The Accuracy of Cup Placement in Total Hip Arthroplasty (THA) Using an Augmented Reality-Based Navigation System.

Background AR HIP Navigation System® (AR-navi; Zimmer-Biomet, Warsaw, IN) is a portable navigation system employing augmented reality via a smartphone app, which was developed in Japan. We retrospectively analyzed the accuracy of cup placement in total hip arthroplasty (THA) using AR-navi, to investigate whether obesity is associated with an absolute value error in cup placement angle. Methods We retrospectively analyzed 45 hips in 43 patients who underwent THA using AR-navi (AR-navi group) and compared them with 45 hips in 45 patients who underwent THA using alignment rods (conventional group). Results The mean absolute error of cup placement (AR-navi group vs. conventional group) was found to be 2.60° (±2.11) in radiographic inclination (RI) for the AR-navi group and 4.61° (±3.28) for the conventional group, which indicates significant difference in the AR-navi group compared to that in the conventional group (p = 0.0036). The mean absolute error of radiographic anteversion (RA) was 3.57° (±3.36) for the AR-navi group and 3.87° (±2.97) for the conventional group (p = 0.4732). The mean absolute error of RI was 2.36° (±2.24) in the obese group and 3.16° (±2.03) in the nonobese group, and the mean absolute error of RA was 4.08° (±4.51) and 3.16° (±2.05) in the obese and nonobese groups, respectively. Conclusions Cup placement accuracy for THA using AR-navi was 2.60 ± 2.11° for RI and 3.87 ± 2.97° for RA. Compared to THA using the conventional method, the RI installation error was significantly improved with AR Navi. There was no significant difference in the mean absolute error of RI and RA among the obese and nonobese groups.

Joint instability in patients with borderline developmental dysplasia of the hip.

BACKGROUND: The treatment strategy for developmental dysplasia of the hip is determined based on the lateral center-edge angle. Nonetheless, an evaluation of joint instability may be important in determining the treatment strategy. This study classified the displacement patterns of the femoral head center during hip abduction. METHODS: Ten patients with borderline developmental dysplasia of the hip, 10 patients with developmental dysplasia of the hip, and 10 patients with normal hips were analyzed. Image matching was performed using X-ray images of hip abduction with a three-dimensional hip model. The displacement of the femoral head center and its trajectory length were measured. A cluster analysis was conducted to classify the displacement pattern of the femoral head center, and trajectory lengths were compared. FINDINGS: Displacement was classified into three patterns: medialization, hinge abduction, and centering. Patients with borderline developmental hip dysplasia exhibited all three patterns. Almost all patients with developmental dysplasia of the hip showed medialization and hinge abduction, whereas all normal patients had the centering type. The mean trajectory length indices for the medialization and hinge abduction types were significantly longer than those for the centering type (P = 0.01 and P = 0.016, respectively). INTERPRETATION: Borderline developmental dysplasia of the hip is a heterogeneous condition characterized by varying hip instability levels. Our findings suggest that uniform evaluation based on the lateral center-edge angle is inappropriate and that joint instability must be evaluated in each patient with borderline developmental dysplasia of the hip.

Patient-specific three-dimensional evaluation of interface micromotion in two different short stem designs in cementless total hip arthroplasty: a finite element analysis.

BACKGROUND: Evaluation of micromotion in various activities in daily life is essential to the assessment of the initial fixation of cementless short stems in total hip arthroplasty. This study sought to evaluate three-dimensionally the micromotion of two types of cementless short stems. METHODS: Two types of stems were used: the Fitmore stem with a rectangular cross-section (rectangular stem) and the octagonal-oval GTS stem with fins (finned stem). Finite element analysis was used to calculate the micromotion of two activities that place a heavy load on the stem (single-leg stance and stair climbing). Three values were measured: the magnitude of micromotion (mean and 95th percentile), the location of micromotion above the 95th percentile value, and the directions of the micromotion vector. RESULTS: 1. There was no significant difference in the magnitude of the micromotion between the rectangular stem and finned stem groups for single-leg stance or stair climbing. 2. In both groups, the micromotion was greatest at the proximal and distal ends. 3. The direction of the micromotion was similar in both groups; internal rotation occurred from the distal to the middle of the stem during stair climbing. CONCLUSIONS: The rectangular stem had comparable initial fixation to that of the finned stem. In both models, the micromotion was greater at the proximal and distal ends. The direction of the micromotion was not dependent on the stem shape but on the direction of the load on the artificial femoral head. These results will be important for stem selection and future stem development.

Successful reimplantation surgery after extraction of well-fixed cementless stems by femoral longitudinal split procedure.

BACKGROUND: Well-fixed cementless stems sometimes need to be extracted in patients with complications including periprosthetic infection, stem-neck breakage, or trunnionosis. The purpose of this study was to report the clinical outcome in patients undergoing reimplantation surgery after removal of a well-fixed porous-coated cementless stem by the femoral longitudinal split (FLS) procedure. METHODS: We conducted a retrospective study and radiographic review of 16 patients who had undergone reimplantation following the FLS procedure to remove a well-fixed stem due to periprosthetic infection, stem-neck breakage, or trunnionosis. The study group consisted of 2 men and 14 women with an average age of 68.4 years. Mean follow-up was 44.6 months. The Kaplan-Meier method was used to evaluate the longevity of the stem. RESULTS: The average operation time was 272 ± 63 minutes and intraoperative bleeding was 420 ± 170 mL. Although postoperative dislocation occurred in 5 hips and subsidence of the stem was found in 2 hips after surgery, no progressive subsidence was observed and the clinical JOA and JHEQ scores were both improved after reimplantation surgery. Reimplantation surgery with Zweymüller-type stems revealed evidence of osseointegration of the stem without femoral fracture. Kaplan-Meier survival analysis of stem revision for any reason as the end point revealed 70.0% survival at 9 years. CONCLUSIONS: In this study, we experienced some complications in patients with trunnionosis or periprosthetic infections. However, the FLS procedure is expected to confer successful clinical results without loosening of the reimplanted cementless stem, after safe extraction of well-fixed porous-coated cementless stems without fracture.