Use of an Artificial Intelligence Device for Evaluating Blood Loss in Complex Major Orthopaedic Surgery Procedures.

BACKGROUND: An artificial intelligence algorithm that analyzes the pulse oximeter waveform in the fingertip can be used to determine the compensatory reserve index (CRI) in trauma patients. This measurement shows the remaining cardiovascular capacity and is known to be more specific and sensitive in detecting blood loss than are routine vital signs. We hypothesized that the CRI measurement could predict loss of reserve cardiovascular capacity in patients undergoing major orthopaedic surgery, and therefore could help in their management. METHODS: A total of 304 patients undergoing lower extremity arthroplasty consented to participate in waveform monitoring. Pulse oximeter waveforms were sensed with a fingertip probe and processed with a tablet computer that remained with the patient during surgery and recovery in the hospital. The CRI, systolic blood pressure, and heart rate were evaluated throughout the postoperative period. RESULTS: The CRI measurement identified a group of patients who were significantly more likely to require transfusions and emergency medical care (P = .000021). Patients who had morbid obesity were especially likely to have low CRI results and a high percentage of clinical events. A CRI of 0.40 or more was evaluated retrospectively as the criterion for withholding transfusion in 54 patients, but that group had a significantly higher incidence of transfusion later in treatment than did the cohort as a whole. The systolic blood pressure and heart rate were not useful in predicting the need for transfusion until late in treatment. CONCLUSIONS: This study suggests that the CRI measurement can identify patients at risk for transfusion and the need for urgent medical care and may aid in the management of blood loss and transfusion in major orthopedic surgery.

Clinical Results of Revision TKA in Patients With Presumed Metal and Cement Allergy.

BACKGROUND: Metal and cement allergy affects a small subset of patients, causing severe pain and often systemic reaction after total knee arthroplasty (TKA). Revision with ceramic-surfaced femoral components has been reported to resolve these symptoms of metal allergy, but no solution currently is available for patients with allergies to metal and bone cement. METHODS: Five patients (5 knees) with documented metal allergy were revised with custom porous-coated ceramic femoral components (Magnesia-stabilized Zirconia) from January 2007 to January 2013. An additional 23 patients (23 knees) met inclusion criteria from 2007 to 2015, but because the ceramic implant was unavailable, they underwent different treatment based on their underlying allergy to metal, cement, or both. Inclusion criteria included the history of clinically documented severe metal allergy, severe pain, swelling, and effusion >1 year after TKA, negative workup for infection, loosening, and ligament imbalance. Knee Society scores were compared for each cohort. RESULTS: Mean Knee Society scores for all 5 patients revised with custom cementless ceramic femoral components improved significantly for objective score (preoperative, 39 ± 5; most recent visit, 90 ± 2) and function score (preoperative, 33 ± 8; most recent visit 93 ± 4) (P < .0001). The 12 knees revised with off-the-shelf cemented ceramic-coated femoral components had similar results. The 7 unrevised knees (including 4 knees with allergy to metal and bone cement) and the 4 knees revised with standard CoCr femoral components did not improve and worsened over time. CONCLUSION: Symptoms resolved in the 5 patients revised with custom ceramic implants and in the 12 patients revised with ceramic-coated components, but did not improve in the patients unrevised or revised with CoCr femoral components. Symptoms presumed to be associated with metal or cement allergy improve with the use of ceramic femoral surfaces, but patients who are allergic both to metals and bone cement would be candidates only for porous-coated ceramic implants fixed without bone cement.

Phase Transformation and Roughening in Artificially Aged and Retrieved Zirconia-Toughened Alumina Femoral Heads.

