The tridimensional geometry of the proximal femur should determine the design of cementless femoral stem in total hip arthroplasty

Short-stem total hip arthroplasty is equivalent to a standard-length stem procedure in an unselected population at mid-term follow-up

PURPOSE

Limitations of standard-length femoral stems persist, including proximal-distal mismatch, non-ideal load transfer, loss of bone tissue, and perioperative fracture. Symbol® (Dedienne Santé, France) is a metaphyseal-engaging short-stem implant designed to address these issues in total hip arthroplasty (THA). While short stems have been well studied in selected and younger patients, it is unclear whether they offer advantages in an unselected population. We hypothesized that short femoral stems offer similar mid-term survivorship at five year minimum follow-up and function score to standard-length femoral stems, in an unselected patient population.

METHODS

We retrospectively reviewed a continuous unselected cohort of patients who undergone THA by one surgeon with a standard-length stem between November 2013 and October 2015, and a short stem between November 2015 and March 2017. We compared modified Harris Hip Score and Oxford Scores with a minimum follow-up of five years and procedural factors that could be associated with worse results with a short stem design.

RESULTS

There was no difference in survival rate between the two groups. Average Harris Hip Score and Oxford Scores at the last follow-up were comparable. A multivariate linear regression was performed to assess the relationship between modified Harrys Hip Score at five years post-operatively and the explanatory variables: age, body mass index, physical status score ASA (American Society of Anesthesiologists), and HHS pre-op. None was associated with the standard-length stem but for the short stem.

CONCLUSION

Short-stem implants provide good survival rate at mid-term; nevertheless, a steep learning curve is necessary to optimize the metaphyseal filling of the implant, especially for osteoporotic bone.

The torsion of the proximal femur in cementless total hip arthroplasty: a 3-dimensional evaluation

INTRODUCTION

The anatomy of the proximal femur at the time of total hip arthroplasty has been widely studied but the horizontal plane was never considered, or only limited to the torsion of the femoral neck.

METHODS

Using CT-scan images from a group of 178 patients scheduled for cementless total hip arthroplasty (THA), we analysed the evolution of the torsion of the proximal femoral metaphysis, in reference to the posterior bicondylar plane of the femur. The evolution of the torsion, between 20 mm below the centre of the lesser trochanter and 20 mm above, was evaluated.

RESULTS

In cases of primary osteoarthritis, osteonecrosis, rheumatoid arthritis and epiphysiolysis capitis femoris, the mean torsion decreased from 46° to 20° without significant differences in average values between the different diagnoses, but important individual variations were found. In the groups of dysplasia and congenital hip dislocation, the torsion values were significantly higher, decreasing in mean from 59° to 25° and 63° to 34° respectively, and with important individual variations.

CONCLUSIONS

These data are important when using cementless femoral stems, since an ideal fit-and-fill in the proximal femur zone has been shown to positively influence bone ingrowth of the stem. However, a strict adaptation of the stem to the medullary canal, without considering its torsion, can lead to an increased or decreased torsion of the prosthesis neck and thus to an instability of the arthroplasty. For these reasons, if a perfect adaptation of the stem to the intramedullary anatomy and an optimal reconstruction of the extramedullary anatomy are to be achieved, 3-dimensional planning should ideally be obtained for every patient. This will allow the best stem choice adapted to every single patient and every kind of anatomy.

Component Asymmetry in Bilateral Cementless Total Hip Arthroplasty

Background

This study investigated the results of component asymmetry (CA) in bilateral cementless total hip arthroplasty (THA).

Methods

This study included 300 patients, who underwent bilateral cementless THA between April 2000 and December 2017. They were divided into the component symmetry (CS) and CA groups; CA group was sub-classified into acetabular component asymmetry (ACA) and femoral component asymmetry (FCA). Radiologic and clinical outcomes of the CA group were compared with those of the CS group.

Results

The incidence of CA was 25.7% (77/300 patients), including 55 patients with ACA, 34 patients with FCA, and 12 with both components asymmetric. The mean time interval between operations in the CA group was significantly longer than that in the CS group (p < 0.001). The mean differences in horizontal and vertical distances from teardrop to the center of rotation of the acetabular component between both hips in the ACA group were significantly larger than those in the CS group (p = 0.033 and p < 0.001, respectively). The mean femoral component alignment angle difference between both hips was significantly larger in the FCA group than in the CS group (p < 0.001). The mean Harris Hip Score at last follow-up of the CA group was similar to that of the CS group.

Conclusions

CA in patients undergoing bilateral cementless THA was not rare, especially with a longer time interval between operations. Regardless of CA, when stable fixation of the components was achieved, satisfactory radiologic and clinical outcomes were obtained.

