Study design and setting
Inclusion criteria: (1) Takakura stage II-IIIb varus ankle osteoarthritis; (2) worsening pain and seriously impaired daily activities after 6 months of conservative treatment; (3) intact lateral tibial articular surface and <50% necrosis of the talus; (4) age 18-65 years with high activity demands; (5) follow-up time >2 year after surgery.
Exclusion criteria: (1) Takakura stage IV ankle osteoarthritis with severe joint degeneration; (2) tibial double osteotomy procedure using internal fixation; (3) extensive bone and soft tissue defects after previous surgeries; (4) complications such as Charcot joint, rheumatoid osteoarthritis, ankle deformity, chronic infection, and comorbidities of diabetes, smoking, osteoporosis, and other vascular and neurological diseases.
Participants
From August 2018 to June 2022, a total of 55 patients with varus ankle osteoarthritis were identified for this study, with 52 patients followed up after surgery and 3 lost follow-up. Among 52 patients, 19 patients in the SMOT with Ilizarov technique group (treatment group) and 33 patients in the SMOT with internal fixation group (control group) were included in this study. All patients underwent weight-bearing anteroposterior ankle X-rays, weight-bearing lateral ankle X-rays, Saltzman X-rays, ankle joint computer tomography (CT) scans, and measurements of tibial articular surface angle (TAS), tibial lateral surface angle (TLS), talar tilt (TT), tibiocrural angle (TC), tibial medial malleolar angle (TMM), hindfoot alignment angle (HAA), and modified Takakura stage by two experienced attending physicians (Figures 1, 2).
Treatment group: The treatment group consisted of 19 patients (19 feet), including 11 males and 8 females, with an average age of 44.21±14.27 years, a body mass index (BMI) of 25.94±4.41 kg/m2, a disease duration of 7.42±6.34 years, and a follow-up time of 37.63±10.57 months. According to the modified Takakura stage, there were 5 cases of stage II, 7 cases of stage IIIa, and 7 cases of stage IIIb. Control Group: The control group consisted of 33 patients (33 feet), including 18 males and 15 females, with an average age of 50.45±14.06 years, a BMI of 25.18±2.71 kg/m2, a disease duration of 8.38±6.36 years, and a follow-up time of 40.09±11.02 months. According to the modified Takakura stage, there were 12 cases of stage II, 15 cases of stage IIIa, and 6 cases of stage IIIb. There were no statistically significant differences in general data between the two groups (P > 0.05) (Table 1).
Preoperative Planning
Weight-bearing examination is necessary, and weight-bearing anteroposterior ankle X-rays, and weight-bearing lateral ankle X-rays play a key role in comparing the affected and unaffected ankles, assessing leg length discrepancy, pelvic tilt, hindfoot varus/valgus deformity, and knee varus/valgus deformity [38]. Ankle joint CT scan has a good evaluation effect on ankle osteoarthritis that are difficult to determine by X-ray, and can accurately define the specific affected area of the ankle joint. In order to achieve complete adjustment of the foot and ankle deformities, this study performed medial wedge osteotomy at the CORA level [39]. Varus ankle osteoarthritis often involve the coronal and/or sagittal planes, affecting multiple joints above and below the ankle, and affecting the overall lower limb alignment. Therefore, comprehensive identification and precise planning must be performed preoperatively [40]. Preoperative planning at a level higher or lower than the deformity level will result in translation displacement. This study performed ankle joint thin-layer CT scanning with a slice thickness and interval of 0.625 mm. Arigin 3D pro (Shanghai Xinjian Medical Technology Co., Ltd.) was used to create a three-dimension (3D) reconstruction model to determine the center of rotation and angulation (CORA). Finite element mechanical analysis was used to create a digital model of varus ankle osteoarthritis, and parameters such as correction angle, osteotomy position, and size of wedge bone graft required for deformity correction were calculated based on the model. The target TAS was set at 90-92°, the target TLS was set at 80-85°, and the target TT was set at 0-4°.
Surgical procedure
The patients were placed in a supine position under general anesthesia with the ipsilateral hip elevated and a tourniquet applied after routine disinfection. An incision was made in the anterior aspect of the ankle, which served as the observation and operation ports for arthroscopy. Arthroscopy was performed to explore and clean the synovial and fibrous scar tissue, bone spurs, and joint spaces. Complete release of the ankle joint was performed until dorsiflexion reached 20°.
SMOT was then performed. A longitudinal incision was made above the medial malleolus, exposing the osteotomy plane. A pre-designed 3D printed guide for SMOT was installed through the medial incision, and Kirschner wires were used to fix the guide. Osteotomy was performed at the designated site using an oscillating saw with guidance from the osteotomy guide. Care was taken to preserve the outer cortex of the tibia on the lateral side as a pivot point. Fluoroscopy was used to confirm the satisfactory position and correction of the osteotomy, and the guide was removed. Then a pre-designed distractor was gently applied to the medial osteotomy surface.
