All cases in this study were followed up for 1.5-5 years. All patients had significant reduction or disappearance of anterior knee pain at 1 month and 1 year after surgery. The Lysholm score, medial pushing distance of the patella, Kujala score, and VAS in the OSM group and the TSM group were significantly improved at the last follow-up than before surgery(P<0.05). Five patients had heamarthrosis postoperatively in the TSM group, and comprehensive treatments such as rest, local compression bandaging, ice compress, raising the affected limb, puncture and drainage of joint cavity, and plaster or brace braking were managed for those patients. All the patients were all relieved and returned to normal. After the symptoms were relieved, functional exercise was restored. Three cases of joint adhesion in the TSM group and 1 cases in the OSM group were relieved after manual loosening. None infection, deep vein thrombosis and other complications were observed in the TSM group. No postoperative complications such as infection, joint hematoma, and deep vein thrombosis occurred in the OSM group. Arthroscopic closing LPRR for the treatment of LPCS can effectively improve the function and symptoms of the patellofemoral joint. It has the advantages of small trauma, rapid recovery and less complications. But, the number of hemarthrosis and joint adhesion were significantly higher in the TSM group than in the OSM group.
Under normal circumstances, the commissure relationship between the patellofemoral joint has good adaptability. When the normal anatomical alignment of patellofemoral joint was disturbed due to various reasons, the muscle strength around the patella will be unbalanced and the LPR will be contracted, resulting in abnormal patella trajectory and abnormal contact of the patellofemoral joint surface during knee flexion and extension. The stress in local articular surface of patella will be increased and the inner and outer pressure distribution will be uneven, which causes damage to secondary articular cartilage [1]. As time goes on, cartilage damage will be aggravated and pain in the knee will be produced, which develops into LPCS. Therefore, arthroscopy could directly measure cartilage contact pressure during surgery to guide the precise release of LPR, which can balance the stress inside and outside of the patellofemoral joint to reduce further cartilage degradation postoperatively. In this study, there were 30 and 27 cases of traumatic history in the TSM group and the OSM group respectively. So trauma was an important cause of LPCS.
Researchers first proposed that the LPR should be released for the cause of this disorder, so that the laterally displaced patella returns to its normal position, and the pressure between the patellofemoral articular cartilage tends to be balanced [16]. The release method includes three types: incision, arthroscopic assisted incision, and arthroscopic closure releasing [14, 17]. The first two methods need to open the patellofemoral joint, and its wound is large. Although it can directly look at the site of the LPRR, it cannot directly look at the improvement of the relationship between the patellofemoral joint during the release process, and often causes insufficient or excessive release to affect the prognosis.
Closed release LPR under arthroscopy could directly observe the change of the patella position, adjust the location and extent of the release, and not need to suture locally[18]. After the surgery, the elastic bandage was pressure-wrapped and fixed in the slightly medial displacement of the patella, which can prevent the formation of blood and hemarthrosis. Besides, early active rehabilitation training for patients after LPRR will significantly improve efficacy and prevent postoperative re-adhesion. Patients in the TSM group and the OSM group were followed up for an average of 3.4 and 3.5 years without serious complications. The position of the patella was basically normal. 3 and 2 cases respectively in the TSM group and the OSM group with severely damaged articular cartilage were not working well. So, patients with Outerbridge grade IV of patella are not suitable for arthroscopic LPRR treatment alone.
Fulkerson et al [19] found that LPRR can effectively correct the lateral petalla tilt by CT scan before and after surgery. In the TSM group, the synovium, joint capsule and LPR were cut apart under arthroscopy from the joint, resulting in partial synovial membrane loss, which easily caused intra-articular hemorrhage and joint adhesion that affect the surgical effect. The biggest feature of the OSM group is to retain the synovial membrane, which can reduce joint hemorrhage and postoperative adhesion due to the intact synovial membrane. Therefore, we found that the incidences of joint hemorrhage and joint adhesion were significantly higher in the TSM group than in the OSM group.
The advantages of closed LPRR under arthroscopy are as follows: ① Small trauma is good for quick recovery, rehabilitation and functional exercise. Besides, arthroscopic debridement can be performed under arthroscopy, which can remove the articular cartilage debris, inflammatory factors and calcium salt crystals that cause pain in the knee joint, and remove the swelling and degeneration of the articular cartilage, tearing meniscus, hyperplastic synovial folds and osteophyte, etc. to improve the internal environment of the joint. ② Patelloplasty could be performed simultaneously to reduce the impact between the lateral articular surface of patellofemoral joint. ③ Arthroscopic closed LPRR can dynamically and intuitively observe the patella trajectory, patellofemoral joint contact pressure and the degree of cartilage degeneration of the affected articular surface. Besides, it also can accurately determine the condition and dynamically observe the release effect in time being beneficial to accurate operation.
The surgeons should pay attention to the following points during the operation. ⑴ The obvious hyperplasia and deformation of the lateral patella should conduct patelloplasty. ⑵ The osteophyte of the patella trajectory should be removed; ⑶ Hemostasis using arthroscopic electrocoagulation needs to be thorough to reduce the risk of blood in the joint and accelerate postoperative recovery. ⑷ The scope of release should be thorough. Most scholars recommend starting from l-2 cm of the proximal end of the patella, at least to the anterio-lateral entrance. Marumoto et al [20] found that retinacula cut from the inferior third of the vastus lateralis tendon down to the tibial tubercle.
The shortcomings of this study are the small number of cases. In addition, this was not a randomized controlled trial (RCT); the clinicians and patients were not totally blinded to the group assignment. All of these observations need further confirmation in large-sample multi-center prospective randomized controlled trials.