The position of the vertebral artery V1 segment relative to the C7 vertebra.

BACKGROUND: The vertebral artery (VA) usually enters the transverse foramen at the C6 level. Thus, surgeons prefer to insert pedicle screws (PSs) at C7, but this does not eliminate the risk of VA injury. We aimed to clarify anatomical features of the VA V1 segment at the C7 pedicle level, based on computed tomographic angiography (CTA) of 81 consecutive patients. METHODS: We examined the course of the VA V1 segment on axial CTA images. VA position was classified according to its alignment with the anterior (A), middle (M), or posterior (P) third of the C7 vertebral body at the pedicle level. We also assessed the prevalence of hypoplastic VA (HVA). We measured the distance (VED) from the optimum C7 PS entry point (Ep) to the center of the VA. We also measured the angles formed by the vertebral midline and a line from the inner edge of the VA to the Ep (the VEA), and by the vertebral midline and a line from the inner edge of the pedicle to the Ep (the PEA). RESULTS: The variant location of the VA to the C7 vertebra was A in 13 courses (8.1%), M in 123 (76.9%), and P in 20 (12.5%). HVA was present in the contralateral side in 7 of 20 courses (35%) in the P group, and in 8 of 127 courses (6.3%) in the M group (p < 0.05). The mean VED was 20.2 mm, the mean VEA 6.9°, and the mean PEA angle was 36.3°. CONCLUSION: The 20 VA courses in the P group (12.5% of the total VA courses) were relatively close to the C7 Ep. HVA was present contralateral to the VA in 7 of 20 courses in the P group. CTA should be considered before proceeding with, even if, C7 PS instrumentation, to avoid unexpected pitfall.

Impact of posterior femoral condylar cartilage and posterior intercondylar distance on rotation of femoral component in total knee arthroplasty.

BACKGROUND: Greater accuracy is needed when determining the final femoral component (FC) rotation during total knee arthroplasty (TKA), because this parameter affects soft tissue balance during flexion and patellar tracking. Anatomical markers, such as the epicondylar axis, are typically used to determine the final FC rotation, although intraoperative confirmation may be challenging. Therefore, rotational position is frequently determined with the posterior condylar axis (PCA) as a landmark. However, the thickness of the posterior condylar cartilage has not been considered and may not be represented on preoperative images. We used plain X-rays to measure the thickness of the medial and lateral posterior condylar cartilage fragments postoperatively, and investigated the effects of differences in cartilage thickness on final FC rotation. METHODS: Fifty knees (19 men, 31 women) underwent primary TKA to treat medial knee osteoarthritis at our hospital between August 2015 and May 2017. All knees were treated using an Attune PS (DePuy Synthes, Inc., Warsaw, IN). We first measured the distance between the posterior femoral condyles, resected the posterior condyle, and measured the thickness of the resected cartilage fragments. We then took X-ray images from a direction tangential to the osteotomy surface, secured the cartilage fragments with digital calipers, and measured the thickness of the cartilage. We investigated the effects of differences in cartilage thickness on final FC rotation of the residual medial and lateral cartilage with a trigonometric function. RESULTS: Medial condylar cartilage thickness averaged 0.6 ± 0.5 mm and the lateral condylar thickness averaged 1.8 ± 0.6 mm; posterior intercondylar distance averaged 46.1 ± 3.3 mm and average impact on rotation of the cartilage remnant was 1.5 ± 0.9° (- 0.1-3.9°). There may be measurement error of up to 4° in the maximum values compared with the preoperative plan in cases with short intercondylar distance. CONCLUSIONS: In cases where the FC external rotation angle is determined using the posterior condyles as landmarks, this angle can be affected by the intercondylar distance, especially in Japanese women who have small physical stature. This angle can potentially be much larger, so caution is advised. Our results suggest that several anatomical landmarks should be referenced to achieve accurate FC rotation.

Enhancement of tendon-bone interface healing and graft maturation with cylindrical titanium-web (TW) in a miniature swine anterior cruciate ligament reconstruction model: histological and collagen-based analysis.

