Role of bariatric surgery in reducing periprosthetic joint infections in total knee arthroplasty. A systematic review and meta-analysis.

BACKGROUND: Obesity represents an epidemic of rising numbers worldwide year after year. In the Orthopedic field, obesity is one of the major causes leading to osteoarthritis needing Total Joint Arthroplasty (TJA). Still, contextually, it represents one of the most significant risk factors for joint replacement complications and failures. So, bariatric Surgery (BS) is becoming a valuable option for weight control and mitigating obesity-related risk factors. This review of the literature and meta-analysis aims to evaluate periprosthetic joint infections (PJI) and surgical site infections (SSI) rates in patients who underwent TKA after BS compared to obese patients without BS. METHODS: Systematic review was performed according to Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines up to October 2023. We included longitudinal studies comparing obese patients who underwent total knee arthroplasty after bariatric surgery (study group) and obese patients who underwent TKA (control group). The surgical site infection and Periprosthetic joint infection rate were compared among groups using a meta-analytical approach. RESULTS: The online database and references investigation identified one hundred and twenty-five studies. PJI rate differed significantly among groups, (z = -21.8928, p < 0.0001), with a lower risk in the BS group (z = -10.3114, p < 0.0001), for SSI, instead, not statistically significance were recorded (z = -0.6784, p = 0.4975). CONCLUSIONS: The current Literature suggests that Bariatric Surgery can reduce infectious complications in TKA, leading to better outcomes and less related costs treating of knee osteoarthritis in obese patients.

Preliminary data on the neurophysiological evaluation of male sexual dysfunction in patients with pelvic ring fractures: a multicenter retrospective study.

OBJECTIVE: Traumatic pelvic ring fractures include several comorbidities due to the close anatomical relationship between the skeletal system, pelvic organs, and neurovascular structures. In this retrospective multicenter study, we evaluated patients complaining of sexual dysfunction following pelvic ring fractures, assessed through different neuro-physiological examinations. PATIENTS AND METHODS: Patients were enrolled one year after the injury according to their reported ASEX scores and evaluated on the basis of the Tile's type of pelvic fracture. Lower limb and sacral somatosensory evoked potentials, pelvic floor electromyography, bulbocavernosus reflex and pelvic floor motor evoked potentials were recorded, according to the neurophysiological indications. RESULTS: A total of 14 male patients (mean age 50.4; 8 subjects Tile-type B and 6 Tile-type C) were enrolled. The ages between the Tile B group and the Tile C group of patients were not significantly different (p=0.187), while the ASEX scores were significantly different (p=0.014). In 57% of patients (n=8), no alterations in nerve conduction and/or pelvic floor neuromuscular responses were found. In 6 patients, electromyographic signs of denervation were revealed (2 patients), and alterations of the sacral efferent nerve component were detected in 4 patients. CONCLUSIONS: Sexual dysfunctions after a traumatic pelvic ring fracture are more common in Tile-type B. Our preliminary data did not reveal a significant association with neurogenic aetiology. Other causes could explain the complaining impairments.

Robotic-assisted unicompartimental knee arthroplasty performed with Navio system: a systematic review.

OBJECTIVE: Robotic-assisted arthroplasty is a relatively modern concept, quickly arising in its use. The aim of this systematic review is to assess, according to the existing literature, which are the functional and clinical outcomes and component positioning and implant survivorship of unicompartmental knee arthroplasty surgery performed using an image-free hand-held robotic system. Moreover, we analyzed whether there are significant differences and advantages compared to conventional surgery. MATERIALS AND METHODS: A systematic review has been performed on studies published between 2004 and 2021, on the electronic library databases, according to the Preferred Reporting Items of Systematic Reviews and Meta-analysis (PRISMA) statement. The inclusion criteria were all studies described as unicompartmental knee arthroplasty performed with the Navio robotic system. RESULTS: Fifteen studies were included, and 1,262 unicondylar knee arthroplasties were analyzed. These studies showed a satisfactory recovery of joint function, with a good range of motion (extension <5° and flexion which ranged from 105° to 130.3°) in patients of the NAVIO group. The revision rate was <2% while the infection rate <1%; no postoperative transfusion was needed in all UKA implanted. CONCLUSIONS: The use of a robotic tool for unicompartmental knee arthroplasty (UKA) could lead to a better implant positioning and joint alignment than conventional surgery. There is still limited evidence to support that the use of this robot in unicompartmental knee arthroplasty is a greater survivorship than other systems or conventional techniques; therefore, a long-term follow-up is needed.

