Aims

The aims of this study were: 1) to describe extended restricted kinematic alignment (E-rKA), a novel alignment strategy during robotic-assisted total knee arthroplasty (RA-TKA); 2) to compare residual medial compartment tightness following virtual surgical planning during RA-TKA using mechanical alignment (MA) and E-rKA, in the same set of osteoarthritic varus knees; 3) to assess the requirement of soft-tissue releases during RA-TKA using E-rKA; and 4) to compare the accuracy of surgical plan execution between knees managed with adjustments in component positioning alone, and those which require additional soft-tissue releases.

Currently implemented accuracy metrics in open-source libraries for segmentation by supervised machine learning are typically one-dimensional scores [1]. While extremely relevant to evaluate applicability in clinics, anatomical location of segmentation errors is often neglected.

This study aims to include the three-dimensional (3D) spatial information in the development of a novel framework for segmentation accuracy evaluation and comparison between different methods.

Predicted and ground truth (manually segmented) segmentation masks are meshed into 3D surfaces. A template mesh of the same anatomical structure is then registered to all ground truth 3D surfaces. This ensures all surface points on the ground truth meshes to be in the same anatomically homologous order. Next, point-wise surface deviations between the registered ground truth mesh and the meshed segmentation prediction are calculated and allow for color plotting of point-wise descriptive statistics. Statistical parametric mapping includes point-wise false discovery rate (FDR) adjusted p-values (also referred to as q-values).

The framework reads volumetric image data containing the segmentation masks of both ground truth and segmentation prediction. 3D color plots containing descriptive statistics (mean absolute value, maximal value,…) on point-wise segmentation errors are rendered. As an example, we compared segmentation results of nnUNet [2], UNet++ [3] and UNETR [4] by visualizing the mean absolute error (surface deviation from ground truth) as a color plot on the 3D model of bone and cartilage of the mean distal femur.

A novel framework to evaluate segmentation accuracy is presented. Output includes anatomical information on the segmentation errors, as well as point-wise comparative statistics on different segmentation algorithms. Clearly, this allows for a better informed decision-making process when selecting the best algorithm for a specific clinical application.

Aims

The aim of this study was to establish a reliable method for producing 3D reconstruction of sonographic callus.

Aims

The morphology of medial malleolar fracture is highly variable and difficult to characterize without 3D reconstruction. There is also no universally accepeted classification system. Thus, we aimed to characterize fracture patterns of the medial malleolus and propose a classification scheme based on 3D CT reconstruction.

Aims. Tibial plateau fractures (TPFs) are complex injuries around the knee caused by high- or low-energy trauma. In the present study, we aimed to define the distribution and frequency of TPF lines using a 3D mapping technique and analyze the rationalization of divisions employed by frequently used classifications. Methods. In total, 759 adult patients with 766 affected knees were retrospectively reviewed. The TPF fragments on CT were multiplanar reconstructed, and virtually reduced to match a 3D model of the proximal tibia. 3D heat mapping was subsequently created by graphically superimposing all fracture lines onto a tibia template. Results. The cohort included 405 (53.4%) cases with left knee injuries, 347 (45.7%) cases with right knee injuries, and seven (0.9%) cases with bilateral injuries. On mapping, the hot zones of the fracture lines were mainly concentrated around the anterior cruciate ligament insertion, posterior cruciate ligament insertion, and the inner part of the lateral condyle that extended to the junctional zone between Gerdy’s tubercle and the tibial tubercle. Moreover, the cold zones were scattered in the posteromedial fragment, superior tibiofibular syndesmosis, Gerdy’s tubercle, and tibial tubercle. TPFs with different Orthopaedic Trauma Association/AO Foundation (OTA/AO) subtypes showed peculiar characteristics. Conclusion. TPFs occurred more frequently in the lateral and intermedial column than in the medial column. Fracture lines of tibial plateau occur frequently in the transition zone with marked changes in cortical thickness. According to 3D mapping, the four-column and nine-segment classification had a high degree of matching as compared to the frequently used classifications. Cite this article: Bone Joint Res 2020;9(6):258–267

Aims

We sought to determine whether cobalt-chromium alloy (CoCr) femoral stem tapers (trunnions) wear more than titanium (Ti) alloy stem tapers (trunnions) when used in a large diameter (LD) metal-on-metal (MoM) hip arthroplasty system.

It is nowadays widely recognized that patient satisfaction following knee arthroplasty strongly depends on ligament balancing. To obtain this balancing, the occurring ligament strain is assumed to play a crucial role. To measure this strain, a method is described in this paper that allows full field 3D evaluation of the strains. The latter is preferred over traditional measurement techniques, e.g. displacement transducers or strain gauges, as human soft tissue is not expected to deform uniformly due to its highly inhomogeneous and anisotropic properties.

To facilitate full field strain measurements, the 3D digital image correlation (DIC) technique was adopted. This technique was previously validated by our research group on human tissue. First, a high contrast speckle pattern was applied on the sMCL. Therefore, the specimens are first coated with a small layer of methylene blue. Following, a random white speckle pattern is applied. During knee flexion, two cameras simultaneously take pictures of the deforming region at predefined flexion angles. Using dedicated software, the captured images are eventually combined and result in 3D full field strains and displacements.

Using this method, the strain distribution was studied in six cadaveric knees during flexion extension movement. Therefore, the femur was rigidly fixed in a custom test rig. The tibia was left unconstrained, allowing the six degrees of freedom in the knee. A load was applied to all major muscles in physiological directions of each muscle by attaching a series of calibrated weights (Farahmand et al., J Orthop Res., 1998;16(1)). The direction of the pulling cables was controlled using a digital inclinometer for each specimen. As a result, a statically balanced muscle loading of the knee was obtained.

From these cadaveric experiments, it is observed that on average the sMCL behaves isometrically between 0° and 90° of flexion. However, high regional differences in strain distribution are observed from the full field measurements. The proximal region of the sMCL experiences relatively high strains upon flexion. These strains are positive (tension) in the anterior part and negative (compression) in the posterior region. In contrast, the distal region remains approximately isometric upon knee flexion (see Figure 1).

It is accordingly concluded that the sMCL behaves isometric, though large regional differences are observed. The proximal region experiences higher strains. Furthermore, the DIC technique provided valuable insights in the deformation of the sMCL. This technique will therefore be applied to study the impact of knee arthroplasty in the near future.

Caption with figure 1: Full field strain distribution in the sMCL's longitudinal direction for specimen in 45° (a) and 90° (b) of knee flexion

Anterior positioning of a cephomedullary nail in the distal femur occurs in up to 88% of cases. This is considered to occur because of a mismatch between the radius of curvature of the femur and that of available implants. The hypothesis for this study was that the relative thicknesses of the cortices of the femur (referenced off the linea aspera) change with age and determine the final position of intramedullary implants.

This study used the data from CT scans undertaken as part of routine clinical practice in 919 patients with intact left femora (median age 66 years, 484 male and 435 female). The linea aspera and transverse intervals were plotted on a template femur between 25% – 60% femoral bone length (5% increments) and