Predicting Leg Forces and Knee Moments Using Inertial Measurement Units: An In Vitro Study.

We compared the ability of seven machine learning algorithms to use wearable inertial measurement unit (IMU) data to identify the severe knee loading cycles known to induce microdamage associated with anterior cruciate ligament rupture. Sixteen cadaveric knee specimens, dissected free of skin and muscle, were mounted in a rig simulating standardized jump landings. One IMU was located above and the other below the knee, the applied three-dimensional action and reaction loads were measured via six-axis load cells, and the three-dimensional knee kinematics were also recorded by a laboratory motion capture system. Machine learning algorithms were used to predict the knee moments and the tibial and femur vertical forces; 13 knees were utilized for training each model, while three were used for testing its accuracy (i.e., normalized root-mean-square error) and reliability (Bland-Altman limits of agreement). The results showed the models predicted force and knee moment values with acceptable levels of error and, although several models exhibited some form of bias, acceptable reliability. Further research will be needed to determine whether these types of models can be modified to attenuate the inevitable in vivo soft tissue motion artifact associated with highly dynamic activities like jump landings.

Neo-Natal Castration Leads to Subtle Differences in Porcine Anterior Cruciate Ligament Morphology and Function in Adolescence.

Female adolescent athletes are at a higher risk of tearing their anterior cruciate ligament (ACL) than male counterparts. While most work related to hormones has focused on the effects of estrogen to understand the increased risk of ACL injury, there are other understudied factors, including testosterone. The purpose of this study was to determine how surgical castration in the male porcine model influences ACL size and function across skeletal growth. Thirty-six male Yorkshire crossbreed pigs were raised to 3 (juvenile), 4.5 (early adolescent), and 6 months (adolescent) of age. Animals were either castrated (barrows) within 2 weeks after birth or were left intact (boars). Posteuthanasia, joint and ACL size were assessed via MRI, and biomechanics were assessed via a robotic testing system. Joint size increased throughout age, yet barrows had smaller joints than boars. ACL cross-sectional area (CSA), length, volume, and in situ stiffness increased with age, as did the percent contribution of the ACL anteromedial (AM) bundle to resisting loads. Boar ACL, AM bundle, and PL bundle volumes were 19%, 25%, and 15% larger than barrows across ages. However, ACL CSA, in situ stiffness, and bundle contribution were similar between boars and barrows. The barrows had smaller temporal increases in AM bundle function than boars, but these data were highly variable. Early and sustained loss in testosterone leads to subtle differences in ACL morphology but may not influence measures associated with increased injury risk, such as CSA or bundle forces in response to applied loads.

Computational study of extrinsic factors affecting ACL strain during single-leg jump landing.

BACKGROUND: Non-contact anterior cruciate ligament (ACL) injuries are a major concern in sport-related activities due to dynamic knee movements. There is a paucity of finite element (FE) studies that have accurately replicated the knee geometry, kinematics, and muscle forces during dynamic activities. The objective of this study was to develop and validate a knee FE model and use it to quantify the relationships between sagittal plane knee kinematics, kinetics and the resulting ACL strain. METHODS: 3D images of a cadaver knee specimen were segmented (bones, cartilage, and meniscus) and meshed to develop the FE model. Knee ligament insertion sites were defined in the FE model via experimental digitization of the specimen's ligaments. The response of the model was validated against multiple physiological knee movements using published experimental data. Single-leg jump landing motions were then simulated on the validated model with muscle forces and kinematic inputs derived from motion capture and rigid body modelling of ten participants. RESULTS: The maximum ACL strain measured with the model during jump landing was 3.5 ± 2.2%, comparable to published experimental results. Bivariate analysis showed no significant correlation between body weight, ground reaction force and sagittal plane parameters (such as joint flexion angles, joint moments, muscle forces, and joint velocity) and ACL strain. Multivariate regression analysis showed increasing trunk, hip and ankle flexion angles decreases ACL strain (R2 = 90.04%, p < 0.05). CONCLUSIONS: Soft landing decreases ACL strain and the relationship could be presented through an empirical equation. The model and the empirical relation developed in this study could be used to better predict ACL injury risk and prevention strategies during dynamic activities.

