Oblique ulnar fracture: lag screw and plate fixation
1. Principles
Options for fixation
For oblique forearm shaft fractures, interfragmentary compression can be achieved either by using an independent primary lag screw, protected by a plate (A), or by using a compression plate as the primary loading device with the addition of a subsequent lag screw through the plate (B).
Note: The first principle (A) will be described using two different techniques.
Absolute stability
Absolute fracture stability, which is defined as the complete abolition of interfragmentary movement, is achieved by interfragmentary compression. It results in direct bone healing (in simple fracture configurations).
Interfragmentary compression
Interfragmentary compression can be achieved by a lag screw, inserted either through a plate hole (1), or separate from the plate (2).
If available, a partially threaded cortical lag screw (shaft screw) can be used to accomplish interfragmentary compression.
Dynamic compression principle
The holes of the plate are shaped like an angled cylinder. The spherical undersurface of the screw head slides down the inclined cylinder as the screw is tightened.
The horizontal movement of the head, as it impacts against the angled side of the hole, results in movement of the bone fragment relative to the plate and leads to compression of the fracture.
Axial compression
Interfragmentary compression can be achieved by loading the oblique fracture site axially, using specific techniques.Axial compression, using self-compressing plates (DCP, LC-DCP, LCP, etc.), is achieved by eccentric screw placement.
Plate position
The plate on the ulna can be positioned under the extensor carpi ulnaris muscle (A), under the flexor carpi ulnaris muscle (B), or in the interval between extensor and flexor carpi ulnaris muscles (C). With a more proximal fracture it can be more difficult to place the plate underneath the extensor muscle. With more distal fractures, plates should be placed in the interval between the extensor and flexor carpi ulnaris muscles (C).
While plate position on the tensile (subcutaneous) aspect of the ulna (C) is biomechanically preferable, plate prominence can be a problem and cause irritation. To avoid too superficial position of the plate, it can be placed towards positions (A) or (B) where it will be covered by the muscle compartment.
In oblique fractures, the plate position should consider the fracture morphology. It is preferable to insert the lag screw through the plate, if possible.
In the following procedure, we demonstrate the plate positioned deep to the extensor carpi ulnaris muscle (A).
While plate position on the tensile (subcutaneous) aspect of the ulna (C) is biomechanically preferable, plate prominence can be a problem and cause irritation. To avoid too superficial position of the plate, it can be placed towards positions (A) or (B) where it will be covered by the muscle compartment.
In oblique fractures, the plate position should consider the fracture morphology. It is preferable to insert the lag screw through the plate, if possible.
In the following procedure, we demonstrate the plate positioned deep to the extensor carpi ulnaris muscle (A).
2. Reduction
Open and anatomical reduction
Reduce the fracture anatomically, using a reduction forceps on each main fragment. The use of blunt, as opposed to pointed, reduction forceps can be helpful, particularly if greater forces are required.
Pearl: leverage technique for oblique fractures
A small bone lever can be used to reduce the fragments.
Pearl: lengthening by twisting of reduction forceps
Reduction of overlapping oblique fractures can sometimes be achieved by twisting a reduction forceps, thereby lengthening the fracture.
Maintain fracture reduction
Maintain the fracture reduction with pointed reduction forceps. Place the forceps such that it will not interfere with the planned plate position.
3. Plate length and number of screws
In the forearm, in addition to any lag screw, three bicortical plate screws are required in each main fracture fragment due to the high torsional stresses. For biomechanical reasons, not every plate hole needs to be occupied by a screw. Therefore, plates with at least 8 or 9 holes are usually used.
4. Fixation – lag screw as primary fixation device separate from plate
If the fracture morphology dictates that the interfragmentary lag screw be positioned separate from the plate, the plate then acts as a neutralization (protection) plate and axial compression should not be applied.
Drill gliding hole
Using a 3.5 mm drill sleeve and a 3.5 mm drill bit, drill a gliding hole in the near cortex.
Ensure that the direction of the drill is as perpendicular to the fracture plane as possible.
Ensure that the direction of the drill is as perpendicular to the fracture plane as possible.
Thread hole: guide in gliding hole
Insert the 3.5 mm / 2.5 mm drill guide into the gliding hole. Check that the anatomical reduction is maintained and use a 2.5 mm drill bit to drill a pilot hole just through the far cortex.
