Transient elastohydrodynamic lubrication analysis of a novel metal-on-metal hip prosthesis with a non-spherical femoral bearing surface

Effective lubrication performance of metal-on-metal hip implants only requires optimum conformity within the main loaded area, while it is advantageous to increase the clearance in the equatorial region. Such a varying clearance can be achieved by using non-spherical bearing surfaces for either acetabular or femoral components. An elastohydrodynamic lubrication model of a novel metal-on-metal hip prosthesis using a non-spherical femoral bearing surface against a spherical cup was solved under loading and motion conditions specified by ISO standard. A full numerical methodology of considering the geometric variation in the rotating non-spherical head in elastohydrodynamic lubrication solution was presented, which is applicable to all non-spherical head designs. The lubrication performance of a hip prosthesis using a specific non-spherical femoral head, Alpharabola, was analysed and compared with those of spherical bearing surfaces and a non-spherical Alpharabola cup investigated in previous studies. The sensitivity of the lubrication performance to the anteversion angle of the Alpharabola head was also investigated. Results showed that the non-spherical head introduced a large squeeze-film action and also led to a large variation in clearance within the loaded area. With the same equatorial clearance, the lubrication performance of the metal-on-metal hip prosthesis using an Alpharabola head was better than that of the conventional spherical bearings but worse than that of the metal-on-metal hip prosthesis using an Alpharabola cup. The reduction in the lubrication performance caused by the initial anteversion angle of the non-spherical head was small, compared with the improvement resulted from the non-spherical geometry

Calculation of wear (f.i. wear modulus) in the plastic cup of a hip joint prosthesis

The wear equation is applied to the wear process in a hip joint prosthesis and a wear modulus is defined. The sliding distance, wear modulus, wear volume, wear area, contact angle and the maximum normal stress were calculated and the theoretical calculations applied to test results.\ud \ud During the wear process the increase of the wear modulus is about 100 Nmm−2 per mm sliding distance in the Charnley and the Charnley-Muller hip joint prosthesis. From the wear volume point of view the Charnley prosthesis is probably superior to the Charnley-Muller prosthesis if run-in before implantation

The Effects of Interlocking a Universal Hip Cementless Stem on Implant Subsidence and Mechanical Properties of Cadaveric Canine Femora.

ObjectiveTo determine if an interlocking bolt would limit subsidence of the biological fixation universal hip (BFX(®)) femoral stem under cyclic loading and enhance construct stiffness, yield, and failure properties.Study designEx vivo biomechanical study.AnimalsCadaveric canine femora (10 pairs).MethodsPaired femora implanted with a traditional stem or an interlocking stem (constructs) were cyclically loaded at walk, trot, and gallop loads while implant and bone motions were captured using kinematic markers and high-speed video. Constructs were then loaded to failure to evaluate failure mechanical properties.ResultsImplant subsidence was greater (P = .037) for the traditional implant (4.19 mm) than the interlocking implant (0.78 mm) only after gallop cyclic loading, and cumulatively after walk, trot, and gallop cyclic loads (5.20 mm vs. 1.28 mm, P = .038). Yield and failure loads were greater (P = .029 and .002, respectively) for the interlocking stem construct (1155 N and 2337 N) than the traditional stem construct (816 N and 1405 N). Version angle change after cyclic loading was greater (P = .020) for the traditional implant (3.89 degrees) than for the interlocking implant (0.16 degrees), whereas stem varus displacement at failure was greater (P = .008) for the interlocking implant (1.5 degrees) than the traditional implant (0.17 degrees).ConclusionAddition of a stabilizing bolt enhanced construct stability and limited subsidence of a BFX(®) femoral stem. Use of the interlocking implant may decrease postoperative subsidence. However, in vivo effects of the interlocking bolt on osseointegration, bone remodeling, and stress shielding are unknown

Revision rates after primary hip and knee replacement in England between 2003 and 2006

<b>Background</b>: Hip and knee replacement are some of the most frequently performed surgical procedures in the world. Resurfacing of the hip and unicondylar knee replacement are increasingly being used. There is relatively little evidence on their performance. To study performance of joint replacement in England, we investigated revision rates in the first 3 y after hip or knee replacement according to prosthesis type. <b>Methods and Findings</b>: We linked records of the National Joint Registry for England and Wales and the Hospital Episode Statistics for patients with a primary hip or knee replacement in the National Health Service in England between April 2003 and September 2006. Hospital Episode Statistics records of succeeding admissions were used to identify revisions for any reason. 76,576 patients with a primary hip replacement and 80,697 with a primary knee replacement were included (51% of all primary hip and knee replacements done in the English National Health Service). In hip patients, 3-y revision rates were 0.9% (95% confidence interval [CI] 0.8%–1.1%) with cemented, 2.0% (1.7%–2.3%) with cementless, 1.5% (1.1%–2.0% CI) with “hybrid” prostheses, and 2.6% (2.1%–3.1%) with hip resurfacing (p < 0.0001). Revision rates after hip resurfacing were increased especially in women. In knee patients, 3-y revision rates were 1.4% (1.2%–1.5% CI) with cemented, 1.5% (1.1%–2.1% CI) with cementless, and 2.8% (1.8%–4.5% CI) with unicondylar prostheses (p < 0.0001). Revision rates after knee replacement strongly decreased with age. <b>Interpretation</b>: Overall, about one in 75 patients needed a revision of their prosthesis within 3 y. On the basis of our data, consideration should be given to using hip resurfacing only in male patients and unicondylar knee replacement only in elderly patients

