Comparison of bone mineral density between porous tantalum and cemented tibial total knee arthroplasty components

Osteoporosis in the setting of knee arthroplasty: a narrative review

Patients undergoing knee replacement, which is mainly indicated in severe osteoarthritis, are frequently co-affected by osteoporosis and osteopenia. With a prevalence standing at around 20% in patients receiving knee arthroplasty, osteoporosis could lead to poor outcomes postoperatively. Some of these complications include periprosthetic fractures and an increased revision rate. Antiresorptive medications have been shown to be beneficial postoperatively. However, no studies have been conducted on whether they had any benefits if given preoperatively. Surgical management may also be beneficial, but this area remains full of controversy.

Prospective randomized study on the effect of concurrent bone filling of tibial peg holes in cementless total knee arthroplasty

BACKGROUND

In total knee arthroplasty (TKA), cementless fixation is initially weaker than cement fixation. This study aimed to examine whether filling the tibial peg holes with bone improves initial fixation strength in cementless TKA.

METHODS

This prospective, comparative study examined 88 joints in 66 patients randomized to the bone filling (48 joints) or conventional group (no bone filling; 40 joints). All patients underwent TKA with the NexGen® trabecular metal modular tibial component. In the bone filling group, resected cancellous bone was filled into the peg holes before insertion of the tibial component. We performed clinical and plain radiographic evaluations after the operation and measured bone mineral density (BMD) at five sites below the component at 1, 3, 6, and 12 months postoperatively.

RESULTS

Operative time and clinical evaluations were not significantly different. Plain radiography showed significant longitudinal thickening of the trabecula below the peg (P<0.05) and decreased occurrence of reactive lines (P=0.07) in the bone filling group compared with the conventional group. BMD was significantly higher in the bone filling group in the medial region below the peg at 1, 3, and 6 months and in the central region at 1 and 3 months (all P<0.05).

CONCLUSIONS

When using the NexGen trabecular metal modular tibial component, concurrent peg hole bone filling increases the initial component fixation strength. Possible effects on long-term stabilization warrant further study.

Factors influencing periprosthetic bone mineral density in total knee arthroplasty: a systematic review

INTRODUCTION

Following total knee arthroplasty (TKA), there is a significant decline in periprosthetic bone mineral density (BMD), potentially resulting in complications such as prosthetic loosening, periprosthetic fracture, and influencing the postoperative recovery. The objective of this study was to summarize the factors influencing periprosthetic BMD in TKA from existing studies.

METHODS

A comprehensive systematic search was performed in 4 databases: Pubmed, Embase, Web of Science, and Cochrane Library. The last search was carried out on October 12, 2023. We used the keywords ''total knee arthroplasty'', ''bone mineral density'' and each of them combined with ''tibia'' and ''femur'' to identify all relevant articles reporting about potential impact factors influencing the periprosthetic BMD in patients after TKA.

RESULTS

Out of 1391 articles, 22 published from 2001 to 2023 were included in this systematic review. Following eligibility screening, six significant categories affecting periprosthetic BMD were recognized: prosthesis type, design of stem, coating, body weight, cement, and peg distance.

CONCLUSION

Mobile-bearing prostheses, modular polyethylene design, short stems, cruciform stems, avoidance of bone cement, higher body mass index, titanium nitride coating, and a smaller medial peg distance could potentially benefit periprosthetic BMD. Comprehensive consideration of diverse factors influencing periprosthetic BMD before surgery and collaboration with post-operative drug therapy are essential.

TRIAL REGISTRY

The PROSPERO registration number is CRD42023472030.

Total Knee Replacement with an Uncemented Porous Tantalum Tibia Component: A Failure Analysis

Porous tantalum has been extensively used in orthopaedic surgery, including uncemented total knee arthroplasty (TKA). Favourable results were reported with earlier monobloc tibial components and the design evolved to modular implants. We aimed to analyse possible causes for extensive medial tibia bone loss, resulting in modular porous tantalum tibia baseplate fracture after primary TKA. Retrieved tissue samples were scanned with 3 MeV focused proton beam for Proton-Induced X-ray Emission (micro-PIXE) elemental analysis. Fractographic and microstructural analysis were performed by stereomicroscopy. A full 3D finite-element model was made for numerical analysis of stress-strain conditions of the tibial baseplate. Histological examination of tissue underneath the broken part of the tibial baseplate revealed dark-stained metal debris, which was confirmed by micro-PIXE to consist of tantalum and titanium. Fractographic analysis and tensile testing showed that the failure of the tibial baseplate fulfilled the criteria of a typical fatigue fracture. Microstructural analysis of the contact surface revealed signs of bone ingrowth in 22.5% of the surface only and was even less pronounced in the medial half of the tibial baseplate. Further studies are needed to confirm the responsibility of metal debris for an increased bone absorption leading to catastrophic tibial tray failure.

Highlighting the advantages and benefits of cementless total knee arthroplasty (Review)

In the field of orthopedic surgery, cemented total knee arthroplasty (TKA) is considered to be one of the gold standards. However, there are categories of patients (i.e., obese and morbidly obese patients, younger than 65 years old) among whom cemented TKA has however a high failure rate. Moreover, the frequency of using uncemented TKA is increasing due to the potential benefits of long-term biological fixation, being an innovative field that addresses a new generation orthopedic surgical treatment which is more suitable for young patients who have good bone quality (good to very good, in terms of density). The survival rates and functional results of the latest generation of cementless TKAs may be similar to functional results and survival rates of cemented prosthesis. In conclusion, this review-type article can be considered a powerful database, extremely informative, dense, and focused on the topic mentioned above, in the interest of all medical professionals and all interested individuals.

Medial peg position of cementless porous tantalum tibial component affects bone mineral density around the prosthesis after total knee arthroplasty: 2-year follow-up study

BACKGROUND

Use of a porous tantalum tibial component for total knee arthroplasty (TKA) was reported to have beneficial effects on periprosthetic bone mineral density (BMD). In some cases, hexagonal peg is placed close to or in contact with the tibial cortex, which may result in stress-shielding around the peg. However, no studies have analyzed the relationship between peg position and BMD. The aim of this study was to compare the peg position and BMD around the peg in a porous tantalum tibial component after TKA.

METHODS

Twenty-seven patients (27 knees) who underwent primary TKA with a cementless porous tantalum tibial component were investigated. BMD was measured by dual-energy X-ray absorptiometry for 2 years after the operation. The distance between the peg and the tibial cortex (peg distance) was measured on the medial and lateral sides.

RESULTS

BMD was decreased in the medial region after the operation (p < 0.01). Relative change in BMD was lower in the medial region than in the central and lateral regions (p < 0.01). Multiple regression analysis showed that medial peg distance was negatively correlated with relative change of BMD in the medial part of the tibia (p = 0.04, R = 0.402).

CONCLUSIONS

The medial peg position affected the postoperative relative change of BMD in the medial part of the tibia, but did not affect the longevity of the implant. As the tibial medial peg became closer to the medial tibial cortex, the BMD loss became larger in the medial part of the tibia at 2 years postoperatively.

Computational tibial bone remodeling over a population after total knee arthroplasty: A comparative study

Periprosthetic bone loss is an important factor in tibial implant failure mechanisms in total knee arthroplasty (TKA). The purpose of this study was to validate computational postoperative bone response using longitudinal clinical DEXA densities. Computational remodeling outcome over a population was obtained by incorporating the strain‐adaptive remodeling theory in finite element (FE) simulations of 26 different tibiae. Physiological loading conditions were applied, and bone mineral density (BMD) in three different regions of interest (ROIs) was considered over a postoperative time of 15 years. BMD outcome was compared directly to previously reported clinical BMD data of a comparable TKA cohort. Similar trends between computational and clinical bone remodeling over time were observed in the two proximal ROIs, with most rapid bone loss taking place in the initial months after TKA and BMD starting to level in the following years. The extent of absolute proximal BMD change was underestimated in the FE population compared with the clinical subject group, which might be the result of significantly higher initial clinical baseline BMD values. Large differences in remodeling response were found in the distal ROI, in which resorption was measured clinically, but a large BMD increase was predicted by the FE models. Multiple computational limitations, related to the FE mesh, loading conditions, and strain‐adaptive algorithm, likely contributed to the extensive local bone formation. Further research incorporating subject‐specific comparisons using follow‐up CT scans and more extensive physiological knee loading is recommended to optimize bone remodeling more distal to the tibial baseplate.

Bone remodeling and implant migration of uncemented femoral and cemented asymmetrical tibial components in total knee arthroplasty - DXA and RSA evaluation with 2-year follow up

BACKGROUND

Aseptic loosening is one of the major reasons for late revision in total knee arthroplasty (TKA). The risk of aseptic loosening can be detected using radiostereometric analysis (RSA), whereby micromovements (migration) can be measured, and thus RSA is recommended in the phased introduction of orthopedic implants. Decrease in bone mineral density (BMD), as measured by dual-energy x ray absorptiometry (DXA), is related to the breaking strength of the bone, which is measured concurrently by RSA. The aim of the study was to evaluate bone remodeling and implant migration with cemented asymmetrical tibial and uncemented femoral components after TKA with a follow up period of 2 years.

METHODS

This was a prospective longitudinal cohort study of 29 patients (number of female/male patients 17/12, mean age 65.2 years), received a hybrid Persona® TKA (Zimmer Biomet, Warsaw, IN, USA) consisting of a cemented tibial, an all-polyethylene patella, and uncemented trabecular metal femoral components. Follow up: preoperative, 1 week, and 3, 6, 12 and 24 months after surgery, and double examinations for RSA and DXA were performed at 12 months. RSA results were presented as maximal total point of motion (MTPM) and segmental motion (translation and rotation), and DXA results were presented as changes in BMD in different regions of interest (ROI).

RESULTS

MTPM at 3, 6, 12, and 24 months was 0.65 mm, 0.84 mm, 0.92 mm, and 0.96 mm for the femoral component and 0.54 mm, 0.60 mm, 0.64 mm, and 0.68 mm, respectively, for the tibial component. The highest MTPM occurred within the first 3 months. Afterwards most of the curves flattened and stabilized. Between 12 and 24 months after surgery, 16% of femoral components had migrated by more than 0.10 mm and 15% of tibial components had migrated by more than 0.2 mm. Percentage change in BMD in each ROI for distal femur was as follows: ROI I 26.7%, ROI II 9.2% and ROI III 3.3%. BMD and at the proximal tibia: ROI I 8.2%, ROI II 8.6% and ROI III 7.0% after 2 years compared with 1 week postoperative results. There was no significant correlation between maximal percentwise change in BMD and MTPM after 2 years.

CONCLUSION

Migration patterns and changes in BMD related to femoral components after TKA in our study correspond well with previous studies; we observed marginally greater migration with the tibial component.

[Progress of change in bone mineral density after knee arthroplasty]

Objective

To summarize research progress of change in bone mineral density (BMD) after knee arthroplasty and its diagnostic methods, influencing factors, and drug prevention and treatment.

Methods

The relevant literature at home and abroad was reviewed and summarized from research status of the advantages and disadvantages of BMD assessment methods, the trend of changes in BMD after knee arthroplasty and its influencing factors, and the differences in effectiveness of drugs.

Results

The central BMD and mean BMD around the prosthesis decrease after knee arthroplasty, which is closely associated with body position, age, weight, daily activities, and the fixation methods, design, and material of prosthesis. Denosumab, bisphosphonates, and teriparatide et al. can decrease BMD loss after knee arthroplasty.

Conclusion

BMD after knee arthroplasty decreases, which is related to various factors, but the mechanism is unclear. At present, some inhibitors of bone resorption can decrease BMD loss after knee arthroplasty. However, its long-term efficacy remains to be further explored.

CHANGES IN BONE MINERAL DENSITY AFTER TOTAL KNEE ARTHROPLASTY

Objective

We aimed to investigate the change in bone mineral density (BMD) in the first postoperative year in patients that underwent total knee arthroplasty (TKA) due to primary osteoarthritis of the knee.

Methods

Preoperative and first postoperative year dual-energy X-ray absorptiometry measurements of 76 patients with knee osteoarthritis, who undergone surgery between 2016 and 2018 due to the recommendation for TKA, were statistically evaluated in the study.

Results

Of the 19 patients with a normal BMD in the preoperative period, 73.7% (n = 14) continued to have a normal BMD in the postoperative period. Of the 34 patients with a low BMD (osteopenia) in the preoperative period, 91.2% (n = 31) did not show any change, whereas osteoporosis was observed in two patients (5.9%) in the postoperative period. Of the 23 patients with osteoporosis in the preoperative period, 95.7% (n = 22) did not show any change, whereas osteopenia was observed in one patient (4.3%) in the postoperative period. Both the T and Z scores of the spine (L1-L4) and proximal femur showed a slightly positive trend, however, with an insignificant statistical difference (p ≥ 0.05).

Conclusion

Patients that underwent TKA experienced a statistically insignificant bone gain at the spine and proximal femur twelve months after the surgery. Level of Evidence III, Therapeutic Studies Investigating the Results of Treatment.

Periprosthetic Loss of Bone Mineral Density After Cementless Porous Tantalum and Cemented Total Knee Arthroplasties: A Mean of 11-Year Concise Follow-Up of a Previous Report

BACKGROUND

Our previous study showed that the decrease in relative change of bone mineral density (BMD) in the lateral part of the tibia was significantly less in the group treated with the cementless porous tantalum component than in the group treated with the cemented cobalt-chromium tibial component up to 5 years after the operation. However, the long-term benefits of porous tantalum tibial component on BMD have not been proven. The aim of this study was to update a matched cohort study at a minimum of 6 years' follow-up period.

