Point-Counterpoint: Are Static Measurements Of Foot Morphology Necessary To Create Custom Foot Orthoses?

Yes.

Citing research as well as his own clinical experience, this author says goniometric measurements play a key role in recognizing the degree and etiology of abnormal function, and help facilitate better prescriptions of custom foot orthoses.   

By Robert D. Phillips, DPM

The necessity of performing goniometric measurements is often a subject of debate in podiatric circles. Many people believe the goniometric examination is something that only happens before making orthotics and a great many will argue today that to make orthotics, one only needs a one-sentence book: Take a neutral cast. Certainly, anyone can point to a plethora of orthotic devices made through the years that have significantly benefitted the wearers yet there was no goniometric examination beforehand.

So of what value are “static measurements?” While we have described foot function as being normal or abnormal for decades and various types of supports have improved foot pain and dysfunction, the search for the causes of foot function has been controversial and elusive as a great many have tried to ascribe abnormal foot function to just one cause.

Muscle weakness was the causative factor that we learned for many years.¹ Morton ascribed the etiology of flatfoot to a structural variation that he called metatarsus atavicus.² Other researchers cited high tension in the Achilles tendon as the cause while others attributed the cause to forefoot varus.^3,4

In 1964, Root wrote about the importance of looking for the causes of foot symptoms in any individual.⁵ He proposed there could be a number of causes for abnormal function and he also suggested that the dysfunction is a continuum and not a dichotomous condition.

In 1971, Root proposed a series of measurements that clinicians could use to quantify the degree of pronation or supination from a neutral position, and quantify a number of causes of abnormal pronation and supination.⁶ What is important to remember is that Root did not say these were the only causes of abnormal pronation or supination. He also emphasized the necessity of performing muscle testing as muscle weaknesses could also contribute to the abnormal function. The Root concept stated that one could measure and calculate the reserve of pronation when a person is in static stance.

Of course, static measurements cannot directly calculate how much the foot uses the reserve of pronation when one walks. However, if one knows the range of motion of the subtalar joint, then using kinematic data, the clinician could still calculate whether the subtalar joint was using its entire reserve of pronation during the gait cycle. Most college curricula quickly adopted Root’s book on taking goniometric examinations of the lower extremity and practitioners markedly increased their use of these measurements.⁶

Raising Questions On Measurement Methodologies And Instrument Quality
However, in the past 20 years, there seems to be a marked decrease in the use of goniometric measurements in the daily clinical practice. Three common reasons for this are the lack of reimbursement, that the measurements do not change the prescription and that there is no reliability in the measurements.

I will be the first to acknowledge that a multitude of papers have brought into question the reliability of current techniques of performing goniometric measurements.^7-10 However, one can reasonably argue that this is not a reason to not perform measurements. Unfortunately, none of the papers that question reliability really discusses the reasons for the unreliability. It is disappointing in studying most of these papers to find a lack of detail in the measurement methodologies and poor quality instruments.

I have found by experience that small differences in techniques can make big differences in measurements.^11-13 For example, the movement of the ankle joint can make a big difference in the range of motion one measures in the subtalar joint. Since ligamentous tension creates the end range of motion of almost all joints, there can be great differences in the measured range of motion according to the amount of force or even the direction of force at the end range of motion. Since the measurement of the forefoot to rearfoot relationship is based on the angle at which one views it, the amount of force exerting against the forefoot and the position of the subtalar joint, it is not surprising that great inter-tester unreliability occurs.

Therefore, I argue that instead of discontinuing these measurements, there needs to be greater attention on standardizing the techniques of measurement. In spite of the number of papers often quoted by those who defend the practice of not performing goniometric examination, further examination of the literature demonstrates that those who utilize better instrumentation for performing examinations show much better reliability results.^14-18

Most practitioners and a great majority of researchers who questioned goniometer measurements utilize goniometers that are of nominal cost (e.g. the simple double arm plastic goniometer printed with 2-degree increments). A look at the instrumentation in most podiatric offices often finds high numbers of palliative care instruments costing $50 to $100 each, expensive examination chairs, vascular analysis units, lasers and various other high quality diagnostic and treatment tools. Yet these offices use goniometric tools that are of the lowest cost and have not been developed for the measurements that are needed or desired. Such failure to utilize high quality scientific instruments to take measurements can only result in poor reliability of the measurements.

