The effect of foot rotation on measuring ankle alignment using simulated radiographs: a safe zone for pre-operative planning

Translation of 3D Anatomy to 2D Radiographic Angle Measurements in the Ankle Joint: Validity and Reliability

Background:

The objective consisted of 2 elements, primarily to define 2 bone geometry variations of the ankle that may be of prognostic value on ankle instability and secondly to translate these bone variations from a 3D model to a simple 2D radiographic measurement for clinical use.

Methods:

The 3D tibial and talar shape differences derived from earlier studies were translated to two 2D radiographic parameters: the medial malleolar height angle (MMHA) and talar convexity angle (TCA) respectively to ensure clinical use. To assess validity, the MMHA and TCA were measured on 3D polygons derived from lower leg computed tomographic (CT) scans and 2D digitally reconstructed radiographs (DRRs) of these polygons. To assess reliability, the MMHA and TCA were measured on standard radiographs by 2 observers calculating the intraclass correlation coefficient (ICC).

Results:

The 3D angle measurements on the polygons showed substantial to excellent agreement with the 2D measurements on DRR for both the MMHA (ICC 0.84-0.93) and TCA (ICC 0.88-0.96). The interobserver reliability was moderate with an ICC of 0.58 and an ICC of 0.64 for both the MMHA and TCA, respectively. The intraobserver reliability was excellent with an ICC of 0.96 and 0.97 for the MMHA and the TCA, respectively.

Conclusion:

Two newly defined radiographic parameters (MMHA and TCA) are valid and can be assessed with excellent intraobserver reliability on standard radiographs. The interobserver reliability was moderate and indicates training is required to ensure uniformity in measurement technique. The current method may be used to translate more variations in bone shape prior to implementation in clinical practice.

Level of Evidence:

Level III, cohort study.

Lower leg symmetry: a Q3D-CT analysis

PURPOSE

In fracture and realignment surgery, the contralateral unaffected side is often used as a model or template for the injured bone even though clinically valuable quantitative data of bilateral symmetry are often unavailable. Therefore, the objective of the present study was to quantify and present the bilateral symmetry of the tibia and fibula.

METHODS

Twenty bilateral lower-leg CT scans were acquired in healthy volunteers. The left and right tibia and fibula were segmented resulting in three-dimensional polygons for geometrical analyses (volume, surface and length). The distal and proximal segment of the right tibia of each individual was subsequently matched to the left tibia to quantify alignment differences (translation and rotation). Bone symmetry on group level was assessed using the Student's t test and intra-individual differences were assessed using mixed-models analyses.

RESULTS

Intra-individuals differences were found for tibia volume (5.2 ± 3.3 cm³), tibia surface (5.2 ± 3.3 cm²), translations in the lateral (X-axis; 9.3 ± 8.9 mm) and anterior direction (Y-axis; 7.1 ± 7.0 mm), for tibia length (translation along Z-axis: 3.1 ± 2.4 mm), varus/valgus (φ_z: 1.7^o ± 1.4°), and endotorsion/exotorsion (φ_z: 4.0^o ± 2.7°).

CONCLUSION

This study shows intra-individual tibia asymmetry in both geometric and alignment parameters of which the surgeon needs to be aware in pre-operative planning. The high correlation between tibia and fibula length allows the ipsilateral fibula to aid in estimating the original tibia length post-injury. Future studies need to establish whether the found asymmetry is clinically relevant when the contralateral side is used as reference in corrective surgery.

LEVEL OF EVIDENCE

III cohort study.

Tibial torsion correlates with talar morphology

BACKGROUND

There is limited literature on axial rotation of the ankle or variations in anatomy of the talus. We aim to evaluate the rotational profile of the distal tibia and its relationship to talus morphology, radiographic foot-type, and tibiotalar tilt in arthritic ankles.

METHODS

Preoperative imaging was reviewed in 173 consecutive patients with ankle arthritis. CT measurements were used to calculate tibial torsion and the talar neck-body angle (TNBA). Tibiotalar tilt and foot-type were measured on weightbearing plain radiographs.

RESULTS

Measurements indicated mean external tibial torsion of 29.2±9.1˚ and TNBA of 35.2±7.5˚ medial. Tibiotalar tilt ranged from 48˚ varus to 23.5˚ valgus. A moderate association between increasing external tibial torsion and decreasing TNBA was found (ρ=-0.576, p<.0001). Weak relationships were found between external tibial torsion and varus tibiotalar tilt (ρ=-0.239, p=.014) and plantarflexion of the talo-first metatarsal angle (ρ=-0.218, p<.025).

CONCLUSION

We observed a statistically significant correlation between tibial torsion and morphology of the talus, tibiotalar tilt, and first ray plantarflexion. This previously unreported association may provide information regarding the development of foot and ankle deformity and pathology.

LEVEL OF EVIDENCE

Level III.

Assessment of Hindfoot Alignment Comparing Weightbearing Radiography to Weightbearing Computed Tomography

BACKGROUND

Hindfoot alignment view (HAV) radiographs are widely utilized for 2-dimensional (2D) radiographic assessment of hindfoot alignment; however, the development of weightbearing computed tomography (WBCT) may provide more accurate methods of quantifying 3-dimensional (3D) hindfoot alignment. The aim of this study was to compare the 2D calcaneal moment arm measurements on HAV radiographs with WBCT.

METHODS

This retrospective cohort study included 375 consecutive patients with both HAV radiographs and WBCT imaging. Measurement of the 2D hindfoot alignment moment arm was compared between both imaging modalities. The potential confounding influence of valgus/varus/neutral alignment, presence of hardware, and motion artifact were further analyzed.

RESULTS

The intraclass correlation coefficients (ICCs) of interobserver and intraobserver reliability for measurements with both imaging modalities were excellent. Both modalities were highly correlated (Spearman coefficient, 0.930; P < .001). HAV radiographs exhibited a mean calcaneal moment arm difference of 3.9 mm in the varus direction compared with WBCT (95% CI, -4.9 to 12.8). The difference of hindfoot alignment between both modalities was comparable in subgroups with neutral/valgus/varus alignment, presence of hardware, and motion artifact.

CONCLUSION

Both HAV radiographs and WBCT are highly reliable and highly correlated imaging methods for assessing hindfoot alignment. Measurements were not influenced by severe malalignment, the presence of hardware, or motion artifact on WBCT. On average, HAV radiographs overestimated 3.9 mm of varus alignment as compared with WBCT.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Imaging Techniques for Assessment of Dynamically Unstable Sports Related Foot and Ankle Injuries

Foot and ankle instability can be seen both in acute and chronic settings, and isolating the diagnosis can be difficult. Imaging can contribute to the clinical presentation not only by identifying abnormal morphology of various supporting soft tissue structures but also by providing referring clinicians with a sense of how functionally incompetent those structures are by utilizing weight-bearing images and with comparison to the contralateral side. Loading the affected joint and visualizing changes in alignment provide clinicians with information regarding the severity of the abnormality and, therefore, how it should be managed.