Abstract
Background
The anterior cruciate ligament is commonly injured and multiple risk factors have been studied. But there is paucity of articles considering predictive risk factors of femoral condyle morphology in south Indian population. This study aims to assess distal femoral condyle sphericity as a risk factor in anterior cruciate ligament injury and to correlate it with proximal tibia morphological risk factors.
Materials and methods
This is a case control study including 80 patients with knee MRI aged between 18 and 60.They were grouped into cases (40) and controls (40). Cases being non-contact ACL injuries without multi ligamentous injuries and controls being MRI with ACL intact. Lateral femoral condyle index, posterior tibial slope, medial and lateral tibial depth were measured and compared. The risk factors were analysed with multiple logistic regression.
Results
The lateral femoral condyle index had a mean value of 0.79 with standard deviation of ± 0.05 in cases group. Control group had a mean value of 0.803 with standard deviation of ± 0.05. Medial tibial slope in cases (8°) was lesser than in control group (7.6°). Lateral tibial slope was found to more among cases group (9.1°) than in control group (7.5°). Medial tibial depth had a mean of 4.07 mm among cases and 3.9 mm among control group. There was a moderate positive correlation between LFCI and Medial Tibial slope among cases that was statistically significant (P = 0.002). In addition, there was a weak negative correlation between LCFI and Medial Tibial Depth that was statistically significant.
Conclusion
The lateral femoral condyle index was not found to be significant statistically among ACL injured patients. In our study we concluded that lateral tibial slope was more reliable risk factor in predicting ACL injury when compared to other parameters.
Keywords: Anterior cruciate ligament injury (ACL), Lateral femoral condyle index (LFCI), Posterior tibial slope, Medial tibial depth, Lateral tibial depth
1. Introduction
The anterior cruciate ligament (ACL) is the primary stabilizer of the knee joint that mainly resists the anterior translation of the tibia and secondarily stabilises the knee to valgus and rotational forces.1, 2, 3
The ACL injury is associated with significant loss of function and significantly altered biomechanics which results in accelerated onset of osteoarthrosis in the knee joint.4 It is therefore important to determine the risk factors predisposing patients to ACL injury and identify risk groups, who may require special gait training or carry out preventive measures.5,6
The asymmetry of the slopes of the posterior medial and lateral tibial plateau can add an internal rotational vector in normal knee biomechanics which can be exaggerated in certain individuals and elicit a greater amount of force on the ACL.1 In addition to the proximal tibia osteology, the morphology of the distal femur has also come into consideration. Recently, reports have assessed the femoral attachment of the ACL and its possible role in predisposing an ACL injury.3,4,7, 8, 9 The sphericity of the distal femur in the sagittal plane would also affect knee biomechanics.1,2,5
We hypothesized that variation in lateral femoral index and proximal tibia morphological parameters are the risk factors for ACL injury. This study aims to analyse, does increase or decrease in distal femoral condyle sphericity measured on MRI increase the chances of ACL tear & Does increase or decrease in various proximal tibia morphological parameters measured on MRI increase the chances of ACL tear.
2. Methods
The study was conducted for a period of one year, between September 2021–August 2022. After obtaining the institutional ethical committee approval, all patients with proven ACL injury on MRI were explained and consented and then included under study group, and patients undergoing MRI of knee for other (non-ACL injury) pathology were taken into control group. MRI was done using 1.5 T machine and standard procedure of MRI knee was done. There were 40 subjects in case group and 40 subjects in control group. The inclusion and exclusion criteria have been represented as flowchart in Fig. 1.
Fig. 1.
Flowchart for inclusion and exclusion criteria of the study.
The following parameters were measured in both the groups.
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I.
Lateral femoral condyle index (LCFI)
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II.
Medial tibial slope (MTS)
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III.
Lateral tibial slope (LTS)
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IV.
Lateral tibial height (LTH)
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V.
Medial tibial depth (MTD).
All the measurements were measured by a single orthopaedic sugeon to avoid interobserver error, using RadiAnt DICOM Viewer 2021.1., with an accuracy of 0.1 mm for linear measurements and 0.1° for angular measurements. All the MRI's were conducted using 1.5-T scanner (MAGNETOM Symphony; Siemens AG, Erlangen, Germany) with a 3-mm section thickness.The orthopaedician who performed the measurements was blinded of patient records.
2.1. Inclusion criteria
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i.
Age 18 years–40 years with MRI proven ACL injury.
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ii.
Non-contact ACL injury.
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iii.
MRI with isolated meniscal injury
2.2. Exclusion criteria
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i.
Multi-ligamentous injury
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ii.
Associated fractures
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iii.