METHODS

Twenty patients with a porous tantalum tibial component and 18 patients with a cemented cobalt-chromium-alloy tibial component were investigated for more than 6 years in the present study. The mean follow-up period was 11.4 years. Dual X-ray absorptiometry was used to measure the BMD.

RESULTS

The decrease in relative change of BMD in the lateral aspect of the tibia was significantly less with the porous tantalum tibial component than that with the cemented cobalt-chromium tibial component up to 5 years. However, at the final follow-up period, no significant difference was observed in the relative change of BMD between the 2 groups. No prosthetic migration or periprosthetic fracture was detected in either group.

CONCLUSION

The present study is one of the studies with the longest follow-up period on BMD after total knee arthroplasty. Porous tantalum tibial component did not have a favorable effect on the BMD of the proximal tibia after total knee arthroplasty for long term.

Peri-prosthetic bone mineral density after simultaneous bilateral total knee arthroplasty under oral bisphosphonate therapy - A comparison between mobile- and fixed-bearing prostheses

BACKGROUND

Peri-prosthetic bone mineral density (BMD) decreases after total knee arthroplasty (TKA). We aimed to specifically compare peri-prosthetic BMD changes between mobile- and fixed-bearing prostheses in patients undergoing oral bisphosphonate therapy, hypothesizing that mobile-bearing components would have a favorable effect on postoperative peri-prosthetic BMD.

METHODS

This prospective cohort study investigated 30 patients who underwent simultaneous bilateral TKA for primary knee osteoarthritis between December 2007 and September 2012. All patients underwent mobile-bearing TKA in one knee and fixed-bearing TKA in the other and received oral alendronate therapy at a dosage of 35 mg/week. Peri-prosthetic and lumbar spine BMDs were measured using dual X-ray absorptiometry scans, with peri-prosthetic BMD changes being compared between the two prostheses in each patient at six months and one, two, three, and five years post-operation.

RESULTS

Clinical results did not significantly differ between two prostheses. Relative change of lumbar spine BMD was significantly greater at five years post-operation than at one year post-operation (p = 0.01), and was significantly correlated at five years post-operation with peri-prosthetic BMD in the central femur (r = 0.39, p = 0.002), posterior femur (r = 0.39, p = 0.002), and medial tibia (r = 0.42, p = 0.007).

CONCLUSIONS

There was no difference in peri-prosthetic BMD changes between two prostheses in patients undergoing oral bisphosphonate therapy. Our results suggest that the influence of oral bisphosphonate therapy might offset the influence of prosthetic design. Thus, oral bisphosphonate therapy may be more effective than prosthetic design selection in preventing post-TKA peri-prosthetic BMD loss.

LEVEL OF EVIDENCE

II.

Despite Improved Survivorship of Uncemented Fixation in Total Knee Arthroplasty for Osteoarthritis, Cemented Fixation Remains the Gold Standard: An Analysis of a National Joint Registry

BACKGROUND

Total knee arthroplasty (TKA) numbers are increasing worldwide. While cement fixation for both femoral and tibial components is commonly used, alternatives include hybrid and uncemented TKAs. This study aimed to evaluate survivorship, revision rates, and patient-reported outcomes for cemented, hybrid, and uncemented TKAs using New Zealand Joint Registry (NZJR) data.

METHODS

NZJR data relating to all TKAs performed during the 19 years up to the end of December 2017 were analyzed. Outcomes were assessed using prosthesis survivorship data (including reasons for revision) and Oxford scores at 6 months, 5 years, and 10 years postoperatively.

RESULTS

A total 96,519 primary TKAs were performed during the period examined. Most (91.5%) were fully cemented with 4.8% hybrid and 3.7% uncemented. Mean Oxford scores at 6 months were highest in cemented and lowest in uncemented TKAs (P < .001). However, this was not clinically significant. There was no difference at 5 or 10 years. Ten-year survival rates were 97%, 94.5%, and 95.8% for cemented, uncemented, and hybrid TKAs, respectively. Revision rates were 0.47, 0.74, and 0.52 per 100 component years for cemented, uncemented, and hybrid prostheses, respectively. The revision rate for uncemented prostheses compared with cemented was higher (P < .001). When stratified by age group, there were differences in survival rates between cemented and uncemented groups (P = .001) and hybrid and uncemented groups (P = .038) in patients aged <55 years; between cemented and uncemented groups in those aged 55-64 years (P = .031); and between cemented and hybrid groups in those aged >75 years (P = .004).

CONCLUSION

Uncemented TKAs had similar patient-reported outcomes but higher revision rates and worse survivorship compared with hybrid or fully cemented TKAs.

Association between bone mineral density distribution and various radiographic parameters in patients with advanced medial osteoarthritis of the knee

PURPOSE

Patients with severe osteoarthritis (OA) of the knee have changes in bone mineral density (BMD) of the distal femur and proximal tibia. Correlations between the medial-to-lateral BMD (M/L-BMD) ratio (which normalizes the potentially confounding effects of body size and sex on BMD) and radiographic parameters that indicate OA progression have not been adequately studied. The purpose of this study was to evaluate correlations between radiographic indicators of OA progression and femoral and tibial M/L-BMD ratios.

METHODS

A consecutive series of 182 knees in 156 patients with advanced medial knee OA who underwent total knee arthroplasty were included. We evaluated correlations between the femoral and tibial M/L-BMD ratios and various radiographic parameters, including tibiofemoral angle (TFA), mechanical axis angle (MAA), tibial coronal angle, tibiofemoral subluxation (%), load-bearing axis deviation at the tibial plateau (%), and medial and lateral laxity.

RESULTS

Univariate analyses using Spearman's correlation coefficient revealed significant positive correlations between femoral and tibial M/L-BMD ratios and both TFA and MAA and negative correlations with tibial coronal angle and load-bearing axis deviation. Multivariate analyses showed significant associations between TFA and the femoral M/L-BMD ratio (β = 0.434, p < 0.001) and between MAA and the tibial M/L-BMD ratio (β = 0.384, p < 0.001).

CONCLUSION

BMD distribution around the knee might be predictable with radiographic parameters such as the TFA for the femur and MAA for the tibia. The findings of this study provide in vivo data on the evaluation of preoperative femoral and tibial M/L-BMD ratios without dual-energy X-ray absorptiometry.

