Reconstruction of the Supple Flatfoot with the Concept of Planal Dominance

Abstract

Management of the adolescent and flexible flatfoot deformity represents a complex task. It requires biomechanical knowledge and analytic mechanics to determine deformity that compensates in a primary plane of dominance. This in-depth review presents clinical presentation, radiographic evaluation and mechanisms of occurrence. It also will propose surgical management for three types of flatfoot deformity as seen compensating in a dominant plane. In discussion of the various types, biomechanical focus concerning articular geometry and its modes of compensation will be highlighted.

1. Introduction

Although an abundance of research into the treatment of congenital flatfoot deformity has led to improved standardization of surgical options, discrepancies still exist in how surgeons best approach this common musculoskeletal condition. Differences in surgical approach appear to be based on geographic location and training. Controversy of opinion still remain on whether planal dominance actually exists (Figure 1). The chief author’s approach tends to the theory of Root and Weed [2]. This chapter will offer insight into flatfoot deformity that is predominant in either the frontal, transverse or sagittal planes. While deformity certainly overlaps into the three planes, dominance in a primary plane often exists. The foot follows the analytic mechanical effect of Cardan coupling. A universal joint connecting rigid shafts whose axes are inclined to each other. The presentation provided will embed a stepwise approach to assess a patient clinically, radiographically and biomechanically. This will determine the surgical procedures necessary to best benefit their anatomy. This will occur once conservative measures have failed.

Figure 1.

Represents the complex geometry of planal dominance [1].

2. Arches of the foot

There are three main arches of the foot (Figure 2). The first represents the medial longitudinal arch. It is constructed of three joints: talonavicular (TN), navicular-medial cuneiform joint (NC) and first metatarsal-medial cuneiform joint (first met-MC). The second is represented by the lateral longitudinal arch. It is composed of the tarsometatarsal (TMT) four and five joints as well as the calcaneocuboid joint (CC). Third, the anterior transverse arch, or Roman arch, created by the metatarsals one through three and their respective cuneiforms and metatarsals four, five and their articulations with the cuboid.

Figure 2.

Graphic depiction of the three arches of the foot.

The medial longitudinal arch consists of two tri-planar axial joints. The TN joint which biomechanically composes the longitudinal midtarsal joint (LMTJ) axis. It deviates 15 degrees from the transverse plane and nine degrees from the sagittal plane. Thus, it provides primarily frontal plane motion. It also consists of the first-met MC joint, articulating with the navicular. This represents the first ray. It angles 45 degrees with both the frontal and sagittal planes and only slightly from the transverse plane. It thus allows primarily biplanar motion. These become effected at forefoot load (at 15% of the gait cycle) and influenced by the ankle and subtalar joints.

The lateral longitudinal arch is composed of TMT 4,5 joints as well as the CC joint. The fourth metatarsal cuboid moves only in the sagittal plane. The fifth metatarsal cuboid TMT 5 represents only motion of the fifth metatarsal. It angles 20 degrees from the transverse plane and 35 from sagittal plane. Thus, it exhibits primarily two planes of motion in equal amounts in the frontal and sagittal planes despite being a tri-planar axis. Of note the central three metatarsal cuneiform joints move according to subtalar joint and midtarsal joint motion. Whereas, the fifth ray is completely independent of their (subtalar joint and midtarsal joint motion).

The CC joint composes the oblique midtarsal joint (OMTJ) axis. It deviates 52 degrees to the transverse and 57 degrees to sagittal plane. Thus, it allows primarily motion in those two planes despite being tri-planar joint.

The anterior transverse arch (or Roman arch as it has been described) represents the TMT 1,2,3. These move minimally in the sagittal plane. They serve to provide inherent stability to the anterior arch of the foot. The lateral portion of the Roman arch remains mobile via fifth ray motion and adapts the lateral midfoot to terrain.

3. Classification of adolescent and adult flexible flatfoot deformity

This discussion will attempt and limit to classify flatfoot deformity in an adult or adolescent that exists only in a flexible deformity. There are no associated signs of neuromuscular (NM) weakness present. Intrinsic joint instability due to axis alteration is a dominant factor. Borrelli and Smith [3] discussed the flexible flatfoot from a planal dominance point of view. The authors described three planes of dominant deformity. Their discussion noted primary frontal plane compensation as STJ subluxation. The STJ is the articulation of the talus and calcaneus. It is also known as a peritalar joint articulating with the navicular as well. Thus, it composes the two tri-planar axes of the STJ and LMTJ as a peritalar complex. Axis deviation altering articular geometry creates intrinsic joint instability. Heel valgus is the primary deformity and arch flattening leads to weight bearing over the NC joint.

Transverse plane dominance was discussed as a lateral column deformity characterized by increased forefoot abduction. As will be seen, the deformity can either be affected at the STJ or OMTJ itself. In either case arch height loss occurs over the NC joint.

