The role of fibular for supramalleolar osteotomy in treatment of varus ankle arthritis: a biomechanical and clinical study

Supramalleolar osteotomy (SMOT) was first introduced by the American authors Speed and Boyd in 1936 [1] and was popularized after Takakura’s report in 1995 for the treatment of early- and mid-stage asymmetric ankle osteoarthritis (OA) [2]. Previous studies have reported that SMOT could restore the weight-bearing alignment of the ankle joint [3‐5], decrease the contact pressure of the medial part of the tibiotalar joint [6], restore the congruence of the tibiotalar joint surface [5, 7, 8], improve the chondromalacia [9], postpone the OA progress [10], and even reverse the radiological ankle OA stages [2, 9, 11, 12].

However, whether a fibular osteotomy is needed in SMOT still in controversial. Some authors have proposed combined fibular osteotomy for all SMOT patients [2, 12‐16], some have suggested that the fibula should always be preserved [3, 11, 17, 18], and some authors have performed fibular osteotomy depending on the conditions [4, 5, 7, 19]. Few studies have focused on the role of the fibula in SMOT. Stufkens et al. [6] reported that the tibiotalar contact force shifted in different directions with and without fibular osteotomy after SMOT. Furthermore, no clinical study has directly compared the outcomes of SMOT patients with and without fibular osteotomy. We hypothesized that (1) the tibiotalar joint contact area and stress changes differ in asymmetric ankles with and without fibular osteotomy, and (2) the patients in these groups have different clinical outcomes.

Ankle OA is a degenerative disease with a high rate of angular deformity of the distal tibial articular surface. Valderrabano et al. [25] reported that 55 % of patients with ankle OA presented with varus malalignment, whereas 8 % had valgus malalignment. It is well known that uneven pressure on the articular surface of the lower extremities is closely related to the degeneration of cartilage, which may induce and accelerate the progress of OA [26]. Realignment surgery based on this theory aims to redistribute the joint’s weight-bearing line and unload the degenerated articular surface onto more viable cartilage to delay the progress of OA.

Biomechanical studies suggest that distal tibial deformities are responsible for the contact pressure changes of the tibiotalar joint [1, 27]. Tarr and colleagues reported that distal tibial articular deformities with an angulation of 15° in the sagittal plane showed a 42 % decrease in the contact area [27]. Stamatis and colleagues found that a 10° valgus supramalleolar osteotomy decreased 42 % of the force on the medial talar dome [1]. Stufkens et al. [6] reported that the mean reduction in contact area was up to 36 % in cases with a 15° valgus deformity. According to the current study, the mean contact area decreased 18 % in 10° varus deformities and 14 % in 10° valgus deformities with the fibula preserved. However, after fibular osteotomy, the mean contact area decreased up to 27 % in 10° varus deformities and 37 % in 10° valgus deformities. Additionally, the mean contact pressure increased from 19 to 44 % under varus conditions after fibular osteotomy and from 17 to 47 % under valgus conditions. This difference likely arises because the fibular and relative lateral ligaments and syndesmotic ligaments prevented the changes in tibiotalar joint contact and stress transfer. Additionally, we agree with Becker and Myerson that the ability of the ankle and foot to tolerate deformity above the ankle joint depends on the flexibility and the ability of the foot to accommodate and compensate for the deformity [28].

Since Takakura’s report in 1995 [2], the published evidence for the use of SMOT as an alternative treatment for persistent painful asymmetric ankle OA increased rapidly during the last two decades [29]. The results showed good short- to mid-term outcomes for pain relief, functional improvement, and the resumption of sports and recreation activities [2‐5, 7‐9, 11, 12, 14‐18, 26]. According to the current results, the functional and radiological outcomes all improved significantly (Table 3). The Maryland foot score was used in the current study because it assigned more points to pain and gait, which were more correlated with the patients’ general activity [5].

