Patient-Specific Guides/Instrumentation in Shoulder Arthroplasty
TAKE-HOME POINTS
- Optimal outcomes following TSA and RSA are dependent on proper implant position.
- Patient-specific guides/instrumentation result in improved accuracy of implant positioning compared to traditional methods.
- Currently, there are no clinical studies demonstrating superiority of patient-specific guide/instrumentation use on patient outcomes.
- At this time there are 3 commercially available single use patient-specific instrumentation systems (DJO Global, Wright Medical Group, and Zimmer Biomet) and 1 commercially available reusable patient-specific instrumentation system (Arthrex).
- Limited research is available comparing the accuracy of different commercially available 3-D planning systems.
Optimal functional recovery and implant longevity following both total shoulder arthroplasty (TSA) and reverse shoulder arthroplasty (RSA) depend, in large part, on proper placement of the glenoid component. Glenoid component malpositioning has an adverse effect on shoulder stability, range of motion (ROM), impingement, and glenoid implant longevity.
Traditionally, glenoid component positioning has been done manually by the surgeons based on their review of preoperative films and knowledge of glenoid anatomy. Anatomic studies have demonstrated high individual variability in the version of the native glenoid, thus making ideal placement of the initial glenoid guide pin difficult using standard guide pin guides.1
The following 2 methods have been described for improving the accuracy of glenoid guide pin insertion and subsequent glenoid implant placement: (1) computerized navigation and (2) patient-specific guides/instrumentation. Although navigated shoulder systems have demonstrated improved accuracy in glenoid placement compared with traditional methods, navigated systems require often large and expensive systems for implementation. The majority of them also require placement of guide pins or arrays on scapular bony landmarks, likely leading to an increase in operative time and possible iatrogenic complications, including fracture and pin site infections.
This review focuses on the use of patient-specific guides/instrumentation in shoulder arthroplasty. This includes the topic of proper glenoid and glenosphere placement as well as patient-specific guides/instrumentation and their accuracy.
GLENOID PLACEMENT
Glenohumeral osteoarthritis is the most common indication for TSA2 and commonly results in glenoid deformity. Using computed tomography (CT) scans of 45 arthritic shoulders and 19 normal shoulders, Mullaji and colleagues3 reported that the anteroposterior dimensions of the glenoid were increased by an average of 5 mm to 8 mm in osteoarthritic shoulders and by an average of 6 mm in rheumatoid arthritic shoulders compared to those in normal shoulders. A retrospective review of serial CT scans performed preoperatively on 113 osteoarthritic shoulders by Walch and colleagues4 demonstrated an average retroversion of 16°, and it has been the basis for the commonly used Walch classification of glenoid wear in osteoarthritis. Increased glenoid wear and increased glenoid retroversion make the proper restoration of glenoid version, inclination, and offset during shoulder arthroplasty more difficult and lead to increased glenoid component malpositioning.
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