Introduction

One of the most common diseases in the world is hip osteoarthritis, which also ranks high among the causes of many injuries1. Along with the increase in life expectancy among the global populace, its occurrence has increased. In hip osteoarthritis, pain and movement restriction occur due to articular cartilage damage. During hip arthroplasty, the damaged cartilage surface is replaced, and functionality is restored2 Total hip arthroplasty (THA) is a frequently performed orthopedic surgical procedure with positive results3 Treatment with uncemented femoral stems with different stem designs in patients with a certain bone quality shows positive results in the long term4. The design of conventional uncemented tapered wedge femoral systems is inspired by the Mueller Straight Stem, which was first used in 19775. This tapered design improves proximal loading and alleviates stress shielding thus leading to better mediolateral stability6. Although the survival time of conventional femoral stems is promising, they have disadvantages such as proximal–distal discrepancy, bone loss, thigh pain, and periprosthetic fracture.7 Different stem designs have been created over time to reduce these drawbacks, and short femoral stems are one of these. Short femoral stems have frequently been used, especially in the past 20 years1. Short femoral stems are shorter than 120 mm and which typically coincides with the metaphyseal–diaphyseal junction8. The stability of these short femoral stems depends upon their stable metaphyseal fixation; a requirement for optimal proximal load transfer8. Biomechanical studies have shown that optimising proximal load transfer can lead to the best chance of bone preservation8. They are generally preferred as they preserve proximal bone reserve and result in an optimal distribution of the proximal load transfer2.

This study compares short uncemented femoral stems with conventional uncemented femoral stems in terms of radiological and clinical results.

Materials and method

Patients

The study design is in accordance with the Declaration of Helsinki, and ethical committee approval was received from the IRB (Ankara Yıldırım Beyazıt University Health Sciences Ethics Committee 2022-651). This study comprised 123 primary THA patients who received short uncemented femoral stems between 2014 and 2017 and 129 primary THA patients who received conventional uncemented femoral stems. An Optimys (Mathys, Bettlach, Switzerland) short femoral stem was administered to the group that underwent THA performed using a shot femoral stem, and a Stryker Accolade II conventional femoral stem (Stryker, Mahwah, NJ) was administered to the group that underwent THA performed using a conventional femoral stem. The number of patients included in the study and the excluded patients are presented in Fig. 1. While having THA with a primary osteoarthritis and femur head avascular necrosis diagnosis was a criterion for inclusion, secondary osteoarthritis (fracture sequala, rheumatoid arthritis, spondyloarthropathies, etc.) femur neck fractures, history with the same hip, coxarthrosis due to developmental hip dysplasia, and neuromuscular diseases comprised the exclusion criteria. Patients who underwent arthroplasty with short uncemented femoral stems were designated Group 1, and those who underwent arthroplasty using conventional femoral stems were designated Group 2. Cementless femoral stem was used in all patients in both groups.

Figure 1
figure 1

Flow chart of patient selection.

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Patients included in the study were compared regarding their ages on operation day, sex, the side of the hip operated on, surgical indications, follow-up time, and Dorr cortical index classification.9 All data was obtained from the patients’ medical records.

Surgical technique

All patients were intravenously administered a 3 × 1 gr/day dose of cefazolin as prophylactic before the operation. Low molecular weight heparin (0.4 mL/day) was used in all patients as the thromboembolism prophylaxis. All surgical procedures were performed by a single experienced orthopedic surgeon using a posterolateral approach. The uncemented acetabular cup was reconstructed using the press-fit technique in both groups. The use of screws following acetabular cup insertion was left to the preference of the surgeon during surgery. The Optimys short uncemented femoral stem was used for femoral reconstruction in Group 1, and the Stryker Accolade II conventional femoral stem was used in Group 2. Patients in both groups received ceramic femoral heads that matched the size of the acetabular cup.

For patients in both groups, the same post-operative protocol was followed. The patients were mobilized with a walker on the day following surgery, ensuring the highest tolerable weight. For the next three weeks, it was ensured that the patients were mobilized and unsupported after walker use.