Osteoarthritic change.
Assessment tools:
The sample size was calculated using the formula:
| n = 2[SD]2 [Zα/2 + Zβ]2 /d2 |
Where,
SD−standard deviation
| d = M1-M2 |
M − mean.
Zα/2=1.96.
Zβ = 0.84.
The data was analysed using SPSS for windows (SPSS ver 22.0, Armonk, NY). The data was normally distributed as assessed by Shapro Wilks test. Comparison for variables between cases controls and gender was done using unpaired't’ test. Pearson correlation was used to measure linear relationship between continuous variables. An ROC curve with area under the curve was calculated for each continuous variables with cut off values. Sensitivity and specificity for significant variables post ROC curve was also determined. Finally, a logistic regression was done to determine the strength of association between risk factor and injury. The level of significance was set at P < 0.05.
2.2.1. Lateral femoral condyle index
Imaging protocols included 2 sequences in sagittal, coronal and axial planes with thickness of 3 mm. First, on the coronal image, the one with most prominent popliteal groove was identified. The lateral femoral condyle width width measurement was done at the popliteal groove. Sagittal section at the level of midpoint of femoral condyle is obtained in T1 image. A circle was used to approximate curvatures of femur condyle in flexion and extension using the T1 weighted sagittal image. A circle which fits best to the bone at subchondral level at 6 o'clock was drawn (inferior most) and 9o'clock (anterior most) position and this forms the extension circle. Another circle which fits best in 3 o’ clock (posterior most) and 6o'clock (inferior most) is drawn. Most congruent overlap with the spherical shape of the lateral femur condyle was obtained by aligning the circles. Lateral Femur Condyle Index was obtained by dividing the flexion circle diameter by extension circle diameter as shown in Fig. 2. This was carried out according to Hodel et al.1 We obtained area of the two circles (A). The diameter (d) was obtained by the formula d = 2x √A/ .
Fig. 2.
Measurement of lateral femoral condyle index on MRI.
2.2.2. Measurements of tibial slope
Measurement of both the medial and lateral tibial slope is must. To obtain this we chose the axial section where popliteal groove was shown the maximum. Along with this coronal section was identified to find the mid-articulating region in sagittal plane of the medial and lateral plateau.
On this sagittal image, a tangential line was drawn along most anterior aspect of the outer cortex of tibial shaft. Another line which connected the highest points of anterior and posterior aspects of medial plateau was drawn, which defined the slope of the medial plateau as shown in Fig. 3. The angle between the two lines was calculated and difference to tangential line was calculated to give the value of Lateral tibial slope as seen in Fig. 4.
Fig. 3.
Measurement of posterior medial tibial slope on MRI.
Fig. 4.
Measurement of lateral tibial slope on MRI.
2.2.3. Medial tibial depth and lateral tibial height
Measurement of depth on the medial and lateral tibial plateau is another important aspect. On the medial side it is done using a line which connects the crests of superior and inferior parts of the plateau of tibia. Another line which runs parallel to this line was then drawn tangentially to the lowest aspect of the concave part which represents the terminal boundary of the subchondral bone. Measurement between these two lines that is perpendicular distance was done and this represented the depth of the medial tibial plateau concavity. A similar approach was followed for the lateral side as shown in Fig. 5, Fig. 6.
Fig. 5.
Measurement of medial tibial depth on MRI.
Fig. 6.
Measurement of lateral tibial depth in MRI.
There was a multivariate analysis done among the age and sex matched case control groups.
3. Results
All the patients with MRI proven ACL injury who met the inclusion and exclusion criteria were included in the study. A total of 40 patients were in the study group and 40 in control group. They were identified and analysed.
3.1. Demographics
The cases group had 80 % of males (n = 29) and 20 % of females (n = 11). Whereas control group had 57.5 % males (n = 23) and 42.5 % females (n = 17). Cases group showing patients with MRI knee with ACL rupture with intact medial collateral ligament, lateral collateral ligament and posterior collateral ligament. Controls group showing patients with MRI knee with intact ACL and isolated meniscal injury.
Mean age in case group- males, was found to be 27.22 years (19–43; SD ± 7.8) and females was 35.5 (21–57; SD ± 12.7). Mean age in control group- male patients was found to be 34.8 (21–54; SD ± 8.9) and in females was 36.5 (18–54; SD ± 12.04).
3.2. Magnetic resonance imaging measurements
3.2.1. Lateral femoral condyle index
The lateral femoral condyle index had a mean value of 0.79 with standard deviation of ± 0.05 in cases group. Control group had a mean value of 0.803 with standard deviation of ± 0.05.
