Mid-flexion stability after total knee arthroplasty (TKA) is dependent, in large part, on implant design. Design variables include retention or sacrifice of the posterior cruciate ligament, conformity of the polyethylene tibial surface, and radius of curvature of the femoral component. In this study, we attempted to isolate the impact of femoral component design by comparing a single-radius design (SR) to a J-Curve design (JC). We selected cruciate-retaining implants to eliminate the effect of a cam-and-post mechanism. Mid-flexion performance these two designs were compared using the Lower-Quarter Y-Balance Test (YBT-LQ), as well as patient reported outcomes and measures of physical performance. The YBT-LQ is a simple functional test of unilateral lower extremity strength and balance. Reach of the contralateral limb is measured in three different directions (Figures 1–3). Our hypothesis was that the SR design would provide superior mid-flexion stability, and therefore, a greater reach distance in the YBT-LQ when compared to the JC group. Patients undergoing primary, unilateral TKA were prospectively enrolled and block randomized to receive either the SR (n=30) or JC (n=30) implant. All surgeries were performed by one surgeon using a gap-balancing technique with a cruciate-retaining implant design. Patients completed outcome measures (KOOS, KSS, UCLA Activity), performed the YBT-LQ, and completed physical performance measures (walking speed, timed up-and-go, sit-to-stand) before surgery and 1 year postoperatively. A series of 2×2 repeated measures ANOVAS (Implant group x Time) were completed.Introduction
Methods
Acetabular cup malpositioning during total hip arthroplasty (THA) is known to lead to impingement, instability, wear-induced osteolysis, and increased rates of revision surgery. The purpose of this study was to independently evaluate the accuracy of acetabular cup orientation using a novel mechanical navigation device. Postoperative acetabular cup orientation was reviewed in 47 primary THAs using the HipSextant mechanical navigation device. Angles were measured with a validated two-dimensional/three-dimensional matching application. An outlier was defined as +/− 10 degrees outside of the preoperative plan for inclination and anteversion.Background
Methods
Cup malposition leads to increased incidences of dislocation, impingement, wear, and revision. The HipSextant navigation system is a smart mechanical navigation device designed to indicate correct cup orientation at surgery. The current study assesses the effect of deliberately mis-docking the device on clinical accuracy. Ten patients (5 men and 5 women) presenting for total hip arthroplasty were assessed. Planning for the HipSextant Navigation System (Surgical Planning Associates, Inc., Boston, MA) was performed as usual. This is done by first creating a 3D surface model from CT imaging, establishing an Anterior Pelvic Plane coordinate system, and then creating a patient-specific HipSextant coordinate system. This coordinate system is defined by three points. The first point, called the basepoint, is located just behind the posterior wall of the acetabulum a fixed distance above the infracotyloid notch. The second point is located on the lateral aspect of the anterior superior iliac spine. The third point is located on the surface of the ilium and equally distant from the other two points. These three points define a patient-specific coordinate system that is known relative to the APP. Clinically, the instrument is then docked according to the plan and two protractors on the top of the instrument allow a direction indicator to point in the direction of desired cup orientation. For each of the hips, after the HipSextant plan was created (Figure 1), two additional plans were created: one where the basepoint was docked 5 mm closer to and one 5 mm further from the infracotyloind notch. The effect of the deliberate mis-docking was measured in degrees of operative anteversion and operative inclination.Introduction:
Methods:
