Expert Insights On Performing The Akin Osteotomy
- Volume 23 - Issue 1 - January 2010
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Kirschner wires. K-wires remain a popular form of fixation. If the hinge is intact, one can insert a single pin through the tip of the toe extending proximally through the interphalangeal joint, crossing the osteotomy site and ending at the base of the proximal phalanx. A more common technique is to use two pins. The surgeon should insert one from distal medial to proximal lateral across the osteotomy site. Insert another pin from the opposite direction. Orient these pins as close to 90 degrees as possible. Anchor the distal aspect of the pins in cortical bone to help ensure four-cortex anchoring. Ideally, the pins should cross just proximal to the osteotomy site.
With the four-cortex anchor and the orientation of the K-wires, this results in a very stable type of fixation. Obviously, a larger diameter pin like a 0.062 K-wire provides greater stability and resistance to bending than a 0.045 pin. Threaded K-wires should provide greater resistance to loosening and displacement. Although this is a very effective form of fixation, it does require removal and this does make some patients apprehensive. Pin tract infection can occur but is rare.
Weighing The Pros And Cons Of Staples For Fixation
Staples. Bone staples are frequently advocated for fixation of the Akin osteotomy. They have the advantage of being easy to insert and, with the correct type of staple and orientation, result in a strong osteotomy site.
Green recommended the use of staples, indicating that they provide excellent compression and eliminate motion at the osteotomy site.17 He inserted them from dorsal medial to lateral plantar. Lerman felt that a power staple provided greater pullout strength than a manually inserted staple.18 He inserted the staples from medial to lateral with the arms parallel to the weightbearing surface. Heat sensitive memory staples have also gained popularity. After inserting the staple into the bone, apply a source of heat. The heat causes the arms to move closer together, resulting in a degree of compression.
Bechtold noted that there were no guidelines to achieve maximum stability with staples.19 He determined that stability of the osteotomy increased with the number of staples used and torsional strength also increased when the surgeon inserted two staples in opposite direction to each other.
Firoozbakhsh determined that a curvilinear square or a square staple leg provided much more pullout strength over a round leg.20 He also discovered that increasing the length of the staple leg increased resistance to pullout force, tension and torsional loading.
Bone Screws And Plates: Can They Provide Optimal Fixation?
Bone screws. Research has shown that interfragmentary compression using bone screws provides a high degree of compression and, more importantly, rigidity at the osteotomy site. Levitsky and colleagues presented a series of eight patients using bone screws for fixation of the Akin site.21 All osteotomies healed without callus formation, which indicated rigid fixation. There were no patients with delayed healing or displacement. The authors concluded that this type of fixation was superior in comparison to other fixation modalities.
Since the proximal phalanx of the hallux is short, this technique can be difficult. One must create an oblique osteotomy and remove the bone wedge without breaking the lateral cortex. The surgeon must insert the bone screw at a 90-degree angle to the osteotomy. The screw should also purchase enough bone medially so one can tighten it without cracking the cortical bone around the screw head.
One bone screw is sufficient with an intact hinge but two screws are necessary when the hinge is not intact. Usually, there is only enough room to use a single 3.5-mm cortical screw but sometimes one can use two 2.7-mm screws. I use this procedure only when the bone is large enough to accommodate the screws necessary to achieve interfragmentary fixation.