The medial portion TMT 1,2,3 of the transverse arch is a stable and relatively rigid articular structure. Disease and injury can lead to abnormal joint instability. The first met MC becomes unstable and thus exhibits abnormal clinical motion creating a midfoot flatfoot with loss of arch height. Weight bearing thus is primarily centered at the medial cuneiform (1st met-MC). STJ and MTJ compensation is normally not effected.

Sagittal plane deformity was defined by medial column subluxation. In this case the talus within the peritalar complex is oblique and subluxed with the talar head being weight bearing at the collapsed medial longitudinal arch.

4. Frontal plane flatfoot deformity

4.1 Biomechanics of the frontal plane flatfoot deformity

In the case of normal biomechanical function of the STJ, the axis deviates 42 degrees to the transverse plane and 16 degrees to the sagittal plane as well as 46 degrees to the frontal plane. It is known that the joint axis is determined by joint geometric anatomy. This indicates frontal plane motion signified clinically by calcaneal eversion, and transverse plane motion noted by talar adduction related nearly 1:1. Sagittal plane motion is much less and presented as talar plantarflexion.

Chambers in 1946 [4] discussed the concept of unsaddling of the STJ. He noted that the posterior, anterior and middle facets were synchronized in their movement and acted like gears. The articular surface geometry is determined by the axis. The talus moves as a cog relative to the calcaneus. In a normal state of function talar movement is determinant by an osseus restraining mechanism. Sigrid Zitzlsperger, MD described this mechanics as self-locking wedges [5]. The talar concave and calcaneal convex surfaces at the posterior, anterior, and middle facets determine talar movement. Beginning as congruous during biomechanical function talar adduction, plantarflexion and calcaneal eversion ultimately become incongruous and thus (lock) preventing further talar motion. This relates to the first 25% of the gait cycle where maximal pronation occurs and the calcaneus everts to six degrees.

When in a pathologic state and the axis becomes deviated more to the frontal plane (less vertical) calcaneal eversion (greater than 20 degrees) will exceed talar adduction. The joint structures (posterior, ant, middle facet) will fail to lock and thus a loss of the osseus restraining mechanism and failure of the self-locking wedges occurs. The end result is the supporting structures (cervical, interosseus and spring ligaments) attempt to restrain talar movement and become strained. Talar movement does not stop until the talar lateral process abuts into the floor of the sinus tarsi. Thus, as the foot proceeds to 50% of the gait cycle it fails to resupinate.

Bruce Sangeorzan, MD and colleagues only recently discussed the “forward movement of the talus” moving like a screw [6]. This factor of the talus sliding forward on the calcaneal facets correlates to radiographic findings that will be discussed. The severity of this movement is determinant upon pathologic compensatory factors such as equinus and torsional forces.

Clinically heel valgus then exceeds the normal six degrees. The forefoot loads at about 10% of the gait cycle. Normally the TN joint and LMTJ axis compensates for the heel valgus by six degrees of inversion. In cases of excessive heel valgus (greater than six degrees), further forefoot compensation will occur at the first met MC/navicular first ray. This is signified as an NC break and elevation of the first metatarsal in reference to the second (Seiberg index). Also further compensatory forces (equinus) strain the soft tissue about the TN joint allowing further motion. This is the concept of forefoot supinatus. This will be discussed in more detail in radiographic analysis. In essence, the foot fails to resupinate and thus at propulsion fails at toe off.

4.2 Radiographic evaluation of the frontal plane flatfoot deformity

When viewing the dorsal plantar (DP) view (Figure 3A), the talo-calcaneal (TC) angle, or Harris-Beath angle is increased. Uncoverage of the talar head varies from 30 to 50% while cuboid abduction angle remains normal. This can be explained by the talus adducting and moving forward and does not use the navicular for lateral rotation.

Figure 3.

A: DP view of a right frontal plane flatfoot; B: Lateral view of a right frontal plane flatfoot with annotated anatomical anomalies; C: Axial view of a frontal plane flatfoot; D: Clinical photograph showing the posterior view of frontal plane flatfeet; E: Clinical photograph showing the front view of frontal plane flatfeet; F: Clinical photograph showing the lateral view of left frontal plane flatfoot.

On the lateral view (Figure 3B), various radiographic deviations are noted. First one notices the orientation of the posterior facet. It is angled about 75 degrees to the weight bearing surface with the STJ axis being less vertical and more perpendicular to the frontal plane. It can be viewed as a “pogo-stick” pulling the posterior facet into that position tilting the entire talus forward, medial and down. We also see obliteration of the sinus tarsi. This is due to a lateral process abutment that led to stoppage of talar movement.

The talar declination angle is increased due to the adducted plantarflexed and forward movement of the talus. Calcaneal inclination is also decreased. This is due to the forward position of the talus over the sustentaculum tali (STT) with weight bearing forces pushing it downward. With associated gastrocnemius soleus equinus contracture it pulls the posterior tuber superior and the anterior portion of the calcaneus inferiorly. An anterior break of the Cyma line is seen. Inferior plantar gapping of the CC joint represents excessive calcaneal eversion as the calcaneus moves away from the cuboid.

