Examining the Distribution of Bone Bruise Patterns in Contact and Noncontact Acute Anterior Cruciate Ligament Injuries

Abstract

Background:

Bone bruises are commonly seen on magnetic resonance imaging (MRI) in acute anterior cruciate ligament (ACL) injuries and can provide insight into the underlying mechanism of injury. There are limited reports that have compared the bone bruise patterns between contact and noncontact mechanisms of ACL injury.

Purpose:

To examine and compare the number and location of bone bruises in contact and noncontact ACL injuries.

Study Design:

Cross-sectional study; Level of evidence, 3.

Methods:

Three hundred twenty patients who underwent ACL reconstruction surgery between 2015 and 2021 were identified. Inclusion criteria were clear documentation of the mechanism of injury and MRI within 30 days of the injury on a 3-T scanner. Patients with concomitant fractures, injuries to the posterolateral corner or posterior cruciate ligament, and/or previous ipsilateral knee injury were excluded. Patients were stratified into 2 cohorts based on a contact or noncontact mechanism. Preoperative MRI scans were retrospectively reviewed by 2 musculoskeletal radiologists for bone bruises. The number and location of the bone bruises were recorded in the coronal and sagittal planes using fat-suppressed T2-weighted images and a standardized mapping technique. Lateral and medial meniscal tears were recorded from the operative notes, while medial collateral ligament (MCL) injuries were graded on MRI.

Results:

A total of 220 patients were included, with 142 (64.5%) noncontact injuries and 78 (35.5%) contact injuries. There was a significantly higher frequency of men in the contact cohort compared with the noncontact cohort (69.2% vs 54.2%, P = .030), while age and body mass index were comparable between the 2 cohorts. The bivariate analysis demonstrated a significantly higher rate of combined lateral tibiofemoral (lateral femoral condyle [LFC] + lateral tibial plateau [LTP]) bone bruises (82.1% vs 48.6%, P < .001) and a lower rate of combined medial tibiofemoral (medial femoral condyle [MFC] + medial tibial plateau [MTP]) bone bruises (39.7% vs 66.2%, P < .001) in knees with contact injuries. Similarly, noncontact injuries had a significantly higher rate of centrally located MFC bone bruises (80.3% vs 61.5%, P = .003) and posteriorly located MTP bruises (66.2% vs 52.6%, P = .047). When controlling for age and sex, the multivariate logistical regression model demonstrated that knees with contact injuries were more likely to have LTP bone bruises (OR, 4.721 [95% CI, 1.147-19.433], P = .032) and less likely to have combined medial tibiofemoral (MFC + MTP) bone bruises (OR, 0.331 [95% CI, 0.144-0.762], P = .009) compared with those with noncontact injuries.

Conclusion:

Significantly different bone bruise patterns were observed on MRI based on ACL injury mechanism, with contact and noncontact injuries demonstrating characteristic findings in the lateral tibiofemoral and medial tibiofemoral compartments, respectively.

Keywords

contact ACL injury bone bruise patterns noncontact ACL injury anterior cruciate ligament mechanism of injury

Acute anterior cruciate ligament (ACL) injuries are typically classified into 2 distinct groups based on their injury mechanism: contact or noncontact injuries.^18,19 Contact ACL injuries are less common and typically occur when there is force directed to the lateral side of the knee.^18,19 In contrast, more than 70% of ACL injuries occur in a noncontact manner, during which rapid movement that confers supraphysiological stresses, such as changing directions, landing, deceleration, or pivoting, can lead to rupture of the ACL.^10,12 While the mechanisms of ACL injury have been thoroughly investigated, the underlying kinematic forces at the time of injury remain debated.

