The most important finding of this study is that in the treatment of medial Hepple IV-V OLT, patients who underwent arthroscopic autologous cancellous bone grafting showed an early advantage in functional recovery at the 3-month follow-up compared to those who underwent medial malleolar osteotomy combined with autologous periosteal iliac bone grafting. By 1 year postoperatively, the outcomes of both methods tended to be equivalent, with the arthroscopic approach avoiding the need for osteotomy. We also found that both surgical methods significantly relieved pain, restored function, and improved cartilage repair. The results of this study confirm that minimally invasive surgery has comparable efficacy to traditional open surgery, with faster functional recovery and shorter surgical time, providing more evidence for the clinical selection of minimally invasive approaches in treating medial Hepple IV-V OLT.

By comparing VAS scores, AOFAS scores, and ankle joint mobility, we found that at 3 months postoperatively, Group A had significantly higher AOFAS scores and ankle joint mobility compared to Group B, while at 1 year postoperatively, there were no significant differences in AOFAS scores and ankle joint mobility between the two groups. This reflects that Group A showed an early advantage in functional recovery at the 3-month follow-up, and by 1 year postoperatively, the outcomes of both groups tended to be equivalent. Additionally, at both 3 months and 1 year postoperatively, VAS scores, AOFAS scores, and ankle joint mobility in both groups were significantly higher compared to preoperative levels, indicating that both surgical methods significantly relieved pain and restored function. To further assess cartilage repair, we evaluated the MOCART 2.0 ankle scores, which showed a significant increase from the early postoperative period to 1 year postoperatively in both groups, with no significant differences between the groups, reflecting a significant improvement in cartilage repair over time in both groups, and the outcomes were comparable. The surgical time for Group A was significantly shorter than Group B. This difference can be attributed to the additional time required for osteotomy and the internal fixation of osteotomy fragments in Group B.

In our study, we tried to evaluate the clinical significance of the observed improvements in both AOFAS scores and VAS pain scores following surgery for both treatment groups. To quantify the magnitude of change that is considered meaningful from a patient’s perspective, we compared our results with established benchmarks known as the Minimal Clinical Important Difference (MCID). Previous research has suggested that the MCID for VAS score changes is set at 2.7, and for AOFAS score changes, it is set at 8.9 [30]. The differences in both AOFAS and VAS scores pre- and postoperatively in our study exceeded these values for both groups, indicating that the observed changes are likely to be clinically meaningful. Regarding the improvement of mobility, our study assessed the total range of motion of the ankle joint, which can provide some insights into the overall mobility of the ankle. A comparison with existing literature on the improvement of mobility in similar clinical scenarios is challenging due to the lack of specific data on dorsiflexion and plantarflexion separately. However, our findings indicate that both surgical techniques resulted in significant improvements in overall ankle joint mobility.

When performing open autologous bone grafting surgery, surgeons typically harvest autologous bone grafts from non-weight-bearing areas to implant into the damaged site and replace damaged cartilage. In the selection of autologous bone grafts, previous studies have compared the clinical effects of autologous osteochondral transplantation with periosteal iliac bone grafting in the treatment of OLT, found that although both methods show positive effects in improving postoperative pain, joint function, and quality of life, periosteal iliac bone grafting performs better in reducing donor site complications and controlling postoperative pain [31]. This study used periosteal iliac bone grafting for Group B, and retrospective studies have shown that this method is effective for OLT and also shows satisfactory effects on the recovery of sports function [18, 32].

