Previous studies showed that a fast-resorbable antibacterial hydrogel coating (DAC®, Novagenit Srl, Mezzolombardo, TN, Italy) composed of covalently linked hyaluronan and poly-D, L-lactide, is able to reduce early post-surgical infection both after joint replacement and osteosynthesis. Aim of the present report is to investigate medium-term safety and efficacy of the coating in patients undergoing primary and revision cementless total hip replacement (THR).

We designed a two-phases study. In both phases, DAC was prepared according to manufacturer's instructions. In brief, the syringe prefilled with 300 mg of sterile DAC powder was mixed, at the time of surgery, with a solution of 5 mL of sterile water and with the tailored antibiotics, at a concentration ranging from 25 mg/mL to 50 mg/mL. The resulting antibacterial hydrogel was then spread on the outer surface of the prosthesis just before implantation.

In the first phase, safety was assessed. Forty-six patients (13 primary and 33 revision THR) were treated with DAC between 2013 and 2015 and evaluated at a 2.8 ± 0.7 years follow up (FU). Antibiotics used for DAC reconstruction were Vancomycin in 33 cases, Vancomycin + Meropenem in 10, Vancomycin + Rifampicin, Teicoplanin or Ceftazidime in 1 case, respectively. Patients were evaluated at 3, 6, 12 months and yearly after with a clinical and radiographic FU. No evidence of infection and no failure/loosening of the prosthesis were observed. No adverse events were reported.

The second phase was designed to evaluate efficacy of DAC in preventing infection recurrences after a two stage revision for infected THR. Twenty-seven patients, treated with DAC coating, were compared with a control group of 32, treated in the same time period, without the coating. Demographics, host type and and identified bacteria were similar in the two groups (18.6% of MRSA in DAC group vs 18.5% MRSA in no-DAC group). Patients were evaluated clinically and radiographically at 3, 6, 12 months and yearly thereafter. At a minimum 2 years FU (mean 2.7), we observed 1 dislocation in each group and 2 cases of loosening in the no-DAC group. 4 cases (11%) of recurrence of infection in the no-DAC group (1 MRSA and 3 St. Epidermidis) and no infection recurrences in the DAC group. Due to the small cohort of patients this difference is not statistically significant (Fisher's exact test, p=0.18).

This is, to our knowledge, the longest observation concerning the safety and efficacy of the DAC antibacterial coating, applied to hip replacement. The results are in line with those previously reported and point out the absence of side effects of the antibacterial coating in this application and the tendency to reduce re-infection in second stage. This finding needs to be confirmed by a larger dataset.

Reliability of microbiological diagnosis of prosthetic joint infection [PJI] strongly depends on the ability to dislodge microorganisms from biofilm and on the rate of contaminating samples during collection in the operating room and processing. The aim of a correct protocol is to avoid false negative and false positive results in order to adapt the correct therapy for each patient.

The object of the present study was to evaluate the impact of a novel closed bag system designed for samples collection and processing based on dithiothreitol (DTT), which is a sulfydryl compound able to remove bacteria from biofilm (MicroDTTect, 4i, Italy), on isolation of contaminant microorganisms in hip prostheses.

Specimens (prostheses, spacers, periprosthetic tissues) were aseptically collected according to a standard protocol into the device, which was transported to the laboratory for culture. Three different models of the system were prospectively evaluated, each being a development of the previous one. The first generation device consisted in an “open” system (DTT eluate was collected with a syringe and dispensed into sterile tubes), the second generation device in a “partially closed” system (DTT eluate collected directly in sterile vacuum tubes) and the third generation device in a “completely closed system” (DTT reservoir directly connected with sealed tubes inside the device). PJI was diagnosed following criteria established by MSIS.

The overall contamination rate, sensitivity and specificity of the first generation “open” system MicroDTTect were respectively 2.6% (1/39), 82.3% and 95.4% in 39 hips. The second generation “partially closed” device was characterized by a contamination rate of 1.96% (1/51), a sensitivity of 84% and a specificity of 96.1% in 51 hips. Contamination rate further decreased in the third generation “closed” system (1.89%, 2/106), while sensitivity (91.3%) and specificity (96.7%) improved in 106 hips. Differences have been also observed in hips (106) when compared to knees (70 cases) prosthetic infections (sensitivity 91.3% vs 89.3% and specificity 96.7% vs 100%).

Our data show as, thanks to its ease of use, low contamination rate and high sensitivity, MicroDTTect can represent a useful tool for improving the microbiological diagnosis of PJIs in hip revisions and has replaced sonication in our practice.