During the SMOT procedure, whether and when a fibular osteotomy is needed remains unclear. In previous studies, the authors recommended fibular osteotomy as a standard procedure for the treatment of varus ankle OA [2, 12, 16]. However, some studies recommended preserving the fibula in all cases [3, 11, 17, 18]. We based the decision to perform the fibular osteotomy on the pre- and intraoperative evaluation. When the TC angle is decreased more than 5° compared with the contralateral side, which indicates a longer fibula or varus change, a fibular osteotomy may facilitate the reduction of the tibial plafond and talus [19]. Stufkens et al. [6] reported that creating a supramalleolar valgus deformity would not cause a shift in contact towards the lateral side of the tibiotalar joint, and the restricting role of the fibula was revealed when an osteotomy was performed. Our biomechanical study confirmed their results and showed that the tibiotalar joint’s loading center moved in opposite directions with and without fibular osteotomy.

According to a current study, in patients with fibular osteotomy (Fig. 5), the TT decreased more than in those without fibular osteotomy (P = 0.02). The role of TT in SMOT is highly controversial. Some authors have reported a significant decrease of the TT [4, 7, 8, 11, 17]; however, others have not [3, 12, 15, 19]. Tanaka et al. [12] reported that in all patients with a preoperative TT greater than 10°, the joint space did not return to normal. Lee et al. [15] reported that the preoperative TT was correlated with the postoperative TT and suggested that an optimal preoperative threshold for predicting high postoperative TT was 7.3°. Mann et al. [18] reported that the clinical results were good, although the mean postoperative TT was 10°. Additionally, Kim et al. [11] reported that no radiological outcome seemed to have a significant influence on the clinical outcomes. We agree with Mann et al. [18] that realignment surgery of the ankle joint with osteotomy is worthwhile, even for high TT patients, because the osteotomy will redistribute the contact forces of the ankle joint and move the mechanical axis point of the ankle laterally [13], prolong the viability of a more normally aligned joint, and even restore the TT to a neutral position (Fig. 6). We agree that the radiological changes need time to appear. Cheng et al. [9] reported that all patients presented opened medial joint spaces that gradually increased over the follow-up time. It was 1 year after SMOT before the radiographic evidence showed that the joint space had widened enough to demonstrate regeneration of the arthritic ankle, and after that point, improvement seemed to continue year by year [9]. However, in the current study, the mean TT degrees postoperatively were similar between the two groups, which might suggest that the patients in the fibular osteotomy group had a larger TT preoperatively. Additionally, we found a significant improvement of the TC angle in the fibular osteotomy group.

We agree that not all SMOT patients require fibular osteotomy. If the varus ankle OA patient presents with a widened mortise, SMOT with fibular preservation may be a good choice [3]. The authors reported that the center of the talus moved laterally, with a mean migration of 5.7 mm (P < 0.01) [3]. Additionally, the fibula should be preserved if the patient has normal lateral anatomic construction, and the ankle joint alignment was corrected to a satisfactory degree during the operation.

The limitations of current study include that only 10° angular deformities were evaluated because we just wanted to evaluate the difference in tibiotalar joint contact conditions between fibular preservation and osteotomy. Additionally, the use of fewer conditions could decrease the error between different loading times. The limitations of using a static cadaver model were also present. The limitation of our clinical study contained the follow-up duration, the retrospective design, and the lack of information regarding intraarticular changes. Although the outcomes will change with time, our early results confirm that the functional outcomes of SMOT were good in terms of pain relief and correction of malalignment, even in patients with high TT angles. Additionally, in appropriate cases, fibular osteotomy was helpful for translating contact pressure and restoring joint congruence. Other limitations included that we only used the Maryland foot score for functional evaluations and that the pre- and postoperative radiological evaluations did not include the weight-bearing full leg anterior-posterior view, which would be useful for the full leg alignment evaluation. Haraguchi et al. [13] used hip-to-calcaneus radiographs to evaluate lower limb alignment in SMOT patients and reported that when the preoperative mechanical axis point was more medial than the tibial plafond, the point was insufficiently moved to the lateral side, and the clinical outcomes were less satisfactory. This finding is important for preoperative evaluations and selecting the proper operation for mid-stage varus ankle OA patients.

In conclusion, supramalleolar osteotomy is recommended for the treatment of early- and mid-stage varus ankle OA and results in substantial functional improvement and malalignment correction. Fibular osteotomy can facilitate the tibiotalar contact pressure translation and is helpful for varus ankle joint OA realignment in patients with large TT and small TC angles.