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Templating femoral offset in patients with coxa valga and antetorta undergoing THA: Critical need for a minimum 5 mm increase
⁎Corresponding author: Conradin Schweizer. conradin.schweizer@gmx.at
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Received: ,
Accepted: ,
This article was originally published by Reed Elsevier India Pvt. Ltd. and was migrated to Scientific Scholar after the change of Publisher.
Abstract
Abstract
Total hip arthroplasty (THA) is a common procedure in which accurate restoration of femoral offset is crucial to prevent complications. In patients with coxa valga and antetorta (CVA), excessive femoral antetorsion may lead to inaccurate prediction of femoral offset during digital templating. The purpose of this study was to assess the accuracy of templated femoral offset in patients with CVA compared to a control group.
A retrospective analysis was conducted on 35 CVA patients and 56 controls who underwent cementless THA. Preoperative and postoperative pelvis radiographs were taken following a standardized procedure. A CVA group was defined by a caput-collum-diaphyseal (CCD) angle >140°, while the control group had a CCD angle of 125°–135°. Femoral antetorsion was assessed using the size of the lesser trochanter on pelvis radiographs. Preoperative templating was performed with mediCAD, and radiographs were analyzed for femoral offset, neck resection level, and leg length discrepancy. Intraoperative head length changes and 90-day postoperative adverse events were also recorded.
CVA patients had a significantly lower native femoral offset than controls (34.9 mm vs. 41.7 mm; p < 0.001). Postoperatively, CVA patients showed an offset increase of only 1.1 mm, despite a templated increase of 5.1 mm (p < 0.001), while the control group had no significant difference between templated and postoperative offsets (p = 0.893). Larger head sizes than templated were used twice as often in the CVA group. No significant leg length differences were observed.
Digital templating for femoral offset in CVA patients proves to be inaccurate, with postoperative radiographs showing a significant reduction compared to the templated femoral offset. To prevent postoperative offset reduction and associated complications, a templated femoral offset increase of at least 5 mm should be targeted when performing THA in CVA patients.
Keywords
Cementless total hip arthroplasty
Coxa valga and antetorta
Femoral offset
Digital templating
Femoral antetorsion
1 Introduction
Total hip arthroplasty (THA) is one of the most successful orthopaedic procedures, and its frequency is expected to increase in the coming years 4. A crucial component of THA is digital preoperative templating, which aims to simulate the restoration of all relevant biomechanical aspects and predict implant size.1 Important biomechanical features include the restoration of femoral offset and leg length, which are essential to avoid negative side effects such as dislocation, trochanteric pain syndrome, and accelerated polyethylene wear.2–4
Some authors report increased abductor strength and improved range of motion with a postoperative increase in femoral offset.5–7 However, the primary objective of THA is to provide a stable construct that replicates the patient's original biomechanics as close as possible to their preoperative state. Current studies indicate that an increase in femoral offset of up to 5 mm is acceptable.8 In contrast, a decrease in femoral offset is linked to poorer functional outcomes and gait irregularities.9–11
Restoration of biomechanical features with templating softwares is routinely performed using standardized radiographs of the pelvis, typically taken preoperatively in 15° internal rotation to account for the physiological femoral anteversion. Patients with coxa valga and antetorta (CVA), who often undergo THA, present excessive femoral antetorsion. A previous study reported that excessive femoral antetorsion results in discrepancies between predicted and implanted femoral component sizes when using digital templating.12 However, the impact of excessive femoral antetorsion on the prediction of femoral offset using two-dimensional templating software has not been investigated.
The primary objective of this study was to assess the accuracy of preoperatively templated femoral offset versus postoperative femoral offset in patients with CVA, compared to a control group. Furthermore, the study aimed to evaluate differences in neck resection level, leg length discrepancy, and the incidence of 90-day postoperative adverse events between the two groups. The study hypothesis was that in patients with CVA, the templated femoral offset will be overestimated compared to the actual postoperative femoral offset.
