INTRODUCTION

An accelerometer-based portable navigation system (KneeAlign2, OrthAlign Inc., Aliso Viejo, CA) is expected to improve mechanical axis and component alignment compared to conventional instrumentation in total knee arthroplasty (TKA). However, past reports have evaluated its accuracy using only radiographic measurements. The purpose of this study was to analyze the accuracy of the KneeAlign2 system with radiography and more detailed three-dimensional (3D) CT.

Introduction

Dysplastic hip has not only deficiency of acetabulum but also femoral deformity. Therefore, selection of stem is important in cementless THA for dysplasia. Especially using of short stem should be challenge for deformed femur. We studied clinical performance and radiological findings after THA with triple tapered short stem (Optimys hip) for dysplastic hip.

Introduction

Patient matched instrumentation (PMI) have been proposed the accuracy of bone cuts through custom cutting blocks and provide the proper alignment of total knee arthroplasty (TKA). On the other hand, there are some reports that the introduction of PMI for guiding bone cuts could increase the incidence of malalignment in primary TKA. Recent comparisons between patient-specific cutting guides and quantitative assessments of postoperative alignment have revealed the presence of outliers with respect to coronal alignment. The purpose of this study was to assess the implanted component alignment post-operatively between one type of MRI based PMI (Visionaire; Smith & Nephew, Inc, Memphis, Tenn) and conventional surgical instrumentation (CI) using radiographs and CT scan.

Introduction

Fixation patterns of cementless stem were known as proximal or distal part. Distal fixation was seen in fully porous coated stem and stress shielding of the proximal femur was indicative. These phenomena did not lower the clinical results, but technical difficulties were more and more in revision surgery because of infection or dislocation. There was lot of reports that alendronate was effective for treatment of osteoporosis by induction of apoptosis in osteoclasts. We can expect alendronate to modify the bone quality around the stem after cementless THA.

Background

Accuracy of implantation is a recognized prognostic factor for the long-term survival of TKA. The purpose of this study was to analyze the accuracy of component orientation and post-operative alignment of the leg following CT-based navigation-assisted TKA and to compare these parameters with those of a conventional surgical technique.

In total knee arthroplasty (TKA), rotational alignment of the femoral component is determined by the measured resection technique, in which anatomical landmarks serve as determinants, or by the gap balancing technique, in which the femoral component is positioned relative to the resected aspect of the tibia. The latter technique is considered logically more favorable for obtaining rectangular extension and flexion gaps. However, in patients with severe changes attributed to osteoarthritis and/or a severely limited range of motion, it is difficult to perform adequate posterior clearance (e.g. bone spur excision) before resecting the posterior femoral condyle, often causing unbalanced extension and flexion gaps after resection. Thus, the gap balancing technique is more technically demanding and requires higher skill. We employed a computed tomography (CT)-based navigation system to develop a simple and standardized surgical technique by performing two assessments: Assessment 1, we investigated the relationship between the position of the femoral component determined by the gap balancing technique and anatomical landmarks; and Assessment 2, we placed the femoral component at the position determined by the measured resection technique and within the acceptable gap-balanced range determined in Assessment 1. In Assessment 1, 18 knees with osteoarthritis were treated by posterior stabilized TKA for varus deformity. The extension-flexion balance after resection of the distal femoral condyle and the proximal tibia was within 3° in all cases. Posterior bone resection was performed parallel to the resected aspect of the tibia and at 90° of flexion under constant compression applied using a tensor. In other words, the rotational alignment of the femoral component was determined by the gap balancing technique, and its position relative to the posterior condylar axis (PCA) and clinical transepicondylar axis (CEA), which are landmarks in the measured resection technique, and the condylar twist angle (CTA; the angle between the CEA and PCA) were measured, and their relationships were quantitatively determined. The CTA, which was determined based on the preoperative CT data, was 4.7– 9.6° (mean, 7.05 ± 1.35°), while the aspect of the femoral resection was 3.0–8.3° externally rotated (mean, 5.6 ± 1.6°) to the PCA; a strong positive correlation was found between the rotational alignment of the femoral component and the CTA (p < 0.0001, R² = 0.871). The aspect of the femoral resection was 0.3–2.6° internally rotated (mean, 1.4 ± 0.6°) to the CEA, and no correlation with the CTA was apparent. In Assessment 2, 39 knees with an extension-flexion balance ≤3° were examined to determine the internal-external rotation balance. Based on the results of Assessment 1, we employed the measured resection technique and placed the femoral component by rotationally aligning the target, which was 1.4° internally rotated to the CEA. The final rotational alignment of the femoral component was 2.0 ± 0.6° internally rotated to the CEA; the internal-external rotation balance at 90° of flexion was good and more toward external rotation by 0.72 ± 1.61°. The results demonstrated that the measured resection technique enables placement of the femoral component within an acceptable range of rotational alignment.