At the midfoot level the presence of an NC fault is noted. As has been described this represents pathologic compensation for excessive heel valgus. This is an osseous adaption and attributes to forefoot varus. At the forefoot level, forefoot supinatus is noted. This represents piling of the metatarsals so when viewed they all appear to be on the same plane. With excessive equinus forces the TN joint is subluxed on the frontal plane due to increased inversion forces that affect the capsuloligamentous structures. The navicular, three cuneiforms and three metatarsals become aligned with metatarsal 4 and 5. This represents a soft tissue contracture.

On the axial view (Figure 3C) we note the talus subluxed medially on the STT. There is sloping and hypoplasia noted. This is due to the anterior talar subluxatory weight bearing forces. This then produces functional adaptation along the lines of force as described by the Law of Wolff [7]. There is then an obvious loss of parallelity between the anterior, medial, and posterior facets. Also, the calcaneal body is in valgus in relation to the weight bearing line of the tibia.

4.3 Clinical evaluation of the frontal plane flatfoot deformity

When viewing the patient from behind (Figure 3D) we see excessive amounts of heel (calcaneus valgus). Also noted is medial bulging of the talus and of note it is not weight bearing. A positive Helbing’s sign is also seen with lateral orientation of the Achilles tendon insertion.

On the frontal view of the patient (Figure 3E), one notes a “reverse peek-a-boo heel sign.” With the lateral aspect of the calcaneus clearly visible due to excessive heel valgus. Also note the lack of forefoot abduction due to forward migration of the talus and lack of rotatory contact with the navicular.

When viewing the foot from the lateral view (Figure 3F), significant collapse of the medial longitudinal arch is noted. One can clearly see the weight bearing center of rotation axis (CORA) of collapse centers at the medial-cuneiform -navicular joint (MCNJ) with the navicular tuberosity being the apex of weight bearing. Talar bulge is noted and significant but does not represent the weight bearing CORA of the longitudinal arch collapse.

4.4 Surgical management of the frontal plane flatfoot deformity

4.4.1 Gastrocnemius and Achilles tendon contracture

The approach begins first by assessing the deforming forces of the Achilles tendon contracture. The Silverskold test is utilized. If contracture exists with the knee extended and eliminated when the knee is flexed, contracture of the gastrocnemius is present. This is best approached by gastrocnemius recession. A Strayer or Baumann type of aponeurotic release is performed. If, however the contracture persists when the knee is flexed it is representative of an Achilles tendon contracture. This is best addressed either open, frontal or z-plasty lengthening (Figure 4A), or more commonly percutaneous length by a Hoke technique. Two medial and a central lateral incision is utilized cutting 1/3 of the tendon at each site. In cases of primary gastrocnemius contracture a two incision percutaneous approach to the Achilles tendon can be utilized bringing the ankle only to 90 degrees. One must also be aware of the presence of an osseus equinus. This can be best evaluated on a lateral view looking for tibiotalar impingement lesions or flattening of the dome of the talus.

Figure 4.

A: Depicts and open z-plasty proximally; B–D: Koutsogiannis osteotomy to stabilize STJ in a frontal plane flatfoot patient; E: Gleich-Dwyer calcaneal osteotomy.

4.4.2 Posterior calcaneal osteotomy

Once the deforming force from the Achilles tendon is addressed, one then turns to the STJ malalignment. The first option is the cresentic calcaneal osteotomy described by Koutsogiannis [8]. Despite being a translated medial in the transverse plane, it allows significant correction in the frontal plane addressing the heel valgus deformity (Figure 4B). It has four primary biomechanical effects: 1. it converts the Achilles tendon insertion from a pronator to a supinator; 2. it aligns the calcaneal tuberosity to the STT; 3. by medial reposition it institutes gravitational forces that create closed kinetic chain supination and thus external leg rotation; and 4. its main biomechanical effect is that it displaces STJ motion by reducing pronation. On a maximal pronation force to the STJ the heel remains vertical. Thus it “displaces” the range of motion but has no effect on altering the STJ axis. The Gleich-Dwyer calcaneal osteotomy is done through the calcaneal body via a medial approach and allows a significant corrective force in the frontal plane. It can be done laterally where a medial wedge is cut in the medial side of the calcaneus (Figure 4C).

4.4.3 STJ arthroeresis

The second option to address STJ malalignment in the frontal plane, is utilization of STJ arthroeresis. Voegler [9] originally described arthroeresis into three separate categories (Figure 5A–C).

Figure 5.

A–C: depict the Vogler classification for three arthroeresis options; D: diagram of Selakovich opening wedge osteotomy of the sustentaculum tali; E: diagram of posterior facet osteotomy with bone graft as described by Baker and Hill; F: diagram of chambers procedure demonstrating application of arthroeresis concept with use of bone graft.

