Long-Term Results of Acetabular Reconstruction Using Ganz Acetabular Rings.

BACKGROUND: Our study examines the long-term results of acetabular reconstruction using the Ganz acetabular reinforcement ring (GRR) in total hip arthroplasty. METHODS: Between 1998 and 2001, 135 hips (119 revision and 16 primary arthroplasties) were consecutively implanted with a GRR at our hospital. The average age was 65 years (range, 26-90). Clinical and radiographic evaluations were carried out. Long-term survivorship was estimated using a competing risks analysis, and multivariate survivorship using Cox regression model was used to identify risk factors for implant failure. RESULTS: At a mean follow-up of 16 years (range, 15-18), 3 patients were lost to follow-up and 19 had implant failure: 4 aseptic loosenings without re-revision, 4 septic, and 11 aseptic re-revisions. Survival was estimated at 86% after 16 years (95% confidence interval [CI], 78.5%-90.9%) using radiographic loosening or revision for any reason as the end point. Using aseptic loosening as the end point, the survival was estimated at 91.2% after 16 years (95% CI, 84.5%-95.0%). Multivariate analysis revealed that age at surgery was a significant risk factor for failure of the GRR. With acetabular revision or loosening as the end point, patients ≤60 years had 71.6% (95% CI, 53%-82.8%) and older patients had 92.2% (95% CI, 84%-96.2%) probability of implant survival after a mean 16-year follow-up. The median Harris Hip Scores and Western Ontario and McMaster Universities Osteoarthritis Index scores were 77 and 64.5, respectively, and mean Numerical Pain Rating Scale score was 1.6 at final follow-up. CONCLUSION: Our long-term study showed acceptable survival and functional results using the GRR in older patients, while young patients had less favorable survival.

The Influence of Cement Morphology Parameters on the Strength of the Cement-Bone Interface in Tibial Tray Fixation.

BACKGROUND: The strength of the cement-bone interface in tibial component fixation depends on the morphology of the cement mantle. The purpose of this study was to identify thresholds of cement morphology parameters to maximize fixation strength using a minimum amount of cement. METHODS: Twenty-three cadaveric tibiae were analyzed that had been implanted with tibial trays in previous studies and for which the pull-out strength of the tray had been measured. Specimens were separated into a group failing at the cement-bone interface (INTERFACE) and one failing in the bulk bone (BULK). Maximum pull-out strength corresponds to the ultimate strength of the bulk bone if the cement-bone interface is sufficiently strong. 3D models of the cement mantle in situ were reconstructed from computed tomography scans. The influences of bone mineral density and 6 cement morphology parameters (reflecting cement penetration, bone-cement interface, cement volume) on pull-out strength of the BULK group were determined using multiple regression analysis. The threshold of each parameter for classification of the specimens into either group was determined using receiver operating characteristic analysis. RESULTS: Cement penetration exceeding a mean of 1.1 mm or with a maximum of 5.6 mm exclusively categorized all BULK bone failure specimens. Failure strength of BULK failure specimens increased with bone mineral density (R2 = 0.67, P < .001) but was independent of the cement morphology parameters. CONCLUSION: To maximize fixation strength, a mean cement penetration depth of at least 1.1 mm should be achieved during tibial tray cementing.

Comparison of different cement application techniques for tibial component fixation in TKA.

PURPOSE: Aseptic loosening of the tibial component remains a major cause for revision surgery in total knee arthroplasty (TKA). A stable initial fixation of the tibial implant has been suggested to reduce micromotion of the implant and could be decisive regarding its long-term performance. Different techniques for applying cement to the tibial surface have been described in the literature, with controversial results. No guidelines in favour of any particular approach are available. METHODS: In this study, we compared three commonly used cementing techniques (layered application, stem cementation, cement gun) with surface-only fingerpacking cementation following pulsed lavage (paired human tibiae, four groups, n = 24). Specimens underwent computed tomography scanning for three-dimensional analysis of cement penetration and mechanical testing for assessing interface strength. RESULTS: Bone cement penetration decreased with increasing bone mineral density (BMD) (R (2) = 0.18, p = 0.023), while interface strength increased with BMD (R (2) = 0.56, p < 0.001). No significant effect of cementation techniques on cement penetration (p ≥ 0.069) or interface strength (p = 0.180) was found in any group. CONCLUSION: Adequate surface preparation using pulsed lavage and copious drying of the tibial surface appears to be of overruling importance, thus limiting the effect of any particular technique applied to improve implant fixation. This study emphasises the fundamental importance of surface preparation and pulsed lavage in TKA.

