Flatfoot





KEY FACTS





  • Arch height is widely variable in the population. A “low-arched foot” is not necessarily pathologic.



  • Acquired flatfoot refers to an abnormal loss of the arch with pain.




    • Acquired flatfoot is a common end point of many etiologies.




  • Posterior tibial tendon (PTT) dysfunction is the most common cause of the adult acquired flatfoot.




    • Other causes include neuropathic (Charcot) degeneration, neuromuscular disease, inflammatory disease, and trauma (fracture malunion or PTT laceration/rupture). Other factors, such as obesity, may play a role.




  • Flatfoot describes the end point of a collapsed medial arch with associated deformities of the hindfoot and forefoot.




    • The hindfoot progresses into the valgus, and the forefoot supinates.




      • Peak pressures and contact forces of the associated joints, such as the subtalar joint, increase.




    • In the sagittal plane, the longitudinal arch collapses with subluxation of the talonavicular (TN), naviculocuneiform (NC), or 1st tarsometatarsal (TMT) joints (or a combination of them).



    • In the axial plane, the forefoot abducts, usually through the TN joint.



    • In the coronal plane, heel valgus is seen.




  • In 3 dimensions, the deformity is perhaps best described as dorsolateral peritalar subluxation, because the foot is subluxing dorsally and laterally around the talus.




    • Although the deformity is primarily through the peritalar joints in many flatfeet, it is important to remember that in some feet, other joints (such as NC or TMT) may be involved.




  • The disease tends to be progressive. Once arch integrity is lost and collapse begins, gravity and weight-bearing forces encourage further destabilization.







The transverse tarsal joint includes the calcaneocuboid and talonavicular joints. In a simplified model, the axes of the joints are divergent in supination, locking the midfoot. When the foot is pronated, the axes are parallel, allowing motion at these joints and unlocking the midfoot.








Inspection and palpation along the course of the posterior tibial tendon may demonstrate pain, swelling, and bogginess.








Lateral radiograph shows a large talar beak . There is C-shaped sclerosis at the subtalar joint . Both findings are secondary signs of a talocalcaneal coalition. (From DI: MSK Non-Trauma.)








Tarsal coalition may cause a deformity that resembles the adult acquired flatfoot. CT confirms the fused medial facet of the subtalar joint , while the posterior facet remains normal. This is a typical intraarticular talocalcaneal coalition, which usually only involves the medial facet. (From DI: MSK Non-Trauma.)






Arches of Foot





  • The medial longitudinal arch comprises the 1st metatarsal, medial cuneiform, navicular, and talus.



  • The lesser longitudinal arch consists of the 4th and 5th metatarsals, cuboid, and lateral calcaneus.



  • A transverse arch spans the midfoot across the midtarsal joints. The 2nd and 3rd metatarsal bases are keystones and help prevent collapse.



Arch Support: Ligaments Are Key Static Supporters of Arch





  • The spring ligament is an important stabilizer of the medial arch. It consists of 2 parts.




    • The superomedial calcaneonavicular (SMCN) ligament arises from the sustentaculum tali and fans out to insert on the edge of the medial navicular facet.



    • The inferior calcaneonavicular ligament runs from the anterior sustentaculum tali and inserts on the plantar aspect of the midnavicular cortex.




  • The superficial deltoid originates on the medial malleolus and inserts on the dorsal edge of the SMCN ligament.




    • Its function is to serve as a check rein for the entire complex.




  • The plantar fascia also contributes to arch integrity.




    • In biomechanical testing, it fails under load at 1.7-3.4 times body weight. (Hintermann 1995).



    • Division of the plantar fascia results in depression of the longitudinal arch and elongation of the medial length of the foot (Sharkey et al 1998).




      • Arch stiffness decreases by 25% (Huang et al 1993).





  • The long plantar ligament runs from the anterior tuberosity of the inferior surface of the calcaneus.




    • The majority of fibers insert on the cuboid, and the more superficial fibers insert on the 2nd-5th metatarsals.




