Comparison of two hydroxyapatite-coated femoral stems: clinical, functional, and bone densitometry evaluation of patients randomized to a regular or modified hydroxyapatite-coated stem aimed at proximal fixation

When the Total Hip Replacement Fails: A Review on the Stress-Shielding Effect

Total hip arthroplasty is one of the most common and successful orthopedic surgeries. Sometimes, periprosthetic osteolysis occurs associated with the stress-shielding effect: it results in the reduction of bone density, where the femur is not correctly loaded, and in the formation of denser bone, where stresses are confined. This paper illustrates the stress shielding effect as a cause of the failing replacement of the hip joint. An extensive literature survey has been accomplished to describe the phenomenon and identify solutions. The latter refer to the design criteria and the choice of innovative materials/treatments for prosthetic device production. Experimental studies and numerical simulations have been reviewed. The paper includes an introduction to explain the scope; a section illustrating the causes of the stress shielding effect; a section focusing on recent attempts to redefine prosthetic device design criteria, current strategies to improve the osteointegration process, and a number of innovative biomaterials; functionally graded materials are presented in a dedicated section: they allow customizing prosthesis features with respect to the host bone. Conclusions recommend an integrated approach for the production of new prosthetic devices: the “engineering community” has to support the “medical community” to assure an effective translation of research results into clinical practice.

Do Cementless Short Tapered Stems Reduce the Incidence of Thigh Pain After Hip Arthroplasty? Systematic Review and Meta-Analysis

BACKGROUND

The purpose of this study was to determine whether short tapered stems reduce the rate of thigh pain through a systematic review and meta-analysis of comparative studies between short tapered stems and standard-length tapered stems.

METHODS

We conducted a meta-analysis of comparative studies: 1) retrospective studies and 2) randomized controlled trials (RCTs), on 2 stem designs: short tapered stem versus standard-length tapered stem. Studies were selected by means of the following criteria: 1) study design: retrospective comparative studies, prospective comparative studies, RCTs; 2) study population: patients with total hip arthroplasty or hemiarthroplasty for hip disease or hip fracture; 3) intervention: short tapered stem and standard tapered stem; and 4) outcomes; thigh pain, other clinical results.

RESULTS

Among the 250 articles that were identified at the initial search, 6 studies, 4 RCTs and 2 retrospective comparative studies, were included in this meta-analysis. In the analysis of retrospective studies, the short tapered stem reduced the risk of thigh pain compared to the standard tapered stem (risk ratio [RR] = 0.13; 95% confidence interval [CI], 0.02-0.09; Z = -2.07; P = 0.039). However, in the analysis of RCTs, the incidence of thigh pain was similar between the two stem designs (RR = 1.21; 95% CI, 0.76-1.93; Z = 0.82; P = 0.410). Overall meta-analysis including all studies showed that the short tapered stem did not reduce the incidence of thigh pain compared to the standard-length tapered stem (RR = 0.91; 95% CI, 0.59-1.40; Z = -0.44, P = 0.663).

CONCLUSIONS

We did not find a significant difference in the incidence of thigh pain between short tapered stem and standard tapered stem in hip arthroplasty.

TRIAL REGISTRATION

PROSPERO Identifier: CRD42021231240.

Short-term success of proximal bone stock preservation in short hip stems: a systematic review of the literature

Total hip arthroplasty is performed more frequently in younger patients nowadays, making long-term bone stock preservation an important topic. A mechanism for late implant failure is periprosthetic bone loss, caused by stress shielding around the hip stem due to different load distribution. Short stems are designed to keep the physical loading in the proximal part of the femur to reduce stress shielding. The aim of this review is to give more insight into how short and anatomic stems behave and whether they succeed in preservation of proximal bone stock.

A systematic literature search was performed to find all published studies on bone mineral density in short and anatomic hip stems. Results on periprosthetic femoral bone mineral density, measured with dual-energy X-ray absorptiometry (DEXA), were compiled and analysed per Gruen zone in percentual change.

A total of 29 studies were included. In short stems, Gruen 1 showed bone loss of 5% after one year (n = 855) and 5% after two years (n = 266). Gruen 7 showed bone loss of 10% after one year and –11% after two years. In anatomic stems, Gruen 1 showed bone loss of 8% after one year (n = 731) and 11% after two years (n = 227). Gruen 7 showed bone loss of 14% after one year and 15% after two years.

Short stems are capable of preserving proximal bone stock and have slightly less proximal bone loss in the first years, compared to anatomic stems.

Cite this article: EFORT Open Rev 2021;6:1040-1051. DOI: 10.1302/2058-5241.6.210030

No Clinically Important Differences in Thigh Pain or Bone Loss Between Short Stems and Conventional-length Stems in THA: A Randomized Clinical Trial

BACKGROUND

Short-length stems were developed to reduce bone loss of the proximal femur and potentially decrease the incidence of thigh pain after cementless THA. However, it remains unknown whether short stems indeed reduce bone loss or the frequency of thigh pain.

