Congenital and Acquired Flatfoot. Hereditary Joint Laxity.

Introduction

The flatfoot — pes planus — encompasses a heterogeneous group of foot morphologies in which the medial longitudinal arch is reduced or absent. The condition ranges from the physiological flexible flatfoot of childhood, requiring no treatment in the asymptomatic patient, through the rigid congenital flatfoot of the talocalcaneal coalition, through the symptomatic adult-acquired flatfoot of progressive posterior tibial tendon dysfunction, to the severely deformed flatfoot of neuromuscular disease. The clinical evaluation of the flat foot must distinguish flexible from rigid forms, identify any underlying neuromuscular condition or systemic joint hypermobility, and determine whether the deformity is producing symptoms or functional limitation. This chapter synthesizes content from Tachdjian’s Pediatric Orthopaedics, Apley & Solomon’s, Miller’s Review, and Netter’s Examination to cover the flexible (physiological) flatfoot of childhood, the rigid (pathological) flatfoot including congenital vertical talus and tarsal coalition, the adult- acquired flatfoot deformity due to posterior tibial tendon dysfunction, and the hereditary joint hypermobility syndromes including the Ehlers-Danlos syndromes.

Flexible Flatfoot of Childhood

Definition and Epidemiology The flexible flatfoot is the most common form of pes planus and is essentially a physiological variant of normal foot development. The young child (up to age 6-8 years) normally has an apparent flatfoot because of the abundant subcutaneous fat in the medial arch, the relative ligamentous laxity of childhood, and the not-yet-developed muscular control of the longitudinal arch; the medial arch develops gradually through childhood and approaches its adult morphology by approximately 8-12 years of age. The prevalence of flexible flatfoot in children below age 5 has been quoted as 25-50%, falling to 5-15% in older children, with the rate of resolution being highest in the youngest age groups. Clinical Features The cardinal feature is reduction or absence of the medial longitudinal arch on weight- bearing, with restoration of the arch on non-weight-bearing examination and on tip-toe testing — the so-called “flexibility test.” On tip-toe standing, the hindfoot rolls into varus and the medial arch re-forms in the flexible flatfoot, while in the rigid flatfoot the hindfoot remains in valgus and no arch develops. Hindfoot valgus and forefoot abduction relative to the midfoot are typical. The foot is supple, asymptomatic, and well-tolerant of ordinary activity in the great majority of children. Investigations The flexible flatfoot in the asymptomatic child requires no specific investigation. Weight- bearing radiographs (AP and lateral views of both feet) are obtained in symptomatic or

atypical cases and demonstrate increased talo-calcaneal angle, plantarflexion of the talus, calcaneal valgus, and forefoot abduction. The Meary angle (the angle between the long axis of the talus and the first metatarsal on the lateral view) is increased in flatfoot, normally being 0°. Treatment The asymptomatic flexible flatfoot of childhood requires no treatment. Reassurance of parents and continued observation is appropriate. The widespread practice of prescribing arch supports, special shoes, and orthotics for the asymptomatic flexible flatfoot has been challenged by long-term studies showing no benefit on foot morphology and no effect on later development. The symptomatic flexible flatfoot — typically with foot fatigue or pain after prolonged activity in the older child — may benefit from supportive orthotic insoles (a soft medial-arch support with hindfoot valgus correction), stretching of a tight Achilles tendon if present, and selective use of activity modification. Surgical management is rarely required in the flexible flatfoot of childhood. When symptoms persist into adolescence despite conservative measures, options include subtalar arthroereisis (an interference implant placed in the sinus tarsi to limit excessive subtalar pronation, with reasonable but not durable results), medial column procedures (medial cuneiform osteotomy with bone graft, Hoke arthrodesis), and Achilles tendon lengthening for the patient with a tight heel cord.