Measure for screw length
Countersink the cortex at the gliding hole.
Use a depth gauge to measure for screw length.
Measure the longer side of the oblique drill hole, as shown, to ensure sufficient screw length.
The lag screw should protrude 1-2 mm through the opposite cortex to ensure maximal thread purchase. However, too long a screw may be tender, or injure soft tissues.
Use a depth gauge to measure for screw length.
Measure the longer side of the oblique drill hole, as shown, to ensure sufficient screw length.
The lag screw should protrude 1-2 mm through the opposite cortex to ensure maximal thread purchase. However, too long a screw may be tender, or injure soft tissues.
Tap the thread hole
Using a 3.5 mm cortical tap with the corresponding drill sleeve to protect adjacent soft tissues, create a thread in the pilot hole of the far cortex.
This maneuver is not necessary when using self-tapping screws.
This maneuver is not necessary when using self-tapping screws.
Lag screw insertion
Insert the lag screw and carefully tighten it, making sure that the fracture stays reduced and is compressed.
Help to maintain the reduction by leaving the pointed reduction forceps in situ.
Help to maintain the reduction by leaving the pointed reduction forceps in situ.
Neutralization (protection) plate
To protect the primary lag screw fixation, a perfectly contoured plate is applied adjacent to the screw head without axial compression (all screws in the neutral position).
The pointed reduction forceps can then be removed.
The pointed reduction forceps can then be removed.
5. Fixation – lag screw as primary fixation device through the plate
In some fracture configurations, it might be advantageous to compress the fracture first by inserting a lag screw through the relevant plate hole.
If this technique is used, then axial compression must not be applied via the plate.
If this technique is used, then axial compression must not be applied via the plate.
Drill gliding hole through plate
After anatomical reduction, the fracture is held by a pointed reduction forceps.
A perfectly contoured plate is now applied to the surface of the anatomically reduced fracture and fixed to one main fragment, either with a neutral screw, or with a bone forceps as illustrated. The interfragmentary lag screw can then be inserted through the appropriate plate hole.
Using a 3.5 mm drill sleeve and a 3.5 mm drill bit, drill a gliding hole in the near cortex.
Ensure that the direction of the drill is as perpendicular to the fracture plane as possible.
A perfectly contoured plate is now applied to the surface of the anatomically reduced fracture and fixed to one main fragment, either with a neutral screw, or with a bone forceps as illustrated. The interfragmentary lag screw can then be inserted through the appropriate plate hole.
Using a 3.5 mm drill sleeve and a 3.5 mm drill bit, drill a gliding hole in the near cortex.
Ensure that the direction of the drill is as perpendicular to the fracture plane as possible.
Thread hole: guide in gliding hole
Insert the sleeve of the 3.5 mm / 2.5 mm drill guide through the plate and into the gliding hole. Check that the anatomical reduction is maintained and use a 2.5 mm drill bit to drill a pilot hole just through the far cortex.
Measure for screw length
Use a depth gauge through the plate to measure for screw length.
Measure the longer side of an oblique drill hole, as shown, to ensure sufficient screw length.
A screw should protrude 1-2 mm through the opposite cortex to ensure maximal thread purchase. However, too long a screw may be tender, or injure soft tissues.
Measure the longer side of an oblique drill hole, as shown, to ensure sufficient screw length.
A screw should protrude 1-2 mm through the opposite cortex to ensure maximal thread purchase. However, too long a screw may be tender, or injure soft tissues.
Tap the pilot hole
Using a 3.5 mm cortical tap with the corresponding drill sleeve to protect adjacent soft tissues, create a thread in the pilot hole of the far cortex.
This maneuver is not necessary when using self-tapping screws.
This maneuver is not necessary when using self-tapping screws.
Lag screw insertion
Insert the lag screw through the plate and carefully tighten it, making sure that the fracture stays reduced, is compressed, and that the plate sits accurately on the bone surface.
Insert the plate screws
Complete the fixation by inserting the plate screws in neutral mode, usually alternately, in both main fragments.
6. Fixation – compression plating with an additional lag screw
Prebending the plate
If the plate which will exert axial compression is exactly contoured to the anatomically reduced fracture surface, there will be some gapping of the opposite cortex, when the plate is tensioned by tightening the load screw.
The solution to this problem is to “over-bend” the plate so that its centre stands off 1-2 mm from the anatomically reduced fracture surface.
