Similar functional outcomes but different remodeling patterns: A minimum 5-years radiographic comparison of short fit-and-fill stem and quadrangular taper stem

Abstract

Purpose

ACTIS and CORAIL are cementless titanium femoral stems with hydroxyapatite (HA) coating but differing macro-geometries: ACTIS features a variable triple-taper with a medial collar, whereas CORAIL is a straight double-tapered design available with or without a collar. We compared mid-term clinical and radiographic outcomes of these stems with a minimum 5-years follow-up.

Methods

We retrospectively reviewed 114 primary total hip arthroplasties using ACTIS (63 hips) or CORAIL (51 hips). Clinical outcomes and standardized radiographic parameters were assessed and compared between groups.

Results

The canal-fill ratio (CFR) was significantly greater at the proximal, middle, and distal levels in the ACTIS group. Spot-weld formation was more frequent with ACTIS than with CORAIL (58.7% vs 35.3%). In logistic regression, proximal CFR significantly predicted spot-weld formation for ACTIS, with an optimal cutoff of 66.2% (sensitivity 91.9%, specificity 72.0%). Rates of subsidence, radiolucent lines, and pedestal formation did not differ significantly between groups. No severe stress shielding was observed with ACTIS, whereas three CORAIL hips demonstrated severe stress shielding (0% vs 5.9%). Clinical scores improved significantly in both groups, with no significant between-group differences at final follow-up.

Conclusions

Both stems yielded favorable radiographic and clinical mid-term outcomes. In ACTIS, greater proximal canal fill was associated with radiographic osseointegration, suggesting proximal CFR as a probabilistic radiographic marker of stem ingrowth.

Keywords

total hip arthroplasty ACTIS CORAIL mid-term outcome retrospective study

Introduction

Total hip arthroplasty (THA) is widely regarded as a highly effective procedure for relieving pain and restoring function in patients with osteoarthritis or osteonecrosis, and has been termed the “operation of the century”.¹ Demand for THA continues to increase, with projections estimating that more than 1.4 millions procedures will be performed annually in the United States by 2040.² In contemporary practice, cementless femoral stems are increasingly preferred because they offer a relatively straightforward surgical technique and may shorten operative time.³ Durable fixation of cementless stems, however, depends on successful osseointegration, which is influenced by implant macro-geometry, surface characteristics, initial mechanical stability, and host bone biology.⁴

The CORAIL Hip System (DePuy Synthes, Warsaw, IN, USA) is a fully hydroxyapatite (HA)–coated cementless stem available in collared and collarless versions (Figure 1(a)–(c)).⁵ It is implanted using a compaction broach–only technique designed to preserve cancellous bone and to create a biologically favorable environment for fixation.⁶ Owing to its minimal radiographic findings and durable performance, CORAIL has been described as a “silent” stem and has demonstrated excellent long-term survivorship with low complication rates.^5–7

Figure 1.

(a–c) CORAIL hip system (DePuy Synthes). CORAIL has a structure with a medial collar, tapered, and coated with hydroxyapatite. CORAIL is tapered from proximal to distal in both the coronal and sagittal planes (double tapered). (d–f) ACTIS Total Hip System (DePuy Synthes). ACTIS has a structure with a medial collar, coated with hydroxyapatite, and a reduced lateral shoulder. ACTIS features a triple taper geometry. Tapered from proximal to distal in the anterior/posterior plane, medial/lateral plane, and lateral to medial in the transverse or axial plane.

In contrast, the ACTIS Total Hip System (DePuy Synthes, Warsaw, IN, USA) is a more recent design based on a short fit-and-fill philosophy and incorporates a medial collar with a variable triple-tapered (MCTT) geometry (Figure 1(d)–(f)). The stem is fully HA-coated and is inserted using a hybrid broaching technique that combines compaction in the anteroposterior (AP) plane with extraction in the mediolateral (ML) plane.⁸ Although early reports have shown encouraging short-term outcomes, comprehensive mid-term radiographic data remain limited.^8,9

Although both ACTIS and CORAIL are fully HA-coated cementless stems, they differ in macro-geometry, broaching technique, and intended fixation strategy. The clinical relevance of these differences with respect to implant performance and patient outcomes has not been fully clarified. Therefore, the objective of this study was to compare mid-term radiographic and functional outcomes between the ACTIS and CORAIL femoral stems in primary THA.