BACKGROUND: Tendon-bone interface healing and ligamentization of the graft in anterior cruciate ligament (ACL) reconstruction with autografts are important factors affecting treatment outcome. This study aimed to investigate the effectiveness of a cylindrical titanium-web (TW) in tendon-bone interface healing and graft maturation in ACL reconstruction. METHODS: Fourteen mature female CLAWN miniature swine underwent bilateral ACL reconstructions with patellar tendon (PT) autografts. In one limb, the TW/tendon complex was placed into the proximal side of the tibial tunnel. Only the graft was transplanted into the tunnel in the control limb. The proximal side of the graft was sutured into the stump of the native ACL and the distal end was stapled to the tibia. The animals were euthanized at 4 and 15 weeks postoperatively, for histological and biochemical analyses. RESULTS: Microscopic images in TW limbs showed that ingrowth of tendon-like tissue and mineralized bone tissue into the TW connected the bone and the tendon directly. In contrast, fibrous tissue intervened between the bone and tendon in the control limbs. The total amount of collagen cross-links (which defines the strength of collagen fibers) and the maturation of collagen cross-links in TW tendons were significantly higher (p < 0.05) than those of control limbs. There was no significant difference in the ratio of dihydroxy-lysinonorleucine to hydroxy-lysinonorleucine (an indicator of tissue specific collagen maturation) between TW tendons and that of the native PT. CONCLUSIONS: TW promoted the maturation and formation of collagen cross-links in the grafted tendon while maintaining the cross-links pattern of native tendon collagen, and enabled direct binding of tendon to bone.

Pre-operative hemoglobin level and use of sedative-hypnotics are independent risk factors for post-operative delirium following total knee arthroplasty.

BACKGROUND: Delirium is a well-known complication following surgery, especially with the increasing age of patients undergoing surgery. The increasing demands resulting from a prolonged healthy life expectancy has resulted in more arthroplasties despite their age and existing comorbidities. The purpose of this study is to explore the various risk factors that may contribute to delirium in unilateral and bilateral total knee arthroplasties in the elderly population. METHODS: 170 patients who underwent unilateral or bilateral total knee arthroplasties were analyzed retrospectively for delirium. Age, sex, comorbidities, use of sedative-hypnotics, peri-operative blood loss, pre- and post-operative laboratory blood test results were investigated and analyzed. RESULTS: The incidence of post-operative delirium was 6.5% (11 out of 170 patients) with a mean age of 79.5 (± 6.9) years, compared to 73.0 (± 9.0) years in the non-delirium group. Higher age, use of sedative-hypnotics, low pre-operative Hb and Ht, low post-operative Hb, Ht and BUN were observed in the delirium group. Multivariate logistic regression analysis identified that the use of sedative-hypnotics and pre-operative Hb level were independent risk factors for post-operative delirium after TKA. The odds ratios for the use of sedative-hypnotics and pre-operative Hb level were 4.6 and 0.53, respectively. Receiver operating characteristic curve analysis showed that pre-operative Hb of less than 11.1 g/dL was a predictor for the development of delirium, with a sensitivity of 54.6% and a specificity of 91.6%. CONCLUSION: Patients with a pre-operative Hb level of < 11.1 g/dL or those using sedative-hypnotics are associated with post-operative delirium. Peri-operative management and preventative measures are therefore needed to reduce the risks of post-operative delirium in such patients.

Redundant and Distinct Roles of Secreted Protein Eap and Cell Wall-Anchored Protein SasG in Biofilm Formation and Pathogenicity of Staphylococcus aureus.

