Five-year DEXA study of 88 hips with cemented femoral stem

Variations in bone mineral density after joint replacement: A systematic review examining different anatomical regions, fixation techniques and implant design

Purpose

This study aims to evaluate postoperative periprosthetic bone mineral density (BMD) at various time points following joint replacement with different implant designs and fixation techniques.

Methods

Database search was conducted on MEDLINE, Scopus, Cochrane Central Register of Controlled Trials, Web of Science, and CINAHL for studies analyzing bone remodelling after joint replacement (March 2002-January 2024). Inclusion criteria: English-language articles; total joint replacement; at least two BMD evaluations; observational studies, cross-sectional, prospective, retrospective, randomised controlled trials, and clinical trials. Exclusion criteria: no BMD measurement within one month after surgery; BMD data only expressed as percentage changes or graphs without numerical values; no Gruen zone evaluation for hip replacement; no periprosthetic bone evaluation for knee replacement; pharmacological treatment or comorbidities affecting BMD; revision joint replacements; irrelevant articles; no full text or no original data.

Results

Sixty-eight articles matched the selection criteria. Fifty-five focused on the hip joint, 12 on the knee, and one on the shoulder. After total hip arthroplasty, the greatest bone resorption occurred in the proximal femur, peaking at 6 months. Cemented implants and tapered stems showed greater bone resorption than cementless implants and anatomical stems. BMD around the acetabular component decreased during the first 6 months but increased in regions subjected to higher loads. In total knee arthroplasty, bone loss occurred in the anterior distal femur and medial tibial plateau, with cemented and posterior-stabilised implants showing greater bone loss than cementless and cruciate-retaining designs.

Conclusions

The periprosthetic BMD decreases progressively after joint replacement. The fixation technique and implant design influence the extent and pattern of this decline. These factors must be considered during the surgical planning, as they can have long-term implications for bone health and implant longevity. Further research is needed to optimise implant design and surgical techniques to mitigate BMD loss and improve patient outcomes.

Level of Evidence

Level IV.

Strain shielding for cemented hip implants

BACKGROUND

Long-term survival of hip implants is of increasing relevance due to the rising life expectancy. The biomechanical effect of strain shielding as a result of implant insertion may lead to bone resorption, thus increasing risk for implant loosening and periprosthetic fractures. Patient-specific quantification of strain shielding could assist orthopedic surgeons in choosing the biomechanically most appropriate prosthesis.

METHODS

Validated quantitative CT-based finite element models of five femurs in intact and implanted states were considered to propose a systematic algorithm for strain shielding quantification. Three different strain measures were investigated and the most appropriate measure for strain shielding quantification is recommended. It is used to demonstrate a practical femur-specific implant selection among three common designs.

FINDINGS

Strain shielding measures demonstrated similar trends in all Gruen zones except zone 1, where the volumetric strain measure differed from von-Mises and maximum principal strains. The volumetric strain measure is in better agreement with clinical bone resorption records. It is also consistent with the biological mechanism of bone remodeling so it is recommended for strain shielding quantification. Applying the strain shielding algorithm on three different implants for a specific femur suggests that the collared design is preferable. Such quantitative biomechanical input is valuable for practical patient specific implant selection.

INTERPRETATION

Volumetric strain should be considered for strain shielding examination. The presented methodology may potentially enable patient-specific pre-operative strain shielding evaluation so to minimize strain shielding. It should be further used in a longitudinal study so to correlate between strain shielding predictions and clinical bone resorption.

Peri-prosthetic bone remodeling and change in bone mineral density in the femur after cemented polished tapered stem implantation

OBJECTIVE

We examined longitudinal changes in bone mineral density (BMD) around the femur for 5 years after total hip arthroplasty (THA) using cemented collarless polished double-tapered stem implantation and investigated the influence of BMD changes on radiological remodeling of the femur.

