If you don't remember your password, you can reset it by entering your email address and clicking the Reset Password button. You will then receive an email that contains a secure link for resetting your password
If the address matches a valid account an email will be sent to __email__ with instructions for resetting your password
To describe differences in radiographic and magnetic resonance imaging (MRI) findings between adult and pediatric patients with known primary anterior cruciate ligament (ACL) injuries.
Methods
We performed a retrospective analysis of surgical patients with a history of ACL tears treated at our institution over a 7-year period. Patients were divided into 2 cohorts based on age (≤15 years and ≥21 years). Patients’ radiographs and MRI studies were used to compare features including fracture incidence, bone bruise pattern, associated ligamentous injuries, and meniscal injuries between the 2 groups. Proportions of associated findings were analyzed using the 2-proportion z test.
Results
Within our cohorts of 52 sex-matched pediatric and adult patients, we found that pediatric patients were more likely to have radiographic evidence of fracture (P = .001) and MRI evidence of lateral femoral condylar bone bruising (P = .012). Adult patients had higher rates of medial femoral condylar bruising (P = .016) and medial proximal tibial bruising (P = .005), as well as popliteal fibular ligament injuries (P = .037), identified on MRI.
Conclusions
In this study, we identified differences in bone bruise patterns between pediatric and adult patients with primary ACL tears. Pediatric patients were more likely to have radiographic evidence of fracture and MRI evidence of lateral femoral condylar bone bruising. Adult patients were more likely to show medial femoral condylar and medial proximal tibial bone bruising, as well as popliteal fibular ligament injuries.
Level of Evidence
Level IV, prognostic case series.
The anterior cruciate ligament (ACL) is crucial for knee stability. Along with the posterior cruciate ligament, the ACL forms a cross within the knee, preventing excessive anterior tibial translation while also assisting with rotational stability that results from varus or valgus stressors.
The annual incidence of ACL tears in the United States is 68.6 per 100,000 person-years, resulting in about 100,000 to 200,000 ACL reconstructions per year and costing approximately $1.7 billion annually.
Magnetic resonance imaging (MRI) is the gold-standard imaging modality for the diagnosis of ACL pathology. The primary signs of an acute complete ACL tear are non-visualization of the ACL, discontinuity of the ligament, and increased T1 and T2 signal. Primary signs of acute partial tears include thickened ligaments with a T2-hyperintense signal with intact ACL fascicles.
In addition to these primary and secondary signs, the femoral notch volume can be measured on MRI because a decreased volume may be associated with ACL-deficient knees in adult and pediatric patients.
Assessment of relationship between three dimensional femoral notch volume and anterior cruciate ligament injury in Chinese Han adults: A retrospective MRI study.
Three-dimensional femoral notch volume in anterior cruciate ligament-deficient versus anterior cruciate ligament-intact patients: A matched case-control study with inter-gender comparison.
Three-dimensional intercondylar notch volumes in a skeletally immature pediatric population: A magnetic resonance imaging-based anatomic comparison of knees with torn and intact anterior cruciate ligaments.
Imaging of ACL injuries in a pediatric population may share similar primary and secondary signs with imaging in an adult population; however, there are many differences that need to be considered in the diagnosis of a pediatric ACL injury versus an adult ACL injury. Pediatric ACL tears may be challenging to characterize owing to the difficulty in differentiating between an incompletely closed physis and an impaction fracture, as well as difficulty in visualizing the thinner pediatric ACL.
Furthermore, skeletally immature patients are more likely to have partial ACL tears and to have associated tibial spine avulsion fractures as compared with their skeletally mature counterparts.
Radiographs are commonly obtained during the evaluation of an ACL injury to determine the presence of fractures or associated risk factors such as an increased posterior tibial slope angle.
Although many imaging studies have been conducted to identify primary and secondary signs of ACL injury, data are limited regarding the relative proportions of associated radiographic findings between adult and pediatric patients with ACL tears. Prior research has investigated radiographic differences in bipolar bone loss between adult and adolescent patients after anterior shoulder dislocation.
The purpose of this article was to describe differences in radiographic and MRI findings between adult and pediatric patients with known primary ACL injuries. We hypothesized that differences in associated injuries and imaging patterns would be observed between the adult and pediatric patients that may be due to differences in biomechanics or mechanisms of injury between the 2 groups.
