Edward T. Davis

Femoral neck fracture following hip resurfacing THE EFFECT OF ALIGNMENT OF THE FEMORAL COMPONENT

A total of 20 pairs of fresh-frozen cadaver femurs were assigned to four alignment groups consisting of relative varus (10 degrees and 20 degrees) and relative valgus (10 degrees and 20 degrees), 75 composite femurs of two neck geometries were also used. In both the cadaver and the composite femurs, placing the component in 20 degrees of valgus resulted in a significant increase in load to failure. Placing the component in 10 degrees of valgus had no appreciable effect on increasing the load to failure except in the composite femurs with varus native femoral necks. Specimens in 10 degrees of varus were significantly weaker than the neutrally-aligned specimens. The results suggest that retention of the intact proximal femoral strength occurs at an implant angulation of > or = 142 degrees . However, the benefit of extreme valgus alignment may be outweighed in clinical practice by the risk of superior femoral neck notching, which was avoided in this study.

A Biomechanical and Finite Element Analysis of Femoral Neck Notching During Hip Resurfacing

Hip resurfacing is an alternative to total hip arthroplasty in which the femoral head surface is replaced with a metallic shell, thus preserving most of the proximal femoral bone stock. Accidental notching of the femoral neck during the procedure may predispose it to fracture. We examined the effect of neck notching on the strength of the proximal femur. Six composite femurs were prepared without a superior femoral neck notch, six were prepared in an inferiorly translated position to create a 2 mm notch, and six were prepared with a 5 mm notch. Six intact synthetic femurs were also tested. The samples were loaded to failure axially. A finite element model of a composite femur with increasing superior notch depths computed maximum equivalent stress and strain distributions. Experimental results showed that resurfaced synthetic femurs were significantly weaker than intact femurs (mean failure of 7034 N, p<0.001). The 2 mm notched group (mean failure of 4034 N) was significantly weaker than the un-notched group (mean failure of 5302 N, p=0.018). The 5 mm notched group (mean failure of 2808 N) was also significantly weaker than both the un-notched and the 2 mm notched groups (p<0.001, p=0.023, respectively). The finite element model showed the maximum equivalent strain in the superior reamed cancellous bone increasing with corresponding notch size. Fracture patterns inferred from equivalent stress distributions were consistent with those obtained from mechanical testing. A superior notch of 2 mm weakened the proximal femur by 24%, and a 5 mm notch weakened it by 47%. The finite element analysis substantiates this showing increasing stress and strain distributions within the prepared femoral neck with increasing notch depth.

Imageless computer navigation for placement of the femoral component in resurfacing arthroplasty of the hip

We have investigated the accuracy of placement of the femoral component using imageless navigation in 100 consecutive Birmingham Hip Resurfacings. Pre-operative templating determined the native neck-shaft angle and planned stem-shaft angle of the implant. The latter were verified post-operatively using digital anteroposterior unilateral radiographs of the hip. The mean neck-shaft angle determined before operation was 132.7 degrees (118 degrees to 160 degrees ). The mean planned stem-shaft angle was a relative valgus alignment of 9.7 degrees (SD 2.6). The stem-shaft angle after operation differed from that planned by a mean of 2.8 degrees (SD 2.0) and in 86% of cases the final angle measured within +/- 5 degrees of that planned. We had no instances of notching of the neck or varus alignment of the implant in our series. A learning curve was observed in the time taken for navigation, but not for accurate placement of the implant. Navigation in hip resurfacing may afford the surgeon a reliable and accurate method of placement of the femoral component.

Long Intergenic Noncoding RNAs Mediate the Human Chondrocyte Inflammatory Response and Are Differentially Expressed in Osteoarthritis Cartilage

To identify long noncoding RNAs (lncRNAs), including long intergenic noncoding RNAs (lincRNAs), antisense RNAs, and pseudogenes, associated with the inflammatory response in human primary osteoarthritis (OA) chondrocytes and to explore their expression and function in OA.

Hip arthroplasty. Part 2: normal and abnormal radiographic findings

This review addresses the normal and abnormal radiographic findings that can be encountered during the follow-up of patients with total hip arthroplasty (THA). The relative significance of different patterns of radiolucency, bone sclerosis, and component position is discussed. The normal or pathological significance of these findings is correlated with design, surface, and fixation of the prosthetic components. It is essential to have a good knowledge of expected and unexpected radiological evolution according to the different types of prostheses. This paper emphasizes the importance of serial studies compared with early postoperative radiographs during follow-up in order to report accurately any sign of prosthetic failure and trigger prompt specialist referral. Basic technical guidelines and schedule recommendations for radiological follow-up are summarized.

