Oxidized Zirconium Components Maintain a Smooth Articular Surface Except Following Hip Dislocation.

BACKGROUND: Oxidized zirconium (OxZr) offers theoretical advantages in total hip and knee arthroplasty (THA and TKA, respectively) relative to other biomaterials by combining the tribological benefits of ceramics with the fracture toughness of metals. Yet, some studies have found that OxZr does not improve outcomes or wear rates relative to traditional bearing materials such as cobalt-chromium (CoCr). Separately, effacement of the thin ceramic surface layer has been reported for OxZr components, though the prevalence and sequelae are unclear. METHODS: To elucidate the in vivo behavior of OxZr implants, the articular surfaces of 94 retrieved THA and TKA femoral components (43 OxZr TKA, 21 OxZr THA, 30 CoCr THA) were analyzed using optical microscopy, non-contact profilometry, and scanning electron microscopy. RESULTS: We found that OxZr components maintain a smooth articular surface except following hip dislocation. Three of four OxZr femoral heads revised following dislocation exhibited severe damage to the articular surface, including macroscopic regions of ceramic-layer effacement and exposure of the underlying metal substrate; these components were 23-32 times rougher than pristine OxZr controls. When revised for dislocation, OxZr femoral heads were substantially rougher than CoCr femoral heads (median Sa = 0.431 v. 0.020 µm, P = .03). In contrast, CoCr femoral heads exhibited low overall roughness values regardless of whether they dislocated (median Sa = 0.020 v. 0.008 µm, P = .09, CoCr dislocators v. non-dislocators). CONCLUSIONS: Effacement of the ceramic surface layer and substantial articular surface roughening is not atypical following dislocation of OxZr femoral heads, making OxZr much less tolerant than CoCr to hip dislocation.

Novel Acetabular Cup for Revision THA Improves Hip Center of Rotation: A Radiographic Evaluation.

BACKGROUND: Bone loss in patients undergoing revision THA poses a considerable challenge for orthopaedic surgeons. Often, to achieve better fixation in remaining bone, larger diameter acetabular components and reaming superiorly may be necessary. However, this is likely to raise the hip center of rotation, which may lead to altered biomechanics, specifically, insufficiency of the abductor muscles, altered gait, and increased risk of dislocation from impingement. More recently, a newer acetabular shell has been designed to more closely replicate the native hip center of rotation in these circumstances while maintaining adequate fixation. QUESTIONS/PURPOSES: The purpose of this study was to compare the radiographic parameters of this newer design with conventional hemispheric cups in revision THA. Specifically, we assessed the differences in (1) vertical center of rotation (COR) displacement and (2) horizontal COR displacement. METHODS: Between January 2016 and April 2016, five reconstructive surgeons at five institutions utilized a newer highly porous acetabular shell designed with peripheral screw holes and vertically eccentric COR to allow for restoration of center of hip rotation in revision THA. We included all patients who received this device. During this time, the general indications at these sites for using the new device included Paprosky Stage IIA, IIB, IIC, or IIIA acetabular defects. This yielded 29 patients who were subsequently matched (one to two) by cup size and sex to a cohort who underwent revision THA with conventional hemispheric cups between January 2015 and May 2016. To determine hip COR, radiographic measurements were performed. A circle contiguous to the acetabulum was drawn and the center was determined as the hip COR. All measurements were made from the interteardrop line for both the revised and native hips. A line through the teardrops was used for all horizontal measurements. Center position adjustments were made based on the manufacturer-specified values. Comparisons were performed using chi-square tests for categorical and t-tests for continuous variables. There was no difference in the severity of bone loss before the revision in the groups, as evidenced by Paprosky staging of preoperative radiographs. RESULTS: The mean vertical COR displacement was smaller in patients who had the novel cup (3.5 mm; range, -12 to 15 mm; mean difference, -7.3 mm; 95% confidence interval [CI], -13.2 to -1.5) as compared with those who had the conventional cup (10.5 mm; range, -4 to 50 mm; mean difference, 7.3 mm; 95% CI, -12.5 to -2.2; p = 0.003). There was no difference in mean horizontal displacement between the two groups (-0.06 ± 6.1 versus 1.7 ± 7.1; mean difference, -1.8; p = 0.903). CONCLUSIONS: Although hip COR was improved based on radiographic measurements with the use of this novel acetabular design, and although this may improve hip biomechanics, more studies are required before its widespread adoption for revision cases of this nature can be recommended. Both implant costs and the risks associated with using a new design in practice will have to be justified by studies that evaluate fixation, clinical function and implant survival, and patient-reported outcome scores, all of which were beyond the scope of this preliminary report. LEVEL OF EVIDENCE: Level III, therapeutic study.