The treatment group used Ilizarov ring fixator for external fixation. Kirschner wires and Schanz pins were inserted into the distal tibia, calcaneus, wedge bone of the midfoot, and metatarsals 1-5. A ring frame was installed in the middle and lower segments of the tibia and a semi-ring frame was installed in the foot. These frames were assembled using connecting rods. Traction was applied to the ankle joint, and the foot and ankle were maintained in a dorsiflexion-neutral position to allow postoperative joint movement. Intraoperative fluoroscopy was used to confirm that the ankle joint space had been stretched to 5mm (Figure 3, 4).
In the control group, autogenous bone graft from the ipsilateral ilium or allograft cortical bone graft was used. These grafts were shaped according to a pre-designed trial model and implanted into the osteotomy site to fill the gap. An appropriate locking plate was selected to fix the distal tibia osteotomy site (Figure 5).
Preoperatively, the need for fibular osteotomy was determined based on fibular length and joint congruity. If necessary, fibular osteotomy was performed above the distal tibiofibular syndesmosis to adjust the position and length of the fibula. For patients with residual hindfoot varus deformity, calcaneal osteotomy was performed. For those with chronic ankle instability, a modified Brostrom procedure was performed intraoperatively. For patients with osteochondral lesions of the talus, the lesions was debrided using microfracture/bone marrow stimulation during arthroscopy. For patients with reduction of medial clear space, triangular ligament release was performed. For patients with limited dorsiflexion range of motion, per Silverskiod test results, either gastrocnemius recession or Achilles tendon lengthening was performed. Fluoroscopy was used to confirm restoration of the tibiofibular joint space and correction of the hindfoot alignment.
Auxiliary procedures in this study included a modified Brostrom procedure in 38 cases, gastrocnemius recession or Achilles tendon lengthening in 32 cases, iliac bone grafting in 32 cases, arthroscopic microfracture in 19 cases, calcaneal osteotomy in 16 cases, posterior ankle arthroscopy in 2 cases, and LARS ligament reconstruction in 1 case.
Aftercare and follow-up routine
In the treatment group, patients were instructed to perform joint distraction with the Ilizarov ring fixator twice a day, with a distraction rate of 0.5mm each time, for at least 3 months. Weight-bearing and ankle joint motion were prohibited for the first 6 weeks after surgery. The Ilizarov ring fixator was removed 3-4 months postoperatively, and ankle joint manipulation was performed under anesthesia to prevent joint adhesion. After the removal of the Ilizarov ring fixator, a inflatable walking boot was immediately used to allow partial weight-bearing for 1 month. After confirming the bony union of the osteotomy site through imaging examination, full weight-bearing could start. Following the removal of internal fixation, physiotherapy was continued for 2 months to improve range of motion, lower limb strength, and proprioception (Figure 6).
In the control group, conventional support fixation was applied using an inflatable walking boot or short leg cast after surgery. Leg elevation training, active toe and ankle joint exercises could be performed from the second day onwards. Weight-bearing was prohibited within the first 6 weeks, and after confirming the formation of callus at 6 weeks postoperatively, the patients were allowed to bear weight with the support. After confirming the bony union of the osteotomy site through imaging examination, full weight-bearing could start (Figure 7).
Outcome measures
Outcome measurements included the AOFAS ankle-hindfoot score, AOS, VAS, ROM, as well as radiographic parameters including TAS, TLS, TT, TC, TMM, HAA, and modified Takakura grade. The AOFAS ankle-hindfoot score assesses pain, function, gait, range of motion, stability, and alignment, with a maximum score of 100. Scores of 90-100 are considered excellent, 75-89 good, 50-74 fair, and below 50 poor. VAS score ranges from 0 to 10, indicating the severity of pain. To analyze changes in imaging grading, a quantitative scoring system was used, with scores of 2, 3, 4, and 5 assigned to modified Takakura grades II, IIIa, IIIb, and IV, respectively. Complications were also observed.
Statistical Analysis
Statistical analysis was performed using SPSS 26.0 software. The Shapiro-Wilk test was used to assess the normality of the data. Normally distributed continuous variables are presented as mean ± standard deviation (x̄ ± s), and paired-sample t-tests were used to compare preoperative and final follow-up measurements within each group. Independent-sample t-tests were used to compare measurements between the two groups. Skewed distributed continuous variables are presented as M (Q1, Q3), and Wilcoxon signed-rank tests were used to compare preoperative and final follow-up measurements within each group. Wilcoxon rank-sum tests were used to compare measurements between the two groups. Spearman’s correlation analysis was used to assess the correlation between radiographic parameters (TAS, TT, TLS, TT, TC, TMM, HAA, modified Takakura stage) and clinical outcomes (VAS and AOFAS scores) at the final follow-up. A p-value < 0.05 was considered statistically significant.