      • It is thought to be of secondary importance in arch support.





Dynamic Arch Stabilizers





  • The posterior tibial tendon (PTT) is a powerful inverter and plantar flexor of the foot.




    • It locks the transverse tarsal joints [talonavicular (TN) and calcaneocuboid joints].



    • Biomechanical and electromyographic studies suggest that the tendon acts as an arch supporter during gait and loading situations.




  • An imbalance between the PTT and its antagonists (tibialis anterior, peroneal longus and brevis, and triceps surae) may lead to arch collapse.




    • This occurs in muscle imbalance disorders, such as cerebral palsy.




  • Extrinsic and intrinsic toe flexors also contribute to arch support but have a secondary role.




    • The flexor tendons fail under repetitive stress without a functional PTT.




  • Hindfoot motion locks and unlocks the transverse tarsal joints.




    • With subtalar eversion, the transverse tarsal joints are flexible, which keep the forefoot supple to accommodate uneven surfaces.



    • When the PTT fires just prior to the heel rise portion of gait, the axes of the TN joint and calcaneocuboid joint are divergent, locking the transverse tarsal joints.




      • This creates a rigid medial column and long lever arm for forceful push-off during gait.





  • In the normal gait cycle, firing of the PTT just prior to heel rise inverts the heel, bringing the Achilles vector medial to the subtalar joint.




    • Achilles contraction then supports the arch and encourages locking of the transverse tarsal joints.




      • This stabilizes the arch for push-off.





3D Deformity





  • Although arch collapse is traditionally noted in the TN joint, deformity can occur with any combination of TN, naviculocuneiform (NC), &/or 1st tarsometatarsal (TMT) subluxation/collapse.



  • Using the “tripod” model of foot structure, loss of the medial post of the tripod through collapse of any of these joints allows the hindfoot to collapse into valgus.



  • Acquired flatfoot is a 3D deformity of hindfoot valgus, longitudinal arch collapse, and forefoot abduction.



  • The talus becomes plantar flexed, the calcaneus everts, and the navicular and cuboid move to a more everted location.



  • With increasing hindfoot valgus, the forefoot assumes a compensatory forefoot supination.



  • The lateral column is effectively shortened as the deformity progresses.



  • The talus slides anteriorly relative to the calcaneus.



  • Hindfoot valgus occurs as a result of rotation through the subtalar and TN joints.



  • Achilles contracture is a deforming force that can both cause and exacerbate arch failure.




    • When the heel is in valgus, the Achilles insertion lies lateral to the axis of the subtalar joint so that Achilles contraction promotes subtalar eversion and, thus, arch collapse.




  • When the PTT fails to invert the hindfoot prior to heel rise, the calcaneal insertion of the Achilles remains lateral to the axis of the subtalar joint.




    • Achilles contraction then leads to hindfoot eversion.



    • The transverse tarsal joints are unlocked, and the arch can sag.




  • Recurrent cycles of this dysfunctional gait can break down the static support of the arch.



  • In some situations, Achilles contracture may precede any other pathology.




    • With Achilles contracture, the talus and calcaneus are plantar flexed.



    • Weight bearing places a dorsiflexion force on the forefoot.



    • Because of the oblique axis of the subtalar joint, subtalar eversion also produces some dorsiflexion.



    • In a foot with a tight Achilles tendon, subtalar eversion is necessary to produce a plantigrade foot.



    • With subtalar eversion, the PTT can become secondarily strained and eventually injured.




  • Many patients with active PTT tendonitis will have a tight gastrocnemius and a low arch on the “normal” foot.



  • A flatfoot deformity exacerbates Achilles contracture by maintaining the foot in hindfoot valgus and equinus.



  • The Achilles may become more contracted, which further antagonizes PTT function and arch integrity with a progressive deformity.



  • So, an acquired flatfoot can be caused by tightness of the Achilles (especially the gastrocnemius component) and can also result in a contracted Achilles tendon.



