Wednesday, October 11, 2017

Patient specific instrumentation - does it add value to total shoulder arthroplasty?

Patient-specific instrumentation for total shoulder arthroplasty: not as accurate as it would seem

These authors sought to assess the effectiveness of total shoulder arthroplasty patient-specific instrumentation in improving positioning of the glenoid component.

Eleven consecutive TSAs (7 TSAs and 4 reverse TSAs) were performed using custom-made patient-specific positioning guides for the glenoid component using the Biomet Comprehensive TSR/PSI Glenoid. Preoperatively, each patient had a CT scan of the affected shoulder with the pre-established protocol using the Zimmer Biomet PSI Shoulder Planner software (Biomet). This protocol comprised coronal and sagittal localizers and high-resolution axial scans performed using an Aquilion PRIME 160-slice CT scanner. These data were then used to create a patient-specific positioning guide for the glenoid  component of the TSA. The guides were produced to allow 0° of glenoid inclination and version in anatomic TSAs and 10° of inferior inclination for reverse TSAs.

Preoperative glenoid types and versions are shown here

At one year after surgery for the conventional TSA group, the mean version was measured at 8° ± 10° retroversion and 1° ± 4° inclination. For reverse TSAs, mean version was 10° ± 10° retroversion and –1° ± 5° inclination. There were 5 cases classified as outliers in terms of version (>10° anteversion or retroversion). They observed a mean correction of version of 22° ± 9° and 17° ± 9° in inclination compared with preoperative measurements.

In their discussion, the authors provide a candid assessment of some of the issues regarding patient specific instrumentation in this group of shoulders with higher degrees of preoperative retroversion. Despite large corrections toward template neutral (or –10° inclination for reverse TSA), they were unable to fully correct the existing glenoid slope. They questioned the benefit of aiming for a neutral version in an anatomically retroverted glenoid. They found that this patient specific guidance system did not allow controlled reaming, and so the depth of central guidewire placement was variable. Shallow guidewire placement could result in toggle and thus less accurate reaming and implantation. Finally, despite the use of guides that were custom designed to fit each patient, they did not know whether the obliquity of bone loss at the glenoid articular surface allowed slight loss of positioning during reaming and thus malpositioning. 

We are left with the question of the value of patient specific instrumentation. What is the incremental cost of its use? What is its effect on operating time? For which surgeons and for which patients might it be of benefit? What is the learning curve for use of this approach? And most importantly, what is its benefit in terms of improved clinical outcomes for the patient?

We've included below a reprise of a prior post demonstrating that routine "correction" of glenoid version, preoperative CT scans, and patient specific instrumentation may not be necessary in total shoulder arthroplasty.

A 76 year old man presented to us with severe right shoulder pain, stiffness and the x-rays shown below. While his AP view suggested straightforward osteoarthritis

his axillary, 'truth' view showed what is known as the 'severe arthritic triad': glenoid retroversion, glenoid biconcavity, and posterior decentering of the humeral head on the glenoid. No CT needed to define the pathoanatomy!

He elected to proceed with a total shoulder using a standard glenoid component. At surgery we reamed the glenoid to a single concavity without trying to change glenoid version. We used an anteriorly eccentric humeral component and a rotator interval plication to optimize posterior stability. Immediately after surgery he was started on the standard total shoulder rehabilitation program with continuous passive motion and assisted flexion. At six weeks he started the supine press and active flexion.

At four months he has a comfortable shoulder, no problems with instability, active flexion over 120 degrees, and is continuing his rehab.

His four month films are shown below.

While this is very short term followup, it does demonstrate that immediate postoperative glenohumeral stability can be achieved with this approach. To date we've not had problems with posterior instability using a standard glenoid component inserted in retroversion.

See also:
Does Postoperative Glenoid Retroversion Affect the 2-Year Clinical and Radiographic Outcomes for Total Shoulder Arthroplasty?
That study analyzed the two year outcomes in 71 TSAs, comparing the 21 in a "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 results in the retroverted group were not inferior to those for the non-retroverted group. 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).

In conclusion, 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 managing this glenoid retroversion commonly found in osteoarthritic glenohumeral joints using posterior glenoid bone grafts, reaming the anterior aspect of the glenoid, and posteriorly augmented glenoid components. The first study reviewed above reports the result of shoulders managed by altering the glenoid version with a posterior humeral head autograft. The second study reviewed above 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:

Information about shoulder exercises can be found at this link.

Use the "Search" box to the right to find other topics of interest to you.