## 2 Materials and Methods  
One hundred fifty patients with a good radiological outcome after implantation of a THA were selected: 50 after implantation of a THA using a conventional femoral stem (CTHA group) and 100 after implantation of a THA using a short stem with primary metaphyseal fixation (STHA group). A good radiological outcome was judged on the postoperative X-rays by three senior surgeons according to the following criteria: under- or oversizing, early subsidence, and intra- or postoperative fractures.  
Undersizing was defined as either a too low fit of the implant that could have been avoided by choosing a bigger size or by the presence of a visible distance between the  
Figure 1: Lateral view of the METHA short stem total hip arthroplasty (STHA), showing the striven positioning parallel to the femoral neck and thus reconstructing the physiological ante torsion of the femoral neck.  
cortical bone and the implant in a region of bone that is crucial for the anchorage of the implant (calcar region and lateral cortex for CTHA and cortical ring of the resected femoral neck basis as well as lateral cortex for STHA). Oversizing was defined as a too high fit of the implant that could have been avoided by choosing a smaller size, indicated by the shoulder of the implant exceeding the highest point of the greater trochanter for CTHA or the shoulder of the implant exceeding the cortical ring of the femoral neck basis by more than 10 mm for STHA. Early subsidence after full load-bearing, which was allowed for all patients, was defined as an unambiguous (>2 mm) migration of the implant within the surrounding bone in a follow-up X-ray examination 3 months after surgery. The occurrence of intra- or postoperative fractures were retrieved from the surgery reports and patients' charts.  
For these patients, who were included consecutively and underwent THA between 2010 and 2011, preoperative and postoperative digital X-rays in pairs were selected from the database of the department of orthopedic surgery of a university hospital. All these patients underwent standardized X-ray examinations, including an a.p. pelvic overview and an lateral view (Lauenstein) of the proximal femur. These X-rays existed for the preoperative and postoperative state and with a follow-up of at least 3 months. All X-rays were taken with a standardized film-focus-distance of 100 cm. An external calibration marker of 25 mm diameter was positioned between the legs of each patient for the preoperative pelvic overview.  
Digital templating was performed by three senior surgeons experienced in THA. When conducting digital templating, the examiners were only able to see the preoperative, but not the postoperative X-rays.  
The software used for digital templating was OrthoView (OrthoView Orthopaedic Digital Planning Version 6.3, Meridian Technique Limited, Southampton, UK). For this software tool, templates for the conventional BICONTACT stem (CTHA) and the METHA short stem (STHA; both Aesculap B. Braun, Tuttlingen, Germany) were available (Figures 2 and 3).  
Figure 2: Digital templating of the BICONTACT stem (CTHA) in an anteroposterior (**a**) and lateral (**b**) view with the corresponding postoperative radiographs (**c**,**d**).  
One hundred patients received a cementless METHA prosthesis with a caput-collum-diaphysis (CCD) angle of 130\({}^{\circ}\), 135\({}^{\circ}\), or 140\({}^{\circ}\). All these stems are available in a size range of 0 to 7. The median stem size of the implanted METHA short stems was 3.  
Fifty patients received a cementless conventional BICONTACT stem. These stems are monobloc-types with different offset variations: S for standard, H for High offset, and SD for dysplastic femurs. In our study, we templated and implanted only S and H types. BICONTACT stems are available in stem sizes 10-21. From the 50 truly implanted hip implants, the median stem size was 14.