Scientific evidence on the use of proprioceptive insoles in patients affected by neurological disorders: literature review

Introduction

The posture is defined as the attitude of the living beings of every animal species that helps their adaptation to the environment. Determining factors for its definition are the set of foreign and proprioceptive inputs, as well as psychological ones. The complex postural system therefore integrates at different levels the peripheral receptors (visual, proprioceptive, skin, joints, vestibules, mandibular), nerves that carry the electrical signals from the first, the neuronal complexes that process, program and provide the right responses and, finally, muscles, tendons and joints that adapt them to the output programs. The mechanisms on which this system is based, are related subsystems: feedback mechanisms, that is, constant and circular automatic adaptations to each exogenous or endogenous modification, and feedforward ones, defined as behavior patterns of predicting actions and finally, the memory: an element capable of using these mechanisms at specific times. Basically, at the cortical level you get at all times a three-dimensional representation of space, man and his movements through a continuous decoding and integration of a very complex pattern of informations. This changes in front of particular conditions of alteration of signal conduction as in elderly and in patients suffering from neurological pathology.

An important source of electrical information directly related to postural balance and on which attention has been focused only at the dawn of the 1950s is the plantar surface, an area anatomically rich of pressure receptors and which, according to recent anthropological studies, has changed over time in favor of a cavism, which would promote better agility and dynamism. It must be remembered that the gait is in fact a function enclosed in the marrow, which is early in ontogenetic development; this guarantees individual autonomy and precedes the acquisition, equally important, of maintaining balance. The latter is a function acquired later because of the fact that the nerve centers of the coordination of gait are contained in the spinal cord, phylogenetically older structure than previous, deputies to the postural balance.

Given the close relationship between foot, balance and posture, especially the elderly and patients with neurological disorders, such as Multiple Sclerosis or Parkinson’s disease or peripheral neuropathy, show an impairment of balance (which translates into the increase of the antero-posterior and medial-lateral sway of the Center of Pressure) and gait, which can be associated with sensory-motor deficits and reduced plantar sensitivity. Sometimes, biomechanical or sensory alterations of the plantar surface itself are pathognomonic signs of neurological disease and even precede the appearance of clinical signs by years.

When posture is altered, plantar skin afferences provide altered information, which can give rise to higher-upcoming compensation strategies that are important to analyze in the prevention of the risk of falls.

Texturized, stimulating and facilitating surfaces in the environment, as well as in footwear, are increasingly being used to improve compromised plantar sensory feedback, balance and gait in patients with these deficits. Insoles, therefore, cannot and should not be seen in the narrow view of deformities correction of the foot, but as a valid preventive and reeducational element of the various structural and postural alterations of the system, especially where this is affected by diseases responsible for deafferentation and central deficits in balance and gait, such as neurological ones.

Method and materials

The review of clinical trials was conducted through research on different platforms such as PubMed Advanced and Scopus. The journals Physiotherapy Journal, Parkinsonism and Related Disorders, Gait & Posture, Journal of NeuroEngineering and Rehabilitation and Plos One Journal were also consulted. 

The design of the review included Randomised or quasi-Randomised Clinical Trials, published in peer-reviewed journals. The comparison of experimental groups-control groups was to involve the use of texturized or stimulating insoles vs placebo/other types of conventional and smooth insoles.

A diagram that reconstructs the revision algorithm is shown below:

Of the forty-one potentially valid studies performing the search for “textured insoles”, only 6 studies met the criteria for inclusion. To these, 2 others were added, which examined sensory stimulation in Parkinson’s disorder.

Of the 8 studies included, one study was of metanalysis and systematic review (liv I-a) (1), two studies were of I-b level with a moderate methodological quality and five studies, of which the orthosis’ descriptions wasn’t very clear and with low quality results, of Level II.

Among the studies included, 4 examined the effects of textured or stimulating insoles on postural balance, 7 examined the gait pattern, 2 examined muscle activity during the latter, and 3 examined plantar sensitivity.

The inclusion criteria of the review were therefore the affection for Multiple Sclerosis or Parkinson’s Disease in idiopathic and non-advanced form. All types of patients with comorbidity or clinical history conditions that could influence their condition were excluded. Sample age and size are best illustrated in Table 1.

