Mastering The Technical Approach To The Scarf Bunionectomy
The blood supply to the first metatarsal head primarily enters from the plantar neck region and to a secondary degree dorsally at the capsular area. The scarf osteotomy respects both of these very nicely. The approach is a medial longitudinal incision, which the surgeon takes down to bone along nearly the entire first metatarsal. Incise the capsule with a lenticular approach. No vertical capsulorrhaphy is necessary. Reflect the abductor hallucis muscle belly plantarly on the proximal aspect for saw blade excursion. Similarly, reflect the area dorsally and proximal to the capsule insertion, protecting the blood supply and offering a clear visual field for the osteotomy.
Perform a minimal medial eminence resection to allow for ease with the scarf cut. Make the longitudinal cut first, determining the angles based on deformity correction needs. Make the longitudinal cut from the metaphyseal region to the metaphyseal region. Make sure the cut remains parallel or nearly so to the ground, not the shaft.
The cut should start superior to the midline and traverse with a plantar orientation to allow plantar translation as one performs the shift. This is beneficial in the majority of cases to allow the medial column an advantage to once again bear the load it was intended to bear and often obviates the need for an adjunctive Weil osteotomy. Then perform dorsal, distal and proximal plantar cuts parallel to each other. One will only need to cut 2 to 3 mm of bone. This reduces the stress riser and if the metatarsal is shortened, it will not be elevated in the process.
If one desires less than 3 mm of length correction, changing the axis of the proximal and distal cuts is all that is necessary. The cuts must remain parallel to allow length change to occur and remain stable. If more than 3 mm of length, usually shortening, is necessary, simply remove a piece of bone to the amount of correction desired from both the proximal and distal ends.
What You Should Know About Shifting The Metatarsal
Now we are ready to shift. This requires a pushing-pulling maneuver. The shift can be substantial, up to three-quarters of the available shelf. Utilize a bone clamp or temporary K-wires to assess the shift. Loading the first ray should show a desirable intermetatarsal correction and a balanced hallux. If not, remove temporary fixation and adjust the shift. If a decrease in range of motion is present, further shortening should correct for this by decreasing tension on the flexor hallucis brevis tendon primarily.
Perform fixation with either two parallel dorsal to plantar screws or one dorsal to plantar screw proximally and one from dorsal and angling 45 degrees toward the metatarsal head. This second orientation decreases troughing and allows compression across the proximal and distal cuts. The troughing is minimal when one extends the longitudinal cut from the metaphyseal bone distally to the metaphyseal bone proximally. The long arm also gives power to the corrective ability and a large surface area for screw placement and bone healing. Resection of any overhanging medial eminence completes the bony work.
Then perform the capsulorrhaphy medially by bringing the longitudinal (lenticular) capsule together. This secures the sesamoids in position beneath the corrected metatarsal head. The vertical capsulorrhaphy is not necessary as this lateral release and the bony correction have reduced the deformity. Tightening the capsule in the vertical plane reduces postoperative range of motion but surgeons can avoid this. Plantarflexing the hallux during the repair and throwing one solid suture at the point of rotation is the key to capsular closure.
If the hallux still has an abductory component, an Akin osteotomy can achieve desired outcomes. One can perform the Akin by extending the medial incision and choosing either a transverse or oblique osteotomy. Akin fixation includes screws, staples or wire.