Implant migration or hardware migration refers to the displacement of an implant or component away from its designated position and is associated with hardware failure and loosening. Examples of implant migration include screw break out or screw back out, cage extrusion, inlay extrusion, choledochal stent migration and intrapelvic cup migration.
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Epidemiology
The frequency of implant and hardware migration various significantly with the type of implant.
Risk factors
Predisposing factors for implant migration include 1-3:
- implant malposition
- imbalance of tissue tension
- improper anchorage or suboptimal implant design
Clinical presentation
Clinical signs and symptoms depend on the type and location of the implant as well as the associated complications and might range from absence to severe pain and/or shock.
Complications
Complications of implant migration highly depend on the implant and its location and include 4:
- hemorrhage
- neurovascular injury
- thrombosis or embolism
- adjacent organ injury
Pathology
Etiology
Implant migration can be caused by altered local biomechanics including 2,5:
- hardware failure
- septic and/or aseptic loosening
- tumor recurrence
Radiographic features
Plain radiograph
Plain radiographs are the first-line imaging modality for assessing implanted hardware and detecting deviations from its expected position 5. Serial radiographs can help in the differentiation from primary implant malposition.
CT
CT can accurately characterize implant position in various locations also with respect to the adjacent structures. It can also delineate associated complications 2.
MRI
MRI can localize and evaluate non-metallic implants and associated complications.
Radiology report
The radiological report should include a description of the following:
- implant position
- associated complications if present
- hardware failure
- neurovascular injury
- associated organ injury
Treatment and prognosis
Management depends on the presence and risk of further complications and includes watchful waiting, removal or revision1.
Differential diagnosis
The main differential diagnosis of implant migration include the following 1: