Art & science | foot and ankle injuries
Accessory ossicles and sesamoid bones: recognition and treatment Anthony Summers explains how emergency nurse practitioners can recognise two common bone variants in X-rays of the foot and ankle that are often mistaken for fracture Correspondence [email protected]. gov.au Anthony Summers is a nurse practitioner at Redlands Hospital emergency department, Cleveland, Queensland, Australia Date of submission December 5 2014 Date of acceptance December 29 2014 Peer review This article has been subject to double-blind review and has been checked using antiplagiarism software Author guidelines journals.rcni.com/r/ en-author-guidelines
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Abstract Accessory ossicles and sesamoid bones are normal variants of bone development. In foot and ankle X-rays these bones can appear similar to, or can obscure, fractures, which makes the X-rays difficult to interpret. This article illustrates and describes some of the more common ossicles and sesamoid bones, and provides a brief description of the management of the patients with foot or ankle pain whose X-rays are inconclusive. Keywords Foot, ankle, sesamoid bones, ossicles, fractures, bone development, X-rays, normal variances, pain BETWEEN ONE million and 1.5 million people with ankle or foot injuries in the UK, and about 100,000 of such people in Australia, present to emergency departments (EDs) every year (Lamb et al 2009, Lau et al 2013). Many of these patients require X-rays and, although these usually provide enough information for clear diagnoses, some are inconclusive. For example, an abnormality identified on X-ray may be assumed to be a fracture but may actually be an accessory ossicle or sesamoid bone that mimics a fracture, or a fracture may be missed because it is obscured by an accessory ossicle or sesamoid bone (Coskun et al 2009). Accessory ossicles and sesamoid bones are commonly seen in X-rays of foot and ankle structures and, in the case of the former, sometimes in X-rays of the wrist and hand. Emergency nurse practitioners (ENPs) should therefore be confident in their ability to recognise them in X-rays and offer appropriate treatment to the patients concerned (Kauffmann and Stacy 2014).
If ENPs are concerned about what they see in X-rays, they can ask the radiographers to make ‘hot’ reports to specialists, who are then expected to assess immediately whether or not abnormalities are present. If ENPs have no such concerns or if the patients concerned have been treated successfully, the radiographers make cold reports (Hardy et al 2008).
Accessory ossicles Nwawka et al (2013) define accessory ossicles as supernumerary bones that commonly derive from unfused primary or secondary ossification centres. They are small, well-corticated bones that can be ovoid or nodular in shape, bipartite or multipartite, and unilateral or bilateral. They are considered to be normal variants of bone development, although their functions are unknown (Nwawka et al 2013). The 12 types of accessory ossicle are described below. Os trigonum Seen in up to 25% of X-rays of people with inflammation of the posterior ankle (Mellado et al 2003), os trigonum is the biggest and most common accessory in the foot and ankle (Figure 1, page 28). It is a secondary ossification centre of the talus and is seen laterally to the groove for the flexor hallucis longus tendon close to the posterior process of the talus (Ahn et al 2013). Patients who present with inflammation of the posterior ankle soft tissues from supination or hyperplantarflexion trauma, or from dancing on a hard surface, may have posterior ankle impingement syndrome (Ahn et al 2013), an impingement of the posterior edge of the tibia and the superior surface of the calcaneus that often causes pain (Ahn et al 2013). March 2015 | Volume 22 | Number 10 27
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Art & science | foot and ankle injuries Figure 1 Os trigonum
Figure 2 Os peroneum
Figure 3 Os intermetatarseum
Figure 4 Os vesalianum
