Meniscofemoral ligaments--structural and material properties

ACL reconstruction combined with anterolateral structures reconstruction for treating ACL rupture and knee injuries: a finite element analysis

Introduction: The biomechanical indication for combining anterolateral structures reconstruction (ASLR) with ACL reconstruction (ACLR) to reduce pivot shift in the knee remains unclear. This study aims to investigate knee functionality after ACL rupture with different combinations of injuries, and to compare the effectiveness of ALSR with ACLR for treating these injuries. Methods: A validated finite element model of a human cadaveric knee was used to simulate pivot shift tests on the joint in different states, including 1) an intact knee; 2) after isolated ACL rupture; 3) after ACL rupture combined with different knee injuries or defect, including a posterior tibial slope (PTS) of 20°, an injury to the anterolateral structures (ALS) and an injury to the posterior meniscotibial ligament of the lateral meniscus (LP); 4) after treating the different injuries using isolated ACLR; v. after treating the different injuries using ACLR with ALSR. The knee kinematics, maximum von Mises stress (Max.S) on the tibial articular cartilage (TC) and force in the ACL graft were compared among the different simulation groups. Results and discussion: Comparing with isolated ACL rupture, combined injury to the ALS caused the largest knee laxity, when a combined PTS of 20° induced the largest Max.S on the TC. The joint stability and Max.S on the TC in the knee with an isolated ACL rupture or a combined rupture of ACL and LP were restored to the intact level after being treated with isolated ACLR. The knee biomechanics after a combined rupture of ACL and ALS were restored to the intact level only when being treated with a combination of ACLR and ALSR using a large graft diameter (6 mm) for ALSR. However, for the knee after ACL rupture combined with a PTS of 20°, the ATT and Max.S on the TC were still greater than the intact knee even after being treated with a combination of ACLR and ALSR. The finite element analysis showed that ACLR should include ALSR when treating ACL ruptures accompanied by ALS rupture. However, pivot shift in knees with a PTS of 20° was not eliminated even after a combined ACLR and ALSR.

Anterior Mobility of the Posterior Horn of the Lateral Meniscus Is Associated With Abnormal Magnetic Resonance Imaging Findings of Anteroinferior Popliteomeniscal Fascicle and Posterosuperior Popliteomeniscal Fascicle as Well as a Clinical History of Catching or Locking Symptoms

Purpose

To identify predictors of anterior mobility of the posterior horn of the lateral meniscus (PHLM) among patient demographics (age, sex), clinical characteristics (a history of catching or locking symptoms [CLS], body mass index, alignment of limb), and magnetic resonance imaging (MRI) findings of 4 restraints: anteroinferior popliteomeniscal fascicle (aiPMF), posterosuperior popliteomeniscal fascicle (psPMF), posteroinferior popliteomeniscal fascicle (piPMF), and meniscofibular ligament (MFibL).

Methods

Between October 2010 and December 2014, patients who underwent arthroscopic measurement of mobility of the PHLM were identified. The Sakai classification was used to classify aiPMF and psPMF on MRI into the following 3 types: type A, the fascicle was depicted with obvious continuity and with a low-intensity band; type B, depicted with continuity but with an ambiguous intensity structure; and type C, depicted with discontinuity or not visible. Magnetic resonance images of the piPMF and MFibL were evaluated as presence or absence. The mobility of the PHLM was measured arthroscopically at traction forces of 10 and 20 N.

Results

A total of 73 patients (47 men, mean age 41.8 ± 19.3 years) were included. Multivariate regression analyses revealed aiPMF type C and psPMF types B and C to be independent factors associated with mobility at both traction forces, and CLS was an independent factor at a traction force of 20 N. Compared with that of type A, the increased mobility of aiPMF type C was 5.0 mm (P = .019) and 5.6 mm (P = .011) at 10 and 20 N, respectively; the increased mobility of psPMF type B was 2.5 mm (P = .007) and 3.5 mm (P = .0003), respectively; and the increased mobility of psPMF type C was 3.3 mm (P = .021) and 3.6 mm (P = .014), respectively. The increased mobility associated with CLS was 3.5 mm at 20 N (P = .022).

Conclusions

Anterior displacement of the PHLM induced by an external traction force at 90° of flexion of the knee joint was associated with abnormal MRI findings of the anteroinferior popliteomeniscal fascicle and posterosuperior popliteomeniscal fascicle, as well as a history of catching or locking symptoms.

Clinical Relevance

Understanding signs and symptoms and associated pathology in patients with symptomatic anterior mobility of the posterior horn of the lateral meniscus may help guide best treatment.

Mechanical properties of animal ligaments: a review and comparative study for the identification of the most suitable human ligament surrogates

The interest in the properties of animal soft tissues is often related to the desire to find an animal model to replace human counterparts due to the unsteady availability of human tissues for experimental purposes. Once the most appropriate animal model is identified, it is possible to carry out ex-vivo and in-vivo studies for the repair of ligamentous tissues and performance testing of replacement and support healing devices. This work aims to present a systematic review of the mechanical properties of ligaments reported in the scientific literature by considering different anatomical regions in humans and several animal species. This study was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) method. Moreover, considering the lack of a standard protocol for preconditioning of tissues, this aspect is also addressed. Ninety-six studies were selected for the systematic review and analysed. The mechanical properties of different animal species are reported and summarised in tables. Only results from studies reporting the strain rate parameter were considered for comparison with human ligaments, as they were deemed more reliable. Elastic modulus, ultimate tensile stress, and ultimate strain properties are graphically reported identifying the range of values for each animal species and to facilitate comparison between values reported in the scientific literature in animal and human ligaments. Useful similarities between the mechanical properties of swine, cow, and rat and human ligaments have been found.

MRI study of the cruciate ligaments and menisco-femoral ligaments of the knee

PURPOSE

It has been argued that the meniscus-femoral ligaments disappear with age. We therefore analyzed the presence of the meniscus-femoral ligaments, in MRI.

MATERIALS AND METHODS

We measured the PCL, ACL and MFL, noting their presence or absence in 120 Knee MRIs, 51 in women and 69 in men. All knees underwent MRI in the coronal, sagittal and axial planes. T1 and T2 weighted sequences were obtained. A descriptive statistical study of all the variables was carried out, and a comparative study was performed between sexes, sides and age groups.