MATERIALS AND METHODS

Sixty hips from 56 patients who underwent cemented THA with a collarless polished double-tapered stem were included. BMD was measured 2 weeks postoperatively (baseline), 3 months, 6 months, 1 year and annually thereafter until 5 years after surgery using dual-energy X-ray absorptiometry on the lumbar spine and proximal femur of the operated side according to the Gruen's zone classification. We analyzed predictable factors for BMD preservation in the proximal femur and compared radiological remodeling of the femur and changes in BMD.

RESULTS

BMD at 5 years in zone 7 decreased less than 10%, whereas BMD in zone 1 increased to over the baseline (+ 1.9%). Multiple linear regression analyses revealed that body weight was a predictor for positive BMD change in the proximal femur. The frequency of radiolucency of the femur was significantly lower in patients who exhibited an increase in BMD at 5 years compared with BMD at 2 weeks in zone 7.

CONCLUSION

BMD preservation of the proximal femur after cemented collarless polished double-tapered stem implantation was more effective in heavier patients. Furthermore, the frequency of radiolucency around the stem was significantly lower in patients who exceeded 100% of the baseline BMD in zone 7 at 5 years.

Bone mineral density as a marker of hip implant longevity: a prospective assessment of a cementless stem with dual-energy X-ray absorptiometry at twenty years

PURPOSE

Bone remodeling around the femoral component after total hip arthroplasty (THA) is considered to be an important factor in long-term stability and seems to be strictly related to the stem design, coating, and fixation. Stress shielding, micro-movement, and high intra-articular fluid pressure might activate macrophages and osteoclasts, causing progressive bone density decreases. Here we analyze the bone mineral density (BMD) around a cementless femoral stem during a 20-year period to better understand the adaptive bone changes around such implants during long-term follow-up.

METHODS

In this retrospective study, 14 patients treated by THA were reviewed from a cohort of 84. Clinical evaluation with Harris Hip Score and radiographic assessment were performed throughout a 20-year follow-up. To evaluate the bone remodeling around the stem, we monitored the femoral BMD in four regions of interest with a dual-energy X-ray absorptiometry (DEXA) post-operatively and at one, two, three, five and 20 years of follow-up.

RESULTS

The main BMD changes between the post-operative examination and the 20-year follow-up varied between + 11.19% and + 24.30%. Patients with signs of loosening, low Harris Hip Scores, and pain showed decreasing BMD values.

CONCLUSIONS

The correlation between the clinical result and BMD values could suggest DEXA results as a predictor of implant loosening or longevity.

Less periprosthetic bone loss following the anterolateral approach to the hip compared with the direct lateral approach

Background and purpose - The loss of bone mineral in the proximal femur following hip arthroplasty may increase the fracture risk around uncemented stems. We hypothesized that the surgical approach to the hip might influence bone mineral changes around the femoral stem in patients with a femoral neck fracture (FNF). Patients and methods - This was a pre-specified subgroup analysis (n = 51) of an ongoing randomized trial (n = 120) in patients with FNF. Participants were allocated to an uncemented hemiarthroplasty inserted through a direct lateral (Hardinge) approach or an anterolateral (modified Watson-Jones) approach. The 51 patients (mean age 83 (70-90) years, 33 women) were measured by dual-energy X-ray absorptiometry (DXA) to assess changes in periprosthetic bone mineral density (BMD). Results - The mean change in total BMD differed between groups at 12 months in favor of the anterolateral group (4.8%, 95% CI 0.0-9.6; p = 0.05). DXA at 3 months displayed BMD loss in the proximal Gruen zones in the lateral group compared with the anterolateral group. Zone 1 (-5.0% vs. 2.7%), zone 2 (-4.3% vs. 4.1%), zone 6 (-6.5% vs. 0.0%) and zone 7 (-11% vs. -2.4%, all p < 0.05). Interpretation - DXA measurements in this study indicate that surgical approach to the hip influences periprosthetic BMD. Clinical implications remain uncertain. Our conclusions should be interpreted with caution as we did not perform adjustments for multiple tests, possibly leading to inflation of false-positive findings.

