Biomechanical reconstruction of the hip: comparison between modular short-stem hip arthroplasty and conventional total hip arthroplasty

Purpose

Short-stem hip arthroplasty preserves femoral bone stock which includes the femoral neck. This implies that the stem has to follow the anatomy of the femoral neck. Therefore, it has been questioned whether biomechanical reconstruction of the hip can be safely achieved with SHA.

Methods

Biomechanical reconstruction of the hip was analysed for 50 modular short-stem hip arthroplasties (SHA) and compared to 50 conventional total hip arthroplasties (THA). Biomechanical parameters were analysed on pre- and postoperative pelvic overviews and compared to those of the contralateral side.

Results

The position of the acetabular cup (vertical and horizontal hip centre of rotation) changed slightly and was comparable for both groups. Horizontal femoral offset increased more in SHA (6.2 mm) than in THA (2.0 mm). Compared to the contralateral side it was significantly greater after SHA (+3.6 mm) but almost balanced after THA (−0.2 mm). Limb length increased with both procedures (8.0 mm SHA, 9.1 mm THA), but showed a significantly greater discrepancy after SHA (3.3 mm) as compared to THA (1.3 mm). According to the different implant designs, the stem-shaft axis showed a wider varus-valgus range for SHA (6.2° varus to 8.8° valgus) than for THA (2.6° varus to 3.3° valgus).

Conclusion

Horizontal femoral offset increased more with modular SHA than with conventional THA, but was within a beneficial range. Restoration of limb length appears more difficult in SHA and has a tendency to prolong limb length, which is probably related to the higher femoral resection level. This should be taken into consideration when considering SHA for a patient as well as during implantation.     

Does stem design influence component positioning in total hip arthroplasty using a minimal invasive posterolateral approach?

Purpose

Limited data exist for the reconstructive potential of short bone-preserving stems in THA using a minimal invasive posterolateral approach. Our study aim was to assess the effect of stem design on the reconstruction of hip offset and leg length in MIS posterolateral THA.

Methods

This retrospective consecutive single-surgeon study compares hip offset and leg length, as well as acetabular component positioning (cup anteversion; inclination) of 129 THAs with a cementless standard-length stem (Synergy®) and 143 THAs with a cementless short bone-preserving stem (Trilock®).

Results

In reference to the contralateral side, the mean difference in hip offset was 0.9 mm (p = 0.067) for the standard stem and 0.1 mm (p = 0.793) for the short stem, respectively. Leg-length discrepancy was 0.7 mm (Synergy®) and 0.9 mm (Trilock®), respectively. A total of 233 (86 %) acetabular components fell within the target zone for anteversion and inclination.

Conclusion

Accurate component positioning in MIS posterolateral approach THA is possible and is not influenced by the type of stem.     

Does total hip arthroplasty restore native hip anatomy? Three-dimensional reconstruction analysis

Purpose

Component orientations and positions in total hip arthroplasty (THA) are important parameters in restoring hip function. However, measurements using plain radiographs and 2D computed tomography (CT) slices are affected by patient position during imaging. This study used 3D CT to determine whether contemporary THA restores native hip geometry.

Methods

Fourteen patients with unilateral THA underwent CT scan for 3D hip reconstruction. Hip models of the nonoperated side were mirrored with the implanted side to quantify the differences in hip geometry between sides.

Results

The study demonstrated that combined hip anteversion (sum of acetabular and femoral anteversion) and vertical hip offset significantly increased by 25.3° ± 29.3° (range, −25.7° to 55.9°, p = 0.003) and 4.1 ± 4.7 mm (range, −7.1 to 9.8 mm, p = 0.009) in THAs.

Conclusions

These data suggest that hip anatomy is not fully restored following THA compared with the contralateral native hip.     

Evaluation of the accuracy of femoral component orientation by the CT-based fluoro-matched navigation system

Purpose

Accurate orientation of acetabular and femoral components are important during THA. However, no study has assessed the use of the CT-based fluoro-matched navigation system during THA. Therefore, we have evaluated the accuracy of stem orientation by CT-based fluoro-matched navigation.

Methods

The accuracy of stem orientation by CT-based fluoro-matched navigation was assessed by postoperative CT data. Furthermore, we compared the postoperative stem orientation with the intraoperative registration errors.

Results

The average antetorsion error of the stem (navigation records − postoperative CT) was −0.5° ± 5.2°. The stem valgus error was 0.4° ± 2.7°. The accuracy of the navigation record for the orientation of the stem valgus was dependent on the intraoperative registration errors.

Conclusions

The clinical accuracy of CT-based fluoro-matched navigation is adequate for stem alignment orientation, and the intraoperative verification of registration errors is valuable for checking the accuracy of stem orientation by navigation.     