BACKGROUND: Zirconia-toughened alumina (ZTA) used in hip arthroplasty contains yttria-stabilized zirconia (Y-TZP) as a toughening agent. However, Y-TZP is well known to degrade in vivo from tetragonal to monoclinic phase transformation. The stability of never-implanted ZTA femoral heads was evaluated in a severe artificial aging test, with retrieved ZTA heads also evaluated for clinical relevance. We hypothesized that ZTA would degrade due to tetragonal-to-monoclinic phase transformation, with changes in surface topography and progressive roughening. Y-TZP specimens served as a positive comparison group, while magnesia-stabilized zirconia (Mg-PSZ), which does not undergo phase transformation, served as a stable comparison group. METHODS: Monoclinic phase concentration, surface topography, and roughness of never-implanted ZTA, Y-TZP, and Mg-PSZ heads were measured by X-ray diffraction and optical profilometry, before and after 2 rounds of 24 hours of hydrothermal aging. Explanted ZTA heads were characterized by the same methods. RESULTS: After 48 hours in an autoclave, the surface of ZTA heads exhibited irregularly spaced protrusions about 20-30 nm high by 100-150 µm in diameter, with significant increases in monoclinic phase concentration (from 12.2% to 21.3%) and surface roughness. Similar features were observed on the surface of explanted ZTA heads, with 33% monoclinic phase after 2.7 years in vivo. CONCLUSION: Based on data collected from ZTA retrievals, this artificial aging test underestimated the amount of phase transformation in vivo. Phase transformation and surface roughening of ZTA heads steadily increased without reaching a plateau, which may lead to stress concentrations and weakening of the ceramic material, and could result in late fracture and wear.

One-stage Revision With Catheter Infusion of Intraarticular Antibiotics Successfully Treats Infected THA.

BACKGROUND: Two-stage revision surgery for infected total hip arthroplasty (THA) is commonly advocated, but substantial morbidity and expense are associated with this technique. In certain cases of infected THA, treatment with one-stage revision surgery and intraarticular infusion of antibiotics may offer a reasonable alternative with the distinct advantage of providing a means of delivering the drug in high concentrations. QUESTIONS/PURPOSES: We describe a protocol for intraarticular delivery of antibiotics to the hip through an indwelling catheter combined with one-stage revision surgery and examine (1) the success as judged by eradication of infection at 1 year when treating chronically infected cemented stems; (2) success in treating late-onset acute infections in well-ingrown cementless stems; and (3) what complications were associated with this approach in a small case series. METHODS: Between January 2002 and July 2013, 30 patients (30 hips) presented to the senior author for treatment of infected THA. Of those, 21 patients (21 hips) with infected cemented THAs underwent débridement and single-stage revision to cementless total hip implants followed by catheter infusion of intraarticular antibiotics. Nine patients (nine hips) with late-onset acute infections in cementless THA had bone-ingrown implants. These patients were all more than 2 years from their original surgery and had acute symptoms of infection for 4 to 9 days. Seven had their original THA elsewhere, and two were the author's patients. All were symptom-free until the onset of their infection, and none had postoperative wound complications, fever, or prolonged pain suggestive of a more chronic process. They were treated with débridement and head and liner exchange, again followed by catheter infusion of intraarticular antibiotics. During this time period, this represented all infected THAs treated by the senior author, and all were treated with this protocol; no patient underwent two-stage exchange during this time, and no patients were lost to followup. At the time of the surgery, two Hickman catheters were placed in each hip to begin intraarticular delivery of antibiotics in the early postoperative period. Antibiotics were infused daily into the hip for 6 weeks with the tubes used for infusion only. Eleven of the single-stage revisions and four of the hips treated with débridement had methicillin-resistant Staphylococcus aureus. Patients were considered free of infection if they had no clinical signs of infection and had a normal C-reactive protein and erythrocyte sedimentation rate at 1 year. Complications were ascertained by chart review. RESULTS: Twenty of 21 (95%) infections in patients who had single-stage revision for chronically infected cemented THA were apparently free from infection and remained so at a mean followup of 63 months (range, 25-157 months). One case grew Candida albicans in the operative cultures and remained free of signs of infection after rerevision followed by infusion of fluconazole. The nine cementless THAs treated with débridement and head/liner exchange all remained free of signs of infection at a mean followup of 74 months (range, 62-121 months). Few complications were associated with the technique. Four patients had elevated serum levels of vancomycin without renal function changes and two patients had transient blood urea nitrogen/creatinine elevations with normal vancomycin levels that resolved with dosage adjustments. No patient had evidence of permanent renal damage. None of the patients in this study developed a chronic fistula or had significant drainage from the catheter site. CONCLUSIONS: Single-stage revision for chronically infected cemented THA and débridement of bone-ingrown cementless THA with late-onset acute infection followed with indwelling catheter antibiotic infusion can result in infection eradication even when resistant organisms are involved. Larger study groups would better assess this technique and prospective comparisons to more traditional one- and two-stage revision techniques for infected THA will likely require multi-institutional approaches. LEVEL OF EVIDENCE: Level IV, therapeutic study.

