Chapter 32: BiomechanicsNormal ValuesCriteria of Normalcy in the Lower ExtremityAdult Biomechanical ExaminationCommon Structural VariationsPlanes of MotionAxes of Joint MotionAngular and Axial DeformitiesAnatomy of Gait: Activity of MusclesObservation of GaitSubtalar Joint MeasurementsSubtalar Joint FunctionMidtarsal Joint Function

BIOMECHANICSNormal Values1. Quick reference chart of normal biomechanical findings:

Part Birth Position Adult PositionThigh/Femur/Hip (frontal plane)

(transverse plane)

Angle of head and neck of femur=150°(angle of Inclination)

Externally rotated 60°Femoral torsion (angle declination)=30°Total range of motion=150°

At age 6 years=125°

At age 6 years=0At age 6 years=10°Past puberty=100°

Knee (Birth) (1&1/2-3yr) (3-6yr) (7-puberty) (puberty-18) (over 18) (over 60) Genu Varum Straight Genu valgum Straight Genu valgum Straight G. valgum

Genu Recurvatum=5-10°Externally rotated=30°Frontal plane rotation=5-10°Transverse plane rotation=5-15°

At age 6 years =0°At age 6 years=0°At age 6 years=0-5°At age 6 years=0-5°

Leg/Tibia Varum(approx. 15°) At age 18 years=0-2° varumTibial torsion at birth=0° 1 yr=6°, 2-3 yr=10-15°, 5-6 yr=18-23°Malleolar torsion at birth=0° 5-6 yr=13-18°Rearfoot At birth= 10° varus approx.

Talocalcaneal angle=30-50° Calcaneal inclination angle=approx. 14° Talar declination angle=approx. 30° Calcaneal stance @ 1 yr=5-10° 5 yr=3-8° Dorsiflexion=45° approx.

At 6 years=2-5° varusAt 6 yrs=25-30°At 6 yrs=20° approx.At 6 yrs=21° approx.8 yr=<2° external rot.After age 18=10V min

Forefoot Varus 10-15° (birth) Metatarsus adductus=15-35° (birth)

At age 6=0-2° varusAdult=15-22°

Criteria of Normalcy in the Lower Extremity 1. Nonwelghtbearing:a. Malleolar torsion should be 13°-18° externally rotatedb. Ankle joint dorsiflexion should be at least 100 with the knee extended c. Ankle joint plantarflexion should be at least 20°d. Total STJ ROM should be 30° (with 20° of inversion and 10° of eversion) e. When the STJ is in neutral position, the calcaneal bisection should be parallel to the bisection of the lower 1/3 of the leg and perpendicular to the supporting surfacef. When the MTJ is maximally pronated and locked the forefoot should be perpendicular to the calcaneal bisection and parallel to the supporting surface and the knee on the frontal plane with the hip neutral at 0° g. There should be equal excursion dorsally and plantarly (5mm) of the 1st ray from a level equal with the 2nd metatarsal when the STJ is in its neutral position and MTJ maximally pronatedh. The 5th ray should have equal excursion dorsally and plantarly from a level equal with the central 3 metatarsals when the STJ is in its neutral position and MTJ maximally pronated

2. Weightbearing:a. The distal 1 /3 of the leg should be verticalb. The knee, ankle, and STJ should lie in transverse planes parallel to the supporting surfacesc. The STJ should rest in its neutral position

d. A bisection of the posterior surface of the calcaneus should be vertical e. The MTJ should be locked in a maximally pronated position about both its axesf. The plantar plane of the forefoot and rearfoot should be parallel to each other and to the supporting surfaceg. The central 3 metatarsals should be completely dorsiflexed and describe a plane parallel to the supporting surfaceh. The 1st and 5th metatarsals should describe a common transverse plane with the central 3 metatarsals

Adult Biomechanical Examination1. Non-weightbearing assessment:a. Ankle dorsiflexion:i. Taken with the patient supineii. The minimum ankle joint dorsiflexion that is necessary for normalambulation is 10° with the knee extended.iii. Dorsiflexion is also measured with the knee flexed

b. Subtalar joint ROM: to calculate neutral positioni. The posterior calcaneus is bisected as is the posterior /distal 1 /3 of the legii. The foot is dorsiflexed to resistance, the MTJ is pronated and locked against the rearfoot, and the rearfoot is supinated maximally and pronated maximally. The total ROM is measured with a goniometer (or tractograph) placed parallel to the bisection of the lower 1/3 of the legiii. The STJ neutral position is defined as that point that divides the medial 2/3 of motion from the lateral 1/3 of motion

iv. The minimal STJ ROM is 8-12° for normal ambulation c. Midtarsal (forefoot):i. The foot is held by the 5th metatarsal and dorsiflexed to resistance and then slowly everted until the STJ reaches neutral positionii. The plantar plane of the rearfoot should be perpendicular to the calcaneal

NOTE* If the amount of dorsiflexion is less than or equal to 100 whether the knee is extended or flexed, then there is an osseus or soleus equinus; if the amount of dorsiflexion is decreased only with extention, then there is a gastrocnemius equinus

NOTE* Calculated neutral position= eversion - total ROM-3For example:From an examination there is revealed to be: 20° inversion + 10° eversion = 30° total ROM. So following the formula from above:Neutral position= eversion (100)- TROM-3 (100)= 0 °A positive number means a valgus or neutral position, while a negative number means a varus or neutral position

bisectord. First ray:i. Dorsiflex the foot to. resistance and bring the STJ into its neutral position, stabilize the 2nd-5th metatarsal heads and grasp the 1st metatarsal head and move it in a dorsal to plantar direction to resistance (this distance should be about 5 mm or 100 to either side of its resting position and its resting position should lie on the same transverse plane as the lesser metatarsals)e. Malleolar torsion:i. Reference marks are placed on the malleoli, the knee placed on the frontal plane, and a measurement made with a gravity goniometerii. Normal malleolar torsion is 13-18° externally rotatedf. Hip motion (transverse plane): internal and external rotation of the femuri. The hip joint functions around its neutral position, in a transverse plane, with the femur rotating the same number of degrees from a neutral position (same with the hip flexed and extended). Total range of internal and external rotation must be equal to be considered normalii. Mark the patella or the femoral condyles and measure internal and external rotation with a goniometeriii. A normal hip rotates 45° internally and 45° externally from a zero degree starting point. This results in a total ROM of 90° and a neutral position of zero (from the neutral position, the hip rotates 45° in each direction)

