Synostosis
A synostosis is a congenital anomaly that allows abnormal contact between two bones. This anomaly can be symptomatic or asymptomatic.
What is a foot synostosis?
A synostosis is an abnormal point of contact between two bones. This is a congenital anomaly that may or may not be symptomatic. Synostoses can occur in various locations; there are several types of synostosis in the ankle and foot, depending on the location and the type of tissue connecting two or more bones:
- If the connection between two bones occurs through a bony bridge, it is called a synostosis.
- If the connection between the two bones is through a fibrous bridge, it is called a synfibrosis.
- If the connection between the two bones is through a cartilaginous bridge, it is called a synchondrosis.
The connection or fusion of the affected bones may be complete or incomplete. This anomaly is part of congenital foot deformities, just like humpback tarsus, which can affect the normal anatomy of the foot and ankle.
What are the symptoms of Synostosis?
A synostosis can be completely asymptomatic and is then described on additional imaging studies performed for another reason. A synostosis can become symptomatic in adolescence or adulthood.
When symptomatic, a synostosis can be painful. The pain is generally mechanical in nature, and is due to a limitation of the joint movement it causes and to the overuse of neighboring joints.
In children, synostosis should be suspected in cases of pain and stiffness in the ankle, hindfoot, or midfoot joints. A history of repeated ankle sprains with minor trauma should prompt consideration of the diagnosis of synostosis. In cases of incomplete synostosis, it is possible to develop arthritic degeneration of the affected joint over time. This foot osteoarthritis can later become painful.
The different types of Synostosis
It corresponds to a bony bridge between the talus and the calcaneus, causing subtalar stiffness. The synostosis is visible on a lateral ankle X-ray, where it is described as the C sign. This abnormality affects the normal anatomy of the ankle and significantly limits the movements of the subtalar joint.
Calcaneo-navicular synostosis is probably the most frequently symptomatic in children and adolescents. It is responsible for pseudo-sprains of the ankle. It is suspected in children who have repeated ankle sprains. The radiographic assessment may show the synostosis, particularly on lateral ankle X-rays or three-quarter foot X-rays. MRI makes it possible to analyze a synchondrosis or a synfibrosis.
Synostosis of the tarsal bones is rarer, and the fusion may involve two or more of the tarsal bones. This synostosis is suspected on weight-bearing frontal X-rays of the feet. CT scan analysis is more accurate for assessing the extent of synostoses and the number of bones involved.
Why choose La Clinique du Pied?
Calling on La Clinique du Pied for the management of synostoses and tarsal coalitions allows you to benefit from specialized surgical and medical expertise in hindfoot disorders. These bone abnormalities require precise evaluation to distinguish asymptomatic forms from those causing pain or functional stiffness.
What are the possible treatments?
In case of a painful flare-up, taking painkillers and anti-inflammatories can help relieve pain. Rehabilitation should be considered if a synostosis is discovered. It involves stretching the posterior muscle chains, strengthening the ankle stabilizers, and working on proprioception. A personalized foot rehabilitation program can help improve joint function despite the limitation imposed by the synostosis.
Wearing orthopedic insoles is not always effective given the joint stiffness associated with synostoses. In case of an old, arthritic synostosis, it is possible to offer an intra-articular cortisone injection. In some symptomatic cases, a temporary immobilization may be necessary to calm acute inflammation.
In case of failure of medical and functional treatment, surgical interventions exist; they depend on the location of the synostosis, the patient’s age, and whether the synostosis is complete or incomplete.
What surgeries are possible?
In cases of incomplete synostosis, it is possible to propose the surgical resection of this synostosis with the interposition of soft tissues, allowing the intra-articular space thus created to be preserved. This is the case for certain talocalcaneal synostoses.
Calcaneonavicular synostoses can be resected without interposition. Tarsal synostoses are rarely symptomatic and are therefore generally not operated on. In cases of long-standing synostosis with arthritis, an arthrodesis of the foot of the affected joint can be proposed.
Tarsal coalitions
Tarsal coalitions refer to an abnormal fusion between two tarsal bones, that is, the bones located at the back and middle of the foot. This is a congenital anomaly of bone development that can be asymptomatic or, on the contrary, cause pain and stiffness in the foot. Depending on the nature of the tissue connecting the bones, the coalition may be osseous (called synostosis), cartilaginous (synchondrosis), or fibrous (syndesmosis). These fusions result in a loss of mobility in the affected joints and can lead to overload on neighboring joints, sometimes causing mechanical pain or early wear.
Tarsal coalitions most often affect the region between the calcaneus (heel bone) and the navicular, or between the talus and the calcaneus. The calcaneo-navicular coalition is the most common and typically appears during adolescence when ossification is complete.
It can cause pain, midfoot stiffness, and recurrent sprains. The talocalcaneal coalition, on the other hand, limits the movements of the subtalar joint and causes discomfort when walking on uneven ground. More rarely, other bone associations can be involved, such as between the talus and the navicular or between the calcaneus and the cuboid.
The diagnosis is based on medical imaging. Standard X-rays of the foot and ankle may sometimes visualize the coalition, particularly thanks to characteristic signs such as the "C sign" seen in talocalcaneal coalitions. The CT scan is the reference examination for determining the exact location and extent of the coalition.
MRI can be useful for identifying non-ossified forms, especially in cases of synchondroses or syndesmoses. A complete assessment generally includes several foot exams to confirm the diagnosis. Foot MRI is particularly useful for assessing cartilaginous or fibrous coalitions not visible on standard X-rays.
Treatment depends on the type of coalition and the discomfort experienced by the patient. In the majority of cases, a conservative approach is recommended initially. This includes wearing appropriate orthopedic insoles, rehabilitation to improve flexibility and proprioception, as well as analgesic or anti-inflammatory treatments to relieve pain.
When symptoms persist despite these measures, surgical intervention may be considered. This involves either resecting the coalition to restore joint mobility, or performing an arthrodesis (intentional fusion) in advanced or arthritic cases when mobility can no longer be preserved.
FAQ
Synostosis is a congenital malformation corresponding to a total or partial fusion of two or more bones. In the case of synostosis, other osteoarticular malformations may be associated.
Rehabilitation can help relieve symptomatic synostoses. The rehabilitation exercises depend on the type of synostosis, its location, and any associated joint stiffness.
Synostosis can be detected with a standard X-ray examination. It can be further specified by a CT scan analysis. In cases of synfibrosis or synchondrosis, MRI allows for a more precise analysis of the cartilaginous and fibrous tissue.