RESULTS

The MFLp was more frequent, found in 67 (55.8%) cases, than the MFLa, in 36 (30%) cases, and both together were present in 27 (22.5%) knees. We found a strong correlation between ACL length and PCL length (p = 0.001), we found no correlation between the presence of the posterior MFL either with age (p = 0.307) or with sex (p = 0.779) or side (p = 0.733). We also found no relationship between the presence of the anterior MFL and age (p = 0.553), or sex (p = 0.913), or laterality (p = 0.082).

CONCLUSION

We found a strong correlation between ACL length and PCL length. In our study, the presence of the posterior MFL was more frequent, being present in 55.68%, while the anterior MFL was found in 30% of the knees. We did not observe that the presence of LMF decreases with age.

Relationship of the Cruciate and Meniscofemoral Ligaments with the Knee Osteology. An Anatomical Study

Objective  To analyze the dimensions of the posterior cruciate ligament (PCL), anterior cruciate ligament (ACL), the presence of meniscus-femoral ligaments MFLs in human knees, and the correlation with the dimensions of the knee skeleton. Methods  Anatomical study on 29 specimens of human knees in which we measured the length and width of the cruciate and meniscus-femoral ligaments and the dimensions of femoral and tibia condyles and the femoral notch. The ACL length was calculated with different degrees of knee flexion. The relationship between the ligaments and bone dimensions were analyzed. Results  The length of the ACL and the PCL were similar. Posterior MFL was more frequent and longer than the anterior MFL. We found the posterior MFL in the 72.41% of the knees and anterior MFL in 20.69%. The ACL presented 30% of its maximum length up to 60°, approximately half of its length between 90° and 120°, reaching its maximum length at 170°. We found a strong correlation between the length of the ACL and that of the PCL ( p  = 0.001). However, the lengths of the ACL and PCL were not related with the bone dimensions. Conclusion  We have found no correlations between the cruciate and MFLs and the anatomical dimensions of the intercondylar notch and the proximal tibia and distal femur. The presence of the posterior MFL was more frequent and longer than that of the anterior ligament.

Importance of posterior tibial slope in joint kinematics with an anterior cruciate ligament-deficient knee

Aims

To fully quantify the effect of posterior tibial slope (PTS) angles on joint kinematics and contact mechanics of intact and anterior cruciate ligament-deficient (ACLD) knees during the gait cycle.

Methods

In this controlled laboratory study, we developed an original multiscale subject-specific finite element musculoskeletal framework model and integrated it with the tibiofemoral and patellofemoral joints with high-fidelity joint motion representations, to investigate the effects of 2.5° increases in PTS angles on joint dynamics and contact mechanics during the gait cycle.

Results

The ACL tensile force in the intact knee was significantly affected with increasing PTS angle. Considerable differences were observed in kinematics and initial posterior femoral translation between the intact and ACLD joints as the PTS angles increased by more than 2.5° (beyond 11.4°). Additionally, a higher contact stress was detected in the peripheral posterior horn areas of the menisci with increasing PTS angle during the gait cycle. The maximum tensile force on the horn of the medial meniscus increased from 73.9 N to 172.4 N in the ACLD joint with increasing PTS angles.

Conclusion

Knee joint instability and larger loading on the medial meniscus were found on the ACLD knee even at a 2.5° increase in PTS angle (larger than 11.4°). Our biomechanical findings support recent clinical evidence of a high risk of failure of ACL reconstruction with steeper PTS and the necessity of ACL reconstruction, which would prevent meniscus tear and thus the development or progression of osteoarthritis.

Cite this article: Bone Joint Res 2022;11(10):739–750.

Outcomes of Combined Lateral Meniscus Posterior Root Repair and Anterior Cruciate Ligament Reconstruction

Background:

Lateral meniscus posterior root tears (LMPRTs) almost always occur in association with anterior cruciate ligament (ACL) tears. Their repair is advocated to restore the stabilizing and load-sharing functions of the meniscus.

Purpose:

To study the functional outcomes of combined arthroscopic repair of LMPRTs and ACL reconstruction (ACLR).

Study Design:

Case series; Level of evidence, 4.

Methods:

The authors evaluated patients who underwent simultaneous arthroscopic ACLR and LMPRT repair. All patients had chronic injuries, with a mean time since ACL rupture of 7.9 months. Patient characteristics, Lachman and pivot-shift test results, type of LMPRT, associated injuries, and surgery details were documented. Pre- and postoperative functional status was assessed using the International Knee Documentation Committee (IKDC) score, Knee injury and Osteoarthritis Outcome Score (KOOS), and Lysholm score. An independent single-tunnel transtibial repair using 2 SutureTapes was performed for Forkel type 1 and 3 tear root avulsions, while side-to-side suture repair was performed for type 2 radial/oblique tears. The Wilcoxon signed rank test and minimal clinically important difference (MCID) of the IKDC score were used for statistical analysis.

Results:

Included were 25 patients with a mean age of 29.6 ± 6.5 years. Of these, 22 patients (88%; 95% CI, 73.1%-100%) had a high-grade (grade 2 or 3) preoperative pivot shift. Diagnosis of the LMPRT on magnetic resonance imaging (MRI) scans was possible only in 5 patients (20%). At final evaluation, performed at 37.4 ± 7.1 months postoperatively, all functional scores had improved significantly from preoperatively: IKDC score, from 47.6 ± 9.5 to 81.8 ± 11.5; KOOS, from 45.5 ± 10.9 to 86.5 ± 10.3, and Lysholm score, from 49.0 ± 11.5 to 88.8 ± 7.6 (P < .001 for all). Twenty-four patients (96%) achieved the MCID for the IKDC score. All knees had a negative pivot shift at final analysis, and no patient underwent revision ACLR or LMPRT repair.

Conclusion:

LMPRT repair combined with ACLR led to good short-term clinical outcomes in this study. An LMPRT may frequently go undetected on preoperative MRI scans, but a high-grade pivot shift is present in a large majority of these patients.

Prevalence, Biomechanics, and Pathologies of the Meniscofemoral Ligaments: A Systematic Review

Purpose

To systematically review the literature to examine current understanding of the meniscofemoral ligaments (MFLs), their function, their importance in clinical management, and known anatomical variants.

