Our results demonstrated that the isolated soft tissue repair surgery (MRP or MPFLR) and the soft tissue repair combined with DFO surgery (DFO + MRP or DFO + MPFLR) for the treatment of RPD with increased femoral anteversion has good clinical outcomes. The VAS score, Kujala score, Lysholm score and IKDC score of 63 patients were significantly improved. No serious patellar shift occurred in all patients during follow-up. A further finding is that this delivers significantly better results in the Lysholm score, Kujala score, IKDC score, CA, and PTA due to combined with DFO. Besides, the FAA, as an independent risk factor for patellar dislocation , has been significantly improved and the FAA has been significantly reduced after combined operations.
Many authors have emphasized that rotational malalignment is a risk factor for patellar instability [4,21,22]. Diederichs et al. suggest that increased femoral torsion may be the currently underestimated major risk factor for patellar dislocation. The mechanical basis for the increased risk may be the increased Q angle due to a greater tendency for genu valgum, which increases the lateral directional force of the patella . Increased FAA results in an abnormal internal rotation gait with the knee joint axis pointing inwards during the forwarding movement of the body. This results in greater internal rotation of the knee axis during the standing position, resulting in excessive lateral force vector of the patella that may favor patellar instability or dislocation [5,23]. For these patients, combined DFO surgery can reduce the FAA of patients and adjust the patella trajectory by improving the rotational malalignment, which can achieve good clinical outcomes. However, there is no uniform standard for FAA threshold for DFO surgery. At least, Our results show that better efficacy is achieved in patients with FAA over 25° for patellar dislocation. For patients with FAA 20° to 25°, as satisfactory results of soft tissue surgery have been achieved, whether combined DFO surgery is still necessary still needs to be further explored.
the postoperative Tegner score of the patients showed no significant improvement in both groups, which was consistent with previous studies [11,18]. We considered that this might be due to the patient’s previous patella dislocation, which led to the patient’s fear of high-intensity activities and their unwillingness to engage in too many intense activities. In the end, the patients are only willing to exercise similar to those before the operation. However, Our study found that the group 2 patients had significantly higher satisfaction than group 1 patients. In group1, the dissatisfied patients expressed that they still felt a small amount of pain during the postoperative activities, and they still felt fear for a large amount of activities after the operation. In group 2, the only unsatisfied patient was due to excessive difficulty in postoperative rehabilitation and excessive pain during the kneeling process. Therefore, we believe that combined surgery will yield better results during long term follow-up.
In this study, we did not undertake tibial tubercle transfer correction of tibial tuberous position in patients with combined surgery, but TT-TG was significantly reduced postoperatively. We consider that this may be due to the rotation of the DFO leading to the outward rotation of the femoral trochlear, which in turn leads to the reduction of the TT-TG distance. In previous studies, the normal range of FAA in the population was stated as around 15°[24,25].However, patients with an increased FAA increase the internal rotation of the femur, which may increase the TT-TG distance theoretically. After soft tissue repair combined with DFO surgery, the TT-TG distance of the patients may be reduced, which has also been preliminarily confirmed in our study. This result is interesting, suggesting that DFO surgery alone may be able to achieve good results in patellar dislocation with increased TT-TG and FAA. Recent studies have also reported that tibial tubercle transfer may have significant effects only in specific patients . Therefore, whether the increase of TT-TG is caused by the internal rotation of the femur or by the external placement of tibial tubercle can be further discussed.
In the past 15 years, the medial patellofemoral ligament reconstruction and medial support for the treatment of patellar dislocation by soft tissue repair has achieved good results [15–17,27]. The medial patellofemoral ligament and the medial retinaculum are important soft tissues that constrain the displacement of the patella, providing considerable medial tension and limiting the displacement of the patella to dislocation of the patella. At the same time, our previous research showed that MRP could yield similar results to MPFLR for recurrent patellar instability in adults . Because DFO + MPFLR has more interference during the operation, DFO + MRP has more obvious surgical advantages. The advantage of MRP is to repair the medial femoral soft tissue directly instead of preparing a tendon graft. Also, the MRP avoids potential interference between the femoral tunnel during the reconstruction of the MPFL and the femoral plate screw. Previous studies have also confirmed that DFO + MRP is effective in patients with increased FAA . Therefore, our surgical team increased the number of operations DFO + MRP surgeries in the treatment process, which not only reduced the difficulty of surgery but also reduced the surgical costs of patients.
However, compared with the isolated soft tissue surgery, the combined operation is more traumatic, the recovery period of patients is longer, and the recovery process is more difficult. In our study, we found that some patients were reluctant to take active functional exercise after combined surgery because of the postoperative pain. In five patients, knee joint activity was still deficient within 8 weeks after the operation. Although it was finally well resolved, the problem of rehabilitation still needs to be paid attention to. In addition, the level of DFO osteotomy performed by various scholars is not consistent. Our recent study found that there is a relationship between the morphology of distal femur and FAA, and we believe that the surgical method of intraosseous osteotomy is also safer and more effectives. Therefore, whether future surgeries can be more minimally invasive and precise needs to be further explored.
In summary, the causes of patella dislocation are multifactorial. Although for patients with patellar dislocation with increased FAA, both isolated soft tissue repair surgery and combined with DFO surgery have good outcomes for patellar dislocation patients with rotational malalignments. Both surgical programs can improve knee function, relieve pain, and adjust the patella trajectory. However, the combined surgical approach can address the major risk factors of patients, correct excessive internal rotation of femur, adjust the rotation line of lower limbs and achieve better postoperative outcomes, which may reduce the recurrence rate of postoperative patellar dislocation in patients. Combination surgery may be an ideal surgical strategy to treat patellar dislocation patients with increased FAA, but individualized strategies should be developed to accurately treat patellar dislocation.