Comparative Analysis of the Biomechanical Behaviour of Two Cementless Short Stems for Hip Replacement: Linea Anatomic and Minihip

Medium-term outcome of the Libra® cemented versus cementless stems in primary dual mobility total hip arthroplasty

INTRODUCTION

Despite the increasing use of cementless stems in total hip arthroplasty, the cemented stem has played a valuable role in the armamentarium of orthopedic surgeons. This study aims to compare two types of Libra® stems SERF, one cemented (Libra® C) and the other cementless hydroxyapatite coated (Libra® HA) that were conducted to analyze the medium-term outcome regarding their behavior and longevity.

METHODS

This is a retrospective study for patients who received primary total hip arthroplasty with Dual Mobility (DM) articulation in the period between January 2014 to January 2020 with a minimum of two years follow-up. Two-hundred hips have been identified in 196 patients. One hundred forty-three Libra® cementless versus fifty-seven Libra cemented stems were implanted and the outcome of these stems is reported. All procedures were performed through the posterior approach and cemented stems were selected for elderly patients with wide medullary canals Dorr Type C. The indications for the index procedure were fractures, avascular necrosis, rheumatoid, and osteoarthritis. One hundred thirty-nine cementless DM cups were used while sixty-one hips had cemented Novae stick cups. Radiological evaluation for cup and stem positions, cement mantle, and radiolucent lines was performed, besides clinical function using the Harris Hip Score.

RESULTS

The average age of patients was 60 ± 14.8. At the latest review, none of the cemented stems was revised or awaiting revision. One cementless stem was revised because of cortical perforation. Five intraoperative fractures were observed in the cementless group, but none of them needed revision or affected the stem stability. Readmission to theatre occurred in four patients to evacuate hematoma in two, a reduction of dislocation in one, and grafting bone lysis in one.

CONCLUSION

Cemented stems have an important role in osteoporotic patients with wide medullary canals with excellent outcomes and minimal risk of fracture.

LEVEL OF EVIDENCE

Level IV.

Patient-specific three-dimensional evaluation of interface micromotion in two different short stem designs in cementless total hip arthroplasty: a finite element analysis

Background

Evaluation of micromotion in various activities in daily life is essential to the assessment of the initial fixation of cementless short stems in total hip arthroplasty. This study sought to evaluate three-dimensionally the micromotion of two types of cementless short stems.

Methods

Two types of stems were used: the Fitmore stem with a rectangular cross-section (rectangular stem) and the octagonal-oval GTS stem with fins (finned stem). Finite element analysis was used to calculate the micromotion of two activities that place a heavy load on the stem (single-leg stance and stair climbing). Three values were measured: the magnitude of micromotion (mean and 95th percentile), the location of micromotion above the 95th percentile value, and the directions of the micromotion vector.

Results

1. There was no significant difference in the magnitude of the micromotion between the rectangular stem and finned stem groups for single-leg stance or stair climbing. 2. In both groups, the micromotion was greatest at the proximal and distal ends. 3. The direction of the micromotion was similar in both groups; internal rotation occurred from the distal to the middle of the stem during stair climbing.

Conclusions

The rectangular stem had comparable initial fixation to that of the finned stem. In both models, the micromotion was greater at the proximal and distal ends. The direction of the micromotion was not dependent on the stem shape but on the direction of the load on the artificial femoral head. These results will be important for stem selection and future stem development.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-022-03329-5.

High prevalence and undertreatment of osteoporosis in elderly patients undergoing total hip arthroplasty

We detected a high prevalence of low bone mineral density assessed by DXA in 268 elderly patients with end-stage osteoarthritis scheduled for total hip arthroplasty (18% osteoporosis, 41% osteopenia). Therefore, and due to the identified concomitant undertreatment, routine DXA measurements should be considered in elderly patients prior to surgery.

INTRODUCTION

Bone quality represents a decisive factor for osseointegration, durability, and complications of an implanted prosthesis. Although the risk of osteoporosis increases with age and the assessment of bone mineral density (BMD) prior to total hip arthroplasty (THA) is recommended in elderly patients, a systematic, unbiased analysis of such patients is not available in the literature.

METHODS

In this retrospective study, we examined 268 elderly patients (age ≥70 years) who underwent dual-energy X-ray absorptiometry (DXA) within 3 months prior to primary THA. Demographics, medical history, radiographic OA grade, and stem fixation method (i.e., cemented or cementless) were obtained.

