1.1

Introduction

Post-polio syndrome (PPS) is a lower motor neuron disorder that affects survivors of paralytic poliomyelitis . The disorder emerges following a stable plateau phase lasting several decades after their recovery from the initial virus attack. Although new reported polio infections are quite rare owing to the polio eradication campaign initiated by the World Health Organization in 1988, there currently are more than 12 million individuals worldwide suffering from PPS. It is estimated that up to 80% of individuals who recovered from their acute poliomyelitis infection, report new neuromuscular complaints . Apart from psychological distress and joint pain , the main symptoms of PPS are progressive weakening of muscles, fatigue, and muscle atrophy .

Deterioration in motor abilities is frequently reported in PPS patients . The main impact of disability for most PPS patients is in mobility-related activities. Ambulatory individuals find it difficult to climb stairs, walk long distances, and perform various normal daily activities. Clinical management of PPS patients aims to restore mobility by means of physiotherapy, muscle training while avoiding overuse, surgical correction of joint deformities, or administration of orthoses and assistive devices . It has been suggested that biomechanical analysis of the PPS gait pattern can lead to optimal design of orthoses for PPS patients .

In light of the need to evaluate the gait characteristic of the PPS patient in order to devise the optimal treatment plan, quantifications of gait parameters may be warranted. Functional tools, e.g. the Timed “Up & Go” test are reliable tools, commonly used to evaluate gait performance . Unfortunately, these tools are not sensitive enough to provide precise quantifications of gait parameters. Therefore, quantitative spatio-temporal parameters are needed in order assess the effectiveness of gait, i.e. gait symmetry and thereby the patient’s risk of falling . Also, these parameters are frequently utilized for patient diagnosis, determining the severity of the patient’s condition, and predicting and monitoring the outcomes of an intervention .

Surprisingly, there is a great paucity in data describing gait of lower motor neuron disease including polio survivors. Importantly, what little data are available is usually lacking better description of the studied PPS group so that the discussion of the results and comparison between studies is compromised. Most studies of PPS gait differ mainly by the inclusion criteria concerning gait and the type of orthotics and walking aids used in the trials. Some of these studies fail to report these crucial data. We therefore aimed to:

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  evaluate the differences in gait characteristics and gait symmetry of PPS patients ambulating with or without shoes and between subgroups walking with different walking aids and orthoses;

  
  
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  study the correlation of these data with personal data, illness condition, physical health, frequency of using aids and orthotics and frequency of falls, and;

  
  
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  derive recommendations for standardization of reporting of descriptive and quantitative data.

In order to reach these goals, we considered two variables as major outcome measures: barefoot/shod gait and type of walking aid/orthosis. Spatio-temporal parameters and gait symmetry were calculated in order to distinct between the different groups and conclude regarding the effectiveness of shoes and the variability of gait patterns in the different stages of the PPS. We further considered data of demographics, physical activity, polio history, falls and walking aids and its relation to the gait characteristics.

1.2

Methods

1.3

Results

We found no difference in gait parameters in PPS sub-groups that differed by gender (male or female), age (above or below 60 years old), body mass index (BMI < 25 or BMI ≤ 25), age of initial poliomyelitis infection (< 2 or ≥ 2 years old), childhood history of weakness in number of limbs (both legs involved or not), walking aids in childhood (yes/no), scoliosis at initial illness (yes/no), education (above or below 12 years), marital status (married or not), perceived physical health (feel healthy or not), exercise during the last month (yes/no), orthopaedic shoes (yes/no), ability to ambulate at home and outdoors (yes with or without difficulty or with aids or assistance or cannot walk), falling outdoors in the last 6 month (yes/no), and working in the last week (yes/no). We did, however, find a connection between several spatio-temporal gait parameters and questionnaire-based subgroups ( Table 1 ). Specifically, PPS subjects who are not using walking aids on a daily basis had significantly higher gait cadence and shorter stride time. Their gait velocity was higher when compared to subjects who did use walking devices on a daily basis, average velocity of 0.673 m/s and 0.454 m/s, respectively, however the difference was not statistically significant. PPS subjects who reported participation in physical activity more than twice a week had better step time and double support symmetry. PPS subjects who did not report falling indoors in the last 6 months had significantly higher gait velocity and cadence, shorter double support stance and step durations, as well as longer step length and better step length SI. PPS subjects who are not using a wheelchair walked with significantly longer step length and had less symmetry of their base width, however only one of these subjects had SI of base width that was above normal. Finally, PPS subjects who went through orthopaedic surgery in childhood walked with a smaller than normal foot progression angle and had significantly wider base width.

