Migration analysis of a metaphyseal anchored short-stem hip prosthesis

[Implant anchorage: In vivo and in vitro analyses : Clusters for implant anchorage and safety]

Aseptic implant loosening is the primary cause of revisions in arthroplasty. Various in vitro and in vivo methods are available for assessing implant fixation and stability. The aim of the Musculoskeletal Biomechanics Research Network (MSB-NET) is to continuously improve or develop these methods. In vitro analyses are often conducted using static and dynamic ISO and ASTM standards, while RSA, DXA, and EBRA analyses are established in vivo methods for evaluating implant fixation. Primary stability analyses, as well as acoustical methods, provide additional opportunities to detect loosening early and precisely evaluate implant stability. The cluster serves as a link between basic research, clinical practice, and end users to promote in vitro and in vivo methods to improve implant safety.

Bone mineral density around cementless short stems after reverse shoulder arthroplasty: changes over time and its relationship to stem positioning

Background

There are numerous reports of bone adaptation observed on plain radiography studies after the use of cementless short stems in reverse shoulder arthroplasty. However, reports on changes in bone mineral density (BMD) around the stem using dual-energy X-ray absorptiometry (DEXA) are prominently absent. In the present study, we measured BMD around the stem using DEXA and investigated changes over time from postoperative year 1 to year 2. Additionally, the relationship between BMD changes, filling ratio, and stem alignment was examined.

Methods

Forty-seven patients with short cementless stems who could be assessed via DEXA at 1-2 years postoperatively were included. After dividing the zones around the stem into 5, the BMD in each zone was measured, in addition to BMD changes and amount of change from postoperative year 1 to year 2. The relationship between filling ratio and stem alignment on postoperative plain radiography was assessed.

Results

A significant decrease in BMD in zone 3 was observed between postoperative year 1 and year 2 (P = .02). Regarding filling ratio and stem alignment, a negative correlation between valgus stem alignment and BMD change observed in zone 1 (r = -0.470, P < .01). In addition, stem valgus greater than 6° correlated with a significant decrease in BMD in zone 1. (P = .01). No significant differences were found in the other zones. Furthermore, there was no correlation between filling ratio and BMD change.

Conclusion

In reverse shoulder arthroplasty cementless short stems, changes that that occurred between postoperative year 1 to year 2 demonstrated a decrease in BMD in zone 3. In addition, a decrease in BMD in zone 1 was observed with a stem alignment of valgus 6° or higher, suggesting that stem alignment within valgus 6° is required to prevent a decrease in BMD.

Sexual activity after short-stem total hip arthroplasty. Does stem size matter?

BACKGROUND

Sexual activity is an important component of quality of life. To date, no studies have examined the impact of stem design on return to sexual activity (RTS) and quality of sex life after total hip arthroplasty (THA).

METHODS

A questionnaire was designed to assess preoperative and postoperative sexual habits, joint awareness and physical activity in working-age patients undergoing short-stem (n = 176) or straight-stem (n = 97) THA.

RESULTS

No differences were noted in time until RTS based on the stem design (short stems vs. straight stems; 6 [IQR: 4-10] vs. 6 [4-10] weeks; p = 0.996). Multivariate analysis revealed that higher patient BMI (p = 0.04), female gender (p < 0.001) and lower FJS-12 (p = 0.006) were significantly associated with delayed RTS. Improved hip mobility and reduced pain mainly contribute to improved quality of sexual activity postoperatively.

CONCLUSION

This study, hence, indicates that stem design has no impact on time until resumption of sexual activity in patients < 65 years. Female obese individuals who are aware of their artificial joint in daily life are at increased risk of delayed RTS after surgery.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

Three-year migration analysis of a new metaphyseal anchoring short femoral stem in THA using EBRA-FCA

Cementless calcar-guided femoral short stems in total hip arthroplasty (THA) have become increasingly popular over the years. Early distal migration of femoral stems measured by Einzel-Bild-Roentgen Analyse, Femoral Component Analyse (EBRA-FCA) has been reported to be a risk factor for aseptic loosening. The aim of this study was to analyse axial migration behavior and subsidence of a new short stem (launched in 2015) over a follow-up period of 3 years. According to the study protocol, 100 hip osteoarthritis patients who consecutively received an unilateral cementless calcar-guided short stem (ANA.NOVA proxy) at a single department were prospectively included in this mid-term follow-up study. Thirteen patients were lost to follow-up, resulting in 87 patients with unilateral THA who fulfilled the criteria for migration analysis with EBRA-FCA. The cohort comprised 41 males (mean age: 60 ± 16.5; mean BMI (Body Mass Index): 30 ± 13) and 46 females (mean age: 61 ± 15.5; mean BMI: 27 ± 10). Seven standardized radiographs per patient were analyzed with EBRA-FCA. An average migration of 2.0 mm (0.95-3.35) was observed within the first 3 years. The median increase during the first year was higher than in the second and third year (1.2 mm [IQR: 0.5-2.15] vs. 0.3 mm [IQR: 0.1-0.6 mm] vs. 0.25 mm [IQR: 0.1-0.5 mm]. Detected migration did not lead to stem loosening, instability, dislocation, or revision surgery in any patient. A higher risk for subsidence was observed in male and heavyweight patients, whereas the female gender was associated with a lower risk. No correlation between migration and revision could be observed. Although moderate subsidence was detectable, the performance of the short stem ANA.NOVA proxy is encouraging. Yet, its use may be re-considered in overweight and male patients due to more pronounced subsidence.

Cementless Short Stems in Total Hip Arthroplasty: Chances and Limits

In recent decades, a large number of cementless short stems have been introduced to the market. The concept aims at saving soft tissue using minimally invasive surgery and at the same time preserving as much bone as possible. In particular, the latest generation of short stems, which are implanted using a calcar-guided round-the-corner technique, are attracting increasing attention. An individualised resection level allows individual stem alignment and thus an ideal reconstruction of the hip anatomy. The early clinical results of short-stem total hip arthroplasty (THA) are promising and have led to an expansion of the indications and limitations for the use of short stems. In particular, the individual positioning in valgus or varus and the resulting individual metaphyseal or metadiaphyseal anchorage offers various possibilities to reconstruct even abnormal joint morphologies. Consequently, short stems are increasingly used in patients with complex anatomical variations or in cases of osteonecrosis of the femoral head. In some various cases, they can also be used in revision or conversion arthroplasty. In some patients, short stems can also be used after femoral neck fracture. Currently, scientific data on those areas of indication of short-stem THA is scarce.

Subsidence of a metaphyseal-anchored press-fit stem after 4-year follow-up: an EBRA-FCA analysis

PURPOSE

Uncemented stem migration analysis by EBRA-FCA (Einzel-Bild-Roentgen Analyse, Femoral Component Analyse) has been seen to be a good predictive indicator for early implant failure. In this study, we investigated the migration behavior of a cementless metaphyseal-anchored press-fit stem after 4-year follow-up.

