The purpose of this study was to evaluate the clinical effect of a personalised biomechanical foot-worn device on spatial-temporal gait parameters, pain, function and quality of life in UK patients suffering from knee OA. Following 3 months of therapy, patients demonstrated significant improvements in both gait and PROM’s, with maintained or further improvements occurring in all parameters after 6 months. The results suggest that most improvements occurred by 3 months, but further improvements occur between 3 and 6 months, apart from SLS in gait and MCS subscale of SF-36. This supports previous work which found that the largest improvements occurred within the initial few months of therapy and are then maintained (32). The improvements in WOMAC scores meet the OMERACT-OARSI guidelines for clinical response to treatment, signifying true positive impacts felt by patients (45). The thresholds for minimal clinical importance differences (MCID) within SF-36 were also met, suggesting improvements in quality of life following treatment (46). In addition, these improvements in self-evaluation questionnaires correlated with the significant improvements in gait.
PROM’s along-with radiographic findings have historically been used to track knee OA outcomes and are leading predictors in guiding the decision upon joint replacement surgery (47). However, the low correlation between radiographic findings and patient symptoms has since become more acknowledged (48), and therefore the importance of more objective and functional measures to evaluate patient symptoms has become apparent. Previous research has proposed spatio-temporal parameters are a good indicator for functional severity (12, 48), with a recent meta-analysis suggesting that stride duration and cadence provided a better reflection of knee OA severity than kinematic and kinetic measures (49).
Using the patients’ cadence and stride lengths as predictor variables for knee OA severity forms the basis of the validated Knee Osteoarthritis Functional Grade or KOFG (13), which in a follow-up study was also validated as a classification tool to measure treatment effect (50). A combination of spatial-temporal parameters objectively classifies patients with knee OA according to functional disease severity, which have been shown to correlate with radiographic evaluation, the level of pain, function and rate of TKR. The benefit of this tool is the ability to quantify the severity of disease and to assess the impact of an intervention, rather than just stating the change in gait analysis parameters (50). The model suggests that a shorter stride length with lower cadence is indicative of a higher functional severity grade (more severe knee OA), while a longer stride length with higher cadence is indicative of a lower functional severity grade (less severe knee OA). Within this current study, there was a significant improvement in KOFG between baseline and 3 months follow-up (p < 0.001), with retained improvement at 6 months. The shift from more severe to less severe KOFG suggest patients not only improvement in symptoms, but actually move away from measures associated with increased rates of TKR (13, 50).
The present study also examined whether there were any differences in the sub-group of patients (20%) that had already been offered joint replacement surgery (TKR/PKR) prior to commencing the therapy. Interestingly, aside from the duration of symptoms, there were no significant differences between cohorts at baseline, suggesting that those patients that had been recommended surgery as a suitable option for their condition, displayed the same characteristics as those that have not had surgical recommendation (Fig. 3). Research reports most patients that are suitable for TKR have WOMAC baseline scores between 40 s to 50’s (47), which could indicate that the cohorts analysed within this study are representative of this population. Furthermore, significant improvements seen across both groups (Table 3) suggests these populations can respond well to this therapy in levels of pain, function and quality of life measures. Differences between these two groups were seen at 6 months, including significantly higher WOMAC pain and stiffness subscales (p = 0.027, and p = 0.019), and significantly lower SLS in both the more and less symptomatic sides (p = 0.04 and p = 0.028) in the recommended surgery group. The reduction of improvements within this group could be explained by significantly longer durations of symptoms experienced by the patients, suggesting more chronicity of the condition. Previous studies have investigated the durations of symptoms and their relationship to clinical improvements and have suggested that optimising the timing that patients access relevant treatments could be key to optimising outcomes (51). Despite this, the overall improvements in both groups are marked and suggestive that the therapy could be an effective alternative for a number of patients that would otherwise have progressed to surgery.
Researchers have presented several theories explaining how this therapy works to improve symptoms in patients with knee OA. Studies have shown that the biomechanical device can reduce the external loads acting on the body to “unload” the painful area, which is said to be important when treating this condition (40, 41). It has been shown to reduce the 1st and 2nd peak KAM and KAAI by 8.4%, 12.7% and 13% after 9 months of therapy respectively (52). An important factor to note with the improvements in biomechanical variables seen with the device is that they remained, even when the patient was not wearing the device. This suggests that a motor learning effect occurs as a result of the neuromuscular retraining received from the therapy (43). Neuromuscular training is delivered by a controlled level of perturbation via the convex nature of the elements (43, 44). The combined features of the biomechanical device allow for repetitive perturbations with diminished pain throughout the gait cycle. Patients wearing the devices for prescribed periods every day means that they gain high repetitions of closed kinetic chain, functional exercises and improved levels of compliance said to be advantageous for motor learning (53–55). This combination of key rehabilitation principles allows the patient to reacquire improved neuromuscular control, thus avoiding pathological patterns previously utilised whilst in pain (31).
Given knee OA is a chronic degenerative condition, symptoms deteriorate over time at varying rates (56). Currently, interventions are directed to the end-stages of the disease and therefore can often be ineffective and palliative in nature (57). Whilst the literature reports that the number of patients progressing to having joint replacement surgery is growing (6), approximately 20–40% of those completed are considered inappropriate. These were classified due to having only slight or moderate symptoms, or not severe enough radiographic findings and therefore TKR deemed unnecessary (58, 59). A paradigm shift is needed to focus efforts on treating patients at high-risk earlier in the disease progression (57), or utilising more specialist modalities that can help minimise this potentially inappropriate flow to surgery. The results of this study display a combination of improvements in both subjective PROM’s and objective spatial-temporal gait parameters which are very promising and may indicate that the biomechanical device used in this study has the ability to be an effective modality in managing this chronic condition.
This study has some limitations. Firstly, the study was a retrospective analysis of patients from the centres database and therefore had no control group. However, a previous study has demonstrated comparable positive effects of this therapy compared to a control group in a double-blind study (31). Secondly, this study had a relatively short follow-up duration of 6 months for this cohort. Long-term follow-up would give more insight into the lasting effects of the treatment. However, it reflects previous research on the therapy on different populations with similar improvements in gait and PROM’s (33–35, 60). Therefore, it could be assumed that the improvements can be maintained with the high compliance rates in the treatment (32). Nevertheless, future research should continue to investigate the long-term clinical effect of the treatment, in prospective, randomised control trial (RCT) design whilst tracking decay rates for joint replacement surgeries. Promisingly, preliminary data from an RCT on the effect of this treatment displays comparable improvements to this study (61).