Superior fixation and less periprosthetic stress-shielding of tibial components with a finned stem versus an I-beam block stem: a randomized RSA and DXA study with minimum 5 years' follow-up

Background and purpose - The stem on the tibial component of total knee arthroplasty provides mechanical resistance to lift-off, shear forces, and torque. We compared tibial components with finned stems (FS) and I-beam block stems (IS) to assess differences in implant migration. Patients and methods - In a patient-blinded RCT, 54 patients/knees (15 men) with knee osteoarthritis at a mean age of 77 years (70-90) were randomly allocated to receive tibial components with either a FS (n = 27) or an IS (n = 27). Through 5 to 7 years' follow-up, implant migration was measured with RSA, periprosthetic bone mineral density (BMD) was measured with DXA, and surgeons reported American Knee Society Score (AKSS). Results - At minimum 5 years' follow-up, maximum total point motion (MTPM) was higher (p = 0.04) for IS (1.48 mm, 95% CI 0.81-2.16) than for FS (0.85 mm, CI 0.38-1.32) tibial components. Likewise, total rotation (TR) was higher (p = 0.03) for IS (1.51˚, CI 0.78-2.24) than for FS (0.81˚, CI 0.36-1.27). Tibial components with IS externally rotated 0.50° (CI -0.06 to 1.06) while FS internally rotated 0.09° (CI -0.20 to 0.38) (p = 0.03). Periprosthetic bone stress-shielding was higher (p < 0.01) up to 2 years' follow-up for IS compared with FS in the regions medial to the stem (-13% vs. -2%) and posterior to the stem (-13% vs. -2%). Below the stem bone loss was also higher (p = 0.01) for IS compared with FS (-6% vs. +1%) up to 1-year follow-up. Knee score improved similarly in both groups up to 5 years' follow-up. Interpretation - Periprosthetic bone stress-shielding medial and posterior to the stem until 2 years, and tibial component migration at 5 years, was less for a finned compared with an I-shaped block stem design.

Uncemented Tantalum Monoblock Tibial Fixation for Total Knee Arthroplasty in Patients Less Than 60 Years of Age: Mean 10-Year Follow-up

BACKGROUND

Although tibial component loosening has been considered a concern after total knee arthroplasty without cement, such implants have been used in younger patients because of the potential for ingrowth and preservation of bone stock. However, mid-term and long-term studies of modern uncemented implants are lacking. We previously reported promising prospective 5-year outcomes after using an uncemented porous tantalum tibial component in patients who underwent surgery before the age of 60 years. The purpose of this study was to determine clinical and radiographic implant survivorship at 10 years in this large series of young patients.

METHODS

The original cohort included 79 patients (96 knees) who were <60 years old at the time of surgery. All procedures were performed with an uncemented, posterior-stabilized femoral component and a porous tantalum monoblock tibial component by 1 high-volume arthroplasty surgeon at a single institution. Patients were followed prospectively. The Knee Society Score (KSS), radiographic findings, and any complications or revisions were recorded.

RESULTS

At the latest follow-up, 76% (60) of the 79 patients (74% [71] of the 96 knees) were available for evaluation or had undergone revision (n = 6); 7 patients had died with the implants in place, and 12 patients were lost to follow-up. The average follow-up for the available implants was 10 years (range, 8 to 12 years). There were no progressive radiolucencies on radiographic review. The mean functional KSS was 68 points (range, 0 to 100 points). All revisions were for reasons unrelated to tibial fixation: femoral component loosening (1), stiffness (1), pain and swelling (2), and instability (2). The all-cause revision rate was 6% (6 of 96 knees).

CONCLUSIONS

Uncemented porous tantalum monoblock tibial components provided reliable fixation, excellent radiographic findings, and satisfactory functional outcomes at a mean of 10 years postoperatively. We identified no cases of tibial component loosening. These promising clinical and radiographic results support the use of uncemented tibial components. Such implants may produce well-integrated, durable long-term constructs in young patients.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Bone Remodeling of the Distal Femur After Uncemented Total Knee Arthroplasty-A 2-Year Prospective DXA Study

Loss of bone stock as a response to the bone trauma, immobilization, and stress shielding related to joint replacement surgery increases the risk of fracture of the distal femur after total knee arthroplasty. Previous studies of uncemented femoral components have reported very high levels of bone loss in the distal femur. This study investigates the adaptive bone remodeling of the distal femur after uncemented total knee arthroplasty. We performed a 2-year follow-up of 53 patients (mean age 61.5 [38-70] years, F/M = 27/26, body mass index 29.5) who because of osteoarthritis received an uncemented total knee arthroplasty. All patients received a NexGen CR-Flex Porous Femoral Component. Measurements of bone mineral density of the distal femur using dual-energy X-ray absorptiometry were performed postoperatively and after 3, 6, 12, and 24 months. Bone mineral density (g/cm²) was measured in 3 regions of interest in the periprosthetic bone of the distal femur. Repeated measures analysis of variance and Tukey post hoc test for bone mineral density changed over time (p < 0.05 were considered significant). In the distal femur, significant changes in bone mineral density were seen after 24 months of follow-up, and bone mineral density decreased by 23.6% in the anterior region behind the anterior flange of the prosthesis (p < 0.001), 10.1% in the posterior region (p < 0.001), and 5.5% in the most proximal region (p < 0.001). We found highly significant bone mineral change in the distal femur after uncemented total knee arthroplasty, most pronounced in the anterior region, where a decrease in bone mineral density of almost 25%, was seen. Taking the expected age-related decay in bone mineral density in this age group into consideration, the decrease was substantial and must be considered to predispose to periprosthetic fractures.

Spatial mapping of humeral head bone density

BACKGROUND

Short-stem humeral replacements achieve fixation by anchoring to the metaphyseal trabecular bone. Fixing the implant in high-density bone can provide strong fixation and reduce the risk of loosening. However, there is a lack of data mapping the bone density distribution in the proximal humerus. The aim of the study was to investigate the bone density in proximal humerus.

METHODS

Eight computed tomography scans of healthy cadaveric humeri were used to map bone density distribution in the humeral head. The proximal humeral head was divided into 12 slices parallel to the humeral anatomic neck. Each slice was then divided into 4 concentric circles. The slices below the anatomic neck, where short-stem implants have their fixation features, were further divided into radial sectors. The average bone density for each of these regions was calculated, and regions of interest were compared using a repeated-measures analysis of variance with significance set at P < .05.

RESULTS

Average apparent bone density was found to decrease from proximal to distal regions, with the majority of higher bone density proximal to the anatomic neck of the humerus (P < .05). Below the anatomic neck, bone density increases from central to peripheral regions, where cortical bone eventually occupies the space (P < .05). In distal slices below the anatomic neck, a higher bone density distribution in the medial calcar region was also observed.

CONCLUSION

This study indicates that it is advantageous with respect to implant fixation to preserve some bone above the anatomic neck and epiphyseal plate and to use the denser bone at the periphery.

Cementless vs Cemented Tibial Fixation in Primary Total Knee Arthroplasty

BACKGROUND

The ideal fixation for modern tibial components in total knee arthroplasty (TKA) remains controversial with uncertainty on whether cementless implants can yield equivalent outcomes to cemented fixation in early follow-up.

