Migration of the acetabular component after revision with impacted morselized allografts: a radiostereometric 2-year follow-up analysis of 21 cases

Implant migration and bone mineral density measured simultaneously by low-dose CT scans: a 2-year study on 17 acetabular revisions with impaction bone grafting

Background and purpose - Early postoperative implant migration predicts failure of joint replacements. Bone mineral density reflects bone quality and bone-graft incorporation. Implant migration and bone densitometry analysis usually require special equipment. We investigated cup migration and bone mineral density changes simultaneously with low-dose CT scans after acetabular revision hip arthroplasty using impaction bone grafting.Patients and methods - We performed a low-dose CT postoperatively, after 6 weeks, and after 2 years in 17 patients, all revised using impaction bone grafting and a graft-compressing titanium shell in the acetabulum. 6 patients had combined segmental and cavitary acetabular defects. Cup migration was analyzed using CT-based micromotion analysis (CTMA). Bone mineral density was determined in the graft and in surrounding native bone using volumetric quantitative computed tomography (QCT). The bone graft volume was calculated from 3D reconstructions.Results - At 2 years, the translations were 1.5 (95% CI 0.4-2.6) mm in proximal direction, -0.6 (CI -1.6 to 0.4) in the medial direction and 0.3 (CI 0.0-0.6) in the anterior direction. The mean volume of impacted bone graft was 40 cm³ (CI 28-52). In the graft bone mineral density increased 14% after 6 weeks and 23% after 2 years. There was 1 mechanical failure.Interpretation - Proximal migration of the acetabular component was low and comparable to previous reports. There was a rapid increase of bone mineral density in the bone graft. Low-dose CT scans make migration analysis and bone densitometry measurements possible in the same setting, offering great diagnostic potential for hip arthroplasty patients.

Bone impaction grafting with trabecular metal augments in large defects in young patients: unravelling a new perspective in surgical technique

Background

Acetabular reconstruction with bone impaction grafting in large defects has yielded conflicting results.

Methods

This was a retrospective study of a case series of five patients with a young age (≤50 years) at the time of surgery who had large acetabular defects reconstructed by bone impaction grafting and trabecular metal augments. The mean follow-up was 79 months. We describe the surgical technique in detail.

Results

Improvement was significant on the WOMAC and SF-36 scales (p < 0.05). The radiographs taken at the last follow-up examination showed no migration of the polyethylene cup (p = 0.31) or differences in the abduction angle (p = 0.27) compared to the radiographs from the immediate postoperative period. One patient presented two dislocation episodes as a complication.

Conclusion

The combination of trabecular metal augments with the bone impaction grafting technique in young patients with large acetabular defects provides satisfactory results in the long term and restores the bone stock.

Acetabular Component Migration Measured Using Radiostereometric Analysis Following Revision Total Hip Arthroplasty: A Scoping Review

* Radiostereometric analysis (RSA) studies of acetabular component migration following revision total hip arthroplasty (THA) have a large variation in their methodology and reporting of results, and, therefore, they may not be directly comparable. Standardization of RSA reporting is recommended. * In our review of RSA studies, there was a trend for cemented acetabular components to have larger amounts of early proximal migration than uncemented acetabular components. Results regarding cemented and uncemented components should be reported separately. * Cohorts that addressed larger acetabular defects were associated with a larger amount of early migration. * Reporting the migration result at 1 and 2 years postoperatively may enable earlier identification of poorly performing implants.

High proximal migration in cemented acetabular revisions operated with bone impaction grafting; 47 revision cups followed with RSA for 17 years

BACKGROUND

Bone impaction grafting is a biologically and mechanically appealing option in acetabular revision surgery, allowing restitution of the bone stock and restoration of the biomechanics. We analysed differences in proximal migration of the revision acetabular components when bone impaction grafting is used together with a cemented or an uncemented cup.

PATIENTS AND METHODS

43 patients (47 hips), revised due to acetabular loosening and judged to have less than 50% host bone-implant contact were included. The hips were randomised to either an uncemented (n = 20) or a cemented (n = 27) revision cup. Radiostereometry and radiography was performed postoperatively, at 3 and 6 months, 1, 2, 3, 5, 7, 10 and 13 and 17 years postoperatively. Clinical follow-up was performed at 1, 2 and 5 years postoperatively and thereafter at the same interval as in the radiographic follow-up.

