Differences in MR signal intensity of lateral collateral ligament of knee joint on fat-suppressed proton density-weighted imaging

The relationship of proximal lateral collateral ligament hyperintensity with knee joint ligament and meniscus pathologies

BACKGROUND

Hyperintensity in the proximal lateral collateral ligament (LCL) is often confusing. This appearance may be alone or accompany other pathologies.

PURPOSE

To investigate the relationship between the signal intensity (SI) change in the proximal LCL and the knee joint pathologies.

MATERIAL AND METHODS

The knee MRI scans taken between 2020 and 2022 were queried retrospectively. Patients with acute trauma, instability, knee surgery, or high-grade osteoarthritis were excluded. Included patients were divided into two groups as normal SI and increased SI according to proximal LCL. The difference in ligamentous and meniscal pathologies between the two groups was analyzed using a chi-square test. Inter-observer agreement analysis was performed on 50 randomly selected patients.

RESULTS

A total of 351 patients (139 men [39.6%], 212 women [60.4%]; median age = 37 years; interquartile range = 67 years) were included. There were 114 (32.5%) LCLs with normal SI and 237 (67.5%) LCLs with increased SI. Normal SI and increased SI groups had a significant difference in terms of joint side, median age, patellar tendon SI, anterior cruciate ligament SI, and medial collateral ligament SI (P = 0.004, P = 0.004, P = 0.001, P = 0.011, P = 0.004, respectively). A significant difference between the results of two separate LCL examinations in coronal + axial and coronal-only planes (P <0.001). Inter-observer agreement was found to be good to excellent.

CONCLUSION

Hyperintensity in the proximal LCL was more common on the right joint side, in older patients, and patients with hyperintensity in the proximal patellar tendon, anterior cruciate ligament, and medial collateral ligament. Evaluating the LCL only in the coronal plane overestimates the hyperintensity.

Increased signal of the fibular collateral ligament of the knee on MRI, clinically significant?

INTRODUCTION

The purpose of this study was to determine the clinical significance of signal hyperintensity in the proximal fibular collateral ligament (FCL) on coronal proton density (PD) fat-saturated (FS) MRI of the knee, a common finding. This study is unique in that it characterizes the FCL of a comprehensive, large cohort of both symptomatic and asymptomatic patients, which to our knowledge represents the first study with such broad inclusion criteria.

METHODS

A large case series was performed analyzing MRI of the knee of 250 patients from July 2021 through September 2021 and retrospectively reviewed. All studies were performed on 3-Tesla MRI scanners with a dedicated knee coil and in accordance with standard institutional knee MRI protocol. Signal in the proximal fibular collateral ligament was assessed on coronal PDFS and axial T2-weighted FS images. Increased signal was classified as none, mild, moderate, or severe. A corresponding chart review of clinic notes was performed to determine the presence or absence of lateral knee pain. An FCL sprain or injury was considered present if the medical record described tenderness on palpation of the lateral knee, positive finding against resistance to the leg (varus stress test) or reverse pivot shift, or any clinical suspicion for lateral complex sprain or posterolateral corner injury.

RESULTS

The majority (74%) of knee MRIs demonstrated the presence of increased signal in the proximal fibular collateral ligament on coronal PD FS images. <5% of these patients had associated clinical findings of fibular collateral ligament and/or lateral supporting structure injury.

DISCUSSION

Although increased signal in the proximal FCL of the knee is a common finding on coronal PDFS images, the majority are not associated with clinical symptoms. Thus, this increased signal is likely not a pathological finding in the absence of clinical findings of fibular collateral ligament sprain/injury. Our study emphasizes the importance of clinical correlation in identifying increased signal in the proximal FCL as pathologic.

Imaging Characteristics of the Proximal Lateral Collateral Ligament of the Knee: Findings on Ultrasound and MRI With Histologic Correlation

OBJECTIVES

Determine prevalence of increased signal intensity of the lateral collateral ligament (LCL) of the knee on MRI and decreased echogenicity on ultrasound, and compare with cadaveric histologic evaluation.

METHODS

After IRB approval of this prospective study with informed consent, patients having knee MRI were additionally evaluated with ultrasound. Signal intensities of LCL on MRI (low, intermediate, high), echogenicity at ultrasound (hyperechoic, hypoechoic, anechoic), and extent of findings were assessed. Descriptive statistics, Wilcoxon signed ranked test, and intraclass correlation coefficient (ICC) were calculated. Two cadaveric knees were imaged with MRI and ultrasound, including histologic LCL evaluation.

RESULTS

Seventy-three subjects were included (39 males, 34 females; mean age 48 ± 14 years) with 77 knee examinations. On MRI, low, intermediate, and high signals were present in 21% (16/77), 75% (58/77), and 4% (3/77), respectively. On ultrasound, echogenicity was assessed as hyperechoic, hypoechoic, and anechoic in 62% (48/77), 38% (29/77), and 0% (0/77), respectively. Mean length of increased signal was 8.6 mm (±4.9) on MRI, and 6.5 mm (±4.8) on ultrasound. The ICC showed a good to excellent intermodality reliability (0.735-0.899) without statistically significant difference for interreader measurements (P = .163-.795). Histology evaluation showed transition of ligament fibers to fibrocartilage at its insertion with increased connective tissue mucin corresponding to MRI and ultrasound findings.

CONCLUSIONS

Increased signal intensity of the proximal LCL on ultrasound and MRI is common and corresponds to normal connective tissue mucin.