Diffusion tensor imaging of the anterior cruciate ligament following primary repair with internal bracing: A longitudinal study

Factors influencing diffusion tensor imaging of knee cartilage in children ages 6-12 years: a prospective study

BACKGROUND

Magnetic resonance diffusion tensor imaging (DTI) has recently been used to evaluate the developing cartilage of children, but the influencing factors have not been well studied.

OBJECTIVE

The objective of this study was to investigate the influence of the diffusion gradient strength (b value), diffusion gradient direction, age and sex on knee cartilage DTI in healthy children aged 6-12 years.

MATERIALS AND METHODS

A total of 30 healthy child volunteers, with an average age of 8.9 ± 1.6 (mean ± standard deviation) years, were enrolled in this study. They were categorized into three groups according to their age range: 6-8 years, 8-10 years and 10-12 years, ensuring equal sex distribution in each group (5 boys and 5 girls). These volunteers underwent routine left knee joint magnetic resonance imaging (MRI) and serial DTI scans. DTI parameters were altered as follows: when b value = 600 s/mm2, diffusion gradient direction was set to 6, 15, 25, 35 and 45; and when diffusion gradient direction = 25, b value was set to 300, 600, 900 and 1200 s/mm2. The values of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were separately acquired using image post-processing techniques. The correlation between various b values, diffusion gradient directions, age and sex on the one hand and FA and ADC values on the other, was investigated.

RESULTS

(1) When diffusion gradient direction was fixed and the b value was varied, both FA and ADC exhibited a decreasing trend as the b value increased (P < 0.001). (2) When the b value was fixed and diffusion gradient direction was varied, the FA of knee cartilage showed a decreasing trend with increasing diffusion gradient direction (P < 0.001). (3) The FA value increased with age (P < 0.05).

CONCLUSION

The b value, diffusion gradient direction value and age exert a significant impact on both FA and ADC values in MR DTI of knee cartilage in children aged 6-12 years. In order to obtain a stable DTI, it is recommended to select a b value ≥ 600 s/mm2 and a diffusion gradient direction ≥ 25 during scanning.

Assessment of Mechanically Induced Changes in Helical Fiber Microstructure Using Diffusion Tensor Imaging

Noninvasive methods to detect microstructural changes in collagen-based fibrous tissues are necessary to differentiate healthy from damaged tissues in vivo but are sparse. Diffusion Tensor Imaging (DTI) is a noninvasive imaging technique used to quantitatively infer tissue microstructure with previous work primarily focused in neuroimaging applications. Yet, it is still unclear how DTI metrics relate to fiber microstructure and function in musculoskeletal tissues such as ligament and tendon, in part because of the high heterogeneity inherent to such tissues. To address this limitation, we assessed the ability of DTI to detect microstructural changes caused by mechanical loading in tissue-mimicking helical fiber constructs of known structure. Using high-resolution optical and micro-computed tomography imaging, we found that static and fatigue loading resulted in decreased sample diameter and a re-alignment of the macro-scale fiber twist angle similar with the direction of loading. However, DTI and micro-computed tomography measurements suggest microstructural differences in the effect of static versus fatigue loading that were not apparent at the bulk level. Specifically, static load resulted in an increase in diffusion anisotropy and a decrease in radial diffusivity suggesting radially uniform fiber compaction. In contrast, fatigue loads resulted in increased diffusivity in all directions and a change in the alignment of the principal diffusion direction away from the constructs' main axis suggesting fiber compaction and microstructural disruptions in fiber architecture. These results provide quantitative evidence of the ability of DTI to detect mechanically induced changes in tissue microstructure that are not apparent at the bulk level, thus confirming its potential as a noninvasive measure of microstructure in helically architected collagen-based tissues, such as ligaments and tendons.

Applications of Diffusion-Weighted MRI to the Musculoskeletal System

Diffusion-weighted imaging (DWI) is an established MRI technique that can investigate tissue microstructure at the scale of a few micrometers. Musculoskeletal tissues typically have a highly ordered structure to fulfill their functions and therefore represent an optimal application of DWI. Even more since disruption of tissue organization affects its biomechanical properties and may indicate irreversible damage. The application of DWI to the musculoskeletal system faces application-specific challenges on data acquisition including susceptibility effects, the low T2 relaxation time of most musculoskeletal tissues (2-70 msec) and the need for sub-millimetric resolution. Thus, musculoskeletal applications have been an area of development of new DWI methods. In this review, we provide an overview of the technical aspects of DWI acquisition including diffusion-weighting, MRI pulse sequences and different diffusion regimes to study tissue microstructure. For each tissue type (growth plate, articular cartilage, muscle, bone marrow, intervertebral discs, ligaments, tendons, menisci, and synovium), the rationale for the use of DWI and clinical studies in support of its use as a biomarker are presented. The review describes studies showing that DTI of the growth plate has predictive value for child growth and that DTI of articular cartilage has potential to predict the radiographic progression of joint damage in early stages of osteoarthritis. DTI has been used extensively in skeletal muscle where it has shown potential to detect microstructural and functional changes in a wide range of muscle pathologies. DWI of bone marrow showed to be a valuable tool for the diagnosis of benign and malignant acute vertebral fractures and bone metastases. DTI and diffusion kurtosis have been investigated as markers of early intervertebral disc degeneration and lower back pain. Finally, promising new applications of DTI to anterior cruciate ligament grafts and synovium are presented. The review ends with an overview of the use of DWI in clinical routine. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 3.

