Femoral Trochlear Dysplasia Is Common in Lower Limbs With Hartofilakidis C2 Hip Dysplasia

BACKGROUND: Patients with developmental dysplasia of the hip (DDH) can also present with deformities of the patellofemoral joint, such as femoral trochlear dysplasia. Although previous studies have reported that trochlear dysplasia is clinically important in some patients with DDH, the association between DDH and trochlear dysplasia is still unclear. QUESTIONS/PURPOSES: (1) Is trochlear dysplasia more common among lower limbs with bilateral DDH, with unilateral DDH, or without DDH (specifically, in the contralateral limb of patients with unilateral DDH)? (2) Is having more severe DDH (as measured by Hartofilakidis classification, Crowe classification, or according to angular measurements) associated with higher odds of having trochlear dysplasia? METHODS: This was a single-center retrospective comparative study. Between November 2018 and February 2024, a total of 439 patients with DDH (of whom 56% [248 of 439] had bilateral DDH and the remainder had unilateral DDH) underwent THA in our center. Of those, we considered as potentially eligible patients who were between ages 18 and 50 years, with a history of DDH that did not undergo surgical treatment prior to the THA, and who had available demographic and radiographic data. We then excluded 31% of the patients because 62 of them had a history of hip or knee treatment, 8 had a history of trauma or infection in the hip or knee, 24 had severe knee osteoarthritis, 9 had a history of neuromuscular disease, and the data from 33 patients were incomplete, leaving 303 patients (of whom 50% [152 of 303] had bilateral DDH, while the remainder had unilateral DDH; 455 affected and 151 unaffected limbs, in total) for the analysis. From those, we formed three study groups: 33% (152) of limbs randomly selected from one of the limbs of each patient with bilateral DDH were assigned to the bilateral group, 33% (151) of limbs selected from the ipsilateral side of patients with unilateral DDH were assigned to the unilateral group, and 33% (151) of limbs selected from the contralateral limbs in patients with unilateral DDH were assigned to the contralateral group. There were no differences in demographics, such as sex, age, and BMI, between patients with bilateral DDH and unilateral DDH. All patients underwent CT as a standard component of the preoperative evaluation process for THA. To answer our first question about in which group trochlear dysplasia is more common, we measured anatomic parameters related to the patellofemoral joint by three-dimensional CT, diagnosed trochlear dysplasia using a sulcus angle of ≥ 145° or a femoral trochlear depth of ≤ 4 mm, and classified trochlear dysplasia according to the Dejour classification; the proportions of trochlear dysplasia among the three groups were compared totally or by sex. To answer the second question about whether more severe DDH is associated with a higher likelihood of trochlear dysplasia, Crowe classification and the Hartofilakidis classification were used to group the limbs with DDH, and hip parameters including the lateral center-edge angle (LCEA), the femoral neck-shaft angle, and the femoral anteversion angle were measured. Two trained observers independently performed all measurements and classifications, with excellent intraobserver and interobserver reliability assessed using intraclass correlation coefficients (> 0.80). RESULTS: The proportion of knees with trochlear dysplasia was higher in both the bilateral and unilateral groups compared with the contralateral group (34% [52 of 152] versus 12% [18 of 151], OR 3.8 [95% confidence interval (CI) 2.1 to 7.0]; p < 0.001 and 31% [47 of 151] versus 12% [18 of 151], OR 3.3 [95% CI 1.8 to 6.1]; p < 0.001, respectively). The bilateral and unilateral groups had a larger sulcus angle (143° ± 7° versus 140° ± 7°, mean difference 4° [95% CI 2° to 5°]; p < 0.001 and 144° ± 9° versus 140° ± 7°, mean difference 5° [95% CI 3° to 6°]; p < 0.001, respectively) and a shallower femoral trochlear depth (5 ± 1 mm versus 6 ± 2 mm, mean difference -1 [95% CI -3 to -1]; p < 0.001 and 5 ± 2 mm versus 6 ± 2 mm, mean difference -1 [95% CI -2 to -1]; p < 0.001, respectively) compared with the contralateral group. When all limbs with DDH were grouped by Hartofilakidis classification, we found that the group of Hartofilakidis C2 hips had a higher odds of trochlear dysplasia (53% [29 of 55], C2 versus the others OR 2.8 [95% CI 1.6 to 5.2]; p = 0.008) and the highest proportion of severe trochlear dysplasia knees (that is, they had both a sulcus angle of ≥ 145° and a femoral trochlear depth of ≤ 4 mm) (72% [21 of 29], C2 versus the others OR 4.0 [95% CI 2.0 to 8.0]; p = 0.03). Compared with the dysplastic hips without trochlear dysplasia, those with trochlear dysplasia had a smaller LCEA (-6° ± 15° versus -2° ± 14°, mean difference -4° [95% CI -8° to 0°]; p = 0.03) and a larger femoral anteversion angle (35° ± 14° versus 31° ± 13°, mean difference 4° [95% CI 1° to 7°]; p = 0.01). CONCLUSION: We found that limbs with DDH, particularly those with Hartofilakidis C2 hip dysplasia, were more prone to having trochlear dysplasia. In contrast, the contralateral limbs of patients with unilateral DDH rarely exhibited trochlear dysplasia. For pediatricians, early screening of hip development, along with timely treatment of DDH, is beneficial to preventing the occurrence and progression of associated deformities. For joint surgeons, it is essential to assess patellofemoral alignment and conditions in such patients. During THA, modular prostheses or subtrochanteric osteotomy should be considered to correct and maintain proper patellofemoral tracking, which may reduce the risk of postoperative patellar instability and anterior knee pain. Future studies might clarify the impact of trochlear dysplasia on preoperative and postoperative patellar instability and knee pain in these patients. LEVEL OF EVIDENCE: Level III, prognostic study.