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ORIGINAL ARTICLE
Year : 2015  |  Volume : 15  |  Issue : 3  |  Page : 214-219

Effects of posterior tibial slopes on noncontact anterior cruciate ligament injury


Department of Orthopaedic Surgery, Institute of Post Graduate Medical Education and Research, Kolkata, West Bengal, India

Date of Web Publication2-Sep-2015

Correspondence Address:
Gopal Ghosh
C/o Bijan Roy, 12 C Garfa 4th Lane, Jadavpur, Kolkata - 700 075, West Bengal
India
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DOI: 10.4103/1319-6308.164275

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  Abstract 

Purpose: In the present study, we measured medial tibial slope (MTS) and lateral tibial slope (LTS) separately, using conventional magnetic resonance images (MRIs) of knee joint. The Purpose of the study was to provide reference value of the posterior tibial slope in normal Indian population, and noncontact anterior cruciate ligament (ACL) injured Indian population and, to assess the association between steeper posterior tibial slope and noncontact ACL injury. Methods: In the present study, 60 ACL injured (I) patients (30 male, 30 female) were compared with 60 ACL uninjured (UI) or control population (30 male, 30 female) regarding LTS and MTS. MTS and LTS of each subject were measured using 1.5 tesla MRI of knee joint. Data were analyzed using appropriate statistical analysis. Results: Mean ± standard deviation (SD) MTS of uninjured male, female and pooled population are 6.94 ± 3.205°, 9.28 ± 2.657° and 7.73 ± 3.204° respectively. Mean ± SD MTS of injured male, female and pooled population are 8.13 ± 2.11°, 10.56 ± 1.691°, 8.73 ± 2.261° respectively. Mean ± SD LTS of uninjured male, female and pooled population are 3.77 ± 1.859°, 6.45 ± 3.364°, 4.68 ± 2.757° respectively. Mean ± SD LTS of injured male, female and pooled population are 4.88 ± 2.032°, 8.85 ± 2.22°, 5.85 ± 2.689° respectively. In normal population, MTS and LTS are steeper in female compared to male P < 0.05). LTS is steeper in injured male and female compared to uninjured (P < 0.05). MTS is steeper in injured male compared to uninjured (P < 0.05). Conclusion: Posterior tibial slope specifically LTS could be considered as a significant risk factor for noncontact ACL injury. Steeper posterior tibial slope (MTS and LTS) in female also is an important risk factor that explains the disparity in ACL injury rates between genders.

