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Purpose To compare the effect of the lateral meniscus (LM) complete radial tear at different tear sites on the load distribution and transmission functions. Methods A compressive load of 300 N was applied to the intact porcine knees ( n  = 30) at 15°, 30°, 60°, 90°, and 120° of flexion. The LM complete radial tears were created at the middle portion (group M), the posterior portion (group P), or the posterior root (group R) ( n  = 10, each group), and the same loading procedure was followed. Finally, the recorded three-dimensional paths were reproduced on the LM-removed knees. The peak contact pressure (contact area) in the lateral compartment and the calculated in situ force of the LM under the principle of superposition were compared among the four groups (intact, group M, group P, and group R). Results At all the flexion angles, the peak contact pressure (contact area) was significantly higher (lower) after creating the LM complete radial tear as compared to that in the intact state ( p  < 0.01). At 120° of flexion, group R represented the highest peak contact pressure (lowest contact area), followed by group P and group M ( p  < 0.05). The results of the in situ force carried by the LM were similar to those of the tibiofemoral contact mechanics. Conclusion The detrimental effect of the LM complete radial tear on the load distribution and transmission functions was greatest in the posterior root tear, followed by the posterior portion tear and the middle portion tear in the deep-flexed position. Complete radial tars of the meniscus, especially at the posterior root, should be repaired to restore the biomechanical function.

Purpose To clarify the effect of longitudinal tears of the medial meniscus on the in situ meniscus force and the tibiofemoral relationship under axial load. Methods Twenty-one intact porcine knees were mounted on a 6-degrees of freedom robotic system, and the force and three-dimensional path of the knee joints were recorded during three cycles under a 250-N axial load at 30°, 60°, 90° and 120° of knee flexion. They were divided into three groups of seven knees with longitudinal tears in the middle to the posterior segment of the medial meniscus based on the tear site: rim, outer one-third and inner one-third of the meniscal body. After creating tears, the same tests were performed. Finally, all paths were reproduced after total medial meniscectomy, and the in situ force of the medial meniscus was calculated based on the principle of superposition. Results With a longitudinal tear, the in situ force of the medial meniscus was significantly decreased at 60°, 90° and 120° of knee flexion, regardless of the tear site. The decrement was greater with a tear in the meniscal body than a tear in the rim. A longitudinal tear in the meniscal body caused a significantly greater tibial varus rotation than a tear in the rim at all flexion angles. Conclusion Longitudinal tears significantly decreased the in situ force of the medial meniscus. Tears in the meniscal body caused a larger decrease of the in situ meniscus force and greater varus tibial rotation than tears in the rim.

The coculture of vascular endothelial cells (ECs) on collagen gels containing smooth muscle cells (SMCs) has been carried out to investigate cellular interactions associated with blood vessel pathophysiology under wall shear stress (WSS) conditions. However, due to a lack of gel stiffness, the previous collagen gel coculture constructs are difficult to use for pathologic higher WSS conditions. Here, we newly constructed a coculture model with centrifugally compressed cell–collagen combined construct (C6), which withstands higher WSS conditions. The elastic modulus of C6 was approximately 6 times higher than that of the uncompressed collagen construct. The level of α-smooth muscle actin, a contractile SMC phenotype marker observed in healthy arteries, was elevated in C6 compared with that of the uncompressed construct, and further increased by exposure to a physiological level WSS of 2 Pa, but not by a pathological level of 20 Pa. WSS conditions of 2 and 20 Pa also induced different expression ratios of matrix metalloproteinases and their inhibitors in the C6 coculture model but did not in monocultured ECs and SMCs. The C6 coculture model will be a powerful tool to investigate interactions between ECs and SMCs under pathologically high WSS conditions.

