POST- BURN HETEROTOPIC JOINT OSSIFICATIONS

Virbicky B.

First Orthopaedic Department, Teaching Hospital, Prague, Czechoslovakia

SUMMARY. In a 10-year period 3322 burn in-patients were treated. Out of this number 68 patients developed heterotopic joint ossifications - either symptomless or limiting joint movement extent in various degrees up to ankylosis. The present work attempts to determine: a) causes which could lead to heterotopic ossifications; b) clinical signs in the period, of presupposed heterotopic ossifications; c) methods for detecting heterotopic ossification maturity prior to planned resection.

Extensive bum trauma leaves almost 50% of patients with changes variously limiting joint movement. The causes of this condition are the following: scar contractures of the skin, tendons and articulare capsule, and heterotopic ossifications (H0) in the joint area. In soft tissue contractures limiting movement, the surgical treatment is clear. HO may be clinically symptomless or may limit joint movement extent in various degree up to ankylosis.

In the years 1976-1986 3322 burn in-patients were treated at our Burns Centre. Out of this number 68 patients w ' ith HO development limiting joint movement were detected by systematic follow-up, including orthopaedic specialist participation, i.e. 2%, which is in agreement with other authors' data (1).

Age of Patients - Table I

Cause of Bum - Table II

Incidence in Indivual Joints - Table III

In the above population of handicapped patients the author attempted to.determine:

1. causes which could lead to HO development already in the acute phase;
2. clinical signs in the period of presupposed HO development;
3. methods for detecting 1-10 maturity prior to planned resection.

A. The evaluation of the acute phase thermal injury was based on case records of patients who subsequently developed HO with joint movement limitation.

The follow-up of these data was based on references(2) dealing with HO development after brain injury accompanied by long-term unconsciousness. Out of our population under study 7 patients were unconscious.
In all of these however the cause of bum was electric current with direct joint destruction; unconsciousness could not therefore play an important role and the probability of this being a factor in HO development is considered very low.

2. Septic fevers

Elevated temperature is a typical feature in thermal trauma: in this study patients with a septicaemia temperature curve lasting more than 3 weeks were followed. This criterion applied to 8 of the patients, in whom intra-articular ankylosis developed. The septic condition might threaten the joint with septic destruction and subsequent intraarticular ankylosis.

3. Escharotomy

Second- and third-degree bums affecting the whole circumference of the limb may lead to the occurrence of the compartment syndro.me(3). Compressed soft tissues in the compartment area undergo necrotic changes which may turn into HO. Escharotomy decreases the danger of compartment syndrome sequelae. In patients treated from the beginning at a Bums Centre the intervention was always timely and of sufficient extent, and there were therefore not so many IjO cases as in patients brought from other surgical departments where escharotomy was not performed in time, or incorrectly.

Out of the population under study with HO in the joint area, 5 patients were found to have a history of severe trauma or malformation of the joint prior to the thermal injury. Although the number of such cases is not high, more attention should be paid to these joints during thermal injury treatment.

5. Individual tendency to HO development

Some case reports (5) mention the development of HO after every blunt trauma. answers were indefinite, the mean value according to the above scale being 1.2. References to the incidence of identical HO types in 2 burned brothers are also known (1). The key to this genetic predisposition may be in the HLA system distribution. A survey by means of HLA B27 showed the HLA distribution in normal population to be 7%, compared to 70% in HO patients. In our patients the response concerning the tendency to HO was never positive, but its possibility should also be considered in burn patients.

B. Radiological evidence of HO begins in the period from 9-18 weeks after the thermal injury. The possibility of HO development may manifest itself by the following facts:

1. Depth, extent and localization of burned skin area

1. In all HO patients studied the burns were predominantly full thickness, with burned skin area exceeding 20%.
2. The occurence of HO was not always at the site of maximal thermal injury: one of our patients had HO of the elbow while the thermal injury was only in the lower part of the body.

2. Total immobility period of the patient

The mean time spent in hospital in our HO patients was 2 months. This confirms the reports of other authors (7, 8) that 2 months' total immobility predisposes to HO development: early mobilization, together with adequate kinesiotherapy,significantly reduces the occurrence of HO.

3. Itching in the site of the affected joint

Some case reports (6) mention itchin& in the site of HO development. Our patients were asked about itching over the site of periarticular HO, the evaluaton of its intensity being as follows: 0 = none, I = slight, 2 = moderate, 3 = severe.

The intensity of pain in the area of the affected joint was tested by means of a subjective sensation scale analogous to that used for itching. The resulting mean value was 1.93. It can therefore be assumed that there may be pain in a joint with developing HO. Other causes of such pain must however also be taken into account, e.g. incipient infection.

