How To Conquer The Accessory Navicular Bone
The original procedure advocated by Kidner involved shelling out of the accessory navicular bone from within the insertional area of the posterior tibial tendon and rerouting this tendon under the navicular bone in hopes of restoring a normal pull of this tendon. When treating younger children, history has shown us that simply shelling out of the accessory navicular bone from within the tendon and remodeling the tuberosity of the navicular bone can give you satisfactory results.
In general, you want to reserve advancement of the posterior tibial tendon for adults or those who have a more significant flatfoot deformity. You may also use this approach after determining that quality custom orthotics are only resulting in a slight decrease of symptoms.
Apply a well-padded ankle tourniquet. After the patient is under IV sedation or general anesthesia, perform a posterior tibial nerve block along with local infiltration in a diamond shape around the navicular bone. Mark the most prominent aspect of the navicular bone and outline the course of the posterior tibial tendon.
Make a linear longitudinal incision along the horizontal midline of the navicular bone, extending approximately 2 cm distal and 5 cm proximal. Mildly angle the proximal cut upward following the course of the posterior tibial tendon. Look out for the great saphenous vein and saphenous nerve, which should be dorsal to the surgical area.
Proceed to use a Metzenbaum scissor to dissect subcutaneous tissues away from the capsule of the talar navicular area. Then make a horizontal incision through the capsule directly over the midline of the navicular down to bone. Reflect the navicular joint capsule both superiorly and inferiorly. You should retract the abductor hallucis plantarly and it may be necessary to use a key periosteal elevator to reflect the capsular tissues from the navicular bone. During the deeper dissection, it also is important to avoid incizing through the posterior tibial tendon.
Using an osteotome and mallet, proceed to resect the hypertrophied portion of the navicular tubercle (which is prominent medially) from distal to proximal. (Getting pre-operative measurements from the AP X-ray will help you determine how much bone you’ll need to remove.) At this time, you can more easily identify the accessory navicular bone proximal to the navicular by its articulation or separation from the larger navicular bone. You can sharply excise the accessory bone with a scalpel or crown and collar scissors.
Examine the posterior tibial tendon by performing a tenolysis proximally until the tendon appears normal in size, continuity and color. Excise any areas of degenerated or abnormal posterior tendon prior to performing tubularization. Then tubularize the frayed or thinned areas distally with 3-0 non-absorbable suture.
When You Should Perform
The Modified Kinder Procedure
If you’ve removed a large portion of hypertrophied navicular bone, you may notice redundant posterior tibial tendon. In addition, when you’re treating severe flatfoot cases or patients with inherent ligamentous laxity, be aware of excessive laxity of the posterior tibial tendon. It is important to check the redundancy or laxity of the tendon with the foot held in subtalar joint (STJ) neutral position.
In these cases, you should perform tendon advancement.
Before you begin, be sure to free the under surface of the navicular bone of soft tissues and rasp the area smooth. Doing so will help facilitate the tenodesis. I prefer to use the Mitek super anchor to assist in a tenodesis. When using the Mitek drill with a measured stop, you drill from medial to lateral directly into the middle of the navicular body. Use the non-absorbable suture attached to the anchor to advance and tack down the posterior tibial tendon plantarly and medially to the navicular bone. While performing the advancement tenodesis, it is important to maintain the foot in STJ neutral or a mildly inverted position.