Evaluating rotational kinematics of the knee in ACL-ruptured and healthy patients using 3.0 Tesla magnetic resonance imaging

Assessment of knee instability in ACL-injured knees using weight-bearing computed tomography (WBCT): a novel protocol and preliminary results

OBJECTIVE

To propose a protocol for assessing knee instability in ACL-injured knees using weight-bearing computed tomography (WBCT).

MATERIALS AND METHODS

We enrolled five patients with unilateral chronic ACL tears referred for WBCT. Bilateral images were obtained in four positions: bilateral knee extension, bilateral knee flexion, single-leg stance with knee flexion and external rotation, and single-leg stance with knee flexion and internal rotation. The radiation dose, time for protocol acquisition, and patients' tolerance of the procedure were recorded. A blinded senior radiologist assessed image quality and measured the anterior tibial translation (ATT) and femorotibial rotation (FTR) angle in the ACL-deficient and contralateral healthy knee.

RESULTS

All five patients were male, aged 23-30 years old. The protocol resulted in a 16.2 mGy radiation dose and a 15-min acquisition time. The procedure was well-tolerated, and patient positioning was uneventful, providing good-quality images. In all positions, the mean ATT and FTR were greater in ACL-deficient knees versus the healthy knee, with more pronounced differences observed in the bilateral knee flexion position. Mean lateral ATT in the flexion position was 9.1±2.8 cm in the ACL-injured knees versus 4.0±1.8 cm in non-injured knees, and mean FTR angle in the bilateral flexion position was 13.5°±7.7 and 8.6°±4.6 in the injured and non-injured knees, respectively.

CONCLUSION

Our protocol quantitatively assesses knee instability with WBCT, measuring ATT and FTR in diverse knee positions. It employs reasonable radiation, is fast, well-tolerated, and yields high-quality images. Preliminary findings suggest ACL-deficient knees show elevated ATT and FTR, particularly in the 30° flexion position.

Effect of ACL Reconstruction on Range of Tibial Rotation: A Systematic Review of Current Literature and a Recommendation for a Standard Measuring Protocol

Background:

Tibial rotation is an important topic in anterior cruciate ligament (ACL) surgery, and many efforts are being made to address rotational stability. The exact role of the ACL in controlling tibial rotation in clinical studies is unknown.

Purpose:

To quantify the effect of ACL reconstruction on the amount of tibial rotation based on the current available literature.

Study Design:

Systematic review; Level of evidence, 4.

Methods:

A literature search of the PubMed and EMBASE databases was performed in August 2019. Two independent reviewers reviewed titles and abstracts as well as full-text articles. A total of 2383 studies were screened for eligibility. After screening of titles and abstracts, 178 articles remained for full-text assessment. Ultimately, 13 studies were included for analysis. A quality assessment was performed by means of the RoB 2.0 (revised tool for Risk of Bias in randomized trials) and the ROBINS-I (Risk Of Bias In Non-randomized Studies–of Interventions) tools.

Results:

According to the studies using computer-assisted surgery that were included in this review, ACL reconstruction resulted in an average reduction in tibial rotation of 17% to 32% compared with preoperatively; whether the range of tibial rotation returned to preinjury levels remained unclear. In the current literature, a gold standard for measuring tibial rotation is lacking. Major differences between the study protocols were found. Several techniques for measuring tibial rotation were used, each with its own limitations. Most studies lacked proper description of accompanying injuries.

Conclusion:

ACL reconstruction reduced the range of tibial rotation by 17% to 32%. Normal values for the range of tibial rotation in patients with ACL deficiency and those who undergo ACL reconstruction could not be provided based on the current available literature owing to a lack of uniform measuring techniques and protocols. Therefore, we advocate uniformity in measuring tibial rotation.

Dynamic MRI for articulating joint evaluation on 1.5 T and 3.0 T scanners: setup, protocols, and real-time sequences

Dynamic magnetic resonance imaging (MRI) is a non-invasive method that can be used to increase the understanding of the pathomechanics of joints. Various types of real-time gradient echo sequences used for dynamic MRI acquisition of joints include balanced steady-state free precession sequence, radiofrequency-spoiled sequence, and ultra-fast gradient echo sequence. Due to their short repetition time and echo time, these sequences provide high temporal resolution, a good signal-to-noise ratio and spatial resolution, and soft tissue contrast. The prerequisites of the evaluation of joints with dynamic MRI include suitable patient installation and optimal positioning of the joint in the coil to allow joint movement, sometimes with dedicated coil support. There are currently few recommendations in the literature regarding appropriate protocol, sequence standardizations, and diagnostic criteria for the use of real-time dynamic MRI to evaluate joints. This article summarizes the technical parameters of these sequences from various manufacturers on 1.5 T and 3.0 T MRI scanners. We have reviewed pertinent details of the patient and coil positioning for dynamic MRI of various joints. The indications and limitations of dynamic MRI of joints are discussed.

