Quality of Life and Patient Satisfaction After the Provision of an Orthopedic Knee Scooter

A Multicenter Randomized Controlled Trial

Background: Partial or total avoidance of weight-bearing by a lower limb is regularly needed after trauma and surgery. There are approximately 200 such cases per 100 000 persons per year. Forearm crutches have mainly been used in Germany until now to keep these patients mobile. For those who lack the strength or coordination needed to use crutches, a wheelchair may become necessary, or they might find themselves forced to continue weight-bearing on the affected limb, with possible impending adverse consequences and complications. 

Methods: The supplementary use of a new type of orthopedic scooter by patients who must avoid weight-bearing by a lower limb, wholly or in part, was studied in a multicenter randomized controlled trial involving 88 subjects. The endpoints were improvement in quality of life (EQ5D, SF36) and improved abilities in everyday life (retrospective registration: DRKS00032980).

Results: Patients who used orthopedic knee scooters (KS) reported a better overall state of health more frequently than those who used forearm crutches (UC) (SF-36 score: 67 [KS group], 95% CI [61; 73]; 59 [UC group], [53; 64]). They also reported less anxiety and depressed mood, greater mobility, and more independence than the patients who used crutches. In addition, they more frequently reported being able to transport themselves 4 x 500 meters in less than 20 minutes (n = 30 [KS], 63.8% [48.5; 77.3]; n = 6 [UC], 14.6% [5.6, 29.2]).

Conclusion: The supplementary use of an orthopedic knee scooter can improve these patients’ mobility and independence and prolong the distance over which they can transport themselves. For many patients, this form of treatment may well shorten the time of their total or partial inability to work and thus lower the socioeconomic costs of lower limb injuries and surgery.

According to studies from the USA and Finland, the incidence of disease or trauma requiring partial or total avoidance of weight-bearing by a lower limb is approximately 200/100 000 persons (1, 2). Many different mobility aids are available, but in Germany mainly forearm crutches (FC) are prescribed (3, 4, 5), or if necessary a wheelchair (5, 6, 7).

A number of clinical trials have demonstrated that even after repeated training, especially elderly patients find it almost impossible to correctly reduce weight-bearing by the lower limb with the use of FC (8, 9). As long as 100 years ago, deficiencies in physical condition and coordination prompted investigation of alternatives to FC (10). Since the mid-1990s various manufacturers, mainly in the USA and the UK, have offered orthopedic knee scooters (KS; also known as knee walkers). Owing to the transmission of force at the tibial head with the knee joint flexed, these devices improve mobility over greater distances and enable patients to support themselves on two legs while reducing the load on their hands (4, 11, 12). It has been shown in healthy volunteers that the amount of energy needed is significantly lower than with FC (12, 13). In a 6-minute walking test, the study participants could walk further using a KS than with FC; moreover, 88% of them preferred the KS to FC (14). Early studies also investigated use of KS by patients who needed reduction or complete avoidance of lower limb weight-bearing (12, 15, 16). In a cohort with a mean age of 57 years, Workman et al. found a satisfaction rate of 96% and a preference for the KS over FC (17). Other researchers confirmed the positive results, although falls were also reported, albeit with lower rates of injury, in persons using KS (15, 18).

Potentially serious injuries also occur occasionally with other mobility aids (3000–5000 cases/year in the USA) (19, 20). While lower limb trauma predominates in those using crutches, more head injuries occur among wheelchair users (19). In an early study on clinical use of KS (15), half of the patients (55.6 ± 13 years) had fallen at least once. However, patient satisfaction was high overall (86%) and actually even higher among those who had fallen (94%).

On the basis of these data, a KS has been approved for use in Germany since 2014. This device was tested by the German Technical Inspection Agency (Technischer Überwachungs-Verein, TÜV), possesses the European CE quality certificate, and complies with the Medical Device Regulation (MDR, 2017/745/EU) (Figure). At the design stage, particular attention was paid to stability, resistance against overturning, and practicality.

After 2 years of clinical application and sharing of experience by the clinicians at the participating centers, a multicenter randomized controlled trial was carried out across four sites in Germany (LMU Munich: Großhadern and city center campuses, Department of Trauma Surgery at the Hessing Foundation Augsburg, Geseke Holy Ghost Hospital). The study question was whether providing a KS to patients who needed to reduce or completely avoid weight-bearing would improve their quality of life and mobility.

