BEARING SURFACE OPTIONS FOR TOTAL HIP REPLACEMENT IN YOUNG PATIENTS

Comprehensive Review on Biomaterials and Their Inherent Behaviors for Hip Repair Applications

Developing biomaterials for hip prostheses is challenging and requires dedicated attention from researchers. Hip replacement is an inevitable and remarkable orthopedic therapy for enhancing the quality of patient life for those who have arthritis as well as trauma. Generally, five types of hip replacement procedures are successfully performed in the current medical market: total hip replacements, hip resurfacing, hemiarthroplasty, bipolar, and dual mobility systems. The average life span of artificial hip joints is about 15 years, and several studies have been conducted over the last 60 years to improve the performance and thereby increase the lifespan of artificial hip joints. Present-day prosthetic hip joints are linked to the wide availability of biomaterials. Metals, ceramics, and polymers are some of the most promising types of biomaterials; nevertheless, each biomaterial has advantages and disadvantages. Metals and ceramics fail in most applications owing to stress shielding and the emission of wear debris; ongoing research is being carried out to find a remedy to these unfavorable responses. Recent research found that polymers and composites based on polymers are significant alternative materials for artificial joints. With growing research and several biomaterials, recent reviews lag in effectively addressing hip implant materials' individual mechanical, tribological, and physiological behaviors. This Review comprehensively investigates the historical evolution of artificial hip replacement procedures and related biomaterials' mechanical, tribological, and biological characteristics. In addition, the most recent advances are also discussed to stimulate and guide future researchers as they seek more effective methods and synthesis of innovative biomaterials for hip arthroplasty application.

Which is the best bearing surface for primary total hip replacement? A New Zealand Joint Registry study

INTRODUCTION

We have investigated the revision rates of all bearing surface combinations for primary total hip replacement (THR) registered on the New Zealand Joint Registry (NZJR) to determine which coupling has been the most durable and successful over the last 16 years.

METHODS

There were 106,139 primary THRs registered, resulting in 4,960 revisions for any cause. We examined all-cause revision rates, reasons for revision and performed survival analyses.

RESULTS

Ceramic-on-highly cross-linked polyethylene (CoPx) had the lowest all-cause revision rate of 0.54/100-component-years (cys) (95% confidence interval 0.48 to 0.61). This was superior to all other hard-on-soft bearing combinations in unadjusted analysis. Furthermore, the age of patients receiving CoPx was significantly lower than for metal-on-polyethylene (mean 62.9; standard deviation [SD] 10.1 vs. 69.1; SD 9.6; p<0.001). Acetabular loosening was the reason for revision in 14.5% of CoPx, compared to 33% of MoP THRs (p<0.001). Metal-on-metal bearings had the highest revision rate of 1.43/100 cys and were significantly inferior to CoPx (p<0.001). Kaplan-Meier analysis and Cox regression analyses were performed and we adjusted the analyses to control for age, femoral head size, surgical approach and fixation.

CONCLUSIONS

CoPx remained the most durable and successful coupling used in primary THR in New Zealand irrespective of age, gender or size of femoral head.

Survivorship and clinical outcome of Birmingham hip resurfacing: a minimum ten years' follow-up

INTRODUCTION

Resurfacing as a percentage of total hip arthroplasty rose from 5.6 % in 2001 to 8.9 % in 2005 in Australia. During the same period the resurfacing to conventional prosthesis rose from 19.6 % to 29 % in the younger age group (less than 55 years). Long term (more than ten years) functional results of BHR are sparingly documented. Among the literatures available, the patient selection criteria vary from osteoarthritis, avascular necrosis, and dysplastic hip to slipped capital femoral epiphysis. The objective of the current study is to evaluate long term survivorship and functional outcome of Birmingham hip resurfacing surgery in osteoarthritic hip patients performed by a single surgeon.

PATIENTS AND METHODS

In this retrospective clinical study, all patients who underwent hip resurfacing for osteoarthritis of hip between 1999 and 2004 are included. All surgeries were performed by single surgeon (SJM) and in all patients Smith & Nephew system (Midland Medical Technologies, Birmingham, United Kingdom)) was used. Revision surgery is considered the end point of survivorship. Means, standard deviations, and confidence interval were calculated for all continuous measures. Survival analysis was performed with the Kaplan-Meier method and 95 % confidence intervals were calculated.

