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The subtalar joint and rheumatoid arthritis
4 The subtalar joint and rheumatoid arthritis L. S M I D T
In recent years, with the increasing understanding of functional anatomy and biomechanics of the lower limb, the importance of the subtalar joint is becoming clearer. It is at the subtalar joint that pronation and supination occur and in the normal well functioning foot it is this joint which is primarily responsible for minimizing stress factors in the hindfoot at, and immediately following heel strike in the gait cycle. ANATOMY OF THE SUBTALAR JOINT The talus articulates with the calcaneum at two points, each having its own joint capsule. The talocalcaneo-navicular articulation is the anterior of the two articulations and is partly between the head of the talus and the anterior and middle articular facets of the calcaneum. The talocalcaneal joint, posteriorly, lies between the inferior surface of the body of the talus and the posterior articular surface of the calcaneum. Pronation and supination occur at the subtalar joint about an oblique axis. This is therefore a triplane movement occurring simultaneously about all three body planes. The axis inclines from the posterior-plantar-lateral to the anterior-dorsal-medial (Figure 1). The movements which occur about the subtalar joint are eversion, abduction and dorsiflexion in relation to the pronatory capabilities of the joint (Figure 2) and conversely inversion, adduction and plantarflexion in relation to the supinatory capabilities of the joint (Figure 3). EXAMINATION OF THE S U B T A L A R JOINT
In order to undertake an examination of the subtalar joint it is necessary to establish the neutral position of the joint. This is best undertaken with the patient in the prone position, lying on a flat examination couch with the feet extended beyond the surface of the couch. Grasp the head of the talus between thumb and forefinger of one hand and holding the foot with the other in a slightly plantarflexed position, move the foot from inversion to eversion until you establish that the head of talus is in a central position with Bailli~re's Clinical Rheurnatology--Vol. 1, No. 2, August1987
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L. SMIDT
16 ~ Figure 1. Diagram to show the axis of the subtaloid joint. All movement of the joint occurs around this triplanal axis.
the margins of the bone equal between your thumb and forefinger. This is the neutral position and the foot is either in pronation or supination. Avoiding the skin overlying the achilles tendon, bisect the lower leg in two or three positions. These points should be connected with a line drawn, using a straight edge, to a position on tl~e posterior aspect of the calcaneum. The calcaneum should be similarly bisected and a line drawn between the points to connect with the line previously drawn. It is important to use the bony margins of the calcaneum and not the soft tissue. The two lines drawn will form an angle, with the foot held in the neutral subtalar position. This angle in normal feet will be between 3-5 degrees of varus (Figure 4).
/~
/
. .
"~ 9 3. Dorsiflexio~nCf/~..2 ~Evelsi~ ~ 3 " D~176 ~/~\'/'A~ ~
2.Abduction ~ Pronation
version Medial
Figure 2. Two diagrams to show the triplane movement of pronation at the subtaloid joint. (a) Anterior view. (b) Posterior view.
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THE SUBTALAR JOINT AND RHEUMATOID ARTHRITIS
~L ~
J ~
Inversion
\
2. Adduction
k~. Lateral
~i
3. Plantar flexion 1. Inversion
~
W Plantar IV" flexion
Adduetion Figure 3. Two diagrams to show the triplane m o v e m e n t s of supination. (a) Anterior view. (b) Posterior view.
The subtalar joint basically functions as a hinge joint and since the axis is oblique and lies relatively close to the sagittal plane (+ 16~ the relative amount of dorsiflexion/plantarflexion is small compared with the amount Of eversion/inversion and abduction/adduction (the axis is inclined at 42 ~ from the transverse plane. In the normal subtalar joint, there should be a smooth gentle quality to the range of movement which will allow greater supination than pronation by a factor of two to one.
Leg bisection
Lateral
La
,I bisection
3-5 ~
Varus Figure 4. Diagram to show the normal varus angle of the calcaneus to the leg bisection with the foot in neutral.
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L. SMIOT
THE RHEUMATOID PROCESS
The subtalar joint, bounded by the talus, calcaneum and navicular is commonly affected by rheumatoid disease resulting in synovitis in the sinus tarsi, in the subtalar joint itself and tenosynovitis in the surrounding and adjacent tendons. It is suggested that rheumatoid synovitis is linked with the presence of immune complexes which trigger the complement system and thus cause phagocytic polymorphonuclear leucocytes to migrate into the joint. The phagocytic action of these polymorphonuclear leucocytes causes the release of lysosomal enzymes leading to an inflammatory response and synovitis. The synovium proliferates as granulation tissue which is known as pannus. This pannus which is a villous, boggy mass becomes fixed to the cartilage. By further enzymatic action the pannus penetrates and invades the cartilage and underlying bone and produces characteristic rheumatoid erosions. As a result of these inflammatory changes the joint is swollen and becomes damaged or even destroyed by the erosive effects of the rheumatoid disease. These effects are accompanied by the synovitis, and of cellulitis, fasciitis and tendinitis and often lead to adhesions between the joint surfaces and consequently secondary osteoarthrosis. Although the majority of patients with rheumatoid disease will have inflammatory synovitis of the subtalar joint and will have pain to a variable degree, relatively few will exhibit significant malalignment of the foot on the leg in the early stages of the disease. However, it is rare to find a patient who has had rheumatoid arthritis for five years or more who does not present with severe and significant hindfoot malalignment. In the presence of inflammatory joint disease, the peri-articular cartilage is extremely liable to degenerative change as a result of the pannus described earlier but also because of the vertical an~t shear forces that occur during gait which tend to further weaken the collagen fibres and thereby allow enzymatic degeneration to occur more readily leading to greater fragility of the cartilage allowing it to be more readily deformed by continuing stress and in effect creating a self-perpetuating vicious circle. Eventually the bone itself becomes affected and erosive changes become apparent. Specifically in the subtalar joint there is an increased stress occurring as a result of the loss of the ability in the structures to absorb shock. Therefore, in gait, each time the foot contacts the ground and moves through its range of motion the ligamentous structures, now weakened, are unable to prevent increased supinatory and pronatory effects. With increased pronation the effects on and remote from the foot become increasingly apparent (Figure
5).
