The Subtalar Joint: Anatomy and Joint Motion

Transcription

1 The Subtalar Joint: Anatomy and Joint Motion Paul A. Rockar, )r., MS, PT, BS, OCS' Paul A. Rockar, Jr. T he subtalar joint is one of many structures of the foot complex. Just as with other parts of the musculoskeletal system, the orthopaedic and sports physical therapist must be familiar with the anatomy and biomechanics of this articulation. Therefore, the purpose of this paper is to discuss the bony, ligamentous, muscular, and vascular anatomy as well as the motions of the subtalar joint so the clinician will have a foundation upon which to base examination and treatment procedures. ANATOMY The Bones and Their Articular Surfaces The skeleton of the foot can be divided into four transverse segments (Figure 1) (17). These divisions are the tarsus (rearfoot), the lesser tarsus (midfoot), the metatarsus, and the digits. The tarsus is comprised of the talus and the calcaneus. The lesser tarsus contains the navicular, the cuboid, and the three cuneiforms. Metatarsals one through five form the metatarsus, and the five toes comprise the digital segment (1.2). Some anatomical texts include the lesser To fully understand the research literature on the efficacy of various clinical procedures, the physical therapist must be knowledgeable in the anatomy and biomechanics of the synovial joints. This paper presents detailed information on the bony, ligamentous, muscular, and vascular anatomy of the subtalar joint. In addition, there is a discussion of the joint axis as well as the joint motions about this axis. This information will prove valuable to the clinician as new examination and treatment procedures are considered for inclusion in the management of patients with foot-ankle dysfunction. Key Words: subtalar, anatomy, motion ' Vice President, CORE Network, McKeesport, PA; Adjunct Assistant Professor, Duquesne University, Pittsburgh, PA; Associate Professor, Slippery Rock University, Slippery Rock, PA. Address for correspondence: Muny Highlands Circle, Munysville, PA tarsus with the tarsus. The tarsus, in these instances, consists of the seven tarsal bones. Accordingly, the foot is then divided into only three segments (2.22). The subtalar joint is the articulation between the talus superiorly and the calcaneus and navicular inferiorly. It consists of two separate chambers. The posterior chamber is formed by the articulation between the inferior posterior facet of the talus and the superior posterior facet of the calcaneus. It is also referred to as the talocalcaneal articulation (2, 11,13,22). The anterior chamber is formed by the articulation of the inferior articular facets of the talus with the superior articular facet(s) of the calcaneus. The floor of the anterior chamber is formed by the plantar calcaneo-navicular ligament. This ligament has a cartilaginous articular surface. The entire articulation is often referred to as the talocalcanealnavicular joint (2,11,13,22). The differentiation of the subtalarjoint into two separate articulations is preferred by anatomists. Orthopaedic surgeons consider the talocalcaneal joint and the talocalcaneonavicular joint to be one functional unit. This is due to the fact that these joints have a common axis of motion. Neither of these joints has movement independent of the other (13). It is helpful to be familiar with the specific characteristics of the three bones of the subtalar articulation. The talus (astralgus) is the second largest of the tarsal bones (2.12). The talus supports the tibia and rests upon the calcaneus. (2) It has been referred to as the mechanical keystone at the apex of the foot (1). More than one-half of the surface area of the talus is covered by articular hyaline cartilage (12). The talus consists of a body, a neck, and a head. The body has superior, inferior, medial, lateral, and posterior surfaces. The superior surface is termed the trochlea. It is covered by articular cartilage and articulates with the mortise of the ankle joint which is formed by the tibia and the fibula (2,22). It is wider anteriorly secondary to a lateral border, which inclines medially in the posterior aspect of the body. The trochlear surface is convex antero-posteriorly and concave medidaterally (22). The inferior, or plantar surface, rests on the dorsal surface of the calcaneus. Posteriorly, there is a large, oval, concave facet for articulation JOSPT Volume 21 Number 6 June 1995

2 FIGURE 1. Bones of the 1987 Ciba-Geigy Corporation. Reprinted with permission from Ciba-Geigy Corporation, illustrated by Frank H. Netter, MD. All rights reserved). with the calcaneus (2,22). This facet of the inferior surface of the body is just one of four facets along the inferior aspect of the talus (2,4,12,22). Some discrepancy can be found in various anatomical texts as to the middle facet being considered a part of the inferior surface of the talus or as a part of the head of the talus. The 29th American edition of Gray's Anatomy includes the small, middle facet in its discussion of the inferior surface of the talar body (2). The 35th British edition of Gray's Anatomy includes this slightly convex facet in its discussion of the head of the talus (22). Hall reports the middle facet as being a prolongation of the articular surface of the head of the talus (4). All three texts do agree the middle facet articulates with the facet on the sustentaculum tali of the calcaneus, and that the middle facet of the talus is separated from the posterior facet of the talus by a deep groove, the sulcus tali (2,4,22). The medial surface of the body of the talus is continuous superiorly with the trochlea. The upper part of this surface serves as a facet for articulation with the medial malleolus. The area below the facet is rough and pitted. It contains numerous vascular foramina and has a deep depression for attachment of the deltoid ligament (2,22). The lateral surface is also continuous with the trochlea. It presents a large triangular facet for articulation with the lateral malleolus (2,22). This articular surface is concave cranial to caudal. Inferiorly, the apex of the articular facet forms the lateral process of the talus (22). Anteriorly, there is a roughened area for the attachment of the anterior talofibular ligament. Another triangular facet exists between the posterior half of the lateral border of the trochlea and posterior aspect of the base of the fibular articular surface. This contacts the inferior tibiofibular ligament during flexion