MR imaging of the posterolateral corner of the knee

Relationship of Fracture Morphological Characteristics with Posterolateral Corner Injuries in Hyperextension Varus Tibial Plateau Fractures

BACKGROUND

Hyperextension varus tibial plateau fracture (HVTPF) is known to present with concomitant injuries to the posterolateral corner (PLC). However, the exact rate and characteristics of these injuries remain unclear. The primary objective of this study was to explore the rate and characteristics of PLC injuries in HVTPFs. The secondary objective was to investigate the relationship between the fracture morphological features and the associated PLC injuries.

METHODS

Patients with HVTPFs were subdivided into 2 groups: group I (without fracture of the posterior column cortex) and group II (with fracture of the posterior column cortex). Fracture characteristics were summarized qualitatively based on fracture maps and quantitatively based on the counts of morphological parameters. Knee ligamentous and meniscal injuries were assessed using magnetic resonance imaging. The association between fracture characteristics and PLC injuries was analyzed.

RESULTS

We included a total of 50 patients with HVTPFs in our study: 28 in group I and 22 in group II. The rate of PLC injuries was 28.6% in group I and 27.3% in group II. In group I, patients with PLC injuries showed fracture lines closer to the anterior rim of the medial plateau and had smaller fracture areas. Furthermore, 6 of the 8 patients with PLC injuries in group I also had posterior cruciate ligament injuries.

CONCLUSIONS

The rate of PLC injuries is relatively high in HVTPFs. In HVTPFs without fracture of the posterior column cortex, a small fracture area strongly suggests an accompanying PLC injury, and PLC injury is frequently combined with posterior cruciate ligament injury.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Diagnosing popliteofibular ligament injuries in anterior cruciate ligament-injured knees: A prospective magnetic resonance imaging study investigating the inter- and intraobserver reliability of identification of the popliteofibular ligament

Purpose

The aim of our study was to investigate the intra- and interobserver reliability for the identification of the popliteofibular ligament (PFL) in magnetic resonance imaging (MRI) scans in patients with an anterior cruciate ligament (ACL) injury and ascertain the prevalence of PFL tears in ACL-injured knees without clinically high-grade posterolateral corner injury.

Methods

MRI readings were performed retrospectively by two surgeons on 84 patients who underwent ACL reconstruction in our department. The presence of the PFL on both sagittal and coronal images as well as the presence of PFL tears was noted. Readings were repeated 6 weeks later for one observer. The κ value was calculated to determine the intra- and interobserver reliability for identification of the PFL and the prevalence of PFL tears was ascertained.

Results

The PFL was visualized in 90.5%-91.7% of MRI scans. The intra- and interobserver reliability of visualizing the PFL on MRI had an κ value of 0.63 and 0.66 (substantially reliable), respectively. The intraobserver reliability for identification of PFL tears had an κ value of 0.26 (fair reliability). We found a 4.8% prevalence of PFL tears in ACL-injured knees.

Conclusions

There is substantially reliable intra- and interobserver reliability for the identification of the PFL on MRI scans but only fair reliability for the identification of PFL tears. A 4.8% prevalence of PFL tears in ACL-injured knees without clinically confirmed high-grade posterolateral corner injury can be observed in our series.

Level of Evidence

Level IV.

Demystifying the "Dark Side of the Knee": An Update on Imaging of the Posterolateral Corner

The posterolateral corner (PLC) of the knee is a complex anatomical-functional unit that includes ligamentous and tendinous structures that are crucial for joint stability. This review discusses the intricate anatomy, biomechanics, and imaging modalities, as well as the current challenges in diagnosing PLC injuries, with an emphasis on magnetic resonance imaging (MRI). Recognizing the normal MRI anatomy is critical in identifying abnormalities and guiding effective treatment strategies. Identification of the smaller structures of the PLC, traditionally difficult to depict on imaging, may not be necessary to diagnose a clinically significant PLC injury. Injuries to the PLC, often associated with cruciate ligament tears, should be promptly identified because failure to recognize them may result in persistent instability, secondary osteoarthritis, and cruciate graft failure.

[Imaging of posterolateral rotational instability of the knee joint]

Posterolateral instability of the knee joint typically occurs with injuries to the posterolateral corner of the joint or with additional combined injuries involving the anterior and posterior cruciate ligaments. In addition to numerous, smaller anatomical structures, the most important are the lateral collateral ligament (LCL), the popliteus muscle with its tendon, and the popliteofibular ligament (PFL), which can usually be assessed using magnetic resonance imaging (MRI). On the contrary, small structures like the arcuate ligament and fabellofibular ligament cannot always be identified. However, they are also of lesser importance in the development of posterolateral rotational instability. Overlooked injuries to the posterolateral joint corner promote instability with the complication of inadequate ligament reconstruction and early onset posttraumatic osteoarthritis. Knowledge of MRI morphology of the anatomical structures involved, taking into account their biomechanical significance, is crucial to recognize and use the corresponding imaging findings.

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.

The diagnostic accuracy of MRI for evaluating the posterolateral corner in acute knee dislocation

OBJECTIVE

To investigate the diagnostic performance of preoperative MRI in evaluating posterolateral corner (PLC) structures after acute knee dislocation (KD) and determine the correlation of MRI with operative findings for grading structure integrity.

METHODS

Acute knee (femorotibial) dislocations between 2005 and 2020 with preoperative MRI and surgical posterolateral corner repair were identified from a single academic institution. From MRI, integrity was evaluated for PLC structures: lateral collateral ligament (LCL), popliteus tendon (PT), biceps femoris tendon (BFT), and ligamento-capsular complex (LCC). Frequency of injury to each structure and number of PLC structures torn in each case were tabulated. Diagnostic performance of MRI was determined using surgery as the reference standard. Correlation between MRI and surgery for each PLC structure was determined using kappa.

