0196-601 1 /85/0606-0324$02.00/0 THE JOURNAL OF ORTHOPAEDIC AND SPORTS PHYSICAL THERAPY Copyright 0 1985 by The Orthopaedic and Sports Physical Therapy Sections of the American Physical Therapy Association Management of Metatarsalgia with Foot Orthotics GORDON E. DOXEY, BS, PT* Various disorders cause pain in the forefoot. Factors contributing to the development of metatarsalgia include: biomechanical alignment, foot biomechanics, anatomical structure of the foot and leg, physical activity, and pathological disease states. The foot functions to balance and support forward locomotion by acting as a mobile adaptor to the ground and as a rigid lever during propulsion at the early and late phases of stance. Forefoot pathomechanics results from an overload of the anterior support or from an irregular distribution of the metatarsal weightbearing load. Orthotic therapy may be provided with insoles made from flexible, semiflexible, or rigid materials. The orthotic should be individualized in each patient's case. The purpose of treatment is to increase weightbearing tolerance by balancing the metatarsal load, assisting proper foot biomechanics, and cushioning or protecting the metatarsal heads. Metatarsalgia is a common foot disorder. The term rnetatarsalgia refers to a pain syndrome in the forefoot and not to a specific diagnosi~.~' Many different diagnoses have been indentified as the cause of the painful forefoot. Excessive stress may result in ligamentous strain, synovitis, capsulitis, fracture, or degenerative arthritis. Me- tatarsalgia may be associated with cerebral palsy, stroke, multiple sclerosis, or other neurological diseases. Metatarsalgia results from pathological alterations in forefoot structure due to rheumatoid arthritis, osteomyelitis, or osteochondrosis. Cir- culatory or metabolic disorders may also produce metatar~algia.~~ The management of metatarsal- gia requires identifying the etiology and treating the primary cause. Treatment may include medi- cal, physical, or surgical therapies but only the use of foot orthotics will be discussed in this article. TYPES OF METATARSALGIA Metatarsalgia may present as an independent disorder or coexist with other foot pathology.14 The types of metatarsalgia may be grouped as primary, secondary, or as forefoot pain without associated plantar keratosis. Primary metatarsal- gia is associated with metatarsalpain and reactive 'St. Benedict's Hospital, Ogden, UT. keratosis due to a chronic imbalance in the weight distribution between the metatarsals. This type may be either structural or functional depending upon whether the imbalance is osseous or due to inadequate muscular function.26 Neale et ahz2 re- fers to this type of mechanical imbalance as func- tional metatarsalgia. This imbalance overloads the metatarsals causing an inflammatory reaction in the metatarsalphalangeal joints. ScrantonZ6 con- siders adult onset static disorders, postoperative iatrogenic imbalances, hallux valgus, hallux rigi- dus, and Morton's foot to be primary metatarsal- gias. Compression of the metatarsals is increased with rigid cavus or pes planus feet, metatarsal fixation, retraction or clawing of the toes, and metatarsal subluxation. Shearing across the met- atarsals is increased with first or fifth metatarsal hypermobility, excessive pronation, or illfitting ~hoes.~'~~ Secondary metatarsalgia is associated with forefoot pain and reactive plantar keratosis due to factors other than the metatarsals themselves. The etiology is due to localized disease within the forefoot. A chronic equinus gait is also a promi- nent factor predisposing an individual to second- ary metatarsalgia. S ~ r a n t o n ~ ~ considers rheuma- toid arthritis, sesamoid disorders, posttraumatic imbalances, neurogenic and stress fractures to be secondary metatarsalgias. The contribution of 324 Journal of Orthopaedic & Sports Physical Therapy® Downloaded from www.jospt.org at on February 26, 2023. For personal use only. No other uses without permission. Copyright © 1985 Journal of Orthopaedic & Sports Physical Therapy®. All rights reserved.
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Management of Metatarsalgia With Foot Orthotics01 96-601 1 /85/0606-0324$02.00/0 THE JOURNAL OF ORTHOPAEDIC AND SPORTS PHYSICAL THERAPY Copyright 0 1985 by The Orthopaedic and Sports Physical Therapy Sections of the American Physical Therapy Association
Management of Metatarsalgia with Foot Orthotics GORDON E. DOXEY, BS, PT*
Various disorders cause pain in the forefoot. Factors contributing to the development of metatarsalgia include: biomechanical alignment, foot biomechanics, anatomical structure of the foot and leg, physical activity, and pathological disease states. The foot functions to balance and support forward locomotion by acting as a mobile adaptor to the ground and as a rigid lever during propulsion at the early and late phases of stance. Forefoot pathomechanics results from an overload of the anterior support or from an irregular distribution of the metatarsal weightbearing load. Orthotic therapy may be provided with insoles made from flexible, semiflexible, or rigid materials. The orthotic should be individualized in each patient's case. The purpose of treatment is to increase weightbearing tolerance by balancing the metatarsal load, assisting proper foot biomechanics, and cushioning or protecting the metatarsal heads.
