Heterotopic ossification

As heterotopic ossification of the reconstruction of soft tissue outside of the skeletal system is referred to in bony tissue, synonymously, the term myositis ossificans is used.

Causes

Heterotopic ossification are generally a result of tissue injury. Most frequently they are seen after implantation of endoprosthesis of the hip joint. However, they also occur in a number of other disease or injury primarily these are juxta-articular fractures of large bones such as hip fractures or shoulder joint fractures. Also at the elbow very often found post-traumatic ossification that occur in up to 55 % after elbow dislocations, in up to 30 % for radial head fractures and in up to 20 % with supracondylar humerus fractures. Even with blast injuries occur due to the strong tissue injury often heterotopic ossification on, just as in polytrauma with long unconsciousness.

In addition, neurogenic heterotopic ossification are especially after a traumatic brain injury, spinal cord injury ( and particularly at a paraplegia), encephalitis or observed a peripheral plexus or nerve injury.

A third large group are ossifications in competitive athletes and in massive repetitive muscular overloads. Examples are ossifications in the adductor muscles and gluteal muscles in the thigh with riders or calcifications on tensor fasciae latae in sprint athletes. In addition, several chronic degenerative diseases such as ankylosing spondylitis heterotopic ossification can be observed.

Pathogenesis

Pathogens table are for the resulting outside of the skeleton ossification usually called mesenchymal precursor cells responsible. Stimulated by so-called morphogens - their concentration in muscle and soft tissue area in trauma and surgery greatly increases - these cells are transformed through various intermediate stages in osteoblast or even the transformation of myoblasts to osteoblasts trigger. The ossification endochondral carried out prior verknorpeltem tissue, finally produces a lamellar bone.

About ten to twelve days after surgery or trauma, the incipient ossification may be clinically apparent by pain, swelling and redness of the skin (usually without the presence of chemical laboratory signs of inflammation ). After three to six weeks, they will radiologically initially visible as a dull, poorly demarcated opacities, they are previously but already in scintigraphy displayed. The heterotopic ossification are gradually converted into solid bone substance in the course from its center to the periphery, but their growth is there after some time by themselves to a standstill. After six months, most Verknöcherunegn are mature, but still shows up to 20 % growth until a year later.

Diagnostics

Heterotopic ossification are already clearly visible in conventional radiographs usually: in projection on the affected muscle and soft tissue, there are some dull, but later also well-defined calcified opacities. For precise localization of the ossification and the assessment of their expansion as part of a treatment planning computed tomography, magnetic resonance imaging and ultrasonography are used. Using scintigraphy can be determined whether the ossification " grown " and then do not show increased bone metabolism more, or are still in the process of growth and maturation with markedly elevated metabolism. This is important for planning a surgical resection, as these should be made only after completion of maturation, to reduce the risk of recurrence.

Symptoms and frequency

Heterotopic ossification can remain completely asymptomatic, but also cause pain and pain-related or mechanically induced movement restrictions of any severity. The extent of radiologically detectable ossification not correlates with the degree of discomfort. Arise after implantation of hip joint prostheses heterotopic ossification - the frequency is given very differently in the literature with 2 to 70 percent - to give approximately 4 percent to a stiffening ( ankylosis ) of the hip joint. After severe hip joint injuries much more frequently ( about 15 percent) are observed severe, joint bridging ossifications with stiffening. After implantation of total knee prostheses disturbing heterotopic ossification are rarely observed; often ( about 15 percent ) one finds kleinherdige, clinically harmless ossification in the course of the quadriceps tendon.

Postoperative heterotopic ossification is seen naturally more common in the older age groups where the need for prostheses increases. The formation of heterotopic ossification after bone and joint injuries, however, is independent of age, but it can be in these cases not possible to discern whether the injury itself or the surgical treatment is the cause of ossification.

The formation of heterotopic ossification is dependent on an individual assessment. On which factors this assessment is based, is not known. Individuals with a predisposition to increased osseous metaplasia is known ( for example, patients with ankylosing spondylitis ( Bechterew's disease ), or diseases of the circle form of disseminated idiopathic Skeletthyperostosen ) are preferentially affected by heterotopic ossification .. Also in men are more common than in heterotopic ossification women observed.

Other predisposing factors are strong intra-operative bleeding and bruising and infections., The type of surgical approach and surgical technique seem to have an effect on the frequency. Especially a further tissue trauma through vigorous movements of the broken bone ends to each other or by brusque Repositionsbewegungen increases the risk of heterotopic ossification as well as a delayed surgical care. On the other hand, the rehabilitation has no effect on the frequency, it is independent of whether a restraint, an active or a passive mobilization is carried out of the relevant joint.

Heterotopic ossification after hip replacement

Heterotopic ossification after total hip replacement with prostheses are classified using the classification by Brooker (1973 ) on the basis of an X-ray image in the frontal plane and divided into four grades:

A disadvantage of this arrangement that the complex three-dimensional structure is classified only on the basis of a single two-dimensional X-ray image. After Rader and Barthel ossification were with clinically relevant symptoms in 10 to 20 percent of patients have been found.

Treatment

Asymptomatic heterotopic ossification usually require no treatment. In movement disorders and / or chronic pain, surgical removal of calcifications should be considered. This must not be forgotten that any surgical manipulation may be the cause of new ossification itself again. Often, a surgical removal of the ossification often does not reach the treatment goal is to improve the mobility objective or subjective sensation of pain.

The time of resection or a arthrolysis is controversial. On the one hand there is evidence of a significantly increased risk of recurrence when the ossification are not yet " mature " at the time of removal and still growing, on the other hand seem to be the functional results especially at the elbow and shoulder joints better if is already operating in the first six months. The functional results appear better after resection of heterotopic ossification, which have formed after traumatic brain injury ..

Prevention

Patients in whom the incidence of heterotopic ossification is already known because of previous surgery or trauma, are often subjected to just before or within three days after a planned major surgery to bone ( hip ) irradiation, which increases the likelihood for re heterotopic ossification of approximately 30 to 10-14% reduced.

Indomethacin has long been heterotopic ossification prophylaxis used. In recent years, this also come in high doses administered nonsteroidal antiinflammatory drugs such as ibuprofen or diclofenac for use. This can also contribute to the reduced incidence of heterotopic ossification, so they are usually administered independently of the analgesic requirements of patients over several weeks after major orthopedic use.