[Femur first in hip arthroplasty--the concept of combined anteversion]

USE OF COMPUTER NAVIGATION IN TOTAL HIP ARTHROPLASTY (LITERATURE REVIEW)

OBJECTIVE

The aim: Analyze the accuracy and ease of use of various computer navigations in total hip arthroplasty.

PATIENTS AND METHODS

Materials and methods: Data from about 50 literature sources for the last two decades have been analysed.

CONCLUSION

Conclusions: Analyzing the accuracy and ease of use of various computer navigations in total hip arthroplasty, we offer two the most promising for further study and improvement systems: a semi-active navigation system and augmented reality system in total hip arthroplasty.

Femur first surgical technique: a smart non-computer-based procedure to achieve the combined anteversion in primary total hip arthroplasty

Background

The relevance of prosthetic component orientation to prevent dislocation and impingement following total hip arthroplasty (THA) has been widely accepted. We investigated the use of a non-computer-based surgery to address the reciprocal orientation of the acetabular and femoral components.

Methods

In the femur first technique, the cup is positioned relative to the stem. When the definitive antetorsion of femoral component is fixed, the cup is positioned in a compliant anteversion to the stem. Clinical and radiographic assessments were performed before and 3 months after THA. Radiographic assessment was performed in standing position with the EOS 2D/3D radiography system. 3D images were used to preoperative anterior pelvic plane (APP) angle, postoperative acetabular inclination (AI) and anteversion (AA), and postoperative stem antetorsion. Clinical assessment was performed with Harris Hip Score (HHS).

Results

Forty patients (40 hips) underwent primary THA with an average age of 61 years (range, 36–84). Average HHS increased from 43 ± 5 (range, 37–52) preoperatively to 97 ± 6 (range, 86–100) at the last follow-up (P < 0.0001). Average combined anteversion value of cup with liner and stem was 38° ± 9° (range, 12°-55°). Average AI value of cup with liner was 39° ± 6° (range, 30°-55°) in the group with standard stem and 45° ± 7° (range, 39°-58°) in the group with varized stem (P = 0.007). Relationship analysis showed no correlation between the combined anteversion values of the cup with liner and stem with APP angle values (r = 0.26, P = 0.87).

Conclusions

Femur first technique allows the surgeon to achieve a combined anteversion ranging from 25° to 50° with a cup inclination ranging from 30° to 50°. The cup is positioned according to the functional plane of the patient regardless the preoperative pelvic tilt.

The Evolution of Computer-Assisted Total Hip Arthroplasty and Relevant Applications

In total hip arthroplasty (THA), the accurate positioning of implants is the key to achieve a good clinical outcome. Computer-assisted orthopaedic surgery (CAOS) has been developed for more accurate positioning of implants during the THA. There are passive, semi-active, and active systems in CAOS for THA. Navigation is a passive system that only provides information and guidance to the surgeon. There are 3 types of navigation: imageless navigation, computed tomography (CT)-based navigation, and fluoroscopy-based navigation. In imageless navigation system, a new method of registration without the need to register the anterior pelvic plane was introduced. CT-based navigation can be efficiently used for pelvic plane reference, the functional pelvic plane in supine which adjusts anterior pelvic plane sagittal tilt for targeting the cup orientation. Robot-assisted system can be either active or semi-active. The active robotic system performs the preparation for implant positioning as programmed preoperatively. It has been used for only femoral implant cavity preparation. Recently, program for cup positioning was additionally developed. Alternatively, for ease of surgeon acceptance, semi-active robot systems are developed. It was initially applied only for cup positioning. However, with the development of enhanced femoral workflows, this system can now be used to position both cup and stem. Though there have been substantial advancements in computer-assisted THA, its use can still be controversial at present due to the steep learning curve, intraoperative technical issues, high cost and etc. However, in the future, CAOS will certainly enable the surgeon to operate more accurately and lead to improved outcomes in THA as the technology continues to evolve rapidly.

Even the Intraoperative Knowledge of Femoral Stem Anteversion Cannot Prevent Impingement in Total Hip Arthroplasty

BACKGROUND

In this prospective study of 66 patients undergoing cementless total hip arthroplasty through a minimally invasive anterolateral approach, we evaluated the impact of an intraoperative hybrid combined anteversion technique on postoperative range of motion (ROM).

METHODS

After navigation of femoral stem anteversion, trial acetabular components were positioned manually, and their position recorded with navigation. Then, final components were implanted with navigation at the goals prescribed by the femur-first impingement detection algorithm. Postoperatively, three-dimensional computed tomographies were performed to determine achieved component position and model impingement-free ROM by virtual hip movement, which was compared with published values necessary for activities of daily living. This model was run a second time with the implants in the position selected by the surgeon rather than the navigation program. In addition, we researched into risk factors for ROM differences between the freehand and navigated cup position.