The first is “self/locking wedges” (Figure 5A) which represent the most common of arthroeresis implants. They are cylindrical implants that are inserted into the canalis tarsi. They serve to center the calcaneus in a vertical position in reference to the ankle joint. They also resaddle the talus into the STJ mortise. Thus while preserving supinatory motion they restrict pronation significantly. This is noted clinically by decreased calcaneal eversion, talar adduction as well as PF and forward migration of the talus. This form of arthroeresis provides corrective force to the STJ and alters its axis. In the past this was addressed with opening-wedge type osteotomy directed at the STT (anterior and middle facet).

The Selakovich opening wedge osteotomy (Figure 5D) was performed at the sustentaculum level. It served to reposition the anterior and middle facets parallel to the weight bearing surface and re-establish talar head support. The Baker and Hill opening wedge osteotomy of the posterior facet (Figure 5E) was created when it was noticed with STJ correction when performing an extra-articular Grice arthrodesis on a young patient with cerebral palsy a large gap was noted at the level of the posterior facet. Thus, rather than performing the arthrodesis they embarked with an opening wedge osteotomy of the posterior facet and restored its congruency. Both of these osteotomies serve to alter the axis of the STJ and re-established its locking mechanism.

The second implant type is the axis altering represented by the Smith Subtalar Arthroeresis (STA) peg (Figure 5B) [10]. Based on the Chambers procedure (Figure 5E) it is placed in front of the posterior facet where it is notched at 90 degrees to the anterior portion and thus raised the floor of the sinus tarsi. It then serves to restrict talar pronatory motion and restores the posterior facet locking mechanism.

The third type of arthroesis implant are the blocking devices (Figure 5C). Smith altered his STA peg to have an inclined anterior thickness to block the talus in adduction by “jamming” the lateral process. Pisani [11] placed a 3.5 mm screw in front of the lateral process in the floor of the sinus tarsi. The STJ was placed in its corrected neutral position and screw placed perpendicular in front of the lateral process. In essence, all three types of arthroesis implants lead to axis alteration in the adolescent. Functional adaption of the anterior, middle, and posterior facets then occurs along the lines of corrective forces as described by Wolff.

Once the STJ is stabilized in the frontal plane, one then turns to address the medial longitudinal arch (medial column changes). As stated prior an NC fault is seen as a persistent fault in the frontal plane. This is a result of compensation for equinus and heel valgus. In cases where the fault appears subtle, a “reverse Coleman block test” may be utilized (Figure 6A). With this test, blocks are placed under the forefoot and the amount of block height needed is to bring the calcaneus to a vertical position. A lateral X-ray is taken and a fault if present will be clearly demonstrated.

Figure 6.

A: reverse Coleman block test used to assess the presence of medial column fault. Block placed under the forefoot to identify NC fault; B: surgical approaches addressing equinus present in a frontal plane flatfoot patient; C: Jack test on a right foot to activate the windlass effect; D–F: cotton osteotomy, Lapidus, hoke navicular trans cuneiform fusion; G: Miller procedure.

In the adolescent and some adults the NC fault can be corrected by Achilles/gastrocnemius lengthening and STJ stabilization (Figure 6B). These procedures address the forefoot supinatus component. In these cases, functional adaption at the NC joint has not occurred. Another way to determine this condition pre-operatively is to perform Jack test (hallux dorsiflexion creating a windlass mechanism action) (Figure 6C).

If the NC fault present on the pre-operative weight bearing x-ray reduces, then there is no need to perform a medial column procedure. In cases where the NC fault persists on performance of the Jack test (first ray compensation), functional adaption occurs by sagittal compression forces about the dorsal portion of the NC joint. Thus, a true forefoot varus is present.

In these cases a cotton osteotomy (opening wedge of MC) or a plantarflexory MC (Mosca) osteotomy is performed. Also, the Hoke type navicular cuneiform fusion which includes the intercuneiform joint is an option. This can also be incorporated with wedging to address additional forms of forefoot abduction. The sagittal plane Lapidus procedure can be considered in the adolescent and addresses the NC fault. It can also be also utilized as a tri-planar correction in the presence of associated hallux abducto valgus deformity (Figure 6D–F). A Miller procedure (Figure 6G) is considered in the case of a longstanding severe equinus and heel valgus. This can lead to a combined medial fault involving the NC and first met-MC joints.

5. Transverse plane flatfoot deformity-subtalar type

5.1 Biomechanics of the transverse plane flatfoot deformity-subtalar type

In the case of the transverse plane dominated flatfoot deformity we see the axis (facet geometry) in a more vertical orientation (Figure 7). In this case transverse plane (talar adduction) exceeds frontal plane calcaneal eversion. The predominant deformity is forefoot abduction. There are two separate etiologies that lead to excessive forefoot abduction.