The results of intra-subject variability of 14 PPS patients who were able to perform the test with (PPS-SHOD) and without (PPS-BRF) their shoes, orthotics and walking aids are presented in Table 2 . Although the mean gait velocity was increased from 0.59 m/s for PPS-BRF to 0.65 m/s for PPS-SHOD, the difference was not statistically significant ( P = 0.572; Table 2 ). Among the 14 PPS subjects, only nine walked faster wearing their shoes and orthotics. A similar finding concerns the mean stride length increase from 77.5 cm for PPS-BRF to 85.1 cm for PPS-SHOD ( Table 2 ). Although 11 subjects increased their stride length, the results were insignificant ( P = 0.158). An example for the difference in step lengths when ambulating barefoot, with shoes, and with orthotics is depicted in Fig. 1 . In this figure, sagittal images of a 43-year-old female PPS patient who ambulated without shoes ( Fig. 1 a), with orthopaedic shoes ( Fig. 1 b) and with KAFO ( Fig. 1 c) are presented at the time of right foot heel strike. The step length of the subject was short when she ambulated without shoes and genu recurvatum of the right leg can be seen. When walking with her orthopaedic shoes, the patient increased her step length by 11.8 cm and when donning the KAFO, the hyperextension of the knee is prevented, however the orthosis imposes a decrease in step length to only 3.6 cm longer than the step length achieved while walking without shoes. All temporal-related SIs decreased when shoes and orthotics were used in the trials ( Table 2 ). The decrease in SI of the swing duration was statistically significant ( P < 0.01).

Sagittal images of a 43-year-old female post-polio syndrome (PPS) patient who ambulated (a) without shoes, (b) with orthopaedic shoes, and (c) with KAFO. The pictures were taken at the time of right foot heel strike. The step lengths are calculated using the algorithm described in subchapter 2.3.1.

When comparing the gait characteristics of PPS patients walking with shoes, with or without AFO (PPS-SHOES), with shoes and KAFO (PPS-KAFO), with shoes, orthotics and wither a walker or crutches (PPS-AIDS) and normal gait (NORM), we found significant differences for most of the spatio-temporal parameters of gait and SIs ( Table 3 ). As could be expected, the normal gait was characterized by higher velocity and cadence, shorter stance duration, longer stride and step lengths. These parameters differed statistically for the NORM group when compared to the three PPS groups ( Table 3 ). Other characteristic of normal gait were smaller base width), longer single support duration, and better SI, however the statistical significance was found interchangeably for one or two of the PPS groups ( Table 3 ).

The PPS-SHOES group walked with a smaller base width and better symmetry in stance and swing durations when compared to the PPS-KAFO group. They also walked with a higher velocity and cadence, longer stride length and single support duration, however these findings were not found to be statistically significant ( Table 3 ).

The PPS-AID group was characterized by the slowest gait velocity, reduced cadence, long stride time, stance and double support duration, short swing and single support durations, short step length and high SIs. The variability and range of SIs for the PPS-AID was very high.

1.4

Discussion

PPS patients exhibit decreased functional ability, mainly impaired due to gait deficiencies. In addition to the custom functional, clinical and electro-physiological examinations, computational gait analysis provides further insight into the motor function and control of the patient. In this study, we compared spatio-temporal data and gait symmetry of PPS patients ambulating barefoot, with shoes, with orthotics and walking aids and compared them to normal gait. The necessity of exploring these differences arose from the great paucity in data describing the gait of PPS patients and more importantly, the lack of uniformity in reporting the personal characteristics of the study group and the conditions of the trials, compromising the conclusions of comparisons made between different studies of PPS gait.

