Femoral neck retention in hip arthroplasty. A cadaver study of mechanical effects

Biomechanical Properties of Bionic Collum Femoris Preserving Hip Prosthesis: A Finite Element Analysis

OBJECTIVE

Compared with total hip replacement, conventional collum femoris preserving prosthesis has a better bone retention effect. However, damage to the trabecular bone of the proximal femur leads to inevitable abnormal stress distribution, which leads to increased risks of femoral neck bone absorption, periprosthetic fracture, prosthesis loosening, rotation, and sinking. Thus, we compare the biomechanical properties of collum femoris preserving (CFP) and bionic collum femoris preserving (BCFP) hip prostheses.

METHODS

The Sawbone digital model (#3503, left, medium) was selected as the research object. We used the Mimics 21.0 software to reconstruct the digital model of the femur and the SolidWorks 2019 software to build and assemble the three-dimensional models of CFP and BCFP prostheses. With the ANSYS Workbench 2021R1 software, the models were meshed and assigned values to simulate the load of a single foot under slow walking. We measured the mechanical distribution of the whole model and obtained the stress nephogram.

RESULTS

For CFP prosthesis, the peak stresses of the medial interface of the stem neck, the lateral interface of the stem neck, and the end of the stem were 64.894, 32.199, and 8.578 MPa, respectively; the peak stresses of the medial surface of the femoral shaft, the lateral surface of femoral shaft, the medial femoral neck bone-prosthesis interface (osteotomy interface), the lateral femoral neck bone-prosthesis interface (basal area), the lateral femoral neck bone-prosthesis interface (osteotomy interface), and the greater trochanter area were 28.093, 24.790, 14.388, 5.118, 4.179, and 8.245 MPa, respectively; the valley stress of the greater trochanter area was 1.134 MPa. For BCFP prosthesis, the peak stresses of the medial interface of the stem neck, the lateral interface of the stem neck, and the end of the stem were 47.015, 26.771, and 47.593 MPa, respectively; the peak stress of tension screw was 15.739 MPa; the peak stresses of the medial surface of the femoral shaft, the lateral surface of femoral shaft, the medial femoral neck bone-prosthesis interface (osteotomy interface), the lateral femoral neck bone-prosthesis interface (basal area), the lateral femoral neck bone-prosthesis interface (osteotomy interface) and the greater trochanter area were 28.581, 25.364, 15.624, 6.434, 4.986, and 8.796 MPa, respectively; the valley stress of the greater trochanter area was 1.419 MPa; the peak stress of bone-metal interface between the tension screw and the lateral surface of the femur was 5.858 MPa.

CONCLUSION

Compared with the CFP prosthesis, the design of the BCFP prosthesis is based on the lever balance theory. With the bionic reconstruction of tension trabeculae, BCFP prosthesis makes up for the defects of CFP prosthesis design, optimizes the stress distribution, and reduces the stress shelter effect of the proximal femur, which has better biomechanical properties.

Neck-sparing short femoral stems: A meta-analysis

BACKGROUND

Neck sparing short femoral stems are supposed to ease restoration of the proximal femoral anatomy and physiological hip biomechanics. This stem design is of particular interest as they have the potential to generate prosthetic hips that have higher functional performance with an improved lifespan, and revise more easily. Unlike previously published meta-analysis, this meta-analysis was initiated to determine if neck sparing short femoral stems compared to conventional stems: (1) resulted in improved functional performance; (2) reduced risk of thigh pain; (3) reduced risk of reoperation/revision, and 4) reduced stress shielding related bone loss in the proximal femur.

MATERIAL AND METHODS

Literature databases were searched between 1st January 2005 and 30th March 2019. The primary search was conducted using the electronic databases MEDLINE, EMBASE, PubMed, Open Grey, Trip Pro, Evidence Search, and Cochrane. Eligible studies were assessed for homogeneity, with continuous outcomes expressed as standardized mean difference with 95% confidence interval and dichotomous data as odds-ratio with 95% confidence interval.