Chronic and fatal infections caused by Staphylococcus aureus are sometimes associated with biofilm formation. Secreted proteins and cell wall-anchored proteins (CWAPs) are important for the development of polysaccharide-independent biofilms, but functional relationships between these proteins are unclear. In the present study, we report the roles of the extracellular adherence protein Eap and the surface CWAP SasG in S. aureus MR23, a clinical methicillin-resistant isolate that forms a robust protein-dependent biofilm and accumulates a large amount of Eap in the extracellular matrix. Double deletion of eap and sasG, but not single eap or sasG deletion, reduced the biomass of the formed biofilm. Mutational analysis demonstrated that cell wall anchorage is essential for the role of SasG in biofilm formation. Confocal laser scanning microscopy revealed that MR23 formed a rugged and thick biofilm; deletion of both eap and sasG reduced biofilm ruggedness and thickness. Although sasG deletion did not affect either of these features, eap deletion reduced the ruggedness but not the thickness of the biofilm. This indicated that Eap contributes to the rough irregular surface structure of the MR23 biofilm and that both Eap and SasG play roles in biofilm thickness. The level of pathogenicity of the Δeap ΔsasG strain in a silkworm larval infection model was significantly lower (P < 0.05) than those of the wild type and single-deletion mutants. Collectively, these findings highlight the redundant and distinct roles of a secreted protein and a CWAP in biofilm formation and pathogenicity of S. aureus and may inform new strategies to control staphylococcal biofilm infections.

Non-invasive skin autofluorescence, blood and urine assays of the advanced glycation end product (AGE) pentosidine as an indirect indicator of AGE content in human bone.

BACKGROUND: Bone mineral density (BMD) measurements are widely used to assess fracture risk. However, the finding that some fracture patients had high BMD together with the low contribution of drugs to osteoporosis suggests that bone strength factors other than BMD contribute to bone quality. We evaluated the amount of advanced glycation end products (AGEs) by non-invasive assays of serum and urine as well as by skin autofluorescence to measure the levels of a representative AGE, pentosidine, to investigate whether pentosidine can serve as an indirect indicator of AGEs formation in bone collagen. METHODS: A total of 100 spinal surgery patients without fragility fracture (54 males and 46 females) treated at our hospital were enrolled. The amount of pentosidine in blood, urine, skin and bone (lumbar lamina) samples from these patients was measured. AGE accumulation was assessed by measuring skin autofluorescence. We examined the correlation between pentosidine content in tissues and body fluid, as well as skin AGEs with age, height, body weight, BMI, and estimated glomerular filtration rate (eGFR). RESULTS: A significant age-related increase in pentosidine levels in tissues was observed, while there was a significant negative correlation between tissue pentosidine and eGFR. The amount of skin pentosidine was significantly and positively correlated with pentosidine content of the bone in those under 50 years of age. Urine pentosidine also correlated positively with bone pentosidine and skin pentosidine, but only in females. The total amount of AGEs in skin did not correlate with bone pentosidine. CONCLUSION: In this study, the strong correlation between the pentosidine content in each sample and eGFR may indicate that renal dysfunction with advancing age increases oxidative stress and induces AGEs formation in collagen-containing tissues. The correlation of skin pentosidine concentration and eGFR, with AGEs formation in bone collagen suggests that pentosidine would be a useful indirect index of decreased bone quality. Skin AGEs estimated by autofluorescence in clinical situations may not be suitable as an indirect assessment of bone quality. Because urine pentosidine correlated positively with bone pentosidine and skin pentosidine in females, urine pentosidine may be a candidate for an indirect assessment of bone quality.

An Autologous Leukocyte-Reduced Platelet-Rich Plasma Therapy for Chronic Injury of the Medial Collateral Ligament in the Knee: A Report of 3 Successful Cases.

Some patients complain of chronic persistent medial knee pain after isolated low-grade injuries of medial collateral ligaments (MCL). These injuries often respond to various conservative treatments but insufficient healing of ligaments is believed to be responsible for symptoms in this group of patients. We report on successful treatment of chronically symptomatic MCL injuries in 3 patients using autologous leukocyte-reduced platelet-rich plasma (PRP) injections. There were 3 men with a mean age of 39.3 years and a mean disease duration of 10 months. Magnetic resonance imaging showed discontinuities of superficial layers and thickness of deep layers in the proximal MCL. After PRP injections, all cases returned to their sport activities at a previous level as without symptoms, and complete healing of proximal ligaments was identified on magnetic resonance images. The outcomes indicated that PRP injections led to successful repair for chronic injuries of MCL in knees.

