Dissociation of modular total hip arthroplasty at the femoral head-neck interface after loosening of the acetabular shell following hip dislocation

Modular component dissociation is a potential problem of current modular total hip arthroplasty (THA) systems. We describe a case of dissociation of the modular THA at the femoral head-neck interface after loosening of the acetabular shell during closed reduction for posterior dislocation of THA. The causes of this dissociation and acetabular shell loosening are discussed. Successful treatment was provided with surgical revision of the acetabular and the femoral head components. The present case serves as a graphic reminder that the acetabular shell overhanging the acetabular bone must be avoided when implanting modular THA components.     

Biomechanics of large femoral heads: what they do and don't do

The stability and durability of total hip reconstruction is dependent on many factors that include the design and anatomic orientation of prosthetic components. An analysis of femoral component head size and acetabular component orientation shows an interdependency of these variables and joint stability. Increased femoral component head size can increase hip stability by increasing the prosthetic impingement-free range of hip motion and by increasing the inferior head displacement required before hip dislocation. Increasing the femoral head size from 22 mm to 40 mm increases the required displacement for dislocation by about 5 mm with the acetabular component at 45 degrees of abduction; however, increasing acetabular component abduction greatly diminishes this stability advantage of larger femoral heads. Vertical acetabular component orientation and femoral component head subluxation are each predicted to more than double the tensile stress with acetabular component polyethylene compared with components at 45 degrees of abduction. With a desirable acetabular component orientation, the use of larger femoral heads may result in improved joint stability and durable use of polyethylene. With high abduction acetabular component orientation, the use of larger femoral heads contributes little to joint stability and contributes to elevated stress within the polyethylene that may result in implant failure.     

The Effects of Acetabular Shell Deformation and Liner Thickness on Frictional Torque in Ultrahigh-Molecular-Weight Polyethylene Acetabular Bearings

The purposes of this study were to determine if there were differences in the frictional torque generated between spherical acetabular shells and acetabular shells deformed as a result of implantation and to evaluate how changes in polyethylene insert thickness and head diameter affected these frictional torque data. An established bench top model was used for mechanical testing. A total of 70 samples were tested. Acetabular shells were impacted into polyurethane foam that was designed to create spherical or deformed shell models. We found that deformed acetabular shells produced higher frictional torque than spherical shells. Also, larger femoral head sizes produced greater frictional torque than smaller femoral head sizes. For the deformed models, the thicker polyethylene inserts produced greater frictional torque than the thinner polyethylene inserts.     

Comparison of Bone Removed During Total Hip Arthroplasty With a Resurfacing or Conventional Femoral Component : A Cadaveric Study

We sought to examine the amount of bone removed during total hip arthroplasty with a resurfacing femoral component, compared to with a conventional, stemmed femoral component, by using 6 male and 4 female cadaveric pelves with attached bilateral proximal femora. Using randomized assignment and order, a total hip arthroplasty with a resurfacing femoral implant was performed on one side, and total hip arthroplasty with a cementless, stemmed femoral implant was performed on the contralateral side. The relationship between native femoral head diameter and the implanted acetabular socket was on average within 2 mm for both procedures. No significant difference was observed in the amount of acetabular bone removed (9.8 g for hip resurfacing vs 8.8 g). However, a resurfacing component resulted in approximated 3 × less bone removal from the femur (25.8 g vs 75.1 g). This study shows that the preservation of femoral bone with a resurfacing femoral component does not result in an increased removal of acetabular bone when compared to the use of a conventional, stemmed femoral component.     

Effect of femoral head size on wear of the polyethylene acetabular component

A technique was developed to determine the wear of the acetabular component of a total hip replacement by examination of standardized initial and follow-up radiographs. Three hundred and eighty-five hips were followed for at least 9.5 years after replacement. The least amount and rate of linear wear were associated with use of a femoral head that had a diameter of twenty-eight millimeters (p less than 0.001). The greatest amount and mean rate of linear wear occurred with twenty-two-millimeter components, but these differences were not statistically significant. The greatest volumetric wear and mean rate rate of volumetric wear were seen with thirty-two-millimeter components (p less than 0.001). A wider radiolucent line in acetabular Zone 1 was associated with use of the thirty-two-millimeter head. The amounts of resorption of the proximal part of the femoral neck and of lysis of the proximal part of the femur both correlated positively with the extent of linear and volumetric wear; this suggests an association between the amount of debris from wear and these changes in the femoral neck and proximal part of the femur.     