Background: Few studies have compared the force distribution between the anterolateral, posterolateral, and medial structures of the knee. Purpose: To investigate the important structures in an intact knee contributing to force distribution in response to anterior tibial load. Study Design: Controlled laboratory study. Methods: Nine fresh-frozen cadaveric knee specimens underwent robotic testing. First, 100 N of anterior tibial load was applied to the intact knee at 0°, 15°, 30°, 60°, and 90° of knee flexion. The anterior cruciate ligament (ACL), anterolateral capsule, lateral collateral ligament, popliteal tendon, posterior root of the lateral meniscus, superficial medial collateral ligament, posterior root of the medial meniscus (MM), and posterior cruciate ligament were then completely transected in sequential order. After each transection, the authors reproduced the intact knee motion when a 100-N anterior tibial load was applied. By applying the principle of superposition, the resultant force of each structure was determined based on the 6 degrees of freedom force/torque data of each state. Results: At every measured knee flexion angle, the resultant force of the ACL was the largest of the tested structures. At knee flexion angles of 60° and 90°, the resultant force of the MM was larger than that of all other structures with the exception of the ACL. Conclusion: The MM was identified as playing an important role in response to anterior tibial load at 60° and 90° of flexion. Clinical Relevance: In clinical settings, the ACL of patients with a poorly functioning MM, such as tear of the MM posterior root, should be monitored considering the large resultant force in response to an anterior tibial load.

Purpose To clarify the effect of the radial tear of the lateral meniscus on the in situ meniscus force and the tibiofemoral relationship under axial loads and valgus torques. Methods Ten intact porcine knees were settled to a 6-degree of freedom robotic system, while the force and 3-dimensional path of the knees were recorded via Universal Force Sensor (UFS) during 3 cycles of 250-N axial load and 5-Nm valgus torque at 15°, 30°, 45°, and 60° of knee flexion. The same examination was performed on the following 3 meniscal states sequentially; 33, 66, and 100% width of radial tears at the middle segment of the lateral meniscus, while recording the force and path of the knees via UFS. Finally, all paths were reproduced after total lateral meniscectomy and the in situ force of the lateral meniscus were calculated with the principle of superposition. Results The radial tear of 100% width significantly decreased the in situ force of the lateral meniscus and caused tibial medial shift and valgus rotation at 30°–60° of knee flexion in both testing protocols. Under a 250-N axial load at 60° of knee flexion, the in situ force decreased to 36 ± 29 N with 100% width of radial tear, which was 122 ± 38 N in the intact state. Additionally, the tibia shifted medially by 2.1 ± 0.9 mm and valgusrotated by 2.5 ± 1.9° with the complete radial tear. However, the radial tear of 33 or 66% width had little effect on either the in situ force or the tibial position. Conclusion A radial tear of 100% width involving the rim significantly decreased the in situ force of the lateral meniscus and caused medial shift and valgus rotation of the tibia, whereas a radial tear of up to 66% width produced only little change. The clinical relevance is that loss of meniscal functions due to complete radial tear can lead to abnormal stress concentration in a focal area of cartilage and can increase the risk of osteoarthritis in the future.

Background Cranial closing wedge osteotomy (CCWO) is a functional stabilisation technique for cranial cruciate ligament (CrCL) ruptures. This biomechanical study aimed to evaluate the influence of CCWO on the stability of the stifle joint. Eighteen Beagle stifle joints were divided into two groups: control and CCWO. The stifle joints were analyzed using a six-degree-of-freedom robotic joint biomechanical testing system. The joints were subjected to 30 N in the craniocaudal (CrCd) drawer and proximal compression tests and 1 Nm in the internal–external (IE) rotation test. Each test was performed with an extension position, 135°, and 120° of joint angle. Results The stifle joints were tested while the CrCLs were intact and then transected. In the drawer test, the CCWO procedure, CrCL transection, and stifle joint flexion increased CrCd displacement. The CCWO procedure and CrCL transection showed an interaction effect. In the compression test, the CCWO procedure decreased and CrCL transection and stifle joint flexion increased displacement. In the IE rotation test, CCWO, CrCL transection, and stifle joint flexion increased the range of motion. Conclusions CCWO was expected to provide stability against compressive force but does not contribute to stability in the drawer or rotational tests. In the CCWO-treated stifle joint, instability during the drawer test worsened with CrCL transection. In other words, performing the CCWO procedure when the CrCL function is present is desirable for stabilizing the stifle joint.

