Graft Forces Research Articles

An Update on Emerging Techniques and Considerations in Revision Anterior Cruciate Ligament Reconstruction.

» The rate of primary anterior cruciate ligament reconstruction (ACLR) failure in at-risk populations remains unacceptably high and necessitates thorough evaluation of native alignment and concomitant injuries.» Posterior tibial slope of >12° is a substantial risk factor of ACLR failure and should be corrected through anterior closing wedge osteotomy.» Varus malalignment of >5° exacerbates stress on the ACL graft, increases ACLR failure risks, and should be considered for correction through high tibial osteotomy at the time of revision ACLR.» Injuries to the anterolateral ligamentous complex are prevalent in ACL ruptures, and high-risk patients have shown benefit from anterolateral ligament reconstruction or lateral extra-articular tenodesis in the revision setting.» Addressing posterolateral corner, collateral ligament, and meniscal injuries, during revision ACLR, is vital to mitigate increased graft forces and optimize knee stability and functional outcomes.

Poster 317: How Steep is Too Steep? Assessing the Limits of Lateral Extra-Articular Tenodesis and Slope-Reducing Osteotomy on ACL Graft Force and Knee Stability

Poster 317: How Steep is Too Steep? Assessing the Limits of Lateral Extra-Articular Tenodesis and Slope-Reducing Osteotomy on ACL Graft Force and Knee Stability

Supratubercle Anterior Closing Wedge Osteotomy: No Changes in Patellar Height and Significant Decreases in Anterior Tibial Translation at 6 Months Postoperatively

Background: Because of the increased prevalence of revision anterior cruciate ligament (ACL) reconstruction, there has been a desire to understand the role of posterior tibial slope on increased anterior tibial translation and increased ACL graft forces. One potential concern in supratubercle anterior closing wedge proximal tibial osteotomy (ACW-PTO) for decreasing the posterior tibial slope is the risk of altering the patellar height. Purpose: To radiographically assess changes in (1) patellar height, (2) anterior tibial translation, and (3) posterior tibial slope after supratubercle ACW-PTO. Study Design: Case series; Level of evidence, 4. Methods: Patients who underwent supratubercle ACW-PTO by a single surgeon between July 2019 and June 2023 were included. Standardized lateral knee weightbearing radiographs to assess patellar height (via the Caton-Deschamps index), anterior tibial translation of the lateral tibial plateau relative to the lateral femoral condyle, and posterior tibial slope were obtained at 4 time points (preoperatively and 1 day, 3 months, and 6 months postoperatively). Paired t test was used to compare differences between preoperative, 1-day, and 3- and 6-month values for patellar height as measured using the Caton-Deschamps index and for posterior tibial slope. Paired t test was also used to compare differences in the preoperative and 6-month postoperative values for anterior tibial translation. Results: In 20 patients after ACW-PTO, the Caton-Deschamps index demonstrated a significant increase in patellar height on postoperative day 1 (P < .001) but no significant differences at 3 (P = .057) and 6 (P = .176) months postoperatively. Anterior tibial translation on standing lateral knee radiographs was significantly decreased by a mean of 8.9 mm from preoperatively to 6 months postoperatively (P < .001). Posterior tibial slope was significantly decreased by a mean of 11.2° from preoperatively to 6 months postoperatively (P < .001). Conclusion: Supratubercle ACW-PTO performed for ACL reconstruction failure in the setting of an increased posterior tibial slope did not induce significant changes in patellar height postoperatively. Furthermore, after ACW-PTO, there was a significant decrease in anterior tibial translation and posterior tibial slope.

In Vitro Assessment of Knee Joint Biomechanics Using a Virtual Anterior Cruciate Ligament Reconstruction.

Understanding the biomechanical impact of injuries and reconstruction of the anterior cruciate ligament (ACL) is vital for improving surgical treatments that restore normal knee function. The purpose of this study was to develop a technique that enables parametric analysis of the effect of the ACL reconstruction (ACLR) in cadaver knees, by replacing its contributions with that of a specimen-specific virtual ACLR that can be enabled, disabled, or modified. Twelve ACLR reconstructed knees were mounted onto a motion simulator. In situ ACLR graft forces were measured using superposition, and these data were used to design specimen-specific virtual ACLRs that would yield the same ligament force-elongation behaviors. Tests were then repeated using the virtual ACLR in place of the real ACLR and following that in ACL deficient knee by disabling the virtual ACLR. In comparison to the ACL deficient state, the virtual ACLRs were able to restore knee stability to the same extent as real ACLRs. The average differences between the anterior tibial translation (ATT) of the virtual ACLR versus the real ACLR were +1.6 ± 0.9 mm (p = 0.4), +2.1 ± 0.4 mm (p = 0.4), and +1.0 ± 0.9 mm (p = 0.4) during Anterior drawer, Lachman and Pivot-shift tests, respectively, which is small in comparison to the full ATT range of motion (ROM) of these knees. Therefore, we conclude that a virtual ACLR can be used in place of real ACLR during biomechanical testing of cadaveric knees. This capability opens the door for future studies that can leverage parameterization of the ACLR for surgical design optimization.