Methods

A systematic review was conducted following Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines using PubMed, EMBASE, and Cochrane databases. Studies were included if they reported on the biomechanical, radiographic, or arthroscopic evaluation of human MFLs, or if they reported on an anatomical variant. These were then categorized as cadaveric, radiographic, or clinical. Biomechanical, radiographic, patient-reported, and functional outcomes data were recorded.

Results

Forty-seven studies were included in the qualitative analysis, and 26 of them were included in the quantitative analysis. Of these, there were 15 cadaveric, 3 arthroscopic, and 9 radiographic studies that reported on the prevalence of MFLs. Overall, when looking at all modalities, the presence of either the anterior or posterior MFL (aMFL, pMFL) has been noted to be 70.8%, with it being the aMFL 17.4% and the pMFL 40.6%. The presence of both ligaments occurs in approximately 17.6% of individuals. Eleven reported on mean MFL length and thickness. When evaluating mean length in both men and women, the aMFL has been reported between 21.6 and 28.3 mm and the pMFL length in this population is between 23.4 and 31.2 mm. Five reported on cross-sectional area. Nine additional papers report anatomical variants.

Conclusions

This review shows that there continues to be a variable incidence of MFLs reported in the literature, but our understanding of their function continues to broaden. A growing number of anatomic and biomechanical studies have demonstrated the importance of the MFLs in supporting knee stability. Specifically, the MFLs serve an important role in protecting the lateral meniscus and augmenting the function of the posterior cruciate ligament.

Clinical Relevance

Our findings will aid the clinician in both identifying and treating pathologies of the meniscofemoral ligaments.

Role of the Meniscofemoral Ligaments in the Stability of the Posterior Lateral Meniscus Root After Injury in the ACL-Deficient Knee

» Injuries to the posterior root of the lateral meniscus occur frequently in acute knee injuries with concomitant tearing of the anterior cruciate ligament (ACL). » The meniscofemoral ligaments (MFLs), consisting of the anterior MFL (ligament of Humphrey) and the posterior MFL (ligament of Wrisberg), as well as the osseous attachment of the meniscal root, stabilize the lateral meniscus, enabling appropriate load transmission and maintenance of contact forces within the lateral compartment of the knee during loading and range of motion. » In the setting of an ACL injury to the knee with osseous root injury of the posterior root of the lateral meniscus, the MFLs (when present) may stabilize the lateral meniscus against meniscal extrusion, thereby maintaining appropriate contact mechanics within the knee, decreasing the risk of subsequent chondral and meniscal injury and the development of premature osteoarthritis. » Additional study on the indications for posterior meniscal root repair during ACL reconstruction is warranted since the ideal management of lateral root injury in the MFL-intact knee remains unknown.

Clinical Anatomy of the Posterior Meniscofemoral Ligament of Wrisberg: An Original MRI Study, Meta-analysis, and Systematic Review

Background

The posterior meniscofemoral ligament (pMFL) of Wrisberg attaches to the posterior horn of the lateral meniscus and the lateral intercondylar aspect of the medial femoral condyle and passes posteriorly to the posterior cruciate ligament (PCL). The pMFL plays a role in recovery after PCL injuries and offers stability to the lateral meniscus, promoting normal knee function.

Purpose/Hypothesis

The aim of the magnetic resonance imaging (MRI) arm of this study was to evaluate the prevalence of the pMFL in Polish patients. The purpose of the systematic review and meta-analysis was to evaluate the clinical relevance of the pMFL in knee surgery. It was hypothesized that extensive variability exists in reports on the prevalence, function, and clinical significance of the pMFL.

Study Design

Cross-sectional study and systematic review; Level of evidence, 3.

Methods

A retrospective MRI investigation was conducted on 100 randomly selected lower limbs of Polish patients (56 male, 44 female) performed in 2019 to determine the prevalence of the pMFL. Additionally, an extensive literature search of major online databases was performed to evaluate all reported data on the pMFL. Assessments of article eligibility and data extraction were completed independently by 2 reviewers, and all disagreements were resolved via a consensus. A quality assessment of the included articles was performed using the Anatomical Quality Assessment tool.

Results

In the MRI arm of this study, the pMFL was observed in 73 of the 100 limbs. In the meta-analysis, 47 studies were included, totaling 4940 lower limbs. The pooled prevalence of the pMFL was found to be 70.4% (95% CI, 63.4%-76.9%); the mean length was 27.7 mm (95% CI, 24.8-30.5 mm) and the mean widths were 4.5, 6.1, and 4.1 mm for the meniscal and femoral attachments and midportion, respectively. The mean pMFL thickness was 2.3 mm (95% CI, 1.8-2.7 mm).

Conclusion

Despite the variability in the literature, the pMFL was found to be a prevalent and large anatomic structure in the knee joint. The shared features of this ligament with the PCL necessitate the consideration of its value in planning and performing arthroscopic procedures of the knee.

Cross-Sectional Area Measurement Techniques of Soft Tissue: A Literature Review

Evaluation of the biomechanical properties of soft tissues by measuring the stress-strain relationships has been the focus of numerous investigations. The accuracy of stress depends, in part, upon the determination of the cross-sectional area (CSA). However, the complex geometry and pliability of soft tissues, especially ligaments and tendons, make it difficult to obtain accurate CSA, and the development of CSA measurement methods of soft tissues continues. Early attempts to determine the CSA of soft tissues include gravimetric method, geometric approximation technique, area micrometer method, and microtomy technique. Since 1990, a series of new methods have emerged, including medical imaging techniques (e.g. magnetic resonance imaging (MRI), computed tomography (CT), and ultrasound imaging (USI)), laser techniques (e.g. the laser micrometer method, the linear laser scanner (LLS) technique, and the laser reflection system (LRS) method), molding techniques, and three-dimensional (3D) scanning techniques.

Complementary Function of the Meniscofemoral Ligament and Lateral Meniscus Posterior Root to Stabilize the Lateral Meniscus Posterior Horn: A Biomechanical Study in a Porcine Knee Model

Background:

It has been demonstrated that the load distribution function of the lateral meniscus (LM) is compromised by resecting both the meniscofemoral ligament (MFL) and LM posterior root (LMPR). However, the effect of resecting these fibers on load transmission through the LM needs to be investigated.

