Point-of-Care Coating of Revision Femoral Stems With Antibiotic-Loaded Calcium Sulfate: Reduction in Infection After 2nd Stage Reimplantation but Not With Aseptic Revisions.

Background: Infection rates in revision total hip arthroplasty are lower when antibiotic loaded cemented stems are utilized. Inspired by this technique, a point-of-care coating of antibiotic-loaded calcium sulfate (CaSO4) was applied to cementless revision stems in aseptic revision and 2nd stage reimplantation total hip arthroplasty. Methods: One hundred eleven consecutive femoral stems were coated. Just prior to insertion, 10 cc of CaSO4 was mixed with 1 g vancomycin and 240 mg tobramycin with the paste applied to the stem. The results were compared to a matched cohort (N = 104) performed across the previous 5 years. The surgical methods were comparable, but for the stem coating. The study group was followed for a minimum of 3 years. Results: In the study cohort of 111 patients, there were 69 aseptic revisions with one periprosthetic joint infection (PJI) (1.4%) and 42 second-stage reimplantations with 2 PJIs (4.8%). In the control cohort of 104 patients, there were 74 aseptic revisions with one PJI (1.4%) and 30 second-stage reimplantations with 7 PJIs (23.3%). There was no significant reduction in PJI rate in the aseptic revision subgroup (1.4% study vs 1.4% control group), P = 1.000. Antibiotic stem coating reduced PJI rate in the 2nd stage reimplantation subgroup (23.3% control vs 4.8% study group), P = .028. In both groups, there were no cases of aseptic stem loosening. Conclusions: Point-of-care antibiotic coating of cementless revision femoral stems reduces PJI infection rate in 2nd stage reimplantations only. We theorize that microbes persist in the endosteal cortices after resection and may contribute to infection recurrence.

The Effect of Prosthetic Joint Infection on Work Status and Quality of Life: A Multicenter, International Study.

BACKGROUND: Periprosthetic joint infection (PJI) and subsequent revision surgeries may affect patients' social and physical health, ability to complete daily activities, and disability status. This study sought to determine how PJI affects patients' quality of life through patient-reported outcome measures with minimum 1-year follow-up. METHODS: Patients who suffered PJI following primary total joint arthroplasty (TJA) from 2012 to 2021 were retrospectively reviewed. Patients met Musculoskeletal Infection Society criteria for acute or chronic PJI, underwent revision TJA surgery, and had at least 1 year of follow-up. Patients were surveyed regarding how PJI affected their work and disability status, as well as their mental and physical health. Outcome measures were compared between acute and chronic PJIs. In total, 318 patients (48.4% total knee arthroplasty and 51.6% total hip arthroplasty) met inclusion criteria. RESULTS: Following surgical treatment for knee and hip PJI, a substantial proportion of patients reported that they were unable to negotiate stairs (20.5%), had worse physical health (39.6%), and suffered worse mental health (25.2%). A high proportion of patients reported worse quality of life (38.5%) and social satisfaction (35.3%) following PJI. Worse reported patient-reported outcome measures including patients' ability to complete daily physical activities were found among patients undergoing treatment for chronic PJI, and also, 23% of patients regretted their initial decision to pursue primary TJA. CONCLUSIONS: A PJI negatively affects patients' ability to carry out everyday activities. This patient population is prone to report challenges overcoming disability and returning to work. Patients should be adequately educated regarding the risk of PJI to decrease later potential regrets. LEVEL OF EVIDENCE: Case series (IV).

CT scan analysis of implant mating comparing APA versus TEA in simultaneous bilateral TKA: One technique per knee.

