Computed tomography-based radiostereometric analysis in orthopedic research: practical guidelines.

Early implant migration is an indicator of the long-term survival/failure of implants. CT-based radio-stereometric analysis (CT-RSA) is a precise method for measuring and visualizing implant migration in vivo using image processing of CT scans. This makes the method widely applicable to orthopedic researcher. Since its development in the early 2000s, CT-RSA has benefited from breakthroughs in CT and computing technology. These advancements have allowed for the acquisition of images with higher resolution at a much lower radiation dose. As a result, the measurement precision of CT-RSA is now comparable to that of the current gold standard technology while still compatible with most ethical considerations regarding radiation exposure. In this review we present bests practices for the successful execution of CT-RSA research projects. These practices are based on experience from projects on the hip, knee, shoulder, lower back, cervical spine, foot, pelvis, and wrist.

A randomized double-blind noninferiority trial, evaluating migration of a cemented vitamin E-stabilized highly crosslinked component compared with a standard polyethylene component in reverse hybrid total hip arthroplasty.

AIMS: Radiostereometric analysis (RSA) studies of vitamin E-doped, highly crosslinked polyethylene (VEPE) liners show low head penetration rates in cementless acetabular components. There is, however, currently no data on cemented VEPE acetabular components in total hip arthroplasty (THA). The aim of this study was to evaluate the safety of a new cemented VEPE component, compared with a conventional polyethylene (PE) component regarding migration, head penetration, and clinical results. PATIENTS AND METHODS: We enrolled 42 patients (21 male, 21 female) with osteoarthritis and a mean age of 67 years (sd 5), in a double-blinded, noninferiority, randomized controlled trial. The subjects were randomized in a 1:1 ratio to receive a reverse hybrid THA with a cemented component of either argon-gas gamma-sterilized PE component (controls) or VEPE, with identical geometry. The primary endpoint was proximal implant migration of the component at two years postoperatively measured with RSA. Secondary endpoints included total migration of the component, penetration of the femoral head into the component, and patient-reported outcome measurements. RESULTS: In total, 19 control implants and 18 implants in the VEPE group were analyzed for the primary endpoint. We found a continuous proximal migration of the component in the VEPE group that was significantly higher with a difference at two years of a mean 0.21 mm (95% confidence interval (CI) 0.05 to 0.37; p = 0.013). The total migration was also significantly higher in the VEPE group, but femoral head penetration was lower. We found no difference in clinical outcomes between the groups. CONCLUSION: At two years, this cemented VEPE component, although having a low head penetration and excellent clinical results, failed to meet noninferiority compared with the conventional implant by a proximal migration above the proposed safety threshold of RSA. The early proximal migration pattern of the VEPE component is a reason for continued monitoring, although a specific threshold for proximal migration and risk for later failure cannot be defined and needs further study. Cite this article: Bone Joint J 2019;101-B:1192-1198.

Osteoclasts in Periprosthetic Osteolysis: The Charnley Arthroplasty Revisited.