2 Material and Methods
2.1 Patients
In this single-center retrospective study, consecutive cohorts of patients with CVA and a control group were established. For the CVA group, a retrospective analysis was conducted on 620 patients with end-stage hip osteoarthritis who underwent cementless THA at our institution between October 2022 and December 2023. For the control group, preoperative radiographs of 224 patients who received cementless THA for the same condition, with radiographs taken between January 2023 and July 2023, were examined. The two cohorts were previously analyzed in a matched control study.12
This study included only patients who underwent both templating and implantation with the cementless CORAIL® Stem and PINNACLE™ Acetabular Cup System (both from DePuy Synthes, Warsaw, Indiana, USA). All surgeries were performed using the posterior approach. Used stem types included standard, high offset, and coxa vara. Patients were excluded if there was a mismatch between the templated and implanted stem types (e.g., standard stem vs. coxa vara stem). Additional exclusion criteria included poor bone quality (Dorr type C), acute fractures, previous osteotomy or osteosynthesis of the proximal femur, and malaligned implanted stems (valgus/varus deviation greater than 1°). The varus/valgus deviation of the stem was measured by determining the angle between the stem axis and the long axis of the femur.
In the CVA group, three patients were excluded due to the use of a tripolar cup and one for a mismatch between templated and implanted stem type, leaving 35 patients for further analysis. In the control group, two patients were excluded due to inadequate level of resection and two for mismatch between templated and implanted stem type, leading to 56 patients for further analysis.
A formal ethics approval was not required, as an exemption was granted by the local ethics committee (2024-300433-WF).
2.2 Methods
All radiographs followed a standardized protocol, with imaging conducted in a standing position and 15° of internal rotation, calibrated using a 25 mm measuring ball. Radiographs displaying a caput-collum-diaphyseal (CCD) angle greater than 140° and anteverted femora, identified by the visibility of the lesser trochanter (LT) of at least 10 mm for men and 8 mm for women, were classified into the CVA group. Inclusion criteria for the control group were a CCD angle between 125° and 135°, and a visible LT ranging from 3 to 10 mm for men and 3–8 mm for women. The assessment of femoral anteversion using the size of the LT, variations in LT size based on sex, as well as the measurement techniques used to assess LT size in this study have been documented in previous studies.13,14Fig. 1 illustrates the flowchart for patient selection for both groups.
Preoperative templating was conducted using pelvis radiographs and mediCAD software (Hectec GmbH, Altdorf/Landshut, Germany) by two trained orthopaedic surgeons (CS & MJ). During the templating process, careful attention was given to accurately restoring the native femoral offset and leg length. In cases where the leg length of the operated side was longer than the opposite side, leg length shortening was avoided.
Femoral offset was determined by the distance from the center of the femoral head to the line bisecting the long axis of the femur. On templated radiographs, the level of neck resection was determined by measuring the distance from the uppermost part of the LT to the medial collar of the stem, after equalizing leg length discrepancy. Intraoperatively, the same distance was measured to determine the level of neck resection. Postoperative radiographs were then used to measure the distance from the same landmark to the resection level. Leg length discrepancy was measured by drawing a line connecting both pelvic tear drops, followed by a perpendicular line extending to the widest part of the LT. These measurements were performed on both templated and postoperative radiographs, and the leg length discrepancy was analyzed subsequently. Fig. 2 illustrates the measurement techniques for femoral offset, leg length discrepancy and level of resection.8,15 All measurements were performed using Weasis DICOM Medical Viewer Version 3.8.0.
Additionally, the frequency of head length changes intraoperatively compared to the template was recorded for both groups. The primary reason for intraoperative adjustment of head length was instability, evaluated based on early dislocation and inadequate tissue tension. In cases where there was a discrepancy between the templated and implanted head lengths, the Pythagorean theorem was employed to adjust the templated femoral offset to account for the implanted head length. The formula used was x22=y, where x represents the difference in head length and y the adjusted femoral offset.
We further assessed the development of 90-day medical complications and readmissions through our Institutional Complications Board, which meets every two months.
2.3 Statistical analysis
Differences between the two groups were assessed using an unpaired t-test for metric data and a Chi-square test for categorical data. When analyzing differences within one group a paired t-test was employed. P-values of less than 0.05 were considered significant. All statistical analyses were performed using IBM SPSS Statistics® (version 29.0.1).