Medial gastrocnemius flap for the treatment of infected knee prostheses.

OBJECTIVE: Muscular flaps may represent a valid treatment option for prosthetic infection after knee arthroplasty. PATIENTS AND METHODS: We present the results of 20 consecutive patients treated with the use of medial gastrocnemius flap for the management of different types of injuries or integumentary defects after total knee arthroplasty. Tissue necrosis or dehiscence occurred within 1 and 2 months after arthroplasty. The mean follow-up was 23.4 (12-60) months. Clinical outcome was evaluated according to the infection control rate and post-operative Knee Society Score (KSS). RESULTS: Prosthesis salvage and complete restoration of skin coverage were achieved in all patients. Functional assessment was performed using the KSS score. The final knee KSS score was classified as excellent (score: 80-100) in 0 patients, good (score: 70-79) in 17 patients, fair (score: 60-69) in 2 patients, and poor (score: 60) in 1 patient. Residual Extension Deficit: 0-20°; Very Satisfactory in 17 patients. 30-70° Satisfactory in 2 patients, 80-90° Unsatisfactory in 1 patient. Patients who successfully underwent flap treatment experienced a much greater increase in both components of the KSS score. CONCLUSIONS: The results highlight the effectiveness of medial gastrocnemius muscular flap for the treatment of prosthetic knee infection, in terms of function, limb salvage, cost-effectiveness and post-surgery quality of life. Further larger studies may consolidate these findings.

Could serum procalcitonin play a role in an emergency setting for patients with pyogenic spondylodiscitis?

OBJECTIVE: Spinal infections, represent quite rare but often severe conditions. However, due to symptoms' non-specificity and the lack of specific laboratory tests, diagnosis is often delayed with serious consequences for the patient's outcomes. The present investigation aimed at evaluating the role of procalcitonin (PCT) and other clinical features on the risk stratification and the clinical outcomes in spondylodiscitis patients treated in our Emergency Department. PATIENTS AND METHODS: The present investigation represents a single-center retrospective study. Clinical records of consecutive patients admitted to our Emergency Department from 1 January 2015 to 31 March 2021 were evaluated and patients with spondylodiscitis diagnosis in this period were recruited. Our primary outcome was the degree of autonomy of patients following the acute event. Our secondary outcome was the resolution of the infection. RESULTS: In the study period, a total of 345 patients were evaluated. Among these, 165 met the inclusion criteria, and constituted the study cohort. Concerning the primary outcome, we observed that the most significant predictive factors for being non-autonomous were elevated serum creatinine (> 1.05 mg/dl), Blood Urea Nitrogen (BUN) > 23 mg/dl, Lactate dehydrogenase > 228 U/L, PCT > 0.11 ng/mL. Patients with higher PCT (PCT > 0.11 ng/mL) and higher BUN (BUN > 23 mg/dl) had higher odds of infection persistence (the Odd Ratio, OR, were respectively 3.78 for PCT and 3.14 for BUN). CONCLUSIONS: PCT assay may play a role in diagnosing spondylodiscitis in an emergency setting. A PCT value > 0.11 ng/mL should be considered as a red flag, a predictor of worse clinical outcomes and persistence of infection.

Megaprosthesis in articular fractures of the lower limbs in fragile patients: a proposal for the therapeutic algorithm.

OBJECTIVE: The use of megaprosthetic implants could provide substantial advantages in elderly population affected by complex fractures. The aim of the study was to identify the patients suitable to megaprosthetic implants in the treatment of lower limbs fractures, as well as periprosthetic fractures. PATIENTS AND METHODS: From January 1st, 2015, to December 31st, 2021, all patients affected by femoral fractures with severe bone loss or previous surgery failure were retrospectively reviewed. ADL, IADL, SF-12 values pre- and post-operative were recorded. Hemoglobin value, NLR, PLR were recorded pre- and peri-operatively for all patients. Complications were recorded. All patients underwent a radiological follow-up. Significance was set at p ≤ 0.05. RESULTS: 23 patients were considered eligible, 10 males and 13 females; the mean age was 72.87 years old (± 12.33), while the mean BMI was 27.2 points (± 5.2). The mean follow-up was 2 years (± 1.4). The mean preoperative ADL and IADL scores were correlated with a positive independence of the patient, while the mean postoperative scores corresponded to a moderate-low independence. Also the mean Mental and Physical SF12 scores saw a decrease in values. NLR values were higher in the first group of patients with complications. CONCLUSIONS: A careful multiparametric and multidisciplinary patient selection is required to identify the suitable patient to this treatment.

