Ist kürzer wirklich besser?: Philosophie der Kurzschaftendoprothesen

Development and Finite Element (FE) analysis of a novel short hip stem concept

Introduction

In order to improve the anchorage behavior of short hip stems, this development project aims at designing a short hip stem concept that preserves the femoral neck and minimizes interference with the physiological stress distribution of the femur. The new design will be evaluated according to ISO 7206-4 which is the standard for testing Implants for surgery.

Methods

Basic CAD models based on an established short stem prosthesis were created and evaluated using finite element analysis. The best design was further developed to achieve a more deformable stem while maintaining stability. The model was validated through in vitro testing.

Results

The "H-Beam" short stem showed a higher degree of deformation of approximately 142-144% compared to the established short stem. The FE model had a relative error of 0.98% and 1.07% compared to the in vitro tests. An operating procedure was outlined for this new short stem design.

Discussion

The FE model is deemed valid due to small differences in comparison to in vitro testing. The short-stem prosthesis is more flexible and can be easily adapted to individual anatomy during surgery. The prosthesis length is similar to conventional prostheses, but the new stem design could allow better and faster osteointegration while preserving the cancellous bone structure.

Twenty-year results of a neck-preserving short-stem prosthesis in primary total hip arthroplasty

PURPOSE

The use of short-stemmed femoral components with preservation of the femoral neck has been advocated for younger and more active patients undergoing joint replacement. This study reports the long-term outcomes of the Collum Femoris-Preserving (CFP) prosthesis on a previous report.

METHODS

Between January 1999 and December 2000, a total of 149 patients underwent total hip arthroplasty procedure using the CFP stem in a single institution. At latest follow-up, 79 patients were available and were included in this study. The mean age of the cohort was 73.4 (range, 44-92 years) with a mean follow-up of 20.7 years (range 20-21). The average age was 52.1 years at index procedure (range, 21-71 years).

RESULTS

The Kaplan-Meier survivorship free from revision for any cause at 5, 10 and 20 years was 93.2% (87.8-96.3%), 93.2% (87.8-96.3%) and 83.0% (75.7-88.3%), respectively. At 20 years follow-up, the revision for any cause occurred in 26.6% (21 of 79) of patients. The most common causes for revision surgery were aseptic loosening, dislocation, and polyethylene wear with 6.3% (5 out of 79), respectively. Periprosthetic fracture occurred in four patients (5.1%) followed by periprosthetic joint infection in two patients (2.5%). Revision surgery of the femoral stem was required in four patients (5.1%). There was a statistically significant improvement of the Harris Hip Scores from 53 to 83.7 (range 56-91).

CONCLUSION

The long-term outcomes of the CFP stem are excellent, demonstrating a low rate of aseptic loosening with an excellent survivorship within 2 decades.

Short Stem for Total Hip Arthroplasty (THA) - Overview, Patient Selection and Perspectives by Using the Metha® Hip Stem System

Short stem hip replacement has not only gained attention but also significance over the past decades. However, there still remains uncertainty regarding the correct indications for these stems. Even companies, producing implants, have varying recommendations that are more likely based on a well-meant advice than on statistically evaluated data. Thus, it is important to evaluate the advantages and disadvantages of a short stem prosthesis. The goal of this paper is to reveal some of the existing uncertainty in this field, by analyzing the Metha^® short hip stem system. This paper does not only focus on general aspects but also discusses some more specific problems, such as avascular necrosis and post-rheumatic diseases, as well as hip dysplasia and coxarthrosis. The aim is also to convey the opportunity to indicate this type of implant for elderly and obese patients as well as for femoral misalignments following post-Perthes disease, post-traumatic deformities or other malpositions of the hip.

Clinical and radiographic outcomes after total hip arthroplasty with the NANOS neck preserving hip stem: a 10 to 16-year follow-up study

BACKGROUND

Short-stem Hip Arthroplasty (SHA) are increasingly implanted in recent years thanks to their potential advantage in preserving metaphyseal bone-stock. Among them, the NANOS® short-stem implant demonstrated satisfactory results to short and mid-term. The purpose of this retrospective study was to evaluate the clinical and radiographic outcome of the Nanos® short stem at a minimum follow-up of 10 years.

