Elastic stable intramedullary nailing (ESIN) has become the method of choice for internal fixation of femoral and tibial shaft fractures in children of 4-14 years of age. In the lower extremity, ESIN treatment may be complicated by loss of reduction following push-out of the nails at the entry site, especially in unstable femoral shaft fractures. The rate of this complication nail migration with subsequent soft-tissue and skin irritation was reported to be as high as 5-12% until end caps (which lock the nails at the entry point) became available. The use of end caps avoids postoperative instability, even in heavier, older patients with unstable fracture types. To maximize stability of ESIN-instrumented unstable fractures, end caps require properly placed nails that are correctly bent. It is essential to cut the nails to a correct length at the entry site to ensure adequate anchoring of the nails in the caps and anchoring of the cap in the cortical bone respectively. The end caps are equipped with a self-cutting device and are put over the cut ends of the nails like a hollow screw that is fixed in the cortical bone at the nail entry site. A special bevelled impactor is mandatory for the final nail positioning. The position of the nail inside the end cap can easily be visualized since the caps are semi-radiolucent. The end caps also protect the soft tissues from the cut nail ends, and improve retrieval because the cap facilitates nail placement and creates a space around the nail ends for the extraction pliers. Only one small, extra instrument, the driver for the caps, is required.

Following the positive experiences with the end caps, there is also a need for small end caps. On the one hand there has been a request for a safer and more comfortable stabilization of clavicle fractures, on the other hand there has been a request for a safer stabilization of problematic forearm fractures in older children.

Biomechanical studies performed by the AO Foundation show that end caps increase the push-out force six times over that of conventionally inserted nails. A clinical study run by the Department of Pediatric Surgery  in Bern demonstrated the clinical efficacy.