Indications for Supramalleolar Osteotomy Based on Arthroscopic Findings for Varus Type Ankle Osteoarthritis

Background: Preoperative arthroscopic examinations were carried out in patients with varus deformity among those with osteoarthritis of the ankle caused by malalignment, and to assess the severity of the disease on the basis of the arthroscopic findings, and the associations of these findings with X-ray findings and the indications for supramalleolar osteotomy were evaluated. Methods: A total of 57 joints in 56 patients were investigated, and the mean follow-up period was 4 years. The proportion of the surface area of the ankle that had become hardened into an eburnation was classified according to a five-grade scale on the basis of preoperative arthroscopy: Grade 1 indicated fibrillation of the articular cartilage alone with no evident eburnation; Grade 2, eburnation was limited to the medial malleolar articular surface; Grade 3, eburnation extended across the medial shoulder of the talus, but covered <25% of the talocrural joint; Grade 4, eburnation covered ≥25% but <50% of the talocrural joint; and Grade 5, eburnation covered ≥50% of the talocrural joint. The surgical procedure used was lateral closing wedge osteotomy, and assessments were carried out using Takakura et al.’s clinical score and Tanaka et al.’s radiographic grading system. Results: Initially, 3 joints were Grade 1, 19 were Grade 2, 15 were Grade 3, 16 were Grade 4, and 4 were Grade 5. Postoperatively, 30 joints were Grade 1, 14 were Grade 2, 7 were Grade 3, 4 were Grade 4, and 2 were Grade 5. Clinical scores showed an improvement from 63.9±11.2 points preoperatively to 81.9±13.2 points postoperatively. Conclusion: Patients who were classed as Grade 3 or below by preoperative arthroscopy showed improved clinical outcomes and radiographic grades. To assess the proportion of cartilage, that may be affect postoperative outcomes, preoperative arthroscopy should be done prior to the supramalleolar osteotomy. Introduction Osteoarthritis of the ankle that is caused by malalignment of the leg is classified as either varus type or valgus type according to the inclination of the talus, with the varus type accounting for the majority of cases. Mild to moderate varus-type osteoarthritis of the ankle is treated surgically with supramalleolar osteotomy, the indication criteria for which are generally determined by plain X-ray evaluation. Takakura’s four-grade classification [1] is conventionally used, and Tanaka et al. have further subdivided Stage 3 into Stage 3a, in which the joint space in the ankle joint has been lost, and Stage 3b, in which narrowing of the joint space extends to the medial side of the talocrural joint, with surgery indicated up to Stage 3a [2]. Although Takakura et al. found that arthroscopy after low tibial osteotomy showed that areas of the joint surface that had been ulcerated preoperatively were covered in fibrous tissue postoperatively, with biopsy demonstrating the presence of fibrous tissue and fibrocartilage within this granulation tissue [1], few studies have yet addressed preoperative arthroscopy of this joint. In this study, preoperative arthroscopy was performed to ascertain the condition inside the joint and to assess the severity of the disease on the basis of the arthroscopic findings, and the associations of these findings with X-ray findings and the indications for supramalleolar osteotomy were evaluated. Material and Methods Fifty seven ankles of 56 patients who underwent supramalleolar osteotomy to treat varus-type osteoarthritis of the ankle caused by malalignment between June 1993 and February 2013 were evaluated in this study. There were 11 joints in men and 46 in women. The patients’ mean age at the time of surgery was 58.3 years (range 36–76 years), and the mean postoperative follow-up period was 4 years (range 1 year to 15 years 1 month). All subjects underwent preoperative arthroscopy with a 2.7-mm-diameter 30o oblique arthroscope, which was repeated 1 year postoperatively when the internal fixation device was removed. The surgical procedure consisted of a lateral closing wedge supramalleolar osteotomy of both the tibia and fibula at a height of 5 cm proximal to the ankle joint, with the osteotomy angle being the angle formed by the sole of the foot and the articular surface of the talar trochlea on weight-bearing frontal X-ray images taken while standing on one leg on the affected leg, and both bones fixed with plates. Postoperatively, after three weeks of casting, the patients were instructed to walk wearing a patellar tendon-bearing orthosis, and range of motion (ROM) exercises of the ankle were performed. After 12 weeks, the orthosis was removed, and the patients were instructed to walk with full weight-bearing. Since arthroscopy reveals eburnation from the malleolar articular surface to the talocrural joint surface, it has been suggested that the eburnation rate may indicate severity; therefore, the disease state was classified into the following