Background. Trabecular metal (TM) cones are designed to fill up major bone defects in total knee arthroplasty. Tibial components can be implanted in combination with a stem, but it is unclear if this is necessary after reconstruction with a TM cone. Implanting a stem may give extra stability, but may also have negative side-effects. Aim of this study was to investigate stability and strain distribution of a tibial plateau reconstruction with a TM cone while the tibal component is implanted with and without a stem, and whether prosthetic stability was influenced by bone mineral density (BMD). Methods. Tibial revision arthroplasties were performed after reconstruction of an AORI 2B bone defect with TM cones. Plateaus were implanted in seven pairs of cadaveric tibiae; of each pair, one was implanted with and the other without stem. All specimens were loaded to one bodyweight alternating between the medial and lateral tibia plateau. Implant-bone micro motions, bone strains, BMD and correlations were measured and/or calculated. Results. Tibial components without a stem showed only more varus tilt (difference in median 0.14 degrees (P<0.05), but this was not considered clinically relevant. Strain distribution did not differ. BMD had only an effect on the anterior/posterior tilt ρ:-0.72 (P<0.01). Conclusions. Tibial components, with or without a stem, which are implanted after reconstruction of major bone defects using TM cones produce very similar biomechanical conditions in terms of stability and strain distribution. Additional stem extension of the tibial component may not be required after reconstruction of major bone defects using TM cones. Level of evidence. IIb. Disclosures. The department of Orthopaedics, University of Groningen, University Medical Center Groningen has received direct funding from the Anna Fonds (Oegstgeest, NL). Zimmer (Warsaw, IN, USA) has provided the instrumentation and tools for this study. The department of Orthopaedics, University of Groningen, University Medical Center Groningen receives research institutional support from InSpine (Schiedam, NL) and Stryker (Kalamazoo, Mich. USA). One of the authors (ALB) will be and has been paid as a consultant by Zimmer (Warsaw, IN, USA) for purposes of education and training in knee arthroplasty

The osteo-regenerative properties of allograft have recently been enhanced by addition of autogenous skeletal stem cells to treat orthopaedic conditions characterised by lost bone stock. There are however, multiple disadvantages to allograft, including cost, availability, consistency and potential for disease transmission, and trabecular tantalum represents a potential alternative. Tantalum is already in widespread orthopaedic use, although in applications where there is poor initial implant stability, or when tantalum is used in conjunction with bone grafting, loading may need to be limited until sound integration has occurred. Development of enhanced bone-implant integration strategies will improve patient outcomes, extending the clinical applications of tantalum as a substitute for allograft.

The aim of this study was to examine the osteoconductive potential of trabecular tantalum in comparison to human allograft to determine its potential as an alternative to allograft.

Human bone marrow stromal cells (500,000 cells per ml) were cultured on blocks of trabecular tantalum or allograft for 28 days in basal and osteogenic media. Molecular profiling, confocal and scanning electron microscopy, as well as live-dead staining and biochemical assays were used to characterise cell adherence, proliferation and phenotype.

Cells displayed extensive adherence and proliferation throughout trabecular tantalum evidenced by CellTracker immunocytochemistry and SEM. Tantalum-cell constructs cultured in osteogenic conditions displayed extensive matrix production. Electron microscopy confirmed significant cellular growth through the tantalum to a depth of 5mm. In contrast to cells cultured with allograft in both basal and osteogenic conditions, cell proliferation assays showed significantly higher activity with tantalum than with allograft (P<0.01). Alkaline phosphatase (ALP) assay and molecular profiling confirmed no significant difference in expression of ALP, Runx-2, Col-1 and Sox-9 between cells cultured on tantalum and allograft.

These studies demonstrate the ability of trabecular tantalum to support skeletal cell growth and osteogenic differentiation comparable to allograft. Trabecular tantalum represents a good alternative to allograft for tissue engineering osteo-regenerative strategies in the context of lost bone stock. Such clinical scenarios will become increasingly common given the ageing demographic, the projected rates of revision arthroplasty requiring bone stock replacement and the limitations of allograft. Further mechanical testing and in vivo studies are on-going.