RESULTS

There were no differences in the base line demographic data between the 2 groups. At the last follow-up (17 years) 14 hips (10 cemented, 4 uncemented) had been re-revised due to loosening. 3 additional cups (1 uncemented and 2 cemented) were radiographically loose. There was a higher early proximal migration in the cemented cups.

DISCUSSION

Cups operated on with cement showed a higher early migration measured with RSA and also a higher number of late revisions. The reason for this is not known, but factors such as inclusion of cases with severe bone defects, use of smaller bone chips and issues related to the impaction technique might have had various degrees of influence.

Does cup-cage reconstruction with oversized cups provide initial stability in THA for osteoporotic acetabular fractures?

BACKGROUND

The incidence of acetabular fractures in osteoporotic patients is increasing. Immediate total hip arthroplasty (THA) has potential advantages, but achieving acetabular component stability is challenging and, at early followup, reported revision rates for loosening are high.

QUESTIONS/PURPOSES

This study measured acetabular component stability and the initial surface contact achieved between the acetabular component and unfractured region of the pelvis after THA using an oversized acetabular component and cup-cage reconstruction.

METHODS

Between November 2011 and November 2013, we treated 40 acute acetabular fractures in patients older than 70 years of age. Of these, 12 (30%) underwent immediate THA using an oversized acetabular component with screws inserted only into the ilium and a cup-cage construct. Postoperatively all patients were mobilized without weightbearing restrictions. Indications for immediate THA after acetabular fractures were displaced articular comminution deemed unreducible. Eleven of the 12 were prospectively studied to evaluate the initial stability of the reconstructions using radiostereometric analysis. One of the patients died of a pulmonary embolism after surgery, and the remaining 10 (median age, 81 years; range, 72-86 years) were studied. Of these, five were analyzed at 1 year and five were analyzed at 2 years. Acetabular component migration was defined as acceptable if less than the limits for primary THA that predict later loosening (1.76 mm of proximal migration and 2.53° of sagittal rotation). The contact surface between the acetabular component and ilium in direct continuity with the sacroiliac joint, and the ischium and pubis in direct continuity with the symphysis pubis, was measured on postoperative CT scans.

RESULTS

At 1 year the median proximal migration was 0.83 mm (range, 0.09-5.13 mm) and sagittal rotation was 1.3° (range, 0.1°-7.4°). Three of the 10 components had migration above the suggested limits for primary THA at 1 year postoperatively. The contact surface achieved at surgery between the acetabular component and pelvis ranged from 11 to 17 cm(2) (15%-27% of each component).

CONCLUSIONS

The majority of acetabular components in this cohort were stable despite the small contact surface achieved between the component and pelvic bone. Three of 10 migrated in excess of the limits that predict later loosening in primary THA but it remains to be seen whether these limits apply to this selected group of frail osteoporotic patients. We continue to use this technique routinely to treat patients with the same indications, but since the analysis of these data we have added screw fixation of the acetabular component to the ischial tuberosity and the superior pubic ramus.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

Results using Trabecular Metal™ augments in combination with acetabular impaction bone grafting in deficient acetabula

We examined whether the use of trabecular metal wedges to fill segmental defects is an effective method of socket reconstruction when used in combination with impaction grafting and implantation of a cemented socket. Fifteen hips in 14 patients underwent impaction grafting in combination with a TM wedge with a minimum of two years follow-up. All patients had their defects assessed using the Paprosky classification. Patients were reviewed with x-rays and migration of the implant was measured. Outcome scores were also collected. Mean follow-up was 39 months (25-83). The mean age at surgery was 67.8 (49-85) years. Seven of the patients had previously undergone impaction grafting with the use of a stainless steel rim mesh to constrain the graft. None of the patients had failed either clinically or radiologically.

A novel technique for impaction bone grafting in acetabular reconstruction of revision total hip arthroplasty using an ex vivo compaction device

BACKGROUND

Impaction bone grafting allows restoration of the acetabular bone stock in revision hip arthroplasty. The success of this technique depends largely on achieving adequate initial stability of the component. To obtain well-compacted, well-graded allograft aggregates, we developed an ex vivo compaction device to apply it in revision total hip arthroplasty on the acetabular side, and characterized mechanical properties and putative osteoconductivity of allograft aggregates.