Unanticipated mid-flight external trunk perturbation increased frontal plane ACL loading variables during sidestep cuttings.

Unanticipated trunk perturbation is commonly observed when anterior cruciate ligament (ACL) injuries occur during direction-changing manoeuvres. This study aimed to quantify the effect of mid-flight medial-lateral external trunk perturbation directions/locations on ACL loading variables during sidestep cuttings. Thirty-two recreational athletes performed sidestep cuttings under combinations of three perturbation directions (no-perturbation, ipsilateral-perturbation, and contralateral-perturbation relative to the cutting leg) and two perturbation locations (upper-trunk versus lower-trunk). The pushing perturbation was created by customised devices releasing a slam ball to contact participants near maximum jump height prior to cutting. Perturbation generally resulted in greater peak vertical ground reaction force and slower cutting velocity. Upper-trunk contralateral perturbation showed the greatest lateral trunk bending away from the travel direction, greatest peak knee flexion and abduction angles, and greatest peak internal knee adduction moments compared to other conditions. Such increased ACL loading variables were likely due to the increased lateral trunk bending and whole-body horizontal velocity away from the cutting direction caused by the contralateral perturbation act at the upper trunk. The findings may help understand the mechanisms of indirect contact ACL injuries and develop effective cutting techniques for ACL injury prevention.

Effect of Hamstring-to-quadriceps Ratio on Knee Forces in Females During Landing.

ACL injuries in the athletic population are a common occurrence with over 70% associated with non-contact mechanisms. The hamstring to quadriceps ratio is a widely used clinical measure to assess an athlete's readiness to return to sport; however, its relationship to knee forces and ACL tension during landing is unknown. Baseline isokinetic testing was completed on 100 college-aged females. Subjects with strength ratios 0.4 (n=20) and those with ratios of 0.6 (n=20) returned for an assessment of their drop landing. A sagittal plane knee model determined the low ratio group demonstrated 16.6% larger ligament shear (p=0.000), a 26% increase in tibiofemoral shear force (p=0.026) and a 6% increase vertical force between the femur and tibial plateau (p=0.026) compared to the high hamstring ratio group within 100 ms upon impact. The lower ratio group also demonstrated 9.5% greater maximal quadriceps (p=0.028) force during landing. These findings suggest that the hamstring to quadriceps ratio may be related to knee forces and ACL loading during landing. This metric may augment clinical decision making regarding an athlete's readiness to return to sport or relative risk for re-injury.

Maintenance of Ligament Homeostasis of Spheroid-Colonized Embroidered and Functionalized Scaffolds after 3D Stretch.

Anterior cruciate ligament (ACL) ruptures are usually treated with autograft implantation to prevent knee instability. Tissue engineered ACL reconstruction is becoming promising to circumvent autograft limitations. The aim was to evaluate the influence of cyclic stretch on lapine (L) ACL fibroblasts on embroidered scaffolds with respect to adhesion, DNA and sulphated glycosaminoglycan (sGAG) contents, gene expression of ligament-associated extracellular matrix genes, such as type I collagen, decorin, tenascin C, tenomodulin, gap junctional connexin 43 and the transcription factor Mohawk. Control scaffolds and those functionalized by gas phase fluorination and cross-linked collagen foam were either pre-cultured with a suspension or with spheroids of LACL cells before being subjected to cyclic stretch (4%, 0.11 Hz, 3 days). Stretch increased significantly the scaffold area colonized with cells but impaired sGAGs and decorin gene expression (functionalized scaffolds seeded with cell suspension). Stretching increased tenascin C, connexin 43 and Mohawk but decreased decorin gene expression (control scaffolds seeded with cell suspension). Pre-cultivation of functionalized scaffolds with spheroids might be the more suitable method for maintaining ligamentogenesis in 3D scaffolds compared to using a cell suspension due to a significantly higher sGAG content in response to stretching and type I collagen gene expression in functionalized scaffolds.

