1 Note on illustrations topenlarge
Throughout this treatment option illustrations of generic fracture patterns are shown, as four different types:
A) Unreduced fracture
B) Reduced fracture
C) Fracture reduced and fixed provisionally
D) Fracture fixed definitively
2 Principles of joint-bridging external fixation topenlarge
A joint-bridging external fixator is fixed to the femur and the tibia while the fracture zone is left virtually untouched (it is bridged). Provisional reduction is achieved with distraction.
When external fixation is used to bridge the knee joint it is always only for temporary fixation. Prolonged immobilization will lead to difficulties with knee mobility.
It is rapidly applied without need for intraoperative x-rays and can be adjusted later.
Details of external fixation are described in the basic technique for application of modular external fixator.
Specific considerations for the knee are given below.
3 Pin insertion (humerus and tibial shaft) topenlarge
For safe pin placement make use of the safe zones and be familiar with the anatomy of the lower leg and the femur.
Any pin placed near a joint should be a minimum of 14 mm away from the joint line to prevent joint sepsis.
In the femur, blunt dissection of the soft tissues and the use of small Langenbeck retractors will minimize muscular damage.
Using a straight clamp, prepare a channel for the insertion of the pin.
Tibial pin placement
Drilling a hole in the thick tibial crest may be associated with excessive heat generation and there is a risk the drill bit may slip medially or laterally damaging the soft tissues. As the anteromedial tibial wall provides adequate thickness for the placement of pins, this trajectory is preferable. A trajectory angle (relative to the sagittal plane) of 20-60° for the proximal fragment and of 30-90° for the distal fragment is recommended.
Alternatively, in order to avoid the frame catching on the opposite leg, the pins may be placed more anteriorly. The drill bit is started with the tip just medial to the anterior crest, and with the drill bit perpendicular to the anteromedial surface (A). As the drill bit starts to penetrate the surface, the drill is gradually moved more anteriorly until the drill bit is in the desired plane (B). This should prevent the tip from sliding down the medial or lateral surface.
4 Frame construction / reduction and fixation (knee) topenlarge
Pearl: oblique distal tube
Angle the rod over the tibia such that it is attached to the pins one on the lateral and one on the medial side. This results in a larger window over the condyle which can be beneficial for later (minimally invasive) surgery if it is necessary to maintain the external fixator during definitive osteosynthesis.
Reduction and fixation
Using the partial frames as handles, manually reduce the fracture in length, rotation and axis.
Restore length with a bolster behind the knee to give slight flexion.
It should be understood that a perfect reduction will not be obtained.