Expert Insights On Performing The Akin Osteotomy
There are numerous surgical procedures designed to correct the variations of bunion deformities. Often, the final step of the operation is to correct the valgus and abduction component of the great toe. This has been the subject of a popular and technically simple procedure that was introduced approximately 85 years ago.
In 1925, Akin proposed a hallux valgus procedure that consisted of removal of a wedge of bone from the great toe to achieve a rectus position.1 His procedure also included resection of the medial aspect of the first metatarsal head and the corresponding portion of the base of the proximal phalanx.
Surprisingly, during the next several decades, there was almost no published literature on this procedure. The popular procedure during this time was the Keller osteotomy with modifications by Lelievre, Viladot and Regnauld.2-5 The emphasis was on the intraarticular correction of hallux abducto valgus rather than extraarticular correction.
In 1967, Colloff and Weitz suggested that the benefit of the Akin procedure was the ability to correct a mild to moderate deformity without disturbing the congruity and soft tissue relationship of the first metatarsophalangeal joint.6 Numerous articles soon followed that addressed indications of the procedure, placement of the osteotomy and types of fixation.
In general, the indications for the Akin procedure include the correction of hallux valgus interphalangeus. Mann has also recommended using the procedure whenever the great toe causes displacement of the second toe.7 Specifically, the Akin procedure can correct an abnormal proximal articular set angle (PASA) by placing the osteotomy proximally on the phalanx. If one places the osteotomy distally, the surgeon can achieve correction of an abnormal distal articular set angle (DASA).
The surgeon can also place the osteotomy centrally and remove a cylindrical section of bone to shorten a long proximal phalanx. When there is a combination of a long proximal phalanx with a hallux interphalangeus deformity, one can correct this by removing a trapezoidal section of bone.8 The surgeon may perform a derotational Akin to correct a valgus rotation of the great toe.9
It is also recommended that the intermetatarsal angle be less than 15 degrees and the first metatarsophalangeal joint be congruous. When this criteria has not been met, it is possible to compensate for the abduction by taking a larger wedge out of the great toe. Surgery can make the toe straighter but clinically, it may have a cosmetically unacceptable, exaggerated concave surface medially. This procedure is known as a “cheater Akin.”
Pertinent Pearls For Ensuring The Optimal Incision And Osteotomy
The most common location for the incision by podiatric surgeons is on the dorsal medial aspect of the first metatarsophalangeal joint. This location provides excellent exposure of the first metatarsal head for distal osteotomies. One can extend this incision as far distal as necessary for access to the entire proximal phalanx. The surgeon can even expose the head of the phalanx for placement of a distal osteotomy.
Another method for exposing the head of the phalanx is to extend the incision distally to the interphalangeal joint. Extend the incision medially and then distally for several millimeters.10 In my experience, just extending the incision distally to the interphalangeal joint provides adequate exposure.
After making the incision, identify the extensor hallucis longus tendon and retract it laterally. Incise the periosteum and retract it only enough to perform the osteotomy. Surgeons should never dissect the periosteum from the lateral cortex because this will disrupt the blood supply and could result in postoperative hinge failure.
Some variation exists regarding placement of the osteotomy and its orientation. Frequently, one places the bone cut transversely in the center of the phalanx, probably as a matter of convenience for the surgeon. This is the area where exposure is good and there is adequate bone on either side of the osteotomy for fixation.
It is also possible to correct an abnormal PASA and DASA from this location. A disadvantage of this location is that the osteotomy is entirely in diaphyseal bone where healing may be prolonged. Most agree that the surgeon should place the cut in the metaphyseal bone and proximally this is usually about 5 to 7 mm distal to the articular surface of the base of the phalanx.11 A distal osteotomy can be challenging because the area of the metaphysis is small.
Use an oblique osteotomy when the goal is to achieve interfragmentary compression. Usually one orients the osteotomy from distal medial to proximal lateral, inserting the bone screw perpendicular to the osteotomy site. An advantage of the oblique osteotomy is that the distal and proximal aspect of the bone cut extends into the metaphysis for faster healing. When performing the oblique osteotomy, take care not to inadvertently cut into the joint. Without good fixation, if the lateral hinge breaks, this osteotomy is very unstable and displacement results in shortening of the toe.
Wherever one places the osteotomy, a good technique is to place a loose Kirschner wire (K-wire) over the phalanx and use fluoroscopy to confirm the position.
When making the osteotomy, it is recommended to score the bone before making the cuts. This allows for final confirmation of the osteotomy prior to making the cut. With a proximal osteotomy, make the first cut parallel to the base and about 5 to 7 mm distal to the joint. Place the second arm of the osteotomy distally with both arms intersecting just medial to the lateral cortex but leaving the lateral cortex intact. One can also use a guide wire to preserve the lateral cortex. Make the cuts from dorsal to plantar, and remove the wedge of bone.
Then position the saw from medial to lateral to feather the lateral cortex. While advancing the saw laterally, apply a gentle adductory pressure to the great toe until the lateral cortex weakens and the osteotomy is closed. Since one does not dissect the soft tissue laterally, this maneuver is essentially a closed or percutaneous procedure.
How Much Bone Should One Remove?
Preoperative planning is necessary to determine the amount of bone to remove.
Gerbert advocated using templates based on the preoperative radiographs.12 Removing just enough bone to make the medial and lateral lengths of the phalanx equal is a good guide, but this may not result in enough correction. McGarvey indicated that usually the width of bone he removed was 2 to 3 mm and this gave a good result.13 Frey had devised a complicated mathematical formula to assist in determining how much bone to remove.11 He determined that removing 1/8-inch (3 mm) of bone resulted in 8 degrees of correction. Removing 3/16-inch (5 mm) yielded 16 degrees of correction and 5/16-inch (8 mm) gave 24 degrees of correction.
Even with this data, determining the amount of bone to remove is often based on the surgeon’s judgment. If one does not remove enough bone, the great toe can remain abducted and if one removes too much of a wedge, this can result in a varus deformity. The variable is the intraoperative instability of the first metatarsophalangeal joint. This makes it difficult to determine if the amount of bone removed is enough or too much.
To reduce this potential source of error, I will align the joint, insert a temporary K-wire and extend it through the base of the proximal phalanx into the metatarsal head. Then balance the capsule and suture it for stability. Perform the Akin osteotomy by resecting the appropriate amount of bone and temporarily fixating it with another K-wire. If the position of the toe is satisfactory when the foot is loaded, proceed to fixate the osteotomy site and remove the K-wires. This technique gives a good idea of what you can expect to see postoperatively.
Why You Should Preserve The Lateral Hinge
Preserving the lateral hinge is paramount in performing the Akin procedure. The hinge provides a natural area of stability that complements the internal fixation. Avoidance of dissection laterally preserves the blood supply and ensures optimal healing.
Christensen determined that osteotomies with an intact hinge demonstrated superior stiffness in comparison to osteotomies without a hinge in first metatarsal osteotomies. Both groups had equal internal fixation.14 Boberg felt there was less chance of hinge failure when performing an oblique osteotomy as opposed to a transverse osteotomy.15
What About Monofilament Wire Or K-Wires For Fixation?
Although the great toe is not the primary weightbearing area of the foot, weightbearing forces occur through the great toe, especially at heel-off.16 This can cause an axial load across the hallux that displaces the distal portion of the proximal phalanx. The goal of fixation is to provide stability, prevent displacement and achieve appropriate healing. Fixation failure can result in postoperative pain, swelling, delayed healing, displacement and nonunion.
When it comes to the Akin osteotomy, surgeons have advocated many types of fixation, including tongue depressors, sutures, monofilament wire, Kirschner pins, staples and bone screws.
Monofilament wire. This type of fixation is probably the most common type surgeons use for the Akin osteotomy although they do not always use it correctly. Often surgeons insert 28-gauge wire in holes drilled only on the dorsal or dorsal medial aspect of the great toe. When the surgeon tightens the wire, it only compresses the dorsal medial surface of the osteotomy site. By itself, this fixation is not stable and does not resist axial load. Weightbearing results in dorsiflexion of the head of the proximal phalanx. Undoubtedly, this dorsal two-cortex technique is effective only if the intact lateral hinge remains intact.
