New concept of orthosis treatment for knee osteoarthritis: Clinical and radiological outcomes

1.Introduction

Knee osteoarthritis (OA) is the most common joint disorder [1]. The lifetime risk of developing symptomatic knee OA is estimated at around 45% [2, 3]. If conservative treatment fails, total knee replacement (TKR) is a highly effective procedure that provides reliable relief from pain and improved physical function with a high level of patient satisfaction [4, 5]. The number of knee replacement operations is increasing yearly. Over 40% of all knee replacements and up to 44% of all total knee revisions are performed in patients under 65 [6]. The known limited lifespan of TKR and the high-demand expectation of a prosthesis from relatively young patients with knee OA together with the increasing number of TKRs constitute costly healthcare [7, 8]. Hence development of alternative treatments for knee OA, specifically those that can postpone a prosthesis is needed. If the primary TKR of a patient can be postponed to a period of life that patients are less demanding, it might give more patient satisfaction after TKR and less revisions of TKR resulting in reducing healthcare costs [9].

Knee joint distraction (KJD) is a promising development that has emerged as a joint-preserving treatment for endstage osteoarthritis [10]. Recent studies suggest that KJD can reverse cartilage tissue structure damage in severe knee OA while yielding significant clinical improvement [11, 12]. This newly formed cartilage-like tissue is stable and mechanically effective to the extent that the joint space width (JSW) increases at radiographic examination [13, 14].

KJD is an invasive surgical intervention that involves placement of an external fixation frame over the patient’s knee for 6–8 weeks. Disadvantages besides two surgical procedures are pin-tract infections, short-term stiffness with muscle atrophy after the distraction period, and possible major psychological burden as it hinders patients during sleep and makes personal hygiene more difficult [15].

To avoid the drawbacks and aiming to keep the benefits of KJD, an orthosis was developed that maintains the conditions thought of as being favorable for cartilage repair: unloading the affected knee during loading activities and maintaining synovial fluid flow by leg flexion and extension, which gives good natural joint homeostasis and might release chondroprotective molecules/Mesenchymal stem cells [16].

The orthosis unloads the knee, although not 100%, since the passive muscle tone and knee capsule are still present and will keep loading the knee. The orthosis allows the knee to flex normally, hoping to give a natural synovial fluid flow. We hypothesize that this orthosis will also result in reduced symptoms and regeneration of cartilage in an osteoarthritic knee joint. Primary objective of this pilot study is to examine the effectiveness of using a load-reducing orthosis for two months on functioning in patients with knee OA. Secondary objective is to examine the effect of using a load-reducing orthosis for two months on pain and disease progression (e.g. amount of damaged cartilage).

2.Materials and methods

2.3Intervention

Figure 1.

Example of the custom-made orthosis worn by a patient.

One orthosis was produced for each patient, the orthosis was modified to match the geometry of every participant. The orthosis design was inspired by upper-leg prosthetics and fixed to the body via an adapted upper-leg socket such as known from upper-leg prosthetics (Fig. 1). The bottom of the socket was removed to allow the upper leg to pass. The body weight is transferred to the orthosis via a combination of tuberosity support, friction to the skin and leg volume containment. In this way the weight is transferred directly to the floor by the orthosis, bypassing and unloading the knee and the ankle – so the patient stands on the orthosis, not on the foot. Another important feature of the orthosis is to preserve movement of the knee joint for maintaining synovial fluid flow and thus nutrition of the cartilage. The lower-leg part of the orthosis is therefore connected to the upper-leg part by two hinges (medial and lateral). The hinges are essentially aligned with the knee joint. The lower leg is not fixed directly to the lower-leg part of the orthosis, but to an extra set of bars that is fixed to the lower-leg part under an angle when the orthosis is in full extension. This prevents the lower leg to reach full extension and thus will avoid that the joint surfaces come into direct contact, which for a healthy knee is the mechanism to stabilise the joint during heel strike. To prevent pelvic tilt, the patient wears a sole that is fixed under the shoe of the other leg. The sole increases the height of the shoe and prevents any leg length discrepancy caused by using the orthosis.