Materials and methods

Study design and participants

This retrospective study was approved by the institutional review boards of the authors’ affiliated institutions (IRB number: 2501-055) and conducted in accordance with the Declaration of Helsinki and applicable national and institutional research ethics standards. Owing to the retrospective design, the requirement for informed consent was waived.

We reviewed data from patients who underwent primary THA using either the ACTIS or CORAIL femoral stem between January 2016 and September 2019 at our centers. From an initial cohort of 146 hips in 123 patients (86 ACTIS, 60 CORAIL), 32 hips were excluded because the patients died or were lost to follow-up before the 5-years time point. The final study population comprised 114 hips in 101 patients: 63 hips (56 patients) treated with ACTIS and 51 hips (45 patients) treated with CORAIL.

Two orthopedic surgeons performed all procedures using either an anterolateral or posterior approach, according to surgeon preference. Importantly, both surgeons implanted both ACTIS and CORAIL stems throughout the study period; thus, there was no systematic allocation of a specific stem to a specific surgeon. All operations were performed with the patient in the lateral decubitus position. Each patient received a PINNACLE^® acetabular cup (DePuy Synthes, Warsaw, IN, USA) secured with two or three screws. Femoral stem size was selected based on preoperative 2D or 3D templating and confirmed intraoperatively by achieving rotational stability; the final broach dictated the implanted stem size. If the trial stem did not seat flush with the osteotomy, residual calcar bone was trimmed using a calcar reamer. All CORAIL stems implanted in this cohort were the collared version. Soft-tissue repair was performed according to the surgical approach, and full weight-bearing ambulation commenced on postoperative day 1.

Radiographic evaluation

Patients were followed at routine intervals—6 weeks, 3 months, 6 months, 1 year, and annually thereafter. Immediate postoperative and final follow-up radiographs were assessed for the following parameters: spot-welds, stress shielding, cortical hypertrophy, subsidence, radiolucent lines, reactive lines, pedestal formation, and stem alignment. Spot-welds were recorded by Gruen zone.¹⁰ Stress shielding was graded according to Engh’s classification, with grades 1–2 considered mild and grades 3–4 severe.¹¹

Stem subsidence was determined by comparing distances between anatomical landmarks on immediate postoperative and final images—(i) the greater trochanter to the lateral shoulder of the stem and (ii) the inferior collar to the lesser trochanter (LT)—with subsidence ≥2 mm deemed significant.¹² Coronal stem alignment was measured relative to the proximal femoral axis on anteroposterior (AP) radiographs and categorized as neutral or varus/valgus (≥2° deviation). On lateral radiographs, stems were categorized as neutral, flexed, or extended.

Stem fixation was classified radiographically according to Engh et al. as bone ingrowth, stable fibrous fixation, or unstable fibrous fixation.¹³ Femoral morphology was characterized using the canal flare index (CFI) and the Dorr classification (types A, B, C).¹⁴ The canal-fill ratio (CFR) was measured at three levels: 20 mm proximal to the LT, 20 mm distal to the LT, and 20 mm proximal to the stem tip.¹⁵

Clinical evaluation

Clinical outcomes were evaluated using the original Harris Hip Score (HHS)¹⁶ and the Japanese Orthopaedic Association (JOA) hip score.¹⁷ The HHS comprises four domains—pain (44 points), function (47 points), absence of deformity (4 points), and range of motion (5 points)—for a maximum of 100 points; lower scores indicate greater disability. The JOA hip score allocates 100 points across pain (40 points), range of motion (20 points), walking ability (20 points), and activities of daily living (20 points). Pre- and postoperative HHS and JOA scores were recorded for both groups. Complications, including infection, dislocation, and periprosthetic fracture, were also documented.

