“Bone is a unique and fascinating material,” he began. “People often think of bone as being relatively inert, but I’d like to dispel that concept. Modeling and remodeling can be occurring in the same bone at the same time–bone is always in all stages of remodeling. Bone does not heal, incorporating the scar tissue as seen in most all other tissues–it regenerates itself. It changes its shape and structure based on its use, and if broken can resume 100% of its former strength and function.”
BROAD CLASSIFICATION OF FRACTURES IN THREE SEGMENTS =
- Complete = loss of function of the limb.
- Incomplete = lameness and localised signs; stress fracture.
- Stable = non-displaced
- Unstable = displaced
SPECFIC FRACTURE CLASSIFICATION
- Configuration = oblique, transverse, spiral, multiple, comminuted.
- Character = articular, non-articular, diaphysial, epiphyseal, Salter-Harris physeal, chip and slab (Nunamaker, 2002).
- Single load = falls, collisions, impact
- Accumulation load = continued fatigue damage from repeated loading beyond biomechanical limits.
Clinical Signs and Symptoms
- Complete fracture
- Rapid inflammation of site
- Immediate distress of animal
- Leg hangs crooked
- End of bone may penetrate skin
- Attempted movement on three legs
- Incomplete fracture
- Mild lameness usually
Methods of Diagnosis
- Nuclear Scintigraphy – useful for detecting a hidden fracture
- Stress fractures (also known as fatigue fractures) are most commonly found in the metacarpus, metatarsus, proximal sesamoid, tibia, humerus and pelvis.
- Fractures of P3 (pedal bone) — commonly occur when a horse kicks out at a wall or lands on an irregular surface. If the fracture does not involve the joint (distal interphalangeal joint – DIP joint), most cases heal with box rest and bar shoes for support. If the fracture does involve the DIP joint, prognosis is lesser.
- Fractures of P1 (pastern bone) — commonly longitudinal and extend down from the fetlock joint.
- Sesamoid bone fracture — occur commonly in young foals, often presenting as avulsion fractures at the attachment of the suspensory ligament. Pain and lameness occur alongside fetlock inflammation, resulting in chronic or recurrent lameness.
- Fracture of metacarpal/metatarsal bone — commonly occur due to a kick or fall, and extend into the fetlock joint.
- Carpal fractures — most occur as chip and slab which can result in pain and joint distension.
- Splint bone fracture
- Olecranon fracture — usually the result of a kick, often compound or comminuted.
- Pelvic fractures — most start as an incomplete stress fracture and will fully heal if given a prompt diagnosis, rest and adequate time. The wing of the illium is particularly predisposed to stress fractures.
In every horse that is presenting an acute onset non-weightbearing lameness, a fracture should be high on the differential diagnosis list (along with bone, joint or tendon sheath infection and hoof abscess).
Some fractures (ie. osteochondral chip fracture of a carpal bone) may only produce low grade lameness.
A cast might be changed as frequently as every 10 days for a foal, or as infrequently as every six weeks for an older horse. The duration depends on how healing progresses and how the horse’s skin and muscle react to the cast.
- Surgical fixation
- Bone fragment removal surgery via arthroscopy
Dependent on a variety of factors:
- Poor prognosis = complete fractures of the radius and tibia in adult horses. This is because it becomes difficult to reconstruct and heal the fracture with enough stability to withstand weight bearing. Weight-bearing on the affected limb is essential, otherwise there is increased risk of laminitis in the contralateral limb. Areas that surround the fracture with a large muscle mass, ie. the pelvis, have a more positive prognosis via conservative therapy.
- Fair prognosis = incomplete fracture with confinement.
Complications during Recovery
- Laminitis in the contralateral limb
- Osteoarthritis of adjacent joints
- Flexural limb deformity
- Increased joint laxity in young horses following immobility in a cast of affected limb; also, angular deformities in contralateral limb.
- Joint stiffness = rare.
The Role of a Veterinary Physiotherapist in Recovery
The healing time of a fracture is dependent upon age, fracture type, every and site. An outline of the age and timescales for canine fractures is listed in the table below.
|Younger than 3 months old||2-4 weeks|
|3-6 months old||4 weeks – 3 months|
|6-12 months old||5 weeks – 5 months|
|Over 1 year old||7 weeks – 12 months|
An equine fracture can take between six to eight weeks to heal, with the rehabilitation extending to four to six months. Successful healing of a fracture is not solely determined by complete bony union presented on radiographs, but also the functional use of the limb. With this in mind, physiotherapy following veterinary management of a fracture can be beneficial to healing quality.
Physiotherapy can begin as soon as the area is accessible ie. when the cast is removed or immediately if internal fixation has been used.