QUESTIONS/PURPOSES

Is there a difference between short- and standard-length stems in terms of: (1) the frequency or severity of thigh pain, (2) modified Harris hip scores, (3) implant loosening, or (4) bone mineral density as measured by dual-energy x-ray absorptiometry?

METHODS

Between March 2013 and January 2014, three surgeons performed 205 primary THAs. To be eligible, patients needed to be at least 20 years of age, have not undergone previous history of hip surgery, and have no metabolic bone disease. A total of 100 patients were randomized to receive THA either with a short stem (n = 56) or with a standard-length stem (n = 44). Both stems were proximally coated, tapered, cementless stems. Compared with standard stems, short stems typically were 30- to 35-mm shorter. A total of 73% (41 of 56) and 77% (34 of 44) of those groups, respectively, were accounted for at a minimum of 5 years and were analyzed. The presence of thigh pain during activity was evaluated using a 10-point VAS, and the modified Harris hip score was calculated by research assistants who were blinded to the treatment groups. Plain radiographs were taken at 6 weeks, 6 months, and 12 months postoperatively, and every 1 year thereafter; loosening was defined as subsidence > 3 mm or a position change > 3° on serial radiographs. Radiological assessment was performed by two researchers who did not participate in the surgery and follow-up evaluations. Bone mineral density of the proximal femur was measured using dual-energy x-ray absorptiometry at 4 days, 1 year, 2 years, and 5 years postoperatively. The primary endpoint of our study was the incidence of thigh pain during 5-year follow-up. Our study was powered at 80% to detect a 10% difference in the proportion of patients reporting thigh pain at the level of 0.05.

RESULTS

With the numbers available, we found no difference between the groups in the proportion of patients with thigh pain; 16% (9 of 56) of patients in the short-stem group and 14% (6 of 44) of patients in the standard-stem group experienced thigh pain during the follow-up period (p = 0.79). In all patients, the pain was mild or moderate (VAS score of 4 or 6 points). Among the 15 available patients who reported thigh pain, there was no difference between the implant groups in mean severity of thigh pain (4.3 ± 0.8 versus 4.2 ± 0.7; p = 0.78). There were no between-group differences in the short versus standard-length stem groups in terms of mean modified Harris hip score by 5 years after surgery (89 ± 13 versus 95 ± 7 points; p = 0.06). No implant was loose and no hip underwent revision in either group. Patients in the short-stem group showed a slightly smaller decrease in bone mineral density in Gruen Zones 2, 3, and 5 than those in the standard-stem group did; the magnitude of the difference seems unlikely to be clinically important.

CONCLUSION

We found no clinically important differences (and few differences overall) between short and standard-length THA stems 5 years after surgery in a randomized trial. Consequently, we recommend that clinicians use standard-length stems in general practice because standard-length stems have a much longer published track record in other studies, and short stems can expose patients to the uncertainty associated with novelty, without any apparent offsetting benefit.

LEVEL OF EVIDENCE

Level I, therapeutic study.

A comparison of short-stem prostheses and conventional stem prostheses in primary total hip arthroplasty: a systematic review and meta-analysis of randomized controlled trials

Background

In total hip arthroplasty (THA), short-stem prostheses (SS) were designed to achieve better preservation of proximal femoral bone stock and stability than conventional stem prostheses (CS), however these effects are controversial. We aimed perform a systematic review and meta-analysis to evaluate the effectiveness of SS and CS in primary THA.

Methods

Relevant randomized controlled trials (RCTs) involving the comparison of SS and CS in primary THA were screened using the electronic databases PubMed, Embase and Web of Science. Data were analyzed with the RevMan 5.3 software program and evaluated with mean difference (MD), risk ratio (RR) and 95% confidence intervals (CIs) by random or fixed-effect models.

Results

Sixteen RCTs involving 1,233 patients (1,486 hips) were included. Compared with CS, the incidence of thigh pain was significantly reduced with Proxima SS (RR 0.13, 95% CI, 0.03–0.51; P=0.004). Bone mineral density (BMD) with femoral neck-preserved SS [SS (I)] showed less decrease in Gruen zone 1 (MD 14.60, 95% CI, 10.67–18.54; P<0.00001) and Gruen zone 7 (MD 9.72, 95% CI, 5.21–14.23; P<0.0001) than CS. However, the changes of BMD were not significantly different between the SS without femoral neck preservation group [SS (II)] and the CS group. In addition, no significant differences were found in the revision rate, Harris Hip Score (HHS), or maximum total point motion (MTPM) between the SS and CS groups.

Conclusions

The results of this study showed that compared with CS, Proxima SS decreased the incidence of thigh pain and that SS (I) provided better proximal bone remodeling than CS. But the revision rates, HHS, and MTPM between SS and CS were similar. However, the findings of this meta-analysis require further verification in high-quality RCTs.

Comparison of 5-year postoperative results between standard-length stems and short stems in one-stage bilateral total hip arthroplasty: a randomized controlled trial

PURPOSE

Short stems have recently become popular in total hip arthroplasty. Previous studies aimed at elucidating the efficacy of short stems did not eliminate the influence of other factors aside from stem length. This study aimed to evaluate the usefulness of short stems compared with that of standard-length stems that have the same proximal morphology, surface coating, and material.

