Hindfoot Alignment Measurements: Rotation-Stability of Measurement Techniques on Hindfoot Alignment View and Long Axial View Radiographs

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1 Musculoskeletal Imaging Original Research Buck et al. Measurements Musculoskeletal Imaging Original Research FOCUS ON: Florian M. Buck 1 Adrienne Hoffmann 1 Nadja Mamisch-Saupe 1 Norman Espinosa 2 Donald Resnick 3 Juerg Hodler 1 Buck FM, Hoffmann A, Mamisch-Saupe N, Espinosa N, Resnick D, Hodler J Keywords: hindfoot alignment measurement, hindfoot alignment view, long axial view, malpositioning, rotation stability DOI: /AJR Received September 6, 2010; accepted after revision January 21, Department of Radiology, Orthopedic University Hospital Balgrist, Forchstrasse 340, CH-8008 Zurich, Switzerland. Address correspondence to F. M. Buck (florian.buck@gmail.com). 2 Department of Orthopedic Surgery, Orthopedic University Hospital Balgrist, Zurich, Switzerland. 3 Department of Radiology, University of California San Diego, San Diego, CA. AJR 2011; 197: X/11/ American Roentgen Ray Society Measurements: Rotation-Stability of s on View and Long Axial View Radiographs OBJECTIVE. The purpose of this article is to identify the most rotation-stable hindfoot alignment measurement techniques on hindfoot alignment view and long axial view radiographs. MATERIALS AND METHODS. Hindfoot alignment was quantified on hindfoot alignment view and long axial view radiographs of a phantom in different rotation positions. Rotation stability of measurements using the calcaneal axis, the medial and lateral calcaneal contour, and the apparent moment arm were graphically compared. Interreader agreement was quantified using intraclass correlation coefficient. RESULTS. On hindfoot alignment view radiographs, measurements using the medial and lateral calcaneal contour were rotation stable (± 5 ). Measurements using the calcaneal axis were not reliable and showed considerable divergence with phantom rotation. Measurements using the apparent moment arm manifested an almost linear relationship to phantom rotation. On long axial view radiographs, all measurements manifested an almost linear relationship to phantom rotation, whereas those using the calcaneal axis were the most rotation stable. Interreader agreement of all measurement techniques was perfect on both hindfoot alignment and long axial view radiographs (intraclass correlation coefficient, ; p < 0.001). Interreader agreement was slightly better on long axial view radiographs. CONCLUSION. Hindfoot alignment measurements should be performed on hindfoot alignment view radiographs using the medial or lateral calcaneal contour or on long axial view radiographs using the calcaneal axis. Interreader agreement of hindfoot alignment measurements is slightly better on long axial view radiographs than on hindfoot alignment view radiographs. H indfoot alignment is routinely evaluated in patients with congenital hindfoot deformity or flat foot deformity, acquired flat foot deformity (e.g., as a result of tibialis posterior tendon dysfunction), ankle instability as a result of ankle joint arthrosis, traumatic or neuropathic subtalar arthrosis, and many other abnormalities to evaluate and quantify static hindfoot axis, decide on treatment options, define the optimal position for arthrodesis, and supervise the postoperative course [1, 2]. Today, hindfoot alignment can be evaluated clinically and radiographically on hindfoot alignment or long axial view radiographs [3, 4]. A previous study described a good correlation between clinical evaluation and measurements on hindfoot alignment view radiographs [5]. However, clinical evaluation of hindfoot alignment can be unreliable because of considerable interreader variation, even between experienced orthopedists [6, 7]. Measurements on hindfoot alignment view and long axial view radiographs offer the advantage of repeated measurements and retrospective evaluation of images. Imaging parameters and acquisition techniques for hindfoot alignment view and long axial view radiographs are well defined and have been described in numerous articles [3, 4, 8, 9]. Nevertheless, it is difficult to find a description regarding how to exactly measure hindfoot alignment on these radiographs. Even more problematic, we could find no information about how reliable these measurements are concerning malrotation of the foot during image acquisition. Correct positioning of the foot seems to be crucial because malrotation could lead to considerable measurement errors on hindfoot alignment view and long axial view radiographs. In the first description of the hindfoot alignment view, Cobey [3] defined the correct position of the foot during image acquisition for hindfoot alignment view radiographs as the one in which the long axis of the second 578 AJR:197, September 2011

Compared with the hindfoot alignment view, the acquisition of long axial view radiographs seems to be less problematic.

