The Basic Biomechanical Exam
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Hello, I am Darrell Phillips, Director of Podiatric Residency at Coatesville Veterans Administration Medical Center in Coatesville, Pennsylvania. Today I will present the basic techniques for performing a biomechanical examination.
Production of this present lecture was made possible by a generous grant from Mile High Orthotics, bringing your expectations to higher elevations.
This is a copy of my basic biomechanical exam form that I use in the office. The biomechanical examination is a very important part of the total podiatric evaluation. From it, we learn a great deal about the alignment of the foot and also the amount of motion that the various segments of the lower extremities have available to work within. The information gained within this examination should be very valuable in helping to make decisions about both the conservative and surgical management of the foot.
Today we see many people failing to perform biomechanical examinations. The reasons given usually include such things as: I still do everything the same, it doesn't change the way I practice; I don't have the time; or studies have shown that the exams are not reliable when such attitudes are entertained, the clinician deprives himself or herself of a valuable opportunity to learn more about the patient's reasons for functions. Most of the reasons for unreliability are due to poor, usually cheap instrumentation and a lack of standardized techniques for evaluation. This presentation will emphasize the techniques to help the clinician be more reliable. Unfortunately, it still takes many examinations before reliability is achieved.
the portions of the examination that will be discussed today will be: the subtalar joint frontal plane range of motion; the forefoot to rear foot alignment on the frontal plane; the ankle joint dorsiflexion; hamstring flexibility; the malleolar torsion; hip rotations; and the frontal plane stance measurements.
Exam of the subtalar joint range of motion is usually done in the frontal plane. It is recognized that the subtalar joint simultaneously produces angular motion in all three body planes, however the frontal plane is the easiest plane to measure and usually is a good indicator of the motion in the other planes. A full examination of the subtalar joint will be the topic of a future lecture.
To begin the subtalar joint range of motion, the patient is placed in the prone position. The foot is hanging over the end of the table. The plantar surface of the heel is bisected to establish the long axis of the rearfoot.
The subtalar joint is moved by placing the thumb against the 5th metatarsal head and mildly dorsiflexing the forefoot. To supinate the foot, push directly medial. To pronate the foot, pull directly lateral. It is important not to try to move the foot plantarly or dorsally in the sagittal plane when moving the subtalar joint. This will move the ankle joint and result in an inaccurate subtalar joint measurement.
It is now important to identify the frontal plane of the foot correctly. One of the sources of unreliability is not measuring the range of motion in the frontal plane, but instead measuring it in some other plane. It is a common misnomer that the subtalar joint hangs naturally in its neutral position. Therefore, find the neutral position of the subtalar joint, and then rotate the entire extremity until the plantar calcaneal bisection is perpendicular to the floor. The plane that is now parallel with the floor is now the frontal plane of the foot and it is in this plane that the range of motion will be taken.
Now that the examiner’s eyesight is directly perpendicular to the frontal plane of the foot, the lower leg is bisected. The bisection is performed below the myotendinous junction of the gastrocnemius muscle, and above the narrowest width of the leg above the ankle. The examiner very lightly touches the skin surface on the medial and lateral side of the lower leg and makes 3-4 marks halfway between the 2 sides. These marks are connected by a straight line. It is important that the examiner not necessarily use the Achilles tendon as a reference for bisecting. In the picture on the right, the Achilles tendon is lying medial to the leg bisector.
Next the posterior calcaneal bisector is drawn with the subtalar joint in neutral. The examiner needs to identify the medial and lateral borders of the posterior surface of the oscalcis. Notice that I have drawn these borders on the skin to identify them. I have bisected the distance between these borders for the calcaneal bisector. It is important to keep skin movement to an absolute minimum when making these marks. The posterior calcaneal bisector should be drawn to extend over the inferior curve of the heel.
