3D printing is rapidly being adopted by manufacturers to produce orthopaedic implants. There is a risk however of structural defects which may impact mechanical integrity. There are also no established standards to guide the design of bone-facing porous structures, meaning that manufacturers may employ different approaches to this. Characterisation of these variables in final-production implants will help understanding of the impact of these on their clinical performance.

We analysed 12 unused, final-production custom-made 3D printed acetabular cups that had been produced by 6 orthopaedic manufacturers. We performed high resolution micro-CT imaging of each cup to characterise the morphometric features of the porous layers: (1) the level of porosity, (2) pore size, (3) thickness of porous struts and (4) the depth of the porous layers. We then examined the internal cup structures to identify the presence of any defects and to characterise: (1) their total number, (2) volume, (3) sphericity, (4) size and (5) location.

There was a variability between designs in the level of porosity (34% to 85%), pore size (0.74 to 1.87mm), strut thickness (0.28 to 0.65mm), and porous layer depth (0.57 to 11.51mm). One manufacturer printed different porous structures between the cup body and flanges; another manufacturer printed two differing porous regions within the cup body.

5 cups contained a median (range) of 90 (58–101) defects. The median defect volume was 5.17 (1.05–17.33) mm3. The median defect sphericity and size were 0.47 (0.19–0.65) and 0.64 (0.27–8.82) mm respectively. The defects were predominantly located adjacent to screw holes, within flanges and at the transition between the flange and main cup body; these were between 0.17 and 4.66mm from the cup surfaces.

There is a wide variability between manufacturers in the porous titanium structures they 3D print. The size, shape and location of the structural defects identified are such that there may be an increased risk of crack initiation from them, potentially leading to a fracture. Regulators, surgeons, and manufacturers should be aware of this variability in final print quality.

Introduction: This prospective study focuses on the issue of a reliable prosthesis/bone fixation and compares the clinical and radiological outcome of the cemented and uncemented version of the prosthesis.

Methods: The prosthesis ensures congruent area contact with physiological kinematics resulting from imitation of the healthy morphology of the femoral condyle and unrestricted movement of the polyethylene bearing. From 1991 to 12/2007 we performed 624 medial implantations with cement (age 51–95, mean 71 years) and 185 cementless (age 40–84, mean 65 years). Other criteria as were similar. The follow up is (1.6–17) mean 9 years and seized 93% of the cases. They are assessed according to the KSRS and analyzed radiologically (F. C. Ewald).

Results: Knee Score (pre/post) cemented 41/93, cement-less 39/95. Function Score (pre/post) cemented 56/90, cementless 59/94. ROM increased for the cemented group Flex/Ex 107°/5° to 121°/2°, for the cementless Flex/Ex 107°/4° to 124°/1°.

Loosening needing revision: 15 times (2.5%) in the cemented group and 3 times (1.7%) in the cementless group. The survival rate (endpoint revision) is at 10 years: cemented 93.7%, cementless 94.5%.

The radiological investigation showed less radiolucent lines in the cementless cases in comparison to the cemented.

Conclusion: The prosthesis gives excellent results in the cemented and cementless application. The knee and function scores show similar improvements. The loosening rate of the cementless cases is even lower despite the higher physical demands of this 6 year younger group. The cementless fixation is attractive for younger patients and is pre-eminent for the mini-invasive implantation technique.

Introduction: Unicompartmental knee Arthroplasty (UKA) is a commonly used and accepted treatment for Osteoarthritis (OA) in the medial compartment. How-ever, despite some good results¹ there is still a reluctance to use this procedure in the lateral compartment for the same indications, as the procedure is considered technically difficult, and not as successful². This study reports the clinical outcome of lateral UKAs in comparison with medial UKAs, TKAs and a normal population group using a knee score designed to highlight the shortcomings of TKA³.

Methods: 20 consecutive patients over 2 years following lateral UKA were functionally assessed. They were compared with 3 groups of 20 age and sex matched patients: those who had undergone medial UKA or TKA in the same time period, or normal controls from an upper limb clinic. Clinical function was assessed at least 2 years postoperatively, using the ‘total knee questionaire’³. This consists of 55 scaled multiple choice questions. The score is derived from the product of three scales: the importance of a specific activity, the frequency with which it is undertaken, and the ease with a patient can perform it.

