Bowing fractures of the forearm in children: pathophysiology, diagnosis and management
Intended for healthcare professionals
Evidence and practice    

Bowing fractures of the forearm in children: pathophysiology, diagnosis and management

Jennifer Worrall Senior emergency practitioner and clinical lead, minor injury unit, Trowbridge Community Hospital, Wiltshire Health and Care, Trowbridge, England

Why you should read this article:
  • To refresh your knowledge of the anatomy of forearm bones and the pathophysiology of bowing fractures

  • To increase your awareness of the diagnostic challenges and complications associated with bowing fractures

  • To enhance your understanding of the management of children with bowing fractures

Bowing fractures of the forearm are characterised by numerous micro-fractures on the concave surface of the affected bone(s), usually caused by a fall on an outstretched arm. Children are more susceptible to this type of injury than adults because their long bones have more elasticity. Bowing fractures of the forearm are challenging to diagnose because there are no obvious cortical defects, which can lead to inappropriate management and associated complications, including loss of movement range and loss of function. This article discusses bowing fractures of the forearm in children, including their pathophysiology, diagnosis and management. It aims to enhance emergency nurses’ awareness and knowledge of this type of injury in children and of the challenges surrounding diagnosis and management.

Emergency Nurse. doi: 10.7748/en.2023.e2167

Peer review

This article has been subject to external double-blind peer review and checked for plagiarism using automated software

Correspondence

Jennifer.worrall1@nhs.net

Conflict of interest

None declared

Worrall J (2023) Bowing fractures of the forearm in children: pathophysiology, diagnosis and management. Emergency Nurse. doi: 10.7748/en.2023.e2167

Published online: 04 July 2023

Forearm fractures are one of the most common injuries in children and are frequently encountered in emergency care settings (Sims-Gould et al 2016, Caruso et al 2021). Traumatic bowing of the forearm, first described by Borden (1974), has proved to be an enduring diagnostic challenge for clinicians (Vervaecke et al 2021). It is a subtle form of fracture that children are more susceptible to than adults because of the biomechanical structure of their tubular long bones (Aponte and Ghiatas 1989). Due to a lack of obvious cortical defects, bowing fractures of the forearm lend themselves to misdiagnosis, inappropriate management and the various complications that can ensue (Aponte and Ghiatas 1989).

This article describes the anatomy of the forearm, bowing fractures of the forearm in children and the related diagnostic challenges and potential complications, and discusses the management options and the need to monitor patients’ progress closely. The author includes a fictionalised case study of a 13-year-old girl who presented to a first-contact service following a fall (Case study 1).

Case study 1

A 13-year-old girl presented to a first-contact service following a fall on the outstretched right arm – her non-dominant upper limb. Clinical examination revealed acute tenderness in the mid-forearm, in the radius and ulna but predominantly in the radius, as well as a visible bowing deformity. The patient was experiencing pain in the right wrist, proximal forearm and elbow. There was no history of previous injury to the right forearm.

Taking into account the mechanism of injury and clinical findings on examination, the suspicion was that the patient had sustained a fracture of one or both forearm bones. Following discussion with the patient and her parents, the girl was referred to the radiology department for an X-ray of the right forearm, including the wrist and elbow.

Radiological findings

An initial review of anterior, posterior and lateral X-ray views did not reveal a visible fracture or evidence of elbow joint effusion. There was, however, obvious dorsal bowing of the radius, as documented in the X-ray report and confirmed in an initial discussion with the radiology department. Estimated to be marginally less than 20°, the radial bowing centred on the distal diaphysis. There was no radiological evidence of previous mid-shaft fracture of the right forearm that could have accounted for this.

The X-ray report also documented diffuse overlying soft tissue swelling on the volar aspect of the radius and ulna. No acute abnormalities of the wrist or elbow were noted. The report concluded that the radiological findings raised the possibility of acute plastic bowing deformity.

Conservative management

The X-ray report was reviewed by a paediatric consultant radiologist who recommended further X-rays at regular intervals, when the patient attended fracture clinic review appointments, to look for evidence of periosteal thickening.

After discussion with the orthopaedic team, it was decided that the patient should be treated conservatively with an above-elbow lightweight cast and reviewed in the acute fracture clinic within one week.

At the review one week later, it was decided that the patient should continue to be managed conservatively and reviewed again in three weeks. By then, there was evidence of periosteal thickening on X-ray. The recommendation was that the patient’s progress should be closely monitored in the orthopaedic fracture clinic, with follow-up at three, six, nine and 12 months or more frequently should she encounter any issues between planned reviews. For example, if issues with forearm rotation were to develop, osteotomy would need to be considered. This was discussed with the patient and her parents.