Can lateral tenodesis improve the rotational stability of the ACL reconstruction? A finite element analysis.

One of the most common knee injuries is the Anterior Cruciate Ligament (ACL) rupture with severe implications on knee stability. The usual treatment is the ACL Reconstruction (ACLR) surgery where the surgeon replaces the torn ligament with a graft in an effort to restore knee kinematics. In case of excessive rotatory instability, Lateral Extra-Articular Tenodesis (LET) can be performed in combination with ACLR. Additionally, LET appears to reduce ACLR graft forces minimizing graft failure chances. However, there are concerns about overconstraining physiological rotation. To gain insight in this controversial topic, we developed an automatic, open-source tool to create a series of Finite Element (FE) models attempting to investigate the interactions of ACLR and LET through simulation. We started by creating a validated model of the healthy knee joint that served as reference for subsequent FE simulations. Then, we created FE models of standalone ACLR and combined ACLR-LET. Each model was assessed by applying a loading profile that resembles the reduction phase of the Pivot-Shift clinical exam. We measured the External Tibia Rotation (ETR), the Posterior Tibia Translation (PTT) of the lateral tibial compartment, and the ACLR graft stress developed around the femoral tunnel insertion site. We observed the following: a) LET reduces ETR and PTT compared to isolated ACLR, b) combined ACLR-LET is more sensitive to LET graft pretension with lower values showcasing performance closer to the healthy joint, c) LET reduces ACLR graft forces for the same pretension values, d) LET exhibits significant overconstraint for higher pretension values. In general, these findings are in agreement with relevant clinical studies and accentuate the potential of the developed framework as a tool that can assist orthopaedists during surgery planning. We provide open access for the FE models of this study to enhance research transparency, reproducibility and extensibility.

Arthroscopic-Assisted Lateral Extra-Articular Tenodesis With Knotless Anchor Fixation

Recent studies have reported the biomechanical and clinical advantages of lateral extraarticular augmentation procedures including the modified lateral extra-articular tenodesis (LET) in the setting of anterior cruciate ligament reconstruction. LET has been shown to significantly decrease re-rupture rates in high-risk patients and decrease anterior cruciate ligament graft forces during pivoting loads and instrumented anterior laxity testing. Many variations of the modified LET approaches have been described. However, concerns including lateral hematoma, wound-healing complications, and increased operative time exist. This minimally invasive, arthroscopic-assisted approach using a knotless, all-suture anchor allows for direct visualization through a 2-cm incision and inherently decreases the morbidity associated with traditional LET techniques.

Computational modelling of the graft-tunnel interaction in single-bundle ACL reconstructed knee.

Tunnel enlargement and graft failure are common complications associated with ACL reconstruction. The mechanical interaction between the graft and the tunnel aperture may play a more important role. This study aims to evaluate graft position within femoral tunnel and the graft force under external loads. An FE model of the femur-graft-tibia complex was constructed from CT images of an anatomically reconstructed knee specimen. The model was subjected to kinematics of passive flexion extension, anterior/posterior translation, internal/external rotation and valgus kinematics, which were collected from experimental testing. Graft shift and rotation of graft-tunnel contact region during flexion/extension and external loadings were recorded and compared to experimental measurements. Model showed that the graft shifted in the femoral tunnel during flexion and under external loads. The graft-tunnel contact area rotated by up to 55° during flexion from full extension to 90° of extension implying that the so-called "wiper effect" occurs during most of flexion angles. Different regions of the femoral tunnel aperture, particularly the anterior region, were under significantly more contact force from the graft than other areas of the aperture during the anterior translation test, potentially leading to femoral tunnel enlargement to the anterior side of the aperture.

Biomechanical Analysis of Tibial Motion and ACL Graft Forces After ACLR With and Without LET at Varying Tibial Slopes.