of the ankle joint. Inferior to this facet, there is a groove for attachment of the posterior talofibular ligament (2). The posterior surface of the talar body is narrow and rough and possesses a projection which is referred to as the posterior process. There is an oblique groove for passage of the tendon of the flexor hallucis longus. This groove is bordered by a lateral and medial tubercle. The lateral tubercle is large and gives attachment to the posterior talofibular ligament. The medial tubercle is less prominent and lies just behind the sustentaculum tali of the calcaneus (2,22). Occasionally, the entire posterior process is independent of the talus. When this occurs, it is referred to as the os trigonum (2). The neck of the talus is situated anterior to the talar body. It is set obliquely and inclines medially. This constricted portion of the talus connects the head and the body. The surfaces are roughened for ligamentous attachments. The medial aspect of the plantar surface is the sulcus tali, the deep groove anterior to the inferior and posterior calcaneal facet of the talus. This area is occupied by the interosseous talocalcaneal ligaments. The concave lateral surface is continuous with this deep groove (2, 22). The junction of the neck with the head of the talus is at the distal aspect of the bone (4). The anterior surface of the head is a large, oval, convex surface which articulates with the navicular (2,22). This articular surface is longer medially-laterally than it is superiorly-inferiorly. This surface does not extend onto the superior aspect of the talar neck (4). The entire head of the talus is directed distally and slightly inferiorly and medially (22). As discussed previously, the middle calcaneal facet of the talus is considered by some to be a part of the body while others consider it a part of the neck (2,4,22). In any event, this facet is oval in outline. It is slightly convex and articulates with the facet on the sustentaculum tali of the calcaneus (2,22). Volume 21 Number 6 June 1995 JOSPT

3 Anterior and lateral to the middle calcaneal facet of the talus is the anterior calcaneal facet of the talus. This flattened facet articulates with the facet on the antero-medial aspect of the superior surface of the calcaneus (2,22). Usually the anterior calcaneal facet of the talus is continuous with the middle calcaneal facet of the talus. The anterior calcaneal facet of the talus is continuous with the portion of the head of the talus which articulates with the navicular (22). Anterior and medial to the anterior and middle calcaneal facets of the talus is the fourth facet on the inferior aspect of the talus. It is a part of the head of the talus and is covered by articular hyaline cartilage. In one aspect, it is continuous with the anterior and middle calcaneal facets, and in the other, it is continuous with the navicular articular surface of the talus. This semi-oval facet articulates with the plantar calcaneonavicular ligament (2,22). The talus, quite obviously, articulates with the calcaneus. The calcaneus is the largest of the tarsal bones. The calcaneus provides firm, yet elastic, support for body weight as it is transferred to the tibia through the talus. The calcaneus also acts as a strong lever for the calf muscles by means of its backward projection beyond the bones of the leg (2,5,22). The calcaneus is cuboidal in shape and has six surfaces. The superior surface can be divided into an anterior and posterior portion. The size of each may vary (2). For explanatory purposes, the superior calcaneal surface will be identified as having an articular portion and a nonarticular portion. The articular portion is anterior and contains three facets which face proximally for articulation with the talus. The posterior talar facet of the calcaneus is the largest of the three. It is oval in outline and is convex antero-posteriorly. Just anterior to the posterior facet is a roughened area. It narrows and takes the form of a groove on the medial side of the su- JOSPT Volume 21 Number 6 June 1995 perior surface. This is the sulcus calcanei (1 1,22). The sulcus calcanei corresponds to the sulcus tali. In the articulated foot, these structures form the tarsal canal, or as some refer to it, the canalis tarsi (2,5,13,22). This is funnelshaped with a wide opening, the sinus tarsi, laterally. The narrow part of the funnel is located medially behind the sustentaculum tali and posterior to the medial malleolus. The tarsal canal carries blood vessels to and from the bone and provides attachment for the thick talocalcaneal interosseous ligament (2,5,13,22). This ligament serves as an anterior wall for the posterior chamber and a posterior wall for the anterior chamber of the subtalar joint (1 3). Anterior and medial to the sinus calcanei is a long articular surface which covers the superior surface of the sustentaculum tali. This surface extends forward and laterally onto the body of the bone. A common variation is the division of this articular surface into two smaller facets by a narrow, nonarticular groove. This groove corresponds to the anterior margin of the sustentaculum tali. If this division occurs, the distal facet is referred to as the anterior talar facet of the calcaneus (1 1,22). It is important to note that some anatomical texts refer to three facets on the superior surface of the calcaneus as being the rule and not the exception (2). The nonarticular posterior portion of the superior surface of the calcaneus is described by some as being rather smooth (22), while others report it is as being a roughened area (2). It is convex medio-laterally and is concave antero-posteriorly. It supports the mass of fibro-adipose tissue which separates the tendo calcaneus from the ankle joint (22). The inferior surface of the calcaneus is a roughened segment of the bone. Posteriorly, it is bounded by the calcaneal tuberosity, which consists of a lateral process and a medial process with a notch between them. These processes extend distally for a short distance. The lateral process is not as prominent as the medial process. The lateral process gives rise to a portion of the abductor digiti minimi. The medial process gives attachment to the abductor hallucis, the flexor digitorum brevis, and the plantar aponeurosis. The notch between these processes gives origin to the bulk of the abductor digiti minimi (2,22). A rough area anterior to the medial and lateral processes provides attachment for the long plantar ligament