The foot itself, in pronation, will be taking on an increased abnormal load on the medial side of the forefoot. The first toe and first metatarsal, in an attempt to stabilize the foot in weight-bearing will take greater load and stress. The metatarsal will attempt to stabilize the medial longitudinal arch resulting in an apparent varus position on forefoot loading. The consequent effects on the great toe are medial rotation and valgus positioning. This is partly to accommodate the position of the first metatarsal and partly to aid
279
THE SUBTALAR JOINT AN D RHEUMATOID ARTHRITIS
~ody stress
Directi of stre
Figure 5. Diagram to show the direction of the lines of stress on the ligamentous structures of the foot.
the stabilization of the first ray in response to the medial 'rolling' effect of the pronating foot. As a result of this, the weight-bearing function of the forefoot becomes altered and is referred to elsewhere in this book. As the foot pronates to a greater degree, the clinician can observe that the patients' shoes become misshapen on the medial side at the margin of the heel counter which will bulge outwards and overhang the heel of the shoe. The lateral margin of the heel becomes excessively worn as a result of the abnormal heel strike position. The forepart of the shoe is also diagnostically important and in its distortion follows, as one would expect, the shape of the foot. The shoe therefore has the following appearance (Figure 6). The Achilles tendon when viewed from behind will bow medially above the insertion into the calcaneum; the inner longitudinal arch appears lowered and the lateral border of the foot bears little, if any, weight. This subtalar pronation which results in eversion, abduction and dorsiflexion causes the leg above the foot to follow the imaginary line drawn through the leg. The medial side of the knee joint is now subjected to considerably increased stress. As the knee moves medially, so the femur is pulled with it through the knee joint to a position lateral to it. This further exacerbates the forces on the knee resulting in an increased likelihood of
280
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SMIDT
b Laces drawn diagonally with foot deformity
nana shoe'
Medial bulging
Figure 6. Diagram to show a badly damaged shoe resulting from the extremes of force applied to it by the pronated foot. (a) Posterior view of a badly deformed shoe from a child with an excessively pronated foot. (b) A 'banana shoe'.
Stress within the knee joint as torsion is set up within the joint. Increased compression occurs on the medial side of the joint.
Excessively pronated foot
Figure 7. Diagram to show how excessive pronation leads to increased trauma in the knee joint.
THE SUBTALAR JOINT AND RHEUMATOID ARTHRITIS
281
greater deformity (Figure 7). The degree of deformity at the subtalar joint may only be of a relatively minor nature being only one or two degrees. This will result in considerable force on the knee joint being approximately 50 cm remote from the subtalar joint and still greater stresses will arise in the hip joint as a result of similar phenomena. The distance from the foot to the hip being that much greater will result in stress of larger magnitude. As the foot progresses into pronation, the posterior tibial tendon which is the prime invertor of the foot becomes strained as it attempts to appose eversion. The tendon is tender on palpation and this can be demonstrated by everting the foot and palpating the tendon as it passes behind and below the medial malleolus. The tendon will occasionally, if subjected to excessive or violent strain, become dislocated from the bony groove which holds it in its relationship to the medial malleolus. The flexor hallucis longus which also provides inversion of the foot may become similarly strained and tender. As the foot continues to pronate the lateral everters become shortened, as do the peroneal muscles and the digital extensors. This adaptive shortening may lead to pain in the dorsal and lateral structures of the foot. The ligament which binds the talus to the calcaneum, and is normally taut when the foot is supinated and slack when the foot is pronated, will allow the tarsal canal to deform. The talocalcaneal joint becomes abnormally mobile unless there is damage to the articular surfaces of the joint. The ligament becomes inflamed and can be palpated in the lateral canal anterior to the lateral malleolus. If there is articular damage as the result of rheumatoid arthritis or secondary osteoarthrosis then the tendency to abnormal mobility will result in spasm of the surrounding soft tissues and considerable discomfort as the subtalar joint is moved. OTHER ARTHROPATHIES WHICH MAY AFFECT THE SUBTALAR JOINT Septic arthritis
This may result from several different infectious processes including viral, bacterial, tubercular and fungal. Commonly, septic arthritis occurs from the haematogenous spread of organisms from a distant site rather than from local infection, the commonest being gonococcal arthritis. Septic arthritis is characterized by pain, tenderness, tenosynovitis, swelling, increased temperature, decreased range of motion and erythema. It should be suspected in all cases of monoarthritis as well as in those patients who exhibit features of joint erythema, fever and elevation of the peripheral white blood cell count. Joint aspiration of pus is the most important diagnostic procedure. Connective tissue diseases
Systemic lupus erythematosus, scleroderma, dermatomyositis, polyarteritis nodosa may give rise to non-articular and articular manifestations which include joint capsular laxity and tendon involvement which may lead to multiple subluxation.
