Improvement of absorbability, osteoconductivity, and strength of a ß-tricalcium phosphate spacer for opening wedge high tibial osteotomy: clinical evaluations with 106 patients.

BACKGROUND: An ideal synthetic spacer for medial opening wedge high tibial osteotomy (MOWHTO) has not yet been developed. The authors have developed a new ß-tricalcium phosphate (ß-TCP) spacer with 60% porosity (N-CP60) by modifying the micro- and macro-pore structures of a conventional ß-TCP spacer (CP60) that is widely used in clinical practice. The purpose of this study was to compare the absorbability, osteoconductivity, and in vivo strength of the N-CP60 spacer with those of the CP60 spacer, when used in MOWHTO. METHODS: First, the porosity, diameter distribution of macro- and micropores, and compressive strength of each ß-TCP block were examined using methodology of biomaterial science. Secondly, a clinical study was performed using a total of 106 patients (106 knees) with MOWHTO, who were followed up for 18 months after surgery. In these knees, the N-CP60 and CP-60 spacers were implanted into 49 tibias and 57 tibias, respectively. The absorbability and osteoconductivity were radiologically evaluated by measuring the area of the implanted spacer remaining unabsorbed and assessing with the Hemert's score, respectively. The incidence of cracking in the implanted spacers was determined using computed radiography. Statistical comparisons were made with non-parametric tests. The significance level was set at p = 0.05. RESULTS: The N-CP60 and CP60 blocks had almost the same porosity (mean, 61.0% and 58.7%, respectively). The diameter of macropores was significantly larger (p < 0.0001) in the N-CP60 block than in the CP60 block, while the diameter of micropores was significantly smaller (p = 0.019) in the N-CP60 block. The ultimate strength of the N-CP60 block (median, 36.8 MPa) was significantly greater (p < 0.01) than that of the CP60 block (31.6 MPa). As for the clinical evaluations, the absorption rate of the N-CP60 spacer at 18 months after implantation (mean, 48.0%) was significantly greater (p < 0.001) than that of the CP60 spacer (29.0%). The osteoconductivity of the N-CP60 spacer was slightly but significantly higher (p = 0.0408) than that of the CP60 spacer only in zone 1. The incidence of in vivo cracking of the posteriorly located N-CP60 spacer at one month (mean, 75.5%) was significantly lower (p = 0.0035) than that of the CP60 spacer (91.2%). CONCLUSIONS: The absorbability, osteoconductivity, and compressive strength of the new N-CP60 spacer were significantly improved by modifying the macro- and micro-pore structures, compared with the conventional CP60 spacer. The N-CP60 spacer is more clinically useful than the CP60 spacer. TRIAL REGISTRATION NUMBER: H29-0002.

Potential relationship between high wall shear stress and plaque rupture causing acute coronary syndrome.

The relationship between high wall shear stress (WSS) and plaque rupture (PR) in longitudinal and circumferential locations remains uncertain. Overall, 100 acute coronary syndrome patients whose culprit lesions had PR, documented by optical coherence tomography (OCT), were enrolled. Lesion-specific three-dimensional coronary artery models were created using OCT data. WSS was computed with computational fluid dynamics analysis. PR was classified into upstream-PR, minimum lumen area-PR, and downstream-PR according to the PR's longitudinal location, and into central-PR and lateral-PR according to the disrupted fibrous cap circumferential location. In the longitudinal 3-mm segmental analysis, multivariate analysis demonstrated that higher WSS in the upstream segment was independently associated with upstream-PR, and thinner fibrous cap was independently associated with downstream-PR. In the PR cross-sections, the PR region had a significantly higher average WSS than non-PR region. In the cross-sectional analysis, the in-lesion peak WSS was frequently observed in the lateral (66.7%) and central regions (70%) in lateral-PR and central-PR, respectively. Multivariate analysis demonstrated that the presence of in-lesion peak WSS at the lateral region, thinner broken fibrous cap, and larger lumen area were independently associated with lateral-PR, while the presence of in-lesion peak WSS at the central region and thicker broken fibrous cap were independently associated with central-PR. In conclusion, OCT-based WSS simulation revealed that high WSS might be related to the longitudinal and circumferential locations of PR.