and the lateral head of the quadratus plantae. The plantar calcaneocuboid ligament attaches to the transverse groove anterior to the calcaneal tuberosity and to a prominent tubercle at the anterior part of the inferior surface (2). The medial surface of the calcaneus is deeply concave. The sustentaculum tali projects from the anterior part of the upper border of the medial surface. The superior aspect of the sustentaculum tali supports a facet for articulation with the talus. The inferior aspect of the sustentaculum tali contains a groove far the tendon of the flexor hallucis longus. This groove is continuous with the one present on the talus (2.22). The medial surface only has attachments of the quadratus plantae muscle, the plantar calcaneo-navicular ligament. and the deltoid ligament (2). The lateral surface of the calcaneus is broad, flat, and easily palpable. Near its center is the attachment of the calcaneo-fibular ligament. Just anterior to this is a small elevation, the peroneal trochlea. This is delineated by two oblique grooves. The superior groove transmits the tendon of the peroneus brevis muscle, and the inferior groove transmits the peroneus longus tendon (2,22). The posterior surface of the calcaneus is evident as the prominence of the heel. It can be divided into three areas. The superior portion is a smooth region which is separated from the tendo-calcaneus by a bursa. The middle portion is a roughened

4 area and receives the insertion of the tendocalcaneus and the plantaris. The inferior portion slopes inferiorly and anteriorly. It is rough and is covered by fatty fibrous tissue. This provides a subcutaneous weight-bearing surface (2,5,22). The anterior surface of the calcaneus is the smallest of the six surfaces. This entire surface provides a The anterior surface of the calcaneus is the smallest of the six surfaces. facet for articulation with the cuboid (2,4,22). The facet is a saddle-shaped joint which faces laterally. It is concave in the superior-inferior direction (4,22), broader superiorly than inferiorly (4.22). The medial border of the anterior surface provides attachment for the plantar calcaneo-navicular ligament (2). The navicular is the third bone involved in the talocalcaneo-navicular articulation. It is situated at the medial side of the tarsus between the talus and the three cuneiform bones (2). The proximal or posterior surface is concave and is shaped reciprocally to the surface of the head of the talus (4). The distal or anterior surface is subdivided into three facets for the articulations with the cuneiforms. The dorsal surface is convex and is roughened for ligamentous attachments. The medial surface is also rough and has a prominent tuberosity inferiorly. The plantar surface is concave and is roughened for ligamentous attachments. The plantar surface is separated from the tuberosity of the medial surface by a groove (2,22). There is a slight projection on the lateral side of the groove. This projection, along with the proximal aspect of the plantar surface, provides the plantar calcaneo-navicular FIGURE 2. Ligaments of ankle and tarsal 1987 Ciba-Geigy Corporation. Reprinted with permission from Ciba-Geigy Corporation, illustrated by Frank H. Netter, MD. All rights reserved). ligament with its distal attachment (22). The lateral surface is rough and irregular (2.22). It receives the attachment of the calcaneo-navicular portion of the bifurcated ligament (22). Occasionally, the lateral surface presents a facet for an articulation with the cuboid bone (2.22). Capsule and Ligaments The subtalar articulation consists of two joints (Figures 2 and 3) (17). The anterior chamber consists of the talocalcaneo-navicular joint. The posterior chamber consists of the talocalcaneal joint (2,22). The division between the chambers is made by the tarsal canal (1). The talocalcaneal joint is formed by the posterior calcaneal facet on the inferior surface of the talus and the posterior facet on the superior surface of the calcaneus (2). This is a discrete joint cavity which is surrounded by a fibrous capsule and synovial membrane that attach at the edges of the articular surfaces (4). The capsule is largely comprised of short fibers which split into distinct slips. There is only a weak fibrous connection between these slips. Various ligaments assist the capsule in uniting the talus and the calcaneus. Kapandji considers the main ligament of the talocalcaneal articulation to be the interosseous talocalcaneal ligament (1 1 ). It consists of two Volume 21 Number 6 June 1995 JOSPT

5 FIGURE 3. Tendon insertions and ligaments of sole of 1987 Ciba-Geigy Corporation. Reprinted with permission from Ciba-Geigy Corporation, illustrated by Frank H. Netter, MD. All rights reserved). strong fibrous bands which occupy the sinus tarsi. The anterior band attaches to the sinus calcanei just behind the anterior surface. It runs o b liquely superiorly, anteriorly, and laterally and inserts into the sinus tali at the inferior surface of the talar neck. This is just posterior to the articular facet of the talar head (1 1). The posterior band lies posterior to the anterior band. It attaches to the sinus calcanei just anterior to the superior posterior articular facet of the calcaneus. These thick fibers run obliquely superiorly, posteriorly, and laterally to insert into the sinus tali just anterior to the posterior inferior articular facet of the talus (1 1). These bands comprise a ligament which is actually a part of the united capsules of the talocalcanecmavicular joint and the talocalcaneal joint (2). They reinforce the joint capsule (4). This description of the interosseous ligament is similar to that by Jones (10). He states the true interosseous ligament occupies the sinus tarsi proper and is not situated in the canalis tarsi proper. The canal is bounded anteriorly and posteriorly by the articular capsules of the anterior and posterior talocalcaneal articulations. It is also occupied by some fatty tissue. Jones reports that the ligamentous tissue which occurs in the canalis tarsi is derived from the calcaneal attachment of the inferior extensor retinaculum (10). Smith differs from Jones, however, in that his description places the interosseous ligament in the canalis tarsi. He refers to it as the ligament of canalis tarsi. Smith also states this structure is distinct from the articular capsules in the tarsal canal. He also describes two other ligamentous structures, the inferior extensor retinaculum and the