METHODS

Morselized allograft bone chips were compacted ex vivo using the creep technique and subsequent impaction technique to form the bone aggregates. Impaction allograft reconstruction of the acetabulum using an ex vivo compaction device was performed on eight hips. The mechanical properties and three-dimensional micro-CT-based structural characteristics of the bone aggregates were investigated.

RESULTS

In clinical practice, this technique offered good reproducibility in reconstructing the cavity and the segmental defects of the acetabulum, with no migration and no loosening of the component. In vitro analysis showed that the aggregates generated from 25 g fresh-frozen bone chips gained compression stiffness of 13.5-15.4 MPa under uniaxial consolidation strain. The recoil of the aggregates after compaction was 2.6-3.9%. The compression stiffness and the recoil did not differ significantly from those measured using a variety of proportions of large- and small-sized bone chips. Micro-CT-based structural analysis revealed average pore sizes of 268-299 μm and average throat diameter of pores in the bone aggregates of more than 100 μm. These sizes are desirable for osteoconduction, although large interconnected pores of more than 500 μm were detectable in association with the proportion of large-sized bone chips. Cement penetration into the aggregates was related to the proportion of large-sized bone chips.

CONCLUSION

This study introduces the value of an ex vivo compaction device in bone graft compaction in clinical applications. In vitro analysis provided evidence that compaction of sequential layers of well-compacted, well-graded bone aggregates, i.e., the aggregates comprising smaller sized chips at the host bone side and larger sized chips at the component side, may have the advantages of initial stability of the acetabular component and biological response of the grafted aggregates.

Reconstruction of peri-implant bone defects using impacted bone allograft and BMP-2 gene-modified bone marrow stromal cells

Impaction bone allografting represents an attractive procedure for bone defects reconstruction in joint replacement. And it was found that bone morphogenetic protein-2(BMP-2) gene therapy can enhance bone healing. The purpose of this study was to determine if combined adenovirus mediated human BMP-2(Adv-hBMP-2) gene-modified bone marrow stromal cells(BMSCs) with allograft enhanced the defects healing and improved the strength of implant fixation in 3-mm bone defect around a titanium alloy implant. Using the impaction grafting technique, the defects were reconstructed using freeze-dried allograft, freeze-dried allografts loaded with autogenous BMSCs, or freeze-dried allografts loaded with autogenous BMSCs modified with the human bone morphogenetic protein-2 (hBMP-2) gene. At 6 and 12 weeks, the Bone-implant Contact rate and strength of the interface in the group with BMP-2 gene medication were significantly higher than those of the non-cell or cell groups. BMP-2 gene medication also showed significant effects on allograft healing and replacement compared with those of two other groups, as evidenced by increased new bone formation and reduced graft remnants. The results suggest that BMP-2 gene medication can enhance allograft healing and osseointegration of the bone-implant interface.

Assessment of the initial stability of the Symax femoral stem with EBRA-FCA: a multicentric study of 85 cases

We report a study of 85 Symax femoral stems that were followed at regular intervals with radiographs at 6, 12, 24 and 36 months. The radiological migration of each stem was measured using the computer-assisted EBRA -FCA method. In 30 cases in which the EBRA method did not provide a complete measurement another computer-assisted method (Roman version 1.7) was employed. In all cases the distal migration of the stems was minimal, The threshold migration value used to define the stability of a stem was 1.5 mm at 24 months. The mean migration within the first two years was -0.17 mm (+/- 0.3) at 6 months, -0.31 mm (+/- 0.4) at 12 months and -0.45 mm (+/- 0.5) at 24 months. Only two cases exceeded the threshold limit of 1.5 mm at the two-year follow-up, but both values were lower than 2 mm. In the 25 cases which reached three-year follow-up the mean distal migration was -0.84 (+/-0.7). In four of them the subsidence exceeded 1.5 mm, but only one exceeded 2 mm. These data represent a positive predictive factor for the minimal risk of future aseptic loosening.