282
L. SM~DT
al
Figure 8. Equinus deformity. This is defined as the inability to gain 10~ dorsiflexion when the foot is in neutral position. The measurement is taken using a tractagraph, bisecting the fibula and measuring the plantar surface from heel to metatarsal region. The foot is maintained in neutral having been dorsiflexed to resistance.
If achilles tendinitis is present, this may lead to shortening of the tendon and a consequent equinus deformity (see Figure 8). In order to allow some dorsiflexion to take place during gait, compensatory pronation will occur (see Figure 9). Joint laxity is another manifestation of this group of diseases and unless early measures are taken to preserve normal anatomy, severe malalignment problems may arise at the subtalar articulations.
Seronegative spondarthritis Included in this group of arthropathies are ankylosing spondylitis, psoriatic arthritis, Reiter's disease and enteropathic arthritis. Within this group of
\ \
\ \ \\
\\\\\
\ Axis line of midtarsal joint
Axis line of subtalar joint
Figure 9. Diagram to show how ankle equinus is compensated for by the more distal joints of the foot. The subtalar joint gains 2-3 ~ dorsiflexion by pronating. The rest (7-8 ~ is gained by midtarsal and metatarsal dorsiflexion.
T H E S U B T A L A R J O I N T A N D R H E U M A T O I D ARTHRITIS
283
arthropathies there is an absence of rheumatoid factors from the serum and involvement of the spine. Common features of spondarthritis in the early stages before symptoms in the back occur are peripheral large joint involvement, symptoms in the extra-articular musculoskeletal system and pain around the heel. The heel pain may be due to plantar fasciitis arising at the insertion of the plantar fascia into the calcaneum, especially the medial tubercle of the calcaneum. At this site, it is common for this to be enthesopathic in origin. Similarly such a lesion may be present at the insertion of the Achilles tendon at the posterior of the calcaneum. The pain associated with this disorder will significantly alter gait as a result of the loss of shock absorption capabilities of the heels. This may exacerbate symptoms in the subtalar joint as well as the spine which will be jarred with each heel strike. As ankylosing spondylitis will give rise to rigidity and possible deformity in the spine, this will alter posture from above. The subtalar joint will attempt to compensate for this and the result may be pronation and supination.
Subtalar osteoarthrosis This is frequently the result of trauma which may be due to long-term sporting activity which gives rise to multiple minor injuries to the joint. It may be due to more major trauma such as that leading to fracture of the calcaneum, or it may be secondary to inflammatory arthritis having affected the subtatar joint. Pain will be produced on passive movement of the joint and usually crepitus will be present. The area will exhibit tenderness if pressure is applied over the sinus tarsi anterior to the lateral malleolus. In an effort to minimize pain there may be muscle spasm present, especially in the peroneii. Conservative treatment should be aimed at reducing movement by the provision of orthoses which stabilize the joint. X-ray will demonstrate irregularities between the talus and the calcaneum. It is important to confirm the diagnosis of subtalar osteoarthrosis by X-ray as some cartilaginous or fibrous tarsal coalition conditions may produce similar symptoms. Treatment for both non-bony talocalcaneal coalition and osteoarthrosis are similar, the former probably warrants surgical fusion more commonly than the latter.
Nenropathic arthritis Neuropathic (Charcot's) joints usually are a feature of diabetes mellitus and occasionally tabes dorsalis and will give rise to osteoarthrosis of many joints in the foot and quite frequently the subtalar joint. Conservative joint stabilization and cushioning, coupled with appropriate footwear is of paramount importance to these patients as they are often at risk of infection because of the vascular complications of their diabetes mellitus.
Congenital anomalies Those such as tarsal conditions referred to above may give rise to symptoms
284
L. SMIDT
in the area of the subtalar join t. The congenital vertical talus presents in its extreme form with a 'rocker sole' to the affected foot, and palpation o f t h e head of talus is not possible at its normal anatomical site. The foot presents often as being in pronation and the patient is unable to invert and evert the foot normally. The degree of 'vertical' talus varies and m o r e frequently an increased angulation of the talus occurs. This condition is not treatable but may be a c c o m m o d a t e d by the provision of insoles which are fabricated to compensate for the unusual sole configuration and will assist with weight bearing (Figure 10).
