Objectives. All-suture anchors are increasingly used in rotator cuff repair procedures. Potential benefits include decreased bone damage. However, there is limited published evidence for the relative strength of fixation for all-suture anchors compared with traditional anchors. Materials and Methods. A total of four commercially available all-suture anchors, the ‘Y-Knot’ (ConMed), Q-FIX (Smith & Nephew), ICONIX (Stryker) and JuggerKnot (Zimmer Biomet) and a traditional anchor control TWINFIX Ultra PK Suture Anchor (Smith & Nephew) were tested in cadaveric human humeral head rotator cuff repair models (n = 24). This construct underwent cyclic loading applied by a mechanical testing rig (Zwick/Roell). Ultimate load to failure, gap formation at 50, 100, 150 and 200 cycles, and failure mechanism were recorded. Significance was set at p < 0.05. Results. Overall, mean maximum tensile strength values were significantly higher for the traditional anchor (181.0 N, standard error (. se). 17.6) compared with the all-suture anchors (mean 133.1 N . se. 16.7) (p = 0.04). The JuggerKnot anchor had greatest displacement at 50, 100 and 150 cycles, and at failure, reaching statistical significance over the control at 100 and 150 cycles (22.6 mm . se. 2.5 versus 12.5 mm . se. 0.3; and 29.6 mm . se. 4.8 versus 17.0 mm . se. 0.7). Every all-suture anchor tested showed substantial (> 5 mm) displacement between 50 and 100 cycles (6.2 to 14.3). All-suture anchors predominantly failed due to anchor pull-out (95% versus 25% of traditional anchors), whereas a higher proportion of traditional anchors failed secondary to suture breakage. Conclusion. We demonstrate decreased failure load, increased total displacement, and variable failure mechanisms in all-suture anchors, compared with traditional anchors designed for rotator cuff repair. These findings will aid the surgeon’s choice of implant, in the context of the clinical scenario. Cite this article: N. S. Nagra, N. Zargar, R. D. J. Smith, A. J. Carr. Mechanical properties of all-suture anchors for rotator cuff repair. Bone Joint Res 2017;6:82–89. DOI: 10.1302/2046-3758.62.BJR-2016-0225.R1

Three distal femoral axes have been described to aid in alignment of the femoral component; the Trans Epicondylar Axis (TEA), the Posterior Condylar Axis (PCA) and the Antero Posterior (AP) axis. Our aim was to identify if there was a reproducible relationship between the axes. Hopefully this will aid the surgeon to more accurately judge the rotation of the femoral cutting block by using the axes with the least variation. This is the first study compare all three distal femoral axes with each other using magnetic resonance imaging (MRI) in a Caucasian population awaiting total knee arthroplasty (TKA). We identified the relationship between these axes by performing MRI scans on 89 patients awaiting TKA with patient-specific instrumentation. Measurements were taken by two observers. Patients had a mean age of 62.5 years (range 32–91). 51 patients were female. The mean angle between the TEA and AP axis was 92.78°, standard deviation (SD) 2.51° (range 88°–99°). The mean angle between the AP axis and PCA was 95.43°, SD 2.75° (range 85°–105°). The mean angle between the TEA and PCA was 2.78°, SD 1.91° (range 0°–10°). We conclude that while there is a reproducible relationship between the differing femoral axes, there is a significant range in the relationship between the femoral axes. This range may lead to greater inaccuracy than has previously been appreciated when defining the rotation of the femoral component. There is most variation between the PCA and the AP axis. Most systems have a cutting block with 3° of external rotation from the PCA and this would be parallel to the TEA in the majority, but not all, cases in this series. This data suggests that if the surgeon is to pick two axes to reference from, one should include the TEA

Despite the increasing use on uncemented implants, cement continues to be used for hip and knee replacement in both primary and revision cases. Whilst the exact clinical relevance of reducing cement porosity, and thereby increasing its strength, is unclear in such applications, successive generations of mixing and implanting have all concentrated on reducing the amount of air in cement. The aim of the present study was to elucidate whether the use of a power tool mixing device could reduce cement porosity more than the use of mixing under vacuum conditions alone. Furthermore, we determined if variability in cement porosity could also be reduced with power tool mixing compared with hand mixing under vacuum conditions. Cement was mixed in three different ways in a Stryker cement mixing cartridge. For group 1, cement was mixed by hand with no vacuum. For group 2, cement was mixed manually under vacuum. For group 3, cement was mixed under vacuum using the Stryker Revolution system. For all three groups, cement was stored and mixed at the same temperature and humidity. To study cement porosity, we used 3-dimensional computerised microtomography, a technique which has previously been used by other investigators. Porosity for the sample in group 1 was 9.4%, and for groups 2 and 3, mean sample porosity was 1.8% (SD 1.3) and 1.1% (SD 1.0) respectively. The large difference in porosity between group 1 and the other groups was evident on visual examination. These pores were absent when vacuum was applied. This confirms the results of several studies that have shown significant cement porosity under non-vacuum mixing conditions, even when there is strict adherence to mixing methods. Under vacuum conditions, using the Stryker Revolution system, further small reduction in cement porosity was achieved compared with manual mixing. Both Groups 2 and 3 showed variations in porosity between specimens from the same batch (intra-batch) and between batches (inter-batch). Individual specimens also demonstrated regional variations in internal porosity. Whilst the absolute reduction in overall porosity was small between the two groups (0.7%), the results favoured mixing using a rotary power tool. In addition the Revolution device was of great benefit from an ergonomic perspective. It enabled low porosity specimens to be mixed with greater ease, homogeneity and reproducibility than with manual mixing. Using the Revolution device was operator independent and involved less effort. This is likely to be of benefit in the operating room. In current practice, staff members often do not work with the same surgical team on a repeated basis, so the surgeon is likely to get greater cement consistency with such a device. It is likely to be easier to mix cement well for less experienced members of the surgical scrub team. Whilst an experience operator may be able to produce a mix of cement with very low porosity by manual mixing, it is still likely to be higher than one mixed using a power assisted device. Also, since porosity of following is related to cement working time, greater reproducibility will aid the surgeon when timing insertion of components, provided other environmental conditions remain constant