  • In the deformity, hindfoot and midfoot joint degeneration may develop secondary to increases in joint reactive pressures.




    • With a flatfoot deformity, the subtalar joint facets sublux, so that only 1/2 of the articular surface is in contact.



    • The decrease in contact area leads to increased contact pressures (Ananthakrisnan et al 1999).




Pain From Flatfoot





  • The pes planovalgus deformity alters joint mechanics as well as foot and ankle alignment.



  • Pain can occur in the foot, ankle, or even more proximal locations.




    • The lower back and hip may be sore from limping or from altered gait mechanics.



    • Continued valgus stress on the knee from a valgus foot can lead to medial compartment disease.



    • Valgus foot alignment can also lead to a valgus ankle deformity with painful joint degeneration.



    • In the foot, pain may be felt medially or laterally and may arise from inflammation, tendinitis, arthritis, &/or impingement.




  • In cases of PTT tendinitis, patients may feel pain only in the medial hindfoot from tenosynovitis or from a complete or longitudinal tear within the tendon.



  • In an advanced flatfoot of any etiology, pain may occur over the medial malleolus and deltoid ligament, as the deltoid fibers are tensioned to oppose the worsening hindfoot valgus.



Talocalcaneal Impingement and Calcaneofibular Impingement





  • With hindfoot valgus, lateral hindfoot pain can occur as a result of the calcaneus impinging on the distal tip of the fibula or lateral process of the talus.



  • Cyst formation &/or sclerosis in this region, either on plain film or computed tomography (CT), should create suspicion of impingement.



  • A CT imaging study compared control subjects with patients with severe deformity under 75 N of axial loading (Malicky et al 2002).




    • It determined that the prevalence of sinus tarsi impingement was 92%, and the prevalence of calcaneofibular impingement was 66% in the flatfoot group vs. 0% and 5%, respectively, in the control group.



    • The study patients who had calcaneofibular impingement also had sinus tarsi impingement.




Arthritis





  • Arthritis may be the causative agent or the end result of a chronic severe deformity.



  • Alteration of joint reaction forces causes abnormal loading of the subtalar, tibiotalar, transverse tarsal, and Lisfranc joints and may result in painful arthritic conditions.



Summary of Etiology of Adult Acquired Flatfoot





  • If the normal balance of arch support is disturbed (such as with fracture malunion, PTT injury, or Achilles tightness), persistent abnormally directed weight-bearing forces will tax the remaining support of the arch (such as the PTT or spring ligament), leading to progressive arch collapse.



  • Once the deformity is established, it may be difficult to determine which came first, the Achilles contracture, PTT dysfunction, or spring ligament rupture.



  • Perhaps the most important treatment for an acquired flatfoot is prevention.




    • If the “at-risk” foot could be identified, early intervention might prevent the deformity.



    • Once the deformity is established, it is often self-perpetuating and progressive.



    • An “at-risk” foot would be one with a very tight Achilles and normal PTT function or one with severe flatfoot deformity but still normal PTT function.






Posterior Tibial Tendon Dysfunction


Tibialis Posterior Anatomy





  • The muscle arises from the posterior tibia as a large muscle in the deep posterior compartment of the calf.



  • The tendon travels in the medial malleolar groove and inserts broadly into the medial foot.




    • It primarily inserts onto the navicular tuberosity, but multiple slips fan out to insert into the 2nd-4th metatarsals, into the plantar surface of the cuneiforms, and on the cuboid on the lateral foot.



    • On the plantar surface, it attaches to the deep fascia, peroneal longus tendon, and long and short toe flexors.




  • A zone of hypovascularity exists 40 mm proximal to the navicular tuberosity and extends proximally over 14 mm of tendon.




    • There is no mesotendon in this region, and surrounding synovial tissue is also hypovascular.




      • This area is subject to mechanical wear.





  • It is possible that a transient ischemia creates tendon insufficiency and sets up the cascade of dynamic instability.




    • A diseased PTT has high relative concentrations of type 3 collagen (it is the main collagen in early tendon healing).