Comparison of Head Center Position and Screw Fixation Options Between a Jumbo Cup and an Offset Center of Rotation Cup in Revision Total Hip Arthroplasty: A Computer Simulation Study.

Jumbo acetabular cups are commonly used in revision total hip arthroplasty (THA). A straightforward reaming technique is used which is similar to primary THA. However, jumbo cups may also be associated with hip center elevation, limited screw fixation options, and anterior soft tissue impingement. A partially truncated hemispherical shell was designed with an offset center of rotation, thick superior rim, and beveled anterior and superior rims as an alternative to a conventional jumbo cup. A three dimensional computer simulation was used to assess head center position and safe screw trajectories. Results of this in vitro study indicate that a modified hemispherical implant geometry can reduce head center elevation while permitting favorable screw fixation trajectories into the pelvis in comparison to a conventional jumbo cup.

Do jumbo cups cause hip center elevation in revision THA? A radiographic evaluation.

BACKGROUND: Acetabular revision THA with use of a large (jumbo) cup is an effective treatment for many cavitary and segmental peripheral bone defects. However, hip center elevation may occur with use of a jumbo cup owing to reaming superiorly and/or because of the increased diameter of the jumbo cup compared with the native acetabulum. QUESTIONS/PURPOSES: In our jumbo cup revision THAs, we attempted to avoid hip center elevation by placing the inferior edge of the cup at the inferior acetabulum. In this study, we asked (1) how much of an elevation in the hip center is observed radiographically with use of jumbo cups, and (2) how effective was our technique in minimizing hip center elevation during revision THA in clinical practice? METHODS: We retrospectively reviewed radiographic data for all patients, from one surgeon's practice, who received a jumbo cup (defined as cup size ≥ 66 mm in men, ≥ 62 mm in women) during an acetabular revision between 1998 and 2012 and who had an anatomically placed THA or no THA on the contralateral side (so as to be able to make comparisons); 98 patients were identified and included. The height of the revised hip center was measured relative to the contralateral normal hip. Cup elevation resulting from superior reaming was determined by measuring the distance from the inferior cup edge to the interteardrop line. The mean hip center elevation and cup position relative to the interteardrop line in male and female patients were compared using unpaired t-tests. RESULTS: Radiographic analysis showed a mean hip center elevation of 11 mm. On average, 1 mm of the measured hip center elevation was the result of cup placement superior to its planned position at the interteardop line. CONCLUSIONS: Our results indicate that revision THA with a jumbo cup is associated with hip center elevation despite placement of the cup at the inferior acetabulum. An increase in femoral head length may be needed to compensate for hip center elevation with use of a jumbo cup. LEVEL OF EVIDENCE: Level III, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

Do jumbo cups cause hip center elevation in revision THA? A computer simulation.