METHODS

Sixty-seven patients aged 53 ± 20 years were enlisted in the study, for a total of 72 hips. Primary outcomes were survivorship of the implant and clinical outcome measured using the Hip disability and Osteoarthritis Outcome scores (HOOS) and the Short Form Survey (SF12) questionnaire. The secondary outcome was a radiological evaluation calculating the inclination and the anteversion angle of the acetabular cup for each implant and investigating osteolysis, heterotopic ossifications and stem position.

RESULTS

We observed a 95.5% stem survivorship. The complication rate was 7.6% and three implants underwent revision because of an aseptic loosening, an infection and a periprosthetic fracture due to trauma. Among 58 patients (63 hips) evaluated in an outpatient visit 10-16 years after surgery, improvement in clinically relevant scores comparing with baseline was observed: HOOS score increased after surgery in all its subcategories (from 32.25 ± 14.07% up to 91.91 ± 9.13%) as well as SF12 which increased by more than 18 percentage points. On clinical assessment, the range of motion (ROM) was restored at follow-up, 1 patient (1.7%) showed a squeaking hip and 2 (3.4%) reported leg-length discrepancy. Neutral stem positioning was achieved in 58 hips and heterotopic ossifications occurred in 10 hips (16%).

CONCLUSIONS

The current study reports good clinical and radiological outcomes following NANOS® short-stem hip implant at minimum 10 years-follow-up. Since the high rate of stem survivorship, the low complication rate demonstrated and the overall patient satisfaction, our results suggest NANOS® neck-preserving prostheses should be considered as a valid alternative to standard implants.

Clinical and radiographic outcomes with the Nanos™ short-stem hip implant at 24 months: A prospective, single-center study

Aim

Short-stem total hip arthroplasty is designed to preserve proximal bone stock in case of eventual revision, potentially benefiting younger and more active patients. This prospective, single-center study assessed the safety and performance of the partially neck-sparing Nanos™ short-stem uncemented prosthesis at 24 months using clinical outcome scores and radiographic results.

Methods

Between April 2011 and February 2015, 52 subjects (mean age, 54.9 years) underwent total hip arthroplasty and were followed up at 3, 6, 12 and 24 months. The primary outcome was improvement in quality of life as measured by the Short-Form 36 Mental Component Score (SF-36 MCS). Secondary clinical outcomes included the Harris Hip Score, Hip Disability and Osteoarthritis Outcome Score, Postel Merle d'Aubigné-Score, Activity Level University of California, Los Angeles score, and Pain Visual Analogue Scale. Complications and radiographic images were also recorded at each follow-up.

Results

Mean SF-36 MCS score significantly improved from baseline to final follow up at 24 months (61.3 vs. 79.5, respectively; p < 0.001). All secondary clinical outcomes also showed significant improvement (p < 0.001) during this time period. Neutral stem positioning was achieved in 45 subjects (86.5%). Two subjects (3.8%) underwent revisions: one for a periprosthetic fracture unrelated to the study device and another due to a prosthetic joint infection. Intraoperatively, one fissure fracture of the acetabulum occurred.

Conclusion

Total hip arthroplasty with the Nanos short-stem led to significant clinical improvements and a high subjective satisfaction rate at 24 months. Further follow-up will determine whether these effects are sustained in the long term.

