Background

Spinal cord injury (SCI) is a pathological condition where affected individuals suffer the loss of one or more body functions due to an injury to the spinal cord as a result of trauma or disease [1]. The majority of SCIs are caused by traffic accidents, falls, assaults, and sports injuries. Lesions can be produced by different mechanisms, such as impact, compression due to bone fragments or hematoma, or partial or total tearing [2].

It is not clear how many people live with SCI worldwide, but international incidence data indicate that 250,000–500,000 people suffer SCI each year, with 40–80 new cases per million inhabitants, most caused by traumatic events. The incidence rate tends to be higher in North America than in Europe. With regard to prevalence, there are no global data that estimate how many people are affected by SCIs. Available data allow us to know the prevalence of SCIs by country. According to Gisem studies, there are between 60 and 70,000 SCI cases in Italy, with an incidence of 20–25 new cases per million inhabitants each year [3, 4].

SCIs can cause loss of strength (paraplegia if it affects only lower limbs, and quadriplegia if it affects both lower and upper limbs) and loss or alteration of sensation, from the level of the lesion downward. The loss of strength can affect not only the limbs, but also the muscles of the back, chest, and internal organs, causing inability or weakness in controlling trunk movements and respiratory, intestinal, and genital functions. Lesions are defined as “complete” or “incomplete” depending on whether there is a total or partial loss of function [5,6,7].

Some fundamental objectives in SCI treatment are: prevention of pressure sores, maintenance of joint mobility, prevention of muscle shortening, and, where possible, recruitment of residual muscles [8, 9].

The main goal of rehabilitation treatment is to achieve the highest possible level of independence in the patient’s movements and daily life activities. In order to achieve these objectives, part of the treatment consists of the execution of movements that enhance joint mobility, either actively or with the manual help of the therapist [10, 11]. The use of electrostimulation is widely recommended. In functional electrical stimulation (FES), the intensity and duration of the contraction can be input into the machine to facilitate residual muscle function of the subject [12,13,14]. Robotics, which are used in the rehabilitation field to generate movements, have made great strides in recent years and sensors are now able to detect even minimal movements. The loss of strength and sensitivity typical of this pathology can cause difficulties maintaining balance, both in an upright and sitting position. Recovery of balance control is possible through the stimulation of proprioceptive receptors lying on the skin, muscles, and joints [15,16,17].

Hydrotherapy plays a key role in the rehabilitation of neurological patients [17,18,19]. The usefulness of therapeutic exercise in water is based on 3 physical principles: temperature, density, and viscosity [20, 21]. The ideal temperature is around 31–33 °C, which avoids heat loss and excessive lowering of pressure and vasodilation while inducing muscle relaxation [22]. The density of the water creates a micro-gravity environment and makes the body immersed in it lighter. In this condition, the patient can perform movements easily because gravity is minimal. Viscosity refers to the resistance exerted by the water, which makes movement slower, thus increasing learning and motor control [23, 24]. The water proprieties can facilitate physical therapy, while land-based therapy can be harder to accomplish with SCI patients. Thanks to the use of buoyancy devices and immersion depths, the therapist can vary the patient’s position by performing exercises in the supine, lying, kneeling, prone, or standing position, varying the amount of weight to be supported [25].

The goal of this study was to evaluate the efficacy of hydro kinesitherapy in patients who suffer from SCIs.

Materials and methods

Eligibility criteria for studies considered in this review: type of study, participants, and intervention

In this systematic review, we searched the literature from May to August 2021 to find all published studies that included the keywords “aquatic therapy”, OR “aquatic exercise”, OR “hydrotherapy”, AND “spinal cord injury” on the CINAHL, PubMed, Scopus, Web of Science, and PEDro databases. Only randomized controlled trials (RCTs) that compared aquatic therapy to land or no therapy were considered.

We considered RCTs on patients with SCIs, both as a result of trauma or other sources. Studies were included that considered different outcomes of rehabilitation, including fatigue, postural balance, muscle strength, muscle deficiencies, gait, sensitivity, cardiorespiratory response, endurance, psychosocial field, and quality of life. Articles that reported studies conducted on animals, focused on other pathologies, or were written in other languages were excluded.

Study selection

At the end of the initial keyword search, editors selected relevant studies and removed duplicates. All articles that the editors agreed upon were included in a second screening. During the second screening, the full text of included studies was analyzed, and a final list of eligible studies was compiled, excluding studies that did not meet the inclusion criteria.