2. Weight-bearing assessment:

NOTE* Other examples of hip ROM:a. Internal rotation = 55° external rotation= 35°Total ROM= 90° 90-2= 45°, 55°(int)-45= 10° therefore, neutral position= 100

internal(from neutral position, the hip rotates 45° in each direction)b. Internal rotation=10° external rotation= 40°Total ROM= 50°, 50-2=25° 10°(int)- 25°=-15° therefore, neutral position= 15° external(from neutral position, the hip rotates 25° in each direction)

NOTE* When there is a variance in the degree of neutral position between the flexed and extended hip position, this indicates soft tissue abnormality limiting hip rotation. This abnormality is called internal or External Femoral Rotation Example of a 15° internal femoral position: Internal rotation with hip extended= 45° external rotation with the hip extended= 15°, total ROM=60° therefore, neutral position with the hip extended=15° internalInternal rotation with the hip flexed=45° external rotation with the hip flexed=45°, total ROM=90° therefore neutral position with the hip flexed=0

NOTE* Lack of symmetry in total ROM between the flexed and extended positions results in asymmetry of the neutral position measurement. This indicates soft tissue abnormality at the hip.

a. Angle and base of gait:i. The angle and base of gait are necessary to measure NCSP, RCSP and tibial varum. This allows for standardization and reproducibility of valuesii. The angle of gait is the number of degrees that the foot is deviated from the line of progression of gait (mid-sagittal plane of the body). Normally the foot is between 7°-10° abducted from the line of progressioniii. The base of gait is defined as the space between the malleoli duringmidstance (normally 1 & 1 /2 inches)

b. Neutral calcaneal stance position (NCSP):i. Defined as the angular relationship between the calcaneus and the ground with the STJ in its neutral position and the patient standing in the angle and base of gaitii. The calcaneus is bisected, the foot is placed in STJ neutral position, and the angular relationship between the calcaneus and (perpendicular to) the ground is assessed

c. Resting or relaxed calcaneal stance position (RCSP): This is measured with the patient standing in the angle and base of gait with the STJ in a relaxed position. A measurement is taken of the number of degrees the calcaneal bisector deviates from perpendicular with the ground

d. Tibial varum: Measured by placing the goniometer on the bisection of the lower 1 /3 of the leg, with the feet in angle and base of gait, and the foot placed in the NCSP

e. Gait evaluation: Things to look fori. What is the position of the calcaneus at heel strike? ii. Does the foot pronate excessively?iii. What is the position of the calcaneus and foot at midstance? iv. Is the heel lifting at the proper time? v. In propulsion: Is it vigorous and active? Does the hallux participate? Does the foot roll medially? Is there a plantarflexion of the ankle?vi. Is the knee joint on the frontal plane at heel strike, internally deviated, or externally deviated?vii. Does the knee joint flex and extend normally or not?viii. Does the pelvis function around the transverse plane or tilt excessively to one side?ix. Does the patient lead with one side excessively?x. Do the arms swing symmetrically?xi. Are the trunk and head in the sagittal plane?

Common Structural Variations: Signs and Symptoms

1. Rearfoot varus: A condition in which the calcaneus is inverted relative to the ground with the STJ in its neutral position. Symptoms: a. Callus, plantar 4th and 5th metatarsal heads b. Tailors bunionc. Haglund's deformityd. Inversion ankle sprainse. Adductovarus 4th and 5th hammertoesf. Mild HAV deformity

2. Rearfoot valgus: A condition in which the calcaneus is everted relative to the ground with the STJ in its neutral position. Symptoms: a. Callus, plantar 2nd metatarsal head (occasionally) b. Fatigue muscle of foot and legc. Arch paind. HAV deformity

3. Forefoot varus: A structural abnormality in which the plantar plane of the forefoot is inverted relative to the supporting surface and a vertical bisection of the posterior surface of the calcaneus when the STJ is in its neutral position and the MTJ is maximally pronated and locked (rearfoot is normal).Symptoms:a. Callus, plantar 2nd, 4th, and/or 5th metatarsal heads b. Muscle fatigue in foot and legc. Tailor's buniond. AdductovaruS 4th and 5th hammertoese. HAV deformityf. Plantar fascitis/heel spur syndrome

NOTE* With rearfoot varus the changes during gait are as follows: The knee would function fully extended both at heel contact and during midstance. The leg may be somewhat internally rotated at heel contact, and some internal rotation would occur if STJ motion were available from this point. During the latter half of stance phase normal external rotation of the leg occurs. Position of the heel at contact would be inverted. If the rearfoot varus is not fully compensated, the heel remains in an inverted position. The STJ is normally supinated at heel contact

NOTE* Rearfoot varus is not a major pronator. It only allows pronation until the heel is vertical

4.

Forefoot valgus (plantarflexed 1st ray with compensation by MTJ longitudinal axis supination): A structural abnormality in which the plantar plane. of the forefoot is everted relative to the supporting surface and the posterior bisection of the rearfoot when the STJ is in its neutral position and the forefoot is maximally pronated and locked about both MTJ axes (the rearfoot is normal). Symptoms:a. Callus, plantar to 1st and 5th metatarsal heads b. Tibial sesamoiditisc. Muscle fatigue in foot and legd. Flexion contractures of the lesser digitse. Lateral knee strain

5. Forefoot valgus (plantarflexed 1st ray with compensation by supination of the STJ and MTJ longitudinal and oblique axes): Symptoms a. Callus, plantar to the 1st and 5th metatarsal heads b. Tibial sesamoiditisc. Flexion contraction of the lesser digitsd. Lateral knee straine. Inversion ankle sprainsf. Haglund's deformityg. Intoe gait seen in children

6. Metatarsus primus elevatus: A structural abnormality in which the 1st ray has a resting position above the plane of the lesser metatarsals. Symptoms:a. Callus, plantar 2nd metatarsal and hallux IP joint b. Fatigue of muscles of the foot and legc. Dorsal buniond. Hallux limitus/rigidus

7. Equinus deformity (adults): Symptoms: a. Corn, 5th toeb. Adductovarus deformities of the 4th and 5th toy c. Fatigue of the muscles of the foot and leg d. HAV deformity