RESULT

The result is based on 222 patients (244 hips). This included 153 males and 69 females. Our mean follow up was 12.05 years and overall survival was 93.7 %. In terms of gender, survival in males was 95.43 % while in females it was 89.86 %. Failure was seen in 14 patients (16 hips), which included seven female (10.14 %) and seven male (4.57 %) patients. Failure of femoral components due to aseptic loosening and varus collapse was seen in eight patients after a mean 9.6 years. Metal allergy was seen in three patients (five hips), all of them were female of which two had bilateral resurfacing. Other complications included femoral neck stress fractures in two patients and acetabular component loosening in one patient. We observed that the failure rate is higher if the BHR femoral component size is 46 or less (ten out of 16 hips revised).

CONCLUSION

If patient selection is judiciously done and surgical technique is meticulously followed, hip resurfacing offers acceptable survivorship, satisfactory range of motion and enables patients to resume high demand activities including sports. Future improvements in the bearing surfaces, and possibly in the design, might alleviate concerns posed by high serum metal level and provide options that continue to benefit younger patients in future.

Wear Debris Characterization and Corresponding Biological Response: Artificial Hip and Knee Joints

Wear debris, of deferent sizes, shapes and quantities, generated in artificial hip and knees is largely confined to the bone and joint interface. This debris interacts with periprosthetic tissue and may cause aseptic loosening. The purpose of this review is to summarize and collate findings of the recent demonstrations on debris characterization and their biological response that influences the occurrence in implant migration. A systematic review of peer-reviewed literature is performed, based on inclusion and exclusion criteria addressing mainly debris isolation, characterization, and biologic responses. Results show that debris characterization largely depends on their appropriate and accurate isolation protocol. The particles are found to be non-uniform in size and non-homogeneously distributed into the periprosthetic tissues. In addition, the sizes, shapes, and volumes of the particles are influenced by the types of joints, bearing geometry, material combination, and lubricant. Phagocytosis of wear debris is size dependent; high doses of submicron-sized particles induce significant level of secretion of bone resorbing factors. However, articles on wear debris from engineered surfaces (patterned and coated) are lacking. The findings suggest considering debris morphology as an important parameter to evaluate joint simulator and newly developed implant materials.

Functional and radiographic evaluation and quality of life analysis after cementless total hip arthroplasty with ceramic bearings: minimum of 5 years follow-up

OBJECTIVE

The aim of the study is to analyze and correlate functional and radiographic results and quality of life in patients undergoing cementless total hip arthroplasty with ceramic surface, performed at Hospital Servidor Publico de Sao Paulo from 2001 to 2006.

METHODS

We retrospectively analyzed 35 hips treated with cementless total hip arthroplasty with ceramic surfaces with a minimum follow-up of 5 years. Functional evaluation was based on the Harris Hip Score (HHS). Radiographic evaluation was based on the method proposed by Charles Engh for evaluation of femoral osseointegration and on DeLee and Charnley zones for acetabulum. Quality of life was assessed by SF-36 questionnaire.

RESULTS

The HHS presented excellent and good results in 91% of patients postoperatively (mean of 93.14 points HHS). As for radiographic evaluation, we found excellent results in 100% of evaluated hips (proven osseointegration). SF-36 scores were not compared to the control group for the following components: pain, vitality, mental health and social aspects. The difference between HHS pre and postoperatively had a statistically significant correlation with physical functioning of the SF-36.

CONCLUSION

Total hip arthroplasty with ceramic surface is a treatment that enables functional improvement of the hip and increases quality of life of patients to levels close to those of people without joint diseases.

Synthetic fiber from a teddy bear causing keratitis and conjunctival granuloma: case report

BACKGROUND

To report a case of keratitis and a case of conjunctivitis caused by synthetic fibers from toy teddy bears.

CASE PRESENTATION

Case stories with histopathological analysis. 1) A two-year-old girl developed a severe case of keratitis and corneal ulceration. The initial treatment with various antibiotics gave no improvement and eventually the patient developed spontaneous perforation of the cornea. The corneal swabs contained no bacteria or fungi. Corneal grafting was performed and the corneal button was sent for histopathological examination. 2) A five-year-old girl presented with ocular irritation in her left eye. Examination revealed a conjunctival granuloma in the inferior fornix. The lesion was excised and histopathologically examined.

RESULTS

Microscopy revealed synthetic fibers embedded in the cornea and in the conjunctival granuloma. The diagnosis was confirmed by demonstration of marked birefringence of the synthetic fibers. Microscopical examination of synthetic fibers from two different types of fur (whiskers and face hairs) from the two-year-old girl's teddy bear was performed. Hairs from the face of the teddy bear were morphologically and microscopically identical with the fibers causing the severe corneal ulceration in the two-year-old girl.

