Restoring femoral offset and leg length; the potential of a short curved stem in total hip arthroplasty

Gender differences in cementless short stem total hip arthroplasty: significantly higher femoral lengthening in female patients

Modern cementless short stems in total hip arthroplasty (THA) enable a precise reconstruction of the native pre-arthritic hip geometry. While gender differences have been reported for older generation straight hip stems, there are hardly reports regarding modern cementless short hip stems. Therefore, we aimed to evaluate the influence of gender differences in hip anatomy in cementless short stem THA. A total of 207 patients (109 females, 98 males) with unilateral THA and absence of contralateral joint space narrowing (Kellgren-Lawrence grade ≤ 2) were included. Acetabular height and offset as well as femoral height and offset were measured on pre- and 3-months-postoperative anteroposterior X-rays of the pelvis and compared to the contralateral hip. Additionally, implant position was evaluated on the postoperative radiograph. In male patients, the loss of acetabular offset was significantly greater than in females (p = 0.012), leading to a compensatory increase in femoral offset (p = 0.041). Femoral height discrepancy was significantly higher in females (p < 0.001), accounting for an increased global hip height discrepancy (p < 0.001). The mean acetabular anteversion was significantly greater in female patients (p < 0.001). Female patients are at higher risk of femoral lengthening in THA with a cementless short stem potentially caused by a further proximally conducted femoral neck osteotomy and show significantly higher cup anteversion angles. Therefore, surgeons should take special care to the level of neck resection and implant positioning in female patients.

Survival and radioclinical evaluation of the Optimys™ short stem at more than 6years' mean follow-up: A retrospective study of 108 cases

INTRODUCTION

The short stems developed in recent years offer an interesting alternative to standard long stems. The Optimys™ short stem has been widely studied, but not according to the National Institute for Health and Care Excellence (NICE) criteria. We therefore conducted a retrospective study of Optimys™ at a minimum 5years' follow-up, to assess: (1) survival on NICE criteria, (2) complications, (3) functional results, and (4) subsidence, restoration of offset and bone remodeling.

HYPOTHESIS

Optimys™ shows survival comparable to that of other non-cemented standard and short stems, with a<0.5% per year revision rate or<2.5% at 5years on NICE criteria.

MATERIAL AND METHODS

A single-center retrospective study included 108 Optimys™ stems at a mean 76.5months' follow-up (range: 60-112months). Clinical [Harris, Oxford-12 and forgotten hip (French version: SHO-12) scores] and radiologic data were collected pre- and postoperatively. Analysis focused on implant survival, complications, functional results and radiological results (restoration of offset, bone remodeling, subsidence and osseointegration) and risk factors for stem migration.

RESULTS

At a mean 76.5months' follow-up (range: 60-112months), Optimys™ survival was 97.7% (95% CI: 0.945-1). Oxford and Harris scores improved significantly: respectively, 16.1 vs. 44.7 [Δ=28.598; 95% CI: 27.410-29.785 (p<0.001)] and 45.3 vs. 95 [Δ=49.662; 95% CI: 47.442-51.882 (p<0.001)]. Mean forgotten hip score (SHO-12) at last follow-up was 82.7±19.6 (range: 35.4-100.0). There was 1 case of aseptic revision at 11months for femoral osseointegration defect. Mean subsidence was 1.64mm (range: 0-20.63mm); no predisposing factors could be identified. Femoral offset increased by a mean 2.41±4.53mm (range: -10.10 to 14.70mm).

CONCLUSION

The present study reports good survival for the Optimys™ stem, which meets NICE criteria. Radiologic and clinical results were encouraging, with a low rate of subsidence, comparable to other series, but with increased femoral offset.

LEVEL OF EVIDENCE

IV; retrospective cohort study.

More than a feeling?-Overruling the preoperatively templated offset option leads to a minor offset increase in short stem total hip arthroplasty

PURPOSE

Short stems are increasingly used in total hip arthroplasty (THA) because of advantages in bone and soft tissue preservation and reconstruction of hip geometry. Digital templating is essential in determining the correct offset option and stem size in THA. However, the preoperative template sizes might be intraoperatively overruled.