Lateral extra-articular tenodesis (LET) is being performed more frequently with anterior cruciate ligament (ACL) reconstruction (ACLR) to decrease graft failure rates. The posterior tibial slope (PTS) affects ACL graft failure rates. The effect of ACLR + LET on tibial motion and graft forces with increasing PTS has not been elucidated. LET would decrease anterior tibial translation (ATT), tibial rotation, and ACL graft force versus ACLR alone with increasing tibial slope throughout knee range of motion. Controlled laboratory study. Twelve fresh-frozen cadaveric knees (mean donor age, 40.5 years; all female) were tested in 4 conditions (intact, ACL cut, ACLR, and ACLR + LET) with varying PTSs (5°, 10°, 15°, and 20°) at 3 flexion angles (0°, 30°, and 60°). Specimens were mounted to a load frame that applied a 500-N axial load with 1 N·m of internal rotation (IR) torque. The amount of tibial translation, IR, and graft force was measured. Increasing PTS revealed a linear and significant increase in graft force at all flexion angles. LET reduced graft force by 8.3% (-5.8 N) compared with ACLR alone at 30° of flexion. At the same position, slope reduction resulted in reduced graft force by 17% to 22% (-12.3 to -15.2 N) per 5° of slope correction, with a 46% (-40.7 N) reduction seen from 20° to 5° of slope correction. For ATT, ACLR returned tibial translation to preinjury levels, as did ACLR + LET at all flexion angles, except full extension, where ACLR + LET reduced ATT by 2.5 mm compared with the intact state (P = .019). Increased PTS was confirmed to increase graft forces linearly. Although ACLR + LET reduced graft force compared with ACLR alone, slope reduction had a larger effect across all testing conditions. No other clinically significant differences were noted between ACLR with versus without LET in regard to graft force, ATT, or IR. Many authors have proposed LET in the setting of ACLR, revision surgery, hyperlaxity, high-grade pivot shift, and elevated PTS, but the indications remain unclear. The biomechanical performance of ACLR + LET at varying PTSs may affect daily practice and provide clarity on these indications.

Modified Lemaire Tenodesis Forces in Cadaveric Specimens Are Not Affected by Random Small-Scale Variations in the Femoral Insertion Point During Active Knee Joint Flexion-Extension

PurposeTo directly measure lateral extra-articular tenodesis (LET) forces supporting anterior cruciate ligament reconstruction (ACLR) during dynamic flexion-extension cycles induced by simulated active muscle forces, to investigate the influence of random surgical variation in the femoral LET insertion point around the target insertion position, and to determine potential changes to the extension behavior of the knee joint in a cadaveric model.MethodsAfter iatrogenic anterior cruciate ligament deficiency and simulated anterolateral rotatory instability, 7 fresh-frozen cadaveric knee joints were treated with isolated ACLR followed by combined ACLR-LET. The specimens were tested on a knee joint test bench during active dynamic flexion-extension with simulated muscle forces. LET forces and the degree of knee joint extension were measured. Random variation in the LET insertion point around the target insertion position was postoperatively quantified by computed tomography.ResultsIn extension, the median LET force increased to 39 ± 2 N (95% confidence interval [CI], 36 to 40 N). In flexion over 70°, the LET was offloaded (2 ± 1 N; 95% CI, 0 to 2 N). In this study, small-scale surgical variation in the femoral LET insertion point around the target position had a negligible effect on the graft forces measured. We detected no difference in the degree of knee joint extension after combined ACLR-LET (median, 1.0° ± 3.0°; 95% CI, −6.2° to 5.2°) in comparison with isolated ACLR (median, 1.1° ± 3.3°; 95% CI, −6.7° to 6.1°; P = .62).ConclusionsLET forces in combined ACLR-LET increased to a limited extent during active knee joint flexion-extension independent of small-scale variation around 1 specific target insertion point. Combined ACLR-LET did not change knee joint extension in comparison with isolated ACLR under the testing conditions used in this biomechanical study.Clinical RelevanceLow LET forces can be expected during flexion-extension of the knee joint. Small-scale deviations in the femoral LET insertion point around the target insertion position in the modified Lemaire technique might have a minor effect on graft forces during active flexion-extension. To directly measure lateral extra-articular tenodesis (LET) forces supporting anterior cruciate ligament reconstruction (ACLR) during dynamic flexion-extension cycles induced by simulated active muscle forces, to investigate the influence of random surgical variation in the femoral LET insertion point around the target insertion position, and to determine potential changes to the extension behavior of the knee joint in a cadaveric model. After iatrogenic anterior cruciate ligament deficiency and simulated anterolateral rotatory instability, 7 fresh-frozen cadaveric knee joints were treated with isolated ACLR followed by combined ACLR-LET. The specimens were tested on a knee joint test bench during active dynamic flexion-extension with simulated muscle forces. LET forces and the degree of knee joint extension were measured. Random variation in the LET insertion point around the target insertion position was postoperatively quantified by computed tomography. In extension, the median LET force increased to 39 ± 2 N (95% confidence interval [CI], 36 to 40 N). In flexion over 70°, the LET was offloaded (2 ± 1 N; 95% CI, 0 to 2 N). In this study, small-scale surgical variation in the femoral LET insertion point around the target position had a negligible effect on the graft forces measured. We detected no difference in the degree of knee joint extension after combined ACLR-LET (median, 1.0° ± 3.0°; 95% CI, −6.2° to 5.2°) in comparison with isolated ACLR (median, 1.1° ± 3.3°; 95% CI, −6.7° to 6.1°; P = .62). LET forces in combined ACLR-LET increased to a limited extent during active knee joint flexion-extension independent of small-scale variation around 1 specific target insertion point. Combined ACLR-LET did not change knee joint extension in comparison with isolated ACLR under the testing conditions used in this biomechanical study.