BACKGROUND: The optimal landmark for setting femoral component rotation in primary TKA remains a debate. This study compares the Anterior-Posterior Axis (APA) versus the Transepicondylar Axis (TEA) in patients undergoing simultaneous bilateral TKA, where one reference line was randomized to each knee. Implant mating was assessed via post-operative CT scans. METHOD: The study included 32 patients with osteoarthritis in both knees with similar varus deformities. All patients underwent the same surgical procedure on both knees, aside from the selected femoral rotation axis line: APA randomized to one side and TEA to the contralateral. Post-operative CT scans were performed in extension to assess in-vivo mating. RESULTS: CT scan analysis showed mean rotation of the femoral implant externally rotated relative to the radiographic TEA with no significant difference between the APA and TEA groups (p = 0.28). Tibial implant rotation was also externally rotated to the radiographic TEA with no significant difference (p = 0.59). Femoral-tibial implant mating showed a mean external rotation of the tibia relative to the femur in both groups: 0.86 ± 4.0° external rotation in the APA group and 0.23 ± 3.7° external rotation in the TEA group. There was no significant difference between groups (p = 0.52). The range of mating mismatch was 15° in the APA group and 16.5° in the TEA group. CONCLUSIONS: When using a measured resection, posterior referencing technique, post-operative femoral-tibial implant mating measured by CT scan showed no superiority comparing the APA method versus the TEA method. LEVEL OF EVIDENCE: 2 Randomized prospective study.

Biphasic bone graft substitute in revision total hip arthroplasty with significant acetabular bone defects : a retrospective analysis.

AIMS: Large acetabular bone defects encountered in revision total hip arthroplasty (THA) are challenging to restore. Metal constructs for structural support are combined with bone graft materials for restoration. Autograft is restricted due to limited volume, and allogenic grafts have downsides including cost, availability, and operative processing. Bone graft substitutes (BGS) are an attractive alternative if they can demonstrate positive remodelling. One potential product is a biphasic injectable mixture (Cerament) that combines a fast-resorbing material (calcium sulphate) with the highly osteoconductive material hydroxyapatite. This study reviews the application of this biomaterial in large acetabular defects. METHODS: We performed a retrospective review at a single institution of patients undergoing revision THA by a single surgeon. We identified 49 consecutive patients with large acetabular defects where the biphasic BGS was applied, with no other products added to the BGS. After placement of metallic acetabular implants, the BGS was injected into the remaining bone defects surrounding the new implants. Patients were followed and monitored for functional outcome scores, implant fixation, radiological graft site remodelling, and revision failures. RESULTS: Mean follow-up was 39.5 months (36 to 71), with a significant improvement in post-revision function compared to preoperative function. Graft site remodelling was rated radiologically as moderate in 31 hips (63%) and strong in 12 hips (24%). There were no cases of complete graft site dissolution. No acetabular loosening was identified. None of the patients developed clinically significant heterotopic ossification. There were twelve reoperations: six patients developed post-revision infections, three experienced dislocations, two sustained periprosthetic femur fractures, and one subject had femoral component aseptic loosening. CONCLUSION: Our series reports bone defect restoration with the sole use of a biphasic injectable BGS in the periacetabular region. We did not observe significant graft dissolution. We emphasize that successful graft site remodelling requires meticulous recipient site preparation.Cite this article: Bone Jt Open 2022;3(12):991-997.

Simulated large joint fluid model for evaluating intra-articular antibiotic delivery systems: initial evaluation using antibiotic-loaded calcium sulfate beads.

Introduction: Local antimicrobial delivery via calcium sulfate (CaSO 4 ) beads is used as an adjunctive treatment for periprosthetic joint infection. There is limited clinical information describing the performance of antimicrobial-loaded CaSO 4 (ALCS) in large-scale applications. We developed a simulated large joint model to study properties of eluting ALCS. Methods: The in vitro testing platform was an adapted standardized model for tribological testing of prosthetic total hips and total knees (ASTM F732). The model was 70 mL total fluid volume, 25 % bovine serum, and 75 % phosphate-buffered saline, using ISO standard 14242-1 for human synovial fluid simulation. Four brands of CaSO 4 were evaluated. Each 10 mL of CaSO 4 was loaded with 1.2 grams (g) of tobramycin and 1 g of vancomycin powders. A 35 mL bead volume, equaling 175 beads, of each product was placed in incubated flasks. The test period was 6 weeks with scheduled interval fluid exchanges. Fluid samples were tested for antibiotic and calcium concentrations and pH. Results: Antibiotic elution showed an initial burst on Day 1, followed by a logarithmic reduction over 1 week. Tobramycin fully eluted within 2.5 weeks. Vancomycin showed sustained release over 6 weeks. Calcium ion concentrations were high, with gradual decrease after 3 weeks. All four CaSO 4 products were inherently acidic. Fluid became more acidic with the addition of antibiotics primarily driven by vancomycin. Discussion: Clinicians should be cognizant of tobramycin elution burst with ALCS in large loads. The main driver of acidic pH levels was vancomycin. We propose that joint complications may result from lowered fluid acidity, and we suggest clinical study of synovial pH.