Effects of Voluntary Quadriceps-Hamstring Cocontraction on Tibiofemoral Force During Isometric Knee Extension and Knee Flexion Exercises With Constant External Resistance.

A biomechanical model has been developed to assess the effects of a voluntary effort of quadriceps-hamstring cocontraction on tibiofemoral force during isometric knee flexion and knee extension exercises with constant external resistance. The model establishes the analytic condition in the moment arms and traction angles of the quadriceps and hamstring muscles that determines the direction (anterior/posterior) of the tibiofemoral shear force developed by the cocontraction. This model also establishes the mechanical effect (loading/unloading) on the anterior cruciate ligament (ACL). At about 15° of knee flexion (where the ACL experiences its maximum quadriceps-induced strain) a voluntary quadriceps-hamstring cocontraction effort yields: (1) nearly the same enhancement in hamstring and quadriceps activation, (2) an increase in hamstring force about 1.5 times higher than that of the quadriceps, and (3) posterior (ACL unloading) tibial pull and compressive tibiofemoral force that increase linearly with the level of quadriceps and hamstring activation. The sensitivity of the results to intersubject variability in the posterior slope of the tibial plateau and muscle moment arms has been estimated with the use of anatomic data available in the literature. An anterior (ACL loading) tibial pull is actually developed at 15° of knee flexion by a voluntary effort of quadriceps-hamstring cocontraction as the posterior tibial slope exceeds 14°.

An exploratory study of the use of ultrasound in the measurement of anterior tibial translation under gastrocnemius muscle stimulation.

Gastrocnemius' role as an agonist or antagonist of the anterior cruciate ligament (ACL) is not well understood. This study explored the use of ultrasound imaging to investigate how gastrocnemius stimulation levels influenced anterior tibial translation. The gastrocnemii of 10 participants were stimulated to four different levels using electrical muscle stimulation. The quadriceps were co-activated at a fixed level. Anterior tibial translation was determined using ultrasound imaging. Intraclass correlation coefficient [ICC (2,1)] was used to assess the intra-rater reliability over two sessions. Intra-rater reliability was good at rest and under most muscle stimulation levels (ICC = 0.84 to 0.92), and moderate with the lowest (ICC = 0.71) and highest stimulation (ICC = 0.61). While anterior tibial translation was not significantly different across simulation levels, ultrasound imaging recorded the anterior movement of the tibia as the gastrocnemius was activated, thus supporting gastrocnemius' role as an antagonist of the ACL.

The femoral posterior fan-like extension of the ACL insertion increases the failure load.

PURPOSE: To examine the role of the posterior fan-like extension of the ACL's femoral footprint on the ACL failure load. METHODS: Sixteen (n = 16) fresh frozen, mature porcine knees were used in this study and randomized into two groups (n = 8): intact femoral ACL insertion (ACL intact group) and cut posterior fan-like extension of the ACL (ACL cut group). In the ACL cut group, flexing the knees to 90°, created a folded border between the posterior fan-like extension and the midsubstance insertion of the femoral ACL footprint and the posterior fan-like extension was dissected and both areas were measured. Specimens were placed in a testing machine at 30° of flexion and subjected to anterior tibial loading (60 mm/min) until ACL failure. RESULTS: The intact ACL group had a femoral insertion area of 182.1 ± 17.1 mm2. In the ACL cut group, the midsubstance insertion area was 113.3 ± 16.6 mm2, and the cut posterior fan-like extension portion area was 67.1 ± 8.3 mm2. The failure load of the ACL intact group was 3599 ± 457 N and was significantly higher (p < 0.001) than the failure load of the ACL cut group 392 ± 83 N. CONCLUSION: Transection of the posterior fan-like extension of the ACL femoral footprint has a significant effect on the failure load of the ligament during anterior loading at full extension. Regarding clinical relevance, this study suggests the importance of the posterior fan-like extension of the ACL footprint which potentially may be retained with remnant preservation during ACL reconstruction. Femoral insertion remnant preservation may allow incorporation of the fan-like structure into the graft increasing graft strength.