INFLUENCE OF DILATION ON THE STABILITY OF OSTEOCHONDRAL AUTOGRAFTS IMPLANTED IN CADAVERIC HUMAN FEMURS

The clinical success of osteochondral autografts is heavily reliant on their mechanical stability, as grafts which protrude above or subside below the native cartilage can have a negative effect on the tribological properties of the joint [1]. Furthermore, high insertion forces have previously been shown to reduce chondrocyte viability [2]. Commercial grafting kits may include a dilation tool to increase the diameter of the recipient site prior to insertion. The aim of this study was to evaluate the influence of dilation on the primary stability of autografts.Six human cadaveric femurs were studied. For each femur, four 8.5 × 8mm autografts were harvested from the trochlear groove and implanted into the femoral condyles using a Smith &amp; Nephew Osteochondral grafting kit. Two grafts were implanted into dilated recipient sites (n=12) and two were implanted with no dilation (n=12). Insertion force was measured by partially inserting the graft and applying a load at a rate of 1 mm/min, until the graft was flush with the surrounding cartilage. Push-in force was measured by applying the same load, until the graft had subsided 4mm below congruency. Significance was taken as (p&lt;0.05).Average maximum insertion force of dilated grafts was significantly lower (p&lt;0.001) than their non-dilated equivalent [28.2N &amp; 176.7N respectively]. There was no significant difference between average maximum push-in force between the dilated and non-dilated groups [1062.8N &amp; 1204.2N respectively].This study demonstrated that significantly less force is required to insert dilated autografts, potentially minimising loss of chondrocyte viability. However, once inserted, the force required to displace the grafts below congruency remained similar, indicating a similar degree of graft stability between both groups.

In situ repair of segmental loss posterior lateral meniscal root tears outperforms meniscofemoral ligament imbrication in the ACL reconstructed knee

PurposeThe purpose of this study was to compare the biomechanical effect of in-situ repair of posterior lateral meniscal root (PLMR) tear with segmental meniscal loss, with and without meniscofemoral ligament (MFL) imbrication, on anterior cruciate ligament (ACL) graft force and knee joint kinematics.MethodsTen fresh-frozen cadaveric knee specimens underwent kinematic evaluation in five states: 1) Native, 2) ACLR, 3) Segmental PLMR loss, 4) In-situ PLMR repair, and 5) MFL augmentation. Kinematic evaluation consisted of five tests, each performed at full extension and at 30° of flexion: 1) Anterior drawer, 2) Internal Rotation, 3) External Rotation, 4) Varus, and 5) Valgus. Additionally, a simulated pivot shift test was performed. Knee kinematics and ACL graft force were measured.ResultsPLMR tear did not significantly increase ACL graft force in any test. However, PLMR repair significantly reduced ACL graft force compared to the ACLR alone (over constraint -26.6 N, p = 0.001). PLMR tear significantly increased ATT during the pivot shift test (+ 2.7 mm, p = 0.0001), and PLMR repair restored native laxity. MFL augmentation did not improve the mechanics.ConclusionsIn-situ PLMR repair eliminated pivot shift laxity through ATT and reduced force on the ACL graft, indicating that this procedure may be ACL graft-protective. MFL augmentation was not shown to have any effect on graft force or knee kinematics and untreated PLMR tears may place an ACL graft at higher risk. This study suggests concomitant repair to minimize additional forces on the ACL graft.

