Impact of Stem Collar-Calcar Gap Distance on Postoperative Bone Remodeling in Fully Hydroxyapatite-coated Stem

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Impact of Stem Collar-Calcar Gap Distance on Postoperative Bone Remodeling in Fully Hydroxyapatite-coated Stem

https://doi.org/10.21203/rs.3.rs-4883665/v1

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The collar of a cementless stem in total hip arthroplasty (THA) improves fixation and stability by connecting with the femoral calcar. Proper attachment is essential for reducing micromotion and preventing periprosthetic fractures of the femur. However, gaps between the femoral calcar and stem collar can occur during surgery, and it is unclear what degree of gap can be tolerated. This study evaluated 156 patients who received primary THA with the CORAIL stem. Medial and lateral gap distance were measured by frontal X-ray of the hip joint at 1 week and 1, 3, 6, 12, 24, and 36 months after THA. Clinical outcomes were assessed using Japanese Orthopaedic Association hip scores, and radiographic assessments included femoral morphology and stem alignment. Gaps were initially observed in 55 patients, with 42 showing complete gap disappearance within 36 months. On logistic regression analysis, lateral gap distance was shown to significantly influence gap disappearance, with an optimal cut-off of 5.5 mm by receiver operating characteristic curve analysis. A smaller lateral gap was correlated with quicker closure. When the gap between the collar and femoral calcar is within 5.5 mm, gap disappearance can be expected due to postoperative bone remodeling.

Physical sciences/Materials science

Physical sciences/Materials science/Techniques and instrumentation

Health sciences/Diseases/Rheumatic diseases

Health sciences/Diseases/Rheumatic diseases/Osteoarthritis

Total hip arthroplasty

Stem collar

Fully hydroxyapatite-coated stem

Bone remodeling

The cementless stem collar design provides better outcomes in total hip arthroplasty (THA). Attaching the stem collar directly to the cut calcar neck offers improved fixation, protection against subsidence, positive dispersion of vertical force into the calcar and resistance to stem rotation in relation to the femoral canal [1–4]. Both basic and clinical research indicate that the implementation of collared stems is associated with decreased risk of periprosthetic fracture of the femur [4–6].

In practical surgical scenarios, however, inability to properly attach the stem collar to the cut calcar neck occasionally occurs. A recent study using finite element analysis indicated that micromotion in the contact model between the stem collar and cut calcar neck was notably reduced compared to non-contact models under both flat-surface walking and stair climbing conditions [7]. In such cases, the stem collar may not fulfill its essential role. Thus, precise placement of the stem collar is important to optimizing outcomes in THA.

A number of types of fully hydroxyapatite (HA)-coated stem with collar is available [8–10]. Several studies have reported the occurrence of bone remodeling in the calcar region when the stem collar is not in contact in the region of the femoral calcar [8, 10]. This suggest that even if a gap occurs intraoperatively, post-operative bone remodeling can eliminate it and allow the collar to fulfil its role. However, the maximally acceptable gap distance between the collar of a fully HA-coated stem and the femoral calcar is unclear. Accordingly, an understanding of the distance of bone remodeling after THA will provide valuable intraoperative guidance for surgeons.

In this study, we investigated the relationship between the gap distance occurring between the calcar and collar during fully HA-coated stem insertion and subsequent bone remodeling after primary THA.

Participants

We enrolled 156 consecutive patients (156 hips) who underwent primary THA with a G7® cup (Zimmer Biomet, Warsaw, IN) and CORAIL® stem (DePuy Synthes, Warsaw, IN, USA) at a single center. All operations were performed using a minimally invasive antero-lateral supine approach. The CORAIL stem is a forged titanium stem with a double-tapered geometry that is plasma-coated with 155 µm of HA. HA is also coated on the back of the stem collar. Collar length increases with stem size, namely 6 mm with sizes 8 to 11, 7 mm with sizes 12 to 15, and 9 mm with sizes 16 and above. Collar thickness is 3.5 mm for all sizes. Patients in this study all received stems sizes 8 to 12.

For inclusion, all patients were required to available for follow-up for 36 months after surgery, and to be ambulatory with advanced or end-stage hip osteoarthritis (HOA) or idiopathic osteonecrosis of the femoral head (ION). We excluded patients with no evidence of a gap on frontal X-ray of the hip joint one week after surgery. We also excluded patients with a history of hip surgery ipsilateral to the THA, intraoperative periprosthetic femoral fracture, subsidence of the stem by more than 2 mm, or reoperation due to aseptic loosening.

