Graft Forces Research Articles

Tibial Slope and Its Effect on Force in Anterior Cruciate Ligament Grafts: Anterior Cruciate Ligament Force Increases Linearly as Posterior Tibial Slope Increases

Background: Previous work has reported that increased tibial slope is directly correlated with increased anterior tibial translation, possibly predisposing patients to higher rates of anterior cruciate ligament (ACL) tears and causing higher rates of ACL graft failures over the long term. However, the effect of changes in sagittal plane tibial slope on ACL reconstruction (ACLR) graft force has not been well defined. Purpose/Hypothesis: The purpose of this study was to quantify the effect of changes in sagittal plane tibial slope on ACLR graft force at varying knee flexion angles. Our null hypothesis was that changing the sagittal plane tibial slope would not affect force on the ACL graft. Study Design: Controlled laboratory study. Methods: Ten male fresh-frozen cadaveric knees had a posterior tibial osteotomy performed and an external fixator placed for testing and accurate slope adjustment. Following ACLR, specimens were compressed with a 200-N axial load at flexion angles of 0°, 15°, 30°, 45°, and 60°, and the graft loads were recorded through a force transducer clamped to the graft. Tibial slope was varied between −2° and 20° of posterior slope at 2° increments under these test conditions. Results: ACL graft force in the loaded testing state increased linearly as slope increased. This effect was independent of flexion angle. The final model utilized a 2-factor linear mixed-effects regression model and noted a significant, highly positive, and linear relationship between tibial slope and ACL graft force in axially loaded knees at all flexion angles tested (slope coefficient = 0.92, SE = 0.08, P < .001). Significantly higher graft force was also observed at 0° of flexion as compared with all other flexion angles for the loaded condition (all P < .001). Conclusion: The authors found that tibial slope had a strong linear relationship to the amount of graft force experienced by an ACL graft in axially loaded knees. Thus, a flatter tibial slope had significantly less loading of ACL grafts, while steeper slopes increased ACL graft loading. Our biomechanical findings support recent clinical evidence of increased ACL graft failure with steeper tibial slope secondary to increased graft loading. Clinical Relevance: Evaluation of the effect of increasing tibial slope on ACL graft force can guide surgeons when deciding if a slope-decreasing proximal tibial osteotomy should be performed before a revision ACLR. Overall, as slope increases, ACL graft force increases, and in our study, flatter slopes had lower ACL graft forces and were protective of the ACLR graft.

Lateral Meniscal Posterior Root Repair With Anterior Cruciate Ligament Reconstruction Better Restores Knee Stability

Background: The effect of lateral meniscal posterior root tear and repair—commonly seen in clinical practice in the setting of anterior cruciate ligament (ACL) reconstruction—is not known. Purpose/Hypothesis: This study evaluated the effect of tear and repair of the lateral meniscal posterior root on the biomechanics of the ACL-reconstructed knee. It was hypothesized that anterior tibial translation would increase under anterior loading and simulated pivot-shift loading with the root tear of the posterior lateral meniscus, while repair of the root tear would reduce it close to the noninjured state. Study Design: Controlled laboratory study. Methods: Thirteen fresh-frozen adult human knees were tested with a robotic testing system under 2 loading conditions: (1) an 89.0-N anterior tibial load applied at full extension and 15°, 30°, 60°, and 90° of knee flexion and (2) a combined 7.0-N·m valgus and 5.0-N·m internal tibial torque (simulated pivot-shift test) applied at full extension and 15° and 30° of knee flexion. The following knee states were tested: intact knee, ACL reconstruction and intact lateral meniscus, ACL reconstruction and lateral meniscal posterior root tear, and ACL reconstruction and lateral meniscal posterior root repair. Results: In the ACL-reconstructed knee, a tear of the lateral meniscal posterior root significantly increased knee laxity under anterior loading by as much as 1 mm. The transosseous pullout suture root repair improved knee stability under anterior tibial and simulated pivot-shift loading. Root repair improved the ACL graft force closer to that of the native ACL under anterior tibial loading. Conclusion: Lateral meniscal posterior root injury further destabilizes the ACL-reconstructed knee, and root repair improves knee stability. Clinical Relevance: This study suggests a rationale for surgical repair of the lateral meniscus, which can restore stability close to that of the premeniscal injury state.

Numerical and Experimental Investigation of Novel Blended Bifurcated Stent Grafts with Taper to Improve Hemodynamic Performance.