Other Factors To Consider With Orthotic Prescriptions
One of the most important contributions that Root and colleagues made was the rejection of the concept of Wright and coworkers that a calcaneus vertical position in static stance meant that the foot was in neutral position.^5,19 Certainly, Root taught that a vertical calcaneus made the heel itself most stable but identifying a vertical calcaneus was no longer in and of itself enough to determine the person had a normal foot. Understanding the relationship of the heel to the leg when standing as well as knowing the range of motion of the subtalar joint available became important factors to consider before one could determine if a person standing with the heel vertical was standing with the subtalar joint neutral, pronated or supinated. If one made an orthotic for such a person, one would need to know whether the orthotic should produce a pronation force on the foot or a supination force on the foot.  

Recognizing The Benefits Of Goniometric Exams
After doing thousands of goniometric examinations, I have discovered that they have been of great value in the following ways.

The measurements help in the documentation of deviations from what is accepted as normal. It is important to realize that not every deviation from normal will result in symptoms. However, by analyzing a patient’s deviations from accepted normal ranges and comparing the deviations with his or her symptoms, the practitioner can best determine the etiology of the symptoms. I believe it is the duty of the practitioner to provide the very best explanation of why patients are experiencing symptoms. The degree of abnormal function and the determination of the etiology of the abnormal function are important in justifying the cost of fabricating custom orthotics.

With the measurements, the practitioner is able better to prescribe to the orthotic laboratory how it should manufacture the orthotic. The patient is paying the physician to determine not only why he or she is developing symptoms, but also to provide expertise in designing the orthotic that will solve the patient’s problem. It is my opinion that it is an abdication of responsibility when the physician turns over to the laboratory the actual design of the orthotic. If the physician does not want to take responsibility for the orthotic design, then there is no need for the physician in the delivering of custom orthotic therapy. Below are just a few examples of the many ways that the physician can modify the orthotic prescription. Many other examples of how and when clinicians should order orthotic modifications are present in books by Anthony, Kirby and Scherer.^20-22

• For patients with partially compensated rearfoot varus, attempting to push the calcaneus toward a more vertical position will result in pronating the foot more. In this case, the orthotic prescription should be trying to bring the calcaneus into a more inverted position than it already is in static stance. For these patients, one needs to take additional steps to prevent lateral ankle instability. These steps may include flaring the heel post laterally, building a higher lateral heel seat and making the orthotic stiffer on the lateral half as opposed to making it stiffer under the medial half.

• For patients with a plantarflexed first ray, the orthotic needs to support the second metatarsal head above the level of the first metatarsal head. It is important for the clinician to determine how many millimeters the orthotic should be elevating the second metatarsal.

• By measuring the linear displacement of the center of the calcaneus relative to the center of the leg, the physician can dictate how many millimeters medially or laterally to offset the center of the heel post.

• For patients with severe equinus, an orthotic that allows more than normal pronation of the subtalar joint may be necessary to prevent knee problems.

The biomechanical examination can help the practitioner determine when orthotics are not going to be effective. Sometimes feet are uncontrollable with orthotics. In these cases, it would be more appropriate after an examination for the physician to recommend to the patient that other types of shoe therapy or brace therapy, or even surgical correction should be the treatment of choice.

In the analysis of the goniometric measurements in the patient with symptoms, the physician also increases his or her own knowledge of the function of the foot. The physician is then able to develop orthotic improvements for an individual as well as find ways of improving his or her own practice of orthotic therapy. Certainly, Root was one of these individuals who, as a simple clinician, started by first taking measurements. He was then able to start seeing patterns, shared this information with his fellow practitioners and then started trying to make improvements in treatment.

Using Goniometric Measurements In Combination With Other Measurements
Do not consider the static measurements that Root proposed as the only measurements one should take. In 1983, Phillips and Phillips proposed taking multiple forefoot to rearfoot measurements with the subtalar joint in several positions in order to better understand how the forefoot to rearfoot relationship changes for various degrees of subtalar joint pronation or supination.²³ In 1987, Kirby emphasized the importance of determining the location of the subtalar joint axis.²⁴ In 1992, Phillips and Lidtke introduced linear translational measurements and demonstrated the varying position of the subtalar joint axis.²⁵ Authors have proposed other measures of abnormal pronation, including the rearfoot valgus index and the navicular drop.^26,27

Final Thoughts
Physicians should not be satisfied with the status quo. Accordingly, I hope the reader will arrive at the following conclusions.

