Migration pattern of a short femoral neck preserving stem

5-year clinical and radiostereometric analysis (RSA) follow-up of 39 CUT femoral neck total hip prostheses in young osteoarthritis patients

BACKGROUND

As the number of young patients receiving total hip arthroplasty increases, bone-saving implantations facilitating possible future revision, such as the CUT femoral neck prosthesis, are gaining importance. There have been few medium-term results reported for this prosthesis, however, and its migration pattern has not been analyzed.

PATIENTS AND METHODS

39 consecutive CUT femoral neck prostheses were implanted in 32 patients, mean age 37 (17-58) years, with symptomatic osteoarthritis and either less than 55 years of age or with an anatomic anomaly preventing implantation of a diaphyseal stem (n = 1). Patients were followed prospectively using routine clinical examination and radiostereometric analysis (RSA) at 6, 12, 26, and 52 weeks postoperatively and annually thereafter. This study evaluated the 5-year follow-up results.

RESULTS

The mean Harris hip score increased from 26 (3-51) points preoperatively to 84 (66-98), 86 (55-98), and 87 (47-98) points at 3, 12, and 60 months. 3 stems were revised: 1 after luxation following excessive subsidence due to an undersized component and 2 due to persistent strong thigh pain. 5-year survival was 95% (95% CI: 87-100). Initial migration varied widely in magnitude; median total tip migration was 0.42 mm (0.09-9.4) at 6 weeks, 0.92 mm (0.18-5.9) at 1 year, and 1.10 mm (0.13-6.4) at 5 years. Even after high initial migration, stabilization was achieved in 31 of the 35 RSA-evaluable implants. 3 prostheses showed progressive continuous migration throughout the entire follow-up period, and were considered to be loose, suggesting reduced long-term survival.

INTERPRETATION

Currently, we cannot recommend the CUT femoral neck prosthesis as a routine treatment option in (young) patients requiring THA. The CUT prosthesis may not reach the 90% survival benchmark at 10 years, and the prosthesis is difficult to implant. If initial stabilization is achieved, however, aseptic loosening is unlikely. A good clinical outcome was seen in the surviving prostheses. We will continue to follow this patient group.

Migration analysis of a metaphyseal anchored short-stem hip prosthesis

BACKGROUND AND PURPOSE

Metaphyseal anchored short-stem hip implants were designed to improve load transmission and preserve femoral bone stock. Until now, only few outcome data have been available and migration studies are one of the few ways of obtaining data that are predictive of implant survival. We therefore evaluated a metaphyseal anchored short-stem hip implant by Ein Bild Roentgen Analyse femoral component analysis (EBRA-FCA).

PATIENTS AND METHODS

First, the EBRA-FCA method was validated for the short-stem hip implant. Then 80 of the first 100 consecutive implants were evaluated after at least 2 years. Clinical assessment was performed using the WOMAC and the UCLA score.

RESULTS

After 2.7 (2.0-4.2), years none of the implants had been revised and by that time the stems had subsided by a mean of 0.7 mm (SD 1.8) (95% CI: 0.3-1.1). Of the 80 implants, 78 were stable after 2 years, with 74 being primary stable and 4 showing secondary stabilization after initial subsidence. Continuous migration was seen in only 2 patients. The clinical outcome showed good results with a mean WOMAC of 11 (SD 13) and a mean UCLA score of 7.3 (SD 2.0).

INTERPRETATION

The metaphyseal anchored short-stem hip implant showed good functional results and a high degree of stability after 2 years. The outcome is comparable to that of clinically proven conventional hip implants and if the results are confirmed by long-term studies, short-stem hip arthroplasty might be an alternative for young patients requiring hip replacement.

Shortening cemented femoral implants: an in vitro investigation to quantify exeter femoral implant rotational stability vs simulated implant length

The Exeter stems vary in length from 90 to 150 mm. The shorter stems generally have lower offsets. The purpose of this study was to determine if length of stem, with fixed offset, affected rotational stability. Mechanical testing was carried out on 10 implant-cement constructs with 2 loading profiles, rising from chair and stair climbing, at different simulated implant lengths using purpose-built apparatus. This paper presents a mechanism for clinically observed rotational stability and explains the mechanical characteristics required for rotational stability in Exeter femoral stems.

A prospective short-term outcome study of a short metaphyseal fitting total hip arthroplasty

The purpose of this study was to determine whether the short, metaphyseal fitting femoral stem would achieve stable fixation without diaphyseal fixation. A total of 126 patients (144 hips) were included in the study, and their mean age was 53.9 years (26-65 years). The mean duration of follow-up was 4.5 years (4-5 years). The predominant diagnosis was osteonecrosis of femoral head (88 of 144 hips, or 61%). The mean preoperative Harris hip score was 45 points, which improved to 96 points by the final follow-up. Western Ontario and McMaster Universities Osteoarthritis score and patient's activity score were improved substantially at the final follow-up. This short, metaphyseal fitting cementless femoral component achieved stable fixation without diaphyseal fixation, and there was minimal stress-shielding bone resorption in the calcar region.

