Same same but different: Introduction of a classification system in calcar-guided short-stem total hip arthroplasty.

Background: The concept of calcar-guided short-stem THA (ssTHA) has largely emerged over the last decade, especially in Europe, and today modern calcar-guided short stems are among the most successful primary femoral implants in terms of complications and revision rates as indicated by multiple registry data. The philosophy originally comprised an individualised reconstruction of the hip anatomy by following the calcar of the femoral neck providing bone- and soft-tissue-sparing characteristics. However, as the stem design allows either metaphyseal fixation alone or additional diaphyseal anchoring, depending on the stem alignment and indication, distinct knowledge is required regarding the implantation technique, the broad variation of positioning and fixation and its potential clinical consequences.

Aim: To report on and highlight the characteristics of different ways of performing calcar-guided ssTHA as well as to introduce a classification in order to systematically account for the variety of strategies and the respective implications on the type of fixation.

Surgical technique: Already when templating preoperatively, surgeons need to weigh up the different fixation types taking into account a number of patient-related factors. Intraoperatively, by individually controlling the level of osteotomy, the intended type of anchorage can be implemented. Intraoperative radiography to confirm the result, is mandatory.

Results: Despite numerous options of stem alignment, depending on the patient's anatomy, the bone quality or the indication for operation, a total of 4 categories were identified to characterise different fixation strategies in calcar-guided ssTHA.

Conclusions: The classification system should be used for the preoperative determination of the intended type of anchorage. Whenever a short-stem philosophy with metaphyseal fixation (Type I (M)) is possible, it should be pursued.