RESULTS

Ten randomised clinical trials were eligible; these trials included 1259 total hip arthroplasty procedures, inclusive of 616 neck sparing short stems and 643 conventional stems. We were not able to find a significant functional advantage of using neck sparing short stems based on Harris Hip scores (0.0850; 95% CI: -0.03 to 0.20 [p=0.40]) and WOMAC scores (-0.0605; 95% CI: -0.03 to 0.15 [p=0.87]). We found a trend in favour of neck sparing short stems to reduce the risk of thigh pain but this was non significant (odds ratio of 0.11; 95% CI: 0.03 to 0.43 [p=0.178]). Neck sparing short stems were associated with similar early- to mid-term dislocation and revision rates compared to conventional stems with odds ratio of 1.435 (95% CI: 0.545 to 3.780 [p=0.968]) and of 0.581 (95% CI: 0.220 to 1.532 [p=0.972]), respectively. Neck sparing short stems were found to have less bone loss in both Gruen zones 1 and 7 (3.324; 95% CI: -7.683 to 1.036 [p<0.001], and of -4.632; 95% CI: -9682 to 0.418 [p<0.001], respectively).

DISCUSSION/CONCLUSION

Neck sparing short femoral stems achieve excellent early to mid-term outcomes in both clinical and radiological outcome scores that are in keeping with conventional stems functionally. Hitherto, results from this meta-analysis suggest that neck-sparing stems may achieve better maintenance of bone mineral density than their conventional counterparts, in addition to fewer cases of thigh pain.

LEVEL OF EVIDENCE

I; meta-analysis.

An Ultra-Short Femoral Neck-Preserving Hip Prosthesis: A 2-Year Follow-up Study with Radiostereometric Analysis and Dual X-Ray Absorptiometry in a Stepwise Introduction

BACKGROUND

Total hip arthroplasty (THA) with a diaphyseal stem may risk bone loss. In order to save proximal bone stock in young patients with a high activity level and a long life expectancy, the interest in short stems has evolved. The purpose of this prospective observational cohort study was to evaluate the fixation of, and bone remodeling around, the Primoris femoral neck-preserving hip implant.

METHODS

Fifty younger patients with end-stage osteoarthritis were managed with the Primoris hip implant. We evaluated bone mineral density (BMD) using dual x-ray absorptiometry (DXA) and implant migration using radiostereometric analysis (RSA). A region-of-interest (ROI) protocol for 4 ROIs was applied to assess BMD. The association between BMD and migration was evaluated to determine the fixation of the Primoris implant and bone remodeling in the proximal part of the femur. Follow-up evaluation was performed at regular intervals from day 1 (baseline) until 24 months after surgery.

RESULTS

The major stem migrations were subsidence (Y axis; mean, 0.38 mm) at 6 weeks and varus tilt (rotation) (Z axis; mean, 0.93°) at 6 to 12 months. In ROI4 (the calcar area), a significant gain in bone was found with a mean difference of 4.1% (95% confidence interval [CI], 0.8% to 7.4%; p < 0.02) at 24 months postoperatively. Significant bone loss was found in ROI1 and ROI2, with a mean difference of -4.9% (95% CI, -7.4% to -2.4%; p = 0.0003) and -8.9% (95% CI, -11.5% to -6.2%; p = 0.0001), respectively. Linear regression and multivariate regression analysis showed a significant negative association between maximal total point motion and BMD (p = 0.02, R = 15%; and p < 0.05, R = 26%, respectively).