Is there an increased stem migration or compromised osteointegration of the Mayo short-stemmed prosthesis following cerclage wiring of an intrasurgical periprosthetic fracture?

AIM

Short-stemmed prostheses are increasingly regarded as implants of first choice in primary THA. As a result of the press-fit fixation in the femoral metaphysis, the occurrence of intraoperative fractures were reported. The aim of this study was to analyze the postoperative results of the Mayo short-stem prosthesis following treatment of an intrasurgical femur fracture with cerclage wiring.

PATIENTS AND METHODS

From 1999 to 2005, in 38 patients (18 females, 20 males; mean age 56 years; mean BMI = 27) with the diagnosis of coxarthrosis in whom a Mayo short-stemmed prosthesis has been implanted, an intraoperative fracture was observed. The fractures were treated with cerclage wiring (1 cerclage, n = 32; 2 cerclages, n = 5; 3 cerclages, n = 1). Postoperatively, all patients were prescribed mobilization without weight-bearing (floor contact) on the treated leg for 6 weeks. Using the Wristing software, longitudinal stem migration and varus-valgus femoral stem alignment were examined digitally in anteroposterior X-rays taken immediately after surgery, after 6 weeks and on average after 5.7 years (Zeh et al., Z Orthop Unfall 149:200-205, 2011). Additionally, the incidence of periprosthetic radiolucent lines was captured in the anteroposterior X-rays and assigned to the Gruen zones. Additionally, a DEXA scan was performed. The X-rays of a matched control group after the implantation of a Mayo prosthesis without femur fracture were analyzed by the same method.

RESULTS

There was no significant migration of the Mayo prosthesis in the study or control groups during postoperative follow-up (t test, P > 0.05). The cerclage group compared with the control group showed a statistically significant valgus tilt of 1.5° on average during the follow-up, which is regarded to be clinically not relevant. The frequency of occurrence of radiolucent lines was not statistically different (chi-square test, χ = 0.42, P = 0.51). DEXA scans showed no differences of the bone mineral density in the Gruen zones compared with a historical control group.

CONCLUSION

After wiring of an intrasurgical fracture, no disadvantage could be proven for Mayo prosthesis regarding stem migration and varus-valgus alignment. Furthermore, due to the absence of differences in the occurrence of radiolucent lines and the same results in the DEXA scan, an unimpaired osseointegration is assumed.

Medium term follow up of the Biodynamic neck sparing prosthesis

Hip resurfacing (HR) and neck sparing prostheses (NSP) have been advocated for the treatment of arthritis in younger patients. Some complications following HR have been documented in the recent literature, but NSP are not yet supported by clinical follow-up studies of sufficient duration. We present an assessment of the neck sparing "Biodynamic" prosthesis. 153 patients were evaluated in a longitudinal cohort prospective study, with survival analysis, clinical score and radiographic assessment of stability and osteointegration at 41.8 months average follow up. Survival and clinical outcome were similar to most traditional prostheses in the literature. On radiographic analysis we recorded good neck preservation and osteointegration. Only two stem failures were recorded. Poor clinical outcome was related to misalignment of prostheses implanted during the 'learning curve'. The NSP system described may be a good alternative to HR for younger patients. The system is characterized by good survival and clinical and radiographic outcome combined with bone stock preservation.

Prospective study of a cementless total hip arthroplasty with a collum femoris preserving stem and a trabeculae oriented pressfit cup: minimun 6-year follow-up

AIM

Tissue sparing hip prostheses are becoming more and more popular especially for the treatment of younger patients. The objective of this study was to evaluate the clinical and radiological results after insertion of a tissue sparing hip prosthesis.

METHOD

In 47 consecutive non-selected patients (50 hips), the clinical and radiographic results of cementless total hip arthroplasty using a collum femoris preserving stem, a pressfit cup and an alumina-polyethylene pairing were prospectively evaluated. The mean age at index-surgery was 58 (36-82) years, there were 38 women and 9 men. After a mean follow-up of 6.8 years (minimum 6.1 years), two patients had died and one patient underwent revision surgery due to aseptic loosening of the stem.

RESULTS

The overall survival rate of the acetabular component was 100% and of the femoral component 98%. The mean Harris hip score at follow-up was 94 points.

CONCLUSION

The mid-term survival with this type of total hip arthroplasty is excellent and compares equal with uncemented straight stems in this age group.