Extrusion of the medial meniscus is a potential predisposing factor for post-arthroscopy osteonecrosis of the knee.

BACKGROUND: Post-arthroscopic osteonecrosis of the knee (PAONK) is a rare condition. No studies have analyzed the relationship between the meniscus extrusion and PAONK. The purpose of this retrospective study is to test a hypothesis that the degree of the medial meniscus (MM) extrusion might be significantly greater in the knees with PAONK than in the matched control knees both before and after the meniscectomy. METHODS: Ten knees with PAONK were detected out of a total of 876 knees which had undergone arthroscopic partial meniscectomy of the MM. Ten matched control knees were randomly selected out of the remaining 866 knees without PAONK. The clinical data of these 20 patients were retrospectively collected from the medical records. To evaluate the location of the menisci on the joint line, Extrusion width and Inner width were defined on a coronal section of magnetic resonance imaging (MRI). The intra- and inter-rater reliability was evaluated by calculating the intra- and inter-class coefficients. Statistical comparisons between the 2 groups were made using the 3 non-parametric tests. RESULTS: Before the meniscectomy, the Extrusion width of the MM (mean 4.7 ± 1.4 mm) was significantly greater than that (3.0 ± 1.3 mm) in the Control group (P = 0.0195). In the MRI taken in a range from 3 to 50 weeks after the meniscectomy, the Extrusion width of the MM (5.9 ± 1.1 mm) in the PAONK group was significantly greater than that (3.4 ± 1.4 mm) in the Control group (P = 0.0009), and the Inner width of the MM (0.6 ± 1.7 mm) in the PAONK group was significantly less than that (3.9 ± 1.0 mm) in the Control group (P = 0.0001). CONCLUSION: A significant relationship was found between the degree of the MM extrusion and the onset of PAONK. This study suggested that the extrusion of the MM is a potential predisposing factor for PAONK.

Integrin α4 mediates ATDC5 cell adhesion to negatively charged synthetic polymer hydrogel leading to chondrogenic differentiation.

Negatively charged synthetic hydrogels have been known to facilitate various cellular responses including cell adhesion, proliferation, and differentiation; however, the molecular mechanism of hydrogel-dependent control of cell behavior remains unclear. Recently, we reported that negatively charged poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) gel induces chondrogenic differentiation of ATDC5 cells via novel protein reservoir function. In this study, we identified the cell adhesion molecules binding to PAMPS gels that act as mechanoreceptors. First, we performed a pull-down assay by particle gels using cell membrane proteins of ATDC5, and found that multiple membrane proteins bound to the PAMPS gel, whereas the uncharged poly(N,N'-dimethylacrylamide) gel as control did not bind to any membrane proteins. Western blot analysis indicated differential binding of integrin (ITG) isoforms to the PAMPS gel, in which the α4 isoform, but not α5 and αv, efficiently bound to the PAMPS gel. ITG α4 knockdown decreased cell spreading of ATDC5 on PAMPS gels, whereas the enhanced expression increased the behavior. Furthermore, ITG α4 depletion suppressed PAMPS gel-induced expression of bone morphogenic protein (BMP) 4 contributing to chondrogenic differentiation, in concordance with the reduction of ERK activation. These results demonstrated that membrane protein binding to PAMPS gels occurred in a charge-dependent manner, and that ITG α4 plays a crucial role in cell spreading on PAMPS gels and acts as a mechanoreceptor triggering cellular signaling leads to chondrogenic differentiation.

Inclination of Blumensaat's line influences on the accuracy of the quadrant method in evaluation for anterior cruciate ligament reconstruction.