Treatment options for proximal periprosthetic femoral fractures in Total Hip Arthroplasty: a single center experience.

OBJECTIVE: Proximal periprosthetic femoral fractures (PPFFs) are gradually increasing and surgical management is often associated with high risk of complications, due to elderly population and associated comorbidities. PATIENTS AND METHODS: We retrospectively assessed 39 patients at least at 2-years follow-up. We identified two study groups, similar for demographic data. Group A included patients surgically treated without involving prosthetic implants, whereas Group B included patients in which an implant revision was performed. RESULTS: Data were recorded from January 2017 to February 2020, and 39 patients were included: 30 females (76.9%) and 9 males (23.1%), with a confirmed diagnosis of periprosthetic fracture of the proximal femur. 23 (58.9%) patients were treated with Open Reduction and Internal Fixation (ORIF), 12 (30.7%) with revision surgery and 4 (10.3%) were treated by modular megaprosthesis. CONCLUSIONS: The treatment options considered in the study, revision arthroplasty and internal fixation had shown no significant differences as a matter of clinical outcomes and postoperative complications.

Liner dissociation in total hip arthroplasty: a systematic review.

OBJECTIVE: Liner dissociation (LD) is a rare catastrophic mechanical failure of total hip arthroplasty (THA). The study aims at reviewing the available literature regarding liner dissociations to point out their prevalence, describing any possible association and highlighting the surgical management at the time of revision. MATERIALS AND METHODS: A systematic review of the literature was conducted from January 2002, until February 2022, according to the PRISMA guidelines. The main keywords were: "dissociation" AND "liner" OR "hip arthroplasty" OR "THA" and their MeSH terms in any possible combination. Cases of liner dissociation with all levels of evidence of any age published in indexed journals were included. The study quality of all included studies was evaluated using the MINORS criteria. The kappa (k) value was used to assess the consensus between reviewers in the selection of articles and methodological quality assessment. Finally, a sub-analysis was performed specifically concerning the elderly population. RESULTS: Thirty-one manuscripts met the inclusion criteria of the systematic review (21 case reports and 10 case series). 124 LD in 123 patients, (53% females and 47% males) were evaluated. The overall prevalence of LD was 0.15%. The mean age at surgery was of 56.5 years (range 31-75 years). LD occurred in a primary surgery setting in 86% of the cases, at a mean time of presentation of 45.8 months after replacement surgery. 39.5% of the cups and 8.8% of the stems required revision. The mean follow-up after the revision was 18.4 months. Complications after revision occurred in 19.6% of cases, including 3 cases of re-dissociations. Re-revision was required in 13.6% of the revisions. The sub-analysis of the elderly population included 28 cases of LD identified in 10 manuscripts, with an average age of 73.5 years. CONCLUSIONS: LD is a rare but catastrophic mechanical complication of modular THA that requires implant revision. The LD is not related to a specific prosthetic implant, liner material or design, acetabular positioning within the safe zone or age group.

The IlluminOss® System: a solution in elderly patients with upper limbs bone metastases.

OBJECTIVE: The IlluminOss® System (IS) based on photodynamic bone stabilization (PBS) is a recent option in between the minimally invasive surgical techniques available to treat bone metastases when medical or radiation therapy is neither effective nor indicated, and major surgery is not possible. In this study, the results obtained using IS in the treatment of impending fractures or bone metastases of the upper limb have been analyzed in terms of improvement in pain, quality of life and recovery of function. PATIENTS AND METHODS: Between January 2017 and October 2019, 8 patients over 65 years old with impending fractures or pathological fractures or myeloma of the upper limb have been treated in our institute with IS. All patients were assessed about pain, general health and function of the affected limb before surgery and 1, 3, 6 (consistent with survival) months after the procedure. RESULTS: Mean VAS score improved from 8.88 before surgery to 1.00 six months after surgery, mean Karnofsky index improved at 1 and 3 months post-operative follow-up, and Musculoskeletal Tumor Society Score (MSTS) raised from 44.6 before surgery to 74.7 six months after surgery. Moreover, good reduction and stable fixation of the osteolytic lesion were achieved in all patients, and no complications were found. CONCLUSIONS: Numerous studies have been reported in the literature on the use of this system in osteoporotic elderly fractures, whereas only few articles are currently available regarding its use in the treatment of bone metastases or pathological fractures. From our study PBS seems to be an effective solution in the management of bone metastases or myeloma in both pathological fractures and impending upper limb fractures in patients with low life expectancy.