Ethical approval for this retrospective observational study was obtained from our Institutional Review Board. The study was conducted in accordance with the Declaration of Helsinki, and all patients gave informed consent to participation.

Clinical assessment

Clinical outcomes were evaluated in accordance with the Japanese Orthopaedic Association (JOA) hip scores at 1 month before and 36 months after surgery. This scoring system consists of four elements, namely pain (0–40 points), range of motion (0–20 points), gait ability (0–20 points), and performance in activities of daily living (0–20 points), and is widely used to investigate hip joint conditions in Japan [11]. A higher score indicates a better condition of the post-operative hip joint.

Radiographic assessment

We assessed the gap between the femoral calcar and collar of the stem using postoperative frontal X-ray of the hip joint. X-rays were assessed at 1 week and 1, 3, 6, 12, 24, and 36 months after THA. To assess gap distance between the femoral calcar and collar, medial and lateral gap distances were investigated with a 1-mm pitch at all time points (Fig. 1). Measurement of gap distance relied on an X-ray taken one week post-surgery, which served as the initial reference point. We then assessed bone remodeling-induced disappearance of the gap over 36 months post-surgery, and determined the time until complete disappearance. Cases in which the gap disappeared within 36 months were classified as the contact group, and those in which the gap did not disappear as the non-contact group. A flowchart of the study is presented in Fig. 2.

We also evaluated the proximal femoral morphology using the Dorr classification [12] by measuring the calcaneal width at the mid-level of the lesser trochanter and the canal width at 10 cm below the lesser trochanter, and then calculating the calcaneal-to-canal ratio to determine bone type. As described elsewhere, femurs with a ratio of 0–0.5 were classified as Type A, 0.51–0.75 as Type B, and 0.76–1 as Type C, [13, 14]. Stem alignment angle was investigated using the postoperative radiographs one week after THA and evaluated to assess stem insertion in varus and valgus, as differentiated by deviation of stem axis from the femoral axis, in which valgus alignment was defined as positive.

We investigated whether the medial and lateral gap distances between the femoral calcar and stem collar influenced gap disappearance within 36 months post-surgery. We also calculated the cut-off values for medial and lateral gap distances at which gap disappearance due to bone remodeling could be expected, and the relationship between medial and lateral gap distances and time to gap disappearance.

Statistical analyses

The results are reported as mean ± standard error unless noted otherwise. To compare patient characteristics between the Contact and Non-contact groups, we used Pearson's chi-square test for categorical variables, parametric t-tests for continuous variables with a normal distribution, and the Mann-Whitney U-test for variables not following a normal distribution. Logistic regression analysis was conducted to investigate the impact of medial and lateral gap distances on disappearance within 36 months post-surgery. Independent variables included age, gender, BMI, Dorr type, stem alignment angle, and medial and lateral gap distance, while the dependent variable was disappearance of the gap within 36 months. We applied receiver operating characteristic (ROC) curve analysis to determine cut-off values for the medial and lateral gaps, aiming to predict gap disappearance within the specified post-surgery timeframe. Additionally, we used Spearman's rank correlation coefficient to assess correlations between gap distance and time to gap disappearance. Two observers independently analysed all radiographic images and resolved any disagreements through consensus. All statistical analyses were conducted with SPSS software (v.26.0; IBM, NY, USA), with statistical significance set at p < 0.05.

Classification of Contact and Non-contact Groups

In this study, gaps between the femoral calcar and collar of the stem were observed in the baseline X-rays of 55 cases. Among these, gaps disappeared within 36 months post-surgery in 42 cases (76.4%). Consequently, 42 cases were classified into the Contact group and 13 cases into the Non-contact group. The two groups did not significantly differ with regard to patient characteristics, including age, gender, BMI, clinical diagnosis, or Dorr type. Additionally, they did not differ with regard to clinical data, including stem alignment angle, and pre- and postoperative JOA hip scores. Details of patient characteristic and clinical data comparisons are shown in Table 1.

