We describe a case of a 63-year old lady with a history of chronic forefoot pain since the age of 13 years. The patient had her first presentation as a child after sustaining an injury. The pain and swelling persisted for many years, requiring several surgical operations throughout the years.
The patient had several radiological investigations in her lifetime with her pathology being brought to attention by the consultant radiologist. The plain radiograph (figure 1) demonstrated severe osteoarthritis (OA) in the first metatarsal joint (MTPJ). The second and third metatarsal bones appeared fused with abnormal interosseous communication at the level of the shaft and chronic periosteal thickening. Appearances were longstanding. A CT scan (figure 2) was subsequently organised to evaluate this further. The CT scan confirmed moderate OA changes in the first MTPJ with loss of joint space, subchondral sclerosis, osteophytes and subchondral cysts. The CT also confirmed an ‘incidental’ fusion of the second and third metatarsals bones with areas of cortical and marrow continuity consistent with congenital metatarsal synostosis. Mild degenerative OA changes with osteophytosis was noted in the second and third MTPJs.
Metatarsal synostosis is a rare condition with an incidence of less than 1% [1]. The commonest area includes the tarsals, involving the calcaneonavicular and talocalcaneal joints [2]. Metatarsal synostosis is exceptionally rare with most cases in the literature reporting the coalition of base of the fourth and fifth or the first and second metatarsal bones [3-5]. The cases reported in the literature are predominantly of children or young adults. Our case is the first to describe synostosis of the 2nd and 3rd metatarsal, with other cases describing a fusion of the 2nd-4th metatarsal along with tarsometatarsal coalition [4,7]. Interestingly, it is the only reported case in a middle-aged individual with a longstanding history of a painful foot, consequently undergoing multiple surgical procedures.
Histologically there are three types of coalitions; fibrous (syndesmosis), cartilaginous (synchondrosis) and osseous (synostosis), with synostosis further classified as congenital or acquired [7]. Congenital coalitions are formed by the fusion of accessory ossicles and/or from the failure of differentiation and segmentation of primitive mesenchyme. Acquired coalition can occur as a result of arthritis, infection, neoplasm and trauma [8].
The commonest presentation is mid-foot pain. With ongoing stress to the surrounding joints, patients later present with stiffness, osteoarthritis, and joint deformities [9].
Radiologically both Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) are invaluable methods of assessment. CT scans are used to differentiate the more straightforward osseous coalitions with the non-osseous. The former is demonstrated as continuity between the two bones. The non-osseous coalitions are demonstrated through abnormal narrowing, joint space irregularity, and subchondral cyst formation, easily misinterpreted as degenerative changes risking a delayed or misdiagnosis. MRI is an important tool in differentiating between the three different types of coalitions. In osseous coalitions, the bone marrow signal is continuous across the fused bones, demonstrated as a high signal intensity on T1-weighted images and low signal intensity on T2-weighted fat-suppressed images. The non-osseous coalitions demonstrate non-specific changes [10]. In addition to radiology, the patient’s clinical presentation and examination must be taken into consideration when reaching this diagnosis.
The management of metatarsal synostosis includes conservative management with analgesia, orthotics, with the only curative measure being operative management [10].
Our case illustrates the importance of detecting this abnormality as an important differential of mid-foot pain to avoid any undue investigations and subsequent extensive surgical interventions as noted in this patient.
Written informed patient consent for publication has been obtained.
Synostosis of the second and third metatarsals
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Based on the provided X-ray and CT reconstruction images, the following observations are noted:
1. There is a bony connection at the bases of the 2nd and 3rd metatarsals, suggesting local bony healing or fusion.
2. Partial narrowing of the adjacent joint space is observed, with irregular thickening or sclerosis of the local cortical bone.
3. In the CT three-dimensional reconstruction, a complete bridging between the 2nd and 3rd metatarsals is clearly visible, consistent with metatarsal fusion (with mild degenerative changes).