PATIENTS AND METHODS

We evaluated the effect of intraoperative overruling of the preoperatively templated offset option of a short curved stem on hip offset, leg length, implant positioning, and femoral canal fill index. The overruling was performed in case of intraoperative instability, telescoping, or both. A series of 1052 consecutive THAs with a cementless short curved stem and press-fit cup was retrospectively screened. One hundred patients with unilateral THA and a contralateral native and morphologically healthy hip as a reference met the inclusion criteria. Measurements were carried out on preoperative and 3 months anterior-posterior postoperative radiographs. Patients were divided according to the overruling by offset option or stem size.

RESULTS

Hip offset was increased in all groups, but only with significant increase if an offset option + 1 was used intraoperatively (p = 0.025). LLD was restored without significance in all groups (p = 0.323; p = 0.157).

CONCLUSION

Intraoperative overruling of the preoperative digital template in cementless short stem total hip arthroplasty results in an increase of hip offset compared to a contralateral healthy hip. However, the increase is marginal and clearly under 5 mm compared to the contralateral healthy hip.

The 'critical trochanter angle' does not show superiority over the CCD angle in predicting varus stem alignment in cementless short-stem total hip arthroplasty

PURPOSE

Varus positioning of the femoral stem can affect the hip offset (HO). The critical trochanter angle (CTA) was introduced in 2019 as a novel geometric angle, to predict varus stem alignment in cementless straight stem THA. The aim of this study was to evaluate the applicability of the CTA as a predictor for stem alignment in THA with a cementless neck resecting short stem.

PATIENTS AND METHODS

In this retrospective study, 106 patients (index surgery 2014-2019) with unilateral THA and a morphologically healthy contralateral hip as a reference (Kellgren-Lawrence ≤ 1) were included. A cementless short stem with meta-diaphyseal fixation and press-fit cup was implanted in all cases. Stem alignment, CCD angle, CTA and offset reconstruction were measured on preoperative and 3 months postoperative AP radiographs of the pelvis.

RESULTS

Preoperative lower CTA and lower CCD angle were positively correlated (r = 0.472; p < 0.001). Higher varus stem alignment is correlated with lower CTA (r = - 0.384; p < 0.001) and lower CCD angle (r = - 0.474; p < 0.001). A CTA of 23.1° or lower showed a sensitivity of 59.1% and a specificity of 87.1% (AUC: 0.733) and a CCD angle of 132.75° or lower a sensitivity of 68.2% and a specificity of 80.6% (AUC: 0.77) for a varus stem alignment > 3°.

CONCLUSION

The CTA is also applicable in cementless THA with a neck resecting short stem to evaluate risk of intraoperative varus stem positioning. The CCD angle shows higher sensitivity with marginally lower specificity. Therefore, the CTA is not superior in predicting varus stem alignment in short-stem THA.

LEVEL OF EVIDENCE

IV.

High varus stem alignment in short-stem total hip arthroplasty: a risk for reconstruction of femoro-acetabular offset, leg length discrepancy and stem undersizing?

PURPOSE

Short stems are increasingly used in in total hip arthroplasty (THA) because of advantages in bone and soft tissue preservation and reconstruction of hip geometry. Short stems can be inserted in a more varus position compared to conventional straight stems. This poses the risk of final varus misplacement of the femoral component, which is not intended in all femoral short stems.

METHODS

We wanted to evaluate the effect of a high varus stem positioning in MIS THA on hip offset, leg length and femoral canal fill index. A series of 1052 consecutive THAs with a singular cementless femoral short stem and press-fit cup was retrospectively screened for inclusion. One hundred six patients with unilateral THA and a contralateral healthy hip met the inclusion criteria. Measurements were carried out on preoperative and 3 months anterior-posterior postoperative radiographs. Patients were divided into Group A (varus stem alignment ≤ 3°) and Group B (varus stem alignment > 3°).

RESULTS

Hip offset (HO) increased significantly in Group B by 4 mm (p = 0.013). No influence on leg length difference was detected in both groups. Preoperative CCD angle was significantly lower in Group B (p < 0.001). Canal Fill Indices (CFI) were significantly lower in Group B (CFI I: p < 0.001; CFI II p = 0.003; CF III p = 0.002).

CONCLUSION

High varus stem alignment > 3° leads to a statistically significant but minor increase in HO and poses the risk of stem undersizing. A preoperatively low genuine CCD angle pose a risk for varus stem positioning.

