Summary Statement. The peripheral neuronal phenotype is significantly altered in rotator cuff tendinopathy (RCT) with a clear upregulation of the Glutaminergic system being present in disease. Introduction. Shoulder pain is the third most frequent cause of chronic musculoskeletal pain in the community and is usually caused by rotator cuff tendinopathy (RCT). The central and peripheral nervous system play an important role in both tissue homoeostasis and tendon healing. The Glutaminergic system is of key importance in driving the peripheral and central neuronal changes which increase the body's sensitivity to pain (1, 2). No study to date has investigated the role of the glutaminergic system in human RCT. We hypothesised that the peripheral neuronal phenotype would be altered in RCT, and would vary according to disease stage as measured by size of tear. The term ‘peripheral neuronal phenotype’ is used to refer to refer to specific characteristics of the peripheral nervous system, neuronal mediators and the receptors for these mediators in peripheral tissue. Methods. Rotator cuff tendon specimens were obtained from 64 patients undergoing the surgical repair of rotator cuff tears. Control supraspinatus tendon was obtained from 10 patients undergoing surgery for anterior instability using an ultrasound guided biopsy technique. Patients with rotator cuff tears were divided into 2 groups: the small/medium group (≤ 3cm size) and the large/massive group (>3cm size). The tendon tissue was histologically stained using Haematoxylin and Eosin, and immunohistochemically stained with primary antibodies visualised using 3, 3′-diaminobenzidine (DAB). Image analysis was performed blindly by 2 observers using Image-J to quantify the amount of DAB positive staining. Data was non-parametric in distribution and Mann-Whitney U tests were carried out using SPSS with significance levels set at a minimum of p<0.025. Results. There were significant changes in the peripheral neuronal phenotype in RCT. The Glutaminergic system was significantly up-regulated with an increase in Glutamate and changes in several related receptors in disease versus control (p<0.01). The standard deviation in nuclei count and mean cell nuclear area were both increased in disease (p<0.01) compared to controls. Tendon vascularity and cell proliferation were reduced in disease vs control (p<0.01). There were no significant correlations between pain scores and the peripheral tissue markers. Discussion/Conclusion. The peripheral neuronal phenotype is significantly altered in rotator cuff tendinopathy (RCT) with clear changes in the Glutaminergic system in disease. These findings are novel and improve our understanding of pain and tissue healing in RCT, potentially providing novel therapeutic targets

Objectives

We aimed to determine the effect of surgical approach on the histology of the femoral head following resurfacing of the hip.

The response of the muscle is critical in determining the functional outcome of limb lengthening. We hypothesised that muscle response would vary with age and therefore studied the response of the muscles during tibial lengthening in ten young and ten mature rabbits. A bromodeoxyuridine technique was used to identify the dividing cells.

The young rabbits demonstrated a significantly greater proliferative response to the distraction stimulus than the mature ones. This was particularly pronounced at the myotendinous junction, but was also evident within the muscle belly.

Younger muscle adapted better to lengthening, suggesting that in patients in whom a large degree of muscle lengthening is required it may be beneficial to carry out this procedure when they are young, in order to achieve the optimal functional result.

The energy-storing human Achilles tendon and equine superficial digital flexor tendon (SDFT) show no adaptation to exercise unlike muscle and bone, and are prone to injury. Injury involves microdamage accumulation until there is sufficient weakening for rupture to occur during normal athletic activity. Anatomically opposing positional tendons, such as the common digital extensor tendon (CDET) in the horse rarely suffer exercise–induced injury. Tenocytes maintain the extra-cellular matrix, but in energy-storing tendons they appear unable to adequately repair microdamage as it occurs. Tenocytes have been classified subjectively into 3 subtypes on the basis of histological nuclear morphology. Long, thin type 1 cells are thought to be less synthetically active than cigar-shaped type 2 cells, but their exact morphology and relative proportions in different tendon sites and ages has not been clearly defined. We hypothesised that tenocytes are separable into morphologically distinct subtypes, reflecting differences in age and functional requirements within and between specific tendons. Samples were taken from tensional and compressed regions of the SDFT and CDET of 5 neonates, 5 foals (1–6 m), 5 young adults (2–6 y) and 5 old horses (18–33 y) Cell nuclei were counted and measured in digital images from histological sections by computerised image analysis. Total tenocyte densities and proportions of the 3 subtypes were calculated for each age group, as were nuclear length:width ratios. Length:width ratio distributions for all horses were evaluated using a normality test followed by a paired t-test. There was a significantly higher total cellularity in the SDFT than the CDET, with a higher proportion of type 1 tenocytes in the CDET. With age, total cellularity decreased in all tendon sites and an increase in the proportion of type 1 tenocytes was observed in tensional regions. Foal and neonatal tendons contained significantly higher proportions of type 2 tenocytes than older tendons. The morphology of the two main subtypes in all age groups was significantly different; type 1 tenocytes had a higher nuclear length:width ratio (mean ± SD = 9.6 ± 2.5) than type 2 (mean ± SD =4.7 ±1.1) (p< 0.001). We were able to objectively separate tenocytes into 3 distinct subtypes based on nuclear length:width ratio measurements. There were significant differences in proportions of subtypes with tendon site and age. The positional tendon had significantly lower cellularity and a higher proportion of type 1 tenocytes; these cells may be less functionally active but sufficient to maintain the matrix in a tendon which is not subjected to high levels of strain. The SDFT continues to grow up to 2 years of age and is subjected to high strains, explaining the need for relatively higher proportions of type 2 cells. There is however an age-related increase in type 1 cells in both tendons which may explain an inability of the adult energy-storing tendon to adapt to exercise and to repair microdamage. Understanding the stimulus for age-related changes in tenocyte subtype proportions in tendons with different functions may help us understand the pathogenesis of exercise-induced tendon injury and to develop more appropriate training regimens