Objectives. We sought to determine if a durable bilayer implant composed of trabecular metal with autologous periosteum on top would be suitable to reconstitute large osteochondral defects. This design would allow for secure implant fixation, subsequent integration and remodeling. Materials and Methods. Adult sheep were randomly assigned to one of three groups (n = 8/group): 1. trabecular metal/periosteal graft (TMPG), 2. trabecular metal (TM), 3. empty defect (ED). Cartilage and bone healing were assessed macroscopically, biochemically (type II collagen, sulfated glycosaminoglycan (sGAG) and double-stranded DNA (dsDNA) content) and histologically. Results. At 16 weeks post-operatively, histological scores amongst treatment groups were not statistically different (TMPG: overall 12.7, cartilage 8.6, bone 4.1; TM: overall 14.2, cartilage 9.5, bone 4.9; ED: overall 13.6, cartilage 9.1, bone 4.5). Metal scaffolds were incorporated into the surrounding bone, both in TM and TMPG. The sGAG yield was lower in the neo-cartilage regions compared with the articular cartilage (AC) controls (TMPG 20.8/AC 39.5, TM 25.6/AC 33.3, ED 32.2/AC 40.2 µg sGAG/1 mg respectively), with statistical significance being achieved for the TMPG group (p < 0.05). Hypercellularity of the neo-cartilage was found in TM and ED, as the dsDNA content was significantly higher (p < 0.05) compared with contralateral AC controls (TM 126.7/AC 71.1, ED 99.3/AC 62.8 ng dsDNA/1 mg). The highest type II collagen content was found in neo-cartilage after TM compared with TMPG and ED (TM 60%/TMPG 40%/ED 39%). Inter-treatment differences were not significant. Conclusions. TM is a highly suitable material for the reconstitution of osseous defects. TM enables excellent bony ingrowth and fast integration. However, combined with autologous periosteum, such a biocomposite failed to promote satisfactory neo-cartilage formation. Cite this article: E. H. Mrosek, H-W. Chung, J. S. Fitzsimmons, S. W. O’Driscoll, G. G. Reinholz, J. C. Schagemann. Porous tantalum biocomposites for osteochondral defect repair: A follow-up study in a sheep model. Bone Joint J 2016;5:403–411. DOI: 10.1302/2046-3758.59.BJR-2016-0070.R1

Summary. The 80% porous structure of trabecular metal allows for bone ingrowth in more than 90% of the available surface. The Nexgen LPS Uncemented Knee using a trabecular metal tibial component has performed well at minimum of 5 years’ follow-up. Introduction. Total Knee Arthroplasty prostheses most frequently used in today's practice have cemented components. These have shown excellent clinical results. The fixation can however weaken with time, and cement debris within the articulation can lead to accelerated wear. Cementless implants are less commonly used, but some have also shown good long-term clinical results. The potential advantages of cementless implants are retention of bone stock, less chance of third-body wear due to the absence of cement, shorter operative time, and easier treatment of periprosthetic fractures. The posterior stabilised knee replacement has been said to increase tangential shear stresses on the tibial component and increases contact stresses on the cam and post mechanism hence the great debate of cruciate retaining or cruciate sacrificing implants. Objectives. We report the results of a prospective cohort of consecutive primary total knee arthroplasties using an uncemented posterior stabilised prosthesis using a trabecular metal (tantalum) tibial component at a minimum 5-year follow-up. Methods. Prospective 5 year follow-up of patients undergone an uncemented posterior stabilised total knee replacement using a trabecular metal tibial component (NexgenLPS). Clinical examination, Oxford knee score, Knee society score, SF12 and radiological evaluation undertaken at review. Results. 81 patients, 45 female, 36 male. Left 31, Right 50. Mean age 74.3 yrs range (51–90). SF12, mean: 31.8 range (25–37). Oxford Knee Score Pre-op Mean 20.1 range (9–36) Post op: Mean 32.1 range (9–48). Knee Society score. Pain Mean 91.8; range (60–100). Functional score mean 76.2; range (30–100). Mean Range of movement 110.5 degrees range (90–125). No evidence of loosening at 5 yrs. No deep infection. No Revisions. Conclusion. Although there are a variety of methods of achieving satisfactory initial fixation in cementless components, trabecular metal has an advantage owing to its cellular structure resembling bone. The 80% porous structure of trabecular metal allows for bone ingrowth in more than 90% of the available surface. The Nexgen LPS Uncemented Knee using a trabecular metal tibial component used in this series has shown no evidence of loosening at a minimum of 5 years’ follow-up and the prosthesis as a whole has performed very well clinically. Its early results are comparable to those prostheses most commonly used as reported by the arthroplasty registers. The longer term results from this prosthesis are awaited with interest

