Early bone ingrowth and segmental stability of a trussed titanium cage versus a polyether ether ketone cage in an ovine lumbar interbody fusion model.

BACKGROUND CONTEXT: Lumbar interbody fusion is an effective treatment for unstable spinal segments. However, the time needed to establish a solid bony interbody fusion between the two vertebrae may be longer than twelve months after surgery. During this time window, the instrumented spinal segment is assumed to be at increased risk for instability related complications such as cage migration or subsidence. It is hypothesized that the design of new interbody cages that enable direct osseointegration of the cage at the vertebral endplates, without requiring full bony fusion between the two vertebral endplates, might shorten the time window that the instrumented spinal segment is susceptible to failure. PURPOSE: To quantify the bone ingrowth and resulting segmental stability during consolidation of lumbar interbody fusion using two different cage types. STUDY DESIGN: Preclinical ovine model. METHODS: Seven skeletally mature sheep underwent bi-segmental lumbar interbody fusion surgery with one conventional polyether ether ketone (PEEK) cage, and one newly developed trussed titanium (TT) cage. After a postoperative time period of 13 weeks, non-destructive range of motion testing, and histologic analysis was performed. Additionally, sample specific finite element (FE) analysis was performed to predict the stability of the interbody fusion region alone. RESULTS: Physiological movement of complete spinal motion segments did not reveal significant differences between the segments operated with PEEK and TT cages. The onset of creeping substitution within the cage seemed to be sooner for PEEK cages, which led to significantly higher bone volume over total volume (BV/TV) compared with the TT cages. TT cages showed significantly more direct bone to implant contact (BIC). Although the mean stability of the interbody fusion region alone was not statistically different between the PEEK and TT cages, the variation within the cage types illustrated an all-or-nothing response for the PEEK cages while a more gradual increase in stability was found for the TT cages. CONCLUSIONS: Spinal segments operated with conventional PEEK cages were not different from those operated with newly developed TT cages in terms of segmental stability but did show a different mechanism of bone ingrowth and attachment. Based on the differences in development of bony fusion, we hypothesize that TT cages might facilitate increased early segmental stability by direct osseointegration of the cage at the vertebral endplates without requiring complete bony bridging through the cage. CLINICAL SIGNIFICANCE: Interbody cage type affects the consolidation process of spinal interbody fusion. Whether different consolidation processes of spinal interbody fusion result in clinically significant differences requires further investigation.

Parenteral and enteral feeding in preterm piglets differently affects extracellular matrix proteins, enterocyte proliferation and apoptosis in the small intestine.

The preterm intestine is immature and responds differently to total parenteral nutrition (TPN) and enteral nutrition, compared with the term intestine. We hypothesised that in preterms, diet composition and feeding route affect mucosal morphology, enterocyte mitosis and apoptosis, and the distribution of laminin-1, fibronectin and collagen IV (extracellular matrix proteins (ECMP)). Preterm piglets (93.5 % of gestation) were delivered via caesarean section and birth weight-matched allocated to one of the four experimental groups: the piglets were either euthanised immediately after delivery, after 3 d of TPN or after 2 d enteral feeding with colostrum or milk formula, following 3 d of TPN. We combined immunohistochemistry, image analysis and stereological measurements to describe the intestinal mucosal layer. No significant changes occurred after 3 d of TPN. Feeding colostrum or milk replacer for 2 d after TPN was associated with an increased crypt depth. Only enteral feeding with colostrum resulted in an increased villus height and mitotic index. Neither TPN nor enteral feeding changed the distribution pattern of ECMP or the occurrence of bifid crypts. The immature distribution pattern of ECMP in TPN-fed piglets, coupled with unchanged enterocyte mitosis and apoptosis indices, illustrates that feeding preterm pigs 3 d TPN does not lead to mucosal atrophy. Despite the invariable distribution of ECMP, colostrum was associated with crypt hyperplasia resulting in an increased villus height. These data illustrate that some mechanisms regulating cell turnover are immature in preterms and may in part explain the abnormal gut responses to TPN and enteral feeding in prematurely born pigs.

Formula induces intestinal apoptosis in preterm pigs within a few hours of feeding.