Results: 90% of the patients reported that they were either satisfied or very satisfied with their lateral UKA, with 95% of the patients in the medial UKA group and 75% in the TKA group reaching this level of satisfaction. The average Composite Score for the lateral UKA group was significantly better compared with the TKA group (p < 0, 05). (Kneeling – (5,72/4,45), Gardening – (7,32/5,18), Pivoting – (7,83/6,78) and Walking with heavy bags (8,2/5,97)). The Total Composite Score was significantly better (p< 0, 05) in Patients after lateral UKA (7,14) compared to patients who underwent TKA (5,99). No statistically significant differences in the Total Composite Score was found between both the lateral & medial UKA patients taken as a single group compared with the control group.

Conclusion: Lateral Unicompartmental Knee Arthroplasty achieves superior knee function in comparison to Total Knee Arthroplasty, so is worth considering as an option in for early OA of the lateral compartment.

Radiological measurements are an essential component of the assessment of outcome following knee arthroplasty. However, plain radiographic techniques can be associated with significant projectional errors because they are a two-dimensional (2D) representation of a three-dimensional (3D) structure. Angles that are considered within the target zone on one film may be outside that zone on other films. Moreover, these parameters can be subject to significant inter-observer differences when measured. The aim of our study therefore was to quantify the variability between observers evaluating plain radiographs following Unicompartmental knee arthroplasty.

Twenty-three observers, made up of Orthopaedic Consultants and trainees, were asked to measure the coronal and sagittal alignment of the tibial and femoral components from the post-operative long-leg plain radiograph of a Unicompartmental knee arthroplasty. A post-operative CT scan using the low dose Imperial knee protocol was obtained as well and analysed with 3D reconstruction software to measure the true values of these parameters. The accuracy and spread of the pain radiographic measurements were then compared with the values obtained on the CT.

On the femoral side, the mean angle in coronal alignment was 1.5° varus (Range 3.8, SD 1, min 0.1, max 3.9), whereas the mean angle in sagittal alignment was 8.6° of flexion (Range 7.5, SD 1.5, Min 3.7, Max 11.2). The true values measured with CT were 2.4° and 11.0° respectively. As for the tibial component, the mean coronal alignment angle was 89.7° (Range 11.6, SD 3.3, Min 83.8, Max 95.4), and the mean posterior slope was 2.4° (Range 8.7, SD 1.6, Min -2, Max 6.7). The CT values for these were 87.6° and 2.7° respectively.

We conclude that the plain radiographic measurements had a large scatter evidenced by the wide ranges in the values obtained by the different observers. If only the means are compared, the plain radiographic values were comparable with the true values obtained with CT (that is; accuracy was good) with differences ranging from 0.3° to 2.4°. The lack of precision can be avoided with the use of CT, particularly with the advent of low-dose scanning protocols.

Introduction: Complications following hip resurfacing (HR) occur primarily because of the surgeon’s inability to achieve optimal implant positioning, and the significant learning curve associated with this demanding procedure. Our study sought to look at the impact of navigation technologies on this learning curve.

Materials and Methods: Twenty medical students doing their BSc project took part in the study. Four types of synthetic femurs were used for the study viz., Normal anatomy (11students), Osteoarthritis (5), Coxa Vara and Coxa Valga(2). Each student was allowed to insert the guide wire according to their judgement in the femoral head using 3 systems:

Conventional instrumentation,

This achieved angle was then compared with the angle originally planned for each bone in all three groups using digitizing arm.

Results: The range of error using the conventional method to insert a guide wire was 23deg (range −9 to 14, SD= 6.3), using the CT plan method, it was 22 deg (range −9 to 13, SD=6.6). Using the Navigation method it was 7 deg (range −5 to 2, SD=2.). Students who progressed from conventional through planning to navigation (group 1) were no more accurate than students who went straight to navigation without ever having used conventional instrumentation (group 3). Students produced similar accuracy even in their maiden attempt, on difficult anatomy when provided with navigation technology.

Discussion & Conclusion: This study has shown that motivated and enthusiastic students can achieve an expert level of accuracy very rapidly when provided with the appropriate level of technology. he development of surgeons who are able to deliver excellent outcomes depends more on technology than training.

A Prospective, randomised controlled trial demonstrates superior outcomes using an active constraint robot compared with conventional surgical technique in unicompartmental knee arthroplasty (UKA). Computer assistance should extinguish outliers in arthroplasty, with robotic systems being able to execute the preoperative plan with millimetre precision.