Development and Assessment of a Microcomputed Tomography Compatible Five Degrees-of-Freedom Knee Joint Motion Simulator

Currently available knee joint kinematic tracking systems fail to nondestructively capture the subtle variation in joint and soft tissue kinematics that occur in native, injured, and reconstructed joint states. Microcomputed tomography (CT) imaging has the potential as a noninvasive, high-resolution kinematic tracking system, but no dynamic simulators exist to take advantage of this. The purpose of this work was to develop and assess a novel micro-CT compatible knee joint simulator to quantify the knee joint's kinematic and kinetic response to clinically (e.g., pivot shift test) and functionally (e.g., gait) relevant loading. The simulator applies closed-loop, load control over four degrees-of-freedom (DOF) (internal/external rotation, varus/valgus rotation, anterior/posterior translation, and compression/distraction), and static control over a fifth degree-of-freedom (flexion/extension). Simulator accuracy (e.g., load error) and repeatability (e.g., coefficient of variation) were assessed with a cylindrical rubber tubing structure and a human cadaveric knee joint by applying clinically and functionally relevant loads along all active axes. Micro-CT images acquired of the joint at a loaded state were then used to calculate joint kinematics. The simulator loaded both the rubber tubing and the cadaveric specimen to within 0.1% of the load target, with an intertrial coefficient of variation below 0.1% for all clinically relevant loading protocols. The resultant kinematics calculated from the acquired images agreed with previously published values, and produced errors of 1.66 mm, 0.90 mm, 4.41 deg, and 1.60 deg with respect to anterior translation, compression, internal rotation, and valgus rotation, respectively. All images were free of artifacts and showed knee joint displacements in response to clinically and functionally loading with isotropic CT image voxel spacing of 0.15 mm. The results of this study demonstrate that the joint-motion simulator is capable of applying accurate, clinically and functionally relevant loads to cadaveric knee joints, concurrent with micro-CT imaging. Nondestructive tracking of bony landmarks allows for the precise calculation of joint kinematics with less error than traditional optical tracking systems.

Establishing outcome measures in early knee osteoarthritis

The classification and monitoring of individuals with early knee osteoarthritis (OA) are important considerations for the design and evaluation of therapeutic interventions and require the identification of appropriate outcome measures. Potential outcome domains to assess for early OA include patient-reported outcomes (such as pain, function and quality of life), features of clinical examination (such as joint line tenderness and crepitus), objective measures of physical function, levels of physical activity, features of imaging modalities (such as of magnetic resonance imaging) and biochemical markers in body fluid. Patient characteristics such as adiposity and biomechanics of the knee could also have relevance to the assessment of early OA. Importantly, research is needed to enable the selection of outcome measures that are feasible, reliable and validated in individuals at risk of knee OA or with early knee OA. In this Perspectives article, potential outcome measures for early symptomatic knee OA are discussed, including those measures that could be of use in clinical practice and/or the research setting.

Global rotation has high sensitivity in ACL lesions within stress MRI

PURPOSE

This study aims to objectively compare side-to-side differences of P-A laxity alone and coupled with rotatory laxity within magnetic resonance imaging, in patients with total anterior cruciate ligament (ACL) rupture.

METHODS

This prospective study enrolled sixty-one patients with signs and symptoms of unilateral total anterior cruciate ligament rupture, which were referred to magnetic resonance evaluation with simultaneous instrumented laxity measurements. Sixteen of those patients were randomly selected to also have the contralateral healthy knee laxity profile tested. Images were acquired for the medial and lateral tibial plateaus without pressure, with postero-anterior translation, and postero-anterior translation coupled with maximum internal and external rotation, respectively.