Factors Affecting Bony Impingement in Hip Arthroplasty

Computer modeling of 10 patients' computed tomographic scans was used to study the variables affecting hip arthroplasty range of motion before bony impingement (ROMBI) including acetabular offset and height, femoral offset, height and anteversion, and osteophyte removal. The ROMBI was compared with the ROM before component impingement and the native hip ROM. The ROMBI decreased with decreased total offset and limb shortening. Acetabular offset and height had a greater effect on ROMBI than femoral offset and height. The ROMBI lost with decreased acetabular offset was not fully recoverable with an increase in femoral offset or osteophyte removal. Bony impingement increased and component impingement decreased with decreased acetabular offset and increased head diameter.     

Experimental and clinical studies concerned with the Jikei femoral head prosthesis (author's transl)

For experimental purposes, femoral head prostheses for dogs, using both high density polyethylene (HDP) or titanium as the material for the head, were developed. Periodic observations of the acetabular cartilage influenced by the prosthetic head were done. The results showed that HDP was not suitable as a material for the artificial head because of rapid degeneration of the acetabular cartilage and marked wear and deformity of the HDP femoral head as soon as the surgery was done. On the other hand, the titanium femoral head was seen as causing much less damage to the acetabular cartilage in those cases where the diameter of the prosthetic head was quite adequate in its size. These findings indicated that the metal prosthetic head was useful for clinical cases. It was also clarified that the fixing of the stem to the bone could be achieved with our self-locking design instead of the use of bone cement. In follow-up studies of clinical cases used by the Jikei titanium femoral head prosthesis based upon our experimental results, it was found that better results could be expected when care is taken to use a femoral head which is not larger against the acetabulum. In addition, it was proved the procedure with the femoral head prosthesis is not indicated in cases where degeneration in acetabular cartilage has already occurred.     

Cementless total hip replacement using second-generation components: a 12- to 16-year follow-up

We reviewed 123 second-generation uncemented total hip replacements performed on 115 patients by a single surgeon between 1993 and 1994. The acetabular component used in all cases was a fully porous-coated threaded hemispheric titanium shell (T-Tap ST) with a calcium ion stearate-free, isostatically compression-moulded polyethylene liner. The titanium femoral component used was a Taperloc with a reduced distal stem. No patient was lost to follow-up. Complete clinical and radiological follow-up was obtained for all 123 hips at a mean of 14 years (12 to 16). One femoral component was revised after a fracture, and three acetabular components for aseptic loosening. No additional femoral or acetabular components were judged loose by radiological criteria. Mild proximal femoral osteolysis was identified in two hips and minor acetabular osteolysis was present in four. The mean rate of penetration of the femoral head was 0.036 mm/year (0.000 to 0.227). These findings suggest that refinements in component design may be associated with excellent long-term fixation in cementless primary total hip replacement.     

Range of motion and stability in total hip arthroplasty with 28-, 32-, 38-, and 44-mm femoral head sizes

The purpose of this study was to evaluate, via experimental models, the effect of larger head sizes for total hip arthroplasty on the type of impingement, range of motion (ROM), and joint stability. Testing was conducted using an anatomic full-size hip model (anatomic goniometer) and a novel anatomic dislocation simulator with 28-, 32-, 38-, and 44-mm diameter femoral heads within a 61-mm acetabular shell. Femoral heads >32-mm provided greater ROM and virtually complete elimination of component-to-component impingement. A significant increase in both flexion before dislocation and displacement between the femoral head and acetabulum to produce dislocation occurred with femoral heads >32-mm in diameter. These data indicate that larger femoral heads offer potential in providing greater hip ROM and joint stability.     

Uncemented acetabular components with bulk femoral head autograft for acetabular reconstruction in developmental dysplasia of the hip: results at five to twelve years.

BACKGROUND: Anterolateral acetabular bone deficiency is one of the technical problems associated with total hip arthroplasty in patients with developmental hip dysplasia. The purpose of this study was to evaluate the results of one method of acetabular reconstruction for hip dysplasia-placement of an uncemented socket in conjunction with a bulk femoral head autograft. METHODS: Forty-four hips in thirty-five patients (twenty-nine female and six male; average age, thirty-nine years) with developmental hip dysplasia were treated with primary total hip arthroplasty with use of an uncemented porous-coated titanium cup fixed with screws and an autogenous bulk femoral head graft. The patients were followed clinically in a prospective fashion for five to 12.3 years (mean, 7.5 years), and radiographs were analyzed retrospectively. RESULTS: Four acetabular components were revised: two, because of severe polyethylene wear and osteolysis; one, because of aseptic loosening; and one, because of fracture of the acetabular shell. The mean Harris hip score for the unrevised hips improved from 51 points preoperatively to 91 points postoperatively. No unrevised socket had definite radiographic evidence of loosening. Forty-three of the forty-four hips had no radiographic evidence of resorption of the graft or had radiographic evidence of resorption limited to the nonstressed area of the graft lateral to the edge of the cup. CONCLUSIONS: This method of reconstruction provided reliable acetabular fixation and appeared to restore acetabular bone stock in patients with developmental hip dysplasia. We use this technique for patients with moderate anterolateral acetabular bone deficiency requiring total hip arthroplasty.     