Metatarsalgia is a common foot disorder. The term rnetatarsalgia refers to a pain syndrome in the forefoot and not to a specific diagnosi~.~' Many different diagnoses have been indentified as the cause of the painful forefoot. Excessive stress may result in ligamentous strain, synovitis, capsulitis, fracture, or degenerative arthritis. Me- tatarsalgia may be associated with cerebral palsy, stroke, multiple sclerosis, or other neurological diseases. Metatarsalgia results from pathological alterations in forefoot structure due to rheumatoid arthritis, osteomyelitis, or osteochondrosis. Cir- culatory or metabolic disorders may also produce metatar~algia.~~ The management of metatarsal- gia requires identifying the etiology and treating the primary cause. Treatment may include medi- cal, physical, or surgical therapies but only the use of foot orthotics will be discussed in this article.
TYPES OF METATARSALGIA
Metatarsalgia may present as an independent disorder or coexist with other foot pathology.14 The types of metatarsalgia may be grouped as primary, secondary, or as forefoot pain without associated plantar keratosis. Primary metatarsal- gia is associated with metatarsal pain and reactive
'St. Benedict's Hospital, Ogden, UT.
keratosis due to a chronic imbalance in the weight distribution between the metatarsals. This type may be either structural or functional depending upon whether the imbalance is osseous or due to inadequate muscular function.26 Neale et ahz2 re- fers to this type of mechanical imbalance as func- tional metatarsalgia. This imbalance overloads the metatarsals causing an inflammatory reaction in the metatarsalphalangeal joints. ScrantonZ6 con- siders adult onset static disorders, postoperative iatrogenic imbalances, hallux valgus, hallux rigi- dus, and Morton's foot to be primary metatarsal- gias.
Compression of the metatarsals is increased with rigid cavus or pes planus feet, metatarsal fixation, retraction or clawing of the toes, and metatarsal subluxation. Shearing across the met- atarsals is increased with first or fifth metatarsal hypermobility, excessive pronation, or illfitting ~ h o e s . ~ ' ~ ~
Secondary metatarsalgia is associated with forefoot pain and reactive plantar keratosis due to factors other than the metatarsals themselves. The etiology is due to localized disease within the forefoot. A chronic equinus gait is also a promi- nent factor predisposing an individual to second- ary metatarsalgia. S ~ r a n t o n ~ ~ considers rheuma- toid arthritis, sesamoid disorders, posttraumatic imbalances, neurogenic and stress fractures to be secondary metatarsalgias. The contribution of
324
JOSPT MaylJune 1985 METATARSALGIA 325
localized disease to metatarsalgia development is decreased stride, prolonged midstance, and de- illustrated with rheumatoid arthritis. This arthritic creased heel rise and toe dors i f le~ion.~~'~ disease produces a chronic synovitis which causes erosion of the articular cartilage and bone, NORMAL BIOMECHANICS OF THE FOOT resulting in deformation of the joint capsule. Sub- sequent metatarsal subluxation, clawing of the toes, and dorsal displacement of the plantar fat pad expose the metatarsals to increased plantar stress and metatarsalgia results.30
It is important to recognize the distinction be- tween disorders of mechanical imbalance across the metatarsals with loss of the fat pad and the presence of keratosis and other clinical disorders that are systemic or those that do not produce a keratic plantar reaction. S ~ r a n t o n ~ ~ considers Morton's neuroma, plantar fascitis, tarsal tunnel syndrome, tumors, gout, and circulatory disorders within this group.
CLINICAL EXAMINATION
The goal of the clinical examination and supple- mentary studies is to correlate the clinical evi- dence into a treatment plan by determining the etiology of the disorder, by examining individual biomechanical, alignment and anatomical struc- ture, and by analyzing biomechanical foot function during gait. The physical examination of the foot and ankle is outlined elsewhere.3.4.11~17~22.29 It is important to attempt to correlate the clinical and biomechanical evidence with respect to what is occurring during dynamic foot function. Grayg has observed that clinical evidence with respect to pain, callosities, and biornechanical structure of the foot may not be closely correlated to what occurs dynamically, due to contributing factors within the proximal lower extremity. For example, some patients who upon clinical examination present a rigid first metatarsal ray, in fact, dem- onstrate a hypermobile first metatarsal ray during level walking due to rearfoot pathomechanics when analyzed by the Electrodynogramo (Electro- dynogram, Langer Laboratories, Deer Park, NY) gait system. In summary, it is important to identify factors that are intrinsic to the foot or that are extrinsic within the lower extremity that produces gait dysfunction.
