Alison M. Biercevicz

In Situ, Noninvasive, T2*-Weighted MRI-Derived Parameters Predict Ex Vivo Structural Properties of an Anterior Cruciate Ligament Reconstruction or Bioenhanced Primary Repair in a Porcine Model

Background: Magnetic resonance imaging (MRI) is a noninvasive technology that can quantitatively assess anterior cruciate ligament (ACL) graft size and signal intensity. However, how those properties relate to reconstructed or repaired ligament strength during the healing process is yet unknown. Hypothesis: Magnetic resonance imaging–derived measures of graft volume and signal intensity are significant predictors of the structural properties of an ACL or ACL graft after 15 weeks and 52 weeks of healing. Study Design: Controlled laboratory study. Methods: The current data were gathered from 2 experiments evaluating ACL reconstruction and repair techniques. In the first experiment, pigs underwent unilateral ACL transection and received (1) ACL reconstruction, (2) ACL reconstruction with collagen-platelet composite (CPC), or (3) no treatment. The surgical legs were harvested after 15 weeks of healing. In the second experiment, pigs underwent ACL transection and received (1) ACL reconstruction, (2) ACL reconstruction with CPC, (3) bioenhanced ACL primary repair with CPC, or (4) no treatment. The surgical legs were harvested after 52 weeks. The harvested knees were imaged using a T2*-weighted 3-dimensional constructive interference in steady state (CISS) sequence. Each ligament was segmented from the scans, and the intra-articular volume and the median grayscale values were determined. Mechanical testing was performed to establish the ligament structural properties. Results: Volume significantly predicted the structural properties (maximum load, yield load, and linear stiffness) of the ligaments and grafts (R2 = 0.56, 0.56, and 0.49, respectively; P ≤ .001). Likewise, the median grayscale values (ie, signal intensity) significantly predicted the structural properties of the ligaments and grafts (R2 = 0.42, 0.37, and 0.40, respectively; P < .001). The combination of these 2 parameters in a multiple regression model improved the predictions (R2 = 0.73, 0.72, and 0.68, respectively; P ≤ .001). Conclusion: Volume and grayscale values from high-resolution T2*-weighted MRI scans are predictive of structural properties of the healing ligament or graft in a porcine model. Clinical Relevance: This study provides a critical step in the development of a noninvasive method to predict the structural properties of the healing ACL graft or repair. This technique may prove beneficial as a surrogate outcome measure in preclinical animal and clinical studies.

MRI Volume and Signal Intensity of ACL Graft Predict Clinical, Functional, and Patient-Oriented Outcome Measures After ACL Reconstruction

Background: Clinical, functional, and patient-oriented outcomes are commonly used to evaluate the efficacy of treatments after anterior cruciate ligament (ACL) injury; however, these evaluation techniques do not directly measure the biomechanical changes that occur with healing. Purpose: To determine if the magnetic resonance (MR) image–derived parameters of graft volume and signal intensity (SI), which have been used to predict the biomechanical (ie, structural) properties of the graft in animal models, correlate with commonly used clinical (anteroposterior [AP] knee laxity), functional (1-legged hop), and patient-oriented outcome measures (Knee Injury and Osteoarthritis Outcome Score [KOOS]) in patients 3 and 5 years after ACL reconstruction. Study Design: Cohort study (diagnosis); Level of evidence, 3. Methods: Based on a subset of participants enrolled in an ongoing ACL reconstruction clinical trial, AP knee laxity, 1-legged hop test, and KOOS were assessed at 3- and 5-year follow-up. Three-dimensional, T1-weighted MR images were collected at each visit. Both the volume and median SI of the healing graft were determined and used as predictors in a multiple regression linear model to predict the traditional outcome measures. Results: Graft volume combined with median SI in a multiple linear regression model predicted 1-legged hop test at both the 3- and 5-year follow-up visits (R 2 = 0.40, P = .008 and R 2 = 0.62, P = .003, respectively). Similar results were found at the 5-year follow-up for the KOOS quality of life (R 2 = 0.49, P = .012), sport/function (R 2 = 0.37, P = .048), pain (R 2 = 0.46, P = .017), and symptoms (R 2 = 0.45, P = .021) subscores, although these variables were not significant at 3 years. The multiple linear regression model for AP knee laxity at 5-year follow-up approached significance (R 2 = 0.36, P = .088). Conclusion: The MR parameters (volume and median SI) used to predict ex vivo biomechanical properties of the graft in an animal model have the ability to predict clinical or in vivo outcome measures in patients at 3- and 5-year follow-up. Clinical Relevance: Results from this study may enhance clinical evaluation of graft health by relating the MR parameters of volume and median SI to traditional outcome measures and could potentially aid researchers in determining the appropriate timing for athletes to return to sport.

