Throckmorton and colleagues21 used 70 cadaveric shoulders with radiographically confirmed arthritis and randomized them to undergo either anatomic or reverse TSA using either a patient-specific guide or standard instrumentation. Postoperative CT scans were used to evaluate the glenoid inclination, version, and starting point. They found that glenoid components implanted using patient-specific guides were more accurate than those placed using traditional instrumentation. The average deviation from intended inclination was 3° for patient-specific guides and 7° for traditional instrumentation, the average deviation from intended version was 5° for patient-specific guides and 8° for traditional instrumentation, and the average deviation in intended starting point was 2 mm for patient-specific guides and 3 mm for traditional instrumentation. They also analyzed significantly malpositioned components as defined by a variation in version or inclination of >10° or >4 mm in starting point. They found that 6 of their 35 glenoids using patient-specific guides were significantly malpositioned compared to 23 of 35 glenoids using traditional instrumentation. They concluded that patient-specific guides were more accurate and reduced the number of significantly malpositioned implants when compared with traditional instrumentation.
Early and colleagues25 analyzed the effect of severe glenoid bone defects on the accuracy of patient-specific guides compared with traditional guides. Using 10 cadaveric shoulders, they created anterior, central, or posterior glenoid defects using a reamer and chisel to erode the bone past the coracoid base. Subsequent CT scans were performed on the specimens, and patient-specific guides were fabricated and used for reverse TSA in 5 of the 10 specimens. A reverse TSA was performed using traditional instrumentation in the remaining 5 specimens. They found that the average deviation in inclination and version from preoperative plan was more accurate in the patient-specific guide cohort than that in the traditional instrument cohort, with an average deviation in inclination and version of 1.2° ± 1.2° and 1.8° ± 1.2° respectively for the cohort using patient-specific instruments vs 2.8° ± 1.8° and 3.5° ± 3° for the cohort using traditional instruments. They also found that their total bone screw lengths were longer in the patient-specific guide group than those in the traditional group, with screws averaging 52% of preoperatively planned length in the traditional instrument cohort vs 89% of preoperatively planned length in the patient-specific instrument cohort.
Gauci and colleagues26 measured the accuracy of patient-specific guides in vivo in 17 patients receiving TSA. Preoperative CT scans were used to fabricate patient-specific guides, and postoperative CT scans were used to measure version, inclination, and error of entry in comparison with the templated goals used to create patient-specific guides. They found a mean error in version and inclination of 3.4° and 1.8°, respectively, and a mean error in entry of 0.9 mm of translation on the glenoid. Dallalana and colleagues27 performed a very similar study on 20 patients and found a mean deviation in glenoid version of 1.8° ± 1.9°, a mean deviation in glenoid inclination of 1.3° ± 1.0°, a mean translation in anterior-posterior plane of 0.5 mm ± 0.3 mm, and a mean translation in the superior-inferior plane of 0.8 mm ± 0.5 mm.
Hendel and colleagues28 performed a randomized prospective clinical trial comparing patient-specific guides with traditional methods for glenoid insertion. They randomized 31 patients to receive a glenoid implant using either a patient-specific guide or traditional methods and compared glenoid retroversion and inclination with their preoperative plan. They found an average version deviation of 6.9° in the traditional method cohort and 4.3° in the patient-specific guide cohort. Their average deviation in inclination was 11.6° in the traditional method cohort and 2.9° in the patient-specific guide cohort. For patients with preoperative retroversion >16°, the average deviation was 10° in the standard surgical cohort and 1.2° in the patient-specific instrument cohort. Their data suggest that increasing preoperative retroversion leads to an increased version variation from preoperative plan.
Iannotti and colleagues29 randomly assigned 46 patients to preoperatively undergo either CT scan with 3-D templating of glenoid component without patient-specific guide fabrication or CT scan with 3-D templating and patient-specific guide fabrication prior to receiving a TSA. They recorded the postoperative inclination and version for each patient and compared them to those of a nonrandomized control group of 17 patients who underwent TSA using standard instrumentation. They found no difference between the cohorts with or without patient-specific guide use with regard to implant location, inclination, or version; however, they did find a difference between the combined 3-D templating cohort compared with their standard instrumentation cohort. They concluded that 3-D templating significantly improved the surgeons’ ability to correctly position the glenoid component with or without the fabrication and the use of a patient-specific guide.
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