Figure 7.

A: depiction of the transverse plane axis; B: DP view of a transverse (subtalar type) plane flatfoot; C: lateral view of a transverse (subtalar type) plane flatfoot; D: axial view of transverse (subtalar type) plane flatfoot; E: clinical photograph showing the posterior view of transverse (subtalar type) plane flatfeet; F: clinical photograph showing the front view of transverse (subtalar type) plane flatfeet.

The first is generated the subtalar joint level. In this case, a significant amount of talar adduction occurs noted with an increase in the TC angle. However, the lateral column of the MTJ CC joint remains normal indicating that forefoot abduction is occurring about lateral translation of the navicular. Heel valgus occurs but remains in the 10–12 degree range. When viewing the lateral view an NC break is noted but is mild and reactant to equinus and heel valgus.

5.1.1 Radiographic evaluation of the transverse plane flatfoot-subtalar joint type

When evaluating the DP view there is a noted significant increase in the TC angle (Harris Beath) (Figure 7B). However, there is no sign of an increase in cuboid abduction (CA) angle. On the lateral view (Figure 7C) there is a paradox as there is a mild NC break but Meary’s angle appears as normal. To explain this one can see the posterior facet (a more vertical axis) appears more parallel to the weight bearing surface. When using the pogo-stick is appears more perpendicular to the weight bearing surface. As the talus thus goes through its excess adduction motion the anterior and middle facets being more parallel to the posterior facet is supported through its full range of motion on the axial view image (Figure 7D). There is minimal PF and forward movement noted.

5.1.2 Clinical presentation of the transverse plane flatfoot-subtalar joint type

When viewing the patient from behind (Figure 7E) one can see a lesser amount of heel valgus at about 10 degrees. Talar bulge is noted. Also, the classic “too-many-toes sign” is present signifying increased forefoot abduction. When viewing the patient from the front (Figure 7F), one can see a significant amount of talar bulge but it is not weight bearing. As can be seen with a more vertical STJ large increases in talar adduction are accommodated by the STT in rotation of the navicular as well as the remaining forefoot occurs. The arch is lower but weight bearing CORA occurs at the NC joint.

5.2 Biomechanics of the transverse plane flatfoot deformity-midtarsal type

In the second case, forefoot abduction is generated at the midtarsal joint level or CC (OMTJ). In this case as the talus moves into its locked adducted position the OMTJ becomes unlocked. The result is that forefoot abduction occurs primarily about that joint. The talus “locked” into the ankle mortise leads to prominence of the medial malleolus. This is created by closed kinetic chain pronation. There is a small amount of heel valgus (approximately eight to ten degrees) and associated equinus contracture, that serves to flatten the longitudinal arch about the NC joint. Also, the dorsiflexion component about the CC joint serves to lower the lateral portion of the longitudinal arch.

5.2.1 Radiographic evaluation of the transverse plane flatfoot-midtarsal type

When viewing the DP view (Figure 8A), again an increase in the TC angle is noted but there is also a significant increase in the CA angle. A paradox exists with the lateral view (Figure 8B) with a mild NC fault (greater than 6 degrees of heel valgus and a near normal Meary’s angle). In this case the pronation of the STJ leads to unlocking of the midtarsal joint and forefoot abduction being generated at this level. Arch lowering thus occurs at the first ray and OMTJ “dorsiflexion.”

Figure 8.

A: DP view of a transverse (midtarsal type) plane flatfeet; B: lateral view of transverse (midtarsal type) plane flatfeet; C: clinical photograph showing the posterior view of transverse (midtarsal type) plane flatfeet; D: clinical photograph showing the front view of transverse (midtarsal type) plane flatfeet; E: clinical photograph showing the side view of transverse (midtarsal type) plane flatfeet; F: Evans calcaneal osteotomy with screw and plate fixation.

5.2.2 Clinical presentation of the transverse plane flatfoot-midtarsal joint type

When viewing the patient from behind again, (Figure 8C) one can see heel valgus of about 8–10 degrees. There is an associated “too-many toes sign” indicating increased forefoot abduction. When viewing the patient from the front no significant talar bulge is noted. The medial malleolus is what appears prominent (Figure 8D). This corresponds with the increased talar adduction but internal tibio-fibular rotation as part of closed kinetic chain pronation. Forefoot abduction is noted here as a result of the unlocked CC joint OMTJ. Dorsiflexion also occurs to lower the longitudinal arch laterally and leads to lowering of the medial longitudinal arch (Figure 8F).

5.3 Surgical management of transverse flatfoot-midtarsal and subtalar types

To be able to differentiate between the two types clinically, one first places the patient’s STJ in a neutral or slightly supinated position. If the forefoot remains locked, then a STJ stabilizing procedure is performed along with a posterior group lengthening. This can be represented by either a posterior calcaneal osteotomy (Koutsogiannis, Gleich-Dwyer) or arthroeresis. The medial column may need a Cotton (opening wedge medical cuneiform osteotomy) or a plantarflexed medial cuneiform osteotomy (Mosca) [12].

