Abstract
Background
ACL injuries are infamously known for disability in young adults and require surgical reconstruction. The need of time is to predict predisposing factors and prevent ACL injuries.The incidence of ACL injuries has been associated with various factors related to the morphology of distal femur and proximal tibia.Hence, purpose of this study was to assess the relationship of morphology of distal femur by assessing Notch Width(NW), Notch Width Index (NWI), and Notch shape calculated preoperatively on MRI in association with an ACL tear.
Methods
The following randomized control study had 60 patients enrolled with non contact injury to knee who were equally divided into 2 groups i.e. ACL injury group and control group. ACL group had patients who had MRI proven ACL tear along with clinical findings suggestive of ACL tear whereas control contained patients with intact ACL. Demographic data was collected and NW, NWI and Notch shape were determined on coronal sections of MRI sequences.
Results
Positive correlation of ACL tear was seen with NW, BCW, NWI, NWP, and NWJ. Smaller Notch Width showed higher incidence of ACL tear (p = 0.019). The mean NWI in the injured and control knee is 0.31 ± 0.01 and 0.27 ± 0.01 respectively and was statistically significant(p < 0.001). A shaped Notch (60%) was commonly seen in ACL tear group and U shaped notch (73.3%) was commonly seen in control group.We found the cut off value for the prediction of ACL tear of NWI was 0.29 with a sensitivity of 90% and specificity of 86.7%.
Conclusion
ACL injuries in the given population have shown higher incidence with narrow femoral intercondylar notch, smaller notch width index, ‘A’ shaped femoral notch. If any of the above findings are present in the MRI, its important to counsel the subjects about the increased risk of ACL injuries in them and take preventive measures.
Keywords: ACL tear, Notch width, Notch width index, Notch shape, Prevention of ACL tear, Risk factors for ACL injury
Abbreviations
- ACL
Anterior Cruciate Ligament
- BCW
Bi-intercondylar Width
- NWI
Notch Width Index
- NW
Notch Width
- NWP
Notch Width At Popliteal Groove
- NWJ
Notch Width At Joint Line
1. Introduction
In recent years, there has been growing trend to be involved in sports activities in young population and anterior cruciate ligament (ACL) remains one of most commonly involved ligament.1 ACL tear has shown long term disability in young adults and requires surgical reconstruction. Hence it is important to know the factors predisposing the ACL injuries to prevent people from having them.
There are many injury risk factors related to intrinsic (non-modifiable) and/or extrinsic (modifiable) factors of ACL-injury. The modifiable risk factor include environmental factors, level and type of sporting activity, footwear, weak muscular strength etc.2 The incidence of ACL injuries has been associated with various non modifiable risk factors related to the morphology of distal femur and proximal tibia like intercondylar notch parameters of femur, depth of medial tibial plateau, and the posterior tibial slope etc.3,4 In epidemiological studies of ACL deficient knees; it was found that females overall and narrow femoral intercondylar notch width in either sex were major correlating factors to injury of the ligament.3 It is known fact that women tend to have narrower notch than males.4 Smaller femoral notches are known to be associated with thin and weak ACLs.6, 7, 8 Because of the stenotic notch, ACL impinges onto the lateral femoral condyle, during which it receives anterior shear forces or tibial rotation causing ACL rupture.9, 10, 11, 12 Though notch width is used to prove this correlation in various studies, the use of notch width index (NWI) has been regarded as a better index because it eliminates variation caused by magnification, body stature and size.13 The Notch width index (NWI), has been defined as the ratio of the width of the intercondylar notch to the width of the distal femur at the level of the Popliteal groove measured on a tunnel view radiograph of the knee or coronal section in MRI(13,14,15).The femoral notch shape has been described into three types: Type A, Type Ω and Type U.14 Among these A-shaped notch tend to be narrow and frequently associated with an ACL tear.
Thereby, the impetus of this study was to assess the interconnection of Notch Width, Notch Width Index (NWI), and Notch shape calculated preoperatively on Magnetic resonance imaging (MRI), in association with an ACL tear.