In vivo kinematics and ligamentous function of the knee during weight-bearing flexion: an investigation on mid-range flexion of the knee.

PURPOSE: To investigate the in vivo femoral condyle motion and synergistic function of the ACL/PCL along the weight-bearing knee flexion. METHODS: Twenty-two healthy human knees were imaged using a combined MRI and dual fluoroscopic imaging technique during a single-legged lunge (0°-120°). The medial and lateral femoral condyle translation and rotation (measured using geometric center axis-GCA), and the length changes of the ACL/PCL were analyzed at: low (0°-30°), mid-range (30°-90°) and high (90°-120°) flexion of the knee. RESULTS: At low flexion (0°-30°), the strains of the ACL and the posterior-medial bundle of the PCL decreased. The medial condyle showed anterior translation and lateral condyle posterior translation, accompanied with a sharp increase in external GCA rotation (internal tibial rotation). As the knee continued flexion in mid-range (30°-90°), both ACL and PCL were slack (with negative strain values). The medial condyle moved anteriorly before 60° of flexion and then posteriorly, accompanied with a slow increase of GCA rotation. As the knee flexed in high flexion (90°-120°), only the PCL had increasingly strains. Both medial and lateral condyles moved posteriorly with a rather constant GCA rotation. CONCLUSIONS: The ACL and PCL were shown to play a reciprocal and synergistic role during knee flexion. Mid-range reciprocal anterior-posterior femoral translation or laxity corresponds to minimal constraints of the ACL and PCL, and may represent a natural motion character of normal knees. The data could be used as a valuable reference when managing the mid-range "instability" and enhancing high flexion capability of the knee after TKAs. LEVEL OF EVIDENCE: Level IV.

Validation of a Device to Measure Knee Joint Angles for a Dynamic Movement.

Participation in sports has risen in the United States over the last few years, increasing the risk of injuries such as tears to the anterior cruciate ligament (ACL) in the knee. Previous studies have shown a correlation between knee kinematics when landing from a jump and this injury. The purpose of this study was to validate the ability of a commercially available inertial measurement units (IMUs) to accurately measure knee joint angles during a dynamic movement. Eight healthy subjects participated in the study. Validation was performed by comparing the angles measured by the wearable device to those obtained through the gold standard motion capture system when landing from a jump. Root mean square, linear regression analysis, and Bland-Altman plots were performed/constructed. The mean difference between the wearable device and the motion capture data was 8.4° (flexion/extension), 4.9° (ab/adduction), and 3.9° (rotation). In addition, the device was more accurate at smaller knee angles. In our study, a commercially available wearable IMU was able to perform fairly well under certain conditions and was less accurate in other conditions.

Effect of stifle flexion on the position of the cranial tibial artery relative to the proximal tibia in dogs.

OBJECTIVE: To determine the effect of stifle flexion on the proximity of the cranial tibial artery to the proximal tibia in canine stifles with an intact or transected cranial cruciate ligament (CCL). STUDY DESIGN: Ex vivo randomized blinded computed tomographic angiographic study. SAMPLE POPULATION: Fifteen pelvic limbs from eight greyhound cadavers. METHODS: The femoral artery and vein were cannulated and injected with 10 mL of iohexol. Each limb was placed in lateral recumbency on an acrylic sheet with predrawn femoral and tibial lines representing angles of stifle extension. Computed tomography was performed before (limbs 1-15) and after (limbs 10-15) CCL transection. The shortest distance between the cranial tibial artery and proximal tibia (dCrTA-PT) was measured at a distance of one patellar length from medial intercondylar tubercle. RESULTS: Median dCrTA-PT in intact specimens at 70°, 90°, 110°, and 135° was 2.04, 2.05, 2.28, and 2.51 mm, respectively (P = .008). Pairwise comparisons identified a difference between 70° and 135° (P = .007). Mean dCrTA-PT in transected specimens at 70°, 90°, 110°, and 135° was 2.60, 2.57, 2.90, and 2.79 mm, respectively (P = .208). Median overall dCrTA-PT was 2.24 mm in intact specimens (limbs 1-15, all four angles of extension combined) and 2.76 mm in transected specimens (limbs 10-15, all angles combined; P = .01). CONCLUSION: Flexion of the stifle resulted in a negligible decrease in dCrTA-PT in intact specimens but had no effect in CCL transected stifles. CLINICAL SIGNIFICANCE: The angle of stifle extension does not appear to have any clinically significant effect on the proximity of cranial tibial artery to the proximal tibia.