Determine goals for the different stages of healing. Some used in this case would be:
- pain management
- aerobic fitness
- avoidance of complications resulting from immobility
- maintaining or improving muscle mass
- retraining of functional activities
- Ultrasound — low intensity, pulsed US (1MHz/1.5MHz/3.3MHz for 10-20 minutes daily beginning day 1 post-operative) has been shown to stimulate endochondral ossification. It also increases the positive stiffness and thus resilience of bone.
- LASER — increases osteoblastic proliferation, collagen deposition, new bone formation, increased bone stiffness (by forming smaller and stronger callus with increased quantity of trabeculae).
- Most effective when carried out in early stages where cell proliferation is occurring.
- Pulsed Electromagnetic Field Therapy (PEMFT) — stimulate osteoblast and chondroblast production, although there are contradictory findings in literature.
- Neuromuscular Electrical Stimulation (NMES) — mineralisation of callus, greater torsional parameters.
- Electrode placed 3cm proximal to fracture site and the other proximal to the first electrode, 25mA, pulse width = 50, 4Hz, 20s on:15s off for one hour daily beginning day four after surgery for 25 days.
- Shockwave — effects bone by up regulating proteins critical for angiogenesis, boosting the release of growth factors which are needed for osteoblast formation.
- Weight bearing and early mobillisation — avoidance of the disuse response, invariably leading to muscle atrophy and weakened bone tissue. Based on this response, the unloaded healing bone will repair in a weaker state due to decreased stress and strain placed upon it (Wolffs Law).
- GRADUATED TREATMENT PROCESS = Hydrotherapy –> graduated weight-bearing exercise programme –> land treadmill –> strength, endurance and balance exercises.
Research Rundown: Fractures in Racehorses
RESEARCH ARTICLE: Fractures – a preventable hazard of racing thoroughbreds?
With 60% of fatal racecourse injuries in the UK being associated with a fracture, hazard prevention is essential.
As racing injuries are “spontaneous”, preventing the hazard of fractures can be difficult as it is not caused by a specific traumatic event.
There is evidence that fractures that occur in racing are mostly stress fractures (57%), the end stage of a series of events relating to fatigue. Consequently, avoiding exercising a horse to an extreme fatigue level can decrease the risk of such injuries.
Stress fractures in racing occur in horses undergoing intense race training; a repetitive, high strain loading form of exercise. In order to reduce the incidence of stress fractures, avoiding repetitive and high strain training can be beneficial.
The fractures show a high degree of consistency in their morphology; they frequently share the same locations as incomplete cracks and they are often associated with pre-existing pathology.
Fatigue of bone is associated with progressive microdamage, which is important in the pathogenesis of stress fractures
Horses exercised before bone repair is complete are likely to be at significantly greater risk of sustaining a catastrophic stress fracture.
Gait and speed as exercise components of risk factors associated with onset of fatigue injury of the third metacarpal bone in 2-year-old Thoroughbred racehorses → as speed increases, the hazard ratioassociated with onset of fatigue injury of the third metacarpal bone increases.
Rooney, J. (1982) → predicts that if the distances at which the horse became extremely fatigued were eliminated, lameness would be reduced about 14% and bone fracture-breakdown about 24%.
Mainwood and Renaud (1985) → found that H+ions are generated rapidly when muscles are maximally activated. This increases the acidity of the musclein combination with lactate increase. This can cause discomfortand mean the muscles will not work to the best of the ability to support bones and joints, allowing for the possibility of injury to occur.
Yoshikawa et al.(1994) → found (in an investigation using foxhounds) that muscle fatigue had an effect on bone strain, with peak principal strain on the tibia being increased by an average of 26–35% following muscular fatigue.
Hesse and Verheyen (2010) → found that the presence of pelvic bony asymmetry, muscle atrophy of the quarters, reduced reflex movements of dorsi- and/or ventroflexion and spasm or tenderness on palpation of the gluteal muscles were significantly associated with subsequent fracture diagnosis. Horses subsequently diagnosed with pelvic or hindlimb fracture were 11.1 times more likely to show pelvic bony asymmetry, 4.7 times more likely to display muscle atrophy of the quarters and 6.6 times more likely to have spasm or tenderness on palpation of the gluteal muscles than those that were not. This highlights the importance of the role of a veterinary physiotherapist in a racehorse training programme.
Factors to decrease incidence of fractures;
- Implementation of training regime
- Allow time for recovery
- Softer, more supportive track surface.
- Allow for bone remodelling.
- Diet – ensuring the horse has nutritional requirements
- Shorter races, lower and less wide fences to reduce fatigue.
Racehorse training regimens that allow time for the skeleton to adapt, reduce the risk of pelvic fracture. Read more on this study here.
Preventable to a certain extent. Dependent upon whether reducing the risk factors is financially viable for the racing industry & owner.