Acquired Flat Foot Deformity: Postoperative Imaging - Thieme Connect

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James M. Linklater, F.R.A.N.Z.C.R.2. 1Department of Radiology, Royal North Shore Hospital, Sydney,. Australia. 2Castlereagh Sports Imaging, St. Leonards, ...
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Acquired Flat Foot Deformity: Postoperative Imaging Simon Dimmick, F.R.A.N.Z.C.R. 1 Avneesh Chhabra, M.D., D.N.B. 3 James M. Linklater, F.R.A.N.Z.C.R. 2

Australia 2 Castlereagh Sports Imaging, St. Leonards, Sydney, Australia 3 Russell H. Morgan Department of Radiology and Radiological Sciences, Johns Hopkins University Hospital, Baltimore, Maryland 4 Orthopædic & Arthritis Specialist Centre, Chatswood, Sydney, Australia

Address for correspondence and reprint requests Simon Dimmick, F.R.A.N.Z.C.R., Department of Radiology, Royal North Shore Hospital, Pacific Highway, St. Leonards, NSW 2065, Australia (e-mail: [email protected]).

Semin Musculoskelet Radiol 2012;16:217–232.

Abstract Keywords

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acquired flat foot pes planus staging imaging surgery

Flat foot (pes planus) is a progressive and disabling pathology that is treated initially with conservative measures and often followed by a variety of surgeries. This article briefly reviews the pathology in acquired flat foot deformity, the classification of posterior tibial tendon dysfunction, discusses surgical techniques for the management of adult flat foot deformity, and reviews potential complications and their relevant imaging appearances.

Pathology of Acquired Adult Flat Foot Deformity Acquired adult flat foot is a progressive abnormality characterized by collapse of the medial longitudinal arch and development of hindfoot valgus. It is caused by mechanical uncoupling of the bones of the tarsus due to failure/ elongation of the tendo-osseo-ligamentous complex that maintains the medial longitudinal arch of the foot. This complex consists of both static and dynamic stabilizers. The key dynamic stabilizer is the posterior tibial tendon (PTT), whose primary function is to adduct the transverse tarsal joint and, secondarily invert the subtalar joint, with resultant elevation of the medial longitudinal arch. The static stabilizers include deltoid ligament, spring ligament, plantar fascia, plantar and talocalcaneal interosseous ligaments, as well as the capsules of the talonavicular and naviculocuneiform joints.1 The most common cause of acquired flatfoot deformity (AFFD) in adults is posterior tibial tendon dysfunction (PTTD). If PTTD is left untreated, there is progressive failure of the static stabilizers of the medial longitudinal arch.1 Most cases of PTTD relate to a degenerative tendinopathy that is attri-

Issue Theme Imaging of the Postoperative Ankle and Foot; Guest Editor, James M. Linklater, F.R.A.N.Z.C.R.

tional, often occurring in middle-age women with a high body mass index. The tendinopathy typically develops at the submalleolar level, where there is a watershed zone in tendon vascularity.2 Less commonly, a chronic tenosynovitis associated with an inflammatory arthropathy may be the cause of dysfunction. Rarely, acute trauma may result in a rupture of the posterior tibial tendon. Posttraumatic posteriorly directed bony spurs arising from the retromalleolar sulcus for the posterior tibial tendon and medial malleolar screws penetrating the posterior cortex may also cause attritional tears of the posterior tibial tendon (►Fig. 1). Insertional posterior tibial tendinopathy is less common than noninsertional tendinopathy. When present, it may be associated with a type 2 accessory navicular that has become partially destabilized, usually occurring in middle age. Isolated acute traumatic tears of the static stabilizers of the medial plantar arch can occasionally occur in the setting of a normal posterior tibial tendon, resulting in plano-valgus deformity, most commonly involving the deltoid and/or spring ligaments.3 ►Table 1 presents a comprehensive list of the causes of AFFD.

Copyright © 2012 by Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York, NY 10001, USA. Tel: +1(212) 584-4662.

DOI http://dx.doi.org/ 10.1055/s-0032-1320122. ISSN 1089-7860.

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1 Department of Radiology, Royal North Shore Hospital, Sydney,

Leslie Grujic, F.R.A.C.S. 4

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Figure 1 A 64-year-old female patient presented with painful flat foot following prior open reduction and internal fixation of a bimalleolar fracture. (A) Lateral ankle X-ray demonstrates a medial malleolar screw that penetrates the posterior cortex. (B) Axial proton-density-weighted MR image demonstrating the screw traverses the retromalleolar sulcus for the posterior tibial tendon. (C) Axial proton-density-weighted MR image inferior to the medial malleolus demonstrates deficiency of the posterior tibial tendon.

Staging of Posterior Tibial Tendon Dysfunction The staging of PTTD is based on the condition and function of the tendon, alignment of the hindfoot, and the suppleness of the deformity.4,5 Stage 1 PTTD is characterized by a posterior tibial tenosynovitis, with or without low-grade tendinopathy, the tendon remaining of normal length. Clinical features consist of painful swelling at the medial aspect of the foot, with no deformity in alignment on weightbearing.6 The patient is able to perform a single-limb and double-limb heel rise.2 X-rays are normal. An MRI or ultrasound may confirm tenosynovitis and low-grade tendinosis and help rule out tendon tear.5 Stage 2 PTTD is characterized by elongation, degeneration, and dysfunction of the posterior tibial tendon,5 presenting clinically with a painful, flexible pes planovalgus deformity. The patient may be unable to perform a single-limb heel rise or may demonstrate fatigue with repetition. Heel inversion is typically demonstrated on double-limb heel rise, indicating a Seminars in Musculoskeletal Radiology

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supple deformity that is passively correctable. Stage 2 PTTD has been subclassified according to the extent of lateral peritalar subluxation/abduction of the foot on weightbearing plain radiographs.7–9 Stage 2a is characterized by minimal forefoot abduction and 50 percent uncovering of the talar head and implies significant forefoot abduction. Stage 2c includes the presence of forefoot varus with concomitant stage 2a or 2b deformity. Stage 3 PTTD is characterized by complete nonfunction of the posterior tibial tendon that may be completely ruptured with resultant fixed plano-valgus deformity. The patient is unable to perform a single-limb or double-limb heel rise. There is often lateral pain due to the talocalcaneal or subfibular impingement. Degenerative arthrosis is often present in the hindfoot or midfoot.5 Stage 4 PTTD is characterized by stage 3 findings plus valgus at the talocrural (ankle) joint due to deltoid ligament attrition and tear, which with chronicity leads to osteoarthritis of the talocrural (ankle) joint.5,6,9

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Acquired Flat Foot Deformity: Postoperative Imaging Table 1 Causes of Acquired Flat Foot Deformity • Posterior tibial tendon dysfunction

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The following section briefly reviews various commonly performed surgical procedures and the imaging of complications related to these procedures.

Degeneration Tears • Ligamentous injury Deltoid ligament Spring ligament Lisfranc ligament • Plantar fascia rupture • Arthritis in hindfoot/midfoot Degenerative Inflammatory Neuropathic arthropathy • Malunited fracture Calcaneal fracture Fibular fracture with shortening and syndesmotic injury • Hypermobility leading to plastic deformation/elongation of medial tendon, ligament, and capsular supports • Tight triceps surae or isolated gastrocnemius tightness • Spastic flatfoot • Neuromuscular imbalance Polio Cerebral palsy Closed head injury Stroke • Iatrogenic Overcorrected clubfoot

Surgical Principles in the Management of Acquired Flat Foot Deformity Conservative treatment is recommended for stage 1 PTTD that may involve immobilization, bracing, a walking boot, and nonsteroidal anti-inflammatory drugs. When conservative measures fail in the treatment of late stage 1 and stage 2 PTTD, surgical intervention is considered. In general, a combination of soft tissue procedures designed to address posterior tibial tendon pathology and augment posterior tibial tendon function are combined with osseous procedures that address the malalignment and alter the mechanical axis of the hindfoot.10–12 In stage 3 PTTD, arthrodesis involving the posterior subtalar joint and sometimes the transverse tarsal joint may be required to maintain correction of the deformity. In stage 4 PTTD, triple or pantalar arthrodesis may be performed, depending on whether the patient experiences pain in the ankle and/or tarsal joints.13

Flexor Digitorum Longus Tendon Transfer Tendon transfers for PTTD are intended to augment the reduced adduction across the transverse tarsal joint and hindfoot inversion strength. The flexor digitorum longus (FDL) is the most commonly transferred tendon. Options for fixation are partly determined by the status of the posterior tibial tendon. If the tendon demonstrates reasonable excursion when proximal traction is applied, the FDL may be interwoven into the posterior tibial tendon.14 If the posterior tibial tendon demonstrates no excursion with proximal traction, osseous fixation is required, generally into the medial process of the navicular. Fixation options include use of a biotenodesis (interference) screw, passage through a drill hole, and suturing the tendon on itself proximal to the drill hole or suture anchor fixation. The distal aspect of the posterior tibial tendon may be resected in this setting.

Complications of FDL Transfer Creation of a bony tunnel for the FDL transfer may be complicated by violation of either the talonavicular or the naviculo-cuneiform joints and complicating arthrosis.15 Intraoperative fracture of the medial wall of the drill hole may require conversion to medial cuneiform fixation of the FDL. Loss of fixation in the postoperative setting results in loss of function of the tendon transfer. This may relate to migration of the interference screw that may be demonstrated on ultrasound or MRI. There may be an associated recurrent static planovalgus deformity that may be evident on weightbearing x-rays and may be appreciable on nonweightbearing MRI. Persistent pain and swelling may occur in the postoperative setting due to tendinitis of the transposed FDL or the residual posterior tibial tendon if it has not been resected, or of the FDL-PTT tenodesis tendon construct if there has been a side-to-side tenodesis (►Figs. 2 and 3). These latter scenarios are more common if there was significant preexisting tendinosis in the PTT.16 Tendinitis in the transposed FDL may reflect a reaction to the suture material or the interference screw. Both ultrasound and MRI can demonstrate a postsurgical tendinitis. There may be tendon thickening, signal hyperintensity on fluid-sensitive MR sequences with corresponding hypoechoic echo-textural change on ultrasound, and thickening of the peritenon space. There is often overlap between the appearance of normal postsurgical change and symptomatic postsurgical tendinitis. Ultrasound examination can be helpful in confirming the site of tenderness and in allowing demonstration of hyperemia that is often present in symptomatic postoperative tendinitis. Ultrasound is also often superior to MRI in differentiating the posterior tibial and FDL tendons as separate structures within the interweave tendon construct and in demonstrating suture material within the tendon construct (►Fig. 4). Seminars in Musculoskeletal Radiology