METHODS

A series of 70 consecutive cases with reverse hybrid cementless fixation were matched to 70 cemented cases from 2008 to 2015 based on implant design and patient demographics.

RESULTS

Cementless TKA demonstrated greater aseptic loosening (7 vs 0, P = .013) and revision surgery (10 vs 0, P = .001) than cemented fixation within 5 years of follow-up, but with no clinically significant differences in outcome scores.

CONCLUSION

It remains unclear whether early aseptic loosening in cementless TKA can be reduced with enhanced adjunct fixation and what proportion of early failure justifies the potential lifelong fixation through biologic ingrowth of cementless tibial components.

Long-term results of a porous tantalum monoblock tibia component: clinical and radiographic results at follow-up of 10 years

Background

The purpose of this study is to assess the long-term follow-up of cementless total knee arthroplasty with the trabecular metal (TM) monoblock tibial component at an average 10-year follow-up. This report is an extension of our previously reported series of 108 TM tibias reported in 2011 (Unger and Duggan, 2011).

Methods

Fifty-eight of the original 108 knees were available for review. Each follow-up patient was evaluated by radiologic and clinical Knee Society Scores. The average follow-up was 10.2 years.

Results

Our results indicate excellent long-term survivorship (96.5%) with 2 confirmed tibia revisions, and 1 femoral revision for periprosthetic fracture and 1 patella open reduction internal fixation. X-ray evaluation demonstrated one patient with 1 mm medial polyethylene wear and a nonprogressive 1 mm of radiolucency on the medial side. All the other tibial components showed full bone apposition and incorporation. Knee Society Scores were excellent in all the patients seen on follow-up.

Conclusions

Long-term follow-up of TM monoblock tibia components confirm excellent survivorship and biologic implant fixation, with excellent outcomes and knee scores.

Posterior Cruciate Ligament Retention or Substitution During Total Knee Arthroplasty Does Not Affect Long-Term Bone Mineral Density or Quality

BACKGROUND

Physical activity is recognized as one of the factors that influence bone mineral density (BMD) and bone quality after total knee arthroplasty (TKA). According to biomechanical analyses after posterior cruciate ligament (PCL) retaining (PCLR) and substituting (PCLS) TKA, each implant design has different kinematics and kinetics. The purposes of this study were: (1) to perform within-patient comparisons of the midterm and long-term effects of PCL retention in mobile-bearing TKA on proximal femur and tibia BMD and calcaneus bone quality measured using ultrasound and (2) to identify correlations between them.

METHODS

A prospective, quasi-randomized design was used. Thirty-seven patients (74 knees) who underwent bilateral TKA (PCLR on one side and PCLS on the other) were evaluated. Mean follow-up periods were 118 months (standard deviation 40) and 117 months (standard deviation 36) in knees with PCLR and PCLS implants, respectively. The BMDs of the total hip and proximal tibia and broadband ultrasound attenuation (BUA; dB/MHz) through the calcaneus were measured.

RESULTS

The mean BMD of PCLR and PCLS were equivalent at the proximal hip and tibia. The BUA of the calcaneus was also the same between implants. There were significant correlations between the 3 anatomic sites.

CONCLUSION

When measured approximately 10 years after TKA, PCL retention had no substantial effect on the BMD of the proximal femur and tibia, or on the bone quality of the calcaneus. The measurement of noninvasive BUA may predict BMD, although further analysis is required.

Clinical and radiologic outcomes of the second-generation Trabecular Metal™ glenoid for total shoulder replacements after 2-6 years follow-up

BACKGROUND

A porous tantalum glenoid component for total shoulder replacements was introduced in 2003 to promote biologic ingrowth. However, reports of component failure prompted design modifications. The purpose of this study is to present the largest series to date, of TSR with the second-generation Trabecular Metal™ glenoid component.

METHOD

A radiologic and clinical evaluation of the second-generation TM glenoid was conducted in consecutive cases of 76 shoulders (66 patients) with a mean follow-up of 43.2 months (range 24-72 months). Pre-operative VAS score, patient self-assessed ASES score, active shoulder range of motion, and radiologic assessment were recorded. Patients were recalled for latest follow-up clinical and radiologic evaluation.

RESULTS

On latest follow-up, the mean VAS scores (pre-op: 6.4-latest: 0.9) and ASES scores (pre-op: 36.9-latest: 88.5) improved. Active range of motion improved in all planes. There was no report of glenoid component migration, loosening, or humeral stem subsidence. The incidence of non-progressive radiolucency in the glenoid was 6.6 % (Franklin 1: 3 cases, Franklin 2: 2 cases). Post-operative complications involved dislocation (n = 2) which were reduced in ED, post-operative stiffness (n = 1), transient axillary nerve neuropraxia (n = 1), and supraspinatus tear which underwent arthroscopic repair at 16 months post-op. There were no revision surgeries for implant loosening nor glenoid component fracture at the peg-base plate junction.

CONCLUSIONS

The modifications established in the second-generation TM glenoid resulted to improve early to mid-term survivorship and clinical outcomes in TSR, with promise of long-term implant stability through bony ingrowth.

LEVEL OF EVIDENCE

Level IV, case series, treatment study.

Preoperative Periarticular Knee Bone Mineral Density in Osteoarthritic Patients Undergoing TKA

BACKGROUND

Preoperative periarticular bone quality is affected by joint loading. The purpose of this study was to determine the periarticular bone mineral density of the knee joint of patients undergoing total knee arthroplasty, and whether the location of the load-bearing axis correlates with the measured bone mineral density.

MATERIALS AND METHODS

The bone mineral densities of the medial and lateral femoral condyles and the medial and lateral tibial condyles were analyzed in consecutive 116 osteoarthritic patients (130 knees) by dual energy x-ray absorptiometry.

RESULTS

The median bone mineral density values in the condyles were 1.138 in femoral medial, 0.767 in femoral lateral, 1.056 in tibial medial, and 0.714 in tibial lateral. The medial condyles showed significantly higher bone mineral densities than the lateral condyles in both the femur and tibia. In addition, the femoral medial showed significantly higher bone mineral density levels than the tibial medial, and the femoral lateral condyle had higher bone mineral density levels than the tibial lateral. The bone mineral density Medial/Lateral ratio was significantly negatively correlated with the location (tibial medial edge 0%, lateral edge 100%) of the load-bearing axis in the femur and tibia.

CONCLUSION

Preoperative bone mineral density values may provide against the changes in bone mineral density after total knee arthroplasty by reflecting the correlation with joint loading axis. These results help explain why total knee arthroplasty has such good long-term clinical outcomes with a low frequency of component loosening and periarticular fractures despite a high degree of postoperative bone loss.

