Calcaneonavicular synchondrosis with concurrent osteochondritis
of navicular in a young athlete

MARKEAS N[1], DROLAPAS A[2], VOLTIS D[1]
[1]2nd Orthopaedic Department, ChildrenÕs Hospital "Pan. and Aglaia Kiriakou", Athens
[2]Radiodiagnostic Department, ChildrenÕs Hospital "Pan. and Aglaia Kiriakou"

ABSTRACT
Calcaneonavicular synchondrosis in the tarsal area of a child is relatively uncommon and considered to be the most common cause of a spastic flatfoot. The case of a 11-year-old young athlete with a spastic flatfoot is described in this study. The diagnostic investigation revealed the presence of a calcaneonavicular synchondrosis in his right foot. The significant changes of the navicular in the same foot suggest the disorder of biomechanics in the tarsal area and the excessive force on the bone under the new conditions. Our suggestions would be the meticulous diagnostic management of any painful foot of a child and the early and proper therapeutic schedule.

Key words: Calcaneonavicular synchondrosis, child, foot, painful flatfoot.

INTRODUCTION
Tarsal coalition represents the bridging between two bones of the tarsus consisting of either fibrous tissue (syndesmosis) or cartilage (synchondrosis) or osseous tissue (true synostosis). This pathologic condition is relatively rare. Estimations approximating 1% of tarsal coalition prevalence are reported[11].
The most common site of such an osseous bar is that between calcaneus and navicular, followed by that between talus and calcaneus[3]. Other sites, such as cuneonavicular, talonavicular, calcanocuboid etc. are reported. In addition, multiple coalitions in the same foot seem to be more common than once thought[2].
In this report we describe the case of a young athlete who came to the Orthopaedic Clinic with the symptoms of painful and rigid flatfoot, due (as consequently proved) to underlying calcaneonavicular synchondrosis. The diagnostic procedure and surgical treatment as well as particular reference about the causes of the concurrent pathologic lesions of the tarsal navicular bone are reported.

CASE REPORT
An 11-year-old boy came with his parents to the Orthopaedic Clinic complaining about a painful right foot for the last 5 months. During the last week the pain deteriorated - particularly after stress - and was accompanied by limp and limitation of physical activities. The patient is a swimmer and has been following a training program of two hours daily-three times weekly.
Physical examination disclosed slight swelling and local tenderness on the dorsal side of the foot, limitation of supination-pronation through the subtalar joint and peroneal muscle spasm. The whole picture was that of rigid and painful (spastic) flatfoot.
The results of blood analysis and biochemical tests were normal and infection signs were negative. The roentgenographic examination was normal, although a tubular prolongation of the anterosuperior calcaneus that almost overlapped the midportion of the navicular was depicted on the lateral projection of the right foot (figure 1).
The young patient was hospitalized for further examination. The Tc-99 bone scanning revealed slightly increased uptake of the radioisotope on the area of the right tarsus during the dynamic and blood pool phases. Increased uptake on the right navicular and the proximal part of the ipsilateral talus with a "cold" area on the distal part of the talus was revealed during the metabolic phase (figure 2).
Axial computed tomography performed at numerous 2 and 3 mm sections in transaxial and coronal projections, in soft and osseous tissue algorithm, revealed a calcaneonavicular synchondrosis. The magnified sections revealed significant lesions of the navicular bone indicating osteochondritis (figure 4).

Figure 1. The lateral roentgenogram reveals the prolongation of the anterosuperior calcaneus (arrow),
which approaches the midportion of the navicular bone.

Figure 2. Metabolic (osteal) phase of Tc-99 bone scanning. The arrow indicates the increased uptake of the radioisotope on the right navicular and the "cold" area on the distal part of the talus.

Figure 3. CT clearly depicts CNS (arrow) with characteristic articular irregularity,
abnormal lipping and cystic joint irregularity.

Figure 4. Magnified coronal section reveals significant lesions of the right navicular bone,
indicating osteochondritis.

Non-operative treatment (splintage and non-weight bearing for 3 weeks) was thought of no use. The patient underwent surgical operation. Under general anaesthesia and tourniquet control an incision was made on the lateral-dorsal aspect of the foot. The approach of the calcaneonavicular synchondrosis was achieved through detachment of the origin of the extensor digitorum brevis muscle and removal of the fat from the tarsal sinus (figure 5). The osseous bar was then excised and with the use of slowly absorbable sutures the origin of the extensor digitorum brevis muscle along with subcutaneous fat were interposed into the space that was created by the excision of the synchondrosis (figure 6). Finally, the subcutaneous fat and skin were sutured and a non-weight bearing cast was applied.
The patient remained hospitalized for 5 days and avoided weight bearing for a total of 4 weeks. His return to sports activities took place after approximately 10 weeks post-operatively. 12 months after the operation the clinical presentation of the foot is excellent, the mobility of the ankle and the other foot joints is full-range and the patient remains symptoms-free, despite his daily long-lasting training course. The roentgenogram of the right foot appears normal (figure 7).

