Clinical outcome and periprosthetic bone remodelling of an uncemented femoral component with taper design

Total hip arthroplasty by using a cementless ultrashort stem: A subject-specific finite element analysis for a young patient clinical case

In this article, a subject-specific finite element analysis has been developed to study a clinical case of a surgically misaligned hip prosthesis with an ultrashort stem. It was set out to study the strain energy density pattern, comparing the results obtained with computed tomography images. The authors developed two other numerical models: the first one analyzes the stress and strain distributions in the healthy femur (without prosthesis) and the second one analyzes the same boneimplant biomechanical system of the clinical case but assuming the prosthesis in the proper position. The misaligned prosthesis produced an overload at the proximal posterior plane of the femur, as confirmed by computed tomography images, which detect the formation of new bone. The numerical model of the correctly positioned prosthesis demonstrated that the bone is not overloaded and that the position of neutral axis does not significantly shift from the physiological condition.

Comparison of bone mineral density changes around short, metaphyseal-fitting, and conventional cementless anatomical femoral components

We investigated the incidence and degree of stress shielding and clinical and radiographic results in 2 groups of patients. Fifty patients (60 hips) in each group were enrolled for a randomized study. One group received a short, metaphyseal-fitting femoral component and another group received a conventional metaphyseal- and diaphyseal-filling femoral component. The mean follow-up was 3.35 years in both groups. Bone mineral density was significantly increased in femoral zone 1 but slightly decreased in zone 7 in the short, metaphyseal-fitting stem group. In the conventional metaphyseal- and diaphyseal-fitting stem group, bone mineral density was markedly decreased in both zones 1 and 7. Clinical and radiographic results were similar between the 2 groups. No hip in either group required revision of the component.

Minimal stress shielding with a Mallory-Head titanium femoral stem with proximal porous coating in total hip arthroplasty

BACKGROUND

As longevity of cementless femoral components enters the third decade, concerns arise with long-term effects of fixation mode on femoral bone morphology. We examined the long-term consequences on femoral remodeling following total hip arthroplasty with a porous plasma-sprayed tapered titanium stem.

METHODS

Clinical data and radiographs were reviewed from a single center for 97 randomly selected cases implanted with the Mallory-Head Porous femoral component during primary total hip arthroplasty. Measurements were taken from preoperative and long-term follow-up radiographs averaging 14 years postoperative. Average changes in the proximal, middle and diaphyseal zones were determined.

RESULTS

On anteroposterior radiographs, the proximal cortical thickness was unchanged medially and the lateral zone increased 1.3%. Middle cortical thickness increased 4.3% medially and 1.2% laterally. Distal cortical thickness increased 9.6% medially and 1.9% laterally. Using the anteroposterior radiographs, canal fill at 100 mm did not correlate with bony changes at any level (Spearman's rank correlation coefficient of -0.18, 0.05, and 0.00; p value = 0.09, 0.67, 0.97). On lateral radiographs, the proximal cortical thickness increased 1.5% medially and 0.98% laterally. Middle cortical thickness increased 2.4% medially and 1.3% laterally. Distal cortical thickness increased 3.5% medially and 2.1% laterally. From lateral radiographs, canal fill at 100 mm correlated with bony hypertrophy at the proximal, mid-level, and distal femur (Spearman's rank correlation coefficient of 0.85, 0.33, and 0.28, respectively; p value = 0.001, 0.016, and 0.01, respectively).

CONCLUSION

Stress shielding is minimized with the Mallory-Head titanium tapered femoral stem with circumferential proximal plasma-sprayed coating in well-fixed and well-functioning total hip arthroplasty. Additionally, the majority of femora demonstrated increased cortical thickness in all zones around the stem prosthesis.

LEVEL OF EVIDENCE

Therapeutic Level III.

Study on the impact of morselized bones on biological binding of HA-coated femoral stem in dogs

The impact of the dog's morselized autologous bone implantation into femoral medullary cavity on binding in the hydroxyapatite-coated femoral stem prosthesis-bone interface was studied. Twenty-four adult mongrel dogs were divided into 2 groups: experimental and control. The experimental group's medullary cavity was filled with morselized autologous bone. Artificial femoral-stem replacements at the right side were then carried out. At 1, 3, and 6 months postoperatively, computed tomography (CT) values reflecting changes in bone density were measured. A histological observation to check prosthesis-bone interface contact ratios and bone growth was conducted. Analysis of radiographs of slices was made using Interactive Data Language (IDL; ITT Visual Information Solutions, Boulder, Colorado) software. Results showed that the experimental group fared better than the control group, and the difference was statistically significant (P<.05). Stereomicroscope-based observation showed that the number of trabecular bones in the experimental group was larger than that of the control group, and bone growth of the experimental group was also better than that of the control group. Inverted microscope observation showed that the binding degree between prosthesis and trabecular bone of the experimental group was higher than that of the control group. Comparatively, the experimental group's trabecular bone had more osteogenic cells. The binding between morselized autologous bone and hydroxyapatite-coated femoral stem prosthesis can improve direct bone-contact ratios, and the experimental group's number of newly formed trabecular bone was significantly larger than that of the control group.