[Internal meniscus resections do not affect anterior knee joint stability]. / Innenmeniskusresektionen beeinflussen nicht die anteriore Kniegelenksstabilität.

BACKGROUND: Meniscus injuries lead to increased knee joint instability. Currently, however, it is unclear whether a relevant medial meniscus part resection leads to an increased ventral tibia translation with intact anterior cruciate ligament. The aim of our study was therefore to clinically examine the stabilizer function of at least 30% resected medial meniscus for anterior tibial translation. MATERIALS AND METHODS: In this prospective study, 18 patients with unilateral medial meniscus lesion were treated before and after arthroscopic medial meniscus resection. They were treated on the healthy and on the sick leg through the use of two different apparatus methods (dynamic translation measurement using hamstring reflex apparatus and KT-1000 arthrometers) as well as a functional test (computer-supported dynamic posturography (CDP)) and a clinical hop test. Further, the mean values for significance using non-parametric Wilcoxon test. RESULTS: After completing all the studies, we were not able to detect any significant differences in our study that would indicate increased ventral instability in the knee joint after arthroscopic medial meniscus resection. CONCLUSIONS: Inner meniscal partial resection does not lead to increased ventral knee instability in intact VKB. Whether in patients with instability (feeling) after partial meniscus resection, a rotation instability is the cause or whether further injuries or disturbances in the capsular ligament apparatus are present, must be examined in further studies. Anterior knee joint instability cannot be adequately explained according to our study.

Reliability of Knee Flexion-Extension Lyapunov Exponent in People With and Without Anterior Cruciate Ligament Deficiency.

OBJECTIVES: The current study assessed the intrasession and intersession reliability of the knee flexion-extension Lyapunov exponent in patients with anterior cruciate ligament deficiency and healthy individuals. STUDY DESIGN: University research laboratory. METHODS: Kinematic data were collected in 14 patients with anterior cruciate ligament deficiency and 14 healthy individuals walked on a treadmill at a self-selected, low, and high speed, with and without cognitive load. The intraclass correlation coefficient, standard error of measurement, minimal metrically detectable change, and percentage of coefficient of variation were calculated to assess the reliability. RESULTS: The knee flexion-extension Lyapunov exponent had high intrasession reliability, with intraclass correlation coefficients ranging from .83 to .98. In addition, the intersession intraclass correlation coefficient values of these measurements ranged from .35 to .85 regardless of group, gait speed, and dual tasking. In general, relative and absolute reliability were higher in the patients with anterior cruciate ligament deficiency than in the healthy individuals. CONCLUSIONS: Although knee flexion-extension Lyapunov exponent demonstrates good intrasession reliability, its low intersession reliability indicates that changes of these measurements between different days should be interpreted with caution.

Silk enhances the ligamentization of the polyethylene terephthalate artificial ligament in a canine anterior cruciate ligament reconstruction model.