The intervention consisted of the use of textured or stimulant insoles, composed of a pattern of different types, including:

1. rubber and fabric insoles with small pyramidal peaks, the centers of which are 2.5 mm apart and 3 mm high, with relief at the back of the heel;
2. Leather insoles up “Wet&Dry”, with layer application of adhered sandpaper, rough enough to create feedback but not to bother;
3. Insoles with vibratory devices (two placed in the forefoot and one under the heel) 18 mm in diameter and 5 mm height included in a conventional silicone polymer elastic insole;
4. Textured insoles of medium density (270) in E.V.A. etylene-vinyl-acetate from 2 to 3.1 mm with comprised granulations measuring 5.0 mm in diameter and 3.1 in height or half spheres of 9 mm in diameter (Table 1).

In all trials, except meta-analysis, there were control groups, in which patients received treatment with medium density and thickness insoles of the same material and the size of the insoles subjected to the experimental groups, therefore no higher than 3 mm, but smooth and conventional.

The comparative elements to assess the evidences were: the range of anteroposterior and middle-lateral sway of the Center of Pressure and his displacements and the velocity of these movements, sometimes measured in conditions of greater difficulty, to assess the postural balance; for the assessment of gait, were considered the space-time and cinematic parameters, such as step time, cadence, step and stride lenght, walking distance, stride duration (double support, swing and their coefficient of variation), related sometimes to the parameters of muscle activation of quadriceps, ischio-crural, gastrocnemi and tibials, measured with wireless electromyography systems. Finally, in three of the studies, there was an assessment of the plantar sensitivity of the heel, medial arc and side area through the evaluation of the Semmes-Weinstein monofilaments.

Study (anno)	Partecipants (M:F)	Intervent – control	Elements of outcome comparison	Risults
[3] Dixon e al. (2014)	46 soggetti (12:34) Età m.: 49 affetti d S.M. autonomi nel cammino per 100 mt	Solette 1:  Algeos (piccole piramidi)  Solette 2: Crocs alte 1 mm con piccole sporgenze Solette 3: media densità EVA alte 3 mm, lisce Misurazione a tempo 0 e a 2 settimane	Equilibrio in doppio appoggio, escursione CoP m-lat/a-post, o.chiusi/aperti   Cammino: velocità, cadenza, lunghezza passo. Tempi	Immediati: + oscillazione in doppio app. o. aperti e solette 2 NO effetti significativi del cammino   Dopo due settimane: NO effetti significativi equilibrio + lunghezza del passo (solette 1 e 2), tempi doppio app. ridotti con soletta 2
[6] Jenkins e al. (2009)	40 soggetti con P.D. idiopatico (24:16 e 40 controlli sani Età: 49 a 77 anni	Soletta 1: facilitatoria di gomma alta 3 mm con 3 mm rilievo retro-tallone; soletta 2: convenzionale, liscia in scarpa standard. Misurazione del cammino con queste ognuna delle due solette	Parametri spazio-temporali del cammino: velocità, variabilità del passo, lunghezza, tempi Attività muscolare: quadricipite,ischiocrur, gastrocnemi, tibiali ant.	Riduz. della lunghezza del passo in pz con P.D., aumento della variabilità del passo, miglioramenti di appoggio con solette 1; Attivazione muscolare anticipata con solette 1 di gastrocnemi e tibiali ant.
[7] Kalron e al.  (2014)	25 soggetti con S.M. recidivo-remittente (9:16) Età m.: 49,6 aa con abilità di cammino autonomo e assenza di crisi negli ultimi 30 gg	Solette di gomma elastica e stoffa con piccole piramidi alte 3 mm, ruvide in modo da creare feedback e non fastidio. Misurazione e confronto dei parametri di entrambe le solette immediati, e confronto param. tra 0 e 4 settimane	Parametri spazio-temporali del cammino (traiettoria del CoP, lunghezza del passo, tempi) ; Spostamenti del CdP durante controllo statico posturale; Sensibilità del tocco lieve e sensibilità pressoria (tallone, med, lat)	Immediati: NO evidenze a occhi aperti, riduzione dell’escursione del CoP o.chiusi; NO evidenze nel cammino   Dopo 4 settimane: NO evid. per parametri controllo posturale; riduzione dell’escursione CoP o.chiusi; NO evid. parametri cammino; NO differenze sensibilità plantare
[8] Kellher e al (2010)	14 soggetti con S.M (8:6) recidivo-remittente o secondaria 10 soggetti sani controllo (5:5) Età m. : 37+-7	Solette di fino cuoio wet&dry con carta vetrata applicata sopra; confronto parametri tra queste e scarpe lisce senza soletta	Parametri spazio-temporali del cammino (6 mt.); Analisi del cammino con dati EMG; Attività muscolare gastrocnemi, tibiali, solei; Sensazione plantare (tallone-med- later)	+ velocità cammino in pz con S.M., NO evid. cadenza; + angolo dorsi-flessione in pz con S.M.; + escursione p.sagittale ginocchio; + accelerazione; + attivazione gastrocnemi fase 1 Riduz. Sensazione plantare specie mediale in pz con S.M.
[9] Novak e Novak (2006)	8 soggetti con dg di P.D. idiopatico (5:3) capaci di 6 minuti di cammino autonomo Età m; 58 +- 12 8 controlli Età m.: 58,9	Soletta 1: con 3 dispositivi vibratili (2 avampiede, 1 tallone),con sincro del passo ON diametro 18 mm, altezza: 5 mm, vibr. 70 Hz inclusi in soletta di polimero di silicone Soletta 2: 3 dispositivi vibratili con sincronizzazione del passo OFF . Pz con P.D. e pz sani: 6 min stimolazione on- 5 min riposo- 6 min stimoazione off	Variabili spazio-temporali del passo: distanza percorsa, velocità, lunghezza del passo, durata, cadenza, oscillazione, tempo di appoggio.	+ velocità del cammino in pz con P.D. + durata del passo, + lunghezza del passo, + cadenza NO altre significative evidenze per parametri della locomozione
[10] Qiu e al. (2013)	20 adulti sani (13:7) 20 pz con P.D. (13:7) Età m.: 65 +-9	Solette 1: densità 270 Etilene-vinile-acetato soffici e alte 3,1  mm con granulazioni di 5 mm diametro e rilievo posteriore al tallone; Controllo: piedi scalzi Controllo 2: Scarpe standard con solette dello stesso materiale e dimensioni delle 1 ma convenzionali, lisce.    Parkinson: Solette 1-controllo-con.2 Sani: solette 1- controllo- controllo 2 Parkinson vs sani	Equilibrio con occhi aperti o chiusi su superficie mobile o ferma: spostamenti del CoP A-P e M-L Equilibrio a piedi nudi o con solette lisce o testurizzate	Riduzione delle oscillazioni M-L su superficie. ferma o.aperti, con entrambe le solette Riduzione delle oscillazioni in pz con P.D. e solette 1 su superficie mobile occhi chiusi (prevenzione cadute)
[1] Alfuth Martin (2017)	Revisione sistematica con tutti gli studi precedenti
[4] Ellen e al. (2017)	10 sogg.sani 9 pz affetti da P.D. idiopatico con cammino autonomo e terapia farmacologica specifica	Solette testurizzate 1: Media densità Etilene- vinile- acetato 2 mm alte, con elevazione di mezze-sfere di diametro 9 mm Solette 2: stesso materiale e dimensioni ma lisce.   Misurazione parametri a tempo 0 confrontati ai parametri dopo 2 settimane; (1 con sperimentali + 1 convenzionali)	Parametri cinematici del cammino Sensazione plantare	Miglioramento della sensibilità plantare mantenuto; + lunghezza del passo; Pattern cammino meno ipometrico