If, however when the STJ is placed in a neutral or slightly supinated position, and the forefoot becomes unlocked, then one would address the deformity at the OMTJ level with an Evans opening wedge calcaneal osteotomy (Figure 8F) or opening-wedge osteotomy of the cuboid. Similarly, an equinus release may be required as well as a medial column procedure of a Cotton or a PF medial cuneiform osteotomy.

5.3.1 Biomechanics of the transverse plane flatfoot-Kidner foot

When considering a Kidner-type flatfoot one must be aware of the three types of accessory navicular bone. The type I represents the true accessory or sesamoid bone called the os tibiale externum (Figure 9A). The second is a so called “pre-hallux” or Gorilloid navicular (Figure 9B). It represents a syndesmotic “fibrous” articulation with the main body of the navicular. The third is cornuate navicular which represents an enlarged navicular tuberosity (Figure 9C).

Figure 9.

A: DP view depicting a type I accessory navicular bone; B: DP view depicting a type II Gorilloid navicular bone; C: DP view depicting a type III cornuate navicular bone; D: DP view of a transverse (Kidner type) plane flatfoot; E: lateral view of a transverse (Kidner type) plane flatfoot; F: clinical photograph showing the posterior view of transverse (Kidner type) plane flatfeet; G: clinical photograph showing the dorsal view of transverse (Kidner type) plane flatfoot; H: clinical photograph showing the lateral view of transverse (Kidner type) plane flatfoot; I: Kidner procedure showing removal of navicular tuberosity; J: pre-operative (left) and post-operative radiographs (right).

In most instances it is the type II accessory navicular that proves to be symptomatic. In this case, the insertion of the tibialis posterior tendon engages primarily the accessory portion. As a result, it becomes functionally weakened. The result is a destabilization of the peritalar complex leading to pronation. The net result is increased talar adduction, plantarflexion and calcaneal eversion. The distal tendinous investments across the midfoot become less effective. With functional alteration of the main insertion of the tibialis posterior tendon and a mechanical advantage to the peroneus brevis is gained. The result is increased forefoot abduction that can be generated at the STJ level but also can evolve about the midtarsal joint (OMTJ). Equinus also can represent a deforming force. Recently fusion or arthrodesis has been performed to stabilize the tibialis posterior tendon function and spring ligament. This was performed on type II navicular conditions [13].

5.3.2 Radiographic evaluation of the transverse plane flatfoot-Kidner foot

In the type I, one can see the presence of an os tibiale externum. In the type II, an associated synchondrosis is present with the main navicular body. The type III has an enlarged cornuate tuberosity. On the DP view (Figure 9D), there is an increase in the TC angle. The CA angle in most instances is increased. On the lateral view (Figure 9E) there is increased talar plantarflexion and a decrease CI. There is also the presence of a NC break. Meary’s angle is decreased due to the inherent degree of heel valgus and equinus.

5.3.3 Clinical presentation of the transverse plane flatfoot-Kidner type

When viewing the patient from behind (Figure 9F) one notes an increased amount of heel valgus with 12–14 degrees. There is also the presence of forefoot abduction noted by the “too-many-toes sign.” One also notes the increased girth and enlargement due to the enlarged navicular tuberosity. Viewing the patient from the front or dorsal view (Figure 9G), one notes increased forefoot abduction and enlarged prominence of the navicular tuberosity. When viewing the patient from the side (Figure 9H), one notes weight bearing primarily over the navicular tuberosity.

5.3.4 Surgical management of transverse plane flatfoot-Kidner type

Initial evaluation includes the Silverskold test to determine presence of gastrocnemius or soleus equinus present. Depending, a Bowman or Strayer technique is utilized for gastroc-soleus contracture and a Hoke percutaneous lengthening for gastroc-soleus contracture.

In the case where on the DP view there is an increased TC angle but the CA angle remains normal, a posterior type Koutsogiannis calcaneal osteotomy is performed. If there is also an associated increase in the CA angle, an Evans type opening wedge type osteotomy of the calcaneus is performed. A double calcaneal osteotomy is considered in the presence of more severe signs of instability at the TC and CC joints.

Next step is the performance of Kidner procedure itself. This involves surgical excision and resection of the remaining body parallel to the talus and medial cuneiform (Figure 9I). Resection of the navicular body is done at an angled approach. As the resection begins superior it angles medial to lateral when reaching the inferior portion. The result is the tibialis posterior tendon is tensioned with the foot fully supinated at the rearfoot and pronated at the forefoot. This is done with a suture anchor technique. This often will correct the NC fault but in some cases a Cotton opening medial wedge osteotomy or Mosca-type closing wedge osteotomy is needed. The Mosca-type plantarflexory osteotomy does create increased forefoot adduction (Figure 9J).