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The os trigonum can be confused with Shepherd’s or Cedell fractures of the lateral or medial tubercles of the posterior processes of the talus (Matthews 2012). A patient who demonstrates posterolateral tenderness with pain on movement of the subtalar joint and with passive movement of the flexor hallucis longus tendon may have a Shepherd’s fracture (Matthews 2012). A patient with similar symptoms but in whom a lump can be felt behind the medial malleolus on palpation may have a Cedell fracture (Matthews 2012, Ahn et al 2013). If these fractures are too small to be fixed with screws, they can be excised by an orthopaedic surgeon (Matthews 2012). To differentiate between either of these fractures and the os trigonum, ENPs should request computed tomography (CT) or magnetic resonance imaging (MRI) scans to identify whether the bone in the affected area is irregular, which indicates a fracture, or smooth, which indicates a non-fractured os trigonum. Os peroneum Technically a sesamoid bone, the os peroneum is embedded in the peroneus longus tendon in the region of the cuboid tunnel at the calcaneocuboid joint (Nwawka et al 2013) (Figure 2). In its cartilaginous form, this ossicle is present in everyone; in its ossified form, it is present in up to 26% of the population (Miller 2002). Os peroneum syndrome can cause lateral pain, tenderness and swelling along the peroneus longus tendon, and lateral pain with resisted plantar flexion of the foot (Miller 2002). Displacement or fracture of the os peroneum can be indicative of a tear in the peroneus longus tendon (Nwawka et al 2013). Os intermetatarseum Usually located in the space between the medial cuneiform and the base of the first and second metatarsals (Figure 3), the os intermetatarseum varies in size and can be round or spindle shaped (Chavali 2012). It usually produces no symptoms but a symptomatic os intermetatarseum can cause pain and tenderness when the dorsum of the midfoot is palpated at the level of the first intermetatarsal space, which compresses the superficial and deep peroneal nerves (Miller 2002, Chavali 2012). The os intermetatarseum can be differentiated from fractures of the base of the second metatarsal, which often occur in Lisfranc fracture dislocations. If there is no site of fracture, no soft tissue swelling and no mechanism of injury, Lisfranc dislocation can be ruled out (Nwawka et al 2013). EMERGENCY NURSE
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Os vesalianum Located proximal to the fifth metatarsal in the peroneus brevis tendon (Figure 4), the os vesalianum is rarely symptomatic (Dorrestijn and Brouwer 2011) although can cause pain similar to that produced by os peroneum syndrome (Wilson et al 2011). The os vesalianum can be differentiated from avulsion fractures of the apophysis of the fifth metatarsal, which lie in the transverse plane. Series of X-rays usually reveal callous formation around a fracture site but no callous formation around an os vesalianum (Mellado et al 2003).
Figure 5 Os calcaneus secundarius
Os calcaneus secundarius This is a round or triangular ossicle found in the space between the anteromedial aspect of the calcaneus, the cuboid, the talar head and the tarsal navicular (Ceroni et al 2006) (Figure 5). The os calcaneus secundarius can be differentiated from an anterior process fracture of the calcaneus by its smooth cortical margin to the bone fragment (Ceroni et al 2006).
Figure 6 Os sustentaculum
Os sustentaculum A small ossicle connected to the posterior aspect of the sustentaculum tali (Figure 6), the os sustentaculum can be confused with fracture of the sustentaculum tali (Mellado et al 2003). This rare fracture can occur at impact on a supinated foot, and results in pain and tenderness along the inner border of the foot. It can be differentiated from an os sustentaculum by its irregular surface and lack of cortication, and by the patient’s history of trauma. Os subtibiale Located below the medial malleolus and usually bilateral (Madhuri et al 2009) (Figure 7), the os subtibiale may occur because of a failure of fusion of a secondary growth centre in the medial malleolus (Bellapianta et al 2011). Fracture of the medial malleolus can be differentiated from an os subtibiale by its irregular surface and lack of cortication, and by the patient’s history of trauma.
