Reliability of estimates of ACL attachment locations in 3-dimensional knee reconstruction based on routine clinical MRI in pediatric patients

Anterior cruciate ligament reconstruction related complications: 2D and 3D high-resolution magnetic resonance imaging evaluation

Anterior cruciate ligament (ACL) injury is a common indication for sports-related major surgery and accounts for a large proportion of ligamentous injuries in athletes. The advancements in 2D and 3D MR imaging have provided considerable potential for a one-stop shop radiation-free assessment with an all-in-one modality examination of the knee, for both soft-tissue and bone evaluations. This article reviews ACL injuries and types of surgical managements with illustrative examples using high resolution 2D and 3D MR imaging. Various complications of ACL reconstruction procedures are highlighted with a focus on the use of advanced MR imaging and relevant arthroscopic correlations.

Current trends in the anterior cruciate ligament part 1: biology and biomechanics

A trend within the orthopedic community is rejection of the belief that "one size fits all." Freddie Fu, among others, strived to individualize the treatment of anterior cruciate ligament (ACL) injuries based on the patient's anatomy. Further, during the last two decades, greater emphasis has been placed on improving the outcomes of ACL reconstruction (ACL-R). Accordingly, anatomic tunnel placement is paramount in preventing graft impingement and restoring knee kinematics. Additionally, identification and management of concomitant knee injuries help to re-establish knee kinematics and prevent lower outcomes and registry studies continue to determine which graft yields the best outcomes. The utilization of registry studies has provided several large-scale epidemiologic studies that have bolstered outcomes data, such as avoiding allografts in pediatric populations and incorporating extra-articular stabilizing procedures in younger athletes to prevent re-rupture. In describing the anatomic and biomechanical understanding of the ACL and the resulting improvements in terms of surgical reconstruction, the purpose of this article is to illustrate how basic science advancements have directly led to improvements in clinical outcomes for ACL-injured patients.Level of evidenceV.

Intra-and interobserver reliability of determining the femoral footprint of the torn anterior cruciate ligament on MRI scans

BACKGROUND

Re-injury rates following reconstruction of the anterior cruciate ligament (ACL) are significant; in more than 20% of patients a rupture of the graft occurs. One of the main reasons for graft failure is malposition of the femoral tunnel. The femoral origin of the torn ACL can be hard to visualize during arthroscopy, plus many individual variation in femoral origin anatomy exists, which may lead to this malpositioning. To develop a patient specific guide that may resolve this problem, a preoperative MRI is needed to identify the patient specific femoral origin of the ACL. The issue here is that there may be a difference in the reliability of identification of the femoral footprint of the ACL on MRI between different observers with different backgrounds and level of experience. The purpose of this study was to determine the intra- and interobserver reliability of identifying the femoral footprint of the torn ACL on MRI and to compare this between orthopedic surgeons, residents in orthopedic surgery and MSK radiologists.

METHODS

MR images of the knee joint were collected retrospectively from 20 subjects with a confirmed rupture of the ACL. The 2D (coronal, sagittal, transversal) proton-density (PD) images were selected for the segmentation procedure to create 3D models of the femurs. The center of the femoral footprint of the ACL on 20 MRI scans, with visual feedback on 3D models (as reference) was determined twice by eight observers. The intra- and interobserver reliability of determining the center of the femoral footprint on MRI was evaluated. Intraclass correlation coefficients (ICCs) were calculated for the X, Y and Z coordinates separately and for a 3D coordinate.

RESULTS

The mean 3D distance between the first and second assessment (intraobserver reliability) was 3.82 mm. The mean 3D distance between observers (interobserver reliability) was 8.67 mm. ICCs were excellent (> 0.95), except for those between the assessments of the two MSK radiologists of the Y and Z coordinates (0.890 and 0.800 respectively). Orthopedic surgeons outscored the residents and radiologists in terms of intra- and interobserver agreement.

CONCLUSION

Excellent intraobserver reliability was demonstrated (< 4 mm). However the results of the interobserver reliability manifested remarkably less agreement between observers (> 8 mm). An orthopedic background seems to increase both intra- and interobserver reliability. Preoperative planning of the femoral tunnel position in ACL reconstruction remains a surgical decision. Experienced orthopedic surgeons should be consulted when planning for patient specific instrumentation in ACL reconstruction.