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Tenosynovitis

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Figure 2 A 46-year-old man presented with persistent medial ankle pain following prior debridement of the posterior tibial tendon and Pulvertaft flexor digitorum longus (FDL) tendon interweave. (A) Axial T2-weighted MR image demonstrates an intact posterior tibial-FDL tendon interweave. (B) Axial fat-suppressed T2-weighted image above the level of the interweave demonstrates posterior tibial tendinosis and an incomplete longitudinal split tear that was believed to account for the patient’s symptoms.

In general, there are interconnections between the FDL and FHL tendons at the midfoot (Henry’s knot) level that allow ongoing flexion of the lesser toes after FDL transfer.17 If there is no interconnection, there may be loss of lesser toe flexion. Tenodesis of the distal FDL stump to the FHL may address this issue, but it may also be complicated by hammer toe deformity.15 Inadequate distal tenodesis may also be complicated by first ray instability.18 When performed in isolation, FDL tendon transfer does not achieve adequate correction of the planovalgus deformity.15 Some patients may develop progressive planovalgus

deformity despite initially successful FDL transfer15 (►Fig. 5). Progressive deformity is readily demonstrated on weightbearing x-rays. Comparison with x-rays of the contralateral foot and with previous x-rays can be helpful. The most common cause of failure of FDL tendon transfer relates to the operation being inappropriate for the stage of the PTTD, with common scenarios being the preoperative presence of fixed forefoot varus >15 degrees, lack of adequate subtalar joint inversion, or lack of transverse tarsal joint adduction16 (►Fig. 6). Equinus contracture (tightness of the

Figure 3 A 43-year-old woman presented with persistent medial pain following isolated flexor digitorum longus (FDL) tendon transfer utilizing Pulvertaft tendon interweave. (A) Axial and (B) sagittal fat-suppressed proton-density-weighted MR images demonstrate signal hyperintensity within the posterior tibial-FDL tendon interweave, consistent with a postoperative tendinitis. Seminars in Musculoskeletal Radiology

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Figure 4 A 48-year-old man who had undergone isolated flexor digitorum longus (FDL) transfer for traumatic insertional rupture of the posterior tibial tendon and presented 16 years later with progressive painful flat foot deformity. (A) Weightbearing anteroposterior x-ray of the foot demonstrating mild lateral peritalar subluxation of the navicular. (B) Longitudinal ultrasound image of the distal aspect of the FDL tendon transfer demonstrating peritendon thickening and hyperemia consistent with a peritendinitis. Note the normal fibrillar echotexture of the FDL tendon. (C) Sagittal and (D) axial proton-density MR images demonstrating the limited ability of MRI to differentiate the FDL tendon transfer from the adjacent posterior tibial tendon and postsurgical scar.

gastrocnemius soleus complex) may contribute to failure of an FDL tendon transfer and is diagnosed clinically.19

Posterior Tibial Tendon Advancement (Kidner Procedure) The Kidner procedure was developed to treat a painful type 2 accessory navicular, typically occurring in an adolescent. In

this context the procedure is generally performed in isolation because there is usually no posterior tibial tendinopathy but rather painful inhibition of posterior tibial tendon function. In the adult, there is frequently concomitant posterior tibial tendinopathy, which may be an indication for additional procedures. Numerous other surgical procedures have been devised to treat the symptomatic accessory navicular. The modified Seminars in Musculoskeletal Radiology

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Figure 5 Flexor digitorum longus (FDL) transfer failure. A 61-year-old woman underwent calcaneal osteotomy and FDL transfer for painful type II accessory navicular. The patient presented with persistent pain and pes planus. (A) Axial proton-density-weighted MR image demonstrates amorphous intermediate signal intensity tissue at the site of prior FDL tendon transfer, with no discernible discrete tendon tissue (white arrows). Note the magnetic susceptibility artifact related to the screw fixation of the calcaneal osteotomy. (B) Coronal proton-density-weighted MR image of the ankle shows susceptibility artifact from screw fixation of the calcaneal osteotomy site (arrow) as well as hindfoot valgus with abnormal tibiocalcaneal angle.