Table 1

Comparison of patient characteristics and clinical data
	Contact group	Non-contact group	p value
Total patients, N	42	13
Sex, male/female, N	13/ 29	3/ 10	0.585
Age, years	60.62 ± 1.44	57.31 ± 3.70	0.319
Height, cm	158.11 ± 1.30	156.37 ± 2.30	0.357
Weight, kg	61.96 ± 1.64	64.41 ± 5.98	0.586
Body mass index, kg/m²	24.75 ± 0.55	26.03 ± 1.97	0.714
Diagnoses, N
HOA/ION	36/ 6	10/ 3	0.677
Dorr classification, N
A/B/C	6/ 36/ 0	2/ 11/ 0	0.922
Stem alignment, °	-0.75 ± 0.26	0.12 ± 0.44	0.106
JOA hip scores
One month before surgery
Pain	14.64 ± 1.41	16.54 ± 2.85	0.754
Range of motion	13.76 ± 0.52	15.85 ± 0.81	0.051
Gait	15.29 ± 0.43	16.39 ± 0.83	0.076
Actives of daily living	13.29 ± 0.49	15.23 ± 0.92	0.093
36 months after surgery
Pain	39.29 ± 0.27	39.62 ± 0.39	0.548
Range of motion	17.52 ± 0.23	17.62 ± 0.42	0.941
Gait	19.52 ± 0.25	19.85 ± 0.15	0.537
Actives of daily living	19.48 ± 0.31	19.85 ± 0.15	0.812

Abbreviations: HOA, hip osteoarthritis; ION, idiopathic osteonecrosis of the femoral head; JOA, the Japanese Orthopaedic Association

Factors Influencing Gap Disappearance

The only factor influencing disappearance of the gap within 36 months post-surgery was lateral gap distance (p = 0.02, Odds ratio = 2.79). There were no significant differences in other independent variables, including age, gender, BMI, Dorr type, stem alignment angle, or medial gap distance (Table 2).

Table 2

Logistic regression analysis of the impact of medial and lateral gap distance between the femoral calcar and stem collar on disappearance within 36 months post-surgery
Predictor	Estimate	SE	p value	Odds ratio	95% Confidence interval
Lateral gap	1.02	0.44	0.020*	2.79	1.18–6.60
Medial gap	-0.29	0.43	0.492	0.74	0.32–1.73
BMI	-0.01	0.09	0.943	0.99	0.83–1.18
Sex	-0.43	1.03	0.675	0.65	0.09–4.85
Age	0.02	0.05	0.741	1.02	0.92–1.13
Diagnosis (HOA or ION)	1.17	1.42	0.410	3.22	0.20–52.0
Dorr type (A or B)	-0.28	1.08	0.796	0.76	0.09–6.31
Stem alignment	0.53	0.30	0.079	1.70	0.94–3.06
Abbreviations: SE, standard error; BMI, body mass index; Cl, confidence interval; *, p<0.05; HOA, hip osteoarthritis; ION, idiopathic osteonecrosis of the femoral head

ROC Curve Analyses for Gap Disappearance Prediction

ROC curve analyses were conducted to determine cut-off values for the medial and lateral gap distances in predicting gap disappearance within 36 months post-surgery (Fig. 3). AUC for the lateral gap distance was found to be 0.90, indicating good predictive accuracy. Optimal cut-off value for lateral gap distance was 5.5 mm, with a sensitivity of 0.85 and specificity of 0.86. For medial gap distance, the AUC was 0.74, suggesting moderate predictive accuracy, and the optimal cut-off value was 2.5 mm, with a sensitivity of 0.69 and specificity of 0.71.

Correlation between Gap Distance and Time until Gap Disappearance

We analyzed correlations between medial and lateral gap distances and time until gap disappearance in patients with the Contact group (Fig. 4). The results indicated a statistically significant correlation with the lateral gap distance (ρ = 0.315, p = 0.042), suggesting that a shorter duration until gap disappearance was associated with a smaller lateral gap distance between the femoral calcar and stem collar. In contrast, there was no significant correlation between medial gap distance and time until gap disappearance.

In this retrospective observational study, we evaluated patients who received primary THA with the CORAIL stem, focusing on the impact of gap distance between the femoral calcar and collar on gap disappearance within 36 months after surgery. Radiographic assessments at multiple post-surgery intervals revealed gaps in 55 cases, of which 42 gaps disappeared and 13 did not. Lateral gap distance was the primary factor influencing gap disappearance, with an optimal cut-off value of 5.5 mm showing high predictive accuracy, whereas medial gap distance with a cut-off value of 2.5 mm showed moderate accuracy. A significant correlation was found between a smaller lateral gap and quicker gap disappearance, underscoring the importance of precise stem collar placement for successful bone remodeling and gap closure.

