Robert F. Spencer

The effect of surgical approach on blood flow to the femoral head during resurfacing

We determined the effect of the surgical approach on perfusion of the femoral head during hip resurfacing arthroplasty by measuring the concentration of cefuroxime in bone samples from the femoral head. A total of 20 operations were performed through either a transgluteal or an extended posterolateral approach. The concentration of cefuroxime in bone was significantly greater when using the transgluteal approach (mean 15.7 mg/kg; 95% confidence interval 12.3 to 19.1) compared with that using the posterolateral approach (mean 5.6 mg/kg; 95% confidence interval 3.5 to 7.8; p < 0.001). In one patient, who had the operation through a posterolateral approach, cefuroxime was undetectable. Using cefuroxime as an indirect measure of blood flow, the posterolateral approach was found to be associated with a significant reduction in the blood supply to the femoral head during resurfacing arthroplasty compared with the transgluteal approach.

Gentamicin concentrations in diagnostic aspirates from 25 patients with hip and knee arthroplasties

Background There is little information on long-term release of antibiotics from impregnated bone cement.Patients and methods We assayed joint fluids obtained for diagnostic purposes from 25 patients for the presence of gentamicin. All patients had presented with failing or painful joints up to 20 years following primary hip or knee arthroplasty, using gentamicinimpregnated cement.Results Gentamicin was detected in the joint fluids from 9 of 15 patients with knee prostheses and 4 of 10 patients with hip prostheses. The concentrations ranged from 0.06 mg/L to 0.85 mg/L with no significant differences in concentration between the patients with hip or knee prostheses, or the type of prosthesis. We found no relationship between the gentamicin concentration and the time after primary arthroplasty.Interpretation Although most concentrations were below the levels required to inhibit susceptible pathogens, we conclude that gentamicin release around failing implants may lead to false negative cultures in some patients and provide selective pressure for the emergence of resistance where infection is present in others.

Maximum temperatures of 89°C recorded during the mechanical preparation of 35 femoral heads for resurfacing

Background and purpose We noticed that our instruments were often too hot to touch after preparing the femoral head for resurfacing, and questioned whether the heat generated could exceed temperatures known to cause osteonecrosis. Patients and methods Using an infra-red thermal imaging camera, we measured real-time femoral head temperatures during femoral head reaming in 35 patients undergoing resurfacing hip arthroplasty. 7 patients received an ASR, 8 received a Cormet, and 20 received a Birmingham resurfacing arthroplasty. Results The maximum temperature recorded was 89°C. The temperature exceeded 47°C in 28 patients and 70°C in 11. The mean duration of most stages of head preparation was less than 1 min. The mean time exceeded 1 min only on peripheral head reaming of the ASR system. At temperatures lower than 47°C, only 2 femoral heads were exposed long enough to cause osteonecrosis. The highest mean maximum temperatures recorded were 54°C when the proximal femoral head was resected with an oscillating saw and 47°C during peripheral reaming with the crown drill. The modified new Birmingham resurfacing proximal femoral head reamer substantially reduced the maximum temperatures generated. Lavage reduced temperatures to a mean of 18°C. Interpretation 11 patients were subjected to temperatures sufficient to cause osteonecrosis secondary to thermal insult, regardless of the duration of reaming. In 2 cases only, the length of reaming was long enough to induce damage at lower temperatures. Lavage and sharp instruments should reduce the risk of thermal insult during hip resurfacing.

Evolution in hip resurfacing design and contemporary experience with an uncemented device.

The concepts of surface replacement of the hip and metal-on-metal articulation date back to the 1930s, and recent hip resurfacing designs have been more successful than their predecessors. Experience with the Cormet device followed initial collaboration with Mr. Derek McMinn. Both hybrid implants (a cementless cup and a cemented head) and entirely cementless implants, inserted with use of a variety of surgical approaches, yielded good results, with the cementless option increasing in popularity. The indications for hip resurfacing have become better understood, with the procedure considered most suitable for young and middle-aged males with a high activity profile. In addition, revision surgery, if necessary, has been associated in most cases with bone and soft-tissue conservation. Caution should be exercised when treating small individuals (especially females) and individuals with accompanying diagnoses other than osteoarthritis (such as hip dysplasia), for whom other bone-conserving options may be more appropriate to avoid an adverse reaction to metal debris. Correct implant placement during hip resurfacing is of critical importance.