Kidner procedure involves the resection of an accessory navicular and/or a prominent navicular tuberosity with advancement of the PTT insertion using suture anchors, biotenodesis screws, or bone tunnels to reattach the posterior tibial tendon.20–23 Simple excision of the accessory navicular has also been described.24–26 Arthrodesis of an accessory navicular to the main body of the navicular has also been described in larger ossicles using one or two cannulated screws.27–29

Complications of the Modified Kidner Procedure and Arthrodesis of the Type 2 Navicular The modified Kidner procedure is considered to have minimal complications. There are conflicting reports of progression of loss of the medial arch after the procedure, however.25,28 Giorgini and colleagues retrospectively reviewed a series of 50 feet in 39 patients who underwent a modified KidnerCobb procedure for the treatment of stage 2 PTTD.23 Complications included two feet with wound dehiscence and one

Figure 6 Progressive hindfoot valgus and talocalcaneal impingement in a 47-year-old man who had undergone medial displacement calcaneal osteotomy, flexor digitorum longus tendon transfer, and insertion of an arthroereisis screw for late stage 2 posterior tibial tendon dysfunction. (A) Sagittal short tau inversion recovery MR image demonstrating features of talocalcaneal impingement due to hindfoot valgus, with bone marrow edema at the margins of an accessory articulation between the lateral process talus and base anterior process calcaneus, with associated posterior subtalar joint synovitis. (B) Coronal proton-density MR image demonstrates narrowing of the sinus tarsi and infiltration of the sinus tarsi and subfibular fat plane. Seminars in Musculoskeletal Radiology

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Spring Ligament Repair Attritional tear of the superomedial fibers of the spring ligament and plastic deformation of the tibio-spring and tibionavicular components of the superficial deltoid ligament are common in the setting of chronic advanced stage 2 and stage 3 PTTD. Several surgeons advocate concomitant repair of a torn superomedial spring ligament when performing an FDL tendon transfer.30 It has been claimed that limited tissue quality due to the attritional nature of the pathology, limited vascularity, and limited repair potential of the partially fibrocartilaginous superomedial spring ligament renders repair in this setting of limited clinical usefulness. Isolated tears of the spring ligament and the deltoid ligament complex are an uncommon cause of planovagus hindfoot deformity that was described by Hintermann as medial ankle instability.3 Untreated medial ankle instability may result in overload of the posterior tibial tendon, tendon degeneration, and elongation.3 Early surgical correction may prevent this progression.3 In acute traumatic tears of the deltoid ligament or spring ligament, isolated primary repair

Figure 7 A 15-year-old girl who presented with ongoing pain and swelling 8 months postexcision of a type 2 accessory navicular due to postsurgical tendinitis and peritendinitis. (A) Axial proton-density-weighted MR image demonstrates intermediate signal intensity along the line of the distal posterior tibial tendon and marked thickening of the peritendon space. (B) After intravenous contrast, axial fat-suppressed T1-weighted MR image demonstrates moderate corresponding contrast enhancement. (C) Long axis grayscale image more clearly differentiates the distal posterior tibial tendon from the thickened peritendon space. (D) Color Doppler image demonstrates hyperemia within the tendon and the thickened peritendon space. Seminars in Musculoskeletal Radiology

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foot with fractured hardware. Kopp and Marcus undertook a modified Kidner procedure on 11 feet. There were no complications and no change in the medial arch at follow-up (average: 104 months).25 Scott et al undertook a modified Kidner in 10 patients. Although there were no immediate postoperative complications, 3 of 10 patients (30%) had persistent midfoot pain and radiographic evidence of progressive loss of the longitudinal arch.28 In the authors’ experience, symptomatic postsurgical posterior tibial tendinopathy and peritendinitis is a relatively common cause of persistent pain after the modified Kidner procedure and can be demonstrated on ultrasound or MRI (►Figs. 7 and 8). Several studies have assessed arthrodesis of a type 2 accessory navicular to the medial process of the navicular.27–29 The most common significant complication is nonunion/loosening of screws, requiring further surgery to excise the ossicle.28,29 Chung et al reported that 6 of 22 feet had loosening of the screw(s). This is best demonstrated on computed tomography (CT). Three patients (four feet) also complained of residual enlargement of the navicular tuberosity.29

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Figure 8 A 40-year-old woman who had undergone prior Kidner procedure and presented years later with posterior tibial tendon dysfunction. (A) Sagittal fat-suppressed proton-density and (B) after intravenous contrast fat-suppressed T1-weighted MR images demonstrate distal posterior tibial tendinosis and peritendinitis. (C) Axial proton-density, (D) fat-suppressed T2, and (E) after intravenous contrast fat-suppressed T1-weighted MR images demonstrate a small superimposed longitudinal split tear.