Statistical analysis

Given the multiple radiographic outcomes assessed, we defined the presence of spot-welds on AP radiographs at final follow-up (minimum 5-years) as the primary radiographic endpoint. Secondary endpoints included other radiographic findings (stress shielding, reactive lines, cortical hypertrophy, subsidence, radiolucent lines, pedestal formation, and stem alignment) as well as clinical outcomes (HHS and JOA scores). Analyses of secondary endpoints were considered supportive/exploratory and were interpreted accordingly. Continuous variables (age, body mass index [BMI], CFI, and CFR) were compared using the Student’s t-test. Binary radiographic outcomes (spot-welds, stress shielding, cortical hypertrophy, subsidence, radiolucent lines, reactive lines, and pedestal formation) were compared using the chi-square test. Categorical variables (sex, Dorr type, and stem alignment) were compared using the chi-square test or Fisher’s exact test, as appropriate; Fisher’s exact test was used when one or more expected cell counts were <5. Groups were further stratified by the presence or absence of spot-welds on AP radiographs. Univariate analyses examined associations between spot-welds and clinical or radiographic variables; variables meeting the entry criterion were included in multivariable logistic regression. Receiver operating characteristic (ROC) analysis was used to determine optimal cutoffs for significant predictors, and areas under the curve (AUCs) with 95% confidence intervals (CIs) were calculated. Stem survivorship was evaluated using the Kaplan–Meier method. The endpoint was stem revision for any reason (including exchange or removal of the femoral stem). Hips without stem revision were censored at the time of the final follow-up. 95% CIs were calculated using Greenwood’s formula. Paired t tests were used to compare pre- and postoperative HHS and JOA scores. All analyses were performed using SPSS Statistics, version 25 (IBM Corp., Armonk, NY, USA).

Results

Baseline patient characteristics are summarized in Table 1. There were no statistically significant differences between the ACTIS and CORAIL groups in age, sex distribution, BMI, diagnosis, follow-up duration, or femoral morphology by Dorr classification.

Table 1.

Patient demographics and radiographic evaluation.

Parameters	ACTIS	CORAIL	p-value
Number of hips	63	51
Gender, male/female^a	12/51	15/36	0.196
Age (years)^b	61.7 ± 8.6 (43–82)	59.1 ± 13.3 (27–80)	0.111
Follow-up duration (months)^b	73 ± 3.6 (60–83)	72 ± 17 (60–110)	0.063
BMI (kg/m²)^b	24 ± 4.3 (16–34)	24 ± 4.1 (16.9–32.7)	0.27
Diagnosis n(%)^a
Osteoarthritis	49 (77.8%)	41 (80.4%)	0.471
Osteonecrosis of femoral head	11 (17.5%)	10 (19.6%)
Rapidly destructive coxarthropathy	2 (3.2%)	0
Rheumatoid arthritis	1 (1.6%)	0
Dorr type n(%)^a
A	6 (9.5%)	5 (9.8%)	0.559
B	48 (76.2%)	42 (82.4%)
C	9 (14.3%)	4 (7.8%)
Alignment (AP)^a (Neutral/Varus/Valgus)	52/5/6	48/1/2	0.165
Alignment (ML)^a (Neutral/Flexion/Extension)	51/12/0	44/7/0	0.448
Spot-welds^a
Anterior-posterior	37 (58.7%)	18 (35.3%)	0.013
Lateral	18 (28.6%)	5 (9.8%)	0.013
Reactive line^a	4 (6.3%)	12 (23.5%)	0.009
Cortical hypertrophy^a	5 (7.9%)	0 (0%)	0.040
Stress shielding^a
All (1st to 4th degree)	18 (28.6%)	17 (33.3%)	0.584
Severe (3rd to 4th degree)	0 (0%)	3 (5.9%)	0.051
Subsidence^a	1 (1.6%)	0 (0%)	0.366
Radiolucent line^a	4 (6.3%)	1 (2.0%)	0.255
Pedestal formation^a	5 (7.9%)	1 (2.0%)	0.155
CFR (%)^b
Proximal of LT	70.4 ± 9.4	54.9 ± 5.5	<0.001
Distal of the LT	72.5 ± 7.0	69.8 ± 5.5	0.015
Distal of the stem	66.0 ± 10.3	60.4 ± 10.6	0.003

BMI: body mass index, AP: Anterior-posterior, ML: Medial-lateral, CFR: canal-fill ratio, LT: lesser trochanter. Differences are considered significant for values of p < 0.05.

^a chi-square test or Fisher’s exact test, as appropriate.

^b Student’s t-test.

Stem alignment was assessed on AP radiographs. In the ACTIS group, 52 hips (82.5%) were neutral, five (7.9%) varus, and six (9.5%) valgus. In the CORAIL group, 48 hips (94.1%) were neutral, one (2.0%) varus, and two (3.9%) valgus. The between-group difference in AP alignment was not significant (p = 0.165). On lateral radiographs, 51 ACTIS stems (81.0%) were neutral and 12 (19.0%) were flexed. In the CORAIL group, 44 stems (86.3%) were neutral and seven (13.7%) were flexed. The between-group difference in lateral alignment was not significant (p = 0.448).