Method

A total of 100 male and female patients who received written information about the trial and gave their signed consent were prospectively included in the trial and allocated randomly to the intervention group (KS) or the control group (FC). Randomization was performed by one of the joint first authors (HC). First, the study participants were randomly assigned the patient numbers 1–100. The numbered envelopes were then equally distributed across the four sites, and the co-authors included the patients in the trial by serial number.

This study was approved by the LMU Munich ethics committee (no. 21–0074) and subsequently registered in the German Registry of Clinical Trials (DRKS00032980). At the time of review the editorial board was in possession of the protocol submitted by the authors to the ethics committee.

The number of cases was set at 100 on the basis of the resources available and practicability. Case number planning involved no consideration of statistical factors. There was no advance prioritization of primary or secondary outcome parameters.

Inclusion criteria

Patients fulfilling the following criteria were included:

• Illness, injury or surgery of the foot, ankle joint, or distal lower leg with partial or complete avoidance of weight-bearing for a period of several weeks
• Age 18–75 years

Exclusion criteria

Patients with any of the following were excluded:

• Involvement of both lower limbs
• Pregnancy/breastfeeding
• Serious impairment of the upper limbs making it impossible to use FC or the orthopedic KS
• Limitations, e.g., prosthetic knee joints, that did not permit use of FC or an orthopedic KS
• A balance disorder contraindicating the use of FC or an orthopedic KS
• Thromboses or serious arteriovenous disorders of the affected limb
• Legal guardianship

Mobility aids used

Forearm crutches

The FC used in the trial were commercially available crutches with an ergonomic grip and spikes that could be fitted for use on slippery surfaces. All FC were individually adjusted for use by the patient concerned, in accordance with the MDR, and all patients were instructed in their use.

Knee scooter

The KS used in the trial (Orthoscoot, Orthoscoot GmbH, Neusäß, Germany) comprises a handlebar, a height- and angle-adjustable knee support, three shock-absorbing wheels with a restricted angle of turn, and a lockable disk brake (Figure 1). The device meets the criteria of the MDR 2017/745/EU). Each KS was individually adjusted, and all patients were instructed in the use of the device.

Figure 1

The KS used in the trial being utilized by a female patient to avoid placing weight on the right lower limb

The MDR stipulates cleaning, disinfection, and technical inspection of the KS following each use (after 12 months at the latest). According to the manufacturer, the device can be used for 5 years or more. Since 13 January 2023 it has been possible for physicians to prescribe the KS. Employers’ liability insurance funds and both statutory and private health insurance funds cover the cost of loaning the KR, provided the indication and purpose are appropriate.

The study participants were recruited in the outpatient clinics and wards of the participating hospitals. The patients in the control group received FC for the duration of partial or total avoidance of weight-bearing. The patients of the intervention group received the KS and also FC for the duration of partial or total avoidance of weight-bearing. Immediately after conclusion of the use of mobility aids, each participant received three questionnaires to be completed and returned: a self-compiled study-specific questionnaire on use of the devices with regard to social participation in routine activities, the short-form 36 (SF-36) questionnaire, and a questionnaire on health-related quality of life (EQ-5D-5L questionnaire).

Statistics

The patient data were analyzed per protocol (PP), because intention-to-treat analysis was not possible. Continuous variables were expressed in terms of the mean, standard deviation, and 95% confidence interval (CI), categorical variables in terms of absolute and relative frequency and 95% CI. A subgroup analysis was conducted for the group of retired persons, defined as those who gave their type of occupational activity as “retired” and/or their age as 65 years or older. All analyses were exploratory. The questionnaires were evaluated according to the official recommendations. The software R, version 4.2.2, was used for statistical analysis.

Results

A total of 100 male and female patients were included in the trial and allocated randomly to the treatment groups. This resulted in a FC group of 47 and a KS group of 53 participants. The recruitment phase ended after inclusion of 100 patients, and the study period came to an end after the last patient questionnaires were returned. The patients were asked to complete the questionnaires immediately following the phase of mobility aid use, which usually lasted 6–8 weeks. Six participants from each group failed to return the questionnaires, so the responses of 88 patients were available for analysis (KS: n = 47, 53.4%; FC: n = 41, 46.6%; eFigure 1). The characteristics of these 88 participants are shown in Table 1.