BACKGROUND: Acetabular revision THA with use of a large (jumbo) cup is an effective treatment for many cavitary and segmental peripheral bone defects. However, the jumbo cup may result in elevation of the hip center and protrusion through the anterior acetabular wall as a result of the oversized geometry of the jumbo cup compared with the physiologic acetabulum. QUESTIONS/PURPOSES: The purpose of this computer simulation was to determine how much elevation of the hip center and anterior wall protrusion occurs in revision THA with use of a jumbo cup technique in which the inferior edge of the jumbo cup is placed at the inferior acetabular rim and the superior edge of the jumbo cup is placed against host bone at the superior margin of a posterosuperior bone defect. METHODS: Two hundred sixty-five pelvic CT scans were analyzed by custom CT analytical software. The computer simulated oversized reaming. The vertical and anterior reamer center shifts were measured, and anterior column bone removal was determined. RESULTS: The computer simulation demonstrated that the hip center shifted 0.27 mm superiorly and 0.02 mm anteriorly, and anterior column bone removal increased 0.86 mm for every 1-mm increase in reamer diameter. CONCLUSIONS: Our results indicate that the jumbo cup technique results in hip center elevation despite placement of the cup adjacent to the inferior acetabulum. For a hypothetical increase from a 54-mm socket to a 72-mm socket, as one might see in the context of the revision of a failed THA, our model would predict an elevation of the hip center of approximately 5 mm and loss of approximately 15 mm of anterior column bone. This suggests that an increase in femoral head length may be needed to compensate for the hip center elevation caused by the use of a large jumbo cup in revision THA. A jumbo cup may also result in protrusion through the anterior wall.

Targeted use of vancomycin as perioperative prophylaxis reduces periprosthetic joint infection in revision TKA.

BACKGROUND: The role of vancomycin in surgical antimicrobial prophylaxis and high-risk patients who are most likely to benefit remains unclear. QUESTIONS/PURPOSES: We determined the impact of targeted use of vancomycin on (1) the incidence of periprosthetic joint infection (PJI); and (2) the incidence of PJI from methicillin-resistant organisms in patients undergoing revision total knee arthroplasty (TKA) at our institution. METHODS: In an effort to reduce PJI rates, we added vancomycin to cefazolin as surgical antimicrobial prophylaxis for patients undergoing revision TKA in October 2010. Internal data indicated a high rate of PJI in revision TKA and in particular PJI resulting from methicillin-resistant organisms, including methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-resistant Staphylococcus epidermidis (MRSE). We retrospectively reviewed infection control surveillance data on 414 revision TKAs performed between July 2008 and June 2012 (fiscal years 2009-2012). RESULTS: The overall rate of PJI in fiscal years 2009-2010 among 190 patients undergoing revision TKA was 7.89%. After the change in surgical antimicrobial prophylaxis, there was a significant reduction in PJI among patients undergoing revision TKA in fiscal years 2011-2012 to 3.13% (p = 0.046). In particular, we observed a reduction in PJI resulting from methicillin-resistant organisms over this same time period, from 4.21% to 0.89% (p = 0.049). CONCLUSIONS: Targeted use of vancomycin in patients undergoing revision TKA was effective in reducing the rate of PJI and PJI resulting from methicillin-resistant organisms in an institution with a high baseline rate of PJI due to MRSA and MRSE. Identification of high-risk subgroups of patients within a surgical population can help target infection prevention strategies to those who are most likely to benefit and thus minimize potential risks (eg, selection of resistant organisms, adverse drug events) associated with broader application of such an intervention.

Total knee arthroplasty in patients with juvenile idiopathic arthritis.

