Hegemann’s disease and fishtail deformity: aetiopathogenesis, radiographic appearance and clinical outcome

Purpose A systematic review regarding clinical studies on Hegemann’s disease and fishtail deformity was performed with the aims to: (1) formulate the most up-to-date theory on aetiology in order to better define these conditions, (2) summarise the most frequent radiographic descriptions on radiographs and (3) give an overview of different treatment options. Methods A systematic review of studies to date on Hegemann’s disease and fishtail deformity was performed. Studies were eligible if: (1) the article provides a description of Hegemann’s disease or fishtail deformity, (2) original data of at least one patient was available, (3) the article was written in English, German or Dutch and (4) a full manuscript was available. Animal studies, reviews and expert opinions were not included. Results We included a total of 22 articles: seven regarding Hegemann’s disease including eight patients and 15 regarding fishtail deformity including 58 patients. Conclusions Fishtail deformity and Hegemann’s disease seem to be a spectrum of vascular disorders of the distal humerus, varying from a benign mild vascular disorder to a complete avascular necrosis after fractures. Additional imaging is advised to confirm the presence of a fishtail deformity, intra-articular loose bodies and signs of osteoarthritis to decide if, and what, operative treatment is needed. As long as no clear aetiology for both diseases exist and the clinical symptoms and radiographic appearance are difficult to distinguish, both entities should preferably be named as ‘vascular disturbance of the trochlear growth plate’ to overcome confusing definitions and discussions.


Introduction
Osteochondrosis is used to describe more than 50 different conditions affecting the immature skeleton [1]. In 1951, Dr. Gerd Hegemann described the radiographic changes of the humeral trochlea in the young adult; therefore, osteochondrosis of the humeral trochlea is known as Hegemann's disease [2]. Studies so far report that osteochondrosis goes through stages, similar to Perthes' disease [3]. Reports on patients with Hegemann's disease are very rare [2]. Fishtail deformity of the elbow is a rare complication after fracture of the distal humerus, usually following a supracondylar, a lateral condyle, a medial condyle or even after Salter-Harris type I epiphyseal fractures in childhood [4].
Aetiology as well as optimal treatment for Hegemann's disease and fishtail deformity are subjects of ongoing debate. A systematic review regarding clinical studies on Hegemann's disease and fishtail deformity was performed with the aims to: (1) formulate the most up-to-date theory on aetiology in order to better define these conditions, (2) summarise the most frequent radiographic descriptions on radiographs and (3) give an overview of different treatment options.

Search strategy
To identify studies focusing on Hegemann's disease and fishtail deformity, the following databases (up to 27th August 2014) were searched: EMBASE, MEDLINE OvidSP, Web of Science, Cochrane Central, PubMed Publisher, Scopus and Google Scholar ( Table 1). The EMBASE search strategy was transferred into similar search strategies for the other databases. References of the included articles were also searched to identify more potentially relevant literature.

Study selection
Study selection was assessed by two independent reviewers (FC and JL). Disagreements were solved by consensus. If no consensus was reached, a third reviewer (MB) solved the disagreement. Studies were eligible if: (1) the article provides a description of Hegemann's disease and/or fishtail deformity, (2) original data of at least one patient were available, (3) the article was written in English, German or Dutch and (4) a full-text article was available. Animal studies, (systematic) reviews and expert opinions were not included.

Methodological quality assessment
Two reviewers (FC and JL) independently assessed the methodological quality of all the included studies. Important aspects of methodology were noted: study design, follow-up time and outcomes, e.g. because all studies were case reports, no pre-printed selection forms or an overall scoring system to evaluate methodological quality was used [5].

Data extraction
Data extraction was performed by the first author (FC). The following data were extracted: study population, patient characteristics, design of study, aetiology, clinical presentation and physical examination, radiological evaluation, treatment and outcome measures.

Literature search
A total of 22 studies were included in the current review ( Fig. 1), comprising seven studies regarding Hegemann's disease and 15 studies regarding fishtail deformity.

