DEFINITION

An accessory navicular is an osseous abnormality that is caused by a secondary ossification center that fails to unite during maturation.

Roughly 5% to 14% of all feet have this accessory bone, which is likely an autosomal dominant trait.1,3 Up to 38.6% of feet with an accessory navicular have a planovalgus deformity.4

 

 

ANATOMY

 

The tuberosity of the navicular forms from a secondary ossification center.

 

 

This ossification center normally does not ossify until 9 years old.

 

 

There are three types of accessory navicular3:

 

 

Type I: small round or ovoid sesamoid within the posterior tibialis tendon (PTT) that is typically located at the plantar aspect of the tendon adjacent to the spring ligament

 

 

 

 

Two to 3 mm in diameter No bony attachment Rarely symptomatic

 

Type II: connected by a synchondrosis of less than 2 mm between the ossicle and the navicular (FIG 1)

 

 

Usually 9 to 12 mm

 

Typically becomes symptomatic with relatively minor trauma to the foot that stresses the previously stable synchondrosis

 

 

 

FIG 1 • External oblique view of a right foot demonstrating a type II accessory navicular, with the navicular attached by a synchondrosis.

 

 

IIA: less acute angle (tension force)

 

 

 

More at risk for an avulsion injury IIB: more inferior (shear force)

 

Type III: united by a bony bridge

 

 

 

Produces a cornuate navicular Occasionally symptomatic

PATHOGENESIS

 

Kidner5 described the relationship of the accessory navicular with pes planus:

 

 

The accessory navicular alters the pull and leverage of the PTT, forcing it to become more of an adductor

than a supinator.

 

As the foot adducts, the talus impinges on the medial malleolus.

 

The abnormal pull of the PTT interferes with normal foot mechanics and can cause a weakness of the medial arch and may lead to pes planus.

 

NATURAL HISTORY

 

Pain is likely due to pressure from shoes in children.

 

 

 

At times, it is associated with flattening of the longitudinal arch due to an abnormal insertion of the PTT. Symptoms can develop after relatively minor ankle sprains, other trauma, or chronic overuse/repetitive stress. Tension, shearing, and compressive forces are transmitted via the PTT to the synchondrosis.

PATIENT HISTORY AND PHYSICAL FINDINGS

 

The patient may complain of an insidious onset of medial foot pain often experienced only during activities or with certain types of shoe wear.

 

On examination, the patient will have a normal neuromuscular examination with minimal to no limitations in ankle or foot range of motion. Subtalar motion is typically well preserved.

 

There may be a prominence over the medial forefoot (FIG 2).

 

 

Tenderness to palpation and edema over the prominence

 

Unilateral pes planus may be present in patients with a symptomatic accessory navicular.

 

 

PTT strength should be tested (plantarflexion and inversion against resistance to isolate the PTT): symptoms usually directly at accessory navicular

 

Single-limb heel rise to isolate PTT function: symptoms usually experienced directly over the accessory navicular

 

The examiner should assess the patient's gait and overall alignment to look for hindfoot valgus and a pes planus deformity.

 

 

34

 

 

 

FIG 2 • A. Medial prominence. B. Note PTT attaching to prominent accessory navicular.

 

IMAGING AND OTHER DIAGNOSTIC STUDIES

 

Standard anteroposterior (AP), lateral, and external oblique x-rays can help determine the type and potential size of the accessory bone (FIG 3A-C).

 

 

A routine internal oblique does not allow visualization of the medial navicular.

 

The external oblique radiograph, opposite of the internal oblique view included in a routine radiographic series of the foot (see FIG 3C)

 

Magnetic resonance imaging (MRI) may suggest a symptomatic synchondrosis with bony edema surrounding the synchondrosis (FIG 3D,E).

 

 

Can be useful in ruling out other potential pathology with similar symptoms, including spring ligament pathology, posterior tibial tendinopathy, and navicular stress fracture

 

Bone scan is highly sensitive for symptomatic accessory navicular but not specific.2

DIFFERENTIAL DIAGNOSIS

PTT tear or tendinopathy Spring ligament tear Navicular stress fracture

 

FIG 3 • A. Weight-bearing AP foot radiograph suggests accessory navicular but provides little detail. B. Weight-bearing lateral radiograph also suggests accessory navicular but with little detail. Note that arch is relatively well preserved in this patient. (continued)

 

 

 

NONOPERATIVE MANAGEMENT

 

Acute phase (after recent injury)

 

 

Cam boot to limit PTT tension on synchondrosis between accessory navicular and main body of navicular

 

 

If severe, temporary short-leg cast

 

Avoid boot or cast pressure over tender medial accessory navicular.