3 Results
A total of 35 patients in the CVA group and 56 patients in the control group were included in this study. The CVA group consisted of 22 right and 13 left hips, while the control group had 33 right and 23 left hips. Demographic comparisons revealed significant differences in age and BMI, indicating a younger population in the CVA group and a slightly higher BMI in the control group. Demographic parameters are detailed in Table 1.
| Demographic parameters | |||
| CVA group | Control group | p-Value | |
| Age (yr) | 62.3 ± 8.0 | 71.0 ± 8.0 | <0.001 |
| Height (cm) | 173.2 ± 8.5 | 170.8 ± 9.6 | 0.233 |
| BMI (kg/m2) | 28.8 ± 6.0 | 26.5 ± 4.8 | 0.04 |
| Female | 24 | 36 | 0.675 |
| Male | 11 | 20 | 0.675 |
| Right | 22 | 33 | – |
| Left | 13 | 23 | – |
| Radiological parameters (mm) | |||
| Native offset | 34.9 ± 5.4 | 41.7 ± 6.0 | <0.001 |
| Templated offset | 40.0 ± 4.2 | 41.6 ± 7.0 | 0.230 |
| Offset increase | 5.1 ± 3.4 | 0.0 ± 3.4 | <0.001 |
| Postoperative offset | 36.0 ± 5.1 | 41.7 ± 5.3 | <0.001 |
| Templated resection height | 11.4 ± 4.0 | 9.6 ± 4.9 | 0.07 |
| Postoperative resection height | 8.6 ± 3.5 | 10.0 ± 4.9 | 0.135 |
| Change in leg length | 1.9 ± 4.4 | 0.0 ± 4.4 | 0.051 |
| Stem Type | |||
| Standard | 34 | 37 | – |
| Coxa vara | 0 | 1 | – |
| High offset | 1 | 18 | – |
Patients with CVA exhibited significantly lower native femoral offset compared to controls (34.9 mm vs. 41.7 mm; p < 0.001). During templating, the CVA group demonstrated a significantly larger increase in femoral offset compared to the controls (5.1 mm vs. 0.0 mm; p < 0.001) (Table 1). The templated femoral offset did not differ significantly between the groups (40.0 mm vs. 41.6 mm; p = 0.230). In contrast, the comparison of postoperative offset demonstrated a significantly smaller femoral offset in patients with CVA (36.0 mm vs. 41.7 mm; p < 0.001). Within the CVA group a reduction in femoral offset was observed when comparing templated and postoperative offsets (40.0 mm vs. 36.0 mm; p < 0.001), whereas the control group maintained a similar offset comparing templated and postoperative measurements (41.6 mm vs. 41.7 mm; p = 0.893) (Table 2). Notably, a larger head size than templated was used twice as often in the CVA group compared to the control group (40 % vs. 18 %). In the CVA group, a shorter head than templated was used in only one case (Fig. 3).
| Templated resection height (mm) | Postoperative resection height (mm) | p-Value | |
| CVA group | 11.4 ± 4.0 | 8.6 ± 3.5 | <0.001 |
| Control group | 9.6 ± 4.9 | 10.0 ± 4.9 | 0.425 |
| Templated offset (mm) | Postoperative offset (mm) | ||
| CVA group | 40.0 ± 4.2 | 36.0 ± 5.1 | <0.001 |
| Control group | 41.6 ± 7.0 | 41.7 ± 5.3 | 0.893 |
Within the CVA group, a significant reduction in resection height was observed on postoperative radiographs compared to templated measurements (11.4 mm vs. 8.6 mm; p < 0.001). The control group showed no significant change in resection height (9.6 mm vs. 10.0 mm; p = 0.425) (Table 2). No significant differences in leg length were observed between the two groups.
There were two 90-day postoperative adverse events reported within the CVA group (one non dislocated acetabular fracture, one superficial wound revision) and none within the control group.
4 Discussion
This study compared templated and postoperative standardized radiographs between patients with CVA and a control group. Although the CVA group was templated with a mean offset increase of 5.1 mm, the postoperative radiographs showed a mean reduction of 4 mm (40.0 mm vs. 36.0 mm), resulting in a mean postoperative offset increase of only 1.1 mm. In contrast, the control group showed almost no difference between the templated and postoperative femoral offset (41.6 mm vs. 41.7 mm). The results clearly support the authors' hypothesis, demonstrating that templated femoral offset in CVA patients is significantly overestimated compared to postoperative measurements. Additionally, surgeons were found to increase the head length intraoperatively in patients with CVA approximately twice as often as in controls. Although the study found a significant difference in resection height accuracy, no significant differences in postoperative leg length were reported.
