The Role of Osteotomies in the Management of Ankle OA

Introduction

Osteoarthritis (OA) of the ankle represents 1% of all OA cases in the world. 80% are post-traumatic, most commonly following lower leg fractures and/or repeated ankle sprains.

The ankle joint carries around 4 times the body weight in the stance phase. Biomechanically, the ankle joint is highly congruent. The cartilage of the ankle joint is thinner than that of the hip and knee, but it can withstand greater shear and tensile forces, which enables the contact pressure to remain low. This helps to explain why symptomatic ankle OA is 9 times less common than knee OA.

Perfect alignment in ankle OA is rare; patients with end-stage ankle OA often present with a concomitant deformity that may be seen at the supramalleolar, intra-articular, or inframalleolar level.

The aims of supramalleolar osteotomy (SMO) include:

restoration of the lower-leg axis
improve intra-articular load distribution
slow down (or even stop) degeneration of the tibiotalar joint

Indications and contraindications for SMO

The SMO is mainly indicated for:

incongruent ankle OA (varus or valgus) with intact medial or lateral tibiotalar joint cartilage
alignment correction of severely deformed, end-stage ankle OA before total ankle arthroplasty

Absolute contraindications include:

hindfoot instability that cannot be managed with ligament reconstruction
severe vascular or neurologic insufficiency
neuroarthropathy
acute or chronic infection of the ankle
non-compliance

Relative contraindications include:

elderly patients (>70 y) due to impaired bone quality or frailty
advanced tibiotalar OA
tobacco smoking, which predisposes to non-union
long-term steroid medication
severe osteoporosis
rheumatoid or inflammatory disease
uncontrolled diabetes

Imaging

Weight-bearing radiographs (including AP, lateral and mortise views) of the ankle and whole leg views are obtained to assess concomitant deformities of the lower extremity and to guide surgical planning.

Recently, Haraguchi described the novel hip-to-calcaneus radiograph used for preoperative and postoperative radiographic assessment in patients who underwent a SMO for varus ankle OA.

For better assessment of degenerative changes in the tibiotalar and adjacent joints, a CT (or weight-bearing CT) scan should be performed.

Preoperative Planning

The following parameters should be used for quantitative assessment of the varus or valgus deformity in the coronal plane:

the medial distal tibial angle (MDTA)
the tibio-talar angle (TTA)

Both angles are measured using a weight-bearing mortise view.

The MDTA is crucial for quantifying the supramalleolar deformity (Fig. 1).

The TTA normally defines the centre of rotation of angulation (CORA).

Talar tilt should be used for quantitative assessment of an intra-articular deformity in the coronal plane. It is defined as the difference between the MDTA and the TTA. Values of >4° are considered to be pathological.

A hindfoot alignment view should be used for quantitative assessment of an inframalleolar deformity in the coronal plane.

For calculating the degree of operative correction, the authors recommend the following formula to determine the required amount of opening or closing of the osteotomy:

H= tan α₁ x W

where H is the height of the wedge, α₁ is the amount of deformity, including approximately 2°-4° of desired overcorrection, and W is the width of the distal tibia.

*awaiting image upload*

Fig.1 Measurements around the ankle joint

Plain weight-bearing radiograph showing the TTA and CORA (blue) and MDTA.

Surgical technique

General and/or regional anaesthesia can be used. The patient is supine with the ipsilateral pelvis lifted to correct for external rotation of the foot. Limb exsanguination and a thigh tourniquet can be applied unless contraindicated. Anterior ankle arthroscopy can be performed to assess for osteochondral lesions that can be debrided or micro-fractured.

There are 3 main options to correct varus or valgus deformity of the ankle:

opening wedge osteotomy
closing wedge osteotomy
focal dome osteotomy

Lateral osteotomies are technically more difficult due to the proximity of the fibula. However, if >10° of correction is needed, a lateral wedge osteotomy is often preferred.

