This study prospectively compared the outcomes of AOPT and AOCT as surgical options for large cystic OLTs. No significant statistical difference was observed between the AOPT and AOCT groups in any of the variables for clinical and radiographic outcomes except for donor-site morbidity, for which the AOPT group showed a better outcome compared to the AOCT group.

The importance of subchondral bone in the pathogenesis of lesions of the subchondral region of the OLT has been well discussed by Deng et al. [21]. They found that when trauma causes damage to the cartilage and subchondral bone plate, high-pressure liquid flows continuously into the subchondral bone, which induces osteolysis and subchondral cysts [21]. In addition, previous studies reported that subchondral cysts had a negative impact on clinical outcomes after surgery such as microfracture or abrasion arthroplasty [22, 23]. Hence, it is necessary for patients to undergo replacement techniques such as AOPT and AOCT in the treatment of OLTs with a large subchondral cyst (a diameter larger than 10 mm). We support the notion that the subchondral bone plate could play an important role in maintaining cartilage metabolism by supporting the normal ankle pressure and blocking the brunt of the continuous high-pressure articular liquid. Therefore, AOPT and AOCT achieve satisfactory outcomes for OLTs with large cystic lesions by reconstructing the normal subchondral bone plate.

In this study, sex, age, BMI, lesion size, lesion location, and second-look arthroscopy history were matched before enrolment in order to decrease the effect of potential confounders such as the degree of lesion chronicity and patients’ activity levels before surgery on outcomes. Symptoms and history of trauma were also compared before analyzing outcomes. In the present study, postoperative clinical and radiologic outcomes were examined in detail in both groups at approximately 12 months of follow-up. In the AOPT group, the AOFAS score significantly improved from a mean of 71.14 to 91.29, the VAS score significantly improved from a mean of 6.08 to 1.02, the AAS significantly improved from a mean of 1.26 to 7.58, the mean postoperative MOCART score was 75.08, and the mean ICRS score was 10.08 at second-look arthroscopy. In the AOCT group, the AOFAS score significantly improved from a mean of 70.51 to 91.74, the VAS score significantly improved from a mean of 6.05 to 1.15, the AAS significantly improved from a mean of 1.18 to 7.34, the mean postoperative MOCART score was 76.85, and the mean ICRS score was 10.32 at second-look arthroscopy. These results show that excellent clinical and radiologic outcomes were achieved when using these two techniques in the treatment of OLTs with large subchondral cysts, which is similar to previous research [7, 8, 10, 24].

Moreover, in this study, compared with the AOCT group, there was no significant statistical difference in postoperative AOFAS score, VAS score, RTA, rate of return to previous sports level, rate of satisfaction, MOCART score, and ICRS score in the AOCT group. We believe that both two techniques are simple, safe, and effective surgical procedures for the treatment of large cystic OLTs, providing effective graft replacement and joint pressure support. However, AOPT yielded a better outcome in donor-site morbidity compared to the AOCT group. In the AOCT group, the graft was harvested from the non-weight-bearing portion of the medial femoral trochlea in the ipsilateral knee, so patients with donor-site morbidity would feel symptomatic and experience pain when climbing stairs. We support the notion that friction of the patella and femoral trochlea during knee flexion may increase donor-site morbidity of the ipsilateral knee. In addition, graft harvesting can cause the release of intra-articular proinflammatory cytokines that can induce pain postoperatively, leading to a symptomatic knee, which has become a concerning shortcoming of AOCT [25].

Various studies have reported clinical outcomes of AOPT for the treatment of large cystic medial OLTs, and grafts were harvested from the ipsilateral anterior superior iliac spine [10, 24, 26,27,28,29,30]. However, in our study, the autografts in the AOPT group were taken from the medial tibia instead of the iliac crest, which is similar to Chen et al [12]. Harvesting autografts from the tibia could reduce surgical incisions, which could reduce the risk of wound infection and sciatic nerve injury.

Cao et al. [31] found that the periosteal bone column of a patient had grown well but that several small low‐density areas appeared on the surface of the bone column, and these areas showed a relatively minor improvement in terms of their postoperative evaluation indicators. These findings may be related to premature weight‐bearing by the patient or to a re‐sprained ankle following surgery [28]. However, in our study, all patients in both groups were immobilized in a short leg cast, there was no weight bearing on the affected limb for 6 weeks after surgery, and partial weight bearing was allowed 7 to 8 weeks after surgery. At 8 weeks after surgery, full weight bearing was allowed, after healing of the osteotomy was confirmed by X-ray. Hence, in our study, all patients in both groups indicated that they were satisfied with the surgery in their overall subjective evaluation because of the scientific postoperative rehabilitation.

It is important to consider the limitations of this study. The duration of the follow-up period in this study was limited to a specific timeframe, and the long-term effects of AOPT versus AOCT therapy were not evaluated. Therefore, we will follow up at 5 years postoperatively in the future. Moreover, future prospective multi-center studies with longer follow-up periods are needed to provide more comprehensive insights into the comparative effects of these two treatment approaches. In addition, the lack of blinding could have introduced observer bias. While our study demonstrated significant positive outcomes of AOPT, several questions remain unanswered, presenting avenues for future research. Because of the limitation of the sample, smokers and osteoporotic patients might also have been included in this study. Firstly, the long-term effects of AOPT versus AOCT on clinical outcomes need to be explored. The biomechanical and histological outcomes of AOPT versus AOCT in the treatment of large cystic OLTs also need to be examined. Future research that endeavours to address these unanswered questions will contribute to a deeper understanding of the therapeutic potential of AOPT and further optimize its application in clinical practice.