Local and systemic concentrations of cobalt (Co) and chromium (Cr) ions may be elevated in patients with accelerated tribo-corrosion at prosthesis bearing surfaces and modular taper junctions. Previous studies by us and others have shown that exposure to these metals negatively affect the viability and function of osteoblasts and osteoclasts in vitro, with implications for bone health. More recently, we have observed an increase in total bone mineral density and reduced bone turnover (TRAP5b and osteocalcin) in patients with well-functioning metal-on-metal hip resurfacing (MOMHR). Here, we provide data to support the hypothesis that osteoclast differentiation and function is altered in this patient population, and that this effect is transferrable through their serum. Patients with well-functioning MOMHR (n=18) at median follow-up of 8 years were individually matched for gender, age and time-since-surgery to a low-exposure group consisting of patients with metal-on-polyethylene total hip arthroplasty (THA). The median circulating concentrations of Co and Cr for the MOMHR group were 2.53µg/L and 2.5µg/L respectively, compared to 0.02µg/L and 0.03µg/L for the THA group. Monocyte fraction of peripheral blood was isolated from these patients, seeded onto dentine wafers and differentiated into osteoclasts using media supplemented with RANKL and M-CSF (osteoclastogenic media, OM). Cultures were monitored for the onset of resorption, following which they were treated with OM, autologous serum or serum from the other individual within the matched MOMHR - THA pair, all supplemented with RANKL and M-CSF. At the end of the culture, cells were TRAP stained and quantified for total osteoclast number, number of resorbing osteoclasts and percentage resorption using the CellD Software Package (Olympus, Southend-on-Sea, U.K.). For cells differentiated in osteoclastogenic media, the resorbing ability of osteoclasts derived from MOMHR patients was reduced by 30% (P=0.046) compared to THA. Correlation analyses showed that chronic exposure to Co and Cr trends towards negative association with resorption ability of these osteoclasts (r = −0.3, P=0.06). Furthermore, the resorbing ability of osteoclasts generated from MOMHR patients and differentiated in autologous serum was reduced 33% (p < 0 .0001), whilst matched THA serum caused a smaller reduction of 14% (p < 0 .01). When cells derived from THA patients were differentiated in autologous serum, the resorbing ability of osteoclasts was similarly reduced by 35% (p < 0 .0001), whilst the matched MOMHR serum also caused a reduction of 21% (p < 0 .0001). Reduced osteoclastogenic response of precursor cells from patients with higher circulating Co and Cr suggests an inherent change in their potential to differentiate into functional osteoclasts. The data also suggests that functional response of mature osteoclasts generated from patient precursor cells are dependent on the prior systemic metal concentrations and the presence of higher circulating CoCr in patients with MOMHR. These effects are modest, but may explain the subtle increase in systemic bone mineral density and decreased bone turnover observed in patients after 8 years exposure compared to age, sex, and exposure-time matched patients who received a conventional THA

Objective. In this study, we aim to compare total bone amount extracted in total knee arthroplasty in implant design and the bone amount extracted through intercondylar femoral notch cut. Material and Method. In this study, we implemented 10 implants on a total of 50 sawbones from 5 different total knee arthroplasty implant brands namely Nex-Gen Legacy (Zimmer, Warsaw, IN, USA), Genesis 2 PS (Smith&Nephew, Memphis, TN, USA), Vanguard (Biomet Orthopedics Inc., Warsaw, IN, USA), Sigma PS (De Puy, Johnson&Johnson, Warsaw, IN, USA), Scorpio NRG PS (Stryker Co., Kalamazoo, USA). Equal or the closest sizes of each brand on anteroposterior plane were selected, and cuts were made following standard technique(see Fig 1 and 2). Extracted bone pieces were measured in terms of volume and length on three planes, and statistically analysed. The volume of all pieces available after each femoral incision was measured according to Archimedes’ principles. Furthermore, the volume of each intercondylar femoral notch pieces was measured separately from other pieces but with the same method. The measurement of intercondylar femoral notch pieces on 3 planes (medial-lateral, anterior-posterior, superior-inferior) was made using Kanon slide gauge (Ermak Ltd, Istanbul, TR). Femoral notch incision pieces were scanned with CAD/CAM technology using three-dimensional scanner 1 SeriesTM (Dental Wings Inc, Montreal, QC, Canada), and the measurements were confirmed with DWOS CAD 4.0.1 software (Dental Wings Inc, Montreal, QC, Canada)(see figure 3a-e). The volume of 10 intercondylar femoral notch pieces performed through the set of each brand was averaged, and considered as the incision volume of that particular brand. Results. The comparison made by excluding femoral notch cuts did not produce any statistically significant difference between the amounts of bone extracted. The least volumetric value measured in extracted intercondylar femoral notch cut was obtained using Vanguard (3,6±0,4 cm3). The gradually increasing volumes were obtained from Nex-Gen (3,7±0,5 cm3), Sigma (5,7±0,4 cm3), Genesis 2 (6,3±0,3 cm3) and Scorpio NRG (6,7±0,7 cm3), respectively. There was no statistical difference between Genesis 2 and Scorpio NRG, and between Nex-Gen and Vanguard. Conclusion. There are significant differences among implant designs in terms of preserving bone stock, and much of these differences stems from intercondylar femoral notch incision

Bone ingrowth fixation of large diameter, beaded cobalt chromium cups is generally considered to be reliable but this is typically judged radiographically. To date, implant retrieval data of attached bone has been limited. This study evaluated correlations between the pre-revision radiographic appearance and the measured amount of bone attachment on one design of porous coated cup. Methods. Twenty-six monoblock, CoCr Birmingham Hip Resurfacing (BHR, Smith and Nephew, TN, USA) cups with macroscopic beads and hydroxyapatite coating were studied. Seventeen were revised for acetabular malposition with the remainder revised for femoral loosening (4), pain (1), infection (1), dislocation (1) or lysis (2). Median time to revision was 35 months (10 – 70 months). Ten patients were female; the median age of all patients was 54 years. The pre-revision radiographs were visually ranked for cup-bone integration as follows: 0 = none, 1 = < 50%, 2 = 50 – 75%, 3 = 76 – 95%, 4 = > 96% integration. Rankings were made for the superior and inferior aspects, without knowledge of the appearance of bone on the retrievals. The revised cups were photographed at an angle so the dome and the cup periphery were visualized. The area of bone in four equal segments in each of the superior and inferior aspects was measured with image analysis software. A probe was used to differentiate bone from soft tissue. Only bone that covered the beads was counted. Correlation coefficients were calculated for the radiographic and image analysis data. Results. Radiographically, most cups were assessed as having more than 50% of bone attachment and 7 cups were ranked as having almost total integration with bone. Only 2 cups were assessed radiographically as fully loose. Measured total bone attachment ranged from none to 55%. Superior and inferior percent ingrowth were highly correlated (corr=0.68, p<0.001) but there was no correlation between percent bone and x-ray rank (inferior corr=0.01, p=0.96; superior corr=0.23, p=0.26). There was no correlation between cup malpositioning as a reason for revision and x-ray integration ranking (superior p=0.34; inferior p=0.80). Discussion. Despite the radiographic appearance of good fixation, there was little or no correlation between percent area of actual bone attachment and x-ray appearance. One study limitation is the assumption that attached bone was indeed integrated with the beads as destructive sectioning was not done to verify this. Published autopsy retrieval studies have shown that even a small amount of actual ingrowth can provide clinically successful fixation. Another possible limitation was the variable quality of the radiographs. Never-the-less these results raise questions about the accuracy of radiographic analysis of bone fixation. The possibility that inadequate fixation is a cause for pain leading to revision should be considered even when the radiographic appearance indicates otherwise

To achieve desirable outcomes in cementless total knee replacement (TKR), sufficient primary stability is essential. The primary stability inhibits excessive motions at the bone-implant interface, hence providing the necessary condition for osseointegration [1]. Primary stability for cementless TKR is provided by press-fit forces between the bone and implant. The press-fit forces depend on several factors including interference fit, friction between bone and implant surface, and the bone material properties. It is expected that bone mineral density (BMD) will affect the stability of cementless TKR [2]. However, the effect of BMD on the primary stability of cementless femoral knee component has not been investigated in vitro. Phantom calibrated CT-scans of 9 distal femora were obtained after the surgical cuts were made by an experienced surgeon. Since the press-fit forces of the femoral component mainly occur in the Anteroposterior (AP) direction, the BMD was measured in the anterior and posterior faces for a depth of 5 mm; this depth was based on stress distributions from a Finite Element Analysis of the same implant design. In addition, four strain gauges were connected to different locations on the implant's outer surface and implant strain measured throughout as an indication of underlying bone strain. A cementless Sigma CR femoral component (DePuy Synthes Joint Reconstruction, Leeds, UK) was then implanted using an MTS machine. In order to simulate a ‘normal’ bone condition, the implanted bone was preconditioned for one hour at a cyclic load of 250–1500 N, and a rate of 1 Hz. Finally, the implants were pushed-off from the bone in a high-flex position. Forces and displacements were recorded both during insertion and push-off tests. Strong correlations were found for insertion and push-off forces with BMD, R. 2. = 0.88 and R. 2. = 0.88, respectively (p < 0.001), so although implantation may be harder in patients with higher BMD, initial stability is also improved. A correlation was also found between final strain and push-off forces (R. 2. = 0.89, p < 0.01) and BMD also showed a strong reverse correlation with total bone relaxation (R. 2. = 0.76, p = 0.023). These results indicate that higher BMD induces higher bone strain, which can lead to improved fixation strength. There is no consensus on the best fixation method for the TKR but some surgeons prefer a cementless design for young and active patients. The results of our study showed that the primary stability of a cementless femoral knee component is directly correlated with the bone mineral density. Therefore, patient selection based on bone quality may increase the likelihood of good osseointegration and adequate long-term fixation for cementless femoral knee components

