Yukihide Minoda

Positive nasal culture of methicillin-resistant Staphylococcus aureus (MRSA) is a risk factor for surgical site infection in orthopedics

Background Although nasal carriage of MRSA has been identified as one of the risk factors for surgical site infection (SSI) with MRSA, there have been no reports of this in the orthopedics field. Methods This prospective observational cohort study included 2,423 consecutive patients who were admitted to our department over 26 months and who underwent orthopedic surgery. We examined the relationship between pre-existing nasal MRSA and subsequent occurrence of SSI with MRSA. Results 63 patients (2.6%) had a positive nasal MRSA culture. 15 patients (0.6%) developed SSI with MRSA. The occurrence of SSI with MRSA in nasal MRSA carriers was significantly higher than that in non-carriers (4 out of 63 (6.3%) vs. 11 out of 2,360 (0.5%); p < 0.001) (adjusted OR: 11; 95% CI: 3–37; p = 0.001). Interpretation We recommend appropriate treatment of patients who are nasal carriers of MRSA before orthopedic surgery.

Acetabular component orientation in 834 total hip arthroplasties using a manual technique.

Acetabular component orientation during total hip arthroplasty affects dislocation, range of motion, polyethylene wear, pelvic osteolysis, and component migration. New total hip arthroplasty navigation systems have been introduced to avoid the errors reported after acetabular component orientation using a manual technique. We investigated acetabular component orientation in 834 consecutive primary total hip arthroplasties performed by one surgeon using a manual technique. We examined the relationship between dislocation and a defined safe range. Vertical tilt and planar anteversion were 44.4 ± 6.5 and 17.9 ± 6.3 (mean ± standard deviation), respectively. The error of vertical tilt and planar anteversion were 5.2 ± 3.9 and 5.3 ± 4 (mean ± standard deviation), respectively. Two hundred thirty-three of 834 hips (27.8 %) were outside the safe range. Logistic regression analysis showed that patients with Group IV class according to the classification system of Crowe et al and right hips had a greater risk of being outside the safe range. Navigation systems should be considered, especially in patients with highly dislocated hips. We found no relationship between risk of dislocation and the safe range. Factors other than acetabular component orientation also might affect dislocation. Level of Evidence: Prognostic Study, Level IV (case series). See the Guidelines for Authors for a complete description of levels of evidence.

The incidence of the patellar clunk syndrome in a recently designed mobile-bearing posteriorly stabilised total knee replacement

The patellar clunk syndrome describes painful catching, grinding or jumping of the patella when the knee moves from a flexed to an extended position after total knee replacement (TKR). The posterior stabilised TKR had been noted to have a higher incidence of this problem. Mobile-bearing posteriorly stabilised TKRs have been introduced to improve patellar tracking and related problems by a mechanism of self-alignment. We evaluated the patellar clunk syndrome in 113 knees in 93 patients with such a TKR at a mean follow-up of 2.3 years (2.0 to 3.2). The syndrome was identified in 15 knees (13.3%). Logistic regression analysis showed that the absolute value of the post-operative angle of patellar tilt was significantly associated with the occurrence of patellar clunk (p = 0.025). Patellar tracking should be carefully checked during surgery.

Polyethylene wear particles in synovial fluid after total knee arthroplasty.

The aims of the current study were to examine polyethylene particles in synovial fluid at an early stage, and to compare a newly introduced medial pivot total knee prosthesis with an established posterior-stabilized total knee prosthesis. Synovial fluid was obtained 1 year after knee arthroplasty from 17 patients with well-functioning prostheses (22 knees, 11 posterior-stabilized prostheses and 11 medial pivot prostheses) under complete sterile conditions. Polyethylene particles were isolated and analyzed by scanning electron microscopy. Particle size (equivalent circle diameter) was 0.78 ± 0.08 μm (mean ± standard error) in posterior-stabilized prostheses and 0.67 ± 0.06 μm in medial pivot prostheses. Particle shape (aspect ratio) was 2.30 ± 0.22 in posterior-stabilized prostheses and 1.90 ± 0.16 in medial pivot prostheses. The total numbers of particles were 1.16 ± 0.57 × 108 in posterior-stabilized prostheses and 9.01 ± 2.95 × 106 in medial pivot prostheses. Particles were smaller and rounder in medial pivot prostheses than in posterior-stabilized prostheses, but the differences were not significant. The difference in the common logarithm of particle number was significant. The medial pivot prosthesis generated less wear particles than the posteriorstabilized prosthesis, and these findings may have an impact on the incidence of osteolysis and aseptic loosening.

