Investigation of Morphometric Factors Associated With Adolescent ACL Rupture

Abstract

Background:

There are no definitive anatomic morphometric risk factors for adolescent anterior cruciate ligament (ACL) injury.

Purpose:

To compare the parameters used to define the tibial and femoral morphometric structure of the knee between adolescent patients with and without ACL rupture.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

Included were magnetic resonance imaging (MRI) scans and radiographs of 115 patients aged 10 to 17 years who were evaluated for ACL rupture at a single institution between February 1, 2019, and January 31, 2022. Images from 115 patients with intact MRI scans were included as controls. We investigated the following imaging parameters: tibial slope (on lateral radiograph), lateral condylar height, tibial sulcus height, medial condylar height, condylar width, intercondylar notch with, intercondylar notch angle, notch index, eminence width, tibial plateau width, eminence width/tibial plateau width, medial/lateral/overall eminence height, medial plateau depth, and 2 different eminence angles. Parameters were compared between groups using the chi-square, Fisher exact, Student t, or Mann-Whitney U test, as appropriate. Receiver operating characteristic analysis was conducted for cutoff values of significant parameters.

Results:

There were no significant differences in age, sex, or side affected between groups. Only the medial plateau depth was found to be statistically significant between the ACL rupture and ACL intact groups (2.6 vs 2.2 mm; P = .015). A statistically significant cutoff value could not be obtained for the medial plateau depth.

Conclusion:

Medial plateau depth was found to be significantly greater in adolescent patients with ACL rupture compared with ACL-intact controls.

Participation in sports activities in childhood and adolescence is increasing in Western countries. ⁸ In the United States, for example, 27 million children and adolescents participate in team sports. ⁸ The increase in the population engaged in such sports also explains the increase in the number of sports injuries. A study conducted in Australia showed that anterior cruciate ligament (ACL) injuries are more common in children and adolescents, especially in recent years, due to increased sports participation. ³³ ACL injuries constitute 30% of knee injuries in the population aged 5 to 18 years, which is a highly significant rate. ²⁴

Considering the long-term effects, ACL injuries are very problematic at such early ages; they can lead to serious medical problems such as meniscal injury, cartilage damage, and posttraumatic osteoarthritis in later stages of life.^18,20 The risk factors for ACL rupture have become a popular subject of research for the adolescent population, and numerous studies have been conducted on this subject.^15,29 In general, the risk factors for ACL rupture are classified as modifiable and nonmodifiable. Neuromuscular conditions and environmental factors can be listed among the modifiable risk factors. Among the nonmodifiable risk factors, we can count variations arising from sex and bone morphology.^12,13 To evaluate the risk factors related to bone morphology, studies have been carried out, especially regarding distal femoral and proximal tibial geometry.^12,13

In this study, we aimed to investigate whether the morphometric parameters used to define tibial and femoral morphology were related to ACL ruptures in adolescents.

Methods

Ethics approval was received for the study protocol, and all included participants provided written informed consent. Included in this study were patients aged 10 to 17 years who were evaluated in the outpatient clinic of a single institution with knee joint-related issues between February 1, 2019, and January 31, 2022 and who underwent MRI within appropriate indications during this period. Excluded were MRI scans with poor image quality due to motion artifact as well as patients with a diagnosed disease causing ligament laxity (eg, Marfan syndrome, Ehler-Danlos syndrome), those with previous knee ligament injury, those with a history of neurovascular injury in the extremity examined, those with a history of previous knee surgery, those with arthrosis findings on MRI scan and radiographs, and those with a history of knee circumference fractures without surgery.

A total of 941 MRI scans in patients with knee joint-related issues were initially identified. Of these patients, 826 patients were excluded, leaving 115 patients in the study group (ACL rupture group). The same number of patients with ACL intact who fulfilled the study enrollment criteria were selected randomly as the control group. Figure 1 shows the patient selection process.

Figure 1.

Flowchart of study group selection. ACL, anterior cruciate ligament; MCL, medial collateral ligament; MRI, magnetic resonance imaging; PCL, posterior cruciate ligament.

Radiological and MRI Measurements

The parameters to be examined based on MRI scans and radiographs were measured and recorded independently by 2 orthopaedic specialists (A.K. and C.C.) for each patient separately. All specified measurements are shown in Figures 2 and 3.

Figure 2.