Figure 7 Os subtibiale
Figure 8 Os subfibulare
Os subfibulare A round or comma-shaped bone located under the tip of the lateral malleolus (Mellado et al 2003) (Figure 8), the os subfibulare is rare. Old, non-united avulsion fracture can be differentiated from an os subfibulare by its irregular surface and lack of cortication, and by the patient’s history of trauma. Os supranaviculare, os supratalare and os talotibiale Located adjacent to the dorsal talus, these rare ossicles are not usually associated with EMERGENCY NURSE
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Art & science | foot and ankle injuries Figure 9
Os supranaviculare
Figure 10 Os supratalare
Figure 11 Os talotibiale
painful conditions (Nwawka et al 2013) (Figures 9, 10 and 11). The os supranaviculare is sometimes referred to as the os talonaviculare dorsale, or Pirie’s bone, and may be associated with stress fractures of the navicular (Ingalls and Wissman 2011). Avulsion fracture can be differentiated from an os supranaviculare, os supratalare or os talotibiale by its irregular surface and lack of cortication, and by the patient’s history of trauma. Accessory navicular Also called the os tibiale, os tibiale externum or naviculare secundarium, the accessory navicular is located next to the posteromedial tuberosity of the navicular bone (Mellado et al 2003) (Figure 12). First described in 1605 by Bauhn (Fredrick et al 2005), the accessory navicular appears in between 40% and 80% of the population, and is usually asymptomatic (Mansoor and Qureshi 2014). Patients with symptomatic accessory navicular usually present with foot pain over the medial side of the navicular (Swords et al 2004). They may also report loss of function in the posterior tibial tendon leading to flattening of the medial plantar arch, valgus deformity of the hindfoot, abduction of the forefoot, and an inability to single-heel lift (Fredrick et al 2005). Initial treatment is usually non-surgical, for example physiotherapy, but in young athletes surgical intervention may be the best option to ensure a rapid return to normal function (Fredrick et al 2005).
Sesamoid bones
Figure 12 Accessory navicular
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Nwawka et al (2013) define sesamoid bones as osseous structures partially or totally embedded in tendons, which they protect from injury by reducing friction. They are round or oval-shaped bones, usually between 5mm and 10mm long, that develop from their own ossification centres (Coskun et al 2009). Their name derives from their similarity to the seed of the Sesamun indicum, a plant of eastern India that was once used as a purgative (Munuera et al 2007). People with sesamoid bones may experience pain due to arthritis, infection, neoplasms or capsular‑ligamentous injury, but the most common cause of pain is from trauma or chronic stress (Karasick and Schweitzer 1998, Mellado et al 2003, Garrido et al 2008). Bipartite or multipartite sesamoid bones can be differentiated from fracture if they do not fit together perfectly as they would in a fracture (Potter et al 1992). EMERGENCY NURSE
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The three types of sesamoid bone are discussed below.
Figure 13 Hallux sesamoid
Hallux sesamoid bones The medial and lateral hallux sesamoids are embedded in the medial and lateral slips of the flexor halluces brevis tendon at the level of the first metatarsal head (Mellado et al 2003) (Figure 13), where they provide mechanical advantage during hallux flexion by reducing friction and reinforcing adjacent soft tissues (Garrido et al 2008). The size and shape of these sesamoids vary greatly, with the medial bones being more elliptical and the lateral more cylindrical in shape (Karasick and Schweitzer 1998). Lesser metatarsal sesamoids Usually embedded in the palmer aspect of the joint capsule of the second to fifth metatarsals (Figure 14), lesser metatarsal sesamoids are less common than hallux sesamoid bones. Best seen on anterior-posterior and oblique view X-rays, they appear in 0.4% of second metatarsal, 0.2% of third metatarsals, 0.1% of fourth metatarsals and 4.3% of fifth metatarsals (Coskun et al 2009). They are rarely associated with any pathology (Nwawka et al 2013).
Figure 14 Lesser metatarsal sesamoid
Interphalangeal joint sesamoid Located at the plantar aspect of the interphalangeal joint of the first toe (Figure 15), the interphalangeal joint sesamoid appears in up to 13% of X-rays of the interphalangeal joint (Coskun et al 2009). The sesamoid is embedded in the interphalangeal joint capsule, and can limit the joint’s motion (Nwawka et al 2013). Patients with dislocated interphalangeal joints and interphalangeal joint sesamoids may require referral to orthopaedic specialists for reduction (Woon 2010).