RESULTS

Thirty-nine KD cases (19 right) in 39 patients (28 male) were included, with mean age of 33 years. Mechanism of injury was as follows: high energy 52%, low energy 38%, ultra-low energy 10%. LCL was most frequently torn, in 95% (37/39) of cases. Most commonly, three of four PLC structures were torn in 54% (21/39) of cases. Diagnostic accuracy of MRI was high for LCL 95%, BFT 87%, PT 82%, and LCC 92%. Correlation between MRI and surgical findings was variable: substantial for BFT, moderate for LCL and PT, and fair for LCC.

CONCLUSION

MRI has high accuracy for detecting tears of posterolateral corner stabilizers in the setting of acute KD. However, for grading structure integrity, the correlation of MRI with surgical findings is variable, ranging from fair to substantial.

KEY POINTS

• In acute knee dislocation, MRI has high diagnostic accuracy for detecting tears of posterolateral corner (PLC) structures. • Preoperative MRI should be considered by orthopedic surgeons when there is clinical concern for posterolateral corner instability following acute knee dislocation. • Although MRI is valuable in the preoperative investigation of knee dislocation, clinical assessment and intraoperative exploration may still be required for definitive diagnosis.

Are the popliteofibular ligament, the arcuate ligament, and the fibular insertion of the popliteus muscle the same structure? An anatomic and terminological study

Lesions in the lateral region of the knee can result in severe disability due to instability and articular degeneration. The structures in the posterolateral side of the knee function as a unit contributes to rotation and translation limits. Anatomical descriptions of the lateral corner of the knee are incomplete and contradictory. This study aims to verify, through anatomical dissections in cadavers, if the fibular insertion of the popliteus muscle, the arcuate ligament, and the popliteofibular ligament are distinct or the same structure with different terminology and descriptions in the literature. Fifteen cadavers were dissected. Photographs were taken, and in some cases, a video was recorded. Also, the correct terminology for ligament and insertion was searched. The dissections allowed the popliteus muscle to be identified proximally in the lateral femoral condyle, in the fibula head's posterolateral region, and through a meniscocapsular insertion. In none of the anatomy books reviewed, this fibular insertion of the popliteus muscle is mentioned. However, our findings and data from other experimental studies provide evidence of its presence. The aponeurotic portion of the arcuate ligament is distinguished from the short lateral ligament, which is the fibular insertion of the popliteus muscle with its tendinous attachment. Therefore, the term popliteofibular ligament should be abandoned based on the anatomic terminology, and the term "fibular insertion of the popliteus muscle" should be used instead.

Varus stress MRI in the refined assessment of the posterolateral corner of the knee joint

Magnetic resonance imaging (MRI) is commonly used to assess traumatic and non-traumatic conditions of the knee. Due to its complex and variable anatomy, the posterolateral corner (PLC)—often referred to as the joint’s dark side—remains diagnostically challenging. We aimed to render the diagnostic evaluation of the PLC more functional by combining MRI, varus loading, and image post-processing in a model of graded PLC injury that used sequential transections of the lateral collateral ligament, popliteus tendon, popliteofibular ligament, and anterior cruciate ligament. Ten human cadaveric knee joint specimens underwent imaging in each condition as above, and both unloaded and loaded using an MR-compatible device that standardized loading (of 147 N) and position (at 30° flexion). Following manual segmentation, 3D joint models were used to computationally measure lateral joint space opening for each specimen, configuration, and condition, while manual measurements provided the reference standard. With more extensive ligament deficiency and loading, lateral joint spaces increased significantly. In conclusion, varus stress MRI allows comprehensive PLC evaluation concerning structural integrity and associated functional capacity. Beyond providing normative values of lateral compartment opening, this study has potential implications for diagnostic and surgical decision-making and treatment monitoring in PLC injuries.

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.

MRI evaluation of the peripheral attachments of the lateral meniscal body: the menisco-tibio-popliteus-fibular complex

PURPOSE

To determine, identify and measure the structures of the menisco-tibio-popliteus-fibular complex (MTPFC) with magnetic resonance imaging (MRI) in knees without structural abnormalities or a history of knee surgery.

METHODS

One-hundred-and-five knees without prior injury or antecedent surgery were analyzed by means of MRI. The average age was 50.1 years ± 14.8. All the measurements were performed by three observers. The peripherical structures of the lateral meniscus body were identified to determine the location, size, and thickness of the entire MTPFC. The distance to other "key areas" in the lateral compartment was also studied and compared by gender and age.

RESULTS

The lateral meniscotibial ligament (LMTL) was found in 97.1% of the MRIs, the popliteofibular ligament (PFL) in 93.3%, the popliteomeniscal ligaments (PML) in 90.4% and the meniscofibular ligament (MFL) in 39%. The anteroposterior distance of the LMTL in an axial view was 20.7 mm ± 3.9, the anterior thickness of the LMTL was 1.1 mm ± 0.3, and the posterior thickness of the LMTL 1.2 mm ± 0.1 and the height in a coronal view was 10.8 mm ± 1.9. The length of the PFL in a coronal view was 8.7 mm ± 2.5, the thickness was 1.4 mm ± 0.4 and the width in an axial view was 7.8 mm ± 2.2.

CONCLUSIONS

The MTPFC has a constant morphological and anatomical pattern for three of its main ligaments and can be easily identified and measured in an MRI; the MFL has a lower prevalence, considering a structure difficult to identify by 1.5 T MRI.