(A) Tibial slope measurement on true lateral radiograph. (B) Axial and (C) coronal MRI scan measurements of femoral condylar width and intercondylar notch width. Femoral condylar width was measured with the line connecting both epicondyles, and notch width was measured by drawing a line parallel to the line connecting the epicondyles from the widest part of the intercondylar notch. (D) Axial and (E) MRI scan measurement of femoral intercondylar notch angle. MRI, magnetic resonance imaging.

Figure 3.

(A) Axial MRI measurements of medial femoral condylar height, tibial sulcus height, and medial femoral condylar height. (B-E) Coronal MRI measurements: (B) eminence width and tibial plateau width, (C) medial and lateral eminence height, (D) eminence angle 1, and (E) eminence angle 2. (F) Medial plateau depth on sagittal MRI. MRI, magnetic resonance imaging.

Tibial slope was measured on true lateral radiographs as defined by Malley et al. ²² Notch type was evaluated on MRI scan and classified according to Van Eck et al ³⁰ as type A, type U, or type W. Femoral trochlear morphology (lateral condylar height, medial condyle height, and trochlear sulcus height) was measured according to a study by Kwak et al ¹⁷ in a Korean population. The femoral condylar width, intercondylar notch width, intercondylar notch angle, and notch width index were measured on both axial and coronal MRI and were used to define condyle morphology and notch morphology as per the study by Stein et al ²⁷ on morphometric parameters that predispose to the rupturing of the adolescent ACL.

A number of measurement techniques were used to reveal the morphology of the tibial eminence. Eminence height was calculated as the perpendicular distance between the line connecting the lowest parts of the articular surface of both tibial condyles and the highest point of eminentia. ²³ Medial, lateral, and overall eminence height were recorded separately. Based on the line connecting the medial plateau and lateral plateau joint lines (the line connecting the lowest parts of the articular surface of both tibial condyles), the tibial plateau surface was determined on the coronal MRI, and the distance between the highest points of the medial and lateral eminence was calculated in the same plane. The ratio of eminence width to plateau width was then recorded. To reveal the morphological structure of the eminence more clearly, 2 angular parameter measurements were made. (1) A line was drawn from the peak of the medial eminence to the intereminence area in the coronal plane, and a line was then drawn from the intereminence area to the peak of the lateral eminence. The angle between these 2 lines was recorded as eminence angle 1. (2) The peaks of the medial and lateral eminences were determined in the coronal plane, and a line connecting them was drawn. The angle made by this line and the joint line was recorded as eminence angle 2. The technique of Akhavi Milani et al ² was used to measure the medial tibial plateau depth.

Statistical Analysis

SPSS Version 25.0 (IBM) was used for statistical analysis of the data. Categorical data were recorded as counts and percentages, and continuous data were recorded as means and standard deviations and ranges, as appropriate. Statistical comparisons between the ACL rupture and ACL intact (control) groups were performed with the chi-square test or Fisher exact test for categorical variables and the Student t test or Mann-Whitney U test for continuous variables that did and did not show normal distribution, respectively. The threshold for statistical significance was set at P < .05.

In addition, we used receiver operating characteristic analysis to evaluate the cutoff values for parameters that were significantly different between groups, with sensitivity and specificity values.

Results

Comparison of patient characteristics between the ACL rupture and ACL intact groups is shown in Table 1. There were no significant group differences in patient characteristics.

Table 1.

Comparison of Patient Characteristics According to Study and Control Groups ^a

	ACL Rupture (n = 115)	ACL Intact (n = 115)	P
Age, y	10.96 (10-17)	10.44 (10-17)	>.999
Sex			.169
Male	46 (65.7)	37 (52.9)
Female	24 (34.3)	33 (47.1)
Side affected			>.999
Right	37 (52.9)	36 (51.4)
Left	33 (47.1)	34 (48.6)

^aData are reported as mean (range) or mean ± SD. ACL, anterior cruciate ligament.

When the groups were compared in terms of notch types, the W notch type was not encountered in either group. In the ACL ruptured group, 41.4% of the patients had A type notch, while 58.6% had a U type notch. This rate was 57.1% and 42.9%, respectively, in the ACL intact group. When the U and A type notch distributions were examined, no statistical difference was found between the groups (P = .091).

The measurement results of the radiographic and MRI parameters are presented in Table 2. Medial plateau depth was significantly deeper in the ACL rupture group versus the control group (2.6 vs 2.2 mm, respectively; P = .015).

