ACCURACY OF PREOPERATIVE TEMPLATING IN HIP REPLACEMENT

Abstract

Restoration of hip biomechanics is an important determinant of outcome in hip replacement. Pre-operative templating is considered important in preoperative planning, and this trend is likely to develop further to satisfy consumer demand and to facilitate navigated surgery, particularly as digitisation of radiographs becomes established.

We aimed to establish how closely natural femoral offset could be reproduced using the manufacturers’ templates for 10 femoral stems in common use in the U.K.

The most frequently used femoral components from the U.K. national joint registry and uncemented) were identified, and the CPS-Plus stem was added, as this is in use in our unit. A series of 24 consecutive pre-operative radiographs from patients who had undergone unilateral total hip replacement for unilateral osteoarthritis of the hip were reviewed.

The non-operated on side of the pelvic radiographs was templated as described by Schmalzreid. 3 surgeons of variable experience (junior trainee, senior trainee, consultant) performed the assessment. The standard deviation of change in offset between the templated centre of rotation and the normal centre of rotation of the set of radiographs for each prosthesis was then calculated allowing a ranking.

The most accurate template was the CPS with a mean standard deviation of 1.92mm followed in rank order by: CPT 2.21mm, C Stem 2.42mm, Stanmore 3.02 mm Exeter 3.06 mm, ABG II 3.54mm, Charnley 3.54 mm, Corail 3.63 mm, Furlong HAC 4.2 mm and Furlong modular 4.86mm.

There is wide variation in the ability of the femoral templates to reproduce normal femoral anatomy in a series of standard pre-operative hip radiographs. The more modern cemented polished tapered stems with high modularity appear best able to reproduce femoral offset. Nevertheless, some older monoblock stems, despite poor templating characteristics, are known to be associated with acceptable clinical results. The coming years are likely to be witness to changes in patient expectations and radiograph storage. Implant design and digital templates will need to improve apace with these changes, to ensure accurate preoperative planning.