A new model of multidimensional discharge planning: continuity of care for frail and complex inpatients.

OBJECTIVE: Delays in patient discharge can adversely affect hospital and emergency room productivity and increase healthcare costs. The discharge should be structured from the hospital admission towards the most appropriate environment. This study aims to investigate the efficacy of the Unit, named "Continuity of Care Center" (CCC), to guarantee a safest and fastest hospital discharge in frail patients and to test the effect of our team-approach on hospital outcomes (length of stay and hospital mortality). MATERIALS AND METHODS: This is a prospective cohort study carried out in an acute care hospital with 1,558 beds and is equipped with 41 operating theaters. We collected data from October 2016 to June 2019. RESULTS: The time of patient discharge had an important reduction: 15.5±30.8 in the first 3 months vs. 11.0±20.1 in the last 3 months considered. The median of the time of discharge in all 12 months considered was 12 day. The length of stay presented an important reduction from 33.3±47.5 during the first 3 months vs. 28.8±39.5 in the last 3 months of activity of CCC; and a significant reduction of hospital deaths was recorded from 20% during the first 3 months to 14% in the last 3 months of activity of CCC. CONCLUSIONS: Results indicate a constant decrease in patient discharge time and length of hospital stay, with a consequent significant reduction of healthcare costs. According to the estimates of Italian Health Ministry concerning Latium region, every hospitalization day has a mean cost of € 674.00. Thus, the CCC activity has contributed to a reduction of approximately 12,832 days of hospitalization, in the considered period, with an estimated hospital saving of € 8,648,761.

Use of ceramic bearings in hip arthroplasty: correct implantation and review of clinical and radiographic results.

Ceramic materials are widely used in hip prosthetic surgery. Faced with important developments in the design and characteristics of the materials, ceramic-on-ceramic (CoC) are today the bearings in Total Hip Replacement (THR) showing the minimal wear rate. Moreover, ceramic wear debris demonstrated the absence of local and systemic toxicity. This makes ceramic bearing particularly suitable for active patients, whatever their age. The results show excellent survival rates of THRs with ceramic components and excellent clinical and radiographic scores with follow-up close to 20 years. However, the excellent outcomes of THRs with ceramic bearings are depending on appropriate and correctly performed surgical technique.

Evaluation of PD1 and PD-L1 expression in high-grade sarcomas of the limbs in the adults: possible implications of immunotherapy.

Sarcomas are a heterogeneous group of rare tumours. Improvements in immunotherapy and the important role of PD1 and PD-L1 expression in advancement and prognosis have opened new fields of research for the treatment of these neoplasia. We evaluated the immunohistochemistry of PD1 and PD-L1 expression in 60 adults' patients affected by high-grade sarcomas of the limbs. PD1 expression was 65% while PD-L1 was 68.3%. PD-L1 expression seems to correlate to Ki67 in liposarcomas, fibrosarcoma's and pleomorphic sarcomas, while it does not show any correlation to chondrosarcomas, while in rhabdomyosarcomas there is a correlation but, given the small sample size, it was not possible to perform a statistic analysis. Our study shows positivity among the different subgroups of positive PD1 lymphocytes infiltration and PD-L1 expression in high-grade sarcomas of the limbs.

Innovations in prevention of infections in oncological megaprostheses: a narrative review.

Infection is a significant complication in oncological megaprostheses. The purpose of our study is to indagate the innovations and new trend about the prevention of infection in this kind of surgery. The research focused on the use of antimicrobic prophylaxis, the defensive antibacterial coating and the use of silver coated.

