Journal Pre-proof The Lateral Femoral Notch Sign Decreases in Pediatric Patients Following Anterior Cruciate Ligament Reconstruction

Anterior cruciate ligament (ACL) ruptures are common amongst pediatric patients, especially those 3 participating in competitive sports. While magnetic resonance imaging (MRI) is typically used to confirm 4 the diagnosis, certain radiologic findings can be indicative of an ACL tear, including a lateral femoral 5 notch sign (LFNS) >1.5 millimeters (mm). No study has focused on understanding the resolution pattern 6 of the LFNS in pediatric patients following ACL reconstruction (ACLR). The aim of this study is to 7 determine whether the depth of the LFNS regresses following ACLR. The authors hypothesize that 8 following ACLR, the LFNS will resolve

All patients who were treated for acute ACL rupture by one of two pediatric orthopedic surgeons between 11 2015 and 2020 were collected. 321 patients the ages of 5 to 18 were collected. Patients were excluded if 12 they underwent previous ipsilateral knee surgeries and if they did not have pre-operative knee 13 radiographs. 274 patients met inclusion criteria. LFNS was measured on pre-operative (PreOp) and most 14 recent post-operative (PostOp) radiographs. A comparison cohort of patients with a LFNS <1.5mm 15 matched by age within 1.5 years, sex, and laterality was also collected. The median difference was 16 calculated by taking the difference between PreOp LFNS and PostOp LFNS of each participant and 17 finding the median of those values. 18

Results: 19
274 pre-operative radiographs were analyzed for a LFNS depth >1.5mm. 17 radiographs met these 20 criteria with a median age of 16.3 years and a median depth of 1.70mm. Of the 17 radiographs, 8 (47.1%) 21 of participants were skeletally immature. The median LFNS depth at most recent follow up and median 22 percent decrease were 1.50 mm and 28%, respectively. Only 11.8% of patients demonstrated no change in 23 LFNS depth from PreOp to PostOp imaging. Wilcoxon Signed-Ranks test indicated that the PreOp LFNS 24 was significantly greater than the PostOp LFNS (p<0.001). Mann Whitney U tests with cases and the 25 comparison cohort demonstrated no difference in the percent decrease (p=0.106). 26

Conclusion: 27
This study sought to understand the resolution of the LFNS depth following initial ACL rupture. At a 28 median of 7.67 months following ACLR, the LFNS depth decreased significantly by 0.60mm. These 29 findings suggest that following ACL rupture, the pediatric LFNS has the potential to resolve. Future 30 studies should aim to further assess the resolution pattern of the LFNS with advanced imaging, such as 31 MRI. • Following ACL rupture, the pediatric LFNS has the potential to resolve • The LFNS had decreased significantly by 28% at approximately 8 months • Intraoperative intervention for LFC depression is not necessarily required J o u r n a l P r e -p r o o f

Introduction: 39
Anterior cruciate ligament (ACL) ruptures have been increasing in the pediatric population, 1-3 40 accounting for approximately 30% of all knee injuries. 4,5 When diagnosing these ruptures, patients 41 typically undergo both radiographic imaging and magnetic resonance imaging (MRI) of their knee. While 42 MRI allows for visualization of the ACL itself, Segond fractures and a lateral femoral notch sign (LFNS) 43 have been noted to suggest ACL rupture on radiographs. 6-12 44 The LFNS is thought to occur due to impaction of the posterior tibia onto the lateral femoral 45 condyle during anterior translation of the tibia at the time of the pivot shift when the ACL rupture 46 occurs. 13,14 Various studies have sought to understand the incidence and typical depth of the LFNS sign 8-47 10,15-17 , however, few studies have focused on the resolution pattern of the LFNS. Wierer et al. analyzed 48 the LFNS following surgery using MRI in the adult population and found that the LFNS depth did not 49 decrease but the total area of the notch did. 18 50 To the authors knowledge, no study has focused on determining the resolution pattern of the 51 LFNS in the pediatric population. This study sought to understand the progression of the LFNS in 52 pediatric patients who suffered acute ACL rupture. We hypothesize that the depth of the LFNS will 53 decrease significantly following ACL reconstruction in the pediatric population. 54 55

Subjects: 57
After Institutional Review Board approval, patients 5 to 18 years old at initial visit seen by either 58 of two pediatric orthopedic surgeons with the Current Procedural Terminology code 29888 59 (arthroscopically aided anterior cruciate ligament repair/augmentation or reconstruction) for acute ACL 60 rupture between January 1 st , 2016 and June 20 th , 2020 were identified. 321 patients met these inclusion 61 J o u r n a l P r e -p r o o f criteria. Patients were excluded if they had undergone previous ipsilateral knee surgeries or if they did not 62 have any pre-operative lateral knee radiographs. A total of 274 patients met these inclusion and exclusion 63 criteria. 64

Comparison Cohort: 65
A comparison cohort of patients meeting inclusion and exclusion criteria with a LFNS depth of 66 less than 1.5 millimeters (mm) were collected. This cohort was matched by sex, laterality, and age at 67 surgery within 1.5 years with cases who had a LFNS greater than 1.5 mm. 68

Measurements: 69
Two blinded observers analyzed pre-operative and post-operative knee radiographs using Spectra 70 IDS7 version 23.1 (Linköping, Sweden). Using the method described by Cobby et al, the LFNS depth 71 was measured using a standard lateral knee radiograph. 19 This involved drawing a tangential line across 72 the lower surface of the lateral femoral condyle to use as a reference line and measuring the depth of the 73 notch perpendicular to the reference line ( Figure 1). 74

