The effect of weight-bearing conditions on toe joint angles in healthy volunteers using weight-bearing CT

doi:10.21203/rs.3.rs-3125546/v1

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The effect of weight-bearing conditions on toe joint angles in healthy volunteers using weight-bearing CT

https://doi.org/10.21203/rs.3.rs-3125546/v1

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Purpose: To determine the effect of weight-bearing (WB) conditions on toe joint angles in healthy volunteers using WB and non-WB (nWB) CT images and to evaluate left and right foot differences.

Methods: In twenty healthy volunteers WB and nWB CT images of both feet were acquired. Bones of the forefoot were segmented and the respective bone models were used to calculate angles for the metatarsophalangeal and interphalangeal joints.

Results: Metatarsophalangeal joint (MTPJ) angles ranged between 6˚ and 40˚, proximal interphalangeal joint (PIPJ) angles between 0.5˚ and 54˚and distal interphalangeal joint (DIPJ) angles between 1˚ and 46˚.MTPJ angles were significantly smaller in WB compared to nWB conditions in the first four digits. The interphalangeal joint angles of the first digit was in WB conditions significantly larger. No left-right foot differences were found for toe joint angles.

Conclusion: Toe joint angles show a wide variety between healthy volunteers although the bilateral symmetry is high. MTPJ angles of the first to fourth toe are smaller under WB conditions, but do not change PIPJ and DIPJ angles compared to nWB conditions.

Weight-bearing computed tomography

Toes

Joint angles

Anatomical axes

Toe alignment

Lesser toe deformities such as claw, hammer and mallet toes are prevalent in the general community and diseased populations and commonly require surgical intervention or treatment with specialized footwear [1–3]. With these deformities, one or more toe joints are in a hyperflexed or hyperextended position. In some forms of toe deformity, loading influences the position of the toe significantly and the impact of these deformities on foot function depends on whether the toe is able to stretch under weight-bearing conditions or if the toe joints remains in flexion or extension [4]. Moreover, it is important to objectify the severity of toe deformities both in a weight-bearing and a non-weight-bearing condition, since this could influence treatment options [5]. Current evaluation methods for decision-making in clinical practice regarding conventional or surgical lesser toe deformity treatment consist of physical examination aided by imaging in more severe cases, without the use of objective quantitative measures [6, 7]. Objective toe angle measurements can be performed using imaging and could aid decision making in clinical practice.

Possible imaging modalities to evaluate toe deformities are radiography, computed tomography (CT) and magnetic resonance imaging (MRI) [8]. Radiography is often used with the main advantage that imaging under weight-bearing conditions is possible. However, imaging of lesser toe deformities which primarily manifest themselves in the sagittal plane are difficult to evaluate from radiographs due to over-projection of the toes and does not allow measurement of the orientation of the bones in three-dimensions (3D) [9, 10]. CT and MRI both have the advantage of image acquisition in 3D, thereby eliminating over-projection issues. This 3D imaging enables objective evaluation of toe deformities in 3D [11]. However, most CT- and MRI-scanners are not suitable for scanning under weight-bearing conditions. This is a limitation since the effects of toe deformity are understandably best studied under weight-bearing conditions [4]. To evaluate lesser toe deformities, weight-bearing CT (WBCT) imaging under natural loading seems a valuable option [12–15]. WBCT is a relatively new modality and literature on measuring toe deformities is sparse [7, 9, 12, 16]. An objective 3D method to measure the angles of the joints in the toes has recently been described and tested for accuracy and reproducibility [17].

For optimal diagnosis, patient treatment, and evaluation, it is essential to assess treatment outcomes accurately, measuring toe angles objectively in both weight-bearing and non-weight-bearing conditions. Therefore, the aims of this study are 1) to evaluate differences in toe angles in weight-bearing (WB) and non-weight-bearing (nWB) conditions, 2) to establish reference values of toes without deformity in a healthy population and 3) to determine if toe angles are different between left and right feet.

Subjects

Twenty healthy volunteers with no history of foot and ankle pathology and no diagnosed toe deformity were included in this study. The WB and nWB CT-scans were obtained in the context of an earlier study about 3D foot and ankle geometry on WB and nWB CT-scans of which Medical ethical approval was obtained (METC2019_038) [15].

Image acquisition

A Verity Cone-beam CT (CBCT) scanner (Planmed Oy, Helsinki, Finland) was used to acquire non-weight-bearing and single-leg-full-weight-bearing images of the left and right forefoot. The field-of-view of approximately 16 x 13 cm was sufficient to capture the entire forefoot [18]. Scan parameters were: tube voltage 96 kV and tube current 6.3 mA with a pulse length of 20 ms and a voxel size of 0.4 x 0.4 x 0.4 mm.