2 Measurements metatarsal bone is rectangular to the surface of the x-ray detector or film that is situated in front of the toes. Because the long axis of the second metatarsal bone is not easily identified, we think that malrotation of plus or minus 5 can easily occur. Compared with the hindfoot alignment view, the acquisition of long axial view radiographs seems to be less problematic. The foot must be placed on the x-ray detector with its medial contour parallel to the x-ray beam, which seems to be easier to guarantee [4]. Thus, the purpose of this study was to identify the most rotation-stable hindfoot alignment measurement technique on hindfoot alignment view and long axial view radiographs. Materials and Methods The study was approved by the institutional review board, and informed consent was obtained. A phantom consisting of the skeleton of a human right distal lower leg and foot embedded in anatomically shaped acrylic glass was used (Fig. 1). Hindfoot alignment view and long axial view radiographs were acquired in neutral position referring to the medial aspect of the foot (90 angle between the medial aspect of the foot and the detector plate); in 2, 4, 6, 8, 10, and internal rotation; and in 2, 4, 6, and 10 external rotation (Fig. 1). The images were acquired using a fully digital radiography system (Ysio, Siemens Healthcare). To record hindfoot alignment view radiographs, the foot was placed with the toes next to the detector plate. The x-ray beam was tilted 20 craniocaudally, and the detector plate was adjusted rectangular to the x-ray beam. The distance between the x-ray tube and the detector plate was 0 cm (Fig. 2). Images were acquired using 60-kV tube voltage and 14-mA tube current. For long axial view radiographs, the detector plate was lying horizontally and the foot was placed on top of the detector plate, as described by Reilingh et al. [4] and Lamm et al. [5]. The x-ray beam was tilted 45 craniocaudally, and the foot was aligned with its medial contour parallel to the x-ray beam. The beam settings were identical to the ones for hindfoot alignment view radiographs. Four different measurement techniques (Fig. 3) were applied to quantify hindfoot alignment using Web-based viewing software (ProVision PACS, version 5.0, Cerner). The measurements were performed independently by two fellowshiptrained musculo skeletal radiologists with 4 and 6 years of experience. All four measurements were based on the axis of the distal tibial shaft as a reference. This axis was defined by the midpoint of two pairs of points on the cortex of the distal tibia (Fig. 3). To maximize measurement reliability, a minimum distance between Fig. 1 Phantom imaging. Phantom consisting of skeleton of human right distal lower leg and foot embedded in anatomically shaped acrylic glass was used. Hindfoot alignment view radiographs were acquired in neutral position referring to medial aspect of foot, with 90 angle between medial aspect of foot and detector plate (left) and in varying degrees of internal and external rotation (right). Foot was placed with toes next to detector plate. these pairs of points of 30 mm was maintained. Because of the broadening of the distal tibia adjacent to the ankle joint, both pairs of points were placed at least 4 cm proximal to the ankle joint space. First, the angle between the tibial shaft axis and the calcaneal axis (Fig. 3A) was measured by means of an axis through the calcaneus. This procedure was described on hindfoot alignment view radiographs by Cobey [3] and on long axial view radiographs by Reilingh et al. [4]. On hindfoot alignment view radiographs, to the best of our knowledge, the calcaneus axis was never properly defined. Therefore, the midpoint between the lateral edge of the calcaneus at the level of the subtalar joint and the corner at the inferior aspect of the sustentaculum base and the midpoint between the medial and lateral contour of the posterior calcaneal process (dots in Fig. 3A) defined the calcaneal axis. Next, the angles between the tibial shaft axis and a line adapted to the medial and lateral osseous contour of the calcaneus were measured