Differences in Femoral Head Penetration Between Highly Cross-Linked Polyethylene Cemented Sockets and Uncemented Liners

BACKGROUND

This study aimed at investigating differences in femoral head penetration between highly cross-linked polyethylene (HXLPE) cemented sockets and uncemented liners during 5 years postoperatively.

METHODS

Ninety-six patients (106 hips) with a mean age of 64.4 (range, 35-83) years underwent total hip arthroplasty using a HXLPE cemented socket or liner and were respectively divided into cemented (35 patients [37 hips]) and uncemented (61 patients [69 hips]) groups. Femoral head penetrations were evaluated on both anteroposterior (AP)-view and Lauenstein-view radiographs, and mean polyethylene (PE) wear rates were calculated based on femoral head penetration from 2 to 5 years. Multivariate analyses were performed to assess risk factors for PE wear.

RESULTS

At 5 years postoperatively, the cemented and uncemented groups exhibited proximal direction femoral head penetrations of 0.103 mm and 0.124 mm (P = .226) and anterior direction penetrations of 0.090 mm and 0.151 mm (P = .002), respectively. The corresponding mean PE wear rates were 0.004 mm/y and 0.009 mm/y in the AP-view (P = .286) and 0.005 mm/y and 0.012 mm/y in the Lauenstein-view (P = .168), respectively. Left-side operation and high activity were independent risk factors for PE wear on AP-view.

CONCLUSION

When HXLPE was used, all mean PE wear rates were very low and those of cemented sockets and uncemented liners were very similar. PE particle theory suggests that the occurrence of osteolysis and related aseptic loosening might consequently decrease.

Daily activity and initial bone mineral density are associated with periprosthetic bone mineral density after total hip arthroplasty

OBJECTIVES

To evaluate periprosthetic bone mineral density (BMD) changes around a cementless short tapered-wedge stem and determine correlations between BMD changes and various clinical factors, including daily activity, after total hip arthroplasty (THA) with a tapered-wedge stem.

METHODS

65 patients underwent THA with a TriLock BPS stem. At baseline and at 6, 12, and 24 months postoperatively the BMD of the 7 Gruen zones were evaluated using dual-energy x-ray absorptiometry. Correlations were determined between BMD changes and clinical factors, including the Harris Hip Score, body mass index, University of California at Los Angeles (UCLA) activity rating score, age at surgery, and initial spine BMD. Radiographic parameters, including the proximal femoral geometry (Dorr Classification), canal filling ratio, canal flare index, and calcar-to-canal ratio were also assessed.

RESULTS

Minimal BMD changes were noted in the distal femur. However, significant BMD loss was noted in zone 7 at each time point. BMD loss was also noted in zone 1 at 6 and 12 months postoperatively, but BMD recovered after 18 months. Significant positive correlations were noted between BMD changes and the UCLA activity score in zones 1, 6, and 7. Additionally, negative correlations were noted between BMD changes and the preoperative lumbar BMD in zones 2 and 3. No correlations were noted between BMD changes and the radiographic parameters. Periprosthetic BMD was was virtually unchanged in the proximal femur, especially Gruen zone 1.

CONCLUSIONS

Daily activity may reflect improvements in periprosthetic bone quality after THA; however, the use of this tapered-wedge stem is not recommended in patients with poor bone quality.

Maintenance of periprosthetic bone mineral density with a cementless three dimensional straight tapered stem

Periprosthetic bone loss is a well documented phenomenon after cementless total hip arthroplasty. We compared the bone mineral density (BMD) in 33 patients using the three dimension taper shape stem and 13 patients with a straight component with a distal taper. Postoperative follow-up was evaluated by dual-energy X-ray absorptiometry. BMD was recorded in seven Gruen zones. BMD was correlated with clinical examination, Harris Hip Score (HHS), Body Mass Index (BMI) and age. Clinical assessment took place at 12 months post operation. Periprosthetic BMD loss using the three dimensional straight tapered stem was consistently much less in comparison with the straight type component with a distal tapered design stem. BMD in Gruen zone 1 was maintained. There was no correlation between periprosthetic bone mineral density and clinical factors.