(a)
\
(b) Figure 10. Two diagrams to show the bony position of a vertical talus deformity. (a) Dorsal aspect showing the vertical position of the talus. (b) Medial aspect of the right foot showing a vertical talus. The 'rocker sole' is very apparent.
THE SUBTALARJOINT AND RHEUMATOID ARTHRITIS
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RELATIONSHIP OF THE H I N D F O O T WITH THE F O R E F O O T
During the inflammatory stage of rheumatoid arthritis the subtalar joint can be painful and as a result the time used for single limb support during walking decreases as does the range of motion. Whether the subtalar joint is pronated which is common in patients with rheumatoid arthritis or supinated which is relatively uncommon in these patients, there will be increased stresses brought to bear on the subtalar joints and its articulations and this is likely to lead to joint destruction. It is therefore of paramount importance that with the early diagnosis of rheumatoid arthritis affecting the subtalar joint, suitable orthoses should be provided together with appropriate footwear at the earliest opportunity in order to maintain as near normal anatomy as is possible. With the occurrence of a valgus rotation of the head of the talus there will be a forward thrust and consequent articular alteration onto the navicular and from there onto the cuneiform and consequently to the first three metatarsals which will be forced into a position of greater relative plantarflexion than the fourth and fifth metatarsals. As a result of attempting to stabilize the medial side of the forefoot the first metatarsal adducts. This allows the hallus to go into a valgus position causing cramping of the lesser toes which in any event are becoming retracted as a result of overpull of the extensor tendons and the likely effects of the rheumatoid arthritis on the metatarsophalangeal joints (Figure 11). Similar effects occur with the seronegative group of arthropathies and with these patients it is common to find that the subtalar joint has virtually collapsed medially. The classic forefoot deformity is produced as a result of the extreme pronatory forces exerted from the hindfoot.
/ Figure 11. Diagram showing the marked effects of prolonged pronation and the compensatory stabilizing that occurs in the foot.
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L. SMIDT
TREATMENT
The full range of therapies available to the various clinicians who will be called upon to treat arthropathy occurring in the subtalar joint include the provision of special footwear or advice regarding footwear, systemic medication, steroid injections, weight relief and dietary advice, surgery and physical measures such as physiotherapy techniques and the provision of correctable or supportive orthoses. I intend to concentrate on physical treatment methods only. The use of ultrasound can be very beneficial to patients during the acute stage of subtalar joint inflammation. Direct application of the ultrasound treatment head using a coupling medium or by directing the ultrasound at the affected area through water are both acceptable methods of application. Exposure time and dosages will vary according to patient tolerance but frequent applications (four times per week) are essential if symptoms are to be relieved. The use of various forms of heart therapy can be of benefit to these patients and should usually be followed by gentle passive mobilization of the joint. This should be undertaken following ultrasound treatment too. The use of orthoses for patients who present with subtalar arthritis is important because they are likely to suffer irreparable joint damage, unless normal anatomy is preserved, during the early stages of the disease. Orthoses manufactured for the individual patient should be provided at the earliest opportunity. The degree of deformity of the joint is assessed as described earlier. A negative cast of the patient's feet are produced whilst the foot is maintained in its neutral position. This is achieved by using plaster-of-Paris impregnation bandage and applying several layers to the foot, having first applied a separating medium to the skin. After the bandage has almost dried the negative cast can be carefully removed taking care not to distort its shape, The inside of the negative mould is coated with a suitable separating medium. There are a number of commercially available separating media, but almost any oil or soapy solution will be adequate for the purpose. A creamy mixture of plaster-of-Paris is prepared and poured into the coated negative casts shaking the casts during the pouring to ensure air is not trapped in the cast. The cast is allowed to dry and is best left for a few days before removing the outer layers of bandage. A good positive impression of the foot should now be available. It is now possible to fabricate the orthosis of choice to this model of the foot. In choosing the type of device to be used there are a number of factors to be considered: 1. 2. 3.
Mobility Inflammation and pain Age and frailty of patient
The detail relating to the types of orthoses which can be provided for these patients is dealt with in the chapter devoted to this subject.
THE SUBTALAR JOINT AND RHEUMATOID ARTHRITIS
287
FURTHER READING Bailey DS, Perillo JT & Forman M (1986) Subtalar Joint Neutral. Journal of the America~ Podiatry Association 76" 5%64. Blake RL (1986) Inverted Functional Orthosis. Journal of the American Podiatry Association 76: 275-276. Cailliet R (1983) Foot and Ankle Pain. 2nd edn. Philadelphia: FA Davis. Hickling P & Golding JR (1984) An Outline of Rheumatology. Bristol: John Wright. Locke M, Perry J, Campbell J & Thomas L (1984) Ankle, Subtalar Motion During Gait. Physical Therapy 64: 504-509. Scott JT (1978) Copeman's Textbook of the Rheumatic Diseases Edinburgh: Churchill Livingstone. Spiegel T & Spiegel J (1982) Rheumatoid Arthritis in the Foot and Ankle--Diagnosis, Pathology and Treatment. Foot and ~4nkle 2: 318-324. Swinson DR & Swinbair WR (1980) Rheumatology. Sevenoaks: Hodder & Stoughton.
