Bone healing of severe acetabular defects after revision arthroplasty

Is 18F-fluoride PET/CT an Accurate Tool to Diagnose Loosening After Total Joint Arthroplasty?

BACKGROUND

Several studies using positron emission tomography (PET) show highly elevated periprosthetic bone uptake of fluorine-18 sodium fluoride (18F-fluoride), suggestive of implant loosening after arthroplasty. Focus so far has been on qualitative but not on quantitative assessment. There is also a lack of intraoperative confirmation of preoperative 18F-fluoride PET findings. Although the method seems to have acceptable accuracy and high sensitivity, an attempt to improve the specificity and an overall validation of the method appear warranted.

QUESTIONS/PURPOSES

(1) Is there a difference in 18F-fluoride uptake around loose versus well-fixed THA and TKA components? (2) Can 18F-fluoride uptake measures provide a threshold that differentiates loose from well-fixed implants undergoing revision for a variety of septic and aseptic indications? (3) In a population restricted to THA and TKA undergoing revision for aseptic indications, can measurement of 18F-fluoride uptake still distinguish loose from well-fixed components? (4) What is the interrater reliability of measuring 18F-fluoride uptake?

METHODS

This was a retrospective assessment of a diagnostic test, 18F-fluoride PET/CT, which was performed prior to revision surgery. We included 63 patients with 31 THAs and 32 TKAs. Sixty-five percent of patients were female, and the mean age at 18F-fluoride PET/CT was 66 years. The THA had different modes of fixation (cemented, cementless, and hybrid; 45%, 32%, and 23%, respectively), whereas all TKAs were cemented. Imaging was conducted using routine protocols 1 hour after tracer injection. The interobserver reproducibility was analyzed using Spearman rank correlations and Bland-Altman analyses. Two independent observers were trained separately by a nuclear physician to measure maximal periprosthetic standardized uptake values (SUVmax) for each arthroplasty component (n = 126). Findings at surgery (whether the components were well fixed or loose, as well as the presence or absence of infection) were used as a reference. Presence of periprosthetic joint infection was retrospectively determined based on the criteria suggested by the European Bone and Joint Infection Society (EBJIS): clinical features in combination with blood analysis, synovial fluid cytologic analysis, and microbiology test results. Receiver operating characteristic (ROC) curves were plotted to assess the area under the curve (AUC) for each investigated component separately, indicating suitable SUVmax thresholds that differentiate loose from well-fixed components. After excluding patients with confirmed or suspected PJI per the EBJIS criteria (n = 12), the above analysis was repeated for the remaining patients with aseptic loosening (n = 51).

RESULTS

We found higher 18F-fluoride uptake around loose versus well-fixed components in all but femoral TKA components (median [range] SUVmax for well-fixed versus loose THA cups 10 [7 to 30] versus 22 [6 to 64], difference of medians 12; p = 0.003; well-fixed versus loose TKA femoral components 14 [4 to 41] versus 19 [9 to 42], difference of medians 5; p = 0.38). We identified favorable ROC curves for all investigated components except femoral TKA components (THA cups AUC 0.81 [best threshold 13.9]; THA femoral stems AUC 0.9 [best threshold 17.3]; femoral TKA components AUC 0.6 [best threshold 14.3]; tibial TKA components AUC 0.83 [best threshold 15.8]). 18F-fluoride was even more accurate at diagnosing loosening when we limited the population to those patients believed not to have prosthetic joint infection (THA cups AUC 0.87 [best threshold 14.2]; THA femoral stems AUC 0.93 [best threshold 15.0]; femoral TKA components AUC 0.65 [best threshold 15.8]; tibial TKA components AUC 0.86 [best threshold 14.7]). We found strong interrater correlation when assessing SUVmax values, with Spearman ρ values ranging from 0.96 to 0.99 and Bland-Altman plots indicating excellent agreement between the two independent observers.

CONCLUSION

Measuring SUVmax after 18F-fluoride PET/CT is a useful adjunct in the diagnostic evaluation for suspected implant loosening after THA and TKA. The method appears to be both accurate and reliable in diagnosing implant loosening for all components except femoral TKA components. In a real-world mixed population with both low-grade infection and aseptic loosening, the method seems to be fairly easy to learn and helpful to subspecialized arthroplasty clinicians. When infection can be ruled out, the method probably performs even better. Further prospective studies are warranted to explore the reason why femoral TKA component loosening was more difficult to ascertain using this novel technique.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Is two-stage revision surgery for infected hip arthroplasty worth the suffering, resources and results compared to one-stage?

PURPOSE

Periprosthetic joint infection (PJI) is the most serious complication of total hip arthroplasty. The treatment is usually revision in either 1 or 2 stages. This study analyses revision with impaction bone grafting for periprosthetic joint infection of the hip and compares 1- and 2-stage strategies.

PATIENTS AND METHODS

We reviewed 55 consecutive cases (54 patients) of revision arthroplasty for PJI carried out at our hospital between 2002 and 2016. Of these, 46 were 2-stage procedures. 21 had vancomycin mixed in with the bone graft, and all had gentamycin-containing bone cement. The total perioperative blood loss, duration of operation, and length of hospital stay were recorded. Clinical and radiological results were analysed for 48 hips at 2-16 years follow-up.

RESULTS

No PJI remained at follow-up. 3 patients (6%) had undergone revision for all causes. 1 had radiological signs of mechanical loosening but was not revised. 2-stage procedures had a significantly longer operating time (409 vs. 238 min) and hospital stay (34 vs. 13 days), greater blood loss (2764 vs. 1638 ml), and lower mean functional hip score (15.9 vs. 17.5) at follow-up than the one-stage procedures.

INTERPRETATION

Revision total hip arthroplasty for PJI with vancomycin-loaded impaction bone grafting is a safe method that achieves both the restoration of bone stock and resolution of the infection. This single-stage procedure could therefore be the new gold standard for treatment of non-complicated PJI in the hip.

Allograft Chip Incorporation in Acetabular Reconstruction: Multiscale Characterization Revealing Osteoconductive Capacity

BACKGROUND

Impacted bone-grafting with morselized allograft chips is commonly used to reconstruct acetabular bone defects in revision total hip arthroplasty (THA). While the overall clinical outcome of this procedure is described to be excellent, the microstructural basis and histological determinants of allograft incorporation remained to be further elucidated.

METHODS

The acetabula of 23 individuals with documented previous use of allograft chips during revision THA were explanted post mortem. The time that the allografts were in situ averaged 10.3 ± 4.5 years (range, 1.2 to 19.8 years). The host bone (HB)-allograft bone (AB) interface was characterized using a suite of high-resolution (HR) imaging techniques including HR-peripheral quantitative computed tomography (HR-pQCT), histological analysis, cellular histomorphometry, and scanning electron microscopy.

RESULTS

AB could be identified in 16 of the 23 cases. The HB and AB showed overlap (i.e., ingrowth) in 91.3% of the total interface. The mean ingrowth was 2.2 ± 1.0 mm with a maximum of 4.7 ± 2.1 mm. The periphery of the AB showed a tight interconnection with the HB associated with increased bone remodeling indices and increased trabecular thickness. While no association between the time in situ and the ingrowth was observed, the bone defect area was positively associated with the thickness of a fibrosis layer separating the ingrowth zone from the AB.

CONCLUSIONS

Allograft chips in revision THA form an adequate osseous foundation with successful incorporation through ingrowth of the HB (i.e., osteoconduction). While complete remodeling was not observed, larger defects were associated with fibrosis formation, which may compromise stability.

CLINICAL RELEVANCE

Our study provides the first systematic, multiscale long-term evaluation of chip allograft incorporation in revision THA to underscore its successful clinical use. As larger defects were associated with fibrous ingrowth, structural allografts may be superior for larger defects in terms of long-term outcomes.

Impaction bone grafting in hip re-revision surgery

AIMS

Bone stock restoration of acetabular bone defects using impaction bone grafting (IBG) in total hip arthroplasty may facilitate future re-revision in the event of failure of the reconstruction. We hypothesized that the acetabular bone defect during re-revision surgery after IBG was smaller than during the previous revision surgery. The clinical and radiological results of re-revisions with repeated use of IBG were also analyzed.

METHODS

In a series of 382 acetabular revisions using IBG and a cemented component, 45 hips (45 patients) that had failed due to aseptic loosening were re-revised between 1992 and 2016. Acetabular bone defects graded according to Paprosky during the first and the re-revision surgery were compared. Clinical and radiological findings were analyzed over time. Survival analysis was performed using a competing risk analysis.

RESULTS

Intraoperative bone defect during the initial revision included 19 Paprosky type IIIA and 29 Paprosky type IIIB hips; at re-revision, seven hips were Paprosky type II, 27 type IIIA and 11 were type IIIB (p = 0.020). The mean preoperative Harris Hip Score was 45.4 (SD 6.4), becoming 80.7 (SD 12.7) at the final follow-up. In all, 12 hips showed radiological migration of the acetabular component, and three required further revision surgery. The nine-year cumulative failure incidence (nine patients at risk) of the acetabular component for further revision surgery was 9.6% (95% confidence interval (CI) 2.9 to 21.0) for any cause, and 7.5% (95% CI 1.9 to 18.5) for aseptic loosening. Hips with a greater hip height had a higher risk for radiological migration (odds ratio 1.09, 95% CI 1.02 to 1.17; p = 0.008).

CONCLUSION

Bone stock restoration can be obtained using IBG in revision hip surgery. This technique is also useful in re-revision surgery; however, a better surgical technique including a closer distance to hip rotation centre could decrease the risk of radiological migration of the acetabular component. A longer follow-up is required to assess potential fixation deterioration. Cite this article: Bone Joint J 2021;103-B(3):492-499.

Novel Musculoskeletal and Orthopedic Applications of 18F-Sodium Fluoride PET

PET imaging with ¹⁸F-sodium fluoride (NaF), combined with computed tomography or magnetic resonance, is a sensitive method of assessing bone turnover. Although NaF-PET is gaining popularity in detecting prostate cancer metastases to bone marrow, osseous changes represent secondary effects of cancer cell growth. PET tracers more appropriate for assessing prostate cancer metastases directly portray malignant activity and include ¹⁸F-fluciclovine and prostatic specific membrane antigen ligands. Recent studies investigating NaF-PET suggest utility in the assessment of benign musculoskeletal disorders. Emerging applications in assessing traumatic injuries, joint disease, back pain, orthopedic complications, and metabolic bone disease are discussed.