A prospective randomised study of periprosthetic femoral bone remodeling using four different bearings in hybrid total hip arthroplasty

We performed a study to assess whether different bearing materials have an impact on femoral bone remodeling within the first four years after a hybrid total hip arthroplasty. 205 of 300 patients were available for 4 years follow-up after being randomly allocated to four prosthetic combinations: A: Zirconia ceramic head, polyethylene cup; B: Cobalt-Chrome-Molybdenum head and cup; C: Zirconia ceramic head, polyethylene moulded on the Titanium shell of the Asian cup; D: Alumina head and cup. Bone mineral density (BMD) was measured with Dual-Energy X-ray Absorptiometry in seven Gruen zones adjacent to the femoral implant. Scans were performed within one week after surgery and four years postoperatively. Clinical outcomes were monitored using the Oxford Hip Score (OHS). A high proportion of patients from group D were excluded due to re-operations (19 patients). BMD decreased significantly in all Gruen zones with the largest declines in group D. BMD changes in Gruen zones 1, 2, 3, 6, and 7 correlated with height, and body weight. Advanced age was associated with an increase in bone loss in Gruen zones 1, 2, 3, 6, and 7. A large stem size was associated with a decline in BMD in Gruen zones 1, 6, and 7.Bone remodeling after total hip arthroplasty may depend on the composition of bearing materials, but age, height, weight, and stem size are also related to changes in BMD.

Bone restoration with cemented Exeter universal stem - Three-years longitudinal DEXA study in 165 hips for femur

BACKGROUND

The pattern of strain distribution in the proximal femur changes following total hip arthroplasty (THA) and decreases in bone mineral density (BMD) occur around the stem following cemented and uncemented THA. We herein prospectively examined changes in BMD for 3 years after THA with a cemented Exeter universal stem.

METHODS

One hundred and sixty five hips from 150 patients who underwent unilateral THA were included as a cohort. Our patients included 20 men (20 hips) and 130 women (145 hips) with a mean age of 63.9 years. BMD was measured 2 weeks postoperatively (baseline) and 3, 6 12, 18, 24, 30, and 36 months (3 years) after surgery using dual-energy X-ray absorptiometry (DEXA) on the lumbar spine and proximal femur of the operated side according to the Gruen zone classification. We quantified longitudinal changes in BMD for more than 3 years after surgery and detected several factors which affected these changes.

RESULTS

In the first year, BMD in the most proximal femur showed a 5.5% reduction at the lateral side (zone 1) and 13% reduction at the medial side (zone 7), with no significant BMD reductions being observed thereafter. BMD reductions at 3 years were the most apparent at the proximal medial part of the femur (zone 7; -10.3%), while BMD ratio change in zone 1 was over the baseline (+2.9%). Especially in zone 7, the BMD ratio decreased with female, decreases in weight, decreases in height, decreases in BMI, and increases in age at the time of surgery.

CONCLUSIONS

Bone restoration is expected with a cemented Exeter universal stem. Male patients, a younger age, a high body weight, being tall, and a high BMI were identified as factors associated with the restoration of BMD in proximal femur.

Activity and Loading Influence the Predicted Bone Remodeling Around Cemented Hip Replacements