For amputated patients, direct attachment of upper leg prosthesis to the skeletal system by a percutaneous implant is an alternative solution to the traditional socket fixation. Currently available implants, the OPRA system (Integrum AB, Göteborg, Sweden) and the ISP Endo/Exo prosthesis (ESKA Implants AG, Lübeck, Germany) [1-2] allow overcoming common soft tissue problems of conventional socket fixation and provide better control of the prosthetic limb [3], higher mobility and comfort [2, 4]. However, restraining issues such as soft-tissue infections, peri-prosthetic bone fractures [3, 5–8] and considerable bone loss around the stem [9], which might lead to implant's loosening, are present. Finally, a long a residual limb is required for implant fitting. In order to overcome the limiting biomechanical issues of the current designs, a new concept of the direct intramedullary fixation was developed. The aim was to restore the natural load transfer in the femur and allow implantations in short femur remnants (Figure 1). We hypothesize that the new design will reduce the peri-prosthetic bone failure risk and adverse bone remodeling. Generic CT-based finite element models of an intact femoral bone and amputated bones implanted with 3 analyzed implants were created for the study. Models were loaded with two loading cases from a normal walking obtained from the experimental measurements with the OPRA device [10-11]. Periprosthetic bone failure risk was evaluated by considering the von Mises stress criterion [12-14]. Subsequently the strain adaptive bone remodeling theory was used to predict long-term changes in bone mineral density (BMD) around the implants. The bone mineral content (BMC) change was measured around implants and the results were visualized in the form of DXA scans. The OPRA and the ISP implants induced the high stress concentration in the proximal region decreasing in the distal direction to values below physiological levels as compared with the intact bone. The stresses around the new design were more uniformly distributed along the cortex and resembled better the intact case. Consequently, the bone failure risk was reduced as compared to the OPRA and the ISP implants. The adaptive bone remodeling simulations showed high bone resorption around distal parts of the OPRA and the ISP implants in the distal end of the femur (on average −75% ISP to −78% OPRA after 60 months). The bone remodeling simulation did not reveal any bone loss around the new design, but more bone densification was seen (Figure 2). In terms of total bone mineral content (BMC) the OPRA and the ISP implants induced only a short-term bone densification in contrast to the new design, which provoked a steady increase in the BMC over the whole analyzed period (Figure 3). In conclusion, we have seen that the new design offers much better bone maintenance and lower failure probability than the current osseointegrated trans-femoral prostheses. This positive outcome should encourage further developments of the presented concept, which in our opinion has a potential to considerably improve safety of the rehabilitation with the direct fixation implants and allow treatment of patients with short stumps