Efficacy of alumina ceramic heads for cemented total hip arthroplasty.

Fifty-seven cemented total hip arthroplasties (THAs) were reviewed in cases of osteoarthrosis secondary to congenital dysplasia or dislocation. The bearing surface of the prosthesis used in this series consists of a polyethylene acetabular component on an alumina ceramic head. All acetabular components were positioned at the same level as the original acetabulum, and an autologous femoral head graft was performed for 18 hips. The follow-up period ranged from five to eight years, averaging six years two months. The latest survey showed excellent and good results for 53 hips (92.9%). Four acetabular components (7%) and two femoral components (3.5%) showed roentgenographic evidence of loosening. Only one hip (1.8%) had to be treated with revision surgery for femoral component loosening. None of the cases suffered a broken ceramic head. The use of a total hip prosthesis with an alumina ceramic head in THA is likely to lead to excellent results for patients with osteoarthrosis of the hip.     

Intrapelvic cementless component extraction with immediate triflange acetabular reconstruction using the retroperitoneal approach

Use of the retroperitoneal approach has been well documented and used for intrapelvic cemented components or cement masses. We report on a single stage revision hip arthroplasty that incorporates a retroperitoneal approach for safe removal of an extensively entrapped porous-coated acetabular component and modular femoral head followed by an immediate reconstruction using a triflange acetabular prosthesis via a posterior approach.     

Acetabular diameter measurement determines proper prosthetic head size in hemiarthroplasty for femoral head osteonecrosis

In hemiarthroplasty for femoral head osteonecrosis, collapse and deformity may make femoral head measurement difficult, thus, precluding the selection of an appropriate prosthetic head. We describe a method for measuring the acetabular diameter using acetabular sizing gauges to estimate the prosthetic head size. We evaluated the precision of this method and found it to be highly accurate and reliable.     

Late liner disassociation of a Pinnacle system acetabular component

This article describes a case of late locking mechanism failure and disassociation of a Pinnacle acetabular cup (DePuy, Warsaw, Indiana) and Marathon polyethylene liner (DePuy) 53 months after routine primary total hip arthroplasty in an active patient. Following an uncomplicated initial postoperative recovery, the patient felt a pop while kneeling for gardening activities. The patient had no prodromal symptoms but reported pain with range of motion and weight bearing following the episode. Radiographs appeared to show a fractured liner with intact acetabular and femoral components. Intraoperatively, the liner was disassociated and dislocated inferior to the acetabulum, and 3 consecutive antirotational tines were sheared off the liner at their bases. The acetabular cup and femoral stem were well fixed. Extensive metallosis existed from the femoral head and acetabular shell articulating in the absence of a liner. The patient underwent revision of the acetabular cup, polyethylene liner, and femoral head due to the concern for osteolysis given the extensive metallosis. Revision of the acetabular cup and liner were performed with no further complications. No conclusions could be made as to the exact mechanism of failure following laboratory analysis of the retrieved polyethylene liner. Several possible mechanisms of failure are possible. Although cases of acute disassociation of this system have been reported, this is the first article to our knowledge to report failure at such a late postoperative time.     

Cementing acetabular sockets into metal-backed acetabular components and antiprotrusio cages: a technical tip

Cementing a polyethylene socket or acetabular liner into a well-fixed metal-backed acetabular shell has become a useful procedure in selected complex primary and revision hip arthroplasties. Polyethylene sockets are frequently cemented into antiprotrusio cages as well. Frequently, these metallic devices are fixed to host bone with acetabular screws. Unfortunately, when polyethylene sockets are cemented into such devices, the cement fills the recess within the screw head and makes subsequent screw removal extremely difficult should the device need to be removed or revised. The author describes a technique of filling the screw heads with bone wax and gel foam before cementation. This keeps the recess within the screw head relatively patent and allows easier removal of the screw in the future should it become necessary.     

Late detachment modular femoral component after primary total hip replacement

Three years after total hip replacement surgery, a patient's modular femoral head separated from the stem portion of a primary total hip replacement while the patient was rising from a chair. The modular femoral head was in a polyethylene acetabular socket. Modular femoral and acetabular components now widely are used in hip replacement. The use of modular components greatly increases the flexibility during primary or revision total hip arthroplasty, but introduces the risks of component dissociation and intraoperative errors in matching. We report an unusually late dislocation of a primary modular total hip replacement.     