The typical helical flow within the human arterial system is widely used when designing cardiovascular devices, as this helical flow can be generated using the “crossed limbs” strategy of the bifurcated stent graft (BSG) and enhanced by the tapered structure of arteries. Here, we propose the use of a deflected blended bifurcated stent graft (BBSG) with various tapers, using conventional blended BSGs with the same degree of taper as a comparison. Hemodynamic performances, including helical strength and wall shear stress- (WSS-) based indicators, were assessed. Displacement forces that may induce stent-graft migration were assessed using numerical simulations and in vitro experiments. The results showed that as the taper increased, the displacement force, helicity strength, and time-averaged wall shear stress (TAWSS) within the iliac grafts increased, whereas the oscillating shear index (OSI) and relative residence time (RRT) gradually decreased for both types of BBSGs. With identical tapers, deflected BBSGs, compared to conventional BBSGs, exhibited a wider helical structure and lower RRT on the iliac graft and lower displacement force; however, there were no differences in hemodynamic indicators. In summary, the presence of tapering facilitated helical flow and produced better hemodynamic performance but posed a higher risk of graft migration. Conventional and deflected BBSGs with taper might be the two optimal configurations for endovascular aneurysm repair, given the helical flow. The deflected BBSG provides a better configuration, compared to the conventional BBSG, when considering the reduction of migration risk.

A Preclinical Model to Study the Influence of Graft Force on the Healing of the Anterior Cruciate Ligament Graft.

The purpose of this study is to establish a small animal anterior cruciate ligament (ACL) reconstruction research model where ACL graft force can be varied to create different graft force patterns with controlled knee motion. Cadaveric (n = 10) and in vivo (n = 10) rat knees underwent ACL resection followed by reconstruction using a soft tissue autograft. Five cadaveric and five in vivo knees received a nonisometric, high-force femoral graft tunnel position. Five cadaveric and five in vivo knees received a more isometric, low-force graft tunnel position. ACL graft force (N) was then recorded as the knee was ranged from extension to 90 degrees using a custom knee flexion device. Our results demonstrate that distinct ACL graft force patterns were generated for the high-force and low-force femoral graft tunnels. For high-force ACL grafts, ACL graft forces increased as the knee was flexed both in cadaveric and in vivo knees. At 90 degrees of knee flexion, high-force ACL grafts had significantly greater mean graft force when compared with baseline (cadaver: 7.76 ± 0.54 N at 90 degrees vs. 4.94 ± 0.14 N at 0 degree, p = 0.004; in vivo: 7.29 ± 0.42 N at 90 degrees vs. 4.74 ± 0.13 N at 0 degree, p = 0.007). In contrast, the graft forces for low-force ACL grafts did not change with knee flexion (cadaver: 4.94 ± 0.11 N at 90 degrees vs. 4.72 ± 0.14 N at 0 degree, p = 0.41; in vivo: 4.78 ± 0.26 N at 90 degrees vs. 4.77 ± 0.06 N at 0 degree, p = 1). Compared with nonisometric ACL grafts, the graft force for grafts placed in an isometric position had significantly lower ACL graft forces at 15, 30, 45, 60, 70, and 90 degrees in both cadaveric and in vivo knees. In conclusion, we have developed a novel ACL reconstruction model that can reproducibly produce two ACL graft force patterns. This model would permit further research on how ACL graft forces may affect subsequent graft healing, maturation, and function.

Anterolateral Structure Reconstruction Unnecessary with Anatomic ACL Reconstruction for Knee Stability: Commentary on an article by Frank R. Noyes, MD, et al.: "The Effect of an ACL Reconstruction in Controlling Rotational Knee Stability in Knees with Intact and Physiologic Laxity of Secondary Restraints as Defined by Tibiofemoral Compartment Translations and Graft Forces".

Anterolateral Structure Reconstruction Unnecessary with Anatomic ACL Reconstruction for Knee Stability: Commentary on an article by Frank R. Noyes, MD, et al.: "The Effect of an ACL Reconstruction in Controlling Rotational Knee Stability in Knees with Intact and Physiologic Laxity of Secondary Restraints as Defined by Tibiofemoral Compartment Translations and Graft Forces".

The Effect of an ACL Reconstruction in Controlling Rotational Knee Stability in Knees with Intact and Physiologic Laxity of Secondary Restraints as Defined by Tibiofemoral Compartment Translations and Graft Forces.