BACKGROUND: Periprosthetic osteolysis by polyethylene wear debris-triggered osteoclasts is viewed as the main pathophysiological pathway in aseptic loosening in total hip arthroplasty. The present aim was to study osteoclast occurrence in osteolytic lesions in early and late revisions of the Charnley low-friction torque arthroplasty (CLFA). METHODS: Biopsies of the soft interface membrane and the adjacent bone were taken from osteolytic lesions during revision of 16 loose CLFA, early (2-6 years) or late (>10 years) after primary surgery. By light microscopy (LM), cell-dense regions with signs of osteoclast-mediated bone resorption were selected for transmission electron microscopy. Three additional patients were studied in LM for osteoclast markers (tartrate-resistant acid phosphatase and Cathepsin K). RESULTS: LM disclosed a low-grade chronic inflammation and birefringent particles in most sections. Multiple conglomerates of tartrate-resistant acid phosphatase positive and Cathepsin K positive mononuclear and multinucleated cells were found deep in the fibrous interface membrane. Transmission electron microscopy showed traces of polyethylene-like particles in 67%-100% of the cells. Osteoclast-like cells exhibiting resorptive activity were few (mean, 0.7%; standard deviation, 0.2%), and multinucleated cells, possibly osteoclast precursor cells, located immediately on the bone were also scarce (mean, 2.7%; standard deviation, 5.3%). Multinucleated (odds ratio, 3.0; 95% confidence interval, 1.7-5.5) and macrophage-like cells (odds ratio, 3.6; 95% confidence interval, 2.2-5.6) were typically located deeper in the inflammatory interface membrane with a pathologic appearance with distension and abundance of phagocytic vacuoles. There were no systematic differences in cell populations between early or late revisions. CONCLUSION: Despite probable ongoing osteoclastogenesis in the osteolytic lesions, there were few sites of osteoclast-mediated bone resorption. These findings attach a contributing biological explanation to the longevity of the CLFA.

Abductor Muscle Function and Trochanteric Tenderness After Hemiarthroplasty for Femoral Neck Fracture.

OBJECTIVES: To compare the abductor muscle function and trochanteric tenderness in patients operated with hemiarthroplasty using the direct lateral (DL) or posterolateral (PL) approach for displaced femoral neck fracture. DESIGN: Prospective cohort study. SETTING: A secondary teaching hospital. PARTICIPANTS: We enrolled 183 hips operated with hemiarthroplasty for displaced femoral neck fracture using the DL or PL approach. INTERVENTIONS: Preoperatively, we evaluated the Harris hip score (HHS) and European Quality of Life-5 Dimensions (EQ-5D). At 1 year postoperatively, lucid patients were clinically examined to evaluate the Trendelenburg sign, abductor muscle strength with a dynamometer, and trochanteric tenderness with an electronic algometer. The 1-year HHS and EQ-5D were documented. MAIN OUTCOME MEASURES: The primary outcome was the incidence of postoperative Trendelenburg sign, whereas the secondary outcomes included patients' reported limp, abductor muscle strength, trochanteric tenderness, HHS, and EQ-5D. RESULTS: There were 48 patients (24 in the DL group and 24 in the PL group) who attended the 1-year clinical follow-up. The 2 groups were comparable (P > 0.05). The DL group showed a higher incidence of the Trendelenburg sign (9/24 vs. 1/24, P = 0.02) and limp (12/24 vs. 2/24, P = 0.004). Further analysis with logistic regression showed the surgical approach to be the only factor that resulted in the increment. No differences regarding HHS, EQ-5D, abductor muscle strength, algometer pressure pain threshold, and radiologic measurements were found (P > 0.05). CONCLUSIONS: The incidence of the Trendelenburg sign and limp were significantly higher in the DL approach although this seemed not to influence abductor muscle strength or the incidence of trochanteric tenderness or compromise the clinical outcome. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Debridement, antibiotics and implant retention in early periprosthetic joint infection.

INTRODUCTION: Periprosthetic joint infection (PJI) is a devastating complication in hip arthroplasty surgery. Debridement, antibiotics (AB) and implant retention (DAIR) is recommended in early PJI in association with stable implants. The aim of this study was to evaluate the success rate of DAIR in early PJI (<4 weeks) and to identify factors predicting the outcome. METHODS: This cohort study included a consecutive series of 35 patients (median age 74 years, 25 women, 26 primary arthroplasties) treated with DAIR for an early PJI in a regional hospital. RESULTS: 28 patients (80%) had their infection eradicated. DAIR-only eradicated the PJI in 22 (63%) patients with a median follow-up of 50 (24-84) months. In 17 (49%) patients, oral AB had been given prior to intraoperative cultures, which delayed first debridement with average 6 days and delayed hospital stay. Primary surgery for a hip fracture increased the risk of DAIR-failure. Surgical experience did not affect the outcome. 17% (n = 6) of the patients sustained a secondary infection during their hospital stay; the majority was beta-lactam resistant coagulase negative Staphylococcus aureus. CONCLUSIONS: The success rate of DAIR was inferior to pervious controls from experienced revision centers. Hip fracture patients should be informed about the increased risk of DAIR treatment failure. In order not to delay surgery, empirically based oral AB should not be administered prior to deep cultures. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT02087020.

