Trochlear dysplasia influences patellotrochlear index when measuring patella alta

Objectives: Patella alta is a risk factor for patellar instability and its recurrence after treatment. The patellotrochlear index (PTI) is a measurement used to quantify patella alta, describing patellar engagement in the trochlea through an index of trochlear overlap with patellar articular surface based on sagittal imaging. Values less than 20% have been reported to indicate patella alta, yet this measurement has primarily been described in normal knees. Trochlear dysplasia is also a common risk factor in patellar instability and can affect the length of the trochlea. Therefore the purpose of this study was to compare PTI measurements in knees with and without trochlear dysplasia, and to describe its relationship with trochlear length. Methods: Knees with trochlear dysplasia (defined by trochlear depth<4mm) based on CT imaging were identified from a series of knees with symptomatic patellar instability and compared to age- and gender matched asymptomatic controls. Measurements of patellar height including PTI and Caton Deschamps Index (CDI) were performed, as well as additional measurements of trochlear dysplasia including lateral trochlear inclination [LTI] and sulcus angle [SA]. Trochlear length was quantified using a previously described method of trochlear center-edge angle (TCEA) measurement, an angle between the posterior femoral cortical line with its intersection with Blumensaat’s line to the most proximal margin of the trochlea, with a smaller angle indicating more proximal extension of the trochlea. TCEA was measured at the central, medial, and lateral trochlea. Measurements were compared between dysplastic and control groups using t-test. Linear and multivariate regression analyses were performed to assess the relationship between PTI and measurements of trochlear dysplasia. Results: 21 knees with trochlear dysplasia (13 female and 8 male) were included in this study, and were compared with 21 age- and gender-matched controls. In the dysplastic group, trochlear depth (TD) was 0.7+/-2.4mm vs 6.8+/-2.5mm (p<0.001) in the control group, SA was 154.2+/-11.5 degrees vs 134.0+/-8.3 degrees (p<0.001), and LTI was 12.1+/-6.2 vs 23.7+/-4.4 degrees (p<0.001) . Despite CDI being greater in the symptomatic group (1.19+/-0.23 vs 1.06+/-0.19, p=0.053), PTI was greater (with more overlap) in the symptomatic group (34.92+/-15.23% vs 25.43+/-21.55%, p=0.076). In the symptomatic group, the trochlear groove extended more proximally at the central (TCEA 58.4 degrees vs 68.6 degrees, p<0.001) and medial aspects (68.9 degrees vs 77.9 degrees, p<0.001). In dysplastic knees, PTI demonstrated a weak negative correlation with TCEA (R=-0.40) and with LTI (R=-0.45). Conclusion: In this study, knees with trochlear dysplasia had a PTI of 35% vs 25% in the control group, indicating greater patellar engagement despite having greater measurements of patella alta based on CDI (1.19 vs 1.06). PTI correlated with increased proximal extension of the trochlea which may account for the greater patellofemoral overlap. As abnormal trochlear length can associated with supratrochlear spurs, greater values on PTI may not necessarily indicate functional patellofemoral engagement. Further studies are needed to identify the functional relationship between trochlear length and patella alta.

Anatomic Magnetic Resonance Imaging Measurements in First-Time Patellar Dislocators by Sex and Age

Context Anatomic differences of the knee in first-time patellar dislocators have not been clearly elucidated. Objective To compare structural differences of the knee in those who have sustained an acute first-time patellar dislocation resulting in a medial patellofemoral ligament (MPFL) tear by sex and age (≤17 years old, ≥18 years old). Design Case series. Setting Retrospective magnetic resonance imaging analysis. Patients or Other Participants Thirty-five acute first-time patellar dislocators with an associated MPFL tear. Main Outcome Measure(s) Patellar height using 3 methods, patellar alignment using congruency angles, and trochlear morphology using the sulcus angle. We compared the means of these variables by sex and age. The intraclass correlation coefficient was then calculated to assess the agreement of the independent reviewers. Results A total of 21 left and 14 right knees were analyzed. The MPFL tear location did not differ by sex (P = .34) or age (P = .43). Patellar height did not differ as measured by the Caton-Deschamps ratio (P = .29 for sex, P = .49 for age), Insall-Salvati index (P = .15 for sex, P = .33 for age), or patellotrochlear index (P = .67 for sex, P = .49 for age). The congruence angle (P = .81 for sex, P = .06 for age) and trochlear morphology as measured by the sulcus angle (P = .64 for sex, P = .45 for age) were similar between groups. Conclusions Patellar height and trochlear morphology did not differ by sex or age among patients whose first-time patellar dislocations resulted in an MPFL tear. In addition, the location of the tear did not appear to vary by sex or age.

