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Purpose This study aimed to identify independent predictive factors for return to sports (RTS) after anterior cruciate ligament (ACL) reconstruction in competitive-level athletes and to determine optimal cut-off values for these factors at 6 months after surgery. Methods A total of 124 competitive athletes (50 males and 74 females; mean age, 17.0 years; preinjury Tegner activity scale > 7) who underwent primary ACL reconstruction were enrolled. Assessments at 6 months after surgery consisted of knee functional tests [quadriceps index, hamstrings index, and single-leg hop for distance (SLH)] and 2 self-report questionnaires [IKDC subjective score and ACL-Return to Sport after Injury scale (ACL-RSI)]. At 1 year after surgery, athletes were classified into the RTS group ( n  = 101) or non-RTS group ( n  = 23) based on self-reported sports activities. After screening possible predictive factors of RTS, multivariate logistic regression and receiver operating characteristic curve analyses were performed to identify independent factors. Results Multivariate logistic regression analysis identified SLH (odds ratio, 2.861 per 10 unit increase; P  < 0.001) and ACL-RSI (odds ratio, 1.810 per 10 unit increase; P  = 0.001) at 6 months as independent predictors of RTS at 1 year after surgery. Optimal cut-off values of SLH and ACL-RSI were 81.3% (sensitivity = 0.891; specificity = 0.609) and 55 points (sensitivity = 0.693; specificity = 0.826), respectively. Conclusion In competitive athletes, SLH < 81% and ACL-RSI < 55 points at 6 months after surgery were associated with a greater risk of unsuccessful RTS at 1 year after surgery. SLH and ACL-RSI at 6 months could serve as screening tools to identify athletes who have difficulties with returning to sports after ACL reconstruction. Level of evidence III.

Anatomic ACL reconstruction is the reasonable approach to restore stability without loss of motion after ACL tear. To mimic the normal ACL like a ribbon, our preferred procedures is the anatomic rectangular tunnel (ART) technique with a bone-patellar tendon-bone (BTB) graft or the anatomic triple bundle (ATB) procedure with a hamstring (HS) tendon graft. It is important to create tunnel apertures inside the attachment areas to lessen the tunnel widening. To identify the crescent-shaped ACL femoral attachment area, the upper cartilage margin, the posterior cartilage margin and the resident’s ridge are used as landmarks. To delineate the C-shaped tibial insertion, medial intercondylar ridge, Parson’s knob and anterior horn of the lateral meniscus are helpful. In ART-BTB procedure which is suitable for male patients engaged in contact sports, the parallelepiped tunnels with rectangular apertures are made within the femoral and tibial attachment areas. In ATBHS technique which is mainly applied to female athletes engaged in non-contact sports including skiing or basketball, 2 femoral and 3 tibial round tunnels are created inside the attachment areas. These techniques make it possible for the grafts to run as the native ACL without impingement to the notch or PCL. After femoral fixation with an interference screw or cortical fixation devices including Endobutton, the graft is pretensioned in situ by repetitive manual pulls at 15–20° of flexion, monitoring the graft tension with tensioners on a tensioning boot installed on the calf. Tibial fixation with pullout sutures is achieved using Double Spike Plate and a screw at the pre-determined amount of tension of 10–20N. While better outcomes with less failure rate are being obtained compared to those in the past, higher graft tear rate remains a problem. Improved preventive training may be required to avoid secondary ACL injuries.

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.

After invasion and replication, intracellular pathogens must egress from infected host cells. Toxoplasma gondii facilitates this process by permeabilizing host cells through induced secretion of perforin-like protein 1 (PLP1). However, the precise mechanism of host cell permeabilization remains enigmatic. Here, we identify the secretory microneme protein MIC11 as a key factor for membrane disruption. A CRISPR-based in vivo screen identifies MIC11 as the top in vivo fitness-conferring gene. Deletion of MIC11 results in severe defects in membrane rupture and egress. Scanning mutagenesis identifies functional motifs in MIC11, and mechanistic analyses support an association between MIC11 and PLP1, suggesting that MIC11 is involved in PLP1-dependent membrane disruption. Moreover, the merozoite-specific paralogue MIC22 functionally complements MIC11 deletion, suggesting a conserved mechanism of egress in the feline-restricted stages of T. gondii . Collectively, the discovery of MIC11 advances our understanding of how parasites disrupt host cells to facilitate rapid egress and successful dissemination. This study reveals how Toxoplasma gondii exits host cells to spread infection. Researchers found that a key protein, MIC11, works with parasite perforin to disrupt membranes—a mechanism conserved even in the feline stages of infection.