    • It has decreased tensile strength, which can cause tendon insufficiency and dysfunction with recurrent use.




  • In an evaluation of spontaneously ruptured tendons and controls in an over-35 population, degenerative pathologic changes, such as hypoxic degeneration, mucoid degeneration, tendolipomatosis, and calcifying tendinopathy, were identified (Kannus and Jozsa 1991).




    • Of note, these changes were observed in 34% of control tendon specimens.



    • Normal tendon structure was not identified in any of the ruptured tendon specimens.



    • These findings suggest that degenerative tendinopathy is common after age 35.




Epidemiology





  • It is more often seen in women between 45-65 years of age.



  • It occurs with increased frequency in obese and ­diabetic patients.



  • About 1/2 of patients will relate a traumatic event to the initiation of symptoms.



  • As previously mentioned, with PTT dysfunction, the transverse tarsal joint will not lock during heel rise. Weight-bearing forces across these unlocked joints lead to fatigue failure of the ligaments. In these cases, PTT dysfunction precedes arch collapse.




    • Weight-bearing forces across these unlocked joints lead to fatigue failure of the ligaments.



    • In these cases, PTT dysfunction precedes arch collapse.




  • Arch-flattening forces, such as a tight gastrocnemius and obesity, may contribute to a flatfoot, as the repetitive forces of weight bearing cause the deformity to progress.




    • This may worsen PTT dysfunction.




  • In some cases, static deformities can cause PTT dysfunction (the arch fails first).




    • The position of forefoot pronation and valgus (arch ­collapse) will lead to PTT failure and worsening ­deformity.



    • If the talocalcaneonavicular complex loses stiffness, the PTT insertion sites are in a valgus position.



    • Lengthening of the tendon even 1 cm reduces its efficiency as the primary dynamic stabilizer of the arch.




Posterior Tibial Tendon Disease Progression





  • PTT disease progression is a continuum.



  • A staging system was introduced in 1989 by Johnson and Strom that included 4 stages.




    • The system was devised to describe the clinical entity and offers guidelines for nonoperative and operative treatment.




  • Unfortunately, there is no evidence that a foot progresses from one stage to the next over time.




    • It is possible that feet at stage 1 represent a different pathophysiology with a different natural history than that of a stage 3 flatfoot.




  • Not all feet at any one stage are the same.



  • Although treatment guidelines are often listed by stage, it is important to assess each foot individually.




    • Treatment, especially surgical, cannot be generalized.




Stage 1





  • Pain and swelling occur along the course of the tendon and are defined as tenosynovitis or tendinosis.



  • Tendon length is unchanged.



  • The subtalar joint is flexible.



  • The heel inverts on single toe rise, and there is no loss of strength.



  • There is no deformity; arch height remains unchanged.



  • Radiographs are normal.



  • Magnetic resonance (MR) imaging will demonstrate edema around the tendon and occasional intrasubstance degeneration.




    • Exuberant tenosynovitis may be a hallmark of an inflammatory or rheumatic etiology.




Stage 2





  • The tendon is elongated and enlarged and is functionally incompetent.



  • On tendon inspection, there are partial tears, and there is evidence of degeneration.



  • The patient may be able to perform a single limb heel rise, but the heel does not invert.



  • The foot assumes a pes planovalgus appearance.




    • The arch is collapsed, the hindfoot is in valgus, the forefoot is abducted, and the subtalar joint is everted.




  • The subtalar joint remains flexible, and the deformity is passively correctable.



  • The Achilles tendon will be contracted.



  • There will be a too many toes sign.



  • Radiographs demonstrate an increased lateral talocalcaneal angle, decreased calcaneal pitch, and lateral peritalar subluxation.



  • MR demonstrates tendon degeneration, possible discontinuity, and changes in the spring ligament.



Stage 3





  • Tendon degeneration is pronounced, and it is attenuated or ruptured.



  • Single-limb heel rise is often impossible, and the heel cannot be inverted with heel rise.