Spot-welds were more frequent in the ACTIS group on both AP (58.7% vs 35.3%; p = 0.013) and lateral views (28.6% vs 9.8%; p = 0.013). In the ACTIS group, spot-welds were observed across AP zones 1–6 and, on lateral views, in all zones except 10 (Figure 2(a) and (c)). In the CORAIL group, spot-welds were predominantly located in lateral zones 9–11 (Figure 2(b) and (d)). Overall, spot-welds were more commonly detected distally in both groups. Reactive lines were observed in four hips in the ACTIS group and 12 hips in the CORAIL group (6.3% vs 23.5%; p = 0.009). Because some hips showed reactive lines in more than one Gruen zone, the following zone-level counts reflect hips per zone (non-mutually exclusive): ACTIS—zone 3 (n = 1), zone 4 (n = 2), zone 5 (n = 1), zone 6 (n = 1), and zone 11 (n = 1); CORAIL—zone 1 (n = 12), zone 7 (n = 2), and zone 14 (n = 2). In the CORAIL group, all reactive lines were confined to the proximal portion of the stem (Figure 3(a)). Cortical hypertrophy occurred more frequently with ACTIS (7.9% vs 0%; p = 0.040; Figure 3(b)). There were no significant between-group differences in the rates of stress shielding (grades 1–4; 28.6% vs 33.3%; p = 0.584), subsidence (1.6% vs 0%; p = 0.366), radiolucent lines (6.3% vs 2.0%; p = 0.255), or pedestal formation (7.9% vs 2.0%; p = 0.155). Severe stress shielding (grades 3–4) was not observed with ACTIS but occurred in three hips in the CORAIL group. The CFR was consistently greater with ACTIS at all three measurement levels (proximal: p < 0.001; middle: p = 0.015; distal: p = 0.003).

Figure 2.

Spot-welds appearance per Gruen zone. (a) ACTIS, coronal plane. (b) ACTIS, sagittal plane. (c) CORAIL, coronal plane. (d) CORAIL, sagittal plane.

Figure 3.

(a) A 40-years-old male with a Dorr type A underwent THA with CORAIL. At 5-years follow-up, a reactive line was observed in Gruen zone 1. (b) A 56-years-old female patient underwent THA using ACTIS. At 6-years follow-up, cortical hypertrophy was observed in Gruen zone 5.

In univariate analyses comparing hips with and without spot-welds on AP radiographs, there were no significant differences in age, sex, BMI, Dorr classification, or stem alignment within either group (Table 2). In the ACTIS cohort, CFR values were significantly higher at all measurement levels among hips with spot-welds (proximal p < 0.001, middle p < 0.001, distal p = 0.030). On multivariable logistic regression of 5-years radiographs, proximal CFR independently predicted spot-weld formation in ACTIS (odds ratio per 1% increase 1.31; 95% CI, 1.14–1.51; p < 0.001; Table 3). The ROC curve for proximal CFR yielded an optimal cutoff of 66.2%, with 91.9% sensitivity and 72.0% specificity (Figure 4). In the CORAIL cohort, hips with spot-welds showed higher CFR at the level distal to the lesser trochanter (p = 0.0075) and at the distal stem (p = 0.020) on univariate analysis; however, these associations were not retained in multivariable models.

Table 2.

The univariate analysis of the presence or absence of spot-welds on anterior-posterior radiographs.

Parameters	ACTIS			CORAIL
Parameters	SW (+) (n = 37)	SW(−) (n = 26)	p-value	SW (+) (n = 18)	SW(−) (n = 33)	p-value
Age (years)^a	62.3 ± 8.1 (45–84)	65.6 ± 9.0 (46–78)	0.068	56.1 ± 8.1 (27–72)	61.1 ± 13.7 (28–80)	0.099
Gender, male/female^b	5/32	6/21	0.361	8/10	7/26	0.082
BMI (kg/m²)^a	23.9 ± 4.4 (15.5–37.3)	25.4 ± 4.0 (18.6–33.5)	0.087	24.9 ± 4.2 (16.9–32.0)	23.4 ± 4.0 (16.9–32.7)	0.10
Dorr type^b
A	5	1	0.437	3	2	0.45
B	27	21		14	28
C	5	4		1	3
Alignment (AP)^b (Neutral/Varus/Valgus)	30/2/5	22/3/1	0.325	17/1/0	31/0/2	0.23
CFR (%)^a
Proximal of the LT	74.9 ± 8.6 (59.3–96)	63.6 ± 5.7 (56–78.9)	<0.001	55.8 ± 4.8 (46.9–68.5)	54.3 ± 4.6 (42.9–64.7)	0.19
Distal of the LT	74.8 ± 6.7 (56–78.9)	67.8 ± 7.9 (53–82.1)	<0.001	72.1 ± 5.1 (65–83.3)	68.2 ± 3.1 (59.1–77.3)	0.0075
Distal of the stem	68.0 ± 9.3 (47.7–83)	62.9 ± 11.4 (43.6–85)	0.030	64.2 ± 11.2 (46.2–86.2)	57.8 ± 5.8 (38.5–76)	0.020

