Infrapatellar fat pad abnormalities are associated with a higher inflammatory synovial fluid cytokine profile in young adults following ACL tear.

OBJECTIVE: To evaluate the degree of knee fat pad abnormalities after acute anterior cruciate ligament (ACL) tear via magnetic resonance fat pad scoring and to assess cross-sectionally its association with synovial fluid biomarkers and with early cartilage damage as quantified via T1ρ and T2 relaxation time measurements. DESIGN: 26 patients with acute ACL tears underwent 3T MR scanning of the injured knee prior to ACL reconstruction. The presence and degree of abnormalities of the infrapatellar (IPFP) and the suprapatellar (SPFP) fat pads were scored on MR images along with grading of effusion-synovitis and synovial proliferations. Knee cartilage composition was assessed by 3T MR T1ρ and T2 mapping in six knee compartments. We quantified concentrations of 20 biomarkers in synovial fluid aspirated at the time of ACL reconstruction. Spearman rank partial correlations with adjustments for age and gender were employed to evaluate correlations of MR, particularly cartilage composition and fat pad abnormalities, and biomarker data. RESULTS: The degree of IPFP abnormality correlated positively with the synovial levels of the inflammatory cytokine markers IFN-γ (ρpartial = 0.64, 95% CI (0.26-0.85)), IL-10 (ρpartial = 0.47, 95% CI (0.04-0.75)), IL-6 (ρpartial = 0.56, 95% CI (0.16-0.81)), IL-8 (ρpartial = 0.49, 95% CI (0.06-0.76)), TNF-α (ρpartial = 0.55, 95% CI (0.14-0.80)) and of the chondrodestructive markers MMP-1 and -3 (MMP-1: ρpartial = 0.57, 95% CI (0.17-0.81); MMP-3: ρpartial = 0.60, 95% CI (0.21-0.83)). IPFP abnormalities were significantly associated with higher T1ρ and T2 values in the trochlear cartilage (T1ρ: ρpartial = 0.55, 95% CI (0.15-0.80); T2: ρpartial = 0.58, 95% CI (0.18-0.81)) and with higher T2 values in the medial femoral, medial tibial as well as in patellar cartilage (0.45 ≤ ρpartial ≤ 0.59). Correlations between SPFP abnormalities and synovial markers were not significant except for IL-6 (ρpartial = 0.57, 95% CI (0.17-0.81)). CONCLUSIONS: This exploratory study suggests that acute ACL rupture can be associated with damage to knee tissues such as the inferior fat pad of the knee. Such fat pad injury could be partially responsible for the apparent post-injury pro-inflammatory response noted in ACL-injured individuals. However, future longitudinal studies are needed to link ACL-rupture associated fat pad injury with important patient outcomes such as the development of posttraumatic osteoarthritis.

IMU Sensor Fusion Algorithm for Monitoring Knee Kinematics in ACL Reconstructed Patients.

In this paper we propose a sensor embedded knee brace to monitor knee flexion and extension and other lower limb joint kinematics after anterior cruciate ligament (ACL) injury. The system can be easily attached to a standard post-surgical brace and uses a novel sensor fusion algorithm that does not require calibration. The wearable system and the sensor fusion algorithm were validated for various physical therapy exercises against a validated motion capture system. The proposed sensor fusion algorithm demonstrated significantly lower root-mean-square error (RMSE) than the benchmark Kalman filtering algorithm and excellent correlation coefficients (CCC and ICC). The demonstrated error for most exercises was lower than other devices in the literature. The quantitative measures obtained by this system can be used to obtain longitudinal range-of-motion and functional biomarkers. These biomarkers can be used to improve patient outcomes through the early detection of at-risk patients, tracking patient function outside of the clinic, and the identification of relationships between patient presentation, intervention, and outcomes.

Longitudinal changes in MR T1ρ/T2 signal of meniscus and its association with cartilage T1p/T2 in ACL-injured patients.