Purpose:

To evaluate using a porcine knee model (1) the in situ forces of the MFL and LMPR and (2) the effect of resecting these fibers on the in situ force of the LM under a compressive load and valgus torque to the lateral knee compartment.

Study Design:

Controlled laboratory study.

Methods:

Twenty fresh-frozen porcine knees and a 6 degrees of freedom robotic system were utilized. An axial compressive load of 250 N and 5 N·m of valgus torque were applied to intact, MFL-deficient, LMPR-deficient, and MFL/LMPR-deficient knees at 30°, 60°, and 90° of flexion. The valgus angles under the applied loads were compared among the 4 states. The in situ forces of the MFL and LMPR under the applied loads were calculated under the principle of superposition. The in situ forces of the LM under the applied loads were also calculated and compared among the 4 conditions (intact, without the MFL, without LMPR, and without the MFL/LMPR).

Results:

The valgus angles significantly increased after resecting both the MFL and LMPR at all the flexion angles. The in situ forces of the MFL and LMPR changed reciprocally as the knee flexed. The in situ forces of the LM significantly decreased after resecting both the MFL and LMPR, although resecting only the MFL or LMPR represented no significant effect.

Conclusion:

The MFL and LMPR functioned complementarily as the posterior attachments of the LM against a compressive load and valgus torque to the lateral knee compartment in porcine knee joints.

Clinical Relevance:

If the LMPR is completely detached and needs to be repaired, the MFL should be preserved because it may provide some stability to the LM posterior horn and protect the repaired LMPR.

Evaluation of age-dependent morphometrics of the meniscofemoral ligaments in reference to the posterior cruciate ligament in routine MRI

OBJECTIVES

To quantify the morphological correlation between the posterior cruciate ligament (PCL) and the meniscofemoral ligaments (MFLs), to propose normal ranges for different age populations, and to define guidelines for correct identification and differentiation of MFLs in routine MRI.

METHODS

Three hundred forty-two subjects were included retrospectively and subdivided into five age groups. Morphometrics of the PCL and the MFLs were measured on standard MRI in the sagittal, coronal, and axial planes. Student's t test, Mann-Whitney U test, and ANOVA and Kruskal-Wallis tests with Bonferroni correction were used for comparison.

RESULTS

The MFLs did not vary significantly between sexes (p > 0.05) or in those older than 10 years (p > 0.05). Longitudinal MFL growth is completed before age 11 years, with cross-sectional area (CSA) increasing until age 20. The CSA of the PCL was significantly (p = 0.028) larger in knees without a pMFL (Mdn = 39.7 mm2) than with a pMFL (Mdn = 35.4 mm2). MFLs were more often detected on sagittal than coronal images.

CONCLUSIONS

This study describes the morphometric relation between the PCL and the MFLs on routine MRI. When reporting imaging findings in preparation for arthroscopic knee surgery, evaluation of MFLs, first in the sagittal and then the coronal plane, will achieve the best results.

KEY POINTS

• The MFLs and the PCL have distinct morphological patterns throughout life. • These patterns show intimate anatomical relationships and a potential biomechanical impact. • Those patterns and relationships can be quantified with MRI. • A correlation exists between age and morphometrics of the MFLs. • Recommendations for correct identification of the MFLs are provided.

3-Tesla MRI: Beneficial visualization of the meniscofemoral ligaments?

BACKGROUND

Recent investigations have confirmed an important stabilizing and protective function of the meniscofemoral ligaments (MFLs) to the knee joint and suggest a clinical relevance. Concerning their incidences, however, there have been discrepancies between data acquired from cadaveric studies and MRI data using 0.3- to 1.5-Tesla field strengths probably due to lower resolution. This study aims to investigate whether imaging with 3-Tesla magnetic resonance imaging (3-T MRI) is beneficial in gaining information regarding the ligaments' incidence, length, width and anatomic variation.

METHODS

3-T MRI images of 448 patients (224 males, 224 females, with, respectively, 32 patients of each sex in the age groups: 0-20, 21-30, 31-40, 41-50, 51-60, 61-70, >70years) were retrospectively reviewed. The influence of the parameters 'sex' and 'age' was determined.

RESULTS

Whereas 71% of the patients had at least one MFL, 22% had an anterior MFL (aMFL), 53% had a posterior MFL (pMFL) and five percent had coexisting ligaments. The pMFLs were more likely to be present in female patients (P<0.05) but if so, they were longer in the males (P<0.05). The pMFL was categorized according to its insertion on the medial femoral condyle.

CONCLUSIONS

3-T MRI enables an excellent illustration of the anatomic variations of pMFLs. By modifying an anatomic classification for radiological use we measured lengths and widths of the MFLs without any difficulties. Despite its increased resolution, 3-T MRI lends no diagnostic benefit in visualizing the course of the aMFL or filigree coexisting ligaments as compared to MRI at lower field strengths.

[Posterior cruciate ligament injuries]

Posterior cruciate ligament (PCL) injuries are still often overlooked and treatment of a ruptured PCL is inherently different in comparison to anterior cruciate ligaments (ACL). Conservative treatment is the first-line therapy for acute isolated PCL injuries leading to good clinical and biomechanical results. Injuries to the PCL combined with rupture of other stabilizing ligaments, such as the collateral ligaments or the posterolateral corner of the knee joint are treated surgically. The same is true for high grade chronic PCL insufficiency. Meticulous classification of PCL injuries taking all stabilizing factors of the knee joint as well as the time from injury into account are essential for successful treatment of PCL injuries.

Anterolateral Meniscofemoral Ligament of the Lateral Meniscus

Anatomical variations of the meniscus are a common anomaly that knee surgeons frequently encounter. However, anomalies of the anterior horn of the lateral meniscus (AHLM) are extremely rare. In this report, we present a newly discovered anomaly of the AHML: an anterolateral meniscofemoral ligament is described with clinical features and radiographic and arthroscopic findings.