Periprosthetic bone remodeling is frequently observed after total hip replacement. Reduced bone density increases the implant and bone fracture risk, and a gross loss of bone density challenges fixation in subsequent revision surgery. Computational approaches allow bone remodeling to be predicted in agreement with the general clinical observations of proximal resorption and distal hypertrophy. However, these models do not reproduce other clinically observed bone density trends, including faster stabilizing mid-stem density losses, and loss-recovery trends around the distal stem. These may resemble trends in postoperative joint loading and activity, during recovery and rehabilitation, but the established remodeling prediction approach is often used with identical pre- and postoperative load and activity assumptions. Therefore, this study aimed to evaluate the influence of pre- to postoperative changes in activity and loading upon the predicted progression of remodeling. A strain-adaptive finite element model of a femur implanted with a cemented Charnley stem was generated, to predict 60 months of periprosthetic remodeling. A control set of model input data assumed identical pre- and postoperative loading and activity, and was compared to the results obtained from another set of inputs with three varying activity and load profiles. These represented activity changes during rehabilitation for weak, intermediate and strong recoveries, and pre- to postoperative joint force changes due to hip center translation and the use of walking aids. Predicted temporal bone density change trends were analyzed, and absolute bone density changes and the time to homeostasis were inspected, alongside virtual X-rays. The predicted periprosthetic bone density changes obtained using modified loading inputs demonstrated closer agreement with clinical measurements than the control. The modified inputs also predicted the clinically observed temporal density change trends, but still under-estimated density loss during the first three postoperative months. This suggests that other mechanobiological factors have an influence, including the repair of surgical micro-fractures, thermal damage and vascular interruption. This study demonstrates the importance of accounting for pre- to postoperative changes in joint loading and patient activity when predicting periprosthetic bone remodeling. The study's main weakness is the use of an individual patient model; computational expense is a limitation of all previously reported iterative remodeling analysis studies. However, this model showed sufficient computational efficiency for application in probabilistic analysis, and is an easily implemented modification of a well-established technique.

Stro-1-positive BMSCs predict postoperative periprosthetic bone mineral density outcomes in uncemented total hip arthroplasty patients

Background

Bone marrow cell profiles are variable after total hip arthroplasty (THA), including variable levels of Stro-1⁺ and bone morphogenetic protein receptor (BMPRs)⁺ cells. We investigated the impact of bone marrow cell profiles on changes in periprosthetic bone mineral density (BMD) in uncemented THA patients.

Material/Methods

Bone marrow aspirates were collected from the metaphyseal region of discarded femoral heads from 24 consecutive THA patients (12 men and 12 women; mean age 66.7±11.0 years; range 52–87 years) treated from March 2009 to March 2011 at a single facility. Perioperative proportions of Stro-1⁺ and BMPR⁺ cells in femoral heads were assessed by flow cytometry. Follow-up examined the proximal femur Gruen zones R1 and R7 at 1 week and at 3, 6, and 12 months after THA, using dual-energy X-ray absorptiometry. Associations between BMD loss and age, gender, BMPRs⁺, and Stro-1⁺ were analyzed.

Results

At 3 months, R1 and R7 BMD decreased by 4.4% and 6.4%, respectively (P<0.05). At 12 months, the overall BMD decreases in R1 and R7 were 10.2% and 1%, respectively (P<0.05). Higher Stro-1⁺ cells proportion predicted R7 BMD increases at all time points (P<0.05) and R1 BMD increases at 6 and 12 months (P<0.05). BMPR1a⁺ proportion was associated with BMD increases at 6 months in the R1 region. BMPR2⁺ was not significantly associated with BMD (P>0.05).

Conclusions

Elevated Stro-1⁺ bone marrow cell profile may be a useful prognostic indicator for uncemented THA patients.

Mid-term study of bone remodeling after femoral cemented stem implantation: comparison between DXA and finite element simulation

This five-year prospective study was designed to investigate periprosthetic bone remodeling associated with two cemented stem models, ABG-II (Stryker) and VerSys (Zimmer), randomly implanted in patients older than 75 years. The sample consisted of 64 cases (32, ABG-II; 32, VerSys). Inclusion criterion was diagnosis of osteoarthritis recommended for cemented total hip arthroplasty. Besides clinical study, Finite Element (FE) simulation was used to analyze biomechanical changes caused by hip arthroplasty. Bone Mineral Density (BMD) measurements showed a progressive increase in bone mass throughout the entire follow-up period for both stems, well correlated with FE results except in Gruen zones 4, 5, 6 for ABG-II and in zones 4, 5 for VerSys, denoting that remodeling in those zones does not depend on mechanical factors but rather on biological or physiological ones.

