Coalition is defined as abnormal bridging between two bones, and the connection can be osseous or nonosseous. Most coalitions in the foot involve the hindfoot. Intermetatarsal coalition is thought to be much rarer than the more common hindfoot coalitions and has only been reported sporadically in the orthopedic literature. We present two patients with nonosseous intermetatarsal coalition presenting with nonspecific dorsolateral foot pain and describe the imaging findings of intermetatarsal coalition with different modalities. We suspect that whilst rarely described, intermetatarsal coalition is quite likely a more common underrecognized entity than a rare entity. This report is aimed at increasing the awareness of coalition in this location, in the radiology community, particularly the nonosseous ones, given that this condition can be debilitating but treatable.
Coalition, or abnormal bridging between two bones, has a prevalence of up to 13% in the foot with majority of the foot coalition occurring in the hindfoot [
A 40-year-old otherwise healthy female had an MRI and X-ray performed for one week’s history of dorsal foot pain following an increase in activity. The imaging was performed for investigation of possible stress fracture. The initial X-ray showed abnormal articulation between the base of the third and fourth metatarsals with concave scalloping of the medial margin of the fourth metatarsals, best appreciated on oblique projection (Figures
40-year-old female with dorsal forefoot pain following a change in activity. AP (a) and oblique (b) radiographs reveal bony prominence of the lateral border of the proximal third metatarsal shaft. Short axis PD (c) and PDFS (d) sequences reveal abnormal articulation between the base of the third and fourth metatarsals. Surrounding reactive bony hypertrophy and intramedullary marrow oedema signal. This is consistent with nonosseous intermetatarsal coalition. Coronal PDFS (e) sequence with nonosseous coalition between the base of the third and fourth metatarsals. Localized marrow oedema signal at the third metatarsal base. Coronal PDFS (f) sequence reveals a bursal-neuroma complex at the third intermetatarsal space corresponding to the location of the coalition. Sagittal PDFS sequences (g) with low-grade marrow oedema in the third metatarsal head. These are speculated to arise from the altered weight-bearing mechanics as a result of the coalition with increased load on the metatarsal head.
MRI (Figures
There is, in addition, a third intermetatarsal bursal-neuroma complex (Figure
A 29-year-old female patient underwent radiologic investigation following 3 years’ history of dorsolateral forefoot and midfoot pain exacerbated by activity. Initial ultrasound examination revealed dorsal surface metatarsal bony irregularity and adjacent soft tissue oedema and hyperaemia at the region of interest, corresponding to the base of the third and fourth metatarsals (Figure
29-year-old female with dorsolateral foot pain. Ultrasound in axial view of the proximal metatarsals (a) shows abnormal bony overgrowth in the dorsal border of the third and fourth intermetatarsal space. This is associated with adventitial bursal formation, soft tissue oedema, and increased vascularity. AP (b) and oblique (c) radiographs show abnormal articulation at the base of the third and fourth metatarsals with sclerosis at the site of the approximation. Coronal PDFS (d) with nonosseous coalition at the third and fourth intermetatarsal spaces. Associated periostitis and intramedullary oedema signal. Axial PD (e) and PDFS (f). Marrow oedema signal. Osteitis and periostitis. Abnormal articulation at this level with surrounding bone spurring.
MRI revealed nonosseous coalition at the base of the third and fourth metatarsals with localized marrow oedema in the third metatarsal, surrounding periostitis and reactive bony changes including osteophyte lipping across this articulation (Figures
A conservative approach was also undertaken, with good results.
Coalition is defined as abnormal bridging between two bones [
Companion case. 30-year-old man with the Apert syndrome. Lateral (a) and frontal (b) foot X-ray with multiple osseous synostosis involving both feet, including intermetatarsal coalition.
Coalition was classically thought to be present in approximately 1% of the population, although more recent studies have suggested prevalence as high as 13%, given the increased accessibility to imaging for detection of the asymptomatic cases [
Intermetatarsal coalition is much less well known and only a small number of cases have been reported in the English literature (Table
Available literature on intermetatarsal coalition on literature search via PubMed. Keyword coalition or synchondrosis or synostosis AND intermetatarsal or metatarsal.