OBJECTIVE: To evaluate the longitudinal changes in meniscal T1ρ/T2 signal post-reconstruction in patients with acute anterior cruciate ligament (ACL) injury and to investigate the association with T1ρ/T2 signal in articular knee cartilage. METHOD: In this prospective study, knees of 37 patients with ACL-injury and reconstruction in addition to 13 healthy controls were scanned using magnetic resonance imaging (MRI) T1ρ/T2 mapping. Quantitative analysis of the meniscus was performed in the anterior/posterior horns of lateral/medial meniscus fourteen sub-compartments of cartilage spanning the medial/lateral area of the tibia and femoral condyles. Meniscus T1ρ/T2 signals were compared between injured, contralateral and control knees at baseline, 6-months, 1-year and 2-years using t-tests for cross-sectional comparisons and a mixed model for longitudinal comparisons. Pearson-partial correlations between meniscal and cartilage T1ρ/T2 were evaluated. RESULTS: There was a significant decrease of T1ρ/T2 signal in the posterior horn of lateral meniscus (PHLAT) of injured knees during a 2-year period. In the posterior horn of medial meniscus (PHMED), T1ρ/T2 signal of injured knees was significantly elevated at all time points post-reconstruction compared to contralateral and control knees. Within injured knees, PHMED T1ρ/T2 signal showed significant positive correlations with medial tibia (MT) cartilage T1ρ/T2 signal at all time points. CONCLUSION: A significant decrease in PHLAT T1ρ/T2 signal by 2-years suggests potential tissue recovery after ACL-injury. Elevated T1ρ/T2 signal in the PHMED of injured knees at 2-years correlating with knee cartilage T1ρ/T2 signal elevations suggests involvement of the PHMED in subacute cartilage degeneration after ACL-injury and reconstruction.

The association between MR T1ρ and T2 of cartilage and patient-reported outcomes after ACL injury and reconstruction.

OBJECTIVE: To determine if cartilage T1ρ and T2 relaxation time measures after ACL injury and prior to reconstruction (baseline) are associated with patient-reported outcomes at baseline, 6-months, and 1-year after surgery. DESIGN: Fifty-four ACL-injured participants were scanned in both knees at baseline using 3T MR T1ρ and T2 mapping. Participants also completed Knee-injury and Osteoarthritis Outcome Score (KOOS) and Marx activity level questionnaires at baseline, 6-months, and 1-year after reconstruction. The difference between cartilage T1ρ or T2 of the injured and contralateral knee (side-to-side difference, SSD) was calculated to account for physiological variations among patients. Linear regression models were built to evaluate the association between the baseline SSD T1ρ or T2 and KOOS or Marx at all time points. RESULTS: Higher baseline SSD T1ρ posterolateral tibia (pLT) was associated with worse KOOS in all subscales except symptoms at baseline, worse KOOS pain at 6-months, and worse KOOS in all subscales except sports function at 1-year. Higher baseline SSD T2 femoral trochlea (TrF) was associated with worse KOOS activities of daily living (ADL) at 1-year. Higher baseline SSD T1ρ pLT was associated with lower Marx activity level at 1-year. More severe cartilage lesions, as assessed by Whole-Organ MRI Scoring (WORMS), was significantly associated with worse KOOS pain at 6-months and 1-year. CONCLUSION: T1ρ and T2 of cartilage after ACL injury were associated with KOOS after injury and both KOOS and Marx after reconstruction. Such associations may help clinicians stratify outcomes post-injury, and thus, improve patient management.

Three-dimensional MRI-based statistical shape model and application to a cohort of knees with acute ACL injury.

OBJECTIVE: The aim of this study is to develop a novel 3D magnetic resonance imaging (MRI)-based Statistical Shape Modeling (SSM) and apply it in knee MRIs in order to extract and compare relevant shapes of the tibia and femur in patients with and without acute Anterior cruciate ligament (ACL) injuries. METHODS: Bilateral MR images were acquired and analyzed for 50 patients with acute ACL injuries and for 19 control subjects. A shape model was extracted for the tibia and femur using an SSM algorithm based on a set of matched landmarks that are computed in a fully automatic manner. RESULTS: Shape differences were detected between the knees in the ACL-injury group and control group, suggesting a common shape feature that may predispose these knees to injury. Some of the detected shape features that discriminate between injured and control knees are related to intercondylar width and posterior tibia slope, features that have been suggested in previous studies as ACL morphological risk factors. However, shape modeling has the great potential to quantify these characteristics with a comprehensive description of the surfaces describing complex 3D deformation that cannot be represented with simple geometric indexes. CONCLUSIONS: 3D MRI-based bone shape quantification has the ability to identify specific anatomic risk factors for ACL injury. A better understanding of the role in bony shape on ligamentous injuries could help in the identification of subjects with an increased risk for an ACL tear and to develop targeted prevention strategies, including education and training.