PURPOSE: The quadrant method is used to evaluate the bone tunnel position with the grid based on the Blumensaat's line in anterior cruciate ligament (ACL) reconstruction. This study aimed to clarify the influence of variation in the Blumensaat's line on the accuracy of the quadrant method measurements. METHODS: A retrospective review of the radiological records of patients aged 18-30 years who underwent computed tomography (CT) scanning of the knee joint was conducted. The Blumensaat's line inclination angle (BIA), along with the most posterior point of the posterior condyle (point P) position using the quadrant method and morphology of the Blumensaat's line were measured on true lateral transparent three-dimensional CT images of the distal femoral condyle in 147 patients. Statistical analysis was conducted to determine associations among these measurements. RESULTS: BIA was 37.5° (standard deviation 4.2°; range 27°-48°). The point P position was significantly correlated with BIA in the high/low (R2 = 0.590, P < 0.0001) and deep/shallow (R2 = 0.461, P < 0.0001) directions. The morphology of the Blumensaat's line was straight in 35 knees (23.8%); whereas, the remaining 112 knees (76.2%) were not straight but had some hill on the Blumensaat's line. No significant difference among the morphological variation of the Blumensaat's line was observed in BIA and the point P position. CONCLUSION: There was a strong correlation between BIA and the point P measured using the quadrant method, suggesting the influence of the Blumensaat's line on the accuracy of the quadrant method measurements in ACL reconstruction. As for the clinical relevance, surgeons should be careful in application of the quadrant method for ACL reconstruction, because the variation of the Blumensaat's line inclination influences the accuracy of this method.

Assessment of valgus laxity after release of the medial structure in medial open-wedge high tibial osteotomy: an in vivo biomechanical study using quantitative valgus stress radiography.

BACKGROUND: To perform medial open-wedge high tibial osteotomy (OWHTO), surgeons expose the medial-proximal tibia by releasing or cutting the superficial layer of the medial collateral ligament (sMCL). Biomechanically, the sMCL provides primary restraint against valgus forces. Therefore, any release of the sMCL can cause valgus instability of the knee joint. The purpose of this study was to assess valgus laxity after release of the medial structure of the knee during OWHTO. METHODS: Between 2009 and 2015, 84 consecutive patients (93 knees) who underwent OWHTO using a locking plate were enrolled in this study. All patients underwent radiological examinations before surgery, during surgery, 1 year after surgery, and after plate removal to objectively assess valgus laxity. The medial joint space (MJS) and the joint line convergence angle (JLCA) of the knee were evaluated using quantitative valgus stress radiography. Clinical evaluation was performed 2 years after surgery. RESULTS: The mean functional knee score improved significantly, from 65.5 to 91.1 points (p < 0.0001). The mechanical axis percentage shifted to pass through a point 69.7% lateral from the medial edge of the tibial plateau. The MJS and JLCA increased significantly during OWHTO surgery (11.0 mm, 7.4 °, p < 0.0001). However, no significant differences were noted in the MJS and JLCA among preoperative, 1-year postoperative periods and after plate removal. CONCLUSION: Valgus laxity was significantly greater after release of the sMCL. However, no significant differences were noted in valgus laxity in preoperative, 1-year postoperative periods and after plate removal. Complete release of the sMCL did not cause postoperative valgus laxity after OWHTO surgery. TRIAL REGISTRATION: Trial registration number: No.012-0360.

Intravascular Ultrasound-Derived Virtual Fractional Flow Reserve for the Assessment of Myocardial Ischemia.

BACKGROUND: Fractional flow reserve (FFR) is widely used for the assessment of myocardial ischemia. Intravascular ultrasound (IVUS) is an intracoronary imaging method that provides information about lumen and vessel morphology. Previous studies on the expanded use of IVUS to identify functional ischemia have noted an association between anatomy and physiology, but IVUS-derived minimum lumen area (MLA) has a weak-moderate correlation with myocardial ischemia compared with FFR. We developed a method to calculate FFR using IVUS-derived anatomical information for the assessment of myocardial ischemia. The aims of this study were to investigate the relationship between wire-based FFR and IVUS-derived FFR (IVUS-FFR) and to compare the usefulness of IVUS-FFR and IVUS-derived MLA for functional assessment.Methods and Results:We retrospectively analyzed 50 lesions in 48 patients with coronary stenosis who underwent IVUS and FFR simultaneously. IVUS-FFR was calculated using our original algorithm and fluid dynamics. Mean percent diameter stenosis determined on quantitative coronary angiography and on FFR was 56.4±10.7 and 0.69±0.08, respectively. IVUS-FFR had a stronger linear correlation with FFR (R=0.78, P<0.001; root mean square error, 0.057 FFR units) than with IVUS-derived MLA (R=0.43, P=0.002). CONCLUSIONS: IVUS-FFR may be a more valuable method to identify myocardial ischemia, compared with IVUS-derived MLA.

