Introduction

This study was performed to investigate the failure mechanism of one specific hip arthroplasty cup design that has shown a high clinical failure rate. The aim of this study was to identify general design problems of this polyethylene inlay.

As there are many reports describing avascular reactions to metal debris (ARMD) after Metal-on-Metal Hip Arthroplasty (MoMHA), the use of MoMHA, especially hip resurfacing, is decreasing worldwide. In cases of ARMD or a rise of metal ion blood levels, revision is commended even in pain free patients with a well integrated implant. The revision of a well integrated implant will cause bone loss. As most of the patients with a hip resurfacing are young and a good bone stock is desirable for further revision surgeries, the purpose of this study was to evaluate the stability of a cemented polyethylene cup in a metal hip resurfacing cup. Two different hip resurfacing systems were investigated in this study (ASR™, DePuy Orthopaedics, Leatherhead, UK; Cormet™, Corin Group, Cirencester, UK).

Six different groups were formed according to the treatment and preparation of the cement-cup-interface (table 1). Before instilling cement in groups 1, 3, 5 the surface, which was contaminated with blood, was cleaned just using a gauze bandage. In groups 2, 4, 6 saline, polyhexanid and a gauze were used to clean the surface prior to the cement application. In group one and two the polyethylene cup (PE) was cemented either into Cormet™ or ASR™, just the ASR™ was further investigated in group three to six. A monoaxial load was applied while the cup was fixed with 45 degrees inclination (group 1–4) and 90 degrees inclination (group 5, 6: rotatory stability) and the failure torque was measured. In contrast to group 1 and 2, the cement penetrated the peripheral groove of the ASR™ in groups 3–6. The mean failure torque of five tests for each group was compared between the groups and the implants.

The ASR™ showed mean failure torque of 0.1 Nm in group one, of 0.14 Nm in group two, of 56.9 Nm in group three, of 61.5 Nm in group four, of 2.96 Nm in group five and of 3.04 Nm in group six. The mean failure torque of the Cormet™ was 0.14 Nm both in groups one and two (table 2). In groups 1–6 there were no significant differences between the different preparations of the interface. Furthermore, in groups 1 and 2 there were no significant differences between the Cormet™ and the ASR™. The mean failure torque of group 4 was significant increased compared to group 3 (p=0.008).

We saw an early failure of the cement fixation due to the smooth surface of the Cormet™ and the ASR™ components in groups 1, 2, 5, 6. In contrast to other hip resurfacing cups the ASR™ has a peripheral groove, which was not cemented except in groups 3 and 4 and therefore the lever-out failure torque was significant increased in these groups. Nevertheless, the groove did not provide stability of the cement-PE compound in case of rotatory movements. In conclusion we do not recommend the use of these methods in clinical routine. The complete removal of hip resurfacing components seems to be the most reasonable procedure.

INTRODUCTION:

Good survival rates of cementless hip stems serve as motivation for further development, just like modular implant systems or short stems. New aims are worth striving for, e.g. soft tissue or bone sparing options with similar survival rates in case of short stems. Even minimal design modifications might result in complications, e.g. missing osseointegration, loosening of the implant or painful stem, as shown in the past.

One of these developments is the Biomet – GTS™ stem [Fig. 1], a hybrid between conventional cementless straight stem and potentially sparing short stem.

Aim of this biomechanical study was to analyze, if the biomechanical behavior of the stem is comparable to a clinically proofed design with respect to the stem fixation in the bone and to the mechanical behavior of the stem itself. That's why the primary stability of the GTS™ stem has been determined and subsequently was compared to the Zimmer – CLS® stem.

Introduction

Infection following total joint arthroplasty is a major and devastating complication. After removal of the initial prosthesis, an antibiotic-impregnated cement spacer is inserted for approx. three months. Treatment is completed by a second stage revision arthroplasty.

Up to now, spacers are produced from conventional bone cements that contain abrasive radio-opaque substances like zirconium dioxide or barium sulphate. As long as spacer wear products (cement particles containing these hard substances) are not fully removed during the final revision surgery they may enter the articulating surfaces of the revision implant leading to third body wear.

In order to reduce the formation of reactive wear particles, a special cement (Copal(r) spacem) without abrasive zirconium dioxide or barium sulphate was developed.

To date, no comparative tribological data for cement spacers have been published. Hence, we carried out a study on the wear properties of Copal(r) spacem (with and without gentamicin) in comparison to conventional bone cements (Palacos(r) R and SmartSet(r) GHV).

Introduction

Up to date there are only few reports in literature on the long term survival of uncemented stems. As for cemented THA, 10 year survival of at least 90% is required for any THA.