The effect of an anterior cruciate ligament (ACL) reconstruction on restoring normal knee kinematics in unstable knees with physiologic laxity of secondary ligamentous restraints remains unknown. The purpose of this study was to determine the stabilizing function of an ACL reconstruction and the resulting ACL graft forces in knees with severely abnormal anterior subluxation due to associated laxity of secondary restraints. A 6-degree-of-freedom robotic simulator was used to test 21 cadaveric knees studied as a whole and in subgroups of lax secondary restraints (Lax-SR) and intact secondary restraints (Intact-SR), based on abnormal translations and tibial rotations. Native, ACL-sectioned, and ACL-reconstructed conditions were tested. An instrumented bone-patellar tendon-bone (BPTB) graft measured ACL graft forces. The loading profile involved the Lachman test (25° of flexion and 100-N anterior load), anterior tibial loading (100-N anterior load across 10° to 90° of flexion), internal rotation (25° of flexion and 5-Nm torque), and 2 pivot-shift simulations (100-N anterior load, 7-Nm valgus, and either 5 Nm of internal rotation [Pivot Shift 1] or 1 Nm of internal rotation [Pivot Shift 2]). Equivalence between conditions was defined as being within 2 mm for compartment translation and within 2° for internal tibial rotation, with p < 0.05. ACL sectioning increased center translation in the Lachman test by a mean of 10.9 mm (95% confidence interval [CI], 9.3 to 12.5 mm; p = 0.99), which was equivalent to native values after ACL reconstruction in all knees (mean difference, 0.0 mm [95% CI, -0.4 to 0.4 mm]; p = 0.0013), and in subgroups of Lax-SR (mean difference, 0.2 mm [95% CI, -0.5 to 0.8 mm]; p = 0.03) and Intact-SR (mean difference, -0.2 mm [95% CI, -0.8 to 0.4 mm]; p = 0.002). ACL sectioning in the pivot-shift (5-Nm) test increased lateral compartment translation to non-native-equivalent levels, which were restored to native-equivalent values after ACL reconstruction in all knees (mean difference, 0.9 mm [95% CI, 0.4 to 1.4 mm]; p = 0.055), in the Intact-SR subgroup (mean difference, 1.1 mm [95% CI, 0.5 to 1.8 mm]; p = 0.03), and to nearly native-equivalence in the Lax-SR subgroup (mean difference, 0.6 mm [95% CI, -0.3 to 1.6 mm; p = 0.06). The highest ACL graft force reached a mean of 190.9 N in the pivot-shift (5-Nm) test. The ACL reconstruction restored native kinematics and native rotational stability in all knees, including knees having laxity of secondary ligamentous restraints and clinically equivalent Grade-3 pivot-shift subluxation, and did so at ACL graft forces that were not excessive. An ACL reconstruction with a BPTB graft restored normal stability parameters regardless of the integrity of secondary ligamentous restraints.

Posterior Cruciate Ligament Reconstruction With Transtibial or Tibial Inlay Techniques: A Meta-analysis of Biomechanical and Clinical Outcomes

Background: Transtibial (TT) or tibial inlay (TI) techniques are commonly used for posterior cruciate ligament reconstruction (PCLR). However, the optimum method for PCLR after PCL injury remains debatable. Hypothesis/Purpose: The hypothesis was that TT and TI techniques would not show significant differences for all outcome measures. The purpose was to determine the biomechanical and clinical outcomes of TT and TI surgical techniques for PCLR. Study Design: Meta-analysis; Level of evidence, 3. Methods: MEDLINE, EMBASE, the Cochrane Central Register of Controlled Trials (CENTRAL), Web of Science, and SCOPUS electronic databases for articles published up until August 2016 were searched to find relevant articles comparing outcomes of TT versus TI techniques for PCLR. Data searching, extraction, analysis, and quality assessment were performed according to Cochrane Collaboration guidelines. Biomechanical outcomes and clinical outcomes of both techniques were compared. Results are presented as risk ratio (RR) for binary outcomes and weighted mean difference (WMD) for continuous outcomes with 95% confidence intervals (CI). Results: Five biomechanical and 5 clinical studies were included. No significant biomechanical differences were found regarding posterior tibial translation (PTT) at a knee flexion angle of 90° or PTT after cyclic loading between the 2 groups. However, a stronger in situ force in the graft was detected in the TT group (WMD = 15.58; 95% CI, 0.22-30.95; I2 = 10%). Although no significant differences were found in clinical outcomes such as Lysholm knee function score, Tegner activity score, side-to-side difference, or posterior drawer test at final follow-up between the 2 groups, the TT technique tended to entail fewer perioperative complications than the TI technique (RR = 0.60; 95% CI, 0.35-1.00; I2 = 0%). Conclusion: TT and TI techniques for PCLR can both restore normal knee kinematics and improve knee function. However, the issue of which yields better improvement in stability and functional recovery of the knee remains unclear. More high-quality trials and randomized controlled trials are needed. Although PCLR via the TT technique resulted in higher graft forces, determining whether this is clinically significant will require further studies. When performing the TI technique, surgeons should inform patients of the risk of complications.