Bone mineralisation adjacent to cemented and uncemented acetabular cups: analysis by [18F]-fluoride-PET in a randomised clinical trial

PURPOSE

We present a randomised clinical trial using F-PET/CT to analyse new bone metabolic mineralisation adjacent to acetabular cups following total hip arthoplasty (THA).

PATIENTS AND METHODS

THA was performed on 26 patients (26 cases) with hip OA. Patients with hip osteoarthritis (OA) were randomly assigned to operations with cemented or uncemented acetabular components. The contralateral, healthy acetabulum was used as referent for normal bone metabolism. The patients were analysed with radiography, clinical scoring, and F-PET/CT preoperatively, and at 6 weeks and 6 months postoperatively.

RESULTS

No major complications were recorded, and clinical results were good in all patients. Radiography showed all cups to be stable. The bone-forming activity, as measured by F-PET/CT, was quantified as standardised uptake values (SUV). The mean SUV was 4.6 (6 weeks) and 3.5 (6 months) around the uncemented cups, and 4.8 and 4.0, respectively, for the cemented cups. Normal healthy bone metabolism in the referent was 2.8 and 2.7 SUV at 6 weeks and 6 months, respectively. P < 0.01 for the cemented group at 6 weeks and 6 months, for the uncemented group only at 6 weeks.

INTERPRETATION

An acetabulum affected by OA has elevated SUV activity. Both cemented and uncemented cups had elevated bone metabolic activity at 6 weeks. The raised activity was interpreted as an effect from bone mineralisation secondary to surgical trauma and healing, and to the OA. At 6 months, activity was more normalised for the uncemented group than for the cemented, suggesting healing may terminate faster in the uncemented group. Postoperative bone metabolic activity can be analysed in detail by F-PET/CT.ClinicalTrials.gov Identifier: NCT01623687.

A novel, multi-level approach to assess allograft incorporation in revision total hip arthroplasty

The successful use of allografts in reconstructive orthopedic surgery, including revision total hip arthroplasty (THA), has been outlined repeatedly. Nonetheless, as previous studies were primarily based on clinical follow-ups, we aimed to create an algorithm that accurately determines the extent of allograft incorporation in the acetabulum and femur using a suite of high-resolution imaging techniques. This study is based on a large patient database including > 4,500 patient data with previous revision THA and simultaneous use of allografts. While the database was continuously matched with the deceased individuals at the local forensic medicine department, complete hips were retrieved in case of a positive match. A positive match was achieved for n = 46 hips at a mean follow-up of 11.8 ± 5.1 years. Comprehensive imaging included contact radiography, high-resolution computed tomography (HR-pQCT), undecalcified histology of ground sections and quantitative backscattered electron imaging (qBEI). We here define a histomorphometric toolkit of parameters to precisely characterize the incorporation of structural (bulk) and morselized (chip) allografts in the acetabulum (n = 38) and femur (n = 8), including the defect area and interface length, microstructural and cellular bone turnover parameters as well as overlap and fibrosis thickness. This collection of samples, through its unique study design and precise definition of incorporation parameters, will provide the scientific community with a valuable source for further in-depth investigation of allograft incorporation and, beyond that, the regenerative potential of this osteoconductive scaffold.

Occult Hip Prosthetic Loosening Diagnosed by [18F] Fluoride-PET/CT

Background

Positron emission tomography using the [18F] fluoride metabolite combined with computerized tomography (F-PET/CT) can be used to analyze the metabolic status of the periprosthetic bone after surgery for total hip arthroplasty.

Methods

To obtain normal PET referent values, 44 patients with 5 models of well-functioning hip prosthetic components were analyzed by F-PET/CT, radiography, and clinical score. Another group of patients having painful total hip arthroplasty, but whose radiography showed no conclusive signs of loosening, was analyzed by F-PET/CT scans before revision surgery.

Results

Preoperative median F-PET scores of the bone metabolic activity were 6.65 (3.3-9.0) for the painful stem group and 1.85 (1.2-3.9) (P < .01) for the referent group having the same stem model. At revision surgery, the stems in the painful group were assessed to be loose. At 2-year follow-up, the revised patients were all pain free.

Conclusion

F-PET/CT may be a new diagnostic tool for assessing occult loose stems that are not seen by radiography.

Fingerprint pattern of bone mineralisation on cemented and uncemented femoral stems: analysis by [18F]-fluoride-PET in a randomised clinical trial

PURPOSE

We present a randomised clinical study using 18F-fluoride positron emission tomography/computed tomography (F-PET/CT) to analyse the osteoblastic part of bone metabolism (new bone mineralisation) in periprosthetic bone adjacent to femoral stems following total hip arthoplasty (THA) surgery. Patients with hip osteoarthritis were randomly assigned to THA surgery with cemented or uncemented femoral components.

PATIENTS AND METHODS

THA was performed on 26 patients (26 cases) with hip osteoarthritis. The patients received either an uncemented HA-coated femoral stem or a cemented one. The contralateral healthy femur was used as referent for normal bone metabolism. The patients were analysed with clinical score, radiography and F-PET/CT preoperatively, and postoperatively at 6 weeks and 6 months. After 2 years, clinical score and radiography was analysed again. We used the Polar Map system for analysing and presenting the PET results in 13 regions of interest adjacent to the whole stem.

