PRELIMINARY STUDY OF THE GLOBAL MORPHOTYPE OF THE LOWER LIMBS AND PELVIS USING THE EOS LOW DOSE IMAGING TECHNOLOGY

Introduction

The gold standard for knee surgery is the restoration of the so-called «neutral mechanical alignment ». Recent literature as pointed out the patients with «constitutional varus »; in these cases, restoring neutral alignment could be abnormal and even undesirable. The same situation can be observed in patients with «constitutional valgus alignment ». To date, these outliers cases have only been explored focusing on the lower limb; the influence of the pelvic morphotype has not been studied. Intuitively, the pelvic width could be a significant factor. The EOS low dose imaging technique provides full body standing X-rays to evaluate the global anatomy of the patient. This work explores the influence of the pelvic parameters on the frontal knee alignment.

Material and methods

– We included 170 patients (340 lower extremities). 2 operators performed measurements once per patient on AP X-rays.

• The classical anatomical parameters were:

  1. –

     Femoral mechanical angle (FMA)

  2. –

     Tibial mechanical angle (TMA)

  3. –

     Hip knee shaft angle (HKS)

  4. –

     Hip knee ankle angle (HKA)

  5. –

     Femoral and tibial lengths

• The morphotype was evaluated by:

  1. –

     the distances between the center of two femoral heads (FHD), between knees (KD) and between ankles (AD)

  2. –

     the medial neck-shaft angle (MNSA)

  3. –

     the femoral offset

• The horizontal distance between the limb mechanical axis (line passing from center of the femoral head to the center of the ankle) and the center of the knee was called the intrinsic mechanical axis deviation (IMAD) (fig 1). The horizontal distance between the pelvic mechanical axis (line from the center of the sacral plate to the center of the ankle) and the center of the knee was called the global mechanical axis deviation (GMAD) (fig 2).

Inter-Operator Reliability was calculated with Intra-class Correlation Coefficient (ICC) and Inter-Reader Agreement was assessed with Bland-Altman test.

A relationship between IMAD and GMAD to the other parameters was assessed using Pearson's correlation coefficient.

Results

• Inter-Operator Reliability was high for femoral offset, TMA and MSNA (ICC > 0,88) and very high for the other parameters (ICC > 0,93). These values are given in table 1 and all the 2D parameters are given in the table 2.

• IMAD was significantly correlated with HKA (r = 0,99), FMA (r = −0,58), TMA (r = −0,61) and KD (r = 0,72).

• GMAD was significantly correlated with HKA (r = 0,94), FMA (r = −0,53), TMA (r = −0,60) and KD (r = 0,67).

• Two groups were identified according to pelvic width (FHD):

  • Group 1 (standard patients): Pelvic width < 18 cm (164 lower extremities)

  • Group 2 (wide pelvis): Pelvic width ≥ 18 cm (176 lower extremities)

For standard patients the FHD is a significant parameter, whereas the proximal femoral anatomy (offset and MNSA) are more relevant for wide pelvis.

Conclusion

Accurate analysis of the morphotype of the lower limbs is essential for planning femoral or tibial osteotomy and knee prostheses. Taking into account pelvic morphotype can provide additional informations for the axes restoration and the detection of outliers patients.