Comparison between highly cross-linked and conventional polyethylene in total knee arthroplasty.

The use of highly cross-linked polyethylene in total knee prostheses is still controversial. The aim of the present study was to compare radiographic and clinical results of using conventional and highly cross-linked polyethylene in cruciate retaining total knee prostheses of completely the same design. Two hundred and two consecutive total knee arthroplasties (NexGen CR, Zimmer) were performed using the same procedure. The first consecutive 113 knees had conventional polyethylene insert and following consecutive 89 knees had highly cross-linked polyethylene insert (Prolong, Zimmer). Differences in the age, gender, and diagnosis between two groups were not statistically significant. Preoperative range of motion (ROM) of the knee, and Knee Society Score (KSS) was better in highly cross-linked polyethylene group. Clinical and radiographic results were evaluated at two years after operation. The difference of ROM and KSS between groups was not statistically significant. There was no revision surgery. No knee exhibited osteolysis, aseptic loosening, or polyethylene failure. There was no early catastrophic clinical failure due to use of the new material.

Palsy of the C5 Nerve Root After Midsagittal-Splitting Laminoplasty of the Cervical Spine

Study Design. The imaging characteristics of postoperative C5 nerve root palsy after midsagittal-splitting laminoplasty for cervical myelopathy, including those observed on plain radiography, computed tomography, and magnetic resonance imaging, were analyzed. Objective. To investigate the imaging findings that predict occurrence of C5 nerve root palsy after midsagittal-splitting laminoplasty. Summary of Background Data. There have been several reports on imaging findings for postoperative nerve root palsy after open-door laminoplasty. However, there have been no detailed reports on imaging characteristics that predict the occurrence of nerve root palsy after midsagittal-splitting laminoplasty. Methods. The study included 45 consecutive patients undergoing midsagittal-splitting laminoplasty with sufficient pre- and postoperative imaging examinations: 27 patients with cervical spondylotic myelopathy (CSM), 14 patients with ossification of the posterior longitudinal ligament (OPLL), and 4 patients with cervical disc herniation. Characteristics of pre- and postoperative plain radiographs, computed tomography scans, and magnetic resonance images were compared between the patients with and those without C5 nerve root palsy. Results. Palsy of the C5 nerve root developed in 4 patients, and did not develop in 41 patients. Of the four patients with C5 nerve root palsy, one had CSM and the other three had OPLL. The incidence of C5 nerve root palsy involved 3 of 14 patients with OPLL patients (21.4%) and 1 of 31 patients without OPLL (3.2%) (P = 0.08). For both diseases, the patients with palsy tended to have increased postoperative cervical lordosis (P = 0.21). As for anterior compression on the spinal cord at C3, the P value for the comparison between the group with and the group without palsy was 0.07 for preoperative compression and 0.01 for postoperative compression. Conclusions. The preliminary data suggest that patients who have OPLL with marked anterior compression on spinal cord at C3 can be at risk for postoperative C5 nerve root palsy after midsagittal-splitting laminoplasty. Also, a postoperative increase in cervical lordosis may be the cause of postoperative nerve root palsy.

TKA Sagittal Alignment with Navigation Systems and Conventional Techniques Vary Only a Few Degrees

Navigation systems have been developed to achieve more reliable prosthetic alignment in TKAs. However, the component alignment in the sagittal plane is reportedly less reliable than in the coronal plane even with navigation systems. We measured and compared sagittal prosthetic alignments for TKAs with the conventional technique and three navigation approaches to establish reference frames, using radiographs of the entire lower extremity while standing. The sagittal alignments simulated on the radiographs with the conventional technique and navigation systems differed by a mean of 2° to 4°. Use of navigation systems resulted in a mean of 1° to 4° hyperextension between the femoral and tibial components and use of the conventional technique resulted in a mean of 1° flexion. Use of different reference points on the distal femoral condyle for the navigation systems resulted in differences of as much as 3° alignment in the sagittal plane. Although optimal prosthetic alignment for TKA in the sagittal plane is unknown, surgeons and technicians using navigation systems should be aware of this difference in the sagittal plane and the risk of hyperextension between the femoral and tibial components, which might be associated with osteolysis and anterior post-cam impingement.