3.2.2. Posterior medial tibial slope
Medial tibial slope had a mean value of 8° with standard deviation of ± 2.6° in cases group. Control group medial tibial slope mean was found to be 7.6° with standard deviation of ± 2.87°.
3.2.3. Posterior lateral tibial slope
Lateral tibial slope among 40 cases group was found to be 9.1° with standard deviation of ± 3.4°. Lateral tibial slope among control group had a mean value of 7.5° with standard deviation of ± 2.7°.
3.2.4. Medial tibial depth
Medial tibial depth was found to have a mean of 2.8 mm with standard deviation of ± 0.88 mm in cases group. Control group had a mean value 3.04 mm with standard deviation of ± 1.04.
3.2.5. Lateral tibial height
Lateral tibial height among cases had a mean value of 4.07 mm with standard deviation of ± 0.89 and among control group 3.9 mm was the mean. Standard deviation was found to be 0.81.
In our study, it was found that Lateral Tibial Slope was statistically significant more among cases than control (P = 0.002). There was no statistically significant difference between cases and controls for Lateral femoral condyle index, medial tibial slope, medial tibial depth and lateral tibial height as shown in Table 1.
Table 1.
MRI measurements of all included parameters among cases and controls. MRI measurements in control and cases groups.The degree of freedom was 78. Level of significance was p < 0.05.Statistical significance was found using Unpaired t-test.
| Group | N | Mean ± SD | df | P value | |
|---|---|---|---|---|---|
| Lateral Femoral Condylar Index | Cases | 40 | 0.79 ± 0.05 | 78 | P = 0.35 |
| Controls | 40 | 0.803 ± 0.05 | |||
| Medial Tibial Slope (in degrees) | Cases | 40 | 8 ± 2.6 | 78 | P = 0.508 |
| Control | 40 | 7.6 ± 2.7 | |||
| Lateral Tibial Slope (in degrees) | Cases | 40 | 9.1 ± 3.4 | 78 | P = 0.022* |
| Control | 40 | 7.5 ± 2.7 | |||
| Medial Tibial Depth (in mm) | Cases | 40 | 2.8 ± 0.88 | 78 | P = 0.41 |
| Control | 40 | 3.04 ± 1.04 | |||
| Lateral Tibial Height (in mm) | Cases | 40 | 4.07 ± 0.89 | 78 | P = 0.57 |
| Control | 40 | 3.9 ± 0.81 |
It was found that there was a moderate positive correlation between LCFI and Medial Tibial slope among cases that was statistically significant (P = 0.002). In addition, there was a weak negative correlation between LCFI and Medial Tibial Depth that was statistically significant as shown in Table 2.
Table 2.
Correlation between LFCI and other risk factors among cases and controls. Level of significance at P < 0.05.*statistically significant using Pearson correlation.
| Cases | Medial Tibial Slope | Lateral Tibial Slope | Medial Tibial Depth | Lateral Tibial Height |
|---|---|---|---|---|
| Lateral Femoral Condylar Index | 0.483 | 0.194 | −0.365 | 0.063 |
| P value | P = 0.002* | P = 0.23 | P = 0.021* | P = 0.69 |
4. Discussion
Femoro tibial biomechanics is studied to have a role in anterior cruciate ligament injury. The lateral compartment is asymmetrical with femorotibial morphology. The posterior tibial slope, tibial depth has been studied as risk factor for the ACL injury. Our study was aimed to study lateral femoral condyle morphology as an added risk factor along with known tibial morphological factors.
In our study, we measured the LFCI, which aimed to quantify the sphericity of the lateral femoral condyle. In addition to this we also measured tibial slopes and tibial plateau depths, which have been reported to be a significant risk factors in previously reported literature.
It was postulated from previous study by Hodel et al.1 that a lower lateral femoral condyle index predisposed patients to an ACL injury. However, in our study we found that the LFCI was not a significant risk factor. Among the other measurements we performed, we found only the lateral tibial slope to have a significant correlation to ACL injury. In the previous literature by Hodel et al.,1 Lansdown et al.,2 Pfeiffer et al.,3 Huggi et al.,7 Shen X et al.8 and Raja et al.9 have found depth, slope and LFCI to be significant risk factors for ACL tear.