Patient characteristics
In all eight case reports, the patient characteristics were described. Seven of the eight patients were male (88 %) and the average age was 11 years (range 7-15 years).

Clinical presentation and physical examination
All included studies described the symptoms and findings at physical examination. In five patients, a swelling of the  [2,6,7]. Pain in the elbow was presented in five patients (63 %) [2,6,7,9]. A limited range of motion at presentation was described in all seven case reports (100 %), and an extension contracture of about 15°at presentation was seen in four patients (50 %) [7][8][9]. In one patient, progressive bowing of the elbow was noted (13 %) [10]. Beyer et al. described a patient with a 15°fl exion limitation and 20°varus deformity (13 %) [1]. In one patient, a flexion and extension limitation at presentation was noted (13 %) [6].

Treatment
In four case reports, the treatment for Hegemann's disease was described. A conservative treatment was recommended [2,6,7,9]. In three patients, rest was described as the treatment for Hegemann's disease (60 %) [7,9]. Szepesi advised less physical activities, Martin and Ehrenpfordt recommended less movement and Ito et al. advised to avoid vigorous sports activities by the epiphyseal closure and to avoid certain forms of sports involving hanging and throwing exercises [6,7,9].

Outcome (measures)
Six case reports described the outcome measurements. The average follow-up time was 32 months (range 12-16 months).
Radiography was used as an outcome measurement in all six studies [1,2,6,7,9,10]. In one patient, a reduced size of the trochlea, with the radius being longer than the ulna at the proximal radio-ulnar joint, was shown (17 %) [6].
In two patients, function of the elbow was used as the outcome measurement [2,9]. In the case presented by Hegemann, a range of motion restriction still existed [2] and loss of extension of the elbow was shown in one patient [9].

Clinical presentation and physical examination
In only one study was the clinical presentation and physical examination described [17]. Pain and limited range of motion was shown in 12 of the 14 patients evaluated in this study (86 %). Varus alignment was noted in five patients (range 3-8°), valgus in six patients (range 6-18°) and neutral in three patients. The average loss of extension is 12°(range 0-40°) and the average flexion loss is 11°(range 0-40°).

Treatment
Only one study described the treatment for fishtail deformity [17]. Glotzbecker et al. [17] recommended observational therapy in patients with a range of motion of 25-130°and minimal pain. In the case of progressive pain or increase in loss of range of motion, painful cracking symptoms or presence of symptomatic loose bodies, arthroscopic joint debridement was advised.