Background. Implant stability and is an important factor for adequate bone remodelling and both are crucial in the long-term clinical survival of total hip arthroplasty (THA). Assessment of early bone remodelling on X-rays during the first 2 years post-operatively is mandatory when stepwise introduction of a new implant is performed. Regardless of fixation type (cemented or cementless), early acetabular component migration is usually the weakest link in THA, eventually leading to loosening. Over the past years, a shift towards uncemented cup designs has occurred. Besides the established hydroxyapatite (HA) coated uncemented cups which provide ongrowth of bone, new uncemented implant designs stimulating ingrowth of bone have increased in popularity. These cups initiate ingrowth of bone into the implant by their open metallic structure with peripheral pores, to obtain a mechanical interlock with the surrounding bone, thereby stabilising the prosthesis in an early stage after implantation. This retrospective study assessed bone remodelling, osseointegration and occurrence of radiolucency around a new ingrowth philosophy acetabular implant. Methods. In a retrospectively, single centre cohort study all patients whom underwent primary THA with a Tritanium acetabular component in 2011 were included. Bone remodelling, osseointegration and occurrence of radiolucency were determined by two reviewers from X-ray images that were made at 6 weeks, 3–6-12 and 24 months post-operatively. Bone contact % was calculated based on the original Charnley and DeLee zones. According to Charnley and DeLee the outer surface of an acetabular cup is divided into 3 zones (1-2-3). For our analysis the original 3 zones were further divided into 2 producing 6 zones 1A to 3B. Each of these 6 zones were then further divided into 4 equal sections. We attributed 25 points per section in which complete bone contact without lucency was observed. If lucency was observed no points were attributed to the section. A fully osteointegrated cup in all 24 sections could therefore attain 600 points. The total of each section and zone was subsequently tallied and recalculated to produce the percentage of bone contact on a 1–100% score. Results. In 2011 131 patients; 54 male and 76 female with average age of 60.83 (SD 12.42) and 60.57 (SD 12.11) year respectively underwent primary THA at our institution and all where included in our study cohort. Majority of this cohort underwent primary THA due to osteoarthrosis and most patients were classified ASO I (18%) or ASA II (65%). At two year clinical follow-up two revision were performed. One constituted a femur and acetabulum revision due to leg length difference and a snapping hip phenomenon. Complications included 3 dislocations (all treated policlinic), 4 deep infections (all treated with Genta PMMA beads with prosthesis in situ and healed) and 1 removal of hematoma. In another patient the femoral component was revised due to a peri-prosthetic fracture. Mean bone contact % values for all Charnley and DeLee zones combined were calculated and improved from 68,18% (SD 22,36) at 6 weeks to 73,61% SD (16,26) at 3 months to 84,21% (SD 19,02) at 6 months to 86,90% (SD 16,0) at 1 year to 92,19% (SD 12,74) at two year follow-up. When analysing the bone contact % per individual zone a remarkable difference was found for zones 2A-B. In contrast to zone 1A-B and 3A-B the initial bone contact % was clearly although not significantly lower until two year follow-up. Conclusions. In this study, the bone apposition around Tritanium actebular component was retrospectively assessed until two year clinical. Our results show excellent bone apposition that continues to improve over time (at least until two year clinical follow-up) suggesting that the open trabecular Ti structure of the Tritanium has a positive effect on cup osseointegration. However, some recent reports have shown the development of reactive lines around cups with porous/trabecular metal surfaces, of which the meaning is still unclear. Our analysis indicated that especially acetabular zone 2A-B according to Charnley&DeLee needs time to establish a direct contact of the implant surface and the surrounding bone tissues. Perhaps this might be explained by reaming technique (underreaming vs line to line reaming) resulting in suboptimal seating of the cup. Therefore, careful follow-up of this new implant technology will remain necessary and continued in this study. We aim to improve cohort size and establish results at longer follow-up times. Furthermore we aim to correlate these results to RSA component migration analysis