METHODS

Applying a retrospective study design, we reviewed all consecutive patients who between 2012 and 2017 received a cementless Accolade II press-fit stem at our Department. We reviewed medical histories and performed radiological measurements using EBRA-FCA software. EBRA-FCA measurements and statistical investigations were performed by two independent investigators.

RESULTS

A total of 102 stems in 91 patients (female 60; male 31) fulfilled our inclusion criteria. Mean age at surgery was 66.2 (range 24.3-92.6) years. EBRA migration analysis showed a mean subsidence of 1.4 mm (range 0.0-12.0) at final follow-up. The angle between stem and femur axis was 0.5° (range 0.0°-2.8°) after 48 months. No correlations between gender or Dorr types and subsidence were found (p > 0.05). A body mass index > 30 kg/m² showed a significant increase in stem subsidence within the first 6 (p = 0.0258) and 12 months (p = 0.0466) postoperative.

CONCLUSIONS

Migration pattern of the metaphyseal-anchored stem and a low subsidence rate at final follow-up may predict a good long-term clinical result.

TRIAL REGISTRATION

Number: 20181024-1875.

Calcar-guided short-stem total hip arthroplasty: Will it be the future standard? Review and perspectives

Short stems in total hip arthroplasty (THA) are becoming increasingly popular. In Germany, already 10.4% of all primary THAs are performed using a cementless short stem. The concept of modern, calcar-guided, short stems aims for an individualized reconstruction of the hip anatomy by following the calcar of the femoral neck, a bone- and soft-tissue-sparing implantation technique, and physiological loading. The stem design uses either metaphyseal fixation alone or additional diaphyseal anchoring, depending on the stem alignment and indication. These individualized anchorage types increase the potential indications for the safe use of a short stem. The design features may account for potential advantages of current short stem implants compared with earlier short-stem designs, particularly in cases of reduced bone quality or osteonecrosis of the femoral head and femoral neck fractures. The implantation technique, however, requires distinct knowledge regarding the characteristics of varus and valgus positioning, with the potential for clinical consequences. A learning curve for surgeons new to this technique must be taken into account. Cortical contact with the distal lateral cortex appears to be crucial to provide sufficient primary stability, and the use of intraoperative imaging to identify “undersizing” is highly recommended. Current results of several national registries indicate that calcar-guided short stems are among the most successful implants in terms of mid-term survivorship. However, long-term data remain scarce. This review introduces the characteristics of calcar-guided short-stem THA and summarizes the current evidence.

Short versus conventional stem in cementless total hip arthroplasty : An evidence-based approach with registry data of mid-term survival

Background

Short-stemmed total hip arthroplasty (THA) is well established and gaining popularity in Germany. The perception that short stems may predispose to primary instability in the femur has resulted in a more thorough follow-up of younger patient cohorts than the typical uncemented THA population. To address this issue, an evidence-based approach is presented for a retrospective mid-term survival analysis of a large registry-based cohort in primary cementless THA comparing short stems with a matched group of conventional stems.

Material and methods

Propensity score matching (PSM, see Infobox 1) was used on 131,580 primary cementless THAs fulfilling the inclusion criteria performed between November 2012 and September 2019 and the cumulative probability of revision (CPR) of short and conventional stems for any reason, for reasons excluding prosthetic joint infection (PJI), and due to PJI were compared.

Results

After PSM at 1:1 balanced groups of 17,526 short stems and of 17,526 conventional stems were achieved demonstrating no significant difference for CPR for any reason and for reasons excluding PJI. Matched CPR for any reason was 2.9% (95% confidence interval, CI, 2.4–3.5%) 5 years after primary THA in the short stem and 3.1% (95% CI 2.7–3.4%) in the conventional stem group. The CPR excluding PJI was 2.2% (95% CI 1.7–2.7%) vs. 2.1% (95% CI 1.8–2.4%). In contrast, the incidence of PJI was statistically significant lower for short stems.

Conclusion

For the considered period, there was no statistically significant survival difference in uncemented THA between comparison groups but a lower incidence for PJI in short-stem THA. Further analyses of registry data are required to rule out range of indications and late mechanical failure of short stems.

Mid-term migration pattern of a calcar-guided short stem: A five-year EBRA-FCA-study

BACKGROUND

Short-term results of several short-stem designs have indicated early axial migration. Mid- and long-term results for most designs are lacking. The objective of this study was to evaluate the mid-term migration pattern of a calcar-guided short stem five years postoperative.

METHODS

Implant migration of 191 calcar-guided short stems was assessed by Ein-Bild-Roentgen-Analysis Femoral-Component- Analysis (EBRA-FCA) 5 years after surgery. Migration pattern of the whole group was analyzed and compared to the migration pattern of implants potentially being "at hazard" with a subsidence of more than 1.5 mm at 2 years postoperatively. Influence of preoperative Dorr types (A vs. B vs. C), age (<70 vs. >70 years), gender (female vs. male), weight (<90 kg vs. >90 kg), BMI (<30 vs. >30) and uni-vs. bilateral procedures on mid-term migration pattern was analyzed. Additionally outcome of varus- and valgus stem alignment was assessed.

RESULTS

Mean axial subsidence was 1.5 mm (SD 1.48 mm) at final follow-up. Two years after surgery 73 short stems were classified "at hazard". Of these stems, 69 cases showed secondary stabilisation in the following period, whereas 4 cases presented unstable with more than 1 mm of further subsidence. Stem revision was not required neither in the group of implants with early stabilisation nor the group with pronounced early onset migration. Male gender and heavy-weight patients had a significant higher risk for axial migration, as well as extensive valgus stem alignment, whereas for Dorr type B, compared to A, no statistical difference could be observed.

CONCLUSIONS

In most cases, even in the group of stems being "at hazard", settling could be documented. While different Dorr types did not show a statistically significant impact on axial migration, particularly in male and heavy-weight patients the risk of continuous subsidence is increased. In those 4 cases with further migration, undersizing of the stem could be recognized. At present, clinical consequences are still uncertain.

Early femoral component migration: comparing the anterior and posterior approach to the hip

PURPOSE

Early femoral component migration is a useful indicator for identifying implants at risk of failure due to aseptic loosening. The goal of this retrospective study was to identify if anterior approach (AA) treated hips are at a higher risk of failure due to aseptic loosening caused by early migration compared to hips operated on using the traditional posterior approach (PA).

METHODS

A total of 388 hips were included in this study, 139 AA and 249 PA treated hips. Femoral component migration was evaluated using EBRA-FCA and radiographs were assessed for radiolucency at latest follow-up. Preoperative and 2-year clinical outcomes were reported.