Retrieved Magnesia-Stabilized Zirconia Femoral Heads Exhibit Minimal Roughening and Abrasive Potential.

BACKGROUND: The degradation of ceramic femoral heads made of yttria-stabilized zirconia (Y-TZP) because of tetragonal-to-monoclinic phase transformation in vivo is well-described, whereas magnesia-stabilized zirconia (Mg-PSZ) ceramics resist phase transformation in a warm aqueous environment. The purpose of this study was to evaluate phase transformation, changes in surface topography, and roughness parameters, including changes in surface polarity and abrasiveness, among retrieved zirconia femoral heads. METHODS: A total of 69 Y-TZP and 86 Mg-PSZ-retrieved femoral heads were examined, with 5 never-implanted heads of each type as controls. Selected heads were scanned by x-ray diffraction, to measure % monoclinic phase. All heads were scanned by optical profilometry to find visual evidence of degradation and to measure surface roughness, surface polarity, and the functional roughness parameters. Monoclinic phase % and roughness data were plotted vs time in vivo. RESULTS: Visual evidence of phase transformation was observed among Y-TZP femoral heads, and some exhibited pitting. Y-TZP femoral heads roughened and become more abrasive in vivo, although those made by CeramTec exhibited less degradation than those by Morgan and Saint Gobain. In contrast, Mg-PSZ heads did not exhibit pitting, undergo phase transformation, or roughen in vivo, and retained a negative surface polarity. CONCLUSION: All Y-TZP femoral heads exhibited increased phase transformation with time in vivo, although not all Y-TZP heads exhibited catastrophic roughening. No phase transformation was observed on Mg-PSZ femoral heads after up to 19.2 years in vivo. The lack of degradation among Mg-PSZ retrievals suggests a lower wear potential in joint replacement.

Reduced UHMWPE wear using magnesia-stabilized zirconia instead of CoCr femoral components in a knee simulator.

Magnesia-stabilized zirconia (Mg-PSZ) is stable and maintains a scratch-resistant surface in hip replacement, but is untested in knees. We assessed whether using Mg-PSZ instead of cobalt-chromium (CoCr) femoral components resulted in less tibial insert wear, and evaluated changes in topography and roughness of the femoral components. Inserts bearing against CoCr or Mg-PSZ were tested using standard (9 Mc) and aggressive (6 Mc) waveforms. Femoral component surface topography and roughness were evaluated before and after testing by optical profilometry. When bearing against Mg-PSZ, UHMWPE wear rate decreased by 73% (standard) and by 59% (aggressive conditions). After 15 Mc, CoCr components featured deep scratches, and roughness increased five-fold, while Mg-PSZ components were unchanged. Mg-PSZ femoral components may be indicated for high-demand patients and those with metal sensitivity.

Stem pain after cementless revision total knee arthroplasty.

Revision total knee arthroplasty (TKA) often requires long diaphyseal supporting stems. Pain at the end of the cemented revision stem has been reported, but no study has been published regarding the incidence in cementless revision TKA. This study reviewed 120 cementless revision TKAs with a diaphyseal slotted stem to compare the incidence of stem pain to that in a control cohort of 100 primary TKA patients with a metaphyseal stem. In the revision cohort, 20 out of 120 patients reported pain at the end of their stem on the tibia, but no patient reported thigh pain. In the primary TKA cohort, seven out of 100 patients reported pain below the tibial stem. No correlation between stem length or stem fit was found. This study found that more than 16% of patients may have pain at the end of their press-fit revision TKA stem, and this complication should be explained to patients before their revision TKA surgery.