Comparison between DEXA and finite element studies in the long-term bone remodeling of an anatomical femoral stem

The implantation of a cemented or cementless femoral stem changes the physiological load transfer on the femur producing an effect on the bone called adaptative remodeling. The patterns of this remodeling are attributed to mechanical and biological factors, and those changes in bone mineral density have been determined in long-term densitometry studies. This technique has proved to be a useful tool able to quantify small changes in bone density in different femoral areas, and it is considered to be ideal for long-term studies. On the other hand, the finite element (FE) simulation allows the study of the biomechanical changes produced in the femur after the implantation of a femoral stem. The aim of this study was to contrast the findings obtained from a 5 year follow-up densitometry study that used a newly designed femoral stem (73 patients were included in this study), with the results obtained using a finite element simulation that reproduces the pattern of load transfer that this stem causes on the femur. In this study we have obtained a good comparison between the results of stress of FE simulation and the bone mass values of the densitometry study establishing a ratio between the increases in stress (%) versus the increases in bone density (%). Hence, the changes in bone density in the long term, compared with the healthy femur, are due to different load transfers after stem implantation. It has been checked that in the Gruen zone 7 at 5 years, the most important reduction in stress (7.85%) is produced, which coincides with the highest loss of bone mass (23.89%). Furthermore, the simulation model can be used with different stems with several load conditions and at different time periods to carry out the study of biomechanical behavior in the interaction between the stem and the femur, explaining the evolution of bone density in accordance to Wolff's law, which validates the simulation model.

Modes of periacetabular load transfer to cortical and cancellous bone after cemented versus uncemented total hip arthroplasty: a prospective study using computed tomography-assisted osteodensitometry

Stress-shielding and periprosthetic bone loss after total hip arthroplasty (THA) may be clinically relevant for high-demand patients. Analysis of cortical and cancellous bone density (BD) changes in vivo after THA is of interest to basic science researchers and joint reconstruction surgeons. An insufficient periprosthetic bone stock may predispose to migration, early mechanical failure, and major problems in revision surgery. We used computed tomography (CT)-assisted osteodensitometry in two prospectively analyzed cohorts after cemented (n = 21) versus noncemented (n = 23) cup fixation. Periacetabular BD (mgCaHa/mL) was determined in five CT scans cranial and five CT scans at the level of the cup 10 days and 26 months postoperatively. For press-fit cups BD decreased significantly in all CT cans except in four out of the five scans of cortical bone cranial to the cup. The decrease was highest for cancellous bone ventral to the cup (-45 to -53%). After cemented cup fixation, significant cortical BD decrease was seen ventral to the cup (-11 to -20%). Cancellous BD decrased only ventral (-21 to -31%) and in two scans cranial (-11 and -12%) to the cup. The modes of load transfer between cemented and uncemented cups differ fundamentally. Cemented cups especially prevent the loss of cancellous bone of the acetabulum while also cortical BD loss was significantly lower in most CT scans surrounding the cemented cup compared to the press-fit component. Long-term results are required to prove whether third-generation cementing technique protects periprosthetic BD and thereby improve implant survival.

Midterm results of the Synergy cementless tapered stem: stress shielding and bone quality

BACKGROUND

Tapered femoral stems have been shown to produce less thigh pain and stress shielding than other cement-less stem designs. The purpose of this study was to examine the performance of this type of femoral stem in Japanese patients.

METHODS

A series of 40 total hip arthroplasties with a Synergy tapered femoral component were performed in 33 patients between March 1999 and February 2001 at our institution. Three hips (in three patients) were lost to follow-up, so 37 hips in 30 patients were followed for an average of 70 months. The patients' average age at the time of surgery was 59 years (range 43-80 years). Clinical evaluation included the Japanese Orthopaedic Association (JOA) Hip Score and the incidence of thigh pain. Preoperative radiographic examination included the cortical index and Dorr's bone type. Postoperative radiographic examination included evaluation of biological fixation, spot welds, cortical hypertrophy, and stress shielding.

