Purpose The purpose of this study was to define the incidence of trochlear dysplasia in an infant cohort being screened for developmental dysplasia of the hip (DDH). Methods Newborns screened for DDH that were evaluated with ultrasound for the presence of trochlear dysplasia were retrospectively reviewed. The sulcus angle and trochlear depth were measured. Based on previous work, trochlear dysplasia was defined as a sulcus angle of > 159°. Our newborn cohort was then analyzed to identify potential risk factors for trochlear dysplasia. Results A total of 383 knees in 196 infants were studied. In total, 52% were referred for breech intrauterine positioning and 21% were ultimately diagnosed with DDH and had treatment initiated with a Pavlik harness. Of the entire cohort, 8% of knees were deemed to have trochlear dysplasia. Breech patients were found to have a flatter sulcus angle than those that were not breech (149.5° (sd 7.2°) versus 147.9° (sd 7.5°); p = 0.028). Similarly, a shallower trochlear depth was identified in breech patients versus non-breech patients (1.6 mm (sd 0.4) versus 1.8 mm (sd 0.4); p = 0.019). Those with trochlear dysplasia (as defined by sulcus angle > 159°) did show a smaller alpha angle (i.e. more dysplastic hip) as compared with those without trochlear dysplasia (59.2° (sd 10.2°) versus 65.9° (sd 7.5°); p < 0.001). Hips with DDH were 2.4-times more likely to have knees with trochlear dysplasia (95% confidence interval 1.1 to 5.3). Conclusion Ultrasound screening of newborn knees reveals that trochlear dysplasia is relatively common in breech babies with DDH. Level of Evidence III

Level III.

Background: Patellar instability among adolescents has an incidence of 29 to 43 per 100,000 per year. Trochlear dysplasia has been found in up to 85% of those with recurrent patellar instability. The prevalence of trochlear dysplasia in the general population has not yet been defined. The purpose of the present study was to determine the prevalence of trochlear dysplasia as defined by ultrasound in a skeletally mature population and to characterize associations of trochlear dysplasia with a history of patellofemoral instability or pain.Methods: Skeletally mature adolescents and parents of patients (£50 years of age) who had presented to orthopaedic clinics were prospectively enrolled from 2019 to 2020. Those presenting with knee pain, open physes, prior intra-articular fracture, total knee arthroplasty, and syndromic ligamentous laxity or neuromuscular disease were excluded. Information regarding a history of anterior knee pain, patellar instability, and/or surgery was obtained, and an abbreviated Anterior Knee Pain Scale (AKPS) was collected. An AKPS score of ‡4 was considered positive. Bilateral ultrasound of the knee was performed, and the osseous sulcus angle of the trochlea and the trochlear depth were measured. Basic descriptive statistics are reported.Results: One hundred and two patients (203 knees) were studied. The mean sulcus angle was 144.1°± 6.8°, and the mean trochlear depth was 5.5 ± 1.4 mm. High-grade trochlear dysplasia was defined as the 95th percentile and above, which was shown to be a sulcus angle of ‡154°or a trochlear depth of £3 mm for female patients and £4 mm for male patients. The prevalence of high-grade trochlear dysplasia was 5.4% based on the sulcus angle and 9.9% based on trochlear depth. Knees with high-grade trochlear dysplasia based on the sulcus angle were 11 times more likely to have had previous patellar instability (p = 0.013). Conclusions:The prevalence of high-grade trochlear dysplasia in the general population is approximately 10%, and there may be an association with patellar instability. The use of ultrasound to diagnose trochlear dysplasia may prove to be a rapid and useful tool for guiding patient education and treatment decisions. Disclosure: The Disclosure of Potential Conflicts of Interest forms are provided with the online version of the article (http://links.lww.com/JBJS/G709).