of the ligament usually fails. Imaging evaluation of spring ligament repair should begin with weightbearing x-rays to assess for maintained correction of deformity. MRI can provide assessment of continuity of the repair but does not assess for plastic deformation of the repair construct (►Fig. 9). Current approaches to the management of medial instability include combining primary repair with medial displacement calcaneal osteotomy (MDCO) and insertion of an arthroereisis screw. FDL tendon transfer is reserved for those patients in whom PTTD has developed. Others advocate reconstruction of the deltoid or spring ligament complex using tendon grafts.31 There are limited case series in the literature of spring ligament repair/reconstruction. Gazdag and Cracchiolo performed three different techniques on 11 patients using the peroneus longus, tibialis anterior, or Achilles tendons.30 Choi and colleagues conducted a biomechanical study comparing three different spring ligament reconstruction techniques in 10 feet using a peroneus longus tendon transfer. The technique that reconstructed both the superomedial and inferomedial bands of the spring ligament was the most successful Seminars in Musculoskeletal Radiology

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in restoring talonavicular joint abduction and subtalar inversion.32 Ellis and colleagues described an Achilles tendon allograft to reconstruct the spring ligament.31 The study by Gazdag and Cracchiolo reported three complications in their 11 patients. These included a postoperative wound infection, numbness of the skin over the medial and plantar surfaces of the great toe, and one case of reflex sympathetic dystrophy.30

Subtalar Arthroereisis Subtalar arthroereisis means ’’jacking up’’ of the subtalar joint and involves the elevation of the subtalar joint and correction of hindfoot valgus through insertion of a prosthetic cylinder screw into the sinus tarsi33,34 (►Fig. 10). Both metallic and bioresorbable sinus tarsi implants have been used. It is speculated that the primary role of the implant is to block nonphysiological eversion (hyperpronation).35 A biomechanical study by Arangio et al demonstrated that the medial two metatarsals support 15% of the total load in the normal foot and 31% in AFFD. Arthroereisis decreases the load on the

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Figure 9 Before and after spring ligament repair. (A) Coronal proton-density-weighted MR image shows marked attenuation and a tear of the superomedial fibers of the spring ligament. (B) Coronal proton-density-weighted MR image demonstrates the normal postoperative appearance of an intact spring ligament repair. Note also the susceptibility artifact from a sinus tarsi implant.

medial two metatarsals to 13% and increases the load on the fifth metatarsal to greater than normal levels.33 Intraoperatively, trial spacers are used until the appropriate size is identified. An appropriate spacer limits pathological eversion without causing hindfoot varus. If the spacer is too small, there will be residual excessive pronation. If the spacer is too big, there will be overcorrection into hindfoot and forefoot varus.36 Most adult implants are between 8 and 12 mm in diameter. The procedure is minimally invasive and may be used as an adjunct procedure with medial column osteotomy and FDL transfer or a modified Kidner proce-

dure.34,36 When used in isolation, an arthroereisis screw may provide inadequate correction.

Complications of Subtalar Arthroereisis Sinus tarsi (lateral hindfoot) pain is a common complication, occurring in 10 to 46% of patients.37–40 It has been speculated that the pain relates to an oversized implant causing overcorrection, locking the subtalar joint and limiting subtalar motion (Needleman). The pain is relieved in most cases after removal of the implant (►Fig. 11). Removal of the implant is required in 15 to 50% of patients.41

Figure 10 Normal appearance of subtalar arthroereisis. (A) Lateral and (B) oblique radiographs demonstrating the normal position of an arthroereisis screw toward the apex of the sinus tarsi. Note also the calcaneal osteotomy and metallic suture anchor in the navicular for fixation of an flexor digitorum longus tendon transfer. (C) Coronal proton-density MR image demonstrates the normal position of the arthroereisis screw at the sinus tarsi apex. Seminars in Musculoskeletal Radiology

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Figure 11 Persistent pain after screw removal. Axial proton-density-weighted MR images at the level of the sinus tarsi (A) without fat saturation and (B) with fat saturation demonstrate mild scar and edema within the sinus tarsi.

Undercorrection and overcorrection may be secondary to insertion of an inappropriate size implant or suboptimal implant placement. Undercorrection and implant migration is associated with implants that are too small42 (►Fig. 12). Improper placement of the implant may lead to arthritis of the subtalar joint.43,44 An implant placed too dorsally may also cause impingement of the implant against the lateral process of the talus.43 Overcorrection may induce hindfoot varus or forefoot supination about the midtarsal joint, causing sinus tarsi pain or pain in the lateral column. This occurs in 5% of cases.41 Schon has also described plug extrusion (2% of cases), transient forefoot varus, swelling from local irritation (5%), and lucency around the implant on x-ray (20%) after subtalar arthroereisis.41 Implant-specific complications have also been reported in several clinical series and case reports with the use of cone-

shaped silastic, cone-shaped implants and fixating screws, and ultrahigh molecular weight polyethylene implants.39,45 The increased use of metallic arthroereisis implants has decreased the incidence of implant-specific complications.43