cervical ligament (21). The cervical ligament is lateral to the sinus tarsi and is attached to the upper surface of the calcaneus. It passes superiorly and medially to a tubercle on the inferior and lateral aspect of the neck of the talus (22). Hall states that some authors refer to these ligaments collectively as "the interosseous ligament" (4). Other ligaments binding the talus to the calcaneus have also been described. The lateral talocalcaneal ligament arises from the lateral tubercle of the talus and runs obliquely inferiorly and posteriorly to its attachment on the lateral surface of the calcaneus. The fibers run parallel and anterior to those of the calcanee fibular ligament (2.11,22). The posterior talocalcaneal ligament connects the lateral tubercle of the talus with the proximal and medial portion of the calcaneus. This is a thin and fibrous band (2,ll). A medial talocalcaneal ligament has also been described. It connects the medial tubercle of the talus with the calcaneus at the posterior aspect of the sustentaculum tali and at the medial surface (2.22). Some authors report the fibers blend with those of the plantar calcanecmavicular ligament (2), while others note the fibers blend with those of the deltoid ligament (22). The most posterior fibers line the groove for the tendon of the flexor hallucis longus muscle between the talus and the calcaneus (22). The talocalcane~navicular joint is in the anterior chamber of the subtalar joint. The anterior aspect of the talar head articulates with the proxi- JOSPT Volume 21 Number 6 June 1995

6 ma1 navicular surface. The inferior aspect of the talar head articulates with the facets on the sustentaculum tali of the calcaneus, and it also rests on the articular surface of the plantar calcaneo-navicular ligament (4). The bones of this articulation are connected by the fibrous capsule, the talonavicular ligament, the plantar calcaneo-navicular ligament, and the calcaneo-navicular portion of the bifurcated ligament (22). The articular capsule is imperfectly developed, except posteriorly. Here it is considerably thickened and, along with the capsule of the talocalcaneal joint, forms the interosseous ligament of the sinus tarsi. The dorsal reinforcement of the cap sule is the talonavicular ligament. It is a broad thin band which connects the neck of the talus to the dorsal surface of the navicular. Extensor tendons lie superior to this ligament (222). The plantar ligament for this articulation is the plantar calcaneonavicular ligament. This is often referred to as the "spring ligament." It is a broad thick band which connects the anterior margin of the sustentaculum tali of the calcaneus to the plantar surface of the navicular. The dorsal surface has a triangular portion of fibrocartilage upon which a portion of the talar head rests. The plantar surface is supported by the tendons of the tibialis posterior muscle medially and of the flexor hallucis longus and flexor digitorum muscles laterally. The medial border of this ligament blends with the superficial fibers of the deltoid ligament of the ankle joint (22). The lateral ligament for the anterior chamber is the calcaneo-navicular portion of the bifurcated ligament. The bifurcated ligament is a strong band which originates from the anterior surface of the calcaneus and divides anteriorly into the calcaneocuboid portion and the calcaneonavicular portion (22). The calcaneocuboid portion lies in the horizontal plane and attaches to the dorsal as- FIGURE 4. Muscles, arteries, and nerves of leg: 1987 Ciba-Geigy Corporation. Reprinted with permission from Ciba-Geigy Corporation, illustrated by Frank H. Netter, MD. All rights reserved). pect of the cuboid. The calcaneonavicular portion lies in the vertical plane and attaches to the lateral aspect of the navicular. This orientation results in the bifurcated ligament being referred to as the "Yshapedw ligament (1 1). Muscles The talus is freely situated between the proximal ankle mortise and the distal tarsal bones (Figures 3-6) (17). Muscles of the leg and foot cross it but do not insert onto it (13). Even though the tendon, the flexor hallucis longus, traverses the posterior talar tubercle, it gives off no attachment and is held in the groove by a retinacular ligament (12). Subsequently, the talus cannot move alone and must follow the motions of the other bones. The subtalar joint motions are linked to the ankle joint motions and to the midtarsal joint motions (13). For this reason, a discussion of the anatomical location of the muscles which act on the subtalar joint entails a description of the foot muscles in general. It should be noted that the actions of the muscles of the foot are dependent on: I) their relationship to the joint axes; 2) their distance from the axes; 3) their relative strength; and 4) the weight-bearing status of the body. This discussion will focus on the relationship of the muscle to the axis of motion. The foot muscles can be divided into two categories. The extrinsic muscles have an attachment away from the foot complex. The intrinsics attach entirely within the foot complex (1). The intrinsic muscles do not cross the subtalar joint but their description will be included as the calcaneus does serve as an attachment. The intrinsic muscles of the foot consist of one muscle on the dorsal surface and four layers of muscles on the plantar surface. The dorsal muscle is the extensor digitorum brevis. It attaches to the distal and lateral surface of the calcaneus, to the proximal phalanx of the great toe, and to the lateral aspect of the extensor Volume 21 Number 6 June 1995 JOSPT

