Femoral neck cut level affects positioning of modular short-stem implant

A comprehensive analysis on contributing factors for varus or valgus malposition of femoral stems in uncemented total hip arthroplasty via DAA

Background

Varus or valgus malposition of uncemented femoral stems have been described to have detrimental effects for long term implant survival. Various pre- and intra-OP factors have been suggested to be relevant, one of them being the approach to the hip. The aim was to investigate several pre- and intra-OP factors associated with femoral stem malpositioning in a large series of DAA hips.

Methods

A series of 400 consecutive patients (416 hips) who underwent navigated (Brainlab) cementless Total Hip Arthroplasty (THA) in 2022 (Corail or Actis stem DePuy Synthes) via a direct anterior approach (DAA) was analyzed. Preoperative data were collected based on patients' demographics, radiographic information [critical trochanteric angle (CTA), centrum collum diaphyseal (CCD) angle, greater trochanter overhang, femoral neck resection angle, femoral neck resection height and Door classification], and these were correlated with the postoperative stem position. Univariable and multivariable linear regression were carried out to determine significant factors that contribute to varus and valgus stem malalignment.

Results

With the DAA approach, 56.5 % of stems were placed in an optimal neutral position, 38.4 % were in acceptable position of 0.1°-2° varus/valgus and only 5 % had a deviation larger than 2° varus/valgus. The critical trochanteric angle (CTA) was statistically significant in determining varus stem placement whereas centrum collum diaphyseal angle (CCD) was found to affect valgus stem malpositioning. All other factors have shown no relevant effect on stem placement using stepwise regression method.

Conclusion

In DAA, 95 % of stems were found in a varus/valgus position of 2° or less. In pre-operative measurement, only femoral morphology (e.g. CTA & CCD) were found to be relevant, affecting varus/valgus stem malposition. All other tested modifiable and non-modifiable factors had no significant effect. Therefore, pre-OP templating including measurement of CTA and CCD, intra-operative assessment as well as proper operative techniques are paramount to prevent excessive varus/valgus mal-position of femoral stem in DAA.

Is the strain pattern of conventional stems negatively affected by a previously short stem THA? An experimental study in cadavaric bone

BACKGROUND

A short stem hip arthroplasty can be revised in many cases using a conventional stem. Furthermore, in some cases the implantation of a short stem is intended, but intraoperatively reasons may lead to the decision to implant a conventional stem after previous preparation of a short stem.

OBJECTIVE

In both cases it is questionable if the anchorage of a conventional stem is negatively affected by the previous preparation of a short stem. In clinical practice mid- or long-term follow up for these special cases hardly exist.

METHODS

The strain patterns for the conventional Bicontact stem in primary implantation and after preparation of the proximal femur for a METHA short stem were tested biomechanically in three pairs of cadaveric femora.

RESULTS

The strain patterns for the conventional Bicontact after preparation of the METHA short stem were similar to conditions after testing the conventional stem in primary conditions.

CONCLUSIONS

These data lead to the consequence that in clinical practise the implantation of a conventional stem after preparation of a short stem and even after revision of a short stem is possible without increased risk of loosening or long-term stress-shielding.

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

Background

Total hip arthroplasty (THA) is a very successful procedure in orthopedics. Still polyethylene wear and gait deficits are limiting the clinical success.It is important to reconstruct leg length (LL) and femoral offset (FO) anatomically in order to have the best possible result of a THA. Gait deficits can arise due to leg length discrepancy as well as changes in the abductor moment arm. In THA, LL and FO are strongly determined by the orientation, size and geometry of the femoral stem.

Methods

This radio-anatomical study used the data of a prospective cases series of 112 patients who underwent 126 primary THAs and had completed a 1-year follow-up examination. FO and LL were compared between the conventional straight stem in vivo and a computed simulated implantation of a short curved stem, using the pre- and postoperative pelvic radiographs of the same patients.

Results

In this simulation of the short curved stem statistically significantly restored native FO (p = 0.010) and LL (p = 0.000) better, compared to the conventional straight stem.

Conclusions

Thus, the short curved stem restores FO and LL better, and could potentially prevent gait deficits.

Comparison of Specific Femoral Short Stems and Conventional-Length Stems in Primary Cementless Total Hip Arthroplasty

There are several reported disadvantages with conventional-length femoral stems in cementless total hip arthroplasty (THA). Therefore, various efforts have been made to develop a specific femoral short stem to improve physiologic bone remodeling at the femoral aspect of a cementless THA. However, there are potential disadvantages with specific femoral short stems, such as malalignment, inadvertent subsidence, and potential proximal femoral fracture. Therefore, the authors quantitatively compared radiographic and clinical outcomes as well as component-specific complications between 2 groups of patients following primary cementless THA. A matched comparison was made between specific femoral short stems (n=50) and conventional-length femoral stems (n=50) in cementless THA procedures performed between January 2008 and January 2012. Patients were matched for age, sex, body mass index, height, surgical approach, and surgeon. No significant differences were found between the 2 groups in mean postoperative radiographic outcomes, functional outcomes, or complications. Both groups showed satisfactory performance at 5-year follow-up. Specific femoral short stems resulted in a higher incidence of malalignment and subsidence and a lower incidence of thigh pain and proximal bone resorption compared with conventional-length femoral stems. Although longer follow-up is required, specific femoral short stems may have clinical and radiographic advantages with equivalent perioperative complications relative to conventional-length femoral stems. However, this technique requires proper patient selection in combination with careful preoperative planning and meticulous surgical technique.