Gluteus Maximus Tendon Reference: A Novel Method to Restore Leg Length in Total Hip Arthroplasty With Femoral Bone Loss

BACKGROUND

Accurate restoration of leg length and proximal femoral geometry is essential for achieving satisfactory outcomes in both primary and revision total hip arthroplasty. Although common landmarks such as the greater trochanter and the lesser trochanter (LT) may be used to measure limb length intraoperatively in primary cases, these landmarks may be absent or disrupted in fractures and revision procedures. We propose the distance between the gluteus maximus tendon gluteal sling (GS) and the center of the femoral head (FHC) as a novel anatomic landmark beyond the zone of injury, which can be used to restore limb length in the setting of proximal femoral bone loss or fracture.

METHODS

One hundred healthy hips were retrospectively reviewed using MRI to determine the distance between the proximal edge of the GS and the FHC. Additional measurements were collected including the distance between the GS and the greater trochanter and LT, as well as the FHC to the LT and greater trochanter.Results: The distance between the GS and the femoral head was consistent and measured 8.0 cm (±1.88 cm, SD = 0.66). A moderate positive correlation (r = 0.37, P < 0.001) was observed between patient height and GS to FHC distance.

DISCUSSION

The distance between the GS and the center of the femoral head consistently measures 8 cm and can be used to set implant height to restore proximal femoral geometry and leg length in total hip arthroplasty with proximal femoral bone loss.

Age-Associated Changes in Proximal Femur Morphology Affect Femoral Component Sizing in Cementless Hip Arthroplasty

Background

In cementless hip arthroplasty, the femoral component should obtain firm fixation within the endosteal bone and achieve adequate reconstruction of hip joint biomechanics simultaneously. Previous anatomical studies described age-related changes of the proximal femoral canal, such as canal widening, which theoretically necessitates the use of larger stem sizes in elderly patients. This study examines a potential association between patients’ age at surgery and the implant size of a cementless femoral component.

Material and methods

A total of 13,423 primary hip arthroplasties with a single cementless stem registered in the Dutch Arthroplasty Register (LROI) were included. Patient characteristics (ie patients’ age, sex, height and weight at time of surgery) and femoral component size were derived. A one-way ANCOVA was used to compare the mean stem size between age groups, and multivariable linear regression analysis was used in order to investigate to which extent ageing impacted stem size.

Results

Each subsequent age- group (ten-year intervals) had a significantly larger mean stem size than the prior age- group. Multivariable linear regression analysis revealed that age is positively correlated with stem size and that this correlation is more prominent in females than in males (beta = .046, P < .001 and beta = .028, P < .001 respectively).

Interpretation

Implant size is positively correlated with age, in particular in females and independently from investigated anthropometric characteristics. The present study endorses that the femoral canal morphology is related to patients’ characteristics such as age and sex. The morphology will subsequently influence implant sizing and therefore may have biomechanical and clinical implications.

Biomechanical study on the stability and strain conduction of intertrochanteric fracture fixed with proximal femoral nail antirotation versus triangular supporting intramedullary nail

OBJECTIVES

Based on the features of the three-dimensional spatial structure of the proximal femoral trabeculae, we developed a bionic triangular supporting intramedullary nail (TSIN) for the treatment of the femoral intertrochanteric fracture. The current study aimed to compare the mechanical stability and restoration of mechanical conduction between proximal femoral nail antirotation (PFNA) and TSIN to fix the intertrochanteric fractures.

METHODS

Firstly, five sets of PFNA and TSIN with the same size were selected and fixed on a biomechanical testing machine, and strain gauges were pasted on the main nail, lag screw, and supporting screw to load to the vertical load to 600 N, and the displacement and strain values were recorded. Secondly, formalin-preserved femurs were selected, and the left and right femurs of the same cadaver were randomly divided into two groups to prepare intertrochanteric femur fractures (AO classification 31-A1), which were fixed with PFNA (n = 15) and TSIN (n = 15), respectively. Sixteen sites around the fracture line were chosen to paste strain gauges and loaded vertically to 600 N, and then, the fracture fragment displacement and strain values were recorded. Finally, a 10,000-cycle test ranging from 10 to 600 N was conducted, and the cycle number and displacement value were recorded.

