Do 3 dimensional CT scans add value to the care of patients with shoulder arthritis?

“This article was published in Journal of Shoulder and Elbow Surgery, Vol 27, William J. Mallon, MD, Einstein, 3 Dimensions, and Chainsaws, 577-578, © Journal of Shoulder and Elbow Surgery Board of Trustees (2018).” The publisher and author have kindly allowed us to reproduce it in its entirety here.

Einstein, 3 Dimensions, and Chainsaws (link)
by William J. Mallon, MD Editor-in-Chief Journal of Shoulder and Elbow Surgery Hilton Head Island, SC, USA

I have little patience with scientists who take a board of wood, look for its thinnest parts, and then drill holes where drilling is easy.—Albert Einstein

Although I eventually attended medical school, my own academic training was in mathematics and physics in college, with research done my senior year in general relativity and tensor analysis, which often involves studying motions in 4 dimensions, and learning about many of the teachings of Albert Einstein.

This was good training for my position as editor-in-chief of the Journal of Shoulder and Elbow Surgery over the last year, because of the proliferation of articles we now receive that do 3-dimensional (3D) studies, usually via computed tomography (CT) scans. Many of these articles analyze the anatomy of the shoulder or elbow, comparing that analysis when done using 2-dimensional (2D) CT scans versus 3D CT scans. Invariably, the 3D analysis is shown to be superior al- though often by very fine margins.

My standard response, when I initially read these sub- missions, is something like “No s—.” Just as Einstein’s 4-dimensional space-time improved upon Newton’s 3D analysis of motion, providing better precision, so we would expect 3 dimensions to show us things about shoulder anatomy that 2 dimensions may miss.

However, we live in Newton’s world, for the most part, and not Einstein’s. Einstein’s 4 dimensions are only necessary at the very small, at the atomic level; the very large, such as black holes; or the very fast, at speeds approaching the speed of light. On planet Earth, Newton’s laws suffice almost in- variably for us to obtain adequate precision in our measurements.

And it seems to me that 2 dimensions likely also suffice in preoperative planning of shoulder anatomy, with rare exception. The old bromide about orthopedic surgeons “Measure with a micrometer, mark it with a piece of chalk, and cut it with a chainsaw” is humorous, but the reason is that, like all humor, there is an element of truth to it.

Many of the 3D studies we receive show differences between 2 dimensions and 3 dimensions of only a few degrees, often as small as 1°-2°, and some of the studies of the glenoid have only shown this difference in certain planes, such as the superior or inferior portions. Does that make a clinical difference in our surgery or how we treat patients? I think it usually does not. During surgery, can we even tell the difference between a glenoid that is retroverted 11° versus one that is retroverted 9°? If we can, how accurate is the cut we make or planing of the glenoid? Can we actually get that accurate to within 1°-2°?

Furthermore, does using 3D analysis in preference to 2D make any difference in outcomes, even if the surgery can be done as accurately as the 3D analysis asks of you? If it does, I have not seen those articles yet, because clinical outcome studies using 3D radiographic analysis have not yet been done.

We also live in a medical world that is now emphasizing cost containment, and this is not just in the United States but worldwide. What about the costs of doing these 3D analyses? How much does the software cost? This is rarely mentioned, although one recent article noted that it was very expensive. While the cost may not be much when amortized over many clinical studies, there is still a cost element that should be studied, and for our journal, it has not been.

Finally, in this world of cost containment, we often use the value equation, in which Value = Outcome/cost. So, we do not have studies showing that 3D analysis provides superior clinical outcomes to 2D, and the cost is rarely mentioned, yet when it is, it is more costly. As such, we have no information about what this analysis does to the value equation, although given the increased costs, it likely decreases the value. We really do not know because none of the studies submitted have yet mentioned this.

So why are these studies done? I think it is because of Einstein’s admonition that these are relatively easy studies to do, so the authors have been drilling holes in boards simply because they have a drill (3D software) and drilling is easy.