Clinical evaluation

The hospital of stay, size of the incision, intra-operative complications, and amount of transfusion and intra-hospital complications were recorded for all patients. The patients were monitored at the post-operative 1st and 3rd months and 1st year. The monitoring included a standard physical examination covering the evaluation of the surgical scar, movement alignment, and functionality of the operated hip. In terms of clinical evaluation, the Harris Hip Score (HHS)10, the SF-36 Life Quality Score11, and the existence of thigh pain12 were considered. Anterior thigh pain Barrack et al. It was done as described by; patients were asked specifically whether or not they had pain in their extremity that they attributed to their hip. If they did have pain, they were asked to shade an area over the location of their perceived pain on an anterior, posterior, and lateral pain drawing. Patients who described the pain in the anterior region were recorded as positive for the presence of anterior thigh pain.

Radiological evaluation

In all pre-operative, immediate post-operative, and final follow-up monitoring sessions, standard anteroposterior and lateral pelvis/hip graphics were taken. In this study, a pre-operative pelvis AP x-ray, pelvis AP x-ray at immediate post-operative, and pelvis AP x-ray were taken in the final follow-up.

The parameters and references considered in the radiological evaluation are as follows (radiological measurements are shown in Fig. 2 and Gruen zones of short and conventional femoral stems are shown Fig. 3):

  1. (1)

    Comparison of the anteversion and inclination of the acetabular cup (pelvis AP x-ray at immediate post-operative and pelvis AP x-ray in the final follow-up were used)13

  2. (2)

    Comparison of the varus/valgus alignment of the femoral stem (pelvis AP x-ray at immediate post-operative and pelvis AP x-ray in the final follow-up were used)14

  3. (3)

    Comparison of total offset (acetabular off-set, femoral off-set) (pre-operative pelvis AP x-ray, pelvis AP x-ray at immediate post-operative, and pelvis AP x-ray in the final follow-up were used)15

  4. (4)

    Comparison of acetabular migration (pelvis AP x-ray at immediate post-operative and pelvis AP x-ray in the final follow-up were used)16

  5. (5)

    Comparison of femoral migration (pelvis AP x-ray at immediate post-operative and pelvis AP x-ray in the final follow-up were used)17

  6. (6)

    Assessment of the periarticular ossification according to Brooker Classification in the pelvis AP x-ray taken in the final follow-up18

  7. (7)

    Determination of acetabular loosening zones according to DeLee and Charnley’s classification in the pelvis AP x-ray taken in the final follow-up19

  8. (8)

    Determination of femoral loosening zones according to Gruen Classification in the pelvis AP x-ray taken in the final follow-up20

Figure 2
figure 2

Reference lines used for acetabular migration measurement (A), reference measurements used for acetabular inclination measurement and acetabular anteversion calculation (B), femoral stem shaft angle measurement (C), pre-operative femoral, acetabular and total off-set measurement (D), post-operative femoral, acetabular and total off-set measurement (E), reference lines used for femoral stem migration (F).

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Figure 3
figure 3

Showing Gruen zones of short and conventional femoral stem.

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Statistical analysis

The SPSS 25.0 statistical software package was used to analyze the data. Numbers and percentages were used to communicate categorical measurements, and mean and standard deviation were used to represent continuous measurements (median and minimum–maximum when required). The Fisher test or the chi-square test were used to compare categorical variables. The distributions were examined to compare continuous variables between the groups. For parameters with normally distributed data, Student’s t-test was employed; for those with non-normally distributed data, the Mann–Whitney U test was used. In each test, the statistical significance level was set at 0.05.

Informed consent

Informed consent was obtained from all individual participants included in the study.