2. Materials and methods
This randomized controlled study was done between, January 2019 to December 2019; involved 330 subjects with non contact injury to knee. Subjects with a previous knee injury, old fractures of the proximal tibial or femoral condyle, knee pathologies altering the morphology of femoral notch and tibial plateau of the knee like osteoarthritis, multi-ligament injury of the knee were excluded from study in both the groups. Patients not willing to participate were also excluded. Institution ethical committee approval was taken and valid informed consent was taken from all patients willing to participate. By using startified systematic random sampling, they were randomly divided into 2 equal groups of 30 each, i.e the injured group, and the control or the uninjured group. The injured group contained subjects with clinical findings suggestive of ACL tear on whom MRI of the knee was done and ACL tear was documented. The control group contained knees of subjects with intact ACL on MRI. Magnetic resonance imaging was performed on all subjects participating in the study(Fig. 1).
Fig. 1.
Represents the flow chart of patient selection.
2.1. Sample size calculation
A minimum of 60 (30 per group) patients was necessary to obtain a 90% chance of detecting, as significant at the 5% level, a mean Notch width index (NWI) in the case group as 0.29 and in the control group to 0.30 with SD as ± 0.02.
Calculation based on the formula:
| n = f(α/2, β) × 2 × σ2 / (μ1 − μ2)2 |
Where μ1 and μ2 are the mean outcome in the study groups respectively, σ is the standard deviation.
2.1.1. MRI technique & measurements
A standard MRI knee was performed on a 1.5 T machine with the patient in supine with the knee joint in extension and slight external rotation. Axial proton density (PD) weighted, sagittal T1 and T2 weighted and coronal T2 weighted images were taken with 4 mm slice thickness to evaluate the extent and confirm the diagnosis of ACL injury, and measurements were made using IPACS imaging software.
Femoral Measurements like Femoral Notch Width, Notch Width Index, and shape were assessed on T2 coronal Fat saturated sequences. (TE: 69 ms, TR: 3890 ms slice thickness 4 mm, Matrix: 256 × 256 and FOV: 160 mm) (Fig. 2).
Fig. 2.
(a) represents the notch width at the level of Popliteal groove and Bi-condylar width at the same level, (b) represents the NWI on the coronal view in MRI, Notch width index = dividing the Notch width at the level of Popliteal groove with Bi-condylar width at the same level.
Notch Width Index was calculated by dividing the Notch width at the level of the Popliteal groove with Bi-condylar width at the same level in T2 suppressed Coronal sequences. The shape of the intercondylar notch was assessed by comparing the Notch width at the levels of Popliteal groove (NWP) and joint line (NWJ).16,17 Three shapes of Intercondylar notch were defined on the coronal sequence. Inverted U shape is in which NWP=NWJ ( ±1 mm). A shape is in which NWP < NWJ. Omega shaped notch is in which NWP > NWJ.16,17
3. Statistics analysis
All the continuous variables was summarized statistically using mean ± standard deviation (SD) and the numbers or percentages were used to represent categorical data, summaries and diagrammatic presentation were used wherever necessary. The two categorical variables association was checked using Chi-square (χ2) test. Unpaired t-test was used to evaluate difference in the means of analysis variables between two independent groups. ROC analysis for Sensitivity-specificity was done to check relative efficiency. The results were considered to be statistically significant if p values calculated was less than 0.05. SPSS software v.23 (IBM Statistics, Chicago, USA) and Microsoft office 2007 was used for data analysis.
4. Results
Our study enrolled a total of 60 subjects fulfilling the inclusion criteria, which were further divided into 2 groups of injured and control, based on with or without ACL injury respectively. There were 22 males (73.3%) and 8 females (26.7%) in each group. MRI was done for the patients and using the Ipacs software, the parameters Notch Width at Popliteal grove (NWP), Notch Width at the Joint Line (NWJ), notch width index (NWI), Notch shape was calculated.
The mean age of males in the injured and control group among males was 32.9 ± 9.7 years and 32.7 ± 7.6 years respectively. In mean age of females in the injured and control group were 33.5 ± 10.5 years and 33 ± 8.6 years respectively.