Benefit of Cup Medialization in Total Hip Arthroplasty is Associated With Femoral Anatomy

Background

Medialization of the cup with a respective increase in femoral offset has been proposed in THA to increase abductor moment arms. Insofar as there are potential disadvantages to cup medialization, it is important to ascertain whether the purported biomechanical benefits of cup medialization are large enough to warrant the downsides; to date, studies regarding this question have disagreed.

Questions/purposes

The purpose of this study was to quantify the effect of cup medialization with a compensatory increase in femoral offset compared with anatomic reconstruction for patients undergoing THA. We tested the hypothesis that there is a (linear) correlation between preoperative anatomic parameters and muscle moment arm increase caused by cup medialization.

Methods

Fifteen patients undergoing THA were selected, covering a typical range of preoperative femoral offsets. For each patient, a finite element model was built based on a preoperative CT scan. The model included the pelvis, femur, gluteus minimus, medius, and maximus. Two reconstructions were compared: (1) anatomic position of the acetabular center of rotation, and (2) cup medialization compensated by an increase in the femoral offset. Passive abduction-adduction and flexion-extension were simulated in the range of normal gait. Muscle moment arms were evaluated and correlated to preoperative femoral offset, acetabular offset, height of the greater trochanter (relative to femoral center of rotation), and femoral antetorsion angle.

Results

The increase of muscle moment arms caused by cup medialization varied among patients. Muscle moment arms increase by 10% to 85% of the amount of cup medialization for abduction-adduction and from −35% (decrease) to 50% for flexion-extension. The change in moment arm was inversely correlated (R² = 0.588, p = 0.001) to femoral antetorsion (anteversion), such that patients with less femoral antetorsion gained more in terms of hip muscle moments. No linear correlation was observed between changes in moment arm and other preoperative parameters in this series.

Conclusions

The benefit of cup medialization is variable and depends on the individual anatomy.

Clinical Relevance

Cup medialization with compensatory increase of the femoral offset may be particularly effective in patients with less femoral antetorsion. However, cup medialization must be balanced against its tradeoffs, including the additional loss of medial acetabular bone stock, and eventual proprioceptive implications of the nonanatomic center of rotation and perhaps joint reaction forces. Clinical studies should better determine the relevance of small changes of moment arms on function and joint reaction forces.

Electronic supplementary material

The online version of this article (doi:10.1007/s11999-014-3787-3) contains supplementary material, which is available to authorized users.     

Accurate Leg Length Measurement in Total Hip Arthroplasty: A Comparison of Computer Navigation and a Simple Manual Measurement Device

Background

Several studies have shown that better placement of the acetabular cup and femoral stem can be achieved in total hip arthroplasty (THA) by using the computer navigation system rather than the free-hand alignment methods. However, there have been no comparisons of the relevant clinical advantages in using the computer navigation as opposed to the manual intraoperative measurement devices. The purpose of this study is to determine whether the use of computer navigation can improve postoperative leg length discrepancy (LLD) compared to the use of the measurement device.

Methods

We performed a retrospective study comparing 30 computer-assisted THAs with 40 THAs performed using a simple manual measurement device.

Results

The postoperative LLD was 3.0 mm (range, 0 to 8 mm) in the computer-assisted group and 2.9 mm (range, 0 to 10 mm) in the device group. Statistically significant difference was not seen between the two groups.

Conclusions

The results showed good equalization of the leg lengths using both computed tomography-based navigation and the simple manual measurement device.     

Total hip arthroplasty versus hemiarthroplasty for displaced femoral neck fractures in the healthy elderly: a meta-analysis and systematic review of randomized trials

Purpose

Displaced femoral neck fractures in healthy elderly patients have traditionally been managed with hemiarthroplasty (HA). Recent data suggest that total hip arthroplasty (THA) may be a better alternative.

Methods

A systematic review of the English literature was conducted. Randomized controlled trials comparing all forms of THA with HA were included. Three authors independently extracted articles and predefined data. Results were pooled using a random effects model.

Results

Eight trials totalling 986 patients were retrieved. After THA 4 % underwent revision surgery versus 7 % after HA. The one-year mortality was equal in both groups: 13 % (THA) versus 15 % (HA). Dislocation rates were 9 % after THA versus 3 % after HA. Equal rates were found for major (25 % in THA versus 24 % in HA) and minor complications (13 % THA versus 14 % HA). The weighted mean of the Harris hip score was 81 points after THA versus 77 after HA. The subdomain pain of the HHS (weighted mean score after THA was 42 versus 39 points for HA), the rate of patients reporting mild to no pain (75 % after THA versus 56 % after HA) and the score of WOMAC (94 points for THA versus 78 for HA) all favored THA. Quality of life measured with the EQ-5D favored THA (0.69 versus 0.57).