Anterior cruciate ligament (ACL) reconstruction is the leading treatment for ACL rupture. Ligament Advanced Reinforcement System (LARS), which is made of polyethylene terephthalate (PET), is the most frequently used artificial ligament for ACL reconstruction. However, PET is hydrophobic, so it is difficult to induce the ingrowth of the autologous tissue. The aim of this study is to explore the effects of silk hybrid on the ligamentization of the PET artificial ligament in a canine ACL reconstruction model. Silk/PET hybrid suspensory ligament was fabricated with silk in the weft yarn and PET in the warp yarn, while PET suspensory ligament was fabricated with PET in both the weft and warp yarns. After fabrication, the micromorphology of the ligaments was observed and mechanical testing was performed. Though the failure loads of the degummed silk/PET hybrid suspensory ligaments were significantly lower than those of the PET suspensory ligaments (P < 0.001), both of them were enough for ACL reconstructions of beagle dogs. In the animal study, 14 beagle dogs were divided into PET suspensory ligament group and silk/PET hybrid suspensory ligament group randomly, with 7 dogs in each. The dogs underwent ACL reconstructions in their right knees. At postoperative 6 months, the dogs were sacrificed, and the specimens were evaluated with gross observation, histology, immunohistochemistry, and mechanical testing. The histological and immunohistochemical results showed that the native ACL of the beagle dog held abundant fibroblasts and collagen. The PET-regenerated ligament was loose, and there was a small amount of autologous tissue and collagen. Compared to the PET-regenerated ligament, the silk/PET hybrid-regenerated ligament had a compact structure, and there was more regenerated autologous tissue and collagen. In conclusion, compared to the PET ligament, the silk/PET hybrid ligament kept greater ability to induce the ingrowth of the autologous tissue, indicating that the silk hybrid had enhanced the ligamentization of the PET artificial ligament.

Biomechanical Function and Size of the Anteromedial and Posterolateral Bundles of the ACL Change Differently with Skeletal Growth in the Pig Model.

BACKGROUND: ACL injuries are becoming increasingly common in children and adolescents, but little is known regarding age-specific ACL function in these patients. To improve our understanding of changes in musculoskeletal tissues during growth and given the limited availability of pediatric human cadaveric specimens, tissue structure and function can be assessed in large animal models, such as the pig. QUESTIONS/PURPOSES: Using cadaveric porcine specimens ranging throughout skeletal growth, we aimed to assess age-dependent changes in (1) joint kinematics under applied AP loads and varus-valgus moments, (2) biomechanical function of the ACL under the same loads, (3) the relative biomechanical function of the anteromedial and posterolateral bundles of the ACL; and (4) size and orientation of the anteromedial and posterolateral bundles. METHODS: Stifle joints (analogous to the human knee) were collected from female Yorkshire crossbreed pigs at five ages ranging from early youth to late adolescence (1.5, 3, 4.5, 6, and 18 months; n = 6 pigs per age group, 30 total), and MRIs were performed. A robotic testing system was used to determine joint kinematics (AP tibial translation and varus-valgus rotation) and in situ forces in the ACL and its bundles in response to applied anterior tibial loads and varus-valgus moments. To see if morphological changes to the ACL compared with biomechanical changes, ACL and bundle cross-sectional area, length, and orientation were calculated from MR images. RESULTS: Joint kinematics decreased with increasing age. Normalized AP tibial translation decreased by 44% from 1.5 months (0.34 ± 0.08) to 18 months (0.19 ± 0.02) at 60° of flexion (p < 0.001) and varus-valgus rotation decreased from 25° ± 2° at 1.5 months to 6° ± 2° at 18 months (p < 0.001). The ACL provided the majority of the resistance to anterior tibial loading at all age groups (75% to 111% of the applied anterior force; p = 0.630 between ages). Anteromedial and posterolateral bundle function in response to anterior loading and varus torque were similar in pigs of young ages. During adolescence (4.5 to 18 months), the in situ force carried by the anteromedial bundle increased relative to that carried by the posterolateral bundle, shifting from 59% ± 22% at 4.5 months to 92% ± 12% at 18 months (data for 60° of flexion, p < 0.001 between 4.5 and 18 months). The cross-sectional area of the anteromedial bundle increased by 30 mm throughout growth from 1.5 months (5 ± 2 mm) through 18 months (35 ± 8 mm; p < 0.001 between 1.5 and 18 months), while the cross-sectional area of the posterolateral bundle increased by 12 mm from 1.5 months (7 ± 2 mm) to 4.5 months (19 ± 5 mm; p = 0.004 between 1.5 and 4.5 months), with no further growth (17 ± 7 mm at 18 months; p = 0.999 between 4.5 and 18 months). However, changes in length and orientation were similar between the bundles. CONCLUSION: We showed that the stifle joint (knee equivalent) in the pig has greater translational and rotational laxity in early youth (1.5 to 3 months) compared with adolescence (4.5 to 18 months), that the ACL functions as a primary stabilizer throughout growth, and that the relative biomechanical function and size of the anteromedial and posterolateral bundles change differently with growth. CLINICAL RELEVANCE: Given the large effects observed here, the age- and bundle-specific function, size, and orientation of the ACL may need to be considered regarding surgical timing, graft selection, and graft placement. In addition, the findings of this study will be used to motivate pre-clinical studies on the impact of partial and complete ACL injuries during skeletal growth.

