MR assessment of meniscal movement during knee flexion: correlation with the severity of cartilage abnormality in the femorotibial joint

PURPOSE: The purpose of this study was to assess the degree of meniscal movement during knee flexion on MR images and to correlate it with the severity of cartilage damage in the femorotibial joint. METHOD: Sagittal MR images were obtained at extension and 45 degrees of flexion in 35 knees. A shortening ratio in the distance between the anterior and posterior horns at 0-45 degrees of knee flexion was calculated in each meniscus and was correlated with the degree of cartilage abnormality in the femorotibial joint. RESULTS: The shortening ratio of the meniscus was reduced in knees with cartilage abnormality in the femorotibial joint. The shortening ratio of the medial meniscus was inversely correlated with the degree of cartilage abnormality in the medial femoral condyle and with that in the medial tibial plateau. CONCLUSION: Restricted shortening ratio of the meniscus may be related to cartilage damage in the femorotibial joint.     

Discoid menisci of the knee: MR imaging appearance

Discoid menisci of the knee are not uncommon, and the criteria for arthrographic diagnosis and the clinical symptoms are well known. Although enlarged menisci have been recognized at magnetic resonance (MR) imaging, there are no criteria for the MR imaging diagnosis. The authors describe 29 discoid menisci imaged by means of MR. A discoid meniscus was said to be present if three or more 5-mm-thick contiguous sagittal images demonstrated continuity of the meniscus between the anterior and posterior horns. High-resolution coronal images allowed more graphic depiction of the abnormally wide meniscus. In approximately one-third of the cases in which coronal images were obtained, the measurable height difference between the discoid and the opposite meniscus was greater than or equal to 2 mm. Arthroscopic correlation (obtained in 10 cases) revealed that six cases of discoid meniscus were diagnosed correctly with MR imaging, although one meniscus was considered discoid at MR imaging but was not considered discoid at arthroscopy. Of three discoid menisci seen to be torn at arthroscopy, two were seen to be torn at MR imaging.     

Effect of chondrocalcinosis on the MR imaging of knee menisci

OBJECTIVE: Our goal was to determine the influence of chondrocalcinosis on MR imaging in the detection of meniscal tears. MATERIALS AND METHODS: A retrospective review was performed of knee MR imaging and arthroscopy records from two university hospitals between 1996 and 1998. Seventy individuals had radiographic evidence of chondrocalcinosis and underwent knee MR imaging. Thirty-seven of these individuals had undergone arthroscopy for further evaluation of their symptoms. MR imaging sensitivity and specificity in the detection of medial and lateral meniscal tears were calculated in these 37 patients who had radiographic evidence of chondrocalcinosis and in a control group of 34 patients who underwent MR imaging and arthroscopy but did not have knee chondrocalcinosis. RESULTS: In the chondrocalcinosis group, MR imaging sensitivity, specificity, and accuracy for meniscal tear were 78%, 71%, and 78%, respectively, for the lateral meniscus, and 89%, 72%, and 81% for the medial meniscus. The control group showed sensitivity, specificity, and accuracy of 93%, 100%, and 97%, respectively, for the lateral meniscus and 100% in all cases for the medial meniscus. The MR imaging detection of meniscal tears in both the lateral and medial compartments combined is significantly poorer in the presence of chondrocalcinosis (p < 0.005). CONCLUSION: MR imaging sensitivity and specificity for detection of meniscal tear is decreased in the presence of meniscal chondrocalcinosis. Chondrocalcinosis appeared as a high-signal-intensity region on T1-weighted, intermediate-weighted, and inversion recovery sequences. The high signal of chondrocalcinosis on inversion recovery sequence is an interesting observation that to our knowledge has not been previously reported. Radiographic correlation with the MR imaging examination can help prevent overdiagnosing meniscal tears.     