Results and discussion

Due to the insufficient amount of medium- and long-term effects data, are more reliable the results of the immediate effects of proprioceptive insoles.

In Dixon’s study, the immediate effect on postural control in S.M. patients was an increase in double-sided swings with Crocs insoles. This effect may be due to the fact that any newly inserted foreign element creates a destabilization situation and requires an adjustment period. In Kalron’s 2014 study, no statistically significant changes in postural control are visible in S.M. patients in opened eyes condition, after wearing elastic rubber insoles with small 3 mm high pyramids. However, there was a reduction in the Centre of Preassure range of displacement with its eyes closed. This indicates that the opened-eyes balance is sufficiently preserved to make the performance improvement, resulting from the insoles, irrelevant.  However, removing the afference of the visual system (closed eyes), there may be greater dependence on the plantar information system and this makes the effects of the insoles more visible. Similarly, in the study conducted by Qiu and al. (10), there was a reduction in medio-lateral sways wearing experimental insoles, on a firm surface with opened eyes, and on a moving surface with closed eyes, in patients with Parkinson’s disease: this intervention would constitute, for these patients, an important means of preventing falls.

Summarizing, even in the heterogeneity of the available data, the use of proprioceptive insoles would be followed, in the immediate, by a postural balance improvement in closed-eyes balance in both kinds of patients affected by M.S. and Parkinson’s disease.