The effect of complete radial lateral meniscus posterior root tear on the knee contact mechanics: a finite element analysis

BACKGROUND

In recent years, with technological advances in arthroscopy and magnetic resonance imaging and improved biomechanical studies of the meniscus, there has been some progress in the diagnosis and treatment of injuries to the roots of the meniscus. However, the biomechanical effect of posterior lateral meniscus root tears on the knee has not yet become clear. The purpose of this study was to determine the effect of a complete radial posterior lateral meniscus root tear on the knee contact mechanics and the function of the posterior meniscofemoral ligament on the knee with tear in the posterior root of lateral meniscus.

METHODS

A finite element model of the knee was developed to simulate different cases for intact knee, a complete radial posterior lateral meniscus root tear, a complete radial posterior lateral meniscus root tear with posterior meniscofemoral ligament deficiency, and total meniscectomy of the lateral meniscus. A compressive load of 1000 N was applied in all cases to calculate contact areas, contact pressure, and meniscal displacements.

RESULTS

The complete radial posterior lateral meniscus root tear decreased the contact area and increased the contact pressure on the lateral compartment under compressive load. We also found a decreased contact area and increased contact pressure in the medial compartment, but it was not obvious compared to the lateral compartment. The lateral meniscus was radially displaced by compressive load after a complete radial posterior lateral meniscus root tear, and the displacement took place mainly in the body and posterior horn of lateral meniscus. There were further decrease in contact area and increases in contact pressure and raidial displacement of the lateral meniscus in the case of the complete posterior lateral meniscus root tear in combination with posterior meniscofemoral ligament deficiency.

CONCLUSIONS

Complete radial posterior lateral meniscus root tear is not functionally equivalent to total meniscectomy. The posterior root torn lateral meniscus continues to provide some load transmission and distribution functions across the joint. The posterior meniscofemoral ligament prevents excessive radial displacement of the posterior root torn lateral meniscus and assists the torn lateral meniscus in transmitting a certain amount of stress in the lateral compartment.

Anterior and posterior meniscofemoral ligaments: MRI evaluation

Although meniscofemoral ligaments are distinct anatomic units, their anatomy and function are controversial from an anatomic and radiologic point of view. Five hundred knee MR examinations were retrospectively studied in an effort to demonstrate the incidence and variations regarding sex and age distribution, as well as the anatomy of the meniscofemoral ligament at magnetic resonance imaging. Patients were mostly men, three hundred and twelve, in contrast with women who were fewer, one hundred eighty-eight patients. The mean age of the patients who were included in this study was 46 years. More than half of them were between 20 and 40 years old; one hundred thirty-three patients among 20 to 30 years old and one hundred and one patients among 31 and 40 years old, in total two hundred thirty-four patients.

The posterior meniscofemoral ligament: morphologic study and anatomic classification

The meniscofemoral ligaments (MFLs) run from the medial femoral condyle to the posterior horn of the lateral meniscus and consist of anterior MFL (aMFL) and/or posterior MFL (pMFL) components according to whether it passes anterior or posterior to the posterior cruciate ligament (PCL). The purpose of this study was to analyze the incidence and morphologic features of the MFLs in Koreans and formulate an anatomic classification system of MFLs to aid the detailed interpretation of medical imaging or biomechanical data. One hundred knees from 52 cadavers were studied. Eighty-seven knees had pMFLs, whereas an aMFL was only found in one knee from a male cadaver. The pMFLs and PCLs were longer in males than in females (P < 0.05). The most common type of MFL was the high crossing of a typical pMFL against the PCL in both genders. Regarding other types, the incidence of absent pMFLs was higher in males than in females and the oblique bundle of the PCL was easily confused with the pMFL in several cases in both genders. These results provide the basis for the classification system of the MFL and will contribute to better outcomes for evaluating the MFL and PCL when using medical imaging such as arthro-CT scan or MRI through a better understanding of the anatomy of the MFL and PCL.

More resistant tendons obtained from the association of Heteropterys aphrodisiaca and endurance training

BACKGROUND

Popular Brazilian medicine uses Heteropterys aphrodisiaca infusion as a tonic or stimulant, for the treatment of nervous debility and breakdown and for muscle and bone weakness. This study investigated the effects of Heteropterys aphrodisiaca infusion on the tendon properties and extracellular matrix of rats under endurance training.

METHODS

Wistar rats were grouped as follows: CS- control sedentary, HS- H. aphrodisiaca sedentary, CT-control trained, HT- H. aphrodisiaca trained. The training protocol consisted in running on a motorized treadmill, five times a week, with weekly increase in treadmill speed and duration. Control groups received water while the HS and HT groups received H. aphrodisiaca infusion, daily, by gavage for the 8 weeks of training. Achilles tendons were frozen for biochemical and biomechanical analysis or preserved in Karnovsky's fixative, then processed for histomorphological analysis with light microscopy.

RESULTS

Biomechanical analysis showed significant increase in maximum load, maximum stress, modulus of elasticity and stiffness of the HT animals' tendons. The metalloproteinase-2 activity was reduced in the HT group. The compression region of HT animals' tendons had a stronger and more intense metachromasy, which suggests an increase in glycosaminoglycan concentration in this region of the tendon. The most intense birefringence was observed in both compression and tension regions of HT animals' tendons, which may indicate a higher organizational level of collagen bundles. The hydroxyproline content increased in the HT group.

CONCLUSIONS

The association of endurance training with H. aphrodisiaca resulted in more organized collagen bundles and more resistant tendons to support higher loads from intense muscle contraction. Despite the clear anabolic effects of Heteropterys aphrodisiaca and the endurance exercise association, no side effects were observed, such as those found for synthetic anabolic androgenic steroids.

Anatomy and biomechanics of the posterior cruciate ligament, medial and lateral sides of the knee

The evaluation and management of posterior cruciate ligament (PCL) injuries presents a clinical challenge to even the most experienced orthopedic surgeons. Increasing emphasis has also been placed on the diagnosis of associated ligamentous and cartilaginous injuries that may contribute to patterns of instability not solely attributed to the PCL deficiency. Although a uniformly accepted surgical technique to restore the anatomy and biomechanics of the multiligament injured knee does not exist, careful identification and management of additional ligamentous injuries are critical in achieving optimum results and avoid further insult or degradation of the knee joint owing to continued instability. Knowledge of the PCL anatomy and associated structures, combined with a clinical understanding of the biomechanics of the native tissues assist the orthopedic surgeon in treating these difficult injuries.