1) Do not consider biomechanical knowledge and theory to be static. We need to make improvements and additions to theories of foot function and pathomechanics.

2) Improvements to goniometric examination techniques and instruments for examination need to happen. We also must develop new measurements to identify pathomechanical forces.

3) Improvements in orthotic prescriptions as well as orthotic manufacturing and materials need to occur.
Failure to perform goniometric examinations prevents the profession from making all three of the aforementioned improvements. I therefore encourage all physicians to use the goniometric examination as an essential part of the processes before orthotic prescription as well as surgery.

Dr. Phillips is affiliated with the Orlando Veterans Affairs Medical Center in Orlando, Fla. He is a Diplomate of the American Board of Foot and Ankle Surgery, and the American Board of Podiatric Medicine. Dr. Phillips is a Professor of Podiatric Medicine with the College of Medicine at the University of Central Florida. He is also a member of the American Society of Biomechanics.

The opinions in this article are those of the author alone and in no way are intended to represent the opinions of any other employee or department of the United States government.

Dr. Phillips has disclosed that he is the owner of the Phillips Biometer, which is currently not in production. He is also the owner of CoM’nalysis, a computer program marketed by Tekscan.

References

1. Keith A. The history of the human foot and its bearing on orthopaedic practice. J Bone Joint Surg Am. 1929; 11(1):10-32.
2. Morton DJ. Metatarsus atavicus. J Bone Joint Surg. 1927; 9(3):531-544.
3. Harris RI, Beath T. Hypermobile flat-foot with short tendo Achilles. J Bone Joint Surg Am. 1948; 30(1):116-150.
4. Hurd WJ, Kavros SJ, Kaufman KR. Comparative biomechanical effectiveness of over-the-counter devices for individuals with a flexible flatfoot secondary to forefoot varus. Clin J Sport Med. 2010;20(6):428-35.
5. Root ML. An approach to foot orthopedics. J Am Podiatr Assoc. 1964; 54(4):115-118
6. Root ML, Orien WP, Weed JH, Hughes RJ. Biomechanical Evaluation of the Foot. Clinical Biomechanics Corporation, Los Angeles, 1971.
7. Smith-Oricchio K, Harris BA. Interrater reliability of subtalar neutral, calcaneal inversion and eversion. J Orthoped Sports Phys Ther. 1990; 12(1):10-15.
8. Menz HB, Keenan AM. Reliability of two instruments in the measurement of closed chain subtalar joint positions. The Foot. 1997; 7(4):194-201.
9. Van Gheluwe B, Kirby KA, Roosen P, Phillips RD. Reliability and accuracy of biomechanical measurements of the lower extremities. J Am Podiatr Med Assoc. 1992; 92(6):317-326.
10. Jarvis HL, Nester CJ, Jones RK, et al. Inter-assessor reliability of practice based biomechanical assessment of the foot and ankle. J Foot Ankle Res. 2012; 5(1):10.
11. Elveru RA, Rothstein JM, Lamb RL, Riddle DL. Methods for taking subtalar joint measurements a clinical report. Physical Therapy. 1988; 68(5):678-682.
12. Chan M, Chu M, Wong S, Hamer P. Reliability of a pedal goniometer for the assessment of ankle inversion in the plantarflexed position: Winner of the 1990 Beiersdorf Sports Physiotherapy Award. Australian J Physiother. 1990; 36(3):155-160.
13. Grebing BR, Coughlin MJ. The effect of ankle position on the exam for first ray mobility. Foot Ankle Int. 2004; 25(7):467-475.
14. Chesworth BM, Vandervoort AA. Reliability of a torque motor system for measurement of passive ankle joint stiffness in control subjects. Physiotherapy Canada. 1988; 40(5):300-303
15. LaPointe SJ, Peebles C, Nakra A, Hillstrom H. The reliability of clinical and caliper-based calcaneal bisection measurements. J Am Podiatr Med Assoc. 2001; 91(3):121-126.
16. Glasoe WM, Allen MK, Ludewig PM. Measuring forefoot alignment with a table-mounted goniometric device. Australian J Physiother. 2002; 48(1):51-53.
17. Glasoe WM, Grebing BR, Beck S, et al. A comparison of device measures of dorsal first ray mobility. Foot Ankle Int. 2005; 26(11):957-961.
18. Freeman D, Jaeger A, Johnson R, et al. Reliability study of the Phillips Biometer™ for the measurement of subtalar joint range of motion. The Foot. 2007; 17(2):102-110.
19. Wright DG, Desai SM, Henderson WH. Action of the subtalar and ankle-joint complex during the stance phase of walking. J Bone Joint Surg. 1964;46A;361-382.
20. Anthony RJ. The Manufacture and Use of the Functional Foot Orthosis. Karger, Basel, Switzerland, 1992, p. 26.
21. Kirby KA. Foot and Lower Extremity Biomechanics: A Ten Year Collection of Precision Intricast Newsletters. Precision Intricast, Inc., Payson, Arizona, 1997.
22. Scherer PR. Recent Advances in Orthotic Therapy: Improving Clinical Outcomes with a Pathology-Specific Approach. Lower Extremity Review LLC, Minneapolis, MN, 2011.
23. Phillips RD, Phillips RL. Quantitative analysis of the locking position of the midtarsal joint. J Am Podiatr Med Assoc. 1983; 73(10):518-522.
24. Kirby KA. Methods for determination of positional variations in the subtalar joint axis. J Am Podiatr Med Assoc. 1987; 77(5):228-234
25. Phillips RD, Lidtke RH. Clinical determination of the linear equation for the subtalar joint axis. J Am Podiatr Med Assoc. 1992; 82(1):1-20.
26. Thomson CE. An investigation into the reliability of the valgus index and its validity as a clinical measurement. The Foot. 1994; 4(4):191-197.
27. Mueller MJ, Host JV, Norton BJ. Navicular drop as a composite measure of excessive pronation. J Am Podiatr Med Assoc. 1993; 83(4):198-202.