Trochleoplasty is a Viable Option for Patellar Instability in Patients with Severe Trochlear Dysplasia: a Minimum 1-year Follow-Up Prospective Study

Objectives: Patellar instability caused by trochlear dysplasia may be addressed by sulcus-deepening trochleoplasty. A paucity of data exists from the United States regarding this procedure and no long term follow up. The purpose of this study was to evaluate the outcome data of patients undergoing sulcus-deepening trochleoplasty for high-grade trochlear dysplasia at our institution. Methods: Sixty-four patients (71 knees) with severe trochlear dysplasia were prospectively enrolled and underwent sulcus-deepening trochleoplasty using the Dejour method from 2011-2018. Thirty-six of 71 knees (50.6%) had prior surgery and failed prior surgical management for patellar instability. Concomitant procedures during trochleoplasty were performed at varying rates. Radiographic analysis, physical examination, and clinical follow-up were obtained for all patients. At enrollment, patients completed preoperative visual analog scores (VAS), international knee documentation committee (IKDC) and Kujala scores, which were repeated at their 6 month, 1 year, 2 year, 3 year, and 4 year follow-up visits. Preoperatively, the patellotrochlear index (PTI), trochlear spur height, and trochlear depth were all measured. The patient’s sulcus angle was measured preoperatively and postoperatively on sunrise (merchant) view xray. Of the entire cohort, 43 patients (49 knees) had at least one year complete follow-up including xrays, physical exam, and patient-reported outcome measures and were included in the study. Results: The majority of patients were female (81.6%) with a mean age of 19.6 (+/- 6.8y). Follow-up ranged from 12 months to 78.4 months (mean 27.7 +/- 15.4). At the time of enrollment, mean BMI was 27.1 kg/m2 (+/-6.3) with one current smoker and one diabetic patient. Mean duration of symptoms prior to surgery was 75.2 months (+/- 72.5; r: 4-370mos). All knees were either Dejour B (81.3%) or D (18.8%) with a mean Caton-Deschamps index (CDI) of 1.20 (+/-0.2). Mean spur height preoperatively was 7.41 mm (+/1.84 mm) with a mean trochlear depth -0.18 (+/-2.71). Mean patellotrochlear index (PTI) was 0.41 (+/0.41). There were zero episodes of recurrent instability. All patients reported clinically significant improvements compared with baseline preoperative outcome scores. The mean preoperative IKDC score was 49.99, which improved to 79.86 (p&lt0.001), and the mean preoperative Kujala score was 55.88, which improved to 85.80 (p&lt0.001). Patients reported high satisfaction rates (9.5 +/-1.6 out of 10). All but 1 patient (96.9%) returned to work while 88.2% of patients were able to return to sport. Ten knees (20.4%) developed arthrofibrosis and required manipulation under anesthesia while eight of which underwent simultaneous arthroscopic lysis of adhesions. At the latest follow-up, mean knee range of motion was 132.4 +/- 13.2 degrees. Preoperative VAS was 3.31 (right) and 4.16 (left) while postoperative was 1.31 (right) and 1.76 (left) (p=0.007 R, 0.002 L). Radiographic analysis of the sulcus angle demonstrated a significant decrease from 148.86 degrees (+/-11.42) preoperatively to 135.11 degrees (+/-8.85) postoperatively (p<0.001). Conclusion: In the setting of severe trochlear dysplasia, sulcus-deepening trochleoplasty can provide a reliable and successful surgical solution to recurrent patellar instability. At a minimum of one year follow-up, the majority of patients were satisfied with their outcome corroborated by their subjective, validated outcome measures.