NOTE* With forefoot varus the changes to the gait cycle are as follows: During gait the individual with compensated forefoot varus functions with the knee internally rotating during forefoot loading (contact). The external rotation of the knee that occurs later in stance phase is decreased. There may be some reduction in the amount of flexion of the knee during stance phase because of the pronated position of the foot. The knee would be fully extended at heel contact and midstance. Following heel contact, normal ankle joint plantarflexion occurs with smooth contact of the forefoot. At heel contact the calcaneus is inverted. The heel everts during the stance phase of gait as the forefoot loads. The STJ will be in a pronated position through the rest of the stance phase of gait

e. Plantar fasciitis/heel spur syndrome f. Neuroma symptomsg. Contracture of all the digits (extensor substitution)

8. Forefoot supinatus: A relatively fixed supinated position of the forefoot relative to the rearfoot with the STJ in its neutral position and the forefoot maximally pronated and locked about both MTJ axes, caused by soft tissue adaptation. The MTJ ROM is typically decreased secondary to soft tissue contracture

Planes of MotionThere are three planes of motion in the body, one perpendicular to the other two, corresponding to the three dimensions in space. The position is one with the body erect, elbows extended, palms facing forward, _and feet slightly separated and parallel1. Sagittal plane: A vertical plane passing through the body from front to back, dividing it into right and left half. The cardinal plane divides the body into equal symmetrical halves

2. Frontal plane: A vertical plane passing through the body from side to side, dividing it into a front and back half. The cardinal frontal plane passes through the center of gravity dividing the body into equal but asymmetrical halves

3. Transverse plane: This is a horizontal plane, which passes through the body from side to side and from front to back, dividing it into an upper and lower half. The cardinal transverse plane passes through the center of gravity and divides the body into equal but asymmetrical halves

NOTE* The gait variations seen are as follows: The compensatory changes for equinus are an early heel-off with the knee slightly flexed throughout the stance phase of gait. The knee will be somewhat flexed at heel contact, the flexion might increase during midstance, but it never fully extends at heel lift. As the leg swings forward, it actually becomes hyperextended relative to the femur and then begins to flex, and is flexed by the time the heel contacts the ground. Rather than being an actual compensatory mechanism for equinus, this seems to protect the knee from abnormal stress in a fully extended position. In severe equinus the knee may go into hyperextention during the stance phase of gait (back-knee function). The ankle will be at 90° at heel contact unless the equinus is severe. Following foot flat, the ankle will then dons flex to the limit of its ROM, at which time heel-off will occur (the earlier the heel lift, the sooner the load to the forefoot, the more stress induced symptomatology there is. The STJ will typically be neutral or slightly inverted at heel contact.

NOTE* It is these planes of motion that are used as coordinates to describe where the axis of motion lies and what motion will occur around the axis

Axes of Joint Motion1. Either single or triplane joint motion:a. An axis can be defined as an invisible line around which all motion takes placeb. The axis of motion is always perpendicular to the plane in which the motion takes place (the motion takes place in one plane and the axis lies in the other 2 planes)c. The frontal-transverse axis is horizontal (its motion is sagittal plane), the sagittal-transverse axis is horizontal (the motion is frontal plane), and the frontal-sagittal axis is vertical (the motion is transverse plane) d. The majority of joints in the lower extremity are hinge-like, therefore when motion occurs around a joint it occurs by rotation about an axis

2. Position of the joint axes:a. Single joint motion: The plane of motion is perpendicular to the axis of motionb. Triplane joint motion: The amount of motion that can occur in that plane will depend upon the degree of angularity the joint axis makes to each individual body plane

3. Motion of specific joints: a. Hip:i. Transverse plane axis (controls sagittal plane motion): Controls the movements of flexion and extension. The range of hip flexion depends upon the position of the knee: When the knee is extended the hip can flex 90° (active flexion) and 140° (passive flexion) With the knee flexed the hip can be flexed 120° (active flexion) and 120° (passive flexion)ii. Anteroposterior axis: lies in the sagittal plane and controls the movements of abduction and adductioniii. Vertical axis (controls transverse plane motion): controls internal and external rotationb. Knee:i. Frontal plane axis (controls sagittal plane motion): Controls the motion of flexion and extension Active flexion of the knee with the hip joint extended can result in 120° of flexion, and 140° with the hip joint flexed Passive flexion of the knee may attain a range of 160°ii. Longitudinal plane axis (controls transverse plane motion): Motion of internal and external rotation Active internal rotation has a range of 30°, while active extended rotation has a range of 40°c. Ankle: The primary motions at the' ankle joint are flexion and extension in the sagittal planei. The axis of the ankle joint passes lateral, plantar, and posterior to medial, dorsal, and anterior passing through the tips of the malleoli. It is deviated from the frontal plane due to malleolar torsion The range of dorsiflexion available at the ankle joint is 20-30°, while the range of plantarflexion is 30-50°

d. Subtalar: The axis is oblique to all 3 body planes which allows for triplanar motion (pronation and supination). Pronation allows the motion of abduction, eversion, and dorsiflexion. Supination allows for adduction, inversion, and plantarflexion

NOTE* The greater the amount of degrees (up to 90°) between an axis of motion and a cardinal body plane, the greater the amount of motion that will occur in that body plane

NOTE* Due to slight deviations in the transverse frontal axis of the ankle joint we will see transverse plane motion of abduction and adduction

i. Subtalar joint axis passes from a plantar, posterior, lateral direction to a dorsal, anterior, medial direction. It enters the heel and exits through the dorsomedial surface of the talar neckii. The axis is directed 42° from the transverse plane and 16° from the sagittal planeiii. As the axis is deviated 42° from the transverse plane positioning it approximately equidistant from being completely vertical or completely horizontal, and equal amount of transverse and frontal plane motion will occur (i.e. Equidistant from both the frontal and transverse planes)iv. Additionally, as the axis is deviated 16° from the sagittal plane, this allows a minimal amount of dorsiflexion and plantarflexionv. The normal values for passive ROM from neutral is 20-35° of inversion to 10-15° of eversion for a total ROM of 30-35°

e. Midtarsal: Has 2 axes of motion which allow for triplanar motioni. The longitudinal axis passes 150 from the transverse plane and 9° from the sagittal plane. It passes dorsal, anterior, medial to plantar, posterior and lateral. It enters the calcaneus and exits medially through the 1st metatarsal-cuneiform joint. Since the longitudinal axis is more longitudinal (close to the transverse-sagittal axis) its permits frontal plane motion of inversion and eversion. The normal ROM is 4-6°