Table 1. Advantages and disadvantages of supramalleolar osteotomies

OPENING AND CLOSING WEDGE OSTEOTOMY

In general, for correction of varus or valgus deformity, use a half pin percutaneously placed as near to the CORA as possible in the distal metaphyseal region of the tibia to serve as the center of rotation for the osteotomy. When the CORA falls at the ankle joint, the pin cannot be placed in the joint but can be placed just proximal, which will cause some translation. The osteotomy is performed in metaphyseal bone and the guide hole that is used is the one that will provide the ability for the osteotomy to exit both the medial and lateral cortexes of the tibia. Multiple holes are made along the planned osteotomy line, and then completed using an osteotome or saw blade to connect the holes.

Lateral closing wedge osteotomy involves a 10 to 12cm longitudinal incision along the anterior margin of the distal fibula. In most cases of a varus deformity, the fibula is shortened to preserve the congruency in the ankle joint; this is done with a bone block removal or Z-shaped osteotomy. K-wires are then drilled through the tibia, converging at the medial cortex, and the osteotomy is performed and secured with a plate. The fibula is secured with screws or plate.

Medial opening wedge osteotomy involves a longitudinal incision along the distal medial metaphysis posterior to the great saphenous vein and nerve. The tibia is exposed, preserving the periosteum. Using fluoroscopy, a guidewire is placed from medial to lateral in the plane of the osteotomy determined by the pre-operative plan. The osteotomy is then completed using a wide saw blade and the correction is made, typically preserving the lateral cortex to enhance the intrinsic stability. The tibial osteotomy is then gently distracted using a lamina spreader and the space is filled with an appropriately sized bone graft. In cases of sagittal plane deformity, an anterior or posterior medial wedge can be performed in a biplanar fashion. Rigid plate fixation with locking screws is recommended to secure the osteotomy. After the supramalleolar correction, the alignment of the heel is reassessed clinically. The aim is to achieve a heel with 1° - 5° valgus.

Lateral cortical fracture is less likely to occur when an opening wedge SMO is at the level of the proximal third of the syndesmosis, the so-called “safe zone,” rather than above, due to thick periosteum, syndesmosis, AITFL, PITFL.

FOCAL DOME OSTEOTOMY

A focal dome osteotomy is typically used for frontal or sagittal plane correction at, or near, the ankle joint. An axis pin is placed in the distal tibial metaphysis at the CORA to avoid producing a secondary deformity. A Rancho cube is used over the pin to allow circular rotation outlining the arc of the osteotomy. The holes in the cube are drilled and connected with an osteotome. An osteotomy of the fibula is then performed to allow mobilization of the distal fragment. Strong fixation is needed for a rigid construct.

Complications

Although multiple studies have found substantial pain relief and functional improvement from SMOs, for both varus and valgus deformities, complications occur:

wound healing problems and infections up to 22%
malunion or nonunion up to 22%

There is little evidence that surgical technique, use of allograft versus autograft, or type of fixation affects union rates in distal tibial osteotomies. The progression of degenerative OA after SMO is reported to be up to 25% in the literature.

Summary

SMO has been shown to have good mid-term results in patients with mid-stage, asymmetric ankle arthritis and varus/valgus distal tibial deformity. The primary indication for SMO is a deformity at the supramalleolar level. Studies have shown it to be an effective option in avoiding joint-destructive procedures for ankle arthritis. With proper patient selection and preoperative planning, the supramalleolar osteotomy can effectively redistribute the forces placed on the ankle, limiting progression of further degenerative changes and improving pain and functionality.

References

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Krähenbühl N, Zwicky L, Bolliger L, Schädelin S, Hintermann B, Knupp M. Mid- to Long-term Results of Supramalleolar Osteotomy. Foot Ankle Int. 2017 Feb;38(2):124-132. doi: 10.1177/1071100716673416. Epub 2016 Oct 11. PMID: 27765869.

Hintermann B, Knupp M, Barg A. Supramalleolar Osteotomies for the Treatment of Ankle Arthritis. J Am Acad Orthop Surg. 2016 Jul;24(7):424-32. doi: 10.5435/JAAOS-D-12-00124. PMID: 27195382.

Edited by Graham Chuter 2021