Increased medial tibial slope in teenage pediatric

Authors: Shail Vyas Carola F van Eck Nina Vyas Freddie H Fu Norman Y Otsuka

Publish Date: 2010/07/30

Volume: 19, Issue: 3, Pages: 372-377

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Abstract

Variations in bony morphology have been associated with anterior cruciate ligament ACL injury risk The primary aim of this study was to compare the tibial slope in the teenage pediatric population with open physes with and without ACL injury The secondary aims were to compare the notch width index NWI and determine the influence of gender and age on tibial slope and NWIThirtynine teenage pediatric subjects were included in this study 16 with and 23 without ACL injury Medial tibial slope and lateral tibial slope and NWI as measured on plain radiographs were compared between the groups using an independent ttest Comparison of tibial slope and NWI was also performed between male and female subjects Pearson correlation coefficient between age and tibial slope and NWI was calculatedThe medial tibial slope averaged 102 ±39 degrees the lateral tibial slope 115 ±39 degrees and the NWI 026 There was a significant difference in medial tibial slope between the ACLinjured 121 degrees subjects and the controls 89 degrees P = 0009 There was no significant difference in lateral tibial slope or NWI between the groups There was no significant difference in the medial tibial slope and lateral tibial slope and NWI between the male and female subjects Subject age was not correlated with medial tibial slope and lateral tibial slope or NWIVariations in bony morphology have long been thought to be associated with anterior cruciate ligament ACL injury risk 13 14 18 26 On the femoral side small intercondylar notch dimensions have been correlated with an increased risk of ACL rupture 26 Similarly tibial bony anatomy may have an effect on the ACL The slope of the proximal tibia averages approximately 10 degrees with a variation of 3 degrees in the adult literature 7 11 12 An increase in tibial slope may predispose to ACL rupture Bony morphology may especially play a role in ACL injuries in children 9 However the relationship between tibial slope and ACL injury in this population has not been studied The primary aim of this study is to compare the tibial slope in the teenage pediatric subjects with open physes with and without ACL injury We hypothesized an increased tibial slope in the subjects with ACL injury The secondary aims were to compare the notch width index NWI between pediatrics subjects with open physes with and without ACL injury to evaluate the influence of gender and age on tibial slope and NWI and to evaluate the reliability of measuring tibial slope and NWI on plain radiographs in pediatric subjectsBetween January 2002 and January 2009 all teenage pediatric subjects undergoing ACL reconstruction were included in this study Inclusion criteria were open physes lateral and anterior–posterior radiographs of the knee of good quality presence of an ACL tear as appreciated on magnetic resonance imaging MRI and/ or observed during surgery Subjects with closed physes and evidence of knee morphological abnormalities were excluded A control group was retrospectively selected from teenage pediatric subjects with open physes of similar age and gender with anterior–posterior and lateral radiographs of the knee of good quality without presence of an ACL tear as confirmed on MRI Retrospective selection of the control group was essential to ensure subjects did not suffer an ACL injury before their physes were closed Subjects with closed physes were excludedThe medial tibial slope is determined by subtracting the angle shown in the above figure from 90 degrees The long axis of the tibia is determined drawing a line defined by two points one midway between the anterior and posterior border of the tibia at the level of the tibial tubercle and the other 5 cm distal to the tubercleThe data were analyzed with PASW Statistics version 170 SPSS Inc Chicago IL The measurements of the first observer were used for statistical analysis of the results The ratio mean range and standard deviation of the gender and age of all included subjects were calculated An independent ttest was performed to assess whether the ACLinjured and control group had comparative baseline characteristics An independent ttest was also used to determine the difference in medial tibial slope lateral tibial slope and NWI between male and female subjects and between ACLinjured and control subjects The Pearson correlation coefficient was calculated to determine the correlation between the medial tibial slope lateral tibial slope and NWI and subject age The a priori alpha level for statistical significance was set at P  005 Lastly the intraclass correlation coefficient ICC was calculated to determine interobserver reliability for the medial tibial slope lateral tibial slope and NWI Before conducting this study a sample size calculation was performed An average PTS of 10 degrees was assumed and a difference equal to or exceeding the variation reported in literature 3 degrees was thought to be clinically relevant This sample size analysis revealed that a total of 16 subjects were needed in both the ACLinjured and the control group to obtain a power of 80

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