as described by Donovan and Rosenberg [10] (Fig. 3B). Finally, the apparent moment arm [11] was measured as the distance of the most distal point of the plantar calcaneal contour to the tibial shaft axis (Fig. 3C). These measurement techniques were compared graphically with respect to rotation stability. On hindfoot alignment view radiographs, special attention was paid to phantom positions close to the hindfoot alignment view radiograph position with the long axis of the second metatarsal bone rectangular to the surface of the x-ray detector in front of the toes [3]. This position was achieved with the foot 3 7 internally rotated. On long axial view radiographs, special attention was paid to phantom positions close to the long axial view foot position with the medial contour of the foot parallel to the x-ray beam direction [4]. Interreader agreement was quantified for the different measurement techniques on hindfoot alignment view and long axial view radiographs using the calculation of intraclass correlation coefficients. SPSS software (version, , SPSS) was used for statistical analysis. Fig year-old man. With hindfoot alignment view positioning, radiographs were acquired with x-ray beam tilted 20 craniocaudally, and film was adjusted rectangular to x-ray beam. Distance between x-ray tube and detector plate was 0 cm. Foot was positioned with toes next to film (asterisks) and with long axis of second metatarsal bone rectangular to surface of film in front of toes (inset). AJR:197, September

3 Buck et al. Results The results of hindfoot alignment measurements on hindfoot alignment view and long axial view radiographs in different rotation positions are provided in Table 1 and Table 2 and are graphically compared in Figure 4 and Figure 5. On hindfoot alignment view radiographs, the most constant hindfoot alignment measurements were obtained using an adapted line to the medial calcaneal contour. The measurements using the lateral calcaneal contour were also quite solid in positions of 3 7 internal rotation of the phantom but showed substantial variability with increasing malpositioning. Measurements using the calcaneal axis as described by Cobey [3] were not at all reliable, and even small degrees of rotation resulted in substantial changes in the hindfoot alignment axis (12.4 difference between positions of 4 internal rotation and 6 internal rotation; Fig. 4). Measurements of the apparent moment arm, as described by Saltzman and El- Khoury [11], manifested a linear relationship between the degree of rotation of the phantom and the measurement results in positions between 0 and 8 internal rotation. Fig. 3 Phantom measurement techniques illustrated on hindfoot alignment view radiograph. A, Angle between tibial shaft axis and calcaneal axis was measured by means of axis through calcaneus, as described by Cobey [3]. Midpoint between lateral edge of calcaneus at level of subtalar joint and corner at inferior aspect of sustentaculum base and midpoint between medial and lateral contour of posterior calcaneal process (dots) defined calcaneal axis. B, Angles between tibial shaft axis and line adapted to medial and lateral osseous contour of calcaneus were measured as described by Donovan and Rosenberg [10]. C, Apparent moment arm, as described by Saltzman and El-Khoury [11], is defined as distance of most distal point at plantar calcaneal contour to tibial shaft axis. On long axial view radiographs, all measurement techniques manifested an almost linear relationship between the degree of rotation of the phantom and the measurement results, whereas the hindfoot alignment angle decreased with increasing internal rotation of the phantom. When we evaluated phantom positions close to the one pursued to acquire long axial view radiographs (between 2 internal and 2 external rotation), the most constant measurements were obtained using the calcaneal axis (Fig. 5). Interreader agreement was perfect for all measurements (Table 3). The agreement was slightly better on long axial view radiographs. Discussion Our results show a substantial predilection of the hindfoot alignment measurement TABLE 1: Measurement Results on View Radiographs in Differently Rotated Positions Phantom Rotation, Calcaneal Axis a ( ) Medial Contour ( ) Lateral Contour ( ) Moment Arm b (mm) Degrees Reader 1 Reader 2 Average Reader 1 Reader 2 Average Reader 1 Reader 2 Average Reader 1 Reader 2 Average External rotation Neutral, Internal rotation c c c Measurements in these two rows are close to position to acquire hindfoot alignment view radiograph. 580 AJR:197, September 2011