Surgical technique: Muscle transfer restores extensor function after failed patella-patellar tendon allograft.

BACKGROUND: Extensor mechanism allograft provides an effective remedy for severe quadriceps deficiency caused by loss of the patella, patellar tendon, and quadriceps tendon in TKA. Late failure is common, however, and major quadriceps deficiency occurs after removal of the allograft material. DESCRIPTION OF TECHNIQUE: Six human cadaver specimens were dissected to evaluate the feasibility of transferring the vastus medialis, vastus lateralis, and medial head of the gastrocnemius muscle to fill the defect caused by loss of the patella and extensor tendon mechanism after failure and removal of allograft material. Transfer of the medial and lateral vastus muscles with their distal attachments into the tibia achieved closure of the defect but did not provide robust tendon material to fill the defect in the anterior knee. The medial gastrocnemius muscle reached easily to the muscular portion of the vastus medialis and lateralis flaps and provided secure closure of the anterior knee and strong attachment of viable muscle and tendon. METHODS: Five knees (five patients) with failed patella-patellar tendon allograft between August 2008 and April 2010 were repaired using this technique. RESULTS: Mean extensor lag was 47° (range, 35°-62°) before surgery and improved to 12° (range, 5°-15°) 1 year after surgery. CONCLUSIONS: These preliminary results suggest that the described muscle transfer technique may provide an approach to salvage the failed extensor mechanism allograft after TKA.

Surgical technique: Gluteus maximus and tensor fascia lata transfer for primary deficiency of the abductors of the hip.

BACKGROUND: Avulsion of the abductor muscles of the hip may cause severe limp and pain. Limited literature is available on treatment approaches for this problem, and each has shortcomings. This study describes a muscle transfer technique to treat complete irreparable avulsion of the hip abductor muscles and tendons. DESCRIPTION OF TECHNIQUE: Ten adult cadaver specimens were dissected to determine nerve and blood supply point of entry in the gluteus maximus and tensor fascia lata (TFL) and evaluate the feasibility and safety of transferring these muscles to substitute for the gluteus medius and minimus. In this technique, the anterior portion of the gluteus maximus and the entire TFL are mobilized and transferred to the greater trochanter such that the muscle fiber direction of the transferred muscles closely matches that of the gluteus medius and minimus. METHODS: Five patients (five hips) were treated for primary irreparable disruption of the hip abductor muscles using this technique between January 2008 and April 2011. All patients had severe or moderate pain, severe abductor limp, and positive Trendelenburg sign. Patients were evaluated for pain and function at a mean of 28 months (range, 18-60 months) after surgery. RESULTS: All patients could actively abduct 3 months postoperatively. At 1 year postoperatively, three patients had no hip pain, two had mild pain that did not limit their activity, three had no limp, and one had mild limp. One patient fell, fractured his greater trochanter, and has persistent limp and abduction weakness. CONCLUSIONS: The anterior portion of the gluteus maximus and the TFL can be transferred to the greater trochanter to substitute for abductor deficiency. In this small series, the surgical procedure was reproducible and effective; further studies with more patients and longer followup are needed to confirm this.

Vancomycin concentration in synovial fluid: direct injection into the knee vs. intravenous infusion.

The purpose of this study was to measure joint and serum levels of vancomycin following intra-articular (IA) or intravenous (IV) administration, and to compare the concentrations achieved in the joint fluid. IA vancomycin was only used to treat revision total knee arthroplasty (TKA) due to infection, while IV vancomycin was used as a prophylactic agent in primary and revision TKA. Both IA and IV vancomycin achieved therapeutic levels in the synovial fluid of the knee, but IA delivery of vancomycin resulted in peak levels that were many orders of magnitude higher, and also resulted in therapeutic serum levels. The half-life of IA-delivered vancomycin was just over three hours, and trough levels remained therapeutic in the joint and in serum for 24hours after IA injection.

Surgical technique: vastus medialis and vastus lateralis as flap transfer for knee extensor mechanism deficiency.