RESULTS

The clinical results were good in all patients; there were no major complications. Radiographically, all stems were stable. PET analyses after 6 weeks showed that bone mineralising activity was significantly higher around the uncemented stems, both compared to the cemented group and to the contralateral healthy reference femur group. The cemented group also had elevated activity but only at a barely significant level.

INTERPRETATION

Mineralising activity analysed with F-PET/CT was significantly higher for the uncemented group and also decreased at a slower rate. F-PET/CT is a useful new tool for analysing secondary stabilisation of femoral stems after THA. The study was registered at ClinicalTrials.gov (identifier NCT01623687).

18F-fluoride as a prognostic indicator of bone regeneration

Positron emission tomography (PET) is a form of nuclear imaging, which quantitatively assesses the metabolic activity through the uptake of radioactive tracers. ¹⁸F-fluoride is a positron-emitting isotope with high affinity for bone. Despite its potential as a non-invasive measure of bone metabolism, quantitative ¹⁸F-fluoride PET has only been used sparsely in orthopaedic applications. It has been speculated that ¹⁸F-fluoride PET characterizes cellular activity of bone forming cells in the early stages of the regenerative process and therefore precedes the mineralization detected by conventional computed tomography (CT). Our aim was thus to combine in vivo PET and CT to map the spatiotemporal course of bone regeneration during fracture healing using an open femur fracture model in the rat and characterize regeneration in untreated and pharmacologically treated fractures using both imaging modalities. We hypothesized that PET ¹⁸F-fluoride tracer activity at an earlier time point is predictive of CT measured bone formation at a later time point. On the basis of the RMSE and R² metrics of linear regression models it was conceivable for bone volumes to be predicted up to three weeks in advance in a rodent model (RMSE: 14 mm³-18 mm³, R²: 0.79-0.82). Moreover, the data suggested that ¹⁸F-fluoride positron-emitting activity had the potential to separate bone formation from resorption and thus could be of interest across a wide array of orthopaedic applications. Based on this data, we conclude that ¹⁸F-fluoride positron-emitting activity is strongly correlated to bone formation and could potentially predict the volume of bone regenerated at fracture sites. The volume of bone regenerated at a fracture site can be interpreted as a measure of the healing response and ¹⁸F-fluoride should be further investigated as a predictive diagnostic tool to identify if bone fractures will heal successfully or result in delayed healing or non-union. STATEMENT OF SIGNIFICANCE: We aimed to combine in vivo PET and CT imaging to map the spatiotemporal course of bone regeneration during fracture healing using an open femur fracture model in the rat and characterize regeneration in untreated and pharmacologically treated fractures using both imaging modalities. We hypothesized that PET ¹⁸F-fluoride tracer activity at an earlier time point is predictive of CT measured bone formation at a later time point. Our data suggest that ¹⁸F-fluoride positron-emitting activity can separate bone formation from resorption and thus could be of interest across a wide array of orthopaedic applications including as a predictive diagnostic tool to identify if fractures will heal successfully or result in delayed healing or non-union.

Cellular Mechanisms Responsible for Success and Failure of Bone Substitute Materials

Bone grafts, i.e., autologous, allogeneic or synthetic bone substitute materials play an increasing role in reconstructive orthopedic surgery. While the indications and materials differ, it is important to understand the cellular mechanisms regarding their integration and remodeling, which are discussed in this review article. Osteoconductivity describes the new bone growth on the graft, while osteoinductivity represents the differentiation of undifferentiated cells into bone forming osteoblasts. The best case is that both mechanisms are accompanied by osteogenesis, i.e., bone modeling and remodeling of the graft material. Graft incorporation is mediated by a number of molecular pathways that signal the differentiation and activity of osteoblasts and osteoclasts (e.g., parathyroid hormone (PTH) and receptor activator of nuclear factor κβ ligand (RANKL), respectively). Direct contact of the graft and host bone as well as the presence of a mechanical load are a prerequisite for the successful function of bone grafts. Interestingly, while bone substitutes show good to excellent clinical outcomes, their histological incorporation has certain limits that are not yet completely understood. For instance, clinical studies have shown contrasting results regarding the complete or incomplete resorption and remodeling of allografts and synthetic grafts. In this context, a foreign body response can lead to complete material degradation via phagocytosis, however it may also cause a fibrotic reaction to the bone substitute. Finally, the success of bone graft incorporation is also limited by other factors, including the bone remodeling capacities of the host, the material itself (e.g., inadequate resorption, toxicity) and the surgical technique or preparation of the graft.