RESULTS

The overall displacement of PFNA was 2.17 ± 0.18 mm, which was significantly greater than the displacement of the TSIN group (1.66 ± 0.05 mm, P < 0.05) under a vertical load of 600 N. The strain below the PFNA lag screw was 868.29 ± 147.85, which was significantly greater than that of the TSIN (456.02 ± 35.06, P < 0.05); the strain value at the medial side of the PFNA nail was 444.00 ± 34.23, which was significantly less than that of the TSIN (613.57 ± 108.00, P < 0.05). Under the vertical load of 600 N, the displacement of the fracture fragments of the PFNA group was 0.95 ± 0.25 mm, which was significantly greater than that of the TSIN group (0.41 ± 0.09 mm, P < 0.05). The femoral specimens in the PFNA group showed significantly greater strains at the anterior (1, 2, and 4), lateral (7, 9, and 10), posterior (11), and medial (15 and 16) sites than those in the TSIN group (all P < 0.05). In the cyclic compression experiment, the displacements of the PFNA group at 2000, 4000, 6000, 8000, and 10,000 cycles were 1.38 mm, 1.81 mm, 2.07 mm, 2.64 mm, and 3.58 mm, respectively, which were greater than the corresponding displacements of the TSIN group: 1.01 mm, 1.48 mm, 1.82 mm, 2.05 mm, and 2.66 mm (P₈₀₀₀ = 0.012, P₁₀₀₀₀ = 0.006).

CONCLUSIONS

The current study showed that TSIN had apparent advantages in stability and stress conduction. TSIN enhanced the stability of intertrochanteric fractures, particularly in superior fracture fragments, improved stress conduction, reduced the stress in the anterior and medial femur, and restored the biomechanical properties of the femur.

Determination of the Gender-Related Differences on Native Femoral Anatomy Using Three-Dimensional Computerized Tomography Models in Caucasian Population

Introduction Three-dimensional (3D) modelling, which has an increasing interest in the literature, could help surgeons to better understand the lesions by visualizing the real anatomical features compared to plain radiographs and two-dimensional (2D) tomography images. We aimed to evaluate the native femoral anatomical features of Turkish females and males using 3D computed tomography models. Methods We evaluated the right femoral anatomical features of 60 females and 60 males between 31 and 65 years of age creating 3D computerized tomography models. The gender-specific differences of femoral neck inclination and anteversion, femoral mechanical-anatomical axis, anatomical and mechanical lateral distal femoral, medial and lateral proximal femoral angles were measured on 3D femoral anatomical models. Results The mean age of our study groups was 50.6 ± 8.5. We determined a statistically significant difference between gender groups in terms of mean femoral neck anteversion angles (p = 0.009). We observed the retroversion of the femoral neck in 12 adults (10%). The mean values of femoral neck inclination, femoral mechanical - anatomical angle, anatomical and mechanical lateral distal femoral angles, medial and lateral proximal femoral angles did not differ any statistical significance between gender groups. Conclusion Although the anatomical angle measurements except femoral neck anteversion, did not differ significantly between gender groups of our study, there were differences between mean anatomical angles when compared to other studies in the literature, which investigate the different races or Caucasian population. Through 3D anatomical data, more compatible implants, prosthesis or biomaterials can be produced by determining gender and race-specific anatomical differences.

Hip implants can restore anatomical and medialized rotation centres in most cases : a 3D templating study comparing four implantation strategies

Aims

Hip arthroplasty does not always restore normal anatomy. This is due to inaccurate surgery or lack of stem sizes. We evaluated the aptitude of four total hip arthroplasty systems to restore an anatomical and medialized hip rotation centre.

Methods

Using 3D templating software in 49 CT scans of non-deformed femora, we virtually implanted: 1) small uncemented calcar-guided stems with two offset options (Optimys, Mathys), 2) uncemented straight stems with two offset options (Summit, DePuy Synthes), 3) cemented undersized stems (Exeter philosophy) with three offset options (CPT, ZimmerBiomet), and 4) cemented line-to-line stems (Kerboul philosophy) with proportional offsets (Centris, Mathys). We measured the distance between the templated and the anatomical and 5 mm medialized hip rotation centre.

Results

Both rotation centres could be restored within 5 mm in 94% and 92% of cases, respectively. The cemented undersized stem performed best, combining freedom of stem positioning and a large offset range. The uncemented straight stem performed well because of its large and well-chosen offset range, and despite the need for cortical bone contact limiting stem positioning. The cemented line-to-line stem performed less well due to a small range of sizes and offsets. The uncemented calcar-guided stem performed worst, despite 24 sizes and a large and well-chosen offset range. This was attributed to the calcar curvature restricting the stem insertion depth along the femoral axis.

Conclusion

In the majority of non-deformed femora, leg length, offset, and anteversion can be restored accurately with non-modular stems during 3D templating. Failure to restore hip biomechanics is mostly due to surgical inaccuracy. Small calcar guided stems offer no advantage to restore hip biomechanics compared to more traditional designs.

Cite this article: Bone Jt Open 2021;2(7):476–485.

