Basic principles of intermedullary nailing

1. Introduction

An intramedullary nail provides the strongest mechanical fixation of any shaft fracture.

There may be practical (eg. existing hardware) or biological reasons (eg. soft tissue concerns) why other methods would be chosen.

Nailing may be performed antegrade (proximal to distal) or retrograde (distal to proximal)

Angular stability

A shaft fracture may be displaced in a variety of ways. An intramedullary nail restores axial alignment and prevents angulation.

Angular stability

Rotational stability

Without locking, an IM nail may not provide rotational control in a simple two-part fracture.

Rotational stability

The fracture plane or interdigitation of the fragments may provide some rotational control, but it is usually more reliable to use proximal and distal locking.

Longitudinal stability (shortening)

In a multifragmentary fracture there will be a tendency for a nail to telescope within the fragments and this must be prevented with locking.

Longitudinal stability

2. Nail entry point

The ideal entry point obviously varies according to the bone but is also influenced by the design of the nail. It can be estimated from the X-rays by extrapolating the axis of the medullary canal backwards.

Once the entry point has been chosen, the entry point is opened with an awl or a drill. In some systems, these may be cannulated.

Opening of medullary canal

3. Insertion of guide wires

Most IM nails are inserted over a guide wire.

Reaming is always performed over a guide wire.

The guide wire is inserted under X-ray control.

Insertion of guide wires

In order to facilitate passing the guide wire across the fracture site, the fracture should be adequately aligned. It may be easier to pass the guide wire if the tip is angulated.

Guide wire passing fracture zone

If the fracture ends cannot be sufficiently aligned for a guide wire to passed, an aiming device may be inserted into the proximal fragment (after reaming if necessary) to manipulate the proximal fragment so that the guide wire can be passed into the distal fragment.

Alternatively, a limited open reduction may be required.

In some cases, there may be soft tissue interposition which prevents reduction. This may require open reduction.

Use of aiming device to aid reduction adequate for guide wire to pass fracture site

An olive tipped guide wire is used for reaming, so that the reamer tip may be extracted if the driveshaft breaks.

Use of olive tip guide wire

4. Reaming

If the medullary canal is narrow, it may be necessary to enlarge the canal by reaming to allow the insertion of a larger diameter nail with sufficient strength.

Reaming also increases the length of contact between the nail and the endosteal surface of the bone at the isthmus.

Although reaming may damage the endosteal blood flow, in practice the periosteal blood supply is still sufficient for fracture healing.

The position of the reamer can be checked intermittently under X-ray control.

Reaming generates heat, particularly if the reamers are blunt, so it is important not to apply excessive force whilst reaming. (A tourniquet should not be used in tibial nailing as blood flow cools the bone during reaming.)

The initial reamers will be removing cancellous bone, so they pass relatively easily. As the diameter of reamer heads increases, they start making contact with the endosteal surface of the cortex; a change in the reaming sound can be heard (chatter) and more resistance can be felt.

Reaming

5. Determination of nail length and diameter

It is helpful to perform preoperative planning. In multifragmentary fractures, or in open fractures with bone loss, preoperative planning on the uninjured leg is more accurate. In bilateral fractures, the less comminuted side should be used to determine the length and diameter of the nail.

Determination of nail lenght

Determination of length using second guide wire

The correct length of the nail is determined by comparing a second guide wire of the same length to the one that has been inserted.

The correct placement of the guide wire in the distal canal should be assessed via image intensifier.

The tip of the second guide wire must be positioned at the entry point in the bone.

Determination of length using second guide wire

Determination of length using second guide wire

Alternatively, a radiographic ruler may be used.

The tip of the ruler should be positioned where the tip of the nail is intended to lie. Nail length is determined by the position of nail entry point.

Determination of length using second guide wire

Determination of diameter

The diameter may be determined from the size of the last reamer used. Alternatively, the radiographic ruler may be used. It is important to measure the medullary diameter at the mid portion of the bone, which represents the narrowest segment of the medullary canal.