Good stability but high periprosthetic bone mineral loss and late-occurring periprosthetic fractures with use of uncemented tapered femoral stems in patients with a femoral neck fracture.

BACKGROUND AND PURPOSE: We previously evaluated a new uncemented femoral stem designed for elderly patients with a femoral neck fracture and found stable implant fixation and good clinical results up to 2 years postoperatively, despite substantial periprosthetic bone mineral loss. We now present the medium-term follow-up results from this study. PATIENTS AND METHODS: In this observational prospective cohort study, we included 50 patients (mean age 81 (70-92) years) with a femoral neck fracture. All patients underwent surgery with a cemented cup and an uncemented stem specifically designed for fracture treatment. Outcome variables were migration of the stem measured with radiostereometry (RSA) and periprosthetic change in bone mineral density (BMD), measured with dual-energy X-ray absorptiometry (DXA). Hip function and health-related quality of life were assessed using the Harris hip score (HHS) and the EuroQol-5D (EQ-5D). DXA and RSA data were collected at regular intervals up to 4 years, and data concerning reoperations and hip-related complications were collected during a mean follow-up time of 5 (0.2-7.5) years. RESULTS: At 5 years, 19 patients had either passed away or were unavailable for further participation and 31 could be followed up. Of the original 50 patients, 6 patients had suffered a periprosthetic fracture, all of them sustained after the 2-year follow-up. In 19 patients, we obtained complete RSA and DXA data and no component had migrated after the 2-year follow-up. We also found a continuous total periprosthetic bone loss amounting to a median of -19% (-39 to 2). No changes in HHS or EQ-5D were observed during the follow-up period. INTERPRETATION: In this medium-term follow-up, the stem remained firmly fixed in bone despite considerable periprosthetic bone mineral loss. However, this bone loss might explain the high number of late-occurring periprosthetic fractures. Based on these results, we would not recommend uncemented femoral stems for the treatment of femoral neck fractures in the elderly.

Ureaplasma urealyticum infection in total hip arthroplasty leading to revision.

We describe an infection with Ureaplasma urealyticum causing rapid loosening of a cemented total hip arthroplasty. When reviewing the literature we found that no such case has been reported previously. Taking intraoperative cultures for U urealyticum during revision surgery is not a standard procedure. In cases with rapid, presumed aseptic, loosening of a total hip arthroplasty, an infection with U urealyticum should be considered.

Large femoral bone loss after hip revision using the uncemented proximally porous-coated Bi-Metric prosthesis: 22 hips followed for a mean of 6 years.

BACKGROUND AND PURPOSE: Periprosthetic bone loss after uncemented femoral hip revision is a matter of concern. We have used a proximally porous- and hydroxyapatite-coated prosthesis (Bi-Metric) in revision since 1989 and now we report the bone changes. This prosthesis is intended to distribute the forces more evenly and to avoid proximal femoral unloading. METHODS: 22 patients were unilaterally reoperated because of aseptic loosening. Only patients with a healthy contralateral hip were included. Mean age at revision was 69 (55-80) years. Bone defects were graded by Gustilo-Pasternak and Endo-Klinik classifications. Clinical assessment was performed with Harris hip score. We used radiographs and dual-energy X-ray absorptiometry to evaluate migration, femoral remodeling, and bone mineral density after 72 (30-158) months. RESULTS: The mean Harris hip score was 74 (30-100) points at follow-up. Mild thigh discomfort was present in 1 patient and moderate thigh pain in 3 patients. There was no loosening or subsidence. Osteolysis seen at revision had diminished in 19 of the 22 hips at follow-up. We noted a large reduction in bone mineral density. It was most pronounced in Gruen regions 1, 2, 6, and 7. INTERPRETATION: Revision with this stem is a reliable procedure; however, we noted a large degree of proximal bone loss that could lead to later mechanical complications or fractures.

