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Scientific Articles   |    
Comparison of Patient-Specific Instruments with Standard Surgical Instruments in Determining Glenoid Component PositionA Randomized Prospective Clinical Trial
Michael D. Hendel, MD, PhD1; Jason A. Bryan, MS1; Wael K. Barsoum, MD1; Eric J. Rodriguez, BS1; John J. Brems, MD1; Peter J. Evans, MD, PhD1; Joseph P. Iannotti, MD, PhD1
1 Department of Orthopaedic Surgery, Orthopaedic and Rheumatologic Institute, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, OH 44195. E-mail address for J.P. Iannotti: iannotj@ccf.org
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Investigation performed at the Department of Orthopaedic Surgery, Orthopaedic and Rheumatologic Institute, Cleveland Clinic, Cleveland, Ohio



Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, one or more of the authors has had another relationship, or has engaged in another activity, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

Copyright © 2012 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2012 Dec 05;94(23):2167-2175. doi: 10.2106/JBJS.K.01209
5 Recommendations (Recommend) | 3 Comments | Saved by 3 Users Save Case

Abstract

Background: 

Glenoid component malposition for anatomic shoulder replacement may result in complications. The purpose of this study was to define the efficacy of a new surgical method to place the glenoid component.

Methods: 

Thirty-one patients were randomized for glenoid component placement with use of either novel three-dimensional computed tomographic scan planning software combined with patient-specific instrumentation (the glenoid positioning system group), or conventional computed tomographic scan, preoperative planning, and surgical technique, utilizing instruments provided by the implant manufacturer (the standard surgical group). The desired position of the component was determined preoperatively. Postoperatively, a computed tomographic scan was used to define and compare the actual implant location with the preoperative plan.

Results: 

In the standard surgical group, the average preoperative glenoid retroversion was −11.3° (range, −39° to 17°). In the glenoid positioning system group, the average glenoid retroversion was −14.8° (range, −27° to 7°). When the standard surgical group was compared with the glenoid positioning system group, patient-specific instrumentation technology significantly decreased (p < 0.05) the average deviation of implant position for inclination and medial-lateral offset. Overall, the average deviation in version was 6.9° in the standard surgical group and 4.3° in the glenoid positioning system group. The average deviation in inclination was 11.6° in the standard surgical group and 2.9° in the glenoid positioning system group. The greatest benefit of patient-specific instrumentation was observed in patients with retroversion in excess of 16°; the average deviation was 10° in the standard surgical group and 1.2° in the glenoid positioning system group (p < 0.001). Preoperative planning and patient-specific instrumentation use resulted in a significant improvement in the selection and use of the optimal type of implant and a significant reduction in the frequency of malpositioned glenoid implants.

Conclusions: 

Novel three-dimensional preoperative planning, coupled with patient and implant-specific instrumentation, allows the surgeon to better define the preoperative pathology, select the optimal implant design and location, and then accurately execute the plan at the time of surgery.

Level of Evidence: 

Therapeutic Level I. See Instructions for Authors for a complete description of levels of evidence.

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    References

    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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    Matthew Hamilton Ph.D.
    Posted on December 31, 2012
    Issues with the fitting technique
    Senior Product Developer, Exactech, Inc., Gainesville, FL, USA

    With the emergence of patient-specific instruments, comes an active debate in the shoulder community as to the risks and benefits of this technology. This Level I paper will no doubt play an important role in shaping the views of this technology going forward. As I read this paper, I noticed a discrepancy with the best-fit lines in Figure 5(a) and (b). It appears that these lines were not created using the standard least-squares regression method for a best-fit, but were constrained to cross the origin (0,0). The assumption inherent in this constraint is that a glenoid with zero retroversion will be placed perfectly by standard instrumentation and patient specific instrumentation. This is not supported by the data shown in the plots themselves, nor is it supported in previous studies of accuracy of implant placement. Figure 1 (not shown here due to technical constraints but sent to the authors of the article under separate cover) shows the original plots as presented in the journal (left side), and the identical plots with a best-fit line through the data using the least-squares methodology (right side). Table 1 (shown here) contains the calculated R2 values for these fits indicating that the published fit is not the best possible fit of the data. The fit greatly changes the apparent trends. The discussion section would not be changed, because the analysis showed no statistically significant difference for patients with less than 20° of preoperative retroversion. However, given these trends, it appears that standard instrumentation may have a more predictable result in patients with mild deformity. Without the original dataset, there is no way to confirm that the fit shown here is actually the best, but it is the best fit of the data published in the plots. I would ask that the authors justify the use of their fitting technique as the slope of the trend, particularly with version, is opposite of that obtained using a standard fitting technique.

    Table I
    Comparison of calculated R2 values for published fits vs. the traditional methodology for best-fit lines. A perfect fit is indicated by an R2 value of 1.0, so values closer to 1.0 are considered a better fit.


    Data Set

    Version Data
    Published Fit R2

    Version Data
    Best Fit R2

    Inclination Data
    Published Fit R2

    Inclination Data
    Best Fit R2

    Standard Instruments

    0.2174

    0.4206

    -1.284

    0.0231

    Patient Specific Instruments

    -0.64

    0.4219

    -0.149

    0.0005

    Figure 1 cannot be shown here, but has been sent to the senior author of the article.  The legend follows:

    Figure 1. (upper-left) Pre-operative Retroversion vs. Post-Operative Version Deviation with a trendline that passes through the origin. (upper-right) Pre-operative Retroversion vs. Post-Operative Version Deviation with a standard best-fit trendline. (lower-left) Pre-operative Retroversion vs. Post-Operative Inclination Deviation with a trendline that passes through the origin. (lower-right) Pre-operative Retroversion vs. Post-Operative Inclination Deviation with a standard best-fit trendline.

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