Objective

The purpose of the present study was to compare the clinical and radiographic results after TKA using a patellofemoral design modified prosthesis and its predecessor. The other purpose was to investigate whether the use of the recent prosthesis increase the risk of posterior tibial cortex injury or patellar fracture.

Introduction

Although total knee arthroplasty (TKA) in end-stage hemophilic arthropathy can reduce the severe joint pain and improve the functional disability, it is technically demanding. In addition, it has generally reported a high rate of complication including periprosthetic joint infection (PJI) and component loosening up to 20%. Although the Knee Society classification system of TKA complication was introduced, the complications of TKA in hemophilic arthropathy has not stratified using this classification system in previous articles to the best of our knowledge.

The purpose of this study was to evaluate the mid-term outcomes and complications of TKA in hemophilic arthropathy.

Background

The knowledge about the common mode of failure and each period in primary and revision TKAs offers useful information to prevent those kinds of failure in each surgery. However, there has been limited report that simultaneously compared the mode of failure between primary and revision TKAs using single prosthesis.

We compared the survival rate, mode of failure, and periods of each mode of failure between primary and revision TKAs.

We analysed the clinical and radiographic results after total knee arthroplasty in the valgus knee. Thirty six knees in 27 patients with a valgus alignment of more than 10 degrees of femorotibial angle underwent TKA. The average followup period was 7 years(range 1 to 14 years). Eighteen knees were implanted with a cruciate retaining prosthesis, 17 knees with a posterior stabilized prosthesis, and one knee with a constrained condylar prosthesis. In knees with a preoperative 15 degrees or greater femorotibial angle, the posterior stabilized prosthesis were necessary in 85%.

Medial parapatellar approach was used in 27 knees with a preoperative valgus 20 degrees or lesser femorotibial angle. With 20 to 29 degrees valgus, medial parapatellar approach was used in 5 knees and lateral parapatellar approach in 2 knees. With 30 degrees or greater valgus, lateral parapatellar approach was used in 2 knees.

The mean postoperative Hospital for Special Surgery knee scores were 89.5 points. Postoperative range of motion averaged 114.4 degrees. Postoperative alignment averaged 6.5 degree valgus. Radiolucent line or loosening was not seen in any knee. There were two deep infections in patients whose preoperative femorotibial angle was greater than valgus 20 degrees using lateral parapatellar approach.

Clinical and functional results after TKA in the valgus knee were similar to those in varus knee. But, prevention of deep infection in patients with marked valgus angle was important, especially using lateral parapatellar approach. A more constrained prosthesis was frequently used in more significant valgus deformity. In patients with severe valgus deformity needing lateral capsular release frequently, lateral parapatellar capsular approach was more reasonable than medial parapatellar approach to avoid medial and lateral capsular release simultaneously.

Recently, it has been reported that the posterior stabilised implant clinically used for the total knee replacement (TKR) may have a risk of failures caused by pressure and stress concentrated on the tibial post. Malalignment of the implant or variable loading applied to the implant are one of the major causes of the failure in posteriori stabilised TKR. The purpose of this study is to biomechanically analyse the effect of implant malalignment on the failure risk of the implant in posteriori stabilised TKR by estimating von-Mises stress on the implant.

Finite element models of a knee joint and a posteriori stabilised implant were developed from 1mm slices of CT images and 3D CAD software, respectively. The posterior stabilised implant consists of a femoral component, a tibial post, and a tibial tray. The finite element models of TKR for the neutral alignment case as well as the different malalignment cases (3° and 5° of valgus and varus angulations, 2° and 4° of anterior and posterior tilts, and 3° of external rotation) were developed. Then, the von-Mises stress, which is which was chosen as the fracture risk parameter, acting on the implant were analysed by using CAE software. Loading condition at the 40% of one whole gait cycle such as 2000N of compressive load, 25N of anterior-posterior load, and 6.5Nm of torque was applied to the TKR models.

The maximum von-Mises stresses were concentrated on the anterior region of the tibial post regardless of the oblique loadings. In the rotationally additional loading (3° of external rotation), excessive stresses occurred in the anterior medial and posterior lateral areas. The maximum stress was 18.3MPa in neutral position. The maximum stress increased by 10% in anterior tilt 2°, 15% in anterior tilt 4°, 25% in posterior tilt 2°, 54% in posterior tilt 4°, 116% in varus 3°, 262% in varus 5°, 318% in valgus 3°, 389% in valgus 5°, 6% in external rotation 3° compared with that in the neutral position case. In addition, 32.0MPa of maximum stress occurred on the posterior lateral area of the base component in rotationally additional loading.