Size and Shape of the Human Anterior Cruciate Ligament and the Impact of Sex and Skeletal Growth: A Systematic Review

BACKGROUND

High rates of anterior cruciate ligament (ACL) injury and surgical reconstruction in both skeletally immature and mature populations have led to many studies investigating the size and shape of the healthy ligament. The purposes of the present study were to compile existing quantitative measurements of the geometry of the ACL, its bundles, and its insertion sites and to describe effects of common covariates such as sex and age.

METHODS

A search of the Web of Science was conducted for studies published from January 1, 1900, to April 11, 2018, describing length, cross-sectional area, volume, orientation, and insertion sites of the ACL. Two reviewers independently screened and reviewed the articles to collect quantitative data for each parameter.

RESULTS

Quantitative data were collected from 92 articles in this systematic review. In studies of adults, reports of average ACL length, cross-sectional area, and volume ranged from 26 to 38 mm, 30 to 53 mm, and 854 to 1,858 mm, respectively. Reported values were commonly found to vary according to sex and skeletal maturity as well as measurement technique.

CONCLUSIONS

Although the geometry of the ACL has been described widely in the literature, quantitative measurements can depend on sex, age, and measurement modality, contributing to variability between studies. As such, care must be taken to account for these factors. The present study condenses measurements describing the geometry of the ACL, its individual bundles, and its insertion sites, accounting for common covariates when possible, to provide a resource to the clinical and scientific communities.

CLINICAL RELEVANCE

Quantitative measures of ACL geometry are informative for developing clinical treatments such as ACL reconstruction. Age and sex can impact these parameters.

Extra-articular, Intraepiphyseal Drilling for Osteochondritis Dissecans of the Knee: Characterization of a Safe and Reproducible Surgical Approach

Background:

Osteochondritis dissecans (OCD) is an idiopathic focal condition affecting the subchondral bone of joints, and it is increasingly prevalent among the active young adult population. For lesions that have failed nonoperative management, transarticular drilling and extra-articular drilling are surgical options. Although the extra-articular approach preserves the articular cartilage, it is technically challenging and could benefit from a study of surgical approach.

Purpose:

To use 3-dimensional modeling of magnetic resonance imaging (MRI) scans from skeletally immature individuals to characterize safe tunnel entry points, trajectories, and distances from the physeal and articular cartilage along the course of the distal femoral epiphysis to the OCD target in their most common location of the medial femoral condyle (MFC).

Study Design:

Descriptive laboratory study.

Methods:

A total of 17 MRI scans from skeletally immature patients were used to create 3-dimensional models of the knee joint. Virtual representations of an OCD lesion were placed in the lateral aspect of the MFC; cylinders simulating tunnel length, diameter, and trajectory were superimposed onto the models; and measurements were taken.

Results:

Two safe tunnels were identified, 1 anterior and 1 posterior to the medial collateral ligament (MCL). The anterior tunnel had a diameter of 10.3 ± 1.4 mm, skin entry point of 16.9 ± 12.1 mm anterior and 7.1 ± 5.9 mm superior to the medial epicondyle, bony entry point of 12.1 ± 3.5 mm anterior and 2.4 ± 3.5 mm inferior to the medial epicondyle, and tunnel length of 31.8 ± 3.7 mm. The posterior tunnel had a diameter of 7.8 ± 1.8 mm, skin entry point of 9.4 ± 5.1 mm posterior and 26.0 ± 14.0 mm superior to the medial epicondyle, bony entry point of 8.6 ± 2.6 mm posterior and 5.1 ± 4.2 mm superior to the medial epicondyle, and tunnel length of 33.5 ± 4.5 mm.

Conclusion:

This anatomic characterization study identifies and defines 2 safe and reproducible tunnel approaches, 1 anterior and 1 posterior to the MCL, for drilling or creating tunnels to OCD lesions of the MFC in an extra-articular fashion.

Clinical Relevance:

The study findings provide valuable anatomic references for surgeons performing extra-articular drilling or tunneling of OCD lesions.