MR Spectroscopic imaging of collagen: Tendons and knee menisci

Water molecules associated with collagen have short transverse (T₂) relaxation times. Projection-reconstruction techniques are able to achieve an echo time (TE) much shorter than conventional techniques, allowing imaging of tissues with T₂ < 5 ms. Using these techniques, a conventional 1.5-T MRI human imaging system can directly image collagen-associated water from knee menisci and tendons in normal volunteers and patients. Long-T₂ suppression improves the contrast between these structures and the surrounding tissue with long-T₂ relaxation times. Spectroscopic imaging provides improved lipid/water registration and information about chemical composition and relaxation times. Direct imaging of tendons and menisci may provide more information about these structures and provide a new way to assess both injury and repair.     

MR imaging of the knee: position related changes of the menisci in asymptomatic volunteers

RATIONALE AND OBJECTIVES: To evaluate position related changes of the menisci in asymptomatic volunteers based on MR imaging of the knee in different positions. METHODS: Twenty-two knees from 22 asymptomatic volunteers with no history of knee injury and no evidence of meniscal tears were examined with a 0.5-T open-configuration MR system. Sagittal and coronal images were obtained with the knee supine in neutral, supine in 90-degree flexion with external and internal rotation, as well as in upright weight-bearing positions. The position of the menisci from the outer inferior edge of the meniscus to the outermost edge of the articular cartilage of the tibial plateau was measured, and meniscal movement was calculated. The Wilcoxon signed-rank test was used for statistical analysis. RESULTS: Meniscal movement in the sagittal plane was greatest in the anterior horn of the medial meniscus upon position change from supine neutral to supine in 90-degree flexion with external rotation (mean, 10.5 millimeters). The least meniscal movement was observed in the anterior horn of the lateral meniscus when changing from the supine neutral to the upright knee position (mean, 0.6 millimeters). Meniscal protrusion (ie, protrusion of any part of the meniscus beyond the tibial plateau) was noted most frequently for the anterior horn of the medial meniscus (14/22 instances; 63.6%) in the sagittal plane with the knee in neutral position (mean, 2.6 millimeters, range, 1.8-2.8 millimeters). In the coronal plane, medial meniscal protrusion was most frequently present in the upright weight-bearing position (11/22 instances (50%; mean, 2 millimeters; range, 1.2-2.6 millimeters). CONCLUSIONS:: Meniscal movement is most prominent in the anterior horn of the medial meniscus with the knee in the supine position in 90-degree flexion with external rotation. Meniscal protrusion is more frequently present in the medial meniscus and averaged less than 3 millimeters in normal volunteers in either the sagittal or coronal MR imaging plane.     

Tears of the anterior cruciate ligament and menisci of the knee: MR imaging evaluation

In 242 of 3,000 patients who underwent magnetic resonance (MR) imaging of the knee between September 1986 and August 1987, original MR imaging reports were compared with subsequent arthroscopic reports to determine the value of MR imaging in the evaluation of suspected meniscal and complete tears of the anterior cruciate ligament. The overall accuracy for the menisci was 93% (sensitivity, 95%; specificity, 91%) with a false-negative rate of 4.8%. For the anterior cruciate ligament the overall accuracy was 95%. T2-weighted sequences were associated with greater sensitivity, specificity, and accuracy than were T1 sequences; the false-negative rate was 0% in the T2-weighted group. MR imaging of the knee is an extremely accurate means for noninvasive assessment of the integrity of the menisci and anterior cruciate ligament, and the accuracy exceeds that usually reported for arthrography.     

Truncation artifact: a potential pitfall in MR imaging of the menisci of the knee

Because truncation artifacts on magnetic resonance (MR) images may be confused with meniscal tears, measures to suppress them were investigated in a human cadaver knee and prospective and retrospective studies of patients. The artifacts were most prominent when the acquisition matrix was 128 x 256 and the 128-pixel (phase-encoded) axis was in a superoinferior (SI) orientation. An anteroposterior (AP) orientation of the 128-pixel axis or use of a 256 x 256 acquisition matrix reduced the prominence of or nearly eliminated the artifacts. A review of reports of MR imaging and arthroscopic examinations of 83 knees yielded eight menisci that were falsely interpreted at MR imaging as having tears. Retrospective review of the images suggested that the errors were due to truncation artifacts in two cases. Truncation artifacts will cause relatively little difficulty if diagnostic observers are aware of their characteristics and simple steps are taken to minimize their prominence, including acquiring images in 192 x 256 or 256 x 256 matrices or AP rather than SI orientation of the phase-encoded (128-pixel) axis of 128 x 256 matrices.     