We observed a significant correlation of ACL tear with Notch Width, Bi-condyle Width, NWI, NWP and NWJ. The mean of the parameters measured in each subgroups injured or ACL tear group and control group were Notch Width 19.9 ± 1.7; 21.1 ± 1.9 (p = 0.019), Bi-condyle Width 72.6 ± 6.7: 68.0 ± 4.8 (p = 0.004), Notch Width Index 0.27 ± 0.01; 0.31 ± 0.01 (p=<0.001), Notch Width Popliteal Groove 19.9 ± 1.7; 21.1 ± 1.9 (p = 0.019), Notch Width Joint Line 19.9 ± 1.7; 21.1 ± 1.9; (p = 0.207) respectively[Table 1].
Table 1.
Shows the mean values of the notch parameters like Notch Width(NW), Bi-condyle Width(BCW), Notch Width Index(NWI), Notch Width at popliteal groove(NWP) and Notch Width at joint line(NWJ) calculated on MRI.
| Notch Parameters | INJURED GROUP (with ACL injury) |
CONTROL GROUP (ACL intact) |
p-value | ||
|---|---|---|---|---|---|
| Mean | SD | Mean | SD | ||
| NW | 19.9 | 1.7 | 21.1 | 1.9 | 0.019∗ |
| BCW | 72.6 | 6.7 | 68.0 | 4.8 | 0.004∗ |
| NWI | 0.27 | 0.01 | 0.31 | 0.01 | <0.001∗ |
| NWP | 19.9 | 1.7 | 21.1 | 1.9 | 0.019∗ |
| NWJ | 20.4 | 2.2 | 21.1 | 2.3 | 0.207 |
Patients with a smaller Notch Width were seen to have a higher incidence of ACL tear (p = 0.019). The incidence of the ACL injuries was statistically significant seen in the age interval 31–40 group and >40 years age interval. The mean for age interval 31–40 year was 20.1 ± 1.5 with p = 0.047 and for age interval >40 years was 18.9 ± 1.0 with a p = 0.023 [Table 2].
Table 2.
Shows the comparison of mean values in Group A and B of Notch width(NW) and Notch Width Index(NWI) with Age Interval.
| Notch Parameters | Age (yrs) | INJURED GROUP (with ACL injury) |
CONTROL GROUP (with ACL injury) |
p-value | ||
|---|---|---|---|---|---|---|
| Mean | SD | Mean | SD | |||
| NW | ≤30 | 19.9 | 2.1 | 20.4 | 2.0 | 0.581 |
| 31–40 | 20.1 | 1.5 | 21.5 | 1.1 | 0.047∗ | |
| >40 | 18.9 | 1.0 | 22.2 | 1.9 | 0.023∗ | |
| NWI | ≤30 | 0.27 | 0.01 | 0.30 | 0.01 | <0.001∗ |
| 31–40 | 0.28 | 0.01 | 0.32 | 0.01 | <0.001∗ | |
| >40 | 0.27 | 0.01 | 0.31 | 0.01 | 0.001∗ | |
It was also found that a lower value NWI is associated with ACL tear compared to the normal knee NWI (p= <0.001). The mean value of the NWI in the ACL tear knee compared to normal knee with are 0.31 ± 0.01 and 0.27 ± 0.01 respectively. The male population has lower NWI compared to the female population (0.27 ± 0.01 and 0.28 ± 0.01 respectively). No variation in NWI is seen with age interval, as mean values in all the three age intervals were near comparable. (<30 years: 0.27 ± 0.01; 31–40 years: 0.28 ± 0.01; >40 years: 0.27 ± 0.01) [Table 2].
There was also a positive correlation seen between Bi-condylar width (BCW) (p = 0.004) and ACL tear. The mean BCW was 72.6 ± 6.7 mm observed to be greater in subjects with ACL injuries compared to the subjects with normal knees having a mean value of 68 ± 4.8 mm. Notch shape (A, Ω, inverted U) was another parameter showing a correlation with incidence with the ACL tear of the knee. Notch shape is calculated using the values of Notch width at the Popliteal groove and joint line. Even though NWI depends on the shape of the notch, it is a simpler entity that can be observed without measurements. In our study, with 30 patients in each group, the most common notch shape in the injured group i.e. subjects with an ACL tear is A shape: 18 (60%), followed by U shape: 8 (26%), and last Ω shape: 4 (14%). However, in the control group i.e. subjects with normal ACL most commonly seen shape is Ushape: 22 (73.3%), followed by A shape: 7 (23.3%) and last Ω shape: 1 (3.3%).