Three-dimensional isotropic magnetic resonance imaging can provide a reliable estimate of the native anterior cruciate ligament insertion site anatomy

PURPOSE

This study quantified the error in anterior cruciate ligament (ACL) insertion site location and area estimated from three-dimensional (3D) isotropic magnetic resonance imaging (MRI) by comparing to native insertion sites determined via 3D laser scanning.

METHODS

Isotropic 3D DESS MRI was acquired from twelve fresh-frozen, ACL-intact cadaver knees. ACL insertion sites were manually outlined in each MRI slice, and the resulting contours combined to determine the 3D insertion site shape. Specimens were then disarticulated, and the boundaries of the ACL insertion sites were digitized using a high-accuracy laser scanner. MRI and laser scan insertion sites were co-registered to determine the percent overlapping area and difference in insertion centroid location.

RESULTS

Femoral ACL insertion site area averaged 112.7 ± 17.9 mm² from MRI and 109.7 ± 10.9 mm² from laser scan (p = 0.345). Tibial insertion area was 134.7 ± 22.9 mm² from MRI and 135.2 ± 15.1 mm² from laser scan (p = 0.881). Percentages of overlapping area between modalities were 82.2 ± 10.2% for femurs and 81.0 ± 9.0% for tibias. The root-mean-square differences for ACL insertion site centroids were 1.87 mm for femurs and 2.49 mm for tibias. The MRI-estimated ACL insertion site centroids were biased on average 0.6 ± 1.6 mm proximally and 0.3 ± 1.9 mm posteriorly for femurs, and 0.3 ± 1.1 mm laterally and 0.5 ± 1.5 mm anteriorly for tibias.

CONCLUSION

Errors in ACL insertion site location and area estimated from 3D-MRI were determined via comparison with a high-accuracy 3D laser scanning. Results indicate that MRI can provide estimates of ACL insertion site area and centroid location with clinically applicable accuracy. MRI-based assessment can provide a reliable estimate of the native ACL anatomy, which can be helpful for surgical planning as well as assessment of graft tunnel placement.

Tibial tunnel placement in anatomic anterior cruciate ligament reconstruction: a comparison study of outcomes between patient-specific drill template versus conventional arthroscopic techniques

INTRODUCTION

Accurate anatomic graft tunnel positioning is essential for the successful application of anatomic anterior cruciate ligament (ACL) reconstruction. The accurate insertion of the tibial tunnel (TT) remains challenging. Here, we explored a novel strategy of patient-specific drill template (PDT) for the placement of TT in ACL reconstruction and assessed its efficacy and accuracy.

MATERIALS AND METHODS

TT placement was randomized and performed by use of the PDT technique in 40 patients (PDT group) and the conventional arthroscopic technique in 38 patients (Arthroscopic group). After surgery, the deviations at the center point of the ACL tibial attachment area and radiological TT positioning were assessed in both groups. The preoperative and follow-up examinations included pivot-shift testing, KT-1000 arthrometer testing, the Lysholm and International Knee Documentation Committee scales were used to compare the knee stability and the functional state.

RESULTS

The ideal center points achieved in the PDT group were more precise than that in the arthroscopic group (p < 0.001). Radiological TT positioning performed by use of the PDT technique was more accurate than that by the arthroscopic technique (p = 0.027). Statistical differences could not be found between the groups in terms of the pivot-shift test, KT-1000 arthrometer laxity measurements, the Lysholm or International Knee Documentation Committee scales. Both groups improved at follow-up compared with the preoperative assessment in terms of the pivot-shift test, the laxity tests, and scoring scales.

CONCLUSIONS

The novel PDT strategy could provide more accurate TT positioning than the traditional arthroscopic technique in ACL reconstruction. However, functional scales and stability tests gave similar results in the PDT and the standard techniques.

LEVEL OF EVIDENCE

I.

A Validation Study of a Novel 3-Dimensional MRI Modeling Technique to Identify the Anatomic Insertions of the Anterior Cruciate Ligament

Background:

Anatomic single bundle anterior cruciate ligament (ACL) reconstruction is the current gold standard in ACL reconstructive surgery. However, placement of femoral and tibial tunnels at the anatomic center of the ACL insertion sites can be difficult intraoperatively. We developed a “virtual arthroscopy” program that allows users to identify ACL insertions on preoperative knee magnetic resonance images (MRIs) and generates a 3-dimensional (3D) bone model that matches the arthroscopic view to help guide intraoperative tunnel placement.

