R. M. Dominic Meek

Periprosthetic fractures evaluation and treatment.

Periprosthetic fracture is a serious complication of total hip arthroplasty (THA) that can be difficult to treat, and can be potentially fraught with complications. The incidence of such fractures is increasing, especially after the use of cementless revision arthroplasty. The prevention of these fractures is achieved by understanding the risk factors involved. If the risks are not understood, the best outcome is achieved when the surgeon has a thorough understanding of the principles of treatment of these fractures and has access to various fixation and prosthetic devices, and allograft bone when necessary. Acetabular fractures are rare and relatively little has been reported on their treatment. Periprosthetic femoral fracture treatment is based on the site of fracture, implant stability, and bone stock. The Vancouver classification offers a reproducible description of these factors with the subsequently easy formation of a treatment plan.

Patient Satisfaction and Functional Status After Treatment of Infection at the Site of a Total Knee Arthroplasty with Use of the PROSTALAC Articulating Spacer

BACKGROUND Two-stage exchange arthroplasty remains the standard treatment of infection at the site of a total knee arthroplasty. The clinical and functional outcomes associated with the use of an articulating antibiotic spacer for two-stage revision for infection are not well established. We conducted a retrospective study to evaluate the outcomes associated with the use of the PROSTALAC articulating spacer between the first and second stages. METHODS Fifty-eight patients underwent two-stage revision total knee arthroplasty for infection between January 1997 and December 1999. Of these, fifty-four were alive at the time of follow-up and forty-seven were available for inclusion in the present retrospective study. In all patients, a prosthesis of antibiotic-loaded acrylic cement (the PROSTALAC system) was implanted during the first stage after débridement. The amount of osteolysis that occurred between the stages and the range of motion of the knee joint were measured. After two years of follow-up, outcomes were assessed with use of the WOMAC, Oxford-12, and SF-12 instruments as well as a satisfaction questionnaire. RESULTS At a minimum of two years (average, forty-one months) after revision arthroplasty, two patients (4%) had had a recurrence of infection. The amount of bone loss was unchanged between stages, and the range of movement of the knee improved from 78.2 degrees before the first stage to 87.1 degrees at two years. The average normalized WOMAC function and pain scores were 68.9 and 77.1, respectively; the average Oxford-12 score was 67.3; the average SF-12 mental and physical scores were 53.7 and 41.2, respectively; and the average satisfaction score was 71.7. CONCLUSION A revision operation for infection at the site of a total knee replacement with use of an articulating spacer was associated with reasonable function and satisfaction scores. These findings may be related to the articulating features of the PROSTALAC system, which permits full active movement of the knee in the early postoperative period.

Intraoperative fracture of the femur in revision total hip arthroplasty with a diaphyseal fitting stem.

BACKGROUND In revision total hip arthroplasty, intraoperative split fractures and cortical perforation fractures are becoming a more common concern with the increasing use of diaphyseal fitting cementless stems. The purpose of this study was to evaluate the risk factors and frequency of intraoperative fractures with the use of these stems and their effect on radiographic and functional outcomes. METHODS We performed a retrospective case-control study of 211 consecutive patients who had undergone revision hip arthroplasty with a diaphyseal fitting cementless stem between December 1998 and March 2002. Sixty-four patients sustained an intraoperative fracture of the femur. One hundred and fifteen patients were followed for a minimum of two years; function was analyzed with self-administered outcome questionnaires, and radiographs were evaluated for evidence of bone ingrowth into the femoral stem. RESULTS Risk factors associated with an intraoperative fracture were a substantial degree of preoperative bone loss, a low femoral cortex-to-canal ratio, underreaming of the cortex, and the use of a large-diameter stem. The majority of the diaphyseal undisplaced linear fractures occurred at the distal end of an extended trochanteric osteotomy during stem insertion. Fracture due to cortical perforation occurred most often during cement removal. These intraoperative fractures had no significant effect on the functional outcome or radiographic evidence of bone ingrowth. CONCLUSIONS There was a surprisingly high rate of intraoperative femoral fractures associated with the use of a diaphyseal fitting stem in revision total hip arthroplasty. Identification of risk factors such as preoperative bone loss and a low cortex-to-canal ratio may permit planning to avoid such fractures. However, the final functional and radiographic outcomes appear to have been unaffected by the fracture when it had been managed appropriately. LEVEL OF EVIDENCE Prognostic study, Level II-1 (retrospective cohort study). See Instructions to Authors for a complete description of levels of evidence.

Biomimetic microtopography to enhance osteogenesis in vitro

Biomimicry is being used in the next generation of biomaterials. Tuning material surface features such as chemistry, stiffness and topography allow the control of cell adhesion, proliferation, growth and differentiation. Here, microtopographical features with nanoscale depths, similar in scale to osteoclast resorption pits, were used to promote in vitro bone formation in basal medium. Primary human osteoblasts were used to represent an orthopaedically relevant cell type and analysis of adhesions, cytoskeleton, osteospecific proteins (phospho-Runx2 and osteopontin) and mineralisation (alizarin red) was performed. The results further demonstrate the potential for biomimicry in material design and show that the osteoblast response can be tuned from changes in feature size.