Use of Morphometry to Quantify Osteolysis after Total Hip Arthroplasty

Background Progressive osteolysis threatens the longevity of hip arthroplasties and radiographic review is recommended. Measurement of osteolytic lesions in a clinical setting has not been achieved easily in the past. Other radiologic investigations provide accurate information but cost and risk to the patient prohibit their use in routine review. Questions/purposes We developed a simple, reliable tool to be used in hip arthroplasty review to quantify osteolytic changes seen on plain film radiographs. Methods A morphometric grid was developed and tested on simulated and actual osteolytic lesions. Four health professionals measured lesions on each of two occasions. Intraclass correlation coefficients (ICC) for interobserver and intraobserver reliabilities were calculated and Bland-Altman plots were constructed for graphic analysis. Results The ICCs for interobserver reliability on the simulated and actual osteolytic lesions were in the range 0.90 to 0.96. The values for intraobserver (test-retest) reliability were 0.97 to 0.98. The Bland-Altman plots confirmed agreement and in each case, proximity of the mean to zero indicated no significant bias. Conclusions The data show a morphometric grid is reliable for measuring osteolytic changes after hip arthroplasty. Clinical Relevance This tool has potential to improve monitoring processes for hip arthroplasty and to be useful in future research studies. Additional work is needed to test for validity and clinical importance of the measurements obtained.BackgroundProgressive osteolysis threatens the longevity of hip arthroplasties and radiographic review is recommended. Measurement of osteolytic lesions in a clinical setting has not been achieved easily in the past. Other radiologic investigations provide accurate information but cost and risk to the patient prohibit their use in routine review.Questions/purposesWe developed a simple, reliable tool to be used in hip arthroplasty review to quantify osteolytic changes seen on plain film radiographs.MethodsA morphometric grid was developed and tested on simulated and actual osteolytic lesions. Four health professionals measured lesions on each of two occasions. Intraclass correlation coefficients (ICC) for interobserver and intraobserver reliabilities were calculated and Bland-Altman plots were constructed for graphic analysis.ResultsThe ICCs for interobserver reliability on the simulated and actual osteolytic lesions were in the range 0.90 to 0.96. The values for intraobserver (test-retest) reliability were 0.97 to 0.98. The Bland-Altman plots confirmed agreement and in each case, proximity of the mean to zero indicated no significant bias.ConclusionsThe data show a morphometric grid is reliable for measuring osteolytic changes after hip arthroplasty.Clinical RelevanceThis tool has potential to improve monitoring processes for hip arthroplasty and to be useful in future research studies. Additional work is needed to test for validity and clinical importance of the measurements obtained.

Variations in the anterolateral approach to the hip

A pictorial questionnaire distributed to 56 hip surgeons who use an anterolateral approach to the hip revealed that only 46% use an approach which conforms closely to the original eponymous descrip...

Extracting the tip of a fractured DHS wire from the hip joint.

Dynamic Hip Screw fixation is a very commonly performed operation, but one not without complications (1-3). To stabilise the fixation the guide wire can be advanced into the subchondral bone. An unusual complication of this, and one not previously documented in the literature, is that the tip of the guide wire can fracture. We describe a simple method of removing the tip of the guide wire.

Cement brand and preparation effects cement-in-cement mantle shear strength

Creating bi-laminar cement mantles as part of revision hip arthroplasty is well-documented but there is a lack of data concerning the effect of cement brand on the procedure. The aim of this study was to compare the shear strength of bi-laminar cement mantles using various combinations of two leading bone cement brands. Bi-laminar cement mantles were created using Simplex P with Tobramycin, and Palacos R+G: Simplex-Simplex (SS); Simplex-Palacos (SP); Palacos-Simplex (PS); and Palacos-Palacos (PP). Additionally, specimens were produced by rasping (R) the surface of the original mantle, or leaving it unrasped (U), leading to a total of eight groups (n = 10). Specimens were loaded in shear, at 0.1 mm/min, until failure, and the maximum shear strength calculated. The highest mean shear strength was found in the PSU and PSR groups (23.69 and 23.89 MPa respectively), and the lowest in the PPU group (14.70 MPa), which was significantly lower than all but two groups. Unrasped groups generally demonstrated greater standard error than rasped groups. In a further comparison to assess the effect of the new cement mantle brand, irrespective of the brand of the original mantle, Simplex significantly increased the shear strength compared to Palacos with equivalent preparation. It is recommended that the original mantle is rasped prior to injection of new cement, and that Simplex P with Tobramycin be used in preference to Palacos R+G irrespective of the existing cement type. Further research is needed to investigate more cement brands, and understand the underlying mechanisms relating to cement-in-cement procedures.

Surface replacement of the hip

Attempts to resurface the hip joint date back to the 1930s. Throughout the last century many designs failed due to defective materials or fixation (or a combination). The metal-on-metal designs pioneered at the end of the century appeared to herald a new era, until difficulties associated with adverse reactions to metal debris were identified. Ultimately, a much narrower range of indications emerged - large, young males appear to be the ideal recipients. Implant design features and component orientation are crucial to the survivorship of these implants.

Where do we stand with metal-on-metal bearings

In this issue we have published advice from a collaborative group of experts representing several societies in relation to the current status and safety of metal-on-metal bearings in hip arthroplasty. Over the last decade, our journal has documented benign and encouraging results following the use of metal-on-metal (MoM) bearings, either in the form of total hip arthroplasty or hip resurfacing, both in relation to tribology and potential metal dissemination (including trans-placental passage) (1-8). The literature, at least in the period from 1990-2004, concentrated mainly on technical details relating to the procedures. Recent awareness of adverse reaction to metal debris combined with the potential effect of metal toxicity have radically altered the climate in relation to this discussion, and have highlighted the more encouraging results of small-bearing MoM total hip arthroplasty (< 32 mm) as well as hip resurfacing in larger males (9-11). While some implant designs are particularly implicated, particularly in relation to large head metal-on-metal total hip arthroplasty, caution should be exercised in relation to all metal-on-metal bearings. Some countries have issued specific guidelines, such as the MHRA requirements for surveillance in the United Kingdom (12). Recent evidence from the Netherlands suggests the acuity of screening may become more intense in the years ahead (13). The guidelines produced in the collaborative statement in the following pages may act as a framework in those countries in which specific recommendations have not yet been produced at a national level. This is an area of constantly evolving knowledge, and therefore new information will probably result in modification of these guidelines in the coming years.