Background: Each band of the deltoid ligament cooperatively contributes to stability of the medial side of the ankle joint. Investigating the function of each band of the deltoid ligament is essential to assess abnormalities and develop treatment options. Purpose: To evaluate the changes in ankle kinematics when each band of the deltoid ligament is injured and to measure the in situ force of each ligamentous band in intact ankle kinematics. Study Design: Descriptive laboratory study. Methods: A total of 8 healthy fresh-frozen cadaveric legs were examined by applying forces through eversion and external rotation of the ankle joint using a 6 degrees of freedom robotic system. The deltoid ligament was separated into 6 discrete bands: tibionavicular ligament, tibiospring ligament, tibiocalcaneal ligament (TCL), anterior tibiotalar ligament, superficial posterior tibiotalar ligament (sPTTL), and deep posterior tibiotalar ligament; the bands were then sequentially transected. A loading test was performed in each model, and the changes in ankle motion and in situ force of each ligamentous band were measured using the robotic system. Results: When an eversion force was applied to the intact ankle, the in situ force of the sPTTL was 21.6 N in dorsiflexion and that of the TCL was 19.4 N in plantarflexion, both of which were significantly greater than those of the other ligamentous bands. Additionally, the amount of eversion under eversion loading increased significantly by 3.3° with sPTTL resection in dorsiflexion and by 4.2° with TCL resection in plantarflexion. Conclusion: The TCL and sPTTL play important roles among the ligamentous bands of the deltoid ligament. The sPTTL played a more significant role in ankle dorsiflexion, whereas the TCL played a more significant role in ankle plantarflexion. Clinical Relevance: The TCL and sPTTL should receive attention in the treatment of deltoid ligamentous injuries.

Background: External rotational stress of the knee leads to several knee problems and persistent pain. Clarifying the role of knee structures in external rotational stability aids in optimizing nonoperative treatment and guiding surgical indications. No previous studies have simultaneously compared the biomechanical contributions of both medial and lateral soft tissue structures to external rotational stress using a robotic system. Purpose: To investigate the influence of multiple soft tissue knee structures on stability during external tibial rotation at 0° to 90° of flexion using a robotic testing system. Study Design: Descriptive laboratory study. Methods: A total of 9 fresh-frozen cadaveric knee specimens and a robotic testing system were used. First, 5 N·m of external tibial rotation was applied to the intact knee at 0°, 15°, 30°, 60°, and 90° of knee flexion. The anterior cruciate ligament, anterolateral capsule, lateral collateral ligament, popliteus tendon (PT), posterior root of the lateral meniscus, superficial medial collateral ligament (sMCL), posterior root of the medial meniscus (MMPR), and posterior cruciate ligament (PCL) were then completely transected in sequence. After each transection, intact knee motion was reproduced for each knee condition, applying 5 N·m of external tibial rotation. By employing the principle of superposition, the resultant force of each structure was determined based on the 6 degrees of freedom force/torque data of each state. Resultant forces were statistically compared using the Kruskal-Wallis test, followed by the post hoc Steel-Dwass test. Results: The sMCL exhibited the greatest resultant force across all knee flexion angles from 0° to 90°. Between 30° and 90°, the MMPR and PT generated the highest resultant forces after the sMCL, while the PCL showed the greatest force at 90° after the sMCL, MMPR, and PT. At 60° of knee flexion, the sMCL, MMPR, and PT showed significantly greater resultant forces than the other structures (P < .05). Conclusion: Our study demonstrated that the sMCL exhibited the greatest resultant force under external tibial rotation across all knee flexion angles from 0° to 90°. Clinical Relevance: This study emphasizes the need to avoid excessive external rotation during the nonoperative or postoperative management of sMCL injuries, as rotational stress may compromise healing and functional recovery of the sMCL.