SW: spot-welds, BMI: body mass index, AP: anterior-posterior, CFR: canal-fill ratio, LT: lesser trochanter. Differences are considered significant for values of p < 0.05.

^aStudent’s t-test.

^bchi-square test.

Table 3.

The multivariate analysis with presence or absence of spot-welds of ACTIS.

Variables	Partial regression coefficient	Standard error	Odds ratio	95% CI		p-value
Variables	Partial regression coefficient	Standard error	Odds ratio	Lower	Upper	p-value
CFR (proximal of the LT)	0.27	0.071	1.31	1.14	1.51	<0.001
CFR (distal of the stem)	0.063	0.040	1.07	0.99	1.15	0.11

CI: confidence interval, CFR: canal-fill ratio, LT: lesser trochanter. Differences are considered significant for values of p < 0.05.

Figure 4.

Receiver operating characteristic curve (ROC) for prediction of the appearance of spot-welds five-years after surgery in ACTIS based on canal-fill ratio (CFR) at 20 mm proximal of the lesser trochanter. AUC: area under curve, CI: confidence interval.

Functional outcomes improved significantly in both groups. In ACTIS, the HHS improved from 54.4 ± 14.6 to 92.4 ± 6.6; in CORAIL, from 61.6 ± 15.5 to 92.1 ± 5.3 (between-group comparison of final scores, p = 0.43). JOA scores increased from 46.0 ± 12.0 to 93.2 ± 9.0 in ACTIS and from 55.3 ± 15.0 to 94.3 ± 7.0 in CORAIL (between-group p = 0.58). No major complications (dislocation, infection, periprosthetic fracture) or revision surgeries were reported. Five-year stem survivorship (Kaplan–Meier estimate; endpoint: stem revision for any reason) was 100%.

Discussion

This study compared 5-years postoperative radiographic and clinical outcomes between two cementless femoral stems—ACTIS and CORAIL—used in primary THA. Both stems yielded excellent clinical outcomes and reliable fixation; however, radiographic differences were evident. CORAIL exhibited a radiographically “silent” profile with fewer spot-welds, consistent with prior reports. By contrast, the ACTIS cohort showed more pronounced cancellous bone remodeling, particularly on AP views, suggesting a different remodeling pattern consistent with its fit-and-fill design and hybrid broaching technique. Across both cohorts, all implants demonstrated secure biologic fixation by bone ingrowth, with no mechanical loosening or prosthesis-related complications throughout the 5-years follow-up. Functional scores—HHS and JOA—improved significantly from baseline in both groups, underscoring the clinical efficacy of both designs.

The CORAIL stem’s distal geometry promotes rotational stability while minimizing cortical contact. Its stepped geometry is designed to resist shear and enhance compressive loading.⁶ Prior studies have reported long-term survivorship rates of 99.1% at 12 years⁷ and 96.3% at 23 years for CORAIL stems.⁶ Although longer-term outcomes for ACTIS are not yet widely available, real-world analyses have shown a low revision risk (1.08%) and favorable healthcare efficiency, including shorter operative time, reduced length of stay, and lower overall costs.^18,19 Early series have also reported high implant survivorship (99.6%) and low complication rates for ACTIS, although detailed radiographic findings were not provided.⁹

Design differences may influence peri-implant stress distribution and bone remodeling. Tapered-wedge stems with a reduced lateral shoulder were developed to facilitate minimally invasive approaches to THA. However, single- and double-wedge (fit-and-fill) femoral implants have been associated with increased rates of periprosthetic femoral fracture (PPF),²⁰ whereas the CORAIL stem has been linked to fewer postoperative PPFs compared with other implants.²¹ In general, conventional fit-and-fill stems achieve robust initial fixation by increasing the canal-fill ratio from the metaphysis into the diaphysis.²² Nevertheless, their straight, elongated profile requires meticulous rasping—particularly with anterior approaches—and may predispose to distal fixation and PPF. In contrast, in THA using the ACTIS stem, no intraoperative complications, including calcar fractures, muscle tears, or PPFs, were reported in one series.⁸ The ACTIS design’s medial collar likely contributes to enhanced primary stability, particularly in the vertical and rotational planes.^21,23