Introduction: During hip stem revisions osteotomies allow to remove well-fixed components. Once removal has been done, cerclage wires should secure the osteotomy and support primary stability of the new stem. Stability is important for a bony ingrowth and therefore the longevity of a cementless revision stem.

Tension wires seem to dominate revision surgery and studies only refer to the advantages of cable wires in general. This in-vitro study analyzed the infiuence of both, tension and cable wires on primary stability of cementless revision stems. We aimed to examine the effectivity of wiring a femoral osteotomy, differences achieved with each method, and whether one wire has advantages regarding the fixation concepts of revision stems (meta- and diaphyseal).

Methods: We studied a Ti-tension- and a CoCrWNi-cable-wire. The Helios-stem stood for the meta- and the Wagner-SL-stem for the diaphyseal fixation concept. Each stem was implanted into 3 synthetic femurs and a standardized extended proximal femoral osteotomy was performed. Spatial movements of bones and stems at several sites were explored under axial torques using a high-resolution measuring device. Movement graphs subjected to the sites defined relative movements RM = ΔαZ/TZ [mdeg/Nm]. The osteotomies were locked consecutively with both wires and all compounds were measured again. Wiring was done by a proximal figure 8 and a diaphyseal circular loop.

Results: Compared to the unlocked osteotomy the tension as well as the cable wires caused a changed RM for the stems (p=0.03). Both wires affect an increased stability within the proximal main fixation area of the Helios. Even for the Wagner-SL, usually fixating diaphyseally, a proximal fixation was reached with both wires. A significantly better stabilization could be observed for the Helios using cable wires (p=0.04). The overall RM reached with tension and cable wires was 16.6 and 11.1 mdeg/Nm. The Wagner-SL^® showed no difference in stability between tension and cable wire treatment (p=0.29).

Discussion: Both, the tension and the cable wires support the revision stems in bridging the artificial defect of an extended proximal femoral osteotomy. Especially for the proximal fixating stem, RMs could largely be reduced, while cable wires seem to be advantageous. Preventing a circular constriction leading to an osseous malnutrition, the use of cable wires, however, should be impeded with regard to diaphyseal fixating stems and proximal osteotomies. Comparable results with both wires were reached and none of the wires showed any advantage in this situation. In conclusion, the wires should be chosen depending on the fixation concept of the revision stem.

Introduction: Postoperative periprosthetic fractures are difficult to investigate clinically in scientifically and statistically valid study samples because they are uncommon. However, the combination of advanced age and poor bone quality has been associated with these fractures in conjunction with cementless hip stems. So far, these speculations have neither been supported by clinical evidence nor been investigated experimentally. The purpose of the present study was to analyze in-vitro if the treatment with cementless hip stems increases the risk of suffering a periprosthetic fracture for older patients compared to younger patients. Regarding this manner, we aimed to clarify parameters which possibly can be used preoperatively to assess age related fracture risk and whether the femoral bone quality really plays a role in fracture development.

Methods: An established biomechanical setup was used to provide an investigation on 16 femoral specimens of different age. Prior, the BMDs were measured in 5 ROIs and a cementless hip stem was implanted into each femur. The load bearing of “normal walking” was applied quasistatically under standardized conditions until the fracture occurred. The specimens were arranged by age in ascending order to divide them in the middle. A group of under septuagenarians (< 70y) (mean: 62y) and a group representing an elderly population (≥77y) (mean: 79y) resulted. Important donor data such as body height and bodyweight were considered in the statistical analysis.

Results: The elderly specimens fractured at significantly lower forces (< 70y: Fmax=5,308N; ≥77y: Fmax=2,519N; p< 0.01). Pearson’s test revealed a correlation for Fmax [N] and age (p < 0.01; r = −0.64); and for Fmax [%BW] and age (p < 0.01; r = −0.69). Fracture loads were found to correlate strongly with age (p=0.01), all used ROIs (e.g. for Ward’s triangle: p< 0.01) and BMI (p=0.04). Decreasing CCD angles were found with increasing age (p < 0.01).

Discussion: In patients with advanced age treated with cementless hip stems the risk of suffering a periprosthetic fracture is significantly higher. The identification of specific fracture development variables in geriatric populations can be extended to a preoperative check list to aid clinicians in practicing effective risk assessment. Criteria such as BMD, BMI and CCD angle should be included: A fracture risk remains in patients around 80 years of age or older, with a Ward’s triangle BMD below a value of 0.500g/cm2, or a BMI > 33kg/m2. Depending on patient activity, one single factor should not be viewed as an exclusion criterion for a cementless hip stem, whereas the cumulation of them should alert the surgeon.