Discussion
Reports on patients with Hegemann's disease and fishtail deformity are very rare.
To our knowledge, this systematic review regarding Hegemann's disease and fishtail deformity is the first to summarise current knowledge on aetiology, radiographic findings and different treatment modalities.
Studies so far report that osteochondrosis goes through stages, similar to Perthes' disease [3]. The aetiology of Hegemann's disease remains unclear, although traumatic events may play a role, as in five of eight cases, a contusion, fracture or chronic repetitive micro-trauma are described. It is known that traumatic events in children may sometimes be overlooked or under-reported; therefore, a traumatic origin in the other three cases may play a role as well [26].
The trochlear epiphysis ossification centre appears after 5 years of age and develops between 8 and 13 years of age in boys. The ossification centre fuses with the metaphysis of the humerus between 13 and 16 years of age [6,27]. The trochlear blood supply comes from two end arterioles. The lateral aspect of the medial crista, the trochlear groove and the trochlear apex are relatively hypovascular. So those structures are prone to disturbances in the blood supply and the development of avascular necrosis [4]. Trochlear avascular necrosis is characterised by disturbance of growth involving the centres of ossification of the trochlea. Therefore, fishtail deformity could be a result of avascular necrosis of the vessels supplying the lateral trochlea [4,28]. If the lateral trochlear ossification centre development is disturbed and the remaining normal physis continues to grow, the distal humerus assumes a typical V shape: the fishtail [4,21].
Hegemann's disease is often diagnosed by radiography months or years after trauma [7,10,29]. This makes Hegemann's disease prone to confusion with a 'fishtail deformity.' Fishtail deformity of the elbow is an uncommon complication usually following a distal humeral fracture in childhood [4]. Usually, the term 'Hegemann's disease' is used for spontaneous or idiopathic osteonecrosis of the humeral trochlea. You can question if a disease can be called Hegemann's disease if it is not of idiopathic origin.
In all reports, standard radiographs were used for diagnosing Hegemann's disease and fishtail deformity. There is no gold standard for diagnosing Hegemann's disease and fishtail deformity. However, signs of fishtail deformity are shown earlier on CT and MRI, although at the time Hegemann's disease was first diagnosed neither CT nor MRI were available. Therefore, the fishtail deformity could be another (next) stage of Hegemann's disease, which is benign after a mild vascular disorder. A complete avascular necrosis could develop after traumatic events. Alternatively Hegemann's disease is a benign, self-limiting stage of fishtail deformity after unrecognised injury or (repetitive) micro-trauma. Hegemann's disease is characterised by irregularity of the trochlea and sclerosis. Schumacher et al. [30] classified Hegemann's disease into five different stages based on radiographs: stage 1: initial loss of density and later plaque-shaped sclerosis of the centre of epiphyseal ossification; stage 2: reduction in size and condensation of the ossification centre; stage 3: loosening, accompanied by onset of new ossification; stage 4: regeneration and enlargement of the ossification centre; and stage 5: final stage (complete or partial recovery) (Fig. 2). A central deficiency of the distal humeral epiphysis is characteristic for fishtail deformity [4]. Radiographs should always be compared to the asymptomatic elbow, as the appearance of the growth plate of the trochlea differs between individuals. Whilst Hegemann's disease was initially presumed to be a benign condition, in four of the six cases where follow-up was done, no full recovery was seen. In early stages, rest and a total ban on all sports activities and exemption from participation in certain forms of sport involving hanging, propping and throwing exercises, together with apparatus gymnastics, have been advised until the epiphysis is closed. It is questionable if a total ban on all physical activities is mandatory in these young children; possibly, a symptomrelated adjustment of activities could be enough. CT and MRI scans are helpful to confirm the presence of a premature fishtail deformity, intra-articular loose bodies and signs of osteoarthritis. If intra-articular loose bodies are found and occur with locking symptoms of the elbow, arthroscopic debridement may be indicated. Long-term follow-up studies showed that patients with fishtail deformity are probably prone to functional impairment, ongoing pain and the development of early osteoarthritis [16,21]. It is unknown whether or not early arthroscopic debridement of the joint prevents osteoarthritis in the future.
Based on this systematic review, many aetiological aspects of Hegemann's disease and fishtail deformity remain unclear. It is presumable that fishtail deformity is a stage of Hegemann's disease or Hegemann's disease is a benign stage of fishtail deformity after unrecognised injury or (repetitive) micro-trauma. Additional imaging is advised to confirm the presence of a premature fishtail deformity, intra-articular loose bodies and signs of osteoarthritis to decide if operative treatment is indicated.
There are several weaknesses in the included studies of this systematic review. The review is based on case reports, and the number of included patients in each study was low and, therefore, the strength of evidence is limited by the quality of the available studies.
Since Hegemann's disease and fishtail deformity are very rare, higher quality studies are not likely to be performed and, thus, this systematic review provides the best level of evidence on what is known about Hegemann's disease.

Conclusion
Future studies on Hegemann's disease and fishtail deformity should ideally investigate the aetiology to prevent those diseases. As long as no clear aetiology for both diseases exist and the clinical symptoms and radiographic appearance are difficult to distinguish, both entities should preferably be named a 'vascular disturbance of the trochlear growth plate' to overcome confusing definitions and discussions.
review. FMAP Claessen has received an unrestricted research grant from the Prins Bernhard Cultuurfonds foundation, Trust Foundation, VSB Foundation and Van Beek-Donner Foundation. For the remaining authors, none were declared.
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