Among the studies examined,7 have looked at the immediate effects on the gait pattern. From Dixon’s study (3) and from Kalron’s one (7), there was no significant effect on the gait in S.M. patients who were subjected to the use of texturized rubber insoles. Nonetheless, from Jenkins’s study (6), which looked at patients with Parkinson’s disease, it has been highlighted a reduction in step length and increased variability from step to step, as well as an improvement in single support time with textured insoles. In addition, although unrelated to descriptive data, there was an anticipation of the activation time of gastrocnemis, anterior tibials, quadriceps and ischio-crurals in the same patients.

Kellher and al. (8), in the study of subjects with S.M. wearing up leather insoles, highlighted: an increase in the step velocity and acceleration, no significant change in the cadence, an increase in the angle of dorsiflexion and ROM on the sagittal level of the knee and ankle when compared with the parameters obtained from the use of flat insoles received by a 3D motor analysis.

In the pilot study conducted by Novak-Novak in 2006 (9), subjects affected by idiopathic Parkinson who were subjected to the use of insoles equipped with vibration devices activated with step synchronisation, had an increased pattern of the gait in speed, step time, step length and cadence.

Although of low quality, finally, the comparative cohort study of 2017 by Ellen-Rodrigo and al. (4) , shows that patients with Parkinson’s and subjected to the use of 2 mm high medium density textured insoles consisting of half-spheres high of 9 mm in diameter showed improvements in the gait, which on the whole appeared less hypometric, probably related to an increased afference in the somato-sensory cortex, at the time of one week measurement.

In the light of what has been analysed, on the whole, even in the case of the effects on the parameters of the clinics, the use of proprioceptive insoles has therefore proved to be in the immediate, modically effective.

The results of this review are similar to those found in other studies that examined healthy elderly or elderly patients at high-risk of falling. An immediate disadvantage, which comes from the use of insoles and which therefore creates initial destabilization and requires a stabilization period, is the reduced gait velocity and step length, when compared to the use of flat and conventional insoles. This is always because newly inserted foreign element intervenes to influence the whole series of proprioceptors that contribute to the maintenance of postural control, destabilizing them and making  it necessary a period of stabilization. Also, in Corbin’s study(2), it is stated that postural control in bipodalic station can be improved by the use of texturized insoles, while the control of the monopodale erect station is not affected by this.

However, a reason why there are differences in static and dynamic outcomes may be that peripheral receptors are more likely to be activated during the gait because of a higher impact of forces and pressures compared to maintaining-balance activities. In particular, an increased plantar sensitivity in regions near the course points of vector forces during stride, proves this thesis.

The reduction of the medio-lateral Centre of Pressure sway that were obtained while the subjects wore textured insoles with their closed eyes, could be well explained by the neuro-sensory feedback compensation mechanism for postural control that occurs when one or more afferent channels are not used. According to this phenomenon, during the disabling of a sensory channel (which can result from a pathological condition of deafferentation or being an experimental study condition), the other channels would increase their capacity to maintain the balance of the subject, also making the effects of what acts on them more manifest. The exclusion of the visual canal results in this study, as well as in many other moments of diagnosis and cognitive therapy, an essential element that isolates the subject and makes more corticalized information from other receptors.

Keller and al. (8) and Jenkins and al. (6) assumed that the improvement in plantar feedback resulting from the use of texturized insoles or postural reprogramming ones, in fact, had positive effects on balance. Less clear are the long-term effects of these, as is also evidenced by the lack of evident effects at 4 weeks in Kalron’s study (7).

Furthermore, the improvement of gait pattern in Parkinsonian seems to be linked to a qualitative action of proprioceptive insoles. In fact, the increase in the step cadence is not always a positive factor in parkinsonian, however overall, gait pattern appears less hypometric. Anyway, for future studies, a better definition of this outcome in relation to pathology considered is necessary.

Another parameter examined by two studies is the influence of the textured insoles on muscle activation: Jenkins and al. (6) observed an improvement in muscle activation time, which would indicate a normalization of the same during the heel contact on the ground in patients suffering from Parkinson’s disease; Keller’s study(8) showed this in particular as regards to lateral gastrocnemis in the 1st phase of gait on subjects with S.M.

Overall, it must be said that plantar skin receptors support postural control and deambulation. However, more information originate by receptors in the neuromuscular fuses and joints of the lower limbs, as well as other sources of sensory feedback. This may be one of the main reasons why the effects of textured  insoles and other types of stimulating ones in this study appeared less incisive and heterogeneous.