Methods
Patient Selection
We performed a retrospective analysis of surgical patients with a history of ACL tears treated by 2 surgeons (N.P. and B.F.) at our institution over a 7-year period (2015-2021). Patients were divided into 2 cohorts based on age at the time of surgery: 15 years or younger (adolescent patients) and 21 years or older (adult patients). We used these age cutoffs to create a gap in years between the 2 groups and thus limit confounding that might occur by including pediatric patients who are skeletally mature and only a few months or years younger than the youngest adult patient in the adult cohort. All included patients had undergone an MRI study in the evaluation of their knee pathology. Only patients presenting for primary ACL tears were included in this study. All adult patients underwent arthroscopic ACL reconstruction with either hamstring autograft or posterior tibialis allograft.
Data Acquisition and Imaging Assessment
Institutional review board approval (No. 21-35878) was obtained before data acquisition began. A cohort of pediatric patients with primary ACL tears from 2015-2021 was first identified. Next, we identified the same number of sex-matched adult patients who had sought treatment for primary ACL tears at our institution. The electronic medical record and provider notes were used to gather demographic data including patient age at the time of surgery, time from injury to first MRI, and mechanism of injury.
Patients’ preoperative radiographs were evaluated to determine the incidence of fractures. Fracture incidence was evaluated in 1 of 2 ways: (1) The report from a board-certified radiologist was compared with the imaging and cross-checked by one of the authors or (2) two of the authors (B.F. and N.P.) (each a board-certified sports medicine orthopaedic surgeon) evaluated the radiographs and cross-checked their findings. Any disagreements between findings were reviewed by all authors together until a consensus was reached. Patients’ MRI findings were then evaluated using the same methodology. The following MRI characteristics were analyzed: bone bruise location, cartilage injury location, other (non-ACL) ligamentous injury, meniscal injury location, and characterization of ACL tear (partial vs complete).
Data Analysis
We compared the relative incidence of fractures identified on radiographs and the various associated MRI findings between the pediatric and adult cohorts by use of the 2-proportion z test. Statistical analyses were performed using Stata MP 16 analytical software (StataCorp, College Station, TX). The level of statistical significance was set at P < .05.
Results
Patient Demographic Characteristics
Our study cohort included 26 adult and 26 pediatric patients. Each cohort consisted of 17 male patients (65.4%) and 9 female patients (34.6%). The pediatric patients had a mean age of 11.8 years (standard deviation, 1.8 years; range, 8-15 years), whereas the adult patients had a mean age of 34.3 years (standard deviation, 8.1 years; range, 24-48 years). The time between injury and MRI was categorized as follows: unknown, 0 to 2 weeks, 2 to 4 weeks, 4 to 8 weeks, or greater than 8 weeks. For both patient cohorts, the most common interval was 0 to 2 weeks. There were no statistically significant differences in time to MRI between the pediatric and adult cohorts (P ≥ .224). The most common mechanisms of injury included skiing and playing soccer. However, most pediatric and adult patients were injured while participating in “other” activities. There was not another specific activity that led to more than 2 patient injuries. There were no statistically significant differences between the 2 groups regarding which activities patients were participating in at the time of injury (P ≥ .731). These data are summarized in Table 1.
Table 1Patient Demographic Characteristics
Variable
Pediatric Patients
Adult Patients
P Value
Sex
Male
17 (65.4)
17 (65.4)
Female
9 (34.6)
9 (34.6)
Age on date of surgery, yr
Mean (SD)
11.8 (1.8)
34.3 (8.1)
Range
8-15
24-48
Time to MRI
Unknown
3 (11.5)
3 (11.5)
>.999
0-2 wk
12 (46.2)
15 (57.7)
.407
2-4 wk
5 (19.2)
3 (11.5)
.441
4-8 wk
5 (19.2)
2 (7.7)
.224
>8 wk
1 (3.8)
3 (11.5)
.296
Mechanism of injury
Skiing
5 (19.2)
6 (23.1)
.731
Soccer
5 (19.2)
5 (19.2)
>.999
Other
16 (61.5)
15 (57.7)
.780
NOTE. Data are presented as number (percentage) unless otherwise indicated.
