1 Principles topenlarge
The patella is the largest sesamoid bone in the human body. It is located in the extensor apparatus of the knee. Anatomical features include the cranial base and the extraarticular caudal apex as well as the anterior extraarticular and the posterior articular surfaces. The rectus femoris and vastus intermedius muscles insert at the base and the vastus medialis and lateralis muscles on either side. The patellar tendon originates from the apex patellae and inserts at the tibial tuberosity. The articular surface has the thickest layer of cartilage in the body, up to 5 mm, rendering the patella susceptible to chondromalacia and degenerative patellofemoral arthritis.
History and examination
Patellar fractures make up about 1% of all fractures and are mostly caused by direct trauma to the front of the knee, for example, a direct fall or a blow onto the flexed knee.
Bone avulsions of the adjacent tendons or pure ruptures of the quadriceps and patellar tendons are caused by indirect forces.
Typical signs are swelling, tenderness, and limited or lost function of the extensor mechanism.
Preservation of active knee extension does not rule out a patellar fracture if the auxiliary extensors of the knee - the medial and lateral retinacula - are intact.
If displacement is significant, the physician can palpate a defect between the fragments and hemarthrosis if present. The examination must include evaluation of the soft tissues, so as not to overlook an injury to the patellar bursa or to omit grading the injury if the fracture is open.
In addition to the standard x-rays of the knee in two planes, a tangential view of the patella may be useful. In the AP view the patella normally projects into the midline of the femoral sulcus. Its apex is located just above a line drawn across the distal profile of the femoral condyles. In the lateral view the proximal tibia must be visible to exclude a bone avulsion of the patellar tendon from the tibial tuberosity. A rupture of the patellar tendon or an abnormal position of the patella like patella alta (high-riding patella) or patella baja (shortening of the tendon) can be recognized with the help of the Insall-Salvati method. This is the relationship of the length of the patella (B) and the patellar tendon (A) on the lateral x-ray, r = A/B. This ratio is normally r = 1+/-0.2, ie 0.8-1.2. A ratio r > 1.2 suggests a high-riding patella (patella alta), or patellar tendon rupture.
The third important plane is the 30° tangential view, which is obtainable in 45° knee flexion. If a longitudinal or osteochondral fracture is suspected, the 30° tangential view is a helpful diagnostic adjunct.
Tendon ruptures and patellar dislocation must be ruled out.
Isolated rupture of the quadriceps, or patellar, tendon must be excluded by clinical evaluation (palpation) and ultrasound scan (or MRI). Dislocation, most commonly occurring to the lateral side, may result in osteochondral shear fractures, with avulsion lesions of the medial margin of the patella, and occasionally with impaction fractures of the lateral lip of the patellar groove of the femur.
2 Reduction and fixation top
Reduction techniques and tools
The knee joint and fracture lines must be irrigated and cleared of blood clots and small debris to allow exact reconstruction.
An image intensifier should always be available so that the final result can be checked in the AP and lateral planes.
Krackow whip stitch
The Krackow whip stitch uses 2 or more locking loops inserted into each side of the patellar tendon. The Krackow whip stitch is stronger than the Kessler, or Bunnell, stitches that are used for repairing smaller tendons.
Open the patellar tendon retinaculum longitudinally. Insert two Krackow stitches of #5 non-absorbable suture into the patellar tendon, as illustrated.
Make holes in the main fragment
Make 4 longitudinal drill holes in the proximal patellar fragment.
Using a suture passer from proximal to distal, pull the free ends of the sutures through the proximal segment.
The sutures are then tightened and tied deep to the quadriceps tendon, with the knee in full extension.
Be sure that there is good contact between the tendon and the bone.
Augmentation of patella ligament tendon repair - patella baja
In order to protect this suture repair during the healing process, a protective cerclage wire can be passed around the upper pole of the patella and through a transverse drill hole at the tibial tubercle.
This wire frequently breaks later, and it is best to remove it once healing is assured at 3-4 months.
If the cerclage wire is tightened too tightly it will not be possible to flex the knee and a patella baja will occur.
This complication must be avoided and can cause severe limitation of knee flexion. If there is need for a cerclage wire to protect the patellar tendon, a patella baja can be produced by misjudging the exact length of the patellar tendon. The opposite knee will indicate the correct position of the patella as described under x-ray evaluation.