Medial Displacement Calcaneal Osteotomy MDCO is the most common approach to correcting the bony deformity associated with AFFD.6 The posterior calcaneus is usually shifted medially 1 cm and fixed with a single screw10 (►Fig. 13). This procedure aims to correct hindfoot valgus and alleviate some of the valgus deforming force of the Achilles tendon due to its insertion being lateral to the subtalar axis in the valgus hindfoot (Hill). After MDCO, the Achilles tendon is medial to the axis of the ankle joint. This restores the function of the Achilles as an inverter of the heel and a stabilizer of the midfoot.6,46 With improvement in the alignment of the

Figure 12 Displaced arthroereisis screw. (A) Lateral and (B) anteroposterior x-ray images demonstrate lateral displacement of an arthroereisis plug that was probably “undersized.” Seminars in Musculoskeletal Radiology

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Figure 13 Normal appearance of medial displacement calcaneal osteotomy. (A) Lateral x-ray demonstrates bony union of a calcaneal osteotomy. (B) Axial x-ray demonstrates step-off deformity of the lateral cortex indicating the degree of medial displacement of the calcaneal osteotomy. (C) Oblique axial proton-density MR image in another patient demonstrates medial displacement of the posterior tubercle.

medial longitudinal arch, MDCO also enhances the mechanics of the PTTD and relieves strain on the medial ligamentous structures, particularly the spring ligament complex.34 MDCO is often combined with FDL tendon transfer in stage 2a PTTD. In stage 2b deformity, some surgeons also undertake arthroereisis screw insertion and spring ligament repair; others perform a lateral column lengthening procedure. This procedure does not address lateral peritalar subluxation of the navicular. Marked hindfoot valgus is often not corrected by MDCO.47

Complications of Medial Displacement Calcaneal Osteotomy Malunion and nonunion of the osteotomy may occur after MDCO [18]. An osteotomy that is vertically orientated, rather than the recommended 45-degree angle to the weightbearing surface of the foot, is more prone to malunion and nonunion due to reduced bony contact for bone healing and increased instability at the osteotomy site.15 Plain x-rays usually provide adequate postoperative assessment of MDCO, with the lateral view providing assessment of bony union and an axial view of the heel providing assessment of the extent of correction. Proximal migration of the posterior fragment is a complication associated with Achilles tendon tightness.15 This may reduce tension on the Achilles tendon and decrease plantar flexion power. There is a theoretical risk of penetration of cortical bone through cancellous bone at the site of the osteotomy. This may lead to collapse of the osteotomy. There are no reported cases of this complication after MDCO, however.15 MDCO may inadvertently increase pressure over the lateral forefoot and heel, which results in lateral foot pain.10

Lateral Column Lengthening Lateral column lengthening (LCL) is a variably performed procedure in patients with grade 2b PTTD with >50% lateral

peritalar subluxation of the navicular on weightbearing anteroposterior radiographs. In many cases, LCL is usually undertaken in combination with MDCO and FDL tendon transfer. The aim of LCL is to transfer the load during weightbearing toward the lateral column, thereby decreasing load on the first metatarsal and the moment about the talonavicular joint.48 The classic Evans procedure involves an osteotomy in the calcaneal neck region, distal to the interosseous talocalcaneal ligament without involvement of the calcaneocuboid joint or the subtalar joint.49–51 A tricortical bone graft or metallic wedge is then inserted into the osteotomy to achieve lengthening. An alternative technique involves a calcaneocuboid distraction arthrodesis. This involves removing the articular surface of the calcaneocuboid joint, inserting a bone graft, and arthrodesing the joint.

Complications of Lateral Column Lengthening Procedure There is a high reported complication rate after LCL procedures.10 These include gait abnormalities, lateral overload, graft failure and collapse, nonunion, and painful hardware10 (►Fig. 14). The LCL procedure also endangers the sural nerve, peroneal tendons, and medial soft tissue structures intraoperatively.52 Nonunion after calcaneocuboid distraction arthrodesis is a common complication.53–56 The Evans calcaneal osteotomy has a much lower reported occurrence of nonunion.13,49 Nonunion of the graft may result in loss of correction, chronic lateral column pain, and hardware failure.18,57 Nonunion is often caused by failure of the fixation. Use of a cervical H-plate has a much lower reported incidence of nonunion in comparison with crossed screws for graft fixation.58 Nonunion may be demonstrated on x-ray. CT provides a more accurate assessment for nonunion or hardware loosening. Acquiring image data with sub 1-mm collimation and reconstructing relatively thick (3 to 5 mm) mitigates most of Seminars in Musculoskeletal Radiology

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Figure 14 A 13-year-old boy who had undergone bilateral lateral column lengthening for flexible flat foot deformity 8 months prior presented with lateral foot pain. (A) Sagittal fat-suppressed proton-density MR image of the right hindfoot demonstrates incomplete union of the lateral column lengthening calcaneal osteotomy. Note the mild malalignment of the calcaneocuboid joint and associated joint effusion and subchondral bone marrow edema. (B) Axial proton-density with fat saturation images demonstrate marked bone edema/stress involving the talus, calcaneus, cuboid, and navicular. Mild edema is also noted within the medial cuneiform. Sagittal fat-suppressed proton-density MR image of the left hindfoot demonstrates union of the lateral column lengthening calcaneal osteotomy and no abnormality at the calcaneocuboid joint.