Subchondral bone marrow edema, also termed edema-like marrow signal intensity or bone bruising, is present on magnetic resonance imaging (MRI) in 80% to 99% of patients who sustain acute ACL injuries.^5,11,19 Bone bruises are believed to result from inflammation, edema, and microtrabecular fractures caused by compression forces between the femur and tibia at the time of ACL injury.^11,13 The resultant tibiofemoral bruises can act as a mechanistic “footprint” of the forces within the joint at the time of ACL injury, potentially lending insight into the kinematic events at the time of injury.^1,4,19 The bone bruise patterns in noncontact ACL injuries are well reported in the literature, and many authors have inferred a combination of anterior tibial translation, valgus stress, and internal or external tibial rotation.^8,15,17,19 However, few studies have investigated the bone bruise patterns in contact ACL injuries, as this mechanism is less common and considered less preventable than those sustained in a noncontact manner.¹³

Viskontas et al¹⁷ examined the bone bruise patterns and mechanistic implications in noncontact and contact ACL injuries in a cohort of 100 patients, of which only 12 patients had a contact mechanism. Noncontact injuries showed bruising that was consistent with valgus stress, anterior tibial translation, and internal tibial rotation. While contact injuries were largely believed to result from pure valgus stress imparted by a direct laterally based force on the knee, the authors inferred from the bone bruise patterns that the predominant mechanism of contact injury appeared to be valgus stress and anterior tibial translation.¹⁷ However, these findings were confined to a limited number of patients with contact injuries. Therefore, examination of the bone bruise patterns in a larger cohort of contact ACL injuries may further improve our understanding of the different kinematic forces experienced at the time of ACL injury.

Given the relative infrequency of contact ACL injuries and the paucity of literature that has examined the associated bone bruises, the primary purpose of this study was to examine and compare the number and location of bone bruises associated with contact and noncontact ACL injuries. The authors hypothesized that the direct contact mechanism of ACL injury would lead to different in bruising patterns in the tibiofemoral compartment when compared with the noncontact mechanism.

Methods

Patient Selection and Identification

Institutional review board approval was granted for this study. A total of 320 consecutive patients were identified using the Current Procedural Terminology code 29888 (representing ACL reconstruction surgery), all of whom underwent surgery by 2 orthopaedic sports medicine fellow-trained surgeons at Yale School of Medicine. Of these, 220 patients met the following inclusion criteria for this study: (1) less than 30 days between date of the reported injury and date of the MRI, (2) T2-weighted fat-suppressed MRI sequences available in both the coronal and sagittal planes, (3) clear documentation of the mechanism of injury in clinical notes, (4) no documentation of previous ipsilateral knee injury, and (5) no concomitant knee dislocation, fractures, or posterolateral corner and/or posterior cruciate ligament injuries. Patient characteristics including age, sex, body mass index (BMI), and time between date of initial injury and preoperative MRI were gathered retrospectively from the electronic medical records.

Determination of Mechanism of Injury

Mechanism of injury and sport or activity involved at the time of injury were retrospectively recorded from preoperative clinical notes. Sport injuries were classified as those that occurred during organized or recreational sports. Nonsport injuries included injuries from jumping on the trampoline, working out or participating in workout classes, misstepping (such as when stepping off a curb), or playing around the house (eg, child collides on parent’s lateral side of the knee). As outlined in previous studies, mechanisms were classified as noncontact or contact and patients were separated into these 2 cohorts for comparison. For patients classified into the contact injury cohort, it was required that a clear external force, such as being tackled in American football and/or a collision at the level of the knee, facilitated the injury. Conversely, if there was no external force at the time of injury, the mechanism was classified as noncontact.¹⁷

Classification of Preoperative Bone Bruises on MRI

All 220 patients underwent MRI on a 3-T scanner using the standard knee protocol at our institution. All the imaging studies were independently and retrospectively reviewed by 2 board-certified musculoskeletal radiologists, one with 8 years of clinical experience (A.W.) and the other with 40 years of clinical experience (L.D.K.). Only fat-suppressed T2-weighted coronal and sagittal images were reviewed to determine the location of bone bruises. The sequence specifics for the images were an average repetition time (TR) of 6500 milliseconds, echo time (TE) of 45 milliseconds, field of view of 14 to 16 cm, and resolution of 256 × 256.^7-9

The location of bone bruises was mapped according to Moran et al,^7-9 whose approach has been used for analysis of bone bruising in previous studies. Medial femoral condyle (MFC) bone bruises were defined as those that occur within the medial, central, notch, and/or trochlear zones on the MFC (Figure 1).