Infection remains among the first reasons for failure of joint prosthesis. Currently, the golden standard for treating prosthetic joint infections (PJIs) is two-stage revision. However, two-stage procedures have been reported to be associated with higher costs and possible higher morbidity and mortality, compared to one-stage. Furthermore, recent studies showed the ability of a fast-resorbable, antibacterial-loaded hydrogel coating to reduce surgical site infections after joint replacement, by preventing bacterial colonization of implants. Aim of this study was then to compare the infection recurrence rate after a one-stage, cemenless exchange, performed with an antibacterial coated implant versus a standardized two-stage revision procedure.

In this two-center prospective study, 22 patients, candidate to revision surgery for PJI, were enrolled to undergo a one-stage revision surgery with cementless implants, coated intra-operatively with a fast-resorbable, antibiotic-loaded hyaluronan and poly-D,L-lactide based hydrogel coating (“Defensive Antibacterial Coating”, DAC, Novagenit, Italy). DAC was reconstructed according to manufacturer indications and loaded with Vancomycin or Vancomycin + Meropenem, according to cultural examinations, and directly spread onto the implant before insertion. This prospective cohort was compared with a retrospective series of 22 consecutive patients, matched for age, sex, host type, site of surgery, that underwent a two stage procedure, using a preformed, antibiotic-loaded spacer (Tecres, Italy) and a cementless implant. The second surgery, for definitive implant placing, was performed only after CRP normalization and no clinical sign of infection. Clinical, laboratory and radiographic evaluation were performed at 3, 6 and 12 months, and every 6 months thereafter. Infection recurrence was defined by the presence of a sinus tract communicating with the joint, or at least two among the following criteria: clinical signs of infections; elevated CRP and ESR; elevated synovial fluid WBC count; elevated synovial fluid leukocyte esterase; a positive cultural examination from synovial fluid; radiographic signs of stem loosening.

The two groups did not differ significantly for age, sex, host type and site of surgery (18 knees and 4 hips, respectively). The DAC hydrogel was loaded intra-operatively, according to cultural examination, with vancomycin (14 patients) or vancomycin and meropenem (8 cases). At a mean follow-up of 20.2 ± 6.3 months, 2 patients (9.1%) in the DAC group showed an infection recurrence, compared to 3 patients (13.6%) in the two-stage group. No adverse events associated with the use of DAC or radiographic loosening of the stem were observed at the latest follow-up months.

This is the first report on one-stage cementless revision surgery for PJI, performed with a fast-resorbable antibacterial hydrogel coating. Our data, although in a limited series of patients and at a relatively short follow-up, show similar infection recurrence rate after one-stage exchange with cementless, coated implants, compared to two-stage revision. These findings warrant further studies in the possible applications of antibacterial coating technologies to treat implant-related infections.

Development of antibacterial surfaces or coatings to prevent bacterial adhesion and hence colonization of implants and biofilm formation is an attractive option, in order to reduce the tremendous impact of implant-related infections associated with modern surgery. To overcome the lack of in vivo and clinical models, able to evaluate the performance of anti-adhesive coatings, we designed an in vitro experimental setting that allows to quantitatively evaluate the ability of a coating to reduce bacterial adhesion on a given surface; this model may efficiently serve as a surrogate endpoint to validate anti-adhesive medical devices and compounds. Here we report the results the evaluation of the anti-adhesive properties of a patented, fast-resorbable hydrogel coating, (“Defensive Antibacterial Coating”, DAC).

Sterile sandblasted titanium discs of approximately 5cm² surface area were used as substrates for bacterial adhesion. The gel was prepared as follows: syringes prefilled with 300 mg of DAC powder (Novagenit Srl) were reconstituted with 5 ml of sterile water to obtain a hydrogel with a DAC concentration of 6%. Two experiments were conducted. In the first, 200 mg of hydrogel were homogenously spread on the surface of titanium disc, with the spreading device provided by the manufacturer. Both coated and uncoated substrates (controls) were overlaid with a standardized inoculum (10⁸ CFU/ml) of a wild methicillin-resistant Staphylococcus aureus strain, previously isolated from a peri-prosthetic joint infection, for 15, 30, 60 and 120 minutes. Afterwards, non-adherent bacteria were removed by rinsing with sterile saline. The remaining adhered cells were seeded on agar plates for CFU count. In the second experiment, the discs were first inoculated with bacterial cells followed by a treatment with the hydrogel and bacterial count as described above. Ten discs were used for each condition and each time interval (total 160 discs).