ii. The oblique axis passes 52° from the transverse plane and 57° from the sagittal plane. It enters the lateral aspect of the calcaneus (plantarly) and exits the talonavicular joint (dorsally). The motion that occurs is adduction and abduction, and dorsiflexion and plantarflexion. Inversion and eversion does occur, but is minimal

f. First ray: Consists of the 1st metatarsal and medial cuneiform

i. The axis of motion passes dorsal, medial, posterior (enters the medial aspect of the talonavicular joint) to plantar, lateral, anterior (exits third metatarsal-lateral cuneiform areaii. It angles approximately 45° to both the frontal and sagittal planes and slightly from the transverse plane. It is a triplanar axis, with most of the motion in the sagittal and frontal planes in a 1:1 ratioiii. When the first ray dorsiflexes, it inverts and when it plantarflexes it everts. For every degree the first ray dorsiflexes it also inverts 1°. The first ray axis is now a pronatory axis. The ankle, STJ, MTJ (longitudinal and oblique) and fifth ray all possess pronatory-supinatory axes. The 2nd, 3rd, and 4th rays as well as the digital IPJ's are all uniplanar and produce sagittal plane motion only

iv. The average ROM is 5 mm for dorsiflexion and 5mm for plantarflexion

g. Fifth ray: Consists of the 5th metatarsal

i. It has an axis of motion from proximal inferior, lateral to distal, superior medial and angles to all body planesii. It angles 20° from the transverse plane and 35° from the sagittal plane, therefore exhibiting triplane motion. The degree of sagittal and frontal plane motion is large, and transverse plane motion is minimaliii. When the 5th ray dorsiflexes it also everts and abducts (pronatory axis)h. Lesser rays: The central 3 rays along with the IPJ's, have axes that are parallel with the frontal and transverse planes, therefore will have motion only in the sagittal plane

NOTE* The digital MPJ's contain 2 axes, a transverse and a vertical. While the vertical axis allows for transverse plane motion, it is the transverse axis which allows for dorsiflexion/plantarflexion to occur. The transverse axis moves in a dorsal-proximal direction with MPJ dorsiflexion. The first MPJ must allow for 65% of joint dorsiflexion. The joint acts as a ginglymus joint for the initial 25° of dorsiflexory motion, and acts as arthrodial joint with the first metatarsal plantarflexing for and MPJ dorsiflexion after the Initial 25°

NOTE* The term "degrees of freedom" refers to the number of axes a joint has. While the ankle and most joints of the foot have one degree of freedom, the MPJ's and the MTJ each have 2 axes and thus 2 degrees of freedom

Angular and Axial Deformities of the LowerExtremity in Children1. Definitions:a. Torsion: is the twisting of a long bone on its longitudinal axisb. Rotation is an axial change in the limb due to changes at the jointc. Anteversion is an anterior axial change in the femur with relation to the head and neck to the distal condyles (refers to rotational and positional changes of the limb at the hip)d. Antetorsion (femoral): Refers to twists in the axis of bone. It is a twisting of the head and neck of the femur on its own body axis while the portion of the femur on its own body axis entering Into the knee joint area remains (more or less) in a fixed position, lining up with the lower leg

e. Retroversion: Is a lack of normal torsion in the femur, less than normal by 10-12°

2. Axial Deformities:a. Tibial torsion: Normally 18-23° (external) in the adult. Measured by malleolar torsion which is 5° lessi. Etiology: Soft tissue origin? osseous origin ?ii. Treatment: The decision whether to treat or not is determined by the degree of the deformity (if any), and the age of the child. In the infant with rigid tibial torsion, serial-above knee casting is effective, followed by maintenance with a Ganley splint or D-B bar

3. Femoral torsion:a. Anteversion (medial femoral torsion): Is an axial deformity within the neck and shaft of the femur, resulting in a medial functioning knee

NOTE* Normally, antetorsion at birth is approximately 390, and eventually untwists to 12° by adulthood. If antetorsion is greater than it should be (femur does not untwist enough), then we have one of the factors influenceing a pigeontoe gait

NOTE* While the bony femur is untwisting after birth, there is a simultaneous inward rotation of the thigh (anteversion) in the region of the hip. The bony external twisting (torsion) is being neutralized by the inward rotation of the thigh to align the extremity for forward progression

NOTE* The actual amount of tibial torsion cannot be measured, so therefore we measure malleolar torsion. From birth to 1 year it measures 0° to 10° (external), 1 year to 5 years it measures 8°to 13 ° (external), and 6 years to adult it measures 13-180 external torsion

i. Normal femoral alignment at birth is approximately 35-40° of anteversion, which gradually derotates to the adult alignment of 12-15°ii. Any delay in this progression should be considered abnormal and treated owing to positional imbalance caused by soft tissue constraints and the adaptability of the epiphysis to external forces. It is usually seen is the older female child and manifested by the "reverse tailor's" sitting positioniii. With this, there is a persistent medial effect of the femoral growth plateiv. Examination reveals excessive medial angle of the femur associated with a limited lateral range of motion suggestive of femoral anteversion v. Treatment: In the older child who presents with a knock knee conformation and who, on examination, shows excessive medial femoral ROM, treatment initially consists of change in sitting habits Later (if necessary) a Ganley femoral derotation splint (this splint is of benefit in the 4-8 year child with excessive medial ROM) In true persistent osseous anteversion in the older child a femoral derotation osteotomy or epiphyseal stapling may be necessary

b. Retroversion (lateral femoral torsion): Felt to be a continuation of lateral rotated position of the femur in infancy. Lateral ROM is excessive. Often found in females, usually obese with heavy thighs. The gait effect is knock-knee

4. Angular deformities:a. Knock knee (genu valgum): An angular problem found more often in the obese female child, it also may be associated with coxa vara, and is often the visual result of the proximal axial problems of medial and lateral femoral torsion. These changes are often associated with torsional changes of the

NOTE* The treatment approach to femoral problems has been difficult since any splinting device attached to the feet or legs is nullified once the knee flexes

lower leg and valgus foot deformity. Depression of the lateral tibial condyle in persistent knock-knee in the older child may also lead to soft tissue strain often reflected as quadriceps and calf pain. This can lead to DJD in the adult

i. Etiology: Physiologic Medial femoral torsion Lateral femoral torsion Anteversion syndrome (Kleiger) Trauma: microtrauma (Hueter-Volkman law of epiphyseal response to pressure states that increased pressure across the epiphyseal plate will decrease the rate of growth), direct trauma, infection b. Bowleg (genu varum): May, be associated with coxa valgai. Types: Physiologic: noted at birth Rickets: result of vitamin D deficiency causing a disturbance in the metabolism of phosphorous and calcium Osteochondritis deformans tibiae (Blount's disease): an angulation is noted only at the proximal tibia causing a characteristic "beaking" of the medial tibial plateau. This disease shows fragmentation of the proximal tibial metaphysis and may not become evident before 24-30 months of age. Additionally, infants with a metaphyseal-diaphyseal angle of 110 or greater (created from the intersection of a bisection of tibial and a bisection of the femur) will eventually develop Blount's disease

