Our research group are regularly publishing exciting new findings from our work, advancing the understanding of tendon injuries. You can find a brief synopsis of our recently published papers here. We will also occasionally highlight some work in progress.
Scientists overcome hurdles for champion race horses
We are now a step closer to preventing the kind of injuries that affect ageing race horses like champion hurdler Rock on Ruby, the winner of Coral Hurdle at Ascot in 2015. For the first time, our team at QMUL’s School of Engineering and Materials Science were able to show how the types of proteins differ in parts of the tendon, and importantly how this changes as the tendon ages.
When a horse runs, its muscles generate a massive amount of energy that is stored and released by the tendons in their legs. These can be likened to massive elastic bands that absorb energy as they are stretched, and release it again when they recoil. The key to the effectiveness of tendons is the ability of the fibres that they are made up of to slide across each other. When this ability to slide is reduced, the energy damages the tendon instead of being stored and released by it.
In this new study, we have identified specific proteins that help the tendon fibres to slide, and this research shows that these proteins are replaced less quickly as aging occurs. This makes injuries of the type that ended Rock on Ruby’s career more likely. Rock on Ruby, the 2012 Cheltenham Champion Hurdle winner, famously went on to win the Coral Hurdle at Ascot last year despite suffering a career ending tendon injury during the race, which resulted in the untimely retirement of champion hurdler. All tendons are made of subunits containing rope-like collagen surrounded by a material called the interfascicular matrix (IFM), which binds them together. The IFM is a soft, extendible material that allows the subunits to slide past one another, enabling the whole tendon to stretch.
In our recent paper published in Scientific Reports we identified which proteins are present and how rapidly many of the proteins in the IFM are refreshed in young tendons. As tendons become older, the IFM becomes stiffer making it harder for the subunits to slide past each other. The results of this study indicate that the rate of proteins renewal drops with ageing in the IFM specifically.
Our research proves that the increase in tendon injuries as horses age may be directly related to the slowdown in the renewal of specific proteins within their tendon tissues.
New research gives clues as to why older people get more tendon injuries
Our recent research into how tendons age has found that the material between tendon fibre bundles stiffens as it gets older and that this is responsible for older people being more susceptible to tendon injuries.
In this study, we repeatedly stretched samples of horse tendons, which are very similar to human ones, to test their elasticity and ability to recover. Experiments in the past have shown that stiffening in ageing tendons contributes to increased injuries in older tendons and this new research shows that it is specifically the stiffening and decreased resistance to repetitive loading of the tissue which holds tendon fibre bundles in place that is responsible. Tendon fibre bundles are surrounded by the interfascicular matrix (IFM), made up of tissue which enables the fibre bundles to slide past each other and stretch independently. In horses, the superficial digital flexor tendon (SDFT), which is used to store energy for propulsion, requires greater stretching of the IFM, than in the common digital extensor tendon (CDET) which aids the positioning of the leg.
While the IFM is more elastic, recovering better after loading in the SDFT it is prone to injury in older age because of the greater strain it is put under, and the stiffening and decreased ability to recover that results. The SDFT is very similar to the human Achilles tendon and so the results of this study can be directly applied to Achilles injury in people.
We now have a much greater understanding of what happens tendon structure as people get older and the role that plays in injuries. This information could be used to develop measures to reduce the risk of tendon injury or to speed recovery.
Tendon ECM damage, degradation and inflammation in response to overload
The role of inflammation in tendon injury is uncertain and a topic of current interest. Inflammation is clearly present in some tendon injuries, but the long term, chronically painful tendon injuries often seen by doctors show no signs of inflammation. This is surprising, and has caused scientists trying to understand how tendon injuries develop some confusion. Without understanding how injury develops, it is hard to successfully develop treatments.
Recent data from our group and others suggests that long term chronic tendon injuries do show inflammation early on after injury, but that inflammation has often disappeared before the patient sees a doctor, which is why it has been missed. In this project we wanted to investigate this further and see how different types of loading may initiate tendon inflammation.
We took small section of tendon, and subjected them to loading simulating different amounts of use, such as low effort exercise like walking, and more demanding exercises like fast running for five or 30 minutes. Following those exercises we looked at the response of the tendon cells to the load, especially focusing on enzymes related to inflammation and tendon matrix breakdown.