Management
Figure 15 Interphalangeal joint sesamoid
When clinicians have determined what is revealed in X-rays and obtained radiographers’ hot or cold reports, the results should be discussed with the patients involved. Areas of concern should be explained to patients so that those who have had similar injuries before can inform clinicians about what has been noted on previous X-rays. If hot or a cold reports are inconclusive, ENPs should discuss potential treatment options, which range from no treatment to plaster casts, with the patients concerned. Follow up, which can be referral to GPs or to orthopaedic specialists in fracture clinics, depends on patients’ treatment choices. EMERGENCY NURSE
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Art & science | foot and ankle injuries If X-rays are inconclusive, the patients concerned can be managed as if they have fractures. This is a safe option but may require them to take time off work. On the other hand, patients who have undiagnosed fractures and are managed accordingly may experience pain unnecessarily. If fractures are suspected but cannot be confirmed, the patients concerned should be managed conservatively with below-knee plasters and encouraged not to weight bear. Patients who have received no form of treatment should be given advice about managing
soft‑tissue injuries of the foot and ankle, including information on mobilisation, compression, use of ice and, if appropriate, elevation and adequate analgesia. Patients should also be advised that, if their pain persists for more than seven days, they should seek further help from their GPs or at EDs. By this time, they may require further X-rays to determine whether injuries have been missed or if there are signs of healing, which would confirm fracture. Appropriate follow-up appointments for the new diagnoses should then be arranged.
Online archive For related information, visit our online archive and search using the keywords Conflict of interest None declared
References Ahn J, Kim Y, Kim H (2013) Arthroscopic versus posterior endoscopic excision of a symptomatic os trigonum. American Journal of Sports Medicine. doi: 10.1177/0363546513480614
Fredrick L, Beall D, Ly J et al (2005) The symptomatic accessory navicular bone: a report and discussion of the clinical presentation. Current Problems in Diagnostic Radiology. doi: 10.1067/j.cpradiol.2004.12.004
Bellapianta J, Andrews J, Ostrander R (2011) Bilateral os subtibiale and talocalcaneal coalitions in a college soccer player: a case report. Journal of Foot and Ankle Surgery. doi: 10.1053/j.jfas.2011.03.016
Garrido I, Bosch M, Gonzalez M et al (2008) Osteochondritis of the hallux sesamoid bones. Foot and Ankle Surgery. doi: 10.1016/j.fas.2008.02.004
Ceroni D, De Coulon G, Spadola L et al (2006) Calcaneus secundarius presenting as calcaneonavicular coalition: a case report. Journal of Foot and Ankle Surgery. doi: 10.1053/j.jfas.2005.10.004 Chavali V (2012) Os intermetatarseum: a case report. Journal of Clinical Orthopaedics and Trauma. doi: 10.1016/j.jcot.2011.11.002 Coskun N, Yuesel M, Cevener M et al (2009) Incidence of accessory ossicles and sesamoid bones in the feet: a radiographic study of Turkish subjects. Surgical Radiology Anatomy. doi: 10.1007/s00276-008-0383-9 Dorrestijn O, Brouwer R (2011) Bilateral symptomatic os vesalianum pedis: a case report. Journal of Foot and Ankle Surgery. doi: 10.1053/j.jfas.2011.03.012
Hardy M, Spencer N, Snaith B (2008) Radiographer emergency department hot reporting: an assessment of service quality and feasibility. Radiography. doi: 10.106/j.radi.2007.10.003 Ingalls J, Wissman R (2011) Os supranaviculare and navicular stress fracture. Skeletal Radiology. doi: 10.1007/s00256-011-1154-y Karasick D, Schweitzer M (1998) Disorders of the hallux sesamoid complex: MR features. Skeletal Radiology. 27, 8, 411-418. Kauffmann G, Stacy G (2014) Os cuboideum secundarium: a rare accessory ossicle with the potential to mimic a mass on magnetic resonance imaging. Skeletal Radiology. doi: 10.1007/s00256-013-1709-1 Lamb S, Marsh J, Hutton J et al (2009) Mechanical supports for acute, severe ankle