Acetabular revision surgery with impacted bone allografts and cemented cups in patients younger than 55 years

This article summarises a clinical and radiographical analysis of 30 acetabular revisions in patients younger than 55 years old, performed with impaction bone grafting and cemented cups. Preoperative Merle D'Aubigne and Postel functional score was an average 7 points. At a mean follow-up of 86.5 months (range 34-228) functional score averaged 16.3 points. Radiolucent lines with no clinical impact were observed in 7% of DeLee and Charnley acetabular zones evaluated. Massive radiological migration, consistent with clinical failure, was observed in two cups. Three patients underwent re-revision surgery (10%): two due to infection and one due to mechanical failure. Reconstruction survival rate was 89% (CI 95% 71.9-96.4) overall, and 96% (CI 95% 82.6-99.3) ruling out cases of infection. Impacted bone allograft constitutes one of the reconstructive techniques of choice in acetabular revision surgery of young patients. Restoration of bone stock is essential in this group of patients due to the possibility of future revisions.

The elastic properties of morsellised cortico-cancellous bone graft are dependent on its prior loading

Confined compression experiments were carried out on cortico-cancellous bone taken from bovine femoral condyles to assess the effect of prior loading on the elastic confined modulus, E(c) of morsellised cortico-cancellous bone (MCB). Measurements were taken to find the values of E(c) for MCB subjected to cyclic loading resulting in axial stresses in the range of 0.5-3.0 N mm(2). Two values of E(c) were considered: E(ic), the instantaneous modulus, and E(dc), the delayed modulus allowing for stress relaxation effects. It was found that the values of E(c) increased with increasing maximum axial stress. It was also found that for each stress level the values of E(c) increased as the number of load cycles increased. The dependence of E(c) on the maximum axial stress and the number of load cycles is seen to explain the wide range of values for the apparent modulus of MCB found in previous studies. Tests examining the stress relaxation behaviour of MCB are also discussed. The results indicate that a minimum of 10 compaction episodes are required for MCB to achieve around 90% of its predicted maximum stiffness for a given compaction force.

Five-year follow-up of socket movements and loosening after revision with impacted morselized allograft bone and cement: a radiostereometric and radiographic analysis

In 1999, we reported on the 2-year results of a series of 21 first-time socket revisions using impacted morselized allograft bone. Seven still migrated between 1.5 and 2 years. Seventeen remained for the current 5-year follow-up. No socket had been rerevised. Five sockets showed signs of radiographic loosening. These 5 cases also exhibited radiographic signs of allograft resorption as well as high rates of socket migration and rotation as measured by radiostereometric analysis. Of the 6 remaining sockets that had migrated between 1.5 and 2 years, 3 stabilized and 3 were among those with signs of radiographic loosening. Fifteen patients (15 hips) revealed pain reduction at the 5-year follow-up. Three had slight pain on walking that disappeared immediately at rest (pain score 4). All the others revealed either no pain (pain score 6) or slight pain that disappeared with activity (pain score 5). No pattern of early socket migration according to radiostereometric analysis could be identified, predicting later socket migration or loosening. The rate of cases with signs of radiographic loosening (29%, 5/17) was comparable to that reported by the Nijmegen group but the follow-up was shorter in the current study. The rate of cases with signs of radiographic loosening was comparable to both conventionally cemented socket revisions and cementless revisions. The future will show if further sockets loosen and if the loose sockets up to date will end up in rerevisions.

Acetabular reconstruction with impacted bone allografts and cemented acetabular components

We reviewed the clinical and radiological results of 131 patients who underwent acetabular revision for aseptic loosening with impacted bone allograft and a cemented acetabular component. The mean follow-up was 51.7 months (24 to 156).

The mean post-operative Merle D’Aubigné and Postel scores were 5.7 points (4 to 6) for pain, 5.2 (3 to 6) for gait and 4.5 (2 to 6) for mobility. Radiological evaluation revealed migration greater than 5 mm in four acetabular components. Radiological failure matched clinical failure. Asymptomatic radiolucent lines were observed in 31 of 426 areas assessed (7%). Further revision was required in six patients (4.5%), this was due to infection in three and mechanical failure in three. The survival rate for the reconstruction was 95.8% (95% confidence interval 92.3 to 99.1) overall, and 98%, excluding revision due to sepsis.