In our study, we have used the ROC curve to analyze the parameters used to predict ACL tear injury. In was found the NWI show a positive correlation with an ACL tear (p = < 0.001). The Area under the curve (AUC) was 0.955 and SE of 0.224. The CI was in a range of 0.908–1 (Table 3).
Table 3.
ROC analysis of notch width Index(NWI) in predicting ACL tear.
| Notch Parameters | AUC | SE | p value | 95% CI |
|
|---|---|---|---|---|---|
| Lower | Upper | ||||
| NWI | 0.955 | 0.024 | <0.001∗ | 0.908 | 1 |
Note: ∗ significant at 5% level of significance (p < 0.05.
We found the cut off value for the prediction of ACL tear of NWI was 0.29. The NWI had a sensitivity of 90% and specificity of 86.7%. The cut off values for NW and BCW were 20.3 and 70.1 respectively but the sensitivity and specificity was less compared to NWI[Table 4](Fig. 3).
Table 4.
Cut-off value of Notch Width Index (NWI), Notch Width(NW), Bicondylar width (BCW) in Predicting ACL Tear.
|
Notch Parameters |
Cut-off value | Sensitivity | Specificity |
|---|---|---|---|
| NWI | 0.29 | 90.0% | 86.7% |
| NW | 20.3 | 66.7% | 63.3% |
| BCW | 70.1 | 73.3% | 63.3% |
Fig. 3.
ROC curve of notch width index (NWI) in predicting ACL tear.
5. Discussion
The ACL is a crucial element in stabilizing the knee joint. It plays an important role in performing other major functions in the knee.9 The cause and mechanism, for an ACL tear, have been known in the literature, however, the factors predisposing for an ACL tear, have yet not been discussed. Hence, in our study, we have tried to assess and find the correlation of the predisposition of ACL injuries concerning the parameters of the distal femur on MRI, such as NW, NWI, and shape of notch.
Stijak et al. studied gender based variation of femoral notch width and concluded females have narrower notch than men.10 However, Anderson et al., found no statistically significant difference of NWI between the sexes(11). Domzalski et al., observed NWI with respect to gender did not make a difference, for factor contributing to ACL injuries.12 In our study, we observed there was no statistically significant difference in the NWI between the sexes(0.27 ± 0.01 in males and 0.28 ± 0.01 in females). Souryalet al, used direct radiographs to determine NW and concluded narrow NW is associated with bilateral ACL injuries.14 LaPradeet al found an association of narrow intercondylar notch with increased risk for Anterior Cruciate Ligament injuries.16 We observed similar findings in our study, the patients with a smaller Notch Width were seen to have a higher incidence of ACL tear (p = 0.019). One of the major drawbacks of previous studies done by Palmer et al., LaPradeet al was that it was done using plain radiographs using tunnel view of the knee joint. This caused errors not only by variation in magnification of plain radiograph but also variations in which tunnel views are taken. Our study is based on a calculation done in coronal sections using the Ipacs system which minimizes the errors due to magnification.
The relationship between ACL injuries and Notch Width as assessed by NWI and notch shape has been described in the literature.10 The use of coronal and sagittal views on MRI have helped to assess the anatomy of the notch, by measuring and calculating the NWI and shape.17 Souryalet al described the use of notch width index (NWI) in preventing ACL injuries. They suggested, young individuals with ACL tear and lower NWI have higher risk of sustaining injury to contralateral knee and should always be counseled about that possibility(14). Domzalski et al. and others compared the knees with ACL injuries to the control group, and concluded that there is increased risk ACL rupture with narrow NW(12,13,18) However, Herzog et al., Schinkendantzet al, and Alizadehet al found that there was no significant relationship between NWI and ACL injury.19,20In our study, we found that there was a positive correlation between narrow NWI with ACL injury (p = 0.019).
