The Predicted Position of the Knee Near the Time of ACL Rupture Is Similar Between 2 Commonly Observed Patterns of Bone Bruising on MRI

Abstract

Background: Bone bruises observed on magnetic resonance imaging (MRI) can provide insight into the mechanisms of noncontact anterior cruciate ligament (ACL) injury. However, it remains unclear whether the position of the knee near the time of injury differs between patients evaluated with different patterns of bone bruising, particularly with regard to valgus angles. Hypothesis: The position of the knee near the time of injury is similar between patients evaluated with 2 commonly occurring patterns of bone bruising. Study Design: Descriptive laboratory study. Methods: Clinical T2- and T1-weighted MRI scans obtained within 6 weeks of noncontact ACL rupture were reviewed. Patients had either 3 (n = 20) or 4 (n = 30) bone bruises. Patients in the 4–bone bruise group had bruising of the medial and lateral compartments of the femur and tibia, whereas patients in the 3–bone bruise group did not have a bruise on the medial femoral condyle. The outer contours of the bones and associated bruises were segmented from the MRI scans and used to create 3-dimensional surface models. For each patient, the position of the knee near the time of injury was predicted by moving the tibial model relative to the femoral model to maximize the overlap of the tibiofemoral bone bruises. Logistic regressions (adjusted for sex, age, and presence of medial collateral ligament injury) were used to assess relationships between predicted injury position (quantified in terms of knee flexion angle, valgus angle, internal rotation angle, and anterior tibial translation) and bone bruise group. Results: The predicted injury position for patients in both groups involved a flexion angle <20°, anterior translation >20 mm, valgus angle <10°, and internal rotation angle <10°. The injury position for the 3–bone bruise group involved less flexion (odds ratio [OR], 0.914; 95% CI, 0.846-0.987; P = .02) and internal rotation (OR, 0.832; 95% CI, 0.739-0.937; P = .002) as compared with patients with 4 bone bruises. Conclusion: The predicted position of injury for patients displaying both 3 and 4 bone bruises involved substantial anterior tibial translation (>20 mm), with the knee in a straight position in both the sagittal (<20°) and the coronal (<10°) planes. Clinical Relevance: Landing on a straight knee with subsequent anterior tibial translation is a potential mechanism of noncontact ACL injury.

Elevated In Vivo ACL Strain Is Associated With a Straight Knee in Both the Sagittal and the Coronal Planes

“…In support of this hypothesis, studies that analyzed bone bruise patterns in ACL-injured participants have suggested that the knee was positioned in extension near the time of noncontact ACL rupture. 47,48,62…”

The Predicted Position of the Knee Near the Time of ACL Rupture Is Similar Between 2 Commonly Observed Patterns of Bone Bruising on MRI: Response

“…Based on prior studies, 16,19 the minimum sample size to detect 3° of valgus difference between the two groups with 80% power was 15 per group. We stated that “20 patients who displayed the 3–bone bruise pattern and 30 patients from a previous study 19 who displayed the 4–bone bruise pattern were included in this analysis.” 15 The number “136” appears in this paper once in the following sentence that addresses previous findings from Kim-Wang et al 14 : “Among a cohort of 136 patients with noncontact ACL injuries, these 2 bone bruising patterns comprised 59% of the patient cohort.” 15 Our methods detail the patient sample and appropriately reference our previously reported data related to bone bruising patterns. 14,19…”

“…We agree that the numbers used by Drs Hewett and Lavender “do not add up.” This is because the numbers cited by Drs Hewett and Lavender do not pertain to the study that is the topic of their letter. In brief, the study by Owusu-Akyaw et al 19 (2018) included 30 patients; the study by Kim-Wang et al 14 (2021) included 136 patients; and the study in question, that by Kim-Wang et al 15 (2023), included 50 patients. The study with 136 patients was a descriptive study of bone bruise patterns.…”

“…In the study by Kim-Wang et al, 15 our Methods section stated that MRI scans that met our inclusion criteria were retrospectively reviewed. Based on prior studies, 16,19 the minimum sample size to detect 3° of valgus difference between the two groups with 80% power was 15 per group.…”

“…The subject of our recently published paper 15 was to compare the predicted position of ACL injury between two commonly observed patterns of bone bruising. At no point in this paper did we measure, address, or discuss whether the timing of an ACL injury can be determined from MRI.…”