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Abnormalities of the pediatric foot
Abnormalities of the Pediatric Foot ' Catherine Maldjian, MD, Stephen Hofkin, MD, Akbar Bonakdarpour, MD Nell Roach, MD, J a m e s J. McCarthy, MD
Deformities of the pediatric foot represent a broad range of disorders. Radiographic detection, definition, and differentiation of specific abnormalities are critical. Herein,
Acad Radio11999; 6:191-199 1From the Department of Diagnostic Imaging, Temple University Hospital, Broad & Ontario Sts, Philadelphia, PA 19140 (C.M., S.H., A.B., N.R.); the Department of Diagnostic Imaging, Shriners Hospital for Children, Philadelphia, Pa (C.M., A.B., N.R.); and the Departments of Orthopedic Surgery, Shriners Hospital for Children and Temple University Hospital, Philadelphia, Pa (J.J.M.). Received July 24, 1998; revision requested August 4; revision received October 13; accepted September 16. Address reprint requests to C.M. ©AUR, 1999
we demonstrate critical measurements and radiographic techniques that will assist in the differentiation of common congenital abnormalities seen in the pediatric foot. Postural deformation of the foot may simulate a congenital abnormality of the foot. However, postural deformations are usually caused by in utero malposition, and they occur after organogenesis; therefore, they are transient and resolve spontaneously (1). The interosseous angles are normal and no structural or permanent bone deformities exist in patients with postural deformities. Structural deformities may have some degree of plasticity. In certain cases the abnormality may be mild and, to some extent, malleable, so that correction can be ob-
b.
Figure 1. (a) AP and (b) lateral views of the normal foot. A line bisecting the long axis of the talus and a similar line through the calcaneus form an angle (black lines) that normally measures 20o-40 ° on the AP view and 350-50 ° on the lateral view. The calcaneus normally demonstrates a mild 5°-10 ° eversion and 20o-30 ° dorsiflexion, or pitch. Normal eversion exists when the long axis of the calcaneus aligns with the long axis of the fourth or fifth metatarsal bone. a.
191
Figure 3. Incomplete correction of clubfoot. Note the residual hindfoot varus deformity. The talocalcaneal angle measures less than 20 ° . This appearance is referred to as parallelism of the talus and calcaneus, since their long axes lie roughly parallel to one another (black lines). A cavus deformity is also present.
a.
b,
Figure 2. Clubfoot. (a) In an isolated hindfoot abnormality, the midtalar line will not traverse the base of the first metatarsal bone and usually lies lateral to it on an AP view. (b) Normal alignment of the talus relative to the calcaneus and the forefoot is restored with manipulation consisting of maximal abduction of the forefoot while the heel is firmly held in a fixed position. The Kite angle (talocalcaneal angle on AP projection) approaches normal. This signifies that the deformity is relatively malleable and a favorable outcome with closed reduction is more likely than if the deformitY were more resistant to manual manipulation.
Figure 4. Surgically treated clubfoot. Internal fixation can be accomplished with pins through the talonavicular and calcaneocuboid joints.
Figure 5. Rockerbottom foot as a complication of treatment for clubfoot. This deformity occurs secondary to dorsiflexion prior to the correction of the equinovarus.
tained with conservative treatment if it is begun early. Foot disorders may also be acquired secondary to neuromuscular disorders, such as cerebral palsy or myelomeningocele.
192
In the normal foot, standing radiographs are routinely obtained in anteroposterior (AP) and lateral projections (2). The talocalcaneal angle in both projections normally measures 200-50 ° (Fig 1). More specifically, the talocalcaneal angle measures 200-40 ° in the AP view and 35 °50 ° in the lateral view (1). The talocalcaneal angle is largest at birth (before ambulation) and decreases gradually with age (3). Normal forefoot alignment is demonstrated by alignment of the long axes of the talus and the first metatarsal bones. The talo-first metatarsal angle
Vol 6, No 3, March 1999
a.
ABNORMALITIES OF THE PEDIATRIC FOOT
b.
Figure 8. Vertical talus. (a) Lateral view of the foot demonstrates a rockerbottom configuration. The talus lies between the calcaneus and cuboid bone. (b) There is persistent dorsal dislocation of the navicular bone on the lateral plantar flexion view. If the navicular bone is not yet ossified, then the long axis of the first metatarsal bone can be used as a reference point, it should lie dorsal to the long axis of the talus in vertical talus.