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sprain: a pragmatic, multicentre, randomised controlled trial. The Lancet. 373, 575-581. Lau L, Kerr D, Law I et al (2013) Nurse practitioners treating ankle and foot injuries using the Ottawa Ankle Rules: a comparative study in the emergency department. Australasian Emergency Nursing Journal. doi: 10.1016/j.aenj.2013.05.007 Madhuri V, Poonnoose P, Lurstep W (2009) Accessory os subtibiale: a case report of misdiagnosed fracture. Foot and Ankle Online Journal. doi: 10.3827/faoj.2009.0206.0003 Mansoor S, Qureshi M (2014) Symptomatic accessory navicular bone: a case series. Annals of Physical and Rehabilitation Medicine. 57S, e194. Matthews S (2012) Fractures of the talus. Orthopaedics and Trauma. doi: 10.1016/j.mporth.2012.06.003 Mellado J, Ramos A, Salvado E et al (2003) Accessory ossicles and sesamoid bones of the ankle and foot: imaging findings, clinical significance and differential diagnosis. European Radiology. doi: 10.1007/s00330-003-2011-8 Miller T (2002) Painful accessory bones of the foot. Seminars in Musculoskeletal Radiology. 6, 153-161.
Munuera P, Dominguez G, Reina M et al (2007) Bipartite halluccal sesamoid bones: relationship with hallux valgus and metatarsal index. Skeletal Radiology. doi: 10.1007/s00256-007-0359-6 Nwawka O, Hayashi D, Diaz L et al (2013) Sesamoids and accessory ossicles of the foot: anatomical variability and related pathology. Insights Imaging. doi: 10.1007/s13244-013-0277-1 Potter H, Pavalov H, Abrahams T (1992) The hallux sesamoids revisited. Skeletal Radiology. 21, 7, 437-444. Swords M, Hansen S, Sangeorzan J (2004) Fusion of the primary and accessory navicular bones: a modification of the Kidner procedure. Operative Techniques in Orthopaedics. doi: 10.1053/j.oto.2004.01.002 Wilson T, Wilson R, Ouzounov K (2011) The symptomatic os vesalianum as an uncommon cause of lateral foot pain: a case report. Journal of American Podiatric Medical Association. 101, 4, 356-359. Woon C (2010) Dislocation of the interphalangeal joint of the great toe: is percutaneous reduction of an incarcerated sesamoid an option? Journal of Bone and Joint Surgery America. doi: 10.2106/JBJS.I.0101
EMERGENCY NURSE
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Accessory ossicles and sesamoid bones: recognition and treatment Anthony Summers explains how emergency nurse practitioners can recognise two common bone variants in X-rays of the foot and ankle that are often mistaken for fracture Correspondence [email protected]. gov.au Anthony Summers is a nurse practitioner at Redlands Hospital emergency department, Cleveland, Queensland, Australia Date of submission December 5 2014 Date of acceptance December 29 2014 Peer review This article has been subject to double-blind review and has been checked using antiplagiarism software Author guidelines journals.rcni.com/r/ en-author-guidelines
EMERGENCY NURSE
Abstract Accessory ossicles and sesamoid bones are normal variants of bone development. In foot and ankle X-rays these bones can appear similar to, or can obscure, fractures, which makes the X-rays difficult to interpret. This article illustrates and describes some of the more common ossicles and sesamoid bones, and provides a brief description of the management of the patients with foot or ankle pain whose X-rays are inconclusive. Keywords Foot, ankle, sesamoid bones, ossicles, fractures, bone development, X-rays, normal variances, pain BETWEEN ONE million and 1.5 million people with ankle or foot injuries in the UK, and about 100,000 of such people in Australia, present to emergency departments (EDs) every year (Lamb et al 2009, Lau et al 2013). Many of these patients require X-rays and, although these usually provide enough information for clear diagnoses, some are inconclusive. For example, an abnormality identified on X-ray may be assumed to be a fracture but may actually be an accessory ossicle or sesamoid bone that mimics a fracture, or a fracture may be missed because it is obscured by an accessory ossicle or sesamoid bone (Coskun et al 2009). Accessory ossicles and sesamoid bones are commonly seen in X-rays of foot and ankle structures and, in the case of the former, sometimes in X-rays of the wrist and hand. Emergency nurse practitioners (ENPs) should therefore be confident in their ability to recognise them in X-rays and offer appropriate treatment to the patients concerned (Kauffmann and Stacy 2014).