Results

In Group 1, 58 (61.1%) of the patients were female and 37 (38.9%) were male. In Group 2, 51 (56.7) of the patients were female and 39 (43.3) were male.The average age was 57.8 ± 10.8 in Group 1 and 58.3 ± 11.9 in Group 2. When the groups were compared in terms of the average age, no statistically significant difference was found (p = 0.745). While 51 patients underwent left hip surgery and 44 underwent right hip surgery in Group 1, 50 underwent right hip surgery and 40 underwent left hip surgery in Group 2. In terms of surgery side and surgical indication, the values comparing Groups 1 and 2 are shown in Table 1.

Table 1 Comparison of group 1 and group 2 in terms of side and surgical endication.
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The mean follow-up time was 5.5 ± 0.6 years in Group 1 and 5.2 ± 0.8 in Group 2. No statistically significant difference was found between the two groups regarding follow-up time (p = 0.055). No statistically significant difference was found between the groups regarding distribution according to Dorr classification (p = 0.083).

Table 2 provides information on the length of stay, incision size, HHS, SF-36, and joint movement alignments. The two groups were compared to assess complications during the surgeries, complications during hospital stay, transfusion amount, and thigh pain. While only one patient in Group 1 had complications during surgery (femoral fissure), six patients experienced complications in Group 2 (femoral fissure, fracture, etc.). Group 2 had a significantly higher complication rate than Group 1 (p = 0.045). As for complications during the hospital stay (wound discharge, embolism, etc.), two patients in Group 1 had complications, while six patients experienced them in Group 2. There was no statistically significant difference between the groups (p = 0.160). When the number of transfusions was compared, patients in Group 2 received substantially higher transfusions (p = 0.0001). Patients in Group 2 received a replacement of 47 units of erythrocyte suspension, whereas only 22 were given to patients in Group 1. Comparing thigh pain between both groups, none of the patients in Group 1 reported having experienced this complication, while 12 patients in Group 2 stated that they had experienced it. Statistically, the thigh pain rate was higher in patients in Group 2 (p = 0.00001).

Table 2 Length of hospital stay, incision size, Harris hip score, Sf-36 quality of life score, and range of motion of the patients are shown.
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Table 3 displays the stem alignment in the x-rays taken on the immediate post-operative, the change in stem alignment in the x-rays taken in the final follow-up, and the ratio of this change in years. The angular change of the short femoral stem was found to be statistically lower when compared to the conventional stem, both in terms of total angle change and change by year.

Table 3 First post-op x-ray and final post-op x-ray show stem angles and annual angular change (SD: standard deviation).
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Group 1 and Group 2 were compared regarding acetabular and femoral migration and migration ratio per year; however, no statistically significant difference could be found between the groups for these parameters. While the change in distance to the Koher Line was 0.052 ± 0.5 for Group 1, it was 0.057 ± 0.6 in Group 2, but no statistically significant difference was found between the two groups.Acetabular migration of both groups was compared using both acetabular margin line and dear drop as reference, but no statistically significant difference was detected between the 2 groups (p = 0.809/p = 0.104).

Table 4 presents information from total off-set values acquired from pre-op (acetabular offset and femoral offset) values, immediate post-op total off-set values, and total off-set values from the final follow-up. A graphic representation of this data is shown in Fig. 4. No statistically significant difference was found between the groups when comparing the change in acetabular anteversion and inclination.

Figure 4
figure 4

Demonstration of changing femoral, acetabular, and total off-set.

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Table 4 Percentage representation of acetabular, femoral and total off-set changes in pre-op, first post-op and last post-op x-rays of group 1 and group 2.
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When heterotopic ossification formations were compared according to the Brooker Classification, Phase 2 heterotypical ossification was found in seven (7.4%) patients and Phase 4 heterotypical ossification in one patient (1.1%) in Group 1. In Group 2, 14 (15.6%) patients had Phase 2 heterotypical ossification, three patients (4.4%) had Phase 3 heterotypical ossification, and one patient (1.1%) had Phase 4 heterotypical ossification. When the two groups were compared, Group 2 had a significantly increased prevalence for non-Phase 1 heterotopic ossification (p = 0.05).

When the data on the existence of acetabular loosening—according to DeLee and Charnley’s classification—and on the distribution of this loosening in zones, if any, were compared, no statistically significant difference between the groups was found (p = 0.320).