METHODS

This was a prospective randomized study comparing 5-year midterm outcomes in 29 patients who underwent one-stage bilateral total hip arthroplasty with short and standard-length stems inserted in each of the two femurs. Clinical, radiographical, and dual-energy X-ray absorptiometry outcomes were compared.

RESULTS

No significant differences were found in perioperative and radiographic characteristics (femoral neck anteversion, flare index, operation sequence, operation side, operation time, stem anteversion, and stem alignment). The number of joints with complications, appearance of radiopaque lines around the stems, or bone mineral density changed in stem regions 5 years postoperatively. However, greater micromotion of the stem was seen on the side of the short stem. Satisfactory improvement in hip function was seen on both sides.

CONCLUSION

Based on the 5-year midterm outcomes, both stems obtained satisfactory clinical outcomes despite the greater micromotion with short stems. Both stems attained bone ingrowth fixation. Moreover, the stems were not significantly different in terms of stress shielding; however, further long-term studies (> 5 years) are required to validate our findings related to stress shielding.

Biomechanical Analysis to Probe Role of Bone Condition and Subject Weight in Stiffness Customization of Femoral Stem for Improved Periprosthetic Biomechanical Response

Stress shielding due to difference in stiffness of bone and implant material is one among the foremost causes of loosening and failure of load-bearing implants. Thus far, femoral geometry has been given priority for the customization of total hip joint replacement (THR) implant design. This study, for the first time, demonstrates the key role of bone condition and subject-weight on the customization of stiffness and design of the femoral stem. In particular, internal hollowness was incorporated to reduce the implant stiffness and such designed structure has been customized based on subject parameters, including bone condition and bodyweight. The primary aim was to tailor these parameters to achieve close to natural strain distribution at periprosthetic bone and to reduce interfacial bone loss over time. The maintenance of interfacial bone density over time has been studied here through analysis of bone remodeling (BR). For normal bodyweight, the highest hollowness exhibited clinically relevant biomechanical response, for all bone conditions. However, for heavier subjects, consideration of bone quality was found to be essential as higher hollowness induced bone failure in weaker bones and implant failure in stronger bones. Moreover, for stronger bone, thinner medial wall was found to reduce bone resorption over time on the proximo-lateral zone of stress shielding, while lateral thinning was found advantageous for weaker bones. The findings of this study are likely to facilitate designing of femoral stems for achieving better physiological outcomes and enhancement of the quality of life of patients undergoing THR surgery.

A comparison of patient-reported outcome measures (PROMs) between short and conventional stem hip replacements: a systematic review and meta-analysis

INTRODUCTION

Short stem hip replacements may allow preservation of proximal bone stock and minimise soft tissue disruption, easing future revision surgery. However patient satisfaction with these implants must be determined before widespread use. We aimed to compare patient reported outcome measures (PROMs) between short and conventional stem hip replacements.

METHODS

A systematic review was conducted according to PRISMA guidelines for studies comparing short and conventional stem hip replacements with validated PROMs. Meta-analyses were performed for studies reporting Harris Hip and WOMAC scores. Study bias was assessed with the Cochrane Risk of Bias tool and Newcastle-Ottawa Scale.

RESULTS

24 studies, incorporating 2593 total hip replacements were included for qualitative analysis. 17 studies were included in the meta-analyses. Of the 7 excluded, 1 study reported the Japanese Orthopaedic Association score and 2 others reported the Oxford Hip score. All three showed no difference between the stems. A meta-analysis of 17 studies reporting Harris hip scores showed no statistically significant difference between short and conventional stems (standard mean difference (SMD) -0.06, 95% CI -0.20-0.07, p = 0.35). 6 studies reported WOMAC scores with higher scores indicating worse outcome. No difference was seen between the two groups (SMD 0.21, 95%CI, -0.01-0.42, p = 0.06). 4 studies reported higher WOMAC scores as better. Once again, a meta-analysis showed no statistically significant difference between the stems (SMD 0.28, 95% CI -0.07-0.63, p = 0.12).

CONCLUSIONS

Our systematic review showed no difference in PROMs between short and conventional stem total hip replacements. This is in keeping with previous evidence but is a more comprehensive analysis. Short stems may have an important role in younger individuals as they allow preservation of proximal femoral bone, minimal access surgery and are amenable to abnormal anatomy. The current literature is hindered by non-uniform methodologies and outcome assessments across studies. Further, standardised, high quality evidence is required before widespread changes in practice.

Comparison of Bone Preservation in Elderly Patients with Femoral Neck Fracture After Bipolar Hemiarthroplasty Using Shorter Femoral Stem and Standard Femoral Stem

BACKGROUND

This randomized control study was designed to compare the clinical and radiological outcomes, including periprosthetic bone mineral density (BMD) changes, between the short and standard stems after using cementless hemiarthroplasty in elderly patients with femur neck fractures.

MATERIALS AND METHODS

From January 2013 to May 2017, 151 patients (aged ≥ 65 years) underwent hemiarthroplasties due to femoral neck fractures. Patients were randomized into two groups; 77 patients in Group A implanting the short femoral stem and 74 patients in Group B implanting the standard femoral stem. Clinical and radiographic evaluations were performed in all patients.