The effect of age and spontaneous exercise on the biomechanical and biochemical properties of chicken superficial digital flexor tendon

The aim of this study was to evaluate if spontaneous (nonforced active) exercise and age (maturation process) alter the biomechanical and biochemical properties of superficial digital flexor tendon. Chickens aged 1, 5, and 8 months were divided into two groups: caged and penned. The caged group was reared in an area of 0.5 m(2) (3 animals/cage), while the penned group was reared in an area of 60 m(2) (3 animals/area). For biochemical analysis, the tendon was divided into tensile and compressive regions for quantification of hydroxyproline and glycosaminoglycan content. Biomechanical properties were analyzed from tensile tests of intact tendons. The biomechanical measurements were taken at maximum load and maximum stress. In both the caged and penned groups, maximum load and energy absorption increased with maturation; however, the elastic modulus, maximum stress, and maximum strain did not increase with maturation. Exercise resulted in a higher load, stress, and elastic modulus in the fifth month. Collagen content increased with age in the penned group and with exercise in the fifth and eighth months. Exercise results in a higher expression of glycosaminoglycans in young tendons compared to mature tendons. Thus, low-intensity mechanical stimuli promote the synthesis and possible rearrangement of molecules in immature tendons, whereas inactivity leads to deleterious effects on the material properties (maximum stress and elastic modulus) during growth and maturation.

Anatomic reconstruction of the posterolateral corner of the knee: a case series with isolated reconstructions in 27 patients

PURPOSE

This study presents clinical results of a case series of isolated reconstruction of the posterolateral corner (PLC) with a new technique that aims to reconstruct the lateral collateral ligament (LCL), popliteus tendon, and popliteofibular ligament.

METHODS

From 1997 to 2005, 27 patients available for follow-up with isolated posterolateral instability were treated with primary reconstruction of the LCL and PLC. The median age was 28 years, and there were 16 male patients. Of the patients, 26% had remaining instability after anterior or posterior cruciate ligament reconstruction. All underwent reconstruction with a novel technique addressing both the LCL and the PLC by use of hamstring autografts. Follow-up was more than 24 months, and patients were examined by an independent observer using the International Knee Documentation Committee objective measures and subjective Knee Injury and Osteoarthritis Outcome Scores.

RESULTS

In our series 95% of patients with isolated lateral rotatory instability had rotatory stability after PLC reconstruction. On the basis of International Knee Documentation Committee scoring, 71% were normal or nearly normal. Subjective Knee Injury and Osteoarthritis Outcome Scores were comparable to scores in patients after meniscectomy. One patient had a deep infection, but none had any peroneal nerve injury.

CONCLUSIONS

This case series presents a new method for combined reconstruction of the LCL and the PLC. Despite the extensiveness of procedure, complications were low. The technique restores lateral stability clinically at 2 years' follow-up.

LEVEL OF EVIDENCE

Level IV, therapeutic case series.

Obesity affects collagen fibril diameter and mechanical properties of tendons in Zucker rats

Obesity is currently considered to be a world epidemic and one of the major public health problems in many countries, whose incidence is increasing at alarming rates. Genetically obese Zucker rats are used as a model of obesity and were employed in the present study. Tendons transmit contractile force from muscles to bone, thus permitting articular movement. The objective of our study was to analyze the ultrastructural, biochemical, and biomechanical alterations that occur in the deep digital flexor tendon of obese Zucker rats compared to lean animals. Ultrastructural analysis showed differences in collagen fibril diameter distribution and mass-average diameter between obese and lean animals. Regarding mechanical parameters, there was a significant difference in maximum displacement and strain. Hydroxyproline content was higher in obese animals. In view of the excess weight and peculiar conditions to which the tendon of obese animals is submitted, we concluded that obesity provokes alterations in the composition and organization of tendon extracellular matrix components. These alterations might be related to organizational and structural modifications in the collagen bundles, influencing the mechanical properties of the tendon and the progression to a pathological state.

Geometry, time-dependent and failure properties of human meniscal attachments

Meniscectomies have been shown to lead to osteoarthritis and the success of meniscal replacements remains questionable. It has been suggested that the success of a meniscal replacement is dependent on several factors, one of which is the secure fixation and firm attachment of the replacement to the tibial plateau at the horn locations. To aid in the development of meniscal replacements, the objectives of the current study were to determine the time-dependent and failure properties of human meniscal attachments. In contrast to the time-dependent tests, during uniaxial failure testing a charge-coupled video camera was used to document the local strain and linear modulus distribution across the surface of the attachments. The lateral attachments were statistically smaller in cross-sectional area and longer than the medial attachments. The anterior attachments were statistically longer and had a smaller cross-sectional area than the posterior attachments. From the stress relaxation tests, the load and stress relaxation rates of the medial anterior attachment were statistically greater than the medial posterior attachment. There were no significant differences in the creep, structural properties or the ultimate stress between the different attachments. Ultimate strain varied between attachments, as well as along the length of the attachment. Ultimate strain in the meniscus region (10.4+/-6.9%) and mid-substance region (12.7+/-16.4%) was smaller than the bony insertion region (32.2+/-21.5%). The lateral and anterior attachments were also found to have statistically greater strain than the medial and posterior attachments, respectively. The linear modulus was statistically weaker in the bony insertion region (69.7+/-33.7MPa) compared to the meniscus region (153+/-123MPa) and mid-substance region (195+/-121MPa). Overall the anterior attachments (169+/-130MPa) were also found to be statistically stronger than the posterior attachments (90.8+/-64.9MPa). These results can be used to help design tissue-engineered replacement menisci and their insertions and show the differences in material properties between attachments, as well as within an attachment.