CONCLUSIONS

The Primoris component showed satisfactory primary stability with promising results at the 24-month follow-up. DXA scans showed limited stress-shielding with the proximal loading pattern of the Primoris. Better bone quality was associated with less implant migration.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Comparison of Patient-Reported Outcome from Neck-Preserving, Short-Stem Arthroplasty and Resurfacing Arthroplasty in Younger Osteoarthritis Patients

Hip resurfacing has been considered a good treatment option for younger, active osteoarthritis patients. However, there are several identified issues concerning risk for neck fractures and issues related to current metal-on-metal implant designs. Neck-preserving short-stem implants have been discussed as a potential alternative, but it is yet unclear which method is better suited for younger adults. We compared hip disability and osteoarthritis outcome scores (HOOS) from a young group of patients (n = 52, age 48.9 ± 6.1 years) who had received hip resurfacing (HR) with a cohort of patients (n = 73, age 48.2 ± 6.6 years) who had received neck-preserving, short-stem implant total hip arthroplasty (THA). Additionally, durations for both types of surgery were compared. HOOS improved significantly preoperatively to last followup (>1 year) in both groups (p < 0.0001, η (2) = 0.69); there were no group effects or interactions. Surgery duration was significantly longer for resurfacing (104.4 min ± 17.8) than MiniHip surgery (62.5 min ± 14.8), U = 85.0, p < 0.0001, η (2) = 0.56. The neck-preserving short-stem approach may be preferable to resurfacing due to the less challenging surgery, similar outcome, and controversy regarding resurfacing implant designs.

Short bone-conserving stems in cementless hip arthroplasty

➤ Short bone-conserving femoral stems in total hip arthroplasty were designed to preserve proximal bone stock.➤ Given the distinct fixation principles and location of loading among these bone-conserving stems, a classification system is essential to compare clinical outcomes.➤ Due to the low quality of currently available evidence, only a weak recommendation can be provided for clinical usage of certain stem designs, while some other designs cannot be recommended at this time.➤ A high prevalence of stem malalignment, incorrect sizing, subsidence, and intraoperative fractures has been reported in a subset of these short stem designs.➤ Stronger evidence, including prospective multicenter randomized trials comparing standard stems with these newer designs, is necessary before widespread use can be recommended.

Ten year results of the collum femoris preserving total hip replacement: a prospective cohort study of seventy five patients

PURPOSE

The collum femoris preserving (CFP) uncemented prosthesis has a bone-preserving, high subcapital neck resection and a short anatomical stem. The ideal arthroplasty option in the younger, active patient is a subject of some debate. We evaluated midterm outcomes of the CFP in this patient population.

METHODS

A prospective, consecutive cohort of 75 CFP total hip replacement (THR) patients with a mean age of 52 years was followed for a mean of 9.3 years. Patients were assessed using the Harris Hip Score (HHS). Pain was assessed using a visual analogue scale (VAS) and activity levels using the University of California, Los Angeles (UCLA) score. Radiographs were evaluated for evidence of loosening. Survivorship was calculated with an endpoint of revision for aseptic loosening or radiographic evidence of loosening.

RESULTS

Mean HHS improved from a mean of 50 pre-operatively to 91 (p < 0.001) postoperatively. Mean pain score was 1, mean patient satisfaction was 9 and mean UCLA score was 6. Two acetabular components were revised for aseptic loosening; no stem required revision. Radiographically, no cases had evidence of loosening. Survivorship was 96.8 % for the acetabular component and 100 % for the stem at ten years. Three patients died from unrelated causes, and five were lost to follow-up.

CONCLUSIONS

Bone-preserving hip replacement has increased in popularity as hip replacement in younger and more active individuals increases. The CFP prosthesis has excellent midterm clinical function and survival and provides high levels of satisfaction in young patients.

Outcomes of short stems in total hip arthroplasty

Short-stem total hip arthroplasty has been proposed as a bone-conserving procedure for the younger and more active population undergoing total hip arthroplasty. Although various short stems are currently available, no studies compare the outcomes between these stems. The aim of the current study was to conduct a systematic review of the clinical and radiographic outcomes of the various short stems that have been approved for use in the United States by the Food and Drug Administration. Outcomes that were assessed included implant survivorship, Harris Hip scores, thigh pain, periprosthetic fracture, subsidence, proximal stress shielding, and the prevalence of stem malalignment and inappropriate implant sizing.