During WB acquisition, subjects stood on one leg inside the weight-bearing CT scanner holding a handlebar on the side of the scanner for support and were instructed to divide their weight equally on their foot. During the nWB acquisition, subjects rested the foot on a stool and had their knee in an angle of ninety degrees. They were instructed to not put any weight on their foot.

Bone segmentation and joint angle measurements

In-house developed semi-automatic image analysis software was used to segment relevant osseous structures [19]. Segmentation was conducted using region growing and manual fine-tuning followed by automatic level-set segmentation. The following bones of the foot were segmented: cuboid bone, cuneiform bones (medial, intermediate, lateral), all metatarsals and all phalanges. Segmentations of the bones were performed in non-weight-bearing images, whereas an automated registration technique was used to determine the position and orientation of these bones in the weight-bearing scan of the same foot [19]. To calculate toe joint angles a centroid axis was used. This method has been tested for consistency and observer agreement in a previous study [17]. This centroid axis runs between the centers of the articulating surfaces on each side of the bone. The in-house software uses this centroid axis to calculate the 3D joint angle. Reference values of metatarsophalangeal joint (MTPJ), proximal interphalangeal joint (PIPJ) and distal interphalangeal joint (DIPJ) angles were measured using weight-bearing (WB) and non-weight-bearing (nWB) CT images of both feet.

Statistical analysis

Data were checked for normality using the Shapiro-Wilk test. Both the left and right feet were used in the analysis. The median, interquartile range (IQR) and range were calculated. A Wilcoxon-signed rank test was used on data that was not normally distributed or where the sample size was small. For the statistical analysis SPSS (version 26, IBM) was used. Tests for significance were two-tailed, paired and the significance level was set at 5%.

Effect of weight-bearing conditions on toe joint angles

The MTPJ angles of the first four toes (MTPJ1-4) decreased significantly under WB compared to nWB conditions with on average 7.2–8.7% across toes (p < 0.001; Table 1; Figs. 1 and 2). The IPJ1 angle significantly increased during weight-bearing with on average 16.6% (p < 0.001). MTPJ5, PIPJ2-5 and DIPJ2-5 showed no significant effect of WB versus nWB conditions (p = 0.083 or higher).

Toe joint angles in a healthy population

MTPJ angles had medians between 15.3˚ and 23.7˚ in nWB conditions (range 7.9˚ – 39.5˚) and between 14.8˚ and 22.1˚ in WB conditions (range 6.2˚ – 38.0˚). The medians of the IPJ/PIPJ angles varied between 15.2˚ and 27.4˚ in nWB conditions (range 0.5˚ – 51.7˚) and 14.6˚ and 25.4˚ in WB conditions (range 1.0˚ – 54.0˚). DIPJ angle medians ranged from 13.5˚ to 19.3˚ in nWB conditions (range 0.5˚ – 36.4˚) and from 15.1˚ to 19.8˚ in WB conditions (range 0.7˚ – 45.6˚) .

Differences between toe joint angles in left and right feet

In nWB conditions, the right and the left foot showed a median difference of 3.5˚ with an IQR 1.3˚ − 7.1˚. In WB conditions, the median difference was 3.6˚ with an IQR 1.7˚ − 8.6˚ The PIPJ angle of the fifth digit in a nWB condition showed a significant difference between the right and left side (median difference 8.4˚; IQR 2.1˚ – 13.7˚; p = 0.028). All other toe angles measurements were not significantly different between both feet in either WB or nWB conditions (p > 0.05).

The present study aimed to assess toe joint angles in healthy volunteers under WB and nWB conditions to establish reference values for these toe angles, assess the effect of WB conditions on differences in toe angles and to assess differences between the left and right foot to optimize patient treatment and evaluation. MTPJ angles ranged between 6˚ and 40˚, PIPJ angles between 0.5˚ and 54˚ and DIPJ angles between 1˚ and 46˚. The angles of MTPJ1-4 and IPJ1 were significantly lower during WB compared to nWB conditions; other toe joint angles did not show significant differences between nWB and WB conditions. Intraindividual toe joint angle of the left and right foot were comparable and mostly not significantly different.

