Pedobarographic evaluation of five commonly used orthoses for the lower extremity

Orthotics are defined as ‘externally applied devices used to compensate for impairments of the structure and function of the neuro-muscular and skeletal systems’ (ISO 8549-1:2020, 3.1.2). General functions include immobilization, protected range of motion, selective load reduction, or the correction of the shape and function of the body. Thereby, they allow for earlier mobilization, pain reduction, and secure non-operative or operative treatment [1‐3].

Orthoses are a frequently applied medical devices. About ten percent of the German population will use one at some point in their life [2]. One field in which orthoses are commonly applied is the foot and ankle, for example, to immobilize the ankle following arthrodesis [4], to unload the hindfoot in calcaneus fractures [5; 6], or to reduce mid- and forefoot forces after hallux valgus surgery [7, 8].

Despite their importance in foot and ankle rehabilitation, the number of studies investigating the selective load reduction of common orthoses within the foot is limited. Various studies have assessed the off-loading capacity of orthoses for the treatment of plantar ulcers in diabetic patients [9‐11]. However, diabetes-associated comorbidities, such as peripheral neuropathy, postural impairments, and altered gait patterns, limit the translation of these results to the general population [12]. Other studies were limited to specific injuries, such as fractures to the fifth metatarsal bone [13], or anatomical locations, such as the hindfoot [14] or forefoot [15]. Consequently, up to date, no study has investigated the off-loading capacity of different types of orthoses for the different regions of the foot.

Therefore, the aim of the present study was to analyze the plantar pressure distribution of five common orthoses for the foot and ankle in a healthy population.

The herein presented study is a laboratory study and was approved by the local Ethics Committee (#18-882).

Eleven healthy volunteers (6 females) with a median age of 29 (range 26–38) years, were included. Their median BMI was 22 kg/m² (range 17.9–25.5), and the median shoe size was 40 EU (range 37–46). The dominant leg was the left leg in six, and the right leg in five participants. The absolute and relative values for all pedobarographic parameters are presented in Supplementary Table 1.

This is the first study to assess the off-loading capacity for specific foot regions of five commonly used orthoses in foot and ankle surgery. Regarding the forefoot, the forefoot relief shoe, the short and high walker boot showed a comparable off-loading capacity. None of the assessed orthoses was capable of off-loading the midfoot, but the calcaneus fracture orthosis and the short walker boot instead increased the load within the midfoot. The calcaneus fracture orthosis was the only device to significantly off-load the hindfoot.

Orthotic devices are used to off-load specific foot regions with the aim to enable earlier mobilization, pain reduction and to secure successful treatment [1, 2, 28]. Despite their frequent use, information regarding the specific off-loading capacity of commonly used orthoses is sparse.

The forefoot relief shoe, short and high walker boot significantly reduced the plantar pressure in the forefoot compared to a running shoe. These findings are in line with previous studies, which reported an equal off-loading effect of the forefoot for vacuum orthoses, such as walker boots, and cushioning orthotic devices, such as forefoot relief shoes [9, 11]. Interestingly, the short walker boot only yielded significant reductions in relative peak pressure values, but did neither affect absolute peak pressure values nor any other assessed pedobarographic parameter. In contrast, the forefoot relief shoe, high walker boot, and calcaneus fracture orthosis significantly reduced absolute and relative values for two or more parameters.

None of the assessed orthotic devices generated a significant pressure reduction in the midfoot. Consequently, none of these orthoses appears to be appropriate for applications, in which an off-loading of the midfoot is aspired. Therefore, if pressure in the midfoot region is to be reduced, an orthosis should be combined with partial-weightbearing. Controversy, in particular the calcaneus fracture orthosis significantly increased the midfoot load, which has been reported previously [14]. This load shift toward the midfoot may lead to secondary displacement in calcaneus fractures affecting the anterior process of the calcaneus, cause pain, or stress fractures in case of long-term use [14]. It might also explain why the calcaneus fracture orthosis is often doomed uncomfortable by patients.

Mazur et al. [14] compared pedobarographic measurements between a running shoe and two different hindfoot relief orthoses—the hindfoot relief shoe and the hindfoot relief orthosis in 25 healthy volunteers. They reported an off-loading capacity for the hindfoot of 52% for the two tested devices, which is in line with the herein observed 57% for the calcaneus fracture orthosis.

Finally, we also assessed the effect of a contralateral shoe lift when using a high walker boot on the plantar pressure characteristics. Palmanovich et al. [29] investigated the load effect of a contralateral leg-length equalizing sole when wearing a forefoot relief shoe in 20 healthy men. Similar to our presented data, they could not detect any significant changes in peak pressure and peak pressure integral. However, previous studies were able to show a reduction of gait asymmetries [30], significant improvements in the modified Oswestry low back pain disability questionnaire, and higher scores in the lower extremity functional scale [23] when an orthotic shoe lift was used.

One limitation of the present study is that only the orthosis-specific plantar pressure distribution was assessed, but not the ability of immobilization. Some orthoses, especially the high walker boot, have fields of application due to their ability to immobilize the hind- and midfoot [31], that go beyond the plantar off-loading. This aspect was not addressed in the present study. Furthermore, we retained the same sequence in testing the orthoses for each participant. This holds a potential bias. Another limitation is the rather small sample size and the focus on healthy individuals. Patients suffering from pain and/or gait insecurity might exhibit considerably different patterns of plantar pressure distribution. Therefore, it remains unclear, whether the present observations can be generalized to a clinical setting. Despite these limitations, this study established a standardized assessment setting that not only focused on the absolute effects of orthoses on specific pedobarographic measures, but also analyzed their relative effect in comparison with a control shoe. Any orthosis must proof its off-loading superiority to a regular shoe. By standardizing our measurements to a control, i.e., running shoe, we were able to highlight this real-life advantage of the respective orthosis.

The results provide new insights into the efficiency of five commonly used orthoses to modify pressure distribution patterns in specific foot regions. The knowledge of the specific pressure distribution of the different orthoses is essential for orthopedics to specifically choose the appropriate device. Therefore, the clinical use of specific off-loading orthoses should be indicated carefully and critically discussed as they might induce the risk to increase pressure distribution at the adjoining foot regions. These results should further be validated in larger healthy and patient cohorts.