CONCLUSIONS

Doctors should especially in small children be aware of the risk of ocular consequences of close exposure of synthetic fibers from stuffed toy animals. Corneal ulceration, clinically presenting as corneal infection with negative culturing and staining, should lead to a different clinical strategy and treatment. The treatment of conjunctival synthetic fiber granuloma is excision and antibiotic eye drops.

Metal ion levels following resurfacing arthroplasty of the hip

We report serum metal ion level data in patients with unilateral and bilateral hip resurfacing over a ten-year period. In these patients there is an increase in both cobalt and chromium levels above the accepted reference ranges during the first 18 months after operation. Metal ion levels remain elevated, but decline slowly for up to five years. However, the levels then appear to start rising again in some patients up to the ten-year mark. There was no significant difference in cobalt or chromium levels between men and women. These findings appear to differ from much of the current literature.

The clinical significance of a raised metal ion level remains under investigation.

Designing Fail-Safe Biomaterials against Wear for Artificial Total Hip Replacement

This review paper presents a fail-safe approach in designing biomaterials against wear for application in an artificial total hip replacement in view of the recent advances in orthopedic bioengineering materials. It has been established that substantially different alloys should be used for minimizing wear in bearing surfaces. Frictional forces at these rubbing counter-faces must be minimized to prevent loosening of the femoral stem and acetabular socket assembly from their positions secured by the fixation agent. A comparative analysis of various wear-resistant biomaterials resulted in the lowest production of wear particles in a total hip where a ceramic socket articulates against the ceramic ball: it produces only 0.004 cubic millimeters of ceramic wear particles. Surface modification, through the application of coatings, offers the potential to reduce the wear rate without compromising the bulk mechanical behavior of the implant material. These hard coatings were found to include diamond-like carbon, amorphous diamond, and titanium nitride.

In vitro characterization of bioactive titanium dioxide/hydroxyapatite surfaces functionalized with BMP-2

Poor implant fixation and bone resorption are two of the major challenges in modern orthopedics and are caused by poor bone/implant integration. In this work, bioactive crystalline titanium dioxide (TiO(2))/hydroxyapatite (HA) surfaces, functionalized with bone morphogenetic protein 2 (BMP-2), were evaluated as potential implant coatings for improved osseointegration. The outer layer consisted of HA, which is known to be osteoconductive, and may promote improved initial bone attachment when functionalized with active molecules such as BMP-2 in a soaking process. The inner layer of crystalline TiO(2) is bioactive and ensures long-term fixation of the implant, once the hydroxyapatite has been resorbed. The in vitro response of mesenchymal stem cells on bioactive crystalline TiO(2)/HA surfaces functionalized with BMP-2 was examined and compared with the cell behavior on nonfunctionalized HA layers, crystalline TiO(2) surfaces, and native titanium oxide surfaces. The crystalline TiO(2) and the HA surfaces showed to be more favorable than the native titanium oxide surface in terms of cell viability and cell morphology as well as initial cell differentiation. Furthermore, cell differentiation on BMP-2-functionalized HA surfaces was found to be significantly higher than on the other surfaces indicating that the simple soaking process can be used for incorporating active molecules, promoting fast bone osseointegration to HA layers.

The influence of wear paths produced by hip replacement patients during normal walking on wear rates

Variation in wear paths is known to greatly affect wear rates in vitro, with multidirectional paths producing much greater wear than unidirectional paths. This study investigated the relationship between multidirectional motion at the hip joint, as measured by aspect ratio, sliding distance, and wear rate for 164 hip replacements. Kinematic input from three-dimensional gait analysis was used to determine the wear paths. Activity cycles were determined for a subgroup of 100 patients using a pedometer study, and the relationship between annual sliding distance and wear rate was analyzed. Poor correlations were found between both aspect ratio and sliding distance and wear rate for the larger group and between annual sliding distance and wear rate for the subgroup. However, patients who experienced a wear rate <0.08 mm/year showed a strong positive correlation between the combination of sliding distance, activity levels, and aspect ratio and wear rate (adjusted r(2) = 55.4%). This group may represent those patients who experience conditions that most closely match those that prevail in simulator and laboratory tests. Although the shape of wear paths, their sliding distance, and the number of articulation cycles at the hip joint affect wear rates in simulator studies, this relationship was not seen in this clinical study. Other factors such as lubrication, loading conditions and roughness of the femoral head may influence the wear rate.