5.4 Biomechanics of the transverse plane flatfoot-Lisfranc type

In this case there has been injury, involving Lisfranc’s ligament or degenerative changes of the medial pillar of Lisfranc’s joint. This involves the medial (first-met-MC) and central columns (TMT 2, 3). As is known these three joints demonstrate only mono-planar motion. When injury to the deep (plantar) portion of the Lisfranc’s ligament occurs, resultant tri-planar instability occurs at the first-met-MC and bi-planar compensation at TMT 2,3. With this instability the first metatarsal dorsiflexes, everts and abducts. This leads to lowering of the arch at the medial cuneiform level and creates a midfoot flatfoot. The central column (TMT 2,3) also dorsiflex and abduct and lower the transverse (Roman) arch. This also serves to shorten the lever arm of the foot which leads to a significant mechanical advantage to the gastrocnemius soleus muscle group and thus equinus contracture. With this pathologic hypermobility pronatory forces are compensated solely at those levels. The clinical result is a midfoot flatfoot with the CORA at the MC joint. Thus, STJ and MTJ compensation will rarely occur, but can in longstanding cases.

5.4.1 Radiographic evaluation of the transverse plane flatfoot-Lisfranc type

On the DP view (Figure 10A), one sees shortening (lateral rotation of the first metatarsal on the medial cuneiform). There is a lateral step off of the second and third metatarsals on their respective cuneiforms. Degenerative joint disease occurs dependent on deformity longevity. One notes normal TC and CA angles.

Figure 10.

A: DP view of transverse (Lisfranc’s type) plane flatfeet; B: lateral view of transverse (Lisfranc’s type) plane flatfeet; C: clinical photograph showing the front view of transverse (Lisfranc type) plane flatfoot; D: clinical photograph showing the side view of transverse (Lisfranc type) plane flatfoot; E: interpositional allograft required as large gap is present upon repositioning of the first metatarsal for surgical management of transverse flatfoot-Lisfranc type; F: surgical management of transverse plane (Lisfranc type) flatfoot.

On the lateral view (Figure 10B), one notes a dorsal step off of the first metatarsal base to the MC indicating joint instability. Also, the fifth metatarsal is parallel to the floor indicating increased lateral column instability. The talar declination and CI angle remain normal indicating lack of STJ and MTJ compensation.

5.4.2 Clinical presentation of the transverse plane flatfoot-Lisfranc type

From behind, the calcaneus may show some compensatory eversion, but in most cases, the STJ and MTJ are not involved in compensation.

On a front view (Figure 10C), the forefoot is abducted at tarsometatarsal joint with the ankle aligned.

On a side view (Figure 10D), the arch is flattened to ground with medial cuneiform weightbearing and loss of transverse arch.

5.4.3 Surgical management of transverse flatfoot-Lisfranc type

The initial approach requires equinus contracture determinant by the Silverskold test. This is effected by the shortened lever arm and most often represents a gastrocnemius contracture. Thus, a Bowman or Strayer-type lengthening is performed.

Next, one must address the instability and if present the degeneration of the medial and central columns. It is critical that the first-met-MC joint be re-established in its plantarflexed, adducted and inverted position. This requires arthrodesis and in some instances due to shortening an interpositional auto or allograft is needed (Figure 10E).

The central column (TMT 2, 3) require plantarflexion and adduction to re-establish proper joint alignment by arthrodesis. Care must be performed not to allow shortening or elevation of those respective metatarsals. Any instability or deformity of the lateral column (TMT 4, 5) is addressed by re-alignment and k-wire fixation, no attempt of arthrodesis is performed at this level (Figure 10F).

6. Sagittal plane flatfoot deformity

6.1 Biomechanics of the sagittal plane flatfoot deformity

In this deformity centering is about the peritalar complex. The axis in this situation will tilt 45 degrees sagittal, 30 degrees to the frontal and 15 degrees to the transverse planes. The result is a severely maligned talus with significant subluxation at the calcaneus and navicular. This condition has been referred to as an oblique talus. The deformity is semi-flexible. The talus is nearly dislocated at the navicular and subluxed off the STT. Resulting in severe heel valgus with the talar head being weight bearing. There is some amount of translation of the talar articular surface with the navicular. Leading to a mild increase in forefoot abduction noted as an increased CA angle. Also, abhorrence of the TN (LMTJ) axis allows excessive motion in response to the severe heel valgus and equinus.

6.2 Radiographic evaluation of the sagittal plane flatfoot

On the DP view (Figure 11A) there is a significant increase in the TC angle. The uncoverage angle can be near 70% or greater. There is an increase in the CA angle leading to increased forefoot abduction.

Figure 11.

