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Journal of Orthopaedics logoLink to Journal of Orthopaedics
. 2020 Sep 11;21:487–490. doi: 10.1016/j.jor.2020.08.032

Study of relationship of posterior tibial slope in anterior cruciate ligament injury

Tapas Kumar Panigrahi a, Amit Das a,, Tanmoy Mohanty a, Swarnendu Samanta b, Suvendu Kumar Mohapatra c
PMCID: PMC7501475  PMID: 32999535

Abstract

Objective

To determine the relationship between Posterior Tibial slope in terms of medial and lateral in Anterior cruciate ligament deficient patients.

Methods

Magnetic resonance images (MRI) of the knee of 100 ACL injured patients and 100 ACL intact patients were studied. Their medial and lateral posterior tibial slopes were measured using MRI. Of 200 subjects, 100 (Male- 63, Female- 37) were controls, other 100 (Male – 68, Female-32) were ACL injured cases. Using DIACOM viewer software,the slopes of both medial and lateral slopes were measured. Range of Variation, mean value and standard deviation of medial tibial plateau slope (MTS), lateral tibia plateau slope (LTS) of controls and ACL injured patients were measured. The data collected were entered into Microsoft excel worksheet and analysed using statistical package for social sciences, Version 15.0 (SPSS Inc. Chicago, IL, USA). Distribution of data was confirmed using Shapiro's Wilk Test and appropriate parametric statistics were applied. For all analysis p value < 0.05 was set to be significant.

Results

In control (ACL uninjured) population mean MTS was 5.95° with SD 3.09°, mean LTS was 6.08° with SD 3.48°. In ACL injured population mean MTS 6.41° with SD 2.66°, mean LTS was 8.12° with SD 3.65°. So ACL injured population had MTS steeper than control population with no statistical significance (p value < 0.27) and LTS was steeper than control population with statistical significance (p value < 0.001),where as there were comparable results between male and females.

Conclusion

Our current results indicate that lateral PTS is a risk factor for patients with primary ACL tears as compared with ligament-intact controls. Therefore,PTS should be considered as independent modifiable risk factors in ACL injury.

Keywords: Anterior cruciate ligament, Magnetic resonance imaging, Posterior tibial slope

1. Introduction

The geometry of the tibial plateau, in particular, has a direct influence on the stability of the knee joint in the sagittal plane in terms of translation, the location of the instantaneous center of rotation, the screw-home mechanism, and the biomechanics of the important ligaments such as the Anterior cruciate ligament (ACL).1 Injuries to the ACL arise due to deterioration of the static and dynamic stabilizers of the knee joint. While the static stability is supplied by ligaments, menisci, joint capsule, and bony geometry, the dynamic stability is an integrated function of the neuromuscular system.22 ACL injury occurs predominantly via non-contact mechanisms. Because of a high incidence of the long-term complications of ACL injury, including pain, impairment of normal knee function, meniscal lesions and early development of osteoarthritis; many studies have been conducted to better understand the mechanisms of ACL injury and the associated risk factors which contribute to increased risk for injury.2, 3, 4 The PTS is defined as the angle between a line parallel to the posterior tibial inclination and a line that bisects the diaphysis of the tibia. Biomechanically, a higher tibial slope in the presence of a compressive load will generate a higher anterior shear component of the tibio-femoral reaction force, resulting in increased strain on ACL.5,6 In a cadaveric study by McLean et al. the mean peak strain in the anteromedial bundle of the ACL was found to be directly proportional to anterior tibial acceleration during a simulated jumplanding task. More remarkably, the tibial slope was significantly correlated with both peak anterior tibial acceleration and peak anteromedial bundle strain.7 Whether the PTS is a risk factor for ACL injury remains debatable. This study aimed to compare ACL-injured and ACL-intact patients as well as males and females in terms of Posterior tibial slope both medial and lateral to determine their association with ACL injury.