Similarly, lateral femoral condyle (LFC) bone bruises were defined as those that occur in the lateral trochlea, notch, central, and/or lateral zones on the LFC (Figure 1). Medial tibial plateau (MTP) bone bruises were defined as those that occur within the medial, central, and/or medial subspine zones on the MTP (Figure 1). Lateral tibial plateau (LTP) bone bruises were classified as those that occur within the lateral subspine, central, and/or lateral zones on the LTP (Figure 1).⁸

Correlation of the Coronal Location of the Bone Bruises With Its Corresponding Sagittal Location

Once the coronal location of the bruise(s) was recorded, sagittal plane sequences were used to define the anterior-posterior location of the bone bruising within the femur and tibia. The sagittal zones for both the lateral and medial femoral condyles were divided into the trochlea, anterior, central, and posterior regions (Figure 2).

The sagittal zones for the lateral and medial tibia plateaus were divided into anterior (A), central (C), and posterior (P) regions (Figure 3). The intersecting coronal-sagittal location of each bruise was recorded. If the bruise was located across multiple zones, each individual zone it extended to was counted. Similarly, if multiple bruises were present, edema was counted to the individual zone(s) it spanned. The signal intensity and volume of the lesions were not recorded.^8,9

Determination of Concomitant Injuries

All operative notes were retrospectively reviewed for all patients. Any description of a meniscal injury during diagnostic arthroscopy, whether treated or not, was recorded. Superficial medial collateral ligament (MCL) injuries were graded (1, 2, or 3) on preoperative MRI scans by both radiologists according to Rasenberg et al.¹⁴

Statistical Analysis

Interrater and intrarater intraclass correlation coefficient (ICC) agreements were calculated for the location and number of bone bruises. Agreement was defined as poor, moderate, good, or excellent reliability: <0.5, 0.5 to 0.75, 0.75 to 0.9, and >0.9, respectively.⁶ After the ICCs were calculated, if there was any disagreement between the presence or absence of bone bruises and/or the location of the bone bruises, the 2 radiologists re-reviewed the cases together until a consensus was reached to make a final determination. Continuous variables were assessed using 2-tailed t tests or their nonparametric equivalent using Real Statistics Add-in Package in Microsoft Excel (Microsoft Corporation). SISA (Simple Interactive Statistical Analysis) was used to analyze bone bruise patterns (categorical variables) using chi-square tests or Fisher’s exact tests. Statistical significance was denoted by a P < .05. A multivariate logistic regression model was then performed on all significant variables identified in the lateral and/or medial tibiofemoral bone bruise bivariate analysis (see Table 3) anything that was significant in the bivariate analysis was included in the model and sex and age were controlled for. Additionally, a receiver operating characteristic (ROC) and area under the curve (AUC) were included to demonstrate the validity of the model. Previous AUC cutoffs were used to assess the quality of the model with an AUC <0.50 equating to random assignment, 0.70 to 0.80 to a reasonable model, and >0.80 to a model that discriminates at a high standard, with 1.0 denoting perfect assignment.

Results

Bivariate Analysis

Of the 220 patients who met inclusion criteria, 78 (35.5%) were categorized as sustaining a contact injury, while 142 (64.5%) sustained a noncontact ACL injury. The bivariate analysis revealed no differences with respect to the mean age and BMI of the 2 cohorts. There was a significantly higher frequency of men in the contact cohort compared with the noncontact cohort (69.2% vs 54.2%, P = .030) (Table 1).