Effect of Dynamic Changes in Anterior Cruciate Ligament In Situ Graft Force on the Biological Healing Response of the Graft-Tunnel Interface

Background: Anterior cruciate ligament (ACL) grafts that are placed for reconstruction are subject to complex forces. Current “anatomic” ACL reconstruction techniques may result in greater in situ graft forces. The biological effect of changing magnitudes of ACL graft force on graft-tunnel osseointegration is not well understood. Purpose: The research objective is to determine how mechanical force on the ACL graft during knee motion affects tendon healing in the tunnel. Study Design: Controlled laboratory study. Methods: Male rats (N = 120) underwent unilateral ACL reconstruction with a soft tissue flexor tendon autograft. ACL graft force was modulated by different femoral tunnel positions at the time of surgery to create different graft force patterns with knee motion. External fixators were used to eliminate graft load during cage activity. A custom knee flexion device was used to deliver graft load through controlled daily knee motion. Graft-tunnel healing was then assessed via biomechanical, micro–computed tomography, and histological analyses. Results: ACL graft-tunnel healing was sensitive to dynamic changes in graft forces with postoperative knee motion. High ACL graft force with joint motion resulted in early inferior ACL graft load to failure as compared with knees that had low-force ACL grafts and joint motion and knees that were immobilized (mean ± SD: 5.50 ± 2.30 N vs 9.91 ± 3.54 N [P = .013] and 10.90 ± 2.8 N [P = .001], respectively). Greater femoral bone volume fraction was seen in immobilized knees and knees with low-force ACL grafts when compared with high-force ACL grafts at 3 and 6 weeks. Conclusion: The authors were able to demonstrate that ACL graft-tunnel incorporation is sensitive to dynamic changes in ACL graft force with joint motion. Early high forces on the ACL graft appear to impair graft-tunnel osseointegration. Clinical Relevance: Current “anatomic” techniques of ACL reconstruction may result in greater graft excursion and force with knee motion. Our results suggest that the postoperative rehabilitation regimen may need to be modified during the early phase of healing to protect the reconstruction.

Femoral Tunnel Drilling Method: Revision Risk After Anterior Cruciate Ligament Reconstruction

Objectives:The femoral tunnel in anterior cruciate ligament reconstruction (ACLR) can be created by the transtibial (TT) or tibial-independent (TI) methods. An anatomically located femoral tunnel can be more consistently achieved by TI methods, which include the medial portal (MP) and lateral (outside-in, retrodrill) techniques. Non-anatomic graft placement in ACLR may result in postoperative instability and meniscal or chondral pathology. An anatomically located graft may be subjected to higher postoperative physiologic forces than one placed non-anatomically. The purpose of this study was to examine isolated primary ACLR and determine the risk of aseptic revision based on femoral tunnel drilling method.Methods:A retrospective cohort study was conducted using an integrated U.S. healthcare system’s ACLR Registry to identify primary isolated unilateral cases from 2009 to 2014. Bilateral, double-bundle and multi-ligament reconstructions were excluded. Patients were divided into two groups based on femoral tunnel drilling method, TT or TI. Drilling method was evaluated as a risk factor for aseptic revision, with adjustment for age, sex, body mass index (BMI), race, and graft type using multivariable Cox proportional-hazards regression models.Results:19,022 primary ACLR patients were included, of whom 6,991 (36.8%) were younger than 22 years old, 11,772 (61.9%) were male, 7,632 (40.1%) had a BMI < 25 kg/m2, 8,894 (46.8%) were White, and 7,403 (38.9%) received an allograft. There were 12,336 (64.9%) ACLRs performed using TI techniques (MP n=10,149, lateral n=2,187) and 6,686 (35.1%) using the TT method. Usage of TI approaches increased from 34% of all ACLR in 2009 to 84% in 2014. The cumulative reoperation probability at 5-year follow-up was lower in the TI group, 7.5% (95% CI 6.6-8.4), compared to the TT group, 8.2% (95% CI 7.4-9.1). After adjusting for the covariates, the cumulative failure probability at 5-year follow-up was higher in the TI group, 6.3% (95% CI 5.6-7.2), compared to the TT group, 5.0% (95% CI 4.3-5.7). [Figure 1] After adjusting for the covariates, the TI group had a higher risk for aseptic revision than the TT group (HR=1.4. 95% CI=1.1-1.7).Conclusion:In the largest known study of its type examining femoral tunnel drilling method for primary ACLR, after adjusting for age, sex, BMI, race and graft type, TI techniques were found to have a 1.4 times higher risk of revision than the TT method. Surgeons should be aware that ACLR grafts placed more anatomically by TI methods have a higher risk of revision, possibly due to higher postoperative physiologic graft forces experienced.

The biomechanical effect of tunnel placement on ACL graft forces in double-bundle ACL reconstruction - A 3D computational simulation.