If ENPs are concerned about what they see in X-rays, they can ask the radiographers to make ‘hot’ reports to specialists, who are then expected to assess immediately whether or not abnormalities are present. If ENPs have no such concerns or if the patients concerned have been treated successfully, the radiographers make cold reports (Hardy et al 2008).
Accessory ossicles Nwawka et al (2013) define accessory ossicles as supernumerary bones that commonly derive from unfused primary or secondary ossification centres. They are small, well-corticated bones that can be ovoid or nodular in shape, bipartite or multipartite, and unilateral or bilateral. They are considered to be normal variants of bone development, although their functions are unknown (Nwawka et al 2013). The 12 types of accessory ossicle are described below. Os trigonum Seen in up to 25% of X-rays of people with inflammation of the posterior ankle (Mellado et al 2003), os trigonum is the biggest and most common accessory in the foot and ankle (Figure 1, page 28). It is a secondary ossification centre of the talus and is seen laterally to the groove for the flexor hallucis longus tendon close to the posterior process of the talus (Ahn et al 2013). Patients who present with inflammation of the posterior ankle soft tissues from supination or hyperplantarflexion trauma, or from dancing on a hard surface, may have posterior ankle impingement syndrome (Ahn et al 2013), an impingement of the posterior edge of the tibia and the superior surface of the calcaneus that often causes pain (Ahn et al 2013). March 2015 | Volume 22 | Number 10 27
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Art & science | foot and ankle injuries Figure 1 Os trigonum
Figure 2 Os peroneum
Figure 3 Os intermetatarseum
Figure 4 Os vesalianum
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The os trigonum can be confused with Shepherd’s or Cedell fractures of the lateral or medial tubercles of the posterior processes of the talus (Matthews 2012). A patient who demonstrates posterolateral tenderness with pain on movement of the subtalar joint and with passive movement of the flexor hallucis longus tendon may have a Shepherd’s fracture (Matthews 2012). A patient with similar symptoms but in whom a lump can be felt behind the medial malleolus on palpation may have a Cedell fracture (Matthews 2012, Ahn et al 2013). If these fractures are too small to be fixed with screws, they can be excised by an orthopaedic surgeon (Matthews 2012). To differentiate between either of these fractures and the os trigonum, ENPs should request computed tomography (CT) or magnetic resonance imaging (MRI) scans to identify whether the bone in the affected area is irregular, which indicates a fracture, or smooth, which indicates a non-fractured os trigonum. Os peroneum Technically a sesamoid bone, the os peroneum is embedded in the peroneus longus tendon in the region of the cuboid tunnel at the calcaneocuboid joint (Nwawka et al 2013) (Figure 2). In its cartilaginous form, this ossicle is present in everyone; in its ossified form, it is present in up to 26% of the population (Miller 2002). Os peroneum syndrome can cause lateral pain, tenderness and swelling along the peroneus longus tendon, and lateral pain with resisted plantar flexion of the foot (Miller 2002). Displacement or fracture of the os peroneum can be indicative of a tear in the peroneus longus tendon (Nwawka et al 2013). Os intermetatarseum Usually located in the space between the medial cuneiform and the base of the first and second metatarsals (Figure 3), the os intermetatarseum varies in size and can be round or spindle shaped (Chavali 2012). It usually produces no symptoms but a symptomatic os intermetatarseum can cause pain and tenderness when the dorsum of the midfoot is palpated at the level of the first intermetatarsal space, which compresses the superficial and deep peroneal nerves (Miller 2002, Chavali 2012). The os intermetatarseum can be differentiated from fractures of the base of the second metatarsal, which often occur in Lisfranc fracture dislocations. If there is no site of fracture, no soft tissue swelling and no mechanism of injury, Lisfranc dislocation can be ruled out (Nwawka et al 2013). EMERGENCY NURSE
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Os vesalianum Located proximal to the fifth metatarsal in the peroneus brevis tendon (Figure 4), the os vesalianum is rarely symptomatic (Dorrestijn and Brouwer 2011) although can cause pain similar to that produced by os peroneum syndrome (Wilson et al 2011). The os vesalianum can be differentiated from avulsion fractures of the apophysis of the fifth metatarsal, which lie in the transverse plane. Series of X-rays usually reveal callous formation around a fracture site but no callous formation around an os vesalianum (Mellado et al 2003).
