1 Lag screw principles for the radial head topenlarge
In two-part partial articular fractures of the radial head, fixation can be achieved by lag screws. The thread pulls the opposite bone fragment towards the head of the screw placing the fracture ends under compression. The portion of the thread in the gliding hole does not purchase in the surrounding bone.
Because the radial head is completely covered by articular cartilage the screw heads must be countersunk just below the level of the articular cartilage. The screw tip must not protrude medially, as it will contact the ulna and interfere with supination/pronation.
2 Screw positioning topenlarge
For the insertion of the screws, choose a location in the radial head that causes the least compromise of full pronation and supination. Insert the lag screw(s) as perpendicularly to the fracture plane as possible.
Safe zone for screw insertion
To determine the location of the "safe zone“, reference marks are made along the radial head and neck, to mark the midpoint of the visible bone surface. Three such marks are made with the forearm in neutral rotation, full pronation, and full supination as shown in the illustration. The posterior limit of the safe zone lies halfway between the reference marks made with the forearm in neutral rotation and full pronation. The anterior limit lies nearly two thirds of the distance between the neutral mark and the mark made in full supination.
The nonarticulating portion of the safe zone for the application of implants to the radial head (or safe zone forprominent fixation) consistently encompasses a 90 degrees angle localized by palpation of the radial styloid andLister's tubercle.
3 Choice of implant topenlarge
Mini fragment 1.5 mm or 2.0 mm screws, or headless compression screws (Herbert or similar screws) are used.
4 Reduction and preliminary fixation topenlarge
Remove interposed joint cartilage
Expose the fracture ends with minimal soft tissue dissection off the bone.
Remove hematoma and irrigate.
Prior to final reduction and temporary fixation, interposed joint cartilage should be removed. If the radial head has been dislocated posteriorly, confirm that it is satisfactorily reduced to the capitellum.
Reduction is achieved directly.
If the annular ligament is still intact, cut and retract it to achieve better access to the fracture site.
Reduce and provisionally fix the fracture with the help of small pointed reduction forceps and one or two K-wires.
5 Lag screw insertion topenlarge
Preplan the number and location of screws. The lag screw must be di-rected perpendicularly to the fracture plane. Drill a gliding hole into the free fragment, sized according to screw size (see fig.). Insert the appropriate drill sleeve into the gliding hole until it reaches the fracture. Now drill the epiphysis of the intact radial head with the appropriate drill bit.
Countersinking and measuring
Countersink the cartilage covering the free fragment in order to prevent protrusion of the screw head.
Measure the depth of the hole and tap the far epiphysis with the appropriate cortical tap and protection sleeve.
Always measure after countersinking to prevent penetration of the screw tip into the joint.
Lag screw insertion
Closely observe the compression effect on the fracture line while tightening the lag screw.
The K-wire(s) should be removed just before the final tightening of the screw.
Second lag screw
If the fracture configuration allows the insertion of a second lag screw, it can be inserted now using the same technique as described above.
Check reduction and screw length with supination/pronation exam. Screws should not obstruct rotation.
Alternative fixation - headless compression screws
When headless compression screws (eg, Herbert or HCS) are used, there is no need for countersinking as the screw head engages inside the bone.
After reduction, provisionally fix the fracture inserting one or two K-wires in the previously planned screw position. Over the K-wire, insert the cannulated screw.
Preparation for screw insertion should be performed according to the surgical technique of the specific screw.
6 Ligament repair topenlarge
Repair the annular ligament using non-absorbable sutures.
The lateral collateral ligament may have been avulsed from the lateral humeral epicondyle, or torn in substance. It should be assessed and repaired as necessary.