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.

Purpose The purpose of this study was to evaluate the change in cross-sectional area (CSA) of bone-patellar tendon-bone (BTB) autografts up to 5 years after the anatomic rectangular tunnel (ART) anterior cruciate ligament reconstruction (ACLR). The changing pattern in CSA might be a potential indicator of the graft remodeling process. Methods Ninety-six (62 males, 34 females, mean age 27.0 years) patients were enrolled in this study with a total of 220 MRI scans after ART BTB ACLR to evaluate the CSA of the ACL autografts. The patients with first time unilateral ACLR that consented to undergo MRI evaluations at postoperative periods were included in this study. Intraoperatively, the CSA of the graft was measured directly using a custom-made area micrometer at the midpoint of the graft. Postoperatively, using an oblique axial slice MRI that was perpendicular to the long axis of the graft, the CSA of the graft was measured with digital radiology viewing program “SYNAPSE” at the midpoint of the graft. The postoperative MRI scans were classified into seven groups according to the period from ACLR to MRI evaluation: Group 0–2 months (m.), Group 3–6 m., Group 7–12 m., Group 1–2 years (y.), Group 2–3 y., Group 3–4 y., and Group 4 y.-. The percent increase of the CSA was calculated by dividing the postoperative CSA by the intraoperative CSA. Results The postoperative CSA was significantly larger than the intraoperative CSA in each group, with the exception of Group 0–2 m. The mean percent increase of the CSA in Group 0–2 m., 3–6 m., 7–12 m., 1–2 y., 2–3 y., 3–4 y., 4 y.- was 101.8 ± 18.2, 188.9 ± 27.4, 190.9 ± 43.7, 183.3 ± 28.9, 175.2 ± 27.9, 163.9 ± 19.8, 164.5 ± 25.4% respectively. The percent increase in Group 3–6 m., 7–12 m., 1–2 y., 2–3 y., 3–4 y., and 4 y.- was significantly greater than that in Group 0–2 m . Conclusions The CSA of the BTB autografts after the ART BTB ACLR increases rapidly by 3–6 months after ACLR, reached a maximum value of 190% at around 1 year, decreases gradually after that, and reaches a plateau at around 3 years. The current study might help clinicians to estimate an individual BTB autograft's remodeling stages when considering returning patients to sports. Level of evidence IV

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.

Purpose This study aimed to retrospectively compare the enlargement and migration of the femoral tunnel aperture after anatomic rectangular tunnel anterior cruciate ligament (ACL) reconstruction with a bone–patella tendon–bone (BTB) or hamstring tendon (HT) graft using three-dimensional (3-D) computer models. Methods Thirty-two patients who underwent ACL reconstruction and postoperative computed tomography (CT) at 3 weeks and 6 months were included in this study. Of these, 20 patients underwent ACL reconstruction with a BTB graft (BTBR group), and the remaining 12 with an HT graft (HTR group). The area of the femoral tunnel aperture was extracted and measured using a 3-D computer model generated from CT images. Changes in the area and migration direction of the femoral tunnel aperture during this period were compared between the two groups. Results In the HTR group, the area of the femoral tunnel aperture was significantly increased at 6 months compared to 3 weeks postoperatively ( P  < 0.05). The average area of the femoral tunnel aperture at 6 months postoperatively was larger by 16.0 ± 12.4% in the BTBR group and 41.9 ± 22.2% in the HTR group, relative to that measured at 3 weeks postoperatively ( P  < 0.05). The femoral tunnel aperture migrated in the anteroinferior direction in the HTR group, and only in the inferior direction in the BTBR group. Conclusions The femoral tunnel aperture in the HTR group was significantly more enlarged and more anteriorly located at 6 months after ACL reconstruction, compared to the BTBR group. Level of evidence IV.