Generally, primary and secondary metatarsalgia is aggravated with weightbearing, ambulation, tip toe activity, and forefoot manipulation. Plantar keratosis may also be present at areas where significant stress is occurring. Observation of the patient's gait reveals an apropulsive push-off, a
The function of the foot during walking is that of balance and support with forward locomotion maintained by the lower extremities and momen- tum of the upper body.25 The foot acts as a mobile adaptor to the ground at heel strike and early stance phase and then stabilizes to function in propulsion at push-off. Identifying abnormality in the lower extremity requires an understanding of normal biomechanics. Variations in anatomical structure and alignment are important to identify, especially with mechanical disorders. The biome- chanics of the whole lower extremity has been described by other author^."^^^^'^^^^
Body weight is accepted into the foot at heel strike and transferred anteriorly during foot flat and push-off. The stance phase of gait occurs for 62% of the gait cycle. Initial foot contact occurs at heel strike, foot flat at 7%, heel-off at 34%, and toe-off at 62% of the gait c y ~ l e . ' ~ The metatarsals and hallux are weightbearing for 85 and 60% of the stance phase.12 The heel first contacts the ground in an inverted position. The adaptation of the foot to the ground occurs by eversion of the calcaneus and pronation of the subtalar and mid- tarsal joints. The medial longitudinal arch under- goes structural change during early stance phase by accepting weight from the talas as it assumes a plantarflexed and adducted position. This mech- anism of pronation normally only occurs during early stance phase. At midstance, external rota- tion of the lower extremity initiates supination of the foot. The calcaneus inverts and the talas moves into abduction and dorsiflexion, thereby locking the midtarsal joint, allowing the foot to become more rigid during pu~h-o f f . ' ~~ '~ Supina- tion is further assisted by the oblique axis be- tween the second and fifth metatarsals (called the metatarsal break) which causes the midfoot to supinate passively as weight is shifted onto the metatarsals. The foot also becomes more stable at push-off due to the windlass mechanism of the plantar fasica and the activity of the gastroc- soleus muscle group. These mechanisms stabilize the medial forefoot and allow the first ray (first metatarsal and first cuneiform) to participate max- imally during push off.2.'5.18.23 The kinetics of lower extremity function during gait are summa- rized in Figure 1.
The forefoot adapts to the ground through the
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WALKING CYCLE
mobility of the first and fifth metatarsals. The other metatarsals, especially the second, are more firmly articulated at their bases and are only ca- pable of movement in the sagittal plane. The stability of the second, third, and fourth metatar- sals results from osseous articulation and normal muscle f u n ~ t i o n . ~ * ~ ~ ~ ~ ~ ~ ~ ~
The neutral position of the subtalar joint is used as a reference to determine the alignment of the foot. Ideal nonweightbearing foot alignment is present when the forefoot is perpendicular to the sagittal calcaneus and when the calcaneus is parallel to the axis of the lower leg.''.17 The first metatarsal should assume a position level with the lesser metatarsals and be capable of an equal amount of plantarflexion and dorsiflexion, but is generally less flexible than the fifth metatarsal." The angle from the ground for the first, second, third, fourth, and fifth metatarsal shafts is 18-25, 15, 10, 8, and 5O, re~pectively.~~
The foot may be classified by toe and metatar-
INITIAL INITIAL FLOOR LIFT FLOOR
CONTACT OFF CONTACT
sal length. Referring to the foot as square, Greek, or Egyptian depends upon whether the first toe is the same, shorter, or longer than the second. The metatarsal length formulas are: index plus, 1 > 2 > 3 > 4 > 5; index plus minus, 1 r 2 > 3 > 4 > 5; and index minus, 2 > 1 > 3 > 4 > 5. V i l a d ~ t ~ ~ examined 1,000 feet and observed 16% index plus, 26% index plus minus, and 56% index mi- nus; considering the Greek and index plus minus formula to be ideal.
The weight distribution across the metatarsals differs in stance and level walking. The distribution of 12 units of load, as outlined by Morton, is transferred so that the heel accepts 6, the first metatarsal 2, and each of the lesser digits 1 .I4
Recently, research has demonstrated that the middle metatarsals accept high pressures and that the heel accepts greater than 50% of the load. In stance, the second and third metatarsals accept significant load^.'.'^,^^
During walking, the ground reaction forces in
PELVIS
FEMUR
TIBIA
CALF MUSCLES
Fig. 1 . Diagram illustrating the joint rotations and muscle activity in the lower extremity during a complete gait cycle. Reproduced with permission from Mann RA, Mechanics of the foot. In: American Academy of Orthopaedic Surgeons: Atlas of orthotics, CV Mosby Co.
m 15% jo( &% 60% 80% lOOX
~~~~~~& -EXTERNAL ROTATION- 0 ~~~~~~~-
I N A C T I V E -
OORSIFLEXION-
PLANTAR 3LEXION+
-INCREASING STABILITY-
"INCREASING A C T I V I T Y o l ,
4-blNACTIVE I
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JOSPT MaylJune 1985 METATARSALGIA 327
Fig. 2. Diagram illustrating the center of pressure in the foot during level walking. The numbers along the line represent the percentage of the stance phase of gait that the pressure is present at one location. Reproduced with permission of Mann18 and WB Saunders Co.