 

Chronic phase (removed from acute onset of symptoms)

 

 

Shoe wear modification with improved support and relatively stiff sole

 

Felt or gel doughnut over the medial prominence to potentially reduce pressure on the prominent accessory navicular

 

Semirigid longitudinal arch support

 

 

Will need a relief area directly at accessory navicular

 

Although arch support is recommended to relieve stress from the PTT on the synchondrosis, direct pressure on the accessory navicular from a high medial arch support may create more symptoms from direct pressure; therefore, a modified orthotic with relief directly over the prominent accessory navicular is recommended.

 

 

35

 

 

 

FIG 3 • (continued) C. External oblique view offers best view of the accessory navicular. Note that this is a type II accessory navicular, separated from the main body of the navicular by a synchondrosis. D. Axial MRI suggests edema at the synchondrosis. E. Sagittal MRI demonstrates synchondrosis and the attachment of the PTT on the

accessory navicular.

 

 

Physical therapy

 

 

Exercises that place high demand on the PTT should be avoided.

 

 

 

Will place more stress on the symptomatic synchondrosis Modalities to calm irritation at the synchondrosis may be of benefit.

 

Ultrasound and/or iontophoresis

 

 

External bone stimulation

 

 

Because a symptomatic type II accessory navicular is due to injury/stress on a cartilaginous/fibrous synchondrosis and is not a fracture, external bone stimulation has no role in management.

 

SURGICAL MANAGEMENT

Preoperative Planning

 

Foot alignment, based on weight-bearing clinical and radiographic evaluation, must be understood.

 

 

With a well-preserved arch, surgery may be limited to the accessory navicular.

 

With pes planus, consideration may need to be given foot realignment in addition to surgical management of the accessory navicular.

 

Characteristics of the type II accessory navicular

 

 

If the accessory navicular is large, consideration may be given to excision of the synchondrosis, preparation of the opposing navicular surfaces, and arthrodesis of the accessory navicular to the main body of the navicular.

 

If the accessory navicular is small, then the only sensible procedure is excision and attachment of the PTT to the medial aspect of the navicular.

 

Detailed review of the imaging studies, including MRI and/or computed tomography (CT) scan

 

 

Identify associated pathology such as PTT pathology or spring ligament pathology that may need to be addressed surgically.

 

Further define the accessory navicular.

 

Anesthesia per the anesthesia team. Although an ankle block is probably sufficient, consideration may be given to a popliteal block. If a tourniquet is used, it may have less propensity to trap the PTT if it can be used higher in the calf (popliteal block) than if used at the ankle (ankle block).

 

Positioning

 

The patient is placed supine on a radiolucent operating room table.

 

The leg should be allowed to externally rotate to facilitate access to the medial navicular.

 

 

Often, a support (bump) under the contralateral hip promotes ideal leg rotation for the operating on the medial foot.

 

Neutral leg alignment is recommended if concomitant foot realignment for pes planus is planned.

 

 

Thereby, access for medial (accessory navicular) and lateral (calcaneal osteotomy) procedures is facilitated.

 

 

36

 

TECHNIQUES

• Exposure and Approach

  A 4-cm longitudinal medial incision is made dorsomedially over the accessory navicular and distal PTT at its insertion on the accessory navicular (TECH FIG 1A).

  The distal PTT tendon sheath is opened to directly expose the PTT's insertion on the accessory navicular (TECH FIG 1B).

  The synchondrosis is identified.

  Preoperative imaging is useful in determining the orientation of the synchondrosis.

  If arthrodesis of the accessory navicular to the main body of the navicular is being considered, minimize periosteal stripping and maintain the PTT insertion on the accessory navicular.

  A 25-gauge needle and fluoroscopy may be used as a probe to find the synchondrosis between the accessory navicular and the navicular body (TECH FIG 1C).