Background: Investigations on the biomechanical characteristics of the anterior horn of the lateral meniscus (AHLM) related to anterior cruciate ligament (ACL) tibial tunnel reaming have revealed increased contact pressure between the femur and tibia, decreased attachment area, and decreased ultimate failure strength. Purpose/Hypothesis: The purpose of this study was to investigate the influence of a complete radial tear of the AHLM on force distribution in response to applied anterior and posterior drawer forces and internal and external rotation torques. We hypothesized that the AHLM plays an important role in knee stability, primarily at lower knee flexion angles. Study Design: Controlled laboratory study. Methods: A total of 9 fresh-frozen cadaveric knee specimens and a robotic testing system were used. Anterior and posterior drawer forces up to 89 N and internal and external rotation torques up to 4 N·m were applied at 0°, 30°, 60°, and 90° of knee flexion. A complete AHLM tear was then made 10 mm from the lateral border of the tibial attachment of the ACL, and the same tests performed in the intact state were repeated. Next, the recorded intact knee motion was reproduced in the AHLM-torn knee, and the change in the resultant force after an AHLM tear was determined by calculating the difference between the 2 states. Results: In the torn AHLM, the reduction in the resultant force at 0° for external rotation torque (34.8 N) was larger than that at 60° (5.2 N; P < .01) and 90° (6.7 N; P < .01). Conclusion: The AHLM played a role in facilitating knee stability against an applied posterior drawer force of 89 N and external rotation torque of 4 N·m, especially at lower knee flexion angles. Clinical Relevance: This study provides information about the effects of AHLM injuries that may occur during single-bundle ACL reconstruction using a round tunnel.

Background: Many different suture methods have been devised for lateral meniscus radial tears but have resulted in inconsistent outcomes. Purpose/Hypothesis: The purpose of this study was to compare the biomechanical performance, specifically resultant force, tibial shift, and rotation, of 3 suturing techniques—horizontal, tie-grip, and cross-grip—for radial lateral meniscus tears across different flexion angles and under repetitive loading, using a 6 degrees of freedom (6-DOF) robotic simulator. It was hypothesized that the cross-grip suture would demonstrate superior biomechanical properties. Study Design: Controlled laboratory study. Methods: Fresh-frozen porcine right knees were mounted on a 6-DOF robotic simulator to mimic knee joint motion accurately. Meniscal conditions, including intact, radial tear, and horizontal, tie-grip, and cross-grip sutures, were tested on 6 specimens each in 2 experiments: (1) flexion-extension movement under valgus torque and (2) repetitive axial loading at 60° of flexion. The resultant force, which was defined as the net force transmitted through the knee joint, and the tibiofemoral relationship, which was defined as the tibial shifts and rotations relative to the femur, were recorded. Results: Radial tears reduced the resultant force on the lateral meniscus by 45% to 78% compared with intact. Horizontal, tie-grip, and cross-grip sutures restored resultant force to within 5% to 15% of intact levels, with cross-grip achieving the highest recovery. Radial tears caused medial shifts up to 2.15 mm and valgus rotations up to 4.88°, while sutures reduced these to within ±0.44 mm and ≤2.49°, respectively. After 300 loading cycles, sutured menisci maintained >90% of intact force, whereas radial tears declined to 33%. The cross-grip suture maintained the highest force values among the techniques. Sutures also limited abnormal tibial shifts and rotations, partially restoring joint stability. Conclusion: All 3 suture techniques effectively restored joint stability caused by radial lateral meniscus tears. The cross-grip suture showed the highest resultant force in dynamic testing, while all techniques demonstrated the same durability under repetitive loading. This is the first comparative study on the durability of meniscal sutures using a 6-DOF simulator, and it may provide new insights for future research on meniscal sutures. Clinical Relevance: The results of this study suggest that the cross-grip suture may be the preferred choice for competitive athletes with lateral meniscus radial tears who require high load tolerance.