Anatomy of Gait: Phasic Activity of MusclesThe human body has evolved bipedalism as the most efficient means of locomotion. Bipedal gait is a repetitive sequence of alternating movements of the lower limbs; one complete sequence represents a gait cycle1. Subdivisions of the gait cycle:a. Stance phase (62% of gait): The period of ground contact and weight support of the footi. Contact period (27% of stance and 17% of the entire gait cycle): initiated by heel strike, the fully dorsiflexed foot Is lowered to the ground as the body moves from a posterior position to one more directly over the foot. The key locomotor events of contact are: Subtalar joint pronation (for shock absorption) which is normal pronation Subtalar supination (closed chain, begins at the end of contact) Internal rotation of the leg and femur (concurrent with STJ pronation) Full loading of the metatarsus is completed by the end of contact Peak vertical ground reactive forces occur for the first time at the end of contact (the first of the two periods where the ground reactive force rises above body weight during late contact phase The foot functions as a mobile adaptor in contact Internal leg rotation initiates STJ pronation At the end of contact the STJ begins supinating and it is initiated primarily by the posterior tibial and is aided somewhat by the other calf

supinators and leg external rotators

ii. Midstance period (40% of stance): Foot flat begins midstance, when it singly bears the body weight (single support), and the alternate foot is in the swing phase. The key locomotor events of midstance are: Conversion of the foot from a mobile adaptor to a rigid lever for propulsion. The primary condition for a rigid lever to occur is STJ supination (when this does not occur you have all types of problems (i.e. flatfoot). This leads to a poor propulsive unit A decrease in vertical ground reaction force to about 75% of body weight, but begins to increase again prior to heel lift Continued external leg rotation The contralateral limb is in swing phase STJ supination as a result of external leg rotation and the supinating calf muscles (especially the posterior tibial and swinging limb). The foot passes through STJ neutral shortly before heel lift. From this point on, the STJ is supinated

iii. Propulsive period (33% of stance): Continuation of the forward shifting body results in heel lift and the initiation of the propulsive period, whereby the weight is shifted to the forefoot and at the end, opposite foot regains contact with the ground by heel strike. The key locomotor events of propulsion are: Continued STJ supination which increases skeletal rigidity and creates a rigid lever Continued external leg rotation Second peak vertical ground reaction force (about 125% of body weight) Shift of forefoot weightbearing from lateral to medial The opposite foot begins to bear weight just after lateral to medial shift and by toe-off the opposite foot is in full contact phase

b. Swing phase (38% of gait): That portion of the gait cycle when the foot is off the ground. During swing the foot pronates first and then supinates. The key events of swing phase are: During swing, the foot is transported from one step to the next The leg continues to externally rotate momentarily after toe-off. Then it begins an internal rotation during the swing Pronation of the foot to aid ground clearance and then resupination to prepare for contact Ankle joint dorsiflexion, and hip/knee flexion to shorten the length of

NOTE* At the beginning of weightbearing, during the entire contact period, the STJ pronates in order to make the foot more flexible and, as such, a better mobile adaptor to variances in terrain.

NOTE* During midstance the STJ is still pronated but starts supinating to convert the foot to a rigid lever

the leg (there would be a tremendous amount of pelvic motion during gait if there were no mechanisms to flex and shorten the leg length)

c. Double support: Both feet are in ground contact at the beginning and end of each stance phase in the walking gait. Both feet are on the ground 25% of the gait cycle (0-12% and then again from 50-62% of the entire gait cycle)

2. Hip and knee motion:a. Motions in gait: At toe off, both the hips extended and knee is flexed while the limb Is posterior to the body. At heel strike the hip is flexed, the knee extended and the limb forms a lever for the movement of the body onto the heel. During stance the limb extends at the hip as the body moves over the stationary foot. Internal rotation of the limb continues from swing phase into the contact period of stance. In midstance, the limb begins external rotation as the opposite side of the pelvis and hip shift forward and medially rotate during swing phase of the opposite limb b. Swing phase muscle action:i. Hip flexors: The primary flexor of the hip is the iliopsoas which is activated shortly after toe off: it is comprised of the iliacus and the psoas major to form a common muscle bellyii. Hip stabilizers and rotators: In swing phase, the hip on- the swing side has lost support from the ground; it needs to shift body weight medially to the stance limb and to resist downward tilt. The unsupported hip, therefore, needs greater muscular stabilization in swing phase than it does when supported in stance Transverse stabilization of the unsupported hip is produced by the erector spinae on the swing side The hip abductors (gluteus medius and minimus) pull down the pelvis on the supported side, and lift and level the pelvis op the swing side. Their primary function on the swing side is to abduct the-thigh The medial hip adductors (adductor longus, adductor brevis, adductor magnus, and pectineus), stabilize the hip and thigh (with the abductors) in both stance and swing, and they contribute to flexion, extension, and internal and external rotation of the hipiii. Knee extensors: The quadriceps femoris (rectus femoris, vastus medialis, vastus lateralis, vastus intermedius) is a biarthrodial muscle acting on hip flexion and knee extension at the same time. The quadriceps is the only extensor of the leg, and in the walking gait, extends the leg near the end of swing (this extention is decelerated by the hamstrings (semimembranosis, semitendinosis, biceps femoris)

NOTE* In running gaits, the swing phase proportionally increases in duration, an instead of stance phase overlap, the limbs overlap in off-ground motion in a period of float; i.e. there is no double support phase during running, also there is an airborne phase with no ground contact and there is never more than one foot in ground contact at one time

iv. Knee flexors and hip extensors: The hamstrings, prior to heel strike, exert a flexor force on the leg, decelerating ongoing extension, and extend the hip in early stance. The semimembranosus and semitendinosus medially and biceps femoris laterally, are synergists of each other in stabilizing rotation at the knee at heel contact. The hamstrings also stabilize both the hip and knee joints at heel strike

c.