RESULTS

All parameters measured were significantly different between healthy and injured knees (P < 0.05), with exception of lateral plateau without stress. The difference between injured and healthy knees for medial and lateral tibial plateaus anterior displacement (P < 0.05) and rotation (P < 0.001) was statistically significant. It was found a significant correlation between the global rotation of the lateral tibial plateau (lateral plateau with internal + external rotation) with pivot-shift, and between the anterior global translation of both tibial plateaus (medial + lateral tibial plateau) with Lachman. The anterior global translation of both tibial plateaus was the most specific test with a cut-off point of 11.1 mm (93.8 %), and the global rotation of the lateral tibial plateau was the most sensitive test with a correspondent cut-off point of 15.1 mm (92.9 %).

CONCLUSION

Objective laxity quantification of ACL-injured knees showed increased sagittal laxity, and simultaneously in sagittal and transversal planes, when compared to their healthy contralateral knee. Moreover, when measuring instability from anterior cruciate ligament ruptures, the anterior global translation of both tibial plateaus and global rotation of the lateral tibial plateau add diagnostic specificity and sensitivity. This work strengthens the evidence that the anterior cruciate ligament plays an important biomechanical role in controlling the anterior translation, but also both internal and external rotation. The high sensitivity and specificity of this device in objectively identifying and measuring the multiplanar instability clearly guides stability restoration clinical procedures. Level of evidence Cross-sectional study, Level III.

Clinical assessment of antero-medial rotational knee laxity: a systematic review

PURPOSE

To inventory the examination methods available to assess antero-medial rotational laxity (AMRL) of the knee following medial collateral ligament injury.

METHODS

Searches were conducted in accordance with the PRISMA guidelines and using four online databases: WEB OF SCIENCE, MEDLINE, EMBASE, and AMED. The Critical Appraisal Skills Programme guidelines for Diagnostic Test Studies were used for the quality assessment of the articles.

RESULTS

A total of 2241 articles were identified from the database searches. From this, four articles were included in the final review. All were case-control studies, considered a combined ACL/MCL injury and had small study populations. Specialised equipment was required in all studies, and one needed additional imaging support before measurements could be taken. Two employed commercially available measuring equipment as part of the assessment process.

CONCLUSION

Clinical assessment of AMRL in relation to a MCL injury remains challenging. Although methods have been developed to support clinical examination, they are limited by a number of factors, including the need for additional time in the clinical environment when setting up equipment, the need for specific equipment to produce and measure rotational movement and imaging support. In addition, there are patient safety concerns from the repeated imaging. A reliable and valid clinical examination remains to be found to truly assess antero-medial rotational laxity of the knee.

LEVEL OF EVIDENCE

IV.

The effect of knee flexion and rotation on the tibial tuberosity-trochlear groove distance

PURPOSE

The purpose was to measure the effect of flexion and additional rotation of the femur relative to the tibia on the tuberosity-trochlear groove distance (TT-TG) in the same subject in 20 cadaveric knees joint.

METHODS

In 20 human adult cadavers, formal fixed knees (age: 81.9 years, SD 12.3; 10 female) CT scans were performed in extension and 30° of flexion as well as in neutral, maximal possible internal (IR), and external rotation (ER). On superimposed CT scan images, TT-TG was measured in each position. TT-TG measurements were correlated in all knee positions.

RESULTS

TT-TG in full extension/neutral rotation was 7.8 mm (SD 3.4, range, 2.4-15.3). TT-TG in full extension and IR was significantly lower, and TT-TG in full extension and ER was significantly higher than in neutral rotation (5.4 ± 2.3 vs. 10.9 ± 4.8 mm; P < 0.001). IR and ER varied between 1.0°-7.6° and 0.2°-9.2°, respectively. TT-TG in 30° flexion/neutral rotation was 3.9 mm (SD 1.8, range, 1.3-7.8), which was significantly lower than in full extension and neutral rotation (P < 0.001). TT-TG in 30° flexion and IR was significantly lower, and TT-TG in 30° flexion and ER was significantly higher than values obtained in neutral rotation (2.7 ± 1.2 vs. 6.5 ± 3.4 mm; P < 0.001). IR and ER in 30° flexion varied between 0.6°-10.7° and 1.9°-13.0°, respectively.

CONCLUSION

Flexion as well as rotation of the knee joint significantly alters the TT-TG. These results may have wider clinical relevance in assessing TT-TG and further decisions based on it.

Rotational Knee Laxity in Anterior Cruciate Ligament Deficiency: An Additional Secondary Sign on MRI

OBJECTIVE

The objective of this study was to evaluate the accuracy of tibial rotation measurement as a secondary sign for diagnosing anterior cruciate ligament (ACL) tears with the use of MRI.

