Radiographic Evolution of Scaphotrapezium Coalition Trough Carpal Ossificaction

Abstract

Carpal coalitions are anatomy variants, consisting of the union of two or more carpal bones. The incidence is low, usually being an incidental diagnosis. Describing the radiographic development through carpal ossification is our objective concerning a clinical case. Our patient is a 15-year-old male, who suffers repeated scaphoid fractures. He was diagnosed with bilateral non-osseous carpal coalitions in the follow-up. The patient had previous radiographs of his left wrist through infancy until skeletal maturation was observed. Thus, it was possible to compare them to reference images of normal skeletal maturation, showing the strongest differences after carpal ossification. Carpal coalitions are scarce, and the diagnosis is only possible after skeletal maturation, showing a higher risk of mechanical stress and present fractures than the general population.

Keywords

carpal coalition - synchondrosis - synostosis - osteogenesis - bone development

Introduction

A carpal coalition is the union of two or more carpal bones.[1] They are considered anatomical variations present in a low percentage of the population, around 0.1%, reaching a prevalence of up to 9% in the west of the African continent.[2] It is more common in women, generally bilaterally and symmetrically affected, and is a genetically hereditary entity, following an autosomal dominant inheritance pattern.[1] Its appearance is related to failures in the joint cavitation process,[3] [4] so More frequently it affects bones in the same carpal row and bilaterally. The most common are those that appear between semilunar - pyramidal,[3] [4] and between large - hamate.[1] The least common is the scaphoid-trapezoidal, which usually appears in the context of malformation syndromes.[3]

The diagnosis of these entities is usually incidental, being a casual finding when performing a wrist x-ray after a trauma,[5] therefore their evolution throughout growth has not been previously described. We intend to present the radiographic evolution of this malformation regarding a case, considering the theories proposed for the appearance of this malformation in the available literature.

Clinical Case

The patient is a 15-year-old white male, referred to the trauma clinic diagnosed in the emergency room with a fracture of the right scaphoid, after suffering a casual fall on that extremity. In less than 1 year he suffered another trauma to the same wrist, again presenting a fracture of the right scaphoid. Both episodes received conservative management by placing the corresponding closed casts. During follow-up, a non-bony carpal coalition was detected between the scaphoid and trapezius ([Figure 1]). Furthermore, the appearance of a scaphoid pseudoarthrosis developed after the second traumatic event on the scaphoid is notable, requiring an MRI of the right wrist ([Figure 2]).

Fig. 1 In these images we see the radiographic evolution of the right wrist after successive traumas; from top to bottom and left to right: 1–X-ray of the first scaphoid fracture (15 years), 2 and 3–consolidation begins at 8 months, 4–second trauma to the right wrist suffering a scaphoid fracture again, 5 and 6–control after conservative treatment of this second traumatic episode.

Fig. 2 MRI images of the right wrist, diagnosis of carpal coalition type synchondrosis between trapezius and scaphoid, associated with a scaphoid pseudoarthrosis.

When radiographs of the contralateral wrist were requested, a carpal coalition between the scaphoid and trapezius was also seen. Reviewing the history, the patient was treated with growth hormone (GH) for years from the age of 6 to 17 due to hypogrowth. During this time, he was subjected to periodic bone age controls using x-rays of the hand and wrist of the left upper limb, where the development of the carpus and the scapho-trapezoidal coalition can be seen upon reaching bone maturity ([Figure 3]). To confirm the diagnosis of bilateral non-osseous scaphotrapezius carpal coalition, an MRI of the left wrist is requested, for a better assessment of the relationship between the two bones ([Figure 4]). Furthermore, scaphoid pseudoarthrosis is also observed in its proximal region, despite the lack of previous trauma reported by the patient in the left extremity. This pseudoarthrosis was a chance finding, without the patient showing related symptoms, so it was decided to opt for expectant management with follow-up consultations.

Fig. 3 X-ray of the left hand to monitor bone age from top to bottom and from left to right 1-6 years (top left); 28 years; 3- 10 years; 4 - 11 years; 5- 12 years; 6- 14 years; 7–15 years; 8–16 years.