What are we to do about this? As editor, I have to make decisions about which papers we will review, and which we will not, and eventually make decisions about which of those we review will be accepted. I am going to say “stop” at this point on 3D studies unless they provide us with more information than simply showing that 3D CT scans are more accurate in defining anatomy than 2D. If I am wrong that 2 dimensions suffice in preoperative planning of shoulder anatomy, prove it to us.

Here is my new policy on 3D studies of shoulder or elbow anatomy: Submit them all you like, but be forewarned that the studies are now required to provide cost information and outcome information, comparing 3D and 2D analysis using clinical outcomes. If they do not contain this information, they will not be reviewed.

Comment: In this editorial, the author has asked the critical question about new technology, "Does that make a clinical difference in our surgery or how we treat patients?" We live at a time when it is easy to make more measurements, but these measurements may cost more in terms of time, money and radiation exposure. In our practice, we find that for almost all cases we can gather the information needed for the management of a shoulder with glenohumeral arthritis from a standardized axillary view as shown below (see this link).

As suggested in the editorial, the burden of proof would seem to fall on those advocating more complex, more costly methods of assessment of glenohumeral pathoanatomy: do they lead to better patient outcomes?

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Arthritic glenoid anatomy - what information do we need to plan surgery?

A statistical shape model to predict the premorbid glenoid cavity

These authors were interested in inferring the "premorbid" glenoid shape and orientation of scapulae affected by glenohumeral osteoarthritis (OA) to inform restorative surgery.

They used a statistical shape model (SSM) built from 64 healthy scapulae to reconstruct the "premorbid" glenoid shape based on anatomic features that are considered unaffected by OA. First, the method was validated on healthy scapulae by quantifying the accuracy of the predicted shape in terms of surface distance, glenoid version, and inclination. 

The SSM-based reconstruction was then applied to 30 OA scapulae. Glenoid version and inclination were measured fully automatically and compared between the original OA glenoids, SSM-based glenoid reconstructions, and healthy scapulae.

Validation on healthy scapulae showed a root-mean-square surface distance between original and predicted glenoids of 1.0 ± 0.2 mm. The prediction error was 2.3° ± 1.8° for glenoid version and 2.1° ± 2.0° for inclination. In other words the model based on healthy scapulae can predict the glenoid position in healthy scapulae.

When applied to an OA dataset, SSM-based reconstruction "restored" average glenoid version and inclination to values similar to the healthy situation. 

The authors concluded that the SSM can predict the "premorbid" glenoid cavity of healthy scapulae with millimeter accuracy. They claim that this technique has the potential to reconstruct the "premorbid glenoid cavity shape, as it was prior to OA, and thus to guide the positioning of glenoid implants in total shoulder arthroplasty."

Comment: While this is an interesting methodology, it may not be completely accurate to state that the model recreates "premorbid" anatomy; for patients with OA we cannot assume that their anatomy was "normal" prior to the development of arthritis. For example, increased "premorbid" retroversion may predispose the shoulder to arthritis.

Secondly (see below) the average deviation of the arthritic anatomy from "normal" is small (6 degrees or less) and the variation among subjects is in many cases greater than the mean value. Are the differences among glenoid types clinically significant?

Thirdly, one must be cautious about suggesting that such measurements should "guide the positioning of glenoid implants in total shoulder arthroplasty." Take for example the B3 glenoid that had 22 degrees of retroversion, yet, by definition, had the humeral head centered in the glenoid (see below)

Is it reasonable to suggest that the glenoid version should be "corrected" by 22 degrees? If so, by what means, anterior reaming, bone graft, posteriorly augmented glenoid component, or reverse total shoulder?

Fourthly, what is the added cost and time necessary to perform this type of modeling in comparison to obtaining a standardized axillary view (see this link). For which patients would this technology be cost-effective?