Severe stress shielding was reported in 11.1% of hips at 5-years follow-up in a previous study of the CORAIL stem.²⁴ In our series, severe stress shielding was observed radiographically only in the CORAIL group. Among CORAIL hips with Dorr type A morphology, 80% exhibited proximal reactive lines. These findings raise concern for increased stress shielding and a tendency toward distal fixation. In narrow canals (e.g., Dorr type A), use of the CORAIL stem may require additional distal reaming to avoid distal fixation. By contrast, although a subset of ACTIS hips also demonstrated Dorr type A morphology, no radiographic signs of distal fixation were observed. This may reflect the ACTIS stem’s shorter length and triple-tapered, fit-and-fill geometry, which are intended to optimize proximal engagement while preserving bone.

In this study, ACTIS showed significantly more spot-welds than CORAIL on AP radiographs. Although spot-welds are commonly regarded as a radiographic sign suggestive of bone ingrowth fixation, their absence does not necessarily indicate inferior osseointegration. Given that both stems achieved secure biologic fixation and equivalent 5-years functional outcomes in the present study, the higher frequency of spot-welds with ACTIS should be interpreted as a different remodeling pattern rather than evidence of clinical superiority.

ACTIS is implanted using a hybrid broaching technique that combines mediolateral extraction with AP compaction to preserve cancellous bone, which may contribute to its fit-and-fill interface and the higher frequency of spot-welds observed on AP views. By contrast, uncemented THA with the CORAIL stem has been linked to less favorable radiographic outcomes in femora with insufficient proximal filling.¹⁵ Although CFR in the CORAIL group was comparable to prior reports, the ACTIS group demonstrated significantly higher CFR at the proximal, middle, and distal levels. Multivariable analysis further showed that greater proximal CFR independently predicted spot-weld formation with ACTIS and was not accompanied by evidence of distal fixation. On lateral radiographs, ACTIS exhibited a radiographically “silent” pattern similar to CORAIL, with cancellous bone compaction except for focal spot-welds where the stem contacts the femoral cortex (Gruen zones 9, 11, and 12).

From a practical standpoint, a proximal CFR ≥66.2% can be interpreted as a probabilistic radiographic marker indicating a higher likelihood of spot-weld formation (osseointegration) for the ACTIS stem. However, we do not advocate intentionally pursuing a specific numeric target through aggressive broaching, because excessive canal fill and/or distal cortical contact may theoretically increase the risk of cortical hypertrophy or periprosthetic fracture. Importantly, in our cohort, a proximal CFR <66.2% did not translate into inferior 5-years clinical outcomes or radiographic loosening; therefore, this cutoff should be viewed as a guide to avoid obvious undersizing rather than a mandatory threshold. Longer-term follow-up and external validation in independent cohorts are warranted to determine whether lower proximal filling has any late clinical implications.

Cortical hypertrophy was observed in a small proportion of ACTIS hips, which may reflect localized load transfer near the distal portion of the stem.²⁵ Prior literature indicates that greater canal fill and tight distal cortical contact can elevate mechanical stress and stimulate bone remodeling.²⁶ Consistent with its fit-and-fill design, ACTIS showed a higher canal-fill ratio and closer apposition to the endosteal cortex, which could increase local loading and contribute to focal cortical hypertrophy. Although cortical hypertrophy was not associated with inferior 5-years clinical scores in our cohort, its longer-term implications—such as thigh pain or distal load transfer–related stress risers—remain uncertain; therefore, continued long-term surveillance is warranted.^26,27

The increasing adoption of minimally invasive surgery (MIS) that preserves muscle and soft tissue has been associated with lower dislocation rates in some series and with earlier functional recovery.²⁸ The ACTIS stem’s compatibility with MIS—even in patients with higher BMI—adds to its clinical appeal. Its shorter overall length and angled insertion feature facilitate placement with reduced soft-tissue disruption, which may be particularly beneficial in anatomically challenging cases.

