Osseous bridging in the foot describes an abnormal condition where two or more tarsal bones in the back of the foot are naturally connected by a bridge of bone tissue. Medically referred to as a tarsal coalition, this unintended fusion severely limits the foot’s natural flexibility. A healthy foot depends on the coordinated movement of these small bones to adapt to various surfaces and absorb shock.
Understanding Osseous Bridging
Osseous bridging is the most rigid form of tarsal coalition, characterized by a complete synostosis, or fusion, of two bones with dense bone tissue. Normally, the joints between the tarsal bones are separated by a small space containing cartilage and synovial fluid, allowing for gliding and rotational movement. When osseous bridging occurs, this functional joint space is eliminated, replaced entirely by a bar of solid bone.
The abnormal connection can also involve less rigid tissues. A fibrous coalition involves dense, ligament-like tissue, while a cartilaginous coalition features a bridge made of cartilage. These non-osseous connections restrict the joint’s movement compared to a normal, unfused joint. The presence of any type of coalition inhibits the small, complex motions of the hindfoot that are needed for proper gait mechanics. This loss of motion forces other joints in the ankle and knee to compensate, often leading to secondary problems over time.
Primary Causes and Common Locations
The vast majority of osseous bridging cases are congenital, meaning the condition is present from birth. This developmental abnormality results from a failure of embryonic tissue to fully separate into distinct bones and joints during fetal development. Although present at birth, the fusion often remains non-bony (cartilaginous or fibrous) and asymptomatic until later childhood or adolescence.
The two most frequent locations for tarsal coalition are the calcaneonavicular and the talocalcaneal joints, accounting for approximately 90% of all cases. A calcaneonavicular coalition connects the calcaneus (heel bone) to the navicular bone in the midfoot. Symptoms typically present between the ages of 8 and 12 years.
The talocalcaneal coalition involves the talus (ankle bone) and the calcaneus, affecting the subtalar joint, which controls side-to-side foot motion. This fusion tends to ossify later, with symptoms commonly emerging between 12 and 16 years of age. The delayed onset occurs when the softer, non-osseous bridge gradually hardens into bone, restricting movement and causing pain.
Osseous bridging can occasionally be acquired later in life due to external factors. Severe trauma, such as a major foot fracture, can result in an abnormal bony connection during healing. Advanced cases of inflammatory conditions like severe arthritis or chronic infections can also lead to the body attempting to fuse painful joints, resulting in an acquired bony bridge.
Recognizing the Signs and Confirmation
The signs of osseous bridging often become apparent when the foot is under increased physical stress or when the non-osseous bridge begins to harden into bone. Common clinical presentations include chronic, deep-seated pain in the foot, particularly below the ankle or in the midfoot area. Patients also report noticeable stiffness, which makes walking on uneven terrain difficult.
A recognizable physical sign is the development of a rigid flatfoot deformity, sometimes called a “peroneal spastic flatfoot.” The foot appears flat and lacks a proper arch, and unlike a flexible flatfoot, the arch does not return when the patient stands on their toes. This rigidity is caused by the coalition preventing normal arch adjustments, and “spastic” refers to the protective muscle spasms that can occur around the ankle.
Diagnosis begins with a physical examination to assess the flexibility and range of motion of the hindfoot joints. Imaging studies confirm the presence and extent of the bony connection. Standard X-rays are typically the first step, clearly showing a fully ossified bridge, especially in a calcaneonavicular coalition.
However, X-rays may not fully visualize a partially bony or cartilaginous bridge, especially in a talocalcaneal coalition. In these more complex cases, advanced imaging like a Computed Tomography (CT) scan or Magnetic Resonance Imaging (MRI) is used. A CT scan provides detailed cross-sectional images of the bone, while an MRI is better at visualizing the soft tissue components, confirming the precise nature of the abnormal connection.
Management and Treatment Pathways
The management of osseous bridging typically follows two pathways: conservative care for symptomatic relief and surgical intervention for definitive correction. Initial treatment focuses on reducing inflammation and pain, often involving a period of rest and immobilization. This may include wearing a short-leg cast or a removable walking boot for several weeks to completely restrict movement of the affected joints.
Non-surgical methods also include the use of non-steroidal anti-inflammatory drugs (NSAIDs) to manage pain and swelling. Specialized foot orthotics are frequently prescribed to provide custom support to the arch and heel, helping to redistribute pressure and reduce strain on the stiffened joints. These conservative treatments aim to manage symptoms, particularly in cases where the coalition is small or the patient’s activity level is low.
Surgical treatment is generally considered when conservative methods fail to provide adequate pain relief or when the coalition is extensive, causing significant deformity or disability. For smaller, less extensive coalitions, a coalition resection is often performed.
Resection involves surgically removing the abnormal bony bridge and placing soft tissue, such as fat or muscle, between the remaining bone surfaces to prevent the fusion from recurring. This procedure aims to restore some of the lost joint motion while eliminating the source of pain. In cases where the coalition is large, involves multiple joints, or is associated with significant, debilitating arthritis, a definitive joint fusion, known as arthrodesis, may be necessary. Arthrodesis intentionally fuses the joint in a corrected position to eliminate all movement and the associated pain.