To Cement or Not? Two-Year Results of a Prospective, Randomized Study Comparing Cemented Vs. Cementless Total Knee Arthroplasty (TKA)

The optimal mode of fixation in total knee arthroplasty (TKA) is a subject of debate. We enrolled 100 TKA patients randomized to cemented or cementless fixation. Knee Society Scores (KSS), Oxford scores and pain visual analog scales (VAS) were collected pre-operatively and post-operatively. Two-year follow-up was obtained for 93 patients. The mean VAS trended higher for the cementless group at 4 months (P=0.06). At 2 years, the KSS functional scores, Oxford scores, and self-reported questions for satisfaction, less pain and better function were similar but the cemented group had higher KSS clinical scores (96.4 vs. 92.3, P=0.03). More radiolucencies were seen in cementless knees (P<0.001). The cementless group had one revision for instability and one cemented knee was revised for infection. Cementless TKA showed equivalent survivorship (revision for any reason as the endpoint) compared to cemented TKA at this early follow-up. Close monitoring of radiolucencies is important with continued follow-up.

Changes in bone mineral density of the proximal tibia after uncemented total knee arthroplasty. A prospective randomized study

PURPOSE

Regenerex is a novel porous titanium construct with a three-dimensional porous structure and biomechanical characteristics close to that of normal trabecular bone. The aim of this study was to evaluate the adaptive bone remodeling of the proximal tibia after uncemented total knee arthroplasty (TKA) using a tibial tray with this novel coating compared to a well-proven standard porous coated (PPS) tibial tray.

MATERIALS

Sixty patients scheduled for TKA were randomized to receive either a Regenerex (n = 31) or a PPS tibial component (n = 29). Changes in bone mineral density (BMD) of the proximal tibia were measured at three, six, 12 and 24 months by dual-energy X-ray absorptiometry (DEXA).

RESULTS

In the lateral region (ROI 3), a significant increase in BMD was seen in both groups at three, six, and 12 months after surgery. The relative increase at 12 months was 8.1 % (P = 0.007) for the PPS group and 6.5 % (P = 0.002) for the Regenerex group. Positive values were retained at 24 months in both groups. At 24 months BMD in the distal region below the central stem (ROI 1) had decreased in the PPS group by 3.4 % (P = 0.005) and in the Regenerex group by 2.4 % (P = 0.17). In the medial region (ROI 2) BMD remained unchanged at all follow-up evaluations in both groups. There were no significant differences between the two groups (P = 0.45) in any ROI at any follow-up evaluation.

CONCLUSION

The significant increase in BMD of the lateral proximal tibia plateau with very limited changes medially and distally seen in both implants suggests that the novel porous titanium construct Regenerex and the PPS implant have a pronounced beneficial effect with regard to maintaining periprosthetic BMD in all regions of interest investigated.

Mobile- vs. fixed-bearing total knee replacement

BACKGROUND AND PURPOSE

It is unclear whether mobile-bearing (MB) total knee arthroplasties reduce the risk of tibial component loosening compared to fixed-bearing (FB) designs. This randomized study investigated implant migration, periprosthetic bone mineral density (BMD), and patient-reported outcomes (Oxford knee score)-all at 2 years-for the P.F.C. Sigma Cruciate Retaining total knee arthroplasty.

PATIENTS AND METHODS

50 osteoarthritis patients were allocated to either FB or MB tibial articulation.

RESULTS AND INTERPRETATION

At 2 years, the mean total translation (implant migration) was higher for the FB implant (0.30 mm, SD 0.22) than for the MB implant (0.17 mm, SD 0.09) (p = 0.04). BMD decreased between baseline and 1-year follow-up. At 2-year follow-up, BMD was close to the baseline level. The knee scores of both groups improved equally well. The FB tibial implant migrated more than the MB, but this was not clinically significant. The mobile polyethylene presumably partly absorbs the force transmitted to the metal tibial tray, thereby reducing micromotion.

Additively manufactured porous tantalum implants

The medical device industry's interest in open porous, metallic biomaterials has increased in response to additive manufacturing techniques enabling the production of complex shapes that cannot be produced with conventional techniques. Tantalum is an important metal for medical devices because of its good biocompatibility. In this study selective laser melting technology was used for the first time to manufacture highly porous pure tantalum implants with fully interconnected open pores. The architecture of the porous structure in combination with the material properties of tantalum result in mechanical properties close to those of human bone and allow for bone ingrowth. The bone regeneration performance of the porous tantalum was evaluated in vivo using an orthotopic load-bearing bone defect model in the rat femur. After 12 weeks, substantial bone ingrowth, good quality of the regenerated bone and a strong, functional implant-bone interface connection were observed. Compared to identical porous Ti-6Al-4V structures, laser-melted tantalum shows excellent osteoconductive properties, has a higher normalized fatigue strength and allows for more plastic deformation due to its high ductility. It is therefore concluded that this is a first step towards a new generation of open porous tantalum implants manufactured using selective laser melting.

Modulation and predictors of periprosthetic bone mineral density following total knee arthroplasty

Total knee arthroplasty (TKA) leads to a loss of periprosthetic bone mineral density (BMD). Great importance is attached to the prevention of periprosthetic bone loss with a view to ensuring a long service life of the prosthesis. In order to provide appropriate recommendations for preventive movement therapy measures to combat peri-implant bone loss, it is necessary to know the predictors of periprosthetic BMD. The aim of this study was (1) to determine the change of periprosthetic BMD of the femur and tibia and (2) to analyse the effects of different predictors on periprosthetic BMD. Twenty-three patients with primary TKA were evaluated 10 days and 3 months postoperatively. The data analysis comprised (1) the change in periprosthetic BMD from pretest to posttest and (2) the correlations between BMD and the variables isometric maximum voluntary force, lean mass, physical activity (step count), and BMI using multiple linear regression and structural equation modelling (SEM). BMD of the distal femur was significantly reduced by 19.7% (P = 0.008) 3 months after surgery, while no changes were found in BMD of the tibia. The results of SEM demonstrate that 55% of the BMD variance was explained by the model (χ² = 0.002; df = 1; P = 0.96; χ²/df = 0.002; RMSEA < 0.01; TLI = 1.5; CFI = 1.0). A significant direct effect was only evidenced by the variable lean mass (β = 0.38; b = 0.15; SE = 0.07; C.R. = 2.0; P = 0.046). It can be assumed that a large muscle mass with accompanying distribution of high mechanical load in the bones can contribute to local changes of periprosthetic BMD. Concrete recommendations for preventing peri-implant bone loss therefore include exercises which have the aim of maintaining or building up muscle mass.

The Mark Coventry Award: Trabecular metal tibial components were durable and reliable in primary total knee arthroplasty: a randomized clinical trial

BACKGROUND

Although highly porous metals have demonstrated excellent bone ingrowth properties and so are an intriguing option for fixation in total knee arthroplasty (TKA), some surgeons are skeptical about the durability of uncemented tibial fixation and the potential for soft tissues to adhere to these porous metals and perhaps cause knee stiffness or pain.

