The surgical procedure as intented by the manufacturer is described as following [1]. Some different hints are given: After correction of the deformity and preparing the bone channel the K-wire, that guides the reamer, hast o be removed from the bone channel. With a second K-wire and a ruler it is possible to do a direct measurement of the hole implant length. Be sure to have a x-ray by C-arm that shows the distal end oft the K-wire in the phyis and not penetrating the joint. Measure the length to the edge of the bone at proximal tibia, femur, humerus or wherever your surgical approach and bone entry is. Now you can notice the maximum length of the whole implant. That means the combination of male and female nail part.
Then - in the common description - the K-wire is removed and the male solid nail is placed in the male driver, making sure that the wings of the male solid nail are fitted into the male driver slot.
The male drivers have the possibility to lock the male component to facilitate maneuvering the nail upon insertion. After insertion of male nail part in the male driver, simply an eccentric ring has to be turned to the lock position.
Then the male solid nail is pushed and threaded down the bone and screwed into the distal epiphysis. For simplification this step can be missed. The same procedure can be done with a solid combination of male and femal part with usage of the canulated female nail driver. But in this way, no positive locking between the arrows of male nail part and the tube of the female nail does exist. The thread of the male part cannot be screwed in the distal physis, it only can be pushed in the distal physis.
The method changing development has to be performed on the table meanwhile the individual preparation of the female nail part. The female part has to be cutted to desired length. The lengths with overlapping with the male part should be as long as anatomical reasonable. The system is, that the rod should telescope for a long time during growth without disconnecting. If the goal of preparing an individual implant is, to cut it as long as for anatomical reasons possible, than it is easy to cut it to a exaclty measured length. This can be arranged with two K-wires and a ruler as desribed above.
Figure 1 shows, how to cut a U-shaped groove in the distal female nail part. This slot has be as long as the arrows of the male nail part. This is about 4-5mm. The edges have to be deburred exactly to avoid jammed telescoping. Figure 2 shows the result. If the slot is too long, the edges of the slotted distal female part could be demaged thru insertion or they could bend. An overlapping of slot an arrows for at least 4-5mm is enough time for a normal bone healing time of 6-8 weeks. After bony consolidation a antirotational mechanism is no longer needed. Figure 3 shows the nail ready to implant with distal antirotational positive locking fitting arrows in slot. Please test smooth telescoping on table before implantation as shown in the video in supplementary material.
Avoid proximal ride out of the male part in the threaded head of the female part, if you intend to lock the nail in the proximal physis in the next step.
The male nail parts have a distal locking hole for a 1.0mm K-Wire. This is challenging to an unexperienced user. But the locking hole makes sense and should be used to avoid penetration of the distal end into the joint. With a lateral exactly positioned C-arm and the magnifying glass, one can use a 2.0 or 2.7 mm drill to drill a hole in freehand technique in exactly overlapping with the maximum round nail hole. It is much easier to come from a great hole to a narrow hole with a thin wire then to navigate it in two similar narrow holes. If you have a threaded 1.0mm K-wire, use it. Figure 4 shows the result of distal locking in an implanted nail. Verify under fluoroscope that the distal thread is not positioned in the growth plate otherwise normal growth may be affected [1]. If there is not enough space as in a lot of tibial cases in OI or CPT, lock the distal end of the male part proximally above the physis in the metaphyseal bone as shown in Figure 4 at the end of a rod changing procedure due to affection of the physis with lack of telescoping. This leads to reduced telescoping effect (only proximal growing of the tibia leads to telescoping) but is mile better than fixation of the physis by screw or K-wires or penetrating the joint.
If the surgeon likes to have a second proximal locking option, it is possible to create a full locked rotational stable nail. Simple use your sterile single use stainless steel drill from metal- removal rescue set. Sterile metal drills can be ordered by many distributants and manufacturers worldwide. We have good experience with the 2.7mm metal drill bit for stainless steel from DePuy Synthes Inc. with a Synthes-Connector for accu machines.
Use the cut block from the high speed cutter to fix the femal nail tight. Then drill the proximal locking hole exactly between the distal two threads of the screwed head. You want to use it in a safe zone, with a perpendicular K-wire that should lock the nail but not penetrate the proximal physis or the joint (if implanted in the tibia). Figure 5 shows the final result after locking the implant proximal with a 2.0mm K-wire.
If you want to remove the implant for any reasons or pull it back a few millimeter before proximal locking, use a needle holder. The original FD nail instruments have no coupling between implant and female nail drivers and no mechanism of sleeve and soul or any other fixation for pulling out the nail.