Quantitative analysis of the fine vascular anatomy of articular ligaments

Creating an Optimal In Vivo Environment to Enhance Outcomes Using Cell Therapy to Repair/Regenerate Injured Tissues of the Musculoskeletal System

Following most injuries to a musculoskeletal tissue which function in unique mechanical environments, an inflammatory response occurs to facilitate endogenous repair. This is a process that usually yields functionally inferior scar tissue. In the case of such injuries occurring in adults, the injury environment no longer expresses the anabolic processes that contributed to growth and maturation. An injury can also contribute to the development of a degenerative process, such as osteoarthritis. Over the past several years, researchers have attempted to use cellular therapies to enhance the repair and regeneration of injured tissues, including Platelet-rich Plasma and mesenchymal stem/medicinal signaling cells (MSC) from a variety of tissue sources, either as free MSC or incorporated into tissue engineered constructs, to facilitate regeneration of such damaged tissues. The use of free MSC can sometimes affect pain symptoms associated with conditions such as OA, but regeneration of damaged tissues has been challenging, particularly as some of these tissues have very complex structures. Therefore, implanting MSC or engineered constructs into an inflammatory environment in an adult may compromise the potential of the cells to facilitate regeneration, and neutralizing the inflammatory environment and enhancing the anabolic environment may be required for MSC-based interventions to fulfill their potential. Thus, success may depend on first eliminating negative influences (e.g., inflammation) in an environment, and secondly, implanting optimally cultured MSC or tissue engineered constructs into an anabolic environment to achieve the best outcomes. Furthermore, such interventions should be considered early rather than later on in a disease process, at a time when sufficient endogenous cells remain to serve as a template for repair and regeneration. This review discusses how the interface between inflammation and cell-based regeneration of damaged tissues may be at odds, and outlines approaches to improve outcomes. In addition, other variables that could contribute to the success of cell therapies are discussed. Thus, there may be a need to adopt a Precision Medicine approach to optimize tissue repair and regeneration following injury to these important tissues.

Neural stimulation does not mediate attenuated vascular response in ACL-deficient knees: potential role of local inflammatory mediators

Chronic inflammation associated with osteoarthritis (OA) alters normal responses and modifies the functionality of the articular vasculature. Altered responsiveness of the vasculature may be due to excessive neural activity associated with chronic pain and inflammation, or from the production of inflammatory mediators which induce vasodilation. Using laser speckle perfusion imaging (LSPI), blood flow to the medial collateral ligament (MCL) of adult rabbits was measured in denervated ACL transected knees (n = 6) and compared to unoperated control (n = 6) and 6-week anterial cruciate ligament (ACL)-transected knees (n = 6). Phenylephrine and neuropeptide Y were applied to the MCL vasculature in topical boluses of 100 microL (dose range 10(-14) to 10(-8) mol and 10(-14) to 10(-9) mol, respectively). Denervation diminished vasoconstrictive responsiveness to phenylephrine compared to both control and ACL-transected knees. Denervation minimally enhanced vascular responses to neuropeptide Y (NPY) compared to ACL deficiency alone, which nevertheless remained significantly diminished from control responses. To evaluate the potential role of inflammatory dilators in the diminished contractile responses, phenylephrine was coadministered with histamine, substance P, and prostaglandin E(2). High-dose histamine, and low-dose substance P and PGE(2) were able to inhibit contractile responses in the MCL of control knees. Excessive neural input does not mediate diminished vasoconstrictive responses in the ACL transected knee; inflammatory mediators may play a role in the deficient vascular responsiveness of the ACL transected knee.

Analysis of asymmetry in mammograms via directional filtering with Gabor wavelets

This paper presents a procedure for the analysis of left-right (bilateral) asymmetry in mammograms. The procedure is based upon the detection of linear directional components by using a multiresolution representation based upon Gabor wavelets. A particular wavelet scheme with two-dimensional Gabor filters as elementary functions with varying tuning frequency and orientation, specifically designed in order to reduce the redundancy in the wavelet-based representation, is applied to the given image. The filter responses for different scales and orientation are analyzed by using the Karhunen-Loève (KL) transform and Otsu's method of thresholding. The KL transform is applied to select the principal components of the filter responses, preserving only the most relevant directional elements appearing at all scales. The selected principal components, thresholded by using Otsu's method, are used to obtain the magnitude and phase of the directional components of the image. Rose diagrams computed from the phase images and statistical measures computed thereof are used for quantitative and qualitative analysis of the oriented patterns. A total of 80 images from 20 normal cases, 14 asymmetric cases, and six architectural distortion cases from the Mini-MIAS (Mammographic Image Analysis Society, London, U.K.) database were used to evaluate the scheme using the leave-one-out methodology. Average classification accuracy rates of up to 74.4% were achieved.