Periprosthetic fracture morphology of a femoral neck prosthesis: An in vitro study

Femoral neck prostheses have been developed for the treatment of osteoarthritis in young and active patients. The concept combines a bone-conserving and minimal invasive technique with proximal load transferring by metaphyseal anchoring, which results in a more physiological loading pattern. However, little is known about the morphology of periprosthetic fractures. Thus, the aim of this study was to describe fracture patterns and to determine patient-specific factors favoring periprosthetic fracture. This study was performed as a biomechanical experimental study using 10 fresh frozen femora and 10 Silent-Hip femoral neck implants (DePuy International Ltd., Leeds, UK). In order to simulate physiological loading, a static muscle reconstruction (abductor muscles and iliotibial band) and a dynamic simulation of the gait cycle were applied. During biomechanical testing (50% and 100% of normal weight-bearing), three periprosthetic fractures with two different morphologies occurred. The first pattern corresponds to an abrupt breakaway. The second type was of spiral configuration extending to the diaphyseal region and emerging from an initial fissure. Specimen-specific factors favoring periprosthetic fracture were body mass index and varus angle of the implant. Periprosthetic fractures may extend to the subtrochanteric/diaphyseal region and may be of spiral configuration. According to the finding of this study, body mass index and varus/valgus position of the implant are important factors influencing the risk of periprosthetic fractures. Furthermore, partial weight-bearing as part of the postoperative regimen may be favorable.

Femoral neck prostheses: A systematic analysis of the literature

Primary total hip arthroplasty (THA) is one of the most successful surgical procedures. Considering the demographic change the use of new ultra-short femoral implants has gained importance especially when treating young patients. Main features are bone conservation, metaphyseal anchoring and thus reducing stress shielding by proximal load transferring. The objective of this study is to give an overview over the subject of femoral neck prostheses. A systematic review was conducted. A total number of 27 publications were taken into this systematic review. Over all, just a few follow-up, biomechanical and radiostereometric studies have been conducted in the past. Still no long-term results (>10 years of follow-up) are available. The available mid-term results indicate unsatisfactory survival rates. Aseptic loosening was the most common reason for revision. Valgus angle and good bone mineral density were considered to be crucial for primary stability of femoral neck prostheses. Register data report a very low percentage of femoral neck prostheses in THA with even more diminishing implantation rates. To conclude, further studies are necessary in order to provide evidence-based recommendations. Currently, due to the inhomogeneous and poor data a reasonable and legitimate recommendation cannot be given.

'Pre-launch' finite element analysis of a short-stem total hip arthroplasty system consisting of two implant types

BACKGROUND

We applied a previously established and validated numerical model to a novel short-stemmed implant for a 'pre-launch' investigation.

METHODS

The implant system consists of two different implant geometries for valgus/varus-positioned proximal femurs with differences in volume distribution, head/neck angle, and calcar alignment. The aim of the design was to achieve a better adaption to the anatomic conditions, resulting in a favourable load transfer. The implant type G showed the best fit to our model, but both stem geometries were implanted; the implant type B was used to compute an 'imperfection scenario'.

FINDINGS

Apparent bone density decreased by 4.3% in the entire femur with the implant type G, and by 12.3% with the implant type B. Bone mass loss was pronounced in the proximal calcar region. Apparent bone density increased at the lateral cortical ring and in the minor trochanter. The apparent bone density in the imperfection scenario was very similar to that of a straight stem, indicating a distal load transfer.

INTERPRETATION

No adverse effects of the A2 short-stemmed implant system on bone remodeling could be detected. The overall bone density reduction was acceptable, and wedge fixation was not observed, indicating that there was no distal load transfer. The simulation of an incongruous implant indicates the sensitivity of our model in response to modifications of implant positioning. Correct implant selection and positioning is crucial when using the A2 system.

Is a short stem suitable for patients with hip dysplasia? A report on technical problems encountered during femoral reconstruction

INTRODUCTION

A wide variety of stems have been used for the treatment of osteoarthritis secondary to advanced hip dysplasia. Since evidence for using short stems in dysplastic hips is limited, we planned to analyse the technical problems encountered when reconstructing the proximal femur of patients with osteoarthritis secondary to congenital dysplasia of the hip treated with total hip arthroplasty (THA) using a type 2B short stem.

METHODS

We prospectively analysed 17 patients (22 hips) treated with primary THA performed with a single-branded short uncemented stem with metaphyseal fixation (MiniHip™; Corin). We excluded cases in which other type of stems were used, or in which retrospective data was only available. Mean follow-up was 41.22 months (minimum 24). We analysed clinical outcome using the modified Harris Hip Score (mHHS) and pain using the visual analogue scale (VAS). Radiographs were examined in order to determine causes of complications and revision surgery.