4 Measurements TABLE 2: Measurement Results on Long Axial View Radiographs in Differently Rotated Positions Phantom Rotation, Degrees External rotation Calcaneal Axis a ( ) Medial Contour ( ) Lateral Contour ( ) Moment Arm b (mm) Reader 1 Reader 2 Average Reader 1 Reader 2 Average Reader 1 Reader 2 Average Reader 1 Reader 2 Average Neutral, 0 c Internal rotation c Measurements in this row are close to position to acquire hindfoot alignment view radiograph Phantom Rotation Phantom Rotation Axis Angle Medial Angle Lateral Angle Moment Arm Axis Angle Medial Angle Lateral Angle Moment Arm Fig. 4 Hindfoot alignment view. Graph shows measurement results of phantom in differently rotated positions. Positive values of phantom rotations indicate internal rotation, and negative values indicate external rotation. Positive measurement results indicate valgus hindfoot axis, and negative measurements indicate varus hindfoot axis. Gray bar between 3 and 7 internal rotation of phantom denotes imaging position desired for hindfoot alignment view radiographs. Angles were measured in degrees, and moment arm was measured in millimeters. Fig. 5 Long axial view. Graph shows measurement results of phantom in differently rotated positions. Positive values of phantom rotations indicate internal rotation, and negative values indicate external rotation. Positive measurement results indicate valgus hindfoot axis, and negative measurements indicate varus hindfoot axis. Gray bar between 2 and 2 rotation of phantom denotes imaging position desired for long axial view radiographs. Angles were measured in degrees, and moment arm was measured in millimeters. AJR:197, September

5 Buck et al. TABLE 3: Interreader Agreement Interreader Agreement (Intraclass Correlation Coefficient) Hindfoot alignment view Calcaneal axis a 0.80 Medial calcaneal contour 0.80 Lateral calcaneal contour 0.90 Moment arm b 0.90 Long axial view Calcaneal axis a 0.98 Medial calcaneal contour 0.97 Lateral calcaneal contour 0.98 Moment arm b 0.94 Note All intraclass correlation coefficients were highly significant (p < 0.001). techniques on hindfoot alignment view and long axial view radiographs for errors that are introduced by rotational misplacement of the foot during image acquisition. Especially on hindfoot alignment view radiographs, hindfoot alignment measurements using the calcaneal axis [3] and the apparent moment arm [11] are very susceptible to rotational misplacement of the foot during image acquisition. Currently, these two measurement techniques are probably the most commonly used in clinical practice. Even small rotation differences of the phantom resulted in substantial differences of hindfoot alignment measurement results, as great as using the calcaneal axis (Fig. 4). The almost linear relationship of measurement results of the apparent moment arm with progressive rotation of the phantom is not surprising, but rather is a logical consequence of the sagittal distance of the two references used for the measurement. Measurements using the medial and lateral calcaneal contour, on the other hand, were rather constant; however, measurements using the medial calcaneal contour seemed to be more reliable than measurements based on the lateral calcaneal contour (Fig. 4). On long axial view radiographs, the measurements were less susceptible to rotational misplacement of the foot, and all measurements showed an almost linear relationship to the degree of rotational misplacement. To our knowledge, there is only one previous study, published by Johnson et al. [12] in 1999, dealing with measurement errors from rotation of the foot. Those authors presented a new coronal hindfoot alignment view