Effects of osteochondral defect size on cartilage regeneration using a double-network hydrogel.

BACKGROUND: There has been increased interest in one-step cell-free procedures to avoid the problems related to cell manipulation and its inherent disadvantages. We have studied the chondrogenic induction ability of a PAMPS/PDMAAm double-network (DN) gel and found it to induce chondrogenesis in animal osteochondral defect models. The purpose of this study was to investigate whether the healing process and the degree of cartilage regeneration induced by the cell-free method using DN gel are influenced by the size of osteochondral defects. METHODS: A total of 63 mature female Japanese white rabbits were used in this study, randomly divided into 3 groups of 21 rabbits each. A 2.5-mm diameter osteochondral defect was created in the femoral trochlea of the patellofemoral joint of bilateral knees in Group I, a 4.3-mm osteochondral defect in Group II, and a 5.8-mm osteochondral defect in Group III. In the right knee of each animal, a DN gel plug was implanted so that a vacant space of 2-mm depth was left above the plug. In the left knee, we did not conduct any treatment to obtain control data. Animals were sacrificed at 2, 4, and 12 weeks after surgery, and gross and histological evaluations were made. RESULTS: The present study demonstrated that all sizes of the DN gel implanted defects as well as the 2.5mm untreated defects showed cartilage regeneration at 4 and 12 weeks. The 4.3-mm and 5.8-mm untreated defects did not show cartilage regeneration during the 12-week period. The quantitative score reported by O'Driscoll et al. was significantly higher in the 4.3-mm and 5.8-mm DN gel-implanted defects than the untreated defects at 4 and 12 weeks (p < 0.05). The 2.5-mm and 4.3-mm DN gel implanted defects maintained relatively high macroscopic and histological scores for the 12-week implantation period, while the histological score of the 5.8-mm DN gel implanted defect had decreased somewhat but statistically significantly at 12 weeks (p = 0.0057). CONCLUSIONS: The DN gel induced cartilage regeneration in defects between 2.5 and 5.8 mm, offering a promising device to establish a cell-free cartilage regeneration therapy and applicable to various sizes of osteochondral defects.

Effects of initial graft tension on clinical outcome after anatomic double-bundle anterior cruciate ligament reconstruction: comparison of two graft tension protocols.

BACKGROUND: In anatomic double-bundle anterior cruciate ligament (ACL) reconstruction, there are great controversies concerning the ideal graft tension protocols. The purpose of this study was to clarify differences in the effect of two graft tension protocols on the clinical outcome after anatomic double-bundle anterior cruciate ligament (ACL) reconstruction by comparing the minimum 2-year clinical results. METHODS: Ninety-seven patients with unilateral anatomic double-bundle ACL reconstruction were divided into two groups. In the first 44 patients (Group I), a 40-N tension was applied to each of the two hamstring autografts at 30° of knee flexion, and simultaneously fixed onto the tibia. In the remaining 53 patients (Group II), a 30-N tension was applied to each graft at 10° of knee flexion, and simultaneously fixed onto the tibia. Each patient was examined 2 years after surgery. RESULTS: There wasn't a significant difference in the background of the two groups. There was no significant difference in the postoperative anterior laxity between the two groups. The average was 1.1 mm and 0.9 mm in Groups I and II, respectively. There wasn't any differences between the two groups in Lysholm knee score, International Knee Documentation Committee (IKDC) evaluation and muscle strength. Four patients had loss of knee extension in a range of 5° and 10° in Group I and none of the patients in Group II exhibited any loss in knee extension; which was statistically significant (p = 0.025). CONCLUSION: The two initial graft tension protocols did not result in any significant differences in the Lysholm knee score and IKDC grade. However, it was noted that the 40-N tension applied to each graft at 30° of knee flexion more significantly induced loss of knee extension in comparison to the 30-N tension applied to each graft at 10°. From a clinical viewpoint, the loss of knee extension is one of the pathological conditions that should be absolutely avoided after ACL reconstruction. Therefore, the 30-N tension applied to each graft at 10° is preferable to the other graft tension protocol.