MRI, magnetic resonance imaging; SD, standard deviation.
Preoperative radiographs were obtained for 16 of the 26 pediatric patients. Of these pediatric patients, 4 (25%) had evidence of fracture on radiographs, consisting of a lateral proximal tibial avulsion fracture (1), patellar avulsion fracture (1), incomplete patellar fracture (1), and notch avulsion fracture (1). Of the 25 adult patients for whom preoperative radiographs were obtained, none had radiographic evidence of fracture. Pediatric patients were significantly more likely to have radiographic evidence of fracture (P = .001). Table 2 summarizes these data.
Within our cohort of pediatric patients, 20 of 26 (76.9%) had MRI evidence of bone bruising as compared with 23 of 26 adults (88.5%) (P = .269). We found statistically significant differences in the location of bone bruising between the 2 groups. Pediatric patients were more likely to have bone bruising noted in the lateral femoral condyle (LFC) (73.1%) as compared with adults (38.5%) (P = .012) (Fig 1). Conversely, adults were more likely to have bruising of the medial femoral condyle (MFC) (46.2% vs 15.4%, P = .016) and medial proximal tibia (34.6% vs 3.8%, P = .005) (Fig 2). We did not observe statistically significant differences in the proportions of patients with bone bruising in the lateral proximal tibia, fibular head, or patella.
Fig 1Axial fast spin echo magnetic resonance image of left knee in 10-year-old girl with lateral femoral condylar bone marrow edema (arrow).
Fig 2Coronal fat-suppressed proton density magnetic resonance image of left knee in 27-year-old man with medial femoral condylar bone marrow edema (arrow).
Next, we examined the relative proportions of MRI evidence of articular cartilage injury between the 2 groups. Cartilage injuries were observed in 5 adult patients (19.2%) versus 2 pediatric patients (7.7%). Of the adult patients, 2 had LFC lesions, 2 had MFC lesions, and 1 had a lateral proximal tibial defect. The pediatric cartilage injuries included 1 injury to the LFC and 1 injury to the lateral patella. There was not a statistically significant difference between the 2 groups regarding the overall rate of cartilage injury (P = .224). Furthermore, we did not find statistically significant differences in cartilage injury location distribution between the adult and pediatric patients.
We additionally examined non-ACL ligamentous injury in our cohort of patients. Of the 26 pediatric patients, 12 (46.2%) had an associated ligamentous injury, whereas 13 adults (50%) had a non-ACL ligamentous injury (P = .784). We found that each group included 8 patients with medial collateral ligament pathology (P > .999). Lateral collateral ligament injury occurred in 6 adults (23.1%) versus 2 pediatric patients (7.7%); however, this result was not statistically significant (P = .124). Adult patients (15.4%) were more likely to have MRI evidence of popliteal fibular ligament (PFL) injury as compared with pediatric patients (0%) (P = .037). Of the 4 adults with PFL injuries, 3 had partial tears whereas 1 had a complete tear.
Meniscal injuries were common in our cohorts of pediatric (57.7%) and adult (69.2%) patients (P = .389). However, we did not find statistically significant differences in the relative proportions of patients with isolated medial or lateral meniscal injury or those with both medial and lateral pathologies.
Finally, although all patients in our cohort were ultimately treated surgically, we found that 11.5% of pediatric patients had partial ACL tears as compared with 0% of adult patients. However, this result was not statistically significant (P = .075). These data are summarized in Table 3.
In this study, we identified differences in bone bruise patterns between pediatric and adult patients with primary ACL tears. We found that pediatric patients were more likely to have radiographic evidence of fracture as compared with adult patients (P = .001). This finding is consistent with the findings of Prince et al.,
who showed that skeletally immature patients were more likely to exhibit tibial spine avulsion fractures on MRI as compared with their more skeletally mature counterparts. We found that 25% of patients in our pediatric cohort had radiographic evidence of fracture. Prince et al. found a tibial spine avulsion fracture rate of 26% among skeletally immature patients. Of the 4 patients in our cohort with evidence of fracture, only 1 had a tibial spine avulsion fracture (6.25% overall). Because our study included analysis of only 16 pediatric radiographs, it is possible that our study is underpowered to detect overall rates of tibial spine fractures specifically. Given that fractures related to the patella occurred in 2 of our patients, it is possible that these patients experienced patellofemoral instability events in addition to their ACL injuries.