The popliteofibular ligament: a cadaveric ultrasound study

OBJECTIVE

The popliteofibular ligament (PFL) is an important stabilizer of the knee found within the posterolateral corner (PLC) of the joint. Injuries to the PLC can cause substantial patient morbidity. Accurate PFL visualization has been historically challenging, impeding injury diagnosis and treatment. The gold standard for in vivo PFL visualization is magnetic resonance imaging (MRI), but this procedure has slice thickness limitations, is costly, and is subject to longer wait times. Ultrasonographic (US) PFL assessment is a potentially viable alternative to MRI. This study aimed to determine the viability of US PFL assessment.

MATERIALS AND METHODS

Ten fresh-frozen lower limb specimens were evaluated for the presence and morphometric characteristics of the PFL via US using an 18.0-MHz linear transducer. The cadavers were then dissected and reassessed for the presence and morphometric characteristics of the PFLs for comparison with US findings. Moreover, the fracture of the fibular styloid process near the site of the insertion of the PFL (the arcuate sign) was simulated and assessed via US.

RESULTS

The PFL was visualized and measured in all ten knees via both US and cadaveric assessments. There were no statistically significant differences in PFL morphometric characteristics determined via US examination and dissection. The fibular styloid fracture was easily identified in US examination.

CONCLUSION

US imaging is a viable alternative for accurate and effective assessment of the normal PFL. Moreover, the arcuate sign can be evaluated via US.

Evidence-Based Clinical Anatomy of the Popliteofibular Ligament and Its Importance in Orthopaedic Surgery: Cadaveric Versus Magnetic Resonance Imaging Meta-analysis and Radiological Study

BACKGROUND

The popliteofibular ligament (PFL) is a static stabilizer of the posterolateral corner of the knee, preventing varus angulation, tibial rotation, and posterior translation. The PFL is anatomically variable, and there is no current review that outlines its prevalence rate and morphological variations.

PURPOSE

To investigate the anatomic prevalence and morphological qualities of the PFL in various global patient populations via a meta-analysis of relevant literature involving both cadaveric dissections and patient-based research using magnetic resonance imaging (MRI) scans.

STUDY DESIGN

Meta-analysis.

METHODS

We pooled literature data detailing PFL prevalence rates and performed a retrospective MRI study of 100 knees to determine the overall PFL prevalence. Data searches and analyses were performed according to Anatomical Quality Assurance and PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines.

RESULTS

There were 30 cadaveric studies and 11 MRI studies (including our radiological investigation), representing a total of 1595 lower limbs. The meta-analysis of cadaveric studies showed a higher prevalence of the PFL than the meta-analysis of MRI studies, with 98.4% (95% CI, 97.5%-99.2%) and 89.0% (95% CI, 73.9%-98.6%), respectively. Our MRI investigation reported a PFL prevalence of 92.0%.

CONCLUSION

The PFL was found to be a constant or rarely absent anatomic structure of the human knee according to the analysis of cadaveric dissection studies, and it was identified notably less on MRI, albeit not significantly. Increasing PFL anatomic knowledge, including awareness of its prevalence and morphological diversity, will improve injury diagnoses, treatment methods, and prognoses.

Arcuate sign-fibular head avulsion fracture and associated injuries in the pediatric and adolescent population

PURPOSE

To describe the first "arcuate sign" case series in the pediatric population, radiologic features of the associated injuries, management, and how they compare with the adult population.

METHODS

Retrospective study included patients under 18 years of age with a classic "arcuate sign" on radiographs. Data collected included patient demographics, mechanism of injury, and management. Radiographs and advanced imaging (MRI, CT) were reviewed by two musculoskeletal radiologists in a blinded fashion and findings recorded.

RESULTS

Seven patients (4 males, 3 females) with mean age 15 years (range 14-17 years) were included in the study. All 7 injuries were related to sports, 5/7 (71%) being non-contact injuries. Five patients had MRI done-1 LCL injury, MPFL sprain, and MCL sprain were reported; 3 popliteofibular ligament and popliteus sprains were seen; and 3 bone contusions were present on imaging. None of the patients had meniscus or cruciate ligament tears. One patient had an additional fracture of the lateral tibial plateau at the ilio-tibial band attachment and an associated peroneal nerve injury. Five out of seven (71.4%) were treated non-operatively and were able to return back to activity at a mean of 7.2 weeks from injury. Two out of seven (28.6%) needed operative intervention for the fracture but not arthroscopic repair.

CONCLUSION

Pediatric patients with a radiographic arcuate sign tend not to have ACL, PCL, or meniscal injuries, and treatment is predominantly non-operative in contrast to literature reported in adults.

The Menisco-Tibio-Popliteus-Fibular Complex: Anatomic Description of the Structures That Could Avoid Lateral Meniscal Extrusion

PURPOSE

To analyze, quantify, and redefine the anatomy of the peripheral attachments of the lateral meniscal body to further understand how the structures might play a part in preventing meniscal extrusion and how it might be applied to surgical techniques.

METHODS

Ten nonpaired fresh-frozen cadaveric knees without prior injury, a surgical history, or gross anatomic abnormality were included. There were 5 right and 5 left knees, and 50% were from male donors and 50% were from female donors. All the dissections were performed by a group of 3 experts in knee surgery (2 knee surgeons and 1 anatomy professor who oversaw the design of the dissection protocol and guided this protocol). The main peripheral structures associated with the lateral meniscus body were dissected to determine the insertion, size, thickness, and location of the lateral meniscotibial ligament (LMTL), popliteofibular ligament (PFL), and popliteomeniscal ligament (PML). The distance to various landmarks in the lateral compartment was also determined using an electronic caliper. Moreover, a histopathologic study was carried out.