We used the Acrobot system to deliver tailor made surgery for each individual patient. A total of 27 patients (28 knees) awaiting unicompartmental knee arthroplasty were randomly assigned to have the operation performed either with the assistance of the Acrobot or conventionally. CT scans were obtained with coarse slices through hips and ankles and fine slices through the knee joint. Preoperative 3D plans were made and transferred to the Acrobot system in theatre, or printed out as a conventional surgical aid. Accurate co-registration was confirmed, prior to the surfaces of the femur and tibia being milled. The outcome parameters included measurements of the American Knee Society (AKS) score and Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index. These measurements were performed pre-operatively and at six, 18 weeks, and 18 months post-operatively. After 18 months two UKA out of the conventional trial (n =15) had been revised into a total knee replacement (TKA), whereas there were no revisions in the Acrobot trial group (n = 13).

Using an active constrained robot to assist the surgeon was significantly more accurate than the conventional surgical technique. This study has shown a direct correlation between accuracy and improvement in knee scores at 6, 18 weeks and 18 months after surgery. At 18 months there continues to be a significant improvement in the knee scores with again a marked correlation between radiological accuracy and clinical outcome with higher accuracy leading to better function based on the WOMAC and American Knee Society Score.

Whilst computer assistance enables more accurate arthroplasty to be performed, demonstrating this is difficult. The superior results of CAOS systems have not been widely appreciated because accurate determination of the position of the implants is impossible with conventional radiographs for they give very little information outside their plane of view.

We report on the use of low dose (approximately a quarter of a conventional pelvic scan), low cost CT to robustly measure and demonstrate the efficacy of computer assisted hip resurfacing. In this study we demonstrate 3 methods of using 3D CT to measure the difference between the planned and achieved positions in both conventional and navigated hip resurfacing.

The initial part of this study was performed by imaging a standard radiological, tissue equivalent phantom pelvis. The 3D surface models extracted from the CT scan were co-registered with a further scan of the same phantom. Subsequently both the femoral and acetabular components were scanned encased in a large block of ice to simulate the equivalent Hounsfield value of human tissue. The CT images of the metal components were then co-registered with their digital images provided by the implant manufactures. The accuracy of the co-registration algorithm developed here was shown to be within 0.5mm.

This technique was subsequently used to evaluate the accuracy of component placement in our patients who were all pre-operatively CT scanned. Their surgery was digitally planned by first defining the anterior pelvic plane (APP), which is then used as the frame of reference to accurately position and size the wire frame models of the implant. This plan greatly aids the surgeon in both groups and in the computer assisted arm the Acrobot Wayfinder uses this pre-operative plan to guide the surgeon.

Following surgery all patients, in both groups were further CT scanned to evaluate the achieved accuracy. This post-operative CT scan is co-registered to the pre-operative CT based plan. The difference between the planned and achieved implant positions is accurately computed in all three planes, giving 3 angular and 3 translational numerical values for each component.

Further analysis of the CT generated results is used to measure the implant intersection volume between the pre-operatively planned and achieved positions. This gives a single numerical value of placement error for each component. These 3D CT datasets have also been used to quantify the volume of bone resected in both groups of patients comparing the simulated resection of the planned position of the implant to that measured on the post-operative CT.

This study uses 3D CT as a surrogate outcome measure to demonstrate the efficacy of CAOS systems.

Complications following hip resurfacing occur primarily because of the surgeon’s inability to achieve optimal implant positioning, and the significant learning curve associated with it. Our study sought to look at the impact of navigation technologies on this learning curve.

Twenty medical students doing their BSc project took part in the study. Four types of synthetic femurs were used for the study viz., Normal anatomy (11students), Osteoarthritis (5), Coxa Vara(2) and Coxa Valga(2). Each student was allowed to insert the guide wire according to their judgement in the femoral head using 3 systems: Conventional instrumentation, 3D plan based on a CT scan of the particular bone, helped by a conventional jig and Navigation system.

This achieved angle was then compared with the angle originally planned for each bone in all three groups using digitizing arm.

The range of error using the conventional method to insert a guide wire was 23deg (range −9 to 14, SD= 6.3), using the CT plan method, it was 22 deg (range −9 to 13, SD=6.6). Using the Navigation method it was 7 deg (range −5 to 2, SD=2.). Students who progressed from conventional through planning to navigation (group 1) were no more accurate than students who went straight to navigation without ever having used conventional instrumentation (group 3). Students produced similar accuracy even in their maiden attempt, on difficult anatomy when provided with navigation technology.

This study has shown that motivated and enthusiastic students can achieve an expert level of accuracy very rapidly when provided with the appropriate level of technology. he development of surgeons who are able to deliver excellent outcomes depends more on technology than training.