  Excision of the Synchondrosis

  With the interval between the two bones identified from the dorsal aspect the synchondrosis, the cartilaginous and fibrous tissue is sharply excised without compromising the PTT or adjacent spring ligament.

  The two opposing surfaces of the main body of the navicular and accessory navicular should be fully exposed.

  Consideration for Arthrodesis of the Accessory Navicular to the Main Body of the Navicular

  If the accessory bone is large enough to support one and preferably two 3-mm cannulated screws, an arthrodesis may be performed.

  Two screws affords more stable fixation and controls rotation of the accessory navicular, thereby potentially increasing the chance for healing.

   

   

   

   

  TECH FIG 1 • A. Medial longitudinal incision over dorsal aspect of navicular and PTT at insertion on navicular. B. Dorsal aspect of PTT sheath opened. C. Hypodermic needle used to identify synchondrosis.

   

   

  In larger patients, larger cannulated screws may be feasible; however, care must be taken to avoid fracturing the accessory navicular.

   

  If the accessory bone is too small to support screw fixation, then a modified Kidner procedure (excision of the accessory navicular) is performed.

   

  If the main navicular bone is prominent even without the accessory navicular, a microsagittal saw can be used to remove some the main navicular.

   

  This may provide a better ingrowth surface for the PTT or for arthrodesis of the accessory navicular.

  Advancing the Posterior Tibialis Tendon

   

  Kidner procedure: Kidner originally described accessory navicular excision and advancing the PTT to the residual medial navicular.

   

  Modified Kidner procedure: Other authors have described accessory navicular excision and attaching the PTT to the medial navicular at its resting tension without advancing the PTT.

   

  Although it may appear that advancing the PTT to the medial navicular, that is, adding more tension, may provide a mechanical advantage, there is no evidence to suggest improved clinical outcome over simply attaching the PTT to the medial navicular at its resting tension.

   

   

  In our experience, after excising the accessory navicular, the PTT must be advanced to some degree to allow satisfactory attachment to the navicular.

   

• Modified Kidner Procedure

  37

   

  The accessory navicular and the synchondrosis are identified within the distal medial PTT (TECH FIG 2A).

   

  While protecting all of the PTT fibers, including the ones coursing toward the plantar foot, the accessory navicular is excised by elevating the PTT attachment directly from the accessory navicular (TECH FIG 2B-D).

   

  The PTT tendon fibers should be maintained in continuity, essentially elevated as a sleeve so that they may be effectively attached to the medial navicular.

   

  The synchondrosis needs to be identified and mobilized to separate the accessory navicular.

   

   

   

  TECH FIG 2 • A. The accessory navicular and the synchondrosis are identified within the distal medial PTT. B. The accessory navicular is excised by elevating the PTT attachment directly from the accessory navicular. C. Accessory navicular extracted from PTT and separated from synchondrosis. D. In this case, relatively small accessory navicular. E. Microsagittal saw to shave medial navicular. F. Exposes more cancellous surface for PTT reattachment healing. G. Sharp resection of residual resected bone. H. Suture

  anchor being inserted. Recommend fluoroscopic guidance to ensure talonavicular joint not violated. I.

  Anchor seated fully in medial navicular. (continued)

   

   

  The medial talonavicular capsule and spring ligament must be protected from inadvertent injury during accessory navicular removal.

   

  The residual synchondrosis should be removed from the medial navicular and the medial navicular should be prepared to expose a bony surface conducive to tendon attachment.

   

  If the residual medial navicular is prominent, it may be shaved with a microsagittal saw (TECH FIG 2E-G).

   

  The PTT is attached to the plantar medial aspect of the navicular using a one or two bone suture anchors (TECH FIG 2H,I).

   

  The PTT attachment to the medial navicular periosteum is reinforced with a combination of absorbable and nonabsorbable 0-0 or 2-0 sutures to the periosteum (TECH FIG 2J-L).

   

  The PTT tendon sheath is closed and the subcutaneous layer and skin are reapproximated.

   

   

  38

   

   

   

  TECH FIG 2 • (continued) J. Anchor sutures being passed through PTT. K. PTT may be advanced to enhance tension, but this is not necessary. L. PTT secured to navicular.

• Accessory Navicular and Navicular Arthrodesis/Open Reduction and Internal Fixation

 

The accessory navicular and synchondrosis are exposed (TECH FIG 3A-C).