When the neutral side of the plate is applied to the bone, slight gapping of the cortex will occur directly underneath the plate.
As the load screw is tightened, the tension generated in the plate compresses the fracture evenly across the full diameter of the bone.
The solution to this problem is to “over-bend” the plate so that its centre stands off 1-2 mm from the anatomically reduced fracture surface.
When the neutral side of the plate is applied to the bone, slight gapping of the cortex will occur directly underneath the plate.
As the load screw is tightened, the tension generated in the plate compresses the fracture evenly across the full diameter of the bone.
After the plate has been contoured anatomically to the reduced bone surface, prebend the plate with the handheld bending pliers, or a pair of bending irons.
Insert 1st screw
The prebent plate is fixed to one of the main fragments with a screw in neutral mode. A reduction forceps is placed on the opposite fragment to hold it in the reduced position against the plate.The aim of this maneuver is to create an “axilla” into which the other fragment can be compressed and locked either with a compression screw or using a push-pull technique.
Note: Because of the design of the LC-DCP holes, the neutral drill guides for the LC-DCP have a very slightly eccentric hole and an arrow, which needs always to point towards the fracture line.
Maintain reduction
A reduction forceps is placed on the opposite fragment to hold it in the reduced position against the plate.
Option: Push-pull reduction technique
If reduction proves difficult, a bone spreader, placed between the end of a plate and an independent cortical screw, can be used to distract the fracture for reduction. Once reduced, the reduction forceps is tightened.
Then, using the same independent screw, axial compression can be obtained by pulling the plate end towards the screw with a small Verbrugge clamp.
Insert 2nd screw eccentrically
Once reduced, a second screw is inserted eccentrically (yellow drill sleeve) into the reduced fragment.
Note: the arrow on the drill sleeve has to point towards the fracture line.
Tighten screw
By tightening the eccentrically-inserted screw, axial compression is achieved.
Insert additional screws
Should it be necessary to increase the axial compression, a second screw can be inserted eccentrically into the same fragment as the first eccentric screw.
As the second eccentric screw is tightened, the first eccentric screw in the same fragment needs to be loosened slightly to allow the plate to slide on the bone.
As the second eccentric screw is tightened, the first eccentric screw in the same fragment needs to be loosened slightly to allow the plate to slide on the bone.
Pearl: alternative drill sleeve
For inserting screws into the limited contact dynamic compression plate (LC-DCP), the Universal Drill Guide can be used as well. When this drill guide is pressed into the plate hole, the screw position will be neutral (A). When it is held against the end of the plate hole, without exerting downward pressure, the screw position will be eccentric (B).
Lag screw
The stability of a plate fixation in oblique fractures can be greatly increased by inserting a lag screw through the plate after primary axial compression has been achieved.
All other plate screws are now inserted in a neutral position (green drill sleeve) and do not serve further to increase compression.
Completed osteosynthesis
This illustration shows the completed compression plate osteosynthesis of an oblique fracture with additional lag screw fixation.
7. Check of osteosynthesis
Check the completed osteosynthesis by image intensification. Make sure that the plate is at a proper location, the screws are of appropriate length and a desired reduction was achieved.
The elbow should be stabilized at the epicondyles and the forearm rotation should be checked between the radial and ulnar styloids.
8. Assessment of Distal Radioulnar Joint (DRUJ)
Before starting the operation the uninjured side should be tested as a reference for the injured side.
After fixation, the distal radioulnar joint should be assessed for forearm rotation, as well as for stability. The forearm should be rotated completely to make certain there is no anatomical block.
Method 1
The elbow is flexed 90° on the arm table and displacement in dorsal palmar direction is tested in a neutral rotation of the forearm with the wrist in neutral position.
This is repeated with the wrist in radial deviation, which stabilizes the DRUJ, if the ulnar collateral complex (TFCC) is not disrupted.
This is repeated with the wrist in full supination and full pronation.
Method 2
In order to test the stability of the distal radioulnar joint, the ulna is compressed against the radius...
...while the forearm is passively put through full supination...
...and pronation.
If there is a palpable “clunk”, then instability of the distal radioulnar joint should be considered. This would be an indication for internal fixation of an ulnar styloid fracture at its base. If the fracture is at the tip of the ulnar styloid consider TFCC stabilization.