In our study, the gait pattern of the PPS subjects was not associated with gender, age, BMI, education, and marital status. Also, apart from association with history of orthopaedic surgery at childhood, no correlation was found between gait characteristics and polio history. Most of the subjects (76.9%) went through corrective orthopaedic surgery at childhood and walked with a significantly smaller than normal foot progression angle and had significantly wider base width. This finding may suggest that altered tendon length at the ankle joints and ankle/foot arthrodesis caused alteration of ankle/foot progression bio-mechanical mechanism, thereby compelling the subject to increase his or her base width to maintain stability and to compensate the lack of bio-mechanical rockers.

The physical health of PPS patients affects their daily activities and participation in the community . In this study, we found that subjects who reported participating in physical activity twice a week or more had significantly better step time and double support symmetry, i.e. lower SI. Gait symmetry and gait double support duration were shown to be the variables most strongly associated with prediction of multiple fallers , and we found correlation between reports of falling indoors in the last 6 months and significantly reduced gait velocity and cadence, longer double support stance and step durations, as well as shorter step length and higher step length SI, indicating high asymmetry. These findings suggest that PPS fallers reduce their gait cadence and maintain double support for longer and uncertain distances and likely use walking aids in order to increase their stability and reduce the risk of falling. These taken precautions cost them their velocity of advancing forward as their step length is reduced.

Walking aids and orthopaedic shoes are an integral part in the life of a PPS patient. The deterioration of the motor condition of the PPS patient involves increasing the need of walking aids and orthotics. Although the symptoms of the syndrome vary for each individual, the typical cluster of symptoms comprises mainly of a gradual increase in muscle weakness, particularly but not exclusive to the muscles injured in the initial virus attack. This condition reduces the control of the patient over his or her joints. Following this first stage of the appearance of the symptoms, the patient will adopt certain motor mechanisms that will compensate for the muscle weakness and allow the PPS patient to continue with daily activities. Since gait asymmetry is now a daily routine in the life of the patient, it imposes alteration of the state of loadbearing on the joints, caused by instability of the joints and prolonged loadbearing on the preferred side, or secondary biomechanical changes. Consequently, joint pain often arises. Coupled with muscle pain as part of the PPS, antalgic gait is common and the gait pattern is affected. At this stage, most patients will require new walking aids and/or orthotics, to be used on a daily basis. These aids will usually restore joint stability, thereby reducing joint pain, allowing the patients to walk longer distances without fatiguing and prevent joint pain.

In this study we found that subjects who use walking aids on a daily basis (69.2%) had significantly higher gait cadence and shorter stride time. Their gait velocity and spatial gait parameters did not significantly differ from subjects who did not use walking aids on a daily basis, although the gait velocity was lower in subjects who daily used walking aids. In an attempt to maintain a high gait velocity, PPS patients who depend on assistive devices increase their cadence. At progressive stages of the PPS, the patient will be less able to walk independently without fatiguing and will resort to using a wheelchair. In our study, although we included only subjects that had functional walking ability with or without walking aids, 26.1% of the subjects reported occasionally using a wheelchair. These subjects had significantly shorter step length, since their physical status was more deteriorated.

When comparing gait characteristics of PPS patients walking with their customary shoes and orthotics and walking barefoot, we found no statistically significant differences, excluding the SI of the swing duration, which was improved for shod gait ( Table 1 ). Although most of the subjects walked faster and increased their stride length during shod gait, the results were not statistically significant. These results suggest that the PPS patients adopt a certain gait pattern, which allows them to optimally compensate for muscle weakness and atrophy, and enables a comfortable gait so that when the shoes and orthotics are doffed, only slight changes in the gait characteristics appear. This conclusion, however, does not imply that the gait pattern of the PPS patient cannot be altered by replacing existing orthotic or walking aid with a new one, but that the patient will require time to acquaint himself or herself with the new restrictions or and liberties provided by the replaced orthotic or aid.

Walking aids and orthotics are prescribed to PPS patients to improve balance during the stance phase and ensure foot clearance in the swing phase so that the risk of falling is minimized. The walking aids also improve endurance, relieve pain and prevent further deterioration of joint degradation . The use of orthopaedic shoes, AFO, KAFO, crutches and walkers, alters the gait pattern by controlling the interaction properties between the shoe and the ground, or decreasing the range of motion of the ankle and knee joints. Although these compensation strategies may enable the patients to make the most of their residual capacities and keep their mobility, in the long term, these strategies can induce joint degeneration .