Cartilage morphology and T1ρ and T2 quantification in ACL-reconstructed knees: a 2-year follow-up.

OBJECTIVE: To describe cartilage matrix and morphology changes, assessed using quantitative magnetic resonance imaging (MRI), after acute anterior cruciate ligament (ACL) injury relative to controls and longitudinally during 2 years following reconstruction. METHOD: Fifteen patients with acute ACL injuries and 16 healthy volunteers with a similar demographic profile but no history of osteoarthritis or knee injury were studied. The injured knee of each participant was imaged with a 3.0 T MR scanner at baseline (prior to ACL reconstruction); patients' knees were re-imaged 1 and 2 years after ACL reconstruction. Cartilage T1ρ and T2 values in full thickness, superficial layers, and deep layers, and cartilage thickness of the full layer were quantified within subcompartments of the knee joint. RESULTS: In the posterolateral tibial cartilage, T1ρ values were significantly higher in ACL-injured knees than control knees at baseline and were not fully recovered 2 after ACL reconstruction. T1ρ values of medial tibiofemoral cartilage in ACL-injured knees increased over the 2-year study and were significantly elevated compared to that of the control knees. T2 values in cartilage of the central aspect of the medial femoral condyle at the 2-year follow-up were significantly elevated compared with control knees. Cartilage in the posterior regions of the lateral tibia was significantly thinner, while cartilage in the central aspect of the medial femur was significantly thicker than that of controls. Patients with lesions in the posterior horn of the medial meniscus exhibited significantly higher T1ρ values in weight-bearing regions of the tibiofemoral cartilage than that of control subjects over the 2-year period, whereas patients without medial meniscal tears did not. CONCLUSION: Quantitative MRI provides powerful in vivo tools to quantitatively evaluate early changes of cartilage matrix and morphology after acute ACL injury and reconstruction, which may possibly relate to the development of post-traumatic osteoarthritis in such joints.

Design of two-dimensional tunable photonic crystals with multiple functionalities.

Negative refraction is an interesting phenomenon which can provide sub-wavelength imaging and a novel way to control the propagation path of photons. Photonic crystals have been intensively researched to achieve negative refraction. In this article, we present design and simulations of a new two-dimensional tunable photonic crystal obtained using the plane wave expansion method. The newly designed photonic crystals exhibit tunability among positive, zero, and negative refractions, when liquid crystals infiltrated in the structures are electrically tuned. The equifrequency surface diagrams of the designed photonic crystal unveil the refraction direction of photons in the structures. The tunability is further confirmed using the finite-difference time-domain simulation.

Agranulocytosis induced by multidrug therapy in leprosy treatment: a case report.

Multidrug therapy (WHO/MDT) in multibacillary leprosy consists of treatment with rifampicin, dapsone and clofazimine. However, adverse effects can cause the patient to abandon treatment. We report on a patient who presented agranulocytosis and hemolytic anemia associated with this treatment regime. We also examined the importance of laboratory exams for diagnosis and follow-up of the patient, and for early detection of adverse effects,with a view to improving adhesion to treatment and contributing to the eradication of Hansen's disease as a public health issue.

A multidisciplinary study of the healing of an intraarticular anterior cruciate ligament graft in a goat model.