Table 2.

Statistical Analysis of the Parameters Used in the Comparison of Both Groups ^a

Parameter b	ACL Rupture (n = 115)	ACL Intact (n = 115)	P
Tibial slope, deg	11 (2-18)	11 (2-18)	.423
Lateral condyle height, mm	57.9 ± 6.2	58.2 ± 5.8	.759
Tibial sulcus height, mm	48.6 ± 6.3	49.0 ± 5.2	.708
Medial condyle height, mm	55.9 ± 6.7	55.8 ± 5.6	.285
Condyle width, mm
Axial plane	77.1 ± 7.4	77.5 ± 7.6	.838
Coronal plane	75.2 ± 7.2	75.2 ± 6.8	.623
Intercondylar notch width, mm
Axial plane	18.5 ± 2.3	18.8 ± 1.9	.757
Coronal plane	17.5 ± 2.6	17.8 ± 2.9	.591
Intercondylar notch angle, deg
Axial plane	59.2 ± 12.3	59.7 ± 10.4	.505
Coronal plane	57.3 ± 9.1	58.1 ± 9.0	.539
Notch index
Axial plane	0.24 ± 0.02	0.24 ± 0.02	.834
Coronal plane	0.23 ± 0.03	0.24 ± 0.03	.978
Eminence width, mm	13.6 ± 1.9	13.7 ± 2.1	.648
Tibial plateau width, mm	71.6 ± 6.7	71.3 ± 6.6	.682
Eminence width/tibial plateau width, mm	0.19 ± 0.02	0.19 ± 0.03	.809
Eminence height, mm
Medial	8.2 ± 1.2	8.1 ± 1.2	.513
Lateral	6.9 ± 1.5	6.6 ± 1.5	.763
Overall	15.1 ± 2.6	14.8 ± 2.5	.338
Eminence angle 1, deg	119.1 ± 9.2	123.7 ± 13.2	.473
Eminence angle 2, deg	4.7 (0.4-11.1)	5.1 (0.4-17.0)	.945
Medial plateau depth, mm	2.6 (0.3-4.9)	2.2 (0.8-3.9)	.015

^aData are reported as mean (range) or mean ± SD. Boldface P value indicates statistically significant difference between groups (P < .05). ACL, anterior cruciate ligament.

^bTibial slope measurements were measured on radiograph; all other parameters were measured on MRI scans.

A statistically significant cutoff value could not be obtained for medial plateau depth. As a result of receiver operating characteristic analysis, when the cutoff value for medial plateau depth was taken as <2.45 mm, the result for expecting an ACL rupture had 57.1% sensitivity, 62.9% specificity, and 61.9% probability (95% CI, 0.51-0.70; P = .015) (Figure 4).

Figure 4.

Graph showing ROC curve analysis of medial plateau depth. ROC, receiver operating characteristic.

Discussion

To our knowledge, the present study is the first to examine the relationship between medial plateau depth and ACL rupture in the adolescent population. We found that the medial plateau depth was significantly greater in the patients with ACL rupture (P = .015), regardless of patient sex. However, we could not determine a significant cutoff value for medial plateau depth between the ACL-rupture and ACL-intact groups.

In their arthroscopic study, van Eck et al ³⁰ defined 3 different types of notching. Al-Saeed et al ⁴ examined the MRI scan results of 560 patients and showed that the type A notch may particularly be associated with ACL rupture. Both of these studies were performed among adolescent populations.^4,30 In a retrospective case-control study of female patients by Bouras ⁷ in 2017, the authors also found that type A notch was associated with ACL rupture. There is no study examining the relationship between notch type and ACL rupture in the adolescent population. In the present study, no statistical difference was found between the ACL rupture and ACL intact groups in terms of notch type distributions. However, the adolescent population has different morphometric characteristics from the nonadolescent population and should be evaluated accordingly.