MATERIALS AND METHODS

A total of 893 MRI studies were retrospectively reviewed, and 239 patients were identified as having either an intact ACL (group 1; n = 182), an arthroscopically confirmed acutely torn ACL (group 2; n = 22), or a chronically torn ACL (group 3; n = 35). Tibial rotation was estimated by measuring the femorotibial angle (FTA).

RESULTS

The mean (± SD) FTA was significantly higher in group 2 (10.7° ± 4.8°) and group 3 (11° ± 5.5°) than in group 1 (3.2° ± 3.3°) (p < 0.001, for all cases). An FTA of 4.9° was the optimal threshold (sensitivity, 93%; specificity, 80%) for separating completely torn ACLs from intact ACLs. An FTA ranging from 4.9° to 5.5° (sensitivity, 95%; specificity, 80%) indicated a complete acute ACL tear, whereas an FTA of 5.6° or greater (sensitivity, 91.4%; specificity, 83.5%) suggested a complete chronic ACL tear.

CONCLUSION

An increased FTA indicates alteration in the femorotibial anatomic relationship and could be of value in assessing ACL tears in patients with equivocal signs on MRI.

MR imaging of healthy knees in varying degrees of flexion using a stretchable coil array provides comparable image quality compared to a standard knee coil array

OBJECTIVE

Stretchable coils allow knee imaging at varying degrees of flexion. Purpose was to compare a new-developed stretchable 8-channel to a standard 8-channel knee coil array by means of quantitative and qualitative image analysis.

MATERIAL AND METHODS

IRB approved prospective study. Knee MR imaging in 10 healthy volunteers was performed at 3T using a standard 8-channel and a new-developed stretchable 8-channel coil array at 0°, 45°, and 60° of flexion and at 0° (standard coil). Image parameters were identical. Signal-to-noise ratio (SNR) was determined by combining the images with separately acquired noise data on a pixel-by-pixel basis using MATLAB routines (Natick, MA, USA). Images were qualitatively analysed by two independent radiologists who graded the visibility of several anatomic structures from 1=not visible to 5=excellent. ANOVA, Wilcoxon and kappa statistics were used.

RESULTS

Mean SNR±standarddeviation of bone was 54.7±10.4 and of muscle 28.0± 4.4 using the stretchable coil array and 54.6±8.2 and 33.4±4.5, respectively, using the standard knee coil array. No statistically significant SNR differences were found between both arrays (bone, p=0.960; muscle, p=0.132). SNR was not degraded at higher degrees of flexion. The qualitative image analysis did not reveal statistically significant differences between the stretchable and standard coil array with regard to the visibility of anatomic structures (p=0.026-1.000). Overall kappa was 0.714.

CONCLUSION

Stretchable 8-channel coil arrays provide similar SNR and visibility of anatomic structures compared to standard 8-channel knee coil arrays. MR imaging with high SNR will now be possible in flexed knees.

Effect of axial loading during knee flexion on ACL end-to-end distance in healthy and ACL-deficient knees

PURPOSE

The purpose of this study was to determine the effect of physiological axial loading during knee flexion on changes in anterior cruciate ligament (ACL) end-to-end distance for normal and ACL-deficient knees.

METHODS

Biomechanical tests were conducted on ten cadaveric knees using an Instron machine. We gathered positional data of the tibia and femur at low to middle flexion angles (0°, 15°, 30°, 45° and 60°) with/without axial loading. First, no external load was applied to the specimens at each angle, and then, a 1000-N axial load was applied to the knees. The same test protocols were repeated after transection of the ACL. Using computer software (Geomagic Studio 10), we regenerated positional data and calculated the end-to-end distances of the anteromedial, posterolateral and the entire ACL bundle at each angle.

RESULTS

Compared with ACL-intact knees without axial loading, knees under axial loading did not show significant increases in end-to-end distance. Under axial loading, we found no significant differences in end-to-end distances between bundles in ACL-intact knees according to the increase in knee flexion angle. After ACL transection, axial loading significantly increased end-to-end distances of all three bundles (P < 0.001), and the distances increased significantly with flexion angle (P < 0.05 at all angles in all bundles).

CONCLUSION

The changing patterns of the ACL end-to-end distance in ACL-deficient knees were different from those in healthy knees after applying physiological axial loading, and the ACL end-to-end distances in ACL-deficient knees increased remarkably as knee flexion angles increased.