Purpose Few studies investigated the enlargement inside the tunnel as well as the morphological change at the aperture after anterior cruciate ligament (ACL) reconstruction, whereas the tunnel enlargement has been well documented. The purposes were to evaluate the change in the cross-sectional area along the femoral tunnel and to morphologically clarify the enlargement at the femoral tunnel aperture after anatomic triple-bundle (ATB) ACL reconstruction. Methods The study included 15 patients with unilateral ACL rupture. ATB ACL reconstruction was performed using semitendinosus tendon autografts. Three-dimensional computer models of the femur and bone tunnels were reconstructed from computed tomography images obtained 3 weeks and 1 year postoperatively. The cross-sectional area at the aperture as well as inside the tunnel was compared between the two periods. Likewise, the location of tunnel walls and center in the tunnel footprint were evaluated. Results The cross-sectional area enlarged by 22.7 % for anteromedial/intermediate graft ( P  = 0.002) and 28.6 % for posterolateral graft ( P  = 0.002) at the aperture, while decreased by 36.2 % at 10 mm from the aperture for anteromedial/intermediate graft ( P  = 0.004). Both the anterior and posterior walls shifted anteriorly, while the distal wall shifted distally in both tunnels. Consequently, the center in the footprint significantly shifted anteriorly (4.9–6.6 %) and distally (2.2–2.6 %) in both tunnels. Conclusions The femoral tunnel enlargement occurred at the aperture after ATB ACL reconstruction, but did not occur in the middle of the femoral tunnel. The morphology at the aperture changed with time after surgery as the tunnel walls translated anteriorly and distally. Level of evidence Case series, Level IV.

Background: Residual posterior sagging may occur after posterior cruciate ligament (PCL) reconstruction (PCLR), yet when it mainly occurs is not fully understood. Purpose: To elucidate sequential changes in radiographic posterior tibial translation (PTT) after PCLR. Study Design: Case-control study; Level of evidence, 3. Methods: The authors retrospectively investigated the radiographic findings from 22 patients who underwent bisocket double-bundle PCLR for isolated PCL injury with at least 2 years of follow-up (mean, 4.5 years; range, 2-10 years). Injury severity was assessed using PTT on lateral radiographs with gravity sag views and was stratified according to side-to-side difference in the tibial-femoral stepoff: grade 1 (<5 mm), grade 2 (5 to <10 mm), or grade 3 (≥10 mm). Measurements were taken preoperatively and then immediately, 3 months, 6 months, 1 year, and ≥2 years postoperatively. The authors also investigated the risk factors for residual posterior sagging, indicated when PTT was ≥5 mm (grade ≥2) at the minimum 2-year follow-up. Results: Preoperatively, 13 patients had a grade 2 injury, and 9 had grade 3 injury. The PTT, restored immediately after PCLR, significantly increased at 3 months (P < .001) but remained unchanged thereafter ≥2 years. There were 7 cases of postoperative PTT ≥5 mm on radiographs. Patients with residual posterior sagging had significantly larger mean PTT than did those without residual posterior sagging at all time points except for immediately postoperatively (preoperatively, 9.1 ± 1.6 vs 12.2 ± 2.3 mm; 3-month follow-up, 2.7 ± 1.6 vs 7.0 ± 1.8 mm; ≥2-year follow-up, 3.4 ± 1.0 vs 6.5 ± 1.4 mm; P < .001 for all). Multivariate logistic regression analysis showed that preoperative grade 3 injury was independently associated with residual posterior sagging (OR, 26.809; 95% CI, 1.257-571.963; P < .001). Conclusion: The initially reduced postoperative PTT significantly increased within 3 months using conventional rehabilitation protocols, but no progression was observed up to 4.5 years after PCLR. Preoperative grade 3 injury was independently associated with residual posterior sagging.