Diluted povidone-iodine irrigation prior to wound closure in primary and revision total joint arthroplasty of hip and knee: a review of the evidence.

Periprosthetic Joint Infection (PJI) of the Hip and of the Knee is a tremendous complication associated with high patient morbidity, cost, and increased health care resource utilization. Over the last few years, several perioperative strategies have been developed in the hopes of reducing the risk of early superficial and deep surgical site infection (SSI). One of the most performed intraoperative treatments to reduce the risk of SSI in total joint arthroplasty is the use of dilute povidone-iodine (DPI) irrigation prior to wound closure. For this reason, we believed a systematic review of the literature was needed to better understand the current literature on the efficacy of dilute betadine in reducing PJI. The search terms for this systematic review was performed for keywords "betadine", "povidone-iodine", "lavage", "irrigation" and "arthroplasty". A total of six studies were included, four of these reported the outcome of primary total joint arthroplasty, and two of these reported the outcome of revision total joint arthroplasty. Some studies reported that the use of DPI is effective to reduce the incidence of infective complications, meanwhile other studies did not find differences when DPI was used. More studies must be addressed to provide the efficacy of DPI irrigation.

Intramedullary antibiotic coated nail in tibial fracture: a systematic review.

Implant-associated infections remain one of the main problems in trauma surgery, particularly for treatment of open tibial fractures. The role of systemic antibiotic prophylaxis is now established and accepted, but recent literature also seems to emphasize the importance of local antibiotic prophylaxis. Antibiotic coated nails play a crucial role, allowing at the same time the prevention of infections and favoring the stabilization of fractures. These devices appear to be a clinically effective and safe solution. The purpose of the study was to investigate the role of antibiotic coated nails in the treatment of tibia fractures. A literature review was performed on MEDLINE through PubMed to identify scientific publications relevant to the use of antibiotic coated nails in tibial fractures. Primary outcomes were infection rate and bone union rate. This review present numerous limits due primarily to the small number and different nature of studies published; the heterogeneity of the devices used.

Ankle fracture and necrotizing fasciitis: a common fracture and a dreadful complication.

Necrotizing fasciitis is a dreadful complication of the soft tissue. This pathology could be triggered by many factors, such as a fracture. We present a case of case of a necrotizing fasciitis in ankle fracture.

Staphylococcus Aureus Panton-Valentine Leukocidin causing hip osteomyelitis, thrombophlebitis and necrotizing pneumonia in an immuocompetent child.

Panton-Valentine leukocidin (PVL) represents an important virulence factor for many strains of Staphylococcus aureus. PVL is an esotoxin causing leucocyte destruction and tissue necrosis. We report on a case of osteomyelitis involving the hip joint with thromblophlebitis complicated by necrotizing pneumonia and life-threatening septic shock. The child required advance respiratory support for 14 days with circulatory support for 7 days in ICU (intensive care unit), surgical draninage via arthrotomy of hip joint and second-line antibiotic treatment for 1 month. Among a wide literature, in Europe over half of Panton-Valentine St. Aureus (PVL-SA) is MSSA. Investigations for PVL are not always available determining an under-recognition of the episodes. Data on prevalence of PVL-SA in Italy are scarce. With this clinical report, we emphasize the recognition of clinical features that must lead to suspect PVL-SA osteomyelitis in children, providing their adequate management.

Predictable risk factors for infections in proximal femur fractures.

Proximal femur fractures are increasing, together with the aging of world population. One of the complications worsening this condition is infection. In this study, we try to identify risk factors that can lead to infection. We identified 122 patients with femoral neck fracture. The occurrence of infectious events were recorded (respiratory, urinary, superficial wound and periprostethic infection). There were 15 infections, mostly urinary and pulmonary, and all were treated using antibiotics. No statistical differences were found between infection and control group regarding waiting time for surgery, mean time of surgery, age, kind of fracture, type of surgery. Fever onset >38° within 72 hours from surgery was statistically correlated with early infections. Future studies must be led to identify risk factors for infection and to create a strategy to prevent this possibly lethal complication.

Reprint of: Thoracolumbar burst fractures associated with incomplete neurological deficit in patients under the age of 40: Is the posterior approach enough? Surgical treatment and results in a case series of 10 patients with a minimum follow-up of 2 years.