Clinical accuracy and precision of hip resurfacing arthroplasty using computed tomography-based navigation.

PURPOSE: To avoid malalignment of components during hip resurfacing arthroplasty (HRA), we used a computed tomography (CT)-based navigation system for guidance. This study aimed to evaluate the clinical accuracy and precision of HRA performed using the CT-based navigation systems. METHODS: HRA was performed on 17 hips guided by the CT-based navigation systems. We measured cup alignment deviation, deviation of the stem position, and alignment from the plan by image matching between pre-operative and post-operative CT images. RESULTS: Cup anteversion was within 5° of that in the plan in all cases. Cup inclination was within 5° of that in the plan in 82.4% and within 10° in all cases. The angular difference of the stem was within 5° in all cases, and the entry point of the stem was within 4 mm in all cases. CONCLUSION: The CT-based navigation system for HRA guided accurate component placement according to the plan.

The Regulation of Bone Metabolism and Disorders by Wnt Signaling.

Wnt, a secreted glycoprotein, has an approximate molecular weight of 40 kDa, and it is a cytokine involved in various biological phenomena including ontogeny, morphogenesis, carcinogenesis, and maintenance of stem cells. The Wnt signaling pathway can be classified into two main pathways: canonical and non-canonical. Of these, the canonical Wnt signaling pathway promotes osteogenesis. Sclerostin produced by osteocytes is an inhibitor of this pathway, thereby inhibiting osteogenesis. Recently, osteoporosis treatment using an anti-sclerostin therapy has been introduced. In this review, the basics of Wnt signaling, its role in bone metabolism and its involvement in skeletal disorders have been covered. Furthermore, the clinical significance and future scopes of Wnt signaling in osteoporosis, osteoarthritis, rheumatoid arthritis and neoplasia are discussed.

Downregulation of CD24 suppresses bone metastasis of lung cancer.

Suppression of bone metastasis can improve patient quality of life. Current drugs for bone metastasis have been shown to prolong progression-free survival but not overall survival; therefore, other potential therapeutic targets for bone metastasis should be investigated. Cell-surface antigens, such as CD24, have been recently shown to be involved in the metastasis of various cancers. However, whether CD24 plays a role in bone metastasis of lung cancer remains unknown. To observe metastasis of lung cancer cells by imaging technology, we introduced a near-infrared fluorescent protein, iRFP720, into a bone-seeking subclone established from lung cancer cells, HARA-B4 cells. The anchorage-independent growth of these cells was then evaluated by colony formation assays. We also compared cancer cell tropism to bone tissue with HARA-B4 cells in the presence or absence of CD24 by cell adhesion assays. To clarify the role of CD24 in bone metastasis, we intracardially injected CD24-knockdown HARA-B4 cells into mice and monitored metastasis through detection of iRFP720 using an in vivo imaging system. CD24-knockdown HARA-B4 cells in vitro showed reduced anchorage-independent growth and cancer cell tropism to bone. Bone metastasis was diminished in mice inoculated with CD24-knockdown HARA-B4 cells, which was rescued by add-back of CD24 in cells. Our findings indicate that iRFP720 is effective for in vivo imaging analysis of bone metastasis and that downregulation of CD24 suppresses bone metastasis of lung cancer cells. These findings collectively indicate that CD24 may be considered a promising new therapeutic candidate for the prevention of bone metastasis of lung cancer.

The Effects of Homocysteine on the Skeleton.