The role of fibers in the femoral attachment of the anterior cruciate ligament in resisting tibial displacement.

PURPOSE: The purpose was to clarify the load-bearing functions of the fibers of the femoral anterior cruciate ligament (ACL) attachment in resisting tibial anterior drawer and rotation. METHODS: A sequential cutting study was performed on 8 fresh-frozen human knees. The femoral attachment of the ACL was divided into a central area that had dense fibers inserting directly into the femur and anterior and posterior fan-like extension areas. The ACL fibers were cut sequentially from the bone: the posterior fan-like area in 2 stages, the central dense area in 4 stages, and then the anterior fan-like area in 2 stages. Each knee was mounted in a robotic joint testing system that applied tibial anteroposterior 6-mm translations and 10° or 15° of internal rotation at 0° to 90° of flexion. The reduction of restraining force or moment was measured after each cut. RESULTS: The central area resisted 82% to 90% of the anterior drawer force; the anterior fan-like area, 2% to 3%; and the posterior fan-like area, 11% to 15%. Among the 4 central areas, most load was carried close to the roof of the intercondylar notch: the anteromedial bundle resisted 66% to 84% of the force and the posterolateral bundle resisted 16% to 9% from 0° to 90° of flexion. There was no clear pattern for tibial internal rotation, with the load shared among the posterodistal and central areas near extension and mostly the central areas in flexion. CONCLUSIONS: Under the experimental conditions described, 66% to 84% of the resistance to tibial anterior drawer arose from the ACL fibers at the central-proximal area of the femoral attachment, corresponding to the anteromedial bundle; the fan-like extension fibers contributed very little. This work did not support moving a single-bundle ACL graft to the side wall of the notch or attempting to cover the whole attachment area if the intention was to mimic how the natural ACL resists tibial displacements. CLINICAL RELEVANCE: There is ongoing debate about how best to reconstruct the ACL to restore normal knee function, including where is the best place for ACL graft tunnels. This study found that the most important area on the femur, in terms of resisting displacement of the tibia, was in the central-anterior part of the femoral ACL attachment, near the roof of the intercondylar notch. The testing protocol did not lead to data that would support using a large ACL graft tunnel that attempts to cover the whole natural femoral attachment area.

Analysis of proteins showing differential changes during ATP oscillations in chondrogenesis.

Prechondrogenic condensation is a critical step for skeletal pattern formation. Our previous study showed that ATP oscillations play an essential role in prechondrogenic condensation because they induce oscillatory secretion. However, the molecular mechanisms that underlie ATP oscillations remain poorly understood. We examined how differential changes in proteins are implicated in ATP oscillations during chondrogenesis by using liquid chromatography/mass spectrometry. Our analysis showed that a number of proteins involved in ATP synthesis/consumption, catabolic/anabolic processes, actin dynamics, cell migration and adhesion were detected at either the peak or the trough of ATP oscillations, which implies that these proteins have oscillatory expression patterns that are coupled to ATP oscillations. On the basis of the results, we suggest that (1) the oscillatory expression of proteins involved in ATP synthesis/consumption and catabolic/anabolic processes can contribute to the generation or maintenance of ATP oscillations and that (2) the oscillatory expression of proteins involved in actin dynamics, cell migration and adhesion plays key roles in prechondrogenic condensation by inducing collective adhesion and migration in cooperation with ATP oscillations.

Hyaluronic acid enhances the effect of the PAMPS/PDMAAm double-network hydrogel on chondrogenic differentiation of ATDC5 cells.