DISCUSSION
The onset of symptoms of calcaneonavicular synchondrosis (CNS) usually takes place right after the age of 8, along with the ossification of a pre-existing syndesmosis. CNS typically presents as recurrent ankle "sprains" which are obviously connected to the sports activities of the young patient. That was the very same reason why our young patient came to us 5 whole months after the onset of symptoms.
The clinical presentation of painful (spastic) flatfoot is not typical. Peroneal muscle spasm may conceal numerous pathologic conditions such as an osteocartilaginous fracture, an accessory navicular of tarsus, an avulsion fracture of the 5th metatarsal base, tumours of the calcaneus or the talus, or an inflammation3. Giokas et al1 describe a case of a 13 yrs old boy with painful and rigid flatfoot that histologically proved to be due to a benign chondroblastoma of the talus. However, clinical presentation of CNC is not always the same. Stuecker and Benett[10] report a patient with CNC and two others with talocalcaneal coalition who presented with cavovarus deformity without an underlying neuromuscular disorder.
Concerning the pain in CNS Kumai et al[6] claim that an incomplete coalition produces microfractures on the boundaries between normal bone and the coalition, as well as degenerative changes. According to the authors, the new biomechanical conditions that encounter seem to induce pain via free nerve endings in the periosteum and in the articular capsule surrounding the coalition.
The diagnostic approach of a CNS begins with plain roentgenograms. Lateral films show an abnormal tubular prolongation of the anterior superior calcaneus, described as the "anteater nose". Oestreich et al[9] report that such a configuration was present in all 30 feet reviewed with CNS. The CNS itself may be however recognized on the oblique Slomann view[3].

Figure 5. During the operation. The arrow indicates the osseous bar of the CNS.

Figure 6. During the operation. The osseous bar has been excised and the origin of the extensor digitorum brevis muscle (big arrow) is about to be sutured into the created space (small arrow).

Tc-99 bone scanning is considered to be of no use in cases of tarsal coalition because of epiphyseal uptake and the fact that positive findings are nonspecific and lack anatomic detail[12]. In our case it came out to be useful because our attention was focused on the region of the navicular and the talonavicular joint.
On the contrary, computed tomography proved to be of particular importance because it directly provided the imaging criteria for the characterisation of CNS. These criteria, according to Wechsler et al[12], are depiction of articular narrowing and cystic joint irregularity, sometimes resulting in an abnormal talar slope. In addition, CT provided the characteristic findings of navicular osteochondritis; an obvious outcome of the excessive stress of the bone due to the limitation of the subtalar motion range and the continuing of the young patientÕs sports activities for 5 months, despite of the persisting symptoms.

Figure 7. Oblique roentgenogram of the right foot, 12 months after the operation,
does not reveal any signs of recurrence.

When clinical or roentgenographic suspicion for coalition is high, CT remains a more cost-effective diagnostic modality[4]. Clarke[2] recommends CT evaluation of both feet in transaxial and coronal planes to rule out additional coalitions before surgical intervention. Newman and Newberg[8] underline that CT (as well as MRI) is valuable for assessment of tarsal coalitions because it allows differentiation of osseous from nonosseous coalitions, depicts the extent of joint involvement as well as degenerative changes and may reveal bone marrow oedema along the margins of the abnormal articulation.
Conservative treatment does not usually result in alleviation of symptoms and full return to athletics. Operative treatment is indicated only for persisting cases or those that resist conservative management. Morgan and Crawford[7] studied 12 adolescent patients with a known diagnosis of tarsal coalition. 5 of 6 patients who had CNS were able to return to competitive athletics after a short post-operative period.
The surgical treatment of CNS is the excision of the osseous bar and the interposition of the origin of the extensor digitorum brevis muscle into the space that is created. Particular care should be taken to remove all cartilaginous remnants of the coalition from the calcaneal and navicular sides and to interpose the origin of the muscle using strong absorbable sutures[11]. Contraindications for this operation are the presence of degenerative lesions, the development of an osteophyte in the talonavicular joint, the complete ossification of the bar and the presence of multiple coalitions in the same foot[3].
The young athlete of our case had a full return to athletics within 10 weeks after the operation. According to Gonzalez and Kumar[5], the best results are in patients with CNS, aged under 16. In addition, patients who had a good or excellent result, immediately after the operation, continued to do as well even after 10 years.

REFERENCES
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