The relationship between tibial slope and ACL rupture is one of the parameters studied most frequently in adolescent patients. The increase in the tibial slope raises the tension on the ACL by increasing the anterior tibial translation; therefore, changes in the tibial slope and ACL are closely related. ¹ In a previous study that included patients of different age ranges, including the adolescent age-group, and examined the relationship between the posterior tibial slope and anterior cruciate rupture, it was found that increase in the posterior tibial slope had a moderate relationship with ACL rupture in this age group. ²² Some studies have also shown that posterior tibial slope increase and ACL rupture are correlated in the adolescent age groups.^5,14,22 However, Todd et al ²⁸ reported that increase in the posterior tibial slope was a risk factor only for the female population. In another study conducted in adolescents, medial tibial slope was found not to be associated with noncontact ACL rupture. ⁶ In the current study, we found that the posterior tibial slope was not associated with ACL rupture among adolescent patients. Studies have shown that more than 1 variable is effective on tibial slope values.^9,21 Therefore, there are wide ranges of values different from the literature.^9,21 Age is also an important variable that has an effect on tibial slope values. ⁹ Comparative studies with larger sample sizes are needed to clearly demonstrate the relationship between tibial slope and adolescent ACL injuries.

The femoral intercondylar notch stops growing at around 10 to 11 years of age, and it decreases slightly in size and reaches its final size around 13 to 14 years of age. ¹⁹ Measurement parameters such as notch width, notch angle, femoral condyle width, and notch width index are used to define 2-dimensional (2-D) intercondylar notch morphology. ²⁷ In a study based on the MRI scan findings of 61 patients, Domzalski et al ¹¹ showed that the risk of ACL rupture was higher among adolescent patients with smaller intercondylar notch widths. There are also studies that explain the relationship between notch width and ACL rupture in the adolescent population.^23,26,32 Although there are not enough studies examining the relationship between notch angle and ACL rupture in adolescents, both Alentorn-Geli et al ³ and Huang et al ¹⁵ showed that intercondylar notch angle and ACL rupture were correlated in this patient population. Notch width index is a parameter obtained using both notch width and femoral condyle width. ²⁷ In the study conducted by Pekala et al, ²³ a lower notch width index value was found to be a risk factor for ACL rupture. Similarly, a study of the MRI scan results of 68 patients younger than 19 years showed that a low notch width index value was a risk factor for ACL rupture. ³² Vyas et al, ³¹ on the other hand, did not find a relationship between notch width index and ACL rupture in 39 adolescent patients. Our findings concur with those of Vyas et al, ³¹ in that none of the considered parameters of intercondylar notch morphology were found to be a risk factor for ACL rupture in 115 healthy and ACL-ruptured patients. In a study of 3-dimensional (3-D) notch volume, it was revealed that 2-D measurements made, and the notch structure revealed, in 3-D did not show a correlation. ²⁹

Tibial plateau geometry has a significant effect on ACL injury. ¹⁰ The morphology of the tibial eminence, which is located on the tibial plateau and is the tibial endpoint of the ACL, is important for ACL kinematics and biomechanics. ²³ However, there are no 2-D measurements similar to those used to describe femoral intercondylar notch morphometry for describing the morphometry of the tibial eminence. In this context, intereminence heights are often used. ²³ Therefore, measurement techniques to define eminence morphometry are often preferred. Although limited, there are publications in the literature revealing that the eminence structure is a risk factor for both ACL ruptures and avulsions of the tibial eminence.^23,25 In the present study, no relationship was found between the parameters defined and ACL rupture.

Tibiofemoral joint geometry is crucial for knee kinematics and therefore ACL kinematics and structure, and one of the tibiofemoral joint components is medial tibial plateau depth. ² Hashemi et al ¹³ concluded in a study based on MRI that a shallow medial plateau depth constituted a risk factor for ACL rupture. In another study, it was revealed that the relationship between medial plateau depth and ACL rupture was a risk factor only for women. ¹⁶ Unlike these studies, Akhavi Milani et al ² found no statistical relationship between medial tibial plateau depth and noncontact ACL injury, although they conducted their study in an adolescent population.

In our adolescent cohort, we established a significant difference in medial plateau depth between the ACL-rupture and ACL-intact groups; however, this morphometric relationship should be clarified to fully reveal the mechanism of noncontact ACL rupture and improve surgical procedures. For this, 3-D measurement studies that include larger patient series should be carried out.

Limitations

One of the limitations of the study is that the groups compared in the study were not compared in terms of variables such as age and gender that might be effective in ACL injuries. In addition, the lack of clear mechanisms of ACL injury, especially the inability to distinguish between contact/noncontact can be counted among the limitations of the study.

Conclusion

Medial plateau depth was significantly greater in adolescent patients with ACL rupture compared with ACL intact patients. However, there is no study, including the current study, that has clearly demonstrated the relationship between noncontact ACL rupture and anatomic/morphometric precursors in the adolescent population.