RESULTS

The average thickness of the LMTL was 0.62 ± 0.18 mm (95% confidence interval [CI], 0.49-0.75 mm); that of the PFL-PML area was 1.05 ± 0.27 mm (95% CI, 0.85-1.24 mm). The anteroposterior distance measured 15.80 ± 4.80 mm (95% CI, 12.40-19.30 mm) for the LMTL and 10.40 ± 1.70 mm (95% CI, 9.21-11.63 mm) for the PFL-PML area. The anteroposterior distance of the whole menisco-tibio-popliteus-fibular complex (MTPFC) was 28.20 ± 4.95 mm (95% CI, 24.70-31.70 mm). The average distance from the MTPFC to the posterior horn of the lateral meniscal root was 29.30 ± 2.29 mm (95% CI, 27.60-30.90 mm), whereas that to the anterior horn was 32.00 ± 4.80 mm (95% CI, 28.60-35.50 mm). The average distance from the tibial insertion of the LMTL to the articular surface was 5.59 ± 1.22 mm (95% CI, 4.72-6.46 mm). In all the anatomic components of the knee, a consistent morphologic and histologic pattern was observed between the fibers of the LMTL, PFL, and PML and those of the lateral meniscal body, making up the proposed MTPFC.

CONCLUSIONS

A consistent anatomic pattern has been identified between the lateral meniscal body and the LMTL, PFL, and PML, forming an interconnected complex that would seem appropriate to denominate the MTPFC. A precise study of this region and appropriate nomenclature for it could contribute to a better understanding of the mechanism of lateral meniscal injuries at this level, as well as the development of surgical techniques to treat these lesions and prevent extrusion.

CLINICAL RELEVANCE

This study contributes to the understanding of the lateral meniscal body attachments and the functions they serve. This will lead to improvements in the treatment of lesions in this region, including the development of surgical techniques.

Recent Issues in Musculoskeletal Anatomy Research and Correlation with MRI

MRI 영상은 관절 내 질환의 평가에 중요한 검사기법이며, 관절 MRI 영상의 해석을 위해선 견고한 해부학적 지식이 바탕이 되어야 한다. 관절의 해부학 분야에서는, 새로운 구조물이 발견되기도 하며, 과거에 보고되었으나 기능을 알지 못하던 구조물이 새롭게 주목을 받기도 한다. 본 종설에서는 최근 십여 년간 활발하게 연구되어온 견관절 회전근개 케이블(rotator cable) 및 상관절막(superior capsule), 슬관절의 후외측(posterolateral corner) 및 전외측 인대 복합(anterolateral ligament complex), 발목관절의 원위부 경비골 인대결합(distal tibiofibular syndesmosis) 등의 최근 연구 결과를 소개하고, 이를 MRI 영상을 통해 확인해 보았다.

A Biomechanical Comparison of the Arciero and LaPrade Reconstruction for Posterolateral Corner Knee Injuries

Background:

Injury to the posterolateral corner (PLC) of the knee requires reconstruction to restore coronal and rotary stability. Two commonly used procedures are the Arciero reconstruction technique (ART) and the LaPrade reconstruction technique (LRT). To the authors’ knowledge, these techniques have not been biomechanically compared against one another.

Purpose:

To identify if one of these reconstruction techniques better restores stability to a PLC-deficient knee and if concomitant injury to the proximal tibiofibular joint or anterior cruciate ligament affects these results.

Study Design:

Controlled laboratory study.

Methods:

Eight matched-paired cadaveric specimens from the midfemur to toes were used. Each specimen was tested in 4 phases: intact PLC (phase 1), PLC sectioned (phase 2), PLC reconstructed (ART or LRT) (phase 3), and tibiofibular (phase 4A) or anterior cruciate ligament (phase 4B) sectioning with PLC reconstructed. Varus angulation and external rotation at 0º, 20º, 30º, 60º, and 90º of knee flexion were quantified at each phase.

Results:

In phase 3, both reconstructions were effective at restoring laxity back to the intact state. However, in phase 4A, both reconstructions were ineffective at stabilizing the joint owing to tibiofibular instability. In phase 4B, both reconstructions had the potential to restrict varus angulation motion. There were no statistically significant differences found between reconstruction techniques for varus angulation or external rotation at any degree of flexion in phase 3 or 4.

Conclusion:

The LRT and ART are equally effective at restoring stability to knees with PLC injuries. Neither reconstruction technique fully restores stability to knees with combined PLC and proximal tibiofibular joint injuries.

Clinical Relevance:

Given these findings, surgeons may select their reconstruction technique based on their experience and training and the specific needs of their patients.

Increased Accuracy of Varus Stress Radiographs Versus Magnetic Resonance Imaging in Diagnosing Fibular Collateral Ligament Grade III Tears

PURPOSE

To evaluate the diagnostic accuracy of magnetic resonance imaging and varus stress radiographs for fibular collateral ligament (FCL) tears, and compare these modalities to intraoperative findings.

METHODS

All patients who underwent an isolated FCL or combined anterior cruciate ligament (ACL)/FCL reconstruction by a single surgeon between 2010 and 2017 with preoperative varus stress radiographs and magnetic resonance imaging (MRI) were included in this study. A control group was composed of patients with an MRI and intact ACL and FCL. Sensitivity and specificity of diagnosing FCL injuries on MRI were determined based on review by a fellowship-trained musculoskeletal radiologist, blinded to the pathology associated with each patient (FCL injury vs control), and compared with the gold standard of examination under anesthesia, followed by surgical confirmation of an FCL tear at the time of FCL reconstruction. The sensitivity of diagnosing an FCL injury based on varus stress radiographs was also determined. Furthermore, the ability of both imaging modalities to identify an FCL injury was stratified based on acute versus chronic etiology.

RESULTS

A total of 232 patients were included: 98 patients in the FCL tear group (mean age: 33.6 ± 12.2 years) and 134 patients in the control group (mean age: 44.0 ± 17.2 years). Varus stress radiographs were determined to be more sensitive in diagnosing FCL injuries compared with MRI, with an overall sensitivity of 70% compared with 66%, respectively. Based on MRI, overall specificity was 68%. Based on chronicity of the injuries, MRI was more accurate for detecting acute FCL injuries than chronic injuries (P = .002), and varus stress radiographs were more accurate for detecting chronic FCL injuries than acute injuries (P = .041).

