First-time revision acetabular components have a 36% re-revision rate at 10 years in Australia, with subsequent revisions known to have even worse results. Acetabular component migration >1mm at two years following revision THA is a surrogate for long term loosening. This study aimed to measure the migration of porous tantalum components used at revision surgery and investigate the effect of achieving press-fit and/or three-point fixation within acetabular bone. Between May 2011 and March 2018, 55 patients (56 hips; 30 female, 25 male) underwent acetabular revision THR with a porous tantalum component, with a post-operative CT scan to assess implant to host bone contact achieved and Radiostereometric Analysis (RSA) examinations on day 2, 3 months, 1 and 2 years. A porous tantalum component was used because the defects treated (Paprosky IIa:IIb:IIc:IIIa:IIIb; 2:6:8:22:18; 13 with pelvic discontinuity) were either deemed too large or in a position preventing screw fixation of an implant with low coefficient of friction. Press-fit and three-point fixation of the implant was assessed intra-operatively and on postoperative imaging. Three-point acetabular fixation was achieved in 51 hips (92%), 34 (62%) of which were press-fit. The mean implant to host bone contact achieved was 36% (range 9-71%). The majority (52/56, 93%) of components demonstrated acceptable early stability. Four components migrated >1mm proximally at two years (1.1, 3.2, 3.6 and 16.4mm). Three of these were in hips with Paprosky IIIB defects, including 2 with pelvic discontinuity. Neither press-fit nor three-point fixation was achieved for these three components and the cup to host bone contact achieved was low (30, 32 and 59%). The majority of porous tantalum components had acceptable stability at two years following revision surgery despite treating large acetabular defects and poor bone quality. Components without press-fit or three-point fixation were associated with unacceptable amounts of early migration

Abstract. Objectives. Stem malalignment in total hip arthroplasty (THA) has been associated with poor long-term outcomes and increased complications (e.g. periprosthetic femoral fractures). Our understanding of the biomechanical impact of stem alignment in cemented and uncemented THA is still limited. This study aimed to investigate the effect of stem fixation method, stem positioning, and compromised bone stock in THA. Methods. Validated FE models of cemented (C-stem – stainless steel) and uncemented (Corail – titanium) THA were developed to match corresponding experimental model datasets; concordance correlation agreement of 0.78 & 0.88 for cemented & uncemented respectively. Comparison of the aforementioned stems was carried out reflecting decisions made in the current clinical practice. FE models of the implant positioned in varus, valgus, and neutral alignment were then developed and altered to represent five different bone defects according to the Paprosky classification (Type I – Type IIIb). Strain was measured on the femur at 0mm (B1), 40mm (B2), and 80mm (B3) from the lesser trochanter. Results. Cemented constructs had lower strain on the implant neck, and higher overall stiffness and strain on bone compared to uncemented THA. Strain on the bone increased further down the shaft of the femoral diaphysis, and with progressing bone defect severity in all stem alignment cases. Highest strain on the femur was found at B2 in all stem alignment and bone defect models. Varus alignment showed higher overall femoral strain in both fixation methods. Interestingly, in uncemented models, highest strain was shown on femoral bone proximally (B1-B2) in varus alignment, but distally (B3) in neutral alignment. Conclusion. Varus stem alignment showed overall higher strain on femur compared to neutral and valgus. This highlights the crucial role of stem alignment in long term outcomes of THA. Differences between the two stem types should be taken in consideration when interpreting results from this study

Revision total hip arthroplasty (THA) presents with increasing challenges, potentially compromising the integrity of a revision. The objective of this study was to assess radiologic outcomes of patients who underwent revision THA with a modular tapered stem (Reclaim, DePuy Synthes). This study retrospectively examined all revision Reclaim THAs between 2012 and 2016. Radiologic assessment compared x-rays at two time points: immediately after surgery and the most recent x-ray available. Leg length discrepancy, subsidence and line-to-line fit was assessed. Significant subsidence was considered ≥10mm. Adequate line-to-line fit was considered ≥30mm of bicortical contact. Descriptive statistics included clinical factors (i.e. age, Paprosky classification). P values <0.05 were considered significant. A total of 81 femoral revisions were completed. There were 42 females and 38 males with a mean age of 71 years (range, 46–89). Of these, 6 were revised (dislocation, fracture or infection), and 7 were lost to follow up. Average follow up time was 18 months (range, 1–46 months). Femoral revisions were classified as Paprosky 3a or 3b. Mean stem subsidence was 4.15mm (range, 0–25.6mm). Subsidence of the femoral stem was <10mm in 88% of patients. A total of 62% of patients had both subsidence <10mm and ≥30mm of bicortical contact. In patients with <10mm subsidence, 70% had ≥30mm of bicortical contact. There was a positive trend between cortical contact and stem stability (OR 2.3). The Reclaim modular femoral system has demonstrated radiographic stability. Inadequate initial fit is a potential determinant of subsidence

Introduction

The objective of this study was to compare the performance of the Explant Acetabular Cup Removal System (Zimmer), which has been the favored system for many surgeons during hip revision surgery, and the new EZout Powered Acetabular Revision System (Stryker).

