Reverse shoulder arthroplasty is the treatment of choice for rotator cuff tear arthroplasty. The success of the procedure depends largely on proper positioning and stable fixation of the glenoid component. Achieving the ideal position of the implant always remains a challenge to the operating surgeon. Various methods have been suggested to improve the initial fixation of the glenosphere intraoperatively. Even though computer navigation has shown encouraging results, it is associated with inherent difficulties and involves a significant learning curve. These difficulties may be overcome by the use of patient-specific instrumentation. The clinical utility and accuracy of patient-specific instrumentation has been studied in the setting of total shoulder arthroplasty. This article describes the use of patient-specific glenoid implant positioning guides in reverse shoulder arthroplasty. After a cadaveric pilot study, reverse shoulder arthroplasty was performed in 7 patients using the patient-specific guides. The patient-specific glenoid implant positioning system provides for preoperative planning on a virtual 3D model of the scapula derived from CT scan images. The accuracy of the patient-specific guides was determined by comparing the postoperative version and inclination of the implant with the preoperatively planned values. The mean native version of the glenoid was 5.2 degrees of retroversion (range, + 0.8 to À 14.38 degrees; SD = 5.3) and mean native inclination was 12.25 degrees of superior tilt (range, 8.07 to 18.24 degrees; SD = 4.04). The mean version of the glenoid component as chosen in the preoperative planning was 0.42 degrees (range, À 1 to 3 degrees; SD = 1.27). The mean inclination chosen was 9.19 degrees (range, À 8 to 10 degrees of inferior tilt; SD = 0.91). Postoperatively, we achieved a mean version of 0.38 degrees (range, À2.85 to 2.0 degrees. SD = 1.98) (negative values denote retroversion and vice versa). Postoperative mean inclination was À 9.15 degrees (range, À 7.5 to À 11.1 degrees; SD = 1.175) (negative values denote inferior tilt). The accuracy of reproducing the planned version was 0.04 ± 0.71 degrees with a maximum error of 2.05 degrees and a minimum error of 0.4 degrees. The accuracy of reproducing the planned inclination was 0.04 ± 0.26 degrees, with a maximum error of 2.5 degrees and a minimum error of 0.3 degrees Thus the patient-specific guides seems to be effective in achieving accurate placement of the glenoid component in reverse shoulder arthroplasty. It may help to overcome the problems native to computer navigation. However, more number of studies with longer duration of follow-up is necessary to prove the long-term benefits.This newly developed patient-specific planning and guiding system allows preoperative determination of the glenoid implant position on a virtual 3D model of the scapula reconstructed from preoperative CT images. The system consists of a software component, SurgiCase Connect, and a hardware component, the Match Point System. FIGURE 4. A and B, The patient-...
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