Introduction

Proper femoral stem and acetabular implant orientation is critical to the initial and long-term success of THA. Post-operative determination of cup and stem anteversion is important in cases of hip instability and planning isolated component revisions. At ISTA 2010 Dubai, we introduced a novel, simple stem modification that can be added to any stem design to help assess stem, and possibly cup anteversion with plain post-operative radiographs throughout the lifespan of the implant. [Figure 1] As the stem is rotated, the visible hole pattern changes. [Figure 2] This study was performed to further validate the accuracy and potential usefulness of this design.

Introduction

Proper total knee arthroplasty balancing relies on accurate component positioning and alignment as well as soft tissue tensioning. Technology for cutting guide alignment has evolved from the “free hand” technique in the 1970's, to traditional intra/extra medullary rods in the 1980's and 1990's, to computer navigated surgery in the 2000's, and finally to patient specific custom cutting blocks in the 2010's. The latest technique is a modification to conventional computer navigation assisted surgery using Brainlab's Dash™ TKA/THA software platform that runs as an application on an Apple IPod held by the surgeon in a sterile pouch in the operative field. The handheld IPod touch screen allows the surgeon to control all aspects of the navigation interface without needing the assistance of an observer to manually run the software. In addition, the surgeon is able to always focus on the operative field while ‘navigating’ without looking up at a remote image monitor. This study represents a prospective analysis of the first 30 U.S. TKA cases performed using the newly commercially released Dash™ software using an IPod during surgery.

The use of tapered titanium femoral stems has gained in popularity for primary total hip arthroplasty. One of the basic stem designs is a fully grit blast square tapered stem with distal fixation (Zweymuller-type). Another stem design (Muller-type), a proximally porous coated flat wedge stem with proximal fixation is associated with a low but significant perioperative femoral fracture risk. Both of these implant types are inserted with a broach-only technique. We theorize that the Zweymuller-type implant can be inserted safely with pneumatic broaching with a very low fracture risk even when broached by rotating residents with no prior experience.

We prospectively reviewed 300 consecutive hip arthroplasty cases using Zweymuller-type stems from eight different manufacturers implanted using the Woodpecker TM pneumatic broaching system. The series included both THA and hemiarthroplasty cases with a wide range of cortical/canal indexes. Patient age ranged from 14 to 98 (avg. 68). Half of the hip stems were inserted through a posterolateral modified Kocher-Gibson approach, and half through an anterolateral Hardinge approach. Approximately 25 rotating residents who were initially unfamiliar with this broaching technique and stem implant type performed the majority of the procedures. We routinely obtained an intra-operative AP pelvis x-ray to confirm trial implant size, alignment, and adjust the leg lengths.

The overall technique/implant-related perioperative complication rate was 2% (6/300). These included intra-operative femoral fractures(2), post-operative femoral fractures (1), dislocations(3), and deep infections(2). There were no cases of nerve palsy or leg length inequality > 1cm. Rates of post-op blood transfusions and venous thromboembolism were not reviewed for the purposes of this study. Only one of the complications (one deep infection) required exchange of the original femoral component. There was no significant difference in complication rates between type of surgical approach, brand of square tapered stem manufacturer, or experience of the operating surgeon.

We conclude that hip arthroplasty using pneumatically broached, square tapered, cementless distal fixation (Zweymuller-type) hip stems has a low learning curve and can be implanted safely even in very osteoporotic bone. This technique/implant gives the surgeon control of stem anteversion for stability and leg length inequality correction. The incidence of certain perioperative complications can be reduced by using Zweymuller-type stems using pneumatic broaching regardless of approach, implant manufacturer, or surgeon experience. These patients will continue to be followed clinically for implant survivorship.