T2* MR relaxometry and ligament volume are associated with the structural properties of the healing ACL

Our objective was to develop a non‐invasive magnetic resonance (MR) method to predict the structural properties of a healing anterior cruciate ligament (ACL) using volume and T2* relaxation time. We also compared our T2*‐based structural property prediction model to a previous model utilizing signal intensity, an acquisition‐dependent variable. Surgical ACL transection followed by no treatment (i.e., natural healing) or bio‐enhanced ACL repair was performed in a porcine model. After 52 weeks of healing, high‐resolution MR images of the ACL tissue were collected. From these images, ligament volumes and T2* maps were established. The structural properties of the ligaments were determined via tensile testing. Using the T2* histogram profile, each ligament voxel was binned based on its T2* value into four discrete tissue sub‐volumes defined by specific T2* intervals. The linear combination of the ligament sub‐volumes binned by T2* value significantly predicted maximum load, yield load, and linear stiffness (R2 = 0.92, 0.82, 0.88; p < 0.001) and were similar to the previous signal intensity based method. In conclusion, the T2* technique offers a highly predictive methodology that is a first step towards the development of a method that can be used to assess ligament healing across scanners, studies, and institutions.

Biomechanical Comparison of Parallel Versus 90-90 Plating of Bicolumn Distal Humerus Fractures With Intra-Articular Comminution

PURPOSE To compare the biomechanical properties of 90-90 versus mediolateral parallel plating of C-3 bicolumn distal humerus fractures. METHODS We created intra-articular AO/Orthopaedic Trauma Association C-3 bicolumn fractures in 10 fresh-frozen matched pairs of cadaveric elbows. We determined bone mineral density of the metaphyseal region with dual-energy x-ray absorptiometry. The matched pairs of elbows were randomly assigned to either 90-90 or parallel plate fixation. We tested anteroposterior displacement at a rate of 0.5 mm/s to a maximum load of ± 100 N for both the articular and entire distal humerus segments. We tested torsional stability at a displacement rate of 0.1 Hz to a maximum torque of ± 2.5 Nm. After cyclical testing, we loaded the specimens in torsion to failure. RESULTS There was no significant difference in the bone density of the paired specimens. Compared with parallel fixation, 90-90 plate fixation had significantly greater torque to failure load. Both plating constructs were equally sensitive to bone density. Both techniques had the same mode of failure in torsion, a spiral fracture extending from the medial plate at the metaphyseal-diaphyseal junction. There was no significant difference in the stiffness of fixation of the articular fragment or the entire distal segment in anteroposterior loading. CONCLUSIONS This study demonstrated that 90-90 and parallel plating had comparable biomechanical properties for fixation of comminuted intra-articular distal humerus fractures, and that 90-90 plating had greater resistance to torsional loading.

T2* Relaxometry and Volume Predict Semi-Quantitative Histological Scoring of an ACL Bridge-enhanced Primary repair in a Porcine Model

Magnetic resonance imaging (MRI) variables, such as T2* and volume, can predict the healing ligament structural properties. How these MR variables relate to semi‐quantitative histology of the healing ACL is yet unknown. We hypothesized that T2* and volume would predict the histological scoring of a healing ACL. Yucatan minipigs underwent ACL transection and received bridge‐enhanced ACL repair or no treatment. The surgical legs were harvested after 52 weeks and imaged using a high resolution 2‐echo sequence. For each ligament, the volume and median T2* values were determined. The ACL specimens were then histologically analyzed using the advanced Ligament Maturity Index (LMI). The T2* of the healing ligaments significantly predicted the total LMI score as well as the cell, collagen and vessel sub‐scores; R2 = 0.78, 0.67, 0.65, and 0.60, respectively (p ≤ 0.001). The ligament volume also predicted the total LMI score, cell, and collagen sub‐scores; R2 = 0.39, 0.33, 0.37, and 0.60, respectively (p ≤ 0.001). A lower ligament T2* or a higher volume was associated with higher histological scores of the healing ligaments. This study provides a critical step in the development of a non‐invasive method to evaluate ligament healing on a microscopic scale.

