BACKGROUND Lower extremity valgus is a commonly described factor associated with patellofemoral instability (PFI) and, if identified before skeletal maturity, can be treated with guided growth. The prevalence of valgus alignment in the pediatric and adolescent PFI population is largely unknown. PURPOSE The aim of this study was to report the prevalence of valgus alignment in adolescent patients presenting with PFI; with secondary assessment of high-grade valgus (zone II or III), coronal asymmetry, and associations of these findings with body mass index (BMI). STUDY DESIGN A retrospective cohort study. METHODS A total of 279 consecutive patients (349 knees) with a diagnosis of PFI presenting to a single orthopedic pediatric sport medicine surgeon were identified. A retrospective chart review was performed to collect demographic and clinical data, chronologic and bone age, sex, BMI, mechanism of injury, and the presence of osteochondral fracture. Full-length standing hip-to-ankle alignment radiographs were graded for knee alignment mechanical zone utilizing standard linear femoral head center to talar center assessment. In addition, mechanical axis deviation, mechanical lateral distal femoral angle and medial proximal tibial angle (MPTA) were also calculated. RESULTS Mean patient age was 14.0±2.5 years. There were 162 (58.1%) females and mean BMI was 24.3±6.4. Seventy patients (25.1%) had bilateral PFI. Standing alignment radiographs were available for 81.4% of knees (n=284). Valgus alignment was present in 172 knees with PFI (60.6%). High-grade valgus, defined as zone 2 or greater, was present in 66 knees (23.3%). Overall, 48.9% had asymmetry of coronal alignment (n=139). The mean mechanical lateral distal femoral angle was 85.4±2.8 and the mean MPTA was 88.2±2.6. There was a greater MPTA in female patients (88.8±2.4 vs. 87.5±2.7, P <0.001). A higher BMI (24.87±6.95, P =0.03) was associated with valgus alignment. CONCLUSIONS There is a high (60%) prevalence of lower extremity valgus in adolescent patients presenting with PFI, with nearly 1 in 4 presenting with high-grade valgus. The treatment team should be aware of this association as it may be an important consideration in the pediatric and adolescent PFI populations. LEVEL OF EVIDENCE Level III.

中文翻译：

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患有髌股不稳的儿科患者出现膝外翻。

背景技术下肢外翻是与髌股不稳（PFI）相关的常见因素，如果在骨骼成熟之前发现，则可以通过引导生长进行治疗。儿童和青少年 PFI 人群中外翻排列的患病率在很大程度上尚不清楚。目的 本研究的目的是报告患有 PFI 的青少年患者中外翻排列的患病率；对高度外翻（II 区或 III 区）、冠状不对称以及这些结果与体重指数 (BMI) 的关联进行二次评估。研究设计 一项回顾性队列研究。方法 共有 279 名连续的患者（349 个膝盖）被诊断为 PFI，并就诊于一位骨科小儿运动医学外科医生。进行回顾性图表审查以收集人口和临床数据、时间和骨龄、性别、BMI、损伤机制以及骨软骨骨折的存在。利用标准线性股骨头中心到距骨中心评估，对全长站立髋踝对准射线照片进行膝关节对准机械区分级。此外，还计算了机械轴偏差、股骨远端机械外侧角和胫骨近端内侧角（MPTA）。结果 患者平均年龄为 14.0±2.5 岁。女性 162 名（58.1%），平均 BMI 为 24.3±6.4。70 名患者 (25.1%) 患有双侧 PFI。81.4% 的膝盖 (n=284) 可获得站立对齐 X 光片。172 例 PFI 膝关节存在外翻排列（60.6%）。66 个膝关节 (23.3%) 存在高度外翻，定义为 2 区或以上。总体而言，48.9% 的人冠状位排列不对称 (n=139)。股骨远端平均机械外侧角为85.4±2.8，平均MPTA为88.2±2.6。女性患者的 MPTA 较高（88.8±2.4 比 87.5±2.7，P <0.001）。较高的BMI（24.87±6.95，P=0.03）与外翻对齐相关。结论 在患有 PFI 的青少年患者中，下肢外翻的患病率很高（60%），其中近四分之一的患者患有高度外翻。治疗团队应该意识到这种关联，因为它可能是儿童和青少年 PFI 人群中的一个重要考虑因素。证据级别 III 级。