RESULTS

75 patients (40 patients in Group A and 35 patients in Group B) completed routine follow-up for a minimum of 2 years. The clinical outcomes, including ambulatory functions and thigh pain, were similar in both groups. All the femoral stems acquired radiologic stability. At postoperative one year, BMD values in Gruen zone (G) seven on the standard stem side were significantly lower than those on the short stem side (P = 0.038). At the second year of follow-up, the BMD values of Group A in G1, G3, G4, and G7 were significantly greater than those of Group B (P = 0.007, 0.032, 0.026, and P < 0.000, respectively).

CONCLUSIONS

Both the clinical outcomes and radiologic stability in both group demonstrated similar results in elderly patients with femoral neck fracture at the latest follow-up. In addition, the periprosthetic BMD of the short femoral stems demonstrated better periprosthetic bone preservation at a minimum of 2 years of follow-up.

LEVEL OF EVIDENCES

Therapeutic Level II.

Preoperative Morphology of the Proximal Femoral Canal Did Not Affect the Postoperative Bone Mineral Density Change Around the Zweymüller-Type Stem

The bone mineral density (BMD) around a femoral component changes after total hip arthroplasty (THA). The aim of this study was to investigate the influence of the morphology of the preoperative proximal femoral canal on the postoperative BMD change of the femur around a Zweymüller-type stem. The authors performed a retrospective review of their institutional arthroplasty database. Patients were classified into following 3 groups according to canal flare index (CFI): CFI<3.0, stovepipe group; 3.0<CFI<4.7, normal group; and CFI>4.7, champagne-flute group. This study included 120 hips of 112 patients (26 hips with stovepipe femurs, 72 hips with normal femurs, and 22 hips with champagne-flute femurs) in patients who had undergone THA using the Zweymüller-type stem. The BMD of the proximal femur (Gruen's zones 1-7) was measured at 3 weeks and 6, 12, and 24 months postoperatively. At each follow-up period, the differences in the relative change in the BMD were not statistically significant in any regions of interest among the 3 groups. This study showed the lack of significant differences in the relative change in the BMD among the different morphologies of the proximal femoral canal. The preoperative morphology of the femoral canal did not affect the postoperative BMD change around the Zweymüller-type stem at 2 years postoperatively. [Orthopedics. 2019; 42(5):e449-e453.].

Are short-stem prostheses superior to conventional stem prostheses in primary total hip arthroplasty? A systematic review and meta-analysis of randomised controlled trials

OBJECTIVE

Cementless total hip arthroplasty (THA) is associated with reliable clinical results and high patient satisfaction. Short-stem prostheses (SS) were designed to achieve superior preservation of proximal bone stock and stability compared with those of conventional-stem prostheses (CS). This meta-analysis was conducted to determine the proximal bone remodelling, revision rate, Harris Hip Score, radiolucent line and maximum total point motion values of both SS and CS for primary THA.

METHOD

Relevant randomised controlled trials (RCTs) involving SS and CS in primary THA were identified from electronic databases, such as EMBASE, PubMed and the Cochrane Library.

RESULT

Ultimately, 12 RCTs involving 1130 patients (1387 hips) were included. The results showed that compared with CS, SS resulted in less bone mineral density (BMD) changes in Gruen zone 7 at 1 year and 2 years postoperatively (mean difference (MD)=5.11; 95% CI, 1.61, 8.61; P=0.30; and MD=4.90; 95% CI, 1.01, 8.79; P=0.17, respectively). No difference in BMD changes was found for Gruen zone 1 (MD=2.66; 95% CI, -3.31, 8.64; P<0.00001), and no differences were observed for the revision rate (relative risk (RR)=1.52; 95% CI, 0.71, 3.26; P=0.94), Harris Hip Score (MD=-0.38; 95% CI, -1.02, 0.26; P=0.89) or stem migration (MD=0.02; 95% CI, -0.07, 0.11; P=0.04).

CONCLUSION

Our results suggest that compared with CS, SS may provide superior bone remodelling and similar survival rates and clinical outcomes. However, the short-term follow-up of the included studies was inadequate to determine the long-term performance of SS.

Periprosthetic bone remodeling of short cementless femoral stems in primary total hip arthroplasty: A systematic review and meta-analysis of randomized-controlled trials

BACKGROUND

Short-stem total hip arthroplasty (SHA) has been increasingly used in the treatment of hip arthroplasty. However, it is unclear whether there is a superiority of SHA in periprosthetic bone remodeling over standard stem total hip arthroplasty (THA). This meta-analysis of randomized-controlled trials (RCTs) compared the periprosthetic bone remodeling after SHA and THA.

METHODS

PubMed and Embase were screened for relevant publications up to May 2017. RCTs that compared periprosthetic bone remodeling with bone mineral density (BMD) changes between SHA and THA were included. Meta-analysis was conducted to calculate weighted mean differences (WMDs) and 95% confidence intervals (CIs) using Stata version 12.0. Quality appraisal was performed by 2 independent reviewers using RevMan 5.3 software and Grades of Recommendation Assessment, Development, and Evaluation criteria.