Development of fibrocartilage layers in the anterior cruciate ligament insertion in rabbits.

BACKGROUND: A detailed evaluation focusing on the fibrocartilage layers in the anterior cruciate ligament (ACL) insertion is necessary to consider regeneration of the insertion. This study examined the development of the fibrocartilage layers in the ACL tibial insertion in rabbits by quantitative morphometric evaluations based on histological and immunohistochemical analyses. METHODS: Male Japanese white rabbits were used because of their history of use for histomorphometric analyses of the ACL insertion and to eliminate the influence of female hormones on the ACL. Six animals were euthanized at each age (1 day and 1, 2, 4, 6, 8, 12, and 24 weeks); in total, 48 animals were used. Proliferation rate, apoptosis rate, Sox9-positive rate, and chondrocyte number were evaluated. Safranin O-stained glycosaminoglycan (GAG) areas, tidemark length, ACL insertion width, and ACL length were also evaluated. All parameters were compared with those at age 24 weeks of age. RESULTS: High levels of chondrocyte proliferation and Sox9 expression continued until 4 and 8 weeks of age, respectively, and then gradually decreased. Chondrocyte apoptosis increased up to 8 weeks. The chondrocyte number, ACL insertion width, ACL length, safranin O-stained GAG areas, and tidemark length gradually increased up to 12 weeks. CONCLUSION: Chondrocytes that displayed chondrocyte proliferation and Sox9 expression increased until 12 weeks of age, in accordance with development of the ACL length and its insertion width. The GAG production and tidemark length also increased until 12 weeks of age. The development of fibrocartilage layers in the ACL insertion was complete at 12 weeks of age.

Abbreviated quantitative UTE imaging in anterior cruciate ligament reconstruction.

BACKGROUND: Existing ultrashort echo time magnetic resonance imaging (UTE MRI) methods require prohibitively long acquisition times (~ 20-40 min) to quantitatively assess the clinically relevant fast decay T2* component in ligaments and tendons. The purpose of this study was to evaluate the feasibility and clinical translatability of a novel abbreviated quantitative UTE MRI paradigm for monitoring graft remodeling after anterior cruciate ligament (ACL) reconstruction. METHODS: Eight patients who had Graftlink™ hamstring autograft reconstruction were recruited for this prospective study. A 3D double-echo UTE sequence at 3.0 Tesla was performed at 3- and 6-months post-surgery. An abbreviated UTE MRI paradigm was established based on numerical simulations and in vivo validation from healthy knees. This proposed approach was used to assess the T2* for fast decay component ([Formula: see text]) and bound water signal fraction (fbw) of ACL graft in regions of interest drawn by a radiologist. RESULTS: Compared to the conventional bi-exponential model, the abbreviated UTE MRI paradigm achieved low relative estimation bias for [Formula: see text] and fbw over a range of clinically relevant values for ACL grafts. A decrease in [Formula: see text] of the intra-articular graft was observed in 7 of the 8 ACL reconstruction patients from 3- to 6-months (- 0.11 ± 0.16 ms, P = 0.10). Increases in [Formula: see text] and fbw from 3- to 6-months were observed in the tibial intra-bone graft ([Formula: see text]: 0.19 ± 0.18 ms, P < 0.05; Δfbw: 4% ± 4%, P < 0.05). Lower [Formula: see text] (- 0.09 ± 0.11 ms, P < 0.05) was observed at 3-months when comparing the intra-bone graft to the graft/bone interface in the femoral tunnel. The same comparisons at the 6-months also yielded relatively lower [Formula: see text] (- 0.09 ± 0.12 ms, P < 0.05). CONCLUSION: The proposed abbreviated 3D UTE MRI paradigm is capable of assessing the ACL graft remodeling process in a clinically translatable acquisition time. Longitudinal changes in [Formula: see text] and fbw of the ACL graft were observed.