RESULTS

In total, 153 (57%) cemented and 115 (43%) cementless stem fixations during THA were performed. Forty-nine patients (18%) were diagnosed with osteoporosis (T-score ≤-2.5), 110 patients (41%) with osteopenia (T-score ≤-1.0), and 109 patients (41%) with normal BMD (T-score >-1.0). Importantly, 36/49 patients (73%) with osteoporosis were not diagnosed before, resulting in a relevant undertreatment. Female sex and low body mass index (BMI) were the main factors negatively influencing the bone mineral density (BMD).

CONCLUSIONS

Due to a high incidence of undiagnosed and untreated osteoporosis in elderly patients with potential effects on the success of osseointegration as well as other clinical outcomes, DXA measurements should be included in the clinical routine for these patients prior to THA.

Transcript-Activated Coatings on Titanium Mediate Cellular Osteogenesis for Enhanced Osteointegration

Osteointegration is one of the most important factors for implant success. Several biomolecules have been used as part of drug delivery systems to improve implant integration into the surrounding bone tissue. Chemically modified mRNA (cmRNA) is a new form of therapeutic that has been used to induce bone healing. Combined with biomaterials, cmRNA can be used to develop transcript-activated matrices for local protein production with osteoinductive potential. In this study, we aimed to utilize this technology to create bone morphogenetic protein 2 (BMP2) transcript-activated coatings for titanium (Ti) implants. Therefore, different coating methodologies as well as cmRNA incorporation strategies were evaluated. Three different biocompatible biomaterials were used for the coating of Ti, namely, poly-d,l-lactic acid (PDLLA), fibrin, and fibrinogen. cmRNA-coated Ti disks were assayed for transfection efficiency, cmRNA release, cell viability and proliferation, and osteogenic activity in vitro. We found that cmRNA release was significantly delayed in Ti surfaces previously coated with biomaterials. Consequently, the transfection efficiency was greatly improved. PDLLA coating improved the transfection efficiency in a concentration-dependent manner. Lower PDLLA concentration used for the coating of Ti resulted in higher transfection efficiency. Fibrin and fibrinogen coatings showed even higher transfection efficiencies compared to all PDLLA concentrations. In those disks, not only the expression was up to 24-fold higher but also the peak of maximal expression was delayed from 24 h to 5 days, and the duration of expression was also extended until 7 days post-transfection. For fibrin, higher transfection efficiencies were obtained in the coatings with the lowest thrombin amounts. Accordingly, fibrinogen coatings gave the best results in terms of cmRNA transfection. All biomaterial-coated Ti surfaces showed improved cell viability and proliferation, though this was more noticeable in the fibrinogen-coated disks. The latter was also the only coating to support significant amounts of BMP2 produced by C2C12 cells in vitro. Osteogenesis was confirmed using BMP2 cmRNA fibrinogen-coated Ti disks, and it was dependent of the cmRNA amount present. Alkaline phosphatase (ALP) activity of C2C12 increased when using fibrinogen coatings containing 250 ng of cmRNA or more. Similarly, mineralization was also observed that increased with increasing cmRNA concentration. Overall, our results support fibrinogen as an optimal material to deliver cmRNA from titanium-coated surfaces.

The experience of an indipendent center with the MINIHIP® femoral stem

The implantation of short femoral stems has significantly increased over the past decade, thanks to their preservation of bone stock, allowing for easier potential revision of components and physiological joint reconstruction. Their main features are metaphyseal fixation and partial retention of the femoral neck which lead to biomechanical advantages and high stability. They also guarantee the preservation of bone stock and insertion through minimally invasive approaches. Fifty-one non-consecutive patients with osteoarthritis or avascular necrosis were treated by two senior surgeons with total hip arthroplasty (THA) with anterior or anterolateral approach between April 2013 and October 2016. Cementless short femoral stem monobloc (Minihip, Corin, Cirencester, UK) was implanted in all patients who were studied retrospectively. Radiographic outcome was analyzed and clinical outcomes were assessed with Harris Hip Score (HHS), Hip handicap and Osteaorthritis Outcome Score (HOOS) and Oxford Hip Score (OHS). Based on radiological results we did not find periprosthetic osteolysis while bone resorption was evaluated in 5 implants which were classified according to Gruen. The MiniHip stem demonstrates adequate metaphyseal grip, excellent implant stability to ensure implant survival.

Biomechanics of a cemented short stem: a comparative in vitro study regarding primary stability and maximum fracture load

PURPOSE

In total hip arthroplasty, uncemented short stems have been used more and more frequently in recent years. Especially for short and curved femoral implants, bone-preserving and soft tissue-sparing properties are postulated. However, indication is limited to sufficient bone quality. At present, there are no curved short stems available which are based on cemented fixation.