Ultimately, in the short term, as regards the parameters of postural balance, the insoles promote:

• An increase in sway of the Centre of Pressure in double support and opened-eyes, in patients suffering from S.M.;
• A reduction in the Centre of Pressure sways on the medium-to-lateral level with opened eyes on a firm surface and closed eyes on a moving surface, in patients with Parkinson’s disease.

As for the immediate effects on the gait there will be:

• Increased velocity and acceleration in the gait, increased angle of movement of the ankle and knee, reaction strength to the ground, an anticipation of the muscle activation of gastrocnemis in the 1st phase of stride, in patients suffering from S.M.;
• In patients with Parkinson’s disease, a reduction in stride length, with increased step-by-step variability and muscle activity underlying this; an improvement in velocity, duration and overall the pattern appears less hypometric.

Basically, it can be said that insoles do not promote significant effects in the condition of opened-eyes balance, but make their effects on static postural balance more visible in the closed-eyes particular condition. Even as regards the gait pattern, the effects seem to be positive from a biomechanical point of view both joint and muscular. 

The long-term effects are not well analysed and the studies themselves have no significant effect at 2 and 4 weeks. Additional RCTs with longer treatment and follow-up periods are definitely needed. These studies should also be useful to understand plantar sensitivity parameters, which can be examined with longitudinal settings, to better analyse skin adaptations in response to the use of textured insoles.

In this regard, seem particularly promising the planning of a protocol study that will examine the long-term effects of the use of textured insoles for 12 weeks on the space-time parameters of gait, the kinematics of the step, the plantar sensitivity and proprioception in 176 patients with S.M.(5).

References

1. Alfuth, M. (2017) Textured and stimulating insoles for balance and gait impairments in patients with multiple sclerosis and Parkinson’s disease: a systematic review and meta-analysis. Gait & Posture. Vol. 51, 132-141
2. Corbin, D.M., & Hart, J.M.,& McKeon, P.O., & Ingersoll, C.D., & Hartel, J. (2007) The effect of Textured insoles on postural control in double and single limb stance. Journal of sport rehabilitation Vol.16, 363-372
3. Dixon, J., & Hatton, A.L., & Robinson, J.,& Gamesby-Iyayi, H.,& Hodgson, D.,& Rome K., et al. (2014) Effect of textured insoles on balance and gait in people with multiple sclerois: an exploratory trial. Chartered Society of Physiotherapy (Elsevier) Vol. 100, 142-149
4. Ellen Lirani, S., & Rodrigo, V.,& Barbieri, F.A.,& Orcioli-Silva, D.,& Simieli, L.,& Gobbi, L.T. (2017) Continuous use of textured insoles improve plantar sensation and stride lenght of people with Parkinson’s disease: A pilot study Gait & Posture. Vol. 58, 495-497
5. Hatton, A.,& Dixon, J.,& Rome, K.,& Brauer, S.G.,& Williams, K.,& Kerr, G. (2016) The effect of prolonged wear of textured shoe insoles on gait, foot sensation and proprioception in the people with multiple sclerosis: study protocol for a randomised controlled trial. Hatton et al. Trials. Vol. 17, 1-1
6. Jenkins, M.E.,& Almeida, Q.J.,& Spaulding, S.J.,& Van Oostveen, R.B.,& Holmes, J.D.,& Johnson, A.M.,et al. (2009) Plantar cutaneous sensory stimulation improves single-limb support time and EMG activation patterns among individuals with Parkinson’s disease- Parkinsonism and related disorders. Vol. 15, 697-702
7. Kalron, A., & Pasitselsky, D., & Greenberg-Abrahami, M.,& Achiron A.(2014) Do textured insoles affect postural control and spatiotemporal parameters of gait and plantar sensation in people with  multiple sclerosis? PM&R Journal. Vol. 20, 1-9
8. Keller, K.J.,& Spence, W.D.,& Solomonidis, S.,& Apatsidis, D. (2010), The effect of textured insoles on gait patterns of people with multiple sclerosis, Gait & Posture. Vol.32, pag. 67 – 71
9.  Novak, P.,& Novak, V. (2006) Effect of step-syncronized vibration stimulation of soles on gait in Parkinson’s disease: a pilot study. Journal of NeuroEngineering and Rehabilitation. Vol. 3, 9
10. Qiu, F., & Cole, M.H., & Davids, K.W., & Hennig, E.M., & Silburn, P.A., & Netsher, H., et al. (2013) Effects of Tìtextured insoles on balance in people with Parkinson’s disease PLoS ONE. Vol.8