Saturday, September 20, 2014

Patient specific guides for glenoid placement, is the benefit worth the cost and time?

Three-dimensional planning and use of patient-specific guides improve glenoid component position: an in vitro study.

These authors performed CT scans on 18 cadaver scapulae, "virtually" placed glenoid components, and then created cadaver-specific guides for positioning a guide pin used for glenoid placement. After placement, a second CT scan was performed to compare the planned to the actual pin position. The actual placement was close the the planned placement.

For us and for many surgeons, standard total shoulder practice is to assess preoperative glenohumeral pathoanatomy using standardized axillary radiographs and to fit the glenoid prosthesis to the bone using conservative reaming and conventional guides for drill hole placement, tailoring component position to balance stability of the articulation with quality bone support for the glenoid prosthesis. Guide pins are avoided because of the concern for breakage or inadvertent advancement toward the thorax during reaming. 

While it is recognized that shoulders with the bad arthritic triad create difficulties for the arthroplasty surgeon and have on average poorer results than those shoulders without glenoid retroversion, posterior humeral subluxation and biconcavity, it has yet to be demonstrated that 'normalizing' glenoid version or the use of posteriorly augmented glenoid components improves the clinical outcomes for patients.

Against this background, some have advocated the use of 3-D scans, reconstructions, and the use of proprietary software to create patient specific instruments to guide the placement of a glenoid guidepin in a position that will change the glenoid version toward that found in unarthritic shoulders. 

This study was performed in dry cadaver scapulae without arthritis and absent the presence of the humerus and the soft tissues we encounter at surgery. It did not proceed to study glenoid component implantation, but stopped at the point of guide pin positioning.

It is not clear whether additional surgical exposure is required to use this system. While the title suggests that patient specific guides 'improves' glenoid component position, there is no comparison of this method to other methods. The study does not indicate the added time, added cost of this approach,  or increased open wound time required for this method nor does it demonstrate its utility in intact shoulder specimens or in the performance of actual shoulder arthroplasty.

The bottom line is that the application of new technology needs to be justified by a documented benefit to the patient that offsets the cost, learning curve, and potential added risks in its use.

It is worthwhile to compare this paper to another recent one: Small Improvements in Mechanical Axis Alignment Achieved With MRI versus CT-based Patient-specific Instruments in TKA: A Randomized Clinical Trial.

These authors compared the accuracy of MRI- and CT-based patient-specific instrumentation with conventional instrumentation and with each other in total knees. The three approaches also were compared with respect to validated outcomes scores and duration of surgery.

They conducted a randomized clinical trial in which 90 patients were enrolled and divided into three groups of comparable patients: CT-based, MRI-based patient-specific instrumentation, and conventional instrumentation. Component rotation was measured on CT scans. 

Compared with conventional instrumentation MRI- and CT-based patient-specific instrumentation showed higher accuracy, but the differences were small. There were no differences in the postoperative Knee Society pain and function and WOMAC scores among the groups.

The authors conclude,  "Although this study supports that patient-specific instrumentation increased accuracy compared with conventional instrumentation and that MRI-based patient-specific instrumentation is more accurate compared with CT-based patient-specific instrumentation regarding coronal mechanical limb axis, differences are only subtle and of questionable clinical relevance. Because there are no differences in the long-term clinical outcome or survivorship yet available, the widespread use of this technique cannot be recommended."

In this vein, recommended reading is the spotlight and the Editorial "our love affair with technology and the choices we make'.  I quote the last sentence, " Finally, as surgeons, we need to be mindful when we use some new implant, technology, or approach as a practice-building move, and to do so only when we are certain – based on thoughtful reading and evaluation – that it really clears the bar in terms of safety and efficacy. If we cannot turn off the projector, let’s at least acknowledge that it is time to roll the credits.

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