7 FIGURE 5. Muscles, arteries, and nerves of leg: deep, 1987 Ciba-Geigy Corporation. Reprinted with permission from Ciba-Geigy Corporation, illustrated by Frank H. Nener, MD. All rights reserved). digitorum longus tendon of toes two, three, and four (2,22). The superficial layer of muscles of the plantar surface of the foot is the abductor hallucis, the flexor digitorum brevis, and abductor digiti minimi. The bony attachments of the abductor hallucis are the medial pre cess of the tuberosity of the calcaneus and the medial side of the base of the first phalanx of the great toe. The flexor digitorum brevis also attaches to the medial process of the calcaneal tuberosity. Its distal attachment is to the second phalanx of each of the four small toes. The calcaneal insertion of the abductor digiti minimi is multiple. It includes the JOSPT Volume 21 Number 6 June 1995 lateral process of the calcaneal tuberosity, the plantar calcaneal surface between the medial and lateral process, and the distal aspect of the medial process of the calcaneal tuberosity. Distally, it attaches to the lateral aspect of the base of the first phalanx of the small toe (2,22). The second layer of plantar muscles consists of the quadratus plantae (flexor digitorum accessorius) and the lumbricales. The quadratus plantae has two proximal attachments to the calcaneus. The medial head is attached to the medial concave surface of the calcaneus. The lateral head attaches to the lateral border of the plantar calcaneal surface. Distally, these heads unite and attach to the tendon of the flexor digitorum longus. The lumbricales are actually four small muscles which attach to the tendons of the flexor digitorum longus and to the dorsal expansion of all the proximal phalanges (2,22). The flexor hallucis brevis, the abductor hallucis, and the flexor digiti minimi brevis comprise the third layer of intrinsics. The bony attachments of the flexor hallucis brevis are the medial aspect of the plantar surface of the cuboid, the adjacent portion of the lateral cuneiform, and the medial and lateral border of the first phalanx. Each portion of the distal tendon contains a sesamoid bone (2922). The abductor hallucis has two heads. The oblique head attaches to the bases of the second, third, and fourth metatarsals. Its distal attachments are to the lateral sesamoid and the base of the first phalanx of the hallux. The flexor digiti minimi brevis attaches to the base of the fifth metatarsal bone proximally and to the base of the first phalanx of the small toe (2,22). The fourth and deepest layer of the intrinsic muscles is formed by the dorsal and plantar interossei. There are four dorsal interossei. Proximally, each attaches to adjacent sides of the metatarsal bones between which it is located. Distally, the tendons of these muscles attach to the base of the first phalanges. The first dorsal interossei attaches to the medial side of the second toe, while the other three attach to the lateral sides of toes three, four, and five, respectively. The plantar interossei, three in number, lie below the metatarsal bones. Proximally, they attach to the baqes and medial sides of the third, fourth, and fifth metatarsal bones. Distally, they attach to the bases of the first phalanges of the same toes (2,22). Essentially, the individual actions of the intrinsic muscles can be postulated from an analysis of their attachments. Their action as a group is illdefined (22). Cailliet states the

8 FIGURE 6. Muscles, arteries, and nerves of leg: 1987 Ciba-Geigy Corporation. Reprinted with permission from Ciba-Geigy Corporation, illustrated by Frank H. Nefter, MD. All rights reserved). muscles of the sole of the foot are primarily responsible for "cupping" the sole of the foot (1). Perhaps this is too simplistic and more research is warranted. The extrinsic muscles of the foot are better understood. The extrinsics act on the foot-ankle complex. This includes the subtalar joint. The following discussion will present a description of the attachments. The extrinsic muscles can be divided into three groups: the anterior group, the lateral group, and the posterior group. The anterior group includes the extensor digitorum Iongus, the peroneus tertius, the extensor hallucis longus, and the tibialis anterior (1). The proximal attachment of the tibialis anterior is the lateral condyle and upper one-half to two-thirds of the lateral surface of the tibia. Its distal tendinous attachment is to the medial and plantar surface of the first cuneiform and to the base of the first metatarsal bone (2.22). Proximally, the bony attachment of the extensor hallucis longus is the middle two-fourths of the fibula. Dis- tally, its tendon is received by the dorsal aspect of the base of the distal phalanx of the great toe. This muscle is deep to the tibialis anterior and to the extensor digitorum longus (2.22). The extensor digitorum longus attaches proximally to the lateral condyle of the tibia and to the upper three-fourths of the medial surface of the fibula. The fibers descend distally where its tendinous expansion splits into four parts. These tendons insert into the second and third phalanges of the four lesser toes. The peroneus tertius is actually a fifth tendon of the extensor digitorum longus. It arises from the distal one-third of the anterior surface of the fibula and inserts distally on the dorsal surface of the base of the first metatarsal bone (2.22). The lateral group of the extrinsic muscles of the foot is comprised of the peroneus brevis and the peroneus longus. The peroneus longus is more superficial. Proximally, its main bony attachment is the head and the upper two-thirds of the lateral surface of the body of the fibula. Its tendon to the lateral malleotly anteriorly to the n passes medially be- ~f the foot. It inserts ipect of the base of sal bone. The belly of ngus muscle covers,evis. The peroneus bony attachment is irds of the lateral ody of the fibula (2, >r group of muscles nto a superficial 3p group. The memrficial group are the :he soleus, and the astrocnemius and solmon distal bony at- :ndo calcaneus. The inserts into the mid- ~osterior surface of the calcaneus. ~roximall~, the medial and lateral heads of the gastrocnemius arise from the posterior aspects of the respective femoral condyles. The soleus lies beneath the gastrocnemius. Its proximal bony attachments are the posterior surface of the fibular head, the proximal one-third of the posterior surface of the fibular body, and from the middle third of the medial border of the tibia. Together the gastrocnemius and the soleus are referred to as the triceps surae (2,22). The plantaris muscle lies between the gastrocnemius and the soleus. Its proximal bony attachment is the lateral part of the supracondylar line of the femur. Its long tendon crosses between the gastrocnemius and the soleus and runs along the medial border of the tendo calcaneus. The plantaris tendon inserts on the posterior part of the calcaneus. Occasionally this muscle occurs in duplicate or is absent (2.22). The deep layer of the posterior group consists of the flexor hallucis longus, the flexor digitorum longus, and the tibialis posterior. The flexor hallucis longus attaches to the lower two-thirds of the posterior surface of the body of the fibula proximally. Its Volume 21 Number 6 June 1995 JOSPT

