A polymeric catheter that comes out in two pieces raises one immediate clinical question and several forensic ones. The clinical question, where the rest of it went, is usually answered by imaging within hours. The forensic questions take longer: whether separation began at a manufacturing flaw, whether the polymer had lost its properties, whether the line was compressed at a fixed point, whether a clamp or instrument cut it, or whether it was pulled apart against resistance. Those mechanisms leave different marks on the same few square millimetres of surface, and that surface survives only if nobody trims it.
What the break is asked to distinguish
Catheter separation is not one failure mode. It is a family of mechanisms that all end in two pieces: a defect present at manufacture, a polymer degraded in service, repeated flexing at a compressed point, a crush or cut from a clamp or instrument, and straightforward overload during placement or removal. Fracture analysis does not begin by choosing among them. It begins by describing the surface in enough detail that most of the list stops fitting.
Single-event overload versus progressive cracking
A polymer pulled past its tensile limit in one event usually shows drawing: local thinning, elongated features, and a surface that crosses the wall in a single pass. It reflects a force applied once that exceeded what the material could carry.
Progressive fracture looks different. It advances a little at a time under repeated loading, leaving a flatter region with arrest markings that fan out from where cracking started, then a final ligament that tore quickly once too little wall remained. Under scanning electron microscopy the distinction is generally legible, and it separates one mishandled moment from weeks of cyclic loading nobody observed.
Where a manufacturing flaw announces itself
Cracks start somewhere, and at magnification the origin is often a discrete feature: a void or inclusion in the wall, a weld line or gate artifact from extrusion or moulding, or an abrupt transition at a bonded hub or a radiopaque stripe. A feature of that kind concentrates stress and lets a crack begin at a load the design should have tolerated. Dimensional work then matters as much as microscopy: wall thickness, concentricity and lumen geometry measured against the drawing tolerance and against exemplars from the same or a nearby lot.
Compression at a fixed anatomical point
Some fractures are located by anatomy rather than caused by the device. Pinch-off, the compression of a central venous catheter in the costoclavicular space, is the recognised example: the catheter is squeezed between clavicle and first rib and flexed with shoulder movement until it cracks. What identifies it is not the fracture alone but a coincidence: a fracture position mapping to that anatomy, imaging showing the catheter's course through the space, and a surface consistent with repeated loading rather than a single pull.
Kinking as a precursor, not only an occlusion
A kink is usually discussed as a flow problem, and it is one. It is also a mechanical history written into the wall. Tubing held in a tight bend by dressing, securement or patient position accumulates a permanent crease, and that crease is where the wall is thinnest and most stressed. Kink-radius and flow testing on exemplar tubing, run in the documented placement geometry, shows whether the bend fell inside what the device tolerates.
Clamp, suture and instrument damage
Not every separation is a fracture. A slide clamp closed on the wrong segment, a securing suture tied over the tube, an introducer needle, or scissors during a dressing change each leave a cut or crush signature: straight edges, a shear plane, or a partial notch that later opened under ordinary tension. These are often the most legible marks on a device, and also the ones most easily obliterated when the specimen is handled with instruments after retrieval.
Insertion and withdrawal forces
Devices are also simply pulled apart. Resistance during removal, from adhesion, a fibrin sheath, an overlying suture or a retention feature that did not release, converts a routine withdrawal into a tensile test. ISO 10555 sets general requirements for sterile single-use intravascular catheters, including tensile performance, and testing exemplars establishes what the device should have withstood. The clinical record establishes what it was asked to withstand. Where the two sit close together, the question shifts from whether force was excessive to how thin the design margin was.
The fragment, the mate and the timeline
A retained fragment is both the injury and the best evidence available. Confirming it came from this catheter means matching cross-section, wall thickness, lumen configuration and any radiopaque striping to the remaining length, then confirming that the two fracture surfaces mate. Radiopacity itself is a specified property, with test methods described in ASTM F640, and a fragment that images poorly is a finding rather than an absence of one.
Imaging locates the fragment, insertion and line-care records bound how long the device was in place, and together they distinguish a fracture at placement from one that developed over weeks.
Where these opinions are challenged
Predictably: that the fracture surface was examined after the device had been cut, flushed or stored against other hardware; that no exemplar of the same configuration or lot was tested; and that the mechanism was inferred from the clinical narrative rather than read off the specimen. Work that photographs the device as received, states what was measured against which specification, and says plainly which mechanisms the surface cannot exclude tends to survive that scrutiny.
This article is general technical orientation, not a failure analysis, an engineering opinion, or advice on any specific matter. Determining the cause of a particular incident requires hands-on examination by a credentialed expert.