Bone mineral density changes in the graft after acetabular impaction bone grafting in primary and revision hip surgery

Background and purpose - Impaction bone grafting (IBG) is an established method in hip revision surgery to reconstruct loss of bone stock. There is limited knowledge concerning the actual bone remodelling process within the allograft. We investigated with repeated bone mineral density (BMD) measurements the biological process of bone remodelling in the allograft in vivo. We hypothesized that an initial decrease in BMD would be followed by an increase towards baseline values. Patients and methods - Dual-energy X-ray absorptiometry (DXA) was used to measure BMD values in 3 regions of interest (ROI) in 20 patients (average age at surgery 70 years, 11 males) after an acetabular reconstruction with IBG and a cemented cup. A postoperative DXA was used as baseline and DXA was repeated at 3 and 6 months and at 1 and 2 years. The Oxford Hip Score (OHS), the 12-Item Short Form Health Survey (SF12), and a 0 to 100 mm visual analogue scale (VAS) for pain and satisfaction were obtained simultaneously. Results - The overall mean BMD in the IBG regions increased significantly by 9% (95% CI 2-15) at 2 years' follow-up. In the cranial ROI BMD increased 14% (CI 6-22), whereas the BMD in the medial and caudal ROI showed an increase of 10% (CI 1-18) and 4% (CI -6-16), respectively. The OHS, SF12-mental, and VAS for pain all improved statistically significantly 2 years after surgery, with a mean VAS for satisfaction of 77 (CI 63-90) out of 100 points. The SF12-physical showed non-significant improvement. Interpretation - The BMD in the allograft gradually increased after IBG for acetabular reconstruction arthroplasties, particularly in the cranial ROI. An initial decrease in the BMD was not encountered. These BMD changes, as proxy measurements for bone remodeling, may indicate progressive apposition of vital new host bone in the grafted area.

A 2- to 16-Year Clinical Follow-Up of Revision Total Hip Arthroplasty Using a New Acetabular Implant Combined With Impacted Bone Allografts and a Cemented Cup

BACKGROUND

Treatment of acetabular bone loss with impaction bone grafting (IBG) at revision total hip arthroplasty is highly dependent on mechanical stability and graft compression for clinical success. Here, we describe a new technique to further compress and stabilize the acetabular graft bed with a thin, perforated titanium shell.

METHODS

We retrospectively analyzed 170 cases of acetabular revision arthroplasty 7 years (standard deviation 2.8) after IBG combined with a graft-compressing titanium shell implant. The patients were reviewed by clinical score and radiography. Three patients were lost to follow-up. The medical journals of the 33 deceased cases were reviewed for any reoperation. Of the 170 cases, 74 had a cavitary acetabular bone defect, 93 had combined segmental and cavitary bone defects, and 3 had a pelvic dissociation. Bone graft incorporation was assessed and correction of the hip center of rotation was calculated.

RESULTS

Five cases (3%) were reoperated for mechanical loosening. One more was assessed as loose but asymptomatic and was not planned for revision. There were 3 reoperations for recurrent dislocation, 2 for deep infection and 1 for technical error. Reoperation for any reason, as the end point of survivorship, showed a survival rate of 92% after 10 years. Hip score according to Merle, d'Aubigne, and Postel increased from 10.8 (preoperatively) to 16.4 at follow-up. The clinical and radiological results were excellent.

CONCLUSION

IBG combined with the compressing shell results in excellent results for this challenging condition.

Evolving Role of Molecular Imaging with (18)F-Sodium Fluoride PET as a Biomarker for Calcium Metabolism

(18)F-sodium fluoride (NaF) as an imaging tracer portrays calcium metabolic activity either in the osseous structures or in soft tissue. Currently, clinical use of NaF-PET is confined to detecting metastasis to the bone, but this approach reveals indirect evidence for disease activity and will have limited use in the future in favor of more direct approaches that visualize cancer cells in the read marrow where they reside. This has proven to be the case with FDG-PET imaging in most cancers. However, a variety of studies support the application of NaF-PET to assess benign osseous diseases. In particular, bone turnover can be measured from NaF uptake to diagnose osteoporosis. Several studies have evaluated the efficacy of bisphosphonates and their lasting effects as treatment for osteoporosis using bone turnover measured by NaF-PET. Additionally, NaF uptake in vessels tracks calcification in the plaques at the molecular level, which is relevant to coronary artery disease. Also, NaF-PET imaging of diseased joints is able to project disease progression in osteoarthritis, rheumatoid arthritis, and ankylosing spondylitis. Further studies suggest potential use of NaF-PET in domains such as back pain, osteosarcoma, stress-related fracture, and bisphosphonate-induced osteonecrosis of the jaw. The critical role of NaF-PET in disease detection and characterization of many musculoskeletal disorders has been clearly demonstrated in the literature, and these methods will become more widespread in the future. The data from PET imaging are quantitative in nature, and as such, it adds a major dimension to assessing disease activity.

THA revisions using impaction allografting with mesh is durable for medial but not lateral acetabular defects

BACKGROUND

Most acetabular revisions are managed with cementless hemispherical or elliptical metal implants relying on bone ingrowth. Nonetheless, loss of acetabular bone stock and inability to achieve secure component fixation represent challenges in the setting of revision total hip arthroplasty. Impaction bone grafting (IBG) using allograft represents one option for treatment of this problem. However, cup migration and bone graft resorption are limitations when IBG is used for large segmental defects, and the precise role of IBG as well as the use of mesh (and the kinds of defects for which mesh does not work well) in this setting remains unknown.

QUESTIONS/PURPOSES

We therefore evaluated patients undergoing acetabular revision surgery using IBG and a cemented cup in large bone defects to determine (1) the frequency with which the hip center could be restored in hips with Paprosky 3A and 3B defects and in hips with or without the use of metallic mesh during surgery; (2) survivorship of IBG acetabular-revision reconstructions in patients with severe Paprosky 3A and 3B defects; and (3) risk factors for failure of the reconstruction, including the use of mesh and defect severity (3A versus 3B).