The adhesion density of S. aureus on titanium discs pre-treated with DAC was significantly lower than that observed on untreated controls at each time point. In particular, the average number of adherent bacteria at 15, 30, 60 and 120 minutes of incubation, was respectively reduced by 86.8%, 80.4%, 74.6% and 66.7%, compared to controls (p<0.001). DAC treatment of discs with previously adhered S. aureus reduced bacterial adhesion, at 15, 30, 60 and 120 minutes of incubation, by, respectively, 84.0% (p<0.05), 72.8%, 72.3% and 64.3% (p<0.001), compared to untreated controls.

Our results shows that DAC, “Defensive Antibacterial Coating”, has anti-adhesive properties that allow to reduce bacterial adhesion on a sanded titanium surface by more than 80%, even in the presence of remarkably high bacterial loads (10⁸ CFU/ml), of multi-resistant bacteria (MRSA) and even in the case of previous contamination. Providing anti-adhesive properties to a surface with a fast-resorbable coating may be a safe option to protect inorganic and organic surfaces and biomaterials. Those observation could be the pre-requisite for its in vivo application.

Aim

The induced membrane technique (IMT) or Masquelet technique is a two-step surgical procedure used to treat bony defects (traumatic or resulting from tumoral resections) and pseudo arthroses, even caused by infections. The relatively small case series reported, sometimes with variants to the original technique, make it difficult to assess the real value of the technique. Aim of this study was then to undertake a systematic review of the literature with a particular focus on bone union, infection eradication and complication rates.

Aim

Aim of this study is to present the first clinical trial on an antibiotic-loaded fast-resorbable hydrogel coating*, in patients undergoing internal osteosynthesis for closed fractures.

Aim

Infection remains among the first reasons of failure of joint prosthesis. According to various preclinical reports, antibacterial coatings of implants may prevent bacterial adhesion and biofilm formation. Aim of this study is to present the first clinical trial on an antibiotic-loaded fast-resorbable hydrogel coating*, in patients undergoing hip or knee prosthesis.

Aim

Implant-related infections, including peri-prosthetic joint infection (PJI) and infected osteosynthesis, are biofilm-related. Intra-operative diagnosis and pathogen identification is currently considered the diagnostic benchmark; however the presence of bacterial biofilm(s) may have a detrimental effect on pathogen detection with traditional microbiological techniques. Sonication and chemical biofilm debonding have been proposed to overcome, at least partially, this issue, however little is known about their possible economical impact. Aim of this study was to examine direct and indirect hospital costs connected with the routine use of anti-biofilm microbiological techniques applied to hip and knee PJIs.

Infection is among the first reasons for failure of orthopedic implants. Various antibacterial coatings for implanted biomaterials are under study, but only few technologies are currently available in the clinical setting. Previous studies showed the in vitro and in vivo efficacy and safety of a fast resorbable (<96 h) hyaluronic and polylactic acid based hydrogel, loaded with antibiotic or antibiofilm agents (DAC®, Novagenit Srl, Mezzolombardo, TN). Aim of this study is to report the results of the largest clinical trial in trauma and orthopedic patients.

In this prospective, controlled, study, a total of 184 patients (86 treated with internal osteosinthesis for closed fractures and 98 undergoing cementless total hip or knee joint prosthesis) were randomly assigned in three European orthopaedic centers to receive antibiotic-loaded DAC coating or to a control group, without coating. Pre- and post-operative assessment of laboratory tests, wound healing (ASEPSIS score), clinical score (SF-12 score) and x-rays were performed at fixed time intervals. Statistical analysis was performed with Fisher exact test or Student's t test. Significance level was set at p<0.05.

The study was approved by the local Ethical Committee and all patients provided a written informed consent.

On average, wound healing, clinical scores, laboratory tests and radiographic findings did not show any significant difference between the two-groups at a mean 12 months follow-up (min: 6, max: 18 months).

Four surgical site infections and two delayed union were observed in the control group compared to none in the treated group.

No local or systemic side effects, that could be related to DAC hydrogel coating, were noted and no detectable interference with bone healing or osteointegration could be found

This is the largest study, with the longest follow-up, reporting on clinical results after the use of a fast-resosrbable anti-bacterial hydrogel coating for orthopaedic and trauma implants. Our results show the safety of the tested coating in different indications; although not statistically significant, the data also show a trend towards surgical site infection reduction, as previously demonstrated in the animal models.