  Abstract in Arabic 

تأثير الانحراف الخلفي لعظم الساق الأعظم على التمزق الغير متصل للرباط الصليبى الأمامي.
الهدف من الدراسة: في الدراسات الحالية قسنا الانحراف الأوسط لعظم الساق الأعظم والانحراف الجانبي منفصلين باستخدام صور الرنين المغنطيسي لمفصل الركبة وقد كان الهدف من هذه الدراسة أن تقدم إشارة إلى مقدار الانحراف الخلفي . وتكمن اهمية الدراسة فى ايجاد القياست المجعية للانحراف الخلفي لعظم الساق الأعظم لدى الهنود العاديين ومقرنة ذلك مع الذين يعنون من عطب الرباط الصليبى الامامي غير اللاصق بالضافة الىى تقييم العلاقة بين ازدياد الأنحراف الخلفي لعظم الساق الأعظم وإصابات الرباط الصليبى الامامي. طريقة الدراسة: في الدراسة الحالية تم اختيار (60) مريضاً من المصابين بإصابات في الرباط الصليبى الأمامي (30 من النساء- 30 من الرجال) وتمت مقارنتهم ب (60) شخصاً من غير المصابين (30 من النساء- 30 من الرجال) أو العينة المحكومة بالنسبة للانحراف الجانبي والأوسط لعظم الساق الأعظم. وتم قياس الانحراف الأوسط والجانبي باستخدام 1.5 تسلا من الرنين المغناطيسي للركبة لكل شخص وقد تم تحليل البيانات باستخدام التحليل الاحصائي الملائم. النتائج: وجد أن متوسط الأنحراف المعياري للاشخاص غير المصابين من الرجال والنساء ومجموع السكان هو (±6.94,3.205 ,±9.28,2.657 ,±7.73,3.204 ) بالترتيب ومتوسط الأنحراف المعياري للمصابين من الرجال والنساء ومجموع السكان هو (±8.13 2.11 ,±10.56 1.691 ,±8.73 2.261 ) بالترتيب وأن متوسط الأنحراف المعياري للانحراف الجانبي للمصابين من الرجال والنساء ومجموع السكان هو (±4.88 2.032 ,±8.85 2.22 , ±5.85 2.689 ) بالترتيب. أن الأنحراف الاوسط والجانبي للعظم الساق الاعظم اكبر عند السيدات مقارنة بالرجال بنسبة (0.05 > P ) في السكان العاديين. وأن الانحراف الجانبي لعظم الساق أعلى عند الرجال والنساء المصابين مقارنة بالاشخاص غير المصابين بنسبة (0.05 > P ) وأن الانحراف الاوسط لعظم الساق أعلى عند المصابين من الرجال بالمقارنة بغير المصابين بنسبة (0.05 > P). الخلاصة: ان الأنحراف الخلفي لعظم الساق الاعظم وتحديداً الأنحراف الجانبي للعظم قد يكون عاملاً فاصلاً في زيادة خطر إصابة الرباط الصليبى غير المتصل للركبة. كما أن ازدياد الانحراف الخلفي لعظم الساق الأعظم لدى النساء ( الانحراف الوسطي والانحراف الجانبي). ايضاً يعدّ عاملاً مهماً في زيادة خطر الإصابة والذي يفسر المفارقات بين الجنسين في معدل الإصابة للرباط الصليبى الامامي.

Keywords: Lateral tibial slope, medial tibial slope, noncontact anterior cruciate ligament injury


How to cite this article:
Ghosh G. Effects of posterior tibial slopes on noncontact anterior cruciate ligament injury. Saudi J Sports Med 2015;15:214-9

How to cite this URL:
Ghosh G. Effects of posterior tibial slopes on noncontact anterior cruciate ligament injury. Saudi J Sports Med [serial online] 2015 [cited 2019 Jul 19];15:214-9. Available from: http://www.sjosm.org/text.asp?2015/15/3/214/164275


  Introduction Top


The tibial plateau is not horizontal. It has posteriorly inclined slope. The posterior tibial slope is directed posteriorly and inferiorly relative to the long axis of the middle of the shaft of the tibia. [1] Posterior tibial slope is defined as the angle between the perpendicular to the middle part of the diaphysis of the tibia and the line representing the posterior inclination of the tibial plateau. [2] Tibial plateau is not uniformly inclined postero-inferiorly. Medial tibial slope (MTS) is different from the lateral tibial slope (LTS). Using conventional magnetic resonance image (MRI) of knee, it is possible to measure MTS and LTS separately. The posterior tibial slope varies widely. [3],[4],[5] It may vary with age [6] and sexes. [1],[3] The posterior tibial slope increased in osteoarthritis of knee. [7]

The risk factors of noncontact anterior cruciate ligament (ACL) injury are multifactorial. Biomechanical study showed increasing slope of the tibial plateau caused increasing stresses on the ACL during compressive load on knee joint as in standing and walking. [8] So person with greater slope might be at higher risk of the ACL injury than the person with lower slope during heavy physical load on knee joint.

We measured MTS and LTS separately, using conventional MRIs of knee joint. The goal of the study was to provide reference value of the posterior tibial plateau slope in normal Indian population and ACL injured population and to assess the association between steeper MTS and LTS and noncontact ACL injury.