Figure 6. Pes planovalgus. The line drawn through the long axis of the talus, navicular, medial cuneiform, and the first metatarsal bones (the talo-first metatarsal axis) should be continuous on the lateral weight-bearing view and perpendicular to the tarsonavicular and naviculocuneiform joints. The site at which the continuity is disrupted by plantar angulation determines the portion of the arch resp,onsible for the flattened appearance. The more common locations for disruption of the arch are at the talonavicular and naviculocuneiform joints. In this case the talus and navicular bones are in proper alignment; however, the cuneiform is not. This indicates that the break in the arch is at the naviculocuneiform articulation.
(measured as the angle between the midtalar line and the middle of the first metatarsal line) normally measures 0 ° to +15 ° (1). HINDFOOT ABNORMALITIES Congenital Talipes Equinovarus In congenital talipes equinovarus (clubfoot), medial and plantar displacement of the talar neck are present (4,5) and the talocalcaneal angle is decreased (Figs 2, 3). A talocalcaneal angle of less than 25 ° on the lateral view
Figure 7. Grice procedure for correction of pes planovalgus. Lateral projection of the foot demonstrates a pin and bone graft that traverses the talocalcaneal joint. Subtalar fusion causes immobility of the joint. This procedure is generally reserved for cases of pes planovalgus caused by paralysis.
is indicative of talipes equinovarus (1). The forefoot deviates in conjunction with the calcaneus and midfoot. The inversion deformity of the calcaneus induces supination of the metatarsal bones. As a consequence, there is increased fanning of the metatarsal bones, with the first metatarsal bone projecting superiorly on the lateral view. There may be stress reactions on the lateral metatarsal bones at their bases since weight bearing occurs primarily on the lateral side of the foot in patients with this condition.
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M A L D J I A N ET A L
a.
Figure 9.
Vol 6, No 3, March 1999
b.
Oblique talus. (a) The navicular bone lies dorsal to the long axis of the talus. (b) In plantar flexion, normal alignment is restored.
Closed reduction can be successfully achieved by casting early when the deformity may be somewhat pliable. If normal bone alignment can be approximated on an AP view with applied abduction, then the deformity is to some extent malleable (Fig 2b) (6). If the deformity does not correct with conservative treatment, then surgical treatment is used (Fig 4). Complications of treatment include undercorrection, overcorrection, ischemic necrosis of the talus or navicular bone, and rockerbottom foot (Figs 3, 5).
Pes Planovalgus Pes planovalgus (also called pes planus or flatfoot) (Fig 6) can be either flexible or rigid. Rigid flatfoot occurs with convex pes valgus (vertical talus), tarsal coalition, tight heel cord, and arthritic and neuromuscular disorders. In pes planus, the plantar arch is decreased. In cases of flexible flatfoot, a normal plantar arch will be restored in non-weight-bearing situations, as the deformity is due to ligamentous laxity (1). Treatment is usually conservative; however, in extreme cases surgery may be used (Fig 7).
Rockerbottom Foot Rockerbottom foot is a descriptive term rather than a singular entity. There are several possible causes of the deformity, including vertical talus, oblique talus, severe flatfoot, and partially treated clubfoot. On the lateral weight-bearing view there is a reversal of the normal plantar arch such that the plantar surface actually appears convex (Fig 8).
194
Figure 10. Metatarsus adductus. In this isolated forefoot abnormality, the midtalar line traverses the base but does not align with the long axis of the first metatarsal bone. Frontal weight-bearing radiographs will demonstrate medial subluxation of the metatarsal bones.
Figure 11. Halluxvalgus. (a) Frontal view of the foot demonstrates increased angulation between the first and second metatarsal bones accompanied by increased angulation of the first metatarsophalangeal joint. (b) After treatment, a frontal view of the foot demonstrates an osteotomy of the base of the first metatarsal bone. A Kirschner wire is frequently inserted to secure positioning and alignment.
a.
b,
The main causes of rockerbottom deformity can be readily distinguished from one another. Vertical talus and oblique talus demonstrate plantar flexion of the talus with dorsal dislocation of the navicular bone. This dis'location is not reducible with plantar flexion in vertical talus; however, it is reducible with plantar flexion in oblique talus (Fig 9). When it causes rockerbottom foot, a severe flatfoot, either rigid or flexible, may show hindfoot valgus, but dorsal dislocation of the navicular bone is not a feature. The hindfoot demonstrates equinus posture in vertical talus. A complication of treated clubfoot is rockerbottom foot, but in these cases the clinical history and other manifestations of treated clubfoot can be used to distinguish between the two conditions.