Stance phase muscle action: In the contact period, those muscle groups that decelerated and stabilized these joints at heel strike continue to perform these functions until the foot achieves full foot support. At midstance most of the weight-support functions are managed by bone and ligament, requiring little primary muscular action. As. the body moves over the standing foot, the limb externally rotates in all segments down to the ankle. This rotation is a reaction both to subtalar supination and to medial rotation of the opposite limb swing phase. After the stance limb passes beneath the hip joint, the hamstrings are again activated to help extend it

3. Ankle motion:a. Motions in gait: Functions on a pronatory/supinatory joint axis with the majority of motion consisting of sagittal plane dorsiflexion and plantarflexion. Any rotation of the leg carries the talus with it when the foot is off the ground, and any subtalar action involving the talus affects leg rotation when the foot is weight bearingb. Dorsiflexors: Dorsiflexion occurs from late contact to the propulsive period, whose action is the result of kinetic forces of the body moving over the limb. The 4 anterior crural tendons pass anterior to the transverse axis of the ankle joint, and therefore dorsiflex the ankle. Distally, the tendons pass to either side of the subtalar and midtarsal joint axes where the tendon passing medially (tibialis anterior) exerts an inverting force, supinating the STJ and MRJ axes. The tendons passing laterally (EDL, peroneus tertius) exert an everting force (these apply a pronatory force to the STJ and MTJ longitudinal axes). The anterior crurals function mainly during swing to dorsiflex the foot to clear the ground. The toe extensors begin to act at the end of the propulsive. period, when they help stabilize the toes. They are joined by the tibialis anterior and peroneus tertius, and together lift. the foot at toe off. After heel strike, they decelerate the foot while it is lowered to the ground.

NOTE* The gluteus maximus (the largest and most powerful of lower extremity muscles) contributes to hip extensor stabilization

NOTE* The tibialis anterior is the main dorsiflexor because of its insertion at the base of the first ray, and acts together with the EHL in elevating the first ray and hallux above the groung during swing (its insertion is also medial to the STJ and MTJ axes making it an effective supinator, and invertor during dorsiflexion)

c. Plantarflexors: Consist of 6 muscles divided into superficial and deep groups (superficial: gastrocnemius, soleus, plantaris) (deep: tibialis posterior, FDL, FHL). The tendo Achilles passes 2 cm posterior to the STJ axis giving itmore leverage to act on the ankle than any other muscle (supinates the ankle). The combined action of the triceps surae (2 heads of the gastroc and the soleus.) together with the deep plantarflexors, produce 4 times as much power as the combined dorsiflexors, and mainly act on the fully loaded limb in single support. The tibialis posterior is the strongest invertor and adductor of the foot. The plantarflexors begin to function in the contact period and continue through midstance and into propulsion. They act to decelerate the momentum of the body as it moves across the fixed foot dorsiflexing the joint. The gastrocnemius also resists hyperextension of the knee prior to heel lift

4. Tarsal joint motion:a. Motions in gait: The definitive feature of the contact period is progressive loading of the foot from its initial contact at the heel, along the lateral border, to full foot support. At this stage, the foot is undergoing pronation, and the leg continues to rotate internally. These joints are characterized by their flexibility (if the MTJ is unlocked, the 1 st ray is not stabilized). By midstance, the weight is progressively more medially distributed as the body center of gravity continues to move over it. From the lateral border of the foot, weight is shifted medially along the metatarsal heads. The stresses on the foot now require rigidity in tarsal structure to transfer weight to the forefoot. As the STJ begins to supinate, the leg, with the hip and the thigh, externally rotate. This supinatory process involves the windless effect as the foot proceeds through propulsion.b. Tarsal stabilizers: In midstance, the soleus, gastrocnemius, and tibialis posterior are the prime movers to supinate the foot with concurrent external rotation of the leg. The peroneus brevis and longus (lateral crural ms.) are inactive in the contact period and only begin to act well into midstance and early propulsion. The peroneus brevis is the prime evertor (pronator) of the foot. The peroneus longus exerts a force on the first ray, pressing the first metatarsal to the ground as well as on the intervening tarsals. The combined result is a compact tarsus. The continuing secondary action of the soleus and supinating tendons from the posterior compartment, maintain pressure on the lateral border of the foot. This maintains a fixed position of the cuboid, which acts as a pulley for the peroneus longus tendon. At the end of midstance, the heel is lifted, and the cuboid is released, permitting the peroneus longus to act more directly on the 1st ray as body weight is lifted

NOTE* Summary of anterior aural function: They become active at toe-off to dorsifex the foot. They remain active throughout swing, and show a peak activity at heel strike as they decelerate the forefoot as it strikes the ground. They are active for the first 10% of stance

NOTE* Summary of posterior aural function: The, triceps surae are active during the middle of stance phase. They begin to fire during contact and terminate during propulsion in order to achieve heel-off

from the lateral metatarsal heads

5. Forefoot motion:a. Motions in gait: Stability in the forefoot begins to develop in the latter part of midstance when the foot is supinating, the MTJ is locked, and the tarsal and metatarsal bones are in a close packed position. At heel lift, the foot forms a lever from the plantarflexing ankle joint to the met heads that form its fulcrum. The MPJ's are transversely stabilized while the toes are firmly braced against the ground forming a stable platform for the fulcrum. The loaded extension at these joints activates the windless effect of the plantar fascia, which is stretched by its attachment to the MPJ and hallux

b. Extrinsic muscle action. The FHL continues to act almost until toe off as the hallux is the last part of the foot to leave the ground and requires a longer period of stabilization than do the lesser toes. The tibialis posterior and the peroneals compress the metatarsal bases as well as the tarsal bones. The peroneus longus stabilizes the 1 st ray through the propulsive period