Does a Monoblock Acetabular Component With a Ceramic Liner Cause More Pelvic Bone Loss Than a Conventional Modular Cementless Acetabular Component? A 2-Year Randomized Clinical Trial

BackgroundCeramic-on-ceramic bearings permit the use of large femoral head size while maintaining a favorable effect on wear rates. However, because of increased device rigidity, periprosthetic bone quality could be negatively affected due to stress shielding. The purpose of this study is to assess pelvic periprosthetic bone remodeling around a monoblock ceramic-on-ceramic acetabular component compared to that around a conventional modular metal-on-polyethylene device.MethodsParticipants were randomized to receive hip replacement using either a porous-coated, modular metal-on-polyethylene acetabular component (n = 46) or a hydroxyapatite and titanium-coated monoblock shell with an integrated ceramic-on-ceramic bearing (n = 40). Radiographic assessments were completed preoperatively and postoperatively, and measurements of bone mineral density (BMD) using dual-energy X-ray absorptiometry with region free analysis were performed postoperatively and over 2-years of follow-up.ResultsThere was no significant difference in BMD between the 2 groups at baseline or over the following 2 years. At follow-up, complete shell-to-bone contact without a radiolucent line was observed in 26 (67%) of the modular devices and in 37 (93%) of monoblock (P < .001). The modular device was an independent predictor of radiolucent lines (odds ratio 19.1, P = .007). No cases underwent revision surgery for acetabular loosening.ConclusionBoth the porous-coated modular and hydroxyapatite-coated monoblock acetabular components showed successful clinical results at short-term follow-up with no difference in pixel-level BMD. Using a large head monoblock device does not appear to be associated with an adverse effect on the local bone environment when compared to a modular device.NCTNCT01558752.     

Metallosis after metal-on-polyethylene total hip arthroplasty

Metal debris should not be generated in a well-fixed, well-functioning metal-on-polyethylene total hip arthroplasty. However, surgeons sometimes encounter periprosthetic metallosis during revision hip surgery. Insert wear, fracture, or dislodgment in modular components may lead to articulation of the prosthetic head with the metallic shell and subsequent metallosis. Metallosis may occur with loose acetabular components as a consequence of fretting of the screws and shell screw holes or shedding of the ingrowth surface of the component. The femoral component can also be a source of metallosis: Wear of a titanium femoral head, loosening of rough surface finish from the femoral stem, and stem fracture all may result in metallic particles being deposited in periarticular tissues. Specific clinical and radiographic findings can help in differentiating these forms of failure and in planning surgery. When metallic debris-induced bone loss is recognized early, surgical intervention may limit its progression.     

A randomised study comparing resection of acetabular bone at resurfacing and total hip replacement

We have undertaken a prospective, randomised study to compare conservation of acetabular bone after total hip replacement and resurfacing arthroplasty of the hip. We randomly assigned 210 hips to one of the two treatment groups. Uncemented, press-fit acetabular components were used for both. No significant difference was found in the mean diameter of acetabular implant inserted in the groups (54.74 mm for total hip replacement and 54.90 mm for resurfacing arthroplasty). In seven resurfacing procedures (6.8%), the surgeon used a larger size of component in order to match the corresponding diameter of the femoral component. With resurfacing arthroplasty, conservation of bone is clearly advantageous on the femoral side. Our study has shown that, with a specific design of acetabular implant and by following a careful surgical technique, removal of bone on the acetabular side is comparable with that of total hip replacement.     

Dissociation of modular hip arthroplasty components after dislocation. A report of three cases at differing dissociation levels.

Modular hip arthroplasty systems, currently widely employed, offer the advantage of increased intraoperative flexibility in component selection with reduced inventory, as well as the disadvantage of modular component dissociation. Dissociation during closed reduction for dislocation is reported in three patients at three different interface levels: (1) fixed acetabular shell-polyethylene linear interface, (2) bipolar acetabular component-femoral head interface, and (3) femoral head-neck interface. Subsequent open reduction was required in each case. Although this potential disadvantage of modular hip systems does not outweigh the benefits, it does warrant that certain precautions be taken when implanting modular components. The acetabular linear should lie flush within the metallic shell after impaction. The femoral head should be firmly impacted onto the neck. Both should resist reasonable manual force of disassembly. Should a modular hip arthroplasty component dislocate, gentle reduction under general anesthesia and fluoroscopic control is warranted. Careful inspection of pre- and postreduction roentgenograms for signs of modular component dissociation is mandatory.