Figure 5 Os calcaneus secundarius
Os calcaneus secundarius This is a round or triangular ossicle found in the space between the anteromedial aspect of the calcaneus, the cuboid, the talar head and the tarsal navicular (Ceroni et al 2006) (Figure 5). The os calcaneus secundarius can be differentiated from an anterior process fracture of the calcaneus by its smooth cortical margin to the bone fragment (Ceroni et al 2006).
Figure 6 Os sustentaculum
Os sustentaculum A small ossicle connected to the posterior aspect of the sustentaculum tali (Figure 6), the os sustentaculum can be confused with fracture of the sustentaculum tali (Mellado et al 2003). This rare fracture can occur at impact on a supinated foot, and results in pain and tenderness along the inner border of the foot. It can be differentiated from an os sustentaculum by its irregular surface and lack of cortication, and by the patient’s history of trauma. Os subtibiale Located below the medial malleolus and usually bilateral (Madhuri et al 2009) (Figure 7), the os subtibiale may occur because of a failure of fusion of a secondary growth centre in the medial malleolus (Bellapianta et al 2011). Fracture of the medial malleolus can be differentiated from an os subtibiale by its irregular surface and lack of cortication, and by the patient’s history of trauma.
Figure 7 Os subtibiale
Figure 8 Os subfibulare
Os subfibulare A round or comma-shaped bone located under the tip of the lateral malleolus (Mellado et al 2003) (Figure 8), the os subfibulare is rare. Old, non-united avulsion fracture can be differentiated from an os subfibulare by its irregular surface and lack of cortication, and by the patient’s history of trauma. Os supranaviculare, os supratalare and os talotibiale Located adjacent to the dorsal talus, these rare ossicles are not usually associated with EMERGENCY NURSE
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Art & science | foot and ankle injuries Figure 9
Os supranaviculare
Figure 10 Os supratalare
Figure 11 Os talotibiale
painful conditions (Nwawka et al 2013) (Figures 9, 10 and 11). The os supranaviculare is sometimes referred to as the os talonaviculare dorsale, or Pirie’s bone, and may be associated with stress fractures of the navicular (Ingalls and Wissman 2011). Avulsion fracture can be differentiated from an os supranaviculare, os supratalare or os talotibiale by its irregular surface and lack of cortication, and by the patient’s history of trauma. Accessory navicular Also called the os tibiale, os tibiale externum or naviculare secundarium, the accessory navicular is located next to the posteromedial tuberosity of the navicular bone (Mellado et al 2003) (Figure 12). First described in 1605 by Bauhn (Fredrick et al 2005), the accessory navicular appears in between 40% and 80% of the population, and is usually asymptomatic (Mansoor and Qureshi 2014). Patients with symptomatic accessory navicular usually present with foot pain over the medial side of the navicular (Swords et al 2004). They may also report loss of function in the posterior tibial tendon leading to flattening of the medial plantar arch, valgus deformity of the hindfoot, abduction of the forefoot, and an inability to single-heel lift (Fredrick et al 2005). Initial treatment is usually non-surgical, for example physiotherapy, but in young athletes surgical intervention may be the best option to ensure a rapid return to normal function (Fredrick et al 2005).