Cementless femoral stem fixation and leg-length discrepancy after total hip arthroplasty in different proximal femoral morphological types

PURPOSE

Leg-length changes at total hip arthroplasty (THA) may result from too proximal position of the femoral component, i.e. not being sunk deep enough into the femoral canal due to the size and shape of both medullary canal and implant. Some femoral implants are designed to achieve such fixation in the mediolateral dimension, while others also engage the bone anteroposteriorly. Our aim was to examine the relationship between proximal femoral morphology, osseointegration and leg-length equalization at THA. We asked whether the Dorr classification, femoral cortical index and canal flare index on preoperative radiographs had significant impact on THA aseptic loosening rates and post-operative leg-length discrepancy (LLD).

METHODS

Literature review included original articles on proximal femoral morphology with post-operative LLD and other clinical outcomes of THA, published in the last decade. Case reports and biomechanical studies without clinical data were excluded.

RESULTS

Higher femoral cortical index and/or canal flare index (corresponding to the Dorr type A) increases the risk of leg lengthening at THA. This is particularly notable in femoral stems with metaphyseal fixation, where high canal flare index has also been linked to osseointegration failure and implant loosening. On the other hand, lower canal flare index (corresponding to the Dorr type C) is more prevalent in the elderly population and increases late periprosthetic fracture rates and stress shielding. Even the most commonly used cementless femoral stems cannot offer optimal fit to intra-/extramedullary geometry or offset restoration in up to 30% of clinical cases.

CONCLUSIONS

Femoral morphology can have significant impact on post-operative LLD and osseointegration of cementless THA. Quantitative measurements of the proximal femoral canal may improve the choice of a particular implant and fixation method.

Upper Femur Anatomy Depends on Age and Gender: A Three-Dimensional Computed Tomography Comparative Bone Morphometric Analysis of 628 Healthy Patients' Hips

BACKGROUND

The knowledge of proximal femur geometry is essential in the understanding and treatment of hip pathologies. Our aim is to evaluate the range of "normal anatomical values of the proximal femur" and their relationship to age, gender, and ethnicity in a cohort of healthy population, using a 3-dimensional computed tomography automated software.

METHODS

The pelvis and bilateral femora of 628 healthy individuals (394 males/234 females, mean age 61.5 ± 16.5 years, mean body mass index [BMI] 26.9 ± 5.2 kg/m²) including 2 ethnicities (226 Asians and 406 Caucasians) were assessed with a 3-dimensional computed tomography scan-based system using algorithm-calculated landmarks. The demographic parameters recorded were age, gender, BMI, and ethnicity. The femoral neck-shaft angle (NSA), femoral neck version, femoral offset (FO), and femoral canal flare index (fCFI) were calculated for each individual. Analyses were performed using SPSS version 22. P-values <.05 were considered to indicate statistical significance.

RESULTS

Overall, the mean NSA was 124.7° (standard deviation [SD] 6.2), mean femoral neck version was 14.5° (SD 8.1), mean FO was 42.9 mm (SD 6.8), and mean fCFI was 3.4 (SD 0.5). Gender was associated with all parameters, with the females presenting more valgus and anteverted hips. Multivariate analysis revealed a lower NSA and fCFI and a higher FO for older individuals. Ethnicity and BMI were not associated with any parameters.

CONCLUSION

Our results showed that there is a direct relationship of age and gender to the variations in the investigated proximal femur anatomical parameters in a large cohort of healthy individuals. Those important gender-based and age-based differences might advocate for more varus and lateralized component to reproduce preoperative anatomy of male and patients older than 50 years.

The optimization of the length of the lower limbs after hip arthroplasty

BACKGROUND

The purpose of this research was to evaluate the effectiveness of hip joint arthroplasty in patients with different correction of the length of the legs and identifying factors that influence the outcome.

MATERIAL AND METHODS

We analyzed 93 patients operated upon with an initial shortening of the limb length by more than 3 cm. The difference in the length of the limbs ranged from 3 to 12 cm, which averaged 5 cm. Immediately after surgery and after three to 12 months, a control examination was performed with measurement of the length of the lower extremities and the function of the joint, using the Harris scale.

RESULTS

The study revealed three versions of the result of the correction of the length of the limb after hip joint arthroplasty: saving limb shortening (n = 16 (17%) with HHS 80 (95% CI, 78.4 to 83.4%); full restoration of limb length (n = 70 (75,5%) with HHS 78 (95% CI, 74.6 to 80.2%); excess limb lengthening (n = 7 (7.5%) with HHS 68 (95% CI, 63.5 to 73.5%).

CONCLUSIONS

So that, incorrect lengthening of the lower limb during arthroplasty leads to lameness, discomfort, muscle tension, which ultimately leads to pain. Optimal result of hip arthroplasty and ensure the necessary amplitude of movements, it is advisable to use prediction criteria of the leveling of the limb length, which are: the duration of the disease, presence of consequences of previous operations, gender, age, degree of tissue rigidity, severity of hip-spine syndrome, and scoliotic deformity.