  Methods Top


It is a observational correlation study. Data were collected from 120 subjects (60 male and 60 female) who attended in a tertiary care hospital for some knee problems from January 2011 to January 2013. In the present study, 60 ACL injured (I) patients (30 male, 30 female) were compared with 60 ACL uninjured (UI) or control population (30 male, 30 female) regarding LTS and MTS. Mean age of the subjects were 33.96 years (range: 23-41 years). Subjects with minor knee problem (mild soft tissue injury, superficial bruise etc.), history and clinical sign suggestive of ACL injury included in the study. Conventional MRI scan of the affected knee was done in all subjects. All measurements were done on a same 1.5 Tesla MRI machine. Patients with minor knee problems but without any ligaments injury that was confirmed by MRI were included in the study as control. Patients with history and clinical sign suggestive of isolated ACL injury that was confirmed by MRI included in the study as ACL injured population (cases). Patients with any old or new tibial plateau fractures, osteoarthritis of knee, prior operations of knee, any congenital anomaly of tibia and multiple ligaments injury were excluded from the study. Cases and controls were matched in respect to weight, height and levels of activity. All measurements were done by annotation tools on soft copy of T1-weighted MRI scans of the tibio femoral joint of the selected subjects. We used the methods proposed by Hashemi et al. [9] for measurement of MTS and LTS. All measurements were taken by three different authors. It was found that there was high InterClass Correlation Coefficient (0.986). Values measured by the senior surgeon were included in the study.

First, the dorsal aspect of the tibial plateau was identified. In this transverse image, the sagittal plane that passed closest to the center of the tibial plateau was identified. In the mid sagittal section of tibia, the longitudinal axis of the tibia was constructed [Figure 1]. This was done by determining the midpoint of the anterior-to-posterior width of the tibia at two points located approximately 4-5 cm apart and as distally in the image as possible then these two midpoints were connected. The longitudinal axis was then reproduced in the middle of the medial tibial plateau on sagittal plane. The peak anterior and posterior points on the medial tibial plateau were identified. The slope of the line extending through these two points represented the MTS, and it was measured with respect to the axis perpendicular to the longitudinal axis [Figure 2]. A similar approach was used to determine the LTS [Figure 3].
Figure 1: Longitudinal axis of the tibia on mid sagittal section (L)

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Figure 2: Medial tibial slope (POA)

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Figure 3: Lateral tibial slope (POA)

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All data were analyzed using Statistica Version 6 (StatSoft Inc., 2001; Tulsa, Oklahoma, USA) software. Mean, median and standard deviation (SD) of the MTS and LTS were calculated for male, female and the entire population in both normal control and ACL injured patients. Kolmogorov-Smirnov test was done to assess whether data were normally distributed or not. Paired Student's t-test was done to tests for differences between MTS and LTS within individual subject. Student's unpaired t-test was done to compare the values of MTS and LTS between male and female. Also, Student's unpaired t-test was done to compare the values of MTS and LTS between normal control and ACL injured population. Finally, correlation tests were performed to determine the strength of the linear relationship between MTS and LTS. For all analysis, P < 0.05 was considered to be statistically significant.


  Results Top


Mean age (±SD) of male and female subjects are 32.30 ± 9.40 years and 31.12 ± 13 years respectively. Mean weight (±SD) of male and female subjects are 62 ± 2.21 kg and 56 ± 1.24 kg respectively. In uninjured (UI) or control population irrespective of gender mean ± SD MTS and LTS were 7.73 ± 3.204° and 4.68 ± 2.757° respectively. In injured (I) population, irrespective of gender mean ± SD MTS and LTS were 8.73 ± 2.261° and 5.85 ± 2.689° respectively. In uninjured (UI) or control male population, mean ± SD MTS and LTS were 6.94 ± 3.205° and 3.77 ± 1.859° respectively. In injured (UI) male population, mean ± SD MTS and LTS were 8.13 ± 2.11° and 4.88 ± 2.032° respectively. In uninjured (UI) or control female population, mean ± SD MTS and LTS were 9.28 ± 2.657° and 6.45 ± 3.364° respectively. In injured (UI) female population, mean ± SD MTS and LTS were 10.56 ± 1.691° and 8.85 ± 2.22° respectively. Descriptive statistics of numerical variables of tibial slopes (MTS, LTS) are summarized in [Table 1]. Kolmogorov-Smirnov test showed that data were normally distributed. Correlation test showed that MTS and LTS were poorly correlated in pooled population as well as in control or uninjured male and female population with r value 0.43, 0.11, 0.42 respectively. MTS and LTS were different within each uninjured or control sex group, and this was statistically significant (P = 0.002). Uninjured or control female had significant steeper MTS (P = 0.013) and LTS (P = 0.001) compared to Uninjured or control male. In pooled population, ACL injured (I) Patients had steeper MTS compared to uninjured (UI) or control population but the difference was not statistically significant (P = 0.058). In pooled population, ACL injured (I) patients had steeper LTS compared to uninjured (UI) or control population but the difference was statistically significant (P = 0.025). In male population, ACL injured (I) patients had steeper MTS and LTS compared to uninjured (UI) or control population and the difference statistically significant with P value 0.049 and 0.015 respectively. In female population, ACL injured (I) patients had steeper MTS compared to uninjured (UI) or control population but the difference was not statistically significant (P = 0.119). In female population, ACL injured (I) patients had steeper LTS compared to uninjured (UI) or control population and the difference was statistically significant (P = 0.025). Statistical significant tests are summarized in [Table 2], [Table 3], [Table 4], [Table 5] and [Table 6].
Table 1: Descriptive statistics of numerical variables of tibial slopes (MTS, LTS)