Extraction of data and risk of bias

Data extraction followed the Cochrane method [26]. The reviewers collected patient demographic information. The following data were extracted from selected studies: author and publication year; included sample characteristics; type of treatment and type of control; outcomes and conclusions.

To evaluate the risk of bias, Jadad and PEDro scales were used [27].

Results

Our initial search returned a total of 402 articles (CINAHL 80; PubMed 193; Web of Science 37; Scopus 92; PEDro 0). After applying the inclusion criteria, 11 articles remained. After removing duplicates, 3 articles were included (Table 1) (Fig. 1).

Table 1 Characteristics of studies.
Fig. 1
figure 1

Flow-chart of included studies, description of the study selection (N° = number).

Characteristics of the studies: type of design and participants

In this systematic review, only RCTs were included. All participants gave their consent to participate in the clinical trials. A total of 71 individuals with SCI were included in the studies: 31 with chronic motor incomplete SCI (CMISCI), 20 with a grade B, C, or D SCI according to AIS classification, and 20 with unspecified SCIs. Age and level of injury varied in each study.

In one of them 20 individuals with the following characteristics were included: 15 male and 5 female with spinal cord injury, average age of 33 years, and injured since a time between 7 and 9 months; the intervention group followed a program including passive range of motion (PROM) twice a day and 20 min of water exercise 3 times per week with a follow-up of 10 weeks, while the control group followed only PROM. Outcomes were measured with Functional Independence Measure (FIM) and Ashworth scale [28,29,30]. In this study no significant differences between the two groups were found; regarding spasm severity and oral baclofen intake, the hydrotherapy group reported greater improvement than the control group. Both groups had an increased FIM score, but it was better in the aquatic therapy group. In the second study 20 individuals with spinal cord injury between C8-L5 were included; the intervention group participated to 60 min sessions of aquatic therapy 3 times per week for 8 weeks with a follow-up of 8 weeks, and the control group followed a land therapy program; the outcome measure was CardioTouch 3000 s in sitting position [31]. The aquatic group showed significant changes in all aspects of pulmonary function. In the third study 31 subjects were included, with chronic motor incomplete spinal cord injury (CMISCI) between C2-T12, age between 18 and 65 years and 1 year since injury time; the intervention group had 36 sessions lasting 40 min of aquatic therapy with a follow-up of 3 months, while the control group was subjected to robotic therapy; outcomes were measured using Quark CPET [32, 33]. No significant differences were noted between the two interventions.

Intra-study risk of bias

The Cochrane Risk of Bias tool was used for the qualitative analysis of the trials included in the systematic review. This evaluation revealed that one study received a score of four and had a high level of quality. The remaining two studies achieved a score indicative of a low level of quality (Figs. 2 and 3).

Fig. 2
figure 2

Risk of bias of included studies, investigators’ judgements about each risk of bias item presented as a percentage across all included studies.

Fig. 3
figure 3

Risk of bias summary, investigators’ judgements about each risk of bias item for each included study.

Discussion

In this review, three important aspects were considered in subjects affected by SCI: (1) cardiorespiratory endurance and exercise capacity reduction, (2) lung function limitation, and (3) spasticity management. We aimed to confirm the beneficial effects of aquatic therapy with regard to other types of physiotherapeutic treatment, such as land-based exercise, robotic therapy, or as an addition or support to SCI patient therapy.

Exercises performed in water allow the patient to be subjected to a minimum, continuous, and global resistance from all three spatial dimensions. During the immersion of a patient in water, it is important to consider the effect of hydrostatic pressure, i.e., the force exerted by a liquid on the surface with which it is in contact. This force depends on two factors, the density of the liquid and the level of body immersion [34, 35].

The aquatic environment provides great benefits in the therapeutic treatment of patients with spinal cord injuries since it provides relaxing physical properties while reinforcing physical exercise [36]. The study carried out by Gorman et al. [33] considered 31 individuals with CMISCI between C2 and T12 one year after injury. They compared aquatic and robotic therapy for a total of 36 sessions lasting 40–45 min. Cardiopulmonary endurance was set as an outcome and measured by Quark cardiopulmonary exercise test (CPET) using arm ergometry. There was no significant difference between the two interventions, however oxygen consumption measured with arm ergometry during exercise was not comparable between the two treatments because of different district and muscle group recruitment. The measurement instrument used is therefore useful for patients with gait problems, but not specific to those who have undergone treatment with a robotic-assisted treadmill.