9 tendon lies in a groove which crosses the posterior surface of the distal end of the tibia, the posterior surface of the talus, and the undersurface of the sustentaculum tali. Distally, it inserts into the base of the terminal phalanx of the great toe (2,22). The flexor digitorum longus arises from the posterior view of the body of the tibia from just inferior to the popliteal line to approximately 7-8 cm above the end of the bone. The tendon passes behind the medial malleolus in a groove it shares with the tibialis posterior. Distally, the main tendon splits into four smaller tendons. After passing through a corresponding hole in the flexor digit* rum brevis, each tendon inserts into the bases of the distal phalanges of the second, third, fourth, and fifth toes (2,22). The tibialis posterior lies between the flexor hallucis longus and the flexor digitorum longus. The proximal bony attachments are an area on the posterior surface of the tibia (inferior to the popliteal line and superior to the lower one-third of the bone) and a medial segment on the upper two-thirds of the posterior surface of the fibula (2,22). The tendon passes behind the medial malleolus and anterior to the flexor digitorum longus. Distally, this tendon inserts into the tuberosity of the navicular. This often gives off fibrous expansions to the sustentaculum tali, the three cuneiforms, the cuboid, and the bases of the second, third, and fourth metatarsal bones (2). Vascular Supply The subtalar joint region has an extraosseous and an intraosseus arterial supply (Figures 4-6) (17). The extraosseus supply is derived from three main arteries. These are the posterior tibial artery, the anterior tibial artery, and the peroneal artery. The anterior tibial artery usually becomes the dorsalis pedis artery at the ankle joint (16,18). The anterior and posterior tibial arteries are extensions JOSPT Volume 21 Number 6 June 1995 of the popliteal artery. The peroneal artery arises from the posterior tibial artery (22). The posterior tibial artery branches before and after its passage beneath the medial malleolus. These anastornose with branches from the anterior tibial artery and the peroneal artery. Approximately 2 cm distal the medial malleolus, the posterior tibial artery gives off a branch, the artery of the tarsal canal. This artery passes in an anterolateral-posteromedial direction (18). It passes anteriorly between the sheaths of the flexor digitorum longus and the flexor hallucis longus to enter the tarsal canal. It lies in the dorsal part of the tarsal canal and is closer to the talus than it is to the calcaneus. Within the canal, the artery gives off a large branch which enters the middle of the talar body and a few small branches which enter the calcaneus. It also anastomoses with the artery of the sinus tarsi within the tarsal canal (16). Before entering the tarsal canal, the artery of the tarsal canal gives off a branch which runs anterior between the talotibial and the talocalcaneal components of the deltoid ligament. This deltoid branch supplies the medial periosteal surface of the talus and anastomoses with branches of the dorsalis pedis artery over the neck of the talus (1 6). Peterson et al describe this deltoid branch slightly different (18). They report division into two branches shortly after its origin. One of these branches penetrates the deltoid ligament and enters the medial part of the body of the talus. The other branch runs anterior and further divides into many branches. One of these branches enters the talus and the others form an anastornotic network with the vessels of the anterior tibial artery (18). These medial vessels of the anterior tibial artery are two in number. There are also two lateral branches of the anterior tibial artery and dorsalis pedis artery. The distal lateral.branch originates from the dorsalis pedis artery and is referred to as the lateral tarsal artery. This anastomoses with the perforating peroneal artery and then passes through the tibiofibular interosseous membrane. From this, the artery of the sinus tarsi arises. This passes medially into the sinus tarsi (18). The lateral tarsal artery may give direct branches to the head of the talus and to the lateral anterior aspect of the body of the talus (16). Also, the dorsalis pedis artery may give off direct branches to the nutrient foramina of the neck of the talus (18). The peroneal artery has many branches posteriorly which anaste mose with branches of the posterior tibial artery (16,18). Some branches of this anastomosis run to the posterior process of the talus and enter the bone. Others run more distally and enter the calcaneus (18). The peroneal artery also branches in the interosseous membrane of the tibia and fibula. This branch is referred to as the perforating peroneal artery. This artery contributes to the plexus of the sinus tarsi (16.18). The intraosseus arteria! pattern centers around the talus. The talus appears to be in a center of a large vascular network ( 18). The talar head is supplied from two sources. The medial superior half receives a branch from the dorsalis pedis artery. The lateral inferior half is supplied by the artery of the tarsal sinus, by branches of the sinus tarsi anastome sis, or from branches of the lateral tarsal artery ( 16). The main vascular supply of the body of the talus is from the anastomotic artery in the tarsal canal and the branches of the dorsalis pedis artery (16,18). The talar body also receives some vascular supply from the deltoid branch of the artery of the tarsal canal. Also, the posterior surface of the talus receives many small branches from the anastomosis in the posterior tubercle region (16). The calcaneus and navicular have a rich vascular connection with the talus by means of the interosseous

