To deal with AO/OTA 34C3 patellar fracture, German、American and Switzerland experts proposed special plate. However, the plate is not easy to popularize because the fragment is small and loose. (For eastern people, the body is short, the fragment is more small and loose. ) There is no space for fixing screws.
Although patellar multi-fragmentary fractures are difficult to treat, they are treated according to two rules. The first is to restore the congruous articular surface and the second is to recover the patellar tensile strength.
To restore articular surface, it is important to fix the free articular fragment. Of the 21 patients with AO/OTA 34C3 patellar fracture that we implemented, there were 8 patients with free articular fragment. The South Korean author suggested to fix the Loose articular fragment with headless compression screw, but we found that the articular fragments usually were thin, we fixed them with Kirschner wire under direct vision. In the follow-up, although no fragments were found to fall off, 2 of the 8 patients still suffered from unevenness of articular surface. In the 12-month follow-up after operation, 5 of the 21 AO/OTA 34C3 patients showed unevenness of the articular surface. Therefore, it is still a long way to restore the articular surface of AO/OTA 34C3 patellar fracture.
To restore the tensile strength of patella, we should not only focus on the treatment of patella, but also focus on the restoration of the extensor mechanism. The fact is that the additional cable fixation between proximal patella and tibial tuberosity can replace knee extension device.
The additional cable fixation requires relatively intact proximal patella. Although patellar fracture is type AO/OTA 34C3, we find that the comminuted area of patellar fracture is often located in the middle or distal part of patella. Actually, from January 2014 to January 2018 in our department, of the 48 patellar fracture, only one was proximal patellar multi-fragmentary fractures, and the rest were middle and distal patellar multi-fragmentary fractures. We think that this is definitely related to the shape and position of the patella and the pulling to the patella. The upper of the patella is large while the lower of the patella is small. The proximal end of the patella is pulled by the quadriceps femoris muscle which is the most powerful in the body. As elaborated by Afsar E who did finite element analysis, the force on the proximal patella is the greatest. The unfractured patella is just in front of the broad distal femur. Once the patella is fractured, because of the pulling of the quadriceps femoris, the proximal patella is pulled away from the broad distal femur, escaping the crushing of the distal femur. The distal patella can't escape the crushing of the distal femur, so severe comminuted patellar fracture is always located in the middle or distal part of patella. Therefore, the proximal end of the proximal patella is intact usually or simple fracture. So the relative integrity of the proximal patella can be achieved easily by simple transverse fixation. Thereby the foundation of the proximal patella can be prepared easily.
If the patient is young, the proximal patellar fragment is big, and the quality of the bone is good, we usually fix the proximal patella by inserting cable through the bone. When the patient is old with osteoporosis, (Because the osteoporosis is easy to occur in cancellous area[13,14], the patella of the elderly becomes like an egg with soft core and hard shell.) or the patellar fragment is short, we will fix the proximal patella with cable similar to the cerclage method. So as to increase the resistance of the patella to cable cutting.
According to Lazaro’s article, who examined the patellar fracture with CT, 88% of patients had distal patellar pole fracture which sometimes made it difficult to fix the fracture area whether using Kirschner wire tension band or cerclage. Some people have proposed the partial patellectomy，while others incline to suture patellar tendon on patella. American and German experts suggested to suture and fix patellar tendon to the plate. But the repairment cannot be checked objectively in the above methods. The cast or brace external fixation sometimes has to be applied to protect the repairment. While the additional iron cable fixation between patella and tibial tuberosity can resolve the problem effectively. As the iron cable can be observed in X-ray. Through spanning the injury area, the additional cable fixation also can avoid the load bearing of the repairing area, which is beneficial to heal.
The minimally invasive technology of percutaneous drilling and subcutaneous inserting of cable in tibial tuberosity region greatly reduces the damage to local soft tissues.
Compared with iron wire fixation between patella and tibial tuberosity, the iron cable with the same diameter of the iron wire has obvious flexibility, which will reduce the probability of cable fracture and the irritation to surrounding tissues. Otherwise, the diameter of the iron cable is big which will delay the bone cutting. With the healing of ligaments, even if the cable partially cut the bone area, it is difficult for the cable to continue cutting the bone because the ligament has played a role.
Although, there were 21 patients with AO/OTA 34C3 patella fracture in our hospital, 9 patients (43%) needed to be fixed by additional figure-8 iron cable fixation, which indicated that modified Kirschner wire tension band with or without cerclage cable was not enough for complicated AO/OTA 34C3 patella fracture. Therefore, the AO/OTA 34C3 patella fracture should be got attention.
Because sufficient stress experiment was carried out during the operation, there was no worry about loosening of internal fixation after the operation, the postoperative rehabilitation of the two groups was the same. Both of two teams were allowed to take active postoperative exercise. The results also proved that all patients achieved excellent postoperative efficacy. Moreover, due to active exercise after operation, it was beneficial to reduce the occurrence of postoperative complications.
Therefore, The additional iron cable fixation between proximal patella and tibial tuberosity is a simple and effective method to treat AO/OTA 34C3 patellar fracture on the basis of modified Kirschner wire tension band fixation with or without the cerclage cable. In the end, the additional iron cable becomes the operator's safety belt and life line.
Because Patellar fractures account for approximately 1% of all fractures , the AO/OTA 34C3 patellar fractures are fewer. We only collected 21 cases through 4 years. So the sample size was relatively small.