Comparison of foot orthoses made by podiatrists, pedorthists and orthotists regarding plantar pressure reduction in The Netherlands

As representatives of their professional groups, ten podiatrists, ten pedorthists and eleven orthotists from the southern part of The Netherlands were asked to construct foot orthoses for three patients with metatarsalgia and elevated forefoot peak pressure. Podiatrists were approached through telephone directories. Companies of pedorthists and orthotic workshops were approached through member lists of the professional associations. Each delegated between one and three therapists for the study. The median professional experience in years was 7.5; 16.5 and 20, respectively for podiatrists, pedorthists and orthotists.

Three patients, 2 females of 60 and 61 years old and a 37 years old male, with forefoot complaints, elevated plantar peak pressures and an indication for foot orthoses were selected from an orthopaedic outpatient clinic. The male patient had foot problems related to psoriatic arthritis, which was inactive during the study period. The specific diagnosis for both female patients was bilateral metatarsalgia due to overloading of the forefoot as consequence of structural defects (table 1) leading to functional anomalies. Additional details about the patients are given in table 1. Before the start of the study, patients were informed about all study procedures and their possible risks. The Research Ethical Committee of the University Hospital Maastricht approved the study.

Two sessions were organised at the University Hospital Maastricht with an interval of three weeks between sessions. The first session included patient examination and casting. Therapists were asked to rate the 'importance of pressure reduction' per patient through line bisection of a 100 millimetre visual analogue scale. The orthoses were constructed in the three weeks between the sessions. During the second session, before final delivery, the therapists had an opportunity to check the constructed orthoses for adequacy. If deemed necessary, accommodations of orthoses were made.

Per patient 31 pairs of foot orthoses were evaluated twice in two sessions. Two pairs of sham orthoses were added to create eleven blocks of three pair of orthoses, one from each discipline. The blocks were randomized to determine the measurement sequence and this sequence was reversed for the second session. All orthoses were evaluated in the patient's own shoes and wearing standard thin socks while walking on a treadmill. The Pedar Insole-system^® (Novel, Munich) was used to measure plantar pressures[26, 27]. The first author performed all measurements. Whether these off the shelf shoes had enough space for adding orthoses and the Pedar insole was checked. Patients individually chose their preferred walking speed (table 1), which was kept the same for all subsequent measurements. To minimize a possible effect of the test sequence, such as a possible effect of fatigue on plantar pressures, an equal number of steps from both sessions were used for evaluation. Data were recorded for approximately 50 seconds with a frequency of 50 frames per second. Plantar peak pressure was estimated by calculating the mean over the readings of 40 steps (20 steps per session). This was done for six separate regions: big toe (BT) and metatarsal one (mt-1) to five (mt-5) through anterior-posterior radiographs and Novel 'create any mask^®' software[28]. Baseline values of inshoe plantar pressures, i.e. without orthoses, were calculated as the mean of 4 measurements: for each session, one before and one at the end of the test series. In order to check the influence of fatigue on peak pressure, we compared the before and after values without orthoses of each test session. After each measurement, patients scored walking convenience for left and right orthosis on a ten-point scale on a questionnaire: How do you rate the walking convenience of these orthoses (0 = extremely bad, 10 = excellent)? Walking convenience was estimated by calculating the mean score of the two sessions.

Differences in plantar pressure reduction amongst the professional groups were evaluated for the region with the highest peak pressure measured under the forefoot without orthosis (table 2). For patient B and C the effect on peak pressure was also evaluated for their right and left BT regions respectively, because pressures in these regions were high compared to the peak pressures under the metatarsals. At first plantar pressure data were investigated for normal distribution by the Kolmogorov-Smirnov test. If the data did not meet the assumptions for parametric analysis, a Friedman test was used for non-parametric overall analysis. If there was a statistically significant difference between the groups, Wilcoxon Signed Ranks Tests were performed for pair-wise comparison. We also evaluated the effect of the orthoses focusing on the region were the peak pressure reduction was maximal. For this, the difference between the peak pressure measured with orthoses and the baseline value was calculated for each forefoot region. The largest difference was used for this evaluation.

Variance of the maximal pressure reduction was used to show the within-group variation and to test for equality of these within group variations between the three disciplines. For this purpose a homogeneity of variance analysis was performed with a repeated measures ANOVA, using the GENOVA computer program[29].

For the assessment of the relationship between achieved pressure reduction and 'importance of pressure reduction' we used the maximal pressure reduction. For this purpose linear regression analysis was performed for the cases were there was a wide distribution of the 'importance of pressure reduction' ratings. Statistical analysis was carried out with SPSS 12.01^® software (SPSS Inc.). An alpha level of 0.05 was chosen to judge statistical significance.