2. Materials and methods

This is an Observational study made in the Department Of Orthopaedics, SCB Medical College and Hospital, Cuttack among a Section of Eastern Indian Population Attending out Patient Department of SCB Medical College And Hospital, Cuttack between December 2017 to March 2019.100 cases (ACL injured) And 100 controls(ACL intact) of Skeletally mature subjects (between 15 years and 55 years) of both sexes. Conventional 3T MRI of the knee joints of the selected subjects were done in the department of Radiology, SCB medical college and Hospital, Cuttack. Angles of Tibial Plateau slopes(MTS,LTS) were measured by Annotation tools from the soft copy of these MRI using DIACOM Viewer Software.

  • Subjects Exclusion Criteria

  • Osteoarthritis of knee.

  • Fractures of tibial plateau.

  • Multi-ligamentous injury of knee.

  • Tumours of proximal Tibia.

  • Congenital Deformities around knee.

  • Age >55 years and <15 years.

Informed Consent was taken in the preferred language of the patient. Permission of the Institutional Ethical committee was obtained prior to commencement of the study.

All measurements were done on T2 weighted coronal, axial, sagittal MRI of knee joints using Annotation tools as proposed by Hudek et al.All patients underwent MRI according to the standard protocol. Patients were placed supine with their legs extended and in neutral position by keeping patella facing towards roof. The involved knee was placed in knee extremity coil with patella centered in the coil. The sagittal slice imaging was aligned perpendicular to a line perpendicular to the posterior margins of the posterior femoral condyles. Sagittal sections were secondarily aligned parallel to the femoral diaphysis on the coronal cut. This standard protocol ensured obtaining true sagittal images in all patients.

Range of Variation, mean value and standard deviation of medial tibial plateau slope (MTS), lateral tibia plateau slope (LTS) of controls and ACL injured patients were measured. Mean, range and standard deviation of MTS, LTS were calculated for male, female and the entire population and Shapiro's Wilk Test was done to assess normal distribution of the data. The mean value of MTS and LTS of normal male and female (controls) population were compared and identify significant variation if any by unpaired Student t-test. The mean value of MTS, LTS of normal male and female population were compared with ACL injured male and female separately and as group, and identify any by unpaired student t-test. For all analysis p value < 0.05 was set to be significant.

3. Results

Total 200 subjects were taken in study. Out of them 131 male and 69 females. Of 200 subjects, 100 (Male- 63, Female- 37) were controls, other 100 (Male – 68, Female-32) were ACL injured cases.

. Numerical values of angle of tibial plateau slope [medial tibial slope (MTS), lateral tibial slope (LTS)] of both cases and controls were entered into master chart and statistical analysis made. The data collected were entered into Microsoft excel worksheet and analysed using statistical package for social sciences, Version 15.0 (SPSS Inc. Chicago, IL, USA). Distribution of data was confirmed using Shapiro's Wilk Test and appropriate parametric statistics were applied. In the present study anatomical variables of tibial plateau such as medial tibial plateau slope (MTS), lateral tibial plateau slope (LTS) were measured in normal population and ACL injured populations. Master chart prepared and Statistical analysis done. Mean age of ACL Injured and Uninjured were 35.70 and 34.86 years respectively. Range of age for ACL Injured were 15–55 yrs and for ACL Uninjured were 16–55 years. In control (ACL uninjured) population mean age was 35.7 ± 10.77 and for ACL injured population mean age was 34.86 ± 10.8(Table 2).

Table 2.

Demographic profile of control and cases.