Changes in the orientation of knee functional flexion axis during passive flexion and extension movements in navigated total knee arthroplasty

Purpose

Recently, the functional flexion axis has been considered to provide a proper rotational alignment of the femoral component in total knee arthroplasty. Several factors could influence the identification of the functional flexion axis. The purpose of this study was to analyse the estimation of the functional flexion axis by separately focusing on passive flexion and extension movements and specifically assessing its orientation compared to the transepicondylar axis, in both the axial plane and the frontal plane.

Methods

Anatomical and kinematic acquisitions were performed using a commercial navigation system on 79 patients undergoing total knee arthroplasty with cruciate substituting prosthesis design. The functional flexion axis was estimated from passive movements, between 0° and 120° of flexion and back. Intra-observer agreement and reliability, internal–external rotation and the angle with the surgical transepicondylar axis, in axial and frontal planes, were separately analysed for flexion and extension, in pre- and post-implant conditions.

Results

The analysis of reliability and agreement showed good results. The identification of the functional flexion axis showed statistically significant differences both in relation to flexion and extension and to pre- and post-implant conditions, both in frontal plane and in axial plane. The analysis of internal–external rotation confirmed these differences in kinematics (p < 0.05, between 25° and 35° of flexion).

Conclusions

The identification of the functional flexion axis changed in relation to passive flexion and extension movements, above all in frontal plane, while it resulted more stable and reliable in axial plane. These findings supported the possible clinical application of the functional flexion axis in the surgical practice by implementing navigated procedures. However, further analyses are required to better understand the factors affecting the identification of the functional flexion axis.

Level of evidence

IV.

     

Alignment in knee flexion position during navigation-assisted total knee arthroplasty

Purpose

The aim of this study was to demonstrate the lower limb alignment in knee flexion position after navigation-assisted total knee arthroplasty using the gap technique and to identify the correlative factors.

Methods

One hundred and twenty consecutive osteoarthritic knees (120 patients) were prospectively enrolled for intraoperative data collection. All TKA surgeries were performed using the navigation system (OrthoPilot?, version 4.0; B. Braun Aesculap, Tuttlingen, Germany). Before and after final prosthesis implantation, the lower limb navigation alignment in both knee extension (0°) and knee flexion (90°) position was recorded. The knee flexion alignment was divided into three groups: varus, neutral and valgus alignment. To determine the factors of the alignment in knee flexion position, preoperative demographics, radiologic and intraoperative data were obtained. Pearson’s correlation (r) analysis was performed to find the correlation. The Knee Society Score and Western Ontario and McMaster Universities Osteoarthritis Index were compared between groups.

Results

Although all postoperative extension alignment was within neutral position (between ?2° and +2°), postoperative knee flexion alignment was divided into three groups: varus (≤?3°), 24 cases (20 %); neutral (between ?2° and +2°), 85 cases (70.8 %) and valgus (≥+3°) alignment, 11 cases (9.2 %). There were a good correlation of alignment in knee flexion position with the rotation of femoral component relative to posterior condylar axis (r = ?0.502, p = 0.000) and weak correlations with posterior femoral cut thickness (lateral condyle) (r = 0.207, p = 0.026), medial flexion (90°) gap after femoral component rotation adjustment (r = 0.276, p = 0.003). Other variables did not show correlations. There were no statistical clinical differences between varus, neutral and valgus knee flexion alignment groups.