A new measure of tibiofemoral subchondral bone interactions that correlates with early cartilage damage in injured sheep

We have demonstrated previously that chondral damage is associated with increased knee surface velocities following ligament and meniscus injuries in sheep. We tested the hypothesis that cartilage damage scores would correlate with a new bone surface interaction measure that captures complex changes in tibiofemoral alignment, "proximity disturbance" (PD). Six sheep underwent combined anterior cruciate and medial collateral ligament transection (ACL/MCLx), five complete lateral meniscectomy (Mx), and four sham arthrotomy (Sham). Tibiofemoral subchondral bone surfaces were modeled, and the post-operative changes in relative separation of the surfaces (i.e., "proximity") were derived from subject-specific in vivo 3D stifle kinematics. Surface areas of regions of near contact were determined, and PD was calculated as the range of change in tibiofemoral proximity, divided by normalized overlapping proximity surface areas between baseline and post-operative time points. Cartilage morphology was graded at dissection. ACL/MCLx PD was significantly elevated relative to Mx and Shams, and correlated with cartilage damage (r(2)  = 0.88-0.98). Although not statistically significant, Mx PD values tended to be higher than those of Shams, and correlated with cartilage damage. Results from both injury models suggest that increasing change in tibiofemoral surface alignment may be increasingly deleterious to long-term cartilage health in sheep.

Individualized ACL reconstruction

The pivot shift test is the only physical examination test capable of predicting knee function and osteoarthritis development after an ACL injury. However, because interpretation and performance of the pivot shift are subjective in nature, the validity of the pivot shift is criticized for not providing objective information for a complete surgical planning for the treatment of rotatory knee laxity. The aim of ACL reconstruction was eliminating the pivot shift sign. Many structures and anatomical characteristics can influence the grading of the pivot shift test and are involved in the genesis and magnitude of rotatory instability after an ACL injury. The objective quantification of the pivot shift may be able to categorize knee laxity and provide adequate information on which structures are affected besides the ACL. A new algorithm for rotational instability treatment is presented, accounting for patients' unique anatomical characteristics and objective measurement of the pivot shift sign allowing for an individualized surgical treatment.

LEVEL OF EVIDENCE

V.

Knee morphology and risk factors for developing an anterior cruciate ligament rupture: an MRI comparison between ACL-ruptured and non-injured knees

PURPOSE

The objective of this study was to evaluate multiple morphological features on MR images in patients with and without ACL rupture to evaluate whether there are certain variables that confer a higher risk for an ACL rupture.

METHODS

MRI measurements were taken from 45 subjects with ACL injury and 43 subjects without ACL injury, by two independent observers. The morphometrics were compared between ACL-injured and non-injured subjects, between men and women and for male and female subjects separately. A factor analysis was performed to determine whether any variables were related in the injured, non-injured, male or female groups.

RESULTS

There were no significant differences in the overall population between the ACL-injured and non-injured group. Significant differences were found in bicondylar (P ≤ 0.001), medial condyle (P ≤ 0.001) and lateral condyle widths (P = 0.001) between men and women. In the male group, there were no significant differences between ACL-injured and non-injured subjects. In the female group, there was a significant difference in bicondylar (P = 0.002) and lateral condyle width (P = 0.002) between ACL-injured and non-injured subjects.

CONCLUSIONS

There were gender-related differences in bony morphology between ACL-injured and non-injured subjects. The morphological features that were different between ACL-injured and non-injured subjects varied between male and female subjects.

LEVEL OF EVIDENCE

Case-Control study, Level III.

A Preliminary In Vivo Assessment of Anterior Cruciate Ligament-Deficient Knee Kinematics With the KneeM Device: A New Method to Assess Rotatory Laxity Using Open MRI

BACKGROUND

Methods of objectively measuring rotational knee laxity are either experimental or difficult to use in daily practice. A new method has been developed to quantitatively assess rotatory laxity using an open MRI system and new tool, the KneeM device.

PURPOSE/HYPOTHESIS

To perform a preliminary evaluation of a novel knee rotation measurement device to assess knee kinematics during flexion in an MRI field, in both anterior cruciate ligament (ACL)-deficient and healthy contralateral knees. The hypothesis was that the KneeM device would allow in vivo reproduction and analysis of knee kinematics during flexion in healthy and ACL-deficient knees.

STUDY DESIGN

Controlled laboratory study.