RESULTS

All patients showed statistically significant improvement when preoperative and postoperative values for mHHS (54.19 vs. 94.57; p = 0.0001) and for pain VAS (8.71 vs. 0.71; p = 0.0003) were compared. No cases of thigh pain, instability or infection were found. 1 case of acetabular cup loosening and 1 case of periprosthetic fracture were diagnosed at 8 months and 45 days, respectively. Overall survival was 84.7% at 5 years (CI 95%, 64.4-105.3) with revision for any reason as an end point. When stem performance was separately evaluated, it showed a survival rate of 100% at 5 years with revision for aseptic loosening as an end point.

CONCLUSIONS

THA with a type 2B short stem for the treatment of dysplastic osteoarthritis showed very few technical intraoperative problems, being a useful alternative for femoral reconstruction.

Eleven-year results of the anatomic coated CFP stem in primary total hip arthroplasty

There is a paucity of intermediate term results relating to short stem prostheses. The current study represents the longest follow-up results of the CFP prosthesis to the authors' best knowledge. Between January 1999 and December 2000, all total hip arthroplasty patients (n = 149), treated with this anatomic neck preserving stem in the authors' institution were enrolled in this study. After a mean follow-up time period of 11.2 years 117 patients were available for the follow-up examination. The mean HHS increased from 53 to 93. Overall, revision surgery was required in 11 patients (9.4%), with implant-associated complications noted in only five cases (4.3%). Aseptic loosening leading to implant removal was noted in four patients (3.4%). The current study's data suggest that the CFP implant, used in young patients undergoing primary total hip arthroplasty, is safe and provides excellent results after 11 years.

Five-year results of a cementless short-hip-stem prosthesis

Hip prosthesis stems with a short stem length and proximal fixation geometry support a bone-preserving and muscle-sparing implantation and should also allow for revision surgery with a standard hip stem. We present 250 prospectively documented clinical and radiological results from the Metha Short Hip Stem prosthesis (B. Braun-Aesculap, Tuttlingen, Germany) after an average follow-up of 4.9 years. The average patient age at surgery was 60 years. Indication for total hip replacement was primary osteoarthrosis (OA) (78% of patients), OA based on developmental dysplasia of the hip (16%), and other indications (6%). At the last follow-up, the average Harris Hip Score was 97 points. 85% of patients were very satisfied and 14% were satisfied after surgery, whereas 1% were dissatisfied. Pain according to the Visual Analogue Scale improved from 7.4 (min 1.6, max 9.5) pre-operatively to 0.23 (min 0, max 6.6). No joint dislocations occurred when predominantly using 28 mm and 32 mm prosthesis heads. Nine short-stems were revised: three after bacterial infections, two after primary via valsa with penetration of the femoral cortex two and three months after surgery, and three after early aseptic cases of loosening within the first year. A further nine osseously consolidated short-stems had to be replaced due to breakage of the modular titanium cone adapter after an average of 3.1 years (min 1.9, max 4.4). All surgical revisions were performed using primary standard stems. Without taking the material-related adapter failures into account, a five year Kaplan-Meier survival rate of 96.7% (95% confidence interval 93.4–98.3) was determined for the short-stem prostheses. There were no radiological signs of loosening in any of the short-stem prostheses at the last examination. Fine sclerotic lines were detected in Gruen's AP zones 1 (19%) and 2 (10.5%), individual hypertrophies in zone 3 (3.5%), fine seams in zones 4 (5.5%) and 5 (4%), without pedestal formations in zone 4, clear cancellous bone compressions in zone 6 (97.5%), as well as single fine scleroses (1.5%) and atrophies (2.5%) in zone 7. The mid-term clinical results with periprosthetic bone remodeling and without radiological signs of loosening confirm this metaphyseal short-stem treatment and fixation concept and the possibility of revision surgery using standard hip stems. Long-term results must be further observed on a prospective basis as part of this collective study.