The results of operative treatment of ununited diaphyseal fractures of the humerus are worse after prior intramedullary rod fixation than after prior nonoperative treatment or plate and screw fixation. 16 This could reflect the damage to the rotator cuff that occurs with anterograde insertion of an intramedullary implant, damage to the shoulder if the implant extrudes from the proximal humerus, and bone loss related to motion of a loose intramedullary implant.
An additional factor could be the damage that the proximal humerus and rotator cuff sustain when the rod is removed. If the rod is properly sunk below the cortex, it can be difficult to find and retrieve. In many cases, a large amount of bone must be removed. The rotator cuff also incurs damage during this process.
Sometimes the intramedullary device is firmly fixed in the distal fracture fragment. Forceful attempts to remove it, particularly when the bone is osteopenic, could cause additional fractures.
The advent of the locking compression plate (Synthes, Paoli, PA) has improved internal fixation of osteopenic bone by virtue of the fact that the screws can thread into and lock to the plate, creating a fixed-angle device that could provide improved fixation osteoporotic bone. The locking compression plate could also provide improved fixation in situations in which many of the screws must be unicortical such as the application of a plate to a bone with an intramedullary implant. We describe the use of the locking compression plate for ununited fractures of the humeral diaphysis without removing an intramedullary implant.
The development of the locking compression plate reflects both attempts to improve fixation of osteopenic bone as well as changing concepts in internal fixation fractures. Techniques for improving plate and screw fixation of osteopenic bone have included cement augmentation of screws, 1,6,18,19,24,25,27 application of a strut of cortical bone (either intramedullary or the cortex opposite the plate) to enhance screw fixation, 3–5,11,26 endosteal substitution (the use of a second intramedullary plate), 8,15 exchanging loose 4.5-mm cortical screws with a deeper threaded 6.5-mm cancellous screwm 21 and the use of blade plates. 2,12,13,22
Mast expanded the concept of fixed-angle internal fixation devices such as the blade plate to alter the function of standard screws. His Schuhli nuts convert standard screws to screws that lock rigidly to the plate, making each screw a fixed-angle blade. 14,23 The Schuhli nut has spikes that engages the bone to improve plate-bone friction. The nuts are placed underneath the plate so that the plate stands away from the bone. Some have likened this to an internal external fixator. It is necessary to use small washers with the screws to ensure that the screw threads engage the Schuhli nut, because standard screws have a threadless area adjacent to the screw head. Use of the Schuhli nut requires anticipation of poor-quality bone and meticulous preoperative planning. A preliminary construct must be constructed and applied with the Schuli nuts held in place by plastic screws. When the construct is in place, standard screws are drilled and placed. The technique greatly enhances fixation of osteoporotic bone 20 but is tedious and demanding and adds several additional steps to the surgery.
This type of locking screw was incorporated in the point-contact fixator (PC-Fix), which represents a new concept in internal fixation emphasizing the biologic aspects of fracture healing. 7 In the PC-Fix, plate-bone contact is limited to sharp points with the undersurface of the plate resembling the roof of a gothic cathedral. The screws initially locked to the plate through an interlocking taper. Later designs used thread screw heads that engaged a threaded plate hole. These locked screws were inserted unicortically to avoid injury to the endosteal blood supply. The mechanical advantages of having the screws lock to the plate made up for the diminished strength associated with the use of unicortical screws.
LOCKING COMPRESSION PLATE
The locking compression plate incorporates the option of threaded screw holes into a standard bone plate. The standard dynamic compression unit plate hole has been replaced by a figure-of eight screw hole with a threaded hole on one end and an oval dynamic compression unit on the other. This avoids the detailed planning and additional operative steps associated with the Schuhli nuts. If osteoporosis sufficient to compromise screw engagement was not anticipated, the surgeon can easily switch to a screw fixed rigidly to the plate. All of the functions of a standard dynamic compression plate are retained.
The locking screws have threads on the head of the screw that engage the plate. The locking screws are slightly larger (5.0-mm diameter) and have more shallow threads (large core diameter) as compared with standard 4.5-mm cortical screws.
When applying a plate over an intramedullary implant, unicortical locking screws can be inserted when it is not possible to drill a bicortical screw. The option of using either a locked or standard screw is useful in this situation because each patient is unique and the screws can be inserted to gain optimal fixation (Fig. 1).
If the intramedullary implant protrudes from the proximal humerus, it should be removed. If a prominent nail cannot be safely removed, it should be trimmed so that it does not affect shoulder function.
The anterolateral exposure of Henry 10 is used for nonunions involving the middle and proximal thirds of the humerus, and a modified posterior exposure without splitting the triceps is used for distal third fractures. 9,17 An attempt is made to limit elevation of periosteum and muscle from bone. The plate is placed extraperiosteally.
The nonunion site is entered and debrided of synovial membrane, fibrous tissue, and any interposed muscle. The sclerotic fracture surfaces are debrided and opened so that bleeding bone is exposed. An attempt is made to realign the fracture and close the fracture gap, although this is often difficult when there is an intramedullary implant. In some cases with oblique fracture lines, an interfragmentary compression screw can be applied between the fragments. The plate is contoured to fit over the often-irregular bone surface. If there is an absolute bony defect, the plate can be contoured to stand away from the bone at the fracture site, the so-called wave plate osteosynthesis. 20
The technique for plate application differs slightly from standard plates. Locking screws require precise engagement of the screw threads with the plate threads. This is achieved by drilling the screw tract through a drill guide that threads into the screw hole in the plate.
Locking screws do not bring the plate to the bone. Plate-bone contact is not as important for a locking compression plate as for standard compression plates (Fig. 2). The diminished contact could even increase the blood supply to the bone and enhance the biologic aspects of healing.
Some plate-bone contact is useful to ensure fracture alignment and diminish the prominence of the implant. Plate-bone contact can be achieved by using a few standard screws to bring the plate to the bone. Alternatively, there is a device that drills into the bone and can be used to bring the plate to the bone (the so-called pull reduction instrument, commonly referred to in the United States as a “whirligig”).
Screws are placed bicortically when possible (standard screws are directed to either side of the intramedullary implant when the bone is of adequate quality and thickness) and unicortically otherwise.
We have used the locking compression plate to repair ununited fractures of the diaphyseal humerus without removing an intramedullary device in several patients. In a combined series with Marti, one of the authors (JBJ) reported on the use of this technique in 6 patients with nonunion of the humeral diaphysis after intramedullary nailing. All 6 nonunions healed and patient satisfaction was high. One patient had slight restriction of shoulder motion and one had slight restriction of elbow motion.
Nonunion of the diaphyseal humerus after intramedullary rod fixation is a challenging reconstructive problem. Removal of intramedullary implants can be difficult and could damage the shoulder joint and diminish ultimate upper limb function. Removal of well-fixed implants can be risky. The use of a locking compression plate without removing a well-buried intramedullary implant avoids these problems while achieving healing.
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