each foot segment varies during different phases of the gait cycle. Weight distribution moves through a line of central pressure. Generally. the center of pressure begins at the lateral heel, moves forward into the midfoot, and then shifts medially where it exits between the first and sec- ond toes at ~ush-off (Fig. 2). However variability of the center of pressure exit from the forefoot has been recorded by Stott et a1.34 The ground reaction forces exit between the first and second or second and third toes in subjects who have an index plus or index minus metatarsal formula. The center of pressure demonstrates to which areas of the foot the forces are distributed and the approximate time they remain at one location. The center of pressure moves rapidly through the heel and midfoot and then slows significantly at the forefo~t . '~ . '~ Weight is present at the forefoot for a longer period of time, requiring the weightbear- ing function of the metatarsals and toes to be three times that of the r e a r f o ~ t . ' ~ ~ ' ~ ~ ~ ~ At push-off all of the ground reaction forces are concentrated on the metatarsals and toes. This force has been calculated to be 120% of body eight.'^^^^ The force acting on just the toes is approximately 40% of body weight.33 The forefoot load is carried to a greater degree at the medial forefoot in younger subjects, while older subjects carry the forefoot load more equally between the medial and lateral f o r e f o ~ t . ' ~ . ~ ~ 3 3 4
V i l a d ~ t ~ ~ studied the sequence of foot contact during gait in 100 subjects and observed that in 70% of the cases, ground contact occurred as follows: 1) heel; 2) heel, metatarsals, and distal
toes; 3) heel, midfoot, and forefoot; 4 ) forefoot and toes; 5) toes; and 6) great toe.
The weightbearing stress at the metatarsals is partly relieved by the muscular activity of the toe flexors which counteracts forces occurring at the metatarsals during push-off. The metatarsals are further protected by the plantar skin, fat pads, and ligamentous structures which act as a natural cushioning mechanism (Fig. 3).20*37
PATHOMECHANICS OF THE FOREFOOT
Biomechanical metatarsalgia results from alter- ations in the weightbearing distribution of forces at the forefoot where the metatarsals become overloaded relative to their neighbors. Alteration in anatomical structure and alignment are major etiological factors. Foot type may contribute to metatarsalgia. Metatarsal weightbearing is in- creased with the cavus foot because a dispropor- tionate amount of weight is borne by the heel and forefoot. It is not uncommon to observe retracted or clawed toes with cavus feet, thus decreasing the toes' contribution to unload the metatarsals at push-off. The pes planus foot type (resulting from genu valgum, rearfoot valgus, or forefoot varus) remains pronated during midstance and inhibits proper supination, thus compromising the propulsive function of the forefoot.
Alterations in forefoot alignment may compro- mise foot function. Forefoot varus may be present where the medial forefoot is inverted relative to the rearfoot when the subtalar joint is in a neutral position. This malalignment decreases the medial stability of the forefoot and causes excessive foot pronatlon, as does rearfoot varus. Forefoot valgus may be present where the medial forefoot is ev- erted relative to the rearfoot when the subtalar joint is in a neutral position. This malalignment may result from the first metatarsal that is plan- tarflexed in a rigid position." Figure 4 illustrates the normal and abnormal nonweightbearing posi- tions for the forefoot. These alignment problems may increase and alter the stress acting at the metatarsals, but may not be clinically significant unless the alignment is excessive or rigid." Em- phasis should be placed upon examining the rear- foot, forefoot, and lower extremity for malalign- ment, since the biomechanics of the foot is de- pendent upon all foot and leg segments.
Foot force analysis has been more commonly performed on subjects with rheumatoid arthritis or hallux valgus deformities. Compared to con- trols free of foot pathology, these subjects dem-
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fibrous flexor sheath plantar ligament
trancrerse mctatars;~i l i rst lunibrical l i g a ~ ~ ~ t * t ~ t and scptunl vertical fihres
R Fig. 3. Illustration of the anatomical structures beneath the metatarsals. Reproduced with permission of MollerZ0 JB Lippincott Co.
I weakness of the toes. Simkin30 determined that the force concentration at the metatarsals was a better indicator of local stress than the quantity of the force because rheumatoid arthritis patients maintained lower forefoot force by decreasing their walking speed and by prolonging midstance.
The preceding research demonstrates the sig- nificant role of the hallux in weightbearing. The weightbearing capacity of the first metatarsal pro- gressively decreases as the hallux valgus deform- ity progre~ses.~ Hallux valgus results from rheu- matoid arthritis, neurological disbases, biome- chanical alignment problems, or develops by an idiopathic process or other Hypermo- bility of the first ray results in a clinical problem where a lack of support compromises its ability to assume adequate weightbearing loads.17 Pa- tients with metatarsalgia should be examined for associated disorders of the hallux. ScrantonZ6, in his series, concluded that 34 of 78 patients with either primary or secondary metatarsalgia had coexisting hallux disorders. Any painful condition of the hallux will shift weightbearing to the lesser
Fig. 4. illustrations of the normal and abnormal nonweight- metatarsals, particularly the second or third.*' bearing forefoot alignment types when the subtalar joint is in the neutral position. A, normal relationship; B, forefoot varus; CLASSIFICATION OF METATARSAL C, plantarflexed first ray; D, forefoot valgus. PATHOMECHANICS
onstrate an inadequate propulsive role of the fore- foot resulting from the center of pressure exiting more laterally, between the second and third or the third and fourth toes10~12~28~30-32~34 and greater stress at the metatarsals due to decreased toe flexor muscle activity, particularly in subjects with hallux valgus.10~12~28~30-32 Sharma et aL2' con- cluded that the lack of medial weightbearing at push-off in rheumatoid arthritis patients was due to either inadequate pronation or flexor muscle
V i l a d ~ t ~ ~ has classified metatarsal pathome- chanics as an overload of anterior support or an irregular distribution of the metatarsal load. Irreg- ular metatarsal load syndromes are further sepa- rated into the following four groups: l ) first ray overload, 2) first ray insufficiency, 3) central ray overload, and 4 ) central ray insufficiency. The different patterns of weight distribution in the ir- regular metatarsal load syndromes are illustrated with pedographs (Fig. 5).
