Mechanical effects of stem cement interface characteristics in total hip replacement.

The influence of cement mantle thickness and stem geometry on fatigue damage in two different cemented hip femoral prostheses

Retrieval studies suggest that the loosening process of the cemented femoral components of total hip arthroplasties is initiated by failure of the bond between the prosthesis and the cement mantle. Finite element (FE) analyses have demonstrated that stem–cement debonding has stress-producing effects in the cement mantle. High interface friction, which corresponds to a degree of surface roughness, reduces these stresses. In experiments, however, debonded rough stems produced more cement damage than polished ones; in the Swedish Hip Register polished stems were clinically superior with respect to stems with a mat surface finish. The purpose of the present study was to investigate this contradiction. For this purpose, global and local FE models with debonded stem–cement interfaces were used to study the effects of prosthesis surface roughness on the cement stresses on a global scale and microscale, respectively. Similar to earlier numerical studies, the global FE model predicted that an increased surface roughness of the stem reduced the stresses in the cement mantle. The local model provided insight in the load-transfer mechanism on a microscale and could explain the experimental and clinical findings. The local cement peak stresses around the asperities of the surface roughness profile increased with increasing surface roughness and decreased again beyond a particular roughness value. Cement abrasion is caused by localized stresses in combination with micromotion. From this study it can be concluded that to minimize cement abrasion, debonded stems should either have a polished microstructure to minimize the local cement stresses or have a profiled macrostructure to minimize micromotions at the stem–cement interface. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 42, 554–559, 1998.

Fatigue crack growth rate does not depend on mantle thickness: an idealized cemented stem construct under torsional loading

Bone creep and short and long term subsidence after cemented stem total hip arthroplasty (THA)

This article describes a case of femoral stem displacement during closed reduction of a redislocated bipolar hemiarthroplasty of the hip in a 72-year-old woman who had undergone bipolar hemiarthroplasty using a polished, tapered cemented femoral stem. The polished, tapered cemented femoral stem is vulnerable to displacement when exposed to traction forces. Six days after bipolar hemiarthroplasty, the patient experienced her first dislocation, and immediate reduction of the dislocated hip was easily achieved. However, on the ninth postoperative day, redislocation occurred, and this time, reduction was not achieved. Subsequent radiographs revealed an unreduced state with posterosuperior dislocation of the hip and dissociation of the femoral stem at the cement-stem interface with proximal migration. Open reduction was then performed, and it was noted that the bipolar prosthesis had dislocated posterosuperiorly, the neck of the femoral stem was incarcerated between the short external rotators, and the femoral stem had migrated proximally by approximately 8 cm. The femoral stem was repositioned by freeing it from the short external rotators and gently tapping it into the cement mantle. Our surgical solution is questionable, because the stability of the stem is likely to be inadequate. According to the established study, no difference in stuffiness was observed before extraction and after reinsertion, which supports the surgical solution we chose. Pre-reduction analysis should be conducted to determine the cause and status of a dislocation, and open reduction should be performed if closed reduction fails when treating dislocated bipolar hemiarthroplasty patients.

This study analyzed 15 patients who underwent revision for loosening at the stem-cement interface. The femoral components were from the same manufacturer and had grit-blast roughened surfaces. An apparent radiographic deficiency in the cement mantle was present in at least one zone in 1 3 patients. In 9 of 12 patients with localized osteolysis, the osteolysis developed in a zone with an apparent radiographic cement mantle defect. Loosening occurred due to tension failure of the stem-cement interface followed by axial subsidence and movement into relative retroversion. Motion between the stem and the cement mantle fueled an abrasive wear mechanism between the roughened metal surface and the cement mantle, generating excessive metal and cement particles that gained access to endosteal bone via defects in the cement mantle and resulting in localized osteolysis. Although the roughened surface played a central role in these failures, it is unlikely the layer of polymethylmethacrylate (precoat) played a role in the mechanism of failure. In some cases, debonding occurred as a result of tension failure of the metal-precoat interface. In others, tension failure occurred within the cement mantle, leaving the precoat and some cement from the mantle on the stems. There was no difference in the mechanism of failure of stems with precoat proximally compared to stems with precoat proximally and distally. One stem had no precoat; findings in this patient were indistinguishable from the others. The significance of debonding depends on the surface roughness of the stem. Debonding carries a poorer prognosis with a rougher stem surface because of abrasive wear with the generation of numerous metal and cement particulates, which can lead to rapid osteolysis if there are cement mantle defects. Stems with a higher metal-cement bond strength may require a higher quality cement mantle for long-term success.