BACKGROUND: A double-network (DN) gel, which was composed of poly-(2-Acrylamido-2-methylpropanesulfonic acid) and poly-(N,N'-dimethyl acrylamide) (PAMPS/PDMAAm), has the potential to induce chondrogenesis both in vitro and in vivo. The present study investigated whether DN gel induced chondrogenic differentiation of ATDC5 cells in a maintenance medium without insulin, and whether supplementation of hyaluronic acid enhanced the chondrogenic differentiation effect of DN gel. METHODS: ATDC5 cells were cultured on the DN gel and the polystyrene (PS) dish in maintenance media without insulin for 21 days. Hyaluronic acid having a molecular weight of approximately 800 kDa was supplemented into the medium so that the concentration became 0.01, 0.1, or 1.0 mg/mL. The cultured cells were evaluated using immunocytochemistry for type-2 collagen and real time PCR for gene expression of type-2 collagen, aggrecan, and Sox9 at 7 and 21 days of culture. RESULTS: The cells cultured on the DN gel formed nodules and were stained with an anti-type-2 collagen antibody, and expression of type-2 collagen and aggrecan mRNA was significantly greater on the DN gel than on the PS dish surface (p < 0.05) in the hyaluronic acid-free maintenance medium. Hyaluronic acid supplementation of a high concentration (1.0 mg/mL) significantly enhanced expression of type-2 collagen and aggrecan mRNA in comparison with culture without hyaluronic acid at 21 days (p < 0.05). CONCLUSIONS: The DN gel induced chondrogenic differentiation of ATDC5 cells without insulin. This effect was significantly affected by hyaluronic acid, depending on the level of concentration. There is a high possibility that hyaluronic acid plays an important role in the in vivo hyaline cartilage regeneration phenomenon induced by the DN gel.

Effects of culture on PAMPS/PDMAAm double-network gel on chondrogenic differentiation of mouse C3H10T1/2 cells: in vitro experimental study.

BACKGROUND: Recently, several animal studies have found that spontaneous hyaline cartilage regeneration can be induced in vivo within a large osteochondral defect by implanting a synthetic double-network (DN) hydrogel, which is composed of poly-(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) and poly-(N,N'-dimethyl acrylamide) (PDMAAm), at the bottom of the defect. However, the effect of hydrogel on hyaline cartilage regeneration remains unexplained. The purpose of this study was to investigate the chondrogenic differentiation of C3H10T1/2 cells on PAMPS/PDMAAm DN gel. METHODS: C3H10T1/2 cells of 1.0 × 105 were cultured on PAMPS/PDMAAm DN gel in polystyrene tissue culture dishes or directly on polystyrene tissue culture dishes. We compared cultured cells on PAMPS/PDMAAm DN gel with those on polystyrene dishes by morphology using phase-contrast microscopy, mRNA expression of aggrecan, type I collagen, type II collagen, Sox 9 and osteocalcin using real-time RT-PCR, and local expression of type II collagen using immunocytochemistry. RESULTS: C3H10T1/2 cells cultured on the PAMPS/PDMAAm DN gels formed focal adhesions, aggregated rapidly and developed into large nodules within 7 days, while the cells cultured on the polystyrene surface did not. The mRNA levels of aggrecan, type I collagen, type II collagen, Sox 9 and osteocalcin were significantly greater in cells cultured on the PAMPS/PDMAAm DN gel than in those cultured on polystyrene dishes. In addition, C3H10T1/2 cells cultured on PAMPS/PDMAAm DN gel expressed more type II collagen at the protein level when compared with cells cultured on polystyrene dishes. CONCLUSIONS: The present study showed that PAMPS/PDMAAm DN gel enhanced chondrogenesis of C3H10T1/2 cells, which are functionally similar to mesenchymal stem cells. This suggests that mesenchymal stem cells from the bone marrow contribute to spontaneous hyaline cartilage regeneration in vivo in large osteochondral defects after implantation of PAMPS/PDMAAm DN gels.

Intra-articular administration of hyaluronic acid increases the volume of the hyaline cartilage regenerated in a large osteochondral defect by implantation of a double-network gel.