Several limitations should be acknowledged. First, because this was a retrospective, non-randomized comparison, unmeasured confounding cannot be excluded. Although both surgeons implanted both stems (minimizing surgeon-dependent allocation), residual confounding related to case selection or subtle technical differences may remain. Second, the cohort size may be insufficient to detect rare complications or to support robust subgroup analyses (e.g., severe stress shielding), and the estimated frequencies of stem alignment and radiographic findings may differ in a larger series. In addition, radiographic assessments were limited to standard radiographs, which are less sensitive than CT for detecting osteolysis and subtle periprosthetic changes. Accordingly, multicenter studies with larger sample sizes and long-term follow-up are needed to further validate these findings.

Conclusion

Both ACTIS and CORAIL femoral stems provided excellent 5-years outcomes in primary THA. ACTIS was associated with more pronounced cancellous bone remodeling, likely reflecting its fixation strategy. A higher proximal canal-fill ratio was significantly associated with spot-weld formation in ACTIS, suggesting proximal CFR as a probabilistic radiographic marker of osseointegration; continued follow-up is warranted to determine whether these mid-term patterns persist and whether lower proximal filling has any late clinical implications.

Footnotes

Acknowledgments

We would like to thank all authors for helpful discussions, and Editage () for English language editing.

ORCID iDs

Tomonori Tetsunaga

Yuki Okazaki

Ethical considerations

This retrospective study was approved by the authors’ affiliated institutions. All procedures were performed following the ethical standards of the institutional and/or national research committee, the 1964 Declaration of Helsinki and its later amendments, or comparable ethical standards.

Consent to participate

Written informed consent was waived because of the retrospective nature of the study.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data Availability Statement

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.*

References

Learmonth

Young

Rorabeck

. The operation of the century: total hip replacement. Lancet 2007; 370: 1508–1519. DOI: https://doi.org/10.1016/S0140-6736(07)60457-7

Singh

Chen

, et al. Rates of total joint replacement in the United States: future projections to 2020–2040 using the national Inpatient sample. J Rheumatol 2019; 46: 1134–1140. DOI: https://doi.org/10.3899/jrheum.170990

Wechter

Comfort

Tatman

, et al. Improved survival of uncemented versus cemented femoral stems in patients aged <70 years in a community total joint registry. Clin Orthop Relat Res 2013; 471: 3588–3595. DOI: https://doi.org/10.1007/s11999-013-3182-5

Khanuja

Vakil

Goddard

, et al. Cementless femoral fixation in total hip arthroplasty. J Bone Joint Surg Am 2011; 93: 500–509. DOI: https://doi.org/10.2106/JBJS.J.00774

Al-Najjim

Khattak

Sim

, et al. Differences in subsidence rate between alternative designs of a commonly used uncemented femoral stem. J Orthop 2016; 13: 322–326. DOI: https://doi.org/10.1016/j.jor.2016.06.026

Vidalain

. Twenty-year results of the cementless corail stem. Int Orthop 2011; 35: 189–194. DOI: https://doi.org/10.1007/s00264-010-1117-2

Chatelet

Setiey

. [Long term bone behavior in total primary hip arthroplasty with a fully hydroxyapatite-coated femoral stem: a continuous series of 120 cases with twelve years follow-up]. Rev Chir Orthop Reparatrice Appar Mot 2004; 90: 628–635. DOI: https://doi.org/10.1016/s0035-1040(04)70723-0

Kaszuba

Cipparrone

Gordon

. The actis and corail femoral stems provide for similar clinical and radiographic outcomes in total hip arthroplasty. HSS J 2020; 16: 412–419. DOI: https://doi.org/10.1007/s11420-020-09792-2

Hunter

Fawley

Diaz

, et al. Five-year survivorship of total hip arthroplasty with a proximally coated, medially collared, triple-tapered femoral stem: a retrospective, multicenter registry review. Cureus 2024; 16(5): e59462. DOI: https://doi.org/10.7759/cureus.59462

10.

Gruen

McNeice

Amstutz

. “Modes of failure” of cemented stem-type femoral components: a radiographic analysis of loosening. Clin Orthop Relat Res 1979: 17–27.

11.

Engh

Bobyn

Glassman

. Porous-coated hip replacement. The factors governing bone ingrowth, stress shielding, and clinical results. J Bone Joint Surg Br 1987; 69: 45–55. DOI: https://doi.org/10.1302/0301-620X.69B1.3818732

12.

Mulliken

Bourne

Rorabeck

, et al. A tapered titanium femoral stem inserted without cement in a total hip arthroplasty. Radiographic evaluation and stability. J Bone Joint Surg Am 1996; 78: 1214–1225. DOI: https://doi.org/10.2106/00004623-199608000-00012

13.