The results showed that the implant malalignment could accelerate the stress concentration on the anterior region of the tibial post as in the result of clinical study. In the case of additional rotation, high stress concentration on the anterior medial and posterior lateral areas as well as on the tibial base surface could generate wear or fracture of tibial post. From the additional rotation case, we can expect that higher conformity implant will generate higher stress concentrations than lower conformity implant even though we did not compare the effect of conformity ratio on the stress concentration in the tibial polyethylene component. This study showed that careful consideration of the implant malalignment would be necessary to improve the clinical outcome in the posteriori stabilised TKR.

The use of stem provides consistent component alignment with immediate stable fixation and protects grafted bone by reducing stress on metaphyseal area in revision total knee arthroplasty. One of major concern with use of stems involves stem tip pain in cementless diaphyseal engaging stem. The purpose of this study is to evaluate the effect of stem design and method of fixation on stem tip pain in revision total knee arthroplasty by finite element analysis.

3D finite element model of normal tibia was reconstructed from CT scan images of 26 year old male and the CAD model of revision total knee arthroplasty was developed using commercial software(CATIA^®, Dassault system, USA, version 8.20). The tibia component models were assembled based on conventional surgical procedure. The design changes of stem such as the length, diameter and slot were performed and methods of fixation including press fit and coefficient of friction was considered. The contact pressure and von-Mises stress around the stem and the micromotion at the interface were evaluated for a 2000 N of external load by finite element analysis to investigate the effect of stem design and methods of fixation on stem tip pain. The longer length and larger diameter press fit stem significantly increase the contact pressure & stress at the end of stem. The distal slot reduces the contact pressure & stress at the end of stem. Less displacement between tibial component and bone was noted in the increased coefficient of friction.

It would be better to avoid using press fit stem with extended length and larger diameter in revision total knee arthroplasty. More flexibility of stem tip would be favorable because of less concentration of stress. Stem fixation with higher coefficient of friction would be recommended for less displacement of tibial component. Stem with shorter length enough to engage proximal diaphysis, closer diameter of proximal canal and minimal press fit could be accepted to reduce stem tip pain if patient’s surgical anatomy such as bone loss and quality is tolerable in revision total knee arthroplasty.

Patellofemoral complications after TKA are mostly avoided with appropriate operative technique. Although most orthopedic surgeons performed using a medial parapatellar approach at TKA, but a large amount of the patellar blood flow is blocked by this procedure. A certain surgical exposure, including the midvastus and subvastus approach, has resulted in good clinical results. It is important to maintain the integrity of the extensor mechanism. But the southern or subvastus approach has inadequate exposure in some patients. And then we have had the primary total knee Arthroplasty using midvastus approach in 98 cases, 68 patients. Mean follow up is 30 months, between from 20 months to 43 months.

We estimated parameters of total blood loss, surgical time, difficulty of exposure, number of lateral releases. The clinical parameters of range of motion, ability to perform a straight leg raise, and the number of operative or postoperative complications were evaluated. The patients who had the midvastus approach had minor blood loss, resonable surgical time, no difficulty of exposure even in patients with severe varus or valgus deformities, required lateral retinacular releases only 5% of the cases. The range of motion was all above 120 degrees flexion, no extension loss, had a higher incidence of ability to straight leg raise and fewer complications as like superficial wound infection. The midvastus surgical approach have some more advantages with less pain and earlier control of the operative leg, and may be discharged from the hospital earlier. Because preserving the integrity of the vastus medialis insertion into the medial border of the quadriceps tendon and limited disruption of the extensor mechanism improves the rapid control of quadriceps muscle and improves the more stable patellofemoral articulation, and then evidenced a marked reduction in the need for lateral retinacular releases.

We recommend the mid-vastus surgical approach for total knee arthroplasty. The Midvastus approach is an efficacious alternative to the medial parapatellar approach for primary total knee arthroplasties in selected patients who are not obese and who have not had previous arthrotomy. And if needed more additional exposure, the muscle can be safely split by further dissection.