A numerical model to reproduce squeaking of ceramic-on-ceramic total hip arthroplasty. Influence of design and material.

BACKGROUND: Modern ceramic (CoC) bearings for hip arthroplasty (THA) have been used in younger patients who expect improved survivorship. However, audible squeaking produced by the implant is an annoying complication. Previous numerical simulations were not able to accurately reproduce in vitro and in vivo observations. Therefore, we developed a finite element model to: (1) reproduce in vitro squeaking and validate the model by comparing it with in vivo recordings, (2) determine why there are differences between in vivo and in vitro squeaking frequencies, (3) identify the stem's role in this squeaking, (4) predict which designs and materials are more likely to produce squeaking. HYPOTHESIS: A CoC THA numerical model can be developed that reproduces the squeaking frequencies observed in vivo. MATERIAL AND METHODS: Numerical methods (finite element analysis [ANSYS]) and experimental methods (using a non-lubricated simulated hip with a cementless 32mm CoC THA) were developed to reproduce squeaking. Numerical analysis was performed to identify the frequencies that cause vibrations perceived as an acoustic emission. The finite element analysis (FEA) model was enhanced by adjusting periprosthetic bone and soft tissue elements in order to reproduce the squeaking frequencies recorded in vivo. A numerical method (complex eigenvalue analysis) was used to find the acoustic frequencies of the squeaking noise. The frequencies obtained from the model and the hip simulator were compared to those recorded in vivo. RESULTS: The numerical results were validated by experiments with the laboratory hip simulator. The frequencies obtained (mean 2790Hz with FEA, 2755Hz with simulator, decreasing to 1759Hz when bone and soft tissue were included in the FEA) were consistent with those of squeaking hips recorded in vivo (1521Hz). The cup and ceramic insert were the source of the vibration, but had little influence on the diffusion of the noise required to make the squeaking audible to the human ear. The FEA showed that diffusion of squeaking was due to an unstable vibration of the stem during frictional contact. The FEA predicted a higher rate of squeaking (at a lower coefficient of friction) when TZMF™ alloy is used instead of Ti6Al4V and when an anatomic press-fit stem is used instead of straight self-locking designs. DISCUSSION: The current FEA model is reliable; it can be used to assess various stem designs and alloys to predict the different rates of squeaking that certain stems will likely produce. LEVEL OF EVIDENCE: Level IV in vitro study.

Total knee replacement following intra-articular malunion.

INTRODUCTION: There is a lack of data on the management of osteoarthritis of the knee associated with intra-articular malunion. The present study sought to analyze and report results of total knee replacement (TKR) in this indication, including complications and technical specificities. HYPOTHESIS: TKR for osteoarthritis of the knee associated with intra-articular malunion entails an elevated risk of complication, with impaired functional results. OBJECTIVES: To test this hypothesis in a retrospective series of 74 cases of osteoarthritis of the knee associated with intra-articular malunion. PATIENTS AND METHODS: A multicenter retrospective series collated the records of 74 patients (mean age, 63 ± 14 years) who underwent TKR for post-traumatic osteoarthritis of the knee associated with intra-articular malunion between 2000 and 2008. Mean trauma-to-TKR interval was 21.8 ± 19 years (range 1 to 56 years). Patients were assessed clinically and radiologically at last follow-up, using the Knee Society score as modified by the Western France Orthopedic Society (Société orthopédique de l'Ouest). RESULTS: At a mean overall follow-up of 4 ± 3 years (range 1 to 9 years), mean knee score improved from 25 ± 12 to 85 ± 7 (P<0.001) and mean functional score from 52 ± 13 to 66 ± 10 (P=0.004). Mean flexion gain was 6°: mean preoperative flexion, 104° ± 28° (10° to 150°), vs. 110° ± 19° (20° to 130°) at follow-up. Nineteen patients (26%) had complications, 13 of which were severe and liable to affect the functional result: three extensor system avulsions, four infections, five cases of stiffness and one of instability. DISCUSSION AND CONCLUSIONS: The present results highlight an elevated rate of complications, with poorer clinical results than those found with osteoarthritis of the knee secondary to constitutional deformity. The initial trauma, with associated hemarthrosis, and sometimes iterative surgery to reduce and fix the initial fracture, induce fibrosis and synovial attachments, leading to stiffness and hindering exposure. The patient should be informed, and warned that postoperative flexion amplitude may be improved but is bound to remain limited, especially in case of initial stiffness. LEVEL OF EVIDENCE: Level IV: non-comparative retrospective study.