Engh

Massin

Suthers

. Roentgenographic assessment of the biologic fixation of porous-surfaced femoral components. Clin Orthop Relat Res 1990: 107–128.

14.

Dorr

Faugere

Mackel

, et al. Structural and cellular assessment of bone quality of proximal femur. Bone 1993; 14: 231–242. DOI: https://doi.org/10.1016/8756-3282(93)90146-2

15.

D'Ambrosio

Peduzzi

Roche

, et al. Influence of femoral morphology and canal fill ratio on early radiological and clinical outcomes of uncemented total hip arthroplasty using a fully coated stem. Bone Joint Res 2020; 9: 182–191. DOI: https://doi.org/10.1302/2046-3758.94.BJR-2019-0149.R2

16.

Harris

. Traumatic arthritis of the hip after dislocation and acetabular fractures: treatment by mold arthroplasty. An end-result study using a new method of result evaluation. J Bone Joint Surg Am 1969; 51: 737–755.

17.

Kuribayashi

Takahashi

Fujioka

, et al. Reliability and validity of the Japanese orthopaedic association hip score. J Orthop Sci 2010; 15: 452–458. DOI: https://doi.org/10.1007/s00776-010-1490-0

18.

Chitnis

Mantel

Ruppenkamp

, et al. Survival analysis for all-cause revision following primary total hip arthroplasty with a medial collared, triple-tapered primary hip stem versus other implants in real-world settings. Curr Med Res Opin 2020; 36: 1839–1845. DOI: https://doi.org/10.1080/03007995.2020.1822309

19.

Diaz

Mantel

Ruppenkamp

, et al. Real-world 2-year clinical and economic outcomes among patients receiving a medial collared, triple tapered primary hip system versus other implants for total hip arthroplasty. Curr Med Res Opin 2023; 39: 1575–1583. DOI: https://doi.org/10.1080/03007995.2023.2181150

20.

Giovanoulis

Kenanidis

Aim

, et al.

Collared versus collarless hydroxyapatite-coated stems for primary cementless total hip arthroplasty; a systematic review of comparative studies. Is there any difference in survival, functional, and radiographic outcomes?

SICOT J 2024; 10: 8. DOI: https://doi.org/10.1051/sicotj/2024003

21.

Laine

Puolakka

Moilanen

, et al. The effects of cementless femoral stem shape and proximal surface texture on ‘fit-and-fill' characteristics and on bone remodeling. Int Orthop 2000; 24: 184–190. DOI: https://doi.org/10.1007/s002640000150

22.

Carli

Negus

Haddad

. Periprosthetic femoral fractures and trying to avoid them: what is the contribution of femoral component design to the increased risk of periprosthetic femoral fracture? Bone Joint J 2017; 99-B: 50–59. DOI: https://doi.org/10.1302/0301-620X.99B1.BJJ-2016-0220.R1

23.

Demey

Fary

Lustig

, et al. Does a collar improve the immediate stability of uncemented femoral hip stems in total hip arthroplasty? A bilateral comparative cadaver study. J Arthroplasty 2011; 26: 1549–1555. DOI: https://doi.org/10.1016/j.arth.2011.03.030

24.

Liu

Wei

Zeng

, et al. Comparison of femoral bone mineral density changes around 3 common designs of cementless stems after total hip Arthroplasty-A retrospective cohort study. Orthop Surg 2022; 14: 1059–1070. DOI: https://doi.org/10.1111/os.13265

25.

Van Rietbergen

Huiskes

Weinans

, et al. ESB research award 1992. The mechanism of bone remodeling and resorption around press-fitted THA stems. J Biomech 1993; 26: 369–382. DOI: https://doi.org/10.1016/0021-9290(93)90001-u

26.

Cho

Chun

Rhyu

, et al. Distal femoral cortical hypertrophy after hip arthroplasty using a cementless doubletapered femoral stem. J Orthop Surg (Hong Kong) 2016; 24: 317–322. DOI: https://doi.org/10.1177/1602400309

27.

Tapadiya

Walker

Schurman

. Prediction of outcome of total hip arthroplasty based on initial postoperative radiographic analysis. Matched, paired comparisons of failed versus successful femoral components. Clin Orthop Relat Res 1984: 5–15.

28.

Restrepo

Mortazavi

Brothers

, et al.

Hip dislocation: are hip precautions necessary in anterior approaches?

Clin Orthop Relat Res 2011; 469: 417–422. DOI: https://doi.org/10.1007/s11999-010-1668-y