We found that when compared to normal gait pattern, PPS inter-subject variability was greater and significant differences were evident in most of the spatio-temporal parameters and SIs ( Table 3 ). Our results show that PPS gait is characterized by slower velocity and cadence, prolonged stance duration, and shorter step lengths. Prolonging the stance duration from the mean normal value of 61.8% to mean values of 67.4%, 71.7%, and 74.3% for the PPS-SHOES, PPS-KAFO, and PPS-AID, respectively, was accompanied by shorter swing and single support durations and longer double support duration ( Table 3 ). These temporal data suggest that the subjects felt imbalanced in swinging the leg forward, thereby transferring their entire body load to the other leg. This insecurity relates to the weakness of the muscles that control the body posture and joint stability during load bearing activities and prevent falling.

PPS patients walking with shoes with or without AFO had a smaller base width and better symmetry in stance and swing durations when compared to the PPS patients ambulating with KAFO ( Table 3 ). The locked KAFO is usually prescribed to patients whose symptoms are progressed so that their knee extensors are weak and is crucial for knee stabilization. However, maneuvering with a locked knee unilaterally is designated to produces gait asymmetry. We presented a visual example of the effects of shoes and KAFO on the step length and knee angle in a PPS patient ( Fig. 1 ). This subject has been using the KAFO for the realignment of the femur and tibia. Realignment of limb segment may prove to be harmful as some of the patient’s deformities and compensations are beneficial to produce functional gait . Therefore, the choice for prescribing a certain type of orthosis and adjusting its parameters of function can critically affect the gait pattern of the patient. Most orthotics prescribed to PPS patients are KAFO, designed to lock the unstable knee joint , therefore augmenting stability during gait. Since the patient cannot flex the knee during swing, this result in compensation in the form of circumduction, vaulting or hip hiking or a combination of these. The design of the stance-control orthosis (SCO) locks the knee during load-bearing state and unlocks during non-load bearing state. Studies have shown that PPS patients walk faster while ambulating with an SCO than with a locked KAFO .

PPS patients who require the assistance of a walker or crutches in addition to orthopaedic shoes and/or orthotics are patients whose gait is the most restricted and affected by their deteriorating condition. Accordingly, the gait of these patients who participated in this study, was characterized by the an extremely slow gait velocity, reduced cadence, long stride time, stance and double support durations, short swing and single support durations, short step length and high SIs. The variability and range of SIs for the PPS-AID was very high.

The main limitation of our study is the small sample group; however we were able to show the differences in gait pattern, obviously from normal gait, but more interestingly between sub-groups ambulating with different orthotics and aids. A study of larger population, where PPS patients are divided into groups according to more specific device types will shed more light on the consequences of prescribing certain orthotics or aids. The presented data herein may already provide the basis for understanding some of the factors, which may link spatio-temporal parameters, gait symmetry, and the progress of the PPS. Another limitation is the single-day measurements that may not be representative of the general gait pattern.

Following the conclusions presented herein, we recommend standardization of the reporting protocol of gait-related data of PPS patients. Studies are usually recruiting small PPS groups, which, as shown herein, have great inter-subject variability so that it is important to present all the personal characteristics that differ between subjects. The specific inclusion criteria relating to diagnosis of PPS and motor abilities at the time of recruitment should be addressed. Also, researchers should provide specific details of orthoses and walking aids used by their subjects and note whether the trial protocol was such that the subject ambulated with their own footwear and aids. Since gait laboratories are equipped with different hardware and software, using different calculation algorithm, and different trial protocols, we believe that following the aforementioned guidelines will reduce the difficulty of comparing results between studies.

Disclosure of interest

The authors declare that they have no conflicts of interest concerning this article.

Acknowledgements

We appreciate the help of Hadassah physiotherapists Asaf Frechtel, Yael Bresler, Yshai Peleg, Adina Forst, and Shira Eisenberg, with the data collection.