Sesamoid bones
Figure 12 Accessory navicular
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Nwawka et al (2013) define sesamoid bones as osseous structures partially or totally embedded in tendons, which they protect from injury by reducing friction. They are round or oval-shaped bones, usually between 5mm and 10mm long, that develop from their own ossification centres (Coskun et al 2009). Their name derives from their similarity to the seed of the Sesamun indicum, a plant of eastern India that was once used as a purgative (Munuera et al 2007). People with sesamoid bones may experience pain due to arthritis, infection, neoplasms or capsular‑ligamentous injury, but the most common cause of pain is from trauma or chronic stress (Karasick and Schweitzer 1998, Mellado et al 2003, Garrido et al 2008). Bipartite or multipartite sesamoid bones can be differentiated from fracture if they do not fit together perfectly as they would in a fracture (Potter et al 1992). EMERGENCY NURSE
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The three types of sesamoid bone are discussed below.
Figure 13 Hallux sesamoid
Hallux sesamoid bones The medial and lateral hallux sesamoids are embedded in the medial and lateral slips of the flexor halluces brevis tendon at the level of the first metatarsal head (Mellado et al 2003) (Figure 13), where they provide mechanical advantage during hallux flexion by reducing friction and reinforcing adjacent soft tissues (Garrido et al 2008). The size and shape of these sesamoids vary greatly, with the medial bones being more elliptical and the lateral more cylindrical in shape (Karasick and Schweitzer 1998). Lesser metatarsal sesamoids Usually embedded in the palmer aspect of the joint capsule of the second to fifth metatarsals (Figure 14), lesser metatarsal sesamoids are less common than hallux sesamoid bones. Best seen on anterior-posterior and oblique view X-rays, they appear in 0.4% of second metatarsal, 0.2% of third metatarsals, 0.1% of fourth metatarsals and 4.3% of fifth metatarsals (Coskun et al 2009). They are rarely associated with any pathology (Nwawka et al 2013).
Figure 14 Lesser metatarsal sesamoid
Interphalangeal joint sesamoid Located at the plantar aspect of the interphalangeal joint of the first toe (Figure 15), the interphalangeal joint sesamoid appears in up to 13% of X-rays of the interphalangeal joint (Coskun et al 2009). The sesamoid is embedded in the interphalangeal joint capsule, and can limit the joint’s motion (Nwawka et al 2013). Patients with dislocated interphalangeal joints and interphalangeal joint sesamoids may require referral to orthopaedic specialists for reduction (Woon 2010).
Management
Figure 15 Interphalangeal joint sesamoid
When clinicians have determined what is revealed in X-rays and obtained radiographers’ hot or cold reports, the results should be discussed with the patients involved. Areas of concern should be explained to patients so that those who have had similar injuries before can inform clinicians about what has been noted on previous X-rays. If hot or a cold reports are inconclusive, ENPs should discuss potential treatment options, which range from no treatment to plaster casts, with the patients concerned. Follow up, which can be referral to GPs or to orthopaedic specialists in fracture clinics, depends on patients’ treatment choices. EMERGENCY NURSE
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Art & science | foot and ankle injuries If X-rays are inconclusive, the patients concerned can be managed as if they have fractures. This is a safe option but may require them to take time off work. On the other hand, patients who have undiagnosed fractures and are managed accordingly may experience pain unnecessarily. If fractures are suspected but cannot be confirmed, the patients concerned should be managed conservatively with below-knee plasters and encouraged not to weight bear. Patients who have received no form of treatment should be given advice about managing
soft‑tissue injuries of the foot and ankle, including information on mobilisation, compression, use of ice and, if appropriate, elevation and adequate analgesia. Patients should also be advised that, if their pain persists for more than seven days, they should seek further help from their GPs or at EDs. By this time, they may require further X-rays to determine whether injuries have been missed or if there are signs of healing, which would confirm fracture. Appropriate follow-up appointments for the new diagnoses should then be arranged.
Online archive For related information, visit our online archive and search using the keywords Conflict of interest None declared
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