the beam hardening artifact due to metal hardware. Dualenergy CT may offer further reduction in metal artifact. Loss of correction has been reported with both LCL techniques, often more severe with calcaneal osteotomy,15 and is best assessed with weightbearing x-rays. Excessive and fixed forefoot varus and supination may cause the patient to walk on the lateral border of the foot and be complicated by stress fracture of the fifth metatarsal.15 Overlengthening of the lateral column may cause stress overload across the fifth tarsometatarsal joint leading to pain and arthrosis.52 Increased pressure in the calcaneocuboid joint and subtalar joint may also be a cause of pain and accelerated arthrosis.49,59 Violation of the anterior or middle calcaneal facets of the subtalar joint may be complicated by degenerative arthrosis.15

Cotton Osteotomy The Cotton osteotomy is an opening wedge medial cuneiform osteotomy that was first described in 1935 to correct a depressed medial arch in pes planus.2 Today, this procedure is considered an excellent adjunct to a comprehensive flatfoot correction for the treatment of stage 2c deformity, particularly in patients who have residual fixed forefoot varus or supination.2,60 The procedure is designed to plantarflex the first ray, stabilize the medial column, and correct forefoot varus.10 A tricortical graft is usually used, with fixation using a single screw, compression staple, plate, or K-wires.2,60

Complications of the Cotton Osteotomy One clinical study evaluating the medial cuneiform osteotomy is described in the literature. Hirose and Johnson included a total of 16 feet. There were no reported major complications, including nonunion or malunion. All patients at follow-up described mild to no pain with ambulation. Screw removal was required in one patient due to pain.61 Seminars in Musculoskeletal Radiology

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Subtalar Arthrodesis Isolated subtalar fusion has been advocated for stage 3 AFFD and in stage 2 in patients with no fixed forefoot varus, no talonavicular or calcaneocuboid joint arthrosis, and no hypermobility of the transverse tarsal joint.5 This procedure is increasingly being performed in preference to a triple arthrodesis. The ideal position for a subtalar arthrodesis is 5 degrees of valgus to permit mobility of the transverse tarsal joint (Di Paola). Subtalar arthrodesis alone may correct hindfoot as well as midfoot deformities.62 The procedure may also be performed in combination with medial procedures where a LCL is contraindicated or not preferred (obesity, inability to be nonweightbearing for an extended period of time, elderly patient, and/or underlying systemic disease, where either unreliable motor function or unstable ligament support is present).46

Complications of Subtalar Arthrodesis Subtalar arthrodesis may be suboptimal for stage 2 AFFD due to undercorrection of the deformity and intolerance of either varus or valgus malpositioning.52 Excessive varus deformity may lock the transverse tarsal joint, which forces the patient to walk on the lateral side of the foot.10 This may lead to overload of the lateral portion of the foot. Excessive valgus malalignment may cause calcaneofibular abutment and lateral foot pain.5 These findings may be demonstrable on MRI. Subtalar arthrodesis does not correct or address forefoot deformity. One of the most common causes of failure of this procedure is not recognizing residual forefoot varus (particularly if >12 degrees) after reduction of hindfoot valgus.46 Postoperatively, the patient may ambulate on the lateral aspect of the midfoot, with subsequent pain and callus formation over the base of the fifth metatarsal. Breakdown of the midfoot may also occur in patients with unrecognized hypermobility of the transverse tarsal joint.5

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Figure 15 A 64-year-old woman complained of anterior ankle pain after subtalar arthrodesis and subsequent arthrodesis screw removal. (A) Sagittal and (B) coronal proton-density-weighted MR images demonstrate focal chondral damage at the anterior aspect of the talar dome and adjacent tibial plafond along the line of prior drilling for the screw fixation of the arthrodesis. There was presumably violation of the talocrural joint during drilling of the track for the screw fixation.

Malunion or malposition of the arthrodesis may contribute to early arthrosis of the ankle and adjacent joints.46,63 (►Fig. 15). Nonunion, however, is an uncommon complication. It is readily demonstrated on CT as periarticular sclerosis and cystic change, with no osseous bridging. On MRI a fluid signal or fibrous cleft may be seen at the site of union.

Talonavicular Arthrodesis Although triple arthrodesis remains the gold standard procedure in the correction of a flatfoot, joint-sparing procedures such as talonavicular arthrodesis have increased in popularity. The ideal indication for an isolated talonavicular fusion remains controversial. Some authors believe this procedure is appropriate for younger patients who have supple deformities.64 Others consider patients with rigid or severe deformity or older patients to be the best candidates.2 Isolated talonavicular arthrodesis in an experimental setting was shown to be capable of correcting forefoot abduction, forefoot supination, and midfoot collapse in patients with AFFD to a similar degree as triple or double arthrodesis, whereas, isolated subtalar and calcaneocuboid fusions did not.65

Complications of Isolated Talonavicular Fusion Complications of isolated talonavicular fusions include lateral midfoot pain, malposition, nonunion, and adjacent joint arthrosis.2,64 There have been insufficient clinical studies to ascertain the incidence of these complications.2 Below and McCluskey reported 80% of their patients with isolated talonavicular fusion had subtalar joint pain and 60% had subtalar arthrosis.66 This same study reported a nonunion rate of 40%. Ankle and midfoot joint arthrosis, in addition to subtalar arthrosis, may also complicate isolated talonavicular fusion.67 There is a single case report that describes osteonecrosis of the talus after isolated talonavicular arthrodesis.68 Avascular necrosis is usually best demonstrated on MRI, as decreased marrow signal intensity on all sequences, bony collapse, and lack of perfusion on contrast imaging.