Adaptation of post-traumatic angiogenesis in the rabbit knee by apposition of torn ligament ends

Apposition of torn ligament ends has been shown to have a beneficial effect on healing of the medial collateral ligament; however, the mechanism underlying this improved recovery is unclear. Excessive post-traumatic angiogenesis, an inherent component of soft-tissue regeneration, may be functionally detrimental in relatively hypovascular tissues such as ligaments. The present study therefore examined the relationship between contact of transected ligament ends and vascular remodeling. Female New Zealand White rabbits were subjected to a gap injury, Z-plasty apposition, or sham operation to the midsubstance of the medial collateral ligament. Six weeks after treatment, the volume of vessels supplying the healing zone of the medial collateral ligament, as well as the ipsilateral lateral collateral ligament, posterior cruciate ligament. menisci, and medial capsule, was quantified by carmine red vascular casting. The volume of vessels supplying the neoligamentous scar formed by gap injury to the medial collateral ligament was found to be twice that of ligaments that had undergone the sham operation, and lateral collateral ligament and meniscal vascularity was also augmented in the injured joint. The medial collateral ligaments that underwent Z-plasty apposition exhibited a level of vascularity comparable with that of the control ligaments that had undergone the sham procedure, whereas meniscal and lateral collateral ligament vascularities remained elevated in this group. Capsular and posterior cruciate ligament vascularities were unaffected by gap injury or Z-plasty to the ipsilateral medial collateral ligament. These findings indicate that injury to the medial collateral ligament not only stimulates angiogenesis in the healing ligament, but other ipsilateral soft tissues also undergo vascular remodeling. Furthermore, apposition of an injured medial collateral ligament modifies these pro-angiogenic events, and this may partly explain why contact of torn ligament ends is beneficial for post-traumatic recovery of an injured joint.

Vascular volume determination of articular tissues in normal and anterior cruciate ligament-deficient rabbit knees

The vasculature of diarthroidal joints has been well documented; however, the volume of vessels supplying different articular tissues is unknown. Angiogenesis, the formation of new vessels from preexisting ones, is difficult to quantify in joints due to the unavailability of a suitable technique. Although angiogenesis is known to occur in rheumatoid arthritis, the development of new vessels following joint injury has not been ascertained. A vascular casting technique was developed using carmine red dye to measure the vascular volume of the medial collateral ligament (MCL), lateral collateral ligament (LCL), menisci, medial capsule, and infrapatellar fat pad of the rabbit knee joint. Vascular volume determinations were repeated at 4 weeks in a group of anterior cruciate ligament (ACL)-transected animals and in a sham-operated control group. The volume of vessels supplying the MCL was estimated to be 0.22 +/- 0.07 microliter (mean +/- S.E.M.), the LCL volume was 0.25 +/- 0.05 microliter, the medial meniscus volume was 0.19 +/- 0.03 microliter, the lateral meniscus volume was 0.40 +/- 0.08 microliter, the medial capsule volume was 0.14 +/- 0.05 microliter, and the infrapatellar fat pad volume was 1.90 +/- 0.62 microliters. Following ACL transection, angiogenesis was found to occur in the MCL only. All other tissue vascularities were not significantly different from sham-operated controls. A quantifiable method for measuring vascular volume of knee joint tissues has been described. Joint instability stimulates angiogenesis in the ipsilateral MCL; however, the absence of angiogenic activity in other articular tissues might help explain the lack of posttraumatic healing associated with these joints.

Abnormality of the contralateral ligament after injuries of the medial collateral ligament. An experimental study in rabbits

The right medial collateral ligament of ninety-four adult, female rabbits was transected operatively. At three, six, fourteen, or forty weeks after the operation, the uninjured, contralateral (left) medial collateral ligaments of seventy-eight of the animals were tested biomechanically and compared with the left medial collateral ligaments of thirty-three normal female rabbits. The diameters of the mid-substance collagen fibrils in the medial collateral ligaments were also measured in the uninjured, contralateral hindlimbs of four animals at each interval and compared with the fibril diameters in three normal animals at each of three corresponding intervals. Subtle but significant differences between the uninjured, contralateral and the normal medial collateral ligaments with regard to biomechanical properties of collagen fibril diameters were found at all time-intervals. These results support the notion of a significant effect on the contralateral ligament after an injury to the medial collateral ligament and suggest that contralateral ligaments cannot be considered as a normal control group even in this relatively benign model of knee injury.