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Table 2: Comparison of numerical variables between male and female gender within control group - student's unpaired t-test

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Table 3: Comparison of numerical variables between male and female gender within ACL injured group - student's unpaired t-test

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Table 4: Comparison of numerical variables between control and ACL injured population irrespective of gender - student's unpaired t-test

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Table 5: Comparison of numerical variables between control and ACL injured population in male gender - student's unpaired t-test

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Table 6: Comparison of numerical variables between control and ACL injured population in female gender - student's unpaired t-test

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  Discussion Top


The knee joint is a composite synovial joint. It has the following component medial tibio femoral joint, lateral tibio femoral joint and patella femoral joint. All the components are covered with one joint capsule and lined by one synovial membrane. During unipedal or bipedal stance, it stabilizes femur on tibia so that the limb can sustain the load of body weight like a pillar. During locomotion, it reduces the distance between the center of gravity and the ground (effective limb length) so that the advancing limb can swing forward with minimum excursion of the center of gravity. The articular surfaces of the tibiofemoral joint in combination with the primary ligaments play an important role in controlling the biomechanical behavior of the joint. [10],[11] In particular, the contact mechanics between the femoral and tibial articular surfaces are complex, are three dimensional, and consist of many unique features. The geometry of the tibial plateau has a direct influence on the biomechanics of the tibiofemoral joint in terms of translation, the location of instantaneous center of rotation, the screw home mechanism, and the strain biomechanics of the knee ligaments such as the ACL. [10],[11],[12] An important characteristic of the tibial plateau is its posterior slope (with the anterior elevation being higher than the posterior elevation); when this characteristic is considered in association with a large compressive joint-reaction force such as that produced during weight-bearing activities, the force may have an interiorly directed shear force component that acts to produce a corresponding interiorly directed translation of the tibia. [10],[13] The importance of posterior tibial slope to anterior tibial translation has been well established in both animal [14] and human models. [10],[13] Analysis of the forces in the sagittal plane of the extended knee shows that they can be resolved into two components, a vertical compression force on the tibial plateau and a shearing force that tends to move the tibia anteriorly. [15] During weight bearing, as the slope of the tibial plateau increases, the magnitude of the anteriorly directed shear force component that is associated with the compressive joint force on the tibia also increases. [2],[14],[16]

