Following ethical approval from the institutional review board at our hospital, we reviewed the clinical and radiological records of all children with primary ATPD between January 2010 and February 2022 retrospectively.
Inclusion criteria
Patients were included if (1) they had primary ATPD within four days,(2)they were under 18 years old, and (3) complete clinical and radiological examination were available. This patellar misalignment is diagnosed on the basis of the trauma history and clinical findings. Some patients may remember feeling the patella in a laterally displaced position. Clinical findings include knee hematoma, a lateralized patella and pain at the site of the medial restraints [17].
Neglected fracture in ATPD is defined as meeting three criteria simultaneously if (1) either our hospital or other hospitals had not diagnosed neglected fractures on initial X-ray,(2)at least one of the three authors (MM, LH and HC) could not confirm the existence of fractures on X-ray, and (3) confirmed the osteochondral fractures through subsequent CT or MRI.
Exclusion criteria
Patients were excluded if (1) there was recurrent/ habitual patellar dislocation or other patellar malalignment; (2) there was obvious fracture on X-ray; (3) fractures were present that did not come from the patellofemoral joint; or (4) there was neither CT nor MRI examination.
Acute knee injury was evaluated by pediatric orthopedic surgeon (Table 1). Knee radiography was completed in all patients. Medical history, physical examination, and radiographic records were reviewed to confirm primary ATPD. Post-ATPD pain, swelling and fear can affect the walking and gait, which needs to be evaluated and divided into four levels (Table 1).
The SP was manually compressed, forcing the joint effusion distally. Knee effusion can be graded in size by compressing the SP. If any fluid was noted, it was scored as knee effusion grade 1, slight lift-off of the patella was scored as grade 2 and a ballotable patella as grade 3, while grade 4 represented a tense effusion with no ability to compress the patella against the femoral sulcus [18]. The data of knee examination were extracted from the medical records.
The greatest dimension of the SP effusion on lateral knee radiograph was measured and documented [16]. This measurement is defined by obtaining the anteroposterior distance from the anterior edge of the pre-femoral fat pad to the posterior edge of the SP fat pad (Fig. 1b) [19, 20]. Further imaging examination is decided on by the surgeon.
ATPD with neglected OCF was defined as Group A, while ATPD without OCF was defined as Group B. Group A was divided into two subgroups according to the maximum fracture diameter. Three-dimensional diameters of the OCF were measured and the longest diameter were recorded. For osteochondral defects with a size greater than 10 mm, they have a better prognosis if the fragment received reduction and fixation [5]. Group A1 was defined as greater than or equal to 10 mm, which were considered severe fractures, and Group A2 was defined as having fractures of less than 10mm.
The primary endpoint is neglected OCFs. The main aim of study is to confirm risk factors of neglected OCFs in primary ATPD. So the sample size we enrolled need to present significant difference between Group A and Group B at least.
Data analyses were performed using SPSS software (SPSS for Windows, v. 20.0; SPSS, Inc., Chicago, IL). Data were shown as mean ± standard deviation). An independent samples test was performed to compare the differences between the two groups. We performed the test of normality for the age, weight and SP measurement through Kolmogorov-Smirnov test. Non-parametric distributions data were performed by Kruskal-Wallis test in our study. A chi-square test was used to analyze the frequency data on gender, side, knee injury pattern, displacement sensation, reduction mode, walking ability, effusion grade, and fracture site. Multivariable linear regression analysis was applied to detect the effect of other independent variables on the OCF in ATPD and fragment size.
The receiver operating characteristic (ROC) curve for the risk factor for neglected OCFs was plotted to determine the optimum cutoff point, and area under the ROC curve (AUC) was used to determine the discrimination power between Group A and Group B. The same were used to compare Group A1 and Group A2. Statistical significance was defined as values of p < 0.05.