FOREFOOT ABNORMALITIES Congenital Metatarsus Adductus Congenital metatarsus adductus is distinguished by medial subluxation at the tarsometatarsal articulations (Fig 10). In this disorder there is adduction of the meta-
tarsal bones. Depending on the severity of the condition, the navicular bone either articulates normally with the talus or demonstrates some degree of lateral subluxation.
Hallux Valgus Hallux valgus was previously thought to be related to congenital metatarsus primus varus (abnormal [>10 °] medial angulation of the first metatarsal bone) (7). However, at least one investigation suggests that hallux valgus is due to a valgus orientation of the second metatarsal bone and widening of the intermetatarsal angle (8). This leads to progressive angulation of the first metatarsophalangeal joint and hallux valgus (Fig 11). This disorder usually becomes manifest in adolescence. The term bunion refers to the joint deviation, hypertrophic bone clianges, and inflammatory changes of the adventitial bursa at the metatarsophalangeal joint. This condition predisposes the forefoot to osteoarthritic changes that limit dorsiflexion of this joint (hallux rigidus). Congenital metatarsus primus varus and hallux valgus are more common in females than males, and there is hereditary predisposition for both disorders.
195
Figure 12. Cavus foot. Lateral view of the foot demonstrates cavus deformity-with dorsiflexion of the calcaneus anteriorly. Note the increased calcaneal pitch. This deformity is often seen in flaccid paralytic states.
Figure 14. Calcaneonavicular coalition. This oblique view demonstrates close apposition of the calcaneus and navicular bone with joint space narrowing and alterations at the articular surfaces.
Cavus Foot In cavus foot, the forefoot maintains an equinus posture relative to the hindfoot. In patients with this condition, a neuromuscular cause should be suspected. Idiopathic cases often occur in families, reflecting a probable hereditary predisposition. The hindfoot usually exhibits exaggerated dorsiflexion of the calcaneus anteriorly when the condition is caused by flaccid paralysis from poliomyelitis or myelomeningocele (Fig 12). Hindfoot varus (cavovarus) may also be present in cases in which a cavus deformity accompanies clubfoot (as may be seen after treatment for clubfoot).
196
Figure 13. Skewfoot. In combined hindfoot and forefoot abnormalities (eg, skewfoot), the long axis of the calcaneus will not parallel the long axis of the fourth or fifth metatarsal bone on the frontal view and the talar neck line will not intersect the base of the first metatarsal bone. The frontal view demonstrates hindfoot valgus, denoted by the medial position of the talus relative to the first metatarsal bone, as well as forefoot varus.
a.
b.
Figure 16. Coronal CT scans of talocalcaneal coalitions. (a) Note the narrowing and deformity at the medial aspect of the talocalcaneal joint. This is consistent with a fibrous coalition. (b) Scan in another case demonstrates a bony coalition. CT can be particularly helpful in cases of anterior and middle talocalcaneal coalitions when Harris views fail to definitively demonstrate an abnormality.
Figure 17. Secondary signs of subtalar coalitions. This lateral radiograph shows talar beaking, a common secondary finding in talocalcaneal coalitions. It is believed to be caused by decreased motion of the subtalar joint resulting in dorsal dislocation of the navicular bone against the head of the talus. There may also be narrowing in the posterior subtalar joint. Note also the pes planus, which in this instance is rigid and due to the talocalcaneal coalition.
Figure 15. Talocalcaneal coalition. The Harris view shows the posterior ¢mgulation of the middle facet. The joint space is nearly obliterated in this location.
Skewfoot Skewfoot deformity consists of a combination of forefoot varus and hindfoot valgus (Fig 13). It may result from late or inadequate treatment of congenital metatarsus v a r u s .
197
a.
Figure 18. Ball-and-socket ankle joint. (a) Frontal and (b) lateral projections of the ankle demonstrate a rounded appearance of the tibial plafond and talar dome. Note the osseous fusion between the talus and the calcaneus on the lateral view. Subtalar (talocalcaneal) coalition and shortening of the involved extremity are frequently found in patients with ball-and-socket ankle joints. b.