INTRODUCTION: Surgical management of thoracolumbar burst fractures is controversial. While the goals of surgical treatment are well accepted (i.e., fracture reduction and stabilization, neural elements decompression, and segmental angular deformity correction), the choice of the best surgical approach (i.e., posterior vs. anterior vs. combined approach) remains controversial. Several studies have debated the advantages of each surgical approach but there is no definitive evidence available to date, particularly in young adult patients. The aim of this study was to assess whether posterior approach alone can be a valid surgical treatment for patient under the age of 40 affected by thoracolumbar burst fractures and incomplete neurological deficits. MATERIAL AND METHODS: A total of 10 consecutive patients affected by thoracolumbar burst fractures associated with incomplete neurological deficits treated at our institution from January 2015 to February 2017 were included in our study. All patients were under the age of 40 at the time of injury and underwent decompression and stabilization using the posterior surgical approach alone. Demographics, clinical, and radiographic parameters were recorded preoperatively, postoperatively and at the latest available follow-up. The minimum follow-up was set at 2 years post-operatively. RESULTS: The mean operative time was 303.6 min (range, 138-486). Average blood loss was 756 mL (range, 440-2100). Nine out of ten patients returned to a normal neurological status after surgery while 1 patient showed some improvement but did not recover completely. Segmental kyphotic deformity improved from a mean of 21.8° before surgery to 14.8° at the time of the last follow-up. The anterior and posterior wall height of the fractured vertebra was restored with an average of 4 mm. The Visual Analogue Scale score reported an improvement from the mean preoperative value of 7.92 to 1.24 at the last follow-up; 8 out of 10 patients resumed physical activity while all of them returned to work. CONCLUSIONS: A single posterior surgical approach is an acceptable option in terms of clinical, radiological and functional outcomes at 2 years follow-up in patients under the age of 40 presenting with a thoracolumbar burst fracture and neurological deficit.

Clinical and radiographic outcomes after antegrade intramedullary nail fixation of humeral fractures.

INTRODUCTION: Humerus fractures are frequent, accounting for about 3-4% of all fractures in adults. Treatment for fractures of the diaphyseal and proximal meta-epiphyseal regions remains controversial: there is no unanimity in the scientific community about the superiority of surgical treatment over non-surgical treatment and which is the best between possible surgical treatments. Among the choices for surgical treatment the most commonly used implants are the locking-compression plate and the intramedullary nailing. The purpose of this study was to perform a clinical and radiographic follow-up in patients who underwent surgical procedures for reduction and osteosynthesis of proximal or diaphyseal humeral fractures by means of anterograde intramedullary nailing with a straight-shaped nail. PATIENTS AND METHODS: A clinical and radiographic follow-up was performed in 56 patients who underwent surgical procedures for reduction and osteosynthesis of proximal or diaphyseal humeral fractures by means of antegrade intramedullary nailing using Synthes MultiLoc® system. Clinical data were collected using subjective quality of life assessment forms (SF12-v2), quality of life related to specific disabilities assessment forms (Quick-DASH, ASES score, WORC) and objective functional assessment forms (Constant-Murley score). The radiographic Follow-Up was performed at 30, 90 and 180 days from the date of the surgery. RESULTS: Almost all patients were able to return to a satisfactory quality of life, comparable with the one before the traumatic episode. The functional results were assessed as excellent or good with almost complete recovery of the range of motion and moderate recovery of strength. The residual pain encountered was moderate or zero. The average QuickDASH score was 17.7 ± 4.3 (range 9.1 - 27.3). The average ASES score was 73.8 ± 8.1 (range 58.3 - 88.3). The average WORC score was 543.3 ± 100 [74% ± 4.8%] (range 310 - 740). The mean Constant-Murley score was 69.6 ± 4.6 (range 61 - 84). All patients had a fair or good consolidation of the fracture on radiographic examinations. The calculated RUST score was 4.2 ± 0.4 (range 4-5) 30 days after surgery, 6.1 ± 0.9 (range 4- 8) 90 days after surgery and 9.8 ± 1.5 (range 7-12) to 180 days after surgery. No major complications were found. CONCLUSIONS: Treatment of the diaphyseal and proximal meta-epiphyseal humeral fractures with antegrade intramedullary nail provides excellent subjective and objective clinical results and good radiographic results. However, clinical studies with larger number of patients and longer follow-up are necessary.