METHODS

Ten subjects (7 men and 3 women; mean age ± standard deviation, 32.3 ± 9.4 years) with ACL-deficient knees and contralateral uninjured knees participated in the study. An open MRI was performed with the KneeM device at a mean 4.9 months (range, 3.0-7 months) after ACL injury. The device exerted on the knee an anterior drawer force of 100 N, with an internal rotation of 20°, through the range of flexion (0°, 20°, 40°, and 60°). Both ACL-deficient and healthy contralateral knees were analyzed using the Iwaki method.

RESULTS

There was no statistical difference of anterior translation in the medial compartment between intact and ACL-deficient knees at all degrees of flexion. However, significant differences in the anterior translation of the lateral compartment were observed between ACL-deficient and intact contralateral knees at 0° and 20° of flexion (P = .005 and P = .002, respectively). Between 20° and 40°, the lateral plateau of ACL-deficient knees translated 7.7 mm posteriorly, whereas the medial compartment remained stable, reflecting a sudden external rotation of the lateral plateau under the femoral condyle.

CONCLUSION

This preliminary study suggests that measurement of tibiofemoral movements in both compartments during flexion using the KneeM device was useful for quantifying rotatory laxity in ACL-deficient knees. Moreover, this device seemed to allow a "mechanized pivot shift" and allowed reproduction of the "pivot" phase in the MRI field between 20° and 40° of flexion.

CLINICAL RELEVANCE

This device could be used for diagnostic purposes or to investigate the outcomes of ACL reconstructions.

Passive anterior tibial subluxation in anterior cruciate ligament-deficient knees

BACKGROUND

Abnormal anterior-posterior and rotational motion secondary to anterior cruciate ligament (ACL) insufficiency is typically described in terms of dynamic laxity. An original description of the abnormal tibiofemoral relationship in the setting of ACL insufficiency has highlighted the presence of a fixed anterior tibial subluxation in this population of failed ACL reconstruction (ACLR); however, no study has quantified the degree of tibial subluxation in both the medial and lateral compartments.

PURPOSE

To measure and compare the amount of anterior tibial subluxation among various states of ACL competency, including (1) intact ACL, (2) acute ACL disruption, and (3) failed ACLR (ie, patients requiring revision ACLR). We hypothesized that anterior tibial displacement would be greater in the lateral compartment and in cases of failed ACLR compared with intact and acute ACL injured states.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

Using sagittal magnetic resonance imaging (MRI) and a standardized measurement technique, we determined the amount of anterior tibial subluxation relative to a constant posterior condylar reference point. Measurements were performed in both the medial and the lateral compartments and were compared with 1-way analysis of variance. The presence of meniscal tears along with meniscal volume loss and chondral damage was correlated with the amount of subluxation in each group.

RESULTS

Compared with the intact ACL state, the medial tibial plateau was positioned more anteriorly relative to the femur in both acute ACL injured knees (mean 1.0 mm) and those that failed ACLR (mean 1.8 mm) (P = .072). In the lateral compartment, there was 0.8 mm of mean anterior tibial displacement after acute ACL injury and 3.9 mm of mean anterior subluxation in patients who failed ACLR (P < .001). Mean anterior displacement of the lateral plateau in patients who failed ACLR was almost 5 times greater than the amount observed in patients with acute ACL injuries. There was no correlation between meniscal/chondral injury and the amount of subluxation.

CONCLUSION

Patients who require revision ACLR have an abnormal tibiofemoral relationship noted on MRI that is most pronounced in the lateral compartment and should be taken into account during revision surgery. These observations may explain the suboptimal clinical results seen in some patients who undergo revision ACLR.

Accurate semiautomatic assessment of ligament length variations from MRI data

PURPOSE

A semiautomatic method for the assessment of ligament length variations during different joint positions based on MRI data is proposed.

METHODS

Ligament lengths are represented as distances between points marking characteristic locations in the ligament insertion regions on the bones. These points are defined manually for one single reference joint position and for all other joint positions they are automatically mapped with high accuracy to the correct locations using image registration methods. The methodology is validated using data from 16 volunteers depicting the coracoclavicular ligaments in the left shoulder during different arm abductions.

RESULTS

The method yielded a superior reproducibility of the point locations over different joint positions compared to manual point marking. Significant ligament length variations were found for different abductions which was not possible with manual measurements. Acquisition related geometric distortions and inaccuracies during the registration and segmentation process were small.

CONCLUSIONS

The proposed method provides superior accuracy for the in vivo analysis of ligament dynamics compared to manual measurements. This permits a better understanding of the ligament behavior during joint motion and offers new possibilities for presurgical planning which to date has not been possible with manual data analysis.