5. Joint movement extent

In patients with HO in joint areas, the extent of joint movement varied from normal to total ankylosis. The movement extent was influenced by:

1. scar soft tissue contractures
2. HO development itself in the joint area.

In many cases only the peroperative finding clarified the contribution of the above factors to the limited joint movement. The joint movement extent cannot therefore in most cases be correlated with X-ray findings. It is only the X-ray picture of joint destruction with intra-articular ankylosis and ankylosis due to massive bone bridging round the joint which corresponds to the clinical findings.

C. Extra-articular HO that limit joint movement are removed by their resection, and in joint devastation followed by intra-articular bone ankylosis by means of arthroplasty. Resection may be performed only in mature bone: after removal of immature bone the ossification process in the joint area recurs resulting again in limited movement.

The following facts were found, in correlation with the examinations mentioned below, in all patients studied:

1. immature skin cover or residual granulations mean that the developing HO are not mature yet and/or are still growing;
2. on the other hand mature scar tissue means that HO ossification ingrowth is finished and either resorption of mature bone or its already unchanging shape may be presumed.

2. Calcium and inorganic phosphorus levels

These were followed up in the period of developing HO as well as in their maturity, which was assessed by other methods. In all patients the level of these minerals in both periods studied was in the normal range, which provides evidence of the dystrophic origin of HO but also shows that it is not necessary to follow these data in HO in everyday practice.

The alkaline phosphatase isoenzyme is without doubt an osteoblastic activity index. The alkaline phosphatase level (in microcatals) was studied in children (4-15 years of age) and adult patients with HO. The assessment was peformed both in the period of HO development and of mature pyrophosphate activity in immature bone, i.e. the disappearance of ostcoblastic activity = maturity of HO. The scintigraphic investigation prior to planned HO resection is therefore highly recommended.

4. Enumeration and evaluation of possible methods for determining HO and their maturity

1. Radiography ranks among the first and basic examinations in the event of suspected HO development. In addition to standard projections, atypical X-rays are used for precise anatomic images, especially prior to planned resection.
2. Tomographic investigation is appropriate for more accurate HO localization as well as the determination of their degree of maturity.
3. Arthrography: no practical use in HO.
4. Angiography: possible use only when HO are suspected to be an ossified tumour.
5. Xeroradiography: possible use for diagnosis of fine, freshly arising calcifications in the elbow area
6. Computer tomography: makes the diagnosis of HO localization much more accurate.
7. MRI (Magnetic Resonance Imaging): as our material dates from the year 1976 this method was not used in HO. However, MRI could help to clarify the contribution of HO and soft structures to limited joint movement.

Alkaline Phosphatase Level (in microcatals) - Our investigations show that: a) the normal alkaline phosphatase not exclude the occurrence of ectopic ossification;level does b) periodical alkaline phosphatase follow-up may significantly contribute to determination of HO maturity.

Scintigraphic investigation: in cooperation with the Institute of Nuclear Medicine, HO osteoblastic activity assessment was performed by the scintigraphic method using short-time labelled pyrophosphate compounds. The investigations were carried out in the period of first-noticed subjective joint difficulties as well as in the period when according to X-ray pictures the bone was considered mature for resection. Comparison of the two examinations showed a marked decrease of the previously high level

Conclusions

1. HO in the joint area develop in patients with predominantly deep bums and burned area above 20% TBSA.
2. The site of periarticular HO development need not always be the site of maximal skin injury, the most commonly affected joint being the elbow.
3. Immobilization longer than 8 weeks predisposes to HO occurrence: early mobilization of the patient on the other hand prevents HO development and often may even cause HO disappearance without further treatment.
4. Unclosed wounds or immature post-burn skin cover contribute to HO development whereas definitive closure and its maturity diminish HO.
5. There may exist an inborn predisposition to HO development. Joints affected by inborn or acquired malformations and illnesses may also more often be affected by HO development after burn trauma.
6. Itching, pain and limited joint movement extent may be the first clinical signs of HO development.
7. Among laboratory investigations, the periodical follow-up of the alkaline phosphatase level is of significance: a decrease in its level correlates with HO maturation.
8. The significance of further accessory examination methods (X-ray, CT, MRI, scintigraphy) for HO diagnosis and assessment of the degree of maturity prior to planned resection is mentioned.

RESUME Pendant une période de 10 ans 3322 patients brélés ont W hospitalisés. D'entre eux é8 ont présenté des ossifications hétérotopiques des articulations, ou sans symptémes ou avec une limitation de la capacité de mouvement des articulations plus ou moins grande, jusqu'd Pankylose. Cet article cherche A déterminer: a) les causes qui pourraient conduire aux ossifications hétérotopiques; b) les signes cliniques pendant la période des ossifications hétérotopiques présupposées; c) les méthodes pour dépister la maturité des ossifications hétérotopiques avant la résection planifiée.

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