RESULTS

Seven studies involving 910 patients and 5 SHA designs (Proxima, Fitmore, Microplasty short, Unique custom, and Omnifit-HA 1017) were included for meta-analysis. The pooled data showed no significant differences in the percentage BMD changes in all Gruen zones, with Gruen zone 1 [mean difference (MD) = 11.33, 95% CI, -1.67 to 24.33; P = .09] and Gruen zone 7 (MD = 8.46, 95% CI, -1.73 to 18.65; P = .10). Subgroup analysis of short SHA stems with lateral flare showed a significant less percentage BMD changes compared with standard THA in Gruen zone 1 (MD = 27.57, 95% CI, 18.03-37.12; P < .0001) and Gruen zone 7 (MD = 18.54, 95% CI, 8.27-28.81; P < .0001).

CONCLUSION

The study shows moderate-quality evidence that periprosthetic bone remodeling around the analyzed SHA stems was similar to standard THA stems. However, short SHA stems with lateral flare revealed a moderate- to low-quality evidence for superiority over the standard THA and highlighted the importance of the different SHA designs. Besides, it has to be noticed that despite a similar pattern of periprosthetic bone remodeling, the femoral length where periprosthetic bone remodeling occurs is clearly shorter in SHA. Due to the moderate- to low-quality evidence and the limited stem designs analyzed, the further large-scale multicenter RCTs including the most recent SHA designs are required. However, the current findings should be considered by surgeons for counseling patients regarding total hip replacement.

Comparison of Bone Remodeling Between an Anatomic Short Stem and a Straight Stem in 1-Stage Bilateral Total Hip Arthroplasty

BACKGROUND

Femurs of dysplastic hips exhibit specific abnormalities, and use of modular or specially designed components is recommended. An anatomic short stem was previously designed specifically for dysplastic hips using 3-dimensional data acquired from dysplastic patients. To investigate effects of stem geometry on bone remodeling, we undertook a prospective, randomized study of patients who had undergone 1-stage bilateral total hip arthroplasty (THA) with the anatomic short stem on one side and a conventional straight stem on the other.

METHODS

The study included 36 patients who underwent the above THA procedure. We assessed bone mineral density as well as the presence of cancellous condensation or bony atrophy due to stress shielding based on the analysis of Gruen's zones and newly defined equal-interval zones, at an average follow-up period of 9.2 years.

RESULTS

All stems were bone ingrown stable. Cancellous condensation was observed more proximally, and areas of bone atrophy were narrower on the anatomic short stem side than on the straight stem side. Bone mineral density values reflected results of cancellous condensation and stress shielding and were higher in more proximal zones on the anatomic short stem side than on the straight stem side.

CONCLUSION

Although radiographic results indicated good midterm outcomes of THA with both stems, the loading pattern differed. The anatomic short stem achieved its design purpose in terms of proximal fixation and load transfer and led to better preservation of the proximal femur.

Comparison of proximal humeral bone stresses between stemless, short stem, and standard stem length: a finite element analysis

BACKGROUND

The stem lengths of humeral components used in shoulder arthroplasty vary; however, the literature on these devices is limited. This finite element study investigates the effect of humeral component length on stresses in the proximal humerus.

METHODS

Intact and 3 reconstructed (standard length, short, and stemless implants) finite element models were created from shoulder computed tomography scan data (N = 5). Loading was simulated at varying abduction angles (15°, 45°, and 75°). The average bone stress (represented as a percentage of intact values) was reported at 8 transverse slices. In addition, the overall average change in cortical and trabecular bone stresses was quantified.

RESULTS

Cortical bone stresses in the most proximal slice for the standard (58% ± 12%) and short (78% ± 10%) stem models were significantly reduced compared with the intact (100%) and stemless (101% ± 6%) models (P = .005). These reductions persisted in the second cortical slice for the standard stem compared with the intact, stemless, and short models (P = .025). Interestingly, stresses in the trabecular bone within these proximal slices were significantly elevated when stemless implants were used compared with all other implants (P < .001), regardless of abduction angle.

CONCLUSION

Reducing stem length produced humeral stresses that more closely matched the intact stress distribution in proximal cortical bone. Opposing trends presented in the proximal trabecular bone, probably because of differences in load transfer when shorter stems are used. Accordingly, the results suggest that implant stem length is 1 variable that can be modified in an attempt to better mimic intact bone stresses during humeral component insertion, provided stem fixation is adequate.