Development of polycaprolactone grafts with improved physical properties and body stability using a screw extrusion-type 3D bioprinter.

Three-dimensional (3D) bioprinter including screw extruder was developed, and the polycaprolactone (PCL) grafts fabricated by screw-type and pneumatic pressure-type bioprinters were comparatively evaluated. The density and tensile strength of the single layers printed by the screw-type were 14.07% and 34.76% higher, respectively, than those of the single layers produced by the pneumatic pressure-type. The adhesive force, tensile strength, and bending strength of the PCL grafts printed by the screw-type bioprinter were 2.72 times, 29.89%, and 67.76% higher, respectively, than those of the PCL grafts prepared by the pneumatic pressure-type bioprinter. By evaluating the consistency with the original image of the PCL grafts, we found that it had a value of about 98.35%. The layer width of the printing structure was 485.2 ± 0.004919 μm, which was 99.5% to 101.8% compared to the set value (500 μm), indicating high accuracy and uniformity. The printed graft had no cytotoxicity, and there were no impurities in the extract test. In the in vivo studies, the tensile strength of the sample 12 months after implantation was reduced by 50.37% and 85.43% compared to the initial point of the sample printed by the screw-type and the pneumatic pressure-type, respectively. Through observing the fractures of the samples at 9- and 12-month samples, we found that the PCL grafts prepared by the screw-type had better in vivo stability. Therefore, the printing system developed in this study can be used as a treatment for regenerative medicine.

Hourglass-shaped grafts are superior to conventional grafts for restoring knee stability and graft force at knee flexion angle of 30° following anterior cruciate ligament reconstruction: A finite element analysis.

Background: Anterior cruciate ligament reconstruction (ACLR) using a generally columnar graft is considered the gold standard for treating anterior cruciate ligament ruptures, but such grafts cannot replicate the geometry and mechanical properties of the native anterior cruciate ligament. Purpose: To evaluate the effectiveness of an innovative hourglass-shaped graft versus a traditional columnar graft for restoring joint stability and graft force, while avoiding notch impingement following anterior cruciate ligament reconstruction. Methods: Finite element models of a human knee were developed to simulate ① An intact state, ② anterior cruciate ligament reconstruction using columnar grafts with different diameters (7.5-12mm in 0.5mm increments), ③ anterior cruciate ligament reconstruction using columnar grafts with different Young's moduli (129.4, 168.0 and 362.2MPa) and ④ anterior cruciate ligament reconstruction using hourglass-shaped grafts with different Young's moduli. The knee model was flexed to 30° and loaded with an anterior tibial load of 103N, internal tibial moment of 7.5Nm, and valgus tibial moment of 6.9Nm. The risk of notch impingement, knee stability and graft forces were compared among the different groups. Results: This study found that columnar grafts could not simultaneously restore knee stability in different degree of freedoms (DOFs) and graft force to a level similar to that of the intact knee. The anterior tibial translation and graft force were restored to a near-normal condition when the internal tibial rotation was over-restrained and valgus tibial rotation was lax. A graft diameter of at least 10mm was needed to restore knee stability and graft force to physiological levels, but such large grafts were found to be at high risk of notch impingement. In contrast, the hourglass-shaped graft was able to simultaneously restore both knee stability and graft force at knee flexion of 30° while also having a much lower risk of impingement. Conclusion: Under knee flexion angle of 30°, an hourglass-shaped graft was better able to restore joint stability and graft force to a near-physiological level than columnar grafts, while also reducing the risk of notch impingement.

A Biomechanical Comparison of 2 Over-the-Top Anterior Cruciate Ligament Reconstruction Techniques: A Cadaveric Study Using a Robotic Simulator.