In recent years, with the increasing understanding of functional anatomy and biomechanics of the lower limb, the importance of the subtalar joint is becoming clearer. It is at the subtalar joint that pronation and supination occur and in the normal well functioning foot it is this joint which is primarily responsible for minimizing stress factors in the hindfoot at, and immediately following heel strike in the gait cycle. ANATOMY OF THE SUBTALAR JOINT The talus articulates with the calcaneum at two points, each having its own joint capsule. The talocalcaneo-navicular articulation is the anterior of the two articulations and is partly between the head of the talus and the anterior and middle articular facets of the calcaneum. The talocalcaneal joint, posteriorly, lies between the inferior surface of the body of the talus and the posterior articular surface of the calcaneum. Pronation and supination occur at the subtalar joint about an oblique axis. This is therefore a triplane movement occurring simultaneously about all three body planes. The axis inclines from the posterior-plantar-lateral to the anterior-dorsal-medial (Figure 1). The movements which occur about the subtalar joint are eversion, abduction and dorsiflexion in relation to the pronatory capabilities of the joint (Figure 2) and conversely inversion, adduction and plantarflexion in relation to the supinatory capabilities of the joint (Figure 3). EXAMINATION OF THE S U B T A L A R JOINT
In order to undertake an examination of the subtalar joint it is necessary to establish the neutral position of the joint. This is best undertaken with the patient in the prone position, lying on a flat examination couch with the feet extended beyond the surface of the couch. Grasp the head of the talus between thumb and forefinger of one hand and holding the foot with the other in a slightly plantarflexed position, move the foot from inversion to eversion until you establish that the head of talus is in a central position with Bailli~re's Clinical Rheurnatology--Vol. 1, No. 2, August1987
275
276
L. SMIDT
16 ~ Figure 1. Diagram to show the axis of the subtaloid joint. All movement of the joint occurs around this triplanal axis.
the margins of the bone equal between your thumb and forefinger. This is the neutral position and the foot is either in pronation or supination. Avoiding the skin overlying the achilles tendon, bisect the lower leg in two or three positions. These points should be connected with a line drawn, using a straight edge, to a position on tl~e posterior aspect of the calcaneum. The calcaneum should be similarly bisected and a line drawn between the points to connect with the line previously drawn. It is important to use the bony margins of the calcaneum and not the soft tissue. The two lines drawn will form an angle, with the foot held in the neutral subtalar position. This angle in normal feet will be between 3-5 degrees of varus (Figure 4).
/~
/
. .
"~ 9 3. Dorsiflexio~nCf/~..2 ~Evelsi~ ~ 3 " D~176 ~/~\'/'A~ ~
2.Abduction ~ Pronation
version Medial
Figure 2. Two diagrams to show the triplane movement of pronation at the subtaloid joint. (a) Anterior view. (b) Posterior view.
277
THE SUBTALAR JOINT AND RHEUMATOID ARTHRITIS
~L ~
J ~
Inversion
\
2. Adduction
k~. Lateral
~i
3. Plantar flexion 1. Inversion
~
W Plantar IV" flexion
Adduetion Figure 3. Two diagrams to show the triplane m o v e m e n t s of supination. (a) Anterior view. (b) Posterior view.
The subtalar joint basically functions as a hinge joint and since the axis is oblique and lies relatively close to the sagittal plane (+ 16~ the relative amount of dorsiflexion/plantarflexion is small compared with the amount Of eversion/inversion and abduction/adduction (the axis is inclined at 42 ~ from the transverse plane. In the normal subtalar joint, there should be a smooth gentle quality to the range of movement which will allow greater supination than pronation by a factor of two to one.
Leg bisection
Lateral
La
,I bisection
3-5 ~
Varus Figure 4. Diagram to show the normal varus angle of the calcaneus to the leg bisection with the foot in neutral.