RESULTS

We found a lower flexion of 8.3° (8.8°, P < .001) and lower internal rotation of 9.2° (9.5°, P < .001) for the freehand implanted cups in contrast to a higher extension of 9.8° (11.8°, P < .001) compared with the navigation-guided technique. For activities of daily living, 58.9% (33/56) in the freehand group compared with 85.7% (48/56) in the navigation group showed free flexion (P < .001) and similarly 50.0% (28/56) compared with 76.8% (43/56) free internal rotation (P < .001). Body mass index, incision length, and cup size were identified as independent risk factors for reduced flexion and internal rotation in the freehand group.

CONCLUSION

For implementation of a combined anteversion algorithm, intraoperative alignment guides for accurate cup positioning are required using a minimally invasive anterolateral approach. Obese patients are especially at risk of cup malpositioning.

No difference in clinical outcome, bone density and polyethylene wear 5-7 years after standard navigated vs. conventional cementfree total hip arthroplasty

INTRODUCTION

The purpose of this investigation was to compare clinical outcome, component loosening, polyethylene cup wear and periprosthetic bone mineral density between "cup first" navigated and conventional cementless total hip arthroplasty (THA) 5-7 years after surgery.

MATERIALS AND METHODS

Fifty patients who received THA with (n = 25) or without (n = 25) the use of an image-free navigation system by a single surgeon were investigated after a mean follow-up of 6.4 (4.8-7.4) years. The Hip Osteoarthritis Outcome Score (HOOS) and the Harris Hip Score (HHS) were obtained; range-of-motion (ROM) was evaluated by a blinded examiner. Radiographic cup inclination, signs of radiographic loosening and polyethylene wear were analysed with the help of digital analysis software on anterio-posterior radiographs by a blinded examiner. Acetabular and femoral periprosthetic bone density was evaluated with the help of dual-energy X-ray absorptiometry.

RESULTS

We were unable to find any statistical significant or clinically relevant difference for the HOOS, HHS, ROM and polyethylene wear between the navigated and the conventional THA group 5-7 years after surgery. Cup inclination was more precise in the navigated THA group in relation to the target value of 45°.

CONCLUSIONS

Standard "cup first" THA navigation does not improve mid-term functional outcome, bony ingrowth and/or polyethylene wear. New concepts in computer-assisted THA, considering cup and stem as coupled biomechanical partners are needed to justify the effort of navigation in routine operations.

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.

Surgeon error in performing intraoperative estimation of stem anteversion in cementless total hip arthroplasty

To examine the accuracy of intraoperative estimation of stem anteversion in total hip arthroplasty (THA), we compared the intraoperatively estimated stem anteversion (estimated prosthetic anteversion) to stem anteversion measured by postoperative computed tomography (true anteversion) in 73 hips in 73 patients. Estimated prosthetic anteversion was significantly greater than true anteversion by 5.8°, and the mean absolute value of surgeon error was 7.3° ranging from 11° underestimation to 25° overestimation. Surgeons tended to overestimate when the true anteversion was smaller. A multivariate analysis showed that advanced knee osteoarthritis significantly increased surgeon error. These results indicated that estimated prosthetic anteversion was generally larger than true anteversion and that the grade of knee osteoarthritis affected the degree of surgeon error.

Increased anteversion of press-fit femoral stems compared with anatomic femur

BACKGROUND

With contemporary canal-filling press-fit stems, there is no adjustability of stem position in the canal and therefore the canal anatomy determines stem version. Stem version will affect head/neck impingement, polyethylene wear from edge loading, and hip stability, but despite this, the postoperative version of a canal-filling press-fit stem is unclear.

QUESTIONS/PURPOSES

Is there a difference between the version of the nonoperated femur and the final version of a canal-filling press-fit femoral component? Could a difference create an alignment problem for the hip replacement?

METHODS

Sixty-four hips were studied with fluoroscopy and 46 nonarthritic and 41 arthritic hips were studied with MRI. A standardized fluoroscopic technique for determining preoperative and postoperative femoral version was developed with the patient supine on a fracture table undergoing supine total hip arthroplasty. To validate the methods, the results were compared with two selected series of axial MRI views of the hip comparing the version of the head with the version of the canal at the base of the neck.

RESULTS

For the operated hips, the mean anatomic hip version was less than the stem version: 18.9° versus 27.0°. The difference on average was 8.1° of increased anteversion (SD, 7.4°). Both MRI series showed the femoral neck was more anteverted on average than the femoral head, thereby explaining the operative findings.

CONCLUSION

With a canal-filling press-fit femoral component there is wide variation of postoperative component anteversion with most stems placed in increased anteversion compared with the anatomic head. The surgical technique may need to adjust for this if causing intraoperative impingement or instability.