We evaluated knee function, tensile properties, and histologic appearance of a healing intraarticular bone-patellar tendon-bone autograft after anterior cruciate ligament reconstruction in a goat model. The patellar tendon graft was fixed such that both bone-to-bone (femoral tunnel) and bone-to-tendon (tibial tunnel) healing could be studied. The total anteroposterior translation significantly increased from 3 to 6 weeks, ranging from increases of 28.8% to 46.7%. In situ forces in the replacement graft decreased as much as 22.2% at 6 weeks. Conversely, tensile properties of the femur-anterior cruciate ligament graft-tibia complex did not change significantly from 3 to 6 weeks. However, the mode of failure changed from the graft pulling out of the tibial tunnel at 3 weeks to a mix of midsubstance failures (N = 2) and pullouts (N = 5) at 6 weeks. Histologic evaluations revealed progressive and complete incorporation of the bone block in the femoral tunnel, but only partial incorporation of the tendinous part of the graft in the tibial tunnel. The differences demonstrated at 3 and 6 weeks may be a result of the remodeling process of the midsubstance of the graft as the interfaces within the osseous tunnels mature.

Structure and function of the healing medial collateral ligament in a goat model.

In this study knee joint function with a healing medial collateral ligament (MCL) at six weeks was examined with a robotic/universal force-moment sensor testing system during the application of two loading conditions: (1) 5 Nm valgus moment and (2) 67 N anterior load. Additionally the structural properties of the femur-MCL-tibia complex and the mechanical properties of the MCL substance were determined by uniaxial tensile tests. The histological appearance of the healing MCL was also observed. At 30 degrees and 60 degrees of knee flexion, valgus rotation of the healing knee was significantly increased compared to the sham. The in situ force in the healing MCL was significantly lower (34+/-17 N vs 54+/-12 N) at the same flexion angles (50+/-10 N vs 62+/-7 N). The anterior translation of the knee had returned to normal values at 30 degrees and 60 degrees of knee flexion. However, no differences could be found between the corresponding in situ forces in the healing MCL at all flexion angles examined during application of an anterior load. The stiffness of the healing group (52.5+/-19.4 N/mm) was significantly lower than the sham group (80.3+/-26.4 N/mm) (p<0.04). The modulus of the healing group was also significantly decreased (p<0.05). The findings suggest that the tensile properties of the healing goat MCL and valgus knee rotation have not returned to normal at six weeks after an isolated MCL rupture, however, anterior translation appeared to return to sham levels.

Interaction between the ACL graft and MCL in a combined ACL+MCL knee injury using a goat model.

The optimal treatment for the MCL in the combined ACL and MCL-injured knee is still controversial. Therefore, we designed this study to examine the mechanical interaction between the ACL graft and the MCL in a goat model using a robotic/universal force-moment sensor testing system. The kinematics of intact, ACL-deficient, ACL-reconstructed, and ACL-reconstructed/ MCL-deficient knees, as well as the in situ forces in the ACL, ACL graft, and MCL were determined in response to two external loading conditions: 1) anterior tibial load of 67 N and 2) valgus moment of 5 N-m. With an anterior tibial load, anterior tibial translation in the ACL-deficient knee significantly increased from 2.0 and 2.2 mm to 15.7 and 18.1 mm at 30 degrees and 60 degrees of knee flexion, respectively. The in situ forces in the MCL also increased from 8 to 27 N at 60 degrees of knee flexion. ACL reconstruction reduced the anterior tibial translation to within 2 mm of the intact knee and significantly reduced the in situ force in the MCL to 17 N. However, in response to a valgus moment, the in situ forces in the ACL graft increased significantly by 34 N after transecting the MCL. These findings show that ACL deficiency can increase the in situ forces in the MCL while ACL reconstruction can reduce the in situ forces in the MCL in response to an anterior tibial load. On the other hand, the ACL graft is subjected to significantly higher in situ forces with MCL deficiency during an applied valgus moment. Therefore, the ACL-reconstructed knee with a combined ACL and MCL injury should be protected from high valgus moments during early healing to avoid excessive loading on the graft.

The forces in the anterior cruciate ligament and knee kinematics during a simulated pivot shift test: A human cadaveric study using robotic technology.

