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Study Supports Root Theory Principle Of Neutral Suspension Casting For Orthoses

Root theory is not dead! In fact, a relatively recent study of patients with functional hallux limitus validated the practice of neutral suspension casting and fabrication of true functional foot orthoses.1

It is interesting that the only study thus far that measured significant improvement of function of the first MPJ with foot orthotic intervention actually followed the Root principle of casting and correcting the foot to subtalar neutral.

Becerro de Bengoa Vallejo and co-workers studied 46 patients and measured first MPJ range of motion while walking with and without custom foot orthoses.1 Employing an electromagnetic tracking device to measure motion of the first metatarsal and hallux, the study authors found that all of the patients met the criteria of having functional hallux limitus by demonstrating passive hallux dorsiflexion range greater than 50 degrees non-weightbearing and less than 40 degrees weightbearing. Researchers fabricated the custom foot orthoses from a neutral suspension cast and balanced the casts using a vertical bisection of the calcaneus according to the criteria of Root and colleagues.2 Using a semi-rigid polypropylene material in fabrication of the orthotic devices, the authors purposefully plantarflexed the first metatarsal during the impression casting process and the orthotic shell had a first metatarsal cutout. These are variations of the traditional Root casting and fabrication technique, but are commonly used by practitioners and labs who follow the Root principles.

When patients walked with the custom, Root-style functional foot orthoses, they demonstrated significantly greater first metatarsal plantarflexion in comparison to walking without orthoses.1 Also, the orthoses caused the first metatarsal to move in the direction of abduction, which is consistent with the axis of motion of the first ray as originally described by Hicks and reaffirmed by other studies.1,3 

A Closer Look At The Mixed Results Of Previous Studies On First MPJ Motion And The Principles Espoused By Root

Limitation of motion of the first MPJ is linked to a myriad of foot pathologies and specific gait compensations.4-7 Clinicians have implemented foot orthotic therapy as a means of improving range of motion of the first MPJ with varying results. Several studies show improvement of symptoms of pain using foot orthoses to treat patients with hallux limitus.8,9 However, these investigations did not measure any change of actual motion across the first MPJ. 

A study using a prefabricated foot orthosis with first metatarsal cutout demonstrated improvement of first MPJ pain but showed no improvement in range of motion.10 Studies that actually attempted to measure motion of the first MPJ in patients with hallux limitus showed no improvement in dorsiflexion range with custom foot orthotic intervention.11-13

In 1971, Root, Weed and Orien published their description of the neutral position casting technique for fabrication of custom foot orthoses.2 That same year, Root and his colleagues published a technique for examination of the foot and proposed a classification system of foot deformities based upon reference to the subtalar joint neutral position.14 Six years later, they expanded upon their previous publications with detailed descriptions of their observations of normal and abnormal foot function.15 Collectively, these works became embodied in a dogma known as the “Root Theory” of lower extremity biomechanics. Since that time, Root theory has fallen prey to harsh criticism and challenge.16-18 Much of the criticism focuses upon the accuracy of the examination techniques taught by Root and colleagues as well as the relevance of subtalar neutral position in clinical decision making. 

Final Notes 

What is important in the aforementioned study by Becerro de Bengoa Vallejo and coworkers is the fact that the Root-style functional foot orthoses actually improved function of the foot.1 This was a kinematic study, which assessed motion of skeletal segments and focused on an area of the human foot implicated in causing more pathologies than any other individual joint. Some have questioned the efficacy of Root-style orthotics in the past because many kinematic studies showed only modest improvements. However, those studies focused on rearfoot joints and many lacked the methodology to accurately measure the discrete motion of skeletal segments.

With studies challenging the foundations of traditional Root orthotic therapy, many practitioners abandoned neutral suspension casting and balancing foot orthoses according to calcaneal bisection. As a result, we see companies promoting foot orthoses fabricated from weightbearing scans of the foot or foam box impressions. An image of the foot in this position prohibits preservation of the shape necessary to allow plantarflexion of the first ray. 

As Becerro de Bengoa Vallejo and coworkers demonstrated, Root-style orthoses can provide their intended benefit when clinicians implement these devices properly.1 That is why this practice of foot orthotic therapy continues to be the preference of foot care providers in this country.