Orthoses made by podiatrists clearly differ from orthoses from pedorthists and orthotists. All podiatrists constructed thin insoles out of rubber, leather and cork, but they varied in the application of corrective and/or supportive elements. In broad outlines, orthoses of pedorthists and orthotists were similar. The pedorthists and orthotists made orthoses that look more like the 'Root style' orthoses[14, 30]. However, within the professional groups, there was a considerable variation in applied materials and the use of corrective and supportive adaptations. All orthoses from podiatrists were fully custom-made while this was only the case for 56% of orthoses from pedorthists and 45% of those from orthotists. The remainder were partly or completely constructed from prefabricated elements. Podiatrists constructed full-length orthoses for all patients. Pedorthists provided 34% full-length orthoses, 20% three-quarter and 46% 'in between' length orthoses. Orthotists provided 58% full-length orthoses, 24% three-quarter and 18% 'in between' length orthoses.

For all three patients, the changes of the plantar pressure measurements without orthoses, from before to after the test series, were very small. The change during session 1 for patient A was 0.4, patient B -4.5, patient C 5.1 kPa. During session 2: patient A -0.3, patient B -4.3, patient C -2.1 kPa. We concluded that there was no relevant effect of fatigue on peak pressures in the course of the measurement sessions.

Results for each region for pair wise statistical testing are listed in the figure 1. The highest baseline peak pressures for patient A were measured in the left mt-2 and the right mt-1 regions (table 2). With respect to the left mt-2 region, orthotists and pedorthists achieved greater median reductions, 117 kPa and 71 kPa, than podiatrists, 13 kPa: p = .022. For the right mt-1 region, both orthotists and pedorthists achieved a greater median reduction of 54 kPa, while the orthoses of podiatrists resulted in an increase of peak pressure by 50 kPa. The differences between orthotists and pedorthists compared to podiatrists were statistically significant: p = .021.

The highest baseline peak pressures for patient B were measured in both mt-3 regions (table 2). Orthotists, pedorthists, and podiatrists achieved median reductions of 93, 91 and 58 kPa respectively: figure 1. For the right mt-3 region, these reductions were 57, 24 and 43 kPa respectively. The difference between orthotists and pedorthists was statistically significant: p = .019 (figure 1).

The highest baseline peak pressures for patient C were also measured in both mt-3 regions (table 2). Orthoses of pedorthists, orthotists and podiatrists achieved a median reduction of 149, 141 and 136 kPa respectively in the left mt-3 region (figure 1). For the right mt-3 region, these reductions were 89, 83 and 65 kPa respectively (figure 1).

For patient B and C, a high peak pressure was measured in the corresponding right and left BT region (table 2). Orthoses of pedorthists, orthotists and podiatrists achieved a median reduction of 46, 44 and 3 kPa respectively, in the right BT region of patient B (figure 1). For the left BT region of patient C, orthoses of orthotists, podiatrists and pedorthists achieved a median reduction of respectively 162, 160 and 120 kPa (figure 1).

The maximal reduction of peak pressure calculated for the whole plantar surface over all forefeet was greater with orthoses of pedorthists (p = .005) and orthotists (p < .001) than orthoses of podiatrists: -96 and -102 versus -75 kPa respectively. The within-group variability, expressed as standard deviation, of the maximal local peak pressure reduction for the whole forefoot were 16.0, 14.2 and 16.3 kPa for podiatrists, pedorthists and orthotists respectively (table 3). The differences of the within-group variances between the disciplines were not statistically significant.

Box and whisker plots show the median scores and quartiles for 'importance of pressure reduction' rated by the therapists (figure 2). The median ratings by podiatrists for patients A, B and C were respectively: 68, 65 and 81 out of 100 mm. The ratings by pedorthists for patients A, B and C were 88, 86 and 93 mm, respectively. The ratings by orthotists for patients A, B and C were 90, 81 and 93 mm respectively.

The relationship between the 'importance of pressure reduction' and the effect on peak pressure for the whole forefoot was only evaluated for patients for which therapists within professional groups had a large variation in their judgement of the importance of pressure reduction: for podiatrists patients A and B and for orthotists patient B (figure 3).

Linear regression analysis showed only statistically significant weak negative associations between the 'importance of pressure reduction' ratings by orthotists and the effect on peak pressure for the left and right foot of patient B. Importance of pressure reduction explained 50% (p = .015) and 48% (p = .019) of the variance of the effect on peak pressure, respectively (figure 3). There was no statistically significant relation between ratings of podiatrists and effect on peak pressure for patient A and B.

Podiatrists had less years of professional experience than pedorthists (p = .037) and orthotists (p = .008), while orthotists and pedorthists did not differ in years professional experience. Multiple regression analysis showed that there was no, or a very weak, relationship between achieved pressure reduction and years professional experience, number of constructed orthoses per week, or importance of pressure reduction (data not shown).

The appreciation of walking convenience by the patients is shown in table 4 (Means were calculated through the mean of two ratings per therapist). Walking convenience was better rated by patients A and B for orthoses of pedorthists and orthotists compared to orthoses of podiatrists. The differences for both feet of patient B were statistically significant (left: p = .005, right: p = .005). For patient A, only the differences between orthotists and podiatrists for both feet were statistically significant (left: p = .019, right: p = .047). According to the ratings of patient C, pedorthists scored, on average, better than podiatrists and podiatrists better than orthotists.