Considering the special anatomical structure of the ankle joint, traditional treatments for medial OLT usually involve medial malleolar osteotomy to achieve adequate exposure of the talus dome [19, 20], which disrupts normal bone anatomy and causes damage to the blood supply around the talus. Lee et al. [33] reported that in a second-look arthroscopy, 7.9% of patients had delayed healing and non-union, and 29% of patients had medial malleolar chondral damage due to osteotomy. Bull et al. [34] found that bi-plane chevron medial malleolar osteotomy fixed with two lag screws had a 30% malunion rate, with an average discrepancy of 2 millimeters on the final follow-up X-rays. Compared with traditional open surgery, the advantages of arthroscopic autologous cancellous bone grafting surgery are: ① Arthroscopic-assisted autologous cancellous bone grafting for OLT is a minimally invasive surgery, performed through small incisions, reducing surgical trauma and protecting the blood supply of local tissues [35], thereby reducing postoperative pain and inflammatory responses, and promoting early activity and functional recovery. ② It reduces the incidence of common complications in traditional open surgery, such as delayed union of grafts, malunion or non-union of osteotomies, infections, soft tissue damage, and osteoarthritis, thereby improving surgical safety and postoperative quality of life for patients, accelerating the recovery process, and potentially reducing patient hospital stays. ③ It does not require implantation of internal fixation devices, so it does not depend on intraoperative fluoroscopy, which makes the surgical time shorter, reduces the patient’s X-ray exposure, and avoids secondary surgery for the removal of internal fixation devices, thereby reducing surgical risks and alleviating the patient’s economic and psychological burden. With the development of arthroscopic technology, the advantages of traditional open surgery in providing a surgical field for OLT can now be achieved through arthroscopic surgery. Arthroscopic cancellous bone grafting in the treatment of OLT has been proven to significantly alleviate pain and restore function [22, 23], and our research findings indicate that its efficacy is not significantly different from that of open surgery. Through arthroscopy, surgeons can precisely remove damaged cartilage and perform grafting, allowing the transplanted cancellous bone to evenly cover the defective bone bed, achieving precise matching, thereby improving the success rate of grafting and the predictability of surgical outcomes. In this study’s arthroscopic autologous cancellous bone grafting surgery, microfracture technology was used in conjunction, drilling holes in the treated bone surface to create nutritional channels between cartilage and subchondral bone, establishing blood flow in the subchondral bone tissue, promoting the proliferation and migration of bone marrow mesenchymal stem cells to the cartilage defect area [1, 36]. The transplanted cancellous bone has a large number of trabecular spaces, providing convenient conditions for the growth of blood vessels and fibrous tissue, facilitating “creeping substitution“ [37,38,39]. In addition, the texture of cancellous bone is relatively soft, which is conducive to its filling of any shape of cavity, and can well adapt to the shape of the injury site, providing effective structural support [37]. This adaptability is particularly important for repairing irregularly shaped bone injuries, helping to restore the integrity and function of the bone [39]. It is reported that the incidence of complications in ankle arthroscopy surgery is about 7.69% [40]. In this study’s Group A cases, no complications related to surgical techniques occurred, and two patients in Group B had mild wound healing issues, which resolved within 1 month postoperatively after local dressing changes.

In our study, we focused on patients with Hepple IV-V OLT with a preoperative injury area greater than 15 mm2 and a maximum depth exceeding 4 mm. This size criterion was chosen because injuries exceeding this range are generally considered to require more aggressive surgical intervention [8, 9, 11, 17]. In our treatment, both surgical techniques were considered for injuries exceeding this size range. The area and depth of the lesion were our indicators of interest, but they did not determine the choice of specific surgical method. The decision to use arthroscopy or medial malleolar osteotomy was based on a comprehensive assessment of the lesion’s complexity, the potential for stable fixation and integration of the graft, as well as the patient’s overall condition and surgical risk factors. Notably, all patients in our study, regardless of the treatment group, met these size criteria, and there were no significant differences in preoperative lesion volume between the two groups, ensuring comparability in lesion characteristics and minimizing the potential for selection bias.

This study explores two effective surgical options for the treatment of medial Hepple IV-V OLT. Arthroscopic autologous cancellous bone grafting surgery, with its rapid recovery, fewer complications, shorter surgical time and avoiding osteotomy, can sometimes be the preferred treatment method, particularly for the young and active patient groups. However, for OLT patients with more complex injury, traditional medial malleolar osteotomy combined with autologous periosteal iliac bone grafting may provide more stable treatment effects, as open surgery provides a more convenient operating space for complex injury than arthroscopy. The choice of treatment method should be based on individuals’ circumstances and characteristics of the injury.

This study has some limitations. One of the primary limitations is related to the power of our study to detect smaller effect sizes for certain outcome measures. Although we conducted a post hoc power analysis, the results indicated that the power values for some of our outcomes were below the conventional threshold of 0.8, which is attributed to our relatively small sample size. Specifically, the power values of the VAS scores and 1-year postoperative ankle joint mobility were higher than 0.8, indicating that we could detect these larger effect indicators with certainty. however, the power values of the AOFAS scores, MOCART scores, and 3-month postoperative ankle mobility were below 0.8, indicating that our study was less powered to detect these smaller effect indicators. A larger sample size will be needed in the future to confirm our findings. Despite the smaller effect sizes of some outcome measures, our results suggest trends that are worthy of further investigation, and provide some insights into the effectiveness of the surgical techniques used. We believe these findings contribute to the existing literature and warrant further exploration in larger, more powered studies. Besides, the sample size is relatively small, which cannot perform subgroup analysis, and may affect the universality and extrapolation of the results. Furthermore, the follow-up time is short, and the long-term effects and potential long-term complications still need further observation. Additionally, the study lacks an assessment of the level of sports activity, especially for young patients.

Future studies should expand the sample size, conduct multicenter studies, and perform long-term follow-ups, to further verify the results of this study. It can also explore the applicability and efficacy of different surgical methods in different OLT typing, as well as the impact of individual differences on surgical outcomes, and assess the patient’s return to sports, while considering the type of sports (high-intensity or low-intensity) and the time required to return to sports, to better assess the long-term efficacy and safety of the two surgical methods.