Table 5 shows the distributions of Group 1 and Group 2 based on Gruen Zones and presents information comparing the two groups.

Table 5 Distribution of group 1 and group 2 according to Gruen’s zones.
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Discussion

The HHS was established in 1969 and is among the most frequently used hip scores today10. The SF-36, created in 1992, is a scale that includes 26 parameters. It is frequently used in orthopedic surgery to evaluate the functional status following hip arthroplasty21. In our study, the average HHS for patients in Group 1 and Group 2 was above 90, so the clinical findings can be considered accurate for both groups. Comparing both groups, we observed no statistically significant difference between groups in either the HHS or the SF-36 score. In prior studies in which short femoral stems and conventional femoral stems were compared in terms of clinical scores, no difference existed between the two groups in terms of HHS and SF-3622,23,24. This shows that hip arthroplasty, in terms of appropriate patient selection and adequate surgical operation, is related to good/perfect clinical results and is independent of the implant selection.

Since hip joint movement alignment is a component in the scores24 used in comparative research on hip arthroplasty, we were unable to find studies that specifically examined this parameter. Our study evaluated joint movement alignment separately in both groups and found that flexion and adduction were significantly higher in Group 1. Similar findings were reached by Sousa et al.24 That study found that they might be related to the rise in overall off-set, which will be discussed later. Specifically, a higher flexion angle makes short femoral stems more popular for use in younger patients with high levels of activity.

One drawback of conventional uncemented femoral stems, aside from their positive results, is the potential for periprosthetic fracture. The periprosthetic fracture incidence varies between 1 and 6% for conventional uncemented femoral stems, as shown in Lindahl25 In this respect, when the two groups were compared, periprosthetic fracture was a significantly more frequent complication in Group 2. In comparative studies22,23,24,25,26 and in Wittenberg’s case series27 which included 250 patients, it was shown that prosthetic fracture complication in short femoral stems is significantly low, parallel to our study, which demonstrated that short femoral stems can minimize the risk of fracture if uncemented femoral stems are used in patients with relatively poor bone quality.

According to Daninger et al., blood transfusions increase the risk of complications, surgical site infections, length of stay in the hospital, and mortality rates in knee and hip arthroplasties28. In addition to these complications, blood transfusions are costly. There are two explanations for Group 1’s reduced transfusion rate. One is the minimal bleeding of soft tissues due to the short incision, and the other is the minimal bleeding of bones due to the minimal bone rasping. Although it is not a direct reason for preference, short femoral stems could be chosen to reduce bleeding in patients who may have difficulty tolerating the decrease in hemoglobin. We believe that this would be beneficial both clinically and cost-effectively.

Thigh pain is one of the problems associated with conventional uncemented femoral stems. There have been several instances where revisions have been made because of thigh pain, even though clinical practice does not place much emphasis on it29. Conversely, it has been demonstrated in our study and Yu and Kim’s study26,30 that thigh pain is not a normal consequence of short femoral stems, which is regarded as a key factor in preference.

Short femoral stems could be placed in a varus position since they have a curve in their body Section31 However, there is no consensus on an acceptable varus position. In our study, the groups were compared in terms of varus/valgus alignment and the annual alignment change to provide information about the rotational and vertical stability of the femoral stem. At the end of the monitoring period, Group 1 had reached a 5-degree varus alignment, having undergone a more angular shift than the other group. However, there was hardly any angular shift in Group 2. Short femoral stems do not entirely fill the medullar canal, according to Luger et al.32 and Blakeney et al.33 Additionally, implant/bone contact is less significant than conventional stems, and it diminishes for varus angles higher than 3 degrees. According to these studies and our investigation, short femoral stems have a higher chance of loosening over time due to their reduced angular stability and smaller bone/implant contact area. However, it should be noted that short femoral stems would render a better biomechanical load transfer in cases with a smaller collodiaphyseal angle and inclination to varus alignments, such as coxa vara34.