CONCLUSIONS

The results support the use of both varus stress radiographs and MRI in diagnosing FCL injuries, because MRI is more sensitive in diagnosing an acute FCL tear, and varus stress radiographs are more sensitive in diagnosing a chronic FCL tear. Both imaging modalities are recommended to diagnose both acute and chronic FCL injuries.

LEVEL OF EVIDENCE

Level II, case-control study.

Incidence and MRI characterization of the spectrum of posterolateral corner injuries occurring in association with ACL rupture

OBJECTIVE

To determine the incidence and MRI characteristics of the spectrum of posterolateral corner (PLC) injuries occurring in association with anterior cruciate ligament (ACL) rupture.

MATERIALS AND METHODS

We carried out a level IV, retrospective case series study. All patients clinically diagnosed with an ACL rupture between July 2015 and June 2016 who underwent MRI of the knee were included in the study. In addition to standard MRI knee reporting, emphasis was placed on identifying injury to the PLC and a description of involvement of these structures by two musculoskeletal radiologists. Association with PLC involvement was sought with concomitant injuries using correlation analysis and logistic regression.

RESULTS

One hundred sixty-two patients with MRI following ACL rupture were evaluated. Thirty-two patients (19.7%) had an injury to at least one structure of the PLC, including the inferior popliteomeniscal fascicle (n = 28), arcuate ligament (n = 20), popliteus tendon (n = 20), superior popliteomeniscal fascicle (n = 18), lateral collateral ligament (n = 8), popliteofibular ligament (n = 7), biceps tendon (n = 4), iliotibial band (n = 3), and fabellofibular ligament (n = 1). Seventy-five percent of all patients with combined ACL and PLC injuries had bone contusions involving the lateral compartment of the knee. The presence of these contusions strongly correlated with superior popliteomeniscal fascicle lesions (p < 0.05). There was no correlation between injuries to other structures of the PLC and other intra-articular lesions.

CONCLUSION

Missed injuries of the PLC lead to considerable morbidity. The relevance of this study is to highlight that these injuries occur more frequently than previously described and that an appropriate index of suspicion, clinical examination, and MRI are all required to reduce the risk of missed diagnoses. The results of this study support previous suggestions that the rate of concomitant PLC injury in the ACL-deficient knee is under-reported. The rate of combined injuries in this series was 19.7%. The key message of this paper is that PLC injury is common in the presence of ACL injury and should be sought both clinically and radiologically.

Imaging of Athletic Injuries of Knee Ligaments and Menisci: Sports Imaging Series

Acute knee injuries are a common source of morbidity in athletes and if overlooked may result in chronic functional impairment. Magnetic resonance (MR) imaging of the knee has become the most commonly performed musculoskeletal MR examination and is an indispensable tool in the appropriate management of the injured athlete. Meniscal and ligamentous tearing are the most frequent indications for surgical intervention in sports injuries and an understanding of the anatomy, biomechanics, mechanisms of injury, and patterns of injury are all critical to accurate diagnosis and appropriate management. These will be discussed in reference to meniscal tears and injuries of the cruciate ligaments as well as injuries of the posterolateral and posteromedial corners of the knee. (©) RSNA, 2016.

Normal Magnetic Resonance Imaging Anatomy of the Capsular Ligamentous Supporting Structures of the Knee

Recognition of the normal magnetic resonance (MR) imaging appearances of the capsular ligaments of the knee is of great importance. These ligaments contribute to stability of the knee joint and are frequently injured. In this article, we describe the normal MR imaging anatomy of the capsular ligaments of the knee including the lateral and medial collateral ligamentous complexes, the extensor mechanism, and the supporting ligamentous structures of the proximal tibiofibular joint. Normal MR imaging findings and important anatomic variants of the neurovascular structures of the knee are also described.

Using three-dimensional isotropic SPACE MRI to detect posterolateral corner injury of the knee

BACKGROUND

Reliable magnetic resonance imaging (MRI) diagnosis is important in cases of posterolateral corner (PLC) injury due to the limitations of physical examination in patients with multi-ligament injury.

PURPOSE

To document the appearance of PLC of the knee on three-dimensional (3D) isotropic MR images, and to determine the significance of MRI findings in patients with confirmed posterolateral rotatory instability.

MATERIAL AND METHODS

Twenty-five patients that underwent surgery for posterolateral instability, and 25 individuals with normal MRI constituted the study cohort. The PLC appearances (popliteofibular, fabellofibular, arcuate ligaments, popliteomeniscal fascicle) were analyzed using 3D isotropic proton density sequence and routine two-dimensional (2D) MRI. In addition, the "fibular cap" sign was evaluated. Statistical analysis was performed using the Chi-square and McNemar's tests.

RESULTS

Thickening of popliteofibular, fabellofibular, arcuate ligaments, and popliteomeniscal fascicle was significantly more frequent in the PLC injury group than in the control group (P < 0.05). The sensitivity and specificity of 3D MRI for popliteofibular, fabellofibular, arcuate ligaments, and popliteomeniscal fascicle injury were 63/92%, 54/100%, 46/100%, and 58/92%, respectively. On comparing 3D and 2D images with respect to injury detectability (grade 3 or 4), both modalities visualized injuries, but 3D detected grade 3 or grade 1 rather than grade 4 or 0, respectively. The fibular cap sign was observed significantly more frequently in PLC group, with 58% sensitivity and 100% specificity, and was better observed by 3D than 2D (P < 0.05).