In the present study, MTS was higher than LTS irrespective of gender in both ACL uninjured or control and ACL injured population, it implies that medial tibial plateau was more stepper than lateral tibial plateau. But according to Hashemi et al., [9] LTS was more stepper than MTS. According to Hudek et al., [7] in normal population, LTS is 4.90 ± 3.20° which was similar to the present study (LTS - 4.680 ± 2.757°) but MTS 4.10 ± 2.80° was lower comparison to present study (MTS - 7.730 ± 3.204°). In our opinion, these difference of MTS and LTS in various study as the geometry of tibial plateau is different in different races. In the present study, it was found that MTS and LTS were different within individual subject, and it was statistically significant (P < 0.05). It implies that the posterior tibial slope is not uniformly inclined anterior to posterior. In the present study, MTS of the female (MTS = 9.280 ± 2.650°) was greater than the male (MTS = 6.940 ± 3.20°) and the difference was statistically significant (P = 0.013) similarly LTS of the female (LTS = 6.450 ± 3.360°) was greater than the male (LTS = 3.770 ± 1.850°) this difference was statistically significant (P = 0.001). As MTS is more steeper than LTS during weight bearing as knee extends femur internally rotated on tibia that causes torsion of ACL. Female has steeper posterior tibial slope as well as MTS compared to male so in case of female ACL is more susceptible to torsional strain.

In the present study, 60 ACL injured (I) patients (30 male, 30 female) were compared with 60 ACL uninjured (UI) or control population (30 male, 30 female) regarding posterior tibial slopes. A preliminary t-test was performed to establish any existing differences between groups. Mean MTS of control or uninjured male was 6.940° compared to 8.130° in injured population and this difference was statistically significant with P = 0.049. So ACL injured male patient had steeper medial tibial plateau slope (MTS) compared to uninjured male population. When considering males and females as a group, the injured participants had increased MTS (8.730°) compared to uninjured population (7.730°) but this difference was not statistically significant (P = 0.058) but according to Hashemi et al. [20] total injured participants had significantly increased MTS compared to uninjured population. Mean LTS of control or uninjured male was 3.770° compared to 4.880° in injured population and this difference was statistically significant with P = 0.015. Mean LTS of control or uninjured female 6.450° was compared to 8.850° in injured population and this difference was statistically significant.

In the present study, we found that LTS was significantly greater in ACL injured (I) population compared to the ACL uninjured (UI) population (P < 0.05) as a whole irrespective of gender and separately both male and female. On the other hand, MTS was significantly greater in ACL injured (I) population compared to the ACL uninjured (UI) population (P < 0.05) only in case of male population. MTS was greater in ACL injured (I) population compared to the ACL uninjured (UI) population as a whole irrespective of gender and female population but the difference was not statistically significant (P > 0.05).

The primary restraint to anterior movement of the tibia is the ACL and rupture of the ACL leads to abnormal anterior tibial translation. Anterior tibial translation is more in ACL deficient patient with greater tibial plateau slope. [4] Similar results were shown in virtual computer simulated study [11] and in vitro examination with cadaveric knee. [16] Biomechanical study showed increasing slope of the tibial plateau caused increasing stresses on the ACL during compressive load on knee joint as in standing and walking. [8] So person with greater slope might be at higher risk of the ACL injury than the person with lower slope during heavy physical load on knee joint. [16] Our study proves this hypothesis. Besides these, according to our study, female had steeper posterior tibial slope and more prone to noncontact ACL injury. Different clinical studies supported that patient with noncontact ACL injury may have significantly higher mean tibial slope than persons with intact ACL. [3],[5],[11],[17],[18],[19],[20] However Meister et al. [5] and Hudek et al. [7] reported that there was no relationship between tibial slope and ACL injury.

There were several limitations of the present study. MRI measurements are subject to observer inconsistencies, landmark identification, and image clarity concerns. Our study done on Indian population and the sample size is small so further larger study by collecting data from various parts of the country needed for more precise results. Further studies regarding the effect of other anatomical aspects of the tibial plateau such as coronal tibial slope on noncontact ACL injury are needed to enhance our knowledge about the mechanism of noncontact ACL injury.


  Conclusion Top


From the present study, we established the associations between steeper posterior tibial slopes and noncontact ACL injury. Posterior tibial slopes measurements could be considered as a significant risk factors for ACL injury in the development of injury risk models. According to various researchers, ACL size, anterior knee laxity, and intercondylar notch size difference between genders explains the disparity in ACL injury rates between genders. However, from this study we proved that, posterior tibial slope also is an important factor that explain the disparity in ACL injury rates between genders.


  Acknowledgments Top


We are thankful to the Institution Ethical Board for giving permission to do the research work.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]



 

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