QUESTIONS/PURPOSES

The purpose of this study was to compare, in the context of a randomized clinical trial, a highly porous metal tibia compared with a traditional modular cemented tibia in terms of survivorship, Knee Society scores, range of motion (ROM), and complications.

METHODS

From 2003 to 2006, 397 patients (age 67.8 ± 8.7 years; 54% female) were randomized to three groups: (1) traditional modular cemented tibia; (2) cemented highly porous metal tibia; and (3) uncemented highly porous metal tibia. The same posterior-stabilized femoral component and patella component were cemented in every case. Stratified randomization was done for surgeon, patient's age, sex, and body mass index. Survivorship at 5 years was compared between the groups, as were Knee Society scores, ROM, and complications. Radiographic assessment included alignment, radiolucency, and implant migration/loosening. Patients were followed until death, revision, or for a minimum of 2 years (mean, 5 years; range, 2-9 years). Four patients were lost to followup before 2 years.

RESULTS

Highly porous metal tibias (both uncemented and cemented) were no different from traditional cemented modular tibial modular components in terms of survivorship at 5 years using a intention-to-treat analysis (96.8% [1]; 97.6% [2]; 96.7% [3]; p = 0.59). A per-protocol analysis revealed that no highly porous metal tibia was revised for aseptic loosening. Highly porous metal tibias performed comparably to traditional cemented modular tibias in terms of Knee Society scores, ROM, and the frequency of complications.

CONCLUSIONS

At 5 years this randomized clinical trial demonstrated that highly porous metal tibias provided comparably durable fixation and reliable pain relief and restoration of function when compared with a traditional cemented modular tibia in TKA.

LEVEL OF EVIDENCE

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

Trabecular bone density of the proximal tibia as it relates to failure of a total knee replacement

The relationship between post-operative bone density and subsequent failure of total knee replacement (TKR) is not known. This retrospective study aimed to determine the relationship between bone density and failure, both overall and according to failure mechanism. All 54 aseptic failures occurring in 50 patients from 7760 consecutive primary cemented TKRs between 1983 and 2004 were matched with non-failing TKRs, and 47 failures in 44 patients involved tibial failures with the matching characteristics of age (65.1 for failed and 69.8 for non-failed), gender (70.2% female), diagnosis (93.6% OA), date of operation, bilaterality, pre-operative alignment (0.4 and 0.3 respectively), and body mass index (30.2 and 30.0 respectively). In each case, the density of bone beneath the tibial component was assessed at each follow-up interval using standardised, calibrated radiographs. Failing knees were compared with controls both overall and, as a subgroup analysis, by failure mechanism. Knees were compared with controls using univariable linear regression.

Significant and continuous elevation in tibial density was found in knees that eventually failed by medial collapse (p < 0.001) and progressive radiolucency (p < 0.001) compared with controls, particularly in the medial region of the tibia. Knees failing due to ligamentous instability demonstrated an initial decline in density (p = 0.0152) followed by a non-decreasing density over time (p = 0.034 for equivalence). Non-failing knees reported a decline in density similar to that reported previously using dual-energy x-ray absorptiometry (DEXA). Differences between failing and non-failing knees were observable as early as two months following surgery. This tool may be used to identify patients at risk of failure following TKR, but more validation work is needed.

Cite this article: Bone Joint J 2014;96-B:1503–9.

Periprosthetic bone loss: diagnostic and therapeutic approaches

Total joint replacement surgery is being performed on an increasingly large part of the population. Clinical longevity of implants depends on their osseointegration, which is influenced by the load, the characteristics of the implant and the bone-implant interface, as well as by the quality and quantity of the surrounding bone. Aseptic loosening due to periprosthetic osteolysis is the most frequent known cause of implant failure. Wear of prosthetic materials results in the formation of numerous particles of debris that cause a complex biological response. Dual-energy X-ray Absorptiometry (DXA) is regarded as an accurate method to evaluate Bone Mineral Density (BMD) around hip or knee prostheses. Further data may be provided by a new device, the Bone Microarchitecture Analysis (BMA), which combines bone microarchitecture quantification and ultra high resolution osteo-articular imaging. Pharmacological strategies have been developed to prevent bone mass loss and to extend implant survival. Numerous trials with bisphosphonates show a protective effect on periprosthetic bone mass, up to 72 months after arthroplasty. Strontium ranelate has been demonstrated to increase the osseointegration of titanium implants in treated animals with improvement of bone microarchitecture and bone biomaterial properties.

Porous tantalum tibial component prevents periprosthetic loss of bone mineral density after total knee arthroplasty for five years-a matched cohort study

In 21 knees receiving porous tantalum tibial component and 21 knees receiving a cemented cobalt-chromium tibial component, dual x-ray absorptiometry scans were performed for five years post-operatively. The postoperative decrease in the bone mineral density in the lateral aspect of the tibia was significantly less in knees with porous tantalum tibial components (11.6%) than in knees with cemented cobalt-chromium tibial components (29.6%) at five years (p < 0.05). No prosthetic migration or periprosthetic fracture was detected in either group. The present study is one of the studies with the longest follow-up period on bone mineral density after total knee arthroplasty. Porous tantalum tibial component has a favorable effect on the bone mineral density of the proximal tibia after total knee arthroplasty up to five years.

Trabecular metal in total knee arthroplasty associated with higher knee scores: a randomized controlled trial

BACKGROUND

Porous tantalum is an option of cementless fixation for TKA, but there is no randomized comparison with a cemented implant in a mid-term followup.

QUESTIONS/PURPOSES

We asked whether a tibial component fixed by a porous tantalum system might achieve (1) better clinical outcome as reflected by the Knee Society Score (KSS) and WOMAC Osteoarthritis Index, (2) fewer complications and reoperations, and (3) improved radiographic results with respect to aseptic loosening compared with a conventional cemented implant.

METHODS

We randomized 145 patients into two groups, either a porous tantalum cementless tibial component group (Group 1) or cemented conventional tibial component in posterior cruciate retaining TKA group (Group 2). Patients were evaluated preoperatively and 15 days, 6 months, and 5 years after surgery, using the KSS and the WOMAC index. Complications, reoperations, and radiographic failures were tallied.

RESULTS

At 5-year followup the KSS mean was 90.4 (range, 68-100; 95% CI, ± 1.6) for Group 1, and 86.5 (range, 56-99; 95% CI, ± 2.4) for Group 2. The effect size, at 95% CI for the difference between means, was 3.88 ± 2.87. The WOMAC mean was 15.1 (range, 0-51; 95% CI, ± 2.6) for the Group 1, and 19.1 (range, 4-61; 95% CI, ± 2.9) for Group 2. The effect size for WOMAC was -4.0 ± 3.9. There were no differences in the frequency of complications or in aseptic loosening between the two groups.

CONCLUSIONS

Our data suggest there are small differences between the uncemented porous tantalum tibial component and the conventional cemented tibial component. It currently is undetermined whether the differences outweigh the cost of the implant and the results of their long-term performance.