Fig. 4 MRI of the left wrist, where the same findings can be seen on the right: synchondrosis between trapezius and scaphoid and carpal scaphoid pseudoarthrosis.

Discussion

The appearance of coalitions is related to the failure in the separation process of the cartilaginous interzone between the adjacent carpal bones, which occurs between 4–8 weeks of gestation. This interface is made up of 3 layers: two denser ones, which will become the articular cartilage, separated by one of lower density, from which the synovial and intracapsular structures will be formed. This theory is applied to those collations that affect bones of the same carpal row and to those that share the same ossification rhythm. For the pisiform bone, which appears between 9–14 years in children, the previously described theory is not accepted; For those coalitions that affect this bone with the adjacent ones, it is related to a transformation of derivatives of the mesoderm.[2]

There are different types of coalitions between the carpal bones, the simplest classification being Brunnet's, which is divided into two groups depending on whether the coalition is bony or not[4]; In the latter case, the coalition can be made of cartilaginous tissue, also known as synchondrosis, or fibrous.[1] Concerning the rest of the classifications, as Defazio explained, both the first classification described by Minaar and that of Singh are not useful for coalitions not bony as they are not included.[1] [4]

All carpal bones ossify from a primary ossification center. In the full-term newborn, none of the carpal bones are ossified.[5] [6] The large and pyramidal bones become visible at 3 months of age, with the large one appearing, which has a larger and more rounded ossification nucleus; these are the only ossification nucleus visible for the next 6 months in the wrist. Between 14 months and 3 years, 3 or 4 carpal bones are recognized; to the large and pyramidal, the semilunar and the trapezoidal are added.[5]

This sequential appearance of the carpal bones allows bone age to be determined by comparison with standardized radiographs of carpal bones by age and sex, following the method of Greulich and Pyle. This is the most used method for determining bone age.[7] In the case of the patient studied, differences can be observed in the skeletal maturation of the carpal bones concerning the standard shown in the Greulich and Pyle method ([Figure 5]), from the age of 12, where the lower edge of the trapezius extends to the scaphoid and, clearly at the age of 14, the alteration of the morphology of the scaphoid and the trapezius can be seen. In the case of our patient, we also observed a complication that patients with carpal coalitions usually have, especially in non-bony ones,[4] which is a bone fracture. Although it has been theorized that the increase in fractures in this pathology may be related to the area where the fibrous tissue joins an area of weakness, in our case, we see that the bilateral fracture takes place in the middle third of the scaphoid.[7] This same pattern of fracture, has already been previously described by Noureldin, in this case, a percutaneous osteosynthesis with a compression screw was performed acutely, observing adequate consolidation after 8 months.[8]

Fig. 5 Reference images of the Greulich and Pile method of carpal development in males corresponding to the ages, from left to right: 9 years, 11 years, 13 years, and 15 years; From the age of 11, the differences in the morphology of the scaphoid and trapezius can be observed more clearly compared to those in the clinical case described. Taken from “Vicente Gilsanz OR. Hand Bone Age - A Digital Atlas of Skeletal Maturity. Springer.

A higher proportion of acute and chronic complications, such as chronic wrist pain, has been observed in patient series in patients with carpal coalitions than we found in the general population, which may be related to the alteration of the biomechanics of the wrist.[1]

Conclusion

Carpal coalitions are a rare entity, which appears due to cavitation between the carpal bones between the 4th and 8th week of gestation, but which goes unnoticed until skeletal maturation of the carpus occurs; especially, considering the lack of symptoms that accompany this condition, whose diagnosis is usually a coincidence. Despite this, it has been seen that they are related to a greater susceptibility to mechanical stress, and a greater risk of presenting fractures after suffering trauma.

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• Bibliography

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Publikationsverlauf

Eingereicht: 20. Oktober 2022

Angenommen: 09. Oktober 2023

Artikel online veröffentlicht:
05. Dezember 2023