Comparison of Anterior-Posterior Axis Versus Transepicondylar Axis in Patients Undergoing Simultaneous Bilateral Total Knee Arthroplasty: One Technique per Knee.

BACKGROUND: In primary total knee arthroplasty (TKA), the preferred reference line for setting femoral component rotation is debatable. This study compared the anterior-posterior axis line (APAL) versus the transepicondylar axis line (TEAL) in patients undergoing simultaneous bilateral TKA using a measured resection technique where one reference line was randomized to each knee. METHODS: This prospective study compared the two reference lines using posterior knee referencing with a cemented posterior stabilized knee. The study included 32 patients with osteoarthritis with both knees having similar varus knee deformities. All patients had the same surgical procedure with the only change being the selected femoral rotation axis line. Patients were followed up for a minimum of two years. RESULTS: There was no significant difference in any of the measured radiographic, operative, and clinical parameters, except for a postoperative radiographic limb alignment (APAL 179.7° vs TEAL 180.1° P = .04). The mean femoral external rotation relative to the posterior condylar axis line (PCAL) was 3.0 degrees (0-7 degrees) using the APAL and 3.3 degrees (2-7 degrees) using the TEAL (P = .46). Two-year knee flexion and revised Oxford Knee Scores showed no difference. Seventy-five percent of patients stated no preference for either knee technique. CONCLUSION: When using a measured resection, a posterior referencing technique, we found no difference in knee function and scores when setting femoral component rotation using the APAL versus TEAL. LEVEL OF EVIDENCE: 2, Randomized prospective study.

Outcomes of Modular Knee Arthrodesis for Challenging Periprosthetic Joint Infections.

BACKGROUND: Modular knee arthrodesis (MKA) is a salvage treatment option for patients with challenging periprosthetic joint infections (PJI). The purpose of this study was to investigate the outcomes of patients who underwent MKA for PJI with a single technique and determine if specific factors are associated with MKA failure. METHODS: This was a retrospective review of 81 patients who underwent MKA at a single institution. Knee Society Scores were recorded before MKA and at the final follow-up (mean 52 months). Poisson regression was used to calculate rate ratios for MKA failure secondary to infection. RESULTS: The mean patient age was 67 years; most patients were McPherson B hosts (56.8%) and had type 3 extremities (53.1%), and all had a type III infection (chronic, >4 wks). Forty-six percent of patients had a prior explantation (59.5% failed 2-stage, 40.5% failed spacer). Staphylococcus epidermidis and Staphylococcus aureus were the most common organisms, 22.2% and 18.5%, respectively. Thirty percent of patients had at least one reoperation, excluding reimplantation (14.8% irrigation and debridement/wound closure, 9.9% MKA exchange, and 7.4% amputation). Of 82.7% of MKA patients with no evidence of infection, 82.1% (56 patients) underwent reimplantation endoprosthetic reconstruction, and 67.3% of these remained infection-free at the final follow-up. DISCUSSION: MKA is a salvage option for challenging PJI cases that may serve as definitive surgical management or as a bridge to endoprosthetic reconstruction for patients who have failed prior infection control procedures.

Fabrication of antibiotic-loaded dissolvable calcium sulfate beads: an in vitro mixing lab utilizing various antibiotic mixing formulas.

