Measuring hindfoot alignment in weight bearing CT: A novel clinical relevant measurement method

doi:10.1016/j.fas.2015.10.002

Foot and Ankle Surgery

Volume 22, Issue 4, December 2016, Pages 233-238

https://doi.org/10.1016/j.fas.2015.10.002 Get rights and content

Highlights

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Weight bearing cone beam CT overcomes numerous measurement errors encountered by standard posterior weight bearing radiographs.
•
Currently no method is available to determine hindfoot alignment using every structural component of the hindfoot.
•
We introduce a hindfoot alignment angle on weightbearing CT which is both clinical relevant and reproducible.
•
The talar translation, on which the angle is based, can help the surgeon in determining how much translation is necessary to obtain a neutral alignment during a calcaneal osteotomy.

Abstract

Background

A precise pre-operative measurement of hindfoot malalignment is paramount to plan and obtain an accurate surgical correction. Hindfoot alignment is currently determined on standard weightbearing radiographs. However this is hampered by the superposition of the skeletal structures. Recent technology developed weightbearing cone beam CT to overcome this problem. The objective is to introduce a clinically relevant and reproducible method to measure hindfoot alignment on weightbearing CT.

Methods

Sixty malalignments of the hindfoot were divided in to two groups; group one containing a valgus alignment (n = 30) and group two a varus alignment (n = 30) of the hindfoot. Imaging techniques used were standard radiographs and a weightbearing CT (pedCAT^®). Following angles were measured by two different authors: standard long axial hindfoot angle both on standard radiographs and on CT, clinical hindfoot, novel hindfoot angle, talar shift (distance from a neutral alignment), tibial inclination angle, talar tilt and subtalar vertical angle on CT.

Results

Hindfoot alignment angles showed to significantly differ from each other (P < 0.001). The novel hindfoot alignment angle showed the highest correlation with the clinical measurement method. Correlation of this novel angle with the talar shift showed a Spearman's correlation coefficient = 0.87. Interclass correlation coefficient of the novel hindfoot alignment angle = 0.72 and was the highest among the hindfoot alignment angles.

Conclusion

Weightbearing CT is allows to objectively assess hindfoot alignment. The proposed novel hindfoot alignment angle showed to be both clinically relevant and reproducible as compared to previous methods. The lateral tibiocalcaneal shift, on which the angle is highly correlated to, can help the surgeon in determining how much translation is necessary to obtain a neutral alignment during a calcaneal osteotomy.

Level of evidence

Level III: retrospective cohort study.

Introduction

Hindfoot alignment has classically been determined using a hindfoot alignment view [1], [2] or a long axial view on plain radiography [3], [4].

Measurements on long axial view radiographs showed a superior inter-observer agreement, compared with hindfoot alignment radiographs [5].

However, all hindfoot alignment measurements based on standard radiographs impose a substantial risk for measurement errors due to malpositioning, superpositioning, inconsistent angulation or enlargement of foot and ankle skeletal structures caused by the radiographic fan beam [6], [7].

An accurate knowledge of both axial and rotational alignment is required to objectify preoperative status and achieve surgical correction of hindfoot malalignment [8], [9].

Computed tomography (CT) provides this accurate anatomical information, but most available CT's in clinical setting are limited to a supine position [10], [11] or to loading by an external apparatus [12]. The importance of load bearing for the interpretation of hindfoot alignment has been shown by Kido et al., with the occurrence of joint instability when loading the hindfoot in patients with pedes plani [13].

Recent advances therefore focused on this importance and newly developed CT scanner technology now allows full bipedal weight bearing [14]. Current results show significant different measurements of both hind, middle and forefoot alignment angles when compared to supine imaging [15], [16]. However current measurements lack a clinically relevant and reproducible method to determine hindfoot alignment on weithbearing CT. This is hampered in addition by the limited amount of distal tibia scanned by current cone beam technology.

Therefore the hypothesis in this study is two-fold. First we hypothesized if it would be possible to determine a clinically relevant and reproducible method to measure hindfoot alignment on weightbearing CT.

The second hypothesis investigated whether the anatomical axis of tibia obtained from the full leg was more reliable than the short end of the tibia scanned by the cone beam CT.

Section snippets

Study population and design

Sixty malalignments of the hindfoot were retrospectively reviewed from forty-six patients referred by the department of orthopaedics for radiographic imaging of the hindfoot.

These were divided into two groups; group one contained a valgus alignment (n = 30) and group two a varus alignment (n = 30) of the hindfoot. This division was based on referral indications of the orthopaedic surgeon.

The indications in group one consisted out of osteoarthritis of the hindfoot (n = 12), tibialis posterior type II

Valgus alignment

Measurements in the valgus alignment group of cohort showed a mean HA_{RX LA} = 16.4°, mean HA_{CT CL} = 25.2°, HA_{CT LA} = 17.7°, HA_{CT NOV} = 20.1° (Table 1). These mean hindfoot angles differed significantly from each other when measured radiographically, clinically and on weight bearing CT (Table 2). Radiographic measurements all showed a positive correlation with clinical measurements on 3D images (Fig. 4a). The highest correlation was seen with the novel hindfoot alignment angle. Talar shift showed a high

Discussion

This study shows a novel method to measure hindfoot alignment in a weightbearing CT. Applying the same long axial measurement method as used in standard radiographs also showed to be possible by inclination of the images (Fig. 1c). However this attributed no added value because weightbearing CT overcomes superposition of the osseous structures and an additional rotation may imply a greater measurement error as shown by lower rater reliability of the HA_{CT LA} (Table 1).

Other methods to determine

Conclusion

This study shows a novel clinical relevant method in weight bearing CT to determine hindfoot alignment. We advocate its use in clinical practice because it answers the first hypothesis by showing a positive correlation with previous hindfoot angles, a high correlation with clinical images and an excellent reproducibility. Moreover the talar shift on which the angle is based can aid the surgeon preoperatively in determining how much translation is necessary to obtain a neutral alignment during a

Conflict of interest statement

The authors declare to have no conflict of interest or a financial disclosure of any support received.

The authors state to approve the manuscript and its submission to the journal.

Acknowledgements

The authors declare no conflict of interest or acceptance of external funding.

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View full text

Measuring hindfoot alignment in weight bearing CT: A novel clinical relevant measurement method

Highlights

Abstract

Background

Methods

Results

Conclusion

Level of evidence

Introduction

Section snippets

Study population and design

Valgus alignment

Discussion

Conclusion

Conflict of interest statement

Acknowledgements

Foot Ankle Clin

Foot Ankle Surg

Knee

Foot

Foot

Posterior roentgenogram of the foot

Clin Orthop Relat Res

The hindfoot alignment view

Foot Ankle Int

A roentgenographic study of the development of the calcaneus by means of the posterior tangential view

J Bone Joint Surg

Static rearfoot alignment: a comparison of clinical and radiographic measures

J Am Podiatr Med Assoc

Measuring hindfoot alignment radiographically: the long axial view is more reliable than the hindfoot alignment view

Skeletal Radiol

Hindfoot alignment measurements: rotation-stability of measurement techniques on hindfoot alignment view and long axial view radiographs

Am J Roentgenol

The reliability and validity of radiographic measurements for determining the three-dimensional position of the talus in varus and valgus osteoarthritic ankles

Skeletal Radiol

Osteotomies of the distal tibia and hindfoot for ankle realignment

Orthopade

Computed tomography of the hindfoot

J Comput Assist Tomogr