five categories: Grade 1, fibrillation of the malleolar articular surface alone with no evident eburnation; Grade 2, eburnation limited to the malleolar articular surface; Grade 3, eburnation that extended across the medial shoulder of the talus but covered <25% of the articular surface of the talocrural joint; Grade 4, eburnation that covered ≥25% but <50% of the articular surface of the talocrural joint; and Grade 5, eburnation covering ≥50% of the articular surface of the talocrural joint. A probe with a scale was used to measure the proportions of healthy and eburnated cartilage, and the severity was assessed by multiple doctors. Preoperative and postoperative clinical assessments were carried out following the assessment method of Takakura et al. [3], and Tanaka et al.’s grading system was used for radiographic assessment. Statistical analysis was performed using Wilcoxon’s signed rank test to test for differences between preoperative and postoperative clinical outcomes. P value of < 0.05 was considered statistically significant. Results In terms of preoperative arthroscopic classification, 3 joints were Grade 1, 19 were Grade 2, 15 were Grade 3, 16 were Grade 4, and 4 were Grade 5. Postoperatively, 30 joints were Grade 1, 14 were Grade 2, 7 were Grade 3, 4 were Grade 4, and 2 were Grade 5. The postoperative arthroscopic classification grade was worse than the preoperative grade for 3 joints (Table 1). The mean clinical assessment score improved significantly from 63.9 ± 11.2 points (range 38–93 points) preoperatively to 81.9 ± 13.2 points (range 43–100 points) 1 year postoperatively and 82.1 ± 12.3 points (range 48– 100 points) at final follow-up. The difference between the preoperative and postoperative scores was significant (p < 0.01). The difference between the preoperative and final follow-up scores was also significant (p < 0.01). In terms of the association between the preoperative arthroscopic assessment and the clinical assessment score, joints that were Grade 4 or above tended to have worse clinical scores (Figure 1). On radiographic assessment preoperatively, 2 joints were Stage 1, 18 were Stage 2, 14 were Stage 3a, and 23 were Stage 3b, while postoperatively, 17 joints were Stage 1, 24 were Stage 2, 11 were Stage 3a, 3 were Stage 3b, and 2 were Stage 4. With respect to the association between preoperative arthroscopic classification and radiographic staging, the modal value for each grade corresponded to the radiographic stage, with Grade 2 of the arthroscopic classification corresponding to radiographic Stage 2, Grade 3 to Stage 3a, and Grade 4 to stage 3b. Stage 3b, however, also included many joints of grades other than Grade 4 (Table 2). In terms of the association between the preoperative arthroscopic assessment and the postoperative radiographic assessment, joints that were Grade 3 or below tended to show much improvement in radiographic stage (Table 3, Figure 2). Two patients, both of whom were Grade 4 on preoperative arthroscopic classification, underwent additional surgery for ankle joint fixation due to the progression of postoperative osteoarthritic change. Discussion Varus-type osteoarthritis of the ankle is believed to be caused by distal tibial malalignment, such as tilting of the tibial plafond, or other conditions, such as lateral ankle ligament insufficiency [4]. In a biomechanical study on cadavers, it was reported that distal tibial deformities showed changes in the contact area, the contact shape, and the contact location [5]. The type of treatment depends on the stage of the disease, and supramalleolar osteotomy generally indicated when it is of mild to moderate severity [1,2,6-8], but studies of the indication criteria for supramalleolar osteotomy are controversial. According to Tanaka et al., supramalleolar osteotomy is indicated in cases that are Stage 2 or Stage 3a on plain X-ray [2]. Barg et al. and Easley et al. stated that the indications for supramalleolar osteotomy comprise asymmetric ankle OA with concomitant valgus or varus deformities and a partially (at least 50%) preserved tibiotalar joint surface [9,10]. Lee et al. reported that it is indicated for patients with minimal talar tilt and neutral or varus heel alignment [11]. According to Colin et al., the surgery is indicated if the ‘sidewalk sign’ (pain relief on a sloped surface tilted in the opposite direction of the deformity) is positive [12]. Haraguchi et al. found that, in ankles in which the preoperative mechanical ankle joint axis point is more medial than the tibial plafond, the point was insufficiently moved to the lateral side, and the clinical outcomes were less satisfactory [13]. There are reports in the literature on arthroscopic assessment before and after supramalleolar osteotomy. Cheng et al. reported improvement in Outerbridge grade [14] from grade 3–4 preoperatively to grade 1–2 postoperatively [15], while Takakura et al. performed arthroscopy following low tibial osteotomy and found that joint surfaces that had been ulcerated preoperatively