Femoral antetorsion after calcar-guided short-stem total hip arthroplasty: A cadaver study

Calcar-guided short stems in total hip arthroplasty (THA) permit surgeons to successfully reconstruct postoperative femoroacetabular offset, accurately restore leg length, and adequately re-establish a wide range of caput-collum-diaphyseal angles. However, their effect on femoral antetorsion is less known. Indeed, controlling antetorsion of the femoral stem can be challenging because of the differences in individual femoral geometry and curvature. Therefore, we investigated if calcar-guided short-stem THA alters femoral antetorsion and compared it with conventional-stem THA. Using 12 Thiel-fixed, full-body cadaver specimens from donors without known hip disorders, we compared an uncemented calcar-guided femoral short-stem prosthesis with an uncemented conventional straight-stem prosthesis. In a paired study setup, each specimen received a calcar-guided short stem on one side and a conventional stem on the other. On the acetabular side, all specimens received a press-fit, monobloc acetabular cup. Femoral antetorsion angles were measured using the Waidelich method, and pre- and post-operative angles of both sides were recorded. The mean preoperative femoral antetorsion angles were similar in both groups (24.8°  ± 7.5° vs. 23.8° ± 6.1°, p = 0.313). Mean postoperative femoral antetorsion angles were 23.0° ± 5.5° in short-stem and 13.5° ± 7.1° in conventional-stem hips. Short-stem hips had a small but nonsignificant difference in femoral antetorsion angles pre- and post-operatively (1.8° ± 3.2°, p = 0.109), while the difference for conventional-stem hips was much larger and highly significant (10.3° ± 5.8°, p < 0.001). Calcar-guided short-stem THA effectively restores femoral antetorsion. However, how this affects long-term clinical outcomes and complications warrants further exploration.

A single-surgeon experience in reconstruction of femoro-acetabular offset and implant positioning in direct anterior approach and anterolateral MIS approach with a curved short stem

PURPOSE

Minimally invasive surgery using short stems in total hip arthroplasty gained more popularity. The differences in change of hip offset and implant positioning in minimally invasive approaches are not fully known. Therefore, this study was conducted to evaluate the difference in reconstruction of hip offset and implant positioning in direct anterior approach (DAA) and minimally invasive anterolateral approach (AL MIS).

METHODS

A single surgeon series of 117 hips (117 patients; mean age 65.54 years ± 11.47; index surgery 2014-2018) were included and allocated into two groups: group A (DAA) with 70 hips and Group B (AL MIS) with 47 patients operated. In both groups the same type of cementless curved short hip stem and press fit cup was used.

RESULTS

Both groups showed an equal statistically significant increase of femoral (p < 0.001) and decrease of acetabular offset (p < 0.001). Between both groups no statistically significant difference in offset reconstruction, leg length difference or implant positioning could be found. Leg length increased in both groups significantly and leg length discrepancy showed no difference (group A: - 0.06 mm; group B: 1.11 mm; p < 0.001). A comparable number of cups were positioned outside the target zone regarding cup anteversion.

CONCLUSION

The usage of a curved short stem shows an equal reconstruction of femoro-acetabular offset, leg length and implant positioning in both MIS approaches. The results of this study show comparable results to the existing literature regarding change of offset and restoration of leg length. Malposition of the acetabular component regarding anteversion poses a risk.

[A new measurement method of offset in total hip arthroplasty]

OBJECTIVE

To report a new offset parameter for total hip arthroplasty (THA)-greater trochanter offset (GTO), and analyze the effectiveness and feasibility of this parameter based on clinical data.

METHODS

The 47 patients who met the selection criteria and admitted between January 2016 and May 2020 were selected as the research object. The global offset (GO) was used as the offset parameter in preoperative design. Firstly, the test-retest reliability and inter-rater reliability of GTO were analyzed based on pelvic X-ray films. The GTO reconstruction was defined as the difference between the operative side and the healthy side within ±5 mm, and 47 patients were divided into the reconstruction group and the non-reconstruction group. General data (age, gender, type and side of fracture, the interval between injury and operation), visual analogue scale (VAS) score, Harris score, gait score, and leg length discrepancy (LLD) were recorded and compared between two groups. Then, the GTO was used as the offset parameter in preoperative design of 21 patients (GTO group) admitted between June 2020 and December 2020. The pre- and post-operative clinical data were compared between GTO group and GO group to explore the feasibility of GTO for THA.