RESULTS

The average JOA Hip Score improved significantly from 35 preoperatively to 91 postoperatively. No patient suffered thigh pain. All femoral components were classified as bony stable. Spot welds and cortical hypertrophy were commonly found in the middle to the distal portion of the component. Severe (third and fourth degree) stress shielding was observed in 24.3% of the cases. A low cortical index, a Dorr type C femur, and a large stem size were associated with severe stress shielding.

CONCLUSIONS

The midterm clinical results with the Synergy femoral component were satisfactory for Japanese patients. Although severe stress shielding was frequently observed in patients with poor bone quality, stem stability was not affected. Extent of grit blasting and stem length may be factors causing severe stress shielding in Japanese patients with poor bone quality. In conclusion, poor bone quality is a less favorable indication for the cementless tapered stem.

Quantitative CT-assisted osteodensitometry of femoral adaptive bone remodelling after uncemented total hip arthroplasty

The aim of this prospective study was to measure bone density changes and to assess adaptive bone remodelling after uncemented total hip arthroplasty with a taper-design femoral component using quantitative computer-tomography-assisted osteodensitometry. This method is able to differentiate cortical and cancellous bone structures. Twenty-seven consecutive patients (29 hips) with degenerative joint disease were enrolled in the study. Serial clinical, radiological and CT-osteodensitometry assessments were performed after the index operation. At the 2-year follow-up, the clinical outcome was rated satisfactory in all hips. The radiological assessment showed signs of osteointegration and stable fixation of all cups and stems. We observed a -17% decrease of cortical bone density and -22% decrease of cancellous bone density in the greater trochanter and femoral neck region. Cortical and cancellous bone density decrease at the level of the lesser trochanter was -9% and respectively -4%. We observed small changes of cortical bone density in the diaphyseal regions; in contrast, cancellous bone density increased (range 6% to 27%) in the diaphyseal regions. Overall, a trend of bone density recovery was observed throughout the follow-up period. Periprosthetic bone density changes at the 2-year follow-up are suggestive of stable osteointegration with proximal femoral diaphysis load transfer and moderate metaphyseal stress-shielding.

Volumetric measurement of periprosthetic bone remodeling: prospective 5 years follow-up after cemented total hip arthroplasty

INTRODUCTION

Periprosthetic bone remodeling after total hip arthroplasty (THA) is a well recognized phenomenon. Many authors have published osteodensitometric data with DEXA analysis. This study based on computerized tomography (CT).

MATERIALS AND METHODS

The objective of the current project is to collect prospective volumetric bone density data with a clinical CT study in six patients after cemented THA (titanium alloy stem). The follow-up time is 5 years. A data set of about 100,000 bone voxels for each femur was collected. Bone density was observed by dint of an osteodensitometric computer program. The median results were shown in seven regions of interest (ROI) around the prosthesis stem, according to Gruen.

RESULTS

The statistical analysis of the six cases after 60 months with respect to the postoperative control demonstrated a significantly lower density in ROI 2 (-125.5HU, P = 0.014), ROI 3 (-116.7HU, P = 0.023), ROI 4 (-54.5HU, P = 0.023), ROI 5 (-90.9HU, P = 0.014) and ROI 6 (-104.9HU, P = 0.014). Maximum density decrease was observed in ROI 2 and 3. The statistical analysis of the six cases after 60 months with respect to the 24 months control demonstrated a significantly lower density in ROI 2 (-62.6HU, P = 0.014), ROI 5 (-62.9HU, P = 0.023). There was a density decrease in ROI 3, 4, 6, 7 which was not significant and a slight increase in ROI 1.

CONCLUSION

To our knowledge, this is the first collection of fully prospective 5 years 3D periprosthetic density data. The CT method used in the study presented here measures three-dimensionally, while the frequently used DEXA (dual X-ray absorptiometry) method measures two-dimensionally. The data are also unique as they are suitable for direct patient-specific 3D finite element meshing and biomechanical calculation. They can be graphically post-processed in order to obtain cross-sectional or 3D displays of density patterns.

Computed tomography assisted osteodensitometry in total hip arthroplasty

BACKGROUND

Periprosthetic bone remodelling is an important issue in total hip arthroplasty, which can compromise long-term outcomes. The aim of this study was to evaluate bone remodelling of the proximal femur with an uncemented hydroxyapatite-coated taper stem.

METHODS

Twenty-three patients (27 hips) were included in this study. The mean age of the patients at the index operation was 57.2 years. There were 15 men and 8 women. Bone remodelling was assessed with quantitative computed tomography and the clinical outcome determined using the Harris Hip Scores. The mean preoperative Harris Hip Score was 38 points and at the 1-year follow up, it was rated 96 points. All hips were radiologically stable.

