Orthopedics - Oleksa A.P. 2006

Congenital and Acquired Deformities of the Lower Extremity
Orthopedic Foot Deformities
Accessory Sesamoid Bones of the Foot

Godunov S.F. (1968), citing literature data, points out that sesamoid bones can potentially be localized in eleven different sites of the FOOT (Fig. 202). While those located, for instance, near the Base of the first metatarsal HEAD are functionally significant, others should be regarded as accessory (ossa sesamoidea accessoria).

From a clinical perspective, only certain accessory sesamoid bones are of practical importance, since radiographs sometimes require differentiating them from marginal fractures of the navicular bone or the posterior process of the talus. The symmetrical presence of these accessory bones in both feet helps establish a correct Diagnosis.

It should be noted that radiography quite frequently reveals the os tibiale externum (os naviculare accessorium), symmetrically located in both feet near the tuberosity of the navicular bones. These sesamoid bones may sometimes tightly abut the tuberosity, even forming a fibrous union with it, and are situated within the region of the tibialis posterior tendon. The accessory bone can be woven into a part of this tendon, which reinforces the arch of the foot and thereby weakens it—a factor that, according to G.I. Turner, N.S. Markelov, and others, sometimes leads to Flatfoot (pes planovalgus). If persistent pain accompanies flat-valgus feet, one may suspect the presence of an os tibiale externum fused with the navicular bone. During surgical removal of this accessory bone, care must be taken not to damage the tibialis posterior tendon.

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Fig. 202. Accessory sesamoid bone of the navicular bone.

The second most frequent is the trigonum sesamoid bone (os trigonum, talus accessorius), which is located near the posterior process of the talus with its broader base adjacent to it. Such a Location OF THE sesamoid bone very often needs to be differentiated from a fracture of the posterior process, and a fracture can be ruled out solely based on the presence of this sesamoid bone in the contralateral foot. The diagnosis can also be clarified by identifying smooth and dense cortical margins of the sesamoid bone where it adjoins the posterior process.

Clinically, this os trigonum is usually asymptomatic, but pain may occur if it is torn away from its attachment site. The os trigonum is excised via an approach along the lateral border of the Achilles tendon.

Of similar clinical significance is the accessory Vesalian sesamoid bone (os vesalianum), which lies separately between the cuboid bone and the tuberosity of the fifth metatarsal, appearing as a detached portion of this tuberosity. Sometimes this sesamoid bone is large enough to be compressed by normal footwear, causing pain. In such cases, it should be excised.

Occasionally, following foot trauma, one must differentiate a tuberosity fracture from the presence of a sesamoid bone, which is invariably present symmetrically in both feet.

When pain is experienced in the region of the sesamoid bones near the first metatarsal head, arch Supports with head-relieving features and physical therapy should be prescribed; surgical removal is unnecessary.

Other accessory sesamoid bones are clinically silent and require no Treatment.