Neck-preserving femoral stems

BACKGROUND

Surgeons undertaking total hip arthroplasty (THA) routinely perform a distal femoral neck resection. It has been argued that retaining the femoral neck during THA can provide mechanical and biological advantages.

PURPOSES

The objectives of this study were to review: (1) the current evidence on the advantages of femoral neck preservation during THA and (2) the clinical and radiological outcome of neck-preserving femoral stems.

METHODS

A search of the English-language literature on neck-preserving THA and on the individual neck-preserving implants was performed using PubMed, Ovid SP and Science Direct.

RESULTS

Studies have indicated that neck preservation offers superior tri-planar implant stability and allows more accurate restoration of the hip geometry and biomechanics. The trend towards tissue sparing surgery has contributed to the development of bone-conserving short-stem implants that offer variable levels of neck preservation. Despite an initial learning curve, these implants have generated promising early clinical results, with low revision rates and high outcome scores. However, radiological evaluation of some neck-preserving implants has detected a characteristic pattern of proximal femoral bone loss with distal cortical hypertrophy. The long-term implications of this finding are not yet known.

CONCLUSIONS

Preserving the femoral neck during THA has biomechanical advantages. However, long-term outcome data are needed on neck-preserving femoral stems to evaluate on-going bone remodelling and assess implant performance and survival.

The Freeman femoral component with hydroxyapatite coating and retention of the neck: an update with a minimum follow-up of 17 years

The outcome at ten years of 100 Freeman hip stems (Finsbury Orthopaedics, Leatherhead, United Kingdom) retaining the neck with a proximal hydroxyapatite coating in a series of 52 men (six bilateral) and 40 women (two bilateral), has been described previously. None required revision for aseptic loosening. We have extended the follow-up to 20 years with a minimum of 17 years. The mean age of the patients at total hip replacement was 58.9 years (19 to 84). Six patients were lost to follow-up, but were included up to their last clinical review. A total of 22 patients (22 hips) had died, all from causes unrelated to their surgery. There have been 43 re-operations for failure of the acetabular component. However, in 38 of these the stem was not revised since it remained stable and there was no associated osteolysis. Two of the revisions were for damage to the trunnion after fracture of a modular ceramic head, and in another two, removal of the femoral component was because of the preference of the surgeon. In all cases the femoral component was well fixed, but could be extracted at the time of acetabular revision. In one case both components were revised for deep infection. There has been one case of aseptic loosening of the stem which occurred at 14 years. This stem had migrated distally by 7.6 mm in ten years and 8.4 mm at the time of revision at which stage it was found to be rotationally loose. With hindsight this component had been undersized at implantation. The survivorship for the stem at 17 years with aseptic loosening as the endpoint was 98.6% (95% confidence interval 95.9 to 100) when 62 hips were at risk. All remaining stems had a satisfactory clinical and radiological outcome. The Freeman proximally hydroxyapatite-coated femoral component is therefore a dependable implant and its continued use can be recommended.

Perspectives on metaphyseal conservative stems

Total hip replacement is showing, during the last decades, a progressive evolution toward principles of reduced bone and soft tissue aggression. These principles have become the basis of a new philosophy, tissue sparing surgery. Regarding hip implants, new conservative components have been proposed and developed as an alternative to conventional stems. Technical and biomechanical characteristics of metaphyseal bone-stock-preserving stems are analyzed on the basis of the available literature and our personal experience. Mayo, Nanos and Metha stems represent, under certain aspects, a design evolution starting from shared concepts: reduced femoral violation, non-anatomic geometry, proximal calcar loading and lateral alignment. However, consistent differences are level of neck preservation, cross-sectional geometry and surface finishing. The Mayo component is the most time-tested component and, in our hands, it showed an excellent survivorship at the mid-term follow-up, with an extremely reduced incidence of aseptic loosening (partially reduced by the association with last generation acetabular couplings). For 160 implants followed for a mean of 4.7 years, survivorship was 97.5% with 4 failed implants: one fracture with unstable stem, 1 septic loosening and 2 aseptic mobilizations. DEXA analysis, performed on 15 cases, showed a good calcar loading and stimulation, but there was significant lateral load transfer to R3–R4 zones, giving to the distal part of the stem a function not simply limited to alignment. Metaphyseal conservative stems demonstrated a wide applicability with an essential surgical technique. Moreover, they offer the options of a “conservative revision” with a conventional primary component in case of failure and a “conservative revision” for failed resurfacing implants.