Because the skin above the Achilles tendon insertion is not anchored to the bone, the superior portion of the calcaneal bisection line will move against the bone when the foot is supinated and pronated. Therefore, the examiner should fully supinate the foot, and redraw the posterior calcaneal bisection. The examiner should then fully pronate the foot and again redraw the posterior calcaneal bisection.
The examiner should now grasp the forefoot with the right hand if the right foot is being measured, or the left hand if the left foot is being measured. Do not hold the heel pad as you will distort the bisection lines when you move the joint; dorsiflex the ankle joint to about 90 degrees. Without allowing the ankle joint to plantar flex, push directly medially to fully supinate the subtalar joint until the gentle end range of motion is felt.
A common mistake in examining the subtalar joint is to allow the ankle joint to plantar flex while supinating - especially when the supination end range of motion is encountered. If the ankle joint plantar flexes, the examiner will measure too much inversion motion in the subtalar joint.
Many different measurement tools have been developed to try to easily and accurately measure the angle of the inversion and eversion. This lecture does not necessarily support the use of one instrument over another. In this slide, a tractograph is utilized; however, even a plain protractor can be used to measure the acute angle between the lower leg bisector and the posterior heel bisector. The important point is to keep the eyesight perpendicular to the frontal plane and to keep the measuring instrument parallel to the frontal plane. Deviation of the eyesight or the instrument will produce an inaccurate measurement. To measure the amount of inversion, with the subtalar joint fully supinated, one edge of the tractograph is aligned with the lower leg bisector. One edge of the other arm of the tractograph is aligned with the calcaneal bisector. Remember to keep the tractograph parallel with the ground. The angle of inversion is now read at the center of the tractograph.
After measurement of maximum inversion, the examiner now fully pronates the subtalar joint to the end range of motion. Again, the examiner should move the subtalar joint without allowing the ankle joint to move. It is recommended that the examiner not release his or her grip on the foot after measuring full supination, in order to prevent the ankle joint from moving while moving the subtalar joint. When the end range of pronation is reached, the tractograph is used in the same manner to measure the angle between the posterior calcaneal bisector and the lower leg bisector. In this particular picture, the maximum eversion of the heel to the leg is 0 degrees.
The average person should have a 2:1 ratio of inversion to eversion motion from neutral position, though there is a wide variation from this in some individuals. If the examiner has performed over 20 examinations and has not found this average, then the examiner should re-evaluate his/her measuring techniques.
Because not everyone has a 2:1 ratio of inversion to eversion from neutral, the examiner should now put the subtalar joint back in its neutral position, dorsiflex the ankle joint and measure the heel to leg angle. You will almost always note that when the subtalar joint is in neutral position, there is symmetry of the curvature of the skin above and below the lateral malleolus.
Subtalar varus may be diagnosed if the heel is inverted to the lower leg when the subtalar joint is in its neutral position. Subtalar valgus may be diagnosed if the heel is everted to the lower leg when the subtalar joint is in its neutral position.
We will now discuss measuring the forefoot to rearfoot alignment on the frontal plane. This is done with the patient in the same position as was used for measuring the subtalar joint range of motion.
The forefoot to rear foot alignment is always measured with the subtalar joint in its neutral position and the midtarsal joint fully pronated. The midtarsal joint is fully pronated by placing the thumb under the 4th and 5th metatarsal heads, and gently dorsiflexing until gentle resistance is met. For the average foot, it takes only ounces of force to reach the end of the pronation range of motion of the midtarsal joint.
The plane containing the first and fifth metatarsal heads can be easily visualized by taping a straight stick to metatarsal heads 1 and 5. A cut-down tongue depressor makes a good marker. Double-sided tape is preferred to adhere the stick to the skin, though single-sided tape can also be used.
It is important to keep the eyesight perpendicular to the floor. If the eyesight is too medial, then the forefoot will appear to be too inverted to the rearfoot. If the eyesight is too lateral then the forefoot will appear to be too everted to the rearfoot.
