Is There a Role for PSI in Shoulder Arthroplasty?
Dr. John Sperling discussed research on the use of patient-specific instrumentation in anatomic shoulder arthroplasty at ICJR’s Pan Pacific Orthopaedic Congress. Following is the abstract of his presentation.
Patient-specific instrumentation (PSI) is becoming more popular in shoulder arthroplasty because unlike traditional instrumentation, PSI can account for glenoid wear patterns and thus improve component placement in anatomic version.
A primary goal of shoulder arthroplasty is to place the components in anatomic version. Traditional instrumentation, however, does not accommodate glenoid wear patterns. Many investigators, therefore, have attempted to use computer modeling or CT based algorithms to create custom targeting guides to achieve this goal.
Several recent studies have investigated the use of custom guides. A 2012 study by Iannotti et al  included 31 patients who were randomized into 2 groups:
- Glenoid positioning system group: Novel 3-dimensional CT scan planning software combined with patient-specific instrumentation
- Standard surgical group: Conventional CT scan, preoperative planning, and surgical technique
The authors found that the planning software and patient specific instrumentation were helpful overall, but were particularly beneficial in patients with retroversion in excess of 16°.  In this group of patients, the mean deviation was 10° in the standard surgical group and 1.2° in the patient specific instrumentation group. 
At the 2013 International Congress of Elbow and Shoulder Surgery, Potts et al presented a study on 18 cadaveric shoulders in which components were placed with patient-specific instrumentation. Placement was evaluated with postoperative CT scans. They found that the custom guides were more accurate in version and inclination than traditional instrumentation.
At the 2014 annual meeting of the American Academy of Orthopaedic Surgeons, Throckmorton presented a study on 70 cadaveric shoulders. The study included 1 high volume surgeon (>100 shoulder arthroplasties a year), 2 middle-volume surgeons (20-50 shoulder arthroplasties a year), and 2 low-volume surgeons (less than 20 shoulder arthroplasties per year).
Overall, the custom guide was significantly more accurate than standard instrumentation. In particular, the custom guides were found to be more accurate among specimens with associated glenoid wear. There were no strong trends to indicate consistent differences between high-, medium-, and low-volume surgeons.
The authors concluded that use of custom guides results in a narrower standard deviation and fewer significant errors than the use of standard instrumentation.
Custom guides continue to evolve for use in shoulder arthroplasty, including some guides that allow the surgeon to decide intraoperatively between anatomic shoulder arthroplasty and reverse arthroplasty. Additional studies will be necessary to further define the role of patient specific instrumentation in practice.
Dr. Sperling’s presentation can be found here.
- Hendel MD, Bryan JA, Barsoum WK, et al.Comparison of patient-specific instruments with standard surgical instruments in determining glenoid component position: a randomized prospective clinical trial. J Bone Joint Surg Am. 2012 Dec 5;94(23):2167-75. doi: 10.2106/JBJS.K.01209.