For skeletally immature patients, over-the-top (OTT) anterior cruciate ligament (ACL) reconstruction (ACLR) is preferred. However, increased anterior laxity at deep knee flexion angles remains concerning. We modified the procedure to proximally shift the graft fixation site on the femur to prevent graft loosening at higher knee flexion angles and named it the supra-OTT procedure. To compare anterior laxity and in situ forces of the ACL graft between conventional OTT and supra-OTT ACLR in a cadaveric model. Controlled laboratory study. A total of 11 fresh-frozen cadaveric knee specimens underwent 4 robotic testing conditions: ACL intact, ACL resected, conventional OTT, and supra-OTT. For each condition, a 100-N load was applied at 0°, 15°, 30°, 60°, and 90° of knee flexion to simulate the Lachman test or anterior drawer test. In addition, a combined load of 5-N·m internal tibial torque and 10-N·m valgus torque was applied at 15° and 30° of knee flexion as a simulated pivot-shift test. Anterior tibial translation and in situ graft forces were recorded. The only difference between conventional OTT and supra-OTT ACLR was the graft fixation site on the femur. For conventional OTT ACLR, graft fixation was performed just on the proximal and lateral ends of the posterior condyle. For supra-OTT ACLR, the fixation point was around the proximal insertion of the lateral head of the gastrocnemius and the lateral edge of the posterior cortex, approximately 2 cm proximal to the conventional OTT position. On the simulated anterior drawer test at 60° and 90° of knee flexion, anterior tibial translation after supra-OTT ACLR was significantly smaller than after conventional OTT ACLR (P < .01). However, no significant differences were noted at other flexion angles or on the simulated pivot-shift test between the conventional OTT and supra-OTT procedures. Some overconstraint and higher graft forces were noted with both techniques, but the supra-OTT technique caused even more overconstraint at higher flexion angles. Supra-OTT ACLR showed better biomechanical performance to control anterior laxity than conventional OTT ACLR at higher knee flexion angles. The supra-OTT procedure may improve anterior stability at deep knee flexion angles.

Graft Diameter Should Reflect the Size of the Native Anterior Cruciate Ligament (ACL) to Improve the Outcome of ACL Reconstruction: A Finite Element Analysis.

The size of the anterior cruciate ligament (ACL) often varies between individuals, but such variation is not typically considered during ACL reconstruction (ACLR). This study aimed to explore how the size of the ACL affects the selection of a suitable graft diameter. A finite element model of a human knee was implanted with intact ACLs of different dimensions (0.95, 1 and 1.05 times the size of the original ACL) and with grafts of different diameters, to simulate ACLR (diameter 7.5–12 mm in 0.5 mm increments). The knee models were flexed to 30° and loaded with an anterior tibial load of 103 N, internal tibial moment of 7.5 Nm, and valgus tibial moment of 6.9 Nm. Knee kinematics (anterior tibial translation (ATT), internal tibial rotation (ITR) and valgus tibial rotation (VTR)) and ligament forces were recorded and compared among the different groups. The results showed that, compared with the intact knee, a graft diameter of 7.5 mm was found to increase the ATT and VTR, but reduce the graft force. Increasing the graft diameter reduced knee laxity and increased the graft force. A 10% increase in the size of the ACL corresponded to a 3 mm larger graft diameter required to restore knee stability and graft force after ACLR. It was concluded that the graft diameter should be selected according to the dimensions of the native ACL, for better restoration of knee functionality. This study may help to improve the clinical treatment of ACL ruptures.

Fast and Accurate Computation of the Displacement Force of Stent Grafts after Endovascular Aneurysm Repair.

Purpose: Currently, the displacement force of stent grafts is generally obtained using computational fluid dynamics (CFD), which requires professional CFD knowledge to perform the correct simulation. This study proposes a fast, simple, and clinician-friendly approach to calculating the patient-specific displacement force after endovascular aneurysm repair (EVAR). Methods: Twenty patient-specific post-EVAR computed tomography angiography images were used to reconstruct the patient-specific three-dimensional models, then the displacement forces were calculated using CFD and the proposed approaches, respectively, and their numerical differences were compared and analyzed. Results: Based on the derivation and simplification of the momentum theorem, the patient-specific displacement forces were obtained using the information of the patient-specific pressure, cross-sectional area, and angulation of the two stent graft ends, and the average relative error was no greater than 1.37% when compared to the displacement forces calculated by CFD. In addition, the linear regression analysis also showed good agreement between the displacement force values calculated by the new approach and CFD (R = 0.999). Conclusions: The proposed approach can quickly and accurately calculate the patient-specific displacement force on a stent graft and can therefore help clinicians quickly evaluate the post-EVAR displacement force.

No Difference in Knee Kinematics Between Anterior Cruciate Ligament-First and Posterior Cruciate Ligament-First Fixation During Single-Stage Multiligament Knee Reconstruction: A Biomechanical Study.