Total knee replacement in post-traumatic arthritic knees with limitation of flexion.

UNLABELLED: The objective of this study is to investigate the results of total knee arthroplasty (TKA) in traumatic osteoarthritis cases with flexion restriction and to describe the technical details of their management. A multicentre series comprising 40 patients with limitation of flexion less than or equal to 90° was selected from 152 cases of post-traumatic knee arthritis with malunion. We hypothesized that the arthroplasty complication rate would be higher than in other etiologies of limitation of flexion and would require specific management strategies. PATIENTS: In 23 cases, intra-articular malunion was present, in 15 cases extra-articular, and in two cases combined. The mean flexion was 72±23°, extension was 6±6°, and total range of motion (ROM) 66±23°. Eight cases of flexion restriction were severe (flexion<50°), six intermediate (flexion, 50-70°) and 26 moderate. In 14 cases, the anterior tibial tuberosity was osteotomized (43% intra-articular malunion and 6% extra-articular malunion). Five simultaneous realignment osteotomies were necessary. In severe cases of limitation of flexion, five extensive quadriceps releases were associated. RESULTS: Four mobilizations under general anesthesia were performed. In the cases of severe limitation of flexion, we noted three avulsions of the patellar tendon, two cases of cutaneous necrosis, one of which was associated with deep infection, and another case of deep infection. In the cases of moderate limitation of flexion, we noted one case of nonunion of the tibial tuberosity and two cases were revised for loosening, one aseptic and the other septic. With a mean follow-up of 5±4 years, the mean flexion was 99.4°±23 for a gain of 26.7±20°. The final flexion and the gain in flexion were correlated with preoperative flexion (r=0.62 and r=-0.47, respectively). The final amplitude was 99±27° for a gain of 33±21°. The flexion gains were comparable for both types of malunion, whether they were intra- or extra-articular. DISCUSSION: Arthroplasty provided a substantial gain in flexion. Osteotomy of the tibial tuberosity and the realignment osteotomies should be performed if necessary, with no risk of compromising the result. Superior gains can be sought in severe cases of limitation of flexion by releasing the extensor apparatus, in absence of cutaneous scar tissue retractions and recent infection. LEVEL OF EVIDENCE: Level 4. Noncomparative retrospective study.

Partial atlE sequencing of Staphylococcus epidermidis strains from prosthetic joint infections.

Partial atlE sequencing (atlE nucleotides 2782 to 3114 [atlE(2782-3114)]) was performed in 41 Staphylococcus epidermidis isolates from prosthetic joint infections (PJIs) and 44 isolates from skin as controls. The atlE(2782-3114) allele 1 (type strain sequence) was significantly more frequent in PJI strains (38/41 versus 29/44 in controls; P = 0.0023). Most PJI strains were positive for mecA, icaA/icaD, and IS256, and most belonged to the sequence type 27 subgroup, suggesting the involvement of few related clones.

Arthrodesis after failed total ankle replacement.

We present a series of 16 patients treated between 1993 and 2006 who had a failed total ankle replacement converted to an arthrodesis using bone grafting with internal fixation. We used tricortical autograft from the iliac crest to preserve the height of the ankle, the malleoli and the subtalar joint. A successful arthrodesis was achieved at a mean of three months (1.5 to 4.5) in all patients except one, with rheumatoid arthritis and severe bone loss, who developed a nonunion and required further fixation with an intramedullary nail at one year after surgery, before obtaining satisfactory fusion. The post-operative American Orthopaedic Foot and Ankle Society score improved to a mean of 70 (41 to 87) with good patient satisfaction. From this series and an extensive review of the literature we have found that rates of fusion after failed total ankle replacement in patients with degenerative arthritis are high. We recommend our method of arthrodesis in this group of patients. A higher rate of nonunion is associated with rheumatoid arthritis which should be treated differently.

Understanding medicinal taste and odour formation in drinking waters.