Purpose:

To test the validity of the ACL insertion sites identified using our 3D modeling program and to determine the accuracy of arthroscopic ACL reconstruction guided by our “virtual arthroscopic” model.

Study Design:

Descriptive laboratory study.

Methods:

Sixteen cadaveric knees were prescanned using routine MRI sequences. A trained, blinded observer then identified the center of the ACL insertions using our program. Eight knees were dissected, and the centers of the ACL footprints were marked with a screw. In the remaining 8 knees, arthroscopic ACL tunnels were drilled into the center of the ACL footprints based on landmarks identified using our virtual arthroscopic model. Postprocedural MRI was performed on all 16 knees. The 3D distance between pre- and postoperative 3D centers of the ACL were calculated by 2 trained, blinded observers and a musculoskeletal radiologist.

Results:

With 2 outliers removed, the postoperative femoral and tibial tunnel placements in the open specimens differed by 2.5 ± 0.9 mm and 2.9 ± 0.7 mm from preoperative centers identified on MRI. Postoperative femoral and tibial tunnel centers in the arthroscopic specimens differed by 3.2 ± 0.9 mm and 2.9 ± 0.7 mm, respectively.

Conclusion:

Our results show that MRI-based 3D localization of the ACL and our virtual arthroscopic modeling program is feasible and does not show a statistically significant difference to an open arthrotomy approach. However, additional refinements will be required to improve the accuracy and consistency of our model to make this an effective tool for surgeons performing anatomic single-bundle ACL reconstructions.

Clinical Relevance:

Arthroscopic anatomic single-bundle ACL reconstruction is the current gold standard for ACL reconstruction; however, the center of the ACL footprint can be difficult to identify arthroscopically. Our novel modeling can improve the identification of this important landmark intraoperatively and decrease the risk of graft malposition and subsequent graft failure.

Reliability of 3D localisation of ACL attachments on MRI: comparison using multi-planar 2D versus high-resolution 3D base sequences

PURPOSE

Anatomic placement of anterior cruciate ligament (ACL) grafts at arthroscopic reconstruction can be challenging. Localising ACL attachments on magnetic resonance imaging (MRI) sequences pre-operatively could aid with planning for anatomic graft placement. Though ACL attachments can be identified on two-dimensional (2D) MRI, slice thickness theoretically limits out-of-plane accuracy and a 3D MRI base sequence with smaller isotropic voxels may improve observer reliability in localising ACL attachment locations. The purpose of this study was to test whether a high-resolution 3D sequence improved inter- and intra-observer reliability of ACL attachment localisation compared with conventional 2D MRI for this application.

METHODS

Twenty paediatric knees were retrospectively scanned at 1.5 Tesla with multi-planar 2D proton density (slice thickness 3-4 mm) and T2-weighted 3D multiple-echo data image combination gradient echo (isotropic 0.8 mm voxels) sequences. Two observers blinded to each others' findings identified ACL attachments on MRI slices, and 3D reconstructions showing ACL attachments were produced. ACL attachment centre locations and areas were calculated, and reliability assessed.

RESULTS

Inter-observer variation of centre locations of ACL attachments identified on 3D versus 2D sequences was not significantly different (mean ± SD): 1.8 ± 0.6 versus 1.5 ± 0.7 mm at femoral attachments, 1.7 ± 0.7 versus 1.5 ± 0.8 mm at tibial attachments (p > 0.05). The 95 % confidence interval for centre locations was <4.0 mm in all cases. Inter-observer reliability of attachment areas was not higher for 3D sequences.

CONCLUSIONS

ACL attachment centres were localised with high and similar inter- and intra-observer reliability on a high-resolution 3D and multi-planar conventional 2D sequences. Using this technique, MRI could potentially be used for planning and intra-operative guidance of anatomic ACL reconstruction, whether from 2D or 3D base sequences. Surgeons in clinical practice need not order a lengthy dedicated 3D MRI to localise ligament attachments, but can confidently use a standard 2D MRI for this application.

LEVEL OF EVIDENCE

III.