RESULTS

The 1- and 2-year migration rates (mm/year), and total migration (mm) at 2-year follow-up were comparable between AA and PA hips, respectively: 0.52 versus 0.41, 0.18 versus 0.19, and 0.64 versus 0.63 (all p > 0.05). Though not statistically significant, a higher percentage of AA hips passed 2-year total migration thresholds that have been associated with aseptic loosening compared to PA hips: 25.4% versus 16.5% for 1.5 mm threshold, and 11.3% versus 4.1% for the 2.7 mm threshold. Migration was not associated with the presence of radiolucent lines. All clinical outcomes improved significantly between preoperative and 2-year follow-up.

CONCLUSIONS

There was no association between the AA and any significant increase in femoral component migration. A higher percentage of AA hips exceeded the migration thresholds associated aseptic loosening; however, these stems had no other indications of instability and therefore suggests that this may be a difference in migration pattern.

Outcome of short- to medium-term migration analysis of a cementless short stem total hip arthroplasty using EBRA-FCA: a radiological and clinical study

INTRODUCTION

Stress shielding may lead to aseptic loosening which is a common reason for implant failure. An established method to identify implants with risk of implant failure caused by aseptic loosening is to measure early migration of the stem with the "Ein Bild Roentgen Analyse" femoral component analysis (EBRA-FCA). Therefore, the aim of this study was to measure the migration of a cementless short stem prosthesis via EBRA-FCA to predict the future performance.

MATERIALS AND METHODS

A total collective of 71 patients were treated with a cementless short hip stem prosthesis. Indications for surgery were primary coxarthrosis, dysplasia coxarthrosis or femoral head necrosis. After surgery, the patients were followed-up immediately after 3, 6, 12, 24, 36, and 48 months and X-ray images for EBRA-FCA measurements were taken. Axial caudal migration as well as the varus/valgus tilting of the prosthesis was determined. Possible influencing factors like BMI, age, diagnosis, gender or Harris Hip Score (HHS) on the migration of the stem were assessed.

RESULTS

HHS increased significantly direct postoperatively (p < 0.001). At the second follow-up the average caudal migration was 0.42 ± 0.52 mm (range: 0.00-2.85 mm) (p < 0.001). A total of 14 patients underwent a caudal migration greater than 1.5 mm until 48 months. The initial varus and valgus tilts within the first 3 months were significant (p < 0.001). No correlations between BMI, age, diagnosis, gender or HHS and the migration as well as the tilting of the cementless short hip stem prosthesis were found.

CONCLUSIONS

Although initial axial caudal migration as well as tilting tendencies in varus or valgus position can be detected, there is no marked migration of the examined prosthesis after the first 48 months. Likewise, no aseptic early loosening was detected throughout the study period, which indicates good osseointegration of the short stem prosthesis.

Mid-term results of a new-generation calcar-guided short stem in THA: clinical and radiological 5-year follow-up of 216 cases

BACKGROUND

In recent years, a variety of short stems have been introduced. To date, mid- and long-term results of calcar-guided short-stem designs have been rarely available.

MATERIALS AND METHODS

Two hundred and sixteen calcar-guided short stems were included in combination with a cementless cup in a prospective study. Patients were allowed full weight-bearing on the first day postoperatively. Harris hip score (HHS) as well as pain and satisfaction on visual analogue scale (VAS) were assessed during a median follow-up of 61.7 months. Standardised radiographs were analysed at predefined time points regarding radiological alterations such as bone resorption and remodelling, radiolucency, osteolysis and cortical hypertrophy using modified Gruen zones.

RESULTS

At mid-term follow-up, no revision surgery of the stem had to be performed in the whole collective. At 5 years, HHS was 97.8 (SD 4.7), satisfaction on VAS was 9.7 (SD 0.7), rest pain on VAS was 0.1 (SD 0.5), and load pain on VAS was 0.6 (SD 1.2). Compared to the 2-year results, femoral bone resorption increased significantly at the 5-year follow-up (3.9% versus 42.3%). Rate of femoral cortical hypertrophy remained stable, occurring in a total of 9 hips (4.5%). At the 5-year follow-up, 2 stems (1.0%) showed non-progressive radiolucent lines with a maximum width of 2 mm. Signs of osteolysis were not observed. Compared to the 2-year follow-up, no further subsidence was observed.

CONCLUSIONS

The rate of stem revision (0%) at the mid-term follow-up was remarkable and indicates the principle of using a calcar-guided short stem as being a safe procedure. However, signs of bone-remodelling, indicating some amount of stress-shielding, must be acknowledged at 5 years depending on stem alignment and type of anchorage.

LEVEL OF EVIDENCE

IV, Prospective observational study Trial registration German Clinical Trials Register, DRKS00012634, 07/07/2017 (retrospectively registered).

Short stems in total hip replacement: evidence on primary stability according to the stem type

BACKGROUND:

As the prevalence of total hip replacement is increasing in younger patients, less invasive implants (short stems) are becoming more favourable. However, despite the advantages of these stems, clinical results with a follow-up of more than 10 years are limited to a very few stem designs. There has been an increase in publications recently - mechanical and clinical studies - concerning the primary stability of short stems. Primary stem stability is an important factor as it reflects final stem stabilisation and is related to the clinical results of the prosthesis.

METHOD:

We conducted a systematic review of the literature to retrieve evidence concerning primary implant stability in short stems - as expressed by implant micromotion and stem subsidence - according to our previously proposed short-stem classification.

RESULTS:

Mechanical in vitro studies on stem micromotion are very few and limited to type 2 "partial collum" short stems. The results are comparable to those of stems with a known long-term excellent clinical course. Clinical results concerning stem migration patterns are also limited to some of the commercially available short stems. Although comparative studies are very few, the results for most of the short stems are similar to those of standard stems.

CONCLUSION:

There are promising results concerning biomechanical studies of the initial micromotion of short stems, as well as clinical results of stem migration patterns. Long-term clinical studies are needed in order to confirm these findings. The existing literature concerns very few of the many commercially available implants.

Mid-term migration analysis of a femoral short-stem prosthesis: a five-year EBRA-FCA-study

INTRODUCTION:

The objective of this study was to evaluate the mid-term migration pattern of a femoral short stem.

METHODS:

Implant migration of 73 femoral short-stems was assessed by Ein-Bild-Roentgen-Analysis Femoral-Component-Analysis (EBRA-FCA) 5 years after surgery. Migration pattern of the whole group was analysed and compared to the migration pattern of implants "at risk" with a subsidence of more than 1.5 mm 2 years postoperative.

RESULTS:

Mean axial subsidence was 1.1 mm (-5.0 mm to 1.5 mm) after 60 months. There was a statistical significant axial migration until 2 years postoperative with settling thereafter. 2 years after surgery 18 of 73 Implants were classified "at risk." Nevertheless, all stems showed secondary stabilisation in the following period with no implant failure neither in the group of implants with early stabilisation nor the group with extensive early onset migration.

CONCLUSION:

In summary, even in the group of stems with more pronounced early subsidence, delayed settling occurred in all cases. The determination of a threshold of critical early femoral short stem subsidence is necessary because of the differing migration pattern described in this study with delayed settling of the Fitmore stem 2 years postoperatively compared to early settling within the first postoperative year described for conventional stems.