Prosthetic implants, periprosthetic and osteoarticular tissues are specimens of choice for diagnosis of bone and joint infections including prosthetic joint infections (PJIs). However, it is widely known that cultures from prostheses and tissues may fail to yield microbial growth in up to one third of patients. In the recent past, treatment of prosthetic implants have been optimized in order to improve sensitivity of microbiological cultures, while less attention has been addressed to tissue samples. For these latter homogenization is considered the best procedure, but it is quite laborious, time-consuming and it is not always performed in all laboratories. Dithiothreitol (DTT) has been proposed as an alternative treatment to sonication for microbiological diagnosis of PJIs. In this study, we evaluated the applicability of MicroDTTect treatment, a closed system developed for transport and treatment of tissues and prosthetic implants with DTT.

For evaluation of applicability of MicroDTTect to tissue specimens, samples (tissues and, in case of PJI, prosthetic implants) from 40 patients (12 PJIs and 5 osteomyelitis and 23 not-infected) were evaluated. MicroDTTect system consists of a sterile plastic bag containing a reservoir which allows for release of a 0.1% (v:v) DTT solution, once the sample is placed into the bag. Comparison of MicroDTTect treatment of prostheses with sonication included samples from 30 patients (14 with aseptic loosening of the prosthesis and 16 with PJIs). Of two tissue samples from the same region, one was placed into MicroDTTect bag and the other was collected in a sterile container with addition of sterile saline. After agitation and centrifugation of the eluate, aliquots of the pellets were plated on agar plates and inoculated into broths which were incubated for 48 hrs and 15 days, respectively.

Treatment of prosthetic implants with MicroDTTect showed a higher specificity and sensitivity than sonication (specificity 92.8% vs 85.7%; sensitivity: 87.5% vs 75.0 % DTT vs sonication). When used for tissue treatment, MicroDTTect showed a sensitivity of 82.3% and a specificity of 97% which were higher than that observed when saline was used (sensitivity: 64.7%; specificity 91%).

Treatment of tissues and prosthetic implants with MicroDTTect may be a practicable strategy to improve microbiological diagnosis of osteoarticular infections, reducing sample manipulation and therefore limiting sample contamination. Moreover, use of MicroDTTect does not require dedicated instrumentation, and is time and cost saving.

Summary Statement

An Implant Disposable Antibacterial Coating (i-DAC®) is described, consisting of a fully resorbable, biocompatible hydrogel, able to release antibacterial and antibiofilm agents. Direct application of the hydrogel on implants prevented infection occurrence in an in vitro model of peri-prosthetic infection.

Reasons for bone loss in septic hip prosthesis include osteolysis caused by the infection in itself and by the mechanical loosening, while implant removal and the necessary bone debridment usually ends in a even more severe bone loss.

In two stage revision surgery the use of a long stem antibiotic-loaded pre-formed cement spacer (Spacer G – Tecres s.r.l., Italy) appears particularly useful to allow mechanical stability and antibiotic local elution even in the presence of wide proximal femoral bone loss. After two months the revision is performed with non-cemented long stem modular implants (Profemur – Wright-Cremascoli) without the need for massive bone grafts. Recently we have also started using growth factors to stimulate bone stock reconstitution. In all the patients a double antibiotic therapy is administered after the first and second stage procedures for 6–8 weeks.

The results obtained (54 patients, follow-up 2 – 5 years) according to this protocol show the absence of infection recurrence, 10 cranial spacer dislocation, not treated, 2 revision prosthesis dislocations, that required open reduction, 1 transient femoral nerve palsy.

The described technique, used according to a proper protocol, allows to obtain good results, in the medium term follow-up.

Septic knee prosthesis revision is particularly challenging either for the eradication of the infection and for functional recovery of the patient.

18 patients treated from year 2000 to 2003, treated according to the same medical and surgical protocol have been reviewed. In all cases the following steps have been followed:

- removal of the septic prosthesis, debridement and implant of an articulated pre-formed cement spacer;

At a mean 18 months follow-up, we observed:

- no infection recurrence in all cases (one patient is lost to follow-up);

Two-stage septic knee prosthesis revision, according to a the described protocol, allows to obtain high infection eradication rate and acceptable functional recovery, in the medium term follow-up.

Different conditions may lead to bone loss in bone infections. Septic non-unions, osteomyelitis, septic joint prosthesis are all conditions that may be associated with the need for bone grafts and/or of bone substitutes. The risk of infection recurrence makes, in these cases, particularly challenging the choice of the type of bone implant.