[Differences between short stem prostheses]

The short stem designs currently available are significantly different and can be differentiated into neck containing, partial containing and neck resection designs. In this article, the differences in the design features are presented. These include the differences in the technique of implantation, the significant differences in the reproducibility of the given anatomy of the patient and also concerning their osteologic competence.

The effect of femoral neck osteotomy on femoral component position of a primary cementless total hip arthroplasty

PURPOSE

The aim of this study was to quantify the femoral canal diameter and version at different femoral neck osteotomy locations, and to investigate the effect of the osteotomy plane on femoral component position in total hip arthroplasty (THA).

METHODS

Preoperative and postoperative three-dimensional models were reconstructed in 15 patients (19 hips) who underwent primary cementless THA with tapered non-anatomical femoral stem. On the pre-operative models, the osteotomy plane was simulated at different levels (-5, 0, 5, and 10 mm from the femoral saddle [piriformis fossa]) and angles (30, 40, 50, and 60° from the femoral anatomical axis). Medullary canal version and mediolateral diameter were measured on the osteotomy surfaces. On the postoperative models, the femoral neck osteotomy plane, stem anteversion and alignment were measured.

RESULTS

The average canal diameter ranged from 22.8 to 26.3 mm at different osteotomy levels and from 20.8 to 29.0 mm at different osteotomy angles. The average canal version ranged from 11.4 to 23.2° at different resection levels and from 12.8 to 21° at different resection angles. The femoral stem anteversion was correlated with neck osteotomy angle (R = 0.72), whereas stem alignment in frontal plane (varus/valgus) was correlated with neck osteotomy level (R = 0.87).

CONCLUSIONS

The femoral neck osteotomy plane in THA affects the postoperative stem position due to the complex morphology of the proximal femoral medullary canal, suggesting that both femoral neck resection level and angle should be considered in optimizing femoral component alignment in THA patients.

Reproducing the hip center with a femoral neck-retaining implant

Because of the recent trend for total hip arthroplasty in younger patients, more bone-preserving implants have been designed, based partly on the premise that maintenance of more bone stock would allow revision with standard primary implants. Another possible advantage of an implant that retains the femoral neck is that it may allow anatomical recreation of the center of the femoral head, femoral neck anteversion, anterior tilt, and caput-collum-diaphysis (CCD) angle, as well as femoral offset and leg length, without the use of modular implants. To determine whether the proximal femoral anatomy could be recreated, this study used computed tomography data and 3-dimensional modeling from 10 cadaver hips in 6 whole body specimens. Three femoral neck resection levels were investigated: 2 mm, 5 mm (recommended resection), and 10 mm from the base of the femoral neck. Results showed that the center of the femoral head, femoral neck anteversion, and CCD angle could all be recreated with available implant sizes, without modularity, within 2° and 1 mm on average. The addition of a modular neck provided no advantage in recreation of the hip center or other anatomical parameters. Use of a short metaphyseal femoral neck retaining-type of stem should allow restoration of anatomical parameters without the use of an exchangeable modular femoral neck.

Patient selection for shorter femoral stems

The right patient selection with the correct surgical treatment are prerequisite for a positive result in total hip arthroplasty (THA). Short stem implants demand a shorter anchoring length in accordance with the proper indication. Although appropriate indications for short stems have been discussed in the literature, there currently is no clear definition. The lack of an accepted categorization of short hip stems complicates the situation further. This article briefly reviews the literature and highlights the authors' results and experiences in short stem THA in an effort to establish a proper discrimination between indications and contraindications for the Metha short stem. Results presented include a retrospective data collection and follow-up examination of 126 patients who underwent short stem THA with 2- and 4-year results. Anchoring principles of the short stem are reviewed, and a complication and failure analysis based on 7 femoral revisions in 1092 short stem THAs is presented. Selection criteria for short stem THA are patients younger than 70 years with primary osteoarthritis and dysplastic femoral deformities, and indications of avascular head necrosis. Adequate bone quality must be confirmed intraoperatively, assessing whether the bone structure in the area of the femoral neck is strong enough to support the short stem load transmission. Coxa vara and high dysplastic femoral neck antetorsion are contraindications for short stems. Wide and short femoral necks, implant undersizing, and a deep stem position below the femoral osteotomy compromise stability and must be avoided with an appropriate surgical technique. Long-term data are not yet available.

