Chronic Osteomyelitis Occurring in Emeus crassus
[Read before the Southland Branch, April 30, 1942; received by the Editor, March 29, 1944; issued separately, September, 1944.]
Among moa remains recovered at Back Beach, Riverton, in 1939 by Mr. John Thomson, jun., and presented by him to the Southland Museum, was a partial skeleton of an immature Emeus crassus (Owen), the right tarso-metatarsus of which showed a decided pathological lesion.
Diseased conditions among moa bones have been noted on previous occasions, Booth (1874, p. 124) for instance, stating; “A disease of the foot appeared to have been very prevalent amongst them, as a great number of the joints presented unmistakeable indications of rot, so much so that some of the toe-joints had even grown together.” More recently, in a letter to one of the authors, Dr. Gilbert Archey, Director of the Auckland Institute and Museum, states that some of the moa bones in his institution show pathological conditions. He states that the type of Pachyornis mappini (Archey) has the claw joint of the outer toe fused to the fourth, whilst an example of Euryapteryx exilis (Hutton) from Doubtless Bay has the basal joint of the hind toe fused to the back of the metatarsus. Dr. Archey also states that inter-muscular or interligamentary bone growth and penetration is common in leg-bones and vertebrae which thereby become very jagged in presumably older specimens.
Dr. R. A. Falla, Director of the Canterbury Museum, has stated that several examples of a diseased state in moa bones occur in the collections under his charge, but the authors have no particulars of the actual condition.
It appears that most, if not all, diseased conditions occurring in moa bones, and previously reported, are degrees of bone fusion and associated with advancing age. The condition to be described by the authors is not one of these and occurs in a juvenile bird.
In order to find out if a similar condition had been noted in other members of the Ratite group, various institutions, both at Home and abroad, were written to, requesting information. Almost all replies were negative ones with the exception of one from the American Museum of Natural History in New York, and one from the New York Zoological Society. John T. Zimmer, Executive Curator of the former institution, stated that, after going over their collections of ostriches and their allies, he found one specimen of a male cassowary of undetermined species which showed decided pathological lesions at the upper ends of both tarsi and extending well down in front. In the rest of the material housed at the, institution he was unable to detect any similar condition.
Lee S. Crandall, Curator of Birds, New York Zoological Society, stated that Dr. L. J. Goss, veterinarian at the institution, had been carefully through the records of his department, but could find nothing describing a pathological condition and could recall nothing of the sort from his own experience. Mr. Crandall stated that he had certainly seen birds of the group with bone enlargements suggestive of healed lesions, but could not recall a complete history of such a case.
The remains to which the diseased tarso-metatarsus belong have been identified as Emeus crassus (Owen). They include a damaged pelvis, some vertebrae, part of the lower mandible, a broken sternum, some ribs, toes and sundry small bones, both femora, both tibio-tarsi and the diseased tarsometatarsus. Immaturity is shown by the lack of fusion of epiphyses at the knee and by the roughening of the ends of the long bones beneath their articular cartilaginous coverings. Of those bones which have been preserved no other shows any macroscopic evidence of disease.
The affected bone presents marked expansion of the shaft with a large central cavity and large anterior and posterior openings in the bone. (Figs. 1 and 2.)
On the anterior surface (Fig. 1) the epiphyseal line is still visible at the proximal end of the bone. The expansion of the bone commences immediately beyond this on the lateral aspect and extends almost to the base of the metatarsal element. The involucrum, or subperiosteal new bone, is very dense throughout this area. This new bone extends across the front of the specimen immediately distal to the large anterior fossa and continues down its medial aspect to the base of the internal metatarsal element. There is a large anterior opening in the bone 4.2 cm. long by 3.5 cm. wide. The neck of the internal metatarsal element shows a patch of subperiosteal roughening on its anterior and medial aspects.
On the posterior surface (Fig. 2), the subperiosteal roughening commences just distal to the twin foramina and extends laterally and medially to the expanded regions of the shaft. The involucrum is particularly thick and spongy on the medial aspect of the large central opening, which is 5 cm. long by 4 cm. wide; its distal limits correspond with those on the anterior aspect of the bone. Distally at the neck of the internal metatarsal element there is a small sinus leading down into the depth of the bone. It is situated at the centre of a small raised roughened area of bone 15 mm. across.
The medial surface of the specimen (Fig. 3) is of particular interest, in that it shows two enormous bosses of involucrum occurring in front of and behind a narrow strip of bone which appears to have been the original medial border. There is a small cloaca at the distal aspect of this furrow and several more in the anterior mass of involucrum. Additional interest is aroused by the fact that a similar narrow groove is present in the same region on a healthy bone, so that one is inclined to presume that this is
caused by the presence of a tendon or similar structure. In contradistinction to the marked thickening and density of the lateral border, the involucrum medially is both thin and spongy, hence the numerous cloacae. Distally, the band of roughening can be seen to extend right across the neck of the internal metatarsal element from front to back.
Comparative antero-posterior radiographs of the specimen (Fig. 4) and of a similar bone from the healthy bird (Fig. 5) show the great changes produced by infection. A large cavity occupies the central portion of the expanded shaft and from here the disease extends both proximally and distally.
Proximally, on the medial aspect of the specimen, the lesion, as shown by the increased density of the bone (osteitic reaction) has extended right to the articular surface, while the intervening bone shows irregularly mingled areas of rarefaction and increased density.
Distally, the infective process appears to have involved the medial aspect of the metatarsal elements rather than the external one, though this same irregular alternation of increased density and rarefaction extends down to the necks of the middle and internal metatarsal elements. There are three or four small areas of necrosis in this region of the middle metatarsal and one large one, approximately 15 mm. in diameter, in the internal element.
The radiograph of the healthy bone shows the bony trabeculae and how the lines of force are distributed normally.
The lateral radiograph (Fig. 6) discloses the density of the bone above and below the lesion and the spongy nature of the involucrum which formed posteriorly; it also gives a very fair idea of the ramifications of the large central cavity. In this film the cavity previously noted in the internal metatarsal is seen to affect mainly the posterior part of the bone.
The macroscopic and radiological appearances are those of a chronic long-standing osteomyelitis of the right tarsometatarsal bone with a small metastatic abscess in the neck of the internal metatarsal element, and with commencing necrosis in the neck of the middle metatarsal. The three features of main interest in the actual specimen itself are (1) the large irregular cavity, (2) the great expansion of the bone and (3) the great density of the lateral aspect of the bone.
No other lesion was discovered in any of the remaining bones recovered.
The authors wish to acknowledge their indebtedness to the Southland Museum for permission to describe the diseased bone and to all those who supplied information upon request.
Booth, B. S., 1874. Description of a Moa Swamp at Hamilton. Trans. N.Z. Inst., vol. vii, p. 124.