Abstract
Background
Accurate placement of the glenoid component in total shoulder arthroplasty (TSA) is critical to optimize implant longevity. Commercially available patient-specific instrumentation systems can improve implant placement, but may involve considerable expense and production delays of up to six weeks. The purpose of this study was to develop a novel technique for in-house production of 3D-printed, patient-specific glenoid guides, and compare the accuracy of glenoid guidepin placement between the patient-specific guide and a standard guide using a cadaveric model.
Methods
Twenty cadaveric shoulder specimens were randomized to receive glenoid guidepin placement via standard TSA guide (Wright Medical, Memphis, TN) or patient-specific guide. Three-dimensional scapular models were reconstructed from CT scans with Mimics 20.0 imaging software (Materialise NV, Leuven, Belgium). A pre-surgical plan was created for all specimens for the central glenoid guidepin of 0º version and inclination angles. Central pin entry and exit points were also calculated. Patient-specific guides were constructed to achieve the planned pin trajectory in Rhino3D software (Robert McNeel & Associates, Seattle, WA). Guides were 3D-printed on a Form2 printer with Formlabs Dental SG Resin (Formlabs, Somerville, MA). Glenoid labrum and cartilage were removed with preservation of other soft tissues in all specimens to mimic intraoperative TSA conditions. A fellowship-trained, board-eligible orthopaedic surgeon placed a 2.5 mm diameter titanium guidepin into each glenoid using the assigned guide for each specimen. After pin placement, repeat CT scans were performed, and a blinded measurer used superimposed 3D scapular reconstructions to calculate deviation from the pre-surgical plan in version and inclination angles, dot product angle, and guide pin entry and exit points. Student's t tests were performed to detect differences between pin placements for the two groups.
Results
Cadaver age, sex, and BMI did not differ between groups (p>0.05 for all). Average production cost and time for the patient-specific guides were $29.95 and 4 hours and 40 minutes per guide, respectively. Guidepin version deviation did not differ between the patient-specific and standard guides (1.59º ± 1.60º versus 2.88 º ± 2.11º, respectively, p=0.141). Guidepin inclination deviation was significantly lower in the patient-specific group (1.54º ± 1.58º versus 6.42º ± 5.03º, p=0.009), similarly the dot product angle was lower in the patient-specific compared to standard guide group (2.35º ± 1.66º versus 7.48º ± 4.76º, p=0.005). Glenoid entry site exhibited less deviation for the patient-specific compared to standard guide (0.75mm ± 0.54mm versus 2.05mm ± 1.19mm, p=0.006). Glenoid exit site also was closer to the target for the patient- specific compared to standard group (1.75mm ± 0.99mm versus 4.75mm ± 2.97mm, p=0.010).
Conclusion
We present a novel technique for in-house production of 3D-printed, patient-specific glenoid guides for TSA glenoid pin placement. These patient-specific guides improved pin placement accuracy based on 3D-CT measurements compared to standard TSA guides in a cadaveric model. Our patient-specific glenoid guides can be produced on-demand, in-house, inexpensively, and with significantly reduced time compared to commercially available guides. Future studies are required to validate these findings in clinical applications and determine the potential impact on implant longevity.