References

1.   Becerro de Bengoa Vallejo R, Sanchez Gomez R, Iglesias ME. Clinical improvement in functional hallux limitus using a cut-out orthosis. Prosthet Orthot Int. 2016;40(2):215–223.
2.   Root ML, Weed JH, Orien WP. Neutral Position Casting Techniques. Los Angeles: Clinical Biomechanics Corporation; 1971.
3.   Hicks JH. The mechanics of the foot. Part I: the joints. J Anat. 1953;87(4):345–357.
4.   Dananberg HJ. Gait style as an etiology to chronic postural pain. Part I: Functional hallux limitus. J Am Podiatr Med Assoc. 1993;83(8):433–441.
5.   Dananberg HJ. Functional hallux limitus and its relationship to gait efficiency. J Am Podiatr Med Assoc. 1986;76(12):648-652.
6.   Dananberg HJ. Gait style and its relevance in the management of chronic lower back pain. In: Vleeming A, Mooney V, Gracovetsky S, Lee D, et al. (eds): Proceedings, 4th Interdisciplinary World Congress of Low Back & Pelvic Pain, Montreal, Canada, November 8-10, 2001, pp. 225-230.
7.   Hall C, Nester C. Sagittal plane compensations for the artificially induced limitation of the first metatarsophalangeal joint: a preliminary study. J Am Podiatr Med Assoc. 2004;94(3):26-274.
8.   Grady JF, Axe TM, Zager EJ, Sheldon LA. A retrospective analysis of 772 patients with hallux limitus. J Am Podiatr Med Assoc. 2002;92(2):102–108.
9.   Welsh BJ, Redmond AC, Chockalingam N, Keenan AM. A case series study to explore the efficacy of foot orthoses in treating first metatarsophalangeal joint pain. J Foot Ankle Res. 2010;3:17.
10. Hogan D, Kidd R. Do functional foot orthoses change the range of motion of the first metatarsophalangeal joint of hallux limitus/hallux rigidus? Australas J Podiatr Med. 2001;35:39–41.
11. Kilmartin TE, Wallace WA, Hill TW. Orthotic effect on metatarsophalangeal joint extension. A preliminary study. J Am Podiatr Med Assoc. 1991;81(8):414–417.
12. Nawoczenski DA, Ludewig PM. The effect of forefoot and arch posting orthotic designs on first metatarsophalangeal joint kinematics during gait. J Orthop Sports Phys Ther. 2004;34(6):317–327.
13. Munteanu SE. Effect of foot posture and inverted foot orthoses on hallux dorsiflexion. J Am Podiatr Med Assoc. 2006;96(1):32–37.
14. Root ML, Orien WP, Weed JH, Hughes RJ. Biomechanical Examination of the Foot, Volume 1. Los Angeles: Clinical Biomechanics Corporation; 1971.
15. Root ML, Orien WP, Weed JH. Normal and Abnormal Function of the Foot. Los Angeles: Clinical Biomechanics Corporation;1977.
16. Kirby KA. Are Root biomechanics dying? Podiatry Today. 2009; 22(4):58-65.
17. Kirby KA. Prescribing orthoses? Has tissue theory supplanted Root theory? Podiatry Today. 2015;28(4):36-44.
18. Jarvis HL, Nester CJ, Bowden PD, Jones RK. Challenging the foundations of the clinical model of foot function: further evidence that the Root model assessments fail to appropriately classify foot function. J Foot Ankle Res. 2017;10(1):7.

Additional Reference

19.  Kelso SF, Richie DH, Cohen IR, Weed JH, Root M. Direction and range of motion of the first ray. J Am Podiatry Assoc. 1982;72(12):600–605.

Comments

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Hi Dr Richie,
Thanks for your take on this. I am not sure this paper really supports Root et al.'s theory for different reasons:
1. We don't know if the M1 cutout really helps to improve first ray plantarflexion as the authors did not compare the results with orthoses without this M1 cutout.
2. We don't know if plantarflexing the first met in the negative casts really helps increasing first ray plantarflexion as no comparisons were made with orthoses made from regular casts.
3. The differences found in this study are very small (2 degrees) and the effect sizes are also very small (0.36). Even thought the differences they found were statistically significant, these are probably not clinically significant.
Regards,
Gabriel Moisan, DPM, MSc, PhD(c)

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Great questions, Gabriel. I pondered all of those issues myself when writing this blog. The study did not intend to compare a "generic" or regular Root style orthosis to one with the variations provided by the casting technique and the first met cutout. Instead, the study attempted to measure the efficacy of the intervention compared to no intervention at all. All we can take from this study is the fact that the casting technique and fabrication technique, which have been previously taught by Root et al did in fact provide a small, but significant improvement of first ray function.

Yes, a possible future study would be comparing a generic Root device to one which had additional strategies applied to enhance first ray function. I was taught by all three of the original Root theory pioneers (Root, Weed and Orien), and learned that many variations of the orthotic prescription could be implemented for specific pedal pathologies. This study verifies that the combination of the basic Root approach with some well accepted and commonly practiced modifications/variations for enhanced first ray function actually made a positive change in foot function. We know from other studies that various designs of foot orthoses improved patient symptoms but did not improve range of motion of the 1st MPJ.

This study unfortunately did not attempt to measure clinical changes. Your assumption that the statistically significant improvement of first ray plantarflexion is "probably not clinically significant" is speculative since there are no studies documenting how much improvement of motion of the first ray is necessary to significantly improve symptoms of functional hallux limitus.

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Thanks Dr. Richie for taking the time to reply to my comments. I agree with the first two paragraphs of your reply.

However, even though I agree that this study did not attempt to correlate the biomechanical results with clinical outcomes, the clinical impact of their results would most likely be minimal. Most experts now recommend to calculate p values, but also effect sizes and confidence intervals to determine if differences are statistically significant. For the differences to be significant, the p value must be <0.05, effect size >0.5 and the confidence intervals should not cross 0.

With these more stringent criteria, the differences found in Becerro de Bengoa Vallejo et al.'s study would not be significant (invaliding what you said in your article). Hence, my point that their results would most likely not be clinically significant.

I just think that stating that Root et al.'s theory is not dead and is supported by this study's weak results may be a little optimistic.

Regards,
Gabriel Moisan, DPM, MSc, PhD(c)

Reference
1. Hopkins WG, Marshall SW, Batterham AM, Hanin J. Progressive statistics for studies in sports medicine and exercise science. Med. Sci. Sports Exerc. 2009;41(1):3-13.

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The authors reported that there was significant improvement of plantar flexion of the first ray when subjects wore the Root style orthosis, compared to the non-orthotic condition. I accurately restated their findings in my blog. Nothing you propose here "invalidates" the findings of the study. Yes, you can question whether there would be clinical improvement with this orthosis design, but you have no data to support your conclusion that the results of the study would "most likely not be clinically significant." To that, I would ask: how many degrees of first ray plantarflexion are needed before clinical improvement will occur?

The readers can take what they want from this study. Many, like me, appreciate the validation of an orthotic design, which has worked well in their hands treating patients with dysfunction of the first ray. Others can remain skeptical and yet continue to implement orthotic designs that have never been tested or proven to improve first ray function.

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