Technique and Normative Values for the Medial Column

Objective Assessment of Foot Radiographs: Technique and Normative Values for the Medial Column Glenn Reinhart, MD1; Jill Friebele, MD2; F. Kamalei Cruz3; Sean Tabaie, MD1; Jon R. Davids, MD1; Vedant Kulkarni, MD1; Anita Bagley MPH, PhD1; Nina Q. Cung, BA, BS1 1 Shriners Hospitals for Children, Northern California; 2 Valley Children’s Hospital; 3 UC Davis School of Medicine

Introduction Weight-bearing foot radiographs are critical to the understanding of foot deformity in children with cerebral palsy (CP) and strongly influence the clinical decision-making process. A commonly used biomechanical model divides the foot into medial and lateral columns and three segments (hindfoot, midfoot, forefoot)1. Different patterns of deformity of the medial column are seen in children with cerebral palsy, as seen below: NORMAL

Participants and Methods Participants were identified from a database of ambulatory children with cerebral palsy who were seen between January 1st, 2012 and October 1st, 2014. The unaffected feet of children with hemiplegic CP were used for measurement. Sample consisted of 20 feet that were considered normal by physical exam: Right Foot (n = 13 Left Foot (n = 7) Male = 9, Female = 11 Mean age of children = 11.3 years (range: 7-17 years)

FLAT FOOT

Previous work has validated quantitative radiographic measures of the overall alignment of the medial column. However, techniques for an objective assessment of the sub-segmental components of medial column alignment of the foot have not been described. The goals of the current study are to develop and validate additional radiographic measures of medial column foot alignment and to establish normative values for these new measures.

M’

1) 2) 3) 4) 5) 6) 7)

AP naviculo-cuneiform AP Cuneiform-1st metatarsal AP 1st metatarsal-proximal phalanx Lateral talo-navicular Lateral naviculo-cuneiform Lateral cuneiform-1st metatarsal Talar pitch

Skeletal Segments/Sub-segment Analysis. Standardized techniques were used to describe the longitudinal axis of each bone. Measurements were performed on all feet by an experienced orthopaedic surgeon and medical student. Normative values. Values for medial column alignment angles were calculated from feet of 20 children, using mean and standard deviations (Table 1).

Measurement AP Talo — 1st MT AP Talo — Nav AP Nav — Cun AP Cun — 1st MT AP 1st MT — PP Lat Talo — 1st MT Lat Talo — Nav Lat Nav — Cun Lat Cun — 1st MT Lat Talar Pitch

Mean (+/- SD) 11◦ 23◦ 4◦ 7◦ -9◦ -8◦ -1◦ -2◦ -5◦ 28◦

(+/- 6◦) (+/- 7◦) (+/- 5◦) (+/- 5◦) (+/- 5◦) (+/- 8◦) (+/- 6◦) (+/- 4◦) (+/- 6◦) (+/- 5◦)

Range 3◦ to 23◦ 8◦ to 36◦ -7◦ to 14◦ 0◦ to 15◦ -18◦ to -1◦ -28◦ to 7◦ -12◦ to 10◦ -9◦ to 7◦ -15◦ to 6◦ 19◦ to 35◦

Table 1. Normative values, standard deviations, and ranges for all ten sub-segmental measurements. (MT = metatarsal, Nav = navicular, PP = proximal phalanx, Cun = cuneiform). On AP, (-) denotes valgus. On Lateral, (-) denotes planus.

C

New Measures

Intra- and inter-observer reliability. Reliability was measured by intra-class correlation coefficients (ICC). Establishing methods to precisely characterize this breakdown would be valuable in the assessment and management of foot deformity in this population.

P’

Standing Anterior-Posterior (AP) and Lateral radiographs were analyzed and three previously validated measures along with seven new measures of medial column segmental alignment were calculated. 1) AP talo-1st metatarsal 2) AP talo-navicular 3) Lateral talo-1st metatarsal

Participants

P

M

Validated Measures

SKEW FOOT

Results Cont.

N T Figure 1. Standing AP radiograph of normal foot with measurement techniques. (T = talus, N = navicular, C = cuneiform, M = 1st metatarsal, P = proximal phalanx).

T

T’ N C M

M’

Figure 2. Standing Lateral radiograph of normal foot with measurement techniques. (T = talus, N = navicular, C = cuneiform, M = 1st metatarsal, P = proximal phalanx).

Results

Discussion The technique for an objective radiographic assessment of the sub-segmental components of medial column alignment of the foot showed good reliability for some, but not all of the measurements. On inter-observer comparison, only three of the seven newly applied sub-segmental measurements were statistically reliable, exhibiting poor to moderate inter-rater reliability. However, when the techniques were performed by an individual examiner, the results were consistent and reliable. The radiographic measures developed in this study will help clinicians better understand medial column alignment in a more detailed quantitative and qualitative manner. Future work will seek to develop additional methods of quantitative assessment of the sub-segments of the medial column, particularly in the midfoot.

Intra-observer reliability, based upon repeated measurements of feet from 10 children by a surgeon, was good (ICC 0.78 to 0.99) across all radiographic measures. However, inter-observer reliability was variable when measurements completed by the surgeon and medical student were compared. Inter-rater reliability was good (ICC 0.78 to 0.89), for the previously validated measures (AP talo-1st metatarsal, AP talo-navicular, Lateral talo-1st metatarsal) and three new measures (AP cuneiform-1st metatarsal, AP 1st metatarsal-proximal phalanx, Talar pitch), yet poor to moderate (ICC -0.089 to 0.697) for the rest of the measures (Lateral naviculo-cuneiform, AP naviculo-cuneiform, Lateral cuneiform-1st metatarsal, Lateral talo-navicular).

References 1) Davids, J.R., Gibson, T.W., Pugh, L.I. Quantitative segmental analysis of weight-bearing radiographs of the foot and ankle for children: normal alignment. J Pediatr Orthop. 2005;25:769–776. 2) Davids, J.R. The Foot and Ankle in Cerebral Palsy. gait profile score and movement analysis profile. Orthopaedic Clinics of North America. 2010;41:579-593.