Why total hip resurfacing

Improvements in materials and fixation have addressed many of the limitations of resurfacing total hip arthroplasty (THA). The functional demands and the longevity of arthroplasty patients are increasing. Many patients have embraced the functional capacity, bone conservation, and revision options of hip resurfacing. Young men have historically been at increased risk for failure of total THA. In this patient subgroup, the survivorship of hybrid metal-metal resurfacing THA has been demonstrated to exceed that of THA, but patient selection is critical. The procedure is now also conservative on the acetabular side, and revision of the cementless acetabular component is rare. The operative parameters of femoral resurfacing revisions (conversion to a THA) are similar to that of a primary THA. Bearing technology will continue to evolve.

Estimation of the wear volume after total hip replacement. A simple access to geometrical concepts

Various formulas have been proposed to calculate the volume of prosthetic wear from the penetration depth of the head as assessed on plain radiographs, based on idealized, three-dimensional geometrical models of a prosthetic hip. However, for most published formulas no (or no simple) derivation is available and not all of them are correct. We describe a simple geometrical model that allows for transparent derivation of equations for various components of prosthetic wear volume and compare the calculated volumes with those obtained from published equations. These components are: (1) a right generalized cylinder resulting from a linear shift of a half spherical part of the prosthetic head into the hemispherical cup, (2) an additional wedge that is "cut" from the cup and (3) the wear from an optional additional cylindrical portion of the cup. We emphasize that calculation of a three-dimensional wear volume from linear penetration depth should be based on a geometrical concept that is transparent and simple enough for clinical research, such as the one presented. The incorrect formula of Kabo et al. should be completely abandoned.

The optimal metal-metal arthroplasty is still a total hip arthroplasty: in opposition

The longevity of any hip arthroplasty in an individual patient cannot be predicted with certainty so revisability of the arthroplasty remains an issue. As the occurrence of loosening and osteolysis decreases, then fatigue failure of femoral stems, complications of modular connections, and infection will become relatively more common modes of failure. Metal-metal hip resurfacing conserves bone stock, which provides better options for revision surgery. Hip resurfacing favors early intervention and has demonstrated excellent outcomes in young active males, the group historically at increased risk for failure of a conventional total hip arthroplasty. The best balance of the benefit-risk ratio for hip resurfacing is in those patients at increased risk for failure of a conventional total hip arthroplasty.

Optimizing patient selection and outcomes with total hip resurfacing

Short-term failures of total hip resurfacing have been related to specific characteristics of the proximal femur. A radiographic arthritic hip grading scale was used to assess four characteristics of the proximal femur: bone density, shape, biomechanics, and focal bone defects. Hips with no unfavorable characteristics were Grade A, hips with one unfavorable characteristic were Grade B, hips with two unfavorable characteristics were Grade C, hips with three unfavorable characteristics were Grade D, and hips with four unfavorable characteristics were Grade F. One hundred forty-seven consecutive hips were treated with metal-on-metal resurfacing by a single surgeon. There were no femoral neck fractures. Of the 91 hips eligible for a minimum 2 year followup, 90% were Grades A or B, 10% were Grade C, and none were Grades D or F. With a minimum 2-year followup, arthritic hip grading was associated with preoperative Harris hip score, occurrence of mild to moderate postoperative pain, preoperative and postoperative range of motion, preoperative and postoperative hip center of rotation, preoperative and postoperative horizontal femoral offset, preoperative and postoperative limb length discrepancy, and acetabular radiolucencies. Hips with a lesser degree of secondary arthritic changes have a higher arthritic hip grade and better outcomes with total hip resurfacing. Relatively strict selection criteria for resurfacing were associated with a low occurrence of short-term failures.

LEVEL OF EVIDENCE

Prognostic study, Level II (retrospective study). See the Guidelines for Authors for a complete description of levels of evidence.

New approaches for the characterization of prosthetic joint biofilms

Indwelling prosthetic joints may become colonized by microbial biofilms, although the biofilm structure, composition of the microbial community, and physiologic activity of the organisms in these devices are not well understood. New approaches that rely on the use of fluorescent stain technology can be used to characterize the structure and community composition in a way that earlier methods, which relied on culturing or scanning electron microscopy, could not. Model systems incorporating parameters relevant for indwelling prosthetic joints also can be designed to evaluate the efficacy of treatments for preventing or eradicating biofilms from these devices. Effectively treating microbial biofilms on indwelling medical devices such as prosthetic joints is a challenging proposition. A clearer understanding of the process in vivo and a defined approach for evaluating treatment strategies provide the best hope for success.