Stable fixation but unpredictable bone remodelling around the Lord stem: minimum 23-year follow-up of 66 total hip arthroplasties

Early designs of uncemented hip implants turned out to be failures mainly because the prerequisites for durable implant fixation were unknown. One exception was the chrome-cobalt stem of the Madreporic Lord prosthesis. We prospectively studied this prosthetic design in 107 hips that underwent surgery in 1979-1986. At the last follow-up, five stems and 54 cups had been revised, corresponding to stem and cup survival rates of 92%±3% and 45%±5% at 26years. In all, 66 hips with remaining Lord stems were available for clinical follow-up 26years (24-29) after the index operation. The mean total Harris hip and pain scores were 81 (SD 14) and 41 (SD 5).

Highly crosslinked polyethylene does not reduce aseptic loosening in cemented THA 10-year findings of a randomized study

BACKGROUND

Polyethylene (PE) wear particles are believed to cause aseptic loosening and thereby impair function in hip arthroplasty. Highly crosslinked polyethylene (XLPE) has low short- and medium-term wear rates. However, the long-term wear characteristics are unknown and it is unclear whether reduced wear particle burden improves function and survival of cemented hip arthroplasty.

QUESTIONS/PURPOSES

We asked whether XLPE wear rates remain low up to 10 years and whether this leads to improved implant fixation, periprosthetic bone quality, and clinical function compared to conventional PE.

METHODS

We randomized 60 patients (61 hips) to receive either PE or XLPE cemented cups combined with a cemented stem. At 10 years postoperatively, 51 patients (52 hips) were evaluated for polyethylene wear and component migration estimation by radiostereometry, for radiolucent lines, bone densitometry, and Harris hip and pain scores. Revisions were recorded.

RESULTS

XLPE cups had a lower mean three-dimensional wear rate between 2 and 10 years compared to conventional PE hips: 0.005 mm/year versus 0.056 mm/year. We found no differences in cup migration, bone mineral density, radiolucencies, functional scores, and revision rate. There was a trend toward improved stem fixation in the XLPE group. The overall stem failure rate was comparably high, without influencing wear rate in XLPE hips.

CONCLUSIONS

XLPE displayed a low wear rate up to 10 years when used in cemented THA, but we found no clear benefits in any other parameters. Further research is needed to determine whether cemented THA designs with XLPE are less prone to stem loosening.

LEVEL OF EVIDENCE

Level I, therapeutic study. See the Instructions for Authors for a complete description of levels of evidence.

Femoral Neck Bone Mineral Density after Resurfacing Hip Arthroplasty

Introduction:

Resurfacing hip arthroplasty (RHA) has been suggested to provide an alternative to conventional total hip arthroplasty in younger, active patients. It seems to have an ability to conserve the bone mass on the femoral side. Some controversy exists regarding to the possible disadvantages of RHA and some of them are connected to poor femoral bone quality after surgery. Hence we wanted to study the bone mineral density changes 3 and 12 months after RHA.

Materials and Methods:

A total of 26 patients (22 men and 4 women, 28 hips) underwent a hip resurfacing arthroplasty. The mean age of the patients was 55,2 (range 38–69) years. Bone mineral density (BMD) of the proximal femur was measured by using the dual-energy X-ray absorptiometry (DXA) postoperatively and within 3 and 12 months from surgery. For analysis, we divided the femoral neck area into four equal-sized regions of interest ranging from the prosthesis to the trochanter level.

Results:

At three months follow-up the BMD changes varied between −5.1% (ROIC) and + 1.9% (ROIA), as compared with the immediate postoperative values. After one year follow-up the BMD changes were + 1.1% in the ROIA, + 5.4% in the ROIB, −3.9% in the ROIC and + 1.3% in the ROID. The changes in BMD were not statistically significant.

Discussion:

While there is still much debate and room for additional research in this topic, the results suggest that BMD is conserved in the femoral neck one year after hip resurfacing arthroplasty.

