gms | German Medical Science

Objectives: The idea of a single mechanical tibiofemoral angle (MTFA) throughout the range of motion does not reflect the biomechanics of native or arthritic knee joints, or total knee arthroplasties (TKAs).The MTFA varies in different degrees of flexion and hence coronal knee alignment is best described through a graph showing a curve of the MTFA through the range of motion. The aim of this study was to investigate the association between coronal plane passive knee kinematic curve morphology and distal femoral and proximal tibial articular anatomy.

Methods: An articulated lower limb surgical education bone model consisting of hemipelvis, femur and tibia was used. Registration was completed with a computer navigation system. A medial opening wedge femoral and tibial osteotomy and a rotational femoral osteotomy were used to create 70 different mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA) and femoral torsion combinations across seven groups (Table 1 [Tab. 1]). For each combination, a MTFA was recorded. The curves were categorized into the morphotypes defined by Young et al. (Figure 1 [Fig. 1]). Continuous data was tested for normality with the D'Agostino and Pearson test. Statistical comparison of central tendencies was performed using the Kruskall-Wallis test with multiple comparisons using Dunn's multiple comparisons test.

Results: Five different curve morphotypes were identified, namely straight, drift, inverse drift, C-shape and inverse C-shape. The median mLDFA and femoral torsional angle differed significantly across curve types (p<0.0001) (Table 2 [Tab. 2]).

After adjustment for multiple comparisons there were significant differences in the mLDFA and in the femoral torsional angle between various pairs of curves. The median proximal tibial angle did not vary across curve types (p=0.0844).

Conclusion: Coronal plane kinematic knee curve morphology is determined by the distal femoral coronal and torsional anatomy. The coronal tibial anatomy influences the position of the curve relative to the zero line but not the curve morphology. Restoring the pre-arthritic kinematic curve in total knee arthroplasty (TKA) requires restoring the pre-arthritic mLDFA and femoral torsion, while producing a neutral straight curve requires adjusting the femoral rotation individually once the pre-arthritic kinematic curve and mLDFA are known. Consistently producing a neutral straight curve is not possible without the use of computer navigation.