The two most frequently seen types of tarsal coalitions are calcaneonavicular and talocalcaneal coalitions. Of these, the calcaneonavicular bar and the medial talocalcaneal bridge are the most common and the most frequent cause of peroneal spastic flatfoot. Tarsal coalitions are believed to be caused by a segmentation anomaly of the primitive mesenchyme, and they show a hereditary predis'position. The intertarsal bridging may be osseous, cartilaginous, or fibrous in nature. Calcaneonavicular fusions are seen to best advantage on a 45 ° oblique view; however, cartilaginous and fibrous unions may be difficult to assess radiographically. Flattening of the adjacent articular surfaces, narrowing of the joint, and elongation of the anterior process of the calcaneus may be secondary findings (Fig 14). For talocalcaneal coalitions, an axial oblique (Harris) view is recommended (Fig 15). In this view, the joint is angled posteriorly rather than horizontally. Definitive diagnosis can be made at computed tomography (CT) by using short-axis imaging of the foot (Fig 16). Secondary signs of a talocalcaneal coalition include dorsal and lateral talar beaking (Fig 17). Tarsal coalition (usually of the talonavicular and calcaneocuboid types) is seen in 60% of cases of ball-and-socket ankle joints (Fig 18) (2). The ball-and-socket ankle joint is a congenital de-
198
formity in which the distal portion of the tibia assumes a more concave configuration and the corresponding articular surface of the talus assumes a more convex configuration than normal. This orientation is best appreciated on a frontal view where the articulation would normally appear fairly horizontal; with this deformity, however, the articulation appears dome shaped. Phocomelia, symphangalia, and arthrogryposis are also associated with tarsal synostoses (1,2). Certain syndromes, such as Apert, Nievergelt, and Fuhrmann syndromes, may be seen in conjunction with tarsal coalitions (1,2). Tarsal coalitions are initially treated conservatively. If pain and muscle spasm are present, then surgery should be performed. Generally, calcaneonavicular bars can be resected in patients under the age of 14 years. When severe arthritic changes of the talonavicular joint exist, a triple arthrodesis is indicated. Although partial excision of medial talocalcaneal bars can be performed, the outcome is less often as satisfactory as it is with excision of calcaneonavicular bars. When the bar is fairly extensive, the primary surgical treatment of choice consists of subtalar or triple arthrodesis. In conclusion, there are a multitude of congenital foot abnormalities. Radiographic examination of the interos-
seous relationships may help differentiate these various entities and provide objective parameters for a specific diagnosis. In particular, alignment of the midtalar line relative to the first metatarsal bone differentiates an isolated hindfoot abnormality from a forefoot abnormality. Evaluation of the talocalcaneal angle, particularly as seen on the lateral weight-bearing view, is useful for identification of hindfoot abnormalities. Once a specific diagnosis is established, radiographic evaluation may help ascertain whether adequate correction has been obtained with treatment. ~,CKNOWLEDGMEN"
This article is dedicated to the memory of Dr Mamed Mesgarzadeh, who passed away during the preparation of the poster that was the predecessor of this article. Many of the cases herein were from his teaching file. We will
always cherish his memory as a mentor, colleague, and friend. His many contributions to radiology will never be forgotten. IEFERENCE~
1. Tachdjian MO. The child's foot. Philadelphia, Pa: Saunders, 1985. 2. Ozonoff MB. Pediatric orthopedic radiology. 2nd ed. Philadelphia, Pa: Saunders, 1992. 3. Vanderwilde R, Staheli LT, Chew DE, Malagon V. Measurements on radiographs of the foot in normal infants and children. J Bone Joint Surg [Am] 1988; 70:407-415. 4. Irani RN, Sherman MS. The pathologic anatomy of idiopathic clubfoot. Clin Orthop 1972; 84:14-20. 5. Settle GW. The anatomy of congenital talipes equinovarus: sixteen dissected specimens. J Bone Joint Surg [Am] 1963; 45:1341. 6. McCauley JC Jr. Surgical treatment of clubfoot. Surg Clin North Am 1951 ; 31:561-574. 7. Mitchell CL, Fleming JL, Allen R, Glenney C, Sanford GA. Osteotomybunionectomy for hallux valgus. J Bone Joint Surg [Am] 1958; 40:41-60. 8. Houghton GR, Dickson RA. Hallux valgus in the younger patient. The structural abnormality. J Bone Joint Surg [Br] 1979; 61:176-177.