For further reading, see “Current Insights On The Benefits Of Custom Orthoses And AFOs” in the February 2014 issue of Podiatry Today.

No.

Citing the “inherent inaccuracy” of heel bisection measurements, this author emphasizes maximum eversion height and determining the location of the subtalar joint axis in the transverse plane as key factors in improving the effectiveness of custom orthoses.

By Eric Fuller, DPM

Measurements based on neutral position and heel bisections are not necessary for the decisions that go into writing a prescription for a custom foot orthotic. I do believe some other measurements are quite useful for determining what orthotic variables one should choose. Different variables will make the orthotic device function quite differently.

Anecdotally, there will be some successful treatment with taking a cast, sending it to a lab and telling the lab to use its discretion in determining how to make the finished orthotic. However, in my practice, I see a fair number of patients who already have orthotics that are not relieving their symptoms. A lot of the time we can relieve symptoms by altering the orthotic or making a new orthotic with different design features. The prescription one uses to make the orthotic can make a big difference in the outcome. The key is choosing the correct variables to measure in making the decisions that go into the prescription.  

One can make an orthotic without doing a heel bisection and one reason for this is the inherent inaccuracy of bisecting the heel. In an unpublished internal study by the faculty members at the California College of Podiatric Medicine, there was a 5-degree range on where these experienced practitioners put the heel bisection. There is additional error beyond the heel bisection when you look at forefoot to rearfoot measurement. In this measurement, the medial forefoot can float to different positions and this will add more randomness to the measurement. These measurements are just not repeatable enough to form the basis of an orthotic prescription.

Even though the measurements are inaccurate, there is a coherent rationale behind the prescription choices that one makes using heel bisection. The rationale in the lecture syllabus of John Weed, DPM, was not to evert the subtalar joint farther than it can go. For example, if you had 5 degrees of tibial varum and 4 degrees of calcaneal eversion to the tibia, Dr. Weed taught that one would balance this cast 1 degree inverted because that would be as far at the heel bisection could evert relative to the ground. Balancing that cast to vertical would be attempting to evert the heel farther than it could go. I believe the concept is correct.

However, the level of accuracy is just not there. You should not try to evert the subtalar joint beyond its maximally pronated position. When an orthotic attempts to do this, the patient can get sinus tarsi pain or pain from excessive pressure along the lateral forefoot. Even if there was accurate measurement of the heel bisection and tibial varum measurement, there are still big problems with this prescription writing concept. Looking at the heel bisection completely ignores the forefoot. The forefoot is much more important for determining whether the orthotic will evert the subtalar joint because the forefoot has a longer lever arm to evert the subtalar joint.