Primary stability of a short bone-conserving femoral stem

Aims

The aim of this study was to determine the stability of a new short femoral stem compared with a conventional femoral stem in patients undergoing cementless total hip arthroplasty (THA), in a prospective randomized controlled trial using radiostereometric analysis (RSA).

Patients and Methods

A total of 53 patients were randomized to receive cementless THA with either a short femoral stem (MiniHip, 26 patients, mean age: 52 years, nine male) or a conventional length femoral stem (MetaFix, 23 patients, mean age: 53 years, 11 male). All patients received the same cementless acetabular component. Two-year follow-up was available on 38 patients. Stability was assessed through migration and dynamically inducible micromotion. Radiographs for RSA were taken postoperatively and at three, six, 12, 18, and 24 months.

Results

At two years, there was significantly less subsidence (inferior migration) of the short femoral stem (head, 0.26 mm, 95% confidence interval (CI) 0.08 to 0.43, sd 0.38; tip, 0.11 mm, 95% CI -0.08 to 0.31, sd 0.42) compared with the conventional stem (head, 0.62 mm, 95% CI 0.34 to 0.90, sd 0.56, p = 0.02; tip, 0.43 mm, 95% CI 0.21 to 0.65, sd 0.44, p = 0.03). There was no significant difference in dynamically inducible micromotion, rate of complications or functional outcome.

Conclusion

This study demonstrates that the short femoral stem has a stable and predictable migration. However, longer-term survival analysis still needs to be determined. Cite this article: Bone Joint J 2018;100-B:1148–56.

1-stage bilateral total hip arthroplasty operation in 22 patients with use of short and standard stem length on either side: gait analysis 1 and 2 years after bilateral THA

BACKGROUND

According to previous gait analyses, insertion of a total hip arthroplasty (THA) will improve the range of hip flexion-extension but not to normal. Use of short stems could have a potential to improve the motion by preservation of more bone and muscular attachments. We evaluated whether a short femoral stem resulted in improved hip motion compared to a conventional stem in patients who underwent 1-stage bilateral THA. The most painful hip was randomised to either design and the 2^nd hip was operated with the design not used on the 1^st side.

METHODS

Gait analysis was performed with an optical tracking system in 22 patients. The follow-up was performed 1 and 2 years after the operation. The mean age was 59 (SD 7.7) years and body mass index was 27.7 (SD 4.3). 66 subjects without hip pathology served as controls.

RESULTS

Minimal differences were observed, between or within the 2 different stem designs during gait at the 2 follow-up occasions. Comparison between each of the 2 stem designs and controls at 2 years revealed reduced stride length (p = 0.009), cadence, hip extension (p<0.001) and hip extension-flexion range (p = 0.021) for both designs. Furthermore, the range of hip adduction-abduction (p = 0.046) and hip abduction moment for both designs in the frontal plane was also reduced bilaterally (p<0.001).

CONCLUSIONS

We found no difference in gait parameters between the short and the conventional stem after 1-stage bilateral THA. Although both hip joints were operated at the same time motions and moments did not normalise after bilateral 1-stage operations.

How can a short stem hip implant preserve the natural, pre-surgery force flow? A finite element analysis on a collar cortex compression concept (CO4)

The present work proposes a simple, novel fixation concept for short stem hip endoprostheses, which preserves the pre-surgery force flow through femoral bone to an unprecedented extent. It is demonstrated by finite element analyses that a standard implant model endowed with minor geometrical changes can overcome bone loading reduction and can achieve almost physiological conditions. The numerical results underpin that the key aspect of the novel, so-called "collar cortex compression concept CO4" is the direct, almost full load transmission from the implant collar to the resected femur cortex, which implies that the implant stem must be smooth and therefore interacts mainly by normal contact with the surrounding bone. For a stem endowed with surface porosity at already small areas, it is mainly the stem which transmits axial forces by shear, whereas the collar shows considerable unloading, which is the standard metaphyseal fixation. Only in the latter case the implant-bone stiffness contrast induces stress shielding, whereas for CO4 stress shielding is avoided almost completely, although the implant is made of a stiff Ti-alloy. CO4 is bionics-inspired in that it mimics force transmission at implant-bone interfaces following the natural conditions and it thereby preserves pre-surgery bone architecture as an optimized solution of nature.

Uncemented short stems in primary total hip arthroplasty: The state of the art

Over the last two decades, several conservative femoral prostheses have been designed. The goals of conservative stems include: the spearing of the trochanteric bone stock; a more physiological loading in the proximal femur reducing the risk of stress shielding; and to avoid a long stem into the diaphysis preventing impingement with the femoral cortex and thigh pain.

All stems designed to be less invasive than conventional uncemented stems are commonly named ‘short stems’. However, this term is misleading because it refers to a heterogeneous group of stems deeply different in terms of design, biomechanics and bearing. In the short-term follow-up, all conservative stems provided excellent survivorship. However, variable rates of complications were reported, including stem malalignment, incorrect stem sizing and intra-operative fracture.

Radiostereometric analysis (RSA) studies demonstrated that some conservative stems were affected by an early slight migration and rotation within the first months after surgery, followed by a secondary stable fixation. Dual-energy x-ray absorptiometry (DEXA) studies demonstrated an implant-specific pattern of bone remodelling.

Although the vast majority of stems demonstrated a good osseointegration, some prostheses transferred loads particularly to the lateral and distal-medial regions, favouring proximal stress shielding and bone atrophy in the great trochanter and calcar regions.

Cite this article: EFORT Open Rev 2018;3:149-159. DOI: 10.1302/2058-5241.3.170052

Total Hip Arthroplasty by the Direct Anterior Approach Using a Neck-preserving Stem: Safety, efficacy and learning curve

BACKGROUND

The concept of femoral neck preservation in total hip replacement (THR) was introduced in 1993. It is postulated that retaining cortical bone of the femoral neck offers triplanar stability, uniform stress distribution, and accommodates physiological anteversion. However, data on safety, efficacy and learning curve are lacking.

MATERIALS AND METHODS

We prospectively assessed all patients who were operated for a THR with a short neck preserving stem (MiniHip) between 2012 and 2014. The safety and learning curve were assessed by recording operative time; stem size; and adverse events including periprosthetic fracture; paresthesia; and limb length discrepancy (LLD). The cohort was divided into equal groups to assess the learning curve effect, and the cumulative sums (CUSUM) test was performed to monitor intraoperative neck fractures. For assessment of efficacy, Oxford Hip Score (OHS) and Short Form-36 (SF-36) scores were compared preoperatively and postoperatively.