Rigid Flatfoot of Childhood — Specific Etiologies

A rigid flatfoot in childhood — that is, a flatfoot that does not correct on tip-toe testing and that lacks the supple character of the flexible flatfoot — is always pathological and requires investigation for an underlying cause. The principal etiologies are tarsal coalition, congenital vertical talus, and acquired conditions including post-traumatic deformity, neuromuscular disease, and inflammatory arthritis. Tarsal Coalition Tarsal coalition is a congenital fibrous, cartilaginous, or osseous union of two or more tarsal bones, producing a rigid hindfoot and the typical “peroneal spastic flatfoot.” The talocalcaneal coalition (most commonly involving the middle facet of the subtalar joint) and the calcaneonavicular coalition together account for the great majority of cases. The condition is autosomal dominant with variable penetrance. Presentation typically occurs in adolescence (age 10-15 years) as the previously cartilaginous coalition begins to ossify, producing progressive rigidity and pain; younger children with fibrous coalitions may be asymptomatic. Examination reveals a rigid flatfoot with absent restoration of the medial arch on tip-toe, restricted subtalar and midtarsal motion, peroneal spasm with attempted inversion (the “peroneal spastic flatfoot”), and tenderness over the affected coalition. Imaging is critical: plain radiographs may show the “C-sign” of talocalcaneal coalition (a continuous arc on the lateral view from the medial talar dome to the inferior surface of the sustentaculum tali, indicating obliteration of the subtalar joint by the coalition), the “anteater nose” sign of calcaneonavicular coalition (elongation of the anterior process of the calcaneus on the

lateral view), and the talar beak (a prominent dorsal talar prominence at the talonavicular joint). Oblique radiographs are most useful for calcaneonavicular coalition; CT is the gold standard for the talocalcaneal coalition and quantifies the extent of involvement. MRI demonstrates fibrous or cartilaginous coalitions that are not visible on plain radiographs. Treatment is initially conservative: cast immobilization (typically below-knee cast for 4-6 weeks), orthotics, and activity modification. Persistent symptoms despite conservative therapy are an indication for surgery. Surgical options are coalition resection with fat or muscle interposition (for younger patients with limited disease and preserved joint surfaces, with calcaneonavicular coalitions responding particularly well to resection with interposition of the extensor digitorum brevis muscle), or arthrodesis (subtalar fusion or triple arthrodesis, for more extensive disease or older patients with established arthritis). Congenital Vertical Talus (CVT) Congenital vertical talus is a rare but severe rigid flatfoot deformity in which the talus is fixed in a vertical position with dorsolateral dislocation of the navicular onto the talar neck, producing the characteristic “rocker-bottom” foot of the newborn. The condition is bilateral in approximately 50% of cases. Approximately half of cases are associated with neuromuscular conditions (myelomeningocele, arthrogryposis, chromosomal abnormalities, distal arthrogryposis); the other half are isolated. Presentation is at birth with the rocker-bottom foot, the dorsal skin of the foot creased and tight while the plantar surface protrudes convexly, the forefoot dorsiflexed and abducted, the hindfoot in equinus and valgus, and the foot rigid with severely restricted passive motion. The differential diagnosis is from the much more common “calcaneovalgus foot” (a positional deformity of the newborn that resolves with simple massage and stretching), oblique talus (a milder variant in which the navicular subluxates but reduces with plantarflexion), and the rocker-bottom foot of severe equinovarus correction. Radiographs in the neonate show the characteristic vertical position of the talus on the lateral view. Stress views — forced plantarflexion of the foot in the lateral projection — distinguish vertical talus from oblique talus: in CVT, the navicular remains dislocated from the talus even with maximal plantarflexion, while in oblique talus the navicular reduces. Treatment has been transformed in recent decades by the Dobbs reverse Ponseti technique, modeled on the Ponseti method for clubfoot but in reverse: serial casts in plantarflexion and inversion gradually correct the dorsolateral dislocation of the navicular, followed by percutaneous reduction of the talonavicular joint and percutaneous Achilles tenotomy. The success rate with the Dobbs technique is high in idiopathic cases, with reduced need for the more extensive surgical reconstruction historically required (open reduction of the talonavicular joint, Achilles tendon lengthening, peroneal tendon transfer, capsulotomies). Foot abduction bracing is continued after the casting phase, similar to Ponseti management of clubfoot.

Other Causes of Rigid Childhood Flatfoot Post-traumatic deformity (typically from talar neck or calcaneal fractures of childhood) produces a rigid flatfoot through bony deformity and joint malalignment. Neuromuscular flatfoot — particularly in cerebral palsy, spina bifida, and the late stages of poliomyelitis — produces a complex deformity with components of valgus, abduction, and equinus that requires individualized assessment and treatment. Inflammatory arthritis — juvenile inflammatory arthritis — produces progressive deformity of the subtalar and midtarsal joints with painful flatfoot.

