The habitual patellar dislocation is often accompanied by multiple anatomical abnormalities and medial retinacular injury of knee joint, and surgical procedure is mostly used clinically[2, 3]. In patients with acute patellar dislocation, there is a high probability of injury of medial patellofemoral ligament of the knee[4, 11, 12]. Furthermore, some studies [4, 6] confirmed that the medial patellofemoral ligament of the knee can provide 50%~60% of the medial restraint of the patella flexed at 0°~30°, and play a major role in maintaining patellar stability. Therefore, MPFL is the leading stable structure of medial patella, and MPFL reconstruction is increasingly focused on[7].
However, it should be noted that MPFL reconstruction can only anatomically restore the static stable structure of medial patella, and cannot correct the abnormality in lower extremity bony lines. Hopper et al[13] found that in their study, among patients undergoing MPFL reconstruction, the relocation rate in patients with severe trochlear dysplasia was 100%, but in patients with low-grade trochlear dysplasia was 9.3%. Schöttle et al.[8] studied the relationship between arthroscopic MPFL repair and trochlear dysplasia, and found that at 12-month follow-up, 0/26 knees had re-dislocation in the none/mild trochlear dysplasia group, while 4/22 knees had re-dislocation in the severe trochlear dysplasia group. In the severer trochlear dysplasia group, the surgical efficacy was limited, indicating that MPFL reconstruction alone was not enough. Therefore, for patients with concurrent changes in bone structure such as high patella, knee valgus or retroflexion deformity, femoral internal and external rotation, tibial tubercle ingression and severe femoral trochlear dysplasia, osteotomy orthopedics, tibial tubercle ingression surgery and femoral trochlear plasty are often required. Therefore, for patients with recurrent patellar dislocation, the appropriate surgical procedure should be selected based on comprehensive analysis and judgment from detailed physical examinations and comprehensive imaging and arthroscopic findings.
For patients with patellar inclination angle > 20°, MPFL reconstruction in combination with lateral patellar retinacular release technique can be performed to increase the ingression degree of patellar. However, some studies have shown that the lateral retinaculum plays only a secondary role in the patellar soft tissue stable structure[14]. Therefore, lateral retinacular release alone may have a good early surgical effect, but the effect will gradually decline over time[15]. In this study, the technique was only used as part of the combined surgery to loosen the lateral patellar traction structure and increase the ingression degree of patellar. During the intraoperative retinacular release under microscopy, at 1–1.5 cm from the outer edge of the patella, use a plasma radiofrequency scalpel to gradually loosen from the proximal end to the distal end to reach deep into the subcutaneous fat layer or muscular layer. Usually after full release, widening of the lateral patellofemoral space or an increase in patellar lateral ROM can be observed. In this study, the patient's patellar tilt angle was corrected from 31.5°±13.7° (20.3°~58.4°) before operation to 10.7°±2.6° (5.6°~15.3°) after operation (P < 0.05), lower than the surgical threshold. The postoperative effect was good.
Stephen et al.[16] studied the effect of different TT-TG distances on the surgical effect in 8 knee joint specimens. The results showed that in the normal anatomical position of the tibial tubercle and within 5 mm range of outward displacement, the MPFL reconstruction can correct the patellar outward displacement and restore normal medial patellofemoral joint pressure and patellar tilt angle, so it is recommended that if the TT-TG distance is > 15 mm, tibial tubercle ingression surgery should be considered. Schöttle et al.[8] believed that the clinical effect of MPFL reconstruction alone or lateral retinacular release alone was not good in patients with concurrent femoral trochlear severe dysplasia. In this study, if TT-TG distance was > 20 mm, the tibial tubercle ingression was performed to make the TT-TG distance close to 10 mm after ingression. With regard to the patellar depression limit, it’s believed that the patellar depression limit was 10.0 mm, or it may cause excessive pressure on the patellofemoral joints and resultant postoperative knee pain. In this study, 20 knees were treated with tibial tubercle osteotomy, of which 11 knees were treated with lateral release + tibial tubercle ingression + MPFL reconstruction, and 9 knees were treated with lateral release + tibial tubercle ingression and depression + MPFL reconstruction. The average postoperative TT-TG distance improved to 4.5 mm ~ 17.1 mm (10.8 ± 4.3) mm (P < 0.05). The average Caton-Deschamps index improved to 1.02 ~ 1.15 (1.07 ± 0.06), (P > 0.05). The clinical efficacy was good.
The initial tension required for MPFL graft fixation should be appropriate, but it is difficult to be determined accurately and there is currently no clear reference standard. In this study, the MPFL reconstruction with 30° flexion was generally used in the study. The knee joint was fully flexed and extended. At the same time, the patellar trajectory and reduction alignment were observed under arthroscopy to confirm that the patella was well stabilized with no lateral dislocation and patellar lateral tilting I°, suggesting that the graft tension was appropriate for fixation.
This study had certain limitations, and minors were not included in this study due to involvement of epiphysis. The sample number was small and the follow-up time was short, so there may be errors in the reported results.