METHODS

Between 1997 and 2009, we performed 226 acetabular revisions using IBG. During that time, indications for using IBG in this setting included Paprosky 3A and 3B defects without pelvic discontinuity. Of these, 204 (90.2%) were available for followup at a minimum of 5 years (mean, 10 years; range, 5-17 years). There were 100 hips with an intraoperative bone defect of Paprosky 3A and 104 with a 3B. Medial or rim acetabular uncontained defects were treated with medial and/or lateral metallic mesh in 142 hips. We determined the postoperative radiological cup position and acetabular reconstruction of the hip center according to Ranawat in both groups. We assessed the appearance of cup loosening and the possible risk factors with regression analysis.

RESULTS

Mean postoperative acetabular abduction angle and vertical, horizontal, and hip rotation center distances improved (p < 0.001 in all parameters). Nine hips showed radiological loosening in the group with bone defect 3A and 16 in Group 3B. The survival rate for loosening at 15 years was 83% (95% confidence interval [CI], 71%-95%) for Group 3A and 73% (95% CI, 60%-84%) for Group 3B (p = 0.04). The survivorship for loosening when using mesh or not at 15 years was: no mesh 89% (95% CI, 74%-99%), medial mesh 85% (95% CI, 72%-97%), lateral mesh 80% (95% CI, 67%-91%), and medial and lateral meshes 54% (95% CI, 31%-76%) (p = 0.008). After controlling the most relevant confounding variables we found that the most important factor associated with loosening was lateral mesh use (p = 0.008; hazard ratio, 2.942; 95% CI, 1.328-6.516).

CONCLUSIONS

IBG provides an improvement in reconstruction of the hip rotation center in acetabular revision surgery. Although results are good for contained or medial large defects, hips with a rim or lateral segmental defect may need other options for reconstruction of these challenging surgeries.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Preliminary evaluation of different biomaterials for defect healing in an experimental osteoporotic rat model with dynamic PET-CT (dPET-CT) using F-18-sodium fluoride (NaF)

The aim of the current study was to measure and compare the effect of calcium phosphate cement (CPC) and CPC enriched with strontium (SrCPC) for the healing of osteoporotic bone defects in the rat femur using (18)F-Sodium Fluoride dPET-CT.

METHODS

Osteoporosis was induced by ovariectomy and a calcium restricted diet. After three months, rats were operated to create a 4 mm defect in the distal metaphyseal femur with internal fixation. 7 Rats have been treated either with CPC (Group 2) or with SrCPC (Group 3) for bone replacement and defect healing. Furthermore, a control group of 7 rats without any biomaterial (Group 1) was used for reference. 18 weeks after osteoporosis induction and 6 weeks following femoral surgery, dPET-CT studies scan were performed with (18)F-Sodium Fluoride. SUVs and a 2-tissue compartmental learning-machine model (K1-k4, VB, influx) were used for quantitative analysis.

RESULTS

VB, reflecting the fractional blood volume and k3, reflecting the formation of fluoroapatite were the most sensitive parameters for the characterisation of healing process and revealed the best differentiation for the control group and the CPC group (Group 2) as well as for the CPC with strontium carbonate group (Group 3) (p<0.05). VB was decreased by the order of Group 1, Group 2 and Group 3, while k3 was increased by the same order. Therefore, the data direct to a decreased fractional blood volume and increased fixation of fluoride in rats with these biomaterials.

CONCLUSION

We found PET scanning using (18)F-Sodium Fluoride to be a sensitive and useful method for evaluation of bone healing after replacement with CPC or SrCPC.

Analysis of bone mineralization on uncemented femoral stems by [18F]-fluoride-PET: a randomized clinical study of 16 hips in 8 patients

PURPOSE

We present the first study using fluoride-positron emission CT (F-PET/CT) to analyze mineralization of bone in the femur adjacent to uncemented stems following total hip arthroplasty (THA). We studied patients who were operated bilaterally for osteoarthritis with 2 different stems during the same surgical session.

PATIENTS AND METHODS

THA was performed bilaterally during the same surgical session in 8 patients with bilateral osteoarthritis of the hip. An SL-PLUS stem was inserted in one hip and a BetaCone stem was inserted in the contralateral hip, with randomization of side and sequence. A second group of 12 individuals with a normal healthy hip was used as reference for normal bone metabolism. Clinical and radiographic evaluation was performed preoperatively, postoperatively, and at 2 years. We used [18F]-fluoride-PET/CT to analyze bone mineralization adjacent to the stems 1 week, 4 months, and 12 months after surgery. We modified the Polar Map system to fit the upper femur for analysis and presentation of the PET results from 12 regions of interest adjacent to the whole stem.

RESULTS

The clinical results were good at 2 years. By radiography, all stems were stable. At PET analyses 1 week after surgery, the activity was higher for the SL-PLUS group than for the BetaCone group. The activity was statistically significantly higher for both stems than the reference values at 4 months, and was most pronounced in the upper femur. At one year, the activity had declined more for the BC group than for the SL group.

INTERPRETATION

The bone mineralization activity varied between different regions for the same stem and between different time periods for each group. F-PET/CT is a novel and valuable tool for analysis of bone mineralization patterns around uncemented femoral stems in detail. The combination of PET/CT analysis and the modified Polar Map system may provide a useful tool for future studies of metabolic bone responses to prosthetic implants.