Examination of cervical spine kinematics in complex, multiplanar motions after anterior cervical discectomy and fusion and total disc replacement

Background The biomechanical behavior of total disc replacement (TDR) and anterior cervical discectomy and fusion (ACDF) incomplex multiplanar motion is incompletely understood. The purpose of this study was to determine whether ACDF or TDR significantly affects in vitro kinematics through a range of complex, multiplanar motions. Methods Seven human cervical spines from C4-7 were used for this study. Intact cervical motion segments with and without implanted TDR and ACDF were tested by use of unconstrained pure bending moment testing fixtures in 7 mechanical modes: axial rotation (AR); flexion/extension (FE); lateral bending (LB); combined FE and LB; combined FE and AR; combined LB and AR; and combined FE, LB, and AR. Statistical testing was performed to determine whether differences existed in range of motion (ROM) and stiffness among spinal segments and treatment groups for each mechanical test mode. Results ACDF specimens showed increased stiffness compared with the intact and TDR specimens (P < .001); stiffness was not found to be different between TDR and intact specimens. ACDF specimens showed decreased ROM in all directions compared with TDR and intact specimens at the treated level. For the coupled motion test, including AR, LB, and FE, the cranial adjacent level (C4/C5) for the intact specimens (2.7°) showed significantly less motion compared with both the TDR (6.1°, P = .009) and ACDF (6.8°, P = .002) treatment groups about the LB axis. Testing of the C4/C5 and C6/C7 levels in all other test modes yielded no significant differences in ROM comparisons, although a trend toward increasing ROM in adjacent levels in ACDF specimens compared with intact and TDR specimens was observed. Conclusions This study compared multiplanar motion under load-displacement testing of subaxial cervical motion segments with and without implanted TDR and ACDF. We found a trend toward increased motion in adjacent levels in ACDF specimens compared with TDR specimens. Biomechanical multiplanar motion testing will be useful in the ongoing development and evaluation of spinal motion–preserving implants.

The uncertainty of predicting intact anterior cruciate ligament degeneration in terms of structural properties using T 2 relaxometry in a human cadaveric model

The combination of healing anterior cruciate ligament (ACL) volume and the distributions of T2(*) relaxation times within it have been shown to predict the biomechanical failure properties in a porcine model. This MR-based prediction model has not yet been used to assess ligament degeneration in the aging human knee. Using a set of 15 human cadaveric knees of varying ages, we obtained in situ MR measures of volume and T2(*) of the intact ACL and then related these MR variables to biomechanical outcomes (maximum and yield loads, linear stiffness) obtained via ex vivo failure testing. Using volume in conjunction with the median T2(*) value, the multiple linear regression model did not predict maximum failure load for the intact human ACL; R(2)=0.23, p=0.200. Similar insignificant results were found for yield load and linear stiffness. Naturally restricted distributions of the intact ligament volume and T2(*) (demonstrated by the respective Z-scores) in an older cadaveric population were the likely reason for the insignificant results. These restricted distributions may negatively affect the ability to detect a correlation when one exists. Further research is necessary to understand the relationship of MRI variables and ligament degeneration. While this study failed to find a significant prediction of human biomechanical outcome using these MR variables, with further research, an MR-based approach may offer a tool to longitudinally assess changes in cruciate ligament degradation.

A Biomechanical Comparison of a Novel Expandable Photodynamic Intramedullary System to a Metal Plate and Screw System in Humerus and Femur Osteotomy Models

The biomechanical performance of a locking compression plate system was compared to an intramedullary photodynamic bone stabilization system in a femur and humerus osteotomy model. The photodynamic bone stabilization system utilizes an angioplasty-like balloon that is introduced into the intramedullary canal of a fractured bone, filled with monomer that is then polymerized and hardened by visible blue light delivered through an optical fiber. This system has been in clinical use since 2010. Synthetic bones engineered to mimic the biomechanical properties of natural bone were cut to produce a 10 mm defect mid-shaft, and two groups of specimens were stabilized by either the compression plate or intramedullary photodynamic bone stabilization system. For each bone model, one locking compression plate system was used, and three different diameter intramedullary photodynamic bone stabilization implants were used. Experimental groups were tested for stiffness, peak load, yield load, peak displacement and yield displacement when a load was applied. Additional samples per experimental group were tested for long-term dynamic stability by cyclically loading until failure. It was found that in all biomechanical parameters measured, the 17 mm intramedullary photodynamic bone stabilization system exceeded the mechanical strength and durability of the locking compression plate system in the femur osteotomy model. It was found that in all biomechanical parameters measured, the 15 mm intramedullary photodynamic bone stabilization system performed equivalently or exceeded the mechanical strength and durability of the locking compression plate system. This testing combined with long-term clinical use, and in vivo data from a large animal model, suggest that femur fixation by an intramedullary photodynamic bone stabilization system will provide equivalent biomechanical properties to a locking compression plate once implanted.