Statistical Analysis: 75
Demographic information including sex, age at imaging, laterality, race, and ethnicity were 76 collected. LFNS depth was measured for all lateral knee radiographs at initial presentation (PreOp) and 77 most recent follow up (PostOp). Inter-rater reliability on a random sample of 10 participants was 78 performed and demonstrated excellent reliability (ICC = 0.979 Median LFNS depth at time of presentation was 1.70 mm (IQR = 1.55 -2.05). PostOp 94 radiographs were performed at a mean 7.7 (IQR = 2.1-19.2) months after surgery and found to have a 95 mean LFNS depth of 1.50 mm (IQR = 1.00 -1.60). This decrease correlated with a median depth 96 decrease of 28% (IQR = 18.9 -35.9) between PreOp and PostOp. PreOp LFNS depth was found to 97 decrease in 88.2% patients, while 2/17 patients saw no change at their most recent radiograph. The 98 median Depth difference was found to be 0.60 mm (IQR = 0.25 -0.70). Wilcoxon Signed Rank Test 99 indicated that PreOp LFNS (mean rank = 8.00) was significantly greater than PostOp LFNS (mean rank = 100 0.00) (p < 0.001). was not determined to be statistically significant (p = 0.093), perhaps due to a limited number of cases. 105 When comparing the cases with the comparison cohort, a significant difference was found in Preop, 106 Postop, and Depth difference, but no difference was noted in the percent decrease (Table 2). 107 108 J o u r n a l P r e -p r o o f

Discussion: 109
This study sought to understand the progression of the LFNS depth in pediatric patients who 110 underwent ACL reconstruction following acute injury. Approximately 8 months following initial 111 imaging, after undergoing ACLR without any additional surgical intervention to address the notch, the 112 LFNS was found to decrease by 0.60 mm or 28%. These findings suggest that in pediatric patients with a 113 positive LFNS, the depth does decrease following ACL reconstruction. 114 Wierer et al. performed a similar analysis on predominately adult patients who underwent ACL 115 reconstruction. 18 Using MRI images from initial presentation and post-operative follow-up, they found 116 that the depth of the LFNS did not decrease in this population, while the total area of the notch did 117 significantly decrease. When patients who underwent primary ACLR present after a second knee injury, 118 knowledge of changes in the LFNS can aid in radiographic assessment of ACL graft rupture. Our study 119 found that at 8 months, the depth of the LFNS on radiograph had decreased significantly by 28% in those 120 with a positive Preop LFNS. This suggests the resolution of the LFNS in pediatric patients who suffer 121 ACL rupture may differ from adult patients. Future studies should aim to use advanced imaging 122 techniques, such as MRI, to evaluate the area of the LFNS in order to compare resolution patterns 123 between pediatric and adult patients. 124 The LFNS is an important identification on radiographs and may be significant in helping to 125 determine if a patient initially presents with an ACL tear before obtaining an MRI. Furthermore, previous 126 studies in adults have shown that the presence of a LFNS correlates with concomitant meniscus and 127 anterolateral ligament (ALL) tears. 8,9 This study demonstrated a significant decrease in LFNS depth over 128 time suggesting the potential resolution of the LFNS. However, MRI analysis is needed to understand if 129 the LFNS sign similarly correlates with meniscal tears, ligamentous tears, or other markers of significant 130 injury in the pediatric population following ACL rupture. 131 J o u r n a l P r e -p r o o f The incidence of a LFNS following ACL rupture has been cited anywhere from 7.5% to 52%. 8,9,20 132 However, these studies focused predominately on the adult population, with a mean age of participants 133 between 23.3 to 29.4 years. The adult population primarily considers a positive LFNS if the depth is 134 greater than 2.0 mm. 8 In this study, on patients with a median age of 16.3 years, 5.8% of patients had a 135 LFNS that met our inclusion criteria of having a LFNS depth greater than 1.5 mm. The incidence found in 136 this study suggests that pediatric LFNS may be less common that in the adult population. Alternatively, 137 the notch created in pediatric patients may be shallower and, therefore, the threshold for a positive LFNS 138 in pediatric knees may be smaller than in adults. Understanding the true incidence of pediatric LFNS can 139 aid in the diagnosis of ACL rupture, thus, further studies should aim to assess the incidence of LFNS in 140 pediatric patients compared to adults. 141 This study has several limitations. Many patients had to be excluded due to lack of post-operative 142 radiographic assessments. Additionally, while our x-ray techniques were standardized, this study did not 143 investigate if there was variability between different x-ray technicians. The small sample size limited the 144 ability to further analyze LFNS depth by timepoint following surgical intervention. However, the authors 145 believe that these limitations do not negate the findings of this study as statistically significant decreases 146 in LFNS depth were found. Future studies should aim to group post-operative imaging by more discrete 147 timepoints to further understand the resolution pattern of the LFNS. 148 149

Conclusion: 150
This study sought to understand the resolution of the LFNS following ACLR in pediatric patients. 151 Following ACLR, the LFNS had decreased significantly by 28% at approximately 8 months. These 152 findings suggest that unlike adults, the pediatric LFNS has the potential to resolve following ACLR.       J o u r n a l P r e -p r o o f