The inner cortical edge should touch with the inner numbered disk of the ruler aperture. In the illustration an inner cortical diameter of 14 mm is shown.

Determination of diameter

6. Nail insertion

It may be necessary to exchange the olive tipped wire for a straight guide wire in order to pass the nail.

An appropriately sized nail is mounted on the introduction handle, which normally incorporates the guides for proximal locking.

If the nailing system has different implants for left and right sides, ensure the correct side has been selected, and the introducer has been assembled correctly to ensure proper positioning of the nail.

Mounting of nail on introduction handle

If a guide wire has been used, slide the nail over the guide wire and introduce it into the bone. Ideally the nail can be pushed down with twisting movements, but in practice some hammering may be needed.

The nail is inserted under X-ray control, with particular care being taken as the tip of the nail negotiates the fracture site.

Care must be taken not to create a fracture particularly in osteoporotic bone.

Nail insertion

Make sure the nail is fully seated in the planned position. Depending on the bone and the nail, the position may be determined by the planned screw insertion, eg into the femoral or humeral head.

In general the top of the nail should be flush with or lie just under the surface of the bone.

Nail fully inserted

Pearl: When performing prophylactic nailing in patients with impending pathological fractures, particular care must be taken when inserting the nail as the bone may be more curved than the nail which is being inserted.

This may result in an iatrogenic fracture at the site of the metastasis, or the tip of the nail may break through the cortex distally.

This risk may be reduced by increasing the difference between the size of the last reamer and the nail diameter.

7. Locking

The guide wire must be removed before locking can be started.

Removal of guide wire

Proximal locking

Proximal locking is normally performed using a guide attached to the nail.

Proximal locking

Distal locking

As the nail has a tendency to deform slightly as it is inserted, guides attached to the proximal end are not accurate enough for distal locking.

Distal locking is usually performed under X-ray control.

Distal locking

Displacemnet

In more proximal or distal fractures, as the metaphysis does not provide much support for the nail, there is a tendency for angular displacement.

Angular displacement of nail tip

If only parallel screws are used for locking, a small metaphyseal segment may still displace along the screw axis.

Displacement along screw axis of parallel screws

Screws should be inserted in different axes, if the design of the nail allows.

Insertion of screws in different axis

Alternatively, blocking screws (Poller) may be used adjacent to the nail.

The position of the blocking screws is dictated by the anticipated direction of displacement, which can be predicted from the fracture configuration.

Poller screws

8. Nail cap

Most modern nailing systems have nail caps. These helps reduce bony ingrowth into the nail. If the top of the nail is seated well below the surface of the bone, a longer end-cap, if available, should be used, as this would require less bone removal to find the end cap if the nail is subsequently removed.

Insertion of nail cap

9. Nail removal

It is not generally necessary to remove IM nails unless patients are symptomatic.

Unless there is an indication for urgent removal of the nail, it should not be removed until the fracture has definitely united.

Remove any bone that has grown over the top of the nail with an osteotome. It may be helpful to have imaging available for this.

Removal of bone covering endcap

Any end cap is removed prior to attachment of the extraction device.

Removal of endcap

The extraction device should be attached first, before removing the locking screws.

Attachment of extraction device

Locking screws are then removed and the nail extracted.

Removal of locking screws and nail removal

10. Removal of broken nail

Various techniques have been described for removal of broken nails.

Specific instruments have been developed for broken nail removal.

If such instruments are not available, the following simple technique using guide wires can be employed.

If the nail is hollow, remove all locking screws but do not remove the proximal fragment.

Broken nail

It should be possible to pass an olive tipped guide wire down to and through the nail tip.

Insertion of olive tipped guide wire

One or more straight guide wires are then also passed out through the tip of the nail. This should block the olive from entering back into the nail.

Some trial and error may be needed to determine the correct size of olive.

Insertion of additional straight guide wires

Once the olive is blocked, a T-handle chuck may be attached to the olive guide wire and the nail backed out using a hammer.

Removal of broke