Although we found no significant difference in the overall rate of bony contusions between pediatric and adult patients, we did find statistically significant differences in the location of bony contusions. Pediatric patients were more likely than adults to have LFC bruises (P = .012), whereas adults were more likely than pediatric patients to have MFC bruising (P = .016) and medial proximal tibial bruising (P = .005). Prince et al.
found that the LFC and posterolateral tibial plateau were the most common locations of bony contusions in patients with ACL pathology among both skeletally immature and skeletally mature patients. Moreover, D’Hooghe et al.
D’Hooghe P, Grassi A, Villa FD, et al. The injury mechanism correlation between MRI and video-analysis in professional football players with an acute ACL knee injury reveals consistent bone bruise patterns [published online June 13, 2022]. Knee Surg Sports Traumatol Arthrosc. https://doi.org/10.1007/s00167-022-07002-6.
studied 19 professional soccer players with ACL tears and found that although 84% had LFC bruising, none had MFC bruising patterns. Similarly, Moran et al.
found that LFC bone bruises were more common than MFC bruises (67% vs 33%) and the lateral tibial plateau was more frequently affected than the medial tibial plateau (65% vs 35%). Within our cohort of pediatric patients, we also observed greater rates of LFC bruising than MFC bruising (73.1% vs 15.4%) and more frequent lateral proximal tibial bruising than medial proximal tibial bruising (69.2% vs 3.8%). These findings are consistent with the results of prior research. However, the 26 adult patients studied exhibited higher rates of MFC bruising than LFC bruising (46.2% vs 38.5%) and showed higher rates of MFC bruising (P = .016) and medial proximal tibial bruising (P = .005) than the pediatric cohort. Viskontas et al.
found that although LFC bruising was more commonly associated with ACL tears than MFC bruising, medial-compartment bone bruising was especially common among patients with noncontact injuries. Furthermore, they found that medial-compartment bruising was associated with sagittal-plane loading more than valgus loading among subjects with noncontact injuries. Kaplan et al.
found that medial-compartment bruising was associated with a contrecoup mechanism of injury. Although we found that the adult and pediatric patients were participating in similar activities at the time of the ACL tear, our chart review did not allow for more granular analysis of noncontact versus contact mechanisms of injury. Thus, it is possible that the increased rates of medial-compartment bone bruising among the adult patients are related to either noncontact sagittal-plane loading or contrecoup or compensatory varus alignment occurring at greater rates within the adult cohort. Future research is warranted to better characterize the cause of these results.
We found similar overall rates of cartilage injury between adult and pediatric patients. In addition, we found that overall, other ligamentous injury rates were similar between the adult and pediatric cohorts. Medial collateral ligament injuries occurred in 8 adult patients and 8 pediatric patients (30.8% in each cohort). Adults were more likely to have lateral collateral ligament injuries (23.1% vs 7.7%); however, this result was not statistically significant (P = .124). We did find that adult patients were more likely to have radiographic evidence of PFL pathology as compared with pediatric patients (P = .037). Posterolateral corner injuries, such as injury to the PFL, rarely occur in isolation and are often associated with ACL pathology.
A prospective magnetic resonance imaging study of the incidence of posterolateral and multiple ligament injuries in acute knee injuries presenting with a hemarthrosis.
Because the PFL contributes to external rotation stability, it is possible that the adult patients were more likely to experience ACL tears as a result of excessive external rotatory forces. It is also possible that the PFL, similarly to the ACL, is thinner in pediatric patients, and thus, it is more difficult to identify pathology on MRI. Further research is necessary to better understand the forces that contribute to PFL tears, especially in the context of ACL pathology. Additional research is also needed to better understand why adult patients may have higher rates of radiographic PFL pathology associated with ACL tears.
We did not find statistically significant differences in the rates of overall meniscal injury between pediatric and adult patients (57.7% and 69.2%, respectively; P = .389). These rates of ACL-associated meniscal injury are in line with the rates of 61% and 63% observed in prior research.