A tractograph can be utilized to take the forefoot to rearfoot measurement, though it is somewhat cumbersome. Place the edge of one arm of the tractograph along the calcaneal bisection line. Line up the bottom edge of the other arm of the tractograph with the forefoot plane marker.
A protractor may also be utilized by lining up the bottom edge with the forefoot marker and then placing the center point on the inferior border of the posterior calcaneal bisector, observe the intersection of the posterior calcaneal bisector with the rim of the protractor.
An inverted forefoot deformity is identified when the forefoot is inverted to the calcaneal perpendicular when the subtalar joint is neutral and the midtarsal joint is fully pronated. Inverted forefoot deformities may be due to lack of valgus rotation of the neck of the talus, or they may be due to a loss of motion in the long axis of the midtarsal joint, a plantar flexed cuboid, a dorsiflexed medial column or any other combination of the above.
An everted forefoot deformity is identified when the forefoot is everted to the calcaneal bisection when the subtalar joint is neutral and the midtarsal joint is fully pronated. Everted forefoot deformities may be due to an excess valgus rotation of the talar neck, or to a plantar flexed medial column, or a dorsiflexed lateral column, or any combination of the above.
Some people have a plantar flexed first ray, which means that the plane containing metatarsal heads 2 through 5 is more inverted to the rearfoot than the plane containing metatarsal heads 1 through 5. If the clinician is suspicious of this, the metatarsal marker may be broken so that it covers only metatarsal heads 2 through 5 and the forefoot measurement should be repeated.
We will next discuss measuring ankle joint dorsiflexion. Lack of ankle joint dorsiflexion is a common cause of abnormal pronation. There are many types of equinus. The clinician needs to check for adequate ankle joint dorsiflexion with the knee in a fully extended position and also in a 90 degree flexed position.
The two reference lines that need to be identified are the lateral leg reference line and the lateral foot reference line. The lateral leg line is a line from the center of the lateral malleolus to the center of the lateral knee. The lateral foot line is a line from the heel, where the plantar skin junctions with the lateral skin, to the plantar fifth metatarsal, where the plantar skin junctions with the lateral skin.
The patient is placed supine with the subtalar joint neutral and the leg is rotated until the foot is vertical. The clinician grasps the forefoot on the medial side and asks the patient to use the anterior tibial muscle to pull the foot upward and slightly inward. The clinician must make sure that the subtalar joint does not pronate, and if necessary must produce a supination force on the foot while the patient is actively dorsiflexing. The clinician must also make sure that the patient does not flex the knee.
The ankle joint dorsiflexion measurement is made by placing one arm of a tractograph along the lateral leg reference line and the other arm along the lateral foot reference line. The number of degrees beyond 90 degrees is read. For most people, 10 degrees of dorsiflexion beyond neutral is considered to be normal. This may be somewhat variable according to the patient’s height, foot length and distribution of body weight. Prepubescent children should have between 15 and 20 degrees of ankle joint dorsiflexion.
After measuring the ankle joint dorsiflexion with the knee fully extended, the ankle joint dorsiflexion is remeasured with the knee joint flexed. This is usually best done with the patient lying prone with the knee flexed at 90 degrees. The clinician places the hand against the medial forefoot and asks the patient to assist in maximally dorsiflexing the ankle joint. The clinician makes sure that the patient does not pronate the foot. The clinician then measures the number of degrees beyond the perpendicular that the lateral foot line can move relative to the lateral leg line.
If the patient has less than 10 degrees of ankle joint dorsiflexion only when the knee is extended, then the clinician can diagnose the patient with a gastrocnemius equinus. If there is less than 10 degrees in both the knee extended and knee flexed states, then the clinician must determine if the problem is osseous or soft tissue. To do this, the clinician maximally passively dorsiflexes the ankle joint with the knee in its flexed position. With the opposite hand, the Achilles tendon is pushed in an anterior direction. If the clinician feels a resistance of the forefoot pushing upward against the hand that is dorsiflexing the forefoot, then the diagnoses of a gastroc-soleus equinus can be made. If no plantar flexing movement of the forefoot is felt when the Achilles is bowed forward, then the diagnosis of osseous equinus can be made. This should be confirmed by radiographic examination as well.