Trade-off between stress shielding and initial stability on an anatomical cementless stem shortening: in-vitro biomechanical study

Shortened cementless femoral stems have become popular with the advent of minimally invasive total hip arthroplasty (THA). Successful THA requires initial stem stability and prevention of stress shielding-mediated bone loss, although the effect of stem shortening is controversial. Here we experimentally examined whether stem shortening affects stress shielding and initial stability. Anatomical stems (length, 120 mm) were cut to an 80 mm or 50 mm length. Ten tri-axial strain gauges measured the cortical strain on each stem-implanted femur to evaluate stress shielding. Two transducers measured axial relative displacement and rotation under single-leg stance loading. The 50 mm stem increased the equivalent strains with respect to the original stem in the proximal calcar region (31.0% relative to intact strain), proximal medial region (63.1%), and proximal lateral region (53.9%). In contrast, axial displacement and rotation increased with a decreasing stem length. However, the axial displacement of the 50 mm stem was below a critical value of 150 µm for bone ingrowth. Our findings indicate that, with regard to a reduction in stem length, there is a tradeoff between stress shielding and initial stability. Shortening the stem up to 50 mm can promote proximal load transfer, but bone loss would be inevitable, even with sufficient initial stability for long-term fixation.

Long-term response of femoral density to hip implant and bone fracture plate: Computational study using a mechano-biochemical model

Although bone fracture plates can provide appropriate stability at the fracture site and lead to early patient mobilization, they significantly change the loading pattern in the bone after union (Stress shielding). This phenomenon results in a bone density decrease, which may cause premature failure of the implant. This paper presents the first study that quantifies the long-term response of femoral density to hip implantation and plating (lateral and anterior plating) using a mechano-biochemical model which considers the coupling effect between mechanical loading and biochemical affinities as stimuli for bone remodeling. The results showed that the regions directly beneath the plate experienced severe bone loss (i.e. up to ∼ -70%). However, some level of bone formation was observed in the vicinity of the most proximal and distal screw holes in both lateral and anterior plated femurs (i.e. up to ∼ +110%). The bone under the plate was divided into six zones. With respect to bone remodeling response, the findings revealed that anterior plating was not superior to lateral plating since the maximum and average bone losses among the zones in the anterior plated femur (i.e. -36% and -24%, respectively) were approximately the same as their corresponding values in the lateral plated femur (i.e. -38% and -24%, respectively).

Comparison of Different Materials and Proximal Coatings Used for Femoral Components in One-Stage Bilateral Total Hip Arthroplasty

To evaluate the mid-term effects of different materials and coatings used for femoral components, we prospectively performed 21 one-stage bilateral total hip arthroplasties using 2 anatomical stems which have identical geometries, randomized to side. One stem was made of Ti6Al4V alloy and had a hydroxyapatite coating on grit-blasted surface proximally, and the other was made of TMZF™ alloy and had a proximal coating of hydroxyapatite in addition to an arc-deposited titanium surface coating. Although we found extensions of radiopaque lines to the surface of coatings of seven grit-blasted stems whereas we found none in the case of the arc-deposited titanium stems, all hips showed excellent clinical and radiological outcomes as shown by radiographs and bone mineral density at the final follow-up, average 5.5 years postoperatively.

Total hip replacement and surface replacement for the treatment of pain and disability resulting from end-stage arthritis of the hip (review of technology appraisal guidance 2 and 44): systematic review and economic evaluation

BACKGROUND

Total hip replacement (THR) involves the replacement of a damaged hip joint with an artificial hip prosthesis. Resurfacing arthroplasty (RS) involves replacement of the joint surface of the femoral head with a metal surface covering.

OBJECTIVES

To undertake clinical effectiveness and cost-effectiveness analysis of different types of THR and RS for the treatment of pain and disability in people with end-stage arthritis of the hip, in particular to compare the clinical effectiveness and cost-effectiveness of (1) different types of primary THR and RS for people in whom both procedures are suitable and (2) different types of primary THR for people who are not suitable for hip RS.

DATA SOURCES

Electronic databases including MEDLINE, EMBASE, The Cochrane Library, Current Controlled Trials and UK Clinical Research Network (UKCRN) Portfolio Database were searched in December 2012, with searches limited to publications from 2008 and sample sizes of ≥ 100 participants. Reference lists and websites of manufacturers and professional organisations were also screened.

REVIEW METHODS

Systematic reviews of the literature were undertaken to appraise the clinical effectiveness and cost-effectiveness of different types of THR and RS for people with end-stage arthritis of the hip. Included randomised controlled trials (RCTs) and systematic reviews were data extracted and risk of bias and methodological quality were independently assessed by two reviewers using the Cochrane Collaboration risk of bias tool and the Assessment of Multiple Systematic Reviews (AMSTAR) tool. A Markov multistate model was developed for the economic evaluation of the technologies. Sensitivity analyses stratified by sex and controlled for age were carried out to assess the robustness of the results.