Implantation of PAMPS/PDMAAm double-network (DN) gel can induce hyaline cartilage regeneration in the osteochondral defect. However, it is a problem that the volume of the regenerated cartilage tissue is gradually reduced at 12 weeks. This study investigated whether intra-articular administration of hyaluronic acid (HA) increases the volume of the cartilage regenerated with the DN gel at 12 weeks. A total of 48 rabbits were used in this study. A cylindrical osteochondral defect created in the bilateral femoral trochlea was treated with DN gel (Group DN) or left without any implantation (Group C). In both Groups, we injected 1.0 mL of HA in the left knee, and 1.0 mL of saline solution in the right knee. Quantitative histological evaluations were performed at 2, 4, and 12 weeks, and PCR analysis was performed at 2 and 4 weeks after surgery. In Group DN, the proteoglycan-rich area was significantly greater in the HA-injected knees than in the saline-injected knees at 12 weeks (P = 0.0247), and expression of type 2 collagen, aggrecan, and Sox9 mRNAs was significantly greater in the HA-injected knees than in the saline-injected knees at 2 weeks (P = 0.0475, P = 0.0257, P = 0.0222, respectively). The intra-articular administration of HA significantly enhanced these gene expression at 2 weeks and significantly increased the volume of the hyaline cartilage regenerated by implantation of a DN gel at 12 weeks. This information is important to develop an additional method to increase the volume of the hyaline cartilage tissue in a potential cartilage regeneration strategy using the DN gel.

Biomechanical analysis of knee laxity with isolated anteromedial or posterolateral bundle-deficient anterior cruciate ligament.

PURPOSE: The purpose of this study was to clarify the changes in the kinematics of the knee that result from isolated deficiency of the anteromedial (AM) or posterolateral (PL) bundle. METHODS: Fourteen cadaveric knees were mounted in a 6-df rig and tested using the following 5 loading conditions: 90-N anterior and posterior tibial loads, 5-Nm internal and external tibial torques, and a simulated pivot-shift test. Tibiofemoral kinematics during flexion-extension was recorded with an optical tracking system for (1) intact knees, (2) knees in which the isolated AM bundle was cut, (3) knees in which the isolated PL bundle was cut, and (4) anterior cruciate ligament (ACL)-deficient knees. The distances between the femoral and tibial attachments of the AM and PL bundles of the ACL were also calculated. RESULTS: Anterior translation laxity under an anterior tibial load, rotational laxity under an internal tibial torque, and anterior translation laxity under pivot-shift loading were significantly different between the knees with AM and PL bundle deficiencies (P < .024), but the changes were small: less than 3 mm or 1.5°. The AM bundle distance increased significantly more after an AM bundle tear (P = .004) than after a PL bundle tear in flexion. Cutting the PL bundle did not have a significant effect on the lengths between the bundle attachments. CONCLUSIONS: An isolated AM or PL bundle tear caused a small increase in laxity (<3 mm or <1.5°). CLINICAL RELEVANCE: If there is a clinically identifiable increase in laxity, then--in addition to the isolated tear of the AM or PL bundle--there must also be a tear of the other bundle of the ACL, or at least a partial tear.

Simultaneous monitoring of intracellular ATP and oxygen levels in chondrogenic differentiation using a dual-color bioluminescence reporter.

A number of assay methods which measure cellular metabolic activity have only measured intracellular ATP levels because it has been speculated that ATP production and oxygen consumption are obligatorily coupled to each other under normal conditions. However, there exist many cases in which ATP production and oxygen consumption are uncoupled. Therefore, measurement of only intracellular ATP levels has a limit for understanding the overall metabolic states during various cellular functions. Here, we report a novel system for simultaneously monitoring intracellular ATP and oxygen levels using a red-emitting Phrixothrix hirtus luciferase (PxRe) and a blue-emitting Renilla luciferase (Rluc). Using this system, we monitored the dynamic changes in both intracellular ATP and oxygen levels during chondrogenesis. We found that the oxygen level oscillated at twice the frequency of ATP in chondrogenesis and the oxygen oscillations have an antiphase mode to the ATP oscillations; we also found an independent mode for the ATP oscillations. This result indicates that both mitochondrial and non-mitochondrial respiration oscillate and thus play a role in chondrogenesis. This dual-color monitoring system is useful for studying metabolic regulations that underlie diverse cellular processes.

Beta-tricalcium phosphate shows superior absorption rate and osteoconductivity compared to hydroxyapatite in open-wedge high tibial osteotomy.