RESULTS

At the 1-year follow up, we found a greater bone-density loss of the cancellous bone (ranging from 16.7 to 28.2%) compared with the cortical bone (ranging from 5.3 to 7.8%). A strong correlation was found between the low density of the cortical bone at the index operation and a higher loss of bone density at the follow up.

CONCLUSION

The newly designed tapered stem showed good clinical and radiological outcomes with a proximal femoral bone loss that compares favourably with other studies.

Changes of bone mineral density after cementless total hip arthroplasty with two different stems

Cementless total hip arthroplasty has achieved reliable long-term results since porous coatings were developed, but postoperative changes around the stem remain poorly documented. In this study, changes of the bone mineral density (BMD) were compared between two types of cementless stem. In group B (28 patients with 31 hips), a straight tapered stem with porous plasma spray coating on the proximal 1/4 was used, while group S (24 patients with 26 hips) was given a fluted, tri-slot stem with porous hydroxyapatite coating on the proximal 1/3. In group B, there was an early decrease of BMD, which recovered after 12 months, indicating that stress shielding was minimal. In group S, however, BMD continued to decrease without recovery. The stem shape and radiological findings suggested that the cause of stress shielding in group S was distal fixation.

Quantitative computer-assisted osteodensitometry in total hip arthroplasty

Several factors can cause bone loss and fixation failure following total hip arthroplasty (THA), including polyethylene wear debris, implant micromotion and stress shielding. Various techniques have been used in an effort to detect bone density loss in vivo, all with varying success. Quantitative computed tomography (qCT)-assisted osteodensitometry has been shown to be useful in assessing the in vivo structural bone changes after THA. It has a high resolution, accuracy and reproducibility, thereby making it a useful tool for research purposes, and it is able to differentiate between cortical and cancellous bone structures and assess the bone/implant interface. This technique also provides valuable information about the pattern of stress shielding which occurs around the prosthesis and can show early bony changes, which may prove informative about the quality of implant fixation and surrounding bone adaptation. In conjunction with finite-element analysis, qCT is able to generate accurate patient-specific meshes on which to model implants and their effect on bone remodelling. This technology can be useful to predict bone remodelling and the quality of implant fixation using prostheses with different design and/or biomaterials. In the future, this tool could be used for pre-clinical validation of new implants before their introduction in the market-place.

No increased migration in cups with ceramic-on-ceramic bearing: an RSA study

Ceramic-on-ceramic hip replacements might stress the bone interface more than a metal-polyethylene because of material stiffness, microseparation, and sensitivity to impingement. To ascertain whether this potentially increased stress caused an increased cup migration we compared a ceramic-on-ceramic with a metal-on-polyethylene implant for cup migration. Sixty one patients (61 hips) undergoing THA for osteoarthritis were randomized to ceramic on ceramic (Ce/Ce) or cobalt-chromium on cross-linked polyethylene bearings (PE) in the same uncemented cup shell. Migration was followed with RSA. At 2 years we observed similar mean cup translations in the 3 directions (0.07-0.40 mm vs. 0.05-0.31 mm, Ce/Ce vs. PE), as well as similar rotations around the 3 axes (0.31-0.92 degrees vs. 0.57-1.40 degrees). WOMAC and SF-36 scores were also similar and no radiolucent lines or osteolysis found. The large migration seen in some cups in both implant groups will require close monitoring to ascertain the reasons. Mean proximal wear of the polyethylene liners measured 0.016 mm between 2 and 24 months. Our data suggest there is no increased cup migration in the ceramic-on-ceramic implant compared with the metal-on-polyethylene, and they seem an equally safe choice. However, the low wear measured with the more versatile and less expensive cross-linked polyethylene makes it a strong contender.

LEVELS OF EVIDENCE

Therapeutic Level I. See the Guidelines for Authors for a complete description of levels of evidence.

Osteodensitometry after total hip replacement with uncemented taper-design stem

We followed 24 patients (26 hips) with uncemented total hip replacement for a minimum of 3 years. Patient mean age was 52 (40-69) years. The aim was to evaluate femoral periprosthetic bone mineral density (BMD) using quantitative computed tomography osteodensitometry. At 3-years' follow-up, 25 hips were clinically rated good or excellent. The mean Harris hip score rose from 58 (49-68) pre-operatively to 94 (81-98) at the last follow-up. All hips were radiologically stable. Mean decrease of the overall BMD in the femoral metaphysis was 14.3%, and mean decrease of cortical BMD was 17.3%. In the diaphysis, mean decrease of overall BMD was 5.5% and mean decrease of cortical BMD was 4.5%. Observed loss was markedly lower than in comparable series with uncemented stems.