Our study, from an independent centre, has reproduced the results of the originators of the method.

Acetabular reconstruction with the Burch-Schneider ring: an EBRA analysis of 40 cup revisions

BACKGROUND

Reconstruction of the bone stock and fixation of the implant remain challenging problems in revision surgery. In this retrospective study, we wanted to gain information on initial stability and wear after revision with the Burch-Schneider ring.

PATIENTS AND METHODS

Between 1994 and 1998, we performed 70 reconstructions of the acetabulum with a Burch-Schneider ring in revision arthroplasty. 63 patients could be followed up clinically and radiographically. 40 cups were suitable for EBRA measurements whereas migration and wear could not be assessed by this method in 23 cases due to lack of comparability of pelvic radiographs. The mean follow-up time was 4.7 years.

RESULTS

2 cups were re-revised and 14 cups had breakage or changes of position of the screws. 30 cups showed detectable migration and 18 cups detectable wear. The mean migration was 2.8 mm and the mean wear rate was 0.12 mm/year. 16 cups had detectable migration after 1 year; 11 of these 16 continued to migrate and 9 of them had screw breakage. Both re-revisions showed early migration. Early migration correlated with later screw breakage and the overall migration correlated with wear. The only risk factor found for early migration was the wear rate.

INTERPRETATION

The Burch-Schneider ring is an established and reliable implant for cup revision with good clinical results, but it seems to be difficult to maintain intraoperative stability. The implants with continuous migration may lead to late clinical failure and require further observation. Wear may contribute to migration and resorption of the bone graft.

O uso de enxerto homólogo na revisão de artroplastias do quadril com cimentação do componente acetabular

A artroplastia total do quadril representa um grande avanço no tratamento das enfermidades ortopédicas que acometem o quadril. A soltura asséptica desta prótese pode causar lesões e perdas ósseas, representando um grande desafio para a reconstrução cirúrgica destas artroplastias. Uma das alternativas para a reconstrução é o uso do enxerto ósseo de banco de ossos, podendo este ser usado em bloco ou na forma picada. Este estudo, baseado em uma revisão da literatura sobre enxertos ósseos, teve como objetivo uma análise quanto à reconstrução com enxertos em bloco e picado e sua integração. O enxerto picado mostrou melhores resultados quanto à integração quando se consegue estabilidade da reconstrução. Quando não conseguimos uma boa estabilidade, o enxerto em bloco associado aos anéis de reforço sobressai como a melhor opção.

The effect of acetabular cup size on the short-term stability of revision hip arthroplasty: A finite element investigation

The study uses idealized two-dimensional finite element models to examine the behaviour of the acetabular construct following revision hip arthroplasty, carried out using the Slooff-Ling impaction grafting technique. The behaviour of bone graft was considered in detail, with non-linear elasticity and non-associated plasticity being adopted. Load was applied to the acetabular construct through a femoral head using smooth sliding surfaces. In particular, four models were subjected to two idealized cyclic load cases to investigate the effect of acetabular cup size on the short-term stability of the acetabular construct. The study suggests that benefits may be gained by using the largest practical size of acetabular cup.

Skeletal tissue engineering-from in vitro studies to large animal models

Bone is a tissue with a strong regenerative potential. New strategies for tissue engineering of bone should therefore only focus on defects with a certain size that will not heal spontaneously. In the development of tissue-engineered constructs many variables may play a role, e.g. the source of the cells used, the design and mechanical properties of the scaffold and the concentration and mode of application of growth factor(s). Models for studying new strategies for tissue engineering of bone should be based on the target tissue to be restored. However, in light of the many potential variables, which may also interact if used in combination(s), there is also a large need for relatively simple models in which variables can be tested in a limited number of animals. Moreover, in compromised bone there may be a problem with the load-bearing capacity of the remaining healthy bone. In this light, an important prerequisite for tissue-engineering constructs is that they can be tested in loaded conditions. Particularly, this latter prerequisite is very difficult to achieve. Therefore, in vitro tests for mechanical stability are very useful for evaluating the mechanical consequences of a particular reconstruction procedure prior to the animal experiment. Before a tissue-engineered construct can be introduced into a clinical trial, a final test should be available in a large animal model that is as close and relevant to a particular problematic clinical situation as possible.In the past, a series of models were developed in our laboratory that are very useful for testing tissue-engineered constructs. In this paper, we focus on the use of relatively new simple in vitro and in vivo models for hip revision surgery, segmental bone defect restoration and tumour surgery.