Adult-Acquired Flatfoot Deformity (AAFD) and Posterior Tibial Tendon

Dysfunction (PTTD) Definition and Pathophysiology Adult-acquired flatfoot deformity is a progressive deformity of the adult foot characterized by collapse of the medial longitudinal arch, hindfoot valgus, forefoot abduction, and eventually first-ray instability. The principal underlying pathology in the great majority of cases is posterior tibial tendon dysfunction, a degenerative tendinopathy and ultimately tendon rupture of the posterior tibial tendon — the dynamic inverter of the foot whose normal function maintains the medial longitudinal arch by elevating it during heel rise. Without an effective posterior tibial tendon, the medial arch progressively collapses, the hindfoot drifts into valgus, the forefoot abducts, and a fixed deformity develops over years. The condition predominantly affects women aged 40-65 years, with risk factors including obesity, hypertension, diabetes mellitus, inflammatory arthritis (rheumatoid, psoriatic), and previous injury to the medial ankle or tendon. The natural history is one of progressive deformity over years; without intervention, a flexible deformity becomes fixed and eventually arthritic. Johnson-Strom Classification (Myerson Modification) The standard classification recognizes four stages: Stage I: Tenosynovitis without deformity. The tendon is inflamed but functionally intact; the foot retains normal morphology. Pain is localized to the medial ankle and tendon course. Stage II: Tendon degeneration with flexible deformity. The flatfoot deformity is present but passively correctable; the hindfoot can be brought into varus and the forefoot abducted to neutral on physical examination. Stage III: Fixed deformity. The hindfoot is in fixed valgus, the forefoot in fixed abduction, and passive correction is no longer possible. Subtalar arthritis is typically present. Stage IV (Myerson addition): Stage III deformity with ankle valgus, often with degenerative changes at the ankle joint, typically from chronic loading in valgus.

Clinical Evaluation Presentation is with medial ankle pain, particularly along the course of the posterior tibial tendon behind the medial malleolus, often progressing over months to years to include lateral hindfoot pain (from subfibular impingement as the calcaneus drifts into valgus), and a progressive flattening of the foot. Examination findings include hindfoot valgus on weight-bearing inspection from behind (the “too many toes” sign — more than the normal one and a half toes visible lateral to the heel when viewed from behind), inability to perform a single-limb heel rise (the most reliable functional test of posterior tibial tendon function), and tenderness along the course of the posterior tibial tendon. The “first metatarsal rise” sign (the medial side of the foot lifts off the ground when the patient stands on tip-toe, even bilaterally) indicates posterior tibial tendon failure. Range of motion of the subtalar and midtarsal joints should be assessed and compared with the contralateral side; loss of motion suggests fixed deformity. Imaging Weight-bearing radiographs (AP and lateral foot, AP ankle) provide the principal imaging assessment. The Meary angle (talus-first metatarsal angle on the lateral view) is increased; the calcaneal pitch is reduced; the talo-navicular coverage angle on the AP view is reduced; and forefoot abduction is evident. MRI is the imaging of choice for assessment of the posterior tibial tendon itself, showing tenosynovitis in early disease and tendon thickening, longitudinal splits, and frank rupture in advanced disease. Ultrasound is a useful alternative for assessing the tendon dynamically. Treatment Stage I disease is treated conservatively: rest, NSAIDs, immobilization in a CAM walker or short-leg walking cast for 4-6 weeks, and physiotherapy directed at strengthening the posterior tibial tendon and stretching the Achilles tendon. Custom orthotics (typically with medial heel posting and medial arch support) provide ongoing support. Persistent disease may require operative tenosynovectomy. Stage II disease (flexible deformity) requires reconstructive surgery in most symptomatic patients. The standard reconstruction combines several procedures: (1) flexor digitorum longus (FDL) tendon transfer to the navicular, providing a new dynamic inverter to replace the failed posterior tibial tendon; (2) medial displacement calcaneal osteotomy (MDCO), an oblique osteotomy of the calcaneal tuberosity with medial displacement of the posterior fragment to correct hindfoot valgus and relieve the heel cord moment; (3) lateral column lengthening (Evans osteotomy through the anterior calcaneus with a tricortical iliac crest bone block, or distraction calcaneocuboid arthrodesis), to correct forefoot abduction and restore the medial arch through a tightening of the spring ligament complex; (4) Cotton osteotomy (medial cuneiform plantar opening-wedge osteotomy with bone graft), to correct first-ray dorsiflexion and restore forefoot tripod equilibrium; (5) Achilles tendon lengthening or gastrocnemius recession, to address the tight heel cord that is present in the great majority of cases. The combination of procedures is individualized to the specific deformity components present in each patient.