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JOSPT MaylJune 7985 METATARSALGIA 329
b&.k&s- metatarsal frontal plane malalignment, subluxa- 3 - - tion, dislocation, claw or hammer toes, or congen- -
- itally long central metatarsals are predisposing - % factors.37 The position and function of the central
+ metatarsals is commonly disturbed by the mal- position and malfunction of their respective digits as they are pinned down by digital retraction or subl~xat ion.~~
I -7 - -- % Lesser metatarsal overload is caused by inad- - - -- _ / ._ -
- -7
metatarsal, forefoot, or rearfoot varus can result
dk in excessive pronation. First metatarsal varus and
- - hypermobility of the first ray are also predisposing .- - - -. factors to pronatory problems.29q37
- - -- - - - -. L- _---- - These syndromes are identified by patient com-
p- r >- - =+mAz - ' plaint, palpation, callus formation, anatomical -r--f; I;: e:k --?- 5-= - structure and alignment, pedograph and x-ray
examination. The Electrodynogram is being uti- 3 ) ~ 3 : - lized with increasing frequency to objectively ana- -7 1 --- - - lyze the quantity and duration of segmental and
- - - - - ' .- -. -- vertical foot forces with computer analysis of foot - . , c:. - . t biomechanics from foot sensor data.g The tem-
poral and distance variables of aait can be ana- Fig. 5. Pedographs representing the different syndromes of iyzed by utilizing the Footswitc~Stride Analyzer irregular load distribution at the metatarsals: A, first ray over- load; B, first ray insufficiency; C, central ray overload; 0, (6 & L Engineering, Santa Fe Springs, CA.) with central ray insuffi6iency.
Overload of anterior support occurs from im-…
Management of Metatarsalgia with Foot Orthotics GORDON E. DOXEY, BS, PT*
Various disorders cause pain in the forefoot. Factors contributing to the development of metatarsalgia include: biomechanical alignment, foot biomechanics, anatomical structure of the foot and leg, physical activity, and pathological disease states. The foot functions to balance and support forward locomotion by acting as a mobile adaptor to the ground and as a rigid lever during propulsion at the early and late phases of stance. Forefoot pathomechanics results from an overload of the anterior support or from an irregular distribution of the metatarsal weightbearing load. Orthotic therapy may be provided with insoles made from flexible, semiflexible, or rigid materials. The orthotic should be individualized in each patient's case. The purpose of treatment is to increase weightbearing tolerance by balancing the metatarsal load, assisting proper foot biomechanics, and cushioning or protecting the metatarsal heads.
Metatarsalgia is a common foot disorder. The term rnetatarsalgia refers to a pain syndrome in the forefoot and not to a specific diagnosi~.~' Many different diagnoses have been indentified as the cause of the painful forefoot. Excessive stress may result in ligamentous strain, synovitis, capsulitis, fracture, or degenerative arthritis. Me- tatarsalgia may be associated with cerebral palsy, stroke, multiple sclerosis, or other neurological diseases. Metatarsalgia results from pathological alterations in forefoot structure due to rheumatoid arthritis, osteomyelitis, or osteochondrosis. Cir- culatory or metabolic disorders may also produce metatar~algia.~~ The management of metatarsal- gia requires identifying the etiology and treating the primary cause. Treatment may include medi- cal, physical, or surgical therapies but only the use of foot orthotics will be discussed in this article.
TYPES OF METATARSALGIA
Metatarsalgia may present as an independent disorder or coexist with other foot pathology.14 The types of metatarsalgia may be grouped as primary, secondary, or as forefoot pain without associated plantar keratosis. Primary metatarsal- gia is associated with metatarsal pain and reactive
'St. Benedict's Hospital, Ogden, UT.
keratosis due to a chronic imbalance in the weight distribution between the metatarsals. This type may be either structural or functional depending upon whether the imbalance is osseous or due to inadequate muscular function.26 Neale et ahz2 re- fers to this type of mechanical imbalance as func- tional metatarsalgia. This imbalance overloads the metatarsals causing an inflammatory reaction in the metatarsalphalangeal joints. ScrantonZ6 con- siders adult onset static disorders, postoperative iatrogenic imbalances, hallux valgus, hallux rigi- dus, and Morton's foot to be primary metatarsal- gias.