CONCLUSION

3D MRI is a valid modality for detecting PLC abnormalities as it visualizes pathologies in each component and exhibits the positive fibular cap sign.

Interposition of the Posterior Cruciate Ligament into the Medial Compartment of the Knee Joint on Coronal Magnetic Resonance Imaging

Objective

The purpose of our study was to evaluate the overall prevalence and clinical significance of interposition of the posterior cruciate ligament (PCL) into the medial compartment of the knee joint in coronal magnetic resonance imaging (MRI).

Materials and Methods

We retrospectively reviewed 317 consecutive patients referred for knee MRI at our institution between October 2009 and December 2009. Interposition of the PCL into the medial compartment of the knee joint on proton coronal MRI was evaluated dichotomously (i.e., present or absent). We analyzed the interposition according to its prevalence as well as its relationship with right-left sidedness, gender, age, and disease categories (osteoarthritis, anterior cruciate ligament tear, and medial meniscus tear).

Results

Prevalence of interposition of PCL into the medial compartment of the knee joint was 47.0% (149/317). There was no right (50.0%, 83/166) to left (43.7%, 66/151) or male (50.3%, 87/173) to female (43.1%, 62/144) differences in the prevalence. There was no significant association between the prevalence and age, or the disease categories.

Conclusion

Interposition of the PCL into the medial compartment of the knee joint is observed in almost half of patients on proton coronal MRI of the knee. Its presence is not associated with any particular factors including knee pathology and may be regarded as a normal MR finding.

Reporting knee meniscal tears: technical aspects, typical pitfalls and how to avoid them

Magnetic resonance imaging (MRI) is the most accurate imaging technique in the diagnosis of meniscal lesions and represents a standard tool in knee evaluation. MRI plays a critical role in influencing the treatment decision and enables information that would obviate unnecessary surgery including diagnostic arthroscopy. An accurate interpretation of the knee depends on several factors, starting with technical aspects including radiofrequency coils, imaging protocol and magnetic field strength. The use of dedicated high-resolution orthopaedic coils with a different number of integrated elements is mandatory in order to ensure high homogeneity of the signal and high-resolution images. The clinical imaging protocol of the knee includes different MRI sequences with high-spatial resolution in all orientations: sagittal, coronal, and axial. Usually, the slice thickness is 3 mm or less, even with standard two-dimensional fast spin echo sequences. A common potential reason for pitfalls and errors of interpretation is the unawareness of the normal tibial attachments and capsular attachment of the menisci. Complete description of meniscal tears implies that the radiologist should be aware of the patterns and the complex classification of the lesions.

TEACHING POINTS

• Technical factors may influence MRI interpretation. • Unawareness of the normal meniscal anatomy may lead to errors of interpretation. • Description of meniscal tears implies the knowledge of meniscal tear classification.

The popliteal fibular ligament in acute knee trauma: patterns of injury on MR imaging

OBJECTIVE

To describe the patterns of injury associated with injury to the popliteofibular ligament injury.

MATERIALS AND METHODS

A retrospective review was performed of 180 MRI scans undertaken for acute knee trauma. Scans were excluded if the time of injury was over 4 weeks from the time of the scan, or if there was a history of septic arthritis, inflammatory arthropathy, previous knee surgery, or significant artefact. An agreed criterion for assessing the structures of the posterolateral ligamentous complex was defined and in each scan, the popliteofibular ligament (PFL) was scored as normal or injured. The menisci, ligaments, and tendons of each knee were also assessed.

RESULTS

The mean age was 25.7 years (range, 9-65 years) and 72.2% (n = 130) patients were male. The PFL was injured in 36 cases (20%). There is a significant association between PFL injury and ACL rupture (p = 0.0001), ITB injury (p = 0.0001), PCL injury (p = 0.0373), in addition to associations with injury to other posterolateral corner structures including the lateral collateral ligament (p = 0.0001), biceps femoris tendon (p = 0.0014), and popliteus tendon (p = 0.0014). Of our series of PFL injuries, nine cases (25%) were associated with further injuries of posterolateral corner structures and in 27 cases (75%) the PFL was the only posterolateral corner structure torn.

CONCLUSIONS

PFL injury is not uncommon in acute knee trauma and is associated with significant internal derangement of the knee, especially anterior cruciate ligament rupture, ITB sprain, and injury to other structures within the posterolateral corner.

The Knee

Sports injuries at the knee are very common, not only in contact sports such as football but also in sports with jumping and pivoting. In addition, overuse injuries can affect the tendons, ligaments, and bone with degeneration, friction, and stress response. Radiologists and sports medicine professionals should be familiar with the range of injury occurring at the knee and patterns of injury that can be used to predict other more subtle pathology. These topics and others will be discussed.

Posterolateral and posteromedial corner injuries of the knee

Posterolateral (PLC) and posteromedial (PMC) corners of the knee represent complex anatomic regions because of intricate soft tissue and osseous relationships in small areas. Concise knowledge of these relationships is necessary before approaching their evaluation at imaging. Magnetic resonance imaging offers an accurate imaging diagnostic tool to establish normal anatomy and diagnose and characterize soft tissue and osseous injury. It is important to carefully evaluate the PLC and PMC structures on magnetic resonance imaging before planned surgical intervention to avoid potential complications resulting from occult injury.

