Introduction

We have been re-evaluating patellofemoral alignment after total knee arthroplasty (TKA) by using a weight- bearing axial radiographic view after detecting patellar maltracking (lateral tilt > 5° or lateral subluxation > 5 mm) on standard non-weight-bearing axial radiographs. However, it is unclear whether the patellar component shape affects this evaluation method. Therefore, we compared 2 differently shaped components on weight-bearing axial radiographs.

Introduction

We have been developed lateral flare stem and have been using it since 1989. It was custom stem at first. After being experienced, using the same software, off-the-shelf version lateral flare stem (Revelation) was developed in 1996 in the U.S. We could start using it since 2001 in our country. Lateral flare stems are designed to reproduce physiological proximal load transfer lateral side as well as medial side. It was obtained by having bigger and more accurate proximal part with lateral flare. The design is optimized by matching with 3D insertion path.

Using many custom stems including different length and off-the-shelf standard stems, we have come to feel that as for this high proximal fit and load transfer design, it is not necessary to having long distal part and sometimes it is harmful to obtain good proximal load transfer in some situation such as type A (champagne flute) canal. So we have developed short version of the stem. Many makes of the hip stems have included short stems recently. Some aimed to improve easier insertion, some aimed to improve the volume of residual bone quantity. We have aimed to improve proximal fit expecting more proximal and more physiological load transfer to the femur.

Introduction

Massive defect of the acetabular bone is one of the severe situation in the hip arthroplasty. Installation of cup supporter or acetabular reinforcement device is one of the important method as well as big cup and bone graft etc. Preparing the device to be suitable shape is very important and installing it at the very position where the shaping was intended is also very important to obtain a stable condition for the arthroplasty. When we use navigation system, the device must be programmed in. But it is impossible to programme a device we have bended by ourselves into the system. If we can use a navigation system for such devices for those cases, we can expect better installation. We can fit the device on the patient's bone during the surgery of course; which is the ordinary procedure fot it; but it requires much time and tissue damage maybe with less accurate fitting.

This study shows the radiographic results of total hip arthroplasty (THA) using Revelation stem ® (Djo surgical USA) for hip joint disease.

We removed cases which we couldn't follow up, the remaining of the patients who had undergone a primary THA July 2007 to December 2009 in our institution using Revelation hip stem® and 58 cases-65 hips (14 men and 44 women) were possible for progress observation on this study, and radiographic evaluation was done at the time of the last observation. The preoperative diagnosis of the hip included osteoarthritis (OA) in 40 patients, idiopatic, necrosis of the hip in 13 patients, Rheumatoid arthritis (RA) in 4 patients, and femoral head fracture in 1 patient.

Three patients had undergone femoral head replacement (FHA) and 55 patients had undergone THA.

At the time of the last evaluation, spot welds were detected in 63 hips (97%) in zone1 and 7. Demarcation lines, which indicates movement of the stem, were detected in zone3,4,5, but not in the proximal of the stem.

Stress shielding were observed in 32 joints, according to Engh's classification, first degree were 27 joints and second degree were 5 joints. Cortical hypertrophy were detected in 13 joints.

The revelation stem features a lateral overhang structure (lateral flare) and the stem has an expanded proximal geometry allowing the device to rest on both medial and lateral cortices at the metaphyseal level. Above all the stem has anterior overhand structure (trapezoidal structure). The medullary cavity occupation rate is made to increase by these structures. Above all, the stability of the stem is increased by a proximal portion by three point support.

The distal stem is tapered and polished, which prevents the stress loading to a distal portion of the device.

Stress shielding more than the third degree is not detected, and spots welds were detected in the proximal of the stem. These facts indicate that the concept of this stem, transmit loading to the femur bone, at the proximal portion of the stem, would be achieved.

Introduction

A Finite Element Analysis (FEA) is often used to examine load transfer between prosthesis and canal. Ordinary, bone elements' type is defined as elastic material. But using this element type for FEA on stem load transfer, the stems will jump out and fly away when the load is removed even friction between the stem and the canal was defined. This is remarkably different from the reality. It happens because the canal elements return to the original shape without the load. But actually, the bone is impacted by the load without returning to the original shape. Meshing the trabecular bone with a collapsible element type, it can collapse and be hardened by the stem pressure.

We have been using Revelation (DJO, USA) with lateral flare for the primary cases whom we can expect high proximal load transfer. We were going to shorten its length to secure proximal load. We have been using Modulus (Lima Corporate, Italy) with conical fixation for the cases we expect mid stem load transfer and neck modification. We were going to extend its length for wider load transfer area. To examine load transfer of the designs the collapsible FEA was used.

Introduction

Overstuffing the patellofemoral joint during total knee arthroplasty (TKA) is considered a potential cause of limited knee flexion and patellar maltracking. We investigated the effect of patellar thickness on intraoperative knee flexion and patellar tracking in navigated TKA.