Compression of the metatarsals is increased with rigid cavus or pes planus feet, metatarsal fixation, retraction or clawing of the toes, and metatarsal subluxation. Shearing across the met- atarsals is increased with first or fifth metatarsal hypermobility, excessive pronation, or illfitting ~ h o e s . ~ ' ~ ~
Secondary metatarsalgia is associated with forefoot pain and reactive plantar keratosis due to factors other than the metatarsals themselves. The etiology is due to localized disease within the forefoot. A chronic equinus gait is also a promi- nent factor predisposing an individual to second- ary metatarsalgia. S ~ r a n t o n ~ ~ considers rheuma- toid arthritis, sesamoid disorders, posttraumatic imbalances, neurogenic and stress fractures to be secondary metatarsalgias. The contribution of
324
JOSPT MaylJune 1985 METATARSALGIA 325
localized disease to metatarsalgia development is decreased stride, prolonged midstance, and de- illustrated with rheumatoid arthritis. This arthritic creased heel rise and toe dors i f le~ion.~~'~ disease produces a chronic synovitis which causes erosion of the articular cartilage and bone, NORMAL BIOMECHANICS OF THE FOOT resulting in deformation of the joint capsule. Sub- sequent metatarsal subluxation, clawing of the toes, and dorsal displacement of the plantar fat pad expose the metatarsals to increased plantar stress and metatarsalgia results.30
It is important to recognize the distinction be- tween disorders of mechanical imbalance across the metatarsals with loss of the fat pad and the presence of keratosis and other clinical disorders that are systemic or those that do not produce a keratic plantar reaction. S ~ r a n t o n ~ ~ considers Morton's neuroma, plantar fascitis, tarsal tunnel syndrome, tumors, gout, and circulatory disorders within this group.
CLINICAL EXAMINATION
The goal of the clinical examination and supple- mentary studies is to correlate the clinical evi- dence into a treatment plan by determining the etiology of the disorder, by examining individual biomechanical, alignment and anatomical struc- ture, and by analyzing biomechanical foot function during gait. The physical examination of the foot and ankle is outlined elsewhere.3.4.11~17~22.29 It is important to attempt to correlate the clinical and biomechanical evidence with respect to what is occurring during dynamic foot function. Grayg has observed that clinical evidence with respect to pain, callosities, and biornechanical structure of the foot may not be closely correlated to what occurs dynamically, due to contributing factors within the proximal lower extremity. For example, some patients who upon clinical examination present a rigid first metatarsal ray, in fact, dem- onstrate a hypermobile first metatarsal ray during level walking due to rearfoot pathomechanics when analyzed by the Electrodynogramo (Electro- dynogram, Langer Laboratories, Deer Park, NY) gait system. In summary, it is important to identify factors that are intrinsic to the foot or that are extrinsic within the lower extremity that produces gait dysfunction.
Generally, primary and secondary metatarsalgia is aggravated with weightbearing, ambulation, tip toe activity, and forefoot manipulation. Plantar keratosis may also be present at areas where significant stress is occurring. Observation of the patient's gait reveals an apropulsive push-off, a
The function of the foot during walking is that of balance and support with forward locomotion maintained by the lower extremities and momen- tum of the upper body.25 The foot acts as a mobile adaptor to the ground at heel strike and early stance phase and then stabilizes to function in propulsion at push-off. Identifying abnormality in the lower extremity requires an understanding of normal biomechanics. Variations in anatomical structure and alignment are important to identify, especially with mechanical disorders. The biome- chanics of the whole lower extremity has been described by other author^."^^^^'^^^^
Body weight is accepted into the foot at heel strike and transferred anteriorly during foot flat and push-off. The stance phase of gait occurs for 62% of the gait cycle. Initial foot contact occurs at heel strike, foot flat at 7%, heel-off at 34%, and toe-off at 62% of the gait c y ~ l e . ' ~ The metatarsals and hallux are weightbearing for 85 and 60% of the stance phase.12 The heel first contacts the ground in an inverted position. The adaptation of the foot to the ground occurs by eversion of the calcaneus and pronation of the subtalar and mid- tarsal joints. The medial longitudinal arch under- goes structural change during early stance phase by accepting weight from the talas as it assumes a plantarflexed and adducted position. This mech- anism of pronation normally only occurs during early stance phase. At midstance, external rota- tion of the lower extremity initiates supination of the foot. The calcaneus inverts and the talas moves into abduction and dorsiflexion, thereby locking the midtarsal joint, allowing the foot to become more rigid during pu~h-o f f . ' ~~ '~ Supina- tion is further assisted by the oblique axis be- tween the second and fifth metatarsals (called the metatarsal break) which causes the midfoot to supinate passively as weight is shifted onto the metatarsals. The foot also becomes more stable at push-off due to the windlass mechanism of the plantar fasica and the activity of the gastroc- soleus muscle group. These mechanisms stabilize the medial forefoot and allow the first ray (first metatarsal and first cuneiform) to participate max- imally during push off.2.'5.18.23 The kinetics of lower extremity function during gait are summa- rized in Figure 1.