Finally, how important is "correction" of glenoid version? See the abstract below which addresses the question, Does Postoperative Glenoid Retroversion Affect the 2-Year Clinical and Radiographic Outcomes for Total Shoulder Arthroplasty?

Background: 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.
Questions/Purposes: In a population of patients undergoing TSA in whom no specific efforts were made to change the version of the glenoid, we 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. 

Methods: Between August 24, 2010 and October 22, 2013, information for 201 TSAs performed using a standard all-polyethylene pegged glenoid component were entered in a longitudinally maintained database. 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. These 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, or history of prior surgery from those included in the analysis. Preoperative retroversion measurements were available for 11 (11 shoulders) of the 22 excluded patients. For these 11 shoulders, the mean (± SD) retroversion was 15.8° ± 14.6°, five had less than 15°, and six had more than 15° retroversion. We analyzed the remaining 71 TSAs, comparing the 21 in which the glenoid component was implanted in 15° or greater retroversion (mean ± SD, 20.7° ± 5.3°) with the 50 in which it was implanted in less than 15° retroversion (mean ± SD, 5.7° ± 6.9°). At the 2-year followup (mean ± SD, 2.5 ± 0.6 years; range, 18–36 months), we determined the latest SST scores and preoperative to postoperative improvement in SST scores, the percentage of maximal possible improvement, glenoid component radiolucencies, posterior humeral head decentering, and percentages of shoulders having revision surgery. Radiographic measurements were performed by three orthopaedic surgeons who were not involved in the care of these patients. The primary study endpoint was the preoperative to postoperative improvement in the SST score. 

Results: With the numbers available, 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 mean difference in improvement between the two groups was 0.9 (95% CI, − 2.5 to 0.7; p = 0.412). 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 mean difference between the two groups was 3% (95% CI, − 18% to 12%; p = 0.857). 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. With the numbers available, 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). With the numbers available, 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). 

Conclusion: In this small series of TSAs, postoperative glenoid retroversion was not associated with inferior clinical results at 2 years after surgery. This suggests that it may be possible to effectively manage arthritic glenohumeral joints without specific attempts to modify glenoid version. Larger, longer-term studies will be necessary to further explore the results of this approach.

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Glenoid components can shift position after total shoulder arthroplasty

Sequential 3-dimensional computed tomography analysis of implant position following total shoulder arthroplasty

These authors sought to evaluate glenoid component position over time using 3-dimensional computed tomography (CT) analysis with minimum 2-year follow-up in 20 patients having primary TSA. 

Fourteen patients had a standard anchor peg glenoid component and 6 had a posteriorly augmented glenoid component (Global STEPTECH).

Each patient had a CT scan of the shoulder before surgery, within 2 weeks of surgery, and at a minimum of 2-years after surgery. 7 of the 20 glenoids showed evidence of component shift and/or grade 1 central peg osteolysis on the third scan were considered at risk of loosening: 6 had component shift (3 with increased inclination alone, 1 had increased retroversion alone, and 2 had both increased inclination and retroversion). 

Significantly more patients with glenoid component shift had grade 1 central peg osteolysis compared with those without shift (83% vs 7%, P = .002). One clinical failure occurred, with the patient undergoing revision to reverse TSA for rotator cuff deficiency. 

As shown in the table below, more severe types of glenoid pathology did not have a greater chance of being at risk

of the 11 Walch type A glenoids, 4 (36%) were at risk

of the 5 Walch B glenoids, 1 (20%) was at risk

of the 2 Walch C glenoids, none (0%) were at risk

of the 2 "other" glenoid types, both (100%) were at risk.

Of the 14 standard glenoid components 4 (29%) were at risk

Of the 6 StepTech posteriorly augmented glenoid components 3 (50%) were at risk.

This article demonstrates an intense (3 CT scans per shoulder) effort to evaluate the radiographic changes in the glenoid component after total shoulder arthroplasty. Interestingly, the results in 20 shoulders do not suggest that more severe forms of glenoid pathology are associated with a greater chance of the component being "at risk" and do not suggest that augmented glenoid components have less chance of the glenoid being at risk

While the paper suggests that sequential 3D CT imaging has the potential to be useful and clinically applicable for evaluating TSA component position over time, the cost, radiation exposure, and Human Subjects considerations would seem to limit this utility.

