Patrick Smolinski

Tibiofemoral Joint Contact Area and Pressure After Single- and Double-Bundle Anterior Cruciate Ligament Reconstruction

PURPOSE The purpose of this study was to compare the tibiofemoral contact area and pressure after single-bundle (SB) and double-bundle (DB) anterior cruciate ligament (ACL) reconstruction by use of 2 femoral and 2 tibial tunnels in intact cadaveric knees. METHODS Tibiofemoral contact area and mean and maximum pressures were measured by pressure-sensitive film (Fujifilm, Valhalla, NY) inserted between the tibia and femur. The knee was subjected to a 1,000-N axial load by use of a uniaxial testing machine at 0 degrees , 15 degrees , 30 degrees , and 45 degrees of flexion. Three conditions were evaluated: (1) intact ACL, (2) SB ACL reconstruction (n = 10 knees), and (3) DB ACL reconstruction (n = 9 knees). RESULTS When compared with the intact knee, DB ACL reconstruction showed no significant difference in tibiofemoral contact area and mean and maximum pressures. SB ACL reconstruction had a significantly smaller contact area on the lateral and medial tibiofemoral joints at 30 degrees and 15 degrees of flexion. SB ACL reconstruction also had significantly higher mean pressures at 15 degrees of flexion on the medial tibiofemoral joint and at 0 degrees and 15 degrees of flexion on the lateral tibiofemoral joint, as well as significantly higher maximum pressures at 15 degrees of flexion on the lateral tibiofemoral joint. CONCLUSIONS SB ACL reconstruction resulted in a significantly smaller tibiofemoral contact area and higher pressures. DB ACL more closely restores the normal contact area and pressure mainly at low flexion angles. CLINICAL RELEVANCE Our findings suggest that the changes in the contact area and pressures after SB ACL reconstruction may be one of the causes of osteoarthritis on long-term follow-up. DB ACL reconstruction may reduce the incidence of osteoarthritis by closely restoring contact area and pressure.

Identification of elastic properties of homogeneous, orthotropic vascular segments in distension

Characterization of the constitutive behavior of normal and pathological blood vessel segments could provide the clinician with a means to predict the onset and assess the severity of certain vascular maladies. Many of the constitutive models that have been proposed to date either fail to properly consider certain features of the anatomic structure and function of vascular tissue or are so mathematically complex that their utilization is intractable. We have developed a material identification technique that first required the adaptation and validation of a constitutive law describing the nonlinear, three-dimensional behavior of orthotropic, compressible, hyperelastic vascular segments. By coupling a nonlinear finite element program and experimental data with a robust nonlinear least-squares regression algorithm, a set of elastic parameters (moduli) is obtained. Regressions on data for a canine carotid artery and rabbit infrarenal aorta yielded coefficients of variation of 0.21 and 0.08, respectively. The estimated moduli demonstrated certain trends found by other investigators: both the canine carotid artery and rabbit aorta were found to be stiffer radially than circumferentially, and the former was found to be stiffer circumferentially than longitudinally. Using these material constants and measured arterial pressures, the stress distribution was computed for each specimen. The predicted radial stress was consistent with a transmural variation of approximately--p (applied luminal pressure) to approximately zero in both specimens, while the circumferential stresses ranged from 2.2p to 0.7p for the canine carotid, and from 6.4p to 3.7p for the rabbit aorta. The stress distributions qualitatively agreed with those reported in previous investigations, as well as with certain physiologic observations. Based on the results of our two sample cases, we believe that our technique could be beneficial to the assessment of the three-dimensional, anisotropic behavior of vascular tissue.