based on landmarks of the calcaneal contour. This technique, however, has not enjoyed broad acceptance, probably because of the need to place markers on the foot. An article by Reilingh et al. [4] concluded that the long axial view is more reliable than the hindfoot alignment view for the angular measurement of hindfoot alignment. Our results confirm these findings. Interreader agreement was very good for all measurements on both views. However, interreader agreement was slightly better on long axial view radiographs. At our hospital, hindfoot axis measurements are performed in accordance with those recommended in the standard reference book by Coughlin et al. [2]. A normal hindfoot axis is defined by a hindfoot valgus angle of 0 5. Clearly, pathologic hindfoot valgus angles are greater than 10, and any degree of hindfoot varus is abnormal. Thus, the values indicating either a physiologic or pathologic hindfoot angle are hard to differentiate when compared with the interreader variability. Our data support the view that it is very difficult to discriminate such small differences between normal and pathologic states using measurements on radiographs or MRI scans. On the basis of our results, hindfoot alignment should be measured on hindfoot alignment view radiographs using the medial or lateral calcaneal contour or on long axial view radiographs using the calcaneal axis. These measurements are least susceptible to errors introduced by small rotational changes at the time of image acquisition and show a high interreader agreement. With regard to rotation errors, however, the measurement methods described on hindfoot alignment view radiographs by Cobey [3] and Saltzman and El-Khoury [11], in our view, are less reliable. Because of the slightly better interreader agreement, long axial view radiographs should be acquired to measure hindfoot alignment. In conclusion, hindfoot alignment measurements should be performed on hindfoot alignment view radiographs using the medial or lateral calcaneal contour or on long axial view radiographs using the calcaneal axis. Interreader agreement of hindfoot alignment measurements is slightly better on long axial view radiographs than on hindfoot alignment view radiographs. References 1. Van Bergeyk AB, Younger A, Carson B. CT analysis of hindfoot alignment in chronic lateral ankle instability. Foot Ankle Int 2002; 23: Coughlin MJ, Mann RA, Saltzman CL. Surgery of the foot and ankle, 8th ed. Philadelphia, PA: Mosby, Cobey JC. Posterior roentgenogram of the foot. Clin Orthop Relat Res 1976; Reilingh ML, Beimers L, Tuijthof GJ, Stufkens SA, Maas M, van Dijk CN. Measuring hindfoot alignment radiographically: the long axial view is more reliable than the hindfoot alignment view. Skeletal Radiol 2010; 39: Lamm BM, Mendicino RW, Catanzariti AR, Hillstrom HJ. Static rearfoot alignment: a comparison of clinical and radiographic measures. J Am Podiatr Med Assoc 2005; 95: Haight HJ, Dahm DL, Smith J, Krause DA. Measuring standing hindfoot alignment: reliability of goniometric and visual measurements. Arch Phys Med Rehabil 2005; 86: Menz HB. Clinical hindfoot measurement: a critical review of the literature. Foot 1995; 5: Hamill J, Bates BT, Knutzen KM, Kirkpatrick GM. Relationship between selected static and dynamic lower extremity measures. Clin Biomech (Bristol, Avon) 1989; 4: Herbsthofer B, Eckardt A, Rompe JD, Küllmer K. Significance of radiographic angle measurements in evaluation of congenital clubfoot. Arch Orthop Trauma Surg 1998; 117: Donovan A, Rosenberg ZS. Extraarticular lateral hindfoot impingement with posterior tibial tendon tear: MRI correlation. AJR 2009; 193: Saltzman CL, El-Khoury GY. The hindfoot alignment view. Foot Ankle Int 1995; 16: Johnson JE, Lamdan R, Granberry WF, Harris GF, Carrera GF. Hindfoot coronal alignment: a modified radiographic method. Foot Ankle Int 1999; 20: AJR:197, September 2011

A new radiographic view of the hindfoot

Ikoma et al. Journal of Foot and Ankle Research 2013, 6:48 JOURNAL OF FOOT AND ANKLE RESEARCH RESEARCH Open Access A new radiographic view of the hindfoot Kazuya Ikoma 1*, Masahiko Noguchi 2, Koji Nagasawa