4. No obvious abnormalities are noted in other metatarsal-tarsal joints, and no significant swelling or abnormal calcification is observed in the soft tissues.
Based on the patient’s long-term chronic forefoot pain, repeated surgical history, and imaging findings of 2nd and 3rd metatarsal fusion, possible diagnoses include:
1. Congenital or Post-Traumatic Metatarsal Synostosis: Congenital metatarsal fusion is relatively rare, but it can be observed due to congenital structural abnormalities or bony fusion caused by trauma or inflammation. Imaging typically shows a bony bridge, which matches the findings in this case. The patient’s onset since childhood, history of trauma, and multiple surgeries suggest a possibility of post-traumatic repeated repair leading to bony fusion.
2. Metatarsal Joint Ankylosis or Degenerative Changes: In cases of severe degeneration or inflammation, there may be indistinct trabecular structures and joint space narrowing, but obvious bony bridging is typically not observed.
3. Other Rare Skeletal Abnormalities or Fibrous Union: If the fusion was only fibrous or cartilaginous, one might consider a fibrous or cartilaginous union. However, the high-density continuity on CT suggests bony fusion is more likely.
Considering the patient’s trauma at around age ten, long-term pain, clinical presentation, and multiple surgeries, along with the X-ray and CT 3D reconstruction showing definitive bony fusion between the 2nd and 3rd metatarsals, the most likely diagnosis is:
“Bony Union of the 2nd and 3rd Metatarsals (Metatarsal Synostosis)”
This is a relatively rare type of metatarsal fusion, which clinically can lead to chronic pain, restricted joint mobility, and increased compensatory load on adjacent joints.
1. Conservative Treatment:
• Suitable for patients with mild pain or high surgical risk. Consider physical therapy and custom foot orthotics (such as forefoot off-loading insoles) to reduce local stress.
• Use nonsteroidal anti-inflammatory drugs (NSAIDs) and other analgesics to control pain, if needed for a short period.
2. Surgical Treatment:
• For severe symptoms, failure of conservative treatments, or significant joint degeneration, surgical options may be considered, including release or incision of the fusion and restoration of joint stability.
• Given the patient’s multiple previous surgeries, it is critical to carefully assess surgical indications and weigh the risks and benefits.
3. Rehabilitation and Exercise Prescription:
• Early Stage (Acute Phase / Significant Pain): Reduce weight-bearing activities, use supportive devices or appropriate orthoses. Perform light non-weight-bearing lower limb muscle strengthening, such as seated or supine ankle dorsiflexion and plantarflexion exercises, 2–3 sessions per day, 10–15 repetitions each session.
• Intermediate Stage (Symptom Relief / Gradual Recovery): Gradually increase weight-bearing activities as tolerated. Consider low-impact aerobic exercises such as swimming or cycling 3–4 times a week for 20–30 minutes at a moderate intensity. Progress to short-distance walking on soft surfaces and incorporate resistance exercises for foot and ankle muscles with resistance bands.
• Later Stage (Strengthening / Functional Training): Enhance lower-limb proprioception and balance with single-leg standing and balance board training to improve overall foot and ankle stability. Increase training frequency to 4–5 times a week for 30–45 minutes, ensuring rest days. Emphasize core and lower-limb strengthening to maintain proper gait and posture.
• Throughout all phases, follow the FITT-VP principles (Frequency, Intensity, Time, Type, Volume, Progression), adjusting exercise methods and intensity according to patient tolerance and cardiopulmonary function. If significant pain or swelling occurs, reduce or discontinue the related exercises and consult a physician.
This report is based on the available imaging and clinical information. It serves as a reference but does not constitute a definitive diagnosis or treatment recommendation for the patient. Actual diagnosis and treatment require clinical evaluation, laboratory tests, and other specialist opinions. The patient should seek further examination and treatment under the guidance of professional medical personnel.
Synostosis of the second and third metatarsals