PURPOSE: Although it is well known that the anterior cruciate ligament (ACL) is a primary restraint of the knee under anterior tibial load, the role of the ACL in resisting internal tibial torque and the pivot shift test is controversial. The objective of this study was to determine the effect of these 2 external loading conditions on the kinematics of the intact and ACL-deficient knee and the in situ force in the ACL. TYPE OF STUDY: This study was a biomechanical study that used cadaveric knees with the intact knee of the specimen serving as a control. MATERIALS AND METHODS: Twelve human cadaveric knees were tested using a robotic/universal force-moment sensor testing system. This system applied (1) a 10-Newton meter (Nm) internal tibial torque and (2) a combined 10-Nm valgus and 10-Nm internal tibial torque (simulated pivot shift test) to the intact and the ACL-deficient knee. RESULTS: In the ACL-deficient knee, the isolated internal tibial torque significantly increased coupled anterior tibial translation over that of the intact knee by 94%, 48%, and 19% at full extension, 15 degrees, and 30 degrees of flexion, respectively (P <.05). In the case of the simulated pivot shift test, there were similar increases in anterior tibial translation, i.e., 103%, 61%, and 32%, respectively (P <.05). Furthermore, the anterior tibial translation under the simulated pivot shift test was significantly greater than under an isolated internal tibial torque (P <.05). Under the simulated pivot shift test, the in situ forces in the ACL were 83 +/- 16 N at full extension and 93 +/- 23 N at 15 degrees of knee flexion. These forces were also significantly higher when compared with those for an isolated internal tibial torque (P <.05). CONCLUSION: Our data indicate that the ACL plays an important role in restraining coupled anterior tibial translation in response to the simulated pivot shift test as well as under an isolated internal tibial torque, especially when the knee is near extension. These findings are also consistent with the clinical observation of anterior tibial subluxation during the pivot shift test with the knee near extension.

The effect of knee flexion angle and application of an anterior tibial load at the time of graft fixation on the biomechanics of a posterior cruciate ligament-reconstructed knee.

Ten knees were studied using a robotic testing system under a 134-N posterior tibial load at five flexion angles. Three knee positions were used to study the effect of flexion angle at the time of graft fixation (full extension, 60 degrees, and 90 degrees) and two were used to study the effect of anterior tibial load (60 degrees and 90 degrees). Knee kinematics and in situ forces were determined for the intact ligament and the graft for each reconstruction. Graft fixation at full extension significantly decreased posterior tibial translation compared with the intact knee by up to 2.9 +/- 2.9 mm at 30 degrees, while in situ forces in the graft were up to 18 +/- 35 N greater than for the intact ligament. Conversely, posterior tibial translation for graft fixation at 90 degrees was significantly greater than that of the intact knee by up to 2.2 +/- 1.1 mm at all flexion angles; in situ forces decreased as much as 33 +/- 30 N. When an anterior tibial load was applied before graft fixation at 90 degrees of flexion, posterior tibial translation did not differ from the intact knee from 30 degrees to 120 degrees, while the in situ force in the graft did not differ from the intact ligament at full extension, 60 degrees, and 120 degrees of flexion. These data suggest that graft fixation at full extension may overconstrain the knee and elevate in situ graft forces. Conversely, fixation with the knee in flexion and an anterior tibial load best restored intact knee biomechanics.

Significance of changes in the reference position for measurements of tibial translation and diagnosis of cruciate ligament deficiency.

