The accurate reconstruction of hip anatomy and
biomechanics is thought to be important in achieveing good clinical
outcomes following total hip arthroplasty (THA). To this end some
newer hip designs have introduced further modularity into the design
of the femoral component such that neckshaft angle and anteversion,
which can be adjusted intra-operatively. The clinical effect of
this increased modularity is unknown. We have investigated the changes
in these anatomical parameters following conventional THA with a
prosthesis of predetermined neck–shaft angle and assessed the effect
of changes in the hip anatomy on clinical outcomes.
In total, 44 patients (mean age 65.3 years (standard deviation
(sd) 7); 17 male/27 female; mean body mass index 26.9 (kg/m²)
(sd 3.1)) underwent a pre- and post-operative three-dimensional
CT scanning of the hip. The pre- and post-operative neck–shaft angle,
offset, hip centre of rotation, femoral anteversion, and stem alignment
were measured. Additionally, a functional assessment and pain score
were evaluated before surgery and at one year post-operatively and
related to the post-operative anatomical changes.
The mean pre-operative neck–shaft angle was significantly increased
by 2.8° from 128° (sd 6.2; 119° to 147°) to 131° (sd 2.1;
127° to 136°) (p = 0.009). The mean pre-operative anteversion was
24.9° (sd 8; 7.9 to 39.1) and reduced to 7.4° (sd 7.3;
-11.6° to 25.9°) post-operatively (p <
0.001). The post-operative
changes had no influence on function and pain. Using a standard
uncemented femoral component, high pre- and post-operative variability
of femoral anteversion and neck–shaft angles was found with a significant
decrease of the post-operative anteversion and slight increase of
the neck–shaft angles, but without any impact on clinical outcome.
Cite this article: Bone Joint J 2015;97-B:1615–22.