Influence of different DXA acquisition modes on monitoring the changes in bone mineral density after hip resurfacing arthroplasty

Dual-energy X-ray absorptiometry (DXA) is a technique enabling the measurement of bone mineral density (BMD) around prostheses after hip resurfacing arthroplasty (HRA). In this study, we evaluated the consistency of different DXA acquisition modes with 33 patients who had undergone HRA. Patients were scanned with DXA immediately after surgery and at 3-, 6-, and 12-mo time points. All the patients were scanned with dual femur and orthopedic hip acquisition modes and analyzed using 10-region ROI model. With both acquisition modes, a statistically significant decrease (p<0.05, Wilcoxon's test) in BMD at 3mo was revealed in 3 ROIs, located to upper and lateral upper femur. Both acquisition modes detected similarly (p<0.01) preservation of the femoral bone stock within 12mo in all but 1 ROI. The applied acquisition protocols involved the use of different footplates for hip fixation. Because the differences between acquisition modes ranged between +1.6% and -7.1% and the reproducibility of BMD values can vary by as much as 28% due to hip rotation, it is proposed that both dual femur and orthopedic hip acquisition modes can be used to monitor the changes in BMD after HRA. However, the same hip rotation is recommended for all DXA measurements.

Periprosthetic bone mineral density with a cementless triple tapered stem is dependent on daily activity

PURPOSE

Periprosthetic bone loss around the femoral stem is frequently found after total hip arthroplasty. We have shown that periprosthetic bone mineral density (BMD) loss using the triple tapered stem is consistently much less in comparison with the straight type component. In this study, we compared periprosthetic BMD change with clinical factors.

METHODS

Postoperative dual-energy X-ray absorptiometry was evaluated at follow-up. BMD was determined based on seven Gruen zones. We further compared BMD with clinical examination: body mass index (BMI), age, Harris hip score (HHS) or University of California at Los Angeles (UCLA) activity rating score.

RESULTS

Periprosthetic BMD loss of the triple tapered stem was maintained. Especially, BMD in Gruen zone 1 which was maintained at 96% in comparison with the straight tapered stem. We compared the BMD change with clinical factors. There is no correlation between BMD and BMI, age or HHS. However, we found significant correlation between BMD and UCLA activity rating score in Gruen zones 1 and 2 of the triple tapered stem. Further, the correlation coefficient was increased at 48 months in comparison with 24 months.

CONCLUSION

The cementless triple tapered stem maintains periprosthetic bone mineral density. Activity may reflect improving periprosthetic bone quality after THA using a triple tapered stem.

Reproducibility of BMD measurements in the prosthetic knee comparing knee-specific software to traditional DXA software: a clinical validation

The aim of this study was to validate new knee-specific dual X-ray absorptiometry (DXA) software for cemented total knee arthroplasty (TKA) before initiation of a randomized controlled trial. Firstly, in a phantom study, we evaluated if cementation influenced the measured BMD (g/cm²), the scan reproducibility with the new knee-specific software, and the consequences of leg rotation around a vertical axis. Secondly, in a clinical study, we assessed the clinical reproducibility in repetitive scans performed with the new knee-specific software and with traditional spine-mode DXA software, and further compared the 2 softwares' ability to point type implant and bone edges correctly. Cementation increased the measured bone mineral density (BMD) (p < 0.01). For reproducibility, the coefficient of variation (CV) was 0.52-0.70% in vitro. Leg rotation around a vertical axis significantly changed the measured BMD in most scans. Automatic point typing of implant and bone edge was of varying quality with frequent need of manual correction for both softwares. CVs of clinical reproducibility ranged from 2.78% to 6.19% for knee-specific software and from 1.45% to 6.06% for spine-mode software. We found the new knee-specific software valid for BMD measurement of the bone in proximity of cemented TKA and with clinical reproducibility and corrections of point typing similar to traditional spine-mode software.