Measurements of tibial translation in response to an external load are used in clinical and laboratory settings to diagnose and characterize knee-ligament injuries. Before these measurements can be quantified, a reference position of the knee must be established (defined as the position of the knee with no external forces or moments applied). The objective of this study was to determine the effects of cruciate ligament deficiency on this reference position and on subsequent measurements of tibial translation and, in so doing, to establish a standard of kinematic measurement for future biomechanical studies. Thirty-six human cadaveric knees were studied with a robotic/universal force-moment sensor testing system. The reference positions of the intact and posterior cruciate ligament-deficient knees of 18 specimens were determined at full extension and at 30, 60, 90, and 120 degrees of flexion, and the remaining five-degree-of-freedom knee motion was unrestricted. Subsequently, under a 134-N anterior-posterior load, the resulting knee kinematics were measured with respect to the reference positions of the intact and posterior cruciate ligament-deficient knees. With posterior cruciate ligament deficiency, the reference position of the knee moved significantly in the posterior direction, reaching a maximal shift of 9.3 +/- 3.8 mm at 90 degrees of flexion. For the posterior cruciate ligament-deficient knee, posterior tibial translation ranged from 13.0 +/- 3.4 to 17.7 +/- 3.6 mm at 30 and 90 degrees, respectively, when measured with respect to the reference positions of the intact knee. When measured with respect to the reference positions of the posterior cruciate ligament-deficient knee, these values were significantly lower, ranging from 11.7 +/- 4.3 mm at 30 degrees of knee flexion to 8.4 +/- 4.8 mm at 90 degrees. A similar protocol was performed to study the effects of anterior cruciate ligament deficiency on 18 additional knees. With anterior cruciate ligament deficiency, only a very small anterior shift in the reference position was observed. Overall, this shift did not significantly affect measurements of tibial translation in the anterior cruciate ligament-deficient knee. Thus, when the tibial translation in the posterior cruciate ligament-injured knee is measured when the reference position of the intact knee is not available, errors can occur and the measurement may not completely reflect the significance of posterior cruciate ligament deficiency. However, there should be less corresponding error when measuring the tibial translation of the anterior cruciate ligament-injured knee because the shift in reference position with anterior cruciate ligament deficiency is too small to be significant. We therefore recommend that in the clinical setting, where the reference position of the knee changes with injury, comparison of total anterior-posterior translation with that of the uninjured knee can be a more reproducible and accurate measurement for assessing cruciate-ligament injury, especially in posterior cruciate ligament-injured knees. Similarly, in biomechanical testing where tibial translations are often reported for the ligament-deficient and reconstructed knees, a fixed reference position should be chosen when measuring knee kinematics. If such a standard is set, measurements of knee kinematics will more accurately reflect the altered condition of the knee and allow valid comparisons between studies.

Biomechanical analysis of a posterior cruciate ligament reconstruction. Deficiency of the posterolateral structures as a cause of graft failure.

We hypothesized that posterior cruciate ligament reconstructions are often compromised by associated injuries to the posterolateral structures. Therefore, we evaluated a posterior cruciate ligament reconstruction in isolated and combined injury models using a robotic/universal force-moment sensor testing system. The resulting knee kinematics and the in situ forces in the native and reconstructed posterior cruciate ligament were determined under four external loading conditions. In the isolated injury model, reconstruction reduced posterior tibial translation to within 1.5+/-1.3 to 2.4+/-1.4 mm of the intact knee at 30 degrees and 90 degrees under a 134-N posterior tibial load. In the combined injury model, deficiency of the posterolateral structures increased posterior tibial translation of the reconstructed knee by 6.0+/-2.7 mm at 30 degrees and 4.6+/-1.5 mm at 90 degrees of flexion. External rotation increased up to 14 degrees while varus rotation increased up to 7 degrees. In situ forces in the posterior cruciate ligament graft also increased significantly (by 22% to 150%) for all loading conditions. Our results demonstrate that a graft that restores knee kinematics for an isolated posterior cruciate ligament deficiency is rendered ineffective and may be overloaded if the posterolateral structures are deficient. Therefore, surgical reconstruction of both structures is recommended in the setting of a combined injury.

Current trends in anterior cruciate ligament reconstruction. Part II. Operative procedures and clinical correlations.

Surgical management of the anterior cruciate ligament-deficient knee has evolved from primary repair to extracapsular augmentation to anterior cruciate ligament reconstruction using biologic tissue grafts. The technique of anterior cruciate ligament reconstruction has improved over the last few decades with the aid of knowledge gained from basic science and clinical research. The biology and biomechanics of anterior cruciate ligament reconstruction were analyzed in the previously published first part of this article. In this second part, current operative concepts of anterior cruciate ligament reconstruction as well as clinical correlations are discussed. The latest information regarding anterior cruciate ligament reconstruction is presented with a goal of demonstrating the correlation between the application of basic science knowledge and the improvement of clinical outcomes.

Current trends in anterior cruciate ligament reconstruction. Part 1: Biology and biomechanics of reconstruction.