Impingement Pressure in the Anatomical and Nonanatomical Anterior Cruciate Ligament Reconstruction A Cadaver Study

Background: Although the literature has extensively discussed impingement after anterior cruciate ligament (ACL) reconstruction, the definition of impingement is vague, and impingement pressure has not been well investigated as a function of tunnel position. Purpose: To determine the amount of impingement pressure between the ACL and posterior cruciate ligament (PCL) and between the ACL and notch roof in the native ACL, the single-bundle ACL reconstruction with different tunnel placements, and the anatomical double-bundle ACL reconstruction. Study design: Controlled laboratory study. Methods: Fifteen fresh-frozen nonpaired human cadaver knees were used. In each knee, different femoral and tibial tunnels were created, which allowed different graft placements. A single graft was placed in 3 positions: tibial anteromedial (AM) to femoral AM (anatomical), tibial posterolateral (PL) to femoral high AM (nonanatomical/mismatch), and tibial AM to femoral high AM. Double grafts were placed in an anatomical fashion (AM to AM and PL to PL). In each case, pressure-measuring films were inserted between the ACL and roof, the ACL and PCL, and the AM and PL bundles (for double-bundle group only). Knees were then moved with 40 N of force and from full flexion to full extension, and the pressure pattern on the film was analyzed. Results: Compared with other groups, only the AM–high AM group showed significantly higher roof impingement pressure (P < .05). There was no significant difference in PCL impingement pressure between the intact ACL group and any of the reconstructed groups. No impingement pressure was observed between the grafts in the anatomical double-bundle ACL reconstruction. Conclusion: This study evaluated the effect of different tunnel placements on the impingement pressure after ACL reconstruction. Anatomical single- or double-bundle ACL reconstruction and nonanatomical tibial PL–femoral high AM ACL reconstruction do not cause roof, PCL, and interbundle impingement. Clinical relevance: Surgeons can perform the anatomical double-bundle ACL, anatomical single-bundle, and nonanatomical tibial PL–femoral high AM reconstructions as impingement-free reconstructions.

Anterior Cruciate Ligament Tunnel Position Measurement Reliability on 3-Dimensional Reconstructed Computed Tomography

PURPOSE The purpose of this study was to evaluate intraobserver and interobserver reliability of anterior cruciate ligament tunnel location measurement by use of 3-dimensional reconstructed computed tomography (CT). METHODS Three-dimensional reconstructed CT images of 31 cadaveric knees were used in this study. Twenty-one knees were operated on with a double-bundle technique, and ten knees were operated on with a single-bundle technique. Femoral tunnel location was measured with 3 methods on the medial-lateral view of the lateral femoral condyle in the strictly lateral position. Tibial tunnel location was measured in the top view of the proximal tibia. The images were evaluated independently by 2 orthopaedic surgeons. A second measurement was performed, by both testers, after a 4-week interval. RESULTS The 3 methods of femoral tunnel location measurement had intraobserver intraclass correlation coefficients (ICCs) that ranged from 0.963 to 0.998 and interobserver ICCs that ranged from 0.993 to 0.999. Tibial tunnel measurement had intraobserver ICCs that varied between 0.957 and 0.998 and interobserver ICCs that varied between 0.993 and 0.996. CONCLUSIONS The measurement of the anterior cruciate ligament tunnel location on 3-dimensional reconstructed CT provided excellent intraobserver and interobserver reliability. CLINICAL RELEVANCE Three-dimensional reconstructed CT can be used for further studies to assess the effect of tunnel position on knee stability and patient outcomes.

Morphology of the tibial insertion of the posterior cruciate ligament.

BACKGROUND It has been demonstrated that double-bundle reconstruction of the posterior cruciate ligament restores knee kinematics better than does single-bundle reconstruction. The objective of this study was to identify the tibial insertion site of the posterior cruciate ligament and the related osseous landmarks to help guide surgeons in the performance of an anatomical double-bundle reconstruction of the posterior cruciate ligament. METHODS Twenty-one unpaired human cadaver knees were evaluated. The geometric data and surface features of the tibial insertion site of the posterior cruciate ligament and its bundles were studied with macroscopic observation and with three-dimensional laser photography. RESULTS The mean surface areas (and standard deviations) of the anterolateral and posteromedial insertion sites were 93.1+/-16.6 mm2 and 150.8+/-31.0 mm2, respectively, and the distance between their centers was 8.2+/-1.3 mm. The mean length and width of the anterolateral insertion site were 7.8+/-1.5 mm and 9.2+/-1.6 mm, and the mean length and width of the posteromedial insertion site were 9.4+/-1.4 mm and 15.0+/-2.7 mm. The average distances from the anterior and medial margins of the tibial plane to the center of the anterolateral insertion, defined as percentage ratios of the anteroposterior and mediolateral dimensions, were 83.4%+/-3.4% and 47.1%+/-1.9%, respectively, and the average distances from the anterior and medial margins of the tibial plane to the center of the posteromedial insertion were 95.5%+/-1.9% and 43.8%+/-2.2%. A notable change in angle, of >10 degrees, was observed between the anterolateral and posteromedial slopes in sixteen of the twenty-one knees. The average angle between the anterolateral and posteromedial slopes was 14.5 degrees+/-6.4 degrees. CONCLUSIONS The tibial insertion site of the posterior cruciate ligament and its bundles is very complex. However, the shapes and positions of the insertion sites of the two bundles are consistent in that they are located in different planes on the posterior intercondylar fossa. We noted a consistent change in slope between the tibial insertion sites of the anterolateral and posteromedial bundles.