Blood perfusion and bone formation before and after minimally invasive periacetabular osteotomy analysed by Positron Emission Tomography combined with Computed Tomography

PURPOSE

Sufficient blood perfusion is essential for successful bone healing after periacetabular osteotomy (PAO). The purpose of this study was to quantify blood perfusion and bone formation before and after PAO analysed by positron emission tomography (PET) combined with computed tomography (CT).

METHODS

Twelve dysplastic patients (nine women) were included consecutively in the study and all were operated upon by the senior author (KS). Median age was 33 (23-55) years. Initially, two patients were PET scanned in a pilot study to test our models for calculation of the physiological parameters. The following ten patients had their hip joints PET/CT scanned immediately before PAO and three to four weeks after. Oxygen-15-water was used to quantify blood perfusion and Flourine-18-fluoride was used to produce quantitative images interpreted as new bone formation in the acetabular fragment.

RESULTS

The blood perfusion of the operated acetabulum before surgery was 0.07 ± 0.02 ml/min/ml, and after surgery 0.19 ± 0.03 ml/min/ml (p = 0.0003). Blood perfusion of the non-operated acetabulum was 0.07 ± 0.02 ml/min/ml before PAO and 0.07 ± 0.02 ml/min/ml after surgery (p = 0.47). The fluoride-clearance per volume bone of the operated acetabulum was 0.02 ± 0.01 ml/min/ml preoperatively, and 0.06 ± 0.01 ml/min/ml postoperatively (p = 0.0005). Fluoride-clearance of the non-operated acetabulum was 0.01 ± 0.01 ml/min/ml before PAO and 0.02 ± 0.01 ml/min/ml after PAO (p = 0.49).

CONCLUSION

Blood perfusion and new bone formation increased significantly in the acetabular fragment. Thus, the results of this study do not support the concern about surgically damaged vascularity after PAO.

Analysis of bone formation on porous and calcium phosphate-coated acetabular cups: a randomised clinical [18F]fluoride PET study

We present a study using Fluoride-Positron Emission Tomography (F-PET/CT) to analyse new bone formation in periacetabular bone adjacent to press fit cups following THA. In 16 THA (8 patients) with bilateral hip osteoarthritis simultaneous bilateral total hip arthroplasty (THA) was performed, employing electrochemically applied calcium phosphate coated (HA) cups or porous-coated (PC) cups allocated at random to compare the two sides. A reference group of 13 individuals with a normal healthy hip was used to determine 'normal' bone metabolism. [18F]fluoride -PET/CT was used to analyze bone formation adjacent to the cups 1 week, 4 months and 12 months after surgery. Clinical and radiographic evaluation was performed preoperatively, postoperatively and at 2 years. Bone forming activity had a mean of 5.71, 4.69 and 3.47 SUV around the HA- and 5.04, 4.80 and 3.50 SUV around the PC-cups at 1 week, 4 months and 12 months respectively. Normal bone metabolism was 3.68 SUV. After 1 year activity had declined to normal levels for both groups. The clinical results were good in all cases. HA coating resulted in higher uptake indicating higher bone forming activity after 1 week. F-PET/CT is a valuable tool to analyse bone formation and secondary stabilisation of an acetabular cup.

Radionuclide imaging in the diagnosis and management of orthopaedic disease

Nuclear medicine imaging is often used in the diagnosis and management of several orthopaedic conditions. Bone scintigraphy measures gamma ray emission to detect the distribution of an injected radiolabeled tracer on multiple image projections. In general, this imaging modality has relatively high sensitivity but low specificity in the diagnosis of occult fractures, bone tumors, metabolic bone disease, and infection. Positron emission tomography measures tissue metabolism and perfusion by detecting short half-life positron ray emission of an injected radiopharmaceutical tracer. Historically, positron emission tomography has been used only to monitor bone metastasis and aid in the diagnosis of osteomyelitis; however, this technology has recently been applied to other orthopaedic conditions for which current imaging modalities are insufficient.

Clinical utility of (18)F-fluoride PET/CT in benign and malignant bone diseases

(18)F labeled sodium fluoride is a positron-emitting, bone seeking agent with more favorable skeletal kinetics than conventional phosphate and diphosphonate compounds. With the expanding clinical usage of PET/CT, there is renewed interest in using (18)F-fluoride PET/CT for imaging bone diseases. Growing evidence indicates that (18)F fluoride PET/CT offers increased sensitivity, specificity, and diagnostic accuracy in evaluating metastatic bone disease compared to (99m)Tc based bone scintigraphy. National Oncologic PET Registry (NOPR) has expanded coverage for (18)F sodium fluoride PET scans since February 2011 for the evaluation of osseous metastatic disease. In this article, we reviewed the pharmacological characteristics of sodium fluoride, as well as the clinical utility of PET/CT using (18)F-fluoride in both benign and malignant bone disorders.

Reconstruction of the acetabulum in THA using femoral head autografts in developmental dysplasia of the hip

Background

Severe acetabular deficiencies in cases of developmental dysplasia of the hip (DDH) often require complex reconstructive procedures in total hip arthroplasty (THA). The use of autologous femoral head grafts for acetabular reconstruction has been described, but few data is available about clinical results, the rates of non-union or aseptic loosening of acetabular components.