Wire mesh allows more revascularization than a strut in impaction bone grafting: an animal study in goats

Segmental defects can be reconstructed with a cortical strut or a metal wire mesh when using bone impaction grafting in the femur. We hypothesized that structural grafts would negatively influence revascularization of the underlying impacted grafts compared with an open wire mesh. A standardized large medial wall defect was reconstructed with a strut or a mesh in six goats per group. In all femurs impaction grafting was done in combination with a cemented collarless double-tapered highly polished Exeter stem. After 6 weeks the femurs were harvested. A high rate of periprosthetic fractures was observed (three of seven and two of six for the strut and mesh groups, respectively). Histologic analysis showed different revascularization and tissue ingrowth patterns for both reconstruction techniques. In the strut group, fibrous tissue ingrowth was limited to the edges of the defect. Medially behind the strut no or limited fibrous tissue ingrowth was found. In the mesh group, fibrous tissue and blood vessels penetrated the mesh and a superficial zone of revascularized grafts was observed. Although revascularization, concomitant graft resorption and bone incorporation may compromise the short-term stability of the stem after surgery, the long-term stability of the stem probably is best guaranteed by graft incorporation.

The role of stainless steel wire mesh and cement in bone allograft incorporation in impaction grafting technique: an experimental study in rabbits

Cages of flexible stainless steel wire mesh were filled with impacted morcellized cancellous allograft. Bone defects were created in both tibial metaphyseal regions of 10 adult white New Zealand rabbits. The base of both defects was plugged with a small amount of bone cement. The cages were implanted in the right tibia while the left tibia was filled with impacted bone allograft. Histologic and histomorphometric evaluation of the retrieved specimens at 3 months showed a statistically significant difference in active bone formation parameters between the 2 groups. Active bone formation was more prominent away from the bone cement. The biological process of bone graft incorporation in the "impaction grafting" technique seems to be adversely affected by stainless steel wire mesh and in areas adjacent to bone cement.

Fibrous tissue armoring increases the mechanical strength of an impacted bone graft

Impacted, morselized bone allografts are used with good clinical results in revision of hip prostheses with loosening and osteolysis. The impacted bone graft appears radiographically to remodel, but histological analyses have shown a heterogeneous picture with a mixture of living and dead bone. Thus, complete remodeling of the graft may be neither a prerequisite nor a cause of the good clinical results. The present study concerns the mechanical effect of the mere armoring of the bone graft by ingrowing fibrous tissue. We compared the compression strength of freshly-impacted grafts to grafts that had been inserted into a bone chamber and thus were penetrated by fibrous tissue growing in between the graft trabeculae. The compressive strength was doubled after 4 weeks of fibrous ingrowth. We conclude that the mechanical properties of an impacted graft are enhanced by armoring with ingrowing fibrous tissue. Strengthening of the parts of the impacted grafts which have not yet remodeled, would be clinically relevant for the outcome of the operation, since these parts are at high stress during the whole remodeling period. Complete osseous remodeling may not be necessary to obtain a good clinical result with a morselized impacted graft.

Radiostereometric analysis in hip revision surgery--optimal time for index examination: 6 patients revised with impacted allografts and cement followed weekly for 6 weeks

We revised the hip (6 stems and 5 sockets) with impacted morselized allografts and cement in 6 patients. We followed prosthetic migration by roentgen radiostereometric analysis (RSA) every 7th day for 6 weeks after the first (index) examination performed on the first postoperative day before mobilization. Most of the migration occurred during the first 2 weeks. In most cases more than half of the distal stem migration was seen between the 1st and 14th days. In all cases, the stem and socket migrations slowed down gradually and several prosthetic components had become stable after 5 weeks. We conclude that it is essential to perform the index RSA examination on the 1st or 2nd day after surgery and to state when and how weight bearing should be permitted. Otherwise it will be difficult to compare prosthetic migration in various studies and define normative values for migration predicting survival.