The influence of the surgical process on implant loosening and periprosthetic fractures (PPF) as major complications in uncemented total hip arthroplasty (THA) have rarely been studied due to the difficult quantification. Meanwhile registry analyses have clearly shown a decrease in complications with increasing experience. The goal of this study was to determine the extent of variability in THA stem implantation between highly experienced surgeons with respect to implant-size, -position, press-fit, contact area, primary stability and the effect of using a powered impaction tool.

Primary hip stems were implanted in 16 cadaveric femur pairs by three experienced surgeons using manual and powered impaction. Quantitative CTs were taken before and after each process step and stem tilt, canal-fill-ratio, pressfit and contact area between bone and implant determined. 11 femur pairs were additionally tested for primary stability under cyclic loading conditions.

Higher variations in press-fit and contact area between the surgeons for manual impactions compared to powered were observed. Stem tilt and implant sizing varied between surgeons but not between impaction methods. Larger stems exhibited less micromotion compared to smaller stems.

Larger implants may increase PPF risk, while smaller implants reduce primary stability. The reduced variation for powered impactions indicates that appropriate measures may promote a more standardized process. The observed variations between the experienced surgeons may represent the acceptable range for this specific stem design. Variability in the implantation process warrants further investigations since certain deviations e.g. a stem tilt towards varus, might increase bone stresses and PPF risk.

INTRODUCTION

The restoration of the anatomical hip rotation center (HRC) has a major influence on the longevity of hip prostheses. Deviations from the HRC of the anatomical joint after total hip arthroplasty (THA) can lead to increased hip joint forces, early wear or loosening of the implant. The contact conditions of acetabular press-fit cups after implantation, including the degree of press-fit, the existence of a polar gap and cup orientation, may affect the HRC restoration, and therefore implant stability. The aim of this study was to determine the influence of acetabular press-fit, polar gap and cup orientation on HRC restoration during THA.

INTRODUCTION

Loosening is a major cause for revision in uncemented hip prostheses due to insufficient primary stability. Primary stability after surgery is achieved through press-fit in an undersized cavity. Cavity preparation is performed either by extraction (removing bone) or compaction (crushing bone) broaching. Densification of trabecular bone has been shown to enhance primary stability in human femora; however, the effect of clinically used compaction and extraction broaches on human bone with varying bone mineral density (BMD) has not yet been quantified. The purpose of this study was to determine the influence of the broach design and BMD on the level of densification at the bone-cavity interface, stem seating, the bone-implant contact area and the press-fit achieved.

Computer navigation in total knee arthroplasty (TKA) has proven to significantly reduce the number of outliers in prosthesis positioning and to improve mechanical leg alignment. Despite these advantages the acceptance of navigation technologies is still low among orthopaedic surgeons. The time required for navigation might be a reason for the low acceptance. The aim of the study was to test whether software and instrument improvements made in an established navigation system could lead to a significant navigation acquisition time reduction.

An improved and the current version of the TKA navigation software were used to perform surgery trials on a human cadaveric specimen by two experienced orthopaedic surgeons.

A significant effect of the “procedure” (navigation software version) on the navigation time (p< 0.001) was found, whereas the difference between surgeons was not significant (p= 0.2). There was no significant interaction between surgeon and navigation software version (p= 0.5). The improved version led to a significant navigation acquisition time reduction of 28%. Software and instrument improvements led to a statistically significant navigation acquisition time reduction. The achieved navigation acquisition time decrease was independent from surgeon.

Specific instrument and software improvements in established navigation systems may significantly decrease the surgery time segments where navigation takes place. However, the total navigation acquisition time is low in comparison to the total surgery time.

Introduction: There is an ongoing discussion about potential risks and benefits of minimally invasive approaches (MIS) in total joint replacement. The aim of this study was to evaluate, whether a higher incidence of malalignments could be observed after minimally invasive navigated TKA and wether the results in the early postoperative period were better compared to standard approaches.