There is a general consensus that restoring femoral offset, or increasing it by up to 5 mm, is associated with superior outcomes in patients undergoing THA5,8,9 whereas its reduction can lead to poor clinical outcomes and altered gait, negatively affecting the longevity of the THA.5,10,11 Literature reports native femoral offset values ranging from 37 to 41 mm, which aligns with the measurements in the control group of this study.16,17 When comparing native femoral offset between both groups, patients with CVA showed significantly lower measurements (34.9 mm vs. 41.7 mm). This discrepancy led to a significant increase in templated femoral offset in the CVA group due to the use of mainly standard necks. Lower femoral offset values in patients with CVA on pelvic radiographs are attributed to the valgus of the neck-shaft angle and increased femoral antetorsion 8. Interestingly, despite the templated offset increase of 5 mm in this group, only a 1.1 mm increase in offset was observed on postoperative radiographs (34.9 mm vs. 36.0 mm). This important finding suggests that increasing the femoral offset by at least 5 mm during templating can be accommodated and should be considered for patients with CVA to prevent a postoperative reduction in femoral offset. Additionally, using short necks to precisely restore femoral offset during templating should be avoided in THA to ensure the preservation of the native femoral offset. Reducing femoral offset not only compromises hip joint stability but also alters load distribution in the knee and ankle joints, potentially accelerating the onset of osteoarthritis.18,19
Horizontal-dimensional parameters, such as femoral offset, are widely recognized to be significantly influenced by femoral rotation.20 However, excessive femoral antetorsion causes an increase in anterior offset, defined as the anterior distance from the center of the femoral head to the proximal femoral axis in a sagittal plane.21 Consequently, it is likely that the templated increase in femoral offset may shift to anterior offset, which cannot be measured on pelvic radiographs. In other words, excessive femoral antetorsion cannot be compensated for during shaft preparation, resulting in an increase in anterior offset rather than femoral offset. Overall, literature on anterior offset is scarce, and the extent to which anterior offset impacts joint stability and clinical outcomes is not well understood. Previous studies have reported increased internal rotation and flexion, but decreased external rotation and extension, due to impingement associated with increased anterior offset.21 Another study suggests that changes in anterior offset may influence the abduction/adduction lever arm, which is predominantly defined by the femoral offset (i.e. horizontal femoral offset).22 The influence of changes in anterior offset after THA on clinical outcomes and implant survival has yet to be thoroughly investigated. The present study did not observe any difference in revision rates between the groups within 90 days postoperatively. However, because standard necks were used, leading to a significant increase in templated offset in the CVA group, the femoral offset on postoperative radiographs was not reduced.
This study has several limitations. One major limitation of this study is the absence of three-dimensional imaging to identify patients with CVA. Additionally, due to the lack of available imaging, anterior offset was not measured. Another limitation is the retrospective design of the present study.
5 Conclusion
Predicting femoral offset in patients with CVA using digital templating has proven to be inaccurate. Although the templated offset aimed for a 5 mm increase, postoperative radiographs showed only a 1 mm increase, resulting in a 4 mm reduction compared to the intended offset. This discrepancy may be due to a shift from horizontal femoral offset to anterior offset in patients with excessive femoral antetorsion. Therefore, when considering femoral offset in patients with CVA, it is essential to account for a templated offset increase of at least 5 mm to prevent a reduction in postoperative femoral offset, which could negatively impact clinical outcomes.
CRediT authorship contribution statement
Conradin Schweizer: Conceptualization, Investigation, Data curation, Formal analysis, Writing – original draft, Writing – review & editing. Oliver Niggemeyer: Writing – review & editing, Supervision. Jan-Hauke Jens: Writing – review & editing. Marius Junker: Conceptualization, Methodology, Investigation, Data curation, Writing – review & editing, Visualization, Project administration, All authors read and approved the final manuscript..
Consent to participate
The requirement for obtaining informed consent was waived due to the retrospective nature of the study.
Ethics statement
A formal ethics approval was not required, as an exemption was granted by the local Ethics Committee of the Medical Association of Hamburg (2024-300433-WF).
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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