Effect of tibial tray design on cement morphology in total knee arthroplasty.

BACKGROUND: Improvements to enforce primary fixation in cemented total knee arthroplasty have been suggested to be a key issue for long-term survival. In this context, it has been questioned whether specific implant design features influence bone cement morphology and hence primary interface strength. The purpose of this study was to investigate in vitro the influence of cement pockets on the tibial tray on cement penetration in the tibia. METHODS: Eight paired cadaveric, human tibiae were available for investigation. One side of a pair was implanted with a fixed bearing tibial tray (FB) featuring cement pockets on the undersurface, while in the other side, a mobile bearing platform (MB) without cement pockets was used. Specimens underwent computed tomography analysis of the cement morphology as well as BMD assessment. RESULTS: While bone cement layer between implant and bone surface was thicker in the FB group (p = 0.032), bone cement penetration was not influenced by implant design (p = 0.529). CONCLUSIONS: The present study suggests that cement pockets do not alter or enforce bone cement penetration under the tibial tray in an in vitro scenario.

An in vitro comparison of tibial tray cementation using gun pressurization or pulsed lavage.

PURPOSE: Aseptic loosening of the tibial component remains a limitation to the highly successful procedure of total knee arthroplasty (TKA). Pulsed lavage improves bone cement penetration and interface strength in tibial tray cementation. This study tested whether pressurized cement application with a cement gun can compensate the use of jet lavage for bone surface preparation. METHODS: Tibial components were implanted in six pairs of cadaveric tibiae. On one side, pulsed lavage of the tibial bone was combined with finger packing of bone cement; on the other side, syringe lavage and gun cementing was used. Cement penetration into the bone was determined from computed tomography scans, and Interface strength was determined by pull-out testing. RESULTS: Cement penetration was greater (p = 0.004) and interface strength was higher (p = 0.028) in the pulsed lavage group. CONCLUSION: Pressurization of cement by gun application could not compensate for the omission of pulsed lavage. Thus, pulsed lavage should be considered a crucial factor in TKA to improve implant fixation, which cannot be compensated for by cement application technique.

Influence of cementing the pin on resistance to fracture in hip resurfacing.

BACKGROUND: Since the introduction of modern hip resurfacing systems, there has been a controversy regarding the fixation of the centering pin in the femoral component. It has been suggested that cementing the pin may increase strength of the femoral neck. This in-vitro analysis investigated the influence of a cemented, femoral pin on resistance to fracture in the resurfaced hip. METHODS: Five pairs of cadaveric, fresh-frozen femora underwent hip resurfacing (ASR™) using a high viscosity cementing technique. In one side of each pair only the inner surface of the implant was cemented, in the other side, cement was additionally hand-pressurized down the pinhole prior to implantation of the femoral component. Specimen were then mounted on a material testing machine and cyclic loading with increasing load steps was applied until fracture of the femoral neck. FINDINGS: Fracture load was increased (P = 0.013) in the cemented pin group (Median = 4200 N) when compared with the cementless pin group (Median = 2800 N). The number of cycles to failure in the group with the cemented pin (Median = 8072) was likewise higher (P = 0.01) when compared to the group, in which the pin was not cemented (Median = 5906). INTERPRETATION: Cementing the pin may provide additional fixation in hips with low bone mineral density or osteonecrotic lesions, as resistance to fracture could be improved in the presented in-vitro scenario. Although this was shown for a specific hip resurfacing system, this effect might be extrapolated to other, similar implant designs.

Pulsed lavage improves fixation strength of cemented tibial components.