There was no significant difference found in our study of WB condition for most PIPJ and DIPJ angles of the healthy volunteers between nWB and WB conditions. This is different from most MTPJ angles and other joint angles in foot and ankle anatomy, such as the intermetatarsal angle between metatarsal (MT) 1 and MT2 and the angle between MT5 and the ground, which show differences between loading and non-loading [15]. We hypothesized that in individual cases the PIPJ and DIPJ angles would generally become smaller when the foot was loaded. However Fig. 2 shows this is not always the case. When analysing individual cases of PIPJ and DIPJ angles to assess why in some cases the these joint angles were larger in WB conditions, we noticed that in those cases the PIPJ or DIPJ joints were often more (hyper)extended in WB conditions compared to a slight extension or flexion in nWB conditions (Fig. 3). Because the measurements were in 3D the angles are measured as absolute values, this resulted in larger toe joint angles in WB conditions. In 2D measurement it would be possible to assign a negative value to extension and a positive value to flexion. In 3D, a coordinate system could have been used for this purpose. This might have resulted in smaller toe joint angles in WB conditions compared to nWB conditions. Additionally, 3D joint angle measurements also take lateral or medial deviations in the transversal plane into account (Fig. 4). Therefore, joint angle measurement might result in higher values than would be expected when assessing only the sagittal image.

To our knowledge, there are no studies on the differences in PIPJ and DIPJ angle between nWB and WB conditions in healthy participants. However, in the presence of toe deformity there is evidence that weight-bearing significantly influences the position of the toe, such as in flexible claw and hammer toes [4]. More research is needed to investigate the diagnostic use of WBCT in examining lesser toe deformities.

The healthy volunteers showed a wide range in toe joint angles, especially in the PIPJ and DIPJ of the lesser toes. This implies that it is impossible to define overall reference values for toe joint angles. A few studies have analysed toe angles either with radiographs or without the use of imaging. Bus et al. [20] used a contact digitizer to assess anatomical landmarks on the toes to analyse the toe joint angles. Their healthy control group showed mean MTPJ, PIPJ and DIPJ angles of 45˚, 14˚ and 30˚, respectively in the second toe. The MTPJ and DIPJ angles were much larger than in our study. This might be because the measurement techniques were different. Mens et al. [21] used lateral weight-bearing radiographs and reported mean MTPJ, PIPJ and DIPJ angles of 24˚, 29˚ and 22˚ after a flexor tenotomy in patients with claw toes and diabetic ulceration of the second toe, which is closer to the findings in our current study. Cyphers et al. [22] and Femino et al. [23] classified an MTPJ and PIPJ angle of < 30˚ as a mild deformity, MTPJ and PIPJ angles of 30˚- 60˚ as moderate deformity and angles of > 60˚ as severe deformity using light photographs. According to their classification, some of the healthy volunteers from our study would be classified as with moderate deformity, even though they have no diagnosis of toe deformity. Ceccarini et al. [24] analysed PIPJ angles on radiographs after a hammer toe subtraction osteotomy. They defined a PIPJ angle of > 20˚ to be a poor result, thus implying these angles might still be a deformity. This is a completely different cut-off value from Cyphers et al. and Femino et al. [22, 23]. Thus, toe joint angles alone might not be sufficient to establish deformity. Elevated bare-foot plantar pressure or complaints by the patient such as pain or callus formation might be needed to diagnose toe deformity.

The intraindividual left-right differences were small. Thus, if a toe joint angle diminishes after surgery it is likely not accidental or due to a different stance of a patient. This fact can be used to analyse the effect of interventions, such as a flexor tenotomy. If a pre-operative scan is not available the contralateral side can be used as a comparator. Not having to perform a pre-operative scan also reduces radiation exposure for the patient. When the nWB and WB scans were performed, patients were encouraged not to move the foot in between scans. It is likely that toe stance differs when the foot is moved or if a patient leans more to one side. That a different stance was possible in our study between the nWB and WB scans, could be considered a limitation and could potentially be a reason for higher toe joint angles in WB conditions in some cases (Fig. 2). Therefore, in future studies it should be considered to combine the WBCT scans with a bare-foot pressure measurement inside the scanner to ensure the patient has the same stance in different scans.

In conclusion, the angles of each of the toe joints of the foot (i.e. MTPJ, PIPJ, and DIPJ) vary strongly across healthy volunteers. WB conditions change MTPJ angles of the first four digits and the IPJ angle of the hallux compared to nWB conditions, but do not alter PIPJ and DIPJ angles. This may affect diagnostics in clinical practice. The left and right feet show similar toe joint angles.

Ethical Approval

Medical ethical approval was provided by the Internal Review Board of the Amsterdam UMC (METC2019_038). The subjects in this study provided informed consent for participation in the study and for publication of the study data.

