1 Principles top
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General considerations
Hoffa fractures involve important load-bearing areas of the knee joint surface, and the principles of anatomical reduction and absolute stability of fixation apply.
In cases of very small posterior fragments, the indirect lag screw technique from anterior is not applicable as the thread will be too long and will not achieve compression of the fragment.
In addition, in small fragments, it is difficult to aim the K-wire from anterior into the fragment.
For this procedure, 3.5 mm cannulated headless compression screws are preferable. Standard 3.5 mm lag screws can be used in larger fragments.
Similar principles apply if both condyles are fractured.
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Screw types
None of the implants is allowed to project above the articular surface. This
can be achieved by countersunk lag screws (A) or headless compression screws
(B).
At least two screws should be used, in order to prevent fragment rotation.
2 Patient preparation and approach top
Patient preparation
This procedure is normally performed with the patient in a prone position
Approach
For this procedure a posterior approach is normally used.
3 Reduction top
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Reduce the fracture using a small ball-spiked pusher and secure it temporarily with a K-wire.
Note: patient is lying prone.
4 Fixation top
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Guide-wire insertion
Insert two guide wires. Make sure not to penetrate the far cortex.
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Check guide-wire insertion
Check the guide-wire position under image intensifier control, in the lateral and oblique views.
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Countersinking
If standard partially threaded lag screws are used, countersink manually prior to screw length measurement.
Do not perform countersinking when planning headless compression screws.
Pitfall: countersinking too deeply
Be aware of countersinking too deeply into the cancellous bone, which often happens using a power tool.
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Screw length measurement
Determine the appropriate screw lengths over the guide wires, making sure that the measuring device enters the countersunk holes.
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Fixation – sunken screw
Insert the screws using the manual, not powered, screw driver. Tighten judiciously, as the denser subchondral bone can be fractured by over-tightening.
Illustration showing the completed osteosynthesis using standard partially threaded lag screws.
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Alternative: headless compression screws
Insert headless compression screws, using the cannulated screw driver, and check under image intensifier control in the lateral view to confirm that the screw length was chosen appropriately.