The formation of bromophenols during chlorination of phenol- and bromide-containing waters can be critical for taste and odour problems in drinking waters. The work performed has confirmed that flavour threshold concentrations of some bromophenols are in the ng/L range. In addition, under typical drinking water conditions, kinetic experiments and model simulations performed have shown that (1) bromination is the predominant reaction pathway, (2) bromophenol reaction kinetics are rapid leading to taste-and-odour episodes that last for short periods of 10-20 min, (3) increasing phenol concentration and pH tends to increase taste and odour intensity, (4) increasing chlorine or bromide concentrations tends to shorten the duration of the taste-and-odour episode.

[Results of reimplantation for infected total knee arthroplasty: 107 cases]. / Résultats des changements de prothèse de genou pour infection: à propos de 107 cas.

PURPOSE OF THE STUDY: The purpose of this study was to assess the results of reimplantations of total knee arthroplasties complicated by infection. Outcome was assessed in terms of eradicated infection and function. MATERIAL AND METHODS: This retrospective multicentric study included 107 cases of infected total knee arthroplasties treated by changing the implants. Seventy-seven patients had a two-stage revision and thirty had a one-stage procedure. Patients were reviewed with a minimal 2-year and an average 52-month follow-up. RESULTS: Revision arthroplasty (one- or two-stage) eradicated infection in two out of three patients. With a two-year follow-up, revision arthroplasty was successful in 77% of patients without any sepsis risk factor, in 65% of patients with one risk factor and in 33% of patients with at least two risk factors. After reimplantation for total knee arthroplasty infection, overall function outcome was good (KS knee score: 74.8 after two-stage revision and 75.5 after one-stage revision, NS). After two-stage procedures, the knee outcome was excellent in one-third of patients, good in another third and fair or poor in the final third. After one-stage reimplantation, 40% of the knees had an excellent outcome, 30% a good outcome and 30% a fair or poor outcome. Regarding functional outcome, overall results were fair (KS function score 62.5 for one-stage and two-stage revisions). Functional outcome was fair or poor in 42% of patients with a two-stage procedure and in 55% of patients with a one-stage revision (NS). DISCUSSION: Our study was unable to disclose any difference between one-stage and two-stage revision for eradicating infection. Unfavorable systemic and local conditions decreased the rate of success after revision total knee arthroplasty for infection. Length of infection before reimplantation, number of surgical procedures and bacterial virulence or resistance were not, in our series, predicting factors for failure of septic revision total knee arthroplasty. No difference was found for the clinical and functional results between one-stage and two-stage procedures. Functional outcome was fair or poor for half of the patients after septic revision total knee arthroplsty. The use of an external device between the two procedures for two-stage revision significantly decreased the functional outcome compared with the use of a spacer. Articulated spacers did not offered any advantage compared with a static spacer for functional outcome.

[Every two year follow-up of arthroplasties: myth or reality?]. / La révision exhaustive biennale des arthroplasties: mythe ou réalité ?

In this article, we propose a simple calculation to project quantitatively the number of consultations implied by a systematic follow-up protocol for arthroplasty surgery. In France, this surveillance schedule has become mandatory and will have a pertinent impact on health care expenditures. The longevity of implanted prostheses as well as patient life expectancies can be used to estimate the number of consultations necessary for a regular follow-up. For example, a surgeon who performs 200 arthroplasty procedures per year will have to see 17 patients per week 20 years later.

Is anyone too old for a total knee replacement?

UNLABELLED: The decision on whether to perform a total knee replacement in extremely elderly patients is controversial. To assess the influence of age as an independent factor for early postoperative morbidity and mortality, we did a case-control study comparing a group of 22 patients 85 years or older that was matched for known predictive factors of nonsurgical postoperative complications with a younger control group. Both groups received the same perioperative and postoperative management. We then compared the number of postoperative complications. Standardized mortality ratios were performed to assess the influence of knee replacement on mortality. The 11 patients (50%) in the elderly group had one or more medical complications, which was similar to those of the five patients (23%) in the control group. Mortality in the elderly group who had knee replacements was almost (1/2) that of the general population (standardized mortality ratio, 0.53). We think age should not be a limitation for total knee replacements in elderly patients, although they should be given consideration for special care while in the hospital. LEVEL OF EVIDENCE: Therapeutic study, Level III (Case control study). See the Guidelines for Authors for a complete description of levels of evidence.