Understanding initiation and propagation of fretting wear on the femoral stem in total hip replacement

Characterisation of the surface topography, tomography and chemistry of fretting corrosion product found on retrieved polished femoral stems

Precooling of the femoral canal enhances shear strength at the cement–prosthesis interface and reduces the polymerization temperature

Introduction:Osteotomy around proximal femur provides excellent exposure and helps in revision of both cemented and uncemented femoral stem. Hereby, describing our case report on wedge episiotomy, a new surgical technique for removal of distal fitting cemented or uncemented femoral stem in conditions were extended trochanteric osteotomy (ETO) becomes inappropriate and episiotomy becomes inadequate.Case Report:A 35-year-old lady presented with painful right hip and difficulty in walking. Her X-rays showed a dissociated bipolar head and long cemented femoral stem prosthesis. She gave history of proximal femur giant cell tumor operated with cemented bipolar which failed in 4 months (Figs. 1, 2, 3). There were no signs of active infection such as discharging sinus and elevated blood infection markers. Hence, she was planned for one-stage revision of the femoral stem and conversion into total hip arthroplasty.Surgical Technique:A small trochanter fragment, along with the abductor and vastus lateralis continuity, was preserved and mobilized away augmenting hip exposure. The long femoral stem was found well fixed with a cement mantle all around in an unacceptable retroversion. There was metallosis with no macroscopic signs of infection. Taking in consideration of her young age and the long femoral prosthesis with cement mantle, the idea of ETO was considered inappropriate and more iatrogenic.Initially, an episiotomy was done along the lateral border of femur with an oscillating saw to interrupt the radio compressive force of the bone along the cement mantle and stem. However, the lateral episiotomy was not sufficient to loosen up the tight fit between bone and cement interface. Hence, a small wedge episiotomy was done along the full length lateral border of the femur (Figs. 5 and 6). A lateral wedge of 5 mm bone was removed increasing the exposure of bone cement interface with intact 3/4th cortical rim. This exposure allowed 2 mm K-wire, drill bit, flexible osteotome, and micro saw to go in between the bone and cement mantle to dissociate it. A 240 x 14 mm long uncemented femoral stem was fixed using bone cement extending along the entire femur length, With utmost care, all the cement mantle and implant were removed. The wound was soaked with three minutes of hydrogen peroxide and betadine solution and washed with high jet pulse lavage. A long 305 × 18 mm Wagner-SL revision uncemented stem was placed with adequate axial and rotational stability (Fig. 7). The long straight stem of 4 mm wider than the extracted was passed along the anterior femoral bowing augmenting the axial fit and the wagner fins helped in getting the much need rotational stability (Fig. 8). The acetabular socket was prepared with uncemented cup size of 46 mm with a posterior lip liner poly and 32 mm metal head was used. The wedge of bone was kept back along the lateral border and help with 5-ethibond sutures. Intraoperative histopathology sampling did not show any evidence of giant cell tumor recurrence, ALVAL score of 5 and microbiology culture grew negative. The physiotherapy protocol included non-weight-bearing walking for 3 months, later then partial loading was started and complete loading was done by end of fourth month. The patient had no complication such as tumor recurrence, periprosthetic joint infection (PJI) and implant failure at end of 2 years(Fig. 9).

Distal stem design and the torsional stability of cementless femoral stems

Recently much attention has been focused on the high incidence of thromboembolism following major hip surgery–and in particular total hip reconstruction. Mortality is at least 1.8% following total hip replacement in the absence of prophylaxis. Because of the difficulties encountered with use of anticoagulants such as warfarin sodium and heparin sodium, attention has been turned toward the dextran solutions as antiplatelet agents. Basic, however, to the use of an antiplatelet agent to prevent thromboembolism is an understanding of the central role of the platelet in thrombogenesis. Histopathologic studies have shown that the development of a mural platelet thrombus is the first stage of thrombus formation, not only in the arterial but also in the venous system. A number of studies have further shown that many patients who develop thromboemboli show an abnormality in platelet adhesiveness. The available evidence suggests that the activation of the venous thrombus may follow the formation

In orthopaedic surgery and particularly in the total hip arthroplasty, the stem fixation is performed in general using a surgical cement which consists essentially of polymer polymethyl-methacrylate (PMMA). During polymerisation of PMMA, residual stresses caused by volumetric and thermal shrinkage (exothermic reaction) are generated in the bulk cement. In this study, the three-dimensional finite element method is used to analyze the distribution stresses in the bone cement. Linear elastic analysis is adapted; von Mises, normal and shear stresses are the criterions that are of concern. The results showed that the inclusion of the residual stresses at the interface stem–cement increase the von Mises and the normal stresses in the different sides of the cement compared to the case without residual stresses.

The fatigue failure of bone cement, leading to loosening of the stem, is likely to be one mode of failure of cemented total hip replacements. There is strong evidence that cracks in the cement are initiated at voids which act as stress risers, particularly at the cement-stem interface. The preferential formation of voids at this site results from shrinkage during polymerisation and the initiation of this process at the warmer cement-bone interface, which causes bone cement to shrink away from the stem. A reversal of the direction of polymerisation would shrink the cement on to the stem and reduce or eliminate the formation of voids at this interface. We have investigated this by implanting hip prostheses, at room temperature or preheated to 44 degrees C, into human cadaver femora kept at 37 degrees C. Two types of bone cement were either hand-mixed or vacuum-mixed before implantation. We found that the area of porosity at the cement-stem interface was dramatically reduced by preheating the stem and that the preheating temperature of 44 degrees C determined by computer analysis of transient heat transfer was the minimum required to induce initial polymerisation at the cement-stem interface. Temperature measurements taken during these experiments in vitro showed that preheating of the stem caused a negligible increase in the temperature of the bone. Reduction of porosity at the cement-stem interface could significantly increase the life of hip arthroplasties.

Fatigue failure analysis of a specific total hip prosthesis stem design