Variable ACL Minimum Maximum Mean Std. Deviation
Age INTACT 16 55 35.70 10.77
INJURED 15 55 34.86 10.08
Medial INTACT −2.80 13.6 5.95 3.09
INJURED 1.9 13.60 6.41 2.66
Lateral INTACT −4.0 14.50 6.08 3.48
INJURED 1.4 18.7 8.12 3.65

In control population range of medial tibial slope (MTS) was −2.80° to 13.60°.And lateral tibial slope was −4.00°–14.50°. In ACl injured population range of medial tibial slope (MTS) was 1.9 °to 13.6° and lateral tibial slope was 1.4°–18.7°. In control (ACL uninjured) population mean MTS was 5.95° with SD 3.09°, mean LTS was 6.08° with SD 3.48°. In ACL injured population mean MTS 6.41° with SD 2.66°, mean LTS was 8.12° with SD 3.65°. So ACL injured population had MTS steeper than control population with no statistical significance (p value < 0.27) and LTS was steeper than control population with statistical significance (p value < 0.001) when male and female considered as one group(Table 4). When considered as whole the posterior tibial slope of ACL injured is steeper than ACL uninjured group with statistical significance. (p value < 0.001)in both the genders (Table 5).

Table 4.

Comparison between medial and lateral slope in both groups.

ACL SITE Mean Std. Deviation Mean difference T p
INTACT Medial 5.95 3.09 −0.12 −0.345 0.73
Lateral 6.08 3.48
INJURED Medial 6.41 2.66 −1.72 −4.345 <0.001
Lateral 8.12 3.65

Table 5.

Comparison between ACL intact & injured groups according to site.

SITE ACL Mean Std. Deviation Mean difference T p
MEDIAL INTACT 5.95 3.09 0.45 1.10 0.27
INJURED 6.41 2.66
LATERAL INTACT 6.08 3.48 2.14 4.05 <0.001
INJURED 8.12 3.65

4. Discussion

The most important finding of this study is that the lateral and medial tibial slope were all significantly higher in the ACL-injured group compared to the control group(Fig. 1). In both groups, the lateral tibial slope was greater than the medial tibial slope (statistically significant in injured group). Further, more in gender comparisons lateral slope increased both in males and females in both groups. The results of this study support previous studies suggesting that increased posterior tibial slope is associated with both an increased risk of primary ACL injury.

Fig. 1.

Fig. 1

Bar Diagram depicting the posterior tibial slope(range) of both injured and control group.

According to Hudek et al.,8 Hashemi et al.,1 Medial tibial slope (MTS) and lateral tibial slope of female were greater than the male. But in present study medial tibial slope of female (MTS = 6.64 ± 2.78) was greater than the male (5.63 ± 3.19) and that difference was statistically not significant. (p value = 0.13) (Table 3). Similarly, lateral tibial slope of female (LTS = 6.56 ± 3.53) was greater than male (LTS = 5.85 ± 3.45) and this difference was statistically not significant. (p value = 0.35). This is similiar to studies by Bisson et al. 9and Stijak et al.,10 where there is no statistically significance between two groups (male and female). Some authors found the correlation between the tibial slope and the ACL injury to be sex-dependent. Females with steeper tibial slope are at greater risk of noncontact ACL injury than males.11, 12, 13, 14, 15 Meister et al.,16 Hudek et al.,8 Waiwaiole et al.17 found no correlation between genders both in controls and cases.

Table 3.

Genderwise comparison between medial and lateral slope within ACL intact and injured groups.

ACL Site Gender Mean Std. Deviation Mean Difference t p
INTACT Medial Female 6.64 2.42 1.01 1,60 0.13
Male 5.63 2.76
Lateral Female 6.56 4.62 0.71 0.94 0.35
Male 5.85 3.13
INJURED Medial Female 6.87 2.78 0.69 1.27 0.22
Male 6.18 3.19
Lateral Female 8.40 4.62 0.41 0.46 0.59
Male 7.99 3.13

Many recent studies have attempted to identify potentially modifiable risk factors related to the PTS and to develop strategies to prevent ACL injuries. Effects of patient demographics, such as gender and age, on the tibial slope have not been fully elucidated. The present study showed that the PTS values does not correlate with increasing age(Table 1). In a study by Sun et al.,18 the PTS follows a trend of first decreasing and then increasing, and its role in ACL injury changes with advancing age. The difference in PTS between the younger and older groups likely is related to the regulation of skeletal growth and degeneration.

Table 1.