If one uses monofilament wire, it should penetrate four cortices. Schlefman described a four-cortex horizontal wire loop technique for a distal Akin.10 Pass the wire from medial to lateral and then from lateral to medial prior to making the osteotomy. After retrieving the wire to the medial surface, perform the osteotomy, thin the cortex and tighten the wire.
Boberg advocated a four-cortex technique that used a vertical loop perpendicular to the plane of the osteotomy.15 He felt this would limit dorsiflexion of the distal phalanx. This technique also relies on an intact lateral hinge. Ideally, for greater stability, one should use another wire dorsal to plantar that is oriented 90 degrees to the first wire. Monofilament wire has the advantage of providing stability, has a low profile and does not need to be removed.
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.
Plates. Bone plates are usually not used for the Akin osteotomy. If the surgeon uses a plate, one can only apply it to the dorsal surface of the phalanx. In addition, there is very little subcutaneous tissue so the plate and screws must be low profile in order to prevent soft tissue irritation. Even if the surgeon is using a locking plate, he or she should utilize bicortical fixation. Research has shown that unilateral fixation has only half the holding power of bicortical fixation.22
Interfragmentary compression with a lag screw generates the greatest amount of compression in an oblique fracture but the surgeon cannot accomplish this with a transverse osteotomy or fracture. However, one can achieve some compression using a straight plate on a transverse osteotomy. This involves drilling the hole eccentrically, away from the osteotomy, within the holes of the plate. As the screws tighten, the bone shifts toward the osteotomy site and compression occurs at the bone-plate junction.
What You Should Know About Complications
Fracture of the lateral hinge is a complication that can occur while making the osteotomy or postoperatively through bone resorption or premature weightbearing. Researchers have reported restriction of motion as well as arthritis of the interphalangeal joint but this appears to have been more of a clinical and radiographic observation with patients remaining asymptomatic.6,11,23 Researchers have also reported inadvertently extending the osteotomy into the metatarsophalangeal joint, resulting in degenerative joint changes.24
Frey noted that the most common technical complication was plantar angulation of the osteotomy site.11 She felt this could be due to the pull of the extensor hallucis longus or malposition of the osteotomy during the procedure. Goldner noted that upward displacement of the distal fragment could occur as one completes the osteotomy.25 Researchers have also reported nonunion and malposition as well as delayed union.11
Authors have also noted overcorrection, under-correction and sagittal plane deformities such as hallux extensus and hallux malleus.12 Other potential complications include: internal fixation failure, resulting in gapping of the osteotomy; extensor tendon irritation; displacement of internal fixation; delayed healing and infection.13,17
Postoperative splints, bandages and surgical shoes have been recommended following the procedure. Usually, one performs the Akin in conjunction with a first metatarsal osteotomy and non-weightbearing with cast immobilization. This provides the best protection against complications like delayed healing, nonunion and displacement.
For the best correction of hallux abductus, perform the procedure only after reducing the intermetatarsal angle and ensuring the joint is congruous.
Do everything you can to preserve the lateral hinge but if it is weak or breaks, use additional internal fixation. When it comes to osteoporotic bone, the cortex is brittle and may easily break.
If one is placing the Akin in diaphyseal bone, it may take longer to heal than the distal first metatarsal osteotomy, which the surgeon would usually place in the metaphysis. I would not permit full weightbearing until I see evidence of radiographic consolidation.
Although the Akin is generally thought of as a minor procedure, complications do occur. Respect the principles of bone healing and internal fixation when performing this procedure.
Dr. Fallat is a Fellow of the American College of Foot and Ankle Surgeons. He is the Director of Podiatric Surgical Residency at Oakwood Annapolis Hospital in Wayne, Mich.
Editor’s note: For related articles, see “Can Alternative Fixation Foster Better Outcomes With The Akin Osteotomy?” in the March 2007 issue of Podiatry Today or “Key Pearls For An Alternative Approach To The Akin Osteotomy” in the August 2006 issue.
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