Chronic periprosthetic joint infection (PJI) is a devastating complication that requires an aggressive eradication protocol. Local antimicrobial delivery via dissolvable calcium sulfate (CaSO 4 ) using small-sized beads (3-8 mm) has been utilized as an adjunctive treatment combined with implant exchange, radical debridement, and antimicrobial loaded acrylic spacers. The non-exothermic setting of CaSO 4 theoretically allows for any antimicrobial agent to be used, so long as mixing methods provide a consistent fabrication within a reasonable set time. This study performed the first in vitro mixing study, in which various antimicrobial agents, used singularly and in combination, were mixed with a synthetic CaSO 4 product to observe and document their interactions. The study was performed in a simulated operating room environment. We report a standard mix formula with set times, testing 22 different antimicrobial agents, combinations, and doses. For some antimicrobials and combinations, set times using the standard formula were either too fast or exceedingly slow. For these 14 antimicrobial agents and combinations, we were able to arrive at individualized mixing methods. We present all mixing formulas and set times. In all, we were able to establish mixing methods that incorporate all antimicrobial agents and combinations that we have seen utilized via surgeon-directed use.

Pseudomonas aeruginosa biofilm killing beyond the spacer by antibiotic-loaded calcium sulfate beads: an in vitro study.

Introduction: Bacterial biofilms are an important virulence factor in chronic periprosthetic joint infection (PJI) and other orthopedic infection since they are highly tolerant to antibiotics and host immunity. Antibiotics are mixed into carriers such as bone cement and calcium sulfate bone void fillers to achieve sustained high concentrations of antibiotics required to more effectively manage biofilm infections through local release. The effect of antibiotic diffusion from antibiotic-loaded calcium sulfate beads (ALCS-B) in combination with PMMA bone cement spacers on the spread and killing of Pseudomonas aeruginosa Xen41 (PA-Xen41) biofilm was investigated using a "large agar plate" model scaled for clinical relevance. Methods: Bioluminescent PA-Xen41 biofilms grown on discs of various orthopedic materials were placed within a large agar plate containing a PMMA full-size mock "spacer" unloaded or loaded with vancomycin and tobramycin, with or without ALCS-B. The amount of biofilm spread and log reduction on discs at varying distances from the spacer was assessed by bioluminescent imaging and viable cell counts. Results: For the unloaded spacer control, PA-Xen41 spread from the biofilm to cover the entire plate. The loaded spacer generated a 3 cm zone of inhibition and significantly reduced biofilm bacteria on the discs immediately adjacent to the spacer but low or zero reductions on those further away. The combination of ALCS-B and a loaded PMMA spacer greatly reduced bacterial spread and resulted in significantly greater biofilm reductions on discs at all distances from the spacer. Discussion: The addition of ALCS-B to an antibiotic-loaded spacer mimic increased the area of antibiotic coverage and efficacy against biofilm, suggesting that a combination of these depots may provide greater physical antibiotic coverage and more effective dead space management, particularly in zones where the spread of antibiotic is limited by diffusion (zones with little or no fluid motion).

Elution Kinetics from Antibiotic-Loaded Calcium Sulfate Beads, Antibiotic-Loaded Polymethacrylate Spacers, and a Powdered Antibiotic Bolus for Surgical Site Infections in a Novel In Vitro Draining Knee Model.

Antibiotic-tolerant bacterial biofilms are notorious in causing PJI. Antibiotic loaded calcium sulfate bead (CSB) bone void fillers and PMMA cement and powdered vancomycin (VP) have been used to achieve high local antibiotic concentrations; however, the effect of drainage on concentration is poorly understood. We designed an in vitro flow reactor which provides post-surgical drainage rates after knee revision surgery to determine antibiotic concentration profiles. Tobramycin and vancomycin concentrations were determined using LCMS, zones of inhibition confirmed potency and the area under the concentration-time curve (AUC) at various time points was used to compare applications. Concentrations of antibiotcs from the PMMA and CSB initially increased then decreased before increasing after 2 to 3 h, correlating with decreased drainage, demonstrating that concentration was controlled by both release and flow rates. VP achieved the greatest AUC after 2 h, but rapidly dropped below inhibitory levels. CSB combined with PMMA achieved the greatest AUC after 2 h. The combination of PMMA and CSB may present an effective combination for killing biofilm bacteria; however, cytotoxicity and appropriate antibiotic stewardship should be considered. The model may be useful in comparing antibiotic concentration profiles when varying fluid exchange is important. However, further studies are required to assess its utility for predicting clinical efficacy.

Patellar Rebar Augmentation in Revision Total Knee Arthroplasty.