Introduction

Navigation system has been used for very accurate surgery. It can also be useful for preoperative planning. A surgeon can understand whole surgery, plan the surgery and perform the surgery three dimensionally and accurately. But the planning procedures should be installed before everything is started. When the surgery will be done in an ordinary method, the surgeon would not find particular difficulties. But in sometimes the surgeon can have unordinary situation such as massive defect that should be treated with acetabular enforcement device and bone grafted. Using postoperative DICOM data which is predicted by preoperative planning using 3D CAD software, we will be able to use the navigation system for those cases with difficulties that is not supported.

Introduction

To obtain a better range of motion and to reduce the risk of dislocation, neck and cup anteversion are considered very important. Especially for the reduction of the risk of dislocation, the mutual alignment between neck and cup anteversion (combined anteversion) is often discussed. A surgeon would compare the neck direction to the calf direction with the knee in 90 degrees flexion. When an excessive anteversion was observed, the neck anteversion would be reduced using modular neck system or setting the stem a little twisted inside the canal with the tradeoff of the stem stability. Another choice would be the adjustment of cup alignment. Combined anteversion is defined the summation of cup anteversion in axial plane and stem anteversion in axial plane. But in realty the impingement occurs with 3 dimensional relationships between neck and cup with very complicated geometries. In that meaning, the definition of the angles could be said ambiguous too. The bowing of the femur also makes the relationships more complicated. Upon those backgrounds, we have been performing 3D preoperative planning for total hip arthroplasty on every case. In the present study, in vivo position of the stem in each case was determined then the anteversion observed on surgical view and anteversion around femoral mechanical axis are compared using 3D CAD software.

We have been using 3-dimensional CAD software for preoperative planning as a desktop tool daily. In ordinary cases, proper size stems and cups can be decided without much labor but in our population, many arthritic hip cases have dysplastic condition and they often come to see us for hip replacement after severe defects were created over the acetabulum. It is often the case that has Crowe's type III, IV hips with leg length difference. For those cases preoperative planning using 3D CAD is a very powerful tool.

Although we only have 2-dimensional display with our computer during preoperative planning, 3 dimensional geometries are not so difficult to be understood, because we can turn the objects with the mouse and can observer from different directions. We can also display their sections and can peep inside of the geometries. It is quite natural desire that a surgeon wishes to see the planed geometries as a 3-dimensional materials. For some complicated cases, we had prepared plastic model and observed at the theater for better understanding. When we ask for a model service, each model costs $2,500. We also have small scale desk top rapid processing tool too, however it takes 2 days to make one side of pelvis. Observation of the geometries using 3-dimensional display can be its substitute without much cost and without taking much time. The problem of using 3D display had been the special goggle to mask either eye alternatively.

In the present paper, we have used a 3D display which has micro arrays of powerful prism to deriver different image for each eye without using any goggle.

Dislocation after total hip arthroplasty (THA) is one of the most serious complications. We recently modified the design of Lateral Flare femoral component (RevelationV2) with six degrees lower anteversion to reproduce the normal hip condition in Japanese. In addition, we added 10-degree slope on the posterior neck to prevent dislocation especially aimed to high anteversion cases. The purpose of this study is to verify the clinical outcome after this design modification.

Hospital records and database were retrospectively reviewed. We investigated 46 consecutive hips in 43 patients who underwent primary total hip arthroplasty using RevelationV2 from September 2007 to August 2009. All patients implicated preoperative planning using CAT scan with their informed consents.

The mean age and BMI at surgery were 63 years old and 23.1. Preoperative diagnosis was osteoarthritis (40/46: 87%), rheumatoid arthritis (2/46: 4%) or avascular necrosis of femoral head (4/46: 9%). There were 41 hips (89.2%) of Crowe I, 3(6.5%) of Crowe II and 2(4.3%) of Crowe III. Preoperative femoral neck anteversion averaged 28 degrees, whereas postoperative combined anteversion (the sum of femoral neck anteversion and anterior cup inclination) averaged 46 degrees. During follow up, 5 complications, in details, 3 mild peroneal nerve palsy, 1 pulmonary embolism and 1 dislocation following deep infection were reported. In conclusion, although no ordinal dislocation was found in this series, longer observation will need to judge appropriateness of this new component.

One of the ironies in modern technology for arthroplasty is the stress shielding in cementless stems. The aim of the development of cementless stems had been reduction of stress shielding which cement stems are not free from. In healthy femur, trabecula start form the femoral head and reach at both medial and lateral cortex in rather narrow area around lesser trochanter. So the load from the femoral head is transferred at the level on both medial and lateral side. Cement stems should have binding to the cortical bone from collar to the tip of the stem where the cement interlays, and then the load is transferred gradually from the tip to the collar, which means mild stress shielding. When distal bonding is removed, the load could be transferred as normal femur. This should have been one of the biggest requests for cementless stem. But in realty many cementless stems have difficulty to obtain a load transfer at the level like normal femur.

Since 1990, we have been mainly using lateral flare stems to obtain contact on both medial and lateral side at proximal level. In the present study, different types and length of the designs were compared by 3-Dimensional fill, 3-Dimensional fit and Finite Element Analysis.