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Deformities of the pediatric foot represent a broad range of disorders. Radiographic detection, definition, and differentiation of specific abnormalities are critical. Herein,
Acad Radio11999; 6:191-199 1From the Department of Diagnostic Imaging, Temple University Hospital, Broad & Ontario Sts, Philadelphia, PA 19140 (C.M., S.H., A.B., N.R.); the Department of Diagnostic Imaging, Shriners Hospital for Children, Philadelphia, Pa (C.M., A.B., N.R.); and the Departments of Orthopedic Surgery, Shriners Hospital for Children and Temple University Hospital, Philadelphia, Pa (J.J.M.). Received July 24, 1998; revision requested August 4; revision received October 13; accepted September 16. Address reprint requests to C.M. ©AUR, 1999
we demonstrate critical measurements and radiographic techniques that will assist in the differentiation of common congenital abnormalities seen in the pediatric foot. Postural deformation of the foot may simulate a congenital abnormality of the foot. However, postural deformations are usually caused by in utero malposition, and they occur after organogenesis; therefore, they are transient and resolve spontaneously (1). The interosseous angles are normal and no structural or permanent bone deformities exist in patients with postural deformities. Structural deformities may have some degree of plasticity. In certain cases the abnormality may be mild and, to some extent, malleable, so that correction can be ob-
b.
Figure 1. (a) AP and (b) lateral views of the normal foot. A line bisecting the long axis of the talus and a similar line through the calcaneus form an angle (black lines) that normally measures 20o-40 ° on the AP view and 350-50 ° on the lateral view. The calcaneus normally demonstrates a mild 5°-10 ° eversion and 20o-30 ° dorsiflexion, or pitch. Normal eversion exists when the long axis of the calcaneus aligns with the long axis of the fourth or fifth metatarsal bone. a.
191
Figure 3. Incomplete correction of clubfoot. Note the residual hindfoot varus deformity. The talocalcaneal angle measures less than 20 ° . This appearance is referred to as parallelism of the talus and calcaneus, since their long axes lie roughly parallel to one another (black lines). A cavus deformity is also present.
a.
b,
Figure 2. Clubfoot. (a) In an isolated hindfoot abnormality, the midtalar line will not traverse the base of the first metatarsal bone and usually lies lateral to it on an AP view. (b) Normal alignment of the talus relative to the calcaneus and the forefoot is restored with manipulation consisting of maximal abduction of the forefoot while the heel is firmly held in a fixed position. The Kite angle (talocalcaneal angle on AP projection) approaches normal. This signifies that the deformity is relatively malleable and a favorable outcome with closed reduction is more likely than if the deformitY were more resistant to manual manipulation.
Figure 4. Surgically treated clubfoot. Internal fixation can be accomplished with pins through the talonavicular and calcaneocuboid joints.
Figure 5. Rockerbottom foot as a complication of treatment for clubfoot. This deformity occurs secondary to dorsiflexion prior to the correction of the equinovarus.
tained with conservative treatment if it is begun early. Foot disorders may also be acquired secondary to neuromuscular disorders, such as cerebral palsy or myelomeningocele.
192
In the normal foot, standing radiographs are routinely obtained in anteroposterior (AP) and lateral projections (2). The talocalcaneal angle in both projections normally measures 200-50 ° (Fig 1). More specifically, the talocalcaneal angle measures 200-40 ° in the AP view and 35 °50 ° in the lateral view (1). The talocalcaneal angle is largest at birth (before ambulation) and decreases gradually with age (3). Normal forefoot alignment is demonstrated by alignment of the long axes of the talus and the first metatarsal bones. The talo-first metatarsal angle
Vol 6, No 3, March 1999
a.
ABNORMALITIES OF THE PEDIATRIC FOOT
b.
Figure 8. Vertical talus. (a) Lateral view of the foot demonstrates a rockerbottom configuration. The talus lies between the calcaneus and cuboid bone. (b) There is persistent dorsal dislocation of the navicular bone on the lateral plantar flexion view. If the navicular bone is not yet ossified, then the long axis of the first metatarsal bone can be used as a reference point, it should lie dorsal to the long axis of the talus in vertical talus.