Meniscofibular ligament: morphology and functional significance of a relatively unknown anatomical structure

Purpose. A relatively unknown ligamentous structure of the posterolateral corner of the knee joint, the so-called meniscofibular ligament (MFL), was investigated as regards its macroscopic morphology, its histological features, and its reaction to knee movements. Material and Methods. MFL was exposed on 21 fresh-frozen unpaired knee joints. Its microscopic morphology was examined utilizing for comparison the fibular collateral and the popliteofibular ligament. Results. MFL was encountered in 100% of the specimens as a thin striplike fibrous band extending between the lower border of the lateral meniscus and the head of the fibula. MFL was tense during knee extension and external rotation of the tibia, whereas its histological features were similar to those of fibular collateral and popliteofibular ligament. Discussion. Its precise histological nature is studied as well as its tension alterations during knee movements. The potential functional significance of the MFL with respect to its role in avoidance of lateral meniscus and lateral coronary ligament tears is discussed. Conclusions. MFL presumably provides an additional protection to the lateral meniscus during the last stages of knee extension, as well as to the lateral coronary ligament reducing the possibility of a potential rupture.

The contribution of MRI to the diagnosis of traumatic tears of the anterior cruciate ligament

When faced with a clinical suspicion of knee ligament injury, MRI nowadays has a central role in the diagnostic strategy. In particular, it is essential for assessing the cruciate ligaments and any associated meniscal tears. The objective of this review is to present the various direct and indirect MRI signs of tearing of the anterior cruciate ligament (ACL) and then describe the lesions associated with it. The anatomical and clinical aspects are also discussed so that the contribution of MRI to the diagnosis and therapeutic management of an ACL tear can be better understood.

Can stress radiography of the knee help characterize posterolateral corner injury?

BACKGROUND

Conventional MRI is limited for characterizing the posterolateral corner of the knee due to the region's anatomic variability and complexity; further, MRI is a static study and cannot demonstrate pathologic laxity. Stress radiography may provide additional information about instability.

QUESTIONS/PURPOSES

We therefore (1) correlated varus stress radiography with MRI findings, (2) compared opening in patients who underwent surgical posterolateral corner stabilization versus those who did not, and (3) determined whether stress radiography findings could supplement MRI for making treatment decisions.

PATIENTS AND METHODS

We retrospectively studied 26 patients (27 knee injuries) and correlated lateral compartment opening on varus stress radiography with severity of posterolateral corner injury on MRI. We compared radiographic findings in 18 patients with complete injuries who underwent posterolateral corner stabilization with five who did not.

RESULTS

A complete posterolateral corner injury on MRI was associated with an average of 18.6 mm (10.0-36.5 mm) of varus opening versus 12.8 mm (7.5-17.0 mm) in partial injuries. Opening in operative cases that underwent stabilization was 16.5 mm (11.0-36.5 mm) versus 11.0 mm (7.5-13.5 mm) for those that did not. Ten of 15 partial injuries underwent stabilization, for which the varus opening was 13.6 mm (11.0-17.0 mm). Average varus opening in partial injuries that did not undergo stabilization was 11.0 mm (7.5-13.5 mm).

CONCLUSIONS

Varus stress radiography correlated to MRI findings for posterolateral corner injury. The injuries we treated with reconstruction were associated with increased varus opening. In patients with partial posterolateral corner injury on MRI, we used degree of opening on varus stress radiography to aid the decision for stabilization.

LEVEL OF EVIDENCE

Level IV, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

Magnetic resonance imaging of anatomical variations in the knee. Part 1: ligamentous and musculotendinous

Magnetic resonance imaging (MRI) is now the modality of choice for the investigation of internal derangement of the knee. Technological advances, including the wider availability of stronger magnets and new sequences, allows improved visualisation of smaller structures. Normal variants must be recognised as such, so that both over-investigation and mis-diagnosis are avoided. This article reviews both the well-recognised and the less common ligamentous and musculotendinous anatomical variants within the knee and illustrates their imaging characteristics on MRI.

Diagnostic ultrasound evaluation of posterolateral corner knee injuries

PURPOSE

The purpose of this study was to determine whether dynamic ultrasound (US) would be able to differentiate posterolateral corner knee injuries that would require surgical intervention.

METHODS

This is a single-group cohort study. A knee sonogram was obtained in patients referred to us with suspected posterolateral knee injury. In addition to static US imaging, a dynamic US stress test was performed by placement of maximum varus stress on the knee at 30 degrees of flexion. The tibiofemoral separation was then measured with US. Results from US and surgery were then compared.

RESULTS

Sixteen patients had US and underwent surgery, and twelve patients had surgical findings requiring surgical intervention to the posterolateral knee structures. With regard to static US images, the sensitivity, specificity, negative predictive value, positive predictive value, and accuracy were 92%, 75%, 92%, 75%, and 88%, respectively, for the lateral collateral ligament; 33%, 100%, 100%, 33%, and 50%, respectively, for the popliteus; and 67%, 75%, 67%, 75%, and 69%, respectively, for the popliteofibular ligament. The dynamic US stress test showing 10.5 mm of lateral joint space width or more during varus stress showed a sensitivity of 83% and specificity of 100% for injury to the lateral collateral ligament and posterolateral corner structures, with a positive predictive value of 100%, negative predictive value of 75%, and accuracy of 88%.

CONCLUSIONS

A positive dynamic US stress test (>or=10.5 mm) positively predicted the need for posterolateral knee surgery in 100% of patients in this study who required posterolateral corner repair or reconstruction.

LEVEL OF EVIDENCE

Level I, testing of previously developed diagnostic criteria in series of consecutive patients with universally applied gold standard.

Analysis of the static function of the popliteus tendon and evaluation of an anatomic reconstruction: the "fifth ligament" of the knee

BACKGROUND

The popliteus tendon has important dynamic and static stabilizing functions at the knee. Evaluation of its static role as the "fifth ligament" of the knee and a subsequent analysis of a popliteus tendon reconstruction has not been performed.

HYPOTHESIS

In vitro knee stability can be restored to a popliteus tendon-deficient knee with an anatomic popliteus tendon reconstruction.

STUDY DESIGN

Controlled laboratory study.