SCI patients have a high risk of developing serious and debilitating conditions, including respiratory conditions, which are the major cause of mortality in SCI patients [37]. Therapeutic exercise in water is an effective means of respiratory gymnastics. When the patient is immersed up to the shoulders, the hydrostatic pressure creates resistance against thoracic expansion, therefore opposing inspiration while promoting exhalation [38]. Aquatic therapy has also been compared to land-based therapy to evaluate its effects on pulmonary function. In the study by Jung et al. [31], 20 individuals with SCI between C8-L5 were randomized into control (land-based) or study (aquatic therapy) groups for 60 min of exercise 3 times/week for 8 weeks. Pulmonary function was assessed by measuring forced vital capacity (FVC), forced expiratory flow rate (FEF), forced expiratory volume at one second (FEV1), and forced expiratory volume at one second/forced vital capacity (FEV1/FVC). Following the intervention, the aquatic group showed significant changes in all aspects of pulmonary function, while the land-based group showed differences in only FEF. These results suggest that aquatic therapy has greater effects than land therapy.

Another important condition to treat in SCI patients is spasticity [39, 40]. Here the water temperature plays a key role. Lower temperatures (26–35 °C) are used for high-intensity exercise, while higher temperatures (36–37 °C) are used for mobility, flexibility, and muscle relaxation exercises [41]. Spasticity is usually treated with passive mobilization, stretching techniques, painkillers, and muscle relaxant drugs [42]. With hydrotherapy, both the high temperature of the water and the buoyancy, which provide a sense of safety and protection, induce body relaxation, which allows for even more effective stretching techniques than those used on land [43]. The greatest effect of hydrotherapy was reported in a study on the treatment of spasticity. Kesiktas et al. [28] selected and randomized 20 individuals (15 males) with an average age of 33 years between 7 and 9 months and various degrees of spasticity, after injury into two groups. They compared the control group, which was subjected to traditional treatment consisting of passive range of motion (PROM) and baclofen drug administration, to the study group, which performed an extra 20 min of aquatic therapy 3 times/week. Functional Independence Measure (FIM) [44] score, Ashworth scale score [45], spasm severity, and oral baclofen intake were set as outcome measurements. After 10 weeks of treatment, there were no significant differences between the two groups as measured by Ashworth scale. Regarding spasm severity and oral baclofen intake, the hydrotherapy group reported greater improvement than the control group. Both groups had an increased FIM score, but there was a larger increase in the aquatic therapy group. Hydrotherapy seems helping decrease spasticity and body relaxation that may also allow the patient to feel more independent in water after an adaptation period. It is likely that in this situation the patient will be able to perform motor skills in a more functional way and to move more freely; as a result, he will feel better in both physical and emotional sphere. The water temperature is an important factor because if it is too hot or cold may have a negative effect on spasticity. One mechanism of hydrotherapy on spasticity may be related to depressing the sensitivity of muscle spindle and a decrease in skin sensitivity, reducing gamma fiber activity. In the study it is not specified the duration of benefic effects on spasticity over time, in fact it would be interesting to deepen this aspect in future studies [28]. Also, Ellapen et al. found that hydrostatic pressure assists in the dissipation of edema, in the gradual increase in joint range of motion and in combatting spasticity [46].

This review included studies that treated the main dysfunctions and complications related to this condition, i.e., cardiorespiratory endurance, lung function, and degree of spasticity, and that compared aquatic therapy interventions (study group) with an alternative treatment group (e.g., control group). Our results contribute to the literature by demonstrating the usefulness of hydrotherapy in different situations.

Limitations of the study

Limitations of our study include the small sample size, few available studies, and low methodological quality. Future trials are recommended to show the efficacy of aquatic therapy.

Conclusions

The physical properties of water and the depth of body immersion led to benefits in patients with SCIs. The study shows that patients who underwent rehabilitation treatment in water had results that were greater than or similar to those obtained in patients who received standard or alternative treatment. In conclusion, the aquatic environment provides a rehabilitation tool able to facilitate movements, physical and cardiovascular exercise, resistance training, and body relaxation. The best results can be expected from the combination of hydrotherapy and land-based interventions.