BACKGROUND: Loss of the quadriceps tendon, patella, and patellar tendon leaves a major anterior defect that is difficult to close and compromises knee extension strength. Gastrocnemius muscle transfer does not sufficiently cover such major defects. This paper describes a new surgical technique that addresses these defects and the results of eight cases of revision TKA managed with this new technique. DESCRIPTION OF TECHNIQUE: The new procedure transfers the vastus medialis or the vastus lateralis and their tibial attachments or both muscles and their distal expansions combined with gastrocnemius and soleus flaps to cover major deficiencies in the anterior knee. Nine cadaver knee specimens were dissected to determine the effect of the transfer on nerve and blood supply of the muscles. METHODS: Eight patients underwent the new procedure between 2005 and 2009. Four knees had vastus medialis transfer, two vastus medialis and vastus lateralis transfer, two vastus medialis and medial gastrocnemius transfer, and two medial gastrocnemius and medial ½ of the soleus muscle transfer. Minimum followup was 15 months (mean, 43 months; range, 15-74 months). Patients were evaluated for anterior knee pain, quality of knee closure, ROM, extensor lag, walking ability, use of assistive devices, and ability to climb stairs with the operated extremity. RESULTS: All patients achieved closure of the knee without synovial leaks by 10 days postoperatively. Mean flexion contracture at last followup was 3° (range, 0°-7°). Mean extension lag was 22° (range, 5°-65°). Extension lag was less in those knees that included gastrocnemius or soleus muscle transfer. None of the flaps developed necrosis. CONCLUSIONS: The vastus medialis and vastus lateralis muscles provide adequate coverage for anterior soft tissue deficits of the knee.

Surgical technique: Transfer of the anterior portion of the gluteus maximus muscle for abductor deficiency of the hip.

BACKGROUND: Loss of the abductor portions of the gluteus medius and gluteus minimus muscles due to THA causes severe limp and often instability. DESCRIPTION OF TECHNIQUE: To minimize the symptoms of limp and instability, the anterior ½ of the gluteus maximus was transferred to the greater trochanter and sutured under the vastus lateralis. A separate posterior flap was transferred under the primary flap to substitute for the gluteus minimus and capsule. To ensure tight repair, the flaps were attached and tensioned in abduction. PATIENTS AND METHODS: The technique was performed in 11 patients (11 hips) with complete loss of abductor attachment; the procedure was performed in nine patients during THA and in two later as a secondary procedure. Preoperatively, all patients had abductor lurch, positive Trendelenburg sign, and no abduction of the hip against gravity. Minimum followup was 16 months (mean, 33 months; range, 16-42 months). RESULTS: Postoperatively, nine patients had strong abduction of the hip against gravity, no abductor lurch, and negative Trendelenburg sign. One patient had weak abduction against gravity, negative Trendelenburg sign, and slight abductor lurch. One patient failed to achieve strong abduction, had severe limp after 6 months of protection and physical therapy, and was lost to followup. CONCLUSIONS: Gluteus maximus transfer can restore abductor function in THA with a high success rate.

Reinfected revised TKA resolves with an aggressive protocol and antibiotic infusion.

BACKGROUND: Revision of failed two-stage revision TKA for infection is challenging, and amputation often is the only alternative. QUESTIONS/PURPOSES: We asked whether reinfection after two-stage revision for infection could be controlled with an aggressive revision protocol and intraarticular antibiotic infusion. METHODS: We retrospectively reviewed 18 patients (12 women, six men) who underwent revision for failed reimplantation between January 1999 and January 2008. Mean time from revision for infection to rerevision for reinfection was 5 months (range, 1-18 months). All knees were treated with an individualized protocol that included aggressive exposure, extensive débridement, uncemented components, closure with muscle flaps (seven knees) and other plastic surgery procedures (three knees), and direct antibiotic infusion through Hickman catheters for 6 weeks. Ten knees had one-stage revision; five had débridement, cement spacer, and revision surgery 3 to 4 months later; and three had extensive soft tissue reconstruction before revision surgery. The minimum followup was 2.3 years (mean, 6.1 years; range, 2.3-12.0 years). RESULTS: The mean Knee Society scores improved from 33 preoperatively to 76. Seventeen of the 18 had control of infection and achieved durable fixation and a closed wound. One patient had recurrent infection 13 months after one-stage revision, was revised, and remained asymptomatic 28 months postoperatively after redébridement and vancomycin infusion for 6 weeks. In one patient, soft tissue closure was not obtained and the patient required amputation. CONCLUSIONS: Extensile exposure, débridement, and soft tissue flaps for closure combined with uncemented fixation of revision implants and antibiotic infusion into the knee controlled reinfection after revision TKA.