The effect of a neck-retaining femoral implant on leg-length inequality following total hip arthroplasty

The aim of this study was to assess whether a femoral component which retained the neck reduced the incidence of leg-length inequality following total hip arthroplasty. A retrospective review was undertaken of 130 consecutive primary total hip arthroplasties performed between April 1996 and April 2004 using such an implant. There were 102 suitable patients for the study. Standardised pre- and post-operative pelvic radiographs were measured by an independent investigator to the nearest millimetre.

The leg-length inequality was reduced from a mean pre-operative value of −0.71 cm to a mean of 0.11 cm post-operatively. Of the 102 patients 24 (23.5%) had an equal leg-length post-operatively, and 95 (93.1%) had a leg-length inequality between −1 cm and 1 cm.

Photoelastic and thermoelastic measurement of stress on the proximal femur before and after implantation of a hip prosthesis with retention of the femoral neck

This study demonstrated the improved medial support and the transfer of load onto the retained neck of the femur using seven fresh frozen femurs. Results confirm the reliability of the thermoelastic stress analysis method, which is comparable to the photoelastic surface coating method, but with greater sensitivity. The loading pattern after stem implantation shows a homogeneous transfer of force onto the preserved femoral neck. After femoral neck removal, an inhomogeneous increase of the intertrochanteric compression loading was observed. Therefore, improved biomechanical conditions are created for a permanently stable implantation of stem prostheses with retention of the femoral neck.

Pre-clinical testing of hip prosthetic designs: a comparison of finite element calculations and laboratory tests

To investigate the accuracy of finite element (FE) models for pre-clinical testing of unbounded hip prostheses, relative to aspects of load transfer and micromobility, two previously published laboratory experiments were simulated, using three-dimensional FE models. It was found for the load-transfer analyses that the experiment and the FE study revealed results that were very similar. The trends in the mobility experiments were also reproduced in the FE simulations, although quantitative differences were found. It is concluded that FE analysis can effectively be used for design evaluation of hip prostheses before prototypes are made.

The effect of retention of the femoral neck and of cement upon the stability of a proximal femoral prosthesis

Radiological measurements of downward femoral component migration are reported for 203 hips in the first 2 years following total hip arthroplasty. The femora differed with respect to the retention of the femoral neck--in 167 it was retained and in 36 it was damaged--and to the use of cement--142 hips were press-fits and 61 were cemented. Multivariate analysis demonstrated that both retention of the neck and the use of cement retarded migration (ie, increased stability) of the femoral component (P = .0003 and .0037, respectively).

Effect of interface conditions on the behaviour of a Freeman hip endoprosthesis

The femoral element of a total hip replacement is a composite structure of two, or perhaps three, components--the endoprosthesis, the bone and, where present, the cement. The interfacial conditions are such that complete structural continuity does not necessarily obtain. That this is so has often been suspected due to the observed loosening which can occur in vivo. In modelling the system, typically for finite element analysis, it has usually been considered to be monolithic, such that tensile and shear stresses could be transmitted across the interfaces as well as the normal compressive stress. Here the femoral component of a Freeman hip replacement is considered, implanted without bone cement, and analyses are carried out under monolithic, i.e. fully bonded, and non-bonded assumptions. Simultaneously the effect of retaining the neck of the femur, one of the features of using this particular prosthesis, is also examined.