 

It typically is obvious where the PTT attaches to the unstable accessory navicular (TECH FIG 3D).

 

 

 

TECH FIG 3 • A. Medial navicular exposed. B. Synchondrosis identified. C. Synchondrosis opened. D. PTT fibers attaching to accessory navicular. With unstable synchondrosis, symptoms are produced with PTT tension on accessory navicular. Preparation for arthrodesis with microsagittal saw to remove residual synchondrosis on the medial (E) and accessory (F) naviculars. (continued)

 

 

With the opposing surface of the accessory navicular fully exposed, a microsagittal saw is used to create a flat surface at the medial aspect of the main body of the navicular, where once the synchondrosis was attached, to create a satisfactory healing surface (TECH FIG 3E).

 

The distal aspect of the accessory bone is prepared in a similar manner to optimize the healing surface (TECH FIG 3F).

 

If desired, more medial navicular may be removed to create a lower profile with reattachment of the accessory navicular.

 

39

 

 

TECH FIG 3 • (continued) The medial (G) and accessory (H) navicular surfaces are prepared with smalldiameter drill to increase surface area for healing. The drill holes in the accessory navicular are superficial to limit risk for stress fracture when screws inserted. I-K. Accessory navicular fixation. I. Reduction with bone clamp, optimizing bony apposition. J. Guidewire insertion for cannulated screw placement. Note that the clamp is placed centrally on the accessory navicular to facilitate placing two screws for definitive fixation. K. Screw placement.

 

 

Similar to any other arthrodesis, the surfaces are drilled to increase surface area to optimize chance for fusion (TECH FIG 3G,H).

 

The accessory navicular's healing surface should be drilled carefully and only superficially to limit risk of stress fracture when screws are inserted.

 

The accessory navicular is advanced to the prepared surface of the navicular.

 

To facilitate approximation of the accessory navicular on the medial navicular, ankle plantarflexion and hindfoot inversion is recommended (relieves tension from the PTT).

 

A bone reduction clamp may be used, best centered on the accessory navicular so that two screws may be inserted, on either side of the clamp (TECH FIG 3I).

 

The guide pins for the cannulated screws are placed through the PTT attachment on the accessory navicular (TECH FIG 3J).

 

Using a scalpel blade, creating careful longitudinal slits within the tendon limits damage to the PTT insertion during pin insertion, drilling, and screw placement.

 

Fluoroscopic evaluation in more than one plane is important to confirm satisfactory bony opposition in multiple planes and optimal position of the guide pins.

 

After overdrilling the guidewires, the cannulated screws are carefully advanced through the PTT attachment on the accessory navicular (TECH FIG 3K).

 

Typically, the screw heads will need to advance under the tendon to effectively engage the cortex of the accessory navicular.

 

The slits made sharply in the PTT tendon insertion may need to be carefully enlarged to accommodate the screw heads.

 

Compression of the accessory navicular to the navicular is desired, but overcompression that may lead to accessory navicular stress fracture must be avoided.

 

Closure is similar to that described for the modified Kidner procedure earlier.

 

 

40

• Addition of Subtalar Arthroereisis (Extra-articular Subtalar/Sinus Tarsi Implant)

Background

 

Patients with a symptomatic accessory navicular may have an associated flexible pes planovalgus deformity. Although this deformity may not need to be corrected, consideration may be given to foot realignment in combination with surgical management of the accessory navicular.

 

Some surgeons recommend an extra-articular subtalar arthroereisis (subtalar/sinus tarsi implant) to realign the foot; subtalar arthroereisis has been used in combination with surgical management of the symptomatic accessory navicular.4,6

 

In the pediatric patient population, subtalar arthroereisis has been used in isolation.

 

In skeletally immature patients with flexible pes planovalgus, the implant may realign the foot in anticipation that bone growth in the foot will adjust to a more neutral position.

 

Once the patient reaches skeletal maturity, the subtalar arthroereisis implant may be removed, and because bone growth has been modified with the implant, foot alignment will remain improved.

 

 

 

TECH FIG 4 • A,B. Silfverskiöld test demonstrating isolated gastrocnemius contracture. A. Equinus with knee in extension. B. No equinus with knee in flexion. C-F. Gastrocnemius-soleus recession. C. Posterior approach at musculotendinous junction. Note sural nerve. D. Gastrocnemius tendon release. E. Gastrocnemius released with soleus fibers remaining intact. F. Sural nerve intact. G. Equinus contracture corrected.