Arthroscopic Anatomic Anterior Cruciate Ligament Primary Repair Restores Anterior Tibial Translation Intraoperatively at Time Zero With No Additional Effect of Suture Augmentation

PURPOSE

To intraoperatively evaluate the ability of anterior cruciate ligament (ACL) primary repair (ACLPR) to restore anterior tibial translation (ATT) at time zero and to assess the influence of additional suture augmentation (SA) on ATT.

METHODS

Patients with proximal ACL tears undergoing arthroscopic ACLPR with dual-suture anchor fixation were included in this time-zero clinical study. Laxity measurements were taken with a digital arthrometer to evaluate ATT stability preoperatively in the office (T0) as a standardized diagnostic tool, preoperatively under anesthesia (T1), at time zero intraoperatively after ACLPR but prior to SA fixation (T2), and after SA fixation (T3).

RESULTS

A total of 27 patients (mean age ± standard deviation [SD], 35.1 ± 12.0 years) with proximal ACL tears and significant preoperative (T0) ATT side-to-side differences (SSDs) (mean ± SD, 4.1 ± 1.5 mm) were evaluated. ACLPR was shown to restore ATT SSD at time zero (mean ± SD, 0.2 ± 1.1 mm) given that a significant reduction in ATT SSD (mean difference ± standard error, -4.7 ± 0.21 mm; P < .001) was achieved when comparing preoperative and intraoperative measurements after separate refixation of both ACL bundles with suture anchors. Additional SA fixation did not further decrease ATT when comparing measurements of the ipsilateral leg after ACL refixation and after SA fixation (mean difference ± SD, 0.03 ± 0.22 mm; P = .496).

CONCLUSIONS

ACLPR with dual-suture anchor fixation restores time-zero ATT laxity in adults with proximal ACL tears. Additional SA fixation in full knee extension does not further decrease ATT.

CLINICAL RELEVANCE

This study provides important information about the effectiveness of ACLPR in restoring ATT. SA with the knee fixed in full knee extension does not further decrease ATT; therefore, augmentation may not lead to overconstraint of the knee or stress shielding of the repaired ACL.

Augmentation with Fibertape Leads to Biomechanically Superior but Similar Clinical Outcomes in ACL Surgeries: Systematic Review and Meta-analysis

Purpose

The current generation has witnessed significant progress in the field of knee arthroscopy. Suture tapes have gained immense popularity due to perceived improved biomechanical support to the graft while it heals. The purpose of the present systematic review is to analyze the biomechanical construct of suture tapes in ACL repairs and reconstructions along with clinical outcomes.

Methods

Cochrane Library, PubMed, and Embase were searched until December 2021. All Biomechanical Studies on animal or cadaver knees that compared construct characteristics of suture tape in ACL repair or reconstruction and clinical studies in English focusing on outcomes following suture tape augmentation in ACL repair or reconstruction were included. The quality of clinical studies using the Modified Coleman Methodology Score (MCMS).

Results

A total of 16 studies biomechanical and 23 clinical studies were included in qualitative synthesis, leaving nine biomechanical studies for final quantitative analyses. Suture tape revealed biomechanical superiority in terms of ultimate strength, stiffness, cyclic displacement, and elongation of graft, while comparing ACLR with internal brace to standard ACLR. No significant difference in retear rates was seen in clinical studies. Clinical score(IKDC score) was found similar in both augmented and non-augmented construct. Similar results were obtained in biomechanical studies.

Conclusion

The use of suture tape as a ligament augmentation in both ACL reconstruction and ACL repair offers more strength, less elongation or displacement, and is biomechanically stable and sound. There is a lack of data to comprehensively comment upon the clinical superiority of the use of internal augmentation. However, a meta-analysis of the retear rates and clinical outcome score revealed similar outcomes between suture tape augmented and nonaugmented groups.

Effects of Angular Resolution and b Value on Diffusion Tensor Imaging in Knee Joint

OBJECTIVE

To investigate the influences of the diffusion gradient directions (angular resolution) and the strength of the diffusion gradient (b value) on diffusion tensor imaging (DTI) metrics and tractography of various connective tissues in knee joint.