PURPOSE OF REVIEW: Homocystinuria is a congenital metabolic disorder in which cystathionine ß-synthase deficiency results in a prominent increase in homocysteine (serum levels > 100 µM), causing mental retardation, atherosclerotic cerebral infarction, and osteoporosis accompanied by fragility fractures. Encountering a case with excessive homocysteinemia such as that seen in hereditary homocystinuria is unlikely during usual medical examinations. However, in individuals who have vitamin B or folate deficiency, serum homocysteine concentrations are known to increase. These individuals may also have a polymorphism in methylenetetrahydrofolate reductase, MTHFR (C677T: TT type), which regulates homocysteine metabolism. These changes in homocysteine levels may elicit symptoms resembling those of homocystinuria (e.g., Alzheimer's disease, atherosclerosis, osteoporosis). RECENT FINDINGS: High serum homocysteine has been shown to have detrimental effects on neural cells, vascular endothelial cells, osteoblasts, and osteoclasts. Homocysteine is also known to increase oxidative stress, disrupt cross-linking of collagen molecules, and increase levels of advanced glycation end products, which results in reduced bone strength through a mechanism that goes beyond low bone density and increased bone resorption. Therefore, high serum homocysteine may be regarded as a factor that can reduce both bone mass and impair bone quality. In this review, we outline the epidemiology and pathophysiology of osteoporosis associated with hyperhomocysteinemia.

Diagnosis and treatment of slipped capital femoral epiphysis: Recent trends to note.

Slipped capital femoral epiphysis (SCFE) is not frequently encountered during routine practice and diagnosis and treatment are often delayed. It is important to understand symptoms and imaging features to avoid delayed diagnosis. After the diagnosis is made correct classification of the disease is required. The classification should be based on the physeal stability in order to choose safe and effective treatment. However, surgeons should bear in mind that the assessment is challenging and actual physeal stability is not always consistent with the stability predicted by a clinical classification method. TREATMENT OF STABLE SCFE: Closed reduction is not indicated for stable SCFE, where continuity between the epiphysis and metaphysis has not been disrupted. Treatment method(s) is (are) chosen from in-situ fixation, osteotomy and femoroacetabular impingement treatment. A single screw fixation is often used to fix the epiphysis and the dynamic method is considered especially for young patients. Traditional three-dimensional trochanteric osteotomies have been associated with procedural complexity and uncertainty. A simpler osteotomy method using an updated imaging analysis technology should be considered. Modified-Dunn procedure is indicated for a severe stable SCFE. However, caution is required because recent studies have reported a high rate of complications including postoperative femoral head avascular necrosis (AVN) and hip instability when this method is indicated for stable SCFE. TREATMENT OF UNSTABLE SCFE: Treatment of unstable SCFE is difficult and complication rate is high. Most of unstable SCFE patients were previously treated with closed method and it was difficult to predict an occurrence of postoperative AVN. However, treatment of unstable SCFE has gradually changed in recent years and many studies have shown that physeal hemodynamics can be assessed during treatment. Preoperative assessments include contrast-enhanced MRI and bone scintigraphy. Intraoperative assessments include confirmation of bleeding after drilling the femoral head and monitoring the intracranial pressure by laser doppler flowmetry. It is expected that postoperative AVN can be prevented in many cases by performing the treatment while assessing the intraoperative physeal hemodynamics. Open surgeries have begun to be indicated in the treatment of unstable SCFE through either of anterior approach or (modified) Dunn procedure. The authors expect that recent improvements in assessment of physeal hemodynamics and open treatment method provide improved clinical outcomes in the treatment of SCFE.

Eldecalcitol, an Active Vitamin D3 Derivative, Prevents Trabecular Bone Loss and Bone Fragility in Type I Diabetic Model Rats.

Diabetes mellitus is known to adversely affect the bones and be associated with increased fracture risk. We examined whether eldecalcitol (ELD), an active vitamin D3 derivative, could inhibit the diabetic bone loss in streptozotocin-induced type I diabetic rats. ELD (10, 20, or 40 ng/kg), alfacalcidol (ALF; 25, 50, or 100 ng/kg), or vehicle was administered 5 times per week for 12 weeks from 1 week after diabetes induction. Normal control rats received the vehicle. Bone turnover markers, bone mineral density (BMD), and biomechanical strength of the lumbar spine and femur were measured, and bone histomorphometry was performed. Content of advanced glycation end products (AGEs) in the femoral shaft was also determined. In diabetic rats, serum osteocalcin (OC) concentration was lower and urinary excretion of deoxypyridinoline (DPD) tended to be higher than in normal rats. Areal BMD and maximum load of the lumbar vertebrae and femoral shaft were lower in diabetic rats than in normal rats. All doses of ELD and the highest dose of ALF reduced urinary DPD excretion, but had no effect on serum OC. The 20 and 40 ng/kg doses of ELD prevented decreases in BMD and the highest dose of ELD prevented the reduction in maximum load of the lumbar vertebrae, while ALF did not change these parameters. ELD and ALF did not affect areal BMD or biomechanical strength of the femoral shaft. In diabetic rats, bone volume and trabecular thickness in the trabecular bone of the lumbar vertebrae decreased and trabecular separation increased compared to normal rats. ELD and ALF prevented diabetes-induced deterioration of trabecular microstructure. AGE content in the femoral cortical bone increased in the diabetic rats, and ELD and ALF did not change AGE content compared to the diabetic rats. These results indicated that ELD suppressed bone resorption and prevented trabecular bone loss and deterioration of trabecular microstructure, resulting in prevention of reduction in biomechanical strength in type I diabetic rats.