Ongoing management and monitoring

The focus of ongoing management was on improving the patient’s range of forearm movement and regaining forearm strength with the help of physiotherapy sessions. The patient was referred for physiotherapy and advised to avoid contact sports and activities. She regained movement and strength in the forearm progressively and was found to have made good progress at each follow-up appointment.

At the 12-month review, the patient was deemed to have recovered entirely and was discharged. The patient and her parents were informed about the increased risk of injury arising from a previous fracture and were advised to select sports and activities with that risk in mind.

Anatomy of forearm bones

The forearm encompasses two long bones, the radius and ulna, which are attached proximally by the annular ligament, separated along their diaphysis by the interosseous membrane and attached distally by the ligaments of the distal radioulnar joint and triangular fibrocartilage complex (Herman and Marshall 2006).

Figure 1 shows an anterior view of the radius and ulna.

Figure 1.

Anterior view of the radius and ulna

en.2023.e2167_0001.jpg

The radius demonstrates a three-dimensional curvature (radial bowing) which is most apparent in the coronal plane. Normal radial bowing is important for the rotational range of movement of the forearm and strength of forearm muscles (Balakrishna and Sweekritha 2018). Abnormal radial bowing can negatively affect proximal and distal radioulnar joints, compromise movement in the forearm and create long-term issues if undiagnosed or misdiagnosed.

The ulna is comparatively straight and static and has an important role in maintaining forearm stability, especially when the forearm is subjected to buckling and torsional stress (Salvi 2006). There is some natural bowing in the ulna but to a much smaller degree than in the radius and the radius is more prone to bowing fractures than the ulna (Brouhard 2021).

The forearm rotates around an axis that passes through the heads of the radius and ulna (Balakrishna and Sweekritha 2018). Forearm pronation and supination are essential to accomplish everyday tasks such as bringing food to the mouth or manipulating objects. To lose range of movement in the forearm renders such tasks more challenging.

In a bowing fracture of the forearm, measuring the extent to which forearm pronation and supination are limited is important for clinical decision-making and evaluating outcomes. In children up to the age of 15 years, forearm pronation of 50° to 80° from neutral, and supination of 80° to 120° from neutral, are considered normal (Colaris et al 2010).

In the case study, pronation and supination of the patient’s right and left forearm were measured at first presentation and found to be:

  • Right forearm: pronation 60° to 65°, supination 80°.

  • Left forearm: pronation 80°, supination 90°.

The range of movement in the patient’s right forearm – which had sustained the injury – was within the normal range but was more limited than in her left forearm.

Key points

  • Bowing fractures of the forearm in children are easily missed due to the ambiguities of clinical presentation

  • Patients with bowing fractures typically present with pain, loss of function and deformity in the injured forearm

  • Bowing fractures do not follow the standard phases of fracture healing that are usually apparent on X-rays

  • Patients require meticulous follow up and regular X-rays

  • There is a lack of consensus regarding the management of bowing fractures of the forearm in children, therefore robust and evidenced-based patient treatment protocols are needed

Quantifying radial bowing

The normal degree of curvature of the radius at different ages is an important diagnostic consideration and it is crucial to be able to distinguish between normal radial bowing and radial bowing through injury. A method for quantifying radial bowing in adults was developed by Schemitsch and Richards (1992) and modified and validated for use in children by Firl and Wünsch (2004).

Firl and Wünsch (2004) used Schemitsch and Richards’ (1992) method in a retrospective study of 100 children aged between one year and 15 years with no forearm fracture. They found that although the length of the radius and maximum radial bowing increased with age, the point of maximum radial bowing did not change. They calculated that the point of maximum radial bowing remained constant at 60.39% of the radial length from the bicipital tuberosity. They also found that radial bowing never exceeded 10% of the radial length (Firl and Wünsch 2004).

The method for quantifying radial bowing (Figure 2) is as follows:

Figure 2.

Method for quantifying radial bowing

en.2023.e2167_0002.jpg
  • After having obtained an anteroposterior radiograph of the injured forearm, the radial length is determined by drawing a line (y) between the distal radioulnar joint and the bicipital tuberosity.

  • 60.39% of the radial length from the bicipital tuberosity is measured (x). This enables determination of the point of maximum radial bowing.

  • Radial bowing in millimetres (z) is determined by drawing a line between the point of maximum radial bowing and the line representing the radial length (y).

Radial bowing can be expressed as a percentage of the radial length [(z divided by y) multiplied by 100]. This enables comparison of radial bowing between patients.