RESULTS

Statistical analysis showed that GTO had good test-retest reliability (P<0.001) and inter-rater reliability (P<0.001). There was no significant difference in gender, age, type and side of fracture, the interval between injury and operation, preoperative VAS score, and LLD at 1 year after operation between the GTO reconstruction group and the non-reconstruction group, as well as between the GO and GTO groups (P>0.05). The Harris score and gait score at 1 year after operation, and difference of VAS score between pre- and post- operation in the reconstruction group and GTO group were significantly better than those in the non-reconstruction group and GO group, respectively (P<0.05). There were 23 cases (48.9%) in the GO group and 19 cases (90.5%) in the GTO group with GTO reconstruction, and the difference was significant (χ²=10.606, P=0.001). There were 25 cases (53.2%) in the GO group and 13 cases (61.9%) in the GTO group with GO reconstruction, and the difference was not significant (χ²=0.447, P=0.504). There were 34 cases (72.3%) in the GO group and 19 cases (90.5%) in the GTO group with LLD reconstruction, and the difference was not significant (χ²=2.777, P=0.096).

CONCLUSION

GTO has reliable test-retest reliability and inter-rater reliability. GTO as a parameter of preoperative offset reconstruction plan of THA can obtain good reconstruction of offset and limb length, and obtain a good effectiveness.

Effect of intraoperative treatment options on hip joint stability following total hip arthroplasty

Dislocation remains the leading indication for revision of total hip arthroplasty (THA). The objective of this study was to use a computational model to compare the overall resistance to both anterior and posterior dislocation for the available THA constructs commonly considered by surgeons attempting to produce a stable joint. Patient-specific musculoskeletal models of THA patients performing activities consistent with anterior and posterior dislocation were developed to calculate joint contact forces and joint positions used for simulations of dislocation in a finite element model of the implanted hip that included an experimentally calibrated hip capsule representation. Dislocations were then performed with consideration of offset using +5 and +9 offset, iteratively with three lipped liner variations in jump distance (10°, 15°, and 20° lips), a size 40 head, and a dual-mobility construct. Dislocation resistance was quantified as the moment required to dislocate the hip and the integral of the moment-flexion angle (dislocation energy). Increasing head diameter increased resistive moment on average for anterior and posterior dislocation by 22% relative to a neutral configuration. A lipped liner resulted in increases in the resistive moment to posterior dislocation of 9%, 19%, and 47% for 10°, 15°, and 20° lips, a sensitivity of approximately 2.8 Nm/mm of additional jump distance. A dual-mobility acetabular design resulted in an average 38% increase in resistive moment and 92% increase in dislocation energy for anterior and posterior dislocation. A quantitative understanding of tradeoffs in the dislocation risk inherent to THA construct options is valuable in supporting surgical decision making.

Femoroacetabular offset restoration in total hip arthroplasty; Digital templating a short stem vs a conventional stem

BACKGROUND

Failure in restoring individual anatomy could be a reason for persistent functional limitations post total hip arthroplasty. Femoroacetabular offset (FAO) plays an important role in anatomic restoration, as loss of offset ≥ 5 mm is associated with altered gait and decreased functional outcome. Preoperative assessment by use of digital templating has shown to be a reliable method for sizing the components in total hip arthroplasty, and can show if anatomic restoration is achieved. In recent years, short stems are growing in popularity as it could allow better restoration due to more variety in placement.

AIM

To assess whether restoration of the FAO differs between a short or a conventional stem by use of digital templating. Additionally, association of the preoperative offset and caput-colllum-diaphyseal angle (CCD-angle) within restoration of both stems was investigated, and the reliability of measurements was assessed.

METHODS

A total of 100 standardized hip radiographs were used for digital templating. Restoration of FAO was classified into “restored” or “not restored”, when a < 5 mm or ≥ 5 mm difference from baseline value presented, respectively. Differences between the two stems concerning proportions of correct restoration of the FAO were analyzed by use of McNemar tests. To assess association between CCD-angle and preoperative FAO with absolute FAO restoration, multi-level analysis was performed by use of a linear mixed model to account for paired measurements. Through determination of the optimal point under the curve in operating curve-analysis, bootstrapping of thousand sets was performed to determine the optimal cutoff point of the preoperative FAO for restoration within the limits of 5 mm. Three observers participated for inter-observer reliability, with two observers measuring the radiographs twice for intra-observer reliability.