The posterolateral (PL) graft experiences a high failure rate in anterior cruciate ligament double-bundle (DB) reconstruction. It is hypothesized that tunnel positions could dramatically affect the graft forces. A validated computational model was used to simulate DB reconstruction with various femoral PL tunnel locations (8-11mm center-center tunnel spacing). Graft fixation was simulated at both 0° and 30°. Knee biomechanics were examined with the knee under a 134N anterior load and 400N quadriceps load at 0°, 30°, 60°, and 90° of flexion. Graft forces, tibial translation, and tibial rotation were calculated. PL graft forces at full extension increased with increasing tunnel spacing under both fixation settings, but the knee kinematics was not dramatically affected. Small changes in the femoral PL tunnel position could result in large changes in graft forces, implying that precise PL tunnel position is an important factor in a successful DB reconstruction.

Anatomy and Biomechanics of the Native and Reconstructed Anterior Cruciate Ligament: Surgical Implications.

➤ Technical errors, such as nonanatomic tunnel placement, are among the most common causes of graft failure after anterior cruciate ligament (ACL) reconstruction.➤ No clinical superiority has been demonstrated for double-bundle ACL reconstruction compared with single-bundle reconstruction.➤ Single-bundle reconstruction of the anteromedial bundle has been shown to restore kinematics to the level of the intact knee, whereas reconstruction of the posterolateral bundle results in high graft forces.➤ Regardless of surgical technique (single-bundle compared with double-bundle or anteromedial portal compared with transtibial), the surgeon should avoid placement of a vertical or low femoral tunnel, as this results in abnormal knee kinematics.➤ ACL reconstruction is a patient-specific procedure, whereby surgeons should attempt to restore the native anatomy of the knee on a case-by-case basis and must take into account specific risk factors for ACL graft failure, such as younger age, higher activity level, and use of allograft, when counseling patients.

Is an Anterolateral Ligament Reconstruction Required in ACL-Reconstructed Knees With Associated Injury to the Anterolateral Structures? A Robotic Analysis of Rotational Knee Stability

Background: The effect of an anterolateral ligament (ALL) reconstruction on rotational knee stability and corresponding anterior cruciate ligament (ACL) graft forces using multiple knee loading conditions including the pivot-shift phenomenon has not been determined. Purpose: First, to determine the rotational stability and ACL graft forces provided by an anatomic bone–patellar tendon–bone ACL reconstruction in the ACL-deficient knee alone and with an associated ALL/iliotibial band (ITB) injury. Second, to determine the added rotational stabilizing effect and reduction in ACL graft forces provided by an ALL reconstruction. Study Design: Controlled laboratory study. Methods: A 6 degrees of freedom robotic simulator was used to test 7 fresh-frozen cadaveric specimens during 5 testing conditions: intact, ACL-sectioned, ACL-reconstructed, ALL/ITB-sectioned, and ALL-reconstructed. Lateral and medial tibiofemoral compartment translations and internal tibial rotations were measured under Lachman test conditions, 5-N·m internal rotation, and 2 pivot-shift simulations. Statistical equivalence within 2 mm and 2° was defined as P < .05. Results: Single-graft ACL reconstruction restored central tibial translation under Lachman testing and internal rotation under 5-N·m internal rotation torque (P < .05). A modest increase in internal rotation under 5-N·m internal rotation torque occurred after ALL/ITB sectioning of 5.1° (95% CI, 3.6° to 6.7°) and 6.7° (95% CI, 4.3° to 9.1°) at 60° and 90° of flexion, respectively (P = .99). Lateral compartment translation increases in the pivot-shift tests were <2 mm. ALL reconstruction restored internal rotation within 0.5° (95% CI, –1.9° to 2.9°) and 0.7° (95% CI, –2.0° to 3.4°) of the ACL-reconstructed state at 60° and 90° of flexion, respectively (P < .05). The ALL procedure reduced ACL graft forces, at most, 75 N in the pivot-shift tests and 81 N in the internal rotation tests. Conclusion: Although the ALL reconstruction corrected the small abnormal changes in the internal rotation limit at high flexion angles, the procedure had no effect in limiting tibiofemoral compartment translations in the pivot-shift test and produced only modest decreases in ACL graft forces. Accordingly, the recommendation to perform an ALL reconstruction to correct pivot-shift abnormalities is questioned. Clinical Relevance: The small changes in rotational stability after ALL/ITB sectioning would not seem to warrant the routine addition of an ALL reconstruction in primary ACL injuries. Clinical exceptions may exist, as in grossly unstable grade 3 pivot-shift knees and revision knees. However, the concern exists of overconstraining normal tibial rotations.

