Clavicle fractures are common and usually heal well without surgery. Most patients recover full shoulder function within a few weeks with conservative treatment, which is the standard in Denmark. However, in cases where the broken ends of the bone do not touch (displaced fractures), there is a higher risk of complications like non-healing (non-union), affecting 11-18% of such cases. Non-union can lead to long-term pain, reduced shoulder function, and a longer recovery time, often requiring multiple follow-up visits.

While surgery might prevent these complications for some patients, operating on all displaced fractures would lead to overtreatment. The current challenge is identifying which patients are at risk for non-union and would benefit most from surgery. This study aims to investigate the risk factors for non-union in patients with displaced clavicle fractures by examining both patient characteristics and fracture-related factors.

The goal is to use multiple data points to develop a score that can support clinicians and patients in shared decision-making regarding the optimal and individualized treatment for clavicle fractures.

This research is important not only for clavicle fractures but also for understanding and treating non-union in other bones like the ulna and tibia, which face similar challenges.

Clavicle fracture The clavicle, the collarbone, connects the arm to the axial skeleton. It is essential to shoulder function as it provides attachment for the primary muscles stabilizing the shoulder joint, and allows an extensive range of motion by the upper limb.

The clavicle fracture is a common skeletal injury that accounts for approximately 5% of all adult fractures and 35-40% of injuries to the shoulder girdle. According to extensive epidemiological studies, the majority of clavicle fractures occur in the middle third, with 50-70% of those being displaced. It means that for every 100 clavicle fractures, approximately half of them are displaced midshaft fractures.

A clavicle fracture is frequently caused by a direct impact to the shoulder, often resulting from same-level falls, bicycle accidents, or sports-related incidents, which makes it a common fracture in Denmark. There is a classic bimodal distribution of the fracture with increased incidence in younger males, usually due to high-energy trauma, and a second peak in the elderly population often associated with low-energy falls. According to the Danish Health Data Authority, the incidence of clavicle fractures is relatively high, approximately 65/100,000 from 1996-2018, and numbers have been increasing throughout the years.

Most clavicle fractures heal uneventfully and are traditionally treated non-operatively with immobilization in an arm sling for a few weeks, typically attaining full recovery and range of motion within six weeks.

Clavicle non-union Fracture non-union is a rare but severe complication that affects 5-10% of all fractures worldwide, depending on fracture location and country. The risk of non-union is higher when the fracture is displaced and bone ends shift out of their normal alignment, especially in the clavicle, which has one of the highest rates of non-union. Non-union can cause long-term pain, physical disability, reduced quality of life, and an extended recovery period before returning to regular work productivity. Often a non-union requires later complex operative treatment.

Although the incidence of non-union in the clavicle is approximately 10%, performing surgery on all displaced clavicle fractures would lead to overtreatment of fractures that would have healed uneventfully without surgery. Therefore, it is essential to identify patients predisposed to non-union and the risk factors involved to personalize the initial treatment. However, it is a major clinical challenge to identify these patients.

Recent studies on clavicle fractures have focused on comparing the outcomes of non-operative and operative treatment. Despite various randomized controlled trials, a Cochrane review from 2019 concluded that there is limited evidence for choosing one treatment over the other and that the choice of care must be determined on an individual patient basis.

Risk factors Various studies have examined the predictors associated with non-union, and many have found it to be a multifactorial issue. The degree of displacement, or the distance between bone ends, is usually the most significant factor in predicting non-union. Other risk factors include female gender, older age, smoking, persistent pain, fracture comminution, fracture shortening, and absence of developing bridging callus at the fracture site. Typically, the more risk factors present, the greater the risk of non-union. When evaluating patient-related factors, studies usually look at factors related to the host's physiological state, including gender, age, comorbidities, smoking and alcohol status, weight, BMI, and occupation. To cover patient-related factors, it is also necessary to assess the patient's molecular environment, meaning biomarkers for bone health to be found in the blood.

Rationale Research exploring risk factors that predispose patients to the development of symptomatic non-union of clavicle fractures is lacking. Before treatment can be individualized, clinical studies assessing possible risk factors are needed to fill this knowledge gap.

Hypothesis Patients suffering a displaced midshaft clavicle fracture are not at equal risk of development of non-union following conservative treatment.

10% is expected to develop a non-union within 6 months following the injury and the investigators expect to uncover specific clinical, radiological and molecular risk factors for non-union.

Purpose

Overall aim:

The purpose of this study is to identify risk factors for the development of non-union following a displaced midshaft clavicle fracture. The investigators aim to combine clinical, radiological, and molecular risk factors for the establishment of a predictive risk score that may help to assess individual susceptibility to non-union. A risk score combining all aspects will be a practical tool to aid clinicians in identifying and managing patients with increased risk of non-union at the time of initial presentation. This enables individualized treatment and a chance to improve overall outcome for the patient.

Inclusion Criteria:

• 18 years of age upon study enrollment
• Admitted to the emergency room (ER) at BBH or HVH with a displaced midshaft clavicle fracture
• Danish social security number
• Understand Danish
• Able to fill out questionnaire by hand or online.
• Provides informed consent prior to initiation of any study-related activities/procedures

Exclusion Criteria:

• Subject incapable of understanding the patient information or unable to provide informed consent
• Open fracture or fracture with risk of skin penetration
• Pathological fracture
• Clavicle fracture due to polytrauma
• Floating shoulder injury
• Vascular injury at fracture site
• Pregnancy

Patients at age 18 years or above with a displaced midshaft clavicle fracture in the are of Bispebjerg Hospital and Hvidovre Hospital.

Not allowed due to study approval from national ethics comite.