To report mid-term results of PJI treated with uncemented stems.

: 80 hips of PJI after THA were treated with uncemented stems from 01/1993 to 12/2012 and followed prospectively. Selection occurred for one- (n=27) or two-stage (n=53) exchange according to the Liestal algorithm. Surgical approaches were transfemoral (n=58), transgluteal (n=9) or transtrochanteric (n=13). A monoblock (Wagner SL, n=58) or modular (Revitan, n=22) revision stem was implanted. On the acetabular side 44 Müller rings, 33 Burch-Schneider cages (combined with a cemented PE-cup) and 3 press-fit cups were used. Kaplan-Meier survival was calculated for endpoints (a) persistence of infection, (b) septic/aseptic stem loosening. Radiographs were analysed for (a) subsidence, (b) distal stem integration, (c) changes in cortical thickness, (d) proximal femur restoration, (e) radiolucency around stem/cup.

Mean FU was 5.2 (2–15) years. PJI was eradicated in 77 of 80 hips (96%). 3 patients (all two-stage) had a treatment failure. 2 were treated successfully with an additional two-stage exchange. In the 3rd patient we were not able to control infection and exarticulation was performed. Furthermore, one stem was revised for aseptic loosening (5 years), 1 for a broken Wagner stem (7 years) and 1 for subsidence (8 months). Stem survival after 5 years was 93% (SD ±2.5 years). 2 cups were revised for aseptic loosening and 1 for recurrent dislocations. Subsidence ≥5mm was found in 6 hips and occurred always within 3 months after surgery independent of stem type (p=0.947) and approach (p=0.691). Proximal femoral remodelling after transfemoral approach was excellent or good in 71% (32 excellent, 9 good) with no difference between one-/two-stage exchanges (p=0.288). Initial distal stem integration was 65mm medial and 66mm lateral and increased to 8mm medial (p=0.716) and 10mm lateral (p<0.001). Cortical thickness was unchanged over the entire FU period (p=0.493). Radiolucencies were seen around 26 stems, only the stem revised after 5years was rated loose.

Eradication of PJI was high using our established protocol even with uncemented revision stems. Mid-term survival was independent from one-/two-stage revision and comparable to results for aseptic loosening revision.

Introduction

Primary stability of the Burch-Schneider ring (BSR) in case of acetabular revision is discussed controversial. In a retrospective two centre cohort study we analyzed the influence of the mode of screw fixation and the restoration of the center of rotation on migration, loosening and other radiographic parameters.

Introduction

The usefulness of minimal invasive hip replacement is frequently discussed but there is a lack of data on the effect of the surgical approach on early results. We wanted to study the effect of the surgical approach on the peri- and early postoperative outcome.

Introduction: In treatment for prosthetic hip joint infection (PHJI), the advantages of a 1-stage exchange over the classic 2-stage approach are the lower morbidity and earlier rehabilitation. Secondly, a recently published treatment algorithm for PHJI using well-defined selection criteria for 1-stage exchange had a 85–100% rate of cure for infection. Patient satisfaction after hip surgery is highly influenced by the functional result. We hypothesized that in our used algorithm the functional and radiological outcomes after a 1-stage exchange due to an implant-associated infection would be similar to a matched control group of 1-stage exchange due to aseptic loosening.

Material and Methods: Twenty-two cases (21 patients), with PHJI according to a well-defined definition, after 1-stage exchange of the prosthesis strictly according to the algorithm, with index-surgery between april 1996 and october 2004, were included in the studygroup. Case-matching was performed with aseptic revised cases for previous surgery, type of implant, use of transfemoral osteotomy, Charnley score, duration of follow-up, age, and sex. Outcome measures were perioperatively complications, functional results (Harris hip score, limping, and use of walking support) at two years, and the occurrence of revision for any reason and radiological loosening at latest follow-up. All outcomes were compared between both groups and with the results of the two stage revisions in our cohort. Finally, the eradication of infection was scored.

Results: In 86% of the 1-stage group (n = 19) there was an event-free follow-up for ≥ 2 years. The mean Harris hip score was 84, the incidence of limping 20% and 10% required two crutches. Two stems were revised due to aseptic loosening. Both functional and radiological outcomes were not different from the matched control group.

