1 Principles top
The patello-femoral joint is biomechanically very stressed when the knee is loaded. Any compromise of the joint surface is likely to lead to degenerative joint disease. It is, therefore, highly desirable, in patellar fractures to strive for anatomical reduction of the joint surface and stable fixation.
An additional treatment goal is restoration of function of the knee extensor mechanism and allow early range of motion of the knee.
Tension band principles
The forces produced by the quadriceps on patellar fractures are significant and may cause early fixation failure. For example, screw fixation alone would generally fail. The physiological forces acting on the patella tend to distract the fragments, more on the anterior than at the posterior aspect.
The anterior tension band converts tensile forces on the anterior aspect of the knee joint ...
... into compression forces at the joint line. In the patella, an anterior figure-of-eight wire loop acts as a tension band during flexion of the knee.
Multifragmentary patellar fractures cannot be fixed with a tension band. To be able to use a tension band, the posterior articular cortex cannot be comminuted as it must provide a buttress to allow compression.
Combination of techniques
Tension band stitch may be used in combination with cerclage stitch/wire and/or lag screws.
Suture fixation may be helpful for inferior pole patellar fractures, especially with comminution and/or patients with significant osteoporosis.
Reduction and fixation can be achieved in two ways, either by first reducing the fracture and then drilling the K-wires through the reduced fragments (outside-in technique) or by first drilling the wires into the unreduced fragments followed by reduction and completion of the fixation (inside-out technique).
Verification of reduction
Anatomical reduction of the articular surface is monitored by palpating the joint from inside, as neither inspection nor the x-ray will reveal a minor step off. This will require creation of a small arthrotomy.
Nevertheless, an image intensifier or X-ray images should always be available, so that the reduction can be checked in the AP and lateral planes if needed.
2 Patient preparation and approach topenlarge
This procedure is normally performed with the patient in a supine position with the knee flexed 30°.
For this procedure a mid-axial longitudinal approach is used.
3 Reduction and K-wire insertion using outside in technique topenlarge
The knee joint and fracture lines must be irrigated and cleared of blood clot and small debris to allow exact reconstruction.
The larger fragments are reduced using a pointed reduction forceps or tenaculum.
In frontal/coronal (transverse) fractures, reduction is easier with the knee extended.
Reduction is held by one or two reduction forceps.
Verify the reduction by palpation of the retropatellar surface.
Using the outside-in technique, drill the first K-wire in an axial direction. The second K-wire is then drilled parallel to the first, through the reduced fragments ensuring the K-wires do not enter the joint. It may be difficult to find the right direction and position for the wires.
Two parallel K-wires should be inserted to give more stable fixation.
Reduction is again verified by palpation of the joint surface.
4 Reduction and K-wire insertion using inside out technique topenlarge
Exact positioning of the K-wires is challenging once the fracture is reduced. Therefore, some surgeons prefer to drill the K-wires in an inside out manner.
Drill two K-wires (pointed at both ends) from the fracture surface through the proximal fragment, exiting superiorly.
Manually reduce the main fragments and hold them with a pointed reduction forceps.
Pearl: If the available K-wires are pointed only at one end, the opposite end can be sharpened by cutting it obliquely with a K-wire cutter.
Finalize K-wire insertion
The ideal level for the K-wires lies approximately 5 mm below the anterior patellar surface. Often the K-wires are closer to the articular than to the anterior surface. Nevertheless, the principle of tension banding is not compromised. The position of the wires may be checked with image intensifier or X-ray at this stage before proceeding to insert the tension band.
5 Tension band insertion topenlarge
Insert a nr. 5 Ethibond non-absorbable stitch in a figure-of-eight fashion.
Push the stitch a close as possible to the angle between the bone and the protruding K-wire tips.
The stitch should be as close as possible to the bone throughout its whole course both superiorly and inferiorly.
Applying the figure-of-eight stitch
While tightening the figure-of-eight stitch with the knee in extension, check the reduction by palpating the retropatellar surface (this will require creation of a small arthrotomy).
Once the stitch is tightened, a second stitch is placed. Care is taken not to damage the first stitch with the sharp needle.
After tightening the figure-of-eight stitch, bend the proximal pin ends, shorten them, turn them towards the quadriceps tendon, and drive them into the patella to prevent skin irritation and loosening.
The distal pin ends are trimmed to remove the sharp points, but not bent, for easier removal.
6 Case topenlarge
Lateral X-ray showing displaced transverse patellar fracture in an elderly woman.
AP image postoperative showing tension band stitch technique with fracture reduced. Note the stitch cannot be seen but is resisting tensile forces on the patella.
Lateral image postoperative showing K-wire fixation and non-visible figure of 8 stitch resisting tensile patellar forces.
3 months AP image showing significant osteoporosis in patellar fracture patient.
Same patient three months postoperatively with healed fracture and good situation for removal of hardware later if indicated.