PURPOSE: The purpose of this study was to clinically and radiologically compare the utility, osteoconductivity, and absorbability of hydroxyapatite (HAp) and beta-tricalcium phosphate (TCP) spacers in medial open-wedge high tibial osteotomy (HTO). METHODS: Thirty-eight patients underwent medial open-wedge HTO with a locking plate. In the first 19 knees, a HAp spacer was implanted in the opening space (HAp group). In the remaining 19 knees, a TCP spacer was implanted in the same manner (TCP group). All patients underwent clinical and radiological examinations before surgery and at 18 months after surgery. RESULTS: Concerning the background factors, there were no statistical differences between the two groups. Post-operatively, the knee score significantly improved in each group. Concerning the post-operative knee alignment and clinical outcome, there was no statistical difference in each parameter between the two groups. Regarding the osteoconductivity, the modified van Hemert's score of the TCP group was significantly higher (p = 0.0009) than that of the HAp group in the most medial osteotomy zone. The absorption rate was significantly greater in the TCP group than in the HAp group (p = 0.00039). CONCLUSIONS: The present study demonstrated that a TCP spacer was significantly superior to a HAp spacer concerning osteoconductivity and absorbability at 18 months after medial open-wedge HTO. LEVEL OF EVIDENCE: Retrospective comparative study, Level III.

Anatomic and histologic analysis of the mid-substance and fan-like extension fibres of the anterior cruciate ligament during knee motion, with special reference to the femoral attachment.

PURPOSE: The purpose of this study is to evaluate the morphology of the mid-substance and fan-like extension fibres of ACL during knee motion with reference to the femoral attachment. METHODS: This study used six fresh-frozen cadaveric knees and 22 embalmed cadaveric knees to macroscopically evaluate morphological changes in the ACL attachment during knee motion. Three embalmed specimens fixed at knee extension and another three specimens fixed at 120° flexion were used for histologic observations. RESULTS: The fan-like extension fibres were adhered to the bone surface and the fibre location and orientation in relation to the femoral surface did not change, regardless of the knee flexion angle, while the orientation of the mid-substance fibres in relation to the femur did change during knee motion. During knee flexion, a fold in the ACL femoral attachment was observed at the border between the mid-substance and the fan-like extension fibres. The attachment of the mid-substance fibres was significantly smaller than the attachment of the fan-like extension fibres. CONCLUSION: The present study clarified anatomic and histologic character of the mid-substance fibres and fan-like extension fibres, and provided critical information for future clinical and biomechanical studies concerning both two different fibres. Specifically for ACL reconstruction, it is difficult to reconstruct the natural fan-like extension fibres by creating a tunnel at the femoral and tibial ends of each fibre bundle, although the mid-substance fibres can be reconstructed by such procedures.

Biomechanical comparison of the strength of adhesion of polymethylmethacrylate cement to zirconia ceramic and cobalt-chromium alloy components in a total knee arthroplasty.

PURPOSE: The purpose of this study was to clarify the biomechanical characteristics of cement-material interfaces for the zirconia ceramic and cobalt-chromium (Co-Cr) alloy femoral components used for total knee arthroplasty. METHODS: In the first sub-study, we compared the strength of adhesion of the cement to flat plates, by tensile testing under dry and moistened conditions. In the second sub-study, we compared the maximum load of the cement-component complex by tensile testing. In the third sub-study, we compared the fatigue characteristics of the cement-component complex by use of a dynamic tensile testing machine. RESULTS: Under dry conditions, the maximum strength of adhesion to the zirconia ceramic plate was the same as that to the Co-Cr alloy plate. Under moistened conditions, however, the strength of adhesion to the zirconia ceramic plate was significantly lower (p = 0.0017) whereas the strength of adhesion to the Co-Cr alloy plate was not reduced. Maximum load for the cement-component complexes for zirconia ceramic and Co-Cr alloy was no different under both dry and moistened conditions. Fatigue testing showed that cement-zirconia adhesion was stronger than cement-Co-Cr alloy adhesion (p = 0.0161). CONCLUSIONS: The strength of adhesion of cement to zirconia ceramic is substantially weaker under wet conditions than under dry conditions. The mechanical properties of cement-zirconia ceramic component complexes and cement-Co-Cr alloy component complexes are equivalent.