METHODS

In this in vitro study, primary stability and maximum fracture load of a newly developed cemented short-stem implant was evaluated in comparison to an already well-established cemented conventional straight stem using six pairs of human cadaver femurs with minor bone quality. Primary stability, including reversible micromotion and irreversible migration, was assessed in a dynamic material-testing machine. Furthermore, a subsequent load-to-failure test revealed the periprosthetic fracture characteristics.

RESULTS

Reversible and irreversible micromotions showed no statistical difference between the two investigated stems. All short stems fractured under maximum load according to Vancouver type B3, whereas 4 out of 6 conventional stems suffered a periprosthetic fracture according to Vancouver type C. Mean fracture load of the short stems was 3062 N versus 3160 N for the conventional stems (p = 0.84).

CONCLUSION

Primary stability of the cemented short stem was not negatively influenced compared to the cemented conventional stem and no significant difference in fracture load was observed. However, a clear difference in the fracture pattern has been identified.

Comparative analysis of the biomechanical behavior of two different design metaphyseal-fitting short stems using digital image correlation

BACKGROUND

The progressive evolution in hip replacement research is directed to follow the principles of bone and soft tissue sparing surgery. Regarding hip implants, a renewed interest has been raised towards short uncemented femoral implants. A heterogeneous group of short stems have been designed with the aim to approximate initial, post-implantation bone strain to the preoperative levels in order to minimize the effects of stress shielding. This study aims to investigate the biomechanical properties of two distinctly designed femoral implants, the TRI-LOCK Bone Preservation Stem, a shortened conventional stem and the Minima S Femoral Stem, an even shorter and anatomically shaped stem, based on experiments and numerical simulations. Furthermore, finite element models of implant-bone constructs should be evaluated for their validity against mechanical tests wherever it is possible. In this work, the validation was performed via a direct comparison of the FE calculated strain fields with their experimental equivalents obtained using the digital image correlation technique.

RESULTS

Design differences between Trilock BPS and Minima S femoral stems conditioned different strain pattern distributions. A distally shifting load distribution pattern as a result of implant insertion and also an obvious decrease of strain in the medial proximal aspect of the femur was noted for both stems. Strain changes induced after the implantation of the Trilock BPS stem at the lateral surface were greater compared to the non-implanted femur response, as opposed to those exhibited by the Minima S stem. Linear correlation analyses revealed a reasonable agreement between the numerical and experimental data in the majority of cases.

CONCLUSION

The study findings support the use of DIC technique as a preclinical evaluation tool of the biomechanical behavior induced by different implants and also identify its potential for experimental FE model validation. Furthermore, a proximal stress-shielding effect was noted after the implantation of both short-stem designs. Design-specific variations in short stems were sufficient to produce dissimilar biomechanical behaviors, although their clinical implication must be investigated through comparative clinical studies.

Migration analysis of a metaphyseal-anchored short femoral stem in cementless THA and factors affecting the stem subsidence

Background

Early femoral stem subsidence following a cementless THA is correlated with aseptic loosening of the femoral component. The short femoral stems allow bone sparing and implantation through a minimally invasive approach; however, due to their metaphyseal anchoring, they might demonstrate different subsidence pattern than the conventional stems.

Methods

In this prospective single-center study, a total of 68 consecutive patients with an average age of 63 years, and a minimum follow-up of 5 years following a cementless THA with a metaphyseal-anchored short femoral stem were included. The femoral stem subsidence was evaluated using “Ein Bild Roentgen Analyse” (EBRA).

Results

Average stem migration was 0.96 +/− 0.76 mm at 3 months, 1.71 +/− 1.26 mm at 24 months, and 2.04+/− 1.42 mm at last follow-up 60 months postoperative. The only factor that affected migration was a stem size of 6 or more (r² = 5.74; p = 0.039). Subdivision analysis revealed, that only in females migration appeared to be affected by stem size irrespective of weight but not in men (female stem size of 6 or more vs. less (Difference = − 1.48 mm, R² = 37.5; p = 0.001). Migration did not have an impact on clinical outcome measures.

Conclusions

The examined metaphyseal-anchored short femoral stem showed the highest subsidence within the first 3 months postoperative, the implant began to stabilize at about 24 months but continued to slowly migrate with average total subsidence of 2.04 mm at 5 years following the THA. The amount of stem subsidence was not associated with worse clinical outcomes such as HHS, patient satisfaction, or pain.