Good results with an uncemented proximally HA-coated stem in hip revision surgery: 62 hips followed for 2-13 years.

BACKGROUND AND PURPOSE: Proximal bone loss due to stress-shielding is a matter of concern after uncemented femoral hip revision. We have used short, proximally hydroxyapatite-coated prostheses in revision since 1989, and we now report the results. METHODS: 60 patients (62 hips) were revised because of aseptic loosening. Bone defects prior to revision were mostly of type II according to the Gustilo-Pasternak and Endo-Klinik classifications. Follow-up time was 73 (24-161) months. 9 patients had died before follow-up; 8 of these still had the stem in place. Clinical assessment was performed with the Harris hip score. Radiographs were evaluated for bone defects at revision, postoperative stem fixation, and periprosthetic bone remodeling. RESULTS: Mean Harris hip score was 75 (30-100) points. There was no stem loosening or progressive subsidence. 8 patients had mild to moderate thigh pain. Osteolysis, present at revision, had diminished, partially or completely, in four-fifths of the hips at follow-up. 4 hips had required re-revision due to fracture or dislocation. The 6-year prosthesis survival rate was 95% (95% CI: 0.83-0.98). INTERPRETATION: Uncemented revision with a short, proximally hydroxyapatite-coated prosthesis is a reliable procedure with encouraging results in the medium term if bone defects at revision are moderate.

Periprosthetic proximal bone loss after uncemented hip arthroplasty is related to stem size: DXA measurements in 138 patients followed for 2-7 years.

BACKGROUND: Periprosthetic bone loss occurs around uncemented femoral stems and may be influenced by the stem size. PATIENTS AND METHODS: We studied 138 consecutive patients, 3 (2-7) years on average after a total hip arthroplasty operation (THA) for unilateral osteoarthritis with the Bi-Metric uncemented femoral stem. We analyzed Harris hip score and bone mineral density. RESULTS: The mean Harris hip score was 97 at follow-up. Bone mineral density decreased proximally by 19% in both Gruen zones 1 and 7. Bone loss in zones 1, 2, 6, and 7 was significantly associated with stem size. Distally, a small gain in bone mass was found in zones 3 and 5 for medium femoral sizes. INTERPRETATION: We found a marked proximal BMD loss, especially for the larger stems, which may be specific for this particular implant. Long-term studies should reveal whether this proximal bone loss will affect the longevity of the THA.

Continuous bone loss around a tapered uncemented femoral stem: a long-term evaluation with DEXA.

BACKGROUND: Periprosthetic bone loss is a well-documented phenomenon after uncemented total hip arthroplasty (THA); however, little is known about how bone mineral density (BMD) changes after 2 years. PATIENTS AND METHODS: 14 patients with hip arthrosis (group A) were operated with a proximally porous- and hydroxyapatite-coated stem and followed for 10 years with DEXA, radiographs and Harris hip score (HHS). Another group of 14 patients (group B) was evaluated at 6 and 14 years using the same prosthesis and protocol. RESULTS: No stem was revised and all stems were well-Fixed. At final follow-up, HHS was 97 points in group A after 10 years and 94 points in group B after 14 years. Bone mineral changes in group A were greatest in Gruen zones 1 and 7, where the losses were 31% and 26%, respectively, after 2 years on the operated side. The decrease in BMD continued after 2 years and in Gruen zone 7 it was faster than the rate of bone loss on the control side. In group B, the annual change in BMD on the operated side was not significantly different from the bone loss in group A. INTERPRETATION: Up to 14 years after implantation of a tapered uncemented stem, the BMD in the calcar region continues to decrease faster than would be expected from normal ageing.