Methods

In a retrospective approach, 101 patients with 118 THA requiring autologous femoral head grafts to the acetabulum because of DDH were included. Six patients had died, another 6 were lost to follow-up, and 104 hips were available for clinical and radiological evaluation at a mean of 68 ± 15 (13 to 159) months.

Results

The average Merle d'Aubigné hip score improved from 9 to 16 points. Seven implants had to be revised due to aseptic loosening (6.7%). The revisions were performed 90 ± 34 (56 to 159) months after implantation. The other hips showed a stable position of the sockets without any signs of bony non-union, severe radiolucencies at the implant-graft interface or significant resorption of the graft.

Conclusion

The use of autologous femoral head grafts with cementless cups in primary THA can achieve promising short- to midterm results in patients with dysplastic hips.

Bone metabolism analyzed by PET and DXA following revision THA using a distally fixed stem. A pilot study

In a pilot study we analyzed bone remodeling using ¹⁸F-PET (positron emission tomography) scanning or DXA (dual-energy x-ray absorptiometry) in 3 patient groups, one with a loose femoral stem and 2 after revision using a modular stem (MP). In loose implants (group 1), bone formation activity compared to the contralateral healthy femur was 261 %. In the proximal part of the femur bone formation was increased by 253 % one week after revision (group 2) and did not normalize within 1 year. In the distal region it decreased to normal after one year. In the second revision group DXA showed decreased bone mineral density at 6 and 24 months (group 3). The PET technique provided evidence of bone healing despite osteolysis and prosthetic loosening which continued after revision. Decreasing BMD after revision in the third group is multifactorial, but suggests that despite intensive bone formation resorption was still higher.

Novel composite implant in craniofacial bone reconstruction

Bioactive glass (BAG) and polymethyl methacrylate (PMMA) have been used in clinical applications. Antimicrobial BAG has the ability to attach chemically to surrounding bone, but it is not possible to bend, drill or shape BAG during the operation. PMMA has advantages in terms of shaping during the operation, but it does not attach chemically to the bone and is an exothermic material. To increase the usefulness of BAG and PMMA in skull bone defect reconstructions, a new composite implant containing BAG and PMMA in craniofacial reconstructions is presented. Three patients had pre-existing large defects in the calvarial and one in the midface area. An additive manufacturing (AM) model was used preoperatively for treatment planning and custom-made implant production. The trunk of the PMMA implant was coated with BAG granules. Clinical and radiological follow-up was performed postoperatively at 1 week, and 3, 6 and 12 months, and thereafter annually up to 5 years. Computer tomography (CT) and positron emission tomography (PET-CT) were performed at 12 and 24 months postoperatively. Uneventful clinical recovery with good esthetic and functional outcome was seen. CT and PET-CT findings supported good clinical outcome. The BAG-PMMA implant seems to be a promising craniofacial reconstruction alternative. However, more clinical experience is needed.

The survival and fate of acetabular reconstruction with impaction grafting for large defects

BACKGROUND

Impaction bone grafting has been used for acetabular reconstruction in revision surgery. However, most series do not establish differences in survival in revisions with differing severity of bone loss.

QUESTIONS/PURPOSES

We therefore determined (1) the survival rate for rerevision associated with varying degrees of bone loss; (2) the frequency with which bone graft resorption occurred; and (3) whether the reconstruction restored the anatomic center of rotation of the hip.

METHODS

We retrospectively reviewed 165 patients (181 hips) who underwent rerevision for major bone loss. Using the classification of Paprosky et al. 98 hips had a Grade 3A defect and 83 a Grade 3B. We determined survival rates for revision and graft resorption. Cup position was determined measuring vertical and horizontal positions and the distance from the center of the prosthetic femoral head to the normal center of rotation of the hip in both groups according to Ranawat. The minimum followup until rerevision or the latest evaluation was 0.3 years months (mean, 7.5 years; range, 0.3-17.7 years).

RESULTS

The survival rate for revision at 8 years was 84% (95% confidence interval: 61-100) for Grade 3A and 82% (95% confidence interval: 68-100) for Grade 3B. Twelve hips were rerevised. Seventeen grafts showed bone resorption. Acetabular cup position was anatomically restored in both Grades 3A and 3B.

CONCLUSIONS

The midterm results for impacted bone allograft and cemented all-polyethylene cups were similar in both Grade 3A and Grade 3B hips. Acetabular reconstruction allows anatomic positioning of the cups and is associated with a low rate of rerevision.

Cord blood--an alternative source for bone regeneration

Bone regeneration is one of the best investigated pathways in mesenchymal stromal cell (MSC) biology. Therefore strong efforts have been made to introduce tissue engineering and cell therapeutics as an alternative treatment option for patients with bone defects. This review of the literature gives an overview of MSC biology aiming for clinical application including advantages but also specific challenges and problems which are associated with cord blood derived stromal cell (CB-MSC) as a source for bone regeneration. The use of postnatal CB-MSC is ethically uncomplicated and requires no invasive harvesting procedure. Moreover, most data document a high osteogenic potential of CB-MCS and also low immunoreactivity compared with other MSC types. The expression profile of CB-MSC during osteogenic differentiation shows similarities to that of other MSC types. Within the umbilical cord different MSC types have been characterized which are potent to differentiate into osteoblasts. In contrast to a large number of in vitro investigations there are only few in vivo studies available so far.