 

 

In skeletally mature patients with symptomatic flexible pes planovalgus, subtalar arthroereisis is rarely effective as a standalone procedure to correct deformity.

 

Most surgeons that use subtalar arthroereisis to treat their patients recommend that the implant is used as an adjunct to correct flexible pes planovalgus.

 

 

Procedures that may be used in combination with subtalar arthroereisis are as follows: Tendo Achilles lengthening versus gastrocnemius recession (TECH FIG 4)

 

Medial displacement calcaneal osteotomy

 

Plantarflexion medial cuneiform osteotomy (Cotton osteotomy)

 

Although perhaps feasible, lateral column lengthening through the anterior calcaneus (Evans procedure) probably should not be used in combination with subtalar arthroereisis because the implant would rest directly on the calcaneal osteotomy, potentially negatively influencing its healing and effectiveness.

Exposure

 

Because the subtalar/sinus tarsi implant is inserted from the lateral foot, the foot should be positioned in neutral position on the operating room table to allow access to both the medial and lateral aspects.

 

41

 

The sinus tarsi is palpated distal and inferior to the tip of the lateral malleolus.

 

A 1- to 2-cm oblique incision, parallel to the typical course of the sural nerve, is created over the sinus tarsi, dorsal to the peroneal tendons.

 

A hemostat is used to bluntly dissect to the tarsal canal, avoiding the sural nerve and the lateral dorsal cutaneous nerve.

Guidewire Placement

 

A blunt guidewire is passed through the sinus tarsi and tarsal canal from lateral to medial (TECH FIG 5A).

 

Provided it is oriented properly, the smooth and blunt guidewire should pass relatively readily through the tarsal canal to the medial foot, anterior to the calcaneal posterior facet, and dorsal to the middle calcaneal facet.

 

 

 

TECH FIG 5 • A. A 1-cm incision is made over sinus tarsi to insert guidewire. B. Guidewire passed through sinus tarsi and exiting medial subtalar joint anterior and distal to medial malleolus and dorsal to PTT; stab incision to pass wire through skin. C,D. Guidewire passed through medial skin. E. Foot positioned for fluoroscopic confirmation of proper guidewire position fluoroscopy. F. AP view. G. Lateral view.

 

 

The desired medial exit point is immediately distal and inferior to the medial malleolus and dorsal to the PTT (TECH FIG 5B).

 

The path of least resistance is usually the correct one and has an oblique axis: anterolateral to

posteromedial.

 

Once the wire passes to the medial skin, immediately dorsal to the PTT, a superficial incision is made at the tip of the wire to allow the wire to be passed through the skin (TECH FIG 5C,D).

 

Optimal wire position should be confirmed fluoroscopically (TECH FIG 5E).

 

In the AP plane, the wire should pass from anterolateral to more posteromedial, directly under the neck of the talus (TECH FIG 5F).

 

In the lateral plane, the wire should be inferior to the talar neck and anterior to the calcaneal posterior facet (TECH FIG 5G).

 

 

42

Sizing

 

Most commercially available subtalar arthroereisis systems have sizing guides in 1- or 2-mm diameter increments.

 

With fluoroscopic confirmation of proper wire position successively, larger subtalar/sinus tarsi sizing guides are inserted until the optimal guide is determined (TECH FIG 6A).

 

The goal of the sizing guide, trial, and implant is to correct deformity by blocking hindfoot eversion but without overcorrection into valgus.

 

With the proper size determined with the guide, the optimal trial is placed over the guidewire (TECH FIG 6B-D).

 

The optimally sized trial is identified.

 

Valgus hindfoot stress should block valgus to a physiologic hindfoot position, preventing excessive valgus hindfoot position (TECH FIG 6E).

 

 

 

TECH FIG 6 • A. Sizing guide to determine optimal implant diameter. With cannulated sizing guide placed over guidewire into sinus tarsi to lateral talar neck and dorsal anterior calcaneus, optimal elimination of excessive hindfoot valgus is determined without overcorrection into varus. B. Trial implant being placed over guide pin. C. Trial implant insertion. The incision must be large enough to avoid soft tissue and nerve injury with trial (and eventual final implant) insertion. D. Full insertion. E. Confirming optimal hindfoot valgus with trial in place. F. Ideally, an AP fluoroscopic view is obtained to determine ideal implant position; this oblique view does not afford ideal view. G. Lateral view.