278
L. SMIOT
THE RHEUMATOID PROCESS
The subtalar joint, bounded by the talus, calcaneum and navicular is commonly affected by rheumatoid disease resulting in synovitis in the sinus tarsi, in the subtalar joint itself and tenosynovitis in the surrounding and adjacent tendons. It is suggested that rheumatoid synovitis is linked with the presence of immune complexes which trigger the complement system and thus cause phagocytic polymorphonuclear leucocytes to migrate into the joint. The phagocytic action of these polymorphonuclear leucocytes causes the release of lysosomal enzymes leading to an inflammatory response and synovitis. The synovium proliferates as granulation tissue which is known as pannus. This pannus which is a villous, boggy mass becomes fixed to the cartilage. By further enzymatic action the pannus penetrates and invades the cartilage and underlying bone and produces characteristic rheumatoid erosions. As a result of these inflammatory changes the joint is swollen and becomes damaged or even destroyed by the erosive effects of the rheumatoid disease. These effects are accompanied by the synovitis, and of cellulitis, fasciitis and tendinitis and often lead to adhesions between the joint surfaces and consequently secondary osteoarthrosis. Although the majority of patients with rheumatoid disease will have inflammatory synovitis of the subtalar joint and will have pain to a variable degree, relatively few will exhibit significant malalignment of the foot on the leg in the early stages of the disease. However, it is rare to find a patient who has had rheumatoid arthritis for five years or more who does not present with severe and significant hindfoot malalignment. In the presence of inflammatory joint disease, the peri-articular cartilage is extremely liable to degenerative change as a result of the pannus described earlier but also because of the vertical an~t shear forces that occur during gait which tend to further weaken the collagen fibres and thereby allow enzymatic degeneration to occur more readily leading to greater fragility of the cartilage allowing it to be more readily deformed by continuing stress and in effect creating a self-perpetuating vicious circle. Eventually the bone itself becomes affected and erosive changes become apparent. Specifically in the subtalar joint there is an increased stress occurring as a result of the loss of the ability in the structures to absorb shock. Therefore, in gait, each time the foot contacts the ground and moves through its range of motion the ligamentous structures, now weakened, are unable to prevent increased supinatory and pronatory effects. With increased pronation the effects on and remote from the foot become increasingly apparent (Figure
5).
The foot itself, in pronation, will be taking on an increased abnormal load on the medial side of the forefoot. The first toe and first metatarsal, in an attempt to stabilize the foot in weight-bearing will take greater load and stress. The metatarsal will attempt to stabilize the medial longitudinal arch resulting in an apparent varus position on forefoot loading. The consequent effects on the great toe are medial rotation and valgus positioning. This is partly to accommodate the position of the first metatarsal and partly to aid
279
THE SUBTALAR JOINT AN D RHEUMATOID ARTHRITIS
~ody stress
Directi of stre
Figure 5. Diagram to show the direction of the lines of stress on the ligamentous structures of the foot.
the stabilization of the first ray in response to the medial 'rolling' effect of the pronating foot. As a result of this, the weight-bearing function of the forefoot becomes altered and is referred to elsewhere in this book. As the foot pronates to a greater degree, the clinician can observe that the patients' shoes become misshapen on the medial side at the margin of the heel counter which will bulge outwards and overhang the heel of the shoe. The lateral margin of the heel becomes excessively worn as a result of the abnormal heel strike position. The forepart of the shoe is also diagnostically important and in its distortion follows, as one would expect, the shape of the foot. The shoe therefore has the following appearance (Figure 6). The Achilles tendon when viewed from behind will bow medially above the insertion into the calcaneum; the inner longitudinal arch appears lowered and the lateral border of the foot bears little, if any, weight. This subtalar pronation which results in eversion, abduction and dorsiflexion causes the leg above the foot to follow the imaginary line drawn through the leg. The medial side of the knee joint is now subjected to considerably increased stress. As the knee moves medially, so the femur is pulled with it through the knee joint to a position lateral to it. This further exacerbates the forces on the knee resulting in an increased likelihood of
280
L.
SMIDT
b Laces drawn diagonally with foot deformity
nana shoe'
Medial bulging
Figure 6. Diagram to show a badly damaged shoe resulting from the extremes of force applied to it by the pronated foot. (a) Posterior view of a badly deformed shoe from a child with an excessively pronated foot. (b) A 'banana shoe'.
Stress within the knee joint as torsion is set up within the joint. Increased compression occurs on the medial side of the joint.
Excessively pronated foot
Figure 7. Diagram to show how excessive pronation leads to increased trauma in the knee joint.
THE SUBTALAR JOINT AND RHEUMATOID ARTHRITIS
281
greater deformity (Figure 7). The degree of deformity at the subtalar joint may only be of a relatively minor nature being only one or two degrees. This will result in considerable force on the knee joint being approximately 50 cm remote from the subtalar joint and still greater stresses will arise in the hip joint as a result of similar phenomena. The distance from the foot to the hip being that much greater will result in stress of larger magnitude. As the foot progresses into pronation, the posterior tibial tendon which is the prime invertor of the foot becomes strained as it attempts to appose eversion. The tendon is tender on palpation and this can be demonstrated by everting the foot and palpating the tendon as it passes behind and below the medial malleolus. The tendon will occasionally, if subjected to excessive or violent strain, become dislocated from the bony groove which holds it in its relationship to the medial malleolus. The flexor hallucis longus which also provides inversion of the foot may become similarly strained and tender. As the foot continues to pronate the lateral everters become shortened, as do the peroneal muscles and the digital extensors. This adaptive shortening may lead to pain in the dorsal and lateral structures of the foot. The ligament which binds the talus to the calcaneum, and is normally taut when the foot is supinated and slack when the foot is pronated, will allow the tarsal canal to deform. The talocalcaneal joint becomes abnormally mobile unless there is damage to the articular surfaces of the joint. The ligament becomes inflamed and can be palpated in the lateral canal anterior to the lateral malleolus. If there is articular damage as the result of rheumatoid arthritis or secondary osteoarthrosis then the tendency to abnormal mobility will result in spasm of the surrounding soft tissues and considerable discomfort as the subtalar joint is moved. OTHER ARTHROPATHIES WHICH MAY AFFECT THE SUBTALAR JOINT Septic arthritis
This may result from several different infectious processes including viral, bacterial, tubercular and fungal. Commonly, septic arthritis occurs from the haematogenous spread of organisms from a distant site rather than from local infection, the commonest being gonococcal arthritis. Septic arthritis is characterized by pain, tenderness, tenosynovitis, swelling, increased temperature, decreased range of motion and erythema. It should be suspected in all cases of monoarthritis as well as in those patients who exhibit features of joint erythema, fever and elevation of the peripheral white blood cell count. Joint aspiration of pus is the most important diagnostic procedure. Connective tissue diseases
Systemic lupus erythematosus, scleroderma, dermatomyositis, polyarteritis nodosa may give rise to non-articular and articular manifestations which include joint capsular laxity and tendon involvement which may lead to multiple subluxation.