Stage III disease (fixed deformity) requires arthrodesis to address the established malalignment and associated arthritis. The standard procedure is triple arthrodesis (talonavicular, subtalar, and calcaneocuboid joint fusion), which provides definitive correction of the deformity with permanent loss of subtalar and midtarsal motion. Modified procedures preserving selected joints (e.g., subtalar arthrodesis alone, or talonavicular and calcaneocuboid arthrodesis preserving the subtalar joint) are used in selected cases. Stage IV disease with ankle involvement requires either total ankle arthroplasty (in patients with adequate alignment and bone stock) or ankle arthrodesis combined with the appropriate hindfoot reconstruction.

Other Causes of Adult-Acquired Flatfoot

Although posterior tibial tendon dysfunction is by far the commonest cause of adult- acquired flatfoot, other etiologies must be considered, particularly when the clinical picture does not fit the classical PTTD presentation. Charcot neuroarthropathy in diabetic patients produces a progressive collapse of the midfoot through neuropathic destruction of the joints, often producing a rocker-bottom deformity in advanced disease. The condition is dealt with at length in the diabetic foot literature; the orthopedic principles are early recognition, total contact casting and immobilization in the acute phase, and reconstructive surgery (typically Charcot reconstructive surgery with extended fusion and intramedullary or plate fixation) for unstable or unbraceable deformity. Spring ligament insufficiency can produce a flexible flatfoot without significant posterior tibial tendon dysfunction. The condition is now increasingly recognized on MRI and arthroscopy. Inflammatory arthritis — particularly rheumatoid arthritis — produces a progressive flatfoot through synovitis of the talonavicular and subtalar joints with progressive joint destruction. Treatment combines systemic medical therapy of the underlying disease with appropriate surgical reconstruction. Traumatic flatfoot deformity follows midfoot or hindfoot fractures and fracture- dislocations (talar neck, calcaneal, midfoot Lisfranc) and is addressed by reconstruction tailored to the bony deformity.

Hereditary Joint Hypermobility

Concept and Spectrum Hereditary joint hypermobility encompasses a spectrum of conditions in which generalized joint laxity is the principal clinical feature. The spectrum extends from the asymptomatic generalized joint hypermobility seen in approximately 10-15% of the general population (more common in younger people, in women, and in certain ethnic groups), through the hypermobile Ehlers-Danlos syndrome (formerly Ehlers-Danlos type III), to the more severe

forms of Ehlers-Danlos syndrome with specific organ involvement, to the related connective tissue disorders Marfan syndrome and Loeys-Dietz syndrome. Beighton Score The Beighton score is the standard clinical tool for assessing generalized joint hypermobility. Nine maneuvers are scored as positive or negative: (1) passive dorsiflexion of the fifth metacarpophalangeal joint beyond 90° (one point each side); (2) passive apposition of the thumb to the forearm (one point each side); (3) hyperextension of the elbow beyond 10° (one point each side); (4) hyperextension of the knee beyond 10° (one point each side); (5) palms flat on the floor with knees fully extended (one point). The maximum score is 9; a score of 4 or more in an adult, or 6 or more in a prepubertal child, indicates generalized joint hypermobility.