 

 

 

Varus hindfoot position suggests that the trial implant diameter is too great. Proper trial position should be confirmed fluoroscopically.

 

Ideally, the implant's leading edge will approach the midaxis of the talar neck (AP fluoroscopic view) and its opposite end will not be completely recessed under the lateral talar neck cortex (TECH FIG 6F).

 

 

The implant should have a slight anterolateral to posteromedial orientation. In our experience, 9- and 10-mm implants are most commonly used.

 

Lateral fluoroscopy should also be obtained to confirm that the implant is in optimal position, immediately inferior to the talar neck and anterior to the calcaneal posterior facet (TECH FIG 6G).

 

 

43

Implant Placement

 

With the optimal size determined clinically and proper trial position confirmed fluoroscopically, the trial is removed and the final implant is placed over the guidewire (TECH FIG 7A-C).

 

The implant should be advanced to the point that it appropriately blocks eversion without overcorrecting the hindfoot into varus (TECH FIG 7D,E).

 

Fluoroscopic confirmation of proper implant position should be performed, as described for the trial earlier.

 

 

 

TECH FIG 7 • A. The final implant is threaded to provide stability. It is also fluted to absorb shock. B. End-on view to show fluted design. C. Final implant insertion. D,E. Confirming proper heel position with final implant in place. D. Valgus heel stress. E. Heel position evaluated. F. AP fluoroscopic view to confirm proper final implant position. Ideally, the implant's leading edge approaches the midaxis of the talar neck without its opposite end completely recessed under the lateral talar neck cortex. G,H. Optimal position based on lateral view with guide pin still in place. I. Guidewire extracted medially. By removing it medially, the implant has less chance of dislodging from its ideal position. (continued)

 

 

Ideally, the implant's leading edge approaches the midaxis of the talar neck (AP fluoroscopic view) without its opposite end completely recessed under the lateral talar neck cortex (TECH FIG 7F-H).

 

The guidewire is removed from the medial side to limit the risk of implant displacement (TECH FIG 7I-L).

Completion

 

Final fluoroscopic confirmation in the AP and lateral planes to confirm the implant is in the optimal position (TECH FIG 8).

 

Routine wound closure.

 

 

44

 

 

 

TECH FIG 7 • (continued) J. Guidewire fully extracted. K. Final lateral fluoroscopic view. L. Final AP fluoroscopic view. Note that the implant's leading edge approaches the midaxis of the talar neck without crossing it and the trailing edge is not fully buried under the lateral talar neck.

 

 

 

TECH FIG 8 • Associated foot realignment. A. Medial displacement calcaneal osteotomy completed prior to subtalar arthroereisis in this case. B. Plantarflexion osteotomy of first cuneiform. C. Graft insertion into medial cuneiform.

• Case Example

   

  In our experience, isolated subtalar arthroereisis does not afford adequate correction in skeletally mature patients with flexible pes planovalgus deformity.

   

  In this particular case, the 26-year-old woman had better correction on the right foot, where foot realignment procedures were added to subtalar arthroereisis, than in the left foot, where subtalar arthroereisis was performed with only gastrocnemius-soleus recession (TECH FIG 9A-F).

   

   

   

  TECH FIG 9 • Example case of a 26-yearold woman with better correction on right foot where foot realignment procedures were added to subtalar arthroereisis when compared to left foot where subtalar arthroereisis was performed with only gastrocnemiussoleus recession. A. AP view. B. Posterior view. (continued)

   

   

  Weight-bearing radiographs of the same patient's right foot with subtalar arthroereisis performed with gastrocnemiussoleus recession, medial displacement calcaneal osteotomy, and plantarflexion osteotomy of the first cuneiform (TECH FIG 9G,H).

   

   

  45

   

   

  TECH FIG 9 • (continued) C. Dorsal foot view. D. Left arch. E. Right arch. F. Lateral view demonstrating incisions for subtalar arthroereisis and calcaneal osteotomy. AP (G) and lateral (H) weight-bearing radiographs of the same patient's right foot with subtalar arthroereisis performed with gastrocnemius-soleus recession, medial displacement calcaneal osteotomy, and plantarflexion osteotomy of the first cuneiform. Note healed calcaneal and first cuneiform osteotomies.