Pulsatile lavage is purported to improve radiographic survival in cemented total knee arthroplasty (TKA). Similarly, a potential improvement of fixation strength of the tibial tray has been assumed based on the increased cement penetration. In this study, the influence of pulsed lavage on fixation strength of the tibial component and bone cement penetration was evaluated in six pairs of cadaveric specimens. Following surgical preparation, the tibial surface was irrigated using pulsatile lavage on one side of a pair, while on the other side syringe lavage was applied. All tibial components were implanted using the same cementing technique. Cement penetration and bone mineral density was assessed based on computed tomography data. Fixation strength of the tibial trays was determined by a pull-out test with a material testing machine. Median pull-out forces and cement penetration were significantly (p = 0.031) improved in the pulsed lavage group as compared to the syringe lavage group. Enhanced fixation strength is suggested as being a key to improved survival of the implant. Consequently, pulsatile lavage should be considered as a mandatory preparation step when cementing tibial components in TKA.

Does impaction matter in hip resurfacing? A cadaveric study.

Eight pairs of fresh frozen human femora were prepared for hip resurfacing. One side of each pair was impacted gently, the other side vigorously. After implantation procedure, specimens were loaded in a material testing machine to the ultimate fracture load. Median impaction loads on the vigorously implanted side were 11,298N compared to 1374N on the gently implanted side. Failure loads in the high-impact group (median, 8873N) were significantly (P = .0078) reduced when compared with the low-impact group (median, 9237N). The study stresses that meticulous reaming of the femoral head and the pinhole is of tremendous importance. Remaining obstacles can lead to excessive loads, while attempting to enforce the correct seating of the implant. Only careful, slight tapping should be applied to ensure final seating.

Effects of impaction on cement mantle and trabecular bone in hip resurfacing.

INTRODUCTION: Failures involving the femoral part in hip resurfacing remain problematic in terms of overall implant survival. In this context, effects of impaction strength on cement mantle morphology and trabecular bone damage have not been studied to date. MATERIALS AND METHODS: Sixteen paired cadaveric femora that had undergone hard and gently impacted hip resurfacing using a manual packing cementing technique in a previous study, were evaluated morphologically. The earlier study had revealed lower failure loads for hard impacted heads. A central slice of each femoral head underwent microradiography. RESULTS: Overall cement mantle thickness averaged 2.0 mm (range 0-5 mm) in the hard and in the low impact group with no significant difference between groups (p = 0.299). No signs of damage in the bone remnants inside the prosthesis of the fractured proximal femurs were detected in the microradiographic analysis. CONCLUSION: Cement mantle thickness was not influenced by impaction strength when using a manual packing cementing technique. No trabecular damage underneath the implant was detected despite lower failure loads, confirming the difficulty to identify small trabecular damage in an in vitro study.

Pre-packed vacuum bone cement mixing systems. A further step in reducing methylmethacrylate exposure in surgery.

OBJECTIVES: Polymethylmethacrylate bone cements are widely used in orthopaedic and trauma surgery as well as in dentistry. The toxic side effects of inhaled methylmethacrylate (MMA) fumes generated during mixing have been well studied. Vacuum cement mixing systems have been shown to reduce the risk of airborne MMA significantly compared to handmixing. In an effort to further reduce MMA exposure, the latest generation of mixing devices are pre-packed with the ingredients and thus allow preparation in nearly closed circuits. Until now, there has been no study proofing the efficacy of those systems in protecting theatre staff from MMA vapours. METHODS: A pre-packed vacuum mixing system (Optipac®) was compared with two standard systems (Palamix® and Easymix®) regarding MMA emission. The latter systems require loading with the bone cement compounds prior to mixing. Following a standardized procedure, 10 mixes were performed with each system and the emission of MMA vapours in the breathing zone was recorded using photoionization detection over a period of 3 min. RESULTS: The mean MMA exposure was reduced when using the pre-packed system compared to the devices that require filling with the components. The highest emission peaks were recorded during the mixing and preparation steps in all systems. CONCLUSIONS: Modern pre-packed vacuum mixing systems further help to reduce the occupational hazards created by bone cement preparation. However, MMA fumes can still be detected using this technique. Although this is an important step in reducing MMA exposure in the operating theatre, further technical effort has to be taken to eliminate the continuous leakage of monomer from the devices while mixing and to minimize necessary manipulation for final delivery.