Short stems have lower load at failure than double-wedged stems in a cadaveric cementless fracture model

Objectives

Periprosthetic femoral fractures (PFFs) have a higher incidence with cementless stems. The highest incidence among various cementless stem types was observed with double-wedged stems. Short stems have been introduced as a bone-preserving alternative with a higher incidence of PFF in some studies. The purpose of this study was a direct load-to-failure comparison of a double-wedged cementless stem and a short cementless stem in a cadaveric fracture model.

Methods

Eight hips from four human cadaveric specimens (age mean 76 years (60 to 89)) and eight fourth-generation composite femurs were used. None of the cadaveric specimens had compromised quality (mean T value 0.4 (-1.0 to 5.7)). Each specimen from a pair randomly received either a double-wedged stem or a short stem. A materials testing machine was used for lateral load-to-failure test of up to a maximal load of 5000 N.

Results

Mean load at failure of the double-wedged stem was 2540 N (1845 to 2995) and 1867 N (1135 to 2345) for the short stem (p < 0.001). All specimens showed the same fracture pattern, consistent with a Vancouver B2 fracture. The double-wedged stem was able to sustain a higher load than its short-stemmed counterpart in all cases. Failure force was not correlated to the bone mineral density (p = 0.718).

Conclusion

Short stems have a significantly lower primary load at failure compared with double-wedged stems in both cadaveric and composite specimens. Surgeons should consider this biomechanical property when deciding on the use of short femoral stem.

Cite this article: A. Klasan, M. Bäumlein, P. Dworschak, C. Bliemel, T. Neri, M. D. Schofer, T. J. Heyse. Short stems have lower load at failure than double-wedged stems in a cadaveric cementless fracture model. Bone Joint Res 2019;8:489–494. DOI: 10.1302/2046-3758.810.BJR-2019-0051.R1.

Stem length in primary cementless total hip arthroplasty: Does it make a difference in bone remodeling?

PURPOSE

Stem design is usually accused for proximal femoral remodeling following total hip arthroplasty (THA). The aim of this prospective study was to compare the in vivo changes in bone mineral density (BMD) of the proximal femur after implantation of cementless THA with two length alternative stems.

METHODS

Between May 2011 and March 2014, 50 patients, who met our selection criteria and received cementless THA, randomized into two groups. Group A received cementless standard femoral stems, while group B received short stems. Harris Hip Score (HHS) and visual analog scale (VAS) were used for clinical assessment. Stem and cup positions and stability were radiologically evaluated. Dual-energy X-ray absorptiometry was used to follow and compare changes in BMD in different zones of proximal femur between both groups.

RESULTS

After a mean follow-up of 21.4 ± 3.53 months, there was a significant (p < 0.05) improvement in mean HHS and VAS with no significant differences (p > 0.05) between groups. There was no significant difference (p > 0.05) between groups regarding radiological results and rates of complications. The mean overall BMD was decreased by 11.26% for group A and 8.68% for group B at the final follow-up (p > 0.05). The greatest loss was found in greater trochanter region for group A and so for group B, but to a lesser extent (p < 0.05).

CONCLUSIONS

Cementless short stem was not able to hold back proximal femoral bone loss, but only can modify or decrease its incidence within limits.

Anatomic grooved stem mitigates strain shielding compared to established total hip arthroplasty stem designs in finite-element models

Aseptic loosening remains a major problem for uncemented femoral components in primary total hip arthroplasty (THA). Ideally, bone adaptation after THA manifests minimally and local bone density reduction is widely avoided. Different design features may help to approximate initial, post-THA bone strain to levels pre-THA. Strain-shielding effects of different SP-CL stem design features are systematically analyzed and compared to CLS Spotorno and CORAIL using finite element models and physiological musculoskeletal loading conditions. All designs show substantial proximal strain-shielding: 50% reduced medial surface strain, 40–50% reduction at lateral surface, >120 µm/m root mean square error (RMSE) compared to intact bone in Gruen zone 1 and >60 µm/m RMSE in Gruen zones 2, 6, and 7. Geometrical changes (ribs, grooves, cross sections, stem length, anatomic curvature) have a considerable effect on strain-shielding; up to 20%. Combinations of reduced stem stiffness with larger proximal contact area (anatomically curved, grooves) lead to less strain-shielding compared to clinically established implant designs. We found that only the combination of a structurally flexible stem with anatomical curvature and grooves improves strain-shielding compared to other designs. The clinical implications in vivo of this initial strain-shielding difference are currently under evaluation in an ongoing clinical analysis.