Elongation Patterns of the Anterior and Posterior Borders of the Anterolateral Ligament of the Knee.

PURPOSE: To compare the elongation patterns of the anterior and posterior borders of the anterolateral ligament (ALL) at varying knee flexion angles with the knee in a neutral position without any external forces and with external forces applied, including anterior-posterior translation, internal-external rotation, and varus-valgus angulation. METHODS: Eight cadaveric knees were tested in a custom knee testing system. Elongation of the anterior and posterior borders of the ALL was measured using a MicroScribe 3DLX system at knee flexion angles of 0°, 30°, 60°, and 90° and after the application of internal-external rotation, anterior-posterior translation, and varus-valgus angulation. RESULTS: The anterior border showed a slight noncontinuous increase in percentage elongation (0.8% ± 2.2%) whereas the posterior border showed a continuous decrease in percentage elongation (-12.0% ± 2.8%) as knee flexion increased (P < .001). Apart from the elongation of the posterior border at 90° of knee flexion, internal rotation, varus angulation, and anterior translation resulted in a significant increase in the percentage elongation of the anterior and posterior borders at each flexion angle compared with external rotation, valgus angulation, and posterior translation, respectively. CONCLUSIONS: The ALL shows different elongation patterns between the anterior and posterior borders, with a continuous decrease in the percentage elongation of the posterior border as knee flexion increases. CLINICAL RELEVANCE: This study presents useful evidence to resolve the uncertainty regarding the change in length of the ALL at various degrees of knee flexion. This information may be helpful for deciding the optimal knee flexion angle during ALL graft fixation. The findings from this study suggest that graft fixation during ALL reconstructions should be performed at close to full extension of the knee.

Supplemental Fixation of Inner Graft Limbs in All-Inside, Quadrupled, Single-Tendon Anterior Cruciate Ligament Reconstruction Graft Construct Yields Improved Biomechanical Properties.

PURPOSE: To compare the time-zero load to failure of a quadrupled, single-tendon, all-inside anterior cruciate ligament (ACL) reconstruction graft construct with (supplemented) and without the incorporation of inner-limb whipstitch sutures (control) into a tibial suspensory fixation button. METHODS: Eight matched pairs of peroneus longus tendons were prepared according to a quadrupled, all-inside ACL soft-tissue graft technique with 1 side serving as a control and the contralateral side supplemented. The constructs were biomechanically tested for strain in the inner and outer limbs during a preconditioning protocol, single-cycle load to failure, and elongation of the whole construct. RESULTS: Ultimate load to failure was significantly higher in the supplemented group: 797.5 ± 49.6 N (95% confidence interval [CI], 763.13-831.87 N) versus 719.6 ± 69.6 N (95% CI, 671.38-767.82 N; P = .044). Less graft elongation at failure was observed in the supplemented group (3.1 ± 1.5 mm; 95% CI, 2.07-4.17 mm) versus the control group (21.0 ± 21.2 mm; 95% CI, 6.31-35.69 mm; P = .052). The number of grafts undergoing a 5-mm or greater change in length at failure was 1 of 8 in the supplemented group versus 5 of 8 in the control group (P = .038). CONCLUSIONS: Inner-limb supplemental tibial fixation results in higher time-zero load to failure and decreased graft elongation in a quadrupled, single-tendon, all-inside ACL reconstruction graft construct. CLINICAL RELEVANCE: The weak point of a single-tendon, quadrupled, all-inside ACL graft construct is the tendon-to-tendon suturing to secure the inner limbs of the graft. Adding supplemental fixation by incorporating the sutures from the inner limb to the tibial suspensory fixation button leads to a higher time-zero load to failure and decreased graft elongation.