In our further analysis, we found the positive correlation between LFCI and medial tibial slope in the ACL injured group. This meant that patients who had a smaller LFCI and a greater lateral tibial slope were at greater risk of sustaining anterior cruciate ligament injury in our study group. In addition, we also noted subjects with a lower LFCI and shallow medial tibial concavity to be at risk for ACL injury. This indicated that, though LFCI as a single measurement was not found to be significant, when combined with a higher posterior lateral tibial slope and shallow medial condyle, it could together predispose patients to ACL injury. Literature has reported LFCI to be an important contributor to knee biomechanics and a higher LFCI was postulated to result in less femoral asymmetry which results in less femoral gliding over the tibia effectively reducing the forces exerted on the ACL.1
It is known that tibial slope and femoral notch width are predisposing risk factors for ACL injury and recent literature has noted a differential tibial slope to apply an increased internal rotation force vector on the knee which can again increase the forces applied on the ACL.1, 2, 3,7,8 In our study we found only that an increase in the lateral tibial plateau slope was a significant risk factor for injury in our study group. This is in agreement with a study by Vasta et al.,6 where he noted that a greater lateral tibial plateau slope predisposed subjects to an ACL injury. They too noted that the medial tibial slope was not a significant risk factor ACL injury. Shen et al.8 found that both the medial and lateral tibial slopes to have statistically significant correlation to ACL injury.8
Hashemi et al. 13in their study concluded that males with increased medial tibial slope and lateral tibial slope along with decreased medial tibial depth were at increased risk of suffering from ACL injury. They also conducted studied in females and found only increased medial tibial slope and decreased medial tibial depth was found to be a risk factor. Our study results were found to be similar to this study, though we didn't differentiate group into male and female.
There appears to be great variation in literature as to what bony morphology predisposes subjects to ACL injury. This could be due to significant variations in measurement protocols and observer errors.
Inter observer variability could be the most probable reason behind different outcome in different studies although the same standard measurement protocols are used. It is a proven fact that exaggerated slope will add exaggerated stress on the ACL.10, 11, 12, 13, 14, 15, 16, 17 This measurements will give an idea to surgeons in identifying the risk of possible ACL ruptures.
Insufficient literature on standard measurement technique for these indices has resulted in inability to identify the risk factors. A section of the population with a specific morphological features might have greater risk for ACL ruptures and may continue to have the same amount of risk following reconstruction surgeries.2
As far as we know, this is one of very few studies done on Indian population. There are a large number of studies to show that the normal anatomical parameters in western population in other regions of the body (femur neck shaft angle, Q angle etc) vary from the averages in Indian population. This could be attributed, most likely to the Indian population being “habitual squatters”. Whether this particular trait alters the anatomy, within the knee with respect to the ACL is unknown. We found that most of the parameters apart from lateral tibial slope do not statistically contribute to the ACL injury risks. There are some limitations in our study in that there was only one observer and we did not measure the femoral notch width which is known to be a significant risk factor. Further study with a great number of subjects including the femoral notch index should be performed to further study our findings.
5. Strengths & limitations
Strength of our study is that there are not much literature on the predictive risk factors for ACL injury in Indian population. Present study helps in correlating the various risk factors and ACL injuries and would be a guide for further studies on this topic.
Limitations of the present study are that the sample size is less, it is a single centre study and a single observer study.
Further study with larger sub group of population including the diffuse age group is warranted to get baseline of various parameters for the Indian population which might enable researchers to articulate preventive strategies.
6. Conclusion
On MRI based study of ours, we conclude that among the morphology and morphometric measurements of tibia on MRI, posterior lateral tibia slope is more reliable and statistically significant risk factor in predicting the ACL injury as compared to other parameters.
Financial aid
Nil.
CRediT authorship contribution statement
Keelara Mahadevappa Pawan Kumar: Study Conception & Design, Analysis And Interpretation Of Results, Draft Manuscript Preperation. Aniruddha Mundargi: Study Conception & Design, Data Collection, Analysis And Interpretation Of Results, Draft Manuscript Preperation. Madhuchandra Puttamaregowda: Data Collection, Analysis And Interpretation Of Results, Draft Manuscript Preperation. Rakshith Kumar Kammagondanahalli: Data Collection, Draft Manuscript Preperation. Sagar Perumalswamy: Data Collection, Draft Manuscript Preperation, All Authors Reviewed The Results And Approved The Final Version Of Manuscript. Shetty M. Shantharam: Study Conception & Design, Analysis And Interpretation Of Results, Draft Manuscript Preperation.
Declaration of competing interest
Nil.
Contributor Information
Keelara Mahadevappa Pawan Kumar, Email: pawankumar852@gmail.com.
Aniruddha Mundargi, Email: pm.aniruddha@gmail.com.
Madhuchandra Puttamaregowda, Email: drmadhuchandrap@gmail.com.
Rakshith Kumar Kammagondanahalli, Email: rakshith337@gmail.com.
Sagar Perumalswamy, Email: sagarsan34@gmail.com.
Shetty M. Shantharam, Email: drshantharamshettyssiot@gmail.com.
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