Nanotopographical Induction of Osteogenesis through Adhesion, Bone Morphogenic Protein Cosignaling, and Regulation of MicroRNAs

It is emerging that nanotopographical information can be used to induce osteogenesis from mesenchymal stromal cells from the bone marrow, and it is hoped that this nanoscale bioactivity can be utilized to engineer next generation implants. However, the osteogenic mechanism of surfaces is currently poorly understood. In this report, we investigate mechanism and implicate bone morphogenic protein (BMP) in up-regulation of RUNX2 and show that RUNX2 and its regulatory miRNAs are BMP sensitive. Our data demonstrate that osteogenic nanotopography promotes colocalization of integrins and BMP2 receptors in order to enhance osteogenic activity and that vitronectin is important in this interface. This provides insight that topographical regulation of adhesion can have effects on signaling cascades outside of cytoskeletal signaling and that adhesions can have roles in augmenting BMP signaling.

2D and 3D Nanopatterning of Titanium for Enhancing Osteoinduction of Stem Cells at Implant Surfaces

The potential for the use of well-defined nanopatterns to control stem cell behaviour on surfaces has been well documented on polymeric substrates. In terms of translation to orthopaedic applications, there is a need to develop nanopatterning techniques for clinically relevant surfaces, such as the load-bearing material titanium (Ti). In this work, a novel nanopatterning method for Ti surfaces is demonstrated, using anodisation in combination with PS-b-P4VP block copolymer templates. The block copolymer templates allows for fabrication of titania nanodot patterns with precisely controlled dimensions and positioning which means that this technique can be used as a lithography-like patterning method of bulk Ti surfaces on both flat 2D and complex shaped 3D surfaces. In vitro studies demonstrate that precise tuning of the height of titania nanodot patterns can modulate the osteogenic differentiation of mesenchymal stem cells. Cells on both the 8 nm and 15 nm patterned surfaces showed a trend towards a greater number of the large, super-mature osteogenic focal adhesions than on the control polished Ti surface, but the osteogenic effect was more pronounced on the 15 nm substrate. Cells on this surface had the longest adhesions of all and produced larger osteocalcin deposits. The results suggest that nanopatterning of Ti using the technique of anodisation through a block copolymer template could provide a novel way to enhance osteoinductivity on Ti surfaces.

Femoral Neck Narrowing After Metal-on-Metal Hip Resurfacing

We reviewed 40 Corin Cormet 2000 (Corin, Cirencester, UK) metal-on-metal resurfacing hips, in 36 patients, for the presence of femoral neck narrowing. A neck-to-prosthesis ratio was calculated by dividing the diameter of the femoral neck with that of the implant. This ratio was measured on plain anteroposterior pelvis radiographs taken immediately and 2 years postoperation. Subsequent radiographs were measured up to a maximum 7 years (mean, 5.3 years) postoperation. Femoral neck narrowing was observed in 90% of hips at 2 years, with the average neck narrowing ranging from a ratio of 0.865 to 0.811. Importantly, no further narrowing occurred beyond this point up to 7 years postoperation. We described a simple reproducible method of measuring neck narrowing on plain radiographs and discuss possible causal factors for neck narrowing after hip resurfacing.

Investigation of the limits of nanoscale filopodial interactions

Mesenchymal stem cells are sensitive to changes in feature height, order and spacing. We had previously noted that there was an inverse relationship between osteoinductive potential and feature height on 15-, 55- and 90 nm-high titania nanopillars, with 15 nm-high pillars being the most effective substrate at inducing osteogenesis of human mesenchymal stem cells. The osteoinductive effect was somewhat diminished by decreasing the feature height to 8 nm, however, which suggested that there was a cut-off point, potentially associated with a change in cell–nanofeature interactions. To investigate this further, in this study, a scanning electron microscopy/three-dimensional scanning electron microscopy approach was used to examine the interactions between mesenchymal stem cells and the 8 and 15 nm nanopillared surfaces. As expected, the cells adopted a predominantly filopodial mode of interaction with the 15 nm-high pillars. Interestingly, fine nanoscale membrane projections, which we have termed ‘nanopodia,’ were also employed by the cells on the 8 nm pillars, and it seems that this is analogous to the cells ‘clinging on with their fingertips’ to this scale of features.

Minimally invasive unicompartmental knee replacement: rationale and correct indications

In the early 1990s, unicompartmental knee replacements (UKRs) were almost forgotten as an option for the management of unicompartmental arthritis of the knee, and the two principal surgical options became proximal tibial osteotomy and total knee replacement. The recent introduction of minimally invasive techniques has renewed interest in uni-compartmental knee replacement. The proposed advantages of UKR over proximal tibial osteotomy include more predictable relief of pain, quicker recovery, and better long-term results. In appropriate cases, it has advantages over total arthroplasty in providing more physiologic function, better range of movement, easier salvage in case of failure, and quicker recovery because of minimally invasive techniques.

Titanium nanofeaturing for enhanced bioactivity of implanted orthopedic and dental devices

Titanium (Ti) is used as a load-bearing material in the production of orthopedic devices. The clinical efficacy of these implants could be greatly enhanced by the addition of nanofeatures that would improve the bioactivity of the implants, in order to promote in situ osteo-induction and -conduction of the patients stem and osteoprogenitor cells, and to enhance osseointegration between the implant and the surrounding bone. Nanofeaturing of Ti is also currently being applied as a tool for the biofunctionalization of commercially available dental implants. In this review, we discuss the different nanofabrication strategies that are available to generate nanofeatures in Ti and the cellular response to the resulting nanofeatures. In vitro research, in vivo studies and clinical trials are considered, and we conclude with a perspective about the future potential for use of nanotopographical features in a therapeutic setting.