Metal-on-metal resurfacing arthroplasty: no way under the sun!--in opposition

The functional demands and the longevity of hip arthroplasty patients are increasing. High volumetric wear and osteolysis limit the durability of metal-ultra high molecular weight polyethylene resurfacing. Cemented femoral hemiresurfacing components (no acetabular component) do not develop osteolysis and rarely loosen. Consistent long-term fixation has been demonstrated with hemispherical cementless acetabular components. Metal-metal bearings have demonstrated low wear and rare osteolysis over 3 decades of use. These facts form foundation for total hip resurfacing with metal-metal bearings.

The role of macrophages in osteolysis of total joint replacement

The osteolysis associated with conventional polyethylene on metal total joint replacements is associated with the formation of an inflamed periprosthetic membrane rich in macrophages, cytokines and implant-derived wear particles. There is a wealth of evidence to indicate that the presence and activation of macrophages in the periprosthetic tissues around joint replacements is stimulated by UHMWPE particles. Particles within the size range 0.1-1.0 microm have been shown to be the most reactive. Animal studies have provided increasing evidence that, of the milieu of cytokines produced by particle-stimulated macrophages, TNF-alpha is a key cytokine involved in osteolysis. Recent advances in the understanding of the mechanisms of osteoclastogenesis and osteoclast activation at the cellular and molecular level have indicated that bone marrow-derived macrophages may play a dual role in osteolysis associated with total joint replacement. Firstly, as the major cell in host defence responding to UHMWPE particles via the production of cytokines and secondly as precursors for the osteoclasts responsible for the ensuing bone resorption.

Un couple de frottement métal-métal peut-il améliorer la longévité des prothèses totales de hanche ?

PURPOSE OF THE STUDY

In total hip arthroplasty (THA), inter-series comparative clinical results cannot be considered worthy before at least 10 years of average follow-up, as shown in the Swedish Arthroplasty Register experience (1978-1993). Last generation metal-on-metal bearings were introduced in France only nine years ago (1995). To date, using mid term information, data from the literature, and our experience, one could assume that this bearing material has the capacity to improve THA longevity. Three types of information were analyzed: 1) comparative radiographic and EBRA studies published on early migration (<2 years) of acetabular implants; 2) preliminary comparative data on wear and osteolysis at the 8-year maximum follow-up; 3) clinical data on dislocation frequency and in vitro and in vivo observations of bearing separation and sliding. Study no 1: primary stability of these metal-on-metal acetabular cups was better than for polyethylene (PE) cups or alumina liners; study no 2: no detectable wear and less osteolysis were observed to date with metal-on-metal bearings versus their alumina-on-PE counterparts. Study no 3: less dislocation and less head sliding were measured with the metal-on-metal versus alumina-on-PR bearings possibly due to the interfacial forces provided by lubricating fluid (suction fit).

CONCLUSION

According to current knowledge, this metal-on-metal bearing still represent, with alumina-on-alumina and highly crosslinked PE, a competitive and comprehensive option to improve THA longevity. The real pending problem concerns the frequency and above all the intensity of metal delayed hypersensitivity reaction and their potential effect on implant loosening.

How I choose a bearing surface for my patients

There is insufficient clinical data to demonstrate the overall superiority of any one bearing couple for all total hip cases. It is therefore reasonable to individualize the choice of bearing surface. The fundamental exercise in choosing a bearing surface is maximizing the benefit to risk ratio. There are at least 3 perspectives to consider: the patient's, the surgeon's, and that of the health care delivery system. The following question should be addressed on a patient-by-patient basis: what available bearing is most likely to meet the needs of this patient, with an acceptable risk of revision surgery during his or her lifetime, is accepted in my community, and is there a means to pay for it?

Total resurfacing for osteonecrosis of the hip

With the resurgence of metal-on-metal bearings, there is renewed interest in total hip resurfacing. A cementless acetabular component used for resurfacing with a wall thickness of fewer than 5 mm is comparable in size to acetabular components used for total hip replacement. The fixation of a porous-ingrowth acetabular component used for resurfacing has been shown to be reliable and durable. There are few clinical reports of total hip resurfacing that stratify results by diagnosis. However, available evidence indicates that the pain relief, function, and activity after total hip resurfacing for osteonecrosis are superior to the results reported for hemiresurfacing and similar to the results of total hip replacement. Femoral-side failure is the main issue occurring with total resurfacing for osteonecrosis, and the femoral side failure rate is higher than that of hemiresurfacing. There are no simple guidelines for the extent of femoral head necrosis that are compatible with successful resurfacing. Refined patient selection and surgical technique can improve the outcomes and durability of total hip resurfacing for osteonecrosis.