The forefoot adapts to the ground through the
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WALKING CYCLE
mobility of the first and fifth metatarsals. The other metatarsals, especially the second, are more firmly articulated at their bases and are only ca- pable of movement in the sagittal plane. The stability of the second, third, and fourth metatar- sals results from osseous articulation and normal muscle f u n ~ t i o n . ~ * ~ ~ ~ ~ ~ ~ ~ ~
The neutral position of the subtalar joint is used as a reference to determine the alignment of the foot. Ideal nonweightbearing foot alignment is present when the forefoot is perpendicular to the sagittal calcaneus and when the calcaneus is parallel to the axis of the lower leg.''.17 The first metatarsal should assume a position level with the lesser metatarsals and be capable of an equal amount of plantarflexion and dorsiflexion, but is generally less flexible than the fifth metatarsal." The angle from the ground for the first, second, third, fourth, and fifth metatarsal shafts is 18-25, 15, 10, 8, and 5O, re~pectively.~~
The foot may be classified by toe and metatar-
INITIAL INITIAL FLOOR LIFT FLOOR
CONTACT OFF CONTACT
sal length. Referring to the foot as square, Greek, or Egyptian depends upon whether the first toe is the same, shorter, or longer than the second. The metatarsal length formulas are: index plus, 1 > 2 > 3 > 4 > 5; index plus minus, 1 r 2 > 3 > 4 > 5; and index minus, 2 > 1 > 3 > 4 > 5. V i l a d ~ t ~ ~ examined 1,000 feet and observed 16% index plus, 26% index plus minus, and 56% index mi- nus; considering the Greek and index plus minus formula to be ideal.
The weight distribution across the metatarsals differs in stance and level walking. The distribution of 12 units of load, as outlined by Morton, is transferred so that the heel accepts 6, the first metatarsal 2, and each of the lesser digits 1 .I4
Recently, research has demonstrated that the middle metatarsals accept high pressures and that the heel accepts greater than 50% of the load. In stance, the second and third metatarsals accept significant load^.'.'^,^^
During walking, the ground reaction forces in
PELVIS
FEMUR
TIBIA
CALF MUSCLES
Fig. 1 . Diagram illustrating the joint rotations and muscle activity in the lower extremity during a complete gait cycle. Reproduced with permission from Mann RA, Mechanics of the foot. In: American Academy of Orthopaedic Surgeons: Atlas of orthotics, CV Mosby Co.
m 15% jo( &% 60% 80% lOOX
~~~~~~& -EXTERNAL ROTATION- 0 ~~~~~~~-
I N A C T I V E -
OORSIFLEXION-
PLANTAR 3LEXION+
-INCREASING STABILITY-
"INCREASING A C T I V I T Y o l ,
4-blNACTIVE I
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JOSPT MaylJune 1985 METATARSALGIA 327
Fig. 2. Diagram illustrating the center of pressure in the foot during level walking. The numbers along the line represent the percentage of the stance phase of gait that the pressure is present at one location. Reproduced with permission of Mann18 and WB Saunders Co.
each foot segment varies during different phases of the gait cycle. Weight distribution moves through a line of central pressure. Generally. the center of pressure begins at the lateral heel, moves forward into the midfoot, and then shifts medially where it exits between the first and sec- ond toes at ~ush-off (Fig. 2). However variability of the center of pressure exit from the forefoot has been recorded by Stott et a1.34 The ground reaction forces exit between the first and second or second and third toes in subjects who have an index plus or index minus metatarsal formula. The center of pressure demonstrates to which areas of the foot the forces are distributed and the approximate time they remain at one location. The center of pressure moves rapidly through the heel and midfoot and then slows significantly at the forefo~t . '~ . '~ Weight is present at the forefoot for a longer period of time, requiring the weightbear- ing function of the metatarsals and toes to be three times that of the r e a r f o ~ t . ' ~ ~ ' ~ ~ ~ ~ At push-off all of the ground reaction forces are concentrated on the metatarsals and toes. This force has been calculated to be 120% of body eight.'^^^^ The force acting on just the toes is approximately 40% of body weight.33 The forefoot load is carried to a greater degree at the medial forefoot in younger subjects, while older subjects carry the forefoot load more equally between the medial and lateral f o r e f o ~ t . ' ~ . ~ ~ 3 3 4
V i l a d ~ t ~ ~ studied the sequence of foot contact during gait in 100 subjects and observed that in 70% of the cases, ground contact occurred as follows: 1) heel; 2) heel, metatarsals, and distal
toes; 3) heel, midfoot, and forefoot; 4 ) forefoot and toes; 5) toes; and 6) great toe.
The weightbearing stress at the metatarsals is partly relieved by the muscular activity of the toe flexors which counteracts forces occurring at the metatarsals during push-off. The metatarsals are further protected by the plantar skin, fat pads, and ligamentous structures which act as a natural cushioning mechanism (Fig. 3).20*37
PATHOMECHANICS OF THE FOREFOOT
Biomechanical metatarsalgia results from alter- ations in the weightbearing distribution of forces at the forefoot where the metatarsals become overloaded relative to their neighbors. Alteration in anatomical structure and alignment are major etiological factors. Foot type may contribute to metatarsalgia. Metatarsal weightbearing is in- creased with the cavus foot because a dispropor- tionate amount of weight is borne by the heel and forefoot. It is not uncommon to observe retracted or clawed toes with cavus feet, thus decreasing the toes' contribution to unload the metatarsals at push-off. The pes planus foot type (resulting from genu valgum, rearfoot valgus, or forefoot varus) remains pronated during midstance and inhibits proper supination, thus compromising the propulsive function of the forefoot.
