1 Principles topenlarge
Anterior and lateral flake fractures may be associated with patellar dislocation/subluxation.
These osteochondral fragments are very often avascular, and their incorporation occurs by “creeping substitution” as vessels grow into the fragment from the living underlying cancellous bone. This requires the abolition of all interfragmentary movement by rigid interfragmentary compression. If this is not achievable, then nonunion and late separation can occur. For this reason, smaller fragments may need to be excised, or washed out of the knee joint.
Osteochondral fractures of the medial, or lateral, ridge of the patellar groove of the femur will usually require open parapatellar approach for reduction and fixation. When full arthroscopic resources, including an expert surgeon, are available, arthroscopic reduction and percutaneous fixation may be considered, but require high levels of skill and expertise.
Check the retropatellar surface for lesions.
Pearl: decision making
In these injuries, there may be small osteochondral defects that are not reconstructable. Every reasonable attempt should be made to reconstruct the articular surface. On the other hand, a loose small fragment in the knee joint is clinically worse than a small articular defect. Therefore, surgical judgment must be exercised in determining whether a fragment is reconstructable, or not.
Specialist knee reconstruction surgeons have available advanced techniques to reconstruct the articular surface. Osteochondral autograft and allograft transfer within the knee are possible. Cultured chondrocyte grafting shows promise for the future.
2 Reduction and temporary fixation topenlarge
Achieve reduction by manipulating the fracture with an elevator. Small ball-spiked pushers, or a dental pick, may also be used.
Alternative: reduction under arthroscopic view
Achieve reduction by manipulating the fracture with the hook (illustrated) using arthroscopic control. Small ball-spiked pushers may also be used, inserted through separate portals.
Insert a K-wire to secure the reduction. Make sure that it does not interfere with the intended implant position.
3 Fixation topenlarge
Fixation can be achieved using a small fragment screw system (A or B), or absorbable pins (C). In general screws provide a better compression of the fracture, but need a certain thickness of the osteochondral flake due to the screw head dimension.
Absorbable pins (C) are preferable for thin and small fragments.
Two screws, or pins, should be used in order to prevent fragment rotation.
None of the implants is allowed to project above the articular surface.
Place the guide wires as perpendicularly as possible to the fracture plane.
Check correct guide-wire placement under image intensifier control.
Countersink manually, deep enough to allow for fully buried screw heads.
Pitfall: countersinking too deep
Be aware of countersinking too deeply into the cancellous bone, which often happens using a power tool.
In screw fixation the lag screw principle is followed. Use partially threaded lag screws so that no gliding hole need to be drilled. It is imperative to countersink for the screw head.
This illustration shows the completed osteosynthesis using sunken screws.
Headless compression screw
Insert 3.0 mm headless compression screws with predrilling, or over a guide wire. Neither gliding hole nor countersinking is required. It is imperative to insert the headless compression screw until the screw head has passed the cartilage surface completely.
This illustration shows the completed osteosynthesis using headless compression screws.
Absorbable pins require predrilling. Use the insertion device to insert the pin with gentle hammer blows. Observe the pin insertion process carefully as the pins might deform during insertion.
In case the pin head does not completely sink into the cartilage use a scalpel to remove the projecting part of the head.
This illustration shows the completed osteosynthesis using absorbable pins.