Biomechanics of the meniscus-meniscal ligament construct of the knee

The menisci of the knee act primarily to redistribute contact force across the tibio-femoral articulation. This meniscal function is achieved through a combination of the material, geometry and attachments of the menisci. The main ligaments that attach the menisci to the tibia (insertional ligaments, deep medial collateral ligament), the femur (meniscofemoral ligaments, deep medial collateral ligament) and each other (the anterior intermeniscal ligament) are the means by which the contact force between tibia and femur is distributed into hoop stresses in the menisci to reduce contact pressure at the joint. This means that the functional biomechanics of the menisci cannot be considered in isolation and should be considered as the functional biomechanics of the meniscus-meniscal ligament construct. This article presents the current knowledge on the anatomy and functional biomechanics of the meniscus and its associated ligaments. Much is known about the function of the meniscus-meniscal ligament construct; however, there still remain significant gaps in the literature in terms of the properties of the anterior intermeniscal ligament and its function, the properties of the insertional ligaments, and the most appropriate ways to reconstruct meniscal function surgically.

A biomechanical study of the meniscofemoral ligaments and their contribution to contact pressure reduction in the knee

The aim of this study was to test the hypothesis that the meniscofemoral ligaments (MFLs) of the human knee assist the lateral meniscal function in reducing tibiofemoral contact pressure. Five human cadaveric knee joints were loaded in axial compression in extension using a 4-degree of freedom rig in a universal materials testing machine. Contact pressures pre- and post-sectioning of the MFLs were measured using pressure sensitive film. Sectioning the MFLs increased the contact pressure significantly in the joints for two of the four measures. In addition to their known function in assisting the posterior cruciate ligament (PCL) to resist tibiofemoral posterior drawer, the MFLs also have a significant role in reducing contact stresses in the lateral compartment. Their retention in PCL and meniscal surgery is therefore to be advised.

Comparative anatomy of the meniscofemoral ligament in humans and some domestic mammals

The purpose of this study was to investigate the presence, position and relative sizes of the meniscofemoral ligaments (MFL) in three quadrupeds and humans and relate these to the caudal slope of the lateral tibial plateau. Canine, ovine and equine stifles and human knees were dissected to identify the presence of MFLs, their obliquity in relation to the caudal cruciate ligaments (CCL), the relative size and shape of the MFLs compared with the CCL, the points of femoral attachment of the MFLs and CCL, and the distance between the MFLs and CCL at their midpoints. The lateral tibial condyle was divided sagittally with a handsaw and the caudal slope was measured. An MFL was present in all quadrupeds. It was caudal to the CCL, being analogous to the human posterior MFL. There was no structure analogous to the human anterior MFL, a structure that has a different femoral attachment from the human posterior MFL and MFLs in other species examined. The meniscotibial attachments were of varying sizes. The size ratio between the MFL and CCL was greater in all three quadrupeds than it was in the human knee. The MFL lies more obliquely than the CCL in all species examined. The caudal tibial slope was steeper in the quadrupeds. In the stifle joints of quadrupeds, the MFL is a substantial structure and appears to be related to the caudal tibial slope. It is known to resist caudal translation of the tibia in conjunction with the lateral meniscus. This must be borne in mind when considering its function in the human knee.

Biomechanical and biochemical properties of chicken calcaneal tendon under effect of age and nonforced active exercise

This study investigated if nonforced active exercise alters the biomechanical and biochemical properties of calcaneal tendon during maturation. Chickens at 1, 5, and 8 months old were divided into two groups: caged and penned. Intact tendons were used for biomechanical analysis, but they were divided into tensile and compressive regions for quantification of hydroxyproline and glycosaminoglycans. The exercise increased tendon strength after the fifth month, energy absorption in the eighth month, and ultimate tensile stress in the first month. Age increased tendon strength and energy storage and reduced stiffness but did not alter stress. There was an increase in collagen content in the fifth month. Glycosaminoglycans showed a progressive decline in the tensile region. Thus, some biomechanical and biochemical changes depend on the maturation process itself and also are influenced by spontaneous exercise, showing that mechanical stimulation of low intensity may help to improve the quality of the tendon.

Arthroscopic appearances of the meniscofemoral ligaments: introducing the "meniscal tug test"

To evaluate the feasibility of identifying the anterior and posterior meniscofemoral ligaments (aMFL and pMFL, respectively) at arthroscopy, both visually and using the "meniscal tug test", which exploits the anatomical attachments of the posterior cruciate ligament (PCL) and MFLs. This is an observational type of study. Arthroscopy using anteromedial and anterolateral portals was performed in 68 knees in 68 patients (36 right, 32 left). The MFLs were identified using several anatomical cues, including their femoral and meniscal attachments, their obliquity relative to the PCL, and the meniscal tug test. Identification was classed as easy or hard by the operating surgeon. From 68 knees, the aMFL was seen and confirmed to be an MFL using the tug test in 60 (88%). Identification of the aMFL was classed as easy in 64 (94%), whilst the pMFL was easy to identify in only 6 (9%) of knees, of which 3 had a ruptured PCL. Thus, with the exception of PCL-deficient knees, it was felt that the meniscal "tug test" as applied in this study was not suitable for the pMFL. The study shows that identification of the aMFL is possible in most knees at arthroscopy, using the "tug test" and other anatomical cues. However, identification of the pMFL may require a posterior portal. A subgroup of PCL injuries in which the MFLs were intact was also observed. The "meniscal tug test" can be used in arthroscopic examinations of the PCL to distinguish between fibres of the true PCL from the MFLs, thus avoiding the misdiagnosis of partial versus complete PCL rupture. This will also aid studies examining the role of the MFLs in stabilising the PCL-deficient knee.

Sensitivities of medial meniscal motion and deformation to material properties of articular cartilage, meniscus and meniscal attachments using design of experiments methods

This study investigated the role of the material properties assumed for articular cartilage, meniscus and meniscal attachments on the fit of a finite element model (FEM) to experimental data for meniscal motion and deformation due to an anterior tibial loading of 45 N in the anterior cruciate ligament-deficient knee. Taguchi style L18 orthogonal arrays were used to identify the most significant factors for further examination. A central composite design was then employed to develop a mathematical model for predicting the fit of the FEM to the experimental data as a function of the material properties and to identify the material property selections that optimize the fit. The cartilage was modeled as isotropic elastic material, the meniscus was modeled as transversely isotropic elastic material, and meniscal horn and the peripheral attachments were modeled as noncompressive and nonlinear in tension spring elements. The ability of the FEM to reproduce the experimentally measured meniscal motion and deformation was most strongly dependent on the initial strain of the meniscal horn attachments (epsilon(1H)), the linear modulus of the meniscal peripheral attachments (E(P)) and the ratio of meniscal moduli in the circumferential and transverse directions (E(theta)E(R)). Our study also successfully identified values for these critical material properties (epsilon(1H) = -5%, E(P) = 5.6 MPa, E(theta)E(R) = 20) to minimize the error in the FEM analysis of experimental results. This study illustrates the most important material properties for future experimental studies, and suggests that modeling work of meniscus, while retaining transverse isotropy, should also focus on the potential influence of nonlinear properties and inhomogeneity.