Correlation between age and site within ACL intact and injured groups.

ACL AGE SITE (Mean ± SD) r P
INTACT 35.7 ± 10.77 Medial
5.95 ± 3.09
−0.21 0.03
Lateral
6.08 ± 3.48
−0.08 0.4
INJURED 34.86 ± 10.8 Medial
6.41 ± 2.66
−0.18 0.07
Lateral
8.12 ± 3.65
−0.07 0.5

In our study Mean LTS of control or uninjured was 6.08° ± 3.48° compared to 8.12° ± 3.65° in injured population. This was considered statistically significant (p value < 0.001). Mean MTS of control or uninjured was 5.95° ± 3.09 compared to 6,41° ± 2.66° in injured group, but not significant (p value = 0.27). So ACL injured patients had increased or steeper lateral tibial plateau slope (LTS) compared to uninjured population, as a whole both male and female. In a study by Emrah et al. 19the patients with complete ACL ruptures had a statistically significantly (p < 0.01) larger PTS on the lateral tibial condyle than the control group (4.5° and 3.8°, respectively). However, there was no statistically significant differences between the two groups’ medial PTS.

Our current results indicate that lateral PTS is a risk factor for patients with primary ACL tears as compared with ligament-intact controls. This correlation was confirmed in biomechanical models that reported increased anterior tibial translation and ACLR graft force with increased PTS. Clinically, it was reported that patients with an increased PTS (>12°) are at a significantly higher risk for ACLR(ACL reconstruction)graft failure. Thus, theoretically, these patients may be at higher risk for ACLR graft rupture; however, further longitudinal research is needed to determine risk stratification for ACLR graft failure and nonmodifiable risk factors such as tibial slope. An increased posterior slope is a risk factor not only for an ACL tear, but also for failure of ACL reconstruction. Webb et al. 20found an increased risk of failure or contralateral injury associated with increased tibial slope, which was most apparent with the posterior slope in excess of 12°. Slope leveling osteotomy has been proposed to correct this risk factor in repeat revision surgery.9

Surgeons should consider measuring LTPs during preoperative assessment of ACL-injured patients, and patients with values > 7.4° should be considered at high risk of ACL-R failure. Static ATT increased significantly in knees with tibial slopes >7°, by approximately 0.3 mm per degree, and that dynamic ATT increased significantly in knees with tibial slope ≥12°, by approximately 0.2 mm per degree. These findings confirm the relationship between tibial slope and ATT first described by Dejour et al.,5 who found a stronger coefficient of 0.6 mm per degree, and confirmed more recently by Schatka et al.21

5. Conclusion

We found a statistically significant difference in the lateral PTS of the complete ACL rupture group and the control group, which is consistent with the literature. This study confirmed that the tibial slopes can be measured reliably using an MRI-based method.

An understanding of the anatomical risk factors for ACL injury and treatment failure is important. As a risk factor, the increased tibial slope is potentially modifiable by osteotomy. Such intervention should be considered in cases of excessive slope. To make the measurement of the tibial slope more reliable, future studies should use a prospective recruitment of consecutive noncontact ACLinjured patients with double-blinded image analysis. Our limitations are that prospective study with Non-contact (pivoting tasks) ACL injured subjects would have been better. Considerations should be given to meniscal tears associated wih ACL tear. Studies with larger sample is essential. however, Knowledge of this study could be used in different operative orthopaedic procedures (like ACl reconstruction, Knee arthroplasty, high tibial osteotomy, tibia plataeu management). Finally, this study highlights the importance of optimizing surgical procedures and rehabilitation protocols to patients with different anatomic and lesional characteristics.

CRediT authorship contribution statement

Tapas Kumar Panigrahi: Methodology, Validation, Formal analysis. Amit Das: Investigation, Writing - original draft, Visualization. Tanmoy Mohanty: Conceptualization, Supervision. Swarnendu Samanta: Software, Writing - review & editing. Suvendu Kumar Mohapatra: Resources, Project administration.

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