Introduction: THA in young and active patients remains a major challenge. Uncemented femoral components have been advocated in young patients, but there are only few reports with more than 10 years follow-up.

Materials and Methods: We followed the first 153 consecutive implantations of an uncemented, straight femoral stem (CLS, Zimmer Inc, Warsaw, USA) in 141 patients. Mean time of follow-up evaluation was 17 years (range, 15–20 years), mean age at surgery was 47 years (23–55).

Results: At follow-up, 20 patients (20 hips) had died, and 7 (7 hips) were lost to follow-up. 10 patients (10 hips) underwent femoral revision–1 for infection, 4 for periprosthetic fracture, and 5 for aseptic loosening of the stem. Overall survival was 91% at 17 years (95%-confidence limits, 88%-94%), survival with femoral revision for aseptic loosening as an end point was 95% (95%-confidence limits, 93%–98%). The mean Harris-Hip-Score at follow-up evaluation was 84 points. 116 hips were available for radiolographic evaluation. Radiolucent lines (< 2mm) in Gruen zones 1 and 7 were present in 12,9% (15 hips) and 13,8% (16 hips), respectively. Radiolucencies in zones 2–6 were found in 0,9% (1 hip) – 2,6% (3 hips) on ap x-rays. Only one case of distal osteolysis was found after a previous Wagner resurfacing. No case of severe femoral osteolysis was found at follow-up.

Conclusions: The long-term results with this type of uncemented femoral component are encouraging and compare favorably with those achieved in primary cemented total hip arthroplasty in this group of young and active patients.

Treatment by continuous passive movement at home is an alternative to immobilisation in a cast after surgery for club foot. Compliance with the recommended treatment, of at least four hours daily, is unknown. The duration of treatment was measured in 24 of 27 consecutive children with a mean age of 24 months (5 to 75) following posteromedial release for idiopathic club foot. Only 21% (5) of the children used the continuous passive movement machine as recommended. The mean duration of treatment at home each day was 126 minutes (11 to 496). The mean range of movement for plantar flexion improved from 15.2° (10.0° to 20.6°) to 18.7° (10.0° to 33.0°) and for dorsiflexion from 12.3° (7.4° to 19.4°) to 18.9° (10.0° to 24.1°) (both, p = 0.0001) when the first third of therapy was compared with the last third.

A low level of patient compliance must be considered when the outcome after treatment at home is interpreted.

Introduction: Aim of the study was to investigate the fixation patterns of cementless short-stem designs compared to the fixation patterns of well-known conventional stems artificially shortened in several steps.

Method: Primary rotational stability and tilting were measured in a standardized and validated simulator set-up. The tested short-stem designs included the Mayo (Zimmer), the CFP (Link), and the CUT (Eska). The “conventional” group consisted of the ABG (Stryker), the S-Rom (DePuy), and the G2 (DePuy). Additionally, these systems were tested when gradually shortened in several steps.

Results: The Mayo stem showed a 2/3 fixation pattern with 11.5 mdeg/Nm relative movement at the level of the lesser trochanter. The CFP showed a more distal fixation with 6.8 mdeg/Nm, and the CUT a proximal fixation with 7.6 mdeg/Nm. The Mayo and the CFP adapted to the femoral canal during ventro-dorsal tilting. The CUT tilted like a rigid body. This pattern of tilting was also shown by the ABG after it was shortened from 12.5 cm to 8.5 cm, by the G2 after a reduction from 15 to 6 cm, and the S-Rom after shortening from 18 to 6.9 cm.

Discussion: The shortened conventional stems showed a similar fixation pattern compared to the short-stem designs, the rotational stability was even better than with the Mayo and CFP stem. The CUT design acts like an extensively shortened conventional stem and seems to tilt in the femoral canal like a rigid body with a pressure increase at the lateral cortex of the femur.

Continuous passive motion has been shown to be effective in the conservative treatment of idiopathic club foot. We wished to determine whether its use after operation could improve the results in resistant club feet which required an extensive soft-tissue release. There were 50 feet in the study. Posteromedial lateral release was performed in 39 feet but two were excluded due to early relapse. The mean age at surgery was eight months (5 to 12). Each foot was assigned a Dimeglio club foot score, which was used as a primary outcome measure, before operation and at 6, 12, 18 and 44 months after. Nineteen feet were randomly selected to receive continuous passive motion and 18 had standard immobilisation in a cast.

After surgery and subsequent immobilisation in a cast the Dimeglio club foot score improved from 10.3 before to 4.17 by 12 months and to 3.89 at 48 months. After operation followed by continuous passive motion the score improved from 9.68 before to 3.11 after 12 months, but deteriorated to 4.47 at 48 months. Analysis of variance adjusted for baseline values indicated a significantly better score in those having continuous passive motion up to one year after surgery, but after 18 and 48 months the outcomes were the same in both groups.