We will now discuss the measurement for adequate hamstring length. Because the hamstring muscles and gastrocnemius muscles both cross the knee joint, tight hamstring muscles can also contribute to the patient walking with an equinus-like gait.
The patient lies supine on the examination table. The reference lines that will be used are the same on the lower leg as was used for measuring ankle joint dorsiflexion. The other reference line is a line along the lateral side of the thigh that connects the center of the knee joint with the greater trochanter of the femur.
The clinician asks the patient to totally relax. The hip joint is passively flexed to 90 degrees while flexing the knee at least 90 degrees. With the hip at 90 degrees of flexion, the knee is passively extended until the tension in the hamstring muscles prevents any additional extension. The patient may complain that he/she feels some tightness in the posterior thigh. It is very important that the patient not allow the opposite knee to flex or the pelvis to rise off the table.
With the hamstrings maximally stretched out, the clinician places one arm of the tractograph along the lateral lower leg line and the other arm of the tractograph along the lateral thigh line. The number of degrees that the knee is flexed is read. The normal is usually accepted as being 20 degrees or less of knee flexion angle.
If the hamstring muscles keep the knee from extending to a 20-degree flexed position, the clinician may want to determine if the hamstrings on both sides of the leg are tight or just on one side. If just one side is tight, it is usually the medial hamstring muscles. To isolate the medial hamstrings, the clinician keeps the hip 90 degrees flexed, and then reflexes the knee to 90 degrees. The hip is then maximally externally rotated and the knee is again maximally extended. The degree that the knee is still flexed is measured. If the medial hamstrings are tighter than the lateral hamstring, then the knee will be more flexed with the hip externally rotated than when the knee was extended in the sagittal plane. In rare cases, the lateral hamstring may be tighter. To isolate the lateral hamstring, repeat this test with the hip in its maximally internally rotated position.
We will now discuss the measurement of malleolar torsion. Malleolar torsion has a marked effect on the angle of gait, and many people, especially children, have abnormalities. Both lack of external rotation and excessive external rotation can be the cause of abnormal pronation, though the types of symptoms may be very different.
A simplified way of assessing the effect of malleolar torsion is to look at the angle of gait when the knee joint is on the frontal plane and the subtalar joint is in its neutral position. With the knee joint on the frontal plane and the subtalar joint in neutral position, the long axis of the foot should be between 0 degrees and 10 degrees abducted to the mean sagittal plane.
To assess the effect of malleolar torsion on foot abduction, the patient is placed supine. The clinician need only to draw a line along the plantar foot from the center of the heel through the second ray. Then rotate the entire limb until the knee is on the frontal plane and place the subtalar joint in its neutral position and maximally pronate the midtarsal joint. Measure the angle the long axis of the foot is from being perpendicular to the ground with a gravity dependent angle finder.
Lack of malleolar torsion or internal malleolar torsion will cause the foot to be adducted to the mean sagittal plane when the knee is on the frontal plane and the subtalar joint is in its neutral position. An adducted foot should always be considered to be an abnormality.
An abnormally high degree of external malleolar torsion will cause the foot to be excessively abducted to the mean sagittal plane when the knee is on the frontal plane and the subtalar joint is in neutral position. If the foot abduction angle is greater than 15 degrees it is almost always considered to be abnormal; angles of 10-15 degrees of abduction may be considered abnormal depending on the degree of metatarsus adductus and the degree of anglulation of the subtalar joint axis with the sagittal plane.
A more accurate method of measuring malleolar torsion is performed by marking the center of the medial and lateral malleolus. It is important to remember that the skin over the malleoli is very mobile, therefore it is important that the subtalar joint be in neutral position and that you not stretch the skin while making this bisection mark.