The influence of sterilization method on articular surface damage of retrieved cruciate-retaining tibial inserts.

This observational study was designed to determine the importance of sterilization method and insert thickness as predictors of articular damage of cruciate-retaining polyethylene components used in total knee arthroplasty. Ninety-nine explanted tibial inserts were evaluated for surface damage. Severe damage modes were observed in 36 of 52 of γ-irradiated inserts but none of those sterilized by ethylene oxide. Articular damage significantly correlated to time in vivo but not to insert thickness. Inserts sterilized by ethylene oxide gas in gas-permeable packaging exhibited a significantly lower damage accumulation rate compared with inserts sterilized by γ radiation and stored in air or an inert environment. γ irradiation and storage in argon instead of air reduced the frequency of severe damage such as delamination but not the overall damage rate.

Methicillin-resistant Staphylococcus aureus in TKA treated with revision and direct intra-articular antibiotic infusion.

BACKGROUND: Resistant organisms are difficult to eradicate in infected total knee arthroplasty. While most surgeons use antibiotic-impregnated cement in these revisions, the delivery of the drug in adequate doses is limited in penetration and duration. Direct infusion is an alternate technique. QUESTIONS/PURPOSES: We asked whether single-stage revision and direct antibiotic infusion for infected TKA would control infection in patients with methicillin-resistant Staphylococcus aureus (MRSA) infections. METHODS: We retrospectively reviewed 18 patients (18 knees) with MRSA with one-stage revision protocol that included débridement, uncemented revision of total knee components, and intraarticular infusion of 500 mg vancomycin via Hickman catheter once or twice daily for 6 weeks; we used no intravenous antibiotics after the first 24 hours. We monitored serum vancomycin levels to maintain levels between 3 and 10 microg/mL. Minimum followup was 27 months (range, 27­75 months). Mean followup was 62 months, (range, 27­96 months). RESULTS: Infection was controlled at last followup in all but one patient with a recurrence of the MRSA. The patient was reoperated at 5 months; a necrotic bone fragment was removed, the knee was débrided and revised, and the antibiotic infusion protocol readministered. The patient remained free of infection 42 months postoperatively. At 2-year followup, the mean Knee Society score was 83. We observed no radiographic evidence of implant migration. CONCLUSIONS: One-stage revision and 6 weeks of intraarticular vancomycin administration controlled infection in MRSA infected TKA with no apparent complications. LEVEL OF EVIDENCE: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Reduced wear of cross-linked UHMWPE using magnesia-stabilized zirconia femoral heads in a hip simulator.

BACKGROUND: To reduce wear, the ideal bearing surface in joint arthroplasty should be smooth and hydrophilic. Ceramics generally offer better wettability than metals and can be polished to a smoother finish. However, clinical studies have found no reduction in liner wear when using yttria-stabilized zirconia (Y-TZP) instead of cobalt chromium alloy (CoCr) femoral heads. QUESTION/PURPOSES: We (1) determined whether a hard, diamond-like carbon (DLC) coating would enhance the wettability of CoCr and magnesia-stabilized zirconia (Mg-PSZ) femoral heads without increasing roughness, and (2) compared their wear performance. METHODS: In an observational study limited to CoCr and Mg-PSZ heads, we measured roughness and contact angle on as-received and DLC-coated heads. Eight heads then were subjected to 11 million cycles of wear in a hip simulator against cross-linked ultrahigh molecular weight polyethylene (XLPE) liners. RESULTS: Mg-PSZ femoral heads were smoother and more hydrophilic than CoCr heads. Although DLC coatings did not reduce roughness, they reduced the contact angle of CoCr and Mg-PSZ substrates, which may provide enhanced lubrication in vivo. In hip simulator tests, liners bearing against CoCr heads wore at a greater rate compared with Mg-PSZ heads. The DLC coating on Mg-PSZ heads did not reduce wear further. CONCLUSIONS: The wear rate of XLPE versus Mg-PSZ was seven times less than CoCr heads, probably owing to lower roughness and greater wettability of Mg-PSZ heads. CLINICAL RELEVANCE: The use of Mg-PSZ femoral heads should lead to reduced wear in vivo compared with CoCr heads, but the clinical benefit of DLC-coated Mg-PSZ is unclear.