c. Intrinsic muscle action: The main function of the intrinsic muscles of the foot is to transversely and axially stabilize the digits against the metatarsal heads and against ground reaction forces. All intrinsic muscles begin to contract in midstance and most continue throughout the propulsive period. Transverse stabilization of the toes is accomplished by the plantar and dorsal interossei. The dorsal interossei are bipennate and 4 in number, originating from the corresponding adjacent sides of their respective intermetatarsal spaces. The first dorsal interosseous attaches medially into the base of the proximal phalanx of the second toe while the 2nd, 3rd, and 4th attach laterally into digits 2, 3, and 4. The plantar interossei are unipennate. These three muscles attach medially into the 3rd, 4th, and 5th digits and originate from the medial aspect of their respective metatarsals. Their combined action resists displacement of the toes to either side. Transverse stability of the hallux is provided by the abductor hallucis on one side and adductor hallucis on the other side. The abductor digiti minimi mimics the function and attachment of the dorsal interosseus on the lateral side of the 5th toe. The FHB, FDB and flexor digiti minimi brevis act synchronously with the long flexors, stabilizing the toes against the ground. The flexor digiti minimi brevis attaches laterally into the 5th toe, as a unipennate muscle and functions with the interossei to provide transverse plane digital stability. The interossei are stance phase muscles and function to plantarflex the MPJ's against the retrograde dorsiflexing buckling force that accompanies the FDL and FDB contraction. The axial tension of the FDL is aided by the quadratus plantae. The lumbricals are 4 muscles originating from the medial aspect of the corresponding FDL slip, and attaching medially into the base of the extensor hood of the lesser toes, as they pass plantar to the deep transverse metatarsal ligament. These have been described as swing phase muscles, stabilizing the MPJ's plantarly while assisting in extending the PIPJ's and DIPJ's, limiting excessive swing phase contraction. This provides a stable insertion to allow the EDL to be an important dorsiflexor of the ankle during

swing phase of gait

d. Muscles acting on the 1st ray and hallux: During supination in the midstance period, the peroneus longus is uniquely significant in plantarflexing the 1st ray. The FHL assists in supination during the earlier part of midstance, plantar stabilization of the, metatarsal head together with the action of the peroneus longus, and stabilization of the hallux in propulsion

6. Summary of joint motion during gait: a. Hip joint motion-sagittal plane:i. Contact: hip extends from flexed positionii. Midstance: hip continues to extendiii. Propulsion: hip flexion

b. Hip joint motion-transverse plane:i. Contact: internal rotation of the thigh in the pelvis, corresponding to internal leg rotation with STJ pronationii. Midstance and propulsion: external rotation of the thigh on the pelvis

c. Knee joint motion sagittal plane:i. Contact: flexion (the major shock absorbing mechanism of the body) ii. Midstance: body weight passes over the knee, so there is extension iii. Propulsion: the knee flexes again for pushoff

d. Knee joint motion-transverse plane: Corresponds to supination and pronation in the STJi. Contact: with STJ pronation comes internal rotation of the tibia ii. Stance: external rotation of the tibia on the femur

e. Ankle joint motion-sagittal plane:i. Contact: plantarflexion until midcontact ii. Late contact to midstance: dorsiflexion iii. Propulsion: plantarflexion

f. Subtalar joint motion:i. Contact: pronationii. Midstance and propulsion: supination

g. Midtarsal joint motion: There are 2 separate axesLongitudinal axis Oblique axis

i. Contact: Supinated Pronated

NOTE* The greatest combined effect of all these muscles is achieved in conjunction with the extensor expansion mechanism, which links the IPJ's & the MPJ's in each toe so that tension on the long extensor extends a row of digital joints at a time

NOTE* Summary: The abductor digiti minimi and EDB become active at about 30% of stance, the FHB, abductor hallucis, and FDB become active at about 40%, 50% and 60% of stance respectively, and the interossei become active at about 25% of stance. Activity of all these muscles ceases near toe-off

ii. Midstance: Fully pronated by heel lift* PronatedIll. Propulsion: Remains pronated and locked Supinates

Observation of Gait1. Stance phase:a. Posterior view:i. Contact: Heel contact is inverted but rapidly everts Contact is slightly lateral to the midline of the heel i. Midstance:Posterior bisection of the posterior of the heel goes from everted to verticali. Propulsion: Posterior bisection of the heel inverts as heel lifts

b. Lateral view:i. Contact: Posterior portion of the heel strikes the ground with the foot dorsiflexed on the ankle Plantarflexion of the ankle begins slightly after contact At contact the knee is extended and flexes rapidly for shock absorptionii. Midstance: Ankle dorsiflexion of 5°-10° as the body weight passes over the planted foot Knee returns to full extension Late midstance heel lifts as the trunk passes over the planted foot, literally peeling the heel up from the flooriii. Propulsion: Ankle plantarflexes to facilitate toe-off Knee flexion as the trunk advances further

c. Anterior view: i. Contact: Forefoot is markedly inverted as the heel contacts the ground Leg is slightly invertedii. Midstance: Forefoot has everted bringing the metatarsals to the ground. The forefoot is loaded 5-4-3-1-2 or 5-4-3-2-1- depending upon the metatarsal length and muscle functioning Leg is slightly internally rotatediii. Propulsion: Marked dorsiflexion of the MPJ's Lateral digits lift-off first Body weight passes through the center of the hallux

NOTE* Longitudinal axis pronation during midstance* is very important for normal propulsion. Negative plaster casts are taken of the feet with the longitudinal axis of the MTJ in pronation

Leg externally rotated

2. Swing phase:a. Lateral view:i. Trunk muscles advance the leg forwardii. Ankle dorsiflexion to decrease leg lengthiii. Hip and knee flexion to assist in shortening

Subtalar Joint Measurements1. Open kinetic chain measurement and neutral position calculation: In the non-weightbearing patient, the bisection of the posterior distal 1 /3 of the leg is the point from which calcaneal inversion and eversion are measured.a. Example 1: The calcaneus can evert 80 from the leg bisection and invert

22° from the lebisction. The total STJ ROM is 30°

To find the neutral position of this STJ we need to find the point from which there is twice as much supination as there is pronation. In this case the neutral position is 2° inverted, as from this point there is 100 of pronation and 20° of supination available

30°(total ROM) X 2= 20° 22°(inversion from leg)- 20°= 20 varus

Total STJ ROM X 2= Inversion from neutral position3

Inversion from the leg -MINUS- Inversion from neutral= Neutral position

3b. Example 2: Calcaneal inversion= 32°, calcaneal eversion= 7°, total ROM= 39° 39°+ 3 x 2= 26° inversion from neutral, 32°-26°=6° varus