RESULTS

138 patients with median age 62 years (range 35-82 years) were included with a median followup of 42 months (range 30-56 months). The minimum followup was 2.5 years. The OHS, SF-36 (physical and mental component) scores improved by a mean score of 26, 28, and 27 points, respectively. All patients had LLD of <10 mm (1.9 mm ± 1.3). Adverse events included intraoperative neck fracture (n = 6), subsidence (n = 1), periprosthetic fracture (n = 1), paresthesia (n = 12), and trochanteric bursitis (n = 2). After early modification of the technique to use a smaller finishing broach, the CUSUM test demonstrated acceptable intraoperative neck fracture risk. The second surgery group had a reduced risk of intraoperative neck fracture (5/69 vs. 1/69 P = 0.2), reduced operative time (66 vs. 61 min, P = 0.06), and increased stem size (5 vs. 6, P = 0.09) although these differences were not statistically significant.

CONCLUSIONS

The MiniHip stem is safe alternative to standard THR with good functional outcomes but with a learning curve for the surgical technique, implants sizing, and the risk of intraoperative neck fractures.

The learning curve in short-stem THA: influence of the surgeon's experience on intraoperative adjustments due to intraoperative radiography

Introduction

Short-stem THA has become increasingly popular over the last decade. However, implantation technique differs from conventional THA and thus possibly involves a distinct learning curve. The purpose of this study was to evaluate the value of intraoperative radiography and the influence of the surgeon’s experience on intraoperative adjustments in short-stem THA.

Methods

A total of 287 consecutive short-stem THAs, operated by a total of 24 senior consultants, consultants and residents in training, were prospectively included. Intraoperative radiography was performed after trial reduction. Preoperative planning and intraoperative outcome with regard to positioning, sizing of components as well as resulting offset and leg length were compared. Frequency, reason and type of intraoperative adjustments were documented in relation to the surgeon’s experience. Operation time was assessed.

Results

One hundred and fifty-six (54.4%) procedures were carried out by one of three senior consultants, and a total of nine consultants and 12 residents in training performed 105 (36.6%) and 26 (9.0%) operations, respectively. In 121 cases (42.2%), intraoperative adjustments were made following intraoperative radiography. Intraoperative adjustments of one or more components were made by senior consultants in 51 cases (32.7%), by consultants in 53 cases (50.5%) and by residents in 17 cases (65.4%), respectively. The most common cause was undersizing of the stem. Operation time varied markedly between groups of surgeons.

Discussion

Short-stem THA involves a learning curve. Intraoperative radiography is decisive for prevention of malpositioning and undersizing of components, as well as loss of offset and leg length discrepancies. Hence, it should be considered mandatory, especially for less experienced surgeons.

Stable migration pattern of an ultra-short anatomical uncemented hip stem: a prospective study with 2 years radiostereometric analysis follow-up

INTRODUCTION

Shorter, anatomically shaped and proximally loading stems have been developed to achieve better stress distribution and be more bone preserving. The purpose of this prospective study was to evaluate the migration pattern of the Proxima™ ultra-short uncemented stem using radiostereometric analysis (RSA), and to review the literature regarding the migration of short stemmed hip arthroplasty.

METHODS

25 patients (28 hips) with hip osteoarthritis received a Proxima stem during total hip arthroplasty (THA). To measure stem migration, repeated RSA examinations were done during a 2 year follow up period. The patients were evaluated with the hip specific (HOOS) and the generic health (EQ5D) scores up to 1 year, and clinically for 6 years postoperatively.

RESULTS

Almost all migration occurred within the first 3 months, with mean subsidence of 0.22 mm and varus rotation of 1.04°, being the primary effect variables. After the third postoperative month and up to the 2 year RSA follow up no further significant migration occurred. The outcome scores showed substantial improvement after 1 year. No revisions were performed or indicated for any stem after a mean clinical follow up of 72.1 months.

CONCLUSIONS

Like many other uncemented stems, the Proxima showed early migration up to 3 months hereafter osseointegration seems to have occurred. The achieved stability and clinical outcomes indicate favorable early results for this stem in younger patients who have good bone quality and average BMI. We found, however, the surgical technique to be slightly more demanding compared to conventional stems owing to the unique implant design that necessitates specific adjusted femoral cutting and broaching procedures.

The Influence of Tribological Pairings and Other Factors on Migration Patterns of Short Stems in Total Hip Arthroplasty

Over the last decade, the number of short stem total hip arthroplasty procedures has increased. Along with the possible benefits associated with short stems is a smaller implant-bone contact surface, which may have a negative influence on primary stability and impair osseointegration. Previous studies observed migration of short stems, especially within the first three months. The variables that influence migration in short stem hip implants remain unknown. Therefore, the purpose of this study was to associate the migration of short stems with its possible influencing variables. Migration data from two different short stem studies were retrospectively analyzed. Migration within the first two postoperative years was determined by model-based Roentgen stereophotogrammetric analysis. Migration was correlated to bearing couple, type and size of stem, size of acetabular cup, and age, gender, weight, and height of patients using a multiple factor analysis. Eigenvalue analysis explained 80.7% of the overall variance for the first three dimensions. The four most dominant variables in the first dimension were weight, stem size, acetabular cup size, and patient height (correlations of 0.81, 0.80, 0.71, and 0.70, resp.). None of the analyzed parameters (bearing couple, type and size of stem, size of acetabular cup, and age, gender, weight, and height of patients) affected the migration pattern of short stem THA with primary metaphyseal fixation.

Three-dimensional analysis of the proximal anterior femoral flare and torsion. Anatomic bases for metaphyseally fixed short stems design

PURPOSE

The use of femoral stems with a short metaphyseal fixation may lead to fractures or subsidence. Such failures may be related to a mismatch between the torsions or the sagittal flares of the stem and the femur. The goal of our study was to perform a 3D analysis of the proximal metaphyseal femur anatomy with a special focus on the anterior proximal flare and torsion. Such data may help to detect the outlier patients for whom a short metaphyseal fixation should be avoided.

METHODS

A prospective study included 80 consecutive patients who underwent a primary cementless THA with a 3D CT-scan based pre-operative planning. A femoral frame was determined in order to analyse the proximal metaphyseal torsion and flares of the femur.

RESULTS

The mean metaphyseal torsion was 21.6° ± 7° at 5 mm above the lesser trochanter (LT) and 34.7° ± 8.8 at 15 mm under LT generating a differential torsion of 13° around the LT. The mean flare index was 4.3 ± 0.9 medially, 3.7 ± 0.8 laterally, 2 ± 0.6 anteriorly and 3.1 ± 0.6 posteriorly. The anterior flare was the only flare significantly correlated to the bone density, to the age and to the femoral off-set: the higher the anterior flare index, the younger the patient, the higher the bone density and the higher the femoral offset. The anterior flare was not significantly correlated to the femoral anteversion, the metaphyseal torsion and the coronal neck-shaft angle.

CONCLUSION

The proximal femoral metaphysis presents a highly variable anterior flare and torsion that may explain a mismatch between the femur and the femoral stem, consequently generating a risk of subsidence or fracture when using shortly fixed stems.

LEVEL OF EVIDENCE

Level IV.