Injury to the core region of energy-storing tendons is a frequent occurrence in both human and equine athletes, the incidence of which increases with age. Such energy-storing tendons include the human Achilles tendon (AT) and the equine superficial digital flexor tendon (SDFT). By definition, energy-storing tendons experience high strains during high-speed athletic activity. In contrast, anatomically opposing tendons (“positional” tendons), such as the common digital extensor tendon (CDET) in the horse and extensor digitorum longus tendon in man act only to transmit muscular force and rarely suffer exercise–induced injury. Functional adaptation of muscle and bone in response to exercise is well – documented, but there has been no convincing evidence to suggest that the energy-storing tendons in adults have the ability to adapt to exercise. We hypothesised that adaptive increases in tenocyte cellularity would occur in the energy-storing and positional tendons of young horses subjected to three specific exercise regimens. Samples were taken from midmeta-carpal regions of the SDFT (periphery and core) and CDET of young Thoroughbred horses from the following groups. Group 1: 6 horses exercised on a high-speed treadmill for 18 months from 21.3 months of age (SD 1.1) with 6 age-matched controls that underwent walking exercise only (long-term); Group 2: 6 horses exercised on a high-speed treadmill for 18 weeks from 19.4 months of age (SD 0.6) with 6 age-matched controls that underwent walking exercise only (short-term) and Group 3: 6 horses trained on pasture in New Zealand for 18 months beginning at 7–10 days of age, with 6 age-matched controls kept at pasture with no additional enforced exercise (Global Equine Research Alliance). Tenocyte nuclei were counted and measured in digital images from histological sections stained with haematoxylin and eosin, by computerised image analysis. Tenocyte densities (per mm2) for exercised and control groups for each study were evaluated using paired t-tests. Tenocyte density was significantly higher in the CDET of exercised horses in Group 3 (mean ± SD =260.4 ± 23.4) compared with the non – exercised controls (mean ± SD =226.9 ± 23.8) (p < 0.01). There was no such difference in the SDFT (core or periphery). There was also no significant exercise-related difference in tenocyte density in either the SDFT (core or periphery) or CDET for Groups 1 or 2. No previous data is available on the effect of exercise on tenocyte populations in equine tendons. The lack of other adaptive changes in previous studies of mature equine tendons had raised the question as to whether immature tendons would be more able to adapt to mechanical stimuli. In this study we were able to show that beginning training of horses shortly after birth (Group 3) stimulated an adaptive response by tenocytes in the positional CDET but not the SDFT. The inability of energy-storing tendons to show functional adaptation to exercise in immature or mature animals may explain the high incidence of strain-induced injury. Understanding the pathway by which exercise-related increases in tenocyte densities occur in immature positional but not energy-storing tendons may increase our understanding of the pathogenesis of strain-induced tendon injury

Little is known about the increase in length of tendons in postnatal life or of their response to limb lengthening procedures. A study was carried out in ten young and nine adult rabbits in which the tibia was lengthened by 20% at two rates 0.8 mm/day and 1.6 mm/day.

The tendon of the flexor digitorum longus (FDL) muscle showed a significant increase in length in response to lengthening of the tibia. The young rabbits exhibited a significantly higher increase in length in the FDL tendon compared with the adults. There was no difference in the amount of lengthening of the FDL tendon at the different rates. Of the increase in length which occurred, 77% was in the proximal half of the tendon.

This investigation demonstrated that tendons have the ability to lengthen during limb distraction. This occurred to a greater extent in the young who showed a higher proliferative response, suggesting that there may be less need for formal tendon lengthening in young children.