RESULTS

A total of 2469 records were screened of which 37 were included, representing 16 RCTs and eight systematic reviews. The mean post-THR Harris Hip Score measured at different follow-up times (from 6 months to 10 years) did not differ between THR groups, including between cross-linked polyethylene and traditional polyethylene cup liners (pooled mean difference 2.29, 95% confidence interval -0.88 to 5.45). Five systematic reviews reported evidence on different types of THR (cemented vs. cementless cup fixation and implant articulation materials) but these reviews were inconclusive. Eleven cost-effectiveness studies were included; four provided relevant cost and utility data for the model. Thirty registry studies were included, with no studies reporting better implant survival for RS than for all types of THR. For all analyses, mean costs for RS were higher than those for THR and mean quality-adjusted life-years (QALYs) were lower. The incremental cost-effectiveness ratio for RS was dominated by THR, that is, THR was cheaper and more effective than RS (for a lifetime horizon in the base-case analysis, the incremental cost of RS was £11,284 and the incremental QALYs were -0.0879). For all age and sex groups RS remained clearly dominated by THR. Cost-effectiveness acceptability curves showed that, for all patients, THR was almost 100% cost-effective at any willingness-to-pay level. There were age and sex differences in the populations with different types of THR and variations in revision rates (from 1.6% to 3.5% at 9 years). For the base-case analysis, for all age and sex groups and a lifetime horizon, mean costs for category E (cemented components with a polyethylene-on-ceramic articulation) were slightly lower and mean QALYs for category E were slightly higher than those for all other THR categories in both deterministic and probabilistic analyses. Hence, category E dominated the other four categories. Sensitivity analysis using an age- and sex-adjusted log-normal model demonstrated that, over a lifetime horizon and at a willingness-to-pay threshold of £20,000 per QALY, categories A and E were equally likely (50%) to be cost-effective.

LIMITATIONS

A large proportion of the included studies were inconclusive because of poor reporting, missing data, inconsistent results and/or great uncertainty in the treatment effect estimates. This warrants cautious interpretation of the findings. The evidence on complications was scarce, which may be because of the absence or rarity of these events or because of under-reporting. The poor reporting meant that it was not possible to explore contextual factors that might have influenced study results and also reduced the applicability of the findings to routine clinical practice in the UK. The scope of the review was limited to evidence published in English in 2008 or later, which could be interpreted as a weakness; however, systematic reviews would provide summary evidence for studies published before 2008.

CONCLUSIONS

Compared with THR, revision rates for RS were higher, mean costs for RS were higher and mean QALYs gained were lower; RS was dominated by THR. Similar results were obtained in the deterministic and probabilistic analyses and for all age and sex groups THR was almost 100% cost-effective at any willingness-to-pay level. Revision rates for all types of THR were low. Category A THR (cemented components with a polyethylene-on-metal articulation) was more cost-effective for older age groups. However, across all age-sex groups combined, the mean cost for category E THR (cemented components with a polyethylene-on-ceramic articulation) was slightly lower and the mean QALYs gained were slightly higher. Category E therefore dominated the other four categories. Certain types of THR appeared to confer some benefit, including larger femoral head sizes, use of a cemented cup, use of a cross-linked polyethylene cup liner and a ceramic-on-ceramic as opposed to a metal-on-polyethylene articulation. Further RCTs with long-term follow-up are needed.

STUDY REGISTRATION

This study is registered as PROSPERO CRD42013003924.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

Is the length of the femoral component important in primary total hip replacement?

Many different lengths of stem are available for use in primary total hip replacement, and the morphology of the proximal femur varies greatly. The more recently developed shortened stems provide a distribution of stress which closely mimics that of the native femur. Shortening the femoral component potentially comes at the cost of decreased initial stability. Clinical studies on the performance of shortened cemented and cementless stems are promising, although long-term follow-up studies are lacking. We provide an overview of the current literature on the anatomical features of the proximal femur and the biomechanical aspects and clinical outcomes associated with the length of the femoral component in primary hip replacement, and suggest a classification system for the length of femoral stems.

Predicting Bone Remodeling in Response to Total Hip Arthroplasty: Computational Study Using Mechanobiochemical Model

Periprosthetic bone loss following total hip arthroplasty (THA) is a serious concern leading to the premature failure of prosthetic implant. Therefore, investigating bone remodeling in response to hip arthroplasty is of paramount for the purpose of designing long lasting prostheses. In this study, a thermodynamic-based theory, which considers the coupling between the mechanical loading and biochemical affinity as stimulus for bone formation and resorption, was used to simulate the femoral density change in response to THA. The results of the numerical simulations using 3D finite element analysis revealed that in Gruen zone 7, after remarkable postoperative bone loss, the bone density started recovering and got stabilized after 9% increase. The most significant periprosthetic bone loss was found in Gruen zone 7 (−17.93%) followed by zone 1 (−13.77%). Conversely, in zone 4, bone densification was observed (+4.63%). The results have also shown that the bone density loss in the posterior region of the proximal metaphysis was greater than that in the anterior side. This study provided a quantitative figure for monitoring the distribution variation of density throughout the femoral bone. The predicted bone density distribution before and after THA agree well with the bone morphology and previous results from the literature.