With today's increasing emphasis on sporting activities, the incidence of anterior cruciate ligament injuries has also increased. Epidemiologic studies estimate that the prevalence of anterior cruciate ligament injuries is about 1 per 3000 Americans. Management of these injuries has evolved from nonoperative treatment to extracapsular augmentation and primary ligament repair to anterior cruciate ligament reconstruction. Treatment of these injuries has significantly improved over the last few decades with the application of knowledge gained from both basic science and clinical research. This article is composed of two parts. The first part reviews the biology and biomechanics of the injured anterior cruciate ligament and the basic science of reconstruction. In the second part, to be published later, current operative concepts of reconstruction, as well as clinical correlations, are reviewed. Summarizing the latest information on basic scientific as well as clinical studies regarding the anterior cruciate ligament, this article intends to demonstrate the correlation between the application of basic science knowledge and improvement of clinical outcomes.

Hamstring graft motion in the femoral bone tunnel when using titanium button/polyester tape fixation.

The objective of this study was to determine the relative motion of a quadruple hamstring graft within the femoral bone tunnel (graft-tunnel motion) under tensile loading. Six graft constructs were prepared from the semitendinosus and gracilis tendons of human cadavers and were fixed with a titanium button and polyester tape within a bone tunnel in a cadaveric femur. Three different lengths of polyester tape (15, 25, and 35 mm loops) were evaluated. The femur was held stationary and uniaxial tensile loads were applied to the distal end of the graft using a materials testing machine. Each construct was subjected to loading for ten cycles with upper limits of 50 N, 100 N, 200 N and 300 N. Graft-tunnel motion was then determined using the distances between reflective tape markers placed on the hamstring graft and at the entrance to the femoral bone tunnel, which were tracked with a high-resolution video system. Graft-tunnel motion was found to range from 0.7 +/- 0.2 mm to 3.3 +/- 0.2 mm, and significant increases in graft-tunnel motion were observed with increasing tensile loads (P < 0.05). Shorter tape length (15 mm) resulted in significantly less motion when compared to longer tape length (35 mm) (P < 0.05). We conclude that graft-tunnel motion is significant and should be considered when using this fixation technique. Early stress on the graft, as seen in postoperative rehabilitation exercises and athletic activities, may cause large graft-tunnel motion before graft incorporation is complete. A shorter distance between the tendon tissue and the titanium button is recommended to minimize the amount of graft-tunnel motion. Alternative fixation materials to polyester tape, or different fixation techniques, need to be developed such that graft-tunnel motion can be reduced. Further studies are needed to evaluate the effect of graft-tunnel motion on graft incorporation in the bone tunnel.

The importance of quadriceps and hamstring muscle loading on knee kinematics and in-situ forces in the ACL.

This study investigated the effect of hamstring co-contraction with quadriceps on the kinematics of the human knee joint and the in-situ forces in the anterior cruciate ligament (ACL) during a simulated isometric extension motion of the knee. Cadaveric human knee specimens (n = 10) were tested using the robotic universal force moment sensor (UFS) system and measurements of knee kinematics and in-situ forces in the ACL were based on reference positions on the path of passive flexion/extension motion of the knee. With an isolated 200 N quadriceps load, the knee underwent anterior and lateral tibial translation as well as internal tibial rotation with respect to the femur. Both translation and rotation increased when the knee was flexed from full extension to 30 of flexion; with further flexion, these motion decreased. The addition of 80 N antagonistic hamstrings load significantly reduced both anterior and lateral tibial translation as well as internal tibial rotation at knee flexion angles tested except at full extension. At 30 of flexion, the anterior tibial translation, lateral tibial translation, and internal tibial rotation were significantly reduced by 18, 46, and 30%, respectively (p<0.05). The in-situ forces in the ACL under the quadriceps load were found to increase from 27.8+/-9.3 N at full extension to a maximum of 44.9+/-13.8 N at 15 of flexion and then decrease to 10 N beyond 60 of flexion. The in-situ force at 15 was significantly higher than that at other flexion angles (p<0.05). The addition of the hamstring load of 80 N significantly reduced the in-situ forces in the ACL at 15, 30 and 60 of flexion by 30, 43, and 44%, respectively (p<0.05). These data demonstrate that maximum knee motion may not necessarily correspond to the highest in-situ forces in the ACL. The data also suggest that hamstring co-contraction with quadriceps is effective in reducing excessive forces in the ACL particularly between 15 and 60 of knee flexion.