Triple Arthrodesis Triple arthrodesis involves fusion of the subtalar, talonavicular, and calcaneocuboid joints, converting the hindfoot into one osseous unit, which negates the need for medial and lateral extrinsic muscular stability at the ankle.69 Historically, triple arthrodesis was the primary procedure to correct a flat foot deformity. This procedure is commonly used in stage 3 disease. Today, the indications include severe rigid deformities, advanced multijoint degenerative change, and as a revision procedure for previously failed joint-sparing procedures.46 The goals of triple arthrodesis are to realign the hindfoot by correcting the subtalar joint, reduction of the dorsolateral peritalar subluxation, restoration of forefoot alignment, and improvement in ankle function. Subfibular impingement is relieved by realignment of the hindfoot.

Complications of Triple Arthrodesis Triple arthrodesis is a technically challenging procedure with numerous potential complications. 70–72 The most common causes of failure include persistent deformity, nonunion, malunion, and lateral ankle instability69,73 (►Fig. 16). Mäenpää and colleagues reported that 66% of failed triple arthrodesis were secondary to malunion or malposition. Between 3 degrees and 10 degrees of hindfoot valgus is the ideal position following triple arthrodesis.71,73 Varus malalignment may result in lateral column overload, metatarsal and supramalleolar pain and stress fractures.71,73 The incidence of pseudoarthrosis or nonunion ranges between 6% and 36%.69,72 The talonavicular joint has the highest rate of nonunion.70–72,74 Mäenpää and colleagues reported that 66% of failed triple arthrodeses were secondary to malunion or malposition.74 Slight rotation or adduction of the talonavicular joint may result in the development of hindfoot varus malunion, whereas undercorrection can result in a persistent valgus deformity.52 Seminars in Musculoskeletal Radiology

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Figure 16 A 63-year-old woman with lateral foot pain following triple arthrodesis for stage 3 posterior tibial tendon dysfunction. (A) Ray-sum image from a dual-energy computed tomography study demonstrating nonunion of the calcaneocuboid component of the triple arthrodesis. (B) Sagittal and (C) axial reconstructions demonstrating the calcaneocuboid joint nonunion. There was solid union of the posterior subtalar arthrodesis and of the mid to dorsal aspect of the talonavicular arthrodesis.

Development of arthrosis in the joints adjacent to a triple arthrodesis may occur due to the increased forces they experience following the triple arthrodesis71,72 (►Fig. 17). Osteonecrosis of the talus may be secondary to compromise of the deltoid or sinus tarsi branches at the time of surgery.15

General Risks of Surgical Intervention Neural Injury Incisional neuromas and neuropraxia of the sural nerve may complicate hindfoot realignment procedures. Symptomatic incisional sural neuromas may interfere with shoewear.19 Injury to the posterior tibial nerve or its branches in the foot may occur during calcaneal osteotomy or during FDL transfer procedures at the time of harvest. This may result in loss of plantar sensation.19 The imaging findings in posttraumatic neuroma are discussed in another article in this issue of Seminars. Postoperative reflex sympathetic dystrophy may cause pain, stiffness, and swelling that may impair and prolong postoperative recovery.19

Vascular Injury The posterior tibial artery and vein lie in close proximity to the PTT. These vessels may potentially be injured during surgery, particularly with retractors. 18 Development of an arteriovenous fistula and chronic edema and phlebitis are also reported complications of triple arthrodesis. 15

Infection The incidence of infection, both soft tissue and bony infection, following surgery for AFFD is similar in comparison with other procedures of the foot and ankle.18 The imaging findings in musculoskeletal infection are discussed in another article in this issue of Seminars.

Conclusion Figure 17 Adjacent joint osteoarthritis. (A) Magnified lateral and (B) oblique radiographs of the foot of a 60-year-old woman who had undergone triple arthrodesis 15 years ago and now presents with disabling ankle and foot pain. The radiographs demonstrate osteoarthritis of the naviculocuneiform and ankle joints. Note a sound triple arthrodesis with significant degenerative changes at the naviculocuneiform and the ankle joints. Seminars in Musculoskeletal Radiology

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The surgical management of acquired flat foot deformity in most circumstances requires a combination of soft tissue and bony corrective surgery. An understanding of these procedures and their potential complications is important in the imaging evaluation of the symptomatic postoperative patient.

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