Background:For combined reconstruction of both the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL), there is no consensus regarding which graft should be tensioned and fixed first.Purpose:The purpose of this study was to determine which sequence of graft tensioning and fixation better restores normal knee kinematics. The hypothesis was that ACL-first fixation would more closely restore normal knee kinematics, graft force, and the tibiofemoral orientation in the neutral (resting) position compared with PCL-first fixation.Study Design:Controlled laboratory study.Methods:A total of 15 unpaired human cadaveric knees were examined using a robotic testing system under the following 4 conditions: (1) 89.0-N anterior tibial load at different knee angles; (2) 89.0-N posterior tibial load at different knee angles; (3) combined rotational 7.0-N·m valgus and 5.0-N·m internal rotation load (simulated pivot shift) at 0°, 15°, and 30° of flexion; and (4) 5.0-N·m external rotation load at 0°, 15°, and 30° of flexion. The 4 evaluated knee states were (1) intact ACL and PCL (intact), (2) ACL and PCL deficient (deficient), (3) combined anatomic ACL-PCL reconstruction fixing the ACL first (ACL-first), and (4) combined anatomic ACL-PCL reconstruction fixing the PCL first (PCL-first). A 9.0 mm–diameter quadriceps tendon autograft was used for the ACL graft, tensioned with 40.0 N at 30° of flexion. A 9.5 mm–diameter hamstring tendon autograft (gracilis and semitendinosus, quadrupled loop, and augmented with an additional allograft strand if needed), tensioned with 40.0 N at 90° of flexion, was used for the PCL graft.Results:There were no statistically significant differences between ACL-first and PCL-first fixation regarding knee kinematics. ACL-first fixation restored anterior tibial translation to the intact state at all tested knee angles, while PCL-first fixation showed higher anterior tibial translation than the intact state at 90° of flexion (9.05 ± 3.05 and 5.87 ± 2.40 mm, respectively; P = .018). Neither sequence restored posterior tibial translation to the intact state at 30°, 60°, and 90° of flexion. At 15° of flexion, PCL-first fixation restored posterior tibial translation to the intact state, whereas ACL-first fixation did not.Conclusion:There were no differences in knee laxity between ACL-first and PCL-first fixation with the ACL graft fixed at 30° and the PCL graft fixed at 90°.Clinical Relevance:This study showed that there was no evidence to support the use of one tensioning sequence over the other in single-stage multiligament knee reconstruction.

Revision Anterior Cruciate Ligament Reconstruction and Increased Tibial Slope: When to Perform a Slope-Altering High Tibial Osteotomy

Background: Slope-correcting high tibial osteotomy (HTO) is gaining popularity for mitigating the impact of posterior tibial slope (PTS) on graft failure in patients requiring revision anterior cruciate ligament (ACL) reconstruction surgery. Biomechanical and clinical studies have demonstrated that PTS reduction results in decreased graft forces and satisfactory patient outcomes, making it an important technique in the setting of complex revision ACL reconstruction (ACL-R). Indications: Slope-correcting HTO can be performed for the management of recurrent knee instability after ACL-R due to a high PTS of 12° or greater. Technique Description: A 3- to 4-inch incision is made along the tibia using an anteromedial approach, and the exposed patellar tendon is protected using a retractor. The anterior compartment is exposed by an incision in the tibialis anterior fascia, followed by elevation of the tibialis anterior and placement of a Hohmann retractor. Subperiosteal elevation of the medial collateral ligament (MCL) is performed on the medial side of the tibial tubercle. The position of eventual screw fixation is marked, and a straight tubercle osteotomy is performed without anteriorization, leaving a freely exposed proximal tibia. Two K-wires are used to mark the location of the osteotomy. Soft tissue structures are protected with Hohmann retractors on both sides while using an oscillating saw to perform the osteotomy. A few degrees (1°-3°) of overcorrection are preferred. The osteotomy is completed, retaining 1cm of posterior hinge. The wedge is removed and reduced by hyperextending the knee under gentle manual traction. Pre-contoured, low-profile plates with locking screws are placed, with 3 screws proximally and another 3 distally. During concurrent ACL-R, the screws should leave room for drilling of the ACL tibial tunnel. Results: Studies investigating the effects of slope-correcting HTO concurrent to revision ACL-R have reported reduced anterior tibial translation and rotatory knee instability, improved patient-reported outcomes, and a reduction in graft failure risk. Description/Conclusion: Slope-reducing HTO is an essential technique in the arsenal of complex ACL surgeons aiming to correct the detrimental effect of an increased PTS on ACL graft integrity in the setting of revision ACL-R.

