Current state and future of joint replacements in the hip and knee

Brake response time before and after total knee arthroplasty: a prospective cohort study

BACKGROUND

Although the numbers of total knee arthroplasty (TKA) are increasing, there is only a small number of studies investigating driving safety after TKA. The parameter 'Brake Response Time (BRT)' is one of the most important criteria for driving safety and was therefore chosen for investigation.The present study was conducted to test the hypotheses that patients with right- or left-sided TKA show a significant increase in BRT from pre-operative (pre-op, 1 day before surgery) to post-operative (post-op, 2 weeks post surgery), and a significant decrease in BRT from post-op to the follow-up investigation (FU, 8 weeks post surgery). Additionally, it was hypothesized that the BRT of patients after TKA is significantly higher than that of healthy controls.

METHODS

31 of 70 consecutive patients (mean age 65.7 +/- 10.2 years) receiving TKA were tested for their BRT pre-op, post-op and at FU. BRT was assessed using a custom-made driving simulator. We used normative BRT data from 31 healthy controls for comparison.

RESULTS

There were no significant increases between pre-op and post-op BRT values for patients who had undergone left- or right-sided TKA. Even the proportion of patients above a BRT threshold of 700 ms was not significantly increased postop. Controls had a BRT which was significantly better than the BRT of patients with right- or left-sided TKA at all three time points.

CONCLUSION

The present study showed a small and insignificant postoperative increase in the BRT of patients who had undergone right- or left-sided TKA. Therefore, we believe it is not justified to impair the patient's quality of social and occupational life post-surgery by imposing restrictions on driving motor vehicles beyond an interval of two weeks after surgery.

Retrograde genocephalic removal of fractured or immovable femoral stems in revision hip surgery

Revision arthroplasty for femoral stem breakage can be challenging. We report a new method for the removal of the distal stem segment performed in 6 cases between 2004 and 2008. After extracting the proximal part of the femoral component, the femoral canal was opened at the knee joint and a modified intramedullary nail was used to dislodge the distal stem under fluoroscopic control. In five cases the surgery was uneventful. In one case femoral perforation occurred due to the contour of the cement mantle at the tip of the stem. In the postoperative period all patients progessed well. Removal of a broken stem using our method has limited indications, and it is not recommended in septic cases or when the cement mantle at the tip of the stem has an oblique contour. It also requires opening of the knee joint, but the technique is simple, saves surgical time and in selected cases it does not weaken the femur.

Osteogenic activity of locally applied small molecule drugs in a rat femur defect model

The long-term success of arthroplastic joints is dependent on the stabilization of the implant within the skeletal site. Movement of the arthroplastic implant within the bone can stimulate osteolysis, and therefore methods which promote rigid fixation or bone growth are expected to enhance implant stability and the long-term success of joint arthroplasty. In the present study, we used a simple bilateral bone defect model to analyze the osteogenic activity of three small-molecule drug implants via microcomputerized tomography (micro-CT) and histomorphometry. In this study, we show that local delivery of alendronate, but not lovastatin or omeprazole, led to significant new bone formation at the defect site. Since alendronate impedes osteoclast-development, it is theorized that alendronate treatment results in a net increase in bone formation by preventing osteoclast mediated remodeling of the newly formed bone and upregulating osteoblasts.

How much tibial resection is required in total knee arthroplasty?

The purpose of our study was to calculate the optimal tibial resection depth in total knee arthroplasty. The data from 464 navigated total knee arthroplasties were analysed. An implant with a minimum insert thickness of 8 mm was used. Data regarding leg axis, joint line, insert thickness and tibial resection depth were recorded by the navigation device. An algorithm was developed to calculate the optimal tibial resection depth. The required tibial resection significantly correlates with the preoperative leg axis (p < 0.001). In valgus deformities the required resection depth averaged 5.1 mm and was significantly reduced compared to knees with a neutral leg axis (6.8 mm, p < 0.001) and varus deformities (8.0 mm, p < 0.001). Manufacturers recommend undercutting the high side of the tibial plateau to the depth of the thinnest insert available. However, our study demonstrates that in valgus deformities a reduced tibial resection depth is preferable. Hence, unnecessary bone loss can be avoided.

Toll-like receptors and aseptic loosening of hip endoprosthesis-a potential to respond against danger signals?

Bacterial remnants and subclinical biofilms residing on prosthesis surfaces have been speculated to play a role in hip implant loosening by opsonizing otherwise relatively inert wear particles. The innate immune system recognizes these microbial pathogen-associated molecular patterns (PAMPs) using Toll-like receptors (TLRs). Our objective was to evaluate the possible presence of TLRs in aseptic synovial membrane-like interface tissue. Bacterial culture-negative, aseptic (n = 4) periprosthetic synovial membrane-like tissue was compared to osteoarthritis synovial membrane (n = 5) for the presence of cells positive for all known human functional TLRs, stained using specific antibodies by immunohistochemistry, and evaluated using morphometry. In comparison to osteoarthtritic synovium, the number of TLR-positive cells was found to be increased in the aseptic setting, reflecting the considerable macrophage infiltration to the tissues investigated. Thus aseptic periprosthetic tissue seems to be very reactive to PAMPs. It has been recently recognized that TLR do not only respond to traditional PAMPs, but also to endogenous alarmings or danger signals released from necrotic and activated cells. Alarming-TLR interaction in the periprosthetic tissue might be a novel mechanism of aseptic loosening of endoprosthesis.

Interaction of staphylococci with bone

Staphylococci, in particular Staphylococcus aureus, are the predominant cause of bone infections worldwide. These infections are painful, debilitating and with the rise in antibiotic-resistant forms, increasingly difficult to treat. The growth in the number of prosthetic joint replacement procedures also provides new opportunities for these infections to take hold. Comprehending the mechanisms by which staphylococci interact with and damage bone is critical to the development of new approaches to meet this challenge. This review summarises current understanding of the mechanisms by which staphylococci infect and damage bone. We address the role of the inflammatory response to staphylococcal infection in disrupting the homeostatic balance of bone matrix deposition and resorption and thereby mediating bone destruction. A number of virulence factors that have been shown to contribute to bone infection and pathology are discussed, however no single factor has been defined as being specific to bone infections. Although traditionally considered an extracellular pathogen, there is increasing evidence that staphylococci are able to invade host cells, and that an intracellular lifestyle may facilitate long-term persistence in bone tissue, enabling evasion of antimicrobials and host immune responses. ‘Small colony variant’ strains, with mutations disabling the electron transport pathway appear particularly adept at invading and persisting within host cells, and exhibit enhanced antimicrobial resistance, and may represent a further complication in the treatment and management of staphylococcal bone disease.