Mechanism of injury and plastic bowing

Typically, the mechanism of injury in a bowing fracture of the forearm is a fall onto an outstretched hand (Musters and Colaris 2017), which exerts longitudinal stress on the radius and ulna causing the bones to deform plastically before the point where they would actually break (Vorlat and De Boeck 2003). The affected bone bends much like an archer’s bow but remains bowed after the force exerted on it has been removed. A plastic deformity remains due to invisible micro-fractures that have occurred on the concave surface of the bone (Borden 1975).

Experimental data provided by Chamay (1970) and studied by Borden (1975) suggested that the approximate force that needs to be exerted on bone to cause plastic deformation is 100% to 150% of the person’s body weight. To produce a bowing fracture, the force exerted must be exactly longitudinal, greater than the maximum strength of the bone but shorter in duration than the time it would need for a gross fracture to occur (Learningradiology.com 2023). Patients typically present with pain, loss of function and deformity in the injured forearm.

Plastic-bowing-type fractures are subtle, incomplete fractures. They may be found in children and adults, but children are more prone to them because of the biomechanical structure of their tubular long bones (Aponte and Ghiatas 1989). In children’s long bones, there is a relative elasticity compared with the long bones of adults, which predisposes children to acute plastic bowing (Zhou et al 2016). The greater ability of children’s bones to bend also reflects the way the cortex and periosteum bind to each other in developing bone and the fact that bone cortex is thinner in children than in adults (Musters and Colaris 2017).

Types and complications

According to Musters and Colaris (2017), there are three types of bowing fractures of the lower arm in children:

  • Bowing of both bones.

  • Bowing of one bone and greenstick fracture of the other bone.

  • Bowing of the ulna and fracture or luxation of the head of the radius (Monteggia fracture-dislocation).

The radiological findings described in the case study suggest that there is a fourth type – bowing of one bone of the forearm only. Vervaecke et al (2021) supported the idea that a bowing fracture of the forearm can present either as an isolated fracture or in conjunction with other injuries such as joint dislocation and/or fracture of the other bone. If no fracture or bowing of the other forearm bone can be detected on an X-ray, clinicians should not dismiss the possibility that such injuries may be detected at a later stage. This stresses the need for meticulous follow-up of patients and review of X-rays.

Complications of bowing fractures of the forearm include (Learningradiology.com 2023):

  • Narrowing of the interosseous space resulting in a restriction of forearm rotational movement.

  • The bone remaining bowed.

  • Bowing maintaining an adjacent fracture in angulation or preventing the reduction of an adjacent dislocation.

Diagnostic challenges

While a forearm fracture with a visible fracture line is comparatively easier to diagnose, traumatic bowing of one or both forearm bones is less easy to determine. This is primarily due to the fact that bowing fractures do not appear to show a visible fracture line (Musters and Colaris 2017). Instead, numerous micro-fractures occur on the concave side of the bone while the cortex remains intact on the convex side of the bone (Borden 1975).

Bowing fractures do not follow the standard phases of fracture healing that are usually apparent on X-ray and there may be no evidence of new bone formation in the first few weeks after injury (Crowe and Swischuk 1977). Having studied sequential X-rays, Borden (1975) suggested that there may be no evidence of new bone formation for up to four weeks after injury, with follow-up X-rays showing that the unreduced bone contains the original plastic deformity. Musters and Colaris (2017) suggested that periosteal thickening may not be evident until five or six weeks after injury.

Vervaecke et al (2021) stated that the diagnostic challenges in bowing fractures of the forearm are the absence of a clear cortical defect radiographically, the fact that plastic deformity may only be visible on a strict anteroposterior or lateral view and the lack or late formation of periosteal callus. Firl and Wünsch (2004) advised that radial bowing is best determined on standardised projections taken in true lateral view, while Zhou et al (2016) emphasised the need to obtain anteroposterior and lateral views of the forearm to account for the fact that bowing may only be visible in one of these views.

Bowing of the bone causes minimal haemorrhage in the periosteum of the entire diaphysis. This leads to a late radiological finding of mild cortical broadening on the concave side of the bone without any periosteal callus, usually determined between four months and six months after injury (Sanders and Heckman 1984).

Sanders and Heckman (1984) said the incidence of plastic deformity of the lower arm in children may be higher than the number of confirmed diagnoses because many cases are only discovered during treatment for other issues affecting the forearm. Musters and Colaris (2017) suggested that the low detection of this type of injury is due not only to the difficulty of interpreting deformities on standard X- rays but also insufficient clinician awareness of the possibility of ambiguous clinical presentations.