You may make a very inexpensive instrument for measuring the malleolar torsion by taping two tongue blades to either side of an inexpensive angle finder that you would find at your local hardware store, the tips of the tongue blades project equally from the bottom edge.
With the knee on the frontal plane, and holding the foot in neutral with the midtarsal joint locked, touch the tips of the projecting tongue blades to the center marks on the medial and lateral malleoli. Read the degree that the malleoli are externally rotated from the frontal plane. The classic normal reading is between 13 and 18 degrees external, however, I have found that most of the time 10-20 degrees external is a good range to be in. Less than 10 degrees of malleolar torsion is almost always abnormal internal malleolar torsion. Likewise, more than 20 degrees external is almost always an abnormal external malleolar torsion. The few times that over 20 degrees external malleolar torsion can be accepted as normal is if the patient has a high degree of forefoot adductus.
We will now discuss the transverse plane rotation of the hip. The total range of motion of the hip in the transverse plane is between 30 degrees and 90 degrees. With less than 30 degrees total range of motion, the patient probably has some sort of “arthritic condition” of the hip. The neutral position of the hip joint is halfway between the maximally internally and maximally externally rotated positions.
To measure the hip joint range of motion in the transverse plane, have the patient lie supine with the hips extended at 180 degrees. If you have a gravity goniometer that can clamp to the sides of the knee joint, that is a preferable instrument. Otherwise, flex the knee to 90 degrees over the edge of a table so the tibia is perpendicular to the ground.
Now maximally internally rotate the hip until gentle resistance is met. If you continue to rotate past this gentle resistance point, you will lift the hip off the ground which will give you a false reading. If you are using the angle finder on the anterior leg, read the number of degrees that the tibia is abducted from being perpendicular to the ground.
Now maximally externally rotate the hip until gentle resistance is met. If you are using the angle finder on the anterior leg, read the number of degrees that the tibia is adducted from being perpendicular to the ground. If you continue to rotate past the gentle resistance point, you will probably abduct the hip which will give you a false reading.
An internal femoral rotation problem exists if there is more internal rotation of the femur than external rotation of the femur. It may be due to high angle of declination of the femoral neck, or it may be due to increased tension of the iliofemoral ligament. To distinguish these two entities, have the patient sit up and repeat the test. If the problem is osseous, the two measurements will be about 5 degrees more internal and external rotation than when the patient was lying down. If the problem is ligamentous, then with the patient sitting, the increase in the external rotation of the femur will be more than the increase in the internal rotation of the femur.
Normally, the external hip rotation should be about 0-20 degrees more than the internal hip rotation. If the external hip rotation is more excessive than this, then the patient should be considered to have an external femoral rotation problem. It may be due to a low angle of declination in the neck of the femur, or it may be due to an increased tension of the ischiofemoral ligament. To distinguish these two entities, have the patient sit up and repeat the internal and external rotation measurements. If the problem is osseous, the internal and external rotation will each increase by about 5 degrees. If the problem is ligamentous, then with the patient sitting the increase in the internal rotation of the femur will be much more than the increase in the external rotation.
We will now discuss the static stance measurements. Once the clinician knows the range of motion that the major joints of the foot and leg can work within, he/she needs to know how much the foot is pronating or supinating in static stance. A stance measurement does not have to completely correlate with the gait analysis; however, since much of the time a person spends on his feet is spent just standing around, there is still quite a bit of valuable information to be gained.
The clinician should ask the patient to walk a few steps to determine their angle and base of gait. Then ask the patient to stand in this position. The angle of gait is the angle to the line of progression each foot makes. The base of gait is the distance between the heels. Variances from the angle and base of gait will distort the stance measurements.
Because there are often shifts of the calcaneal fat pad in stance due to friction from the ground, it is necessary to often correct the calcaneal bisection line in static stance. Often in a pronating foot, the inferior portion of the line shifts laterally, and vice versa. The clinician should repalpate the posterior calcaneal surface and remark the bisector line before taking any stance measurements.
