shoulder arthroplasty shoulder these procedures become necessary in the future of this young person.

Long term followup of well-characterized patients treated with the different methods for managing glenoid retroversion will be required to define the relative risks, benefits, effectiveness and durability of each of them.

The reader may also be interested in these posts:

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