BACKGROUND: Total knee arthroplasty (TKA) for juvenile idiopathic arthritis is rare but is nonetheless indicated for many patients with this disease. Few reports exist on the results of TKA in patients with juvenile idiopathic arthritis. QUESTIONS/PURPOSES: It was sought to determine (1) survivorship and (2) functional outcomes of TKAs in patients with juvenile idiopathic arthritis. METHODS: Results were combined from patients treated by experienced surgeons at five hospitals between 1979 and 2011. Two hundred nineteen patients (349 TKAs) were identified and contacted to survey their outcomes at a minimum followup of 2 years (mean, 12 ± 8 years; range, 2-33 years). The average age at surgery was 28.9 ± 9.7 years (range, 11-58 years). Data on revision surgery and ability to perform daily activities were collected. RESULTS: The 10-year survivorship was 95%, decreasing to 82% by 20 years. At latest followup, 31 of 349 TKAs (8.9%) had been revised for either polyethylene failure or loosening (18 TKAs), infection (four), stiffness (three), periprosthetic fractures (two), bilateral amputation for vascular reasons (two), patellar resurfacing (one), and instability (one). Walking tolerance was unlimited in 49%, five to 10 blocks in 23%, and less than five blocks in 28%. Eleven percent could not manage stairs, and another 59% depended on railings. A cane was used by 12% and crutches by 7%; 12% were wheelchair-dependent. CONCLUSIONS: TKA survivorship in patients with juvenile idiopathic arthritis was inferior to that typically seen in younger patients with osteoarthritis or even rheumatoid arthritis confirming results of earlier studies with smaller patient numbers. This is especially disconcerting because younger patients require better durability of their TKAs.

Advances in acetabular osteolysis: biomarkers, imaging, and pharmacologic management.

Acetabular osteolysis can be difficult to diagnose because patients often have no clinical symptoms even when there is substantial bone loss. Ideally, early detection would lead to early interventions. Imaging continues to be the frontline modality for the early detection of acetabular osteolysis. Although plain radiography is the current imaging modality most commonly used in routine follow-up examinations, its low sensitivity limits its usefulness. CT and MRI have proven to be better imaging modalities for the early detection of osteolysis; however, their use is limited by cost, radiation exposure, and time. Biomarkers hold promise for the early detection of osteolysis; however, their efficacy requires more rigorous research for validation. Early diagnosis and treatment of osteolysis may lead to better outcomes for patients.

Maximizing function and outcomes in acetabular reconstruction: segmental bony defects and pelvic discontinuity.

Acetabular reconstruction in revision total hip arthroplasty can be complicated by acetabular bone loss. In patients with severe acetabular bone deficiency with segmental bone defects or pelvic discontinuity, obtaining a stable, well-fixed acetabular component can be challenging. Although porous-coated, uncemented hemispheric cups can be used in most acetabular revisions, as the severity of acetabular deficiency increases, more complex alternatives are needed. Antiprotrusio cages have traditionally been used in the presence of acetabular columnar deficits, but higher failure rates and complications necessitated the development of alternative treatments. More recently, porous-coated acetabular augments have become an attractive alternative to structural allograft and oblong components when segmental bone loss is present. In the setting of severe bone loss or pelvic discontinuity, multiple reconstructive options are available. Depending on individual patient characteristics, plating of the pelvic discontinuity along with structural allografts, custom components, and modular or standard reconstructive cages can be used to obtain a stable acetabular component.

Advances in acetabular reconstruction in revision total hip arthroplasty: maximizing function and outcomes after treatment of periacetabular osteolysis around the well-fixed shell.

As the incidence of primary and revision hip arthroplasty increases, the need for a comprehensive approach to acetabular revision cannot be overstated. In the presence of osteolysis, there is a substantial population of patients with a well-fixed acetabular shell. It will be helpful to orthopaedic surgeons to review the classification of acetabular defects, techniques for exposing an acetabular component when the femoral component will be retained, methods of facilitating access to osteolytic lesions, the principles of bone grafting, options for liner fixation, and when removal of a well-fixed shell is necessary.

Acetabular reconstruction in revision total hip arthroplasty: maximizing function and outcomes in protrusio and cavitary defects.

Osteolysis in the periacetabular region is a common long-term complication of total hip arthroplasty that can lead to bone loss, implant loosening, and protrusio. Several systems have been developed for classifying osteolysis and guiding treatment. Options such as bone grafting or augmentation, with exchange of the bearing surface and, in some cases, revision of the acetabular component, can be used for treatment. Most cavitary and protrusio defects can be treated with a cementless revision cup using screw fixation and grafting with morcellized bone. However, structural augmentation, custom components, or cage reconstruction may occasionally be necessary for managing larger defects with severe loss of acetabular bone stock.