Table 1

Patient Characteristics for the Entire Cohort^a

	Contact (n = 78)	Noncontact (n = 142)	P Value
Age, y	23.1 ± 9.6	25.6 ± 12.0	.097
Sex			.030
Female	24 (30.8)	65 (45.8)
Male	54 (69.2)	77 (54.2)
BMI	26.1 ± 5.9	25.7 ± 5.4	.962
Any bone bruise	75 (96.2)	138 (97.2)	.563
Lateral bone bruises only	10 (12.8)	9 (6.3)	.102
Medial bone bruises only	4 (5.1)	11 (7.7)	.494
Both lateral and medial bone bruises	61 (78.2)	118 (83.1)	.373

Values are presented as mean ± SD or n (%). Boldface type indicates statistical significance (P < .05). BMI, body mass index.

The bivariate analysis did not reveal any significant differences between the rates of lateral meniscal, medial meniscal, and MCL tears in contact and noncontact injuries (Table 2).

Table 2

Concomitant Injuries in Knees with Contact and Noncontact ACL Injuries^a

	Contact (n = 78)	Noncontact (n = 142)	P Value
MM tears	28 (35.9)	37 (26.1)	.126
LM tears	27 (34.6)	59 (41.5)	.313
MCL injury	23 (29.5)	26 (18.3)	.057
MCL injury grade			.229
0	54 (69.2)	116 (81.7)
1	6 (7.7)	8 (5.6)
2	11 (14.1)	10 (7.0)
3	6 (7.7)	8 (5.6)

Values are presented as mean ± SD or n (%). ACL, anterior cruciate ligament; LM, lateral meniscus; MCL, superficial medial collateral ligament; MM, medial meniscus.

Coronal: LFC, LTP, MFC, and MTP Bone Bruises

The interrater reliability for the location of bone bruises demonstrated good agreement (ICC, 0.882). The bivariate analysis revealed that contact injuries had a significantly higher frequency of bone bruises involving the LTP compared with noncontact injuries (89.7% vs 54.2%, P < .001). In addition, contact injuries sustained a greater frequency of combined lateral tibiofemoral (LFC + LTP) bone bruises compared with noncontact injuries (82.1% vs 48.6%, P < .001). Conversely, noncontact injuries had a higher frequency of bruising on the MFC compared with contact injuries (84.5% vs 62.8%, P < .001). Noncontact injuries also had a higher frequency of combined medial tibiofemoral (MFC + MTP) bone bruises than contact injuries (66.2% vs 39.7%, P < .001) (Figure 4). The number of patients and frequencies of different combinations of lateral and medial bone bruises are described in Table 3.

Table 3

Number of Patients With at Least 1 Bone Bruise in the Lateral and/or Medial Tibiofemoral Compartment in Contact and Noncontact ACL Injuries^a

	Contact (n = 78)	Noncontact (n = 142)	P Value
Lateral side
LFC + LTP	64 (82.1)	69 (48.6)	<.001
LFC	65 (83.3)	119 (83.8)	>.999
LTP	70 (89.7)	77 (54.2)	<.001
Medial side
MFC + MTP	31 (39.7)	94 (66.2)	<.001
MFC	49 (62.8)	120 (84.5)	<.001
MTP	47 (60.3)	102 (71.8)	.079

Values are presented as n (%). Boldface type indicates statistical significance (P < .05). ACL, anterior cruciate ligament; LFC, lateral femoral condyle; LTP, lateral tibial plateau; MFC, medial femoral condyle; MTP, medial tibial plateau.

Location of the Femoral and Tibial Bone Bruises in the Sagittal Plane (Anterior, Central, and/or Posterior)

The contact cohort had significantly more posterior bone bruises on the LTP compared with the noncontact group (85.9% vs 32.4%, P < .001). Conversely, the noncontact group demonstrated more bruises on both the central MFC (80.3% vs 61.5%, P = .003) and posterior MFC (38.7% vs 3.8%, P < .001). The noncontact cohort also demonstrated a higher frequency of bone bruises in the posterior MTP (66.2% vs 52.6%, P = .047). All coronal-sagittal bone bruising patterns are described in Table 4.