RESULTS

The mean preoperative FAO was 79.7 mm (range 62.5-113 mm), with a mean CCD-angle of 128.6° (range 114.5°-145°). The conventional stem could only restore the FAO in 72 of the cases, whereas the short stem restored the FAO in all cases. CCD-angle was not a predictor, but the preoperative FAO was. A cut-off point of 81.25 mm (95% confidence interval of 80.75-84.75 mm) in preoperative FAO was found where the conventional stem was unable to restore the FAO. Reliability of measurements was excellent, with an intra-observer reliability of 0.99 and inter-observer reliability in baseline measurements higher than 0.9 between the three observers.

CONCLUSION

In preoperative planning of FAO restoration in total hip arthroplasty, digital templating shows that short stems with a curve following the medial calcar are potentially better at restoring the FAO compared to conventional stems if the preoperative offset is ≥ 80.0 mm.

The morphology of the proximal femur in cementless short-stem total hip arthroplasty: No negative effect on offset reconstruction, leg length difference and implant positioning

Background

Correct reconstruction of hip offset (HO) and leg length are important for clinical–functional outcome and patient satisfaction in total hip arthroplasty (THA). The morphology of the proximal femur can pose a risk for increased leg length difference (LLD) in cementless straight-stem THA. We therefore wanted to evaluate, if this is also applicable in THA with a cementless meta-diaphyseal short stem.

Methods

In a retrospective study, 106 patients (index surgery 2014–2019) with unilateral THA and a morphologically healthy hip as a reference (Kellgren–Lawrence ≤ 1) were included. The same cementless short stem with meta-diaphyseal fixation and cementless press-fit cup was implanted. The proximal femur was rated by Dorr’s classification, and subgroups were formed afterward. Measurements were carried out on preoperative and 3 months postoperative anterior–posterior radiographs of the pelvis. Kruskal–Wallis test, Fisher’s exact test and binary logistic regression were performed to evaluate the influence of the anatomical shape on postoperative leg length difference and offset reconstruction.

Results

The Dorr type did not show any significance influence on LLD (p = 0.532), or postoperative difference in femoral offset (p = 0.243), acetabular offset (p = 0.106) and hip offset (p = 0.698). Stem alignment (p = 0.705) and canal fill indices (CFI I: p = 0.321; CFI II: p = 0.411; CFI III: p = 0.478) were also without significant differences. Logistic regression did not show any significant increased risk for a LLD ≥ 5 mm or ≥ 10 mm as well as HO ≥ 5 mm or ≥ 10 mm.

Conclusion

Reconstruction of hip offset and postoperative leg length difference is not negatively influenced by Dorr type, canal flare index, cortical index and canal-to-calcar ratio in cementless short-stem THA. Implant positioning and canal fill are also not negatively affected by the anatomical shape of the proximal femur.

Level of evidence: Level IV.

Greater increase in femoral offset with use of collum femoris-preserving stem than Tri-Lock stem in primary total hip arthroplasty

OBJECTIVE

This study was performed to compare the clinical outcomes and performance of the collum femoris-preserving (CFP) stem (Waldemar Link GmbH & Co., Hamburg, Germany) and the Tri-Lock stem (DePuy Orthopaedics, Warsaw, IN, USA) in terms of femoral offset (FO) and leg length reconstruction.

METHODS

Clinical and radiographic data of patients who underwent total hip arthroplasty with either a CFP stem or Tri-Lock stem from January 2016 to March 2017 were compared (65 and 57 patients, respectively). The Harris hip score and Western Ontario and McMaster Universities Osteoarthritis Index were recorded. The FO, femoral vertical offset, and neck-shaft angle were measured at the last follow-up. The occurrence of dislocation and periprosthetic fracture during the follow-up period was recorded.

RESULTS

The CFP stem induced significantly more FO than did the Tri-Lock stem on the operated side than contralateral side (3.63 ± 4.28 vs. 0.83 ± 5.46 mm). Significantly fewer patients had a >5-mm decrease in FO on the unaffected side in the CFP stem group (n = 1) than Tri-Lock stem group (n = 10).

CONCLUSION

Both stems similarly improved hip function and reconstructed the leg length, but the CFP stem was superior to the Tri-Lock stem in reconstructing FO.