Conclusion

About 30 % of the cases showed malalignment of more than 3° in knee flexion position although with neutral alignment in extension position. The knee flexion alignment had a good correlation with the rotation of femoral component relative to posterior condylar axis. Neutral alignment in knee flexion position may be adjusted by femoral component rotation especially by the use of navigation system.

Level of evidence

IV.

     

MR imaging evaluation of the postoperative knee: ligaments, menisci, and articular cartilage

The surgical management of knee injuries has increased in recent years. Postoperative magnetic resonance (MR) imaging of the knee following surgical intervention serves an important role in the diagnostic evaluation of patients with recurrent or residual symptoms following surgical intervention. MR imaging additionally assists in the noninvasive documentation of temporal changes at the surgical site potentially reflective of procedural success, or failure. Background understanding of the common surgical procedures performed, their normal postoperative MR imaging appearance, and imaging features of potential procedural complications are essential in the accurate evaluation of patients following prior knee surgery. The focus of the following article is to review the clinical and MR imaging features of the postoperative knee following prior surgical treatment of ligamentous, meniscal, and articular cartilage injuries of the joint.     

Magnetic resonance of the knee menisci and cartilage

This contribution is designed to present magnetic resonance (MR) of the menisci and cartilage to the orthopedic surgeon in a practical manner. The investigators describe those MR sequences and techniques that optimally show injury, as well as the expected morphology of the menisci. Criteria for diagnosis of meniscal tears are outlined. Common “equivocal” meniscal tear appearances are shown and strategies for resolving such equivocal cases are suggested. The difficult problem of diagnosing a meniscal remnant tear or reinjury of a repaired meniscus is covered. Finally, MR imaging of chondromalacia and osteochondral injuries is discussed.     

Magnetic resonance imaging of the knee menisci

MRI remains the most useful noninvasive test for diagnosis of meniscal tears. Knowledge of normal anatomy and familiarity with patterns of meniscal tears are prerequisites when interpreting MRI studies of the knee. Radiologists should pay close attention to technical factors, normal variants, and associated abnormalities to maintain high diagnostic accuracy. Details of meniscal tears should be described as to best aid in orthopedic decision-making.     

Trunk flexion during walking in people with knee osteoarthritis

BackgroundOver 50% of the body’s mass is concentrated within the head, arms and trunk. Thus, small deviations in the orientation of the trunk, during normal walking, could influence the position of the centre of mass relative to the lower limb joint centres and impact on lower limb biomechanics. However, there are minimal data available on sagittal kinematics of the trunk in people with knee osteoarthritis (OA) during walking.Research questionDo people with knee OA have altered kinematic patterns of the trunk, pelvis or hip compared with healthy control participants during walking?MethodsStatistical parametric mapping was used to compare sagittal and frontal plane kinematic patterns, during walking, between a healthy group and cohort of people with knee OA.ResultsIndividuals with knee OA walked with a mean increase in trunk flexion of 2.6°. Although this difference was more pronounced during early stance, it was maintained across the whole of stance phase. There were no differences, between the groups, in sagittal plane pelvic or hip kinematics. There were also no differences in trunk, pelvic or hip kinematics in the frontal plane.SignificanceMost previous gait research investigating trunk motion in people with knee OA has focused on the frontal plane. However, our data suggest that an increase in sagittal trunk flexion may be a clinical hallmark of people with this disease. Altered trunk flexion could affect joint moments and muscle patterns and therefore our results motivate further research in this area.     

Infrapatellar plica of the knee: revisited with MR arthrographies undertaken in the knee flexion position mimicking operative arthroscopic posture

Purpose

To describe the appearance of the infrapatellar plica (IPP) on magnetic resonance arthrography (MRA) taken in 70° knee flexion, corresponding to the arthroscopic posture.

Materials and methods

Twenty-two patients (23 knee joints) who underwent MRA with 70° knee flexion were enrolled. All patients underwent MRA with 70° knee flexion to simulate operative arthroscopy. The images included fat-suppressed T1-weighted spin echo axial, sagittal, and coronal images. The visualization and morphology of the IPP were retrospectively assessed by two musculoskeletal radiologists.