In the 2-stage group (n = 50) results were lower but not significantly, with 80, 30% and 28% respectively, and 2 stems and 1 cup were revised due to aseptic loosening.

One case (after one stage) developed an infection with a different pathogen and one case (after two stage exchange) had a relaps of infection.

Conclusion: By using the identical surgical technique in both septic and aseptic revision hip surgery, functional results are comparable between groups. These results indicate that 1-stage exchange according to a strict algorithm leads to a successful outcome in both maintaining functional mobility and eradicating infection.

Background: Bacteria form a biofilm on the surface of orthopaedic devices, causing persistent and infection. Little is known about biofilms formation on bone grafts and bone substitutes. We analyzed various representative materials regarding their propensity for biofilm formation caused by Staphylococcus aureus.

Methods: As bone graft beta-tricalciumphosphate (b-TCP, CyclOsTM) and as bone substitute a tantalum metal mesh (trabecular metalTM) and PMMA (Pala-cosTM) were investigated. As test organism S. aureus (strain ATCC 29213) was used. Test materials were incubated with bacterial solution of 105 colony-forming units (cfu)/ml at 37°C for 24 h without shaking. After 24 h, the test materials were removed and washed 3 times in normal saline, followed by sonication in 50 ml Ringer solution at 40 kHz for 5 minutes. The resulting sonication fluid was plated in aliquots of 0.1 ml onto aerobe blood agar with 5% sheep blood and incubated at 37°C with 5% CO2 for 24 h. Then, bacterial counts were enumerated and expressed as cfu/ml. All experiments were performed in triplicate to calculate the mean ± standard deviation. The Wilcoxon test was used for statistical calculations.

Results: The three investigated materials show a differing specific surface with b-TCB> trabecular metal> PMMA per mm2. S. aureus formed biofilm on all test materials as confirmed by quantitative culture after washing and sonication. The bacterial counts in sonication fluid (in cfu/ml) were higher in b-TCP (5.1 x 106 ± 0.6 x 106) and trabecular metal (3.7 x 106 ± 0.6 x 106) than in PMMA (3.9 x 104 ± 1.8 x 104), p< 0.05.

Conclusion: Our results demonstrate that about 100-times more bacteria adhere on b-TCP and trabecular metal than on PMMA, reflecting the larger surface of b-TCP and trabecuar metal compared to the one of PMMA. This in-vitro data indicates that bone grafts are susceptible to infection. Further studies are needed to evaluate efficient approaches to prevent and treat infections associated with bone grafts and substitutes, including modification of the surface or antibacterial coating.

Introduction: The original Müller straight stem (MSS, Zimmer^®; Winterthur, Switzerland) is made out of CoNiCr and showed excellent 20 year results but later modifications of the stem proved to be inferior. Aim of this study was to analyse the effect of shape, material and surface roughness on aseptic loosening of cemented Müller type straight stems.

Materials and patients: Between 1984 and 1996 a total of 926 THR were operated with four different versions of cemented Müller type straight stems and followed prospectively in the in-house register at our institution. Two different shapes of cemented Müller type straight stems (MSS and SL), both made out of two different alloys (CoNiCr and TiAl), were included in this study. All four versions differed in surface roughness (MSS CoNiCr Ra 1.0μm (satin); SL CoNiCr Ra 1.2μm (satin); MSS TiAl Ra 2.0μm (rough); SL TiAl Ra > 2.0μm (rough)). Survival analysis was done using Kaplan-Meier curves with aseptic loosening as endpoint, risk factors were tested with regression analysis.