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Patient-specific instrument guidance - is it of value in shoulder arthroplasty?

Patient-specific instrument guidance of glenoid component implantation reduces inclination variability in total and reverse shoulder arthroplasty

These authors assessed the influence of 3-dimensional preoperative planning and patient-specific instrument (PSI) guidance of glenoid component positioning on its inclination in total shoulder arthroplasty (TSA) and reverse shoulder arthroplasty (RSA).
CoC
Thirty-six shoulder arthroplasties (12 TSAs, 24 RSAs) were analyzed, of which 18 procedures (6 TSAs, 12 RSAs) were executed using preoperative 3D planning and patient-specific guides to position the central guide pin for glenoid component implantation.

The inclination of the glenoid component was measured by 2 observers, using the angle between the glenoid baseplate and the floor of the supraspinatus fossa (angle β) on postoperative radiographs.

The results are shown in the table below.

Comment: As is the case for almost all articles describing the use of 3D planning software and patient-specific instrumentation, this report does not provide data on the cost, time or training needed for these complex technologies. As the table above and figure below comparing a non PSI reverse on the left to a PSI reverse on the right show, the apparent benefit of PSI can be subtle.

We find that the optimal position of the glenoid component depends in large part on the arthritic anatomy and the quality of the bone available to support the prosthesis. To us this seems a higher priority than trying to align the prosthesis with a line drawn through the floor of the supraspinus fossa

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MRI imaging of cuff tears - is 3D imaging worth it?

Rotator cuff tear shape characterization: a comparison of two-dimensional imaging and three-dimensional magnetic resonance reconstructions

These authors performed a retrospective review of 34 patients with arthroscopically proven full-thickness rotator cuff tears which were classified by the surgeons with respect to tear shape:  crescent, longitudinal, U- or L-shaped longitudinal, and massive type. 

Two musculoskeletal radiologists reviewed the corresponding MRI studies to characterize the shape on the basis of the tear's retraction and size using 2D MRI. 3D reconstructions of each cuff tear were reviewed by each radiologist to characterize the shape. 

The accuracy for differentiating between crescent-shaped, longitudinal, and massive tears using measurements on 2D MRI was 70.6% for reader 1 and 67.6% for reader 2. The accuracy for tear shape characterization into crescent and longitudinal U- or L-shaped using 3D MRI was 97.1% for reader 1 and 82.4% for reader 2. When further characterizing the longitudinal tears as massive or not using 3D MRI, both readers had an accuracy of 76.9% (10 of 13). The overall accuracy of 3D MRI was 82.4% (56 of 68), significantly different (P = .021) from 2D MRI accuracy (64.7%).

Comment: "The authors assert that the shape of a rotator cuff tear can play an important role in the surgeon’s approach and election to repair as well as in the likelihood of clinical success after the repair. Having this information before surgery is useful to the surgeon as it will permit more complete surgical planning and allow the surgeon to provide prognostic information to the patient based on the surgical success of certain shaped tears.The accurate determination of the shape of the tear could also help in deciding whether the tear is reparable as well as if it would be worthwhile to proceed with surgery. In addition, a correctly defined tear shape could help determine if there is enough tendon tissue remaining to allow marginal convergence during the repair."

In trying to determine the value of the 3D reconstructions we need to know (1) whether the 3D images were predictive of the reparability of the cuff defect in these 34 patients (in other words, was the rationale proposed in the quote above demonstrated in this group of patients)? and (2) what was the incremental cost in terms of time and money for the 3D reconstructions?

It is always tempting to apply high levels of technology, but higher tech is higher cost. However, unless the increased cost produces better results for the patient, we may want to spend our precious health care on something more valuable.

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