Changes in tibial bone density measured from standard radiographs in cemented and uncemented total knee replacements after ten years’ follow-up

Stress shielding resulting in diminished bone density following total knee replacement (TKR) may increase the risk of migration and loosening of the prosthesis. This retrospective study was designed to quantify the effects of the method of fixation on peri-prosthetic tibial bone density beneath cemented and uncemented tibial components of similar design and with similar long-term survival rates. Standard radiographs taken between two months and 15 years post-operatively were digitised from a matched group of TKRs using cemented (n = 67) and uncemented (n = 67) AGC tibial prostheses. Digital radiograph densitometry was used to quantify changes in bone density over time. Age, length of follow-up, gender, body mass index and alignment each significantly influenced the long-term pattern of peri-prosthetic bone density. Similar long-term changes in density irrespective of the method of fixation correlated well with the high rate of survival of this TKR at 20 years, and suggest that cemented and uncemented fixation are both equally viable.

Cite this article: Bone Joint J 2013;95-B:911–16.

Bone ingrowth in well-fixed retrieved porous tantalum implants

While first generation porous coatings have had clinical success, aseptic loosening remains a leading cause of revision. The purpose of this study was to investigate the reasons for revision and to assess the amount of bone ingrowth in retrieved porous tantalum components. In a prospective multicenter retrieval program, 76 porous tantalum acetabular shells, 5 femoral stems, 7 patellas and 36 tibial trays were collected from revision surgeries. A subset of the implants was analyzed for bone ingrowth. The main reason for revision was infection for acetabular shells (1.4 years implantation time) and instability for tibial trays (1.8 years implantation time). Two of the thirty primary surgery acetabular shells and one of the thirty-six primary surgery tibial trays were revised for implant loosening. We observed full depth penetration of bone into the porous tantalum layer for the acetabular shells and femoral stems.

Periprosthetic bone mineral density changes after unicondylar knee arthroplasty

BACKGROUND

Unicompartmental knee arthroplasty (UKA) has received renewed interest in the last decade. UKA involves minor injury to soft tissues, limited removal of bone and delicate preservation of knee anatomy and geometry. In theory, UKA provides an opportunity to restore post-surgical knee kinematics to near normal.

HYPOTHESIS

UKA leaves patellofemoral joint free to meet high mechanical forces with no stress-shielding and therefore might preserve bone mineral density (BMD).

PATIENTS AND METHODS

We studied 21 patients with osteoarthritis (OA), who had received medial compartment UKA at Kuopio University Hospital between October 1997 and September 2000. BMD was measured by dual-energy X-ray absorptiometry (DEXA), at baseline (within a week after surgery) and at intervals until 7 years.

RESULTS

DEXA results were reproducible. The highest rate of periprosthetic bone loss occurred during the first 3 months after UKA. The average loss in BMD was 4.4% (p = 0.039) in the femoral diaphysis and it ranged from 11.2% (p < 0.001) to 11.9% (p = 0.002) in the distal femoral metaphysis; however, BMD changes in these regions, from 2 years to 7 years, were nonsignificant. At the 1-year follow-up, the BMD of the medial tibial metaphysis had increased by 8.9% (p = 0.02), whereas those in the lateral tibial metaphysial (-2.4%) and diaphysial regions (-2.0%) did not change significantly.

INTERPRETATIONS

UKA did not preserve periprosthetic BMD in the distal femoral metaphysis, whereas BMD changes in the tibial metaphysis were minor, consistent with a mechanical balance between the medial and lateral tibial compartments. LEVEL OF EVIDENCE 2B: Prospective case control study.

Minimum 6year results of an uncemented trabecular metal tibial component in total knee arthroplasty

INTRODUCTION

There are theoretical advantages of using a trabecular metal tibial component in total knee replacement (TKR) for long-term survival. We have previously reported outcomes at 3 years. We now report the clinical and radiological outcome of an unselected series of 109 knees at a minimum of 6 years follow up.

METHODS

Patient function was assessed in a research clinic using Oxford Knee Score (OKS), Clinical and Functional Knee Society Score (KSS) and SF-12 physical score. Up to date weight bearing radiographs were obtained.

RESULTS

Seventy-six knees in 72 patients were available for assessment. OKS scores were maintained from the 3-year assessment with a mean of 36.1 (8.6). KSS and SF-12 scores declined slightly but only to a degree previously reported as normal age related change. The mean KSS at follow up was 87.2 (17.7). There was no radiographic evidence of loosening in any implant. There has been 1 revision for unexplained pain at 27 months.

CONCLUSION

The uncemented TMT in an unselected group is performing as well as any TKR implant at this stage. Future follow up is required to ensure this is maintained. The theoretical advantages may make this the prosthesis of choice in younger patients.

LEVEL OF EVIDENCE

IV. Case series.

Influence of time in-situ and implant type on fixation strength of cemented tibial trays - a post mortem retrieval analysis

BACKGROUND

Loosening of the tibial tray is cited as the most common cause of failure in total knee arthroplasty but the mechanism remains unclear. Post mortem specimens provide a unique opportunity to investigate the clinical condition.

METHODS

Twenty two cemented components were serially retrieved in situ at autopsy from a university clinic. They were investigated for mechanical stability by pull-out, which was related to cement morphology and bone quality from CT scans, and to polyethylene wear by score analysis. Implants were grouped into three types: a particular fixed bearing design (n=8), a particular rotating platform design (n=5) and other mixed designs (n=9).

FINDINGS

Trends were observed for pull-out force to decrease with time in situ and increase with cement penetration but was unrelated to bone density or polyethylene wear. For the fixed bearing implants decreasing pull-out strength was related to an increasing proportion of failure at the bone-cement interface. For the mixed designs the opposite was observed. The rotating platform implants failed at the implant-cement interface.

INTERPRETATION

The analysis demonstrated that interface failure is dependent on the implant design, but that both the stem and the bone interfaces weaken with time in situ. Published findings for laboratory implantations have demonstrated that greater cement penetration improves fixation and this was reflected for clinical samples in this study.

Midterm results of a porous tantalum monoblock tibia component clinical and radiographic results of 108 knees

The use of Trabecular Metal (TM), a biomaterial manufactured from elemental tantalum metal, has recently increased in orthopedics. One hundred eight consecutive TM monoblock tibias were implanted in 95 patients and followed for a minimum of 2 years. The average follow-up was 4.5 years. The average age was 65 years. The Knee Society score of 36 improved to 89. One hundred five of the knees were rated good/excellent, and 3 knees were rated poor. Two patellar revisions were performed for loose components and one for patellar misalignment. One patella fracture required open reduction and internal fixation. One femur was revised. There were no tibia revisions. There were no progressive radiographic lucencies. Midterm clinical and radiographic results of 108 consecutive TM tibia components have a high rate of success.