Mid-term results of 155 patients treated with a collum femoris preserving (CFP) short stem prosthesis

Short stem prostheses that preserve the femoral neck are becoming more and more popular. The CFP (collum femoris preserving) has been introduced especially for the treatment of younger patients. However, information about remodelling, complications and learning curve are thus far rare. We present a retrospective study of 155 patients (average age 59.3 ± 9.9 years) who underwent total hip replacement with the CFP prosthesis. Follow-up was obtained 74.3 ± 9.4 months postoperatively. The Harris hip score revealed excellent and good results in 96%. One stem had to be exchanged due to aseptic loosening revealing a survival rate of 99% and 100% for stem and cup, respectively. Radiological analysis showed typical patterns of remodelling with appearance of cortical thickening predominantly in the distal part of the prosthesis. Implant related revision rate was <1%, with further complication rate independent of the surgeon's individual experience. With regard to outcome, survivorship and complication rate, the medium-term results of the CFP prosthesis are promising.

Bone remodeling characteristics of a short-stemmed total hip replacement

Bone remodeling of a metaphyseal fixed femoral stem, Mayo Conservative Hip (Zimmer International, Warsaw, Ind), was characterized by the dual-energy x-ray absorptiometry and a mathematical remodeling model. The mean age of the patient was 50.8 years, and the mean follow-up was 5.7 years. As anticipated, bony structure underwent significant remodeling after the short-stemmed femoral arthroplasty with resorption proximally and ingrowth distally/laterally. Theoretical prediction further suggested that the remodeling was largely regulated by the mechanical loading distribution pattern determined by implant design.

Biomechanical comparison of 2 proximally coated femoral stems: effects of stem length and surface finish

Proximally hydroxyapatite-coated stems have performed well clinically but produced moderate proximal stress shielding and midstem cancellous condensation. Stem modification (stem shortening and distal tip polishing) has resulted in greater incidence of thigh pain. We performed a retrospective finite element analysis of the effects of stem length and surface finish to determine if midstem fixation could be avoided and the results could relate to the clinical outcomes. The modified short stem not only produced moderately less proximal bone resorption but also exhibited greater instability with 40% to 94% greater bone-implant relative motion at the stem tip. Bone formation potential at the transition between the coated and uncoated regions of both stems was observed based on changes in strain energy density. These findings are consistent with previous radiographic and clinical comparisons of short- and long-stem designs. Increased pain incidence for short-stem patients may be related to decreased implant instability and increased interface relative motion.

Differentially loaded radiostereometric analysis to monitor fracture stiffness: a feasibility study

Inability to accurately and objectively assess the mechanical properties of healing fractures in vivo hampers clinical fracture management and research. We describe a method to monitor fracture stiffness during healing in a clinical research setting by detecting changes in fracture displacement using radiostereometric analysis and simultaneously measuring applied axial loads. A method was developed for load application, positioning of the patient, and radiographic setup to establish the technique of differentially loaded radiostereometric analysis (DLRSA). A DLRSA examination consists of radiostereometric analysis radiographs taken without load (preload), under different increments of load, and without load (postload). Six patients with distal femur fractures had DLRSA examinations at 6, 12, 18, and 26 weeks postoperatively. The DLRSA method was feasible in a clinical setting. The method provides objective and quantifiable data for internally fixed fractures and may be used in clinical research as a tool to monitor the in vivo stiffness of healing femoral fractures managed with nonrigid internal fixation.

Medium term results of the collum femoris preserving hydroxyapatite coated total hip replacement

We describe the survival of 75 collum femoris preserving (CFP) hydroxyapatite (HA) coated uncemented total hip replacement stems with a mean follow-up of 43 months (range 12-60). Patients were assessed using the Harris Hip Score. Radiographs were evaluated using Gruen zones and DeLee and Charnley zones. The criteria for failure were revision or impending revision. The mean Harris Hip Score was 50 preoperatively improving to 94 at final review, with 3 patients lost to follow-up. One cup was revised for aseptic loosening, whilst none of the stems required revision. Survivorship was 97% and 100% at 3 years for the cup and stem respectively. Our findings suggest that the medium term results of the CFP stem are excellent.

[Short-stemmed endoprostheses in total hip arthroplasty]

Short-stemmed endoprostheses in total hip arthroplasty are anchored exclusively in the metaphysis and the proximal part of the diaphysis. Therefore, they are much shorter than the classic standard stems. These implants are specially favourable in terms of eventual revision surgery, and also due to the fact that with close diaphyseal bone marrow spaces a sufficient proximal size dimensioning is possible. In this study, the best known short-stemmed systems in clinical use are introduced. Positive long-term results are so far available only with the Pipino and Mayo stems, short and partially medium-term experience with the remaining short stems (C.F.P.(R), Metha, PROXIMA, ESKA) are--with the available learning curve--encouraging. Despite the call for sufficient experience and scientific evaluation, short-stemmed endoprostheses already represent a valuable alternative in endoprosthetics for younger patients.