Anatomy of the posterior cruciate ligament and the meniscofemoral ligaments

This paper describes the anatomy of the posterior cruciate ligament (PCL) and the meniscofemoral ligaments (MFLs). The fibres of the PCL may be split into two functional bundles; the anterolateral bundle (ALB) and the posteromedial bundle (PMB), relating to their femoral attachments. The tibial attachment is relatively compact, with the ALB anterior to the PLB. These bundles are not isometric: the ALB is tightest in the mid-arc of knee flexion, the PMB is tight at both extension and deep flexion. At least one MFL is present in 93% of knees. On the femur, the anterior MFL attaches distal to the PCL, close to the articular cartilage; the posterior MFL attaches proximal to the PCL. They both attach distally to the posterior horn of the lateral meniscus. Their slanting orientation allows the MFLs to resist tibial posterior drawer.

The measurement of the variation in the surface strains of Achilles tendon grafts using imaging techniques

Uniaxial tensile tests are commonly used to characterize the structural and material properties of tendons and ligaments. During these tests, the stress and strain distributions applied to the specimen are assumed to be uniform. However, few studies have investigated the strain distributions throughout the tissue. The purpose of this study was to use imaging techniques to measure the strains around the circumference of 11 mm wide Achilles tendon grafts during a uniaxial tensile test. Pairs of radiopaque beads with a diameter of 2mm were affixed around the mid-substance of the tendon in four different locations. The motion of the beads was recorded using a cine fluoroscope. This system was shown to measure the displacement of the beads with an accuracy of 0.02 mm. During the uniaxial tensile test, large variations in local tissue strains were observed. At 10 MPa of applied stress, the local tissue strain varied from an average of 2.5-8.7%, an increase in strain of more than three times. As a result of these large variations, the modulus calculated from the stress-strain data varied from an average of 217 to 897 MPa, an increase of approximately 4 times. Furthermore, these data suggest that underestimates of the elastic modulus may result if a uniform strain distribution is assumed. These results indicate that during uniaxial tensile tests, the assumption of uniform stress and strain distributions should be carefully considered and small, uniform specimens should be used when measuring the material properties of soft tissues.

Mutable collagenous tissue: overview and biotechnological perspective

The mutable collagenous tissue (MCT) of echinoderms can undergo extreme changes in passive mechanical properties within a timescale of less than 1 s to a few minutes, involving a mechanism that is under direct neural control and coordinated with the activities of muscles. MCT occurs at a variety of anatomical locations in all echinoderm classes, is involved in every investigated echinoderm autotomy mechanism, and provides a mechanism for the energy-sparing maintenance of posture. It is therefore crucially important for the biology of extant echinoderms. This chapter summarises current knowledge of the physiology and organisation of MCT, with particular attention being given to its molecular organisation and the molecular mechanism of mutability. The biotechnological potential of MCT is discussed. It is argued that MCT could be a source of, or inspiration for, (1) new pharmacological agents and strategies designed to manipulate therapeutically connective tissue mechanical properties and (2) new composite materials with biomedical applications.

Stresses and Strains in the Medial Meniscus of an ACL Deficient Knee under Anterior Loading: A Finite Element Analysis with Image-Based Experimental Validation

The menisci are believed to play a stabilizing role in the ACL-deficient knee, and are known to be at risk for degradation in the chronically unstable knee. Much of our understanding of this behavior is based on ex vivo experiments or clinical studies in which we must infer the function of the menisci from external measures of knee motion. More recently, studies using magnetic resonance (MR) imaging have provided more clear visualization of the motion and deformation of the menisci within the tibio-femoral articulation. In this study, we used such images to generate a finite element model of the medial compartment of an ACL-deficient knee to reproduce the meniscal position under anterior loads of 45, 76, and 107N. Comparisons of the model predictions to boundaries digitized from images acquired in the loaded states demonstrated general agreement, with errors localized to the anterior and posterior regions of the meniscus, areas in which large shear stresses were present. Our model results suggest that further attention is needed to characterize material properties of the peripheral and horn attachments. Although overall translation of the meniscus was predicted well, the changes in curvature and distortion of the meniscus in the posterior region were not captured by the model, suggesting the need for refinement of meniscal tissue properties.

The sensitivity of tibiofemoral contact pressure to the size and shape of the lateral and medial menisci

In an effort to prevent degeneration of articular cartilage associated with meniscectomies, both meniscal allografts and synthetic replacements have been studied. A number of biomechanical criteria may be important for a meniscal replacement to restore normal tibiofemoral contact pressure in the knee joint and hence be clinically successful. One of these criteria is geometric similarity. The objectives of the current study were to: determine the sensitivity of the contact variables of the tibial plateau to the transverse depth and width of both the lateral and medial menisci; determine the sensitivity of the contact variables of the tibial plateau to the cross-sectional width and height of the lateral and medial menisci; and determine the tolerances on each of the four parameters for both menisci. To satisfy these objectives, a previously developed finite element model of the tibiofemoral joint was used to compute the contact pressure distribution on the tibial plateau. The effect of the above-mentioned geometric parameters on the contact behavior was studied by perturbing the finite element model. Results showed that the contact variables are similarly sensitive to both the transverse and cross-sectional parameters of the menisci. Additionally the medial meniscal parameters have a greater effect on the contact variables than do the lateral meniscal parameters. Finally, less than a 0.5 mm change in the medial meniscal height and greater than a 1 mm change in the lateral meniscal height could be tolerated before the relative difference in the contact variables from those for the original geometry exceeded 10%. Thus in the design or selection of meniscal replacements, each of the four parameters should be measured when sizing a replacement tissue. Also tighter tolerances should be placed on the medial meniscal parameters compared to the lateral meniscal parameters.