• Subtalar Arthroereisis with Foot Realignment and Accessory Navicular Excision

 

 

Flexible pes planus with forefoot supination (TECH FIG 10A) Equinus contracture (TECH FIG 10B,C)

 

Gastrocnemius-soleus recession (TECH FIG 10D)

 

 

Plantarflexion osteotomy of the first cuneiform to correct forefoot supination (TECH FIG 10E-I) Subtalar arthroereisis performed

 

Guidewire placed (TECH FIG 10J-L)

 

 

Trial and final implant insertion over guidewire (TECH FIG 10M,N) Fluoroscopic confirmation of proper implant position (TECH FIG 10O)

 

Guide pin removed medially (TECH FIG 10P)

 

Guide pin typically exits in planned medial approach for modified Kidner procedure.

 

Modified Kidner procedure performed (TECH FIG 10Q)

 

 

46

 

 

 

 

TECH FIG 10 • A. Patient with symptomatic flexible pes planus and forefoot supination. Gastrocnemius contracture demonstrated with Silfverskiöld test: equinus with knee in extension (B); no equinus with knee in flexion (C). D. Gastrocnemius-soleus recession. E. Osteotomy with microsagittal saw. F. Triple osteotome technique to gradually open osteotomy, leaving plantar cortex intact. G. Dorsal distraction. H. Forefoot supination corrected. I. Graft inserted. J. Guidewire insertion into sinus tarsi. (continued)

 

 

47

 

 

TECH FIG 10 • (continued) K. Optimal medial exit point. Note that wire exists within planned incision for modified Kidner procedure. L. AP view. M. Trial implant insertion. N. Final implant insertion based on trial. O. Fluoroscopic confirmation of proper final implant position. P. Guidewire removed medially. Q. Modified Kidner procedure. Accessory navicular excised and PTT attachment to main body of navicular.

 

 

PEARLS AND PITFALLS
	Imaging the accessory ▪ The external oblique radiograph, different from the internal oblique navicular obtained in routine three views of the foot, provides the best perspective on the accessory navicular.     Excising the accessory ▪ Preserve as much as the medial PTT tendon fibers as possible. navicular ▪ Preserve the plantar PTT fibers that course to the plantar midfoot. Avoid injury to the spring ligament.     Arthrodesis of the ▪ Prepare the synchondrosis like any other arthrodesis. accessory navicular to the ▪ Remove all fibrous and cartilaginous tissue and prepare the bony

Subtalar arthroereisis

• The implant should not be used as a stand-alone device.

• The guidewire should be removed from the medial side to avoid displacing the implant.

surfaces of the navicular and the accessory navicular.

• Oppose the prepared bony surfaces and secure with one or two screws.

main body of the navicular

 

 

 

48

POSTOPERATIVE CARE

 

Sterile dressings are applied to the wounds.

 

 

With satisfactory stability of the PTT or accessory navicular to the medial navicular, the ankle and hindfoot may be splinted in neutral position.

 

 

Slight ankle plantarflexion and hindfoot inversion relieves tension at the repair site but should not be excessive, as it could lead to contracture and be counterproductive if concomitant tendo Achilles lengthening was performed.

 

A subtalar arthroereisis implant is typically stable and does not warrant special consideration in the postoperative management.

 

Follow-up in 2 to 3 weeks for suture removal and short-leg cast versus cam boot. We favor casting for an additional 3 to 4 weeks to protect the medial repair.

 

 

The ankle and hindfoot are generally placed in neutral at this time, but if there is any concern about the stability, then slight hindfoot inversion may be maintained.

 

Touchdown weight bearing is maintained for 6 weeks.

 

At the 6-week follow-up, the patient may typically begin gentle range-of-motion exercises and gradually advance weight bearing in a cam boot to advance to full weight bearing by 10 weeks.

 

 

If an accessory navicular arthrodesis was performed, then an external oblique radiograph should be obtained to confirm satisfactory healing of the accessory navicular to the navicular.

 

 

If healing is delayed, then casting and limited weight bearing must be continued.