Figure 6. Pes planovalgus. The line drawn through the long axis of the talus, navicular, medial cuneiform, and the first metatarsal bones (the talo-first metatarsal axis) should be continuous on the lateral weight-bearing view and perpendicular to the tarsonavicular and naviculocuneiform joints. The site at which the continuity is disrupted by plantar angulation determines the portion of the arch resp,onsible for the flattened appearance. The more common locations for disruption of the arch are at the talonavicular and naviculocuneiform joints. In this case the talus and navicular bones are in proper alignment; however, the cuneiform is not. This indicates that the break in the arch is at the naviculocuneiform articulation.
(measured as the angle between the midtalar line and the middle of the first metatarsal line) normally measures 0 ° to +15 ° (1). HINDFOOT ABNORMALITIES Congenital Talipes Equinovarus In congenital talipes equinovarus (clubfoot), medial and plantar displacement of the talar neck are present (4,5) and the talocalcaneal angle is decreased (Figs 2, 3). A talocalcaneal angle of less than 25 ° on the lateral view
Figure 7. Grice procedure for correction of pes planovalgus. Lateral projection of the foot demonstrates a pin and bone graft that traverses the talocalcaneal joint. Subtalar fusion causes immobility of the joint. This procedure is generally reserved for cases of pes planovalgus caused by paralysis.
is indicative of talipes equinovarus (1). The forefoot deviates in conjunction with the calcaneus and midfoot. The inversion deformity of the calcaneus induces supination of the metatarsal bones. As a consequence, there is increased fanning of the metatarsal bones, with the first metatarsal bone projecting superiorly on the lateral view. There may be stress reactions on the lateral metatarsal bones at their bases since weight bearing occurs primarily on the lateral side of the foot in patients with this condition.
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M A L D J I A N ET A L
a.
Figure 9.
Vol 6, No 3, March 1999
b.
Oblique talus. (a) The navicular bone lies dorsal to the long axis of the talus. (b) In plantar flexion, normal alignment is restored.
Closed reduction can be successfully achieved by casting early when the deformity may be somewhat pliable. If normal bone alignment can be approximated on an AP view with applied abduction, then the deformity is to some extent malleable (Fig 2b) (6). If the deformity does not correct with conservative treatment, then surgical treatment is used (Fig 4). Complications of treatment include undercorrection, overcorrection, ischemic necrosis of the talus or navicular bone, and rockerbottom foot (Figs 3, 5).
Pes Planovalgus Pes planovalgus (also called pes planus or flatfoot) (Fig 6) can be either flexible or rigid. Rigid flatfoot occurs with convex pes valgus (vertical talus), tarsal coalition, tight heel cord, and arthritic and neuromuscular disorders. In pes planus, the plantar arch is decreased. In cases of flexible flatfoot, a normal plantar arch will be restored in non-weight-bearing situations, as the deformity is due to ligamentous laxity (1). Treatment is usually conservative; however, in extreme cases surgery may be used (Fig 7).
Rockerbottom Foot Rockerbottom foot is a descriptive term rather than a singular entity. There are several possible causes of the deformity, including vertical talus, oblique talus, severe flatfoot, and partially treated clubfoot. On the lateral weight-bearing view there is a reversal of the normal plantar arch such that the plantar surface actually appears convex (Fig 8).
194
Figure 10. Metatarsus adductus. In this isolated forefoot abnormality, the midtalar line traverses the base but does not align with the long axis of the first metatarsal bone. Frontal weight-bearing radiographs will demonstrate medial subluxation of the metatarsal bones.
Figure 11. Halluxvalgus. (a) Frontal view of the foot demonstrates increased angulation between the first and second metatarsal bones accompanied by increased angulation of the first metatarsophalangeal joint. (b) After treatment, a frontal view of the foot demonstrates an osteotomy of the base of the first metatarsal bone. A Kirschner wire is frequently inserted to secure positioning and alignment.
a.
b,
The main causes of rockerbottom deformity can be readily distinguished from one another. Vertical talus and oblique talus demonstrate plantar flexion of the talus with dorsal dislocation of the navicular bone. This dis'location is not reducible with plantar flexion in vertical talus; however, it is reducible with plantar flexion in oblique talus (Fig 9). When it causes rockerbottom foot, a severe flatfoot, either rigid or flexible, may show hindfoot valgus, but dorsal dislocation of the navicular bone is not a feature. The hindfoot demonstrates equinus posture in vertical talus. A complication of treated clubfoot is rockerbottom foot, but in these cases the clinical history and other manifestations of treated clubfoot can be used to distinguish between the two conditions.
