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.
In wedge or multifragmentary complete articular fractures, anatomical reduction of the joint surface in relation to all the fragments, combined with durable restoration of the integrity of the extensor mechanism is not commonly achievable. K-wires with heavy sutures applied in standard "tension band configuration" draws the fragments together as anatomically as possible and permits controlled quadriceps rehabilitation in the medium to late healing phases. The joint surface commonly heals with some irregularity, predisposing to secondary degenerative joint disease.
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.
In young patients with good quality bone, tension band principles are firm. But in older patients with bad quality bone, the tension band principle is less important to adhere to and obtaining fracture healing is more important. Often the posterior articular surface is less injured than the dorsal anterior surface and so tension band stitch will work nicely to obtain fracture union.
The knee joint and fracture lines must be irrigated and cleared of blood clot and small debris to allow exact reconstruction.
Reduce the major fracture fragments using a pointed bone reduction forceps or tenaculum. Transverse fractures are more easily reduced with the leg in extension and sagittal fractures are more easily reduced with the leg in flexion.
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.
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. The direction is verified by lateral imaging.
Two parallel K-wires should be inserted to give more stable fixation.
Reduction is again verified by palpation of the joint surface.
4. Suture insertion
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.
Further stabilization may be achieved with the addition of with cerclage stitch/wire and/or lag screws.
5. Aftercare following tension band wiring/lag screw/plate fixation of the patella
Active knee function requires an intact knee extensor mechanism, a mobile patella, a well-preserved patello-femoral joint and muscle strength. After satisfactory reduction and fixation of patellar fractures, early controlled range of motion exercises are combined with static quadriceps strengthening exercises. The progressive increase in loading of the patello-femoral joint depends on many factors and requires planned individual programs, designed by the surgeon and physical therapists.
Patellar fixation is generally quite stable. Early progressive, active mobilization is beneficial after surgery. Despite, wearing a splint to protect against never losing complete extension, range of motion is done throughout the day with the splint off. Static isometric quadriceps exercises should be started on postoperative day 1 with the splint in place. Usually the anterior incision is slow to heal as it is over a flexion surface and so it is usually best to leave the knee in extension for at least a week. Afterwards, special emphasis should be given on active knee and hip movement.
A removable full extension knee splint is applied and worn until good quadriceps control is regained. Full weight bearing may be performed with a straight knee, using crutches or a walker, from postoperative day 1.
Wound healing should be assessed regularly during the first two weeks. X-rays should be taken at 2, 6 and 12 weeks. A longer period may be required if fracture healing is delayed.
Implant removal may be required, as the wires may be prominent under the skin. Implant removal should not be undertaken until a minimum of 1 year postoperatively.
Consideration should be given to thrombo-embolic prophylaxis, according to local treatment guidelines.