Comparison of Bone Mineral Density Between Porous Tantalum and Cemented Tibial Total Knee Arthroplasty Components

BACKGROUND Porous tantalum was recently introduced as a metallic implant material for total knee arthroplasty. Its porosity, low modulus of elasticity, and high frictional characteristics were expected to provide physiologic load transfer and relative preservation of bone stock. However, to our knowledge, the effect of a Trabecular Metal tibial component on bone mineral density has not been reported. The purpose of the present study was to compare the periprosthetic bone mineral density between patients managed with uncemented Trabecular Metal and cemented tibial components. METHODS Twenty-eight knees receiving a Trabecular Metal tibial component and twenty-eight knees receiving a cemented cobalt-chromium tibial component had dual x-ray absorptiometry scans at two weeks preoperatively and at two weeks and six, twelve, eighteen, and twenty-four months postoperatively, to assess periprosthetic bone mineral density. All of the operations were performed by one surgeon through a medial parapatellar approach. RESULTS None of the differences between the two groups in terms of preoperative bone mineral density in the femoral neck, wrist, lumbar spine, or knee were significant. In both groups, the bone mineral density in the tibia decreased postoperatively. However, the postoperative decrease in bone mineral density in the lateral aspect of the tibia was significantly less in knees with Trabecular Metal components than in knees with cemented tibial components at twenty-four months (mean and standard deviation, -6.7% +/- 22.9% compared with -36.8% +/- 24.2%; p = 0.002). At twenty-four months postoperatively, there was no significant difference between the two groups in terms of the Knee Society score, range of motion of the knee, or bone mineral density in the lumbar spine. No prosthetic migration or periprosthetic fracture was detected in either group. CONCLUSIONS The decrease in bone mineral density of the lateral tibial plateau was less in knees with a Trabecular Metal tibial component following total knee arthroplasty than in knees with a cemented tibial component. Additional research is needed to determine whether long-term clinical benefits are realized with the use of porous tantalum tibial components for total knee arthroplasty.

In Vivo Analysis of Polyethylene Wear Particles After Total Knee Arthroplasty: The Influence of Improved Materials and Designs

Polyethylene wear particles induce macrophages to release cytokines, which can lead to osteolysis and aseptic loosening of total joint prostheses1. The generation of polyethylene wear particles is one of the most important factors that affects the midterm and long-term clinical results associated with total knee arthroplasty2,3. The generation of polyethylene wear particles is correlated with the activity level of the patient4, and greater demands are placed on a total knee prosthesis when it is implanted in a younger, more active patient5. Therefore, to achieve better long-term results for patients who have higher activity levels, modifications of materials (i.e., highly cross-linked polyethylene and alumina ceramic) and design (i.e., mobile bearing and medial pivot) have been developed to reduce polyethylene wear after total knee arthroplasty. It takes decades to evaluate the long-term results of newly introduced total knee prostheses. Thus, it is particularly important to examine in vivo polyethylene wear generation in new prostheses before they come into widespread use. It is difficult to determine the in vivo polyethylene wear of total joint prostheses (with the exception of total hips) with use of postoperative radiographs. To measure polyethylene wear in vivo, we developed and employed a method in which we isolated and analyzed polyethylene wear particles in the synovial fluid of knees that had a well-functioning total knee prosthesis6-9. The number, size, and shape of polyethylene wear particles have been reported to be critical factors in the development of osteolysis. Greater volume, submicrometer size, and an elongated shape of polyethylene wear particles all stimulate an increased macrophage response10-12. Our hypothesis was that modification of total knee arthroplasty materials and designs can influence the generation of polyethylene wear particles in vivo. In the present study, …

Range of Motion of Standard and High-Flexion Cruciate Retaining Total Knee Prostheses

Recently, use of high-flexion design was introduced in cruciate-retaining (CR) total knee prostheses. The purpose of this study was to prospectively compare the ranges of motion (ROMs) of 89 knees with standard and 87 knees with high-flexion CR total knee prostheses. Differences in age, gender, diagnosis, preoperative ROM of the knee, and Knee Society Score between the 2 groups were not statistically significant. At 12-month follow-up, average ROM was 112.0 degrees +/- 12.6 degrees for standard, and 115.3 degrees +/- 13.4 degrees for high-flexion CR prosthesis (P = .101). To our knowledge, this is the first report on the ROM with the high-flexion CR total knee prosthesis. Using the technique of anterior referencing for femoral component sizing and using a fixed 7 degrees slope for the tibial component, we found no significant differences between groups with regard to ROM, clinical, or radiographic parameters.