We found out that a small amount of inflammation occurred early on after any exercise, but that with more exercise, the amount of inflammation increased. This is interesting, as it suggests that tendons do consistently respond to loading with inflammation, but that this might actually be beneficial and an important part of how they stay healthy, helping them respond to any damage from use. We now need to learn more about how to manage the inflammation and help the tendon heal effectively after injury
Tendon inflammation in response to overuse
Tendon injuries are common both in athletes and the general population. Unfortunately, the ability of tendon to repair is very poor, so injuries will often persist for many years. We have a limited understanding of how tendon injuries develop, which has restricted our ability to produce effective treatments.
Scientists have always thought that tendons are damaged as a result of overuse, and that the cells in tendons are unable to repair the damage. Many previous studies have not shown any evidence of inflammation in damaged tendon tissue. However, these studies were often carried out on tendons several months after the injury occurred, and so do not help us to understand the early stages of injury development.
In this study, we specifically looked at the immediate response to tendon injury, in order to try and understand the process more fully. We took pieces of tendon and subjected to them to high loads, simulating the conditions leading to injury. We then looked at the tendon response to damage straight away.
We found that damaged tendon had higher levels of various markers of inflammation, as well as increased levels of tissue breakdown, all indicating an early inflammatory response from the tendon cells. This inflammation soon after an injury may actually be beneficial to the healing of tendons. The potential to change this response provides exciting avenues for future research, and may help us prevent long term tendon damage altogether.
Extracorporeal Shock Wave Therapy
Extracorporeal shock wave therapy (ESWT) is a common treatment for tendinopathy in the lower limbs, including greater trochanteric pain syndrome (GTPS), patellar tendinopathy (PT) and Achilles tendinopathy (AT). It involves applying shockwaves to the injured portion of tendon. The shockwaves are generated in a hand piece and delivered to the tendon via a compressed air impulse, radiating out to cover the area where pain occurs.
There is currently limited evaluation for the effectiveness of ESWT in treating tendinopathies. This paper reviewed the literature, to try to understand the most effective way of using the treatment.
We established that ESWT appears to be an effective intervention for tendinopathy, and should be considered for use, particularly where other conservative management has failed. Studies evaluating the most effective energy level, number of sessions, number of impulses and the use of local anaesthetic are required to optimise treatment protocols for each condition.
Understanding tendon fatigue damage with age
Tendons provide a link between muscle and bone, and are involved in moving and positioning the limbs. Some tendons, such as the human Achilles and horse superficial digital flexor tendon (SDFT) have an additional role to make movement more efficient. They do this by being stretchy; just like a rubber band, they can store energy when stretched, which they return by springing back, or recoiling, as they are released. These types of tendons are called energy storing tendons, and we are interested in trying to understand how their structure enables them to stretch and recoil so well. We have previously shown that the subunits of energy storing tendons are all helically arranged like individual springs, so when the tendon is stretched, the springs can stretch to store energy and recoil very effectively. However, even with these specialised springs, energy storing tendons are prone to age-related injury, which we think may be due to alterations in how tightly the springs are coiled.
In this study, we assessed how repetitive loading affects subunits from the energy storing SDFT in both young and old horses. We found that, in young horses, repeated loading caused low levels of damage and whilst the tendon was still elastic and spring-like, the loading began to cause the coil to unwind and become less effective. By contrast, when we looked at old horses, we found that the coil was already compromised and unwound, such that the samples were not able to resist further loading and showed high levels of damage when loaded. These findings may help to explain why the risk of tendon injury increases with age. They provide the first fundamental data of how an energy-storing tendon functions normally, and what happens when it is damaged or injured. Now we know this, we can start to develop solutions to help resolve the problem.
The tendon cell response to damage
This publication explores why and how tendon gets damaged. We think tendon injuries begin as a result of overuse, where the constant cycling of tendon when we run or walk creates microdamage to the structure. However, unlike other materials, in which fatigue damage accumulates with use, our tendons are living tissues, and have cells which can try to repair them. The cells respond to the local strains round them, and repair the matrix based on the strain signals they receive.
Sometime the repair works well and sometimes it doesn’t but we don’t understand why. We want to understand why, and try to control it, so it always works well. To do this, we need to understand the strains seen by the tendon cells during use, and how microdamage affects them. Our research shows that early microdamage does not seem to immediately affect the cell strains, suggesting that other factors must be responsible for the immediate cell response to injury.
However, we have also show that cells are not tightly attached to their surrounding tissue, so are protected from some of the strains applied at a tissue level. This is very interesting as it means we need to learn more about how cells and tissues interact to understand how cells respond to strain and repair tissue. It seems cells may be protected from too much strain though the design of tissues.