Second-generation locking mechanisms and ethylene oxide sterilization reduce tibial insert backside damage in total knee arthroplasty.

This study evaluated the effects of polyethylene quality and locking mechanism on damage to the nonarticulating (backside) surface of retrieved tibial inserts in total knee arthroplasty. Inserts with peripheral capture (PC) locking mechanisms and ethylene oxide (EtO)-sterilized polyethylene were hypothesized to prevent major backside damage. A total of 156 inserts were sorted by locking mechanism and sterilization method and analyzed by damage scoring methods. Ninety-seven specimens exhibited burnishing. Significant positive linear correlations were observed between damage score and age in vivo for all combinations, but damage occurred at a significantly lower rate for second-generation PC implants with EtO sterilization. Most specimens in this group were undamaged (46/72), with others exhibiting only burnishing. Sex, body mass index, and weight did not influence backside damage.

Minimal backside surface changes observed in retrieved acetabular liners.

Modular polyethylene liners offer versatility in total hip arthroplasty, but the locking mechanism may allow micromotion and backside wear. We evaluated the backside surface of 56 retrieved acetabular liners (mean 5.54 years in vivo, range 0.003-13.1 years) to determine whether damage correlated with liner age in vivo, patient factors associated with higher activity, and polyethylene quality. Half of the liners exhibited minimal damage, half exhibited no damage and none exhibited severe damage. Backside damage significantly correlated only to liner age in vivo. Ten of the 28 liners revised for osteolysis exhibited no backside damage, but the osteolytic cysts were peripheral and did not originate from screw holes. The results suggest that modular polyethylene liners in a porous titanium-coated shell with screw holes can be designed such that clinically significant backside wear is minimal.

Cobalt-chromium femoral components developed scratches and released metal debris in simulated wear whereas ceramic femoral components did not.

AIMS: The aims of this study were to evaluate wear on the surface of cobalt-chromium (CoCr) femoral components used in total knee arthroplasty (TKA) and compare the wear of these components with that of ceramic femoral components. METHODS: Optical profilometry was used to evaluate surface roughness and to examine the features created by the wear process in a knee wear simulator. We developed a method of measuring surface changes on five CoCr femoral components and quantifying the loss of material from the articular surface during the wear process. We also examined the articular surface of three ceramic femoral components from a previous test for evidence of surface damage, and compared it with that of CoCr components. RESULTS: We found that the surface roughness of CoCr components rapidly increased during the first 1,000 wear cycles, then reached a steady state, but material loss from the surface continued at a rate of 1,778,000 µm3 per million cycles as carbides were removed from its matrix. These carbides formed third-body wear particles, leading to the formation of new scratches even as older scratches were worn away. In contrast, no scratching, loss of material, or other surface damage, when evaluated with one nanometer resolution, was found on the surface of the ceramic components after a 15 M wear cycle test. CONCLUSION: This study showed wear and loss of CoCr material from scratching and microabrasive wear in TKA. The material loss from the surface continued in a linear relationship with increasing cycles. We also found the absence of scratching and roughening of ceramic femoral components in simulated wear, suggesting an advantage in wear rate and avoiding metal sensitivity. This may have implications in the management of persistent pain after TKA. Cite this article: Bone Joint J 2021;103-B(6 Supple A):94-101.