Os peroneum is an accessory ossicle that is located within the peroneus longus tendon, typically close to the cuboid, at the level of the lateral cuboid groove.
The physical characteristics of this small sesamoid bone include a flattened oval shape, with one or two concave articular deep surfaces. Its average thickness is recorded as 4 mm and length as 13 mm.
It is reported to be fully ossified in about 26% of the population, with a bipartite bone commonly seen in around 30% of cases. The presence of this condition must be considered while evaluating patients with pain in the lateral aspect of the midfoot.
As mentioned by Dr. Stephen V. Corey, painful os peroneum syndrome can result from a spectrum of conditions that may include any one or more of the following:
Clinical diagnosis of os peroneum syndrome should involve physical examination that can help reveal swelling over the cuboid with pain felt during palpation. The patient will feel this pain intensify during plantar flexion, and during the heel elevation stage of the gait process.
Radiographic images can help in demonstrating any abnormal displacement of the os peroneum, fracture, or diatasis of a bipartite sesamoid. MRI is considered to be the gold standard for the detection of painful os peroneum syndrome.
Using MRI can help in determining the location of the os peroneum; the os peroneum is usually located in a transition zone between the lateral and plantar course of the peroneus longus tendon.
Any pathologic changes to the bone marrow of the os peroneum and cuboid, or the soft tissues can also be easily identified using MRI. Computed tomography can help in the precise evaluation of the os peroneum particularly in differentiating a multipartite os peroneum from a non-displaced fracture.
An early diagnosis can help in the formulation of effective management strategies for os peroneum syndrome. There is considerable speculation regarding the contribution of a cavovarus foot position to peroneal tendinopathy.
Aminian et al. describe the biomechanics of a pes cavus foot as involving narrowing of the talo-calcaneal angle which causes the navicular to move to a superior position in relation to the cuboid, as opposed to medially; this can result in a stiffer midfoot fulcrum which can affect the optimal functioning of the peroneus longus tendon.
MASS4D® custom orthotics can be used as a preventative measure to minimise foot postural disparities that can potentially increase the predisposition of an individual to pathologies such as the painful os peroneum syndrome.
By offering maximum reduction in local peak pressures and proper support to the foot, a healthy distribution of weight is facilitated. Additionally, there is an increase in the contact area across the plantar surface of the foot, with reduced excessive supination and increased healthy pronation.
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Repetitive plantarflexion can lead to pain and mechanical limitation in the posterior ankle joint which is known as posterior ankle impingement syndrome. This pathology commonly occurs in ballet dancers and football players.