AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 77529-531 (1988)

Calcaneus Secundarius: An Osteo-Archaeological Note TREVOR ANDERSON Department o f Prehistory and Archeology, Sheffield University, Sheffield, S. Yorkshire SlO 8T1: England

KEY WORDS Trondheim

Osteo-archaeology, Foot anomaly, Medieval

ABSTRACT Calcaneus secundarius, a minor anatomical variant in the foot, is subclinical and its true prevalence in modern populations is uncertain. The trait is clearly visible in dry bones, and osteo-archeological evidence suggests that it may be a more frequent occurrence than was formerly thought. The etiology of the trait is outlined, and its possible value is assessing “biolog- ical distance” in past populations is considered.

The calcaneous secundarius, an accessory bone, is a small ossicle located at the antero- medial angle of the dorsal calcaneal surface (Anderson, 1968: Fig. 13; Sarrafian, 1983: Fig. 2-68). It was first described by Steida in 1867 (cited in Biermann, 1922). Approxi- mately 30 tarsal accessoria have been identi- fied (Klenerman, 1982:361; O’Rahilly, 19531, either as independent ossicles, such as the 0s intercuneiforme, or as abnormal separation from a tarsal element, 0s trigonum and cal- caneus secundarius. In archeological mate- rial the latter type will be recognised as a notch in the dry bone. The independent ossi- cles, even if recovered, will be largely indis- tinguishable from other accessoria and from pedal sesamoids.

The calcaneous secundarius, attached to its tarsal element by a ligamentous band, is asymptomatic, and thus its prevalence in modern populations is uncertain. Earlier sources, quoted in Sarrafian (1983:94), gave occurrences of 0.14-2.5% in nineteenth cen- tury Europe, An examination of 750 British calcanei revealed three cases, 0.4% (Laidlaw, 1905). An example is known from an Egyp- tian mummy (Holland, cited in O’Rahilly, 1953) but, in general, the trait has been over- looked by osteo-archeologists.

MATERIALS AND METHODS

The evidence from a medieval cemetery in Trondheim, Norway, suggests that the anom- aly may be more common than is presently thought. The trait was found in 5.4% of the skeletons (n = 149), that is, 4.8% of individ- ual calcanei (13/268). The youngest occur- rence was in a 12-14-year old (SK 240);

however, only eight bones under 12 years of age were sufXciently complete for study. There was no clear evidence for a sex or age influence. The trait was slightly more fre- quent in the earlier phases (12-13th centu- ries: 6.25%) than in the later period (13-17th centuries: 4.3%), but this does not represent a significant chronological variation.

The morphology of calcaneus secundarius is presented in Table 1. A rounded notch was the commonest form, 77%, which is in opposition in Kohler and Zimmer’s view (1968) that a triangular ossicle is more fre- quently observed. The rounded notches are subdivided by depth: crescent (shallower); lunate (intermediate); semicircle (deeper). The trait occurs almost equally in conjunc- tion with continuous (Fig. 1) and separated (Fig. 2) calcaneal facets (Table 1). In the skeletal sample as a whole, the separated facet (n = 104) is less frequent than the con- tinuous form (n = 166). Thus, calcaneus se- cundarius manifestation is associated more with separated 6.7% (7/104) than continuous 3.6% (6466) facet morphology.

ETIOLOGY

It is known that tarsal accessoria, includ- ing calcaneus secundarius, appear as inde- pendent cartilaginous elements during fetal life (Klenerman, 1982; O’Rahilly, 1953). If an element forms at the dorsal surface of the anteromedial calcaneal angle and fails to co- alesce the resultant bony ossicle is a calca- neus secundarius. A similar etiology has been

Received March 7, 1988; revlsion accepted April 26, 1988

0 1988 ALAN R. LISS, INC

530 T. ANDERSON

TABLE 1. Calcaneus secundarius morphology1

Morphology SKNo. Sex Age p-d Right p-d Left

166 M 37-42 12.5 Rectangle b 18.0 Triangle b 281 M Maturus 40-50 - - 8.0 Lunate a 70 M ? ? 5.5 Lunate b X b

199 F Youngadultus 18-22 3.0 Lunate a 8.0 Lunate a 356 F Young adultus 20-25 X b 4.0 Triangle a 210 F Adultus 25-35 7.0 Semicircle a 9.0 Semicircle a 294 F Maturus 35-40 6.0 Crescent b 5.0 Lunate b 240 ? Juvenalis 12-14 8.5 Crescent b 6.0 Crescent b

’-, trait not scoreable (bone unavailable); X, trait not present; a, calcaneal anterior and medial facets continuous; b, calcaneal anterior and medial facets separated; p-d, proximo-distal notch diameter (mm).

Fig. 1. SK 199, St. Olav’s, Trondheim. Right calca- neus. Displaying a notch (arrowed) representing calca- neus secundarius. The anterior and medial facets are continuous. separate.

Fig. 2. SK 294, St. Olav’s, Trondheim. Right calca- neus. Displaying a notch (arrowed) representing calca- neus secundarius. The anterior and medial facets are

demonstrated for 0s trigonum (O’Rahilly, 1953) and emarginate patella (Green, 1975).

not always synonymous with genetic causa- tion since external, nongenetic, influences (such as viruses and drugs) may act upon the fetus.