We found no difference in JOA hip score at 36 months after surgery between the two groups. Further, no participant experienced periprosthetic femoral fracture or aseptic loosening of the stem after surgery. Recent evidence also indicated that the presence or absence of contact between the collar of a fully hydroxyapatite-coated stem and the femoral neck did not affect clinical outcomes during the first postoperative year [15]. However, several previous studies have indicated that use of a collared stem decreases risk of periprosthetic femur fractures [5, 6, 16]. In their recent multivariate logistic analysis with adjustment for age, sex, and BMI, Rodriguez et al. reported that non-collared cementless stems were associated with an approximately threefold increased risk of periprosthetic femoral fracture compared to fully HA coated and collared cementless stems in patients aged over 65 years who underwent primary THA [6]. Considering that the absence of contact between the collar and femoral calcar is equivalent to the use of a collarless stem, these findings emphasize the importance of precise placement of the stem collar in optimizing outcomes in THA.

Although several studies have suggested the occurrence of bone remodeling between femoral calcar and stem collar, details have remained unclear. Vidalain reported the occurrence of bone remodeling in the calcar region with the CORAIL stem, and that on multivariate analysis femoral remodeling was not influenced to any significant extent by either patient- or prosthesis-related factors [8]. Our results are consistent with the findings of these studies. We revealed that disappearance of the gap due to bone remodeling was not influenced by age, gender, BMI, Dorr type, or stem alignment angle; rather, lateral gap distance was the only significant factor. These results indicate that the HA applied to the back of the stem collar may induce osteoinduction in the calcar region of the stem.

Previous studies on bone remodeling in the stem collar and calcar gap did not considered gap distance [8, 10, 17]. In the present study, we found that the optimal cut-off value for lateral gap distance between the calcar and stem collar for gap disappearance was 5.5 mm (2.5mm for medial gap distance). Additionally, we identified a positive correlation between lateral gap distance and time to gap disappearance. These results suggest that achieving contact between the calcar and collar during the postoperative course requires a lateral gap distance during stem placement within 5.5 mm, and that the smaller the lateral gap distance, the earlier the calcar and collar will be in contact. Two basic studies have investigated risks associated with the femoral calcar-collar gap [7, 18]. Watanabe et al. indicated that micromotion in the collar contact model was notably reduced compared to the non-contact model under both flat walking and stair climbing conditions [7]. In their study of the use of a composite femur in the CORAIL stem, Lamb et al. suggested that fracture torque and torsional stiffness were greater in the calcar-collar contact group than in the non-contact group [18]. They also reported that odds ratio for not achieving collar contact increased 3.8-fold for each mm of separation in the regression model [18]. Many fully HA-coated stems now have the collared option [19]. The angle and size of the stem collar varies from model to model. Surgeons therefore need to be more attentive to the angle and length in femoral neck osteotomy and in the placement of collared stems.

There are a number of potential limitations to this study. First, only one stem product was used, and other stem models may give different results. Second, due to the relatively small sample size and limited number of follow-up time points, no differences between the two groups were observed in clinical outcome. Despite these limitations, we hope our results will serve as an important intraoperative indicator for surgeons using this stem.

This retrospective observational study evaluated the impact of gap distance between the femoral calcar and stem collar on gap disappearance within 36 months post-surgery in patients undergoing primary THA with the CORAIL stem. Our findings indicate that lateral gap distance is a significant factor influencing gap disappearance, with an optimal cut-off value of 5.5 mm. A smaller lateral gap is associated with more rapid gap closure, emphasizing the importance of precise stem collar placement to successful bone remodeling. Our results provide valuable intraoperative guidance for surgeons. When the gap between the collar and femoral calcar is within 5.5 mm, gap disappearance due to postoperative bone remodeling can be expected.

Acknowledgements

We would like to thank Dmed for English language editing.

Author contributions

All authors contributed to the literature search, critical review, data analysis, and manuscript preparation. All authors read and approved the final manuscript.

Data availability

The datasets supporting the conclusions of this article are included within the article. The raw data can be requested from the corresponding author, YO.

Competing Interests

The authors have no relevant financial or non-financial interests to disclose.

Funding

The authors declare that no funds, grants, or other support were received during the preparation of this manuscript.

Ethics Approval

Approval was granted by the Institutional Review Board of Kitasato University Hospital (Number: B22-089).

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No competing interests reported.

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You are reading this latest preprint version

Impact of Stem Collar-Calcar Gap Distance on Postoperative Bone Remodeling in Fully Hydroxyapatite-coated Stem

Status:

Version 1

Abstract

Figures

Introduction

Materials and Methods

Participants

Clinical assessment

Radiographic assessment

Statistical analyses

Results

Classification of Contact and Non-contact Groups

Factors Influencing Gap Disappearance

ROC Curve Analyses for Gap Disappearance Prediction

Correlation between Gap Distance and Time until Gap Disappearance

Discussion

Conclusion

Declarations

References

Additional Declarations

Status:

Version 1