DESIGN

Two rat knee joints were scanned on a preclinical 9.4-T system using a 3-dimensional diffusion-weighted spin echo pulse sequence. One protocol with b value of 500, 1500, and 2500 s/mm² were acquired separately using 43 diffusion gradient directions. The other protocol with b value of 1000 s/mm² was performed using 147 diffusion gradient directions. The in-plane resolution was 45 µm isotropic. Fractional anisotropy (FA) and mean diffusivity (MD) were compared at different angular resolution. Tractography was quantitatively evaluated at different b values and angular resolutions in cartilage, ligament, meniscus, and growth plate.

RESULTS

The ligament showed higher FA value compared with growth plate and cartilage. The FA values were largely overestimated at the angular resolution of 6. Compared with FA, MD showed less sensitivity to the angular resolution. The fiber tracking was failed at low angular resolution (6 diffusion gradient directions) or high b value (2500 s/mm²). The quantitative measurements of tract length and track volume were strongly dependent on angular resolution and b value.

CONCLUSIONS

To obtain consistent DTI outputs and tractography in knee joint, the scan may require a proper b value (ranging from 500 to 1500 s/mm²) and sufficient angular resolution (>14) with signal-to-noise ratio >10.

Suture tape augmentation ACL repair, stable knee, and favorable PROMs, but a re-rupture rate of 11% within 2 years

PURPOSE

The aim of this study is to investigate clinical and magnetic resonance imaging (MRI) outcomes after anterior cruciate ligament (ACL) repair using the suture tape augmentation (STA) technique.

METHODS

This prospective interventional case series included 35 patients who underwent STA ACL repair and were all followed up for 2 years. The ACL rupture was between 4 and 12 weeks old and per-operatively confirmed repairable. The International Knee Documentation Committee (IKDC), and Lysholm and Tegner scores were collected together with return to work (RTW), return to sport (RTS), re-rupture, and re-intervention rate. Lachman testing was performed and ACL healing was evaluated on MRI using a grading scale based on the ACL's morphology and signal intensity with grade 1 representing good ACL healing and grade 3 representing poor ACL healing.

RESULTS

The number of patients who returned to their pre-rupture level for IKDC, Lysholm, and Tegner scores at 2 years of follow-up are 17/26 (65.4%), 13/25 (52.0%), and 18/27 (66.7%) patients, respectively. Median RTW and RTS periods were 5.5 weeks (range 0-32 weeks) and 6 months (range 2-22 months), respectively. The Lachman side-to-side difference decreased significantly (P < 0.001) to less than 3 mm after surgery and remained stable. Four patients [11.4%, 95% CI (3.2, 26.7)] suffered from a re-rupture and three other patients [8.6%, 95% CI (1.8, 23.1)] needed a re-intervention for another reason than re-rupture. MRI follow-up of 31 patients showed overall grade 1 ACL healing in 14 (45.2%) patients, grade 2 ACL healing in 11 (35.5%) patients, and grade 3 ACL healing in 6 (19.4%) patients. A higher risk of re-rupture was associated with grade 3 ACL healing at 6 months post-operatively and a pre-operative Tegner score of  ≥  7.

CONCLUSION

This study shows that treatment of the acute, repairable ACL with the STA technique leads to a stable knee and favorable patient-reported outcome measures (PROMs). However, the re-rupture rate of 11.4% within the 2-year follow-up is a concern.

LEVEL OF EVIDENCE

IV.

Diffusion tensor imaging of the anterior cruciate ligament graft following reconstruction: a longitudinal study

OBJECTIVE

To longitudinally monitor remodeling of human autograft following anterior cruciate ligament (ACL) reconstruction with DTI.

METHODS

Twenty-eight patients underwent DTI follow-up at 3, 8, and 14 months after clinically successful ACL reconstruction with tendon autograft. Among these, 18 patients had a concomitant lateral extra-articular procedure (LET). DTI data from 7 healthy volunteers was also obtained. Diffusion parameters (fractional anisotropy, FA; mean diffusivity, MD; axial diffusivity, AD; and radial diffusivity, RD) were evaluated within the fiber tractography volumes of the ACL graft and posterior cruciate ligament (PCL) in all patients. Data were analyzed using a linear mixed-effects model with post hoc testing using Bonferroni-Holm correction for multiple testing. The effect of additional LET was studied.

RESULTS

The ACL graft showed a significant decrease of FA over time (F = 4.00, p = 0.025), while the diffusivities did not significantly change over time. For PCL there were no significant DTI changes over time. A different evolution over time between patients with and without LET was noted for all diffusivity values of the ACL graft with reduced AD values in patients with LET at 8 months postoperatively (p = 0.048; adjusted p = 0.387). DTI metrics of the ACL graft differed largely from both native ACL and tendon at 14 months postoperatively.

CONCLUSION

Our study has shown the potential of DTI to longitudinally monitor the remodeling process in human ACL reconstruction. DTI analysis indicates that graft remodeling is incomplete at 14 months postoperatively.

KEY POINTS

• DTI can be used to longitudinally monitor the remodeling process in human ACL reconstruction. • DTI analysis indicates that autograft remodeling is incomplete at 14 months postoperatively. • DTI may be helpful for evaluating new ACL treatments.