Distance from the magnification device contributes to differences in lower leg length measured in patients with TSF correction

Abstract

Introduction In absence of deformity or injury of the contralateral leg, the contralateral leg length is used to plan limb lengthening. Length variability on long-leg weight-bearing radiographs (LLR) can lead to inaccurate deformity correction. The aim of the study was to (1) examine the variability of the measured limb length on LLR and (2) to examine the influence of the position of the magnification device. Materials and methods The limb lengths of 38 patients during deformity correction with a taylor-spatial-frame were measured retrospectively on 7.3 ± 2.6 (4–13) LLR per patient. The measured length of the untreated limb between LLR were used to determine length variability between LLR in each patient. To answer the secondary aim, we took LLR from a 90 cm validation distance. A magnification device was placed in different positions: at the middle of the 90 cm distance (z-position), 5 cm anterior and 5 cm posterior from the z-position, at the bottom and top of the validation distance as well as 5 cm medial and 15 cm lateral from the z-position. Results The measured length variability ranged within a patient from 10 to 50 mm. 76% of patients had a measured limb length difference of ≥ 2 cm between taken LLR. Compared to length measurement of the 90 cm test object with the magnification device in the z-position (90.1 cm), positioning the device 5 cm anterior led to smaller (88.6 cm) and 5 cm posterior led to larger measurements (91.7 cm). The measured length with the magnification device at the bottom, top, medial or lateral (90.4; 89.9; 90.2; 89.8 cm) to the object differed not relevantly. Conclusions High variability of limb length between different LLR within one patient was observed. This can result from different positions of the magnification device in the sagittal plane. These small changes in positioning the device should be avoided to achieve accurate deformity correction and bone lengthening. This should be considered for all length and size measurements on radiographs.

Accuracy, inter- and intrarater reliability, and user-experience of high tibial osteotomy angle measurements for preoperative planning: manual planning PACS versus semi-automatic software programs

“…For optimal osteotomy planning using long‐leg full weight‐bearing radiographs, guidelines for system setup and an easy‐to‐implement protocol for patient positioning should be developed to minimize measurement errors during acquisition of radiographs [2, 3, 5, 22, 33]. Additionally, orthopaedic surgeons have to bear in mind that the alignment of adjacent joints may be unintentionally altered as a result of a planned osteotomy which could lead to undesirable effects, such as secondary OA of the ankle [1, 12].…”

“…Inaccurate preoperative osteotomy planning can be caused by known insufficiencies including inconsistent patient positioning and system setup during radiograph acquisition [2, 3, 5, 22, 33], and lack of awareness of unintentional alteration of adjacent joints [1, 12]. Other than the aforementioned insufficiencies, the accuracy of the preoperative angle measurements and planning of the correction angle utilising software programs is important to take into account.…”

Influence of axial limb rotation on radiographic lower limb alignment: a systematic review

“…Additionally, due to the large heterogeneity, a quality assessment of the different studies was not performed. Moreover, we are aware that, besides malrotation, other factors might alter alignment measurements, such as weight-bearing conditions [23,46,61] and magnification errors [3]. One general drawback of LLR is that the hindfoot is not included.…”

Assessment of comparative parameters of leg length discrepancy in children using temporary epiphysiodesis with 8-plates

“…Во-первых, значительная вариабельность результатов у детей разного роста (и, соответственно, с разной конституциональной длиной нижних конечностей), во-вторых, невозможность объективного и безоговорочного использования метода при эпифизеодезе удлиненной конечности. Кроме того, нельзя не принимать во внимание и технические аспекты метрических расчетов, обусловленные погрешностью измерений по рентгенограммам [19]. Применение относительных параметров разновеликости позволяет избежать вышеупомянутых сложностей и может способствовать повышению точности измерений при прогнозировании и оценке результатов лечения.…”