Assessing Risk Indicators of Allograft Survival of Renal Transplant: An Application of Joint Modeling of Longitudinal and Time-to-Event Analysis

After kidney transplantation, many risk factors can lead to graft rejection and force the patient to return to dialysis treatment. Objectives: This study aims to identify risk indicators of renal graft failure, such as serum creatinine, on long-term graft survival, using a novel statistical technique. Methods: In this historical cohort study, 129 patients who underwent kidney transplants were assessed and followed up from September 2003 to December 2014 in Urmia, Iran. The main outcome of the study was assessing the survival rate of kidney transplant in these subjects. In addition, the serum creatinine levels were measured repeatedly for one year after the operation, as the most important risk indicator of graft failure. In addition, the effect of other indicators on graft survival were assessed using a joint modeling of longitudinal and survival technique, using the R software, version 3.0.2. Results: One-, three-, five-, and ten-year graft survival was 93.8%, 86.8%, 76.6%, and 37.4%, respectively. The results of the joint model showed that risk indicators, such as serum creatinine level (P < 0.0001, HR = 1.82), patient’s age (P = 0.006, HR = 1.03), and antithymocytes globulin (P = 0.019, HR = 2.57) had a significant relationship to graft survival. Conclusions: In general, our study showed that short-term graft failure in Iran is almost equal to the reported rates in some developed countries, but its long-term failure is rather high compared to these same countries. In this context, monitoring the postoperative risk indicators of graft rejection, such as the serum creatinine level, plays an important role in increasing the survival rate of kidney transplantation. The present model can be used to design similarly structured datasets

Anterior laxity, graft-tunnel interaction and surgical design variations during anterior cruciate ligament reconstruction: A probabilistic simulation of the surgery

Anterior cruciate ligament (ACL) reconstructive surgeries, employing a total of 48 models, were conducted by virtually removing the ACL and then modeling the surgical preparation, tunnel architecture, graft pre-tensioning and fixation angle of a bone-patellar-tendon-bone autograft. Multifactorial sensitivity analyses were performed to assess the relative influence of these surgical factors on the intraoperative joint laxity, graft-tunnel contact mechanics and graft forces. The sensitivity results indicated that the combined variation in tunnel architecture and graft pre-tension at the time of fixation accounts for most of the estimated variance of the three outcomes. Joint laxity was largely influenced by tunnel placement with a modest contribution of the pre-tensioning force. However, variations in pre-tensioning force yielded a significant effect on both the in tunnel and intra-articular graft forces. Tunnel directions played the dominant role in the expressions of the contact shear between the graft and tunnel aperture in the fully extended and reconstructed joint. Given the proposed significance of the shear mediated graft abrasion at the graft-tunnel aperture, these sensitivity results are consistent with the general observation in the Multicenter ACL Revision Study (MARS), femoral tunnel architecture is most correlated with incidences of graft failures. Tunnel direction and graft pre-tension had similar effect on the estimated variance of the contact pressure in the fully extended joint. Data derived from the 48 ACL reconstructed models indicated that the anatomic surgical design may not be the only design that recovers the healthy joint laxity. In the context of the design of prospective studies, our findings highlight the need to include the graft tension and not fixation angle at the time of fixation as a variable in the evaluation of the surgery.

ACL Graft Position Affects in Situ Graft Force Following ACL Reconstruction

The purpose of our study was to evaluate the relationship between graft placement and in situ graft force after anterior cruciate ligament (ACL) reconstruction. Magnetic resonance imaging (MRI) was obtained for twelve human cadaveric knees. The knees, in intact and deficient-ACL states, were subjected to external loading conditions as follows: an anterior tibial load of 89 N at 0°, 15°, 30°, 45°, 60°, and 90° of flexion and a combined rotatory (simulated pivot-shift) load of 5 Nm of internal tibial torque and 7 Nm of valgus torque at 0°, 15°, and 30° of flexion. Three ACL reconstructions were performed in a randomized order: from the center of the tibial insertion site to the center of the femoral insertion site (Mid), the center of the tibial insertion site to a more vertical femoral position (S1), and the center of the tibial insertion site to an even more vertical femoral position (S2). The reconstructions were tested following the same protocol used for the intact state, and graft in situ force was calculated for the two loadings at each flexion angle. MRI was used to measure the graft inclination angle after each ACL reconstruction. The mean inclination angle (and standard deviation) was 51.7° ± 5.0° for the native ACL, 51.6° ± 4.1° for the Mid reconstruction (p = 0.85), 58.7° ± 5.4° for S1 (p < 0.001), and 64.7° ± 6.5° for S2 (p < 0.001). At 0°, 15°, and 30° of knee flexion, the Mid reconstruction showed in situ graft force that was closer to that of the native ACL during both anterior tibial loading and simulated pivot-shift loading than was the case for S1 and S2 reconstructions. At greater flexion angles, S1 and S2 had in situ graft force that was closer to that of the native ACL than was the case for the Mid reconstruction. Anatomic ACL reconstruction exposes grafts to higher loads at lower angles of knee flexion. Rehabilitation and return to sports progression may need to be modified to protect an anatomically placed graft after ACL reconstruction.