Methods: A total of 50 patients were treated with a navigated (OrthoPilot 4.2) Columbus knee prosthesis (BBraun Aesculap, Germany). In 25 patients either a standard or a minimally invasive (mini-mid-vastus) approach was carried out. In both groups the same exclusion criteria for MIS were adopted. Initially during surgery (Nav1a) and finally after implantation of the original components (Nav1b) the mechanical leg axis, passive range of motion and stability were measured by navigation according to the common workflow of the system. After restarting the software the same parameters were evaluated once more in a second procedure (Nav2) by reacquisition of joint centers both kinematically and by anatomical landmark palpation with the original prosthesis already implanted. Nav2 was conducted independantly from the initial surgical procedure. To validate the intraoperative measurements additional pre- and postoperative long-leg-standing radiographs were made. During the the first 10 days postoperatively daily range of motion (ROM) and pain (VAS) were measured. Perioperative blood loss and complications were documented. Results were analyzed by student’s t-test.

Results: Both groups were comparable with regard to preoperative demografic, radiologic and intraoperative data (Nav1a). There were no significant differences between the groups concerning intraoperative measurements of mechanical leg axis, passive range of motion and stability by Nav1b and Nav2. Additionally no differences were found for the alignment in the postoperative radiographs. The length of the skin incisions were significantly shorter in the minimally invasive group. Postoperative ROM was significantly higher and pain was significantly less intensive in the MIS group. Blood loss and complication rates were comparable.

Discussion: If the exclusion criteria for MIS were accepted no differences regarding the quality of alignment, passive range of motion and ligament stability could be demonstrated between conventional and MIS navigated TKA. Patients with MIS navigated TKA performed superior in terms of early p.o. function and pain. From the authors point of view the technically demanding minimally invasive implantation of knee prostheses should be exclusively performed with support of navigation.

Introduction: There is an ongoing discussion about potential risks and benefits of minimally invasive approaches (MIS) in total joint replacement. The aim of this study was to evaluate, whether a higher incidence of misalignments could be observed after minimally invasive navigated TKA and whether the results in the early postoperative period were better compared to standard approaches.

Methods: A total of 50 patients were treated with a navigated (OrthoPilot 4.2) Columbus knee prosthesis (BBraun Aesculap, Tuttlingen, Germany). In 25 patients either a standard or a minimally invasive (mini-mid-vastus) approach was carried out. In both groups the same exclusion criteria for MIS were adopted. Initially during surgery (Nav1a) and finally after implantation of the original components (Nav1b) the mechanical leg axis, passive range of motion and stability were measured by navigation according the common workflow of the system. After restarting the software the same parameters were evaluated once more in a second procedure (Nav2) by reacquisition of joint centres both kinematically and by anatomical landmark palpation with the original prosthesis already implanted. Nav2 was conducted independently from the initial surgical procedure. To validate the intraoperative measurements additional pre- and postoperative long-leg-standing radiographs were made. During the first 10 days postoperatively daily range of motion (ROM) and pain (VAS) were measured. Perioperative blood loss and complications were documented. Results were analyzed by student’s t-test.

Results: Both groups were comparable with regards to preoperative demographic, radiological and intraoperative data (Nav1a). There were no significant differences between the groups concerning intraoperative measurements of mechanical leg axis, passive range of motion and stability by Nav1b and Nav2. Additionally no differences were found for the alignment in the postoperative radiographs. The length of the skin incision was significantly shorter in the minimally invasive group. Postoperative ROM was significantly higher and pain was significantly less intensive in the MIS group. Blood loss and complication rates were comparable.

Discussion: If the exclusion criteria for MIS were accepted no differences regarding the quality of alignment, passive range of motion and ligament stability could be demonstrated between conventional and MIS navigated TKA. Patients with MIS navigated TKA performed superior in terms of early postoperative function and pain. From the authors point of view the technically demanding minimally invasive implantation of the knee prosthesis should be exclusively performed with support of navigation.

The video shows the detailed surgical technique of minimally invasive navigated total knee arthroplasty. A Columbus (BBraun Aesculap, Tuttlingen, Germany) total knee prosthesis is implanted using the OrthoPilot navigated system and the specially designed small MIOS instruments (BBraun Aesculap, Tuttlingen, Germany). A mini-mid-vastus approach is carried out with an 8 cm skin incision.