The use of growth factors, eventually associated with autologous or homologous bone grafts or with bone substitutes, may be helpful in restoring the bone stock, allowing to fill large bone defects, once the infection is controlled.

We present the preliminary results in 10 patients in which autologous Platelet Rich Plasma (PRP) has been used to treat large bone defect in two stage hip reconstruction (7 cases) and in previously infected non-unions (3 patients).

At a minimum follow-up of 6 months (maximum 18 months) a significant new bone formation occurred at the site of PRP application in all the cases treated and no signs of infection recurrence are present at the time of writing.

This is the first report on the short-term safety of use of PRP for the treatment of bone loss in previously infected bones in humans. The limited number of patients and the follow-up do not allow at the moment to drive any conclusion regarding the efficacy and safety in the long term, and the use of PRP with this indications should be limited to selected cases.

Introduction: Reports about the usefulness of FDG-PET in detecting infections were few in the last years but are greatly increasing in number in the recent years. The interest for this method is related to the demonstration that FDG uptake is increased in cells with elevated glycolitic activity as neoplastic cells, neutrophils, activated macrophages, probably bacteria. As far as a neoplasm is excluded, FDG uptake is increased in inflammatory sites. This study was done to test the possible use of this method in painful total hip-replacement diagnosis.

Materials and methods: A prospective study on 24 patients (33 hip arthroplasties) affected by painful total hip replacement was conducted. All patient has blood test, X-ray examinations of hips and chest, Ultrasound scan, cultures from sinus tract or hip aspiration, Tc^99m MDC bone scan (SPECT), FDG-PET. Areas of uptake were evaluated and compared. Fifteen patients were operated on (9 two-stage revisions, debridements), during operation cultures were repeated and bone biopsy were done at the sites of icreased PET uptake. Bone and soft tissue debridement was specifically performed on site of PET uptake with maximal preservation of bone stock.

Results: Infected hips were 20. Infection was demonstrated by positive culture and positive biopsy in all cases. Sensibility and specificity of PET were respectively 100% and 92%. The study of tracers uptake showed that these are complementary and give different information. All patients who were operated on were reviewed with a mean follow up of 7 months (range 3 months-15 months ). The nine patients who had revision were free of infection at follow-up.

Discussion: from our experience PET is easy to perform, has an excellent sensibility and good specificity and can be placed at the end point of the flow-chart for diagnosis of total hip replacement infection (preceeded in any case by standard X-Rays and bone scan). Moreover PET scan could be useful in pre-operative planning of revision surgery as it has better anatomical definition than traditional scans and may allows surgeon to localize on three planes infected bone and soft tissues. Therefore at the moment this tool has high costs so should be used in selected cases. Its real usefulness in revision surgery has to be confirmed by a longer follow-up of treated cases.

Introduction: In 1995 we started using, at the G. Pini Orthopaedic Istitute of Milano, a system for bone healing stimulation based on low intensity pulsed ultrasound. Advantages of the method are: home therapy (20 minutes per day); no side effects, even in the presence of metallic devices or infection; ease of use. Indications of low intensità pulsed ultrasound are bone healing after fresh frarctures, in which a significant bone healing accelation can be observed, delayed and non-unions. We share our experience in a challenging field of application: septic non-unions.

Materials and methods: We retrospectively evaluated 30 patients, treated from 1996 to 2003, affected by septic non-unions (a fracture that, in the presence of infection, did not show any significant increase in callus formation at 8 months from the time of fracture). The patients had a mean 1.7 ± 2 previous failed intervention. Patients were treated, in the absence of other medical or surgical treatment (excluding antibiotic therapy), with low intensity pulsed ultrasound (EXOGEN S.A.F.H.S. or, since year 2002, IGEA F.A.S.T.). The treatment was applied, after the necessary instructions, directly from the patient, at home, 20 minutes per day. Failures of the treatment were considered need for further surgery to stimulate bone healing, persistence of non-union at follow-up. Exclusion criteria included: evident instability of the synthesis, soft tissue loss and bone exposure, wide bone loss (> 2 cm).

Results: 24 bone healing (86 %), 4 failures (need for surgery), 2 treatment discontinuation. Mean treatment duration: 123 ± 43 days (minimum 90, maximum 240 days). No side effects local or general were observed. In 18 cases a bone debridment and/or hardware removal intervention had been performed after bone healing. At follow-up, 28 patients are free from infection, while two showed infection recurrence.

Conclusions: Low intensity pulsed ultrasound is an effective options in the treatment of septic non-unions, without side effects. An accurate indication and patient selection provide an advantageous cost/benefit ratio.