BACKGROUND: In revision total knee arthroplasty, osteolysis, mechanical abrasion, and infection may leave patellar bone stock severely attenuated with cavitary and/or segmental rim deficiencies that compromise fixation of patellar implant pegs. The purpose of this study was to retrospectively review the use of cortical "rebar" screws to augment cement fixation in revision patelloplasty. METHODS: From 2006 to 2018, dorsal patellar rebar technique was used for patellar reconstruction in 128 of 1037 revision total knee arthroplasty cases (12.3%). Follow-up was achieved with serial radiographs and prospective comparison of Knee Society Scores (KSSs) for clinical outcome. Complications and implant failures requiring reoperation or modified rehabilitation were also assessed. RESULTS: Of the 128 patellar revisions performed using the rebar technique, 69 patients were women and 59 patients were men. The average age of the group was 69.5 years (range, 32-83 years). The mean follow-up of the cohort was 37 months (range, 13-109 months). The most common causes for revision were kinematic conflict, periprosthetic joint infection, and aseptic loosening. The median number of rebar screws used was 5 (range, 1-13). Preoperative KSSs for the study cohort averaged 50 (range, 0-90) At latest follow-up, mean KSS was 85 (range, 54-100). There were 4 patellar-related complications (3.1%) with no implant failures at study conclusion. Retrieval analysis revealed rigid fixation of the reconstructed patellar component in all cases. CONCLUSIONS: Patellar rebar screw augmentation is a useful technique when there are significant cavitary deficiencies and limited segmental rim deficiencies. This technique allows the surgeon to extend indications for patellar revision arthroplasty.

Comparison of Gap Balancing vs Measured Resection Technique in Patients Undergoing Simultaneous Bilateral Total Knee Arthroplasty: One Technique per Knee.

BACKGROUND: Total knee arthroplasty requires careful surgical technique to attain the goal of a well-aligned and symmetrically balanced knee. Soft tissue balance and correct femoral component rotation are paramount in achieving these goals. The two competing techniques to select femoral component rotation and soft tissue balance are the gap balance technique and the measured resection technique. METHODS: We performed a randomized, prospective study to compare the two techniques in patients undergoing simultaneous bilateral total knee arthroplasty, whereby one technique was performed in each knee. Fifty (50) subjects were enrolled into the study. The inclusion criteria were osteoarthritic varus knee deformities with similar deformities in both knees. Subjects were followed up for a minimum of two years. RESULTS: The knees balanced via the gap balance technique had significantly more posterior medial bone removed from the femur than those knees balanced via the measured resection technique (P < .001). Knees in the gap balance group tended to require more medial knee releases in extension and tended to have smaller sized femoral components as a result of cutting more bone from the femur in flexion. The modular tibial polyethylene bearing tended to be thicker in the gap balance group. Despite these differences, average knee flexion and functional revised Oxford Knee Scores at 2-year follow-up were not statistically different. CONCLUSION: At 2-year follow-up, there were no differences between the function and scores using the two techniques. Long-term follow-up will be necessary to evaluate any differences in long-term durability.

Periosteal pseudotumor in complex total knee arthroplasty resembling a neoplastic process.

This case report describes in detail an erosive distal diaphyseal pseudotumor that occurred 6 years after a complex endoprosthetic hinge total knee arthroplasty (TKA). A female patient had conversion of a knee fusion to an endoprosthetic hinge TKA at the age of 62. At her scheduled 6-year follow-up, she presented with mild distal thigh pain and radiographs showing a 6-7 cm erosive lytic diaphyseal lesion that looked very suspicious for a neoplastic process. An en bloc resection of the distal femur and femoral endoprosthesis was performed. Histologic review showed the mass to be a pseudotumor with the wear debris emanating from within the femoral canal due to distal stem loosening. We deduce that mechanized stem abrasion created microscopic titanium alloy particles that escaped via a small diaphyseal crack and stimulated an inflammatory response resulting in a periosteal erosive pseudotumor. The main lesson of this report is that, in the face of a joint replacement surgery of the knee, pseudotumor formation is a more likely diagnosis than a neoplastic process when encountering an expanding bony mass. Thus, a biopsy prior to en bloc resection, would be our recommended course of action any time a suspicious mass is encountered close to a TKA.