Functional midterm outcome in 131 consecutive cases of surgical clubfoot treatment.

INTRODUCTION: Since introduction and widespread use of the Ponseti method in the last decade, the need for surgical treatment of clubfeet is nowadays limited to resistant cases. In the time before, surgery via dorsomedial release was a very common treatment option. METHOD: Very few long-term follow-up studies cover the outcome of surgical methods, which is particularly interesting, as clinical results rather worsen with time. In the present study, 98 children (131 clubfeet), who underwent surgical correction using the Imhauser method at the age of 4.5 months were included. Follow-up time was 8.2 years (0-11.8 years) at average. RESULTS: Data could be retrieved from 46 patients (71 feet), only 5 patients (7 feet) were lost to follow-up. The rate of relapses was high, as 47 patients (53 feet) needed surgical revision for recurrence, while clinical scores showed a good result in the Laaveg and Ponseti Score and the Foot-Function-Index. Isokinetic testing and clinical data indicated a significant weakness of the treated foot, when compared to the healthy side in 12 patients with unilateral deformity. The presented study supports like others the issue that the clinical outcome of a surgical, posteromedial release in terms of relapses is disappointing. This fact is apparently not sufficiently reflected in the current clinical scores, which showed rather good results. CONCLUSION: As the question of evaluation methods for results of clubfoot treatment remains controversial, isokinetic testing is an easy to use alternative that provides detailed information about functional limitations and may help in reducing the need for repeated radiographic examinations.

Mueller reinforcement rings in acetabular revision: outcome in 164 hips followed for 2-17 years.

BACKGROUND: In revision hip arthroplasty, cages are commonly used for acetabular reconstruction in cases with loss of bone stock. It is important to follow this patient group closely, in order to better understand failure mechanisms and the chance of long-term success. PATIENTS AND METHODS: We followed our first 164 acetabular revisions with the Mueller reinforcement ring (ARR) in 164 patients, with an average follow-up period of 6 (2-17) years. Mean age at surgery was 69 (29-92) years. 39 patients died (39 hips) during follow-up, but only 3 patients (3 hips) were lost to follow-up. RESULTS: In the observation period, 13 of the hips had to undergo acetabular re-revision for aseptic and septic loosening. Overall survival at 5 years was 95% (CI: 89%-98%) and 90% (CI: 76%-95%) at 8 years using acetabular re-revision or implant removal for all reasons as endpoint. In addition, mechanical and clinical failure was seen in 2 cases. The mean Harris hip score was 70 points, whilst the Merle d'Aubigné score averaged 7 points. Radiolucent lines according to DeLee and Charnley were observed twice in zone I, 6 times in zone II and 14 times in zone III. INTERPRETATION: We found that mid- to long-term survival of the ARR is acceptable. However, failure of the implant due to allograft collapse/resorption or deep infection, and also poor clinical outcome, remain major concerns in acetabular revision arthroplasty. This should be recognized when advising patients.

Efficacy of vacuum bone cement mixing systems in reducing methylmethacrylate fume exposure: comparison of 7 different mixing devices and handmixing.

BACKGROUND: Polymethylmethacrylate (PMMA) bone cements are mainly used for implant fixation in joint replacement surgery. During cement preparation for application, all staff in the operating theatre are exposed to methylmethacrylate (MMA) fumes, which are known to have toxic side effects. METHODS AND RESULTS: In this study we found that vacuum mixing of bone cement with 7 commercially available mixing devices significantly reduced the emission of MMA vapors in the breathing zone when compared with classic hand mixing in an open bowl. Gas chromatography appears to be more sensitive for detection of MMA fumes than Photo Inonization Detection. INTERPRETATION: According to present knowledge, even repeated mixing of PMMA bone cement during a normal working day does not seem to constitute an increased health risk, particularly if vacuum mixing is implemented.