BACKGROUND: Nutrition regimens influence postnatal small intestinal development, which shows prominent changes after 6 hours of suckling. Such influences are particularly important in preterm neonates as inappropriate feeding responses may predispose to gastrointestinal disorders such as necrotizing enterocolitis (NEC). The authors investigated the early morphological responses to enteral feeding, prior to the time period when a large proportion of preterm pigs normally develop clinical NEC symptoms. METHODS: Preterm piglets (106-107 days of gestation) were fed parenteral nutrition (PN) for 2 days with or without a subsequent 8-hour or 17-hour period of enteral nutrition (EN) with sow's colostrum or formula. Another group of piglets was delivered at 108-109 days of gestation and used for comparison to PN pigs before enteral feeding. Stereological measurements of the mucosal surface density and the volume densities of the tunica mucosa, tunica muscularis, proliferative, and apoptotic cells were made and related to microscopical NEC-lesion score. In addition, villus length and crypt depth were measured. RESULTS: PN-fed piglets showed minimal PN-induced mucosal atrophy, although their crypts were deeper, together with lower cell proliferation and higher apoptotic indices, than newborn (NB) unfed piglets. After PN, enteral feeding with colostrum, for just 8 hours, induced a rapid increase in the mucosal volume density while formula feeding was associated with an elevated number of both proliferating and apoptotic cells and a higher NEC lesion score than PN- or colostrum-fed pigs. CONCLUSION: Enteral feeding of formula, for only a few hours, induces rapid enterocyte turnover and mucosal structural changes that may predispose to later development of NEC.

Diet-dependent mucosal colonization and interleukin-1beta responses in preterm pigs susceptible to necrotizing enterocolitis.

OBJECTIVES: Intestinal colonization challenges the neonatal innate immune system, especially in newborns with an immature immune response lacking the supportive bioactive components from mother's milk. Accordingly, formula-fed preterm pigs frequently show bacterial overgrowth, mucosal atrophy, and gut lesions reflecting necrotizing enterocolitis (NEC) within the first days after birth. We hypothesized that NEC development is related to a diet-dependent bacterial adherence and a subsequent proinflammatory cytokine response in the gut mucosa immediately after introduction of enteral food. MATERIALS AND METHODS: Premature piglets (92% gestation) received 2 to 3 days of total parenteral nutrition followed by 0, 8, or 17 hours of enteral formula or sow's colostrum feeding. RESULTS: Following 8 hours, but not 17 hours, of colostrum feeding, a reduced number of intestinal samples with adherent bacteria (both Gram-negative and Gram-positive bacteria) was counted compared with 0 or 8 hours of formula feeding. Besides a more dense colonization, formula feeding leads to higher intestinal interleukin-1beta (IL-1beta) levels and more NEC-like lesions from 8 hours onward. The load of adherent bacteria was especially high in NEC lesions. Toll-like receptor 4 was detected in enteroendocrine, neuronal, and smooth muscle cells, potentially mediating the increase in IL-1beta levels by Gram-negative bacteria. CONCLUSIONS: Formula feeding facilitates bacterial adherence and the development of a proinflammatory state of the intestine, which may be among the key factors that predispose formula-fed preterm neonates to NEC.

Enteral feeding reduces endothelial nitric oxide synthase in the caudal intestinal microvasculature of preterm piglets.

The initiation of enteral feeding represents a challenge to the neonatal intestinal microcirculation, especially in preterms where it predisposes to necrotizing enterocolitis (NEC). We hypothesized that a structural microvascular deficiency may occur when enteral feeding is initiated in preterm piglets susceptible to NEC. Stereologic volume densities of a pan-endothelial marker (vWF), and the main vasodilator endothelial nitric oxide synthase (eNOS), were determined along the small intestine of 1) unfed preterm piglets, 2) piglets receiving total parenteral nutrition (TPN) for 2-3 d, and 3) piglets fed 2 d sow's colostrum (TPN+SOW) or milk formula (TPN+FOR) following TPN. In the mucosa, vWF-density decreased in a cranio-caudal direction. A corresponding mucosal eNOS gradient appeared only after initiating enteral feeding. In TPN+SOW, eNOS induction may lag behind the mucosal growth of the caudal region. In TPN+FOR, formula-related factors (i.e. bacteria, cytokines) may suppress mucosal eNOS, indicated by increased stress-sensitive nuclear HIF1alpha staining. The low mucosal endothelial eNOS density was related to the presence of NEC lesions, maybe via increased hypoxia-sensitivity, especially in the caudal region as indicated by nuclear HIF1alpha-staining. Our results suggest an insufficient structural adaptation of the microvasculature to enteral feeding, especially of mucosal eNOS, which may lead to NEC.