Accuracy of Computed Tomography-Based Navigation-Assisted Total Knee Arthroplasty: Outlier Analysis.

BACKGROUND: Achieving neutral limb alignment during total knee arthroplasty (TKA) has been identified as a potential factor in long-term prosthesis survival. This study aimed to analyze the accuracy of component orientation and postoperative alignment of the leg after computed tomography (CT)-based navigation-assisted TKA, compare these parameters with those of a conventional technique, and analyze differences in the data of outliers. METHODS: We retrospectively compared the alignment of 130 TKAs performed with a CT-based navigation system with that of 67 arthroplasties done with a conventional system. The knee joints were evaluated using radiographs. RESULTS: Mean hip-knee-ankle (HKA) angle, frontal femoral component angle, and frontal tibial component angle were 180.7°, 88.8°, and 90.6°, respectively, for the navigation-assisted arthroplasties and 181.1°, 88.7°, and 90.2°, respectively, for the conventional arthroplasties. All preoperative leg axes of 10 outliers in the navigation group were >193°, whereas the data of 17 outliers in the conventional group were scattered. CONCLUSION: This study demonstrates significant improvements in component positioning with the CT-based navigation system. Furthermore, when analyzing cases with preoperative HKA angles ≤192°, no outliers were found in the navigation group, indicating high alignment accuracy. However, in cases with preoperative HKA angles ≥193°, outliers were found in both groups, and no significant difference between the groups was observed (P = .08). Detailed analysis of the outlier cases in the navigation group revealed that the femoral component was placed in the varus position. These findings indicate that the varus knee is an important factor influencing accurate positioning of the femoral component and the postoperative leg axis.

[New methods for the evaluation of bone quality. How does decay bone quality?]

The degree of mineralization and microstructure are regulated by bone turnover. Bone collagen enzymatic cross-links and advanced glycation end products(AGEs)are affected by various factors such as the levels of oxidative stress and glycation as well as tissue lifespan. Deterioration of bone material properties markedly advances due to increases in oxidative stress, glycation stress, reactive oxygen species, carbonyl stress associated with aging and reduced sex hormone levels, and glucocorticoid use. In this review, we described determinants of bone quality and strength.

[Calcium and bone metabolism across women's life stages. Bone quality and treatment of osteoporosis by SERM.]

Estrogen deficiency induces bone resorption and bone collagen crosslink abnormalities such as reductions in enzymatic cross-links and accumulation of Advanced glycation end products(AGEs). In this review, we described that the mechanism of poor bone quality in estrogen deficiency and how selective estrogen receptor modulators such as raloxifene and bazedoxifene improve bone structural and material properties.

[Bone quality in COPD.]

Chronic obstructive pulmonary disease(COPD)is a chronic inflammatory disease associated with an increase of fracture risk. Bone strength is determined by bone mass and quality.Bone quality is thought to encompass the structural and material properties of bone. Bone collagen crosslinking plays important roles in bone strength. The quantitative and qualitative deterioration of lysyl oxidase control and non enzymatic cross-links(advanced glycation end products, AGEs, pentosidine)of collagen in patients with osteoporotic femoral neck fracture and diabetes, and COPD might be affected by increased oxidative stress and glycation.