Anterior cruciate ligament reconstruction and cartilage contact forces—A 3D computational simulation

BackgroundClinical outcome studies showed a high incidence of knee osteoarthritis after anterior cruciate ligament reconstruction. Abnormal joint kinematics and loading conditions were assumed as risking factors. However, little is known on cartilage contact forces after the surgery. MethodsA validated computational model was used to simulate anatomic and transtibial single-bundle anterior cruciate ligament reconstructions. Two graft fixation angles (0° and 30°) were simulated for each reconstruction. Biomechanics of the knee was investigated in intact, anterior cruciate ligament deficient and reconstructed conditions when the knee was subjected to 134N anterior load and 400N quadriceps load at 0°, 30°, 60° and 90° of flexion. The tibial translation and rotation, graft forces, medial and lateral contact forces were calculated. FindingsWhen the graft was fixed at 0°, the anatomic reconstruction resulted in slightly larger lateral contact force at 0° compared to the intact knee while the transtibial technique led to higher contact force at both 0° and 30° under the muscle load. When graft was fixed at 30°, the anatomic reconstruction overstrained the knee at 0° with larger contact forces, while the transtibial technique resulted in slightly larger contact forces at 30°. InterpretationThis study suggests that neither the anatomic nor the transtibial reconstruction can consistently restore normal knee biomechanics at different flexion angles. The anatomic reconstruction may better restore anteroposterior stability and contact force with the graft fixed at 0°. The transtibial technique may better restore knee anteroposterior stability and articular contact force with the graft fixed at 30° of flexion.

The effect of graft strength on knee laxity and graft in-situ forces after posterior cruciate ligament reconstruction.

Surgical reconstruction is generally recommended for posterior cruciate ligament (PCL) injuries; however, the use of grafts is still a controversial problem. In this study, a three-dimensional finite element model of the human tibiofemoral joint with articular cartilage layers, menisci, and four main ligaments was constructed to investigate the effects of graft strengths on knee kinematics and in-situ forces of PCL grafts. Nine different graft strengths with stiffness ranging from 0% (PCL rupture) to 200%, in increments of 25%, of an intact PCL’s strength were used to simulate the PCL reconstruction. A 100 N posterior tibial drawer load was applied to the knee joint at full extension. Results revealed that the maximum posterior translation of the PCL rupture model (0% stiffness) was 6.77 mm in the medial compartment, which resulted in tibial internal rotation of about 3.01°. After PCL reconstruction with any graft strength, the laxity of the medial tibial compartment was noticeably improved. Tibial translation and rotation were similar to the intact knee after PCL reconstruction with graft strengths ranging from 75% to 125% of an intact PCL. When the graft’s strength surpassed 150%, the medial tibia moved forward and external tibial rotation greatly increased. The in-situ forces generated in the PCL grafts ranged from 13.15 N to 75.82 N, depending on the stiffness. In conclusion, the strength of PCL grafts have has a noticeable effect on anterior-posterior translation of the medial tibial compartment and its in-situ force. Similar kinematic response may happen in the models when the PCL graft’s strength lies between 75% and 125% of an intact PCL.

A phenomenological contact model: Understanding the graft–tunnel interaction in anterior cruciate ligament reconstructive surgery

In this paper, we sought to expand the fidelity of a validated model of the anterior cruciate ligament reconstruction (ACL-R) procedure by incorporating a stick–slip contact model with linear pressure–overclosure relationship at the interface. The suggested model is characterized by three unknown parameters, friction coefficient, shear stress softening and contact stiffness. In the absence of any isolated experiments exploring the graft–tunnel interactions during an aggregate joint load, the calibration data used in this study are derived from a reported biomechanical study. A Bayesian calibration procedure was employed to find the unknown probability distribution function (PDF) of these contact parameters. Initially, the response surface approximations of the predicted graft forces from laxity test simulations was adopted to estimate the likelihood of noisy experimental data reported in the literature. Then, the wide domain of contact parameters was sampled sequentially based on the Marcov Chain Monte Carlo (MCMC) method with acceptance–rejection criteria to search for population of samples in significantly narrower domain of unknown parameters that are associated with the highest occurrence likelihood of noisy experimental data. Our simulations with calibrated contact parameters indicate that pre-tensioning applied at 30° of flexion leads to larger graft force after the joint is fully extended compared to the graft force when the same pre-tensioning force is applied at full extension. Moreover, regardless of the pre-tensioning force, the graft–tunnel contact pressure is larger when the fixation of the graft is performed at full extension, increasing with the pre-tensioning force.