Introduction. Bicompartmental osteoarthritis involving the medial tibiofemoral and the patellofemoral compartments is often treated with total knee replacement. Improved implants and surgical techniques have led to renewed interest in bicompartmental arthroplasty. This study evaluates the radiographic and early clinical results of bicompartmental arthroplasty with separate unlinked components implanted with the assistance of a robotic surgical arm. In addition, we examine the amount of bone resected using unlinked bicompartmental components compared to total knee replacement. Finally, a retrospective review of total knee cases examines the applicability of this early intervention procedure. Methods. 97 patients received simultaneous but geometrically separate medial tibiofemoral and patellofemoral arthroplasties with implants specifically designed to take advantage of a new bone and tissue sparing implantation technique using haptic robotics. These patients came from four surgeons at four different hospitals. The average follow-up was 9 months. Pre- and post-operative radiographs were taken. ROM, KSS and WOMAC scores were recorded. The patients had an average age of 67 yrs (range: 45-95), BMI of 29 ± 4kg/m. 2. 47% of the patients were male. We retrospectively reviewed pre and post operative notes from 406 consecutive TKA patients from a single surgeon. Intraoperative data included the integrity of the three compartments and the ACL. Results. At only six weeks follow-up, patients recovered their pre-operative ROM (p=0.37). Knee Society Knee scores (knee and function) and WOMAC scores (pain, function and total) significantly improved from pre-operative values at every follow-up of 6 weeks, 6 months and 1 year (p<0.05). Radiographically, there was no evidence of loosening, wear or progression of OA. There were also no perioperative complications. Using computer simulation, the amount of bone removed using bicompartmental arthroplasty compared to traditional TKA was predicted. Total bone removed on the femur and the tibia using a standard TKA implant is 3.5 times the bone removed using a bicompartmental onlay implant and 4 times the bone removed when using a bicompartmental inlay implant. In the review of 406 TKA cases, the ACL was intact in 66% of these cases. Based on these data alone, 16% of these TKA patients were indicated for a unicondylar arthroplasty, 12% medial UKA, 3% lateral UKA and 1% PFA. In addition, 31% were indicated for bicompartmental arthroplasty with 4% bicondylar (medial and lateral UKA), 6% lateral UKA and PFA and 21% medial UKA and PFA. While these data don't yet account for fixed versus flexible deformities, excessive osteophytes or other contraindications, it seems clear that the disease often treated with a TKA does not actually involve all three compartments. Conclusions. Modular bicompartmental arthroplasty is an effective method for treating arthritis of the knee restricted to the medial and patellofemoral compartments. Early results using contemporary prostheses are encouraging and should prompt further mid- and long-term study. Robotic assistance of bicompartmental arthroplasty has shown good early clinical and radiographic success. In addition, bicompartmental arthroplasty removes significantly less bone than total knee arthroplasty. Also, data indicates that may total knee patients have healthy cruciates and disease in only two of the three compartments, indicating that TKA is an overtreatment of earlier stage osteoarthritis. Longer term studies will determine the clinical significance of preserving healthy cartilage and ligaments routinely resected with traditional tricompartmental TKA

Purposes of the study. To assess safety, lengths gained, frame time and perform cost analysis of the technique of submuscular plating to the femur and tibia following distraction osteogenesis. Introduction. Since 2005 we have performed submuscular plating to the femur and tibia after distraction osteogenesis in order to shorten time in external fixator. Aim. To assess safety, lengths gained, frame time and perform cost analysis. Methods. Retrospective analysis using notes and digital radiographs, with cost codes for 2011 prices. Patients. 23 patients (14 male), mean age 11 (range 4 to 17). 14 diagnosed as congenital longitudinal deficiency. Total 37 bones lengthened (14 femur and tibia, 7 tibia only, 2 femur only). Ilizarov fixator most commonly used for tibia, LRS fixator for femur. Results. Mean length gained 68 mm per patient, 43 mm per bone. Mean frame time 121 days. Fixator index 0.59 months/cm per patient, 0.90 months/cm per bone. Mean cost £20100 per patient, £12500 per bone, £2800 per cm length. Cost attributable to plating £5100 per patient, £3300 per bone. Complications: 5/24 had pinsite infections, 2/24 required tendon releases, 1/24 had deformity, 1/24 sustained a fracture proximal to femoral plate. No deep infections. Conclusions. Plating after lengthening is a safe procedure with no deep infections. The frame time is low (0.6 months/cm per patient) but increases overall costs by an extra £5000

Aims. Since 2005 we have performed submuscular plating to the femur and tibia after distraction osteogenesis in selected cases in order to shorten the time in external fixator. The aim was to assess safety, lengths gained, frame time and perform cost analysis. Methods. Retrospective analysis using notes and digital radiographs, with cost codes for 2011 prices. 23 patients (14 male), mean age 11 (range 4 to 17) were analysed. 14 were diagnosed as congenital longitudinal deficiency. Total 37 bones lengthened (14 femur and tibia, 7 tibia only, 2 femur only). Ilizarov fixator most commonly used for tibia, LRS fixator for femur. Results. Mean length gained 68mm per patient, 43mm per bone. Mean frame time 121 days, with mean 75 days of lengthening, and mean 46 days between the cessation of lengthening and the plating procedure. Fixator index 0.59 months/cm per patient, 0.90 months/cm per bone. Mean cost £20100 per patient, £12500 per bone, £2800 per cm length. Cost attributable to plating £5100 per patient, £3300 per bone. Complications: 5/24 had pinsite infections, 2/24 required tendon releases, 1/24 had deformity, 1/24 sustained a fracture proximal to femoral plate. No deep infections. In terms of patient satisfaction, families of patients who had also undergone a prior lengthening with frame only, 80% preferred plate after lengthening. Conclusions. Plating after lengthening is a safe procedure with no deep infections. The frame time is low (0.6 months/cm per patient) but increases overall costs by an extra £5000 per patient. There is room to improve the fixator index further if the time between cessation of lengthening and the plating procedure (currently 46 days) is shortened