Low Short-Stem Revision Rates: 1-11 Year Results From 1888 Total Hip Arthroplasties

BACKGROUND

In total hip arthroplasty, short stems were developed as a bone-conserving alternative to traditional cementless stems. So far, there have been very few recorded medium to long-term results of these comparatively new implants. The aim of our retrospective study was to report on the survival of calcar-loading short stems.

METHODS

All Metha stem implantations from 2004 to 2014 were recorded from the operation protocols (n = 1888). Due to the chronological development of the stem, 3 different versions were implanted: modular titanium stems with neck adapters from titanium or cobalt-chrome and monoblock stems. Patients were questioned by post about revision, dislocation, and satisfaction.

RESULTS

Data were complete for 93% of the procedures (1090 monoblock stems, 314 modular stems with titanium neck, and 230 modular stems with cobalt chrome neck). Mean follow-up was 6 years (1-11 years). Fifteen modular titanium implants were affected by cone fractures (4%). Therefore, monoblock, modular cobalt chrome, and modular titanium implants were analyzed separately. The 7-year revision rate for monoblock stems was 1.5%; for modular cobalt-chrome stems it was 1.8%, and for modular titanium stems it was 5.3%.

CONCLUSION

Our data show the midterm survival of the monoblock and modular cobalt-chrome implants equivalent to the traditional cementless stems. These might, therefore, be considered as a bone-conserving alternative for young and active patients.

Two- to 4-Year Followup of a Short Stem THA Construct: Excellent Fixation, Thigh Pain a Concern

BACKGROUND

Short stem cementless femoral components were developed to aid insertion through smaller incisions, preserve metaphyseal bone, and potentially decrease or limit the incidence of thigh pain. Despite some clinical success, the senior author (DDG) believed a higher percentage of his patients who had received a cementless short stem design were experiencing thigh pain, which, coupled with concerns about bone ingrowth fixation, motivated the review of this case series.

QUESTIONS/PURPOSES

(1) What is the proportion of patients treated with a short stem cementless THA femoral component that develop thigh pain and what are the hip scores of this population? (2) What are the radiographic results, specifically with respect to bone ingrowth fixation and stress shielding, of this design? (3) Are there particular patient or procedural factors that are associated with thigh pain with this short stem design?

METHODS

Two hundred sixty-one primary THAs were performed in 238 patients by one surgeon between November 2010 and August 2012. During this time period, all patients undergoing primary THA by this surgeon received the same cementless short titanium taper stem. Seven patients (eight hips) died and five patients (five hips) were lost to followup, leaving 226 patients (248 hips) with a mean followup of 3 years (range, 2-5 years). Patients rated their thigh pain during activity or rest at final followup on a 10-point visual analog scale. Harris hip scores (HHS) were obtained at every clinic appointment. Thigh pain was evaluated at the final followup or by contacting the patient by phone. Radiographs were evaluated for bone-implant fixation, bone remodeling, and osteolysis. An attempt was made to correlate thigh pain with patient demographics, implant specifications, or radiographic findings.

RESULTS

Seventy-six percent of hips (180 of 238) had no thigh pain, 16% of hips (37 of 238) had mild thigh pain, and 9% (21 of 238) had moderate or severe thigh pain. Preoperatively, mean HHS was 47 (SD, 16) and at last followup, mean HHS was 88 (SD, 13). There were two femoral revisions, one for severe thigh pain and the other for infection. All but two components demonstrated bone ingrowth fixation (99%). Femoral stress shielding was mild in 64% of hips (135 of 212), moderate in 0.5% (one of 212), and severe in no hips. There is an inverse linear relationship between age and severity of thigh pain (r = -0.196; p < 0.0024).

CONCLUSIONS

Although reliable fixation was achieved and good HHS were attained, the frequency and severity of thigh pain with this short cementless stem were concerning. The surgeon has subsequently abandoned this short stem design and returned to a conventional length stem. Future study direction might investigate the biomechanical grounds for the thigh pain associated with this stem design.

LEVEL OF EVIDENCE

Level IV, therapeutic study.

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

A comparative study between two stems (Linea Anatomic and Minihip) has been performed in order to analyse the differences in their biomechanical behaviour, concerning stem micromotions and load transmission between stem and bone. From the corresponding finite element models, a parametric study was carried out to quantify ranges of micromotions taking into account: friction coefficient in the stem-bone interface, press-fit and two types of gait cycle. Micromotions were evaluated for each stem at six different levels along repeated gait cycles. An initial and marked stem subsidence at the beginning of the simulation was observed, followed by an asymptotic decrease due to friction forces. Once migration occurs, a repeated reversible cyclic micromotion is developed and stabilized as gait cycle times are simulated. The general motion pattern exhibited higher amplitude of micromotion for Minihip compared to Linea stem. The load transmission mechanism was analyzed, identifying the main internal forces. The results show higher local forces for Minihip stem up to 80% greater than for Linea stem. The differences of design between Minihip and Linea conditioned different distributions of load, influencing the posterior stress-shielding. Consequently, short stems require high bone stock and quality should, being indicated for young patients with high bone quality.

Radiographic alterations in short-stem total hip arthroplasty: a 2-year follow-up study of 216 cases

INTRODUCTION

In recent years a variety of short-stems have been introduced. Stable osteointegration is a key factor for a satisfactory long-term result. The purpose of this study was to evaluate postoperative radiological alterations and subsidence, as a result of using a newly developed device, over a 2-year follow-up.

METHODS

216 short-stems were implanted in combination with a cementless cup. Patients were allowed full weight-bearing on the first day postoperatively. Pre- and postoperative x-rays were done using a standardised technique. Radiological alterations, such as bone resorption, radiolucency, osteolysis and cortical hypertrophy were detected and located using modified Gruen zones, and subsidence was measured via a conventional digital technique over a 2-year follow-up. In addition, Harris Hip Score (HHS), rest pain and load pain on the visual analogue scale (VAS) were assessed respectively.

RESULTS

At 2-year follow-up 6 stems (2.9%) showed nonprogressive radiolucent lines with a maximum width of 2 mm. Resorption of femoral bone stock was detected in a total of 8 cases (3.9%). Femoral cortical hypertrophy was seen in a total of 9 hips (4.4%). No patient showed osteolysis. A measureable subsidence of at least 2 mm was observed in a total of 15.7% (32 cases) after 6 weeks, corresponding to an initial settlement given full weight-bearing ambulation. Only 1.1% (2 cases) showed further progression at the 6-month follow-up, whereas at the 1- and 2-year follow-ups no further subsidence was observed. After 2 years HHS was 98.1 (65.0-100.0), rest pain on the VAS was 0.2 (0.0-7.0) while load pain was 0.4 (0.0-7.0).

CONCLUSIONS

The results of this radiographic analysis give support to the principle of using metaphyseal anchoring, calcar guided short-stems. The low incidence of bony alterations after a follow-up of 2 years indicates a physiological load distribution. After mild initial subsidence a stable osteointegration can be achieved over time.