Background Periacetabular osteotomy (PAO) increases acetabular coverage of the femoral head and medializes the hip’s center, restoring normal joint biomechanics. Past studies have reported data regarding the degree of medialization achieved by PAO, but measurement of medialization has never been validated through a comparison of imaging modalities or measurement techniques. The ilioischial line appears to be altered by PAO and may be better visualized at the level of the inferior one-third of the femoral head, thus, an alternative method of measuring medialization that begins at the inferior one-third of the femoral head may be beneficial. Questions/purposes (1) What is the true amount and variability of medialization of the hip’s center that is achieved with PAO? (2) Which radiographic factors (such as lateral center-edge angle [LCEA] and acetabular inclination [AI]) correlate with the degree of medialization achieved? (3) Does measurement of medialization on plain radiographs at the center of the femoral head (traditional method) or inferior one-third of the femoral head (alternative method) better correlate with true medialization? (4) Are intraoperative fluoroscopy images different than postoperative radiographs for measuring hip medialization? Methods We performed a retrospective study using a previously established cohort of patients who underwent low-dose CT after PAO. Inclusion criteria for this study included PAO as indicated for symptomatic acetabular dysplasia, preoperative CT scan, and follow-up between 9 months and 5 years. A total of 333 patients who underwent PAO from February 2009 to July 2018 met these criteria. Additionally, only patients who were between 16 and 50 years old at the time of surgery were included. Exclusion criteria included prior ipsilateral surgery, femoroacetabular impingement (FAI), pregnancy, neuromuscular disorder, Perthes-like deformity, inadequate preoperative CT, and inability to participate. Thirty-nine hips in 39 patients were included in the final study group; 87% (34 of 39) were in female patients and 13% (5 of 39 hips) were in male patients. The median (range) age at the time of surgery was 27 years (16 to 49). Low-dose CT images were obtained preoperatively and at the time of enrollment postoperatively; we also obtained preoperative and postoperative radiographs and intraoperative fluoroscopic images. The LCEA and AI were assessed on plain radiographs. Hip medialization was assessed on all imaging modalities by an independent, blinded assessor. On plain radiographs, the traditional and alternative methods of measuring hip medialization were used. Subgroups of good and fair radiographs, which were determined by the amount of pelvic rotation that was visible, were used for subgroup analyses. To answer our first question, medialization of all hips was assessed via measurements made on three-dimensional (3-D) CT hip reconstruction models. For our second question, Pearson correlation coefficients, one-way ANOVA, and the Student t-test were calculated to assess the correlation between radiographic parameters (such as LCEA and AI) and the amount of medialization achieved. For our third question, statistical analyses were performed that included a linear regression analysis to determine the correlation between the two radiographic methods of measuring medialization and the true medialization on CT using Pearson correlation coefficients, as well as 95% confidence intervals and standard error of the estimate. For our fourth question, Pearson correlation coefficients were calculated to determine whether using intraoperative fluoroscopy to make medialization measurements differs from measurements made on radiographs. Results The true amount of medialization of the hip center achieved by PAO in our study as assessed by reference-standard CT measurements was 4 ± 3 mm; 46% (18 of 39 hips) were medialized 0 to 5 mm, 36% (14 hips) were medialized 5 to 10 mm, and 5% (2 hips) were medialized greater than 10 mm. Thirteen percent (5 hips) were lateralized (medialized < 0 mm). There were small differences in medialization between LCEA subgroups (6 ± 3 mm for an LCEA of ≤ 15°, 4 ± 4 mm for an LCEA between 15° and 20°, and 2 ± 3 mm for an LCEA of 20° to 25° [p = 0.04]). Hips with AI ≥ 15° (6 ± 3 mm) achieved greater amounts of medialization than did hips with AI of < 15° (2 ± 3 mm; p < 0.001). Measurement of medialization on plain radiographs at the center of the femoral head (traditional method) had a weaker correlation than using the inferior one-third of the femoral head (alternative method) when compared with CT scan measurements, which were used as the reference standard. The traditional method was not correlated across all radiographs or only good radiographs (r = 0.16 [95% CI -0.17 to 0.45]; p = 0.34 and r = 0.26 [95% CI -0.06 to 0.53]; p = 0.30), whereas the alternative method had strong and very strong correlations when assessed across all radiographs and only good radiographs, respectively (r = 0.71 [95% CI 0.51 to 0.84]; p < 0.001 and r = 0.80 [95% CI 0.64 to 0.89]; p < 0.001). Measurements of hip medialization made on intraoperative fluoroscopic images were not found to be different than measurements made on postoperative radiographs (r = 0.85; p < 0.001 across all hips and r = 0.90; p < 0.001 across only good radiographs). Conclusion Using measurements made on preoperative and postoperative CT, the current study demonstrates a mean true medialization achieved by PAO of 4 mm but with substantial variability. The traditional method of measuring medialization at the center of the femoral head may not be accurate; the alternate method of measuring medialization at the lower one-third of the femoral head is a superior way of assessing the hip center’s location. We suggest transitioning to using this alternative method to obtain the best clinical and research data, with the realization that both methods using plain radiography appear to underestimate the true amount of medialization achieved with PAO. Lastly, this study provides evidence that the hip center’s location and medialization can be accurately assessed intraoperatively using fluoroscopy. Level of Evidence Level III, diagnostic study.