Conclusions

Total hip arthroplasty for displaced femoral neck fractures in the fit elderly may lead to higher patient-based outcomes but has higher dislocation rates compared with hemiarthroplasty. Further high-quality randomized clinical trails are needed to provide robust evidence and to definitively answer this clinical question.     

Dual mobility cup reduces dislocation and re-operation when used to treat displaced femoral neck fractures

Purpose

Total hip arthroplasty (THA) as primary treatment for displaced femoral neck fractures is controversial as THA is associated with higher rates of dislocation but lower rates of re-operation compared to hemiarthroplasty (HA). A dual mobility cup (DMC) design is associated with lower dislocation and re-operation rates in elective surgery. Is this also the case when used to treat displaced femoral neck fractures? The aim of this study is to compare rates of dislocation and re-operation of any kind following treatment for displaced femoral neck fractures with either bipolar HA or THA with DMC.

Methods

Two consecutive groups of patients treated for displaced femoral neck fractures at the Regional Hospital in Viborg in Denmark were included. In 2007–2008 171 patients (mean age 84.1 years) were treated with bipolar HA. In 2009–2010 175 patients (mean age 75.2 years) were treated with THA with DMC. Data regarding rates of dislocation and re-operation were obtained by retrospective review of medical records.

Results

We found a statistically significant difference regarding rates of dislocation and re-operation of any kind in favour of THA with DMC. Dislocation occurred in 25/171 patients [95 % confidence interval (CI) 9.3–19.9 %] treated with bipolar HA and 8/175 patients (95 % CI 1.5–7.7 %) treated with THA with DMC (p = 0.002). Re-operations were required in 32/171 patients (95 % CI 12.9–24.6 %) treated with bipolar HA and 16/175 patients (95 % CI 4.8–13.4 %) treated with THA with DMC (p = 0.01).

Conclusions

Our findings indicate that THA with DMC is superior to bipolar HA following treatment for displaced femoral neck fractures in regard to rates of dislocation and re-operation.     

Can Fluoroscopy-based Computer Navigation Improve Entry Point Selection for Intramedullary Nailing of Femur Fractures?

Background

The entry point is crucial to an accurate reduction in femoral nailing. Fluoroscopy-based navigation was developed to aid in reducing femur fractures and selecting entry points.

Questions/purposes

We asked: (1) Can the piriformis fossa (PF) and tip of the greater trochanter (TT) be identified with high reproducibility? (2) What is the range of nonneutral images clinically acceptable for entry point selection? (3) Does navigation improve accuracy and precision of landmarking the TT and PF? And (4) does off-angle fluoroscopy within the acceptable range affect landmark accuracy?

Methods

Three orthopaedic surgeons digitized the PF and TT under direct visualization on 10 cadaveric femurs, quantifying the reproducibility of the targeted PF and TT landmarks. Arcs of acceptable AP and lateral images of each femur were acquired in increments of 5° with a C-arm. An experienced orthopaedic surgeon rejected or accepted images for entry point selection by qualitatively assessing the relative positions and sizes of the greater trochanter, lesser trochanter, and femoral neck. Entry points were identified on each image using fluoroscopy and navigation. Hierarchical linear modeling was used to compare accuracy and precision between navigation and fluoroscopy and the effects of image angle.

Results

A 29° average arc of acceptable images was found. Reproducibility of the target landmarks for the PF and TT under direct visualization was excellent. Navigation had similar accuracy to fluoroscopy for PF localization but less for TT. Navigation increased precision compared to fluoroscopy for both PF and TT. Image angle affected accuracy of the PF and TT under fluoroscopy and navigation.

Conclusions

Nonorthogonal images reduce accuracy of PF and TT identification with both navigation and fluoroscopy. Navigation increased precision but decreased accuracy and cannot overcome inaccuracies induced by nonorthogonal images.     

The direct anterior approach in hemiarthroplasty for displaced femoral neck fractures

Purpose

Hip replacement is the most common treatment for displaced femoral neck fractures in the elderly, and minimally invasive surgery is popular in the field of orthopaedic surgery. This study evaluated the outcome of monopolar hemiarthroplasty by the direct anterior approach over a postoperative period up to 2.5 years.

Methods

A total of 86 patients with displaced femoral neck fractures were included (mean age of 86.5 years). Surviving patients were reviewed three months (retrospectively) and one to 2.5 years (prospectively) after surgery. One-year mortality was 36 %.