282
L. SM~DT
al
Figure 8. Equinus deformity. This is defined as the inability to gain 10~ dorsiflexion when the foot is in neutral position. The measurement is taken using a tractagraph, bisecting the fibula and measuring the plantar surface from heel to metatarsal region. The foot is maintained in neutral having been dorsiflexed to resistance.
If achilles tendinitis is present, this may lead to shortening of the tendon and a consequent equinus deformity (see Figure 8). In order to allow some dorsiflexion to take place during gait, compensatory pronation will occur (see Figure 9). Joint laxity is another manifestation of this group of diseases and unless early measures are taken to preserve normal anatomy, severe malalignment problems may arise at the subtalar articulations.
Seronegative spondarthritis Included in this group of arthropathies are ankylosing spondylitis, psoriatic arthritis, Reiter's disease and enteropathic arthritis. Within this group of
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\ Axis line of midtarsal joint
Axis line of subtalar joint
Figure 9. Diagram to show how ankle equinus is compensated for by the more distal joints of the foot. The subtalar joint gains 2-3 ~ dorsiflexion by pronating. The rest (7-8 ~ is gained by midtarsal and metatarsal dorsiflexion.
T H E S U B T A L A R J O I N T A N D R H E U M A T O I D ARTHRITIS
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arthropathies there is an absence of rheumatoid factors from the serum and involvement of the spine. Common features of spondarthritis in the early stages before symptoms in the back occur are peripheral large joint involvement, symptoms in the extra-articular musculoskeletal system and pain around the heel. The heel pain may be due to plantar fasciitis arising at the insertion of the plantar fascia into the calcaneum, especially the medial tubercle of the calcaneum. At this site, it is common for this to be enthesopathic in origin. Similarly such a lesion may be present at the insertion of the Achilles tendon at the posterior of the calcaneum. The pain associated with this disorder will significantly alter gait as a result of the loss of shock absorption capabilities of the heels. This may exacerbate symptoms in the subtalar joint as well as the spine which will be jarred with each heel strike. As ankylosing spondylitis will give rise to rigidity and possible deformity in the spine, this will alter posture from above. The subtalar joint will attempt to compensate for this and the result may be pronation and supination.
Subtalar osteoarthrosis This is frequently the result of trauma which may be due to long-term sporting activity which gives rise to multiple minor injuries to the joint. It may be due to more major trauma such as that leading to fracture of the calcaneum, or it may be secondary to inflammatory arthritis having affected the subtatar joint. Pain will be produced on passive movement of the joint and usually crepitus will be present. The area will exhibit tenderness if pressure is applied over the sinus tarsi anterior to the lateral malleolus. In an effort to minimize pain there may be muscle spasm present, especially in the peroneii. Conservative treatment should be aimed at reducing movement by the provision of orthoses which stabilize the joint. X-ray will demonstrate irregularities between the talus and the calcaneum. It is important to confirm the diagnosis of subtalar osteoarthrosis by X-ray as some cartilaginous or fibrous tarsal coalition conditions may produce similar symptoms. Treatment for both non-bony talocalcaneal coalition and osteoarthrosis are similar, the former probably warrants surgical fusion more commonly than the latter.
Nenropathic arthritis Neuropathic (Charcot's) joints usually are a feature of diabetes mellitus and occasionally tabes dorsalis and will give rise to osteoarthrosis of many joints in the foot and quite frequently the subtalar joint. Conservative joint stabilization and cushioning, coupled with appropriate footwear is of paramount importance to these patients as they are often at risk of infection because of the vascular complications of their diabetes mellitus.
Congenital anomalies Those such as tarsal conditions referred to above may give rise to symptoms
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in the area of the subtalar join t. The congenital vertical talus presents in its extreme form with a 'rocker sole' to the affected foot, and palpation o f t h e head of talus is not possible at its normal anatomical site. The foot presents often as being in pronation and the patient is unable to invert and evert the foot normally. The degree of 'vertical' talus varies and m o r e frequently an increased angulation of the talus occurs. This condition is not treatable but may be a c c o m m o d a t e d by the provision of insoles which are fabricated to compensate for the unusual sole configuration and will assist with weight bearing (Figure 10).