One-stage bilateral versus unilateral short-stem total hip arthroplasty: comparison of migration patterns using "Ein-Bild-Roentgen-Analysis Femoral-Component-Analysis"

PURPOSE

The hypothesis of this study was that femoral implant migration would not differ between simultaneous bilateral or unilateral short-stem THA.

METHOD

Implant migration of 202 femoral short-stems (100 unilateral and 102 one-stage bilateral cases) in 151 patients was assessed by "Ein-Bild-Roentgen-Analysis Femoral-Component-Analysis" in a two years follow-up (2.0-3.0 years). Migration patterns of unilateral and simultaneous cases were analysed and compared.

RESULTS

There was no difference between the two groups regarding age, body mass index and gender. After two years mean subsidence of all 202 implants was 1.43 mm (-6.5 mm to 2.0 mm). After initial subsidence of 0.37 mm per month within the first six weeks, the mean monthly migration was reduced to 0.02 mm between one and two years post-operative. There was no statistical difference in mean migration between unilateral (1.34 mm) and simultaneous bilateral (1.51 mm) THA (p = 0.33).

CONCLUSION

In summary, two years post-operative there was no difference in the amount of mean implant subsidence between unilateral compared to simultaneous bilateral short-stem THA. This suggests that regarding implant fixation simultaneous bilateral short-stem THA is as safe and successful as a solely unilateral intervention.

Influence of patient-related characteristics on early migration in calcar-guided short-stem total hip arthroplasty: a 2-year migration analysis using EBRA-FCA

Background

Short stems have gained popularity in recent years. Because of encouraging clinical results, indications have been expended from young to elderly and obese patients. However, long-term results are lacking. The purpose of this study was to evaluate the influence of gender, age, body weight, body mass index (BMI), and offset version on short-stem migration in correlation to the clinical outcome.

Methods

The implant migration of 202 metaphyseal-anchoring, calcar-guided short stems in 151 patients was assessed by “Einzel-Bild-Roentgen-Analyse” femoral component analysis (EBRA-FCA, femoral component analysis) in a 2-year follow-up. Full weight bearing was allowed directly after surgery. Patients were divided into groups regarding gender, age, body weight, BMI, and offset version. The Harris hip score (HHS) and satisfaction on visual analogue scale (VAS) were analyzed.

Results

After 2 years, mean axial subsidence of all 202 implants was 1.43 mm (standard deviation, SD 1.45 mm). A continuous reduction of initially pronounced subsidence over time could be observed. None of the stems had to be revised. Statistically significant increased rates of subsidence were seen in male (1.68 mm; SD 1.56 mm; p = 0.005) and heavy patients (1.54 mm; SD 1.48 mm; p = 0.022). No differences in implant migration were found regarding age, BMI, and different offset versions. HHS improved markedly from 45.8 (SD 15.9) to 98.1 (SD 4.7) while satisfaction on VAS improved from 1.8 (SD 2.2) to 9.7 (SD 0.9) after 2 years.

Conclusions

The results suggest a migration pattern with initially pronounced subsidence followed by subsequent stabilization. Male and obese patients show a slightly increased initial subsidence without any signs of sustained micromovement. No correlation was found concerning clinical results and pronounced initial subsidence above the threshold of 1.5 mm. No aseptic loosening or other signs of implant failure were seen within the observation period of 2 years.

Trial registration

German Clinical Trials Register, DRKS00009834.

Analysis of migration of the Nanos® short-stem hip implant within two years after surgery

PURPOSE

Short-stem implants provide a bone-preserving alternative in total hip arthroplasty. However, some evidence exists that the smaller implant-bone contact surface may compromise primary stability and impair osseo-integration. The purpose of this study was to analyse the migration characteristics of the Nanos® short stem over two years by means of model-based roentgen stereophotogrammetric analysis (MBRSA).

METHODS

Eighteen patients aged 53.6 ± 7.2 years were included. After being treated with a Nanos implant, 14 patients were followed-up radiologically at three, six, 12 and 24 months by means of MBRSA. Early implant migration was calculated. Clinical data have been assessed in addition.

RESULTS

Highest translational migration was observed with a mean value of -0.22 ± 0.39 mm along the proximo-distal axis after three months and highest rotational migration with 0.8 ± 3.2° also around the y-axis after two years. The resulting total migration was 0.46 ± 0.31 mm, with the largest proportion occurring within three months after surgery (0.40 ± 0.34 mm).

CONCLUSION

The Nanos short-stem hip implant shows only a slight initial migration within three months after implantation, followed by secondary stabilisation. These results suggest both good primary stability and osseo-integration, suggesting a low risk of aseptic loosening.

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.

A randomised trial comparing a short and a standard-length metaphyseal engaging cementless femoral stem using radiostereometric analysis

This was a randomised controlled trial studying the safety of a new short metaphyseal fixation (SMF) stem. We hypothesised that it would have similar early clinical results and micromovement to those of a standard-length tapered Synergy metaphyseal fixation stem. Using radiostereometric analysis (RSA) we compared the two stems in 43 patients. A short metaphyseal fixation stem was used in 22 patients and a Synergy stem in 21 patients. No difference was found in the clinical outcomes pre- or post-operatively between groups. RSA showed no significant differences two years post-operatively in mean micromovement between the two stems (except for varus/valgus tilt at p = 0.05) (subsidence 0.94 mm (sd 1.71) vs 0.32 mm (sd 0.45), p = 0.66; rotation 0.96° (sd 1.49) vs 1.41° (sd 2.95), p = 0.88; and total migration 1.09 mm (sd 1.74) vs 0.73 mm (sd 0.72), p = 0.51). A few stems (four SMF and three Synergy) had initial migration > 1.0 mm but stabilised by three to six months, with the exception of one SMF stem which required revision three years post-operatively. For most stems, total micromovement was very low at two years (subsidence < 0.5 mm, rotation < 1.0°, total migration < 0.5 mm), which was consistent with osseous ingrowth. The small sample makes it difficult to confirm the universal applicability of or elucidate the potential contraindications to the use of this particular new design of stem.

Cite this article: Bone Joint J 2015; 97-B:595–602.

10-year experience with short stem total hip arthroplasty

Since 1998, short stem total hip arthroplasty (THA) has been performed at the authors' institution. Currently, 30% of THAs are performed with short stems. This article reports on complications that required revision of a short stem THA. Between September 2005 and February 2012, a total of 1953 Metha short stem THAs were performed; of these, 38 required revision due to mechanical complications. In 12 cases, the modular titanium neck adapter failed. In 19 cases, aseptic implant loosening occurred; of these, 11 cases were due to major stem subsidence. In 2 cases, via falsa (cortical penetration) implantation occurred. In 5 cases, periprosthetic fractures led to revision. This corresponds to an aseptic total revision rate of 1.3% for 26 short stems and 1.9% including the cases of all 38 documented revision cases. Thirty-four cases were revised with cementless standard hip stems, 2 cases were revised with short stems, and 2 cases were revised with long revision stems. Undersizing was analyzed in 58% of aseptic revisions. Fifty-four percent of revisions were performed in male patients - 23% with osteonecrosis of the femoral head, and 7% with short hip stems positioned in varus in coxa vara deformities. Seventy-two percent of revisions after marked early stem subsidence and position change into valgus were performed in female patients. Dysplastic hips with coxa valga did not show elevated revision rates. No revisions were performed for dislocation or femoral thigh pain. Short stem THA with the Metha implant is a bone-preserving option for various indications in select patient groups.