2. Closed kinetic chain measurement and neutral position calculation: a. Example 1:Maximum calcaneal inversion 12° (right), 150 (left), maximum calcaneal eversion 6° (right), 3° (left), tibial varum 1 ° bilaterallyi. To calculate neutral position: Total ROM 18° bilaterally18+ 3 x 2= 12° 12°- 12°= 00 (right), 15°- 12°= 30 varus (left)

ii. To calculate NCSP: Add the tibial varum component to the neutral position measurementTibial varum is 1 ° (left) + 30 varus (left)= 40 rearfoot varus (left) Tibial varum is 1 ° (right) + 0° (right)= 1° rearfoot varus (right)

iii. To calculate the RCSP: Since these values indicate a rearfoot varus component, this individual will compensate at the STJ to bring the calcaneus perpendicular to the ground, by using all STJ pronatory ROM that it needs (the pronatory ROM of the STJ is 1/3 the total ROM or 6°). On the right the NCSP= 1° varus so the RCSP= 0° On the left the NCSP= 40 varus, so the RCSP= 0° (using 2/3 available pronatory ROM)

b. Example 2:Maximum calcaneal inversion 16° (right), 15° (left), maximum calcaneal eversion 2° (right), 3° (left), tibial varum 30 (right), 2° (left) i. Calculate the neutral STJ position:Total ROM (right)= 18° Total ROM (left)= 18°18-3 x 2= 12° (bilateral) inversion from neutral16°- 12°= 40 varus (right), 15°- 12°= 30 varus (left) neutral position

ii. To calculate the NCSP:Tibial varum 3° (right) + 4° varus neutral (right)= 7° rearfoot varus NCSP (right)Tibial varum 2° (left) + 3° varus neutral (left)= 50 rearfoot varus NCSP (left)

iii. To calculate the RCSP: Know that 1/3 the total STJ ROM is 6°. 7° rearfoot varus (right)- 6° (1/3 available pronation)= 1° RCSP (right)5° rearfoot varus (left)- 6° (1/3 available pronation)= 0° RCSP (the STJ still has 1° more of available compensatory motion left)

NOTE* Another method for calculation is: Total ROM- Eversion = Neutral 3

If the resulting number is (+), then there is a varus or neutral positionIf the resulting number is (-), then the resulting number is valgus or neutral

Subtalar Joint FunctionDuring the gait cycle, the STJ functions during the weightbearing (closed kinetic chain) and nonweightbearing portions (open kinetic chain). 1. Open kinetic chain (OKC):a. During the 1st half of the swing phase, the STJ pronates, and during the last half of swing the STJ supinatesb. In OKC function, the STJ pronatory and supinatory components are exhibited exclusively by the calcaneus (with OKC pronation, the calcaneus abducts, everts, and dorsiflexes)c. In OKC motion, the calcaneus moves around the talus, which functions as an immobile extension of the leg

2. Closed kinetic chain (CKC):a. In CKC the STJ motion, the calcaneus and talus both move, the calcaneus moves only in the frontal plane (inversion and eversion), and the talus moves in the transverse and sagittal planes

b. In CKC STJ pronation, the calcaneus will still evert, but the talus will plantarflex and adduct

c. In CKC STJ supination, the calcaneus will invert and the talus dorsiflex and abduct (the talus abducts and dorsiflexes because it is proximal to the STJ joint axis) (transverse plane talar excursion reflects the transverse plane movement of the leg)

NOTE* Forefoot varus is compensated (mostly) by STJ pronation, and minimally by some MTJ pronation. If the amount of forefoot varus is 3° or less, the STJ will only compensate that sped lc number of degrees. lf, however, the forefoot varus is greater than 3° the STJ will (usually) maximally pronate to the end of its ROM. Therefore it will pronate more than the number of degrees required to bring the forefoot's medial surface into contact with the ground. The reason the STJ maximally pronates with a forefoot varus deformity greater than 3° is that once the calcaneus is everted more than 3° the force of the body's weight pushes it to the end of the STJ's pronatory ROM. If, however, the STJ cannot completely compensate the forefoot varus deformity, then and only then will the MTJ pronate to help with the compensation (on the longitudinal axis), leading to first ray dorsiflexion and inversion

NOTE* In a rearfoot valgus greater than 2° the body weight on the evertedcalcaneus will cause the STJ to pronate to the end of its ROM. A rearfoot valgus of less than 2° does not change the STJ position from the NCSP. If a greater than 10° rearfoot valgus exists, the head of the talus will usually plantarflex toward the ground before the STJ completely pronates. While this produces a severe flatfoot, the STJ may not be pronated to the end of its ROM

NOTE* The bones of the STJ move around the STJ's axis of motion, and if any motion takes place in a bone which is proximal to that axis, the motion will be in the opposite direction of the named major motion.

d. Internal rotation of the tibia is associated with CKC STJ pronation, and the converse is true with CKC STJ supination

e. The 2 major functions of CKC pronation are shock absorption and adapting to uneven terrain

3. Measurement of STJ motion:a. There is really no good way to measure STJ motion in all 3 planes, therefore, the frontal plane motion of the calcaneus is used as an index of STJ motion (a bone distal to the STJ axis)b. From the STJ neutral position, the normal foot can supinate twice asmuch as it can pronate. The average total ROM for the STJ is about 30° ofcalcaneal frontal plane motion (minimum normal STJ ROM is 8-12° for normal ambulation)

Midtarsal Joint FunctionAlthough triplane motion occurs about both the MTJ axes, some planes of motion are so small as to be clinically insignificant 1. MTJ function:a. Motion about the longitudinal axis will occur primarily in the frontal plane (inversion and eversion)b. The oblique axis allows primarily for sagittal and transverse plane motion

NOTE* During the contact period (STJ pronation) the calcaneus is everting, while the talus is plantarflexing and adducting. During midstance and propulsion the calcaneus is inverting while the talus abducts and dorsiflexes (STJ supination)

NOTE* Since 2 planes of motion occur about the MTJ oblique axis, it is necessary to know which motions are coupled. As the axis is a pronatory/ supinatory axis, the following occurs by necessity:a. With plantarflexion: adduction also occursb. With dorsiflexion: abduction also occurs

NOTE* The MTJ's total ROM is dependent upon the STJ's position. The axes of the articular facets are just about parallel when the STJ is maximally pronated. This allows for a certain congruity to the 2 joints (T-N and C C joints). As the STJ goes from a maximally pronated position toward a more supinated position, the axis of the 2 joints progressively diverge from one another, congruity is lost, and with it ROM decreases

c. The MTJ longitudinal axis has an average ROM of 4°-6° (ROM of the oblique axis is unknown)

d. When the STJ is maximally pronated, the MTJ's ROM is increased and the forefoot becomes mobile. When the STJ is maximally supinated the MTJ's ROM is decreased and the forefoot inverts with the rearfoot