Results: The 4 groups did not differ in age, gender and diagnosis, the mean follow up was 11.4 (0.1 to 23.0) years. Survival with aseptic loosening as endpoint was 97.7% (MSS CoNiCr), 96.4% (SL CoNiCr), 82.5% (MSS TiAl) and 67.4% (SL TiAl), respectively, at ten years. At final follow up all four groups differed significantly (p=0.044 Log rank test). Increasing roughness increased the risk for aseptic loosening and the harder CoCr had better survival than TiAl. results were significantly worse for the combination of the soft TiAl with a rough surface (SL TiAL, Ra > 2.0μm). For both stem designs the MSS shape had better survival than the SL shape (p=0.001)

Discussion: Wear modalities (abrasion vs. fretting) in the cement-stem interface are directly correlated with surface roughness, the amount of the released particles correlates with loosening. All examined stems had a roughness exceeding the limit of Ra =0.4 μm, producing abrasive wear with a higher volume of wear particles as compared to established polished stems which show fretting wear. Stem roughness and hardness are more important for long-term survival than some modifications in the shape.

Conclusion: Cemented Müller type straight stems should have a polished surface (Ra < 0.4 μm) and be made out of a hard material (CoNiCr) to minimize surface wear. This might be true for all types of cemented stems.

Background: Bacteria form biofilms on the surface of orthopaedic devices, causing persistent infections. Monitoring biofilm formation on bone grafts and bone substitutes is challenging due to heterogeneous surface characteristics. We analyzed various bone grafts and bone substitutes regarding their propensity for in-vitro biofilm formation caused by S. aureus and S. epidermidis.

Methods: Beta-tricalciumphosphate (β-TCP, Chro-nOsTM), processed human spongiosa (TutoplastTM) and PMMA (EndobonTM) were investigated. PE was added as a growth control. As test strains S. aureus (ATCC 29213) and S. epidermidis RP62A (ATCC 35984) were used. Test materials were incubated with defined bacterial solution (105 colony-forming units (cfu)/ml) at 37°C for 24 h without shaking. After 24 h, the test materials were removed and washed 3 times in PBS, followed by a standardised sonication protocol (Trampuz et al. 2007, NEJM). The resulting sonication fluid was plated in aliquots of 100μl onto aerobe blood agar with 5% sheep blood and incubated at 37°C with 5% CO2 for 24 h. Bacterial counts were enumerated and expressed as cfu/ml. Sonicated samples were transferred to a microcalorimeter (TA Instrument) and heat flow at 37°C was continuously monitored over a 24h period with a precision of 0.0001°C and a sensitiviy of 200μW. All experiments were performed in triplicates to calculate the mean ± standard deviation. ANOVA analysis was used for statistical calculations.

Results: For S. aureus bacterial counts (log10 cfu/ sample) were significantly higher (p< 0.001) for the porous (β-TCP 7.67 ± 0.17, Tutoplast 7.65 ± 0.15) than for the solid samples (PMMA 6.12 ± 0.18, PE 5.17 ± 0.22). Bacterial density (log10 cfu/surface) was 10^1–10^2 times higher for the S. epidermidis than for the S. aureus. In calorimetry the shape of the heat flow curves was characteristic for the individual strain and was not influenced by the test materials. The time to detection (TTD) was shortest for β-TCP for both strains and TTD was always shorter for S. aureus than S. epidermidis with corresponding material. Cfu/sample calculated from the calorimetric data was concordant with the standard culturing method.

Conclusion: Our results demonstrate biofilm formation with both strains on all tested materials. The calorimetry in all cases was able to detect quantitatively the amount of biofilm. Further studies are needed to see whether calorimetry is a suitable tool also to monitor approaches to prevent and treat infections associated with bone grafts and bone substitutes.

Introduction: The biological activity of PE-particles released due to wear is an established risk-factor for osteolysis and loosening after Total Hip Arthroplasty (THA). Cup position and orientation might have an effect on the risk of impingement and wear, thus contribute to the risk of aseptic loosening in the long-term what should be studied.

Methods: Between 1984 and 1987 a total of 149 cemented total hips (Müller all-poly cup, Müller straight stem, 32 mm head) have been implanted. All implants had a standardised clinical and radiological follow-up. The pre- and postoperative centre of rotation of the hip and the orientation of the cup were determined. Migration, linear wear and direction of wear were measured twice with standard Methods: and the digital EBRA method. Wear-volume was calculated, taking direction of wear and cup orientation into account. Radiographs were analysed for progressive osteolysis and loosening.