Table 4

Frequency and Location of Bone Bruises in the Sagittal Plane on the LFC, LTP, MFC, and MTP for the Contact and Noncontact Cohorts^a

	Contact (n = 78)	Noncontact (n = 142)	P Value
Lateral femoral condyle
Anterior	22 (28.2)	42 (29.6)	.830
Central	55 (70.5)	93 (65.5)	.448
Posterior	6 (7.7)	5 (3.5)	.153
Lateral tibial plateau
Anterior	7 (9.0)	9 (6.3)	.471
Central	28 (35.9)	42 (29.6)	.336
Posterior	67 (85.9)	46 (32.4)	<.001
Medial femoral condyle
Anterior	10 (12.8)	22 (15.5)	.591
Central	48 (61.5)	114 (80.3)	.003
Posterior	3 (3.8)	55 (38.7)	<.001
Medial tibial plateau
Anterior	6 (7.7)	18 (12.7)	.257
Central	11 (14.1)	28 (19.7)	.297
Posterior	41 (52.6)	94 (66.2)	.047

Values are presented as n (%). Boldface type indicates statistical significance (P < .05). LFC, lateral femoral condyle; LTP, lateral tibial plateau; MFC, medial femoral condyle; MTP, medial tibial plateau.

Regression Analysis

Results of the multivariate logistic regression analysis indicated that contact injuries were significantly more likely to have LTP bone bruises (OR, 4.721 [95% CI, 1.147-19.433], P = .032) and less likely to have combined medial tibiofemoral [MFC + MTP] bone bruises (OR, 0.331 [95% CI, 0.144-0.762], P = .009) compared with noncontact injuries when controlling for age and sex. The results of the multivariate logistic regression model are summarized in Table 5.

Table 5

Multivariate Logistic Regression Variables and Results^a

Variable	OR	P Value	Lower CI	Upper CI
LTP	4.721	.032	1.147	19.433
MFC + MTP	0.331	.009	0.144	0.762

Boldface type indicates statistical significance (P < .05). LTP, lateral tibial plateau; MFC, medial femoral condyle; MTP, medial tibial plateau.

ROC Curve Analysis

The ROC curve of the predicted probabilities from the final logistic regression model demonstrated reasonable discrimination for LTP bone bruises and combined medial tibiofemoral bruises, with an AUC of 0.786.

Discussion

The most important finding in this study was that patients who sustained a contact ACL injury demonstrated significantly different tibiofemoral bone bruise patterns compared with patients who sustained a noncontact injury. Therefore, these findings confirmed the primary hypothesis tested. When controlling for age and sex, contact ACL injuries were significantly more likely to have posterior LTP bruising and less likely to have combined medial tibiofemoral [MFC + MTP] bone bruises on preoperative MRI. These findings may further improve our understanding of the different kinematic forces experienced at the time of contact and noncontact ACL injury.

Bone bruises in the medial tibiofemoral compartment have been reported to occur in up to 83% of patients with noncontact ACL injuries.^2,3,19 Viskontas et al¹⁷ reported that patients with noncontact ACL injury experienced significantly more bone bruising on the MTP compared with patients who sustained a contact ACL injury. Similarly, the present study found that combined medial tibiofemoral (MFC + MTP) bone bruises were significantly more common in knees with noncontact injuries when compared with those with contact injuries. These findings indicate that more frequent collisions occurred between the MFC and MTP in the noncontact mechanism. Biomechanical studies, such as the one conducted by Quatman et al,¹³ have shown that anterior tibial translation is a key underlying mechanism in noncontact ACL injuries. In addition, previous studies on noncontact ACL bone bruise patterns have inferred a degree of anterior tibial translation from central MFC and posterior MTP bruising, which is consistent with the sagittal location of the medial sided bruising in both mechanisms of injury in the present study.^5,8,15 However, the significantly lower rates of combined medial tibiofemoral bone bruises seen with contact ACL injuries may offer insight into the degree of anterior tibial translation when compared with noncontact injuries.