Complications of Resection Arthroplasty in Two-Stage Revision for the Treatment of Periprosthetic Hip Joint Infection

Little data is available regarding complications associated with resection arthroplasty in the treatment of hip periprosthetic joint infection (PJI). We assessed complications during and after two-stage revision using resection arthroplasty. In this retrospective study, 93 patients undergoing resection arthroplasty for hip PJI were included. Patients were assigned to a prosthesis-free interval of ≤10 weeks (group 1; 49 patients) or >10 weeks (group 2; 44 patients). The complication rates between groups were compared using the chi-squared test. The revision-free and infection-free survival was estimated using a Kaplan-Meier survival analysis. Seventy-one patients (76%) experienced at least one local complication (overall 146 complications). Common complications were blood loss during reimplantation (n = 25) or during explantation (n = 23), persistent infection (n = 16), leg length discrepancy (n = 13) and reinfection (n = 9). Patients in group 1 experienced less complications after reimplantation (p = 0.012). With increasing severity of acetabular bone defects, higher incidence of complications (p = 0.008), periprosthetic bone fractures (p = 0.05) and blood loss (p = 0.039) was observed. The infection-free survival rate at 24 months was 93.9% in group 1 and 85.9% in group 2. The indication for resection arthroplasty needs to be evaluated carefully, considering the high rate of complications and reduced mobility, particularly if longer prosthesis-free intervals are used

Prosthetic joint infections

Objectives: To review the available literature on prosthetic joint infections and provide recommendations on management particularly the importance of identifying the causative organism and starting the most appropriate antimicrobial therapy. Methods: The medical literature was searched using PubMed, employing the key words prosthetic joint infections. There appears to be no UK consensus guidelines on the management of prosthetic joint infections or the use of prophylactic antibiotics to prevent them. There is however a number of key documents and trust policies which deal with the subject extensively. We also made use of ‘The Sanford Guide to Antimicrobial therapy 2012’ for the latest recommendations on the correct antimicrobial therapy. Conclusion: Although diagnosis is often difficult, there are a number of investigations which can help us identify the organism. We recommend that the local prevalence of such infections is studied together with identification of the commonest organisms. Work is already underway between the infectious disease team and orthopaedic surgeons to devise locally adapted protocols for the identification and management of such infections. They should work in close liaison to implement the correct treatment which often involves a combination of both surgical and antimicrobial therapy.peer-reviewe

Patient-individual hip cups: simulation-based design and sheet metal forming manufacturing

The revision of an hip prosthesis can have different reasons. One frequent cause, especialley after implantation of a conventional cup, is the so called stress-shielding effect which can lead to a migration or loosening. Patientspecific hip cups can be used to counteract this. However, individual hip cups are only implanted for the treatment of great deformations or tumours because of the cost-intensive manufacturing. Within this project a patient-specific hip cup prosthesis has to be developed and manufactured. Besides the numerical design by means of a coupling between multi-body simulation (MBS) and finite element method (FEM), an inovative concept for the production of patientindividual hip prosthesis out of titanium sheets is introduced in this study.DF

Performance of the resurfaced hip. Part 1: the influence of the prosthesis size and positioning on the remodelling and fracture of the femoral neck

Hip resurfacing is an established treatment for osteoarthritis in young active patients. Failure modes include femoral neck fracture and prosthesis loosening, which may be associated with medium-term bone adaptation, including femoral neck narrowing and densification around the prosthesis stem.Finite element modelling was used to indicate the effects of prosthesis sizing and positioning on the bone remodelling and fracture strength under a range of normal and traumatic loads, with the aim of understanding these failure modes better.The simulations predicted increased superior femoral neck stress shielding in young patients with small prostheses, which required shortening of the femoral neck to give an acceptable implant–bone interface. However, with a larger prosthesis, natural femoral head centre recreation in the implanted state was possible; therefore stress shielding was restricted to the prosthesis interior, and its extent was less sensitive to prosthesis orientation. With valgus orientation, the implanted neck strength was, at worst, within 3 per cent of its intact strength.The study suggests that femoral neck narrowing may be linked to a reduction in the horizontal femoral offset, occurring if the prosthesis is excessively undersized. As such, hip resurfacing should aim to reproduce the natural femoral head centre, and, for valgus prosthesis orientation, to avoid femoral neck fracture

Towards a working methodology for using total hip and knee joint replacements to support identification

Hip and knee prostheses have occasionally been used to support identification of unknown persons along with other medical devices and implants. This paper looks at the specific issues around using hip and knee implants, suggesting a working methodology for their use in supporting identification during and after a post-mortem. The value of Total Knee Replacements (TKR) and Total Hip Replacements (THR) as a means of identification along with other implants is a very recent area of interest in Forensic Science considering the long history of implants. This together with the recent introduction of Joint Replacement Registries means that using hip and knee implants to support identification is likely to become automatic in the future but is not currently automatic. The paper looks at the accumulative collection of evidence as well as the range of issues including; the types and changes in early prostheses, examination of the body for external indications of implants, radiological recording prior to autopsy for confirmation of identification using matching of features with ante-mortem images, actual harvesting and collection of all parts of the joint replacement including cement and any other components, specific differences between TKR and THR. In developing an approach to the problems associated with identifications using TKRs and THRs a stepwise process and the full recording of all of the features associated with the implant as well as manufacturers details and identification numbers is suggested so that the cumulative nature of these features will help to narrow down possibilities towards a more certain identification and confirmation of that identification