Table 1

Patient characteristics

eFigure 1

CONSORT flow chart

To explore the effect of age on how participants got on with the mobility aid, they were divided into two age groups that were then evaluated separately. The cut-off point was the median age of the whole cohort (52 years). This yielded two groups of similar size: “young” (< 52 years; n = 42) and “old” (≥ 52 years; n = 46).

Descriptive patient analysis revealed that more patients in the KS than in the FC group were employed in occupations in which they mostly had to move around (KS: 5%, 95% CI [40; 70], FC: 27% [14; 43]). The FC group contained more retired persons than the KS group (FC: 32% [18; 48], KS: 11% [4; 23]).

EQ-5D-5L questionnaire

A higher proportion of patients in the KS group reported that they experienced no problems in taking care of themselves (KS: 68% [53; 81], FC: 51% [35; 67]). Also, many more patients in the KS group stated that they were not anxious/depressed (KS: 68% [53; 81], FC: 39% [24; 55]) (Figure 2).

Figure 2

Results of the EQ-5D-5L questionnaire, expressed as frequency

The self-assessed health status was better in the KS group than in the FC group (KS: EQ-5D-5L score 67 [61; 74], FC: EQ-5D-5L score 63 [57; 69]), but the difference was not clinically relevant (eFigure 2). Analysis of the subgroup of retired persons showed no clinically relevant difference in quality of life between the KS group and the FC group.

eFigure 2

Box plot showing the median (minimum, maximum) self-assessed health status from the EQ-5D-5L questionnaire

SF-36 questionnaire

In accordance with the manual, we divided the items into the following scales representing the eight dimensions of health: (Figure 3):

Figure 3

Spider chart showing all eight dimensions of the SF-36 scales by group

• Physical functionality (PF)
• Role physical (RP)
• Bodily pain (BP)
• General health (GH)
• Vitality (VT)
• Social functionality (SF)
• Role emotional (RE)
• Mental health (MH)

General health was rated higher in the KS group than in the FC group (KS: SF-36 score 67 [61; 73], FC: SF-36 score 59 [53; 64]) (eFigure 3). In retired persons, the subgroup analysis showed a clinically relevant difference of 18 points in general health in favor of the KS group (KS: SF-36 score 69 [54; 84], FC: SF-36 score 51 [40; 61]).

eFigure 3

Box plot showing the median (minimum, maximum) scores for the “general health” dimension of the SF-36 questionnaire

Trial-specific questionnaire

In the questionnaire compiled specifically for the trial, the patients of the KS group scored higher than those in the FC group on all questions except those relating to use of public transport and discomfort or complications (Table 2). Particularly striking are the much higher scores for mobility (inside and outside the home), the superior degree of autonomy, and the greater ease in walking longer distances (4 × 500 m).

Table 2

Evaluation of the study-specific questionnaire

Because of the slightly higher number of retired persons (age > 65) in the FC group (n = 13) than in the KS group (n = 10), a subgroup analysis was performed. No deviation from the analysis across all age groups was found (Table 2).

Analysis by age was carried out to find out whether there were any age-related differences within the treatment groups. Distinct differences between age groups were found in the KS group. Mobility outdoors was reported as greater by younger than by older persons, and the younger patients also reported it easier to work in a standing position. The majority of the young age group (14 of 23 participants, 60.9%) stated no positive effect of the KS on the ease of using public transport. On closer examination, excluding the patients who did not use public transport anyway (n = 14 in the young and n = 9 in the older age group), the findings changed insofar as more young patients than older patients used public transport (6 of 9 [66.7%] versus 3 of 15 participants [20.0%], p = 0.0361).

Analysis of the FC group by age showed no essential difference in the responses.

Complications

The most frequently reported problem was pain in the upper or lower limb (in 11 and 9 patients, respectively) (eTable). Pain in the lower limb was reported by patients in the KS group (n = 9), pain in the upper limb by patients in the FC group (n =  11).

eTable

Type of complication/problem

Discussion

This trial is the first to show that the use of a KS in combination with FC is safe and greatly improves the patients’ self-assessed health status in comparison with patients who use FC alone.

Despite the frquent problems in providing FC, provision of KS is not yet standard in Germany.