[Determinants of bone quality and strength independent of bone remodeling].

Bone mineral density(BMD)and bone microstructure are regulated mainly by bone remodeling. In contrast, bone collagen enzymatic immature and mature cross-links and advanced glycation end products such as pentosidine and carboxyl methyl lysine are affected by various factors. Aging bone tissue is repaired in the process of bone remodeling. However, deterioration of bone material properties markedly advances due to increases in oxidative stress, glycation stress, reactive oxygen species, carbonyl stress associated with aging and reduced sex hormone levels, and glucocorticoid use. To improve bone material properties in osteoporosis, we should use different drug (Saito M, Calcif Tissue Int, REVIEW, 97;242-261, 2015). In this review, we summarized determinants of bone quality and strength independent of bone remodeling.

Effects of Collagen Crosslinking on Bone Material Properties in Health and Disease.

Data have accumulated to show that various types of collagen crosslinking are implicated in the health of individuals, as well as in a number of disease states, such as osteoporosis, diabetes mellitus, chronic kidney disease, inflammatory bowel disease, or in conditions of mild hyperhomocysteinemia, or when glucocorticoid use is indicated. Collagen crosslinking is a posttranslational modification of collagen molecules and plays important roles in tissue differentiation and in the mechanical properties of collagenous tissue. The crosslinking of collagen in the body can form via two mechanisms: one is enzymatic crosslinking and the other is nonenzymatic crosslinking. Lysyl hydroxylases and lysyl oxidases regulate tissue-specific crosslinking patterns and quantities. Enzymatic crosslinks initially form via immature divalent crosslinking, and a portion of them convert into mature trivalent forms such as pyridinoline and pyrrole crosslinks. Nonenzymatic crosslinks form as a result of reactions which create advanced glycation end products (AGEs), such as pentosidine and glucosepane. These types of crosslinks differ in terms of their mechanisms of formation and function. Impaired enzymatic crosslinking and/or an increase of AGEs have been proposed as a major cause of bone fragility associated with aging and numerous disease states. This review focuses on the effects of collagen crosslinking on bone material properties in health and disease.

Distinctive collagen maturation process in fibroblasts derived from rabbit anterior cruciate ligament, medial collateral ligament, and patellar tendon in vitro.

PURPOSE: Differences in the tissue-specific collagen maturation process between tendon and ligament are still unknown. Collagen cross-link formation is crucial for the collagen maturation process. The aim of this study is to examine collagen maturation processes of anterior cruciate ligament (ACL), medial collateral ligament (MCL), and patellar tendon (PT) in vitro, in order to determine the optimal cell source for tissue engineering of ligament. METHODS: Cells derived from the ACL, MCL, and PT of New Zealand white rabbits were isolated. Each cell type was cultured for up to 4 weeks after reaching confluence. Cell-matrix layers were evaluated and compared for their morphology, collagen cross-links, and gene expression levels of lysine hydroxylase 1 and 2, lysyl oxidase (LOX), tenomodulin, collagen1A1 (Col1A1), and collagen3A1 (Col3A1). RESULTS: Transmission electron microscopy photomicrographs verified that collagen fibrils were secreted from all three types of fibroblasts. A higher ratio of dihydroxylysinonorleucine/hydroxylysinonorleucine was evident in the ligament compared to the tendon, which was consistent with lysine hydroxylase 2/lysine hydroxylase 1 gene expression. The gene expression of LOX, which regulates the total amount of enzymatic cross-linking, and the gene expression levels of Col1A1 and Col3A1 were higher in the ACL matrix than in the MCL and PT matrices. CONCLUSION: ACL, MCL, and PT cells have distinct collagen maturation processes at the cellular level. In addition, the collagen maturation of ACL cells is not necessarily inferior to that of MCL and PT cells in that all three cell types have a good ability to synthesize collagen and induce collagen maturation. This bioactivity of ACL cells in terms of ligament-specific mature collagen induction can be applied to tissue-engineered ACL reconstruction or remnant preserving procedure with ACL reconstruction.