It is interesting to note that adult patients had more isolated medial meniscal injuries (26.9% vs 19.2%) and fewer isolated lateral meniscal injuries (7.7% vs 15.4%); however, these results were not statistically significant. Because adult patients in our cohort also had increased radiographic evidence of medial-compartment bone bruising (P = .016 for MFC bruising and P = .005 for medial proximal tibia bruising), it is possible that medial knee damage globally was more common among our skeletally mature patients, although our sample size may have been underpowered to detect such differences in meniscal injury rates. Future work is needed to better elucidate these findings.
Finally, we found that 11.5% of pediatric patients had partial ACL tears as compared with 0% of adult patients (P = .075). Prince et al.
have shown that partial ACL tears are more common among skeletally immature patients; thus, our results are in line with this prior research, although our data only approach the level of statistical significance.
Limitations
There are certain limitations related to the design of this study. First, the modest sample size of the study may not be sufficient to detect differences between the pediatric and adult populations. Furthermore, skiing and soccer were the most common activities associated with an ACL tear in our study population. Our findings are specific to this study population, and our patients may differ from those in other regions where different sports are more popular. Furthermore, there may have been patients who were skeletally mature within the pediatric group, which may influence the injury patterns observed. The time from initial injury to imaging was unknown in a proportion of our patients, and certain pediatric patients lacked radiographs. This may impact bone bruising patterns as well as the identification of secondary injuries, which is a limitation of the study design. Similarly, it is possible that certain patients, especially within the adult cohort, had pre-existing injuries prior to ACL injury, such as articular cartilage defects. In addition, there are inherent limitations in characterizing rates of injury based on the interpretation of radiographic studies. For example, there are likely differences between physicians regarding what degree of bone marrow edema seen on MRI is interpreted as a bone bruise. We attempted to mitigate this phenomenon either by having at least 1 study author cross-check the images and radiology reports or by having 2 authors evaluate the imaging findings to increase validity. However, there is still potential for error and variation in the imaging interpretations. Additionally, although we controlled for the proportions of adult patients and pediatric patients who were male or female, there may be other factors that were not available in the electronic medical record that could influence the results of this study, such as a patient’s body mass index. Finally, our study focused on patients who underwent operative treatment of symptomatic ACL tears. However, there may be radiographic findings associated with both adult and pediatric patients who choose nonoperative management.
Conclusions
In this study, we identified differences in bone bruise patterns between pediatric and adult patients with primary ACL tears. Pediatric patients were more likely to have radiographic evidence of fracture and MRI evidence of LFC bone bruising. Adult patients were more likely to show MFC and medial proximal tibial bone bruising, as well as PFL injuries.
Assessment of relationship between three dimensional femoral notch volume and anterior cruciate ligament injury in Chinese Han adults: A retrospective MRI study.
Three-dimensional femoral notch volume in anterior cruciate ligament-deficient versus anterior cruciate ligament-intact patients: A matched case-control study with inter-gender comparison.
Three-dimensional intercondylar notch volumes in a skeletally immature pediatric population: A magnetic resonance imaging-based anatomic comparison of knees with torn and intact anterior cruciate ligaments.
D’Hooghe P, Grassi A, Villa FD, et al. The injury mechanism correlation between MRI and video-analysis in professional football players with an acute ACL knee injury reveals consistent bone bruise patterns [published online June 13, 2022]. Knee Surg Sports Traumatol Arthrosc. https://doi.org/10.1007/s00167-022-07002-6.
A prospective magnetic resonance imaging study of the incidence of posterolateral and multiple ligament injuries in acute knee injuries presenting with a hemarthrosis.
The authors report the following potential conflicts of interest or sources of funding: B.F. receives grants or pending grants from National Institutes of Health, OREF, and Orthofix; has a patent pending for a suture anchor; and owns stock or stock options in Bioniks and Kaliber AI, outside the submitted work. N.P. is a consultant for OrthoPediatrics, outside the submitted work. Full ICMJE author disclosure forms are available for this article online, as supplementary material.
00178-X&id=gr1.jpg){kind=link}
00178-X&id=gr2.jpg){kind=link}