Earlier studies in healthy volunteers showed potential advantages of the KS with regard to the energy required, walking distance, and satisfaction (12, 13, 14). These findings are in close agreement with our data, which show a considerable increase in walking distance and improvement of mobility both at home and outdoors.

The enhanced quality of life and the high patient satisfaction found in our cohort of patients are also in accordance with the published data (15, 16, 17). The improvements in mobility and distance are particularly relevant from the social medicine viewpoint. The German Federal Social Court has ruled that to avoid being classed as unable to work, patients must, in addition to the ability to lift and carry objects, demonstrate that they can walk a distance of 500 m four times a day. While these stipulations cannot be fulfilled with FC, additional use of a KS could enabler swifter return to work and avoid socioeconomic follow-on costs (21). Although theoretically older patients could also benefit from provision of a KS, geriatric patients and those with dementia were specifically excluded from our trial because to date there are no validated data showing whether this group of patients possesses sufficient coordination to use a KS safely. The time of use of a mobility aid is highly likely to be subject to a learning curve, with use becoming both safer and more effective after a few weeks. Nevertheless, the positive benefits must always be weighed against any disadvantages that may arise from prolonged reduction of weight-bearing, with the ultimate aim of rapid restoration of physiological gait.

Complications

As expected, some of the patients in the KS group experienced lower limb pain. The elevated occurrence of falls reported from earlier studies of KS use (15, 17) were not confirmed. This is in agreement with the results of other studies, which also found no increased tendency to falls among KS users (16).

The inconsistency of the research findings may be explained by the construction of the mobility aids. While most orthopedic scooters have four wheels mounted on two short axles (17), the model used in our trial is constructed to provide greater stability, with three wheels, a longer axle, and a restricted steering angle. Higher rates of falls could also be explained by a lack of instruction in the use of the mobility aid. In contrast to our trial, the earlier studies state that up to two thirds of patients received no instruction (18).

A further potential disadvantage is the flexed position of the knee joint, with verifiable reduction of venous flow velocity (22, 23). Although no thromboses have yet been described (17), this complication must be regarded as theoretically possible and should therefore be taken into consideration when discussing the options for patients at risk. Because medication to prevent thrombosis is indicated in any patient with reduced or no weight-bearing by a lower limb, the risk that thrombosis will result from the use of an orthopedic scooter can be viewed as small.

Limitations

Both patients with disease (predominantly diabetic foot syndrome) and patients with trauma (younger and older adults) were included in the trial, so the cohort was extremely heterogeneous. Moreover, the presence of comorbidities (e.g., dementia or coordination problems) may have distorted the results.

A further limitation lies in the retrospective nature of the analysis and the fact that patients were not included until they had already become immobile, precluding any baseline measurements for comparison.

Patients over the age of 75 years were excluded from the trial. However, this is just the age group that often has difficulty using forearm crutches, so a future trial should explore the effectiveness of a knee scooter in a geriatric cohort.

Acknowledgments

We thank the physiotherapists at the trial sites for instructing the patients in the use of the different mobility aids, the manufacturer for providing the orthopedic knee scooters, and Dr. Manfred Thomas for his advice during trial planning.

Data sharing

The authors are open to all reasonable requests for original data addressed to the corresponding author, provided that the data requested relate to the data published in the article and do not compromise a future publication or any associated matters. These data comprise the primary data from the patient survey. The data will become generally accessible 5 years after the date of publication.

Conflict of interest statement
The authors declare that no conflict of interests exists.

Manuscript received on 26 October 2023, revised version accepted on 29 May 2024.

Translated from the original German by David Roseveare.

Corresponding author
PD Dr. med. Christian Ehrnthaller

Klinik für Orthopädie und Unfallchirurgie

Muskuloskelettales Universitätszentrum München (MUM)

Klinikum der Universität München, LMU München

Marchioninistr. 15

81737 München, Germany

Cite this as:
Clas H, Ehrnthaller C, Herrmann O, Schraeder DT, Böcker W, Manz K, Thaller P: Quality of life and patient satisfaction after the provision of an orthopedic knee scooter—a multicenter randomized controlled trial. Dtsch Arztebl Int 2024; 121: 519–26. DOI: 10.3238/arztebl.m2024.0121

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