A Novel Small Animal Model of Differential Anterior Cruciate Ligament Reconstruction Graft Strain

The aim of the study was to establish a small animal research model of anterior cruciate ligament (ACL) reconstruction where ACL graft force can be predictably altered with knee motion. Cadaveric rat knees (n = 12) underwent ACL resection followed by reconstruction. Six knees received anterior (high-tension) femoral graft tunnels and six knees received posterior (isometric) graft tunnels. All the 12 knees and ACL grafts were pretensioned to 3 N at 15 or 45 degrees of knee flexion. ACL graft force (N) was recorded as the knee was ranged from extension to 90-degree flexion. Distinct ACL graft force patterns were generated for a high-tension and isometric femoral graft tunnels. For a high-tension femoral tunnel, the rat ACL graft remained relatively isometric at lower knee flexion angles but increased as the knee was flexed beyond 45 degrees. At 90 degrees, high-tension grafts had significantly greater mean graft tension for both pretensioning at 15 degrees (5.58 ± 1.34 N, p = 0.005) and 45 degrees (6.35 ± 1.24 N, p = 0.001). In contrast, the graft forces for isometric ACL grafts remained relatively constant with knee flexion. Compared with a high-tension ACL grafts, the graft force for grafts placed in an isometric tunnel had significantly lower ACL graft forces at 60, 75, and 90 degrees of knee flexion for both pretensioning at 15 and 45 degrees, respectively. We were able to demonstrate that ACL graft forces in our rat model of ACL reconstruction were sensitive to femoral tunnel position similar to human knees. We were also able to establish two reproducible femoral graft tunnel positions in this small animal model, which yielded significantly different ACL graft tension patterns with knee range of motion. This model would permit further research on how ACL graft tension may affect graft healing.

Posterior Cruciate Ligament Graft Fixation Angles, Part 2

Background: Prior studies have suggested that anatomic double-bundle (DB) posterior cruciate ligament reconstruction (PCLR) reduces residual laxity compared with the intact state better than single-bundle PCLR. Although the anterolateral bundle (ALB) and posteromedial bundle (PMB) reportedly act codominantly, few studies have compared commonly used graft fixation angles and the influence that graft fixation angles have on overall graft forces and knee laxity. Hypothesis: Graft fixation angle combinations of 0°/75° (PMB/ALB), 0°/90°, 0°/105°, 15°/75°, 15°/90°, and 15°/105° would significantly reduce knee laxity from the sectioned PCL state while preventing in vitro graft forces from being overloaded between any of the graft fixation angles. Study Design: Controlled laboratory study. Methods: Nine cadaveric knees were evaluated for the kinematics of the intact, PCL-sectioned, and DB PCLR techniques. The DB technique was varied by fixing the PMB and ALB grafts at the following 6 randomly ordered fixation angle combinations: 0°/75° (PMB/ALB), 0°/90°, 0°/105°, 15°/75°, 15°/90°, and 15°/105°. A 6 degrees of freedom robotic testing system subjected each specimen to an applied 134-N posterior tibial load at 0° to 120° of flexion and 5-N·m external, 5-N·m internal, and 10-N·m valgus rotation torques applied at 60°, 75°, 90°, 105°, and 120° of flexion. The ALB and PMB grafts were fixed to load cells that concurrently measured graft forces throughout kinematic testing. t tests compared the kinematics between groups, and 2-factor models assessed the contribution of ALB and PMB grafts after DB PCLR (P < .05). Results: Consistently, DB PCLR significantly reduced posterior translation compared with the sectioned PCL and was comparable with the intact state during applied posterior tibial loads at flexion angles of greater than 90°; a mean residual laxity of 1.5 mm remained compared with the intact state during applied posterior tibial loads. Additionally, fixing the PMB graft at 15° resulted in significantly larger PMB graft forces compared with fixation at 0° during applied posterior loading, internal rotation, external rotation, and valgus rotation. Similarly, fixing the ALB graft at 75° resulted in significantly larger ALB graft forces compared with fixation of the ALB graft at 90° or 105° during all loading conditions. Conclusion: Fixation of the PMB graft at 0° to 15° and the ALB graft at 75° to 105° during DB PCLR were successful in significantly reducing knee laxity from the sectioned state. However, fixation of the PMB graft at 15° versus 0° resulted in significantly increased loads through the PMB graft, and fixation of the ALB graft at 75° versus 90° or 105° resulted in significantly increased loads through the ALB graft. Clinical Relevance: This study found that all 6 fixation angle combinations significantly improved knee kinematics compared with the sectioned state at time zero; however, it is recommended that fixation of the PMB graft be performed at 0° because of the significant increases in PMB graft loading that occur with fixation at 15° and that fixation of the ALB graft be performed at 90° or 105° rather than 75° to minimize ALB graft forces, which could lead to graft attenuation or failure over time.