Results: 1 patient was lost to follow-up, 47 had died, 7 had been revised before 10 years follow-up. 18 patients had a missing or poor final radiograph, leaving 75 hips for long-term analysis. 41 were in male patients, mean age was 66.2 (+/− 11.0) years, mean follow-up 15.4 (+/−4.1) years. Mean inclination was 40.7° (+/− 7.1), mean anteversion was 14.8° (+/−8.4) And the mean cup positioning was 3.8 mm (+/− 4.3) medial and 5.3 mm (+/− 3.5) cranial.

Osteolysis was found in 36 cups, 18 of them have been revised.

The average linear wear was 1.1 (+/− 0.9) mm, the average wear volume 798.7 (+/−622.3) mm3, the linear wear rate 0.07 (+/−0.06) mm/year and the volumetric wear rate 54.5 (+/− 43.2) mm3/year.

Younger patients had increased linear wear rates (p=0.035). Osteolysis of the cup, cup migration and cup revision were correlated with linear and volumetric wear (all p=< 0.001).

There was no correlation of the cup position, inclination and anteversion with osteolysis, loosening and any of the wear parameters. Volume calculation did not provide further information.

Conclusion: We found a strong correlation between wear and loosening of PE cups, but cup position and orientation did not affect osteolysis and loosening. Thus in contrast to hard-hard bearings polyethylene is a forgiving bearing surface and improvement of the cup orientation (e.g. due to navigation) will not result in increased cup survival, as long as extreme positioning errors are avoided.

Introduction: Changes of the proximal femur like oste-olysis, stress shielding and osteopenia are frequently observed after total hip arthroplasty (THA). Such find-ings might be considered as risk factors for aseptic loosening and later revision. Cortical thinning is observed of healthy femora too and it is questioned whether the effect of the implant can be discriminated from age-related changes.

Aim of our study was to analyze cortical bone changes in prosthetic hips with time and compare those changes with the contra lateral non operated femur.

Materials and Methods:From 1984–87 165 hips were operated with a cemented Muller straight stem. Regular clinical and radiological follow up was scheduled after 1, 2, 5, 10, 15 years. We included only patients operated for osteoarthritis without revision and complete follow-up of more than 10 years. 37 THA hips in 35 patients remained for inclusion in the study. The mean follow-up was 16±4,6 years. Thickness of cortices was measured medially and laterally in 6 locations according to the 2nd to 6th Gruen zones and mean cortical thinning was calculated. The measurements were taken on standardized anterior-posterior x-rays of the pelvis. All measurements were analyzed with Image Access 4 Software calibrated with the reference to 32 mm femoral head.

10 patients were not operated on the contralateral hip and were measured in standardized manner in the same locations as in THA femurs.

Results: All included patients had pain free hips and did not require revision surgery at the last follow-up. Mean cortical thinning was 0,17±0,15 mm/year and it was mostly expressed in mid part of the stem (Gruen 2 and 6 zones). Most thinning occurred within the first 5 years (0,32±0,34 mm/year), later thinning was slower (0.09±0,37 mm/year). For the group with non operated contralateral hip mean thickness loss in THA hip was 0,2±0,17 mm/year and there was thickness loss of the contralateral femur too (0,03±0,12 mm/year), being much less as compared to the operated side (p< 0.001).

Conclusions: Loss of cortical thickness in THA hip with the Muller straight stem is frequently observed in long term and is not associated to expression of clinical symptoms and subsequent revision surgery. The effect is pronounced in the first postoperative years, mainly being explained by stress shielding. Additionally there is cortical thinning due to ageing, being much less than the influence of the implant. Thinning of the cortical bone must not be interpreted a sign of aseptic loosening.

Introduction: Since its introduction in 1977 the Müller straight stem and its various copies have become one of the most often used cemented stems worldwide (about 1.1 million stems, figure quoted by manufacturer). Though, there is still a lack of long-term follow-up data.