Results

The IPP was demonstrated in 78.3% (n = 18/23) and was best visualized on the sagittal section through the intercondylar notch. The IPP manifested as a linear hypointense structure with variable thicknesses. The intercondylar component was delineated clearly, arising from the anterior intercondylar notch in parallel with the ACL and curving gently downward to attach to the infrapatellar fat pad. On the other hand, the Hoffa's fat pad component was not depicted clearly. The morphology of the IPP was either a separate type (60.9%) or a split type (17.4%).

Conclusion

The IPPs can be visualized with a high rate of detection and various morphologic appearances must be appreciated under the review of a flexed knee MRA.     

Lesions of the menisci of the knee: value of MR imaging criteria for recognition of unstable lesions

OBJECTIVE: This study aimed to determine the value of four MR imaging criteria for evaluating unstable meniscal lesions. MATERIALS AND METHODS: Criteria for unstable meniscal lesions were the presence of a displaced meniscal fragment, visibility on more than three 3-mm-thick coronal and two 4-mm-thick sagittal images, having more than one orientation plane or more than one pattern (contour irregularity, peripheral separation, tear), and having intrameniscal high signal intensity on T2-weighted spin-echo images. Sensitivity, specificity, and positive and negative predictive values for recognition of instability among all meniscal lesions were determined for the presence of each individual criterion and for the presence of at least one criterion in 50 consecutive patients (mean age, 46 years) who underwent MR imaging and subsequent arthroscopy. RESULTS: Sensitivities and specificities of these four criteria ranged between 18% and 54% and between 94% and 100%, respectively. Positive and negative predictive values ranged between 92% and 100% and between 39% and 52%, respectively. The presence of at least one criterion enabled recognition of unstable lesions with a sensitivity and specificity of 82% and with positive and negative predictive values of 90% and 70%, respectively. CONCLUSION: The four MR imaging criteria have high specificities and positive predictive values and low sensitivities and negative predictive values when evaluating unstable meniscal lesions.     

Patellar tendon length during knee flexion of meniscal-bearing and rotating total knee arthroplasty implants

Purpose

The length of the patellar tendon after total knee arthroplasty (TKA) has most commonly been compared with preoperative measurements. However, there are no reports that discuss changes in the length of the patellar tendon during knee flexion after TKA. The purpose of this study was to evaluate changes in the length of the patellar tendon during knee flexion and to clarify the impact of changes in patellar tendon strain on the length of the patellar tendon and post-operative range of motion (ROM) after TKA.

Methods

Thirty-six patients undergoing sequential bilateral TKA for osteoarthritis were evaluated. Patients received a meniscal-bearing (MB) implant on one side and a rotating platform (RP) implant on the other and were followed for a median of 115 months (range 60–211 months). The lengths of the patellar tendon at maximum extension, 30°, 60°, 90° and maximum flexion were measured, and the post-operative ROM of both knees were assessed. The effects of implant design and the knee flexion angle on the length of the patellar tendon were analysed using a linear mixed-effects model. The relationship between patellar tendon strain and post-operative knee ROM was assessed using Pearson’s correlation coefficients.

Results

Post-operative clinical scores were similar for MB and RP implants. Neither the implant design nor the knee flexion angle significantly affected the length of the patellar tendon. The ROMs in the two designs at final follow-up were equivocal (114° in MB, 113° in RP). There was no correlation between patellar tendon strain and ROM in knees with either implant type.

Conclusions

Patellar tendon lengths after mobile-bearing TKA with implants that permitted different anteroposterior constraints were relatively constant at varying degrees of knee flexion. Differences in patellar tendon strain may not impact ROM. These results provide conclusive evidence that the quality of the patellar tendon may play a less important role in ROM after TKA.

Level of evidence

Therapeutic study, Level II.