 

If a subtalar arthroereisis was performed, then routine weight-bearing radiographs of the foot should be obtained to confirm appropriate implant position and foot realignment.

 

 

To optimize return to full function, consideration may be given to physical therapy at 10 to 12 weeks. In general, return to full activities including athletic activities takes 4 to 6 months.

 

The subtalar implant may be eventually removed (>6 months), but in our experience, if left in place to afford more favorable foot alignment and support for the medial repair, it typically does not cause symptoms.

 

OUTCOMES

Prospective evaluation of 20 patients with a symptomatic type II accessory navicular7

Ten patients had a modified Kidner and 10 patients had an open reduction and internal fixation (ORIF) of

 

 

the accessory navicular.

After an average follow-up of 35 months, the 10 patients who underwent ORIF had a significant improvement in their American Orthopaedic Foot and Ankle Society (AOFAS) scores (greater improvement than the Kidner group, but the postoperative scores were no significantly different).

One patient had to return to the operating room for painful hardware.

Two others had nonunion and one had symptoms. There were no signs of medial arch collapse.

The 10 patients who underwent the modified Kidner had a significant improvement in their AOFAS scores.

Three of 10 showed progressive loss of medial arch.

Retrospective study of 23 feet with painful type II accessory naviculars who underwent a combined modified Kidner and subtalar arthroereisis with planovalgus deformity at 53.9 months and average age of 18 years

Significantly improved AOFAS scores

Significantly decreased visual analog scale pain scores Improvement in Meary angle and talar head uncoverage

Three patients had the implant removed for pain. Deformity correction was maintained after removal. Nineteen had good or excellent results.

 

COMPLICATIONS

Modified Kidner procedure

Incomplete PTT healing to the medial navicular May warrant revision surgery

Development/progression of symptomatic pes planovalgus May warrant bracing versus flatfoot corrective surgery

Prominent symptomatic medial suture anchor knots

Once tendon has healed to medial navicular, these knots may be excised. Ideally, the suture knots are buried as deep as possible.

ORIF of the accessory navicular

Loss of fixation/delayed union/nonunion

May warrant revision surgery or conversion to modified Kidner procedure Development/progression of symptomatic pes planovalgus

May warrant bracing versus flatfoot corrective surgery Prominent hardware

May warrant removal of hardware once arthrodesis has progressed to fusion Subtalar arthroereisis

Impingement pain

Sinus tarsi pain with eversion

 

May warrant implant removal Subtalar stiffness

May warrant implant removal Forefoot supination

In patients with long-standing pes planovalgus, the forefoot may have subtle fixed deformity.

Subtalar arthroereisis may exacerbate forefoot supination, creating symptomatic lack of loading on the medial column of the foot and potential lateral column overload.

Implant migration

If inserted properly and used with proper indications, typically, the implant does not migrate.

Subtalar arthritis Rare

Typically, only occurs if implant placed incorrectly

 

 

REFERENCES

1. Bennett GL, Weiner DS, Leighley B. Surgical treatment of symptomatic accessory tarsal navicular. J Pediatr Orthop 1990;10(4):445-449.

    

    

2. Chiu NT, Jou IM, Lee BF, et al. Symptomatic and asymptomatic accessory navicular bones: findings of Tc-99m MDP bone scintigraphy. Clin Radiol 2000;55(5):353-355.

    

    

3. Coughlin M. Sesamoids and accessory bones of the foot. In: Coughlin M, Mann R, Saltzman C, eds. Surgery of the Foot and Ankle, ed 8. Philadelphia: Mosby, 2007:531-610.

    

    

4. Garras DN, Hansen PL, Miller AG, et al. Outcome of modified Kidner procedure with subtalar arthroereisis for painful accessory navicular associated with planovalgus deformity. Foot Ankle Int 2012;33(11):934-939.

    

    

5. Kidner FC. The prehallux (accessory scaphoid) in its relation to flatfoot. J Bone Joint Surg Am 1929;11:831-837.

    

    

6. Schon LC. Subtalar arthroereisis: a new exploration of an old concept. Foot Ankle Clin 2007;12(2):329-339.

    

    

7. Scott AT, Sabesan VJ, Saluta JR, et al. Fusion versus excision of the symptomatic Type II accessory navicular: a prospective study. Foot Ankle Int 2009;30:10-15.