Paper 80: Biomechanical Analysis of Tibial Motion and ACL Graft Forces After ACLR With and Without LET at Varying Tibial Slopes

Objectives:Lateral extra-articular tenodesis (LET) is being performed more frequently with anterior cruciate ligament reconstruction (ACLR) to decrease graft failure rates. Posterior tibial slope (PTS) affects ACL graft failure rates.2 The impact of LET plus ACLR on tibial motion and graft forces with increasing PTS has not been elucidated. We hypothesized LET will decrease anterior tibial translation (ATT), tibial rotation, and ACL graft force versus ACLR alone with increasing tibial slope throughout knee range of motion.Methods:Twelve cadaveric knees (40.5 mean age, all female) were tested in four conditions (intact, ACL cut, ACLR, ACLR + LET) with varying PTS (5°, 10°, 15°, 20°) at three flexion angles (0°, 30°, 60°). Specimens were mounted to a load frame which applied a 500-N axial load with 1 Nm of internal rotation (IR) torque (Figure 1). The amount of tibial translation, IR, and graft forces were measured.Results:Increasing PTS revealed a linear and statistically significant increase in graft force at all flexion angles. LET reduced graft force by 8.3% (6N) compared to ACLR alone at 30° of flexion. At the same position, slope-correcting osteotomy reduced graft force by 17-22% per 5° of slope correction, with a 46% reduction seen from 20° to 5°slope correction. For ATT, ACLR returned tibial translation to pre-injury levels, as did ACLR + LET at all flexion angles, except full extension where ACLR + LET over-reduced ATT by 2.47mm (p<0.05).Conclusions:Increased PTS was confirmed to increase graft forces linearly. Additionally, while the ACLR + LET reduced graft force compared to ACLR alone, slope correcting osteotomies are a more powerful method to minimize graft force. No other clinically significant differences were noted between ACLR with or without LET in regards to graft force, ATT, or IR. Many authors have proposed LET in the setting of ACLR, revision surgery, hyperlaxity, high grade pivot shift and elevated PTS, but the indications remain unclear. The biomechanical performance of LET plus ACLR at varying PTSs may impact daily practice and provide clarity on these indications.

Modified Lemaire tenodesis reduces anterior cruciate ligament graft forces during internal tibial torque loading

PurposeThe aim of the study was to directly measure graft forces of an anterior cruciate ligament reconstruction (ACLR) and a lateral extra-articular tenodesis (LET) using the modified Lemaire technique in combined anterior cruciate ligament (ACL) deficient and anterolateral rotatory instable knees and to analyse the changes in knee joint motion resulting from combined ACLR + LET.MethodsOn a knee joint test bench, six fresh-frozen cadaveric specimens were tested at 0°, 30°, 60°, and 90° of knee flexion in the following states: 1) intact; 2) with resected ACL; 3) with resected ACL combined with anterolateral rotatory instability; 4) with an isolated ACLR; and 5) with combined ACLR + LET. The specimens were examined under various external loads: 1) unloaded; 2) with an anterior tibial translation force (ATF) of 98 N; 3) with an internal tibial torque (IT) of 5 Nm; and 4) with a combined internal tibial torque of 5 Nm and an anterior tibial translation force of 98 N (IT + ATF). The graft forces of the ACLR and LET were recorded by load cells incorporated into custom devices, which were screwed into the femoral tunnels. Motion of the knee joint was analysed using a 3D camera system.ResultsDuring IT and IT + ATF, the addition of a LET reduced the ACLR graft forces up to 61% between 0° and 60° of flexion (P = 0.028). During IT + ATF, the LET graft forces reached 112 N. ACLR alone did not restore native internal tibial rotation after combined ACL deficiency and anterolateral rotatory instability. Combined ACLR + LET was able to restore native internal tibial rotation values for 0°, 60° and 90° of knee flexion with decreased internal tibial rotation at 30° of flexion.ConclusionThe study demonstrates that the addition of a LET decreases the forces seen by the ACLR graft and reduces residual rotational laxity after isolated ACLR during internal tibial torque loading. Due to load sharing, a LET could support the ACLR graft and perhaps be the reason for reduced repeat rupture rates seen in clinical studies. Care must be taken not to limit the internal tibial rotation when performing a LET.