Results

For all stems, implant positioning with respect to stem alignment, restoration of leg length and femoral offset was correct. Acetabular protrusion was observed in 55 % of the patients one to 2.5 years postoperatively. Subsidence and intraoperative periprosthetic fractures occurred in three patients (3 %) each. All revision stems for postoperative periprosthetic fractures could be implanted using the initial surgical technique without extension of the previous approach. The mean Harris hip score was 85 points at the one to 2.5-year follow-up; 85 % of the patients were satisfied with their hip and 57 % returned to their preoperative level of mobility.

Conclusion

Based on these findings, hemiarthroplasty for hip fractures can be performed safely and effectively via the direct anterior approach with good functional outcome and high patient satisfaction.     

The accuracy of digital templating: a comparison of short-stem total hip arthroplasty and conventional total hip arthroplasty

Purpose

Selection of the correct femoral stem size is crucial in total hip arthroplasty for an uncomplicated implantation and good initial stability. Pre-operative templating has been shown to be a valuable tool in predicting the correct implant size. For short-stem total hip arthroplasty (SHA), which recently is increasingly used, it is unknown if templating can be performed as reliable as conventional total hip arthroplasty (THA).

Methods

A total of 100 hip arthroplasties, 50 with SHA and 50 with THA, were templated by four orthopaedic surgeons each. The surgeons had different levels of professional experience and performed a digital template of the acetabular and femoral component on the pre-operative radiographs. The results were compared with the truly inserted implant size.

Results

For the femoral stems the average percentage of agreement (±1 size) was 89.0 % in SHA and 88.5 % in THA. There was no significant difference among surgeons in the accuracy of templating the correct stem size and no significant difference between templating SHA and THA. For the acetabular component the average percentage of agreement (±1 size) was 75.8 %. However, the more experienced surgeons showed a significant higher accuracy for templating the correct cup size than the less experienced surgeons.

Conclusion

Digital templating of SHA can predict the stem sizes as accurately as conventional THA. Therefore digital templating is also recommendable for SHA, as it helps to predict the implant size prior to surgery and thereby might help to avoid complications.     

Influencing factors for the increased stem version compared to the native femur in cementless total hip arthroplasty

Purpose

Stem version is not always equivalent to femoral neck version (native version) in cementless total hip arthroplasty (THA). We therefore examined the discrepancy of version between the native femoral neck and stem using pre- and postoperative computed tomography (CT), the level of the femur where the canal version most closely fit the stem version, and the factors influencing version discrepancy between the native femoral neck and stem.

Methods

A total of 122 hips in 122 patients who underwent primary THA using a metaphyseal-fit stem through the postero-lateral approach were included. Pre- and postoperative CT images were utilized to measure native and stem version, and the version of the femoral canal at four levels relative to the lesser trochanter.

Results

The mean native and stem versions were 28.1 ± 11.0° and 38.0 ± 11.2°, respectively, revealing increased stem version with a mean difference of 9.8° (p < 0.0001). A total of 84 hips (68.9 %) revealed an increase in version greater than 5°. Femoral canal version at the level of the lesser trochanter most closely approximated that of stem version. Among the factors analysed, both univariate and multivariate analysis showed that greater degrees of native version and anterior stem tilt significantly reduced the version discrepancy between the native femoral neck and stem version.

Conclusions

Since a cementless stem has little version adjustability in the femoral canal, these findings are useful for surgeons in preoperative planning and to achieve proper component placement in THA.     

Total hip arthroplasty with acetabular reconstruction using a bulk autograft for patients with developmental dysplasia of the hip results in high loosening rates at mid-term follow-up

Purpose

Managing a deficient acetabulum in patients with developmental dysplasia of the hip (DDH) can be challenging. The purpose of the study was to determine the mid-term results of total hip arthroplasty (THA) using a bulk structural autograft for reconstruction of the acetabular roof in patients with DDH.

Methods

Between 1982 and 1999, 112 patients underwent THA with acetabular roof-plasty using a bulk structural autograft for secondary osteoarthritis related to DDH. A total of 106 patients (115 hips) met inclusion criteria and were followed for an average of 11.6 years (seven to 24 years). The mean age was 52.5 years at the index operation. Clinical and radiological evaluations were performed according to the methods of Merle d’Aubigné and Postel, Johnston et al. and DeLee and Charnley.

Results

The overall Merle d’Aubigné hip score significantly improved (3.7 vs 10.4, p < 0.01). The limb length discrepancy decreased from 30 to 6 mm (p < 0.01). The average distance that the hip centre was distalised was 22.3 mm (0–56 mm). However, radiolucent lines were observed in 27 % of patients at final follow-up, and the overall rate of revision for aseptic loosening was 16 %. Further, Kaplan-Meier survivorship curves predicted a rapid increase in the failure rate at 15 years.

Conclusions

The mid-term functional outcome of THA with an acetabular roof-plasty using a bulk autograft is satisfactory; however, the long-term results are questionable.