In symptomatic osteochondral defects of the talus surgical treatment is indicated when nonoperative treatment has failed [28
]. The choice for open versus arthroscopic surgery depends on the location and size of the defect as well as the type of treatment [1
]. The preferred technique for primary lesions smaller than 15 mm is debridement and bone marrow stimulation by means of arthroscopy [29
]. For secondary and larger lesions there are various treatment options, including autologous cancellous bone grafting, osteochondral autograft transfer (OATS), autologous chondrocyte implantation (ACI), screw fixation, biodegradable double-layer implants, metallic implants, and allografts [30
]. If the lesion is located on the medial side of the talar dome (63% of cases) [31
], most of these treatment options require a medial malleolar osteotomy in order to obtain access to the talar dome [1
The purposes of this study were to determine the direction of the oblique medial malleolar osteotomy relative to the long tibial axis, the interindividual variation, and reliability of the radiographic methods used. The direction of the osteotomy was shown to be 30 ± 4° relative to the long tibial axis. This axis is determined intraoperatively by the center of the knee (i.e., tibial tuberosity) proximally and the center of the ankle (i.e., middle of both malleoli) distally. Applying the osteotomy direction of 30° should minimize the occurrence of a step off of the articular surface after reduction. Radiographic and CT-measurements were reliable, and indicated that the interindividual variation was small in the studied patient group. Since there was little dispersion (Fig. ), the average 30° angle may be applicable to a larger group of patients. However, if required, the precise osteotomy can be determined reliably for each individual patient according to the methodology described.
The direction of the oblique medial malleolar osteotomy is addressed in few publications. Several authors suggested a direction of approximately 45° to the tibial plafond [15
], which is more horizontal than the direction found in the present study. Others reported a direction ranging from horizontal [5
] to almost vertical [32
]. However, none of these directions are based on measurements, and operative methods to achieve the reported angles were not described.
In addition to the direction and location of the osteotomy, the placement of the fixation screws is important. The lag screws are ideally inserted perpendicularly to the osteotomy cut to achieve optimal compression and a congruent joint surface (Fig. ) [7
]. This corresponds to a 60° angle relative to the long tibial axis. If the screws are inserted either more horizontally or more vertically, an intra-articular step off might result (Fig. ). The optimal screw direction is thus rather horizontal, which has the additional advantage of preserving the deltoid ligament that originates more distally.
Reports on outcome and complications after oblique medial malleolar osteotomy vary. In a series of 30 patients described by Jarde and colleagues [33
], there was no significant difference in outcome between patients treated through a medial malleolar osteotomy, arthrotomy without osteotomy, or arthroscopy. Likewise, Bazaz and Ferkel [14
] reported no osteotomy complications in nine patients. Conversely, Gaulrapp et al. [17
] found that a medial malleolar osteotomy frequently led to local osteoarthritis and less favorable clinical findings than arthrotomy without osteotomy. Osteoarthritic changes were seen in more than 50% of 22 patients within 5 years after treatment [17
]. Baltzer and Arnold [34
] reported malunion in one of 20 cases. In their series, a slight reduction in plantar flexion capacity remained after performing a medial malleolar osteotomy, while the range of motion after using an anterior arthrotomy (23 patients) became equal to the contralateral ankle joint [34
]. Unfortunately, it is not possible to relate these outcomes to the direction of the osteotomy used, as the direction was only reported by Gaulrapp et al. who applied 45°.
Although there are different osteotomy techniques of the medial malleolus (Fig. ), each has disadvantages. A transverse approach [5
] is relatively straightforward but exposure of the talar dome may be insufficient because it is covered by the contours of the tibial plafond. Accordingly, with the inverted V [6
] and inverted U [10
] osteotomies, visualization of the talar dome may be inadequate, and they are contraindicated in patients who have large lesions, limited range of motion, or narrow ankle joints [10
]. A crescentic osteotomy [8
] has the advantage of conforming to the contour of the talar dome but is made in a horizontal direction, which restricts perpendicular access to the talar dome. A step-cut osteotomy, introduced in 1991 [9
] and modified in 2008 [35
], provides excellent access but perpendicular fixation of the distal fragment at the articular surface is difficult because the osteotomy enters the joint vertically while the screws are inserted obliquely [36
]. The oblique osteotomy is therefore our technique of choice.
There are some limitations of the present study. The measurements utilized a method that relied on two-dimensional measurements of a three-dimensional structure. Comparing the intersection angle at the anterior, middle, and posterior portion of the tibia as measured using CT, the biggest difference was found between the anterior and the middle portions (mean, 7.5°; Table ). This difference corresponds to a difference in osteotomy direction of 3.8°. Hence, the osteotomy is ideally created in different directions from anteriorly to posteriorly. However, it would be difficult to reproducibly create the osteotomy in this manner because the oscillating saw blade and osteotome are straight. Hence, a straight osteotomy is made in clinical practice. The mean of the anterior, middle, and posterior osteotomy is therefore the best alternative, and this angle corresponded well to the osteotomy determined by radiography. Another limitation is the absence of intraobserver reliability of CT. The radiographic measurements were repeated by an observer but the CT-measurements were not. We considered the radiographic measurements the most important because these provide a clinical guideline, while the CT measurements were made to verify the radiographically measured intersection angle and determine the course of the intersection. Advantages of radiography are the availability, the low costs, and the depiction of approximately half of the tibia, allowing assessment of the tibial axis, which makes it specifically useful for preoperative planning. Although the proximal tibia was not completely visible, the results of our study and those of another study [24
] indicate that the described methodology for assessing the tibial axis is reliable (Table ). However, it remains unknown whether this radiographic tibial axis perfectly corresponds to the intraoperative tibial axis, and if the proposed radiographic osteotomy direction corresponds to the clinical direction. We currently perform the osteotomy routinely in the described direction by using the tibial axis as a reference. Clinical studies are indicated to assess whether this angle results in congruent fixation and prevents secondary osteoarthritis.