Correction of the Flexible Flatfoot

Jonathan T. Deland

Mackenzie T. Jones

Positioning

The patient is placed in the supine position.
Place a bump under the hip so that the toes point straight to the ceiling.

Surgical Approach

Medial Approach for Posterior Tibial Tendon and Flexor Digitorum Longus (FDL) Tendon

Make an incision from the posterior tip of the medial malleolus to the inferior border of the navicular and first metatarsal tarsal joint distally (Figure 5-1).

Figure 5-1. Incision for exposure of posterior tibial tendon and flexor digitorum longus tendon and possible spring ligament repair.
- This incision can be shorter if a Bio-Tenodesis screw is used for the FDL transfer. The screw allows for a shorter harvesting of the FDL tendon.
Expose and examine the posterior tibial tendon (Figure 5-2).
- If one-half of the diameter of the tendon is not severely degenerated, then retain the tendon and trim the most degenerated portion.
- If the tendon is too degenerated, release it and leave a stump at the navicular. It can be useful to tie the transfer to at the end of the procedure.
  
  Figure 5-2. Exposure showing dorsal Penrose around posterior tibial tendon and inferior Penrose showing the flexor digitorum longus tendon.
Incise the FDL sheath along a line that is parallel and just inferior to the posterior tibial tendon.
- Moving lesser toes may allow palpation of the tendon through the sheath.
Expose the FDL tendon down to a level distal to the navicular, staying on the inferior aspect of the navicular and medial cuneiform to avoid large veins.
Release the FDL tendon at the level underneath the medial cuneiform.
- The authors’ preference is to expose the FDL underneath the metatarsal tarsal joint, which results in more dissection but allows for easier tensioning of the transfer at the end of the procedure (if the tendon is tied down at the dorsal exit of the navicular instead of using a Bio-Tenodesis screw).
Underneath the metatarsal tarsal joint, expose the attachment of the flexor hallucis brevis, incise it longitudinally, and identify the flexor hallucis longus (FHL) tendon.
Isolate the FDL tendon more laterally.
Identify the interconnection from the FHL to the FDL and release the FDL tendon, but not the interconnection, and place a whipstitch in the proximal end of the tendon.
- Do not release the interconnection of the FHL to the second and third toes.
Expose the dorsal navicular and use an awl to mark the dorsal entry point for the guide pin in between the talonavicular and navicular cuneiform joints.
Point the drill toward the medial inferior aspect of the plantar navicular and drill the guidewire through the awl hole from dorsal to plantar (Figure 5-3).
Overdrill on the guidewire using a 4.5- or 5.0-mm hole according to the size of the tendon.

Figure 5-3. Guide pin for drill hole in navicular in place.

Dorsal Approach

If there is severe elevation of the first ray, a first metatarsal tarsal fusion is more effective than a Cotton osteotomy in bringing the first ray down and correcting metatarsus primus varus.

Make an incision in between the first and the second metatarsals so that there is an adequate skin bridge if a long medial incision for the FDL transfer has been used (Figure 5-4).

Expose the first metatarsal tarsal joint, being careful not to injure the superficial peroneal nerve proximally, place retractors, and open the joint dorsally.

Figure 5-4. Incision for metatarsal tarsal fusion (blue). If Cotton osteotomy, just use the proximal one-third of this incision with a one sonometer proximal extension. The most posterior incision is for calcaneal osteotomy (green), with adequate skin bridge to the adjacent incision for lateral column lengthening (red).

Remove the cartilage from the joint.
Assess the amount of elevation of the first ray and metatarsus primus varus if present. Use saw cuts to take minimal bone (in the range of a millimeter) to correct the position of the metatarsal (Figure 5-5).
After confirming that the joint is reduced in good position, perforate the fusion surfaces and oppose them, being careful to have excellent apposition along the fusion site, particularly plantarly.
Using fluoroscopy, confirm good position of the first metatarsal and good apposition once the joint is pinned with K-wires.
Confirm that the metatarsal head is slightly plantar or equal to the second metatarsal head.
Do not place screws, because there is a small possibility that the position of the metatarsal may need to be adjusted after correction of the hindfoot. This is rare with experience.

Figure 5-5. Saw cut for metatarsal tarsal fusion. Note minimal amount of bone being removed.

Cotton Osteotomy

If there is mild to moderate elevation of the first ray with minimal instability and no metatarsus primus varus, a Cotton osteotomy can be used, which is much simpler.

Make an incision dorsally over the lateral border of the medial cuneiform (Figure 5-4).
Blunt dissection is done while identifying and avoiding the dorsal branch of the superficial peroneal nerve.
Expose the medial cuneiform dorsally.
Place one 0.45 K-wire in the more distal aspect of the medial cuneiform and the other in the more proximal aspect, both perpendicular to the bone and allowing for the osteotomy in between.
Check the lateral view of the medial cuneiform for good position.
Once the position is confirmed, make a saw cut down to within 5 mm of the plantar cortex and hinge the osteotomy open with an osteotome dorsally.
Using a pin distractor, adjust the amount of opening to correct the elevation of the first ray so that it is in good alignment with the second and fifth metatarsal head when the foot is plantigrade.
Place a tricortical allograft according to the shape of the proper amount of the opening.
A 2.4-mm screw is then used from the proximal dorsal cuneiform fragment to the plantar distal corner of the medial cuneiform (Figure 5-6).