The limited ability of reconstructing femoral off-set in conventional femoral stems has been studied extensively in the literature35 Therefore, attempts have been made to remove this limitation in short femoral designs. Off-set (especially femoral off-set) is a parameter that affects clinical results, the dislocation rate, abrasion, revision rates, and leg length. The restoration of femoral off-set increases the post-operative joint movement distance and has a positive effect on polyethylene abrasion35 It has been proven that short femoral stems increase femoral off-set based on the varus alignment, and acetabular off-set is decreased based on the medialization during the acetabular component placement32,36. In our study, we found that both femoral off-set and total off-set increased in both groups compared to the pre-op values. However, unlike other studies, the increase in femoral off-set in short femoral stems was significantly higher than in conventional femoral stems. This was because we preferred a higher varus position in implanting the short femoral stems. Therefore, short femoral stems provide a better reconstruction facility in cases of abductor muscle weakness, in which an increased femoro-acetabular off-set reconstruction is required.

Heterotopic ossification is a frequent complication of hip arthroplasty, and its prevalence is not the same in all patient groups. The prevalence varies between 15 and 90%. It could easily be diagnosed in the pelvis AP x-ray. The Brooker classification, which categorizes heterotopic ossification into 4 groups, is often used37 Heterotopic ossification is a problematic complication because it can shadow the ameliorating effect of surgery, limit the movement distance in the hip joint, and even force the patient to have revision surgery. No study in the literature shows the heterotopic ossification frequency of short femoral stems or compares them with conventional stems. However, studies indicating that heterotopic ossification prevalence is low following hip arthroplasties performed with short femoral stems can be found38,39 In this study, in which short femoral stems and conventional femoral stems were assessed, we concluded that heterotypical ossification is less frequent in the group given short femoral stems.

Different femoral stems used for THA affect periprosthetic bone mineral density. However, there is no clear consensus about this effect. Short femoral stems are believed to have a greater potential to preserve more bone and soft tissue than conventional femoral stems40 Different prosthetic designs might have a bone re-modelization pattern in different variations. Therefore, we evaluated the osteointegration around the femoral stem using the Gruen classification for both groups. Examining the data from our study, we can observe that osteointegration occurs in the proximal regions (Gruen Zones 1, 2 and 6, 7) in the group with the short femoral stem and in the distal regions (Gruen Zones 3 and 5) in the group with the conventional femoral stem. This shows that the conventional femoral stems provided distal load transfer while short femoral stems mainly provided proximal load transfer. Both radiological and densitometric studies in the literature support our findings23,24,26,41 However, Yan et al. discovered in their meta-analysis that the level of this information’s evidence-basedness is low41. They argued that comparative, long-monitoring-based, and large-series studies should be conducted to gain a more accurate perspective41. Accordingly, it could be argued that short femoral stems could be preferred to preserve the periprosthetic bone reserve, especially in the younger patient population, considering the need for revisions40. The data in the literature and our study support this view.

This study, in which both femoral stems were assessed from a wider angle, has some limitations. It was retrospective, and the functional score data are based on patient declarations, leaving them open to interpretation. The migration measures were conducted manually, so the participant pool was relatively small.

The present study compared short femoral stems and conventional femoral stems in a broad yet detailed perspective. Although it showed their beneficial qualities and was in line with the literature, it demonstrated that there are several medium-term consequences of short femoral stems that are contrary to their intended use.

Conclusion

In general, hip arthroplasty is a productive procedure if conducted with the appropriate surgical techniques and implants. When the mid-term clinical and radiological comparison of short femoral stems and conventional femoral stems is considered, short femoral stems are more appropriate with the right type of patients (with low collo-diaphyseal angle, coxa vara, and younger arthroplasty patients, etc.) if we consider the cost/benefit rate. Compared to conventional stems, short femoral stems provide less anterior thigh pain, fewer intra-operative complications, higher degree of flexion/adduction and better angular stability, according to mid-term results. However, comparative studies with extensive series that result in long-term findings are required to obtain better results.