FOREFOOT ABNORMALITIES Congenital Metatarsus Adductus Congenital metatarsus adductus is distinguished by medial subluxation at the tarsometatarsal articulations (Fig 10). In this disorder there is adduction of the meta-
tarsal bones. Depending on the severity of the condition, the navicular bone either articulates normally with the talus or demonstrates some degree of lateral subluxation.
Hallux Valgus Hallux valgus was previously thought to be related to congenital metatarsus primus varus (abnormal [>10 °] medial angulation of the first metatarsal bone) (7). However, at least one investigation suggests that hallux valgus is due to a valgus orientation of the second metatarsal bone and widening of the intermetatarsal angle (8). This leads to progressive angulation of the first metatarsophalangeal joint and hallux valgus (Fig 11). This disorder usually becomes manifest in adolescence. The term bunion refers to the joint deviation, hypertrophic bone clianges, and inflammatory changes of the adventitial bursa at the metatarsophalangeal joint. This condition predisposes the forefoot to osteoarthritic changes that limit dorsiflexion of this joint (hallux rigidus). Congenital metatarsus primus varus and hallux valgus are more common in females than males, and there is hereditary predisposition for both disorders.
195
Figure 12. Cavus foot. Lateral view of the foot demonstrates cavus deformity-with dorsiflexion of the calcaneus anteriorly. Note the increased calcaneal pitch. This deformity is often seen in flaccid paralytic states.
Figure 14. Calcaneonavicular coalition. This oblique view demonstrates close apposition of the calcaneus and navicular bone with joint space narrowing and alterations at the articular surfaces.
Cavus Foot In cavus foot, the forefoot maintains an equinus posture relative to the hindfoot. In patients with this condition, a neuromuscular cause should be suspected. Idiopathic cases often occur in families, reflecting a probable hereditary predisposition. The hindfoot usually exhibits exaggerated dorsiflexion of the calcaneus anteriorly when the condition is caused by flaccid paralysis from poliomyelitis or myelomeningocele (Fig 12). Hindfoot varus (cavovarus) may also be present in cases in which a cavus deformity accompanies clubfoot (as may be seen after treatment for clubfoot).
196
Figure 13. Skewfoot. In combined hindfoot and forefoot abnormalities (eg, skewfoot), the long axis of the calcaneus will not parallel the long axis of the fourth or fifth metatarsal bone on the frontal view and the talar neck line will not intersect the base of the first metatarsal bone. The frontal view demonstrates hindfoot valgus, denoted by the medial position of the talus relative to the first metatarsal bone, as well as forefoot varus.
a.
b.
Figure 16. Coronal CT scans of talocalcaneal coalitions. (a) Note the narrowing and deformity at the medial aspect of the talocalcaneal joint. This is consistent with a fibrous coalition. (b) Scan in another case demonstrates a bony coalition. CT can be particularly helpful in cases of anterior and middle talocalcaneal coalitions when Harris views fail to definitively demonstrate an abnormality.
Figure 17. Secondary signs of subtalar coalitions. This lateral radiograph shows talar beaking, a common secondary finding in talocalcaneal coalitions. It is believed to be caused by decreased motion of the subtalar joint resulting in dorsal dislocation of the navicular bone against the head of the talus. There may also be narrowing in the posterior subtalar joint. Note also the pes planus, which in this instance is rigid and due to the talocalcaneal coalition.
Figure 15. Talocalcaneal coalition. The Harris view shows the posterior ¢mgulation of the middle facet. The joint space is nearly obliterated in this location.
Skewfoot Skewfoot deformity consists of a combination of forefoot varus and hindfoot valgus (Fig 13). It may result from late or inadequate treatment of congenital metatarsus v a r u s .
197
a.
Figure 18. Ball-and-socket ankle joint. (a) Frontal and (b) lateral projections of the ankle demonstrate a rounded appearance of the tibial plafond and talar dome. Note the osseous fusion between the talus and the calcaneus on the lateral view. Subtalar (talocalcaneal) coalition and shortening of the involved extremity are frequently found in patients with ball-and-socket ankle joints. b.