METHODS

Eleven nonpaired cadaveric knees were tested under the following popliteus tendon states: intact, sectioned, and reconstructed using an autogenous semitendinosus graft. Each knee was subjected to 10-N.m varus moments, 5-N.m external and internal torques, and 88-N anterior and posterior loads at flexion angles of 0 degrees , 20 degrees , 30 degrees , 60 degrees , and 90 degrees . A 6 degrees of freedom electromagnetic motion tracking system was used to assess motion changes of the tibia with respect to the femur.

RESULTS

Significant increases in external rotation and small but significant increases in internal rotation, varus angulation, and anterior translation motion were found after sectioning the popliteus tendon compared to the intact state. Significant decreases in external rotation were found in the reconstructed state compared with the sectioned state at knee flexion angles of 20 degrees , 30 degrees , 60 degrees , and 90 degrees . Comparing the reconstructed state to the intact state, there were no significant differences at knee flexion angles of 0 degrees and 20 degrees , but significant decreases of external rotation were found at knee flexion angles of 30 degrees , 60 degrees , and 90 degrees . Additionally, there were small but significant differences between the reconstructed and intact state with respect to varus angulation at knee flexion angles of 20 degrees , 30 degrees , and 60 degrees ; anterior translation at 20 degrees and 30 degrees ; and internal rotation at all flexion angles.

CONCLUSION

The popliteus tendon has important primary stabilization roles at the knee. The authors also found that an anatomic popliteus tendon reconstruction significantly reduced the increase in external rotation that occurred with sectioning the popliteus tendon; however, differences seen with respect to internal rotation, varus angulation, and anterior translation were not restored.

CLINICAL SIGNIFICANCE

The popliteus tendon functions essentially as the fifth major ligament of the knee. An anatomic popliteus tendon reconstruction can restore external rotation stability to knees with popliteus tendon injury.

Correlation between the rotational degree of the dial test and arthroscopic and physical findings in posterolateral rotatory instability

Diagnosing posterolateral rotatory instability (PLRI) is difficult because it occurs rarely, takes time to manifest, and no single definitive tool exists in diagnosing posterolateral corner injuries. We sought to evaluate the correlation between rotational degrees in the dial test and physical and arthroscopic findings that surgically verified PLRI in the knee joint. Patients (n = 67) who were diagnosed as having PLRI and received posterolateral reconstruction (n = 57) and repair (n = 10) from 1998 to 2006 were recruited. Preoperative physical findings were evaluated under anesthesia, and arthroscopic findings during surgeries were analyzed. A dial test with post-anesthesia (spinal or general) was conducted. We divided patients into three subgroups (A: <15 degrees, B: 15-20 degrees, and C: >20 degrees), according to differences in rotational degrees in the dial test. All tests showed significant differences among the three groups and positive findings increased as the rotational degrees increased. No test showed a statistically significant difference in the specific group. All tests except for popliteal hiatus widening showed significant differences among the three groups and positive findings also increased as the rotational degrees increased. The total incidence and positive rate of each physical examination and the popliteal hiatus arthroscopic findings in PLRI significantly increased as the rotational degree in the dial test increased. The number of positive findings on physical examination was larger than the number of positive findings by arthroscopy in all three groups.

The meniscofibular ligament: an MRI study

AIM

To describe the appearances and determine the prevalence of the meniscofibular ligament (ligamentum fibulare-MFibL) on MRI of the knee.

SUBJECTS AND METHODS

Retrospective observational review of 160 knee MRI studies (152 patients) which was performed for a variety of clinical presentations over a period of 31 months. The images were assessed independently by two musculoskeletal radiology Fellows.

RESULTS

The MFibL was optimally visualised on far lateral sagittal oblique fat suppressed PDW FSE images. The MFibL appeared as a curvilinear or straight, hypointense band of variable thickness extending between the inferior margin of the posterior third of the lateral meniscus and the fibular head. The ligament was demonstrated in 42.5% (n=68) of the total knee MRI studies, but this prevalence increased to 63% (56/88) in the presence of fluid in the posterolateral corner of the joint.

CONCLUSION

The MFibL is commonly seen on far lateral fat suppressed oblique sagittal PD weighted MR images, particularly in the presence of fluid in the posterolateral corner, and should be recognised as a normal structure in the posterolateral corner of the knee.

MRI of the popliteofibular ligament: isotropic 3D WE-DESS versus coronal oblique fat-suppressed T2W MRI

OBJECTIVE

The objective was to compare isotropic 3D water excitation double-echo steady state (WE-DESS) MRI with coronal oblique fat-suppressed T2-weighted (FS T2W) images in the identification of the popliteofibular ligament (PFL).

MATERIALS AND METHODS

A prospective analysis of 122 consecutive knee MRIs was performed in patients referred for knee pain from the orthopaedic clinic. In addition to the standard knee sequences, isotropic WE-DESS volume acquisition through the whole knee and coronal oblique FS T2W fast spin echo sequences through the posterolateral corner were obtained. The presence of the popliteus and biceps femoris tendons, lateral collateral and PFL was documented. Anterior cruciate ligament injury was present in 33 cases and these were excluded from the study because of the risk of associated PFL injury, leaving a total of 89 cases. Of the 42 patients in whom arthroscopic evaluation was subsequently obtained, none were found to have an injury to the PFL.

RESULTS

The lateral collateral ligament, biceps femoris and popliteus tendon were identified in all cases on all sequences. The PFL was seen in 81 (91.0%; 95% CI 85.1-97.0%) patients using the WE-DESS sequence and 63 (70.8%; 95% CI 61.3-80.2%) patients using the coronal oblique FS T2W sequence, a statistically significant difference (p < 0.00005).

CONCLUSION

Isotropic 3D WE-DESS MRI significantly enhances our ability to identify the popliteofibular ligament compared with coronal oblique fat-suppressed T2-weighted images.