(a)
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(b) Figure 10. Two diagrams to show the bony position of a vertical talus deformity. (a) Dorsal aspect showing the vertical position of the talus. (b) Medial aspect of the right foot showing a vertical talus. The 'rocker sole' is very apparent.
THE SUBTALARJOINT AND RHEUMATOID ARTHRITIS
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RELATIONSHIP OF THE H I N D F O O T WITH THE F O R E F O O T
During the inflammatory stage of rheumatoid arthritis the subtalar joint can be painful and as a result the time used for single limb support during walking decreases as does the range of motion. Whether the subtalar joint is pronated which is common in patients with rheumatoid arthritis or supinated which is relatively uncommon in these patients, there will be increased stresses brought to bear on the subtalar joints and its articulations and this is likely to lead to joint destruction. It is therefore of paramount importance that with the early diagnosis of rheumatoid arthritis affecting the subtalar joint, suitable orthoses should be provided together with appropriate footwear at the earliest opportunity in order to maintain as near normal anatomy as is possible. With the occurrence of a valgus rotation of the head of the talus there will be a forward thrust and consequent articular alteration onto the navicular and from there onto the cuneiform and consequently to the first three metatarsals which will be forced into a position of greater relative plantarflexion than the fourth and fifth metatarsals. As a result of attempting to stabilize the medial side of the forefoot the first metatarsal adducts. This allows the hallus to go into a valgus position causing cramping of the lesser toes which in any event are becoming retracted as a result of overpull of the extensor tendons and the likely effects of the rheumatoid arthritis on the metatarsophalangeal joints (Figure 11). Similar effects occur with the seronegative group of arthropathies and with these patients it is common to find that the subtalar joint has virtually collapsed medially. The classic forefoot deformity is produced as a result of the extreme pronatory forces exerted from the hindfoot.
/ Figure 11. Diagram showing the marked effects of prolonged pronation and the compensatory stabilizing that occurs in the foot.
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TREATMENT
The full range of therapies available to the various clinicians who will be called upon to treat arthropathy occurring in the subtalar joint include the provision of special footwear or advice regarding footwear, systemic medication, steroid injections, weight relief and dietary advice, surgery and physical measures such as physiotherapy techniques and the provision of correctable or supportive orthoses. I intend to concentrate on physical treatment methods only. The use of ultrasound can be very beneficial to patients during the acute stage of subtalar joint inflammation. Direct application of the ultrasound treatment head using a coupling medium or by directing the ultrasound at the affected area through water are both acceptable methods of application. Exposure time and dosages will vary according to patient tolerance but frequent applications (four times per week) are essential if symptoms are to be relieved. The use of various forms of heart therapy can be of benefit to these patients and should usually be followed by gentle passive mobilization of the joint. This should be undertaken following ultrasound treatment too. The use of orthoses for patients who present with subtalar arthritis is important because they are likely to suffer irreparable joint damage, unless normal anatomy is preserved, during the early stages of the disease. Orthoses manufactured for the individual patient should be provided at the earliest opportunity. The degree of deformity of the joint is assessed as described earlier. A negative cast of the patient's feet are produced whilst the foot is maintained in its neutral position. This is achieved by using plaster-of-Paris impregnation bandage and applying several layers to the foot, having first applied a separating medium to the skin. After the bandage has almost dried the negative cast can be carefully removed taking care not to distort its shape, The inside of the negative mould is coated with a suitable separating medium. There are a number of commercially available separating media, but almost any oil or soapy solution will be adequate for the purpose. A creamy mixture of plaster-of-Paris is prepared and poured into the coated negative casts shaking the casts during the pouring to ensure air is not trapped in the cast. The cast is allowed to dry and is best left for a few days before removing the outer layers of bandage. A good positive impression of the foot should now be available. It is now possible to fabricate the orthosis of choice to this model of the foot. In choosing the type of device to be used there are a number of factors to be considered: 1. 2. 3.
Mobility Inflammation and pain Age and frailty of patient
The detail relating to the types of orthoses which can be provided for these patients is dealt with in the chapter devoted to this subject.
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FURTHER READING Bailey DS, Perillo JT & Forman M (1986) Subtalar Joint Neutral. Journal of the America~ Podiatry Association 76" 5%64. Blake RL (1986) Inverted Functional Orthosis. Journal of the American Podiatry Association 76: 275-276. Cailliet R (1983) Foot and Ankle Pain. 2nd edn. Philadelphia: FA Davis. Hickling P & Golding JR (1984) An Outline of Rheumatology. Bristol: John Wright. Locke M, Perry J, Campbell J & Thomas L (1984) Ankle, Subtalar Motion During Gait. Physical Therapy 64: 504-509. Scott JT (1978) Copeman's Textbook of the Rheumatic Diseases Edinburgh: Churchill Livingstone. Spiegel T & Spiegel J (1982) Rheumatoid Arthritis in the Foot and Ankle--Diagnosis, Pathology and Treatment. Foot and ~4nkle 2: 318-324. Swinson DR & Swinbair WR (1980) Rheumatology. Sevenoaks: Hodder & Stoughton.