Although total hip arthroplasty (THA) has been one of the most successful, reliable and common prosthetic techniques since the introduction of cemented low-friction arthroplasty by Charnley in the early 1960s, aseptic loosening due to stem-cement and cement-bone interface failures as well as cement fractures have been known to occur. To overcome this loosening, the stem should be mechanically retentive and stable for long term repetitive loading. Migration studies have shown that all stems migrate within their cement mantle, sometimes leading to the stem being debonded from the cement [1]. If we adopt the hypothesis that the stems debond from the cement mantle, the stem surface should be polished. For the polished stem, the concept of a double taper design, which is tapered in the anteroposterior (AP) and mediolateral (ML) planes, and a triple-tapered design, which has trapezoidal cross-section with the double tapered, have been popularized. Both concepts performed equally well clinically [2]. In this study, we aimed to analyze stress patterns for both models in detail using the finite element (FE) method. An ideal cemented stem with bone was made using three dimensional FE analyses (ANSYS 13). The cortical bone was 105 mm long and 7 mm thick and the PMMA cement mantle was 5 mm in thickness surrounding the stem. Young's modulus was set at 200 GPa for the bone and 2.2 GPa for the cement. Poisson's ratio was 0.3 for both materials. The bone-cement interface was completely bonded and cement-stem interface was not bonded in cases where a polished stem surface was used. The two types of stems were compared. One being the double tapered (Fig 1 left) and the other the triple tapered (Fig 1 right). The coefficient of friction (μ) at the stem-cement interface was set at 0 for both models. The distal ends of the stems were not capsulated by the PMMA and therefore the stems were free to subside. All materials were assumed to be linearly isotropic and homogeneous. The distal ends of the bone were completely constrained against any movements and rotations. An axial load of 1200 N and a transverse load of 600 N were applied at the same time simulating the bending condition [3].Introduction
Methods
There are some critical points of Cruciate retaining (CR) TKA. We recognized that it is one of the most important issue how to manage for release of PCL contracture. PCL contracture would lead to poor ROM, stiff or painful knee after CR TKA. PCL release at insertion of femoral / tibial side or cut in PCL itself, “pie craft” were reported. However, for retaining of PCL function after TKA, peeling off PCL itself would be not desirable. Therefore, we proposed to perform V shape-osteotomy at PCL insertion of tibia with osteotome (Fig.1,2) and cancellous bone graft at osteotomy site to get bony union (V-shape osteotomy with cancellous bone graft: VOCG). We would present how to perform VOCG at CR TKA and clinical results. 188 knees in 126 patients were received NRG CR TKA (Stryker) at Nagano Matsushiro General Hospital between February 2008 and August 2009. Mean age at operation was 75.1±5.9 years old. The indications for VOCG were positive of POLO test positive, inadequate soft tissue balance because of PCL contracture, or poor pre-operative ROM et al. All patients were reviewed with clinical and radiographic assessments. Clinical evaluation was carried out using the Knee Society Score (knee score and functional score). The range of motion (ROM) was pre- and post-operatively. In order to evaluate the effect of VOCG, clinical outcomes were compared between two groups (with VOCG vs without VOCG).Background
Patients and Methods
The use of cervical pedicle screws as anchors in posterior reconstruction surgery has not been widely accepted due to the neurological or vascular injury. We thus sought to investigate the accuracy of free-handed pedicle screw placement in the cervical and upper thoracic spine at the early stage of clinical application. Eight patients (five males and three females) were included in this study. Mean age was 63 years (31 to 78 years). There were three patients with rheumatoid arthritis, three with cervical fracture-dislocation, and two with spinal metastasis. Twenty-four pedicle screws (3.5 mm diameter: Vertex, Medtronic Sofamordanek) were placed into the pedicle from C2 to T2 level by free-handed technique2). Grade of breaching of pedicle cortex was divided into four groups (Grade 0–3). In addition, screw axis angle (SAA) were calculated from the horizontal and sagittal CT images and compared with pedicle transverse angle (PTA). Furthermore, perioperative complications were also examined. Our free-handed pedicle screw placement with carving technique is as follows: A longitudinal gutter was created at the lamina-lateral mass junction and then transverse gutter perpendicular to the longitudinal gutter was made at the lateral notch of lateral mass. The entry point of the pedicle screw was on the midline of lateral mass. Medial pedicle cortex through the ventral lamina was identified using the probes to create the hole within the pedicle. The hole was tapped and the screw was gently introduced into the pedicle to ensure the sagittal trajectory using fluoroscopy. In the transverse direction, 22 out of 24 screws (92%) were entirely contained within the pedicle (Grade 0). In contrast, only teo screws (8%) produced breaches less than half the screw diameter (Grade 1). In the sagittal direction, all screws were within the pedicle (Grade 0). Screw trajectories were not consistent with anatomical pedicle axis angle; the mean SAA were smaller than the mean PTA at all levels. The pedicle diameter ranged from 3.9 to 9.2 mm. The mean value gradually increased toward the caudal level. There were no neurological and vascular complications related to screw placement.
The Mayo-Stem is short and tapered in the anteroposterior and mediolateral directions, designed to enhance early fixation through multiple point contact in the proximal medullary cavity. The purpose of this study was to investigate the clinical and radiographic results of total hip arthroplasty (THA) using this short stem in younger patients. A total of 97 cementless THAs using this short stem were investigated. The length of the stem used ranged from 90mm to 110 mm. The average age of the patients at the time of surgery was 50.9 years (33–64 years). The average follow-up period was 64 months (38–108 months). The Harris hip score was used for clinical evaluation. The valgus angles of the stems and the changes in radiographic findings around the stems after surgery were investigated on the AP radiographs of hip. The average Harris hip score was 52.0 points pre-operatively and 93.9 points at the latest follow-up. An intraoperative femoral fissure fracture of the proximal femur occurred in 15 hips (15.4%), which were treated by circlage wires. The average valgus angle of the stem was 3.5° (range: −6°–18°). The development of bone trabeculae was seen around the curve of the stem (Gruen zones 3 and 5) in 79.4 % of hips one year after surgery. A radiolucent line was found on the lateral side of the stem (Gruen zones 1, 2, and 3) in 13.4 % of hips, which occurred in connection with the development of bone trabeculae. Subsidence of the stems (>
2mm) was seen in three hips in which intraoperative femoral fissure fracture had not occurred. These hips did not get the development of bone trabeculae. In two hips of the three hips, the valgus angles of the stems were 15° and 17° respectively. In the case of the third hip, the stem was small to the proximal femur. Overall the clinical result of THA using a short-stem was basically gratifying. The development of bone trabeculae, the stem size to the proximal femur and the stem position were important factors for the fixation of stem. Intraoperative fissure fracture treated by circlage wires and radiolucent lines with the development of bone trabeculae did not affect the fixation of stem.