Although noncontact injuries demonstrated a high frequency of lateral tibiofemoral bruising, contact injuries demonstrated significantly more posterior LTP bone bruises. It is important to note that the current classification of contact injuries included only patients who described an external force or a lateral-sided collision to the knee, and the reported lateral tibiofemoral bruising findings should be interpreted within the context of this inclusion criterion. In comparison with noncontact injuries, it is plausible that a higher-energy mechanism is imparted by the direct valgus forces sustained during contact ACL injuries, leading to more bone bruising within the lateral tibiofemoral compartment. However, secondary to exclusion of contact cases in many reports or the previously low number of cases reported, statements about the frequency of lateral tibiofemoral bruising seen in contact injuries are also limited. Several biomechanical and ACL bone bruise studies on noncontact injuries have suggested a degree of valgus stress leading to direct impact between the LFC and LTP with simultaneous distraction of the medial compartment.^13,16 In contact ACL injuries, biomechanical studies that elucidate the underlying kinematics are limited, but there is a consensus that the majority of these injuries originate from a lateral-sided collision to the knee, resulting in increased valgus stress and lateral compartment compression. Further studies are warranted to establish direct associations between the lateral-sided bone bruise patterns and valgus kinematics during contact and noncontact ACL injuries, as the current methodology can only provide speculation based on imaging data.

Limitations

There were some inherent limitations to this retrospective study that should be considered. First, the classification of the mechanisms of injury and stratification of the cohort into contact versus noncontact groups were gathered from a retrospective review of clinical notes and based purely on patient recall and physician documentation. While this introduces potential recall bias, the design attempted to obviate this by only including patients who received an MRI within 30 days of the injury, and the clinical notes from the emergency department or first clinical encounter were documented well before the MRI. In return, this decreased the time elapsed from the date of injury, which is known to decrease recall bias. Second, our department frequently sees patients who are evaluated at our level 1 trauma center, which may increase the chances of encountering more contact ACL injuries. However, the rate of contact injuries in our cohort (35.5%) is on the higher end but within the accepted range reported in the literature. Although statistically significant findings were identified when the 2 mechanisms of injury were compared, there were only 78 patients in the contact cohort and certain analyses may have been underpowered. While propensity score matching could have been utilized to match the 2 cohorts, this analysis could have limited the number of included patients who sustained a contact ACL injury. To address any confounding patient variables between the 2 mechanisms of injury, a multivariable logistic regression was utilized to determine the significant bruise patterns.

Bone bruises can be difficult to localize on MRI and can be misinterpreted when the time between the injury and MRI is delayed, and our inclusion of the 30-day cutoff also mitigated any bias with bone bruise healing. It is also important to note that all MRI scans were performed on a 3-T scanner, and given that 1.5-T scanners are used in the majority of clinical practices, this could potentially affect the generalizability of the current results, as 3-T scanners provide greater resolution and higher-quality images. Whether the bone bruises occurred at the time of ACL injury or if they were a consequence of sequelae afterward may represent a limitation in inferring the underlying kinematics at the time of injury. However, we can be certain that high-energy tibiofemoral impaction occurred and the distribution of such bruises was significantly different in the 2 groups.⁸ Bone bruise patterns have the potential to be misinterpreted with variable tibiofemoral locations. The study design sought to obviate this potential limitation via the use of 2 radiologists, blinded to all clinical data except MRI scans, in order to report the bruise findings in this study and showed good interrater agreement (ICC, 0.882). In addition, a validated and previously published standardized mapping technique was utilized for localization of bruises.

Conclusion

Footnotes

Submitted September 7, 2022; accepted January 24, 2023.

One or more of the authors has declared the following potential conflict of interest or source of funding: R.F.L. has received research support from Arthrex, Conmed Linvatec, Ossur, and Smith & Nephew; consulting fees from Arthrex, Ossur, and Smith & Nephew; and royalties from Arthrex, Ossur, and Smith & Nephew. M.J.M. has received consulting fees from Smith & Nephew. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

ORCID iDs

Jay Moran

Michael Lee

Kyle N. Kunze

William M. McLaughlin

Stephen M. Gillinov

Andrew E. Jimenez

Timothy E. Hewett

Michael J. Medvecky

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