The two most frequently seen types of tarsal coalitions are calcaneonavicular and talocalcaneal coalitions. Of these, the calcaneonavicular bar and the medial talocalcaneal bridge are the most common and the most frequent cause of peroneal spastic flatfoot. Tarsal coalitions are believed to be caused by a segmentation anomaly of the primitive mesenchyme, and they show a hereditary predis'position. The intertarsal bridging may be osseous, cartilaginous, or fibrous in nature. Calcaneonavicular fusions are seen to best advantage on a 45 ° oblique view; however, cartilaginous and fibrous unions may be difficult to assess radiographically. Flattening of the adjacent articular surfaces, narrowing of the joint, and elongation of the anterior process of the calcaneus may be secondary findings (Fig 14). For talocalcaneal coalitions, an axial oblique (Harris) view is recommended (Fig 15). In this view, the joint is angled posteriorly rather than horizontally. Definitive diagnosis can be made at computed tomography (CT) by using short-axis imaging of the foot (Fig 16). Secondary signs of a talocalcaneal coalition include dorsal and lateral talar beaking (Fig 17). Tarsal coalition (usually of the talonavicular and calcaneocuboid types) is seen in 60% of cases of ball-and-socket ankle joints (Fig 18) (2). The ball-and-socket ankle joint is a congenital de-
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formity in which the distal portion of the tibia assumes a more concave configuration and the corresponding articular surface of the talus assumes a more convex configuration than normal. This orientation is best appreciated on a frontal view where the articulation would normally appear fairly horizontal; with this deformity, however, the articulation appears dome shaped. Phocomelia, symphangalia, and arthrogryposis are also associated with tarsal synostoses (1,2). Certain syndromes, such as Apert, Nievergelt, and Fuhrmann syndromes, may be seen in conjunction with tarsal coalitions (1,2). Tarsal coalitions are initially treated conservatively. If pain and muscle spasm are present, then surgery should be performed. Generally, calcaneonavicular bars can be resected in patients under the age of 14 years. When severe arthritic changes of the talonavicular joint exist, a triple arthrodesis is indicated. Although partial excision of medial talocalcaneal bars can be performed, the outcome is less often as satisfactory as it is with excision of calcaneonavicular bars. When the bar is fairly extensive, the primary surgical treatment of choice consists of subtalar or triple arthrodesis. In conclusion, there are a multitude of congenital foot abnormalities. Radiographic examination of the interos-
seous relationships may help differentiate these various entities and provide objective parameters for a specific diagnosis. In particular, alignment of the midtalar line relative to the first metatarsal bone differentiates an isolated hindfoot abnormality from a forefoot abnormality. Evaluation of the talocalcaneal angle, particularly as seen on the lateral weight-bearing view, is useful for identification of hindfoot abnormalities. Once a specific diagnosis is established, radiographic evaluation may help ascertain whether adequate correction has been obtained with treatment. ~,CKNOWLEDGMEN"
This article is dedicated to the memory of Dr Mamed Mesgarzadeh, who passed away during the preparation of the poster that was the predecessor of this article. Many of the cases herein were from his teaching file. We will
always cherish his memory as a mentor, colleague, and friend. His many contributions to radiology will never be forgotten. IEFERENCE~
1. Tachdjian MO. The child's foot. Philadelphia, Pa: Saunders, 1985. 2. Ozonoff MB. Pediatric orthopedic radiology. 2nd ed. Philadelphia, Pa: Saunders, 1992. 3. Vanderwilde R, Staheli LT, Chew DE, Malagon V. Measurements on radiographs of the foot in normal infants and children. J Bone Joint Surg [Am] 1988; 70:407-415. 4. Irani RN, Sherman MS. The pathologic anatomy of idiopathic clubfoot. Clin Orthop 1972; 84:14-20. 5. Settle GW. The anatomy of congenital talipes equinovarus: sixteen dissected specimens. J Bone Joint Surg [Am] 1963; 45:1341. 6. McCauley JC Jr. Surgical treatment of clubfoot. Surg Clin North Am 1951 ; 31:561-574. 7. Mitchell CL, Fleming JL, Allen R, Glenney C, Sanford GA. Osteotomybunionectomy for hallux valgus. J Bone Joint Surg [Am] 1958; 40:41-60. 8. Houghton GR, Dickson RA. Hallux valgus in the younger patient. The structural abnormality. J Bone Joint Surg [Br] 1979; 61:176-177.
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