Now utilize an instrument, such as a tractograph to determine how many degrees from perpendicular the posterior calcaneal bisection line is angled. One arm of the tractograph is laid on the ground. The other arm is aligned with the posterior calcaneal bisector. The angle may be in an inverted or averted position. It is important to remember that the angle is not necessarily the number of degrees that the subtalar joint is pronated. More will be said about this later.
Now hold the tractograph in a plane that is in the same plane that the patella is facing. If the patella is facing outward, hold the tractograph facing outward the same degree. Keep the one arm of the tractograph on the ground. Align the other arm with the posterior leg bisector and measure the degree to which the lower leg is inverted or averted from perpendicular.
Now calculate the calcaneal to lower leg angle. This is the subtraction of the relaxed calcaneal stance position from the relaxed tibial stance position. For example, if the calcaneus is 5 degrees averted from perpendicular and the tibia is 10 degrees inverted from perpendicular, then the calcaneus would be calculated to be 15 degrees averted to the tibia. Compare this angle with the measurements of subtalar joint range of motion available performed earlier to determine if the subtalar joint is in its neutral position, if it is partially pronated, if it is partially supinated, if it is fully pronated, or even if it has pronated beyond the end of its range of motion.
After you have determined the degree that the subtalar joint is pronated or supinated in relaxed stance, you need to obtain the same information with the patient standing in neutral. You must do this with both feet standing simultaneously in neutral. If you allow one foot to be in neutral and the other to be relaxed, the patient will shift his/her body weight to the relaxed side, which will distort your neutral stance measurements.
If the patient is pronated or supinated from neutral in static stance, ask the patient to voluntarily move both subtalar joints to neutral position. You will need to palpate the subtalar joint line below the medial and lateral malleolus and give instructions to the patient to invert or avert the foot until the joint lines are congruous under both malleoli. Do not depend on the congruency of the talonavicular joint for determination of subtalar joint neutral position. If the patient has a limb length discrepancy, it is advisable to put a full foot-length elevator of the proper height under the short limb.
With the patient standing with the subtalar joints in neutral position, you may find that that the calcaneal fat pad has shifted again, so correct the posterior calcaneal bisector line before taking measurements. Now measure the neutral calcaneal stance position by placing one arm of the tractograph on the ground, and align the other arm with the posterior calcaneal bisection. Read the angle that the rearfoot is inverted or averted from perpendicular.
Next measure the neutral tibial stance position by keeping one arm of the tractograph on the ground, and aligning the other arm with the posterior leg bisection line. Make sure that the angle finder is facing the same direction that the patella is facing. Read and record the angle that the lower tibia is angulated from perpendicular. This is the true tibial varum or valgum angle.
Now that you have performed and recorded your goniometric examination, you will next have to make treatment decisions for your patient. These may be conservative and/or surgical decisions. Just like any other portion of an examination or radiographic study or laboratory test, the results may or may not have a marked affect on your decision process, however, you don’t know that until after the examination is complete. After your examination, you should be able to explain in detail why the foot is developing the symptoms or deformities that it is experiencing. You should be able to answer the question whether this type of foot needs orthotic therapy or whether orthotics will even work for this foot. If you decide to use orthotics, will a standard orthotic prescription work or is there a need to change something in the prescription? If you are going to do surgery for this foot, what is the goal of doing that surgery and what will be the function of the foot after the surgery is performed? If you are going to do surgery, will the patient be likely to develop new symptoms after the surgery? If so, is there something that can be done to prevent these new symptoms? You will find that as you discipline yourself to perform the goniometric examination that you will become more reliable and you will take into consideration more variables that will dictate what treatment modifications need to be made to produce the best results for your patient. Further lectures will address how each of these portions of the tests can change your approach to treating the patient.
Production of this PRESENT lecture was made possible by a generous grant from Mile High Orthotics, bringing your expectations to higher elevations.