Competing interests

None to disclose

Author’s contributions

MA Mens: Protocol and project development, data collection and management, data analysis, manuscript writing and editing. CMB Bouman: Protocol and project development, manuscript writing and editing. JGG Dobbe: Data management, data analysis, manuscript writing and editing. SA Bus: Protocol and project development, manuscript writing and editing. M Nieuwdorp: Protocol and project development, manuscript writing and editing. M Maas: Protocol and project development, manuscript writing and editing. RHH Wellenberg: Protocol and project development, data collection and management, data analysis, manuscript writing and editing. GJ Streekstra: Protocol and project development, data collection and management, data analysis, manuscript writing and editing.

Funding

M.A.M. is supported by a personal AMC-PhD scholarship 2019. M.N. is supported by a personal ZonMw VICI grant 2020 [09150182010020].

Availability of data and materials

Datasets can be accessed upon request via the authors.

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Table 1 Toe joint angle measurements in both feet of 20 healthy volunteers under weight-bearing (WB) and non-weight-bearing (nWB) conditions

	nWB		WB		P-value
	Median (IQR)	Range	Median (IQR)	Range
MTPJ 1 (˚)	15.3 (12.7 – 20.0)	7.9 – 27.7	14.8 (12.0 – 17.6)	7.1 – 28.8	< 0.001*
MTPJ 2 (˚)	23.7 (19.3 – 27.3)	15.8 - 31.3	22.1 (17.6 – 25.4)	12.3 – 31.0	< 0.001*
MTPJ 3 (˚)	22.0 (91.6 – 25.6)	14.5 – 35.0	20.3 (17.9 – 23.7)	13.8 – 33.4	< 0.001*
MTPJ 4 (˚)	15.5 (12.6 – 19.5)	9.2 – 23.7	15.0 (12.2 – 17.9)	6.2 – 22.8	< 0.001*
MTPJ 5 (˚)	17.4 (15.6 – 21.0)	10.6 – 39.5	18.1 (15.1 – 21.6)	10.5 – 38.0	0.253
IPJ 1 (˚)	17.4 (11.5 – 21.0)	7.5 – 25.2	20.8 (13.8 – 23.2)	6.9 – 30.6	< 0.001*
PIPJ 2 (˚)	15.2 (8.6 – 21.0)	0.5 – 41.7	14.1 (7.8 – 22.1)	1.0 – 49.0	0.925
PIPJ 3 (˚)	18.8 (8.8 – 27.7)	4.1 – 41.5	14.6 (7.2 – 25.1)	1.8 – 43.5	0.211
PIPJ 4 (˚)	20.3 (15.1 – 26.8)	6.4 – 47.1	18.7 (12.7 – 26.4)	3.5 – 51.9	0.559
PIPJ 5 (˚)	27.4 (23.6 – 31.7)	11.1 – 51.7	25.4 (20.9 – 33.9)	11.5 – 54.0	0.536
DIPJ 2 (˚)	13.5 (13.5 – 20.1)	1.1 – 36.4	16.5 (10.0 – 28.3)	0.7 – 40.7	0.083
DIPJ 3 (˚)	15.5 (10.5 – 21.0)	2.5 – 35.5	15.1 (10.4 – 24.6)	1.0 – 44.7	0.861
DIPJ 4 (˚)	18.5 (15.7 – 23.1)	4.2 – 44.6	18.7 (11.9 – 23.3)	6.6 – 45.6	0.382
DIPJ 5 (˚)	19.3 (13.5 – 24.6)	0.5 – 34.0	19.8 (12.2 – 24.8)	0.8 – 35.4	0.902

Note: WB: weight-bearing; nWB: non-weight-bearing; IQR: interquartile range; MTPJ: metatarsal phalangeal joint; IPJ: interphalangeal joint; PIPJ: proximal interphalangeal joint; DIPJ: distal interphalangeal joint; * Statistically significant difference between WB and nWB conditions. To calculate the p-value the Wilcoxon-signed rank test was used. This represents the data of both the left and right feet in one group.

No competing interests reported.

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The effect of weight-bearing conditions on toe joint angles in healthy volunteers using weight-bearing CT

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Version 1

Abstract

Figures

Introduction

Material and Methods

Subjects

Image acquisition

Bone segmentation and joint angle measurements

Statistical analysis

Results

Effect of weight-bearing conditions on toe joint angles

Toe joint angles in a healthy population

Differences between toe joint angles in left and right feet

Discussion

Declarations

References

Table

Additional Declarations

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