Stability of an explicit multi-time step integration algorithm for linear structural dynamics equations

A proof of stability is developed for an explicit multi-time step integration method of the second order differential equations which result from a semidiscretization of the equations of structural dynamics. The proof is applicable to an algorithm that partitions the mesh into subdomains according to nodal groups which are updated with different time steps. The stability of the algorithm is demonstrated by showing that the eigenvalues of the amplification matrices lie within the unit circle and that a pseudo-energy remains constant. Bounds on the stable time steps for the nodal partitions are developed in terms of element frequencies.

Intercondylar roof impingement pressure after anterior cruciate ligament reconstruction in a porcine model

Anterior cruciate ligament (ACL) graft impingement against the intercondylar roof has been postulated, but not thoroughly investigated. The roof impingement pressure changes with different tibial and femoral tunnel positions in ACL reconstruction. Anterior tibial translation is also affected by the tunnel positions of ACL reconstruction. The study design included a controlled laboratory study. In 15 pig knees, the impingement pressure between ACL and intercondylar roof was measured using pressure sensitive film before and after ACL single bundle reconstruction. ACL reconstructions were performed in each knee with two different tibial and femoral tunnel position combinations: (1) tibial antero-medial (AM) tunnel to femoral AM tunnel (AM to AM) and (2) tibial postero-lateral (PL) tunnel to femoral High-AM tunnel (PL to High-AM). Anterior tibial translation (ATT) was evaluated after each ACL reconstruction using robotic/universal force-moment sensor testing system. Neither the AM to AM nor the PL to High-AM ACL reconstruction groups showed significant difference when compared with intact ACL in roof impingement pressure. The AM to AM group had a significantly higher failure load than PL to High-AM group. This study showed how different tunnel placements affect the ACL-roof impingement pressure and anterior-posterior laxity in ACL reconstruction. Anatomical ACL reconstruction does not cause roof impingement and it has a biomechanical advantage in ATT when compared with non-anatomical ACL reconstructions in the pig knee. There is no intercondylar roof impingement after anatomical single bundle ACL reconstruction.

Comparison of In Situ Forces and Knee Kinematics in Anteromedial and High Anteromedial Bundle Augmentation for Partially Ruptured Anterior Cruciate Ligament

Background: High tunnel placement is common in single- and double-bundle anterior cruciate ligament (ACL) reconstructions. Similar nonanatomic tunnel placement may also occur in ACL augmentation surgery. Purpose: In this study, in situ forces and knee kinematics were compared between nonanatomic high anteromedial (AM) and anatomic AM augmentation in a knee with isolated AM bundle injury. Study Design: Controlled laboratory study. Methods: Seven fresh-frozen cadaver knees were used (age, 48 ± 12.5 years). First, intact knee kinematics was tested with a robotic–universal force sensor testing system under 2 loading conditions. An 89-N anterior load was applied, and an anterior tibial translation was measured at knee flexion angles of 0°, 30°, 60°, and 90°. Then, combined rotatory loads of 7-N·m valgus and 5-N·m internal tibial rotation were applied at 15° and 30° of knee flexion angles, which mimic the pivot shift. Afterward, only the AM bundle of the ACL was cut arthroscopically, keeping the posterolateral bundle intact. The knee was again tested using the intact knee kinematics to measure the in situ force of the AM bundle. Then, arthroscopic anatomic AM bundle reconstruction was performed with an allograft, and the knee was tested to give the in situ force of the reconstructed AM bundle. Knee kinematics under the 3 conditions (intact, anatomic AM augmentation, and nonanatomic high AM augmentation) and the in situ force were compared and analyzed. Result: The high AM graft had significantly lower in situ force than the intact and anatomic reconstructed AM bundle at 0° of knee flexion (P < .05) and the intact AM bundle at 30° of knee flexion under anterior tibial loading. There were no differences between anatomic graft and intact AM bundle. The high AM graft also had a significantly lower in situ force than the intact and anatomic reconstructed AM with simulated pivot-shift loading at 15° and 30° of flexion (P < .05). Under anterior tibial and rotatory loading, there was a difference in tibial displacement between anatomic and high AM reconstructions and between the high AM graft and intact ACL under rotational loading with the knee at 15° of flexion. Clinical Relevance: Anatomic AM augmentation can lead to biomechanical advantages at time zero when compared with the nonanatomic (high AM) augmentation. Anatomic AM augmentation better restores the knee kinematics to the intact ACL state.