We performed an experimental study to determine the effectiveness of computer assisted robotic bone preparation with regard to primary rotational stability in comparison to hand broaching. Forty-five synthetic femora were prepared by one of two robotic systems (Robodoc n = 12 and CASPAR n = 12) or by one experienced surgeon (n = 21). Seven different types of cementless femoral components were implanted using a standard protocol and measured in a specially designed testing machine with displacement in six degrees of freedom. For each implant at lease 3 measurements were taken for the handbroached and the robotic milled group, respectively. In addition the contact areas between the stems and the bone were visualised.

S-ROM, Antega and ABG stems were lightly more stable in hand broached femora. Osteolock (prepared by both robotic systems) and Vision 2000 stems were more stable in the robot group without changing the movement pattern. G2 and Versys ET performed higher stability with a change to more proximal fixation in the robotic group. Finally four of seven stems had an increase in rotational stability with the robotically milled cavities. The findings highlight the current difficulties in creating a perfect match of robotically milled cavity and stem geometry to achieve enhanced stability. The contact areas differed in some prosthesis in the way of preparation. In some stem geometries area of fixation and the movement pattern of the stem differ with the mode of preparation.

Aim: The early results of cementless femoral components in young patients have been reported, but there are only few reports with more than 10 years follow-up. Methods: We evaluated the clinical and radiographic results of the þrst consecutive 154 implantations of a cementless, double tapered straight femoral stem (cementless Spotorno (CLS), Sulzer Orthopedics) in 141 patients under the age of 55 (mean 47, 13–55) years. Results: After a mean follow-up of 12 (10Ð15) years, 11 patients (11 hips) had died and 7 (7 hips) could not be located. 5 patients (5 hips) underwent femoral revision- 1 for infection, 1 for periprosthetic fracture and 3 for aseptic loosening of the stem. Overall survival was 97% at 12 years (95%-conþdence limits, 93% Ð 100%), survival with femoral revision for aseptic loosening as an end point was 98% (95%-conþdence limits, 95% Ð 100%). The median Harris-Hip-Score at follow-up was 84 points. No thigh pain was found. Radiolucent lines in Gruen regions 1 and 7 were present in 21 hips (17%). 2 hips had radiolucent lines in regions 2 Ð 6 on anterio-posterior (AP) radiographs. No femoral osteolysis was found. Conclusions: The mid- to long-term survival with this type of femoral component is excellent and compares favorably with cemented stems in this age group. However the high rate of cup loosening and the low Harris Hip Scores are concerning in this group of young patients.

We followed the first 354 consecutive implantations of a cementless, double-tapered straight femoral stem in 326 patients. Follow-up was at a mean of 12 years (10 to 15). The mean age of the patients was 57 years (13 to 81). At follow-up, 56 patients (59 hips) had died, and eight (eight hips) had been lost to follow-up. Twenty-five hips underwent femoral revision, eight for infection, three for periprosthetic fracture and 14 for aseptic loosening.

The overall survival was 92% at 12 years (95% CI 88 to 95). Survival with femoral revision for aseptic loosening as an endpoint was 95% (95% CI 92 to 98). The median Harris hip score at follow-up was 84 points (23 to 100). Radiolucent lines (< 2 mm) in Gruen zones 1 and 7 were present in 38 (16%) and 34 hips (14%), respectively. Radiolucencies in zones 2 to 6 were found in five hips (2%).

The results for mid- to long-term survival with this femoral component are encouraging and compare with those achieved in primary cemented total hip arthroplasty. The high rate of loosening of the cup and the high rate of pain are, however, a source of concern.

We report our results using three different threaded acetabular components (Mecring A, Mecring B and Weill) in 715 hips with a follow-up of between one and ten years (median: 99.1, 56.5, 38.3 months, respectively). All cups were implanted with one type of cementless stem.

The clinical results were good or acceptable in about 70% of the hips, but signs of loosening with radiolucency and/or migration were found in 10.1%. Radiological evidence of loosening did not correlate significantly with the clinical outcome. Pain was not a reliable indicator of loosening and its absence sometimes allowed severe osteolysis to develop. Twenty-five hips were revised (3.5%) for aseptic loosening of the acetabular component. Kaplan-Meier estimates of the cumulative rate of failure showed a rapid increase five years after the initial operation, but no significant correlation with gender, age or weight.

The high rate of failure indicates that further use of these acetabular components cannot be recommended. Annual radiographs are required to assess osteolysis even if the patients are free from pain.