Total Hip Arthroplasty Following Failure of Free Vascularized Fibular Graft

BACKGROUND Many treatments for osteonecrosis of the femoral head, including the use of a free vascularized fibular graft, have been advocated in an attempt to delay the need for hip arthroplasty. The purpose of this study was to document the clinical and radiographic results of total hip arthroplasty performed following failure of a free vascularized fibular grafting procedure. METHODS Twenty total hip arthroplasties in eighteen patients who had previously undergone a free vascularized fibular grafting procedure for the treatment of osteonecrosis were retrospectively reviewed. A straight-stem femoral component was used in twelve hips, a tapered femoral component with removal of residual fibular graft was used in five hips, and a tapered stem without graft removal was used in three hips. The twelve hips with a straight-stem femoral component and previous vascularized fibular grafting were compared with thirty-six osteonecrotic hips in thirty other patients who had undergone total hip arthroplasty but had not had previous free vascularized fibular grafting. The radiographic outcomes with respect to initial femoral component alignment and subsequent migration and the clinical outcomes were compared. RESULTS Analysis of the immediate postoperative radiographs demonstrated significantly improved alignment of the femoral component when a high-speed burr had been used to remove residual fibular graft (p = 0.001), although doing so did significantly increase both the intraoperative blood loss (p = 0.017) and the operative time (p = 0.0002). There was no significant difference in the amount of migration of either the acetabular or the femoral component between the control and study groups at the time of the most recent follow-up. When comparing patients with or without a previous free vascularized fibular graft, the mean postoperative scores at three years were significantly worse in patients who had undergone a previous free vascularized fibular graft (p = 0.03). One revision occurred in the study group at seventy-two months due to acetabular wear, and one revision occurred in the control group at 108 months due to aseptic loosening. CONCLUSIONS This study raises concern that the outcome of total hip arthroplasty in patients who previously underwent a free vascularized fibular graft for the treatment of osteonecrosis of the femoral head may be worse than that in patients without previous free vascularized fibular grafting. The intraoperative use of a high-speed burr can improve the alignment of the femoral component by removing more of the residual graft. However, this technique does increase intraoperative blood loss and operative time. LEVEL OF EVIDENCE Therapeutic Level IV. See Instructions to Authors on jbjs.org for a complete description of levels of evidence.

The Reliability of Radiographic Assessment of Femoral Neck-Shaft and Implant Angulation in Hip Resurfacing Arthroplasty

Fifteen sets of patient radiographs were analyzed by 3 different observers on 2 occasions. Each observer measured the femoral neck-shaft angles (NSAs) of the preoperative digital radiographs and stem-shaft angles (SSAs) of the postoperative radiographs. The effect of femur position on SSA measured by digital radiographs was also investigated using a resurfaced synthetic femur. Radiographs were taken with the synthetic specimen positioned in 10 degrees increments of either flexion or rotation. Measurement by digital radiographs proved less than optimal in assessing preoperative NSA but was better in assessing the postoperative component SSA. External rotation of 30 degrees and flexion of 40 degrees resulted in a clinically significant disparity in SSA measurements. Patient malposition during radiographic imaging can contribute to erroneous NSA and SSA results.

Developing anti-inflammatory therapeutics for patients with osteoarthritis

OA is the most common joint disorder in the world, but there are no approved therapeutics to prevent disease progression. Historically, OA has been considered a wear-and-tear joint disease, and efforts to identify and develop disease-modifying therapeutics have predominantly focused on direct inhibition of cartilage degeneration. However, there is now increasing evidence that inflammation is a key mediator of OA joint pathology, and also that the link between obesity and OA is not solely due to excessive load-bearing, suggesting therefore that targeting inflammation in OA could be a rewarding therapeutic strategy. In this review we therefore re-evaluate historical clinical trial data on anti-inflammatory therapeutics in OA patients, highlight some of the more promising emerging therapeutic targets and discuss the implications for future clinical trial design.

IL-6 secretion in osteoarthritis patients is mediated by chondrocyte-synovial fibroblast cross-talk and is enhanced by obesity

Increasing evidence suggests that inflammation plays a central role in driving joint pathology in certain patients with osteoarthritis (OA). Since many patients with OA are obese and increased adiposity is associated with chronic inflammation, we investigated whether obese patients with hip OA exhibited differential pro-inflammatory cytokine signalling and peripheral and local lymphocyte populations, compared to normal weight hip OA patients. No differences in either peripheral blood or local lymphocyte populations were found between obese and normal-weight hip OA patients. However, synovial fibroblasts from obese OA patients were found to secrete greater amounts of the pro-inflammatory cytokine IL-6, compared to those from normal-weight patients (p < 0.05), which reflected the greater levels of IL-6 detected in the synovial fluid of the obese OA patients. Investigation into the inflammatory mechanism demonstrated that IL-6 secretion from synovial fibroblasts was induced by chondrocyte-derived IL-6. Furthermore, this IL-6 inflammatory response, mediated by chondrocyte-synovial fibroblast cross-talk, was enhanced by the obesity-related adipokine leptin. This study suggests that obesity enhances the cross-talk between chondrocytes and synovial fibroblasts via raised levels of the pro-inflammatory adipokine leptin, leading to greater production of IL-6 in OA patients.

Defining the errors in the registration process during imageless computer navigation in total knee arthroplasty: a cadaveric study.

Computer assisted arthroplasty was introduced as a means to optimally align implants in order to improve function and longevity. The error during the manual registration of landmarks and its effect on component alignment was investigated in this study. Five fresh frozen lower limbs were used and the registration process was performed five times by five surgeons. The error range of the mechanical axis of the femur in the coronal plane was 5.2 degrees of valgus to 2.9 degrees of varus whilst the transepicondylar axis error was 11.1 degrees of external to 6.3 of internal rotation. Those figures suggest that the registration error alone can have a significant effect on the alignment of the implant.