  • The deformity is severe and may be fixed.



  • The subtalar joint may be rigid.



  • The forefoot is abducted and may be supinated.



  • The navicular is in a laterally subluxed position.



  • Pain may occur both medially and laterally.



  • The too many toes sign is grossly positive.



  • Radiographs demonstrate peritalar subluxation, plantar flexion of the talus, and, often, degenerative changes in the subtalar and transverse tarsal joints.




    • Lateral impingement may cause a fibular stress fracture.




  • MR is not needed to assess the tibial tendon but may give information about the degree of degeneration of the hindfoot joints.



  • CT may also be helpful in assessing degeneration of the midfoot and hindfoot joints.




    • Weight-bearing CT, if available, can give more information about the 3D deformity.




Stage 4





  • Stage 4 includes all findings in stage 3 along with valgus angulation of the talus at the tibiotalar joint secondary to deltoid failure and lateral ankle erosion.



  • Radiographs will demonstrate a plantarflexed valgus talus as well as tibiotalar degenerative arthritis.



Other Etiologies of Adult Acquired Flatfoot Deformity





  • Rheumatoid or other inflammatory arthropathies can cause PTT dysfunction.




    • Arthrosis can occur at any of the hindfoot or midfoot joints primarily.




      • Subluxation of these arthritic joints will lead to a flatfoot, independent of PTT function.




    • Inflammatory arthritides can also affect tendons with all the symptoms of PTT dysfunction.




  • Posttraumatic deformity




    • Soft tissue trauma as an etiology of flatfoot is often a subtle diagnosis, as the end-stage deformity, forefoot abduction, and hindfoot valgus are the same.



    • Malunion from navicular, Lisfranc, 1st metatarsal, and calcaneus fracture can cause settling of the medial longitudinal arch, creating a flatfoot deformity.



    • Flatfoot secondary to midfoot (Lisfranc) malunion is secondary to loss of medial column stability, often at the TMT joint.




      • At the level of the midfoot, the longitudinal arch will break, and the forefoot will drift into abduction.



      • Hindfoot valgus is a secondary compensatory change.




    • A PTT laceration or traumatic rupture will also lead to arch collapse as dynamic support of the arch fails, causing muscle imbalance and eventual arthrosis.




  • Neuropathic deformity




    • The characteristic flatfoot deformity has been described in the diabetic neuropathic population, spinal cord patients, and those with Hansen disease and other neuropathic conditions.



    • Charcot neuroarthropathy in the midfoot causes collapse of the medial arch, often with marked deformity.




      • In these cases, it is not PTT dysfunction but rather a loss of the normal bony architecture.





Tarsal Coalition and Peroneal Spasm





  • Peroneal spasm can be a sign of disease in the peritalar region.



  • Protective contraction of any or all of the muscles bridging the peritalar joints may be induced in response to a peritalar insult.



  • Patients with a hindfoot coalition have been traditionally thought of as having spastic peroneal tendons.




    • However, the majority of these patients do not have spasm, and peroneal spasm has been identified in patients without tarsal coalitions.



    • These patients should be examined for other peritalar lesions.




  • A patient with a tarsal coalition classically will have a unilateral flatfoot, decreased motion, vague foot pain, and peroneal spasm.




    • However, the foot may be normally shaped with no peroneal spasm.



    • The typical patient presents only with hindfoot pain.




      • The astute clinician will detect a lack of hindfoot motion.





  • The coalition may be osseous, cartilaginous, or fibrous, and it may be complete or incomplete.



  • Plain x-rays may show dorsal talar beaking.



  • CT examination of the foot can diagnose a coalition.




    • Fibrous coalitions require a high index of suspicion when analyzing the CT.




  • The most common coalition is between the calcaneus and the navicular.



  • A middle facet subtalar coalition is the next most common tarsal coalition.



  • Once diagnosed, involved joints should be investigated for arthritic changes.



  • Coalition resection is appropriate treatment in a nondegenerated calcaneal-navicular coalition.