Patients were given permission to take the orthosis at home and use it after a supervised training session, during the 60 days study period without further supervision. To ensure full unloading of the knee joint during the intervention period, patients used the orthosis every day for 60 days during all activities that comprised knee loading (e.g. standing, walking). Cycling could be complex with the orthosis, so it was not allowed. Also stair climbing could be complex, so it is done without orthosis and with crutches. At night in bed, or while sitting for a longer period where no loading of the knee was required, the orthosis could be removed. The orthosis was also removed when showering, with patients using an external support to remain stable and not load the knee. To compare the orthosis with Knee Joint Distraction (KJD) treatment, the same duration of 2 month (60 days) intervention was chosen [13]. After the intervention period patients were instructed to use physical therapy to retain muscle strength, stability, and mobility.

3.Results

3.2Imaging

Table 2

Results of the MRI analysis and KIDA X-ray of the MAC (most affected compartment)

	Baseline	1-year follow-up	2-year follow-up	p-value (0-1)	p-value (0-2)	p-value (1-2)
MRI ThCtAB (mm)	1.2 (0.5), (0.7–2.3)	1.1 (0.5), (0.6–2.3)	1.0 (0.4), (0.6–2.2)	0.007*	0.005*	0.047*
MRI dABp (%)	20.3 (21.2), (0.7–64.0)	23.2 (23.6), (0.9–65.8)	25.1 (23.3), (1.0–64.4)	0.005*	0.005*	0.169
MRI ThCcAB (mm)	1.5 (0.4), (1.4–2.3)	1.4 (0.4), (1.2–2.3)	1.4 (0.4), (1.2–2.2)	0.009*	0.005*	0.028*
MRI VC (mm3)	1418 (913), (856–2719)	1287 (876), (695–2718)	1220 (773), (765–2586)	0.005*	0.005*	0.022*
KIDA mJSW (mm)	0.0 (1.2), (0.0–4.3)	0.1 (0.4), (0.0–4.7)	0.0 (0.8), (0.0–4.7)	0.574	0.441	0.256

Presented are: median (IQR), (min-max), p-value (Wilcoxon signed rank test) of differences between timepoints 0 (baseline), 1 (1-year follow-up), and 2 (2-years follow-up). ThCtAB: cartilage thickness over the total subchondral bone area (denuded areas included); dABp: denuded part of the subchondral bone area; ThCcAB: cartilage thickness over cartilaginous area of the subchondral bone area (denuded areas excluded), VC: cartilage volume; mJSW: minimal joint space width.

Figure 2.

Upper graph: median WOMAC score and VAS pain score in time for the 10 patients. Lower graph: median WOMAC scores per subscale in time for the 10 patients.

Table 2 presents the MRI and KIDA X-rays results. All MRI cartilage parameters show a significant worsening at 1- and 2-years follow-up compared to baseline. Between the 2-year and 1-year timepoints a significant worsening was found on all parameters, except for the percentage of subchondral bone area that was denuded. Median mJSW based on the KIDA X-rays was zero at each timepoints. No significant difference between timepoints was found on this outcome.

4.Discussion

The current study had a comparable design as that of Wiegant et al. [13], who investigated the effectiveness of knee joint distraction as a joint-preserving procedure in young patients with endstage knee OA. Theirs, as well as other knee-joint distraction studies [12], demonstrated clinical improvement as well as cartilage repair post-surgery lasting at least 2 years. In the current study using the same outcome measures – WOMAC and VAS pain – a similar pattern of a quick clinical improvement was observed already at 3 months, reaching a plateau at 6 months that was sustained until 18 months for the WOMAC score and 24 months for the VAS pain score. For both outcome measures the improvement found in scores exceeds the minimal clinically important differences and can therefore considered as clinically relevant [25, 26]. These findings are in agreement with and reflected by the self-perceived satisfaction scores obtained at 24-months follow-up, where 80% of patients indicated being satisfied/very satisfied with the treatment results. Despite these similar clinical findings, we found no improvements on cartilage parameters, probably as a result of the substantially different nature of the two interventions [27].