Progressive Chondrocyte Death After Impact Injury Indicates a Need for Chondroprotective Therapy

Background Impact injury to articular cartilage can lead to posttraumatic osteoarthritis. Hypotheses This study tests the hypotheses that (1) chondrocyte injury occurs after impact at energies insufficient to fracture the cartilage surface, and that (2) cartilage injury patterns vary with impact energy, time after injury, and cartilage thickness. Study Design Controlled laboratory study. Methods Fresh bovine osteochondral cores were randomly divided into 5 groups: (1) control, (2) 0.35 J, (3) 0.71 J, (4) 1.07 J, and (5) 1.43 J impact energies. Cores were subjected to computer-controlled impact loading and full-thickness sections were then prepared and incubated in Dulbecco’s Modified Eagle’s Medium/F12 at 37°C. Adjacent sections were harvested 1 and 4 days after impact for viability staining and fluorescent imaging. The area of dead and living chondrocytes was quantified using custom image analysis software and reported as a percentage of total cartilage area. Results The highest impact energy fractured the cartilage in all cores (1.43 J, n = 17). Seventy-three percent and 64% of the osteochondral cores remained intact after lower energy impacts of 0.71 J and 1.07 J, respectively. At lower energy levels, fractured cores were thinner (P <.01) than those remaining intact. In cores remaining intact after impact injury, chondrocyte death increased with increasing impact energy (P <.05) and with greater time after impact (P <.05). A progressive increase in dead cells near the bone/cartilage interface and at the articular surface was observed. Conclusion These data showing progressive chondrocyte death after impact injury at energies insufficient to fracture the cartilage surface demonstrate a potential need for early chondroprotective therapy. Clinical Relevance These data show that efforts to reduce chondrocyte morbidity after joint injury may be a useful strategy to delay or prevent the onset of posttraumatic osteoarthritis.

Changes in ACL length at different knee flexion angles: an in vivo biomechanical study

Recently, there has been a tremendous impetus on anatomical reconstruction of the anterior cruciate ligament (ACL), and the double-bundle reconstruction concept has been advocated by many authors. It is, therefore, important to understand how the lengths of the two bundles of the ACL vary during different knee flexion angles as this could influence the angle of graft fixation during surgery. The aim of this study is to determine the change in length of the ACL bundles during different knee flexion angles. Ten subjects with normal knees were evaluated. A high-resolution computer tomography scan was performed, and 3D knee images were obtained. These images were then imported to customized software, and digital length measurement of four virtual bundles (anatomical single bundle, AM, PL and over the top) was evaluated from fixed points on the femur and tibia. Length-versus-flexion curves were drawn, and statistical analysis was performed to evaluate changes in length for each bundle at varying angles of knee flexion (0°, 45°, 90° and 135°). All virtual bundles achieved greatest lengths at full extension. There was a significant difference between the posterolateral bundle length when compared to the other bundles at full extension. There were no significant differences between the lengths of the anteromedial and the over the top single bundles at all angles of knee flexion. Three-dimensional computer tomography can be used to assess the length changes of the virtual anterior cruciate ligament bundles, thereby allowing a better understanding of bundle function in clinical situations.