10 ligament. and the joint capsules. There is also a vascular connection between the tibia and the talus by the capsule and ligament. which join the two bones (18). The arterial supply of this region is large. Subtalar Joint Axis\ h ANTERIOR I Ilongitudinal Axis of Foot The calcaneus and navicular have a rich vascular connection with the talus by means of the in terosseous ligaments and the joint capsules. - - The venous return of the foot and leg is also great and accompanies the arteries and their branches. There are plantar digital veins which originate from the plexus of the plantar surfaces of the digits. After communicating with the dorsal digital veins, they unite to form the metatarsal veins. These veins run proximally along the metatarsal spaces and join each other to form the deep plantar venous arch. The medial and lateral plantar veins arise from this arch. These two veins ana..tomose with the great and small saphenous veins. They unite posterior to the medial malleolus and form the posterior tib ial veins (2,22). The posterior tibial veins accompany the posterior tibial artery and its branches. The peroneal veins join the posterior tibial veins. Ultimately, the posterior tibial veins join the anterior tibial veins. The anterior tibial veins are the proximal portions of the veins of the dorsalis pedis artery. This juncture at the lower border of the popliteus forms the popliteal vein (2,22). Such an anastomotic venous and arterial network provides the subtalar joint region with a rich vascular supply. MEDIAL Tibialis Anterior Tertius LATERAL Tibialis Talocrural Posterior Flexor Flexor Peroneus Longus Hallucis Longus Triceps I Surae POSTERIOR \ FIGURE 7. The subtalar axis of motion and the relationship of the distal insertion of the subtalar muscb to the axis o( motion. MOTION AT THE SUBTALAR JOINT Axis of Motion The subtalar joint is rather complicated when one considers its descriptive anatomy (Figure 7). As discussed, it is comprised of three articulations between the talus and the calcaneus. The posterior articulation occurs between a convex calcaneal facet and a concave talar facet. The middle and anterior articulations occur between convex talar surfaces and concave calcaneal surfaces (15). Functionally, these three articulations act as a single unit and move about a single joint axis (15). This axis of motion passes obliquely from a posterior, plantar, and lateral position to an anterior, dorsal, and medial position (6,7,8,14,19,20,21). From studies on 16 cadaver speci- mens, Manter reports the axis inclines 42" from the horizontal plane and 16" from a sagittal plane through the heel to the space between the first and second toes (14). He notes a range of 8-24" for the angulation from the sagittal plane and a range of 29-47" for the inclination from the horizontal plane (14). Isman and Inman report similar findings from their measurements on 46 cadaver feet (9). However, they found a wider range of individual variation. They note the range for deviation from the horizontal plane to be 20-68" while the deviation from the sagittal plane ranged from 4 to 47" (9). Although this wide variation is noted, other authors also describe the subtalar joint axis as being 42" from the horizontal plane and 16" from the sagittal plane (3,19,20). Volume 21 Number 6 June 1995 JOSFT

11 Specific Motions Motion at the subtalar joint occurs in a single plane perpendicular to the axis (19,20). Since the subtalar joint axis is oblique and consists of an antero-posterior component, a vertical component, and a transverse component, the plane of motion does not correspond to any cardinal body plane (1 l,l3,19,20). The angulation with all three body planes results in triplanar motion (19.20). Movement in the frontal plane occurs about the longitudinal/sagittal component of the axis. These motions are referred to as inversion or eversion (1.13). Inversion is the motion which elevates the medial border of the foot and depresses the lateral border of the foot. Eversion consists of elevation of the lateral border and depression of the medial border of the foot (1). It is important to note that much confusion exists regarding this terminology. Many texts refer to inversioneversion as supination-pronation, respectively (2,11,22). Movement in the transverse plane occurs about the vertical component of the axis. These movements are referred to as abduction or adduction. Abduction is an outward rotation of the foot, and adduction is an inward rotation of the foot (1). The movement in the sagittal plane occurs about the frontal plane component of the axis and is dorsiflexion/plantar flexion (1). Dorsiflexion is the movement in which the foot is elevated so the dorsum of the foot approaches the anterior aspect of the leg. Plantar flexion consists of lowering the foot so the dorsal surface moves away from the anterior aspect of the leg (22). The motions in the three planes occur simultaneously upon movement of the subtalar joint. The resultant triplanar motion is referred to as either pronation or supination. Pronation consists of eversion, abduction, and dorsiflexion. Supination consists of inversion, adduction, and plantar flexion. According to Root et JOSFT Volume 21 Number 6 June 1995 al, there exists a neutral position in the normal foot in which the subtalar joint is neither supinated nor pronated. From this position, two-thirds of the frontal plane movement is inversion and one-third is eversion. This two-to-one ratio of supination-to-pronation is considered "normal" (19, 20). No clinical method of measuring the range of supination and pronation has been devised. The measurement which is utilized is a goniometric measure of the degree of calcaneal inversion or eversion with respect to the longitudinal axis of the leg. Normal locomotion requires an average minimum range of 4-6" of calcaneal inversion and 4-6" of calcaneal eversion. An inadequate available range will result in an abnormal gait pattern and dysfunction (19.20). Obviously, movement at the sub talar joint can occur in the weightbearing as well as nonweight-bearing position. The movements of the talus and calcaneus varies according to the weight-bearing state. The motion which occurs during nonweight-bearing is termed open chain movement. The calcaneus moves in all three body planes, and the talus does not move. Open chain supination consists of calcaneal inversion, adduction, and plantar flexion. Open chain pronation consists of calcaneal eversion, abduction, and dorsiflexion (19,20). Weight-bearing movement at the subtalar joint is referred to as closed chain motion. Due to ground reaction forces, the calcaneus moves in the frontal plane, and the talus moves in the transverse and sagittal planes. Closed chain supination consists of calcaneal inversion and talar dorsiflexion and abduction. Closed chain pronation consists of calcaneal eversion and talar plantar flexion and adduction (l9,2o). The movements of the subtalar joint are a key element in the relationship between the leg, the ankle joint, and the distal articulations of the foot. The leg internally rotates 'during the first one-third of the gait cycle and externally rotates during the remaining two-thirds. The average amount of tibia1 rotation is 