Another reason that using the heel bisection is not useful for writing the prescription is that it makes the assumption that the heel cup of the orthosis holds the calcaneus exactly where the cast was balanced. This can obviously be untrue because anyone standing on an orthosis can move the subtalar joint through its range of motion. The heel cup of the orthosis does not hold the calcaneus in the position in which the cast was balanced.

What You Should Know About Measuring Maximum Eversion Height
So, if the heel bisection cannot be helpful in determining the prescription, what measurements can be helpful in determining which design variables one should use? I have developed a measurement that I call maximum eversion height. One takes this measurement with the patient standing and then everting the foot without moving the leg. As the patient attempts to evert, one can see the peroneal muscles contract and subsequently note the height of the lateral forefoot off the ground. Some people have range of motion available in the direction of eversion of their subtalar and midtarsal joints, and other people do not. This measure looks directly at whether eversion range of motion is available without having to worry about the measurement error associated with heel bisection, calcaneal eversion and forefoot to rearfoot measurements.

The maximum eversion height measurement is important because an intrinsic forefoot valgus post in an orthotic will attempt to evert both the midtarsal joint and subtalar joint. If the height of the intrinsic forefoot valgus post is greater than the maximum eversion height, then the orthotic will be trying to evert the foot farther than the available range of motion of the midtarsal and subtalar joints. Intrinsic forefoot valgus posts are an important design variable because research has shown valgus wedging to reduce tension in the plantar fascia.¹ It can be beneficial to add an intrinsic forefoot valgus post but one needs to know how much post is too much. We cannot determine if an amount is too much with heel bisection and forefoot to rearfoot measurements.

Why Determining The Location Of The Subtalar Joint Axis In The Transverse Plane Is Key
Another measure that is very important for choosing design features in an orthotic is determining the location of the subtalar joint axis in the transverse plane. This is a simple clinical exam.² The subtalar joint axis is quite variable from patient to patient and is very important for determining how the foot functions.

The center of pressure is the average point of ground reaction force. The distance from the center of pressure to the transverse plane projection of the axis will determine the moment (torque) from ground reaction force.³ The moment from ground reaction force determines how hard the ground will push the foot into pronation or supination. Design features in an orthotic can change the location of the ground reaction force.

A medial heel skive will create a varus wedge in the heel cup of the orthosis and will tend to shift the center of pressure more medially.⁴ A more medial shift in the center of pressure will decrease the pronation moment from the ground. This is usually a good thing for feet that have problems related to a high pronation moment from the ground. However, lateral instability can become worse with a medial heel skive. Those feet with a more medial subtalar joint axis should get medial heel skives. Those feet with a more lateral subtalar joint axis should not get medial heel skives and possibly should get a lateral heel skive (a valgus wedge in the heel cup of the device). This is why it is important to measure the location of the subtalar joint axis in the transverse plane.

Heel skives and intrinsic forefoot valgus posts are design variables that can alter the effectiveness of an orthotic. Measurements that help one decide whether or how much to use these design variables can greatly improve an orthotic’s effectiveness. However, some of the measurements based on heel and leg bisections are not accurate enough to use for orthotic prescription writing.

Dr. Fuller taught biomechanics at the California College of Podiatric Medicine for 14 years. He is in private practice in Berkeley, Calif.

References

1. Landorf KB, Keenan AM. Efficacy of foot orthoses: what does the literature tell us? J Am Podiatr Med Assoc. 2000; 90(3):149-58.
2. Kirby KA. Methods for determination of positional variations in the subtalar joint axis. J Am Podiatr Med Assoc. 1987; 77(5):228-234.
3. Fuller EA. Center of pressure and its theoretical relationship to foot pathology. J Am Podiatr Med Assoc. 1999; 89(6):278-91.
4. Kirby KA. The medial heel skive technique. Improving pronation control in foot orthoses. J Am Podiatr Med Assoc. 1992; 82(4):177-88.   

For further reading, see “Pertinent Pearls On Custom Orthoses And Modifications” in the April 2012 issue of Podiatry Today.

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