Bipartite sesamoid is a frequent by csgirla

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									                                    Clinical Picture Quiz 51
             T E Kilmartin PhD FCPod(Surg), Department of Podiatric Surgery,
     Ilkeston Hospital and Nottingham Community Trust. E-mail:

        ipartite sesamoid is a frequent

B       and usually insignificant radio-
        logical finding (Figure 1).
However, the presence of bipartite
sesamoid in combination with pain
requires differential diagnosis for frac-
ture, sesamoiditis, osteoarthrosis, avas-
cular necrosis or infection.

Q1. What is the rule of thumb that will
    differentiate bipartite sesamoid
    from fractured sesamoid?

Q2. Where pain under the medial
    sesamoid cannot be alleviated by
    conservative measures, which
    surgical procedures may be

Answers on page 236

Similar questions with answers and
discussion are invited.

                                                                July 1999 Podiatry Now   229
                  Answers to Clinical Picture Quiz 51
                                   (from page 229)
                                                     Answer 1.
                                                     In Figure 1 (p229) the tibial sesamoid is
                                                     bipartite. It is in effect two quite sepa-
                                                     rate ossicles joined by a fibrocartilagi-
                                                     nous bridge which can be easily appre-
                                                     ciated intra-operatively (Figure 2). The
                                                     combined length of the two ossicles is
                                                     roughly twice the length of the fibular
                                                     sesamoid, which is just a single ossicle.
                                                     In fractured sesamoid, bone length is
                                                     equal, though there may be quite a size-
                                                     able gap between the fragments.
                                                         The gap in fractured sesamoid is a
                                                     consequence of the mechanism of
                                                     injury where the hallux hyperextends
                                                     violently and the consequent tension on
                                                     the flexor brevis/abductor hallucis mus-
                                                     cle complex divides the sesamoid.
                                                         While bipartite sesamoids commonly
 3                             5                     occur bilaterally, the first diagnostic test
                                                     in suspected fracture should be bilateral
                                                     weight-bearing x-rays to compare the
                                                     normal with abnormal side. Technetium
                                                     12 Bone scan should then be used to con-
                                                     firm the presence of pathology. A frac-
                                                     tured sesamoid will produce a hot spot
                                                     while a bipartite sesamoid will not. It
                                                     must however be remembered that bone
                                                     scans are non-specific for inflammation.
                                                     Figure 3 demonstrates an inflamed calci-
                                                     fied bursa which was incorrectly diag-
                                                     nosed on bone scan as fractured
                                                     sesamoid (Figure 4).
                                                         Figure 5 represents a fractured
                                                     bipartite sesamoid. The rule of
                                                     sesamoid length can also be put to effect
 4                                                   here, as the rarely occurring tripartite
                                                     sesamoids appear as three separate
                                                     ossicles, each of similar dimensions.

                                                     Answer 2.

                                                     A fractured sesamoid is a cause of
                                                     chronic recalcitrant pain on the plantar
                                                     surface of the first metatarsophalangeal
                                                         The separation of the fragments is
6                                                    the usual cause of the non-healing, while
                                                     their position and gliding function
                                                     makes fixation very difficult. In many
                                                     cases the sesamoid is removed surgical-
                                                     ly but this carries a risk of iatrogenic hal-
                                                     lux valgus development. Alternatively,
                                                     the sesamoid can be planed to reduce its
                                                     bulk (Figure 6). Painful weight bearing
                                                     on the area will then also be reduced.

236   Podiatry Now July 1999

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