Alterations in forefoot alignment may compro- mise foot function. Forefoot varus may be present where the medial forefoot is inverted relative to the rearfoot when the subtalar joint is in a neutral position. This malalignment decreases the medial stability of the forefoot and causes excessive foot pronatlon, as does rearfoot varus. Forefoot valgus may be present where the medial forefoot is ev- erted relative to the rearfoot when the subtalar joint is in a neutral position. This malalignment may result from the first metatarsal that is plan- tarflexed in a rigid position." Figure 4 illustrates the normal and abnormal nonweightbearing posi- tions for the forefoot. These alignment problems may increase and alter the stress acting at the metatarsals, but may not be clinically significant unless the alignment is excessive or rigid." Em- phasis should be placed upon examining the rear- foot, forefoot, and lower extremity for malalign- ment, since the biomechanics of the foot is de- pendent upon all foot and leg segments.
Foot force analysis has been more commonly performed on subjects with rheumatoid arthritis or hallux valgus deformities. Compared to con- trols free of foot pathology, these subjects dem-
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fibrous flexor sheath plantar ligament
trancrerse mctatars;~i l i rst lunibrical l i g a ~ ~ ~ t * t ~ t and scptunl vertical fihres
R Fig. 3. Illustration of the anatomical structures beneath the metatarsals. Reproduced with permission of MollerZ0 JB Lippincott Co.
I weakness of the toes. Simkin30 determined that the force concentration at the metatarsals was a better indicator of local stress than the quantity of the force because rheumatoid arthritis patients maintained lower forefoot force by decreasing their walking speed and by prolonging midstance.
The preceding research demonstrates the sig- nificant role of the hallux in weightbearing. The weightbearing capacity of the first metatarsal pro- gressively decreases as the hallux valgus deform- ity progre~ses.~ Hallux valgus results from rheu- matoid arthritis, neurological disbases, biome- chanical alignment problems, or develops by an idiopathic process or other Hypermo- bility of the first ray results in a clinical problem where a lack of support compromises its ability to assume adequate weightbearing loads.17 Pa- tients with metatarsalgia should be examined for associated disorders of the hallux. ScrantonZ6, in his series, concluded that 34 of 78 patients with either primary or secondary metatarsalgia had coexisting hallux disorders. Any painful condition of the hallux will shift weightbearing to the lesser
Fig. 4. illustrations of the normal and abnormal nonweight- metatarsals, particularly the second or third.*' bearing forefoot alignment types when the subtalar joint is in the neutral position. A, normal relationship; B, forefoot varus; CLASSIFICATION OF METATARSAL C, plantarflexed first ray; D, forefoot valgus. PATHOMECHANICS
onstrate an inadequate propulsive role of the fore- foot resulting from the center of pressure exiting more laterally, between the second and third or the third and fourth toes10~12~28~30-32~34 and greater stress at the metatarsals due to decreased toe flexor muscle activity, particularly in subjects with hallux valgus.10~12~28~30-32 Sharma et aL2' con- cluded that the lack of medial weightbearing at push-off in rheumatoid arthritis patients was due to either inadequate pronation or flexor muscle
V i l a d ~ t ~ ~ has classified metatarsal pathome- chanics as an overload of anterior support or an irregular distribution of the metatarsal load. Irreg- ular metatarsal load syndromes are further sepa- rated into the following four groups: l ) first ray overload, 2) first ray insufficiency, 3) central ray overload, and 4 ) central ray insufficiency. The different patterns of weight distribution in the ir- regular metatarsal load syndromes are illustrated with pedographs (Fig. 5).
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JOSPT MaylJune 7985 METATARSALGIA 329
b&.k&s- metatarsal frontal plane malalignment, subluxa- 3 - - tion, dislocation, claw or hammer toes, or congen- -
- itally long central metatarsals are predisposing - % factors.37 The position and function of the central
+ metatarsals is commonly disturbed by the mal- position and malfunction of their respective digits as they are pinned down by digital retraction or subl~xat ion.~~
I -7 - -- % Lesser metatarsal overload is caused by inad- - - -- _ / ._ -
- -7
metatarsal, forefoot, or rearfoot varus can result
dk in excessive pronation. First metatarsal varus and
- - hypermobility of the first ray are also predisposing .- - - -. factors to pronatory problems.29q37
- - -- - - - -. L- _---- - These syndromes are identified by patient com-
p- r >- - =+mAz - ' plaint, palpation, callus formation, anatomical -r--f; I;: e:k --?- 5-= - structure and alignment, pedograph and x-ray
examination. The Electrodynogram is being uti- 3 ) ~ 3 : - lized with increasing frequency to objectively ana- -7 1 --- - - lyze the quantity and duration of segmental and
- - - - - ' .- -. -- vertical foot forces with computer analysis of foot - . , c:. - . t biomechanics from foot sensor data.g The tem-
poral and distance variables of aait can be ana- Fig. 5. Pedographs representing the different syndromes of iyzed by utilizing the Footswitc~Stride Analyzer irregular load distribution at the metatarsals: A, first ray over- load; B, first ray insufficiency; C, central ray overload; 0, (6 & L Engineering, Santa Fe Springs, CA.) with central ray insuffi6iency.
Overload of anterior support occurs from im-…
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