A: DP radiograph view of a left foot sagittal plane flatfoot; B: axial radiograph view of a sagittal plane flatfoot; C: lateral radiograph view of a left foot sagittal plane flatfoot; D: clinical photograph showing the lateral view of right sagittal plane flatfoot; E: clinical photograph showing the posterior view of sagittal plane flatfeet; F: clinical photograph showing the front view of sagittal plane flatfeet; G: surgical management of a sagittal plane flatfoot depicting sub-capital talar head wedge resection; H: proposed surgical management of a sagittal plane flatfoot with z-plasty of tendoachilles lengthening, Koutsogiannis calcaneal osteotomy.

The axial view (Figure 11B) will note hypoplasia of the sustentaculum with the talus subluxed medial and forward. Loss of facet parallelity is present. The anterior and middle facets are not visualized.

On the lateral view (Figure 11C) the talus is oblique and an uncharacteristic TN fault is present. The neck of the talus is shortened due to increased compressive intraarticular forces created by the semi flexible, subluxed condition and associated severe equinus. The calcaneal inclination angle (CI) is often negative due to the weight bearing force directed forward and medial at the STT. Equinus force also pulls the calcaneal tuber superiorly. Forefoot supinatus is noted as a piling of the metatarsals due to the longitudinal midtarsal joint abhorrence and alteration. One when viewing the axial and lateral views would consider a STJ coalition.

6.3 Clinical presentation of the sagittal plane flatfoot

When viewing the patient in a non-weight bearing position (Figure 11D) the foot appears flattened with loss of the longitudinal arch. This differs from frontal and transverse plane dominated flatfoot deformities which are flexible and the arch appears normal where the longitudinal arch collapses with weight bearing. The lack of flexibility due to TN subluxation allows this clinical condition.

When viewing the patient from behind (Figure 11E) one notes severe heel valgus, the plantar heels are not weight bearing secondary to the severe equinus contractures. There is considerable increased girth of the foot due to significant subluxed position of the talus. It appears similar to a patient with a STJ coalition.

One can see when viewing the patient from the front (Figure 11F) one can see severe hallux abducto valgus but the forefoot is abducted in the transverse plane. Weight bearing and CORA occur at the talar head level.

6.4 Surgical management of sagittal plane flatfoot deformity

The initial approach is to address the equinus contracture that involves the Achilles tendon. An open z-plasty is required to allow sagittal plane correction of the calcaneus (to increase the calcaneal pitch). A biplane calcaneal osteotomy corrects valgalization and create a vertical heel position. The calcaneal pitch is also corrected.

Due to the fact it is an adolescent or young adult, one needs preserve joint function and avoid arthrodesis if possible. Thus, a talar closing sub capital adductory wedge osteotomy allows correction of the TN fault by shortening the medial column (Figure 11G). A Steinmann pin is utilized to correct the compensatory soft tissue contracture of forefoot supinatus by de-rotation around the TN joint. The osteotomy is secured with a staple. One can see by the dissection technique that preservation of the blood supply to the talus is accomplished (Figure 11H). It may require lengthening of the tibialis anterior tendon to fully reduce the deformity.

7. Conclusion

In the clinical pictures presented below, the concept of planal dominance via Cardan coupling is presented. Considering primary frontal plane compensation. Figure 12.1A demonstrates collapse of the medial longitudinal arch. Clearly the point of weight bearing CORA lies at the navicular and MC articulation. In Figure 12.1B, one notes significant calcaneal valgus exceeding 12–16 degrees. In Figure 12.1C, one sees the reverse “peek-a-boo” heel sign due to increased heel valgus but also the forefoot is relatively well aligned.

Figure 12.

Summary chart with images depicts the various planal appearances of flat feet.

Considering transverse plane dominance we can see four separate modes of compensation. In Figure 12.2A, we see STJ compensation with extreme medial talar bulging but the talus not the CORA of weight bearing. A large amount of forefoot abduction at the TN level and a lowered arch with weight bearing at the NC joint. In Figure 12.2B, we see the midtarsal joint level, compensation with increased forefoot abduction but prominence medially is the medial malleolus. Arch collapse over the NC joint in Figure 12.3C. A Kidner foot with significant forefoot abduction at the midtarsal joint level due to the mechanical imbalance of the peroneus brevis. Again, the NC serves as the weight bearing CORA of the longitudinal arch. Figure 12.2D, we have the “midfoot flatfoot” due to a Lisfranc’s medial and central column insufficiency. The weight bearing CORA is at the medial cuneiform itself. Forefoot abduction is at the metatarsal level itself as well as medial and central column of Lisfranc’s joint.

In sagittal plane primary compensation one sees from Figure 12.3A, from behind, severe heel valgus, the calcaneus not weight bearing due to severe equinus. Significant increase in medial girth is present from the oblique positioning of the talus. On Figure 12.3B, clearly the CORA is at the talar head itself where the longitudinal arch appears broken.

Thus not all flatfeet are the same. Axis alteration due to joint morphology determines the major plane of compensation amongst these multiple tri-planar joint.

Conflict of interest

The authors declare no conflict of interest.