Modern radiological investigation suggests that calcaneus secundarius is more frequent in children: 6-7% in girls and 7-11% in boys

DISCUSSION

The genetic basis of skeletal nonmetrics is still poorly understood (Riising, 1984). It must be remembered that a congenital origin is

CALCANEUS SECUNDARIUS 531

CHoerr et al., 19621, than in adults. This is related to the fact that supernumerary ossi- ficational centra are known to coalesce dur- ing childhood in the talus (Schreiber et al., 1985), calcaneus (BazBnt, 1964; Szaboky et al., 19701, and the patella (George, 1935; Green, 1975). The etiologically related 0s tri- gonum is also known to undergo synostosis (Lapidus, 1972; Sewell, 1904).

Little work was been carried out on the causation and persistence of tarsal accesso- ria. However, the accessory patellar ossicle may remain separate due to muscle traction (Insall, 1984:780). Both hares (Pearson and Davin, 1921) and kangaroos (Shulman, 1955) often display emarginate patellae, which also suggests that stress is an important factor in the persistence of additional ossicles. The asymmetrical expression of calcaneus secun- darius (28.6%) may be the result of environ- mental influence (Trinkaus, 1978). The available evidence suggests that calcaneus secundarius is a congenital anomaly whose phenotypic manifestation may be influenced by environmental factors.

The fact that calcaneus secundarius is not clearly inherited on a simple genetic basis means that its value for assessing “biological distance” is still unproven. The trait is brought to the attention of workers so that a greater knowledge of its prevalence and in- cidence in other skeletal series may be ob- tained. The examination of modern populations, as has been employed for atlan- toid bridging (Saunders and Popovich, 1978; Selby et al., 19551, will also be necessary €or a fuller understanding of the traits pattern of heritability.

CONCLUSIONS A minor skeletal nonmetric, calcaneus se-

cundarius, is presented. The evidence from Trondheim suggests that it is not rare. There was no clear evidence for an age or sex influ- ence on the trait, but it may bear a slight relationship to calcaneal facet morphology. The trait is related to 0s trigonum and emar- ginate patella on etiological grounds, also examples of additional ossification centra re- maining separate. The present evidence sug- gests that its manifestation is inherited on a

multifactorial basis. Further work on both modern living populations, as well as skele- tal samples, will hopefully add to our knowl- edge of this neglected non-metric variant.

LITERATURE CITED

Anderson J E (1968) Skeletal “anomalies” as genetic in- dicators. In DR Brothwell (ed.): The Skeletal Biology of Earlier Populations. London: Pergamon, pp. 135- 147.

Bazgnt B (1964) Doppelter ossifikationskern im Fersen- bein. Z. Orthop. 98t523-527.

Biermann MI (1922) The supernumerary pedal bones. Am. J. Roentgenol. 9t404-411.

George R (1935) Bilateral bipartite patella. Br. J. Surg. 22t555-560.

Green LT Jr (1975) Painful bipartite patellae-a case report of three cases. Clin. Orthop. 110:197-200.

Hoerr NL, Pyle DI, and Francis CC (1962) Radiographic Atlas of Skeletal Development of the Foot and Ankle: A Standard of Reference. Springfield: C.C. Thomas.

Insall J N (1984) Surgery of the Knee. Edinburgh: Churchill-Livingstone.

Klenerman L (1982) The Foot and its Disorders. 2nd ed. Oxford Blackwell.

Kohler A, and Zimmer EZ (1968) Borderlands of the Normal and Early Pathologic in Skeletal Roentgenol- ogy. 11th ed. New York: Grune and Stratton.

Laidlaw PP (1905) The 0s calcis. Part 11. J. Anat. Physiol. 39t161-178.

Lapidus PW (1972) A note on the fracture of 0s trigonum. Report of a case. Bull. Hosp. Joint Dis. 35:150-154.

O’Rahilly R (1953) A survey of carpal and tarsal anoma- lies. J. Bone Joint Surg. [Am.] 35r626-642.

Pearson K, and Davin AG (1921) On the sesamoids of the knee joint. Part I. Man. Biometrika 13r133-172.

Rosing FW (1984) Discreta of the human skeleton: A critical review. J. Hum. Evol. 13t319-323.

Sarrafian SK (1983) Anatomy of the Foot and Ankle. Philadelphia: J. & B. Lippincott.

Saunders SR, and Popovich F (1978) A family study of two skeletal variants: atlas bridging and clinoid bridg- ing. Am J. Phys. Anthropol. 49t193-203.

Schreiber A, Diferding P, and Zollinger H (1985) Talus partitus a case report. J . Bone Joint Surg. [Br.] 67t430- 431.

Selby S, Garn SM, and Kanareff V (1955) The incidence and familial nature of a bony bridge on the first cervi- cal vertebra. Am. J. Phys. Anthropol. 13t129-141.

Sewell RBS (1904) A study of the astragalus. Part 11. J. Anat. Physiol. 38t423-434.

Shulman S (1955) Unilateral congenital duplication of the patella. Br. J . Radio]. 28t164-165.

Szaboky GT, Anderson JJ , and Wiltsie RA (1970) Bifid 0s calcis an anomalous ossification of the calcaneus. Clin. Orthop. 68:136-139.

Trinkaus E (1978) Bilateral asymmetry of human skele- tal non-metric traits. Am. J. Phys. Anthropol. 49t315- 318.