Primary author/reference | Metatarsals involved and location of coalition | Type of coalition |
---|---|---|
Cordoba-Fernandez A [ | 4th-5th base | Osseous |
Dunn KW [ | 3rd-4th base | Nonosseous |
Kachuk KB [ | 4th-5th base | Not applicable |
Novak EJ [ | 1st-2nd base | Osseous |
Russell N [ | 3rd-4th distal | Nonosseous |
Vun SH [ | 4th-5th distal | Osseous |
Yang C [ | 1st-2nd base | Nonosseous |
Mohammed F [ | 1st-2nd base | Osseous |
Aspros D [ | 4th-5th distal | Osseous |
The common presentations described are nonspecific dorsolateral or forefoot pain corresponding to the site of the coalition. This is similar to how our cases presented. The cause for the pain is thought to be due to the altered weight-bearing mechanics, with reduced mobility and flexibility as a result of the coalition which then results in inefficient weight distribution between the metatarsal heads and hence increased stress on the forefoot [
Radiographs are usually the first imaging modality for investigation of foot pain given the availability and relative low cost. Osseous bridging or hypertrophy of the metatarsals can be readily apparent but is frequently not recognized by the reporting radiologists due to the rarity of the condition. One can be alerted to nonosseous coalition by observing osseous deformity along the margins of the coalition [
Computed tomography (CT) with thin slices and 3-dimensional reconstruction ability via surface rendering offers a better appreciation of the anatomy depicted on radiographs without the overlapping composite shadowing. Osseous coalition is defined by its osseous continuity between normally separate structures. Nonosseous coalition can be differentiated from normal joints by its irregular opposing margins, subchondral cyst formation, and usually narrowed space [
Sagittal hindfoot in a 20-year-old female demonstrating a nonosseous calcaneonavicular coalition. Note the irregular, opposing joint margins.
Ultrasound, whilst of limited value in the diagnosis of coalition, is useful in localizing the pathology and in assessing for secondary inflammatory changes associated with coalition as a potential cause for pain (Figure
Magnetic resonance imaging (MRI) findings are relatively similar to CT with the addition of being able to distinguish between fibrous and cartilaginous coalition and visualization of bone marrow oedema signal. Cartilaginous coalition is T2 hyperintense, and T1 isointense to muscle, whilst fibrous coalition is T2 and T1 iso-hypointense. There are often overlapping imaging features; hence, for simplicity, these can be termed fibrocartilaginous coalition. MRI can also demonstrate bone marrow oedema signal or any stress response associated with the coalition more elegantly, to confirm the coalition being a pain generator.
Other potential soft tissue complications of coalition to assess for, apart from interdigital bursal-neuroma complexes as mentioned above, are plantar plate degeneration and metatarsal head oedema from the altered weight-bearing dynamics [
Technetium-99m with single-photon-emission tomography (SPECT) may also show increased uptake at the site of coalition if there is active stress or inflammatory response. None of our patients have undergone any functional imaging.
The treatments described in the literature for the treatment of symptomatic metatarsal coalition include the conservative or surgical approach. The primary aim of the treatment is to correct the foot deformity for better anatomic alignment and function. In general, surgery is usually reserved for cases recalcitrant to conservative management and usually involves resection or disconnection of the coalition [
In conclusion, intermetatarsal coalition is rarely described, but it is almost certainly an underrecognized condition, particularly in the radiology community. This report adds to the literature by presenting two different cases of intermetatarsal coalitions and describing the imaging findings of different imaging modalities. Potential downstream complications of intermetatarsal coalition are also discussed. Prompt diagnosis of coalition for patients presenting with nonspecific metatarsalgia is important as this condition can be debilitating but treatable and when addressed early, progression to degeneration can be halted. Potential future research includes more large-scale radiology studies to determine the prevalence of the isolated, nonsyndromic intermetatarsal coalition.
Not applicable
Ethics approval for consent waiver was obtained via the institution’s ethics board (CHCA-HREC Ref No: 20-CHREC-E012). This report does not contain any personal information which may lead to the identification of the patients.
The authors declare that they have no conflicts of interest.