Hypermobile Ehlers-Danlos Syndrome and the Joint Hypermobility Spectrum Disorders The hypermobile Ehlers-Danlos syndrome and related joint hypermobility spectrum disorders share the clinical features of generalized joint hypermobility with chronic widespread musculoskeletal pain, recurrent joint dislocations and subluxations, soft and hyperextensible skin (less pronounced than in classical Ehlers-Danlos), easy bruising, and a variety of systemic features including autonomic dysfunction (postural orthostatic tachycardia syndrome, gastrointestinal dysmotility), anxiety and depression. The genetic basis of hypermobile Ehlers-Danlos is not yet fully characterized, and the diagnosis is currently clinical based on the 2017 International Classification of the Ehlers-Danlos Syndromes criteria. Other Ehlers-Danlos Subtypes The classical Ehlers-Danlos syndrome (Types I and II in older nomenclature) is caused by mutations in COL5A1 or COL5A2 encoding type V collagen, and presents with hyperextensible skin with atrophic scarring, joint hypermobility, and easy bruising. The vascular Ehlers-Danlos syndrome (Type IV) is caused by mutations in COL3A1 encoding type III collagen and is characterized by a thin, translucent skin, easy bruising, and the catastrophic complications of spontaneous arterial rupture, bowel perforation, and uterine rupture in pregnancy. The kyphoscoliotic, dermatosparaxis, arthrochalasis, and other rare subtypes each have distinct molecular bases and clinical features. Marfan Syndrome Marfan syndrome is caused by mutations in FBN1 encoding fibrillin-1, the principal component of the elastic microfibrils in the extracellular matrix. Clinical features include tall stature with long extremities and digits (arachnodactyly), pectus excavatum or carinatum, scoliosis, dural ectasia, lens subluxation, mitral valve prolapse, and — most importantly — aortic root dilation with risk of dissection and rupture. The Ghent criteria, recently revised, integrate cardiovascular, ocular, musculoskeletal, dural, and family history features for diagnosis. Orthopedic features include scoliosis (often requiring bracing or surgical correction), protrusio acetabuli, pes planus, hindfoot valgus, and joint

hypermobility. The orthopedic surgeon must be aware of the cardiovascular implications of Marfan syndrome and must coordinate care with the cardiac specialist. Loeys-Dietz Syndrome Loeys-Dietz syndrome, caused by mutations in TGFBR1 or TGFBR2, shares many features of Marfan syndrome but with more aggressive aortic disease and a wider arterial involvement. The same orthopedic features may be present, but the cardiovascular implications dominate management. Clinical Management of the Hypermobile Patient The orthopedic care of the hypermobile patient requires attention to several specific issues. Recurrent joint dislocation — particularly of the patella, shoulder, and hip — is common; conservative management with bracing and physiotherapy is the first line, while operative stabilization of the persistently dislocating joint must consider the higher-than- usual rate of failure of soft-tissue procedures and the higher rate of complications generally. Chronic widespread pain in the hypermobile patient often responds poorly to typical analgesic strategies and benefits from a multidisciplinary approach including physical therapy, pacing strategies, and management of comorbid anxiety and depression. Preoperative considerations include the cardiovascular risks in Marfan and Loeys-Dietz syndromes (aortic dissection during surgery is a recognized risk), the increased risk of poor wound healing and atrophic scarring in classical Ehlers-Danlos, and the increased risk of subluxation and dislocation under anesthesia.

Summary and Take-Home Points

The flatfoot is a heterogeneous group of foot morphologies and disorders ranging from the physiological flexible flatfoot of childhood — requiring no treatment when asymptomatic — through the rigid pathological flatfoot of tarsal coalition and congenital vertical talus — requiring specific surgical management — to the adult-acquired flatfoot deformity of posterior tibial tendon dysfunction — staged by the Johnson-Strom-Myerson classification and treated with progressively more extensive surgery as the disease advances. Hereditary joint hypermobility, assessed by the Beighton score, extends from asymptomatic generalized joint laxity through the hypermobile Ehlers-Danlos syndrome and related spectrum disorders to the more severe connective tissue disorders Marfan and Loeys- Dietz, each with characteristic orthopedic manifestations and specific perioperative considerations. The clinical evaluation of the flat foot must distinguish flexible from rigid forms, identify any underlying neuromuscular or systemic condition, and determine whether the deformity is producing symptoms or functional limitation; the management must be tailored to the specific etiology, the severity and reducibility of the deformity, and the individual patient’s functional demands and comorbidities.