Literature on the effectiveness of knee-unloading braces suggests that the custom-made orthosis under investigation is more in line with these types of braces than with knee joint-distraction surgery. A review from 2016 concluded that even though use of an unloading brace results in both pain and functional improvement, similarly to the current findings, biomechanical evidence does not demonstrate a beneficial effect on disease progression [28]. Beck et al. [27] recently provided some new evidence by studying the effect of bracing on damaged cartilage using enhanced MRI (dGEMERIC) mapping, demonstrating not only a clinical effect (reduction in pain and functioning) but also some positive effects on biomechanical properties of the damaged cartilage in patients with unicompartmental knee OA and varus or valgus malalignment. At 3-months follow-up beneficial effects were found in amount of collagen, proteoglycan concentration, and cartilage edema. But in agreement with the current study no positive effects could be evidenced in T1-dGEMERIC and T2* relaxation times, thickness, or extent of damaged cartilage area [27]. Considering the working mechanisms of orthoses and braces, these similar findings are perhaps unsurprising. Where the orthosis in our study was largely designed to unload the entire knee joint, knee-unloading braces aim to minimize compressive forces on the affected knee joint compartment too, by applying an external force to the joint that distracts the stress from the affected compartment  [28].

An explanation for the discrepancy between clinical and radiological outcomes in this study is that the clinical outcomes are all patient-reported and might therefore be subject to a placebo effect. Similarly to what was found in knee-unloading studies, where discomfort like skin irritation and poor brace fit is common [28], resulting in low compliance [29] and a low likelihood of continued use of the brace after 1–2 years (28% and 25% regular use) [30], the intervention was experienced as intensive, given the use of the custom-made orthosis for 60 days during all knee-loading activities. In the current trial patients only needed to wear the orthosis during one 60-day period, and all patients who agreed to participate sustained this period, even though it was experienced as hard and demanding, physically as well as mentally. This probably reflects patients’ belief in the potential of the treatment, giving credibility to the suggestion of the presence of a placebo effect. Another explanation for the improvement in symptoms, with the cartilage parameters showing the natural worsening course of the OA, is that after six months 60% of patients indicated having physical therapy (under the supervision of a physical therapist) after the intervention period. They all had muscle atrophy to a certain degree – the orthosis had to be adjusted at least once during the intervention period for becoming too wide – and needed to regain their strength, coordination, and gait. This rehabilitation period with physical therapy, which continued at least until the 12-month follow-up timepoint in 40% of patients, may have resulted in a reduction of symptoms, considering the high-quality evidence that pain and physical functioning in patients with knee OA can be improved by exercise and weight loss [31].

Even though this study has it strengths in that it aimed to investigate the effectiveness of a relatively non-invasive knee orthosis, with a design similar to a previous study [13] to make comparison possible, several limitations need to be discussed. First, the lack of a control group: without a control group there is no direct insight into the natural course of clinical and radiological outcomes of a similar patient group during the study period, or into the use of another treatment like physical therapy under therapist supervision as primary intervention. Another limitation is the relatively short follow-up period of 24 months. Even though this is comparable to other studies on knee joint distraction [32, 33], it would be interesting to investigate the effectiveness at longer follow-up. A third limitation is that it is unknown how much load on the knee remained when using the knee unloading orthosis, as a result of that in-vivo load measurements are not possible. Last, there is our small group of participating patients, with no a priori sample size calculation conducted beforehand, as it was a pilot study. The reduced number of patients has risks resulting in a low power, with a higher chance of a type-II error – which means the inability to demonstrate a significant effect, when there is in fact a difference in timepoints or between groups. This does not seem to be an issue in the current study, since several significant differences were found on clinical as well as MRI parameters.

5.Conclusions

This study demonstrates that using a custom-made knee-unloading orthosis for two months can lower pain and improve functional ability in relatively young patients (< 60 years) with knee OA. No effect on disease progression (joint space width or MRI-derived cartilage parameters) could be evidenced though.

Ethics statement

All methods were carried out in accordance with relevant guidelines and regulations. The RTPO medical ethics committee in Leeuwarden approved the study protocol (RTPO 982). All participants provided signed informed consent before participation.

Availability of data and materials

The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.

Funding

This work was supported by the Martini Research Fund, the D.H. Heijne foundation, and the Gratama foundation (grant number 2018/012). These funding sources had no involvement in the study design, data collection, analysis, data interpretation, or writing of the report, nor in the decision to submit the article for publication.

Author contributions

MRH performed patient inclusion and data interpretation, and drafted and submitted the manuscript. AJdV coordinated the study; conducted data collection, statistical analysis, and data interpretation; and reviewed the manuscript. GJV initiated the study, designed the orthosis under investigation, and reviewed the manuscript. RWB designed the study, performed patient inclusion, and reviewed the manuscript. All authors read and approved the final manuscript.