Femoral bone density changes after total hip arthroplasty with uncemented taper-design stem: a five year follow-up study

We measured bone density (BD) changes to assess adaptive bone remodelling five years after uncemented total hip arthroplasty with taper-design femoral component using quantitative computed-tomography-assisted osteodensitometry (qCT). Nineteen consecutive patients (21 hips) with degenerative joint disease were enrolled in the study. A press-fit cup and a tapered uncemented stem ceramic-ceramic pairing were used in all patients. Serial clinical, radiological and qCT osteodensitometry assessments were performed after the index operation and at the one, two and five year follow-ups. At the latest follow-up, the clinical outcome was rated satisfactory in all hips. The radiological assessment showed signs of osteointegration with stable fixation of all cups and stems. Overall, there was evidence of a BD loss at year five (p = 0.004). We estimate that BD loss was between 2.2% and 12.1% in comparison with baseline postoperative values. Progressive loss of BD in the metaphyseal region was observed in all hips. We found unremarkable BD changes of diaphyseal cortical BD throughout the five year follow-up period. qCT osteodensitometry technology allows differentiation of cortical and cancellous BD changes over time. Periprosthetic BD changes at the five year follow-up are suggestive of stable stem osteointegration with proximal femoral diaphysis load transfer and metaphyseal stress shielding.

Knee flexion influences periprosthetic BMD measurement in the tibia. Suggestions for a reproducible clinical scan protocol

BACKGROUND AND PURPOSE

The quality and quantity of bone is important for the success of joint prostheses and may be monitored by dual energy X-ray absorptiometry (DXA). Available protocols suggest that the knee should be positioned in full extension. This is not possible for most patients in the first days after surgery; however, deficits in extension normalize with rehabilitation. Individual knee flexion between the baseline and follow-up investigations may therefore be different. We investigated the sensitivity of bone mineral density (BMD) measurements to knee flexion in a phantom study and in patients. We suggest a protocol for clinical use.

METHODS

2 phantom tibial bones with tibia components were secured in a clamp and BMD measurements were repeated 5 times at every 5 degrees change in flexion from 0 degrees to 20 degrees. For clinical use, a soft foam positioner was produced, in which the lower leg could be placed in neutral rotation and with the knee in approximately 25 degrees of flexion. The clinical repeatability was tested with double examinations in 38 patients. We investigated 3 regions of interest (ROIs) below the tibial plateau.

RESULTS

In the phantom study, just 5 degrees of flexion was found to change the measured mean BMD. The reproducibility of clinical measurements (coefficient of variation) in the 3 ROIs assessed ranged from 1.8% to 3.7% for the anteroposterior scans, and from 3.4% to 6.2% for the lateral scans.

INTERPRETATION

Knee flexion does affect the measured periprosthetic tibial BMD, and knee flexion should be the same at all clinical follow-ups. The protocol and soft foam positioner that we suggest permit precise and reliable assessment of BMD in the proximal tibia and they can be used in clinical work.

Changes in bone mineral density of the distal femur after revision total knee arthroplasty with metaphyseal press-fit stem

Background

The effect of postoperative adaptive bone remodeling following a stemmed femoral implant in revision total knee arthroplasty (rTKA) is unknown. The aim of this study was to evaluate bone mineral density (BMD) changes of the distal femur following cemented rTKA with a 100-mm press-fit stem.

Materials and methods

Sixteen consecutive patients were included in the study (age range 40–85 years; mean 63.5 years). NexGen^® (Zimmer, Warsaw, IN, USA) cemented revision implants were used. All implants had the same press-fit femoral stem length of 100 mm. Clinical examinations with evaluation of the knee function using the Knee Society’s Knee Scoring System were used. Measurements of BMD (g/cm²) were performed by dual-energy X-ray absorptiometry (DEXA) using a Norland XR-46 (Norland Corp. Fort Atkinson, WI, USA) bone densitometer.

Results

Knee and function scores improved significantly (P = 0.005) from the preoperative values to 1 year of follow-up. In regions of interest (ROI) 1–4, a significant increase in BMD (3.5–6.0%) after 6 months was seen. This increase only remained significant in ROI 4 (4.0%, P = 0.01) at 1 year of follow-up.

Conclusions

The increase in BMD is probably the result of increased mobility and load on the extremity after implantation of a well-functioning rTKA.