Accuracy of reverse shoulder arthroplasty angle according to the size of the baseplate.

BACKGROUND: Glenoid inclination must be assessed precisely during preoperative planning for reverse shoulder arthroplasty (RSA) to position the glenoid baseplate correctly. We hypothesized that a more dynamic measurement method would better match the diversity of glenoid heights in the population and the variety of commercialized glenoid baseplates. Our purpose was to describe a new method to measure the RSA angle accounting for the baseplate size. METHODS: Computed tomography scans of 50 shoulders that underwent RSA for primary osteoarthritis or cuff tear arthropathy between June 2019 and February 2020 were included (mean age, 76 years). Three variants of the RSA angle were measured: the RSA angle as originally described by Boileau et al, the relative RSA 25 angle (which simulates the implantation of a 25-mm baseplate), and the relative RSA 29 angle (which simulates the implantation of a 29-mm baseplate). Measurements in the 2-dimensional true reformatted scapular plane were made by 3 independent operators. RESULTS: The mean R-S distance (ie, distance between point R [intersection of supraspinatus fossa line with glenoid surface] and point S [inferior border of glenoid]) was 24.2 ± 4.0 mm. The mean RSA angle was 20.3° ± 8.4°, whereas the mean relative RSA 25 angle was 19.3° ± 7.8° and the mean relative RSA 29 angle was 15.6° ± 7.6°. The mean difference between the RSA angle and the relative RSA 25 angle was 1.0° ± 4.1° (P = .16). The mean difference between the RSA angle and the relative RSA 29 angle was 4.7° ± 3.8° (P < .0001). In half of the shoulders in our series, the difference between the RSA angle and the RSA 29 angle exceeded 5°. CONCLUSION: The RSA angle is a reproducible measure of the inclination of the inferior part of the glenoid that is reliable in most cases for glenoid baseplates of 24-25 mm in height. However, surgeons should be aware that the RSA angle may overestimate the superior orientation of the inferior glenoid for baseplates of different sizes or for small- or large-stature patients. In these cases, the relative RSA angle adapted to the size of the baseplate more accurately evaluates the inclination of the inferior glenoid.

Femoral condyle bone mineral density in osteoarthritis differs significantly between knees with valgus vs. varus deformity.

BACKGROUND: The objective of this study was to measure bone mineral density (BMD) of the cancellous bone in both femoral condyles and to compare the results according to the hip-knee-ankle (HKA) angle in patients with knee osteoarthritis. HYPOTHESIS: BMD of cancellous bone in the medial condyle is markedly lower in valgus knees compared to that in the lateral condyle in varus knees. METHODS: Consecutive patients with computed tomography (CT) of the knee and long-leg radiographs obtained in preparation for total knee arthroplasty were included. The 189 knees were divided into five groups based on whether the hip-knee-ankle angle was<170° (major varus deformity), 171°-177° (varus deformity), 178°-182° (normal alignment), 183°-189° (valgus deformity), and>190° (major valgus deformity). A protocol for CT measurement of BMD values at the femoral condyles was developed. Correlations between the HKA angle and BMD were assessed using the ratio of medial-to-lateral condyle BMD values (M/L). RESULTS: M/L was lower for knees with valgus deformity than for normally aligned knees (0.7 vs. 1, p<0.001). This difference was larger in the group with major valgus deformity, with a mean M/L value of 0.5 (p<0.001). M/L was higher for knees with major varus (mean, 1.2; p=0.035). The correlation coefficients showed excellent intra-observer and inter-observer agreement for the BMD measurements. CONCLUSION: The BMD values of the femoral condyles correlate with the HKA angle. BMD is lower at the medial femoral condyle of valgus knees, particularly when the deformity exceeds 10°. This finding may deserve consideration when planning total knee arthroplasty. LEVEL OF EVIDENCE: IV; retrospective study.