Zhou et al (2016) emphasised that bowing fractures may be missed if X-rays are not interpreted by a specialist paediatric radiologist and if a paediatric orthopaedic specialist’s opinion is not sought. Shelmerdine et al (2022a) noted that emergency care clinicians may be less skilled than specialist paediatric radiologists in differentiating between children and adults in terms of bone appearance, bone maturation, injury pattern and injury mechanism. Atrey et al (2010) highlighted the risks incurred when bowing fractures of the forearm are undetected or misdiagnosed, including inappropriate management, ensuing long-term issues and litigation.

Using artificial intelligence to aid diagnosis

Shelmerdine et al (2022a, 2022b) suggested that using artificial intelligence (AI) tools for imaging may aid the diagnosis of bowing fractures and help prevent issues arising from undetected or misdiagnosed injuries. However, these authors noted that there is a lack of education and resources for integrating AI tools in clinical practice. To date, AI diagnostic tools have mostly been used to enhance plain radiography (Shelmerdine et al 2022a). Magnetic resonance imaging and computed tomography assisted by AI diagnostic tools have been reported as helpful but are not used regularly (Zhou et al 2016).

‘Angulation’ is a measure of the angle at the suspected fracture site and is considered adequate to describe a fracture where there are two sides. Zhou et al (2016) considered that angulation fails to provide an accurate measurement of plastic bowing deformity where there is no angular point. To try to address this, Zhou et al (2016) designed and implemented a computer-aided semi-automated method of measuring bowing fractures of the forearm in children that uses optimal thresholds to distinguish abnormal bowing from normal bowing. The researchers argued that their method can reduce manual measurement errors and create normalised data sets for statistical comparisons (Zhou et al 2016).

There is scant evidence on the use of AI tools for diagnosing forearm fractures in children. This suggests that further study and collaboration between clinical settings are required.

Management and monitoring

There appears to have been little published literature on the management of bowing fractures of the forearm in children since Borden’s (1974) influential article.

Vorlat and De Boeck (2003) noted that the management of plastic bone deformities depends on the patient’s age, the severity of bowing and the presence of other injuries. According to Vorlat and De Boeck (2003), fracture reduction should be considered in children over the age of ten years because they have less remodelling potential than younger children. They also said reduction is advised when the bowing of one long bone complicates the reduction of a fracture or dislocation in the other long bone, regardless of the child’s age.

For Vervaecke et al (2021), crucial factors in deciding how to manage bowing fractures of the forearm in children are early detection, the patient’s age and any associated injury. In the case of an initial subtle bowing fracture, Vervaecke et al (2021) suggested that conservative treatment such as an above elbow cast may be appropriate. However, they also suggested that closed fracture reduction should be considered in children over the age of ten years.

Musters and Colaris (2017) found no protocols in the literature for the treatment of plastic deformity of the forearm in children, but identified some consensus that children below the age of four years can be treated conservatively with a cast unless bowing is 20° or more, in which case fracture reduction is advisable. They found no consensus regarding children aged between four years and ten years – which is the age range at which bowing fractures of the forearm most commonly occur – with management advice ranging from conservative treatment and reduction if function is limited at presentation to reduction when bowing is 20° or more (Musters and Colaris 2017).

According to Jones et al (2022), while some studies advocate the reduction of a bowing fracture where bowing is 20° or more, most authors agree that manipulation and reduction are not necessary and that a removable splint is sufficient when bowing is less than 20°. According to Musters and Colaris (2017), all significant bowing fractures of the forearm in children accompanied by functional limitations should be reduced, but it is unclear what amount of bowing can be considered acceptable – and can therefore be entirely managed conservatively – when there is no associated loss of function.

The management of a bowing fracture of the forearm in children in the absence of any other signs and symptoms is still debated.

What is clear, however, is that patients’ progress must be closely monitored to minimise the risk of long-term complications, ensure optimal restoration of limb function and reduce negative repercussions on patients’ well-being, education and development.

Conclusion

Bowing fractures of the forearm in children are easily missed due to the ambiguities of clinical presentation and potentially due to a lack of awareness and knowledge among clinicians. Diagnostic challenges include the absence of a visible fracture line, the absence of obvious cortical defects and the absence of new bone formation in the first few weeks after injury, as well as the difficulty of interpreting plastic bowing deformities on X- rays and that these may only be visible on a strict anteroposterior or lateral view. It is important, therefore, to involve paediatric radiologists and paediatric orthopaedic specialists in the interpretation of X-rays. AI diagnostic tools may aid diagnosis but are still in their infancy. There appears to be a paucity of literature and a lack of consensus regarding the management of bowing fractures of the forearm in children, so robust and evidenced-based patient treatment protocols are needed.

References

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