Ashwini et al., in their study on the Indian population, concluded patients with ACL injury had NWI of 0.29 ± 0.02 or lesser compared to those who didn’t have an ACL injury. Bhasukala et al., showed NWI to be 0.28 ± 0.06.21 However, GormeliCA et al. showed cut-off values of NWI of 0.22 ± 0.008 in bilateral injured knees and 0.24 ± 0.01 in the unilateral injured knee(18). Another study by, Hirtlet et al., showed NWI at the level of Popliteal groove to be 0.25± 0.03.17 Many scholars have concluded the critical value NWI ranging from 0.19 to 0.26.16,22,23 We found the cut off value for the prediction of ACL tear of NWI of 0.29. Although our values of NWI were slightly more than the previous studies, it correlates with a study done by Ashwini et al. which is also a study done on the Indian population. The cut off values for NW and BCW were 20.3 and 70.1 mm respectively but the sensitivity and specificity was very less compared to NWI. So NWI is better indicator than NW or BCW to predict the risk of ACL injury.
The intercondylar notch shape is another useful parameter of the complex distal femur morphology that is related to the ACL injuries. A semi-quantitative approach is used to classify the shape of the intercondylar notch of the distal femur as three shapes i.e. A, Inverse U, and Omega (Ω).In our study, we found a positive correlation of the shape with an ACL injury. The A shape (60%)of the intercondylar notch was associated with ACL injury knee. However the most common intercondylar shape in the normal knee was shaped Inverted U(53.3%). Van Eck et al. described three shapes of femoral as types ‘A’, ‘U’, and ‘Ω’ in which type A had narrow notch than type U(24). Al-seed et al. observed A shaped femoral notch had increased incidence of ACL tear.25,26 However, Ashwini et al. concluded the ACL injuries are more commonly associated with Omega shape notch.26 In our study, 60% of subjects with ACL tears had A-shaped notch whereas 73.3% of subjects in the control group had type U notch. Thus A-shaped notch tends to predispose subject to an ACL injury. There have been limited evidence of variation of notch parameters with age in literature. F.M. Lima et al.(27), in their study on pediatric population, concluded that there is relative stabilization of growth of intercondylar notch at around 13–14years and recognition of the normal developmental changes of the intercondylar notch is important for successful ACL graft placement. V.C. Stein et all(28)in their study on older people with osteoarthritis concluded that narrow notch is a significant risk factor for ACL injury even in patients with osteoarthritis. In our study, there was no variation of NWI with age interval, as mean values in all the three age intervals were near comparable and difference between the groups were significant at all age intervals. Thus age interval does not effect the positive correlation of NWI with ACL injury.
No study is devoid of any limitations, small sample size with more males in the study as compared to the females is our major limitation. Though we matched both the groups with mean age, method of calculation, etc it would have been ideal to have an equal distribution of males and females. Also ACL injury prediction cannot be solely determined using the radio-logical parameters taken in the study, as it also depends on multiple factors like age, hormonal changes, and lifestyle etc.
6. Conclusion
We conclude that narrow femoral intercondylar notch, lower notch width index, A-shaped of the femoral notch increases the risk of an ACL injury in the given population. With an increased interest in sports activities, this can help us predict the high-risk individuals who are predisposed to an ACL injury which in turn would help us planning the preventive strategies to avoid ACL injury.
CRediT authorship contribution statement
Sheik Mohammed Fahim: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Data curation, Writing - review & editing, Supervision. Tushar Dhawan: Methodology, Validation, Data curation, Investigation, Writing - original draft, Writing - review & editing. Nuthan Jagadeesh: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Resources, Data curation, Writing - original draft, Writing - review & editing, Visualization, Supervision, Project administration. Yogesh Putane Ashwathnarayan: Investigation, Data curation, Writing - review & editing.
Contributor Information
Sheik Mohammed Fahim, Email: sheikfahim@hotmail.com.
Tushar Dhawan, Email: tushardhawan92@gmail.com.
Nuthan Jagadeesh, Email: nuthanjagadeesh@yahoo.com.
Yogesh Putane Ashwathnarayan, Email: dryogeshpa@yahoo.com.
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