Patient selection for shorter femoral stems

The right patient selection with the correct surgical treatment are prerequisite for a positive result in total hip arthroplasty (THA). Short stem implants demand a shorter anchoring length in accordance with the proper indication. Although appropriate indications for short stems have been discussed in the literature, there currently is no clear definition. The lack of an accepted categorization of short hip stems complicates the situation further. This article briefly reviews the literature and highlights the authors' results and experiences in short stem THA in an effort to establish a proper discrimination between indications and contraindications for the Metha short stem. Results presented include a retrospective data collection and follow-up examination of 126 patients who underwent short stem THA with 2- and 4-year results. Anchoring principles of the short stem are reviewed, and a complication and failure analysis based on 7 femoral revisions in 1092 short stem THAs is presented. Selection criteria for short stem THA are patients younger than 70 years with primary osteoarthritis and dysplastic femoral deformities, and indications of avascular head necrosis. Adequate bone quality must be confirmed intraoperatively, assessing whether the bone structure in the area of the femoral neck is strong enough to support the short stem load transmission. Coxa vara and high dysplastic femoral neck antetorsion are contraindications for short stems. Wide and short femoral necks, implant undersizing, and a deep stem position below the femoral osteotomy compromise stability and must be avoided with an appropriate surgical technique. Long-term data are not yet available.

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.

Short stems in total hip replacement: current status and future

Short stem hip implants have been introduced as a bone preserving surgery for younger and more active people undergoing hip arthroplasty. Although many short stems are now available, clinical results and long-term survival are controversial. The aim of this paper is to describe the features of the short stems and to analyse their clinical results and long-term survival. The short-stem implants reproduce a stress distribution at the level of the proximal femur more similar to the physiological femur limiting the stress-shielding that occur with conventional cementless stems. Though short stems are an alternative to conventional stems, their use is not yet justified despite the promising short and mid-term survival results. Higher incidence of complications, such as periprosthetic fractures and malpositioning of the stem, and the lack of long-term results do not allow to predict what role in the future short stems in total hip replacement may have.

Migration pattern of a femoral short-stem prosthesis: a 2-year EBRA-FCA-study

INTRODUCTION

Short-stem prostheses enable bone stock preserving total hip arthroplasty. However, little is known about the durability of this group of implants. The most common cause for implant failure is aseptic loosening. Early implant migration is supposed to be the best indicator for mechanical failure of femoral stems. The purpose of this study was to evaluate the migration pattern of a short stem implant and the influence of BMI, gender and femoral offset on implant migration.

MATERIALS AND METHODS

After a minimum follow-up of 2 years, 72 hips were included in this EBRA-FCA-study. The mean age at surgery of the 34 female and 32 male patients was 54 years (range 22-75 years). The mean BMI was 29 kg/m(2) (range 21-51 kg/m(2)).

RESULTS

Mean axial subsidence was 1 mm (±1.4 mm) after 24 months. BMI, gender and implant offset did not influence implant migration on a statistical significant level. Nevertheless, a tendency towards more migration in obese and female patients was observed.

CONCLUSION

The evaluated short stem prosthesis showed a migration pattern similar to clinical proven standard straight stem implants. The indication of short-stem prostheses should be critically evaluated in obese and female patients.

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.

Revision rate after short-stem total hip arthroplasty: a systematic review of 49 studies

BACKGROUND AND PURPOSE

The aim of short-stem total hip arthroplasty is to preserve proximal bone stock for future revisions, to improve biomechanical reconstruction, and to make minimally invasive approaches easier. It is therefore being increasingly considered to be a sound alternative to conventional total hip arthroplasty, especially for young and active patients. However, it is still unknown whether survival rates of short-stem hips match current standards. We made a systematic summary of reported overall survival after short-stem total hip arthroplasty.

MATERIALS AND METHODS

We conducted a systematic review of English, French, German, and Dutch literature. 2 assessors independently identified clinical studies on short-stem hip arthroplasty. After recalculating reported revision rates, we determined whether each implant had a projected revision rate of 10% or less at 10 years of follow-up or a revision rate per 100 observed component years of 1 or less. Stems were classified as "collum", "partial collum", or "trochanter-sparing".

RESULTS AND INTERPRETATION

We found 49 studies, or 51 cohorts, involving 19 different stems. There was a large increase in recent publications. The majority of studies included had a follow-up of less than 5 years. We found a large number of observational studies on "partial collum" and "trochanter-sparing" stems, demonstrating adequate survival rates at medium-term follow-up. Clinical evidence from "collum stem" studies was limited to a small number of studies with a medium-term follow-up period. These studies did not show a satisfactory overall survival rate.

The rationale for short uncemented stems in total hip arthroplasty

Uncemented femoral implants of various designs have proved to provide stable initial and long-term fixation in patients who undergo total hip arthroplasty. Challenges in primary total hip arthroplasty have led to the evolution of short stem designs. These challenges include proximal/metaphyseal and distal/diaphyseal mismatch; facilitation of less-invasive surgical exposures, especially the direct anterior approach; and bone preservation for potential revision surgery.

Clinical comparison of THA with a standard-length or short femoral component

The purposes of this 2-part study were to determine whether reduced distal femoral component geometry allows for routinely larger component sizes to be used and whether clinical or radiographic outcomes differ between total hip arthroplasty (THA) patients treated with either standard-length or short femoral components. Femoral component size and ongrowth surface area were retrospectively compared in a group of bilateral THA patients that had both a standard-length component and a contralateral short component. Then, clinical and radiographic outcomes were compared between matched groups of THA patients that had either a standard-length or short femoral component. The use of the short component resulted in a significantly larger femoral component size being used (P=.01), and the potential ongrowth surface area was significantly larger for the short component than for the standard component (median, 36.69 vs 35.55 cm2; P=.02). In the matched-pairs analysis, no group differences were noted in modified Harris Hip Scores (P=.43) or femoral component subsidence (P=.35), but there was a significantly greater prevalence of radiolucent lines in Gruen zone 8 with the short component (P=.008). The use of a short femoral component was associated with consistently larger component sizes being used, which corresponded with a larger potential ongrowth surface area. Short-term clinical and radiographic outcomes did not differ between standard-length and short femoral components. Studies are necessary to determine whether the increased proximal ongrowth surface area may result in improved long-term fixation or, on the contrary, may increase the risk of periprosthetic fracture.

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

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