  • Subtalar arthrodesis may be necessary for subtalar coalitions, as decreased motion, deformity, and peroneal spasm probably exist at the time of diagnosis.



Physical Examination of Flatfoot





  • The physical examination comprises inspection, palpation, range of motion examination, and dynamic strength testing.



  • Inspection




    • Arch height in comparison with the contralateral side should be noted.



    • The too many toes sign confirms forefoot abduction deformity.




      • When viewed from behind, the abducted forefoot will show more toes visible lateral to the leg than normal.




    • Heel rise testing




      • In the normal foot, elevation of foot to a tiptoe stance requires a functional PTT to invert the subtalar joint.




        • If normal, this will bring the heel into varus.




      • Comparison of the affected and unaffected foot can confirm if the PTT is insufficient by an asymmetric heel position on double heel rise testing.



      • An inability to rise up on the affected foot indicates PTT insufficiency or dysfunction.



      • It can also serve as a stress test if the patient is unable to perform more than 1 or 2 single heel rises.





  • Motion examination




    • The flatfoot is diagnosed as either flexible or rigid based on subtalar motion.




      • A rigid deformity implies muscle spasm, advanced arthritis, or a coalition.




    • To examine for an Achilles contracture, the subtalar joint must 1st be reduced to a neutral starting position.




      • This also allows the examiner to appreciate the degree of forefoot varus and the rigidity of the deformity.





  • Palpation




    • Tenderness can occur over the course of the PTT, plantar fascia, or spring and deltoid ligaments.



    • Tenderness may also occur on the lateral hindfoot as a result of calcaneofibular or talocalcaneal impingement.



    • Peroneal or tibialis anterior spasm may coexist in patients with a tarsal coalition.




Imaging Studies





  • Weight-bearing anteroposterior and lateral views of the foot and an anteroposterior view of the ankle are essential aids in diagnosis.



  • Anteroposterior foot




    • The degree of abnormality in talar alignment can be assessed.




      • The talus becomes increasingly uncovered as the navicular subluxes laterally.




    • The TN coverage angle can determine the degree of uncovering that has occurred.




  • Lateral foot




    • It confirms the loss of alignment between the 1st metatarsal and talus.



    • Subluxation or sagging is identified at the TN and the NC joints.



    • The talus assumes a plantar flexed configuration, and the calcaneal pitch decreases as the deformity progresses.




  • Anteroposterior ankle




    • Talar tilt is determined in this view.



    • Stage 4 disease is characterized by tibiotalar subluxation secondary to deltoid insufficiency.



    • Degeneration at the midfoot and hindfoot joints can be determined by observing subluxation and loss of joint space, osteophyte formation, and sclerosis.



    • Dorsal talar beaking or bossing, if observed, may be suggestive of a coexisting tarsal coalition.




  • MR is a sensitive and specific test in the determination of PTT pathology.




    • It provides insight into the morphology and internal structure of the tendon.



    • Another use of MR is to evaluate the mid- and hindfoot for underlying disease when determining surgical treatment.



    • Its expense must be considered, as most tendinosis can be determined by history and physical examination.




  • Ultrasound is a noninvasive, less expensive modality by which the PTT can be examined.




    • Ultrasound can diagnose increased tendon diameter and increased peritendinous space and compare it with the contralateral side.



    • Ultrasound diagnosis of stage 1 PTT dysfunction correlates with surgical findings.




  • Simulated weight-bearing CT may be useful to better understand the 3D deformity but hard to obtain in many medical centers.



  • Weight-bearing CT may be most helpful when assessing deformity of the stage 2 flatfoot.




    • Although there are no strict criteria, weight-bearing CT may aid in surgical planning, especially for medial column fusions and calcaneal osteotomies.




  • Non-weight-bearing CT will more accurately show the presence of radiographic arthritis than plain films.


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Oct 29, 2019 | Posted by in ORTHOPEDIC | Comments Off on Flatfoot
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