Hindfoot Alignment Assessed by Weight Bearing CT: Presence of a Constitutional Valgus?

, Francois Lintz2, Cesar de Cesar Netto3, Alexej Barg4, Arne Burssens5 and Scott Ellis6



(1)
Department for Foot and Ankle Surgery, Hospital Rummelsberg, Schwarzenbruck, Germany

(2)
Foot and Ankle Surgery Centre, Clinique de l’Union, Toulouse, France

(3)
Department of Orthopedics and Rehab, University of Iowa, Iowa City, IA, USA

(4)
University Orthopedic Center, University of Utah, Salt Lake City, UT, USA

(5)
Department of Orthopedics and Trauma, University Hospital of Ghent, Ghent, OVL, Belgium

(6)
Department of Orthopedic Surgery, Hospital for Special Surgery, New York, NY, USA

 



Keywords

Hindfoot alignmentWeight bearing CTHindfoot correctionNormal alignment


Introduction


Hindfoot alignment has classically been determined using a long axial or hindfoot alignment view [1]. Studies using these radiographic methods in normal asymptomatic feet report values between 2° and 5° of valgus in the general population [2]. Clinical measurements of the hindfoot are situated between 5.61° and 6.50° of valgus [3]. These findings give the impression of a physiological valgus alignment of the hindfoot. However, results are based on small cohorts [2, 4], lack a clear correlation between clinical/radiographical data [5], and impose important measurement errors due to bony superposition present in plane weight bearing radiographs [6]. The latter is currently overcome by the use of weight bearing CT which provides an accurate bone position and allows a natural stance of the patient [7]. Various methods now have been described to determine hindfoot alignment using weight-bearing CT [7, 8]. This study will use a method composed out of the anatomical axis of the tibia and the talocalcaneal axis based on the inferior point of the calcaneus as described previously [9]. To investigate not only the radiological relevance of this point but also a possible biomechanical role, a density analysis will be performed. An increased ossification around the inferior point would indicate a higher load application as stated by Wolff’s law [10]. Currently the measurement method was only used in malalignments of the hindfoot and lacks reference values. Therefore, the goal of this study is to obtain measurements from a population with clinical and radiological absence of hindfoot pathology. These will be compared to hindfoot measurements obtained from the long axial view based on the anatomical axis of the tibia and the calcaneal axis, to point out possible differences attributed to the measurement method [1]. Although surgical hindfoot corrections are frequently performed either extra-articular by osteotomies or intra-articular by arthrodesis, still numerous debate exists on the amount of correction and the ideal foot position after arthrodesis [11, 12]. Per-operative tools are already used to obtain a more accurate correction [13] or a physiological load distribution [14], but a preoperative planning remains paramount. This study will contribute to the preoperative planning by providing further insights into a physiological hindfoot alignment. The null hypothesis is the existence of an overall physiological valgus alignment in the hindfoot.


Materials and Methods


Study Population and Design


Forty-eight patients, mean age of 39.6 ± 13.2 years, with clinical and radiological absence of hindfoot pathology were included. Indications for imaging consisted out of minor foot and ankle trauma with persistent complaints in purpose to rule out an occult fracture, but appeared to be negative or nonsignificant (n = 31), suspicion of osteoartrosis but not detectible on weight bearing CT imaging (n = 11), and MTP I fusion to assess consolidation (n = 4) (Table 9.1).


Table 9.1

Patient characteristics


























Characteristic


Total (N = 48)


Age (±) SD


39.6 ± 13.2 years


Sex (M/F)


28/20


Minor trauma


31


Absence osteoarthritis


11


MTP I fusion


4


Patient Characteristics


Each time the contralateral not affected foot was used for analysis. This was performed using CurveBeam® software applied on the images retrieved from the weight bearing CT (pedCAT®). Ethical committee gave permission in performing the study (OG10601102015). Following imaging protocol was used: radiation source was set at 4 mAs and 50 kV, with a focus distance of 100 cm, with the beam pointed at the ankle joint. PedCAT used the following settings: tube voltage, 96 kV; tube current, 7.5 mAs; CTDIvol 4.3 mGy; matrix, 160,160,130; pixel size, 0.4 mm; and slice interval 0.4 mm. At the department of radiology, patients were asked to attain a natural stance with both feet parallel to each other and straight ahead at shoulder width.


Hindfoot measurements were performed by two authors AB and EDV. Each measurement was repeated three times; after the complete set of measurements, the mean out of three measurements was used for further analysis. The hindfoot angle was determined based on the inferior point of the calcaneus (HAIC) as described previously [9]. In brief the foot is positioned according to the second ray, and the angle is composed out of the intersection between the anatomical tibial axis (TAx) and the talocalcaneal axis (TCAx) (Figs. 9.1a and 9.2a). The latter is formed by connecting the inferior point of the calcaneus with the middle of the upper surface of the talus (Fig. 9.3a, b). This will be compared to the hindfoot angle measured on the long axial view (HALA), for which firstly the foot needed to be aligned with second ray and inclined 45° by applying the reconstruction mode built in to the used software (Figs. 9.1b and 9.2b, c). Secondly the calcaneus needed to be divided 50–50% in the upper part and 40–60% in the lower part to determine the calcaneal axis (CAx) as described by van Dijk et al. [1] (Fig. 9.3c). The HALA was composed out of the intersection between the TAx and the CAx on the inclined foot (Fig. 9.3d).

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Fig. 9.1

(a) Overview of the measurement method (HAIC) based on the inferior calcaneal point (lower right quadrant) after alignment of the foot according to second ray (upper right quadrant, green line) (b). In comparison to the long axial method (HALA) based on dividing the calcaneus (lower right quadrant) after inclination of the feet towards 45° and aligning with the second ray (upper right quadrant, green line)


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Fig. 9.2

(ac) Correlation between both measurement methods showed to be good with an R2 = 0.74, indicating that both can be used to determine hindfoot alignment but with higher valgus values obtained in the HALA


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Fig. 9.3

Schematic overview of both hindfoot measurement methods (a). HAIC composed out of the anatomical tibia axis (TAx) , by dividing the tibia shaft 50–50% each one third (green points) and talocalcaneal axis (TCAx) by connecting the inferior calcaneus point (IC, red point) with the middle of the talar dome (blue point) (b). Distribution of the (TCAx) (c). Distribution of the (CAx) pointing out a shift towards a valgus value (d). HALA composed out of the anatomical tibia axis (TAx) and the calcaneal axis (CAx) after dividing the calcaneus and inclining the foot 45°


To investigate the relevance of the inferior calcaneus point, a bone density analysis was performed by calculating the pixel density of this region of interest (ROI) in the coronal plane and comparing it to a regional area with the same surface window by using an OsiriX®-based plug in software (Fig. 9.4a, b). A higher pixel density would concur with an increased calcium/bone density, and by applying Wolff’s law, this would indicate a higher load exposure [10]. To avoid the influence of traction exerted by the fascia plantaris on the bone formation in this inferior calcaneal region, the ROI was set at a distance of 5 mm from the medial calcaneal tuberosity in the sagittal plane (Fig. 9.4c, d).

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Apr 25, 2020 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Hindfoot Alignment Assessed by Weight Bearing CT: Presence of a Constitutional Valgus?
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