Reconstruction of severe acetabular defects during revision hip arthroplasty presents a significant surgical challenge. Such defects are associated with significant loss of host bone stock, which must be addressed in order to achieve stable implant fixation. A number of imaging techniques including CT scanning with 3D image reconstruction are available to assist the surgeon in the pre-operative planning of such procedures. We describe the use of a novel technique to assist the pre-operative planning of severe acetabular defects during revision hip arthroplasty. Patient and Methods – We present the use of this technique in the case of a 78 year old patient who presented 20 years from index procedure with severe hip pain and inability to weight bear due aseptic loosening of a previously revised total hip arthroplasty. A Paprosky 3B defect was noted with intra-pelvic migration of the acetabular component. Pre-operative investigations included: inflammatory markers, pelvic CT scan with 3D reconstruction, pelvic angiography and hip aspiration. Using DICOM images obtained from the CT scan, we used free open source software to carry out a 3D surface render of the bony pelvis. This was processed and converted to a suitable format for 3D printing. Using selective laser sintering, a physical 3D model of the pelvis, acetabular component and proximal femur were produced. Using this model the surgeon was able to gain an accurate representation of both the position of the intra-pelvic cup and more accurately assess the loss of bone stock. This novel technique is particularly useful in the pre-operative planning of such complex acetabular defects in order to determine if/which reconstruction technique is most likely to be successful. 3D printing is a relatively recent technology, which has numerous potential clinical applications. This is the first reported case of this technology being used to assess acetabular defects during revision hip arthroplasty. The use of this technology gives the surgeon a 3D model of the pelvis, quickly (7 days from CT) and at a tenth of the cost (£280) of producing such a model through the traditional commercial routes. The model allowed the surgeon to size potential implant, quantify the amount of bone graft required (if applicable) and to more accurately classify the loss of acetabular bone stock

Summary. This work proposes a novel, automatic method to obtain an anatomical reconstruction for 3D segmented bones with large acetabular defects. The method works through the fitting of a Statistical Shape Model to the non-defect parts of the bone. Introduction. Patient-specific implants can be used to treat patients with large acetabular bone defects (IIa-c, IIIb, Paprosky 1994). These implants require a full 3D preoperative planning that includes segmentation of volumetric images (CT or MRI), extraction of the 3D shape, reconstruction of the bone defect into its anatomic (non-defect) state, design of an implant with a perfect fit and optimal placement of the screws. The anatomic reconstruction of the bone defect will play a key role in diagnosing the amount of bone loss and in the design of the implant. Previous reconstruction methods rely on a healthy contralateral (Gelaude 2007); however this is not always available (e.g. partial scan or implant present). Statistical shape models (SSM) of healthy bones can help to increase the accuracy and usability of the reconstruction and will decrease the manual labor and user dependency. Skadlubowicz (2009) illustrated the use of an SSM to reconstruct pelvic bones with tumor defects; however tumors generally affect a smaller region of the bone so that the reconstruction will be easier than in large acetabular bone defects. Also, the tumor reconstruction method uses 80 manually indicated landmarks, while the proposed method only uses 14. Patients & Methods. CT-scans from subjects with a healthy hemi-pelvis (15 male, 33 female, mean age: 69±20) were used to generate an SSM. The CT-scans were segmented using Mimics (Materialise NV, Belgium) to create a triangulated mesh. Preprocessing of the meshes ensured that the triangulation was smooth and uniform to help solve the corresponding point problem. An algorithm based on Redert (1999) was used to morph the template hemi-pelvis onto each dataset entity, creating a dataset with corresponding points. From this dataset the SSM was calculated using principal component analysis, so that the principal components serve as parameters for the mathematical model of the hemi-pelvis. To fit the SSM to a new defect hemi-pelvis, a matching algorithm was used. The algorithm varies the Principal Components independently optimizing the distance of the non-defect parts of the defect hemi-pelvis to the SSM sample. To validate the reconstruction method, 6 healthy bone meshes were used to generate a synthetic defect in the acetabular region. The original mesh was used as ‘golden standard’ to measure the reconstruction error. To illustrate the clinical use of the reconstruction method, one hemi-pelvis with a substantial defect was reconstructed. Results. The correspondence error for the morphing algorithm was 4.68±0.78 mm. The leave-one-out error for the SSM was 1.30±0.96 mm. The reconstruction error for the non-defect part was 1.44±1.13mm and for the reconstructed part 2.15±1.53mm. Discussion/Conclusion. The proposed method performs comparable to the contralateral method and the tumor reconstruction method, without the need of a healthy contralateral geometry. Consequently, the validation and the clinical illustration show that the proposed method is promising for automatic reconstruction of large acetabular defects

We used a biodegradable mesh to convert an acetabular defect into a contained defect in six patients at total hip replacement. Their mean age was 61 years (46 to 69). The mean follow-up was 32 months (19 to 50). Before clinical use, the strength retention and hydrolytic in vitro degradation properties of the implants were studied in the laboratory over a two-year period. A successful clinical outcome was determined by the radiological findings and the Harris hip score.

All the patients had a satisfactory outcome and no mechanical failures or other complications were observed. No protrusion of any of the impacted grafts was observed beyond the mesh. According to our preliminary laboratory and clinical results the biodegradable mesh is suitable for augmenting uncontained acetabular defects in which the primary stability of the implanted acetabular component is provided by the host bone. In the case of defects of the acetabular floor this new application provides a safe method of preventing graft material from protruding excessively into the pelvis and the mesh seems to tolerate bone-impaction grafting in selected patients with primary and revision total hip replacement.