1 Bent vs straight nails topenlarge
Interference with the rotator cuff footprint
The entry point for a bent nail may go through the bony attachment of the rotator cuff. This bony defect in the footprint cannot be reconstructed later.
The entry point for a straight nail lies under the rotator cuff so the nail is inserted through the rotator cuff. This requires an incision, which should be made in the line of the tendon fibers which can then be closed effectively by a side to side suture.
Fixation in osteoporotic bone, fifth anchoring point
Due to the bone density in osteopenic bone straight nails provide a better fixation in the proximal humerus in the region of their entry point. Bent nails run through the greater tuberosity which has a lower bone density compared to the superior humeral head.
Interference with fracture lines
In proximal humeral fractures which consist of a fracture of the greater tuberosity the trajectory of bent nails often passes through the fracture line between the greater tuberosity and the humeral head whereas straight nails penetrate the humeral head medial to the fracture line.
Fixation pattern of screws
Straight nails run more medial in the axis of the medullary cavity. Therefore, it is possible to perform a direct fixation of the lesser tuberosity through the nail.
2 Principles topenlarge
Correct nail entry point
A precise entry point of the humeral nail is crucial. An incorrect entry site results in malreduction of the metaphyseal fracture.
It might be difficult or even not possible to access the correct entry point if the humeral head is displaced severely into a varus position. Therefore, it is strongly recommended to expose the entry point by manipulating the humeral head. K-wire “joy-sticks” (as illustrated) or sutures through the rotator cuff insertions can be used to achieve this.
Reduction of the metaphyseal fracture component
If the entry point has been chosen correctly, insertion of the nail will help reduce the fracture.
Protection of axillary nerve
The main structure at risk is the axillary nerve. The axillary nerve should be protected by limiting the incision to less than 5 cm distal to the acromial edge, by palpating the nerve, and by avoiding maneuvers that stretch the nerve during reduction and fixation.
In addition, any suspicious screw trajectory should be made to the bone with blunt dissection and checked with finger palpation if necessary.
Remember the course of the nerve when placing the distal screws.
An anterolateral incision is recommended for nailing of proximal humeral fractures. The need for additional access depends upon fracture type.
3 Reduction of humeral head topenlarge
Before opening the humeral entry point reduce the humeral head. A “joy-stick” technique, as illustrated, is helpful.
Alternatively, or in addition one can use stay sutures through the tendon of the rotator cuff in order to manipulate the humeral head.
4 Determination of entry point and opening of the canal topenlarge
Determination of entry point
The nail insertion site is located at the bone-cartilage junction of the humeral head. It is not lateral to the greater tuberosity. It is slightly anterior to the center of the greater tuberosity.
Be aware, that the correct entry point depends on the type and design of nail used.
A supraspinatus split may be necessary.
Insert a K-wire through the correct entry point and confirm proper placement by image intensification.
Open the humerus
A cannulated awl is recommended for opening the proximal humerus. This awl can be inserted over the previously placed guide wire. It should be advanced into the proximal medullary canal.
5 Nail insertion topenlarge
Mount nail on insertion handle
The humeral nail is mounted on an insertion handle. The nail must be rotated correctly relative to the insertion handle.
If an angled nail is used (as illustrated) ensure that the apex of the nail curvature points away from the insertion handle.
Insert nail and reduce fracture
Insert the nail with slightly rotating movements down to the metaphyseal fracture line. Pass the fracture zone under image intensification and make sure that the nail enters the distal fragment properly.
Make sure the proximal end of the nail is placed beneath the bony surface of the humeral head.
No protrusion of the nail may be tolerated. Confirm with appropriately oriented C-arm images that the nail is below the bone.
Depending upon the selected humeral nail, different preoperative planning is necessary for its locking devices.
Retrotorsion of locking device
In order to lock the nail in the correct trajectory, mount the aiming arm and swivel it approximately 25° anteriorly in order to follow the retroverted axis of the humeral head. (Due to the physiological retrotorsion of the humeral head, the axis of the humeral head is directed approximately 25° posteriorly to the condylar plane of the distal humerus.)
To obtain a true AP view of the proximal humerus, the forearm has to be rotated approximately 25° externally relative to the sagittal plane.
Within the humeral head, the spiral blade should be placed at the transition of the middle to the lower third, slightly below the equator.
Mount aiming device and insert trocar combination
Mount the aiming device in the insertion handle. Confirm that the retroversion angle is correct. Make a skin incision for the aiming device, dissect the muscles bluntly down to the bone, and fully insert the trocar.
Insert guide wire
Check once more the retrotorsion of the handle.
Remove the central trocar and drill the guide wire for the spiral blade onto the medial cortex of the humeral head.
The position of the guide wire should be checked under image intensification.
Take care not to perforate the humeral head in order not to insert a too long spiral blade.
Determine length of spiral blade
Determine the correct length of the spiral blade with the appropriate depth gauge.
Open the lateral cortex
Perforate the lateral cortex with the appropriate cannulated drill.
Insert spiral blade
Attach the spiral blade to the inserter and introduce both over the guide wire.
Align the handle of the inserter parallel to the aiming arm.
The initial rotation of the T-handle of the spiral blade inserter relative to the aiming arm depends on patient anatomy. If the distance from the lateral cortex to the nail is less than 10 mm, start the inserter slightly clockwise from parallel. If the distance from the lateral cortex to the nail is more than 10 mm, start the T-handle slightly counter-clockwise from parallel.
By applying light controlled hammer blows to the connecting screw, advance the spiral blade to the desired depth. This causes the handle to rotate 90°.
Monitor the depth of the spiral blade with image intensification. If attaching sutures to the spiral blade, pause when the spiral blade is approximately 1.5 cm to 2.0 cm short of its intended position so that the suture ends can be placed through the appropriate holes in the base blade.
Check position of spiral blade
Check the position of the spiral blade by image intensification.
Pitfall: If the nail has locking screws that might pass through the bicipital groove, be careful that they do not trap the biceps tendon.
Insertion of additional head screw
If necessary, an additional 4.0 mm screw can be inserted in the inferior quarter of the humeral head.
Drill and determine length of locking screw
For distal locking, insert the two-piece trocar combination (aiming arm). Through an appropriately placed trocar, drill through both humeral cortices until the bit just breaks through the medial cortex and read the depth from the drill bit. Alternatively, a depth gauge can be used.
Insert a locking screw through the trocar. A second screw is recommended, especially in osteoporotic bone.
Pearl: Make one incision large enough to allow palpation of the axillary nerve.
Insert the end cap
The end cap prevents tissue from plugging the inner thread of the nail. Furthermore, it offers the option of angular stability, by compressing the spiral blade.
End caps are available in different sizes and can, if necessary, be used to extend the nail. The top of the end cap must not protrude above the surface of the bone.
Repair rotator cuff
Suture the supraspinatus split.