All wounds, whether internal or external, result in the formation of scar tissue.
This tough, fibrous tissue is a natural side-effect of wound healing, according to Sue Taylor MRCVS of Connaught House Vets.
“The body’s natural healing process is triggered immediately after injury,” she says. “Although nature makes a good attempt to restore normal tissue function as quickly as possible, it cannot recreate the exact, original anatomy at the site of the injury.”
Sue explains that the collagen (a protein which acts as a scaffold, providing strength) produced at the site reforms in a random arrangement compared to its previous, highly organised structure.
“This new collagen is of a different type to the original,” she explains. “This not only makes the resulting tissue less elastic, but leaves it vulnerable to reinjury — especially if the tissue protrudes and is more prone to being knocked. Reinjured scar tissue takes a long time to heal, due to a reduced blood supply and also because the new tissue is abnormal in type.”
During the healing process, the amount of fibrous tissue in the wound increases.
“These fibrous cells cause the wound to contract, pulling the edges inwards,” adds Sue. “While this makes the scar look smaller, the fibrous cells in the wound become much less elastic and the site loses natural flexibility. Because of this, scar tissue can cause stiffness — particularly over a joint such as the hock or fetlock, where it can result in a lack of flexion.”
Internally, scarring occurs at the site of surgical wounds.
“This can have serious secondary consequences,” Sue explains. “The scar made to repair a twisted gut in the case of colic, for example, can develop into a narrowing of the gut and result in an obstruction.”
Most scar tissue is found on the limbs, Sue adds, explaining that the further down the limb the injury occurs, the less efficient healing will be.
“This is because the skin on the limbs is naturally tight, particularly on the distal limb below the hock and the knee,” she says. “It is also recognised that distal limb wounds are slower to heal due to a lack of blood supply to the skin. This causes a greater tendency for infection and the production of ‘proud flesh’ [an excessive growth of granulation tissue, a normal component of healing].
“The process of scarring can also be problematic. In some cases, the scar ends up much larger than expected because an excessive amount of tissue is created. This is known as a hypertrophic scar. Another abnormal type is a cheloid scar, where the skin takes on a reptilian appearance with a thick, scaly crust over the wound site.”
Because damaged skin is more delicate, care must be taken to protect scars from trauma or extreme temperatures.
“Scar tissue can be more susceptible to sunburn, particularly in pink-skinned horses,” adds Sue.
Treatment of a wound will have an impact on how well it heals and how much scar tissue develops.
“Keeping infection at bay and minimising proud flesh are the two key aims, initially,” says Sue, who advises good wound hygiene and the use of antibacterial creams and dressings where necessary. “Proud flesh is produced during the proliferative phase of wound healing [when new tissue is produced] and can be minimised with the application of pressure bandaging, under the guidance of your vet.
“Your vet may also remove prominent proud flesh with a scalpel, depending upon where it is,” she adds.
“Dressings should be changed as infrequently as possible, so as not to disturb the wound. An oozing, bleeding wound may need a dressing change more often, perhaps every 24 to 48 hours, but otherwise bandages can be left on for up to a week. The aim is to prevent damage and disturbance to the new tissue growing around the edges of the wound.”
Sue points out that bandaging a wound in an awkward place, such as over a joint, can be difficult and could lead to bandage sores.
“The topical gel Vulketan, which helps to promote wound healing and prevent the formation of proud flesh, can be applied to the area in these cases without the need for a bandage or dressing,” she says.
“Once a good granulation bed [a covering of new tissue] has been laid over the wound, gentle massage of the surrounding area and over the scar itself can help improve circulation. This will lay the internal fibres and collagen in a more linear arrangement, preventing the scar from becoming too stiff and immobile.
“As long as your vet and physiotherapist say it is appropriate, passive flexion of the joints through their range of movement will also help stop a scar becoming restrictive,” adds Sue.
“The more you ‘work’ scar tissue as it is healing, the more elastic it will be.”
A wise buy?
So you’ve found what seems to be the perfect horse, apart from some scarring from an old injury. Should you still buy him?
“Not knowing how the injury occurred or how the horse was treated can leave too many questions unanswered,” says Sue. “Did the wound reach internal structures such as a tendon sheath or joint capsule, for example? If so, the injury may have far more implications than meet the eye.
“Septic joints, bone chips and tendon damage are not as easy to identify or rectify once the wound has healed, but can render the horse impractical for a ridden career,” she adds.
“Another issue to consider is managing the scar tissue, because an old wound that reopens can be difficult to heal.
“A big, ugly scar in itself should not stop you from buying, however, as long as you are aware of the full extent of the injury and can be sure that there are no underlying issues.”
Ref Horse & Hound; 13 July 2017