A prospective study on 24 patients (33 hip arthroplasties) affected by painful total hip replacement was conducted. All patient had a blood test, X-rays, ultrasound scan, cultures, Tc ^99m bone scan (SPECT), and F¹⁸FDG-PET. Fifteen patients were operated on (nine two-stage revisions, six débridements). During operation, cultures were repeated and bone biopsy was performed at the sites of increased PET uptake. Bone and soft tissue débridement was specifically performed at the site of PET uptake with maximal preservation of bone stock.

There were 20 infected prostheses. Infection was demonstrated by positive culture in all cases and positive biopsy in operated cases. Sensibility and specificity of PET were 100% and 92%, respectively. All patients who were operated on were reviewed with a mean follow-up of 7 months. The nine patients who had revision were free of infection at follow-up.

In our experience PET is easy to perform, has an excellent sensitivity and good specificity and can be placed at the end point of the flow-chart for diagnosis of total hip replacement infection. Moreover, PET scan could be useful in pre-operative planning of revision surgery as it has better anatomical definition than traditional scans. Presently, it involves high costs and should only be used in selected cases. Its real usefulness in revision surgery has to be confirmed by a longer follow-up of treated cases.

Bone loss, either due to a septic process or to surgical débridements, is frequently associated with bone infections. Bone loss may be present in septic non-unions, osteomyelitis or septic joint prosthesis. In each of these conditions the use of bone or bone substitutes may be indicated. However, the risk of septic recurrence makes the choice of the right implant in these patients particularly difficult.

Clinical cases are presented to show the different choices available. Attention is focussed on: (1) when, in the presence of bone loss, a bone graft can be avoided and with which suitable procedures good results can be obtained; (2) when and how autologous bone grafts should be used; (3) when homologous bone grafts or bone substitutes are indicated; (4) how bone grafts should be protected against bacterial adesion and proliferation; and (5) the role of new technologies, such as bone growth factors. In this regard the clinical results are presented of the use of platelet-rich plasma (PRP) added to autologous or homologous bone after bone débridement in six patients treated with two-stage non-cemented revision of septic hip prosthesis and in two patients with septic non-union of the femur. At a minimum follow-up of 6 months (max. 1 year), we did not observe any infection recurrence, while bone remodelling and clinical outcome were favourable.

The use of bone growth factors such as PRP possibly added to autologous or homologous bone appears to be a promising technique to achieve bone reconstruction in débrided bone infections. However, with the limited numbers of patients and the short-term follow-up conclusions cannot be drawn and the use of growth factors with this indication should be limited to selected cases: patients with wide bone loss and with no signs of active infections.

No international guidelines are available concerning bone reconstruction in infections. Clinical experience shows that different surgical procedures are effective and the choice should take into considerations the type and site of bone defect, the host type and the pathogenesis of the bone loss. Growth factors may be a useful tool in these conditions and further studies are indicated.

A modular neck allows to choose the offset of the femoral head and the degree of anti-retroversion, lateralization and varus-valgus intraoperatively. At the G. Pini Institute we have been using modular necks in custom prostheses since 1989. Excellent results in this application did open the way to a larger use in off-the-shelf prostheses. Modular necks can be now coupled with different stems, leaving the surgeon free to use the preferred prosthetic stem design. Modular necks have been implanted in more than 50,000 in the world. Medium term results in custom prosthesis and the experience in off-the-shelf non-cemented stems are presented, together with further improvements of this technology under study.

From 1989 to December 1999, 481 custom stems have been implanted. All patients but ten received modular necks. The prostheses were made of a titanium alloy and HA coated. 61 % of patients had dysplastic oxarthrosis. 372 implants performed between 1989 and 1996 were retrospectively evaluated. Data from off-the-shelf prosthesis, at a shorter follow-up, are also reported. Laboratory data showed that the use of an elliptical Morse cone of the neck reduced wear debris production to less than 1 mg/year. In custom implants, (mean follow-up: 7 years), we did not observe any thigh pain or radiological signs of osteolysis or fretting. Mean leg-length discrepancy was 2.8 cm pre-op and 0.3 cm post-operatively. Off-the-shelf implants also showed good clinical and radiological results. New design modular necks will increase the possible range of motion and provide more solutions for positioning the center of rotation. Modular neck is a safe and reliable solution to obtain the correct position of the center of rotation intra-operatively, without side effects. Applications in off-the-shelf prostheses allow to reduce costs while maintaining the advantages of this technology.