[Radiological study of the accessory skeletal elements in the foot and ankle (author's transl)]

The accessory bones and ossification centers in the foot and ankle were studied in 3,460 radiographs of patients over 7 years of age who consulted our clinic for various reasons from January 1967 to December 1979. The patients comprised of 1,639 males and 1,821 females. The accessory ossicles commonly observed were os tibiale externum, os trigonum, and os peroneum in order of frequency. The os tibiale externum is the commonest accessory bones in the foot and is situated at the point where the tendon of the posterior tibial muscle inserts itself into navicular bone. This ossicle was found to be present in 733 out of 3,460 feet (21.3%). As some authors have pointed out, they are observed somewhat more frequently in females than in males. The os trigonum is an accessory bone which is situated behind the posterior process of the talus. This ossicle was found in 438 feet (12.7%). The os peroneum is a sesamoid in the long peroneal tendon where it bends toward the sole of the foot. This was found in 311 feet (9.0%). Other inconstant skeletal elements were less commonly observed. This os intermetatarseum which is usually located in the first, rarely in the fourth, intermetatarsal space, was found in 91 feet (2.6%). When studied meticulously, this ossicle is found more often than is generally believed. The os subfibulare, situated just under the lateral malleolus, was found in 71 feet (2.1%). The os supranaviculare, situated above the talonavicular joint, was found in 35 feet (1.0%). The os subtibiale, situated just under the medial malleolus, was found in 31 feet (0.9%). The os supratalare, situated above the neck of the talus, was found in 25 feet (0.9%). The calcaneus secundarius, surrounded by calcaneus, talus, os naviculare and os cuboideum, was found in 20 feet (0.6%). The os talotibiale, situated in front of the talocrural joint, was found in 16 feet (0.5%). The os sustentaculi, situated beside the sustentaculum tali, was found in 9 feet (0.3%). The talus accessorius, situated beside the trochlea tali, was found in 6 feet (0.2%). The os vesalianum, situated adjacent to the tuberositas ossis metatarsalis V, was found in 4 feet of the adult patients (0.1%). The talus secundarius, situated near the trochlea peronealis calcanei, was found in 3 feet (0.1%). The os intercuneiforme, located between first and second cuneiform and the navicular bone, was found in only one foot of a 33-year-old male (0.03%). This case may be the first observation in Japan of this extremely rare accessory ossicle. The majority of the patients who had these accessory bones in their feet and ankles seemed to have no clinical complaints. Identification of these ossicles is of importance because they may easily be mistaken as fragments of avulsion fractures. An extra center of ossification for the medical malleolus was observed in 11 feet of the children aged 8 to 11 years. The ossification center for the tuberositas ossis metatarsalis V was found in 56 feet of the adolescents...