Patellar dislocation is a common disease caused by abnormal development, loose ligaments, trauma, and so on22–25. Untimely and ineffective treatment often results in permanent patellar dislocation. Permanent patellar dislocation means that the patella cannot be reduced during knee straightening and flexion10, 12. The abnormal soft tissue structure around the knee joint is the leading cause of permanent dislocation of the patella: lengthening and relaxation of the medial joint capsule and retinaculum of the knee joint, contracture of the lateral joint capsule and retinaculum, contracture of the lateral part of the quadriceps tendon, and contracture of the iliotibial band. Patellar dislocation will cause knee extension delay, weakness, valgus deformity, knee joint degeneration and secondary osteoarthritis. TKA is an effective treatment for end-stage osteoarthritis.
TKA can correct the deformity of the knee joint, but there are different opinions on whether to restore the patellar track during TKA. In earlier studies, scholars suggested preserving lateral patellar dislocation in TKA patients, arguing that restoring the patellar trajectory in surgery is more complicated, and that repairing the defect in the lateral capsule and expanding the knee after correction of the patellar trajectory are difficult, thus affecting the patient’s ability to perform postoperative rehabilitation exercises14, 26.
During TKA, we corrected the patellar trajectory for the following reasons: ①maintaining lateral patellar dislocation will result in residual knee extension retardation ;
We chose to correct the patellar trajectory during TKA for the following reasons: ①maintaining lateral patellar dislocation will cause residual knee extension retardation and weakness; ② Correcting the patellar trajectory can restore the force arm of the quadriceps femoris, improve knee biomechanics, and prevent complications; ③ it is more conducive to correcting valgus deformity and restoring the normal line of force of the lower limbs. This is consistent with the views of articles published in recent years8, 10, 12, 13.
In theory, the external dislocation of the patella can be corrected. First, the normal movement track of the patella can be restored, and then TKA can be performed in the second stage. We complete TKA and correct the patella trajectory in one operation for the following reasons: ①Most of the patients have obvious valgus deformity of the knee joint, the patella can only be reduced by one-stage operation, the valgus deformity cannot be corrected, and the tendency of patellar dislocation still exists, which can easily lead to patellar dislocation.②The symptoms of osteoarthritis are severe, and the simple reduction of the patella cannot relieve the pain.③ Patients with abnormal femoral pulley anatomy and patella reduction cannot meet the knee flexion and extension function exercise, which will affect the second-stage TKA.
For patients with knee osteoarthritis complicated with permanent patellar dislocation, bony structural abnormalities have been corrected in TKA osteotomy. It has been reported that several surgical techniques can restore the trajectory of the patella: release the lateral articular capsule and retinaculum of contracture, rearrange the knee extension device, reconstruct the medial retinaculum, etc.8, 12, 25, 27–31. According to the conditions during the operation, the patellar trajectory can be restored by the combination of one or more surgical techniques. However, a significant defect will be formed in the lateral articular capsule of the knee joint after patellar reduction.
Effective repair of the lateral articular capsule is a challenge for surgeons, affecting rehabilitation after TKA. Few studies have reported the following ways to repair the joint capsule: ① Anterolateral knee approach, the lateral joint capsule of the knee joint can be repaired by delamination incision and staggered suture10, 18. The lateral approach can only release the lateral capsule of the knee but cannot correct the relaxed medial capsule, which is not conducive to restoring the patellar track. Moreover, the method of delamination incision and staggered suture to enlarge the lateral capsule is often limited because the width of the lateral capsule in patients with permanent patellar dislocation is very narrow, especially when the lateral capsule has scars, and it is often impossible to delaminate the incision.
②The joint capsule of a lateral defect was repaired with an iliotibial band, lateral infrapatellar fat pad, meniscus, and subcutaneous fat12, 17. However, there are many disadvantages, such as limited scope of repair, difficulty in closing large joint capsule defects, leakage of synovial fluid after the operation, and limited rehabilitation exercises 10, 12, 17, 18.
There are many advantages to using the medial synovial flap to repair the lateral joint capsule of the knee: ① It can restore the anatomical level of the joint capsule and is beneficial to the functional rehabilitation of the joint. ② It can be repaired in a wide range, including the lateral tendon of the quadriceps femoris, the lateral articular capsule of the patella and the lateral defect of the patellar ligament. ③ The synovial flap can be trimmed into a suitable shape according to the need of an operation, and the joint capsule can be repaired strictly to avoid synovial fluid leakage. ④ There is no restriction on early rehabilitation after TKA.
At present, only a few studies have reported the effect of knee osteoarthritis with permanent dislocation of the patella on the repair of the joint capsule in TKA; most are case reports, and the number of patients included is small8, 12, 25, 30, 31 because knee osteoarthritis with permanent patellar dislocation is a complex deformity with a relatively low incidence8, 12, 25, 30, 31. Due to the different follow-up times of each study, the functional scores used are also different, and most studies do not record specific pain scores8, 12, 25, 30, 31. Therefore, prospective studies with larger sample sizes are needed to compare the differences between different methods of joint capsule repair.
Prosthesis
TKA for patients with permanent patellar dislocation requires extensive release, and some scholars suggest using restricted prostheses18. Some scholars have successfully used unrestricted prostheses to perform TKA for this kind of patient32. Therefore, a restricted prosthesis is not necessary for osteoarthritis patients with permanent patellar dislocation. The key lies in the degree of knee valgus and intraoperative soft tissue balance. In this study, the balance of the collateral ligament was well restored, and an ordinary knee prosthesis was selected. Only two patients chose a plus spacer because of a slight relaxation of the unilateral ligament.
Limitations
This study also has the following limitations: osteoarthritis with permanent patellar dislocation is a rare disease, so the number of patients included in this study is relatively small; the follow-up time in this study is short, and we cannot determine the long-term survival rate of the postoperative prosthesis; and in this study, without a control group and randomization, it is impossible to compare the differences in different methods of repairing joint capsules. In future research, the therapeutic effect of this new medial synovial flap transposition repair method can be compared with that of other surgical methods.