Patient with previous operative treatment of a humeral fracture at the end of 2025, with plate and screw osteosynthesis in situ. In January 2026, revision surgery was performed because of a postoperative abscess/infection, followed by antibiotic treatment.
The patient subsequently developed recurrent local erythema, swelling, warmth, and pain at the operative site. Centrally within the erythematous area, there was a small white nodular elevation of the skin.
Ultrasound demonstrates extensive inflammatory change and swelling of the subcutaneous soft tissues, containing an irregularly marginated hypoechoic area.
At the site of the white cutaneous elevation, there is a focal fluid collection measuring approximately 5.8 × 5.2 × 9 mm, suspicious for a small abscess.
The abnormal hypoechoic tissue appears to extend, at its closest visible point, to approximately 7 mm from the osteosynthesis material. However, because of the irregular margins of the abnormal tissue and the technical limitations of ultrasound immediately adjacent to bone and metallic fixation material, the exact deep extent and relationship to the plate cannot be reliably determined.
Mild local hyperaemia is present on Doppler examination.
Limitations of the examination
This represents a relatively uncommon postoperative presentation in the examiner's own ultrasound practice, involving a potentially recurrent infectious process adjacent to osteosynthesis material. Diagnostic confidence in interpretation of this specific appearance is therefore lower than for more frequently encountered musculoskeletal pathology.
Ultrasound expertise is partly experience-dependent and subject to a learning curve. The number of examinations required to achieve stable competence varies according to anatomical region, pathology, and diagnostic task; there is no universally applicable evidence-based threshold of exactly 100 cases for every individual pathology. The limited personal experience with this specific postoperative presentation therefore provides an additional reason for correlation with other diagnostic modalities and specialist assessment.
1. Final diagnosis
Extensive inflammatory subcutaneous soft-tissue abnormality with a central fluid collection measuring approximately 5.8 × 5.2 × 9 mm, suspicious for abscess formation. Given the previous postoperative infection, recurrent erythema, warmth, swelling, and pain, together with the close proximity of the abnormal tissue to the fixation material, the findings raised significant concern for recurrent infection, including possible fracture-related infection.
Ultrasound could not reliably demonstrate or exclude extension of the inflammatory/infectious process to the osteosynthesis material or underlying humerus.
2. Differential diagnosis
The most clinically important consideration was recurrent fracture-related infection with superficial abscess formation. Alternative considerations included a superficial subcutaneous abscess/cellulitis without implant involvement and, less likely given the clinical presentation, a postoperative inflammatory or foreign-body reaction with associated fluid collection.
3. Teaching points
Ultrasound can identify superficial postoperative fluid collections, inflammatory soft-tissue changes, and hyperaemia and can help guide aspiration of accessible collections. However, ultrasound has important limitations when assessing the deep extent of infection immediately adjacent to cortical bone and metallic osteosynthesis material.
In a patient with previous postoperative infection and recurrent local inflammatory signs, a small superficial collection should not automatically be interpreted as an isolated superficial abscess. Deep communication with an implant may be present even when this cannot be demonstrated sonographically.
This case also illustrates the importance of explicitly communicating diagnostic uncertainty. When sonographic experience with a specific postoperative complication is limited and the consequences of missing deep implant-related infection are substantial, correlation with specialist assessment and additional imaging is appropriate.
4. Injury/disease information
Fracture-related infection may involve the soft tissues, bone, fracture site, and fixation hardware. Clinical findings such as recurrent erythema, warmth, swelling, pain, wound breakdown, or drainage should raise suspicion, particularly in a patient with a previous postoperative infection.
Specialist surgical assessment is important when fracture-related infection is suspected. Additional diagnostic evaluation may include conventional radiography, CT, and/or MRI using metal-artefact-reduction techniques, depending on the clinical question.
Ultrasound-guided aspiration may be useful when a superficial collection is accessible, but a negative aspiration or sampling of only the superficial component does not exclude deeper implant-related infection.
5. Update
Approximately one month after the ultrasound examination, the patient reported that the osteosynthesis plate had been surgically removed following a four-day hospital admission. At surgery, a fistulous tract was found extending to the plate, confirming deep communication with the osteosynthesis material. The operative region was irrigated/debrided, and the patient was subsequently treated with intravenous antibiotics in combination with oral antibiotic therapy.
The subsequent surgical findings therefore confirmed that the initially suspected infectious process was not confined to the superficial soft tissues and was consistent with a fracture-related infection involving the fixation hardware.
A CT report obtained during the subsequent work-up described the postoperative state after humeral fracture fixation with plate and screws. The fracture line remained visible at the caudomedial aspect and was sclerotically marginated. Elsewhere, there appeared to be osseous bridging/healing, although assessment was substantially limited by extensive metal-related scattering artefact despite use of a metal-artefact-reduction protocol. Prominent axillary lymph nodes were also described and considered most likely reactive.
This follow-up is an important retrospective teaching point: the initial ultrasound correctly demonstrated a superficial abscess and extensive inflammatory change but could not establish whether the process reached the osteosynthesis material. Subsequent surgery demonstrated a fistulous connection to the plate, confirming the clinical importance of maintaining a high suspicion for deeper implant-related infection when superficial inflammatory abnormalities occur in this postoperative setting.
Marc is founder of, and trainer at, SonoSkills. SonoSkills is an organization dedicated to MSK ultrasound education. He's also an MSK Sonographer at EchoConsult in Roermond, the Netherlands.
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