Short stem total hip arthroplasty in patients with rheumatoid arthritis

Total hip arthroplasty (THA) has proven successful in patients with rheumatoid arthritis (RA). Patients with RA often require multiple revisions, and bone conservation is mandatory. A variety of short stems is currently available with mid-term results for osteoarthritis. This retrospective study evaluated mid-term clinical results of short stem THA in a series of patients with RA. Between 2005 and 2009, a total of 105 cementless short stems were implanted in patients with RA. Average patient age at the time of the index THA was 44.2 years, and average length of follow-up was 5 years. Clinical evaluation included physical examination and documentation of potential adverse events during the postoperative period. No radiographic failures occurred. Femoral and cup components showed some minor radiolucencies with sclerotic lines, but none involved 100% of the bone-prosthesis interface. Complications included femoral component subsidence in 2 hips after initial full weight bearing; 1 case resolved after 3 months, and the other case was revised to a standard shaft. One intraoperative dorsolateral stem tip perforation occurred with revision to a conventional length stem. Migration in 1 cup led to revision without removal of the short stem implant. No infections or joint dislocations were observed. The transfer of the short stem concept to an additional treatment option for patients with RA proved successful in the early to mid-term postoperative period. Complications and revisions were limited to early migration and early loosening of the implants in line with the results reported in the literature of cementless conventional THA in patients with RA.

Learning curve analysis of the Collum Femoris Preserving total hip surgical technique

The aim of this study was to determine whether femoral neck preserving total hip arthroplasty would become less difficult and more efficient during the first 20 cases and to identify potential pitfalls during the introduction of this procedure. The difficulty and efficiency of the initial 20 procedures performed by four surgeons was prospectively determined by analysing a total of 68 video recordings using time-action analysis. This method measures the duration and efficiency of individual actions needed for a surgeon to achieve his or her goal. Afterwards, we reviewed all actions with a long duration and discussed possible causes of delay with the surgeons to identify possible pitfalls. We found a decrease of difficulty and an increase of efficiency during the first 20 cases and a more consistent execution after the initial five cases. Estimating the correct osteotomy level and stem curvature was often difficult, which resulted in a variable stem position. Radiologic analysis demonstrated a tendency for varus position and increased leg length throughout the series, even after the surgeons demonstrated technical proficiency.

The influence of resection height on proximal femoral strain patterns after Metha short stem hip arthroplasty: an experimental study on composite femora

PURPOSE

The number of candidates for a total hip arthroplasty (THA) is steadily increasing, while the average patient age is decreasing for primary THA. The rise in THA is mainly due to excellent clinical outcomes and the extended longevity of modern implants. Short stem arthroplasties with predominantly metaphyseal fixation such as the Metha® stem are suggested for young patients. It is hypothesised that the more physiological load transfer of these devices reduces stress shielding, which in turn may reduce the risk of aseptic loosening. However, patients with femoral deformities often require a deviation of the resection height. To this end, our aim was to evaluate how resection height influences strain patterns in order to characterise possible limits for short stem implantation.

METHODS

Biomechanical testing using ten strain gauges on synthetic bone illustrated the strain patterns of three different resection heights (0, +5 and +10 mm) for the Metha stem.

RESULTS

The greatest differences in strains were displayed at the "high" (most proximal) resection height (+10 mm) when compared to the non-implanted strain pattern. At the medial calcar, the strain was 143% for +10 mm, 96% for +5 mm and 94% for 0 mm. Overall, discrepancies were less for deeper resections.

CONCLUSIONS

The deeper the resection, the more similar the strain patterns are when compared to a non-implanted synthetic bone. Changes in strain patterns are induced by variation in the varus/valgus positioning of the implant and by different offsets.

The difference between stretching and splitting muscle trauma during THA seems not to play a dominant role in influencing periprosthetic BMD changes

BACKGROUND

Periprosthetic bone adaptation in the proximal femur after total hip arthroplasty can result in reduced bone mineral density that may contribute to increased risk of aseptic loosening or fracture. Functional loading of the proximal femur postoperatively may depend upon the type of surgical muscle trauma - splitting or stretching - and is likely to influence the preservation of periprosthetic bone mineral. Since the maintenance of bone is known to be highly age and gender dependent, the aim of this study was to investigate the interplay between muscle trauma and age and gender influences on periprosthetic bone adaptation.

METHODS

Ninet y-three patients were consecutively recruited into either a transgluteal (splitting) or anterolateral (stretching) surgical approach and examined 7 days and 12 months after an elective primary hip arthroplasty (Zweymüller Alloclassic stem), using dual-energy X-ray absorptiometry measurements to quantify proximal femoral bone mineral density.

FINDINGS

The results indicate that neither gender, age nor surgical trauma type, but only the combination of age and gender, were significant predictors of postoperative remodelling rate, with younger men (<65) and older women exhibiting the largest bone atrophy.

INTERPRETATION

This study has demonstrated that the difference between stretching and splitting surgical trauma to the muscles during total hip replacement does not play a dominant role in influencing periprosthetic bone mineral changes. However, this data does suggest that certain patient populations may particularly benefit from muscle and bone preserving procedures.