Improving peri-prosthetic bone adaptation around cementless hip stems: a clinical and finite element study

This study assessed whether the Symax™ implant, a modification of the Omnifit(®) stem (in terms of shape, proximal coating and distal surface treatment), would yield improved bone remodelling in a clinical DEXA study, and if these results could be predicted in a finite element (FE) simulation study. In a randomized clinical trial, 2 year DEXA measurements between the uncemented Symax™ and Omnifit(®) stem (both n=25) showed bone mineral density (BMD) loss in Gruen zone 7 of 14% and 20%, respectively (p<0.05). In contrast, the FE models predicted a 28% (Symax™) and 26% (Omnifit(®)) bone loss. When the distal treatment to the Symax™ was not modelled in the simulation, bone loss of 35% was predicted, suggesting the benefit of this surface treatment for proximal bone maintenance. The theoretical concept for enhanced proximal bone loading by the Symax™, and the predicted remodelling pattern were confirmed by DEXA-results, but there was no quantitative match between clinical and FE findings. This was due to a simulation based on incomplete assumptions concerning the yet unknown biological and mechanical effects of the new coating and surface treatment. Study listed under ClinicalTrials.gov with number NCT01695213.

Comparison of different distal designs of femoral components and their effects on bone remodeling in 1-stage bilateral total hip arthroplasty

To evaluate the effects of distal design of a proximally coated femoral component on periprosthetic bone remodeling, we prospectively performed 21 one-stage bilateral total hip arthroplasties using a distally tapered and a distally cylindrical stem with the same proximal design, randomized to side. All hips showed good outcomes clinically and radiographically at the final follow-up, average of 7 years postoperatively. Cancellous condensation was always found in Gruen's zones 2 and 6 around the cylindrical stem and in regions between zones 2 and 3 and between zones 6 and 5 around the tapered stem. Bone mineral density of Gruen's zones 2 and 6 was significantly lower around the tapered stem. These results suggested more distal loading in hips with the tapered stem than in those with the cylindrical stem.

Investigation of stress shielding around the Stryker Omnifit and Exeter periprosthetic hip implants using an irreversible thermodynamic-based model

This study investigates stress shielding by predicting bone density around two different implants following total hip arthroplasty using a new thermodynamic-based model for bone remodeling. This model is based on chemical kinetics and irreversible thermodynamics in which bone is treated as a self-organizing system capable of exchanging matter, energy, and entropy with its surroundings. Unlike the previous works in which mechanical loading is regarded as the only stimulus for bone remodeling, this model establishes a coupling between mechanical loading and the chemical reactions involved in the process of bone remodeling. This model is incorporated into the finite element software ANSYS by means of a macro to investigate stress shielding around two different implants: Stryker Omnifit and Exeter periprosthetic hip stems. The results of the simulation showing bone density reductions of 17% in Gruen zone 1 and 27% in Gruen zones 7 around the Omnifit hip stem agree well with dual-energy X-ray absorptiometry (DEXA) measurements reported in the literature. On the other hand, the Exeter implant is found to result in more severe resorption in the proximal femur. This is consistent with clinical studies, which report a higher survivorship rate for HA-coated Omnifit hip stems.

On the optimal shape of hip implants

The success of a total hip arthroplasty is strongly related to the initial stability of the femoral component and to the stress shielding effect. In fact, for cementless stems, initial stability is essential to promote bone ingrowth into the stem coating. An inefficient primary stability is also a cause of thigh pain. In addition, the bone adaptation after the surgery can lead to an excessive bone loss and, consequently, can compromise the success of the implant. These factors depend on prosthesis design, namely on material, interface conditions and shape. Although, surgeons use stems with very different geometries, new computational tools using structural optimization methods have been used to achieve a better design in order to improve initial stability and therefore, the implant durability. In this work, a multi-criteria shape optimization process is developed to study the relationship between implants performance and geometry. The multi-criteria objective function takes into account the initial stability of the femoral stem and the effect of stress shielding on bone adaptation after the surgery. Then, the optimized stems are tested using a concurrent model for bone remodeling and osseointegration to evaluate long-term performance. Additionally, the sensitivity to misalignments is analyzed, since femoral stems are often placed in varus or valgus position. Results show that the different criteria are contradictory resulting in different characteristics for the hip stem. However, the multi-criteria formulation leads to compromise solutions, with a combination of the geometric characteristics obtained for each criterion separately.

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.

Cortical and interfacial bone changes around a non-cemented hip implant: simulations using a combined strain/damage remodelling algorithm

Prostheses alter the loading pattern in bones. For example femoral hip implants cause the cortical bone to remodel and the implant/bone interface to react. To date, simulations of peri-prosthetic bone adaptations have succeeded for the bulk bone remodelling only. In this study we use an approach based on a combined strain/damage algorithm to simultaneously predict both bulk and interfacial peri-prosthetic bone adaptation around a non-cemented hip prosthesis. The influence of stem stiffness is investigated; a flexible iso-elastic stem (20GPa), an titanium alloy stem (110GPa), and a stiff cobalt chrome (CoCrMo) stem (210GPa). The results predict that an iso-elastic stem reduces proximal bone loss because stress shielding is prevented but it increases proximal interface resorption due to damage-stimulated resorption. On the other hand, a stiff cobalt chrome stem increases proximal strain-stimulated resorption but does not induce proximal interfacial damage-stimulated resorption; however damage-stimulated resorption surrounding the distal tip is predicted to increase with stiffer stems. Simulations for the titanium stem were predicted to minimise both strain and damage related remodelling. We propose that this combined strain/damage remodelling algorithm can provide realistic simulations of the response of bone around load-bearing orthopaedic implants.