19" with a range of 13-25" (8). The obliquity of the ankle joint transmits a portion of this rotation by permitting abduction of the foot with dorsiflexion and adduction of the foot with plantar flexion. However, at a maximum, the ankle joint can only account for 1 lo of rotation. Therefore, the subtalar joint must accommodate the additional rotation (8). For this reason, Inman (7) and Inman and Mann (8) refer to the subtalar joint as a "mitered hinge" connecting the leg to the foot. Transverse motion of the talus imparts rotation to the tibia and vice versa. This only takes place during weight bearing as the talus does not move during open chain motion. The talar abduction during closed chain supination causes external rotation of the tibia. Likewise, the talar adduction of closed chain pronation imparts internal rotation to the tibia (7,8,19,20). The tibia also follows the sagittal plane movement of the talus. The talus dorsiflexes during closed chain supination and moves the proximal aspect of the tibia posteriorly. In closed chain pronation, the talar plantar flexion causes an anterior movement of the proximal tibia (19, 20). In essence, the talus is an extension of the tibia in the sagittal and transverse planes (7). Actions of the Muscles The orientation of the tendons of the extrinsic muscles to the subtalar joint determines the movements the muscles are capable of producing. Figure 7 illustrates the position of the various muscles with respect to the subtalar axis, the talocrural axis, and the longitudinal axis of the foot. One can visualize from this diagram which muscles would produce supination and pronation. Essentially, the muscles medial to the subtalar joint axis are supinators

12 of the subtalar joint, and the muscles lateral to it are pronators (19). As a review, the following brief discussion of the action of each extrinsic muscle is presented. The extensor hallucis longus tendon is nearly parallel to the subtalar joint axis. For this reason, it imparts no pronatory nor supinatory action on the subtalar joint. Dorsiflexion of the foot occurs in the neutral position (19). The tibialis anterior muscle is a weak supinator. This "weakness" is due to the tendon's proximity to the subtalar axis. The small distance provides this muscle with only a small lever arm for movement. In contrast, the tibialis posterior lever arm is rather great. Subsequently, it can exert a strong supinatory force upon the subtalar joint (19). The flexor hallucis longus and flexor digitorum longus muscles are also supinators of the subtalar joint. However, they differ in that the flexor hallucis longus is a weak supinator while the flexor digitorum longus muscle can exert an average degree of force on the subtalar joint secondary to its long lever arm. Ironically, the lever arm of the flexor hallucis is also very long. However, it passes the subtalar joint axis at an angle less than perpendicular, resulting in decreased efficiency (19). The triceps surae group also supinates the subtalar joint a. their distal insertion passes medial to the axis of motion. The soleus has a significant lever arm to develop supination force (19). The muscles lateral to the subtalar joint axis are the pronators of the joint. The muscles in the antero-latera1 aspect are the extensor digitorum longus and peroneus tertius. The lever arm of the extensor digitorum longus is significant. The peroneus tertius is a synergist of this muscle (19). The muscles of the postero-latera1 aspect are the peroneus longus and brevis. The peroneus longus passes posterior to the lateral malleolus and inferior to the peroneal tubercle. The distance between the tendon and the axis is large. This lever arm gives this muscle its capability to produce a pronation force. Similarly, the lever arm of the peroneus is also long. This muscle is a strong pronator of the subtalar joint (19). CONCLUSION The subtalar joint is a complex articulation in both its structure and function. The orthopaedic and sports physical therapist must be familiar with these areas to better understand the rationale for examination and treatment procedures. JOSFT ACKNOWLEDGMENT The author extends his appreciation to Mildred Wood, PhD, PT for her assistance in gaining a better understanding of the subtalar joint region. REFERENCES Cailliet R: Foot and Ankle Pain, Philadelphia: F.A. Davis Company, 1968 Goss CM (4: Gray's Anatomy (29th Am Ed), Philadelphia: Lea & Febiger, 1973 Green OR, Whitney AK, Walters P: Subtalar joint motion. J Am Podiatr Assoc 69(1):83-91, 1979 Hall MC: The Locomotor System: Functional Anatomy, Springfield, IL : Charles C. Thomas Publishers, 1965 Harty M: Anatomic considerations in injuries of the calcaneus. Orthop Clin North Am 4(1): , 1973 Hicks JH: The mechanics of the foot. I. The Joints. J Anat 87: , 1953 lnman VT: The Joints of the Ankle, Baltimore: Williams & Wilkins, 1976 lnman VT, Mann RA: Biomechanics of the foot and ankle. In: Mann RA (ed), DuVries' Surgery of the Foot (4th Ed), St. Louis: C. V. Mosby Company, 1978 Isman RE, lnman VT: Anthropometric studies of the human foot and ankle. In: lnman VT (41, The Joints of the Ankle, Baltimore: Williams & Wilkins, 1976 Jones FW: The talo-calcaneal articulation. Lancet 8: ?, 1944 Kapandji IA: The Physiology of the Joints (2nd Ed), New York: Churchill Livingstone Inc., 1970 Kleiger B, Ahmed M: Injuries of the talus and its joints. Clin Orthop 121: , 1976 Lapidus PW: Subtalar joint, its anatomy and mechanics. Bull Hosp Jt Dis 16: , 1955 Manter IT: Movements of the subtalar and transverse tarsal joints. Anat Rec 80(4): , Morris J: Biomechanics of the Foot and Ankle. Clin Orthop 122:lO-17, 1977 Mu finger GL, Trueta J: The blood supply of the talus. J Bone Joint Suq 52B(1):16O-167, 1970 Netter FH: The Ciba Collection of Medical Illustrations (Volume 8). Musculoskeletal System. Part I. Anatomy, Ph ysiology, and Metabolic Disorders. Summit, NJ: Ciba-Geigy Corporation, 1987 Peterson L, Goldie IF, Lindell D: The arterial supply of the talus. Acta Orthop Scand 45: , Root ML, Orien WP, Weed JH: Normal and Abnormal Function of the Foot, Los Angeles, CA: Clinical Biomechanics Corporation, 1977 Root ML, Orien WP, WeedJH, Hughes RJ: Biomechanical Examination of the Foot, Los Angeles, CA: Clinical Biomechanics Corporation, 1971 Smith JW: The ligamentous structures in the canalis and sinus tarsi. J Anat 92(4): , Warwick R, Williams P (eds): Gray's Anatomy (35th Br Ed), Philadelphia: W.B. Saunders Company, 1973 Volume 21 Number 6 June 1W5 JOSPT