Material/Methods: A consecutive series of 165 primary hip replacements (161 patients) with the original forged Müller straight stem (CoNiCr) was operated between July 1984 and June 1987 and followed prospectively. Mean age at operation was 68.9 years (25.6 to 86.3 years). 70 stems were implanted in female patients. Operation was done in supine position through a transgluteal approach with no trochanteric osteotomy. All stems were cemented with a second-generation technique (distal plug, cement syringe). The head diameter was 32 mm diameter, 134 heads were out of metal, 31 out of ceramic. 151 hips had a cemented polyethylene cup (52 with armament screws). 13 were combined with an acetabular reinforcement ring (Müller ring) and one with an anti-protrusion cage (Burch-Schneider).

Clinical and radiological follow-up was planned at 4 months 1, 2, 5, 10, 15 and 20 years. Clinical follow-up included a standardised examination and the completion of an IDES form. Cumulative survival rates were calculated by Kaplan-Meier analysis. Radiographs were analysed for osteolysis according to Gruen et al. (zones 1–7) and radiolucent lines.

Results: 3 patients (3 stems) were lost to follow-up (two postoperative and one after 16.8 years), 103 patients (with 106 hips) had died without revision and 55 patients (56 hips) remained for follow-up. 15 stems were revised, 11 for aseptic loosening (9 in combination with the cup), two for infection and two for other reasons. 13 further patients had isolated cup revision. Survival with aseptic loosening of the stem as endpoint was 86% (95%-CI: 82 to 90%) at 20 years.

The median HHS at the last follow-up was 80 points (range 30–98 points).

31% of the non-revised 41 stems showed osteolysis, most of them in zone 7 (21.9%). Two stems with isolated cup revision had a continuous radiolucent line. Incomplete radiolucent lines appeared most frequently in zone 1. Cup revision was associated with increased radiological changes on the femoral side (p=0.094, Mann-Whitney U-test).

Conclusion: The Müller straight stem shows excellent clinical and radiological results in the long-term, comparable to those achieved with other well established cemented and non-cemented stems. From our data further clinical use of the Muller straight stem can highly be recommended.

Introduction: The Acetabular Reinforcement Ring (ARR) (ME Müller®) was introduced in 1977 as successor of the Endler ring, especially to allow total hip replacement (THR) in patients with congenital hip dislocation, serious dysplasia and revision of loose cups. The Polyethylen (PE)-inlay can be freely oriented in the fixed ARR. It is the first implant with screws having angular stability as the screw-heads are blocked when cementing the inlay in the ring.

Patients and Methods: Out of 2251 primary THR performed between 1984 and 2005 at our hospital the ARR was used in 399 hips (363 patients). The indication for a THR with ARR was mainly a deficient acetabular bone stock as judged by the operating surgeon. 51 % of the patients had osteoarthritis, 22% dysplasia, 7% fractures, 6,5% osteonecrosis, 5% protrusion acetabuli, 4% rheumatoid arthritis and 4,5% other diagnosis. The mean age at operation was 66.4 years, 64% were females.

Intraoperatively, the ARR was placed with its medial border adjacent to the tear drop figure. The weight bearing area was fixed with 3–4 cancellous screws in the acetabular bone stock. Regular clinical and radiological follow-up 3months, 1, 2, 5, 10,15 and 20 years was planned. The radiographs were assessed for osteolysis, radiolucent lines and screw breakage after 15 years. Survival for revision due to aseptic loosening was calculated by Kaplan Meier.

Results: The overall survival regarding aseptic loosening of the cup was 100% after 10 years, 97,2% after 15 and 93,2% after 20 years.

Of the 96 patients (104 rings) operated at least 15 years ago, one was lost for follow-up. Three rings were revised due to aseptic loosening (11, 12, 16 years after implantation) and one was removed due to infection (1,8 years after implantation). 54 patients (with 56 rings) died before they reached the 15 years control. None of them was revised for aseptic loosening of the ring. 37 patients (43 hips) remained for 15-years control, six of them refused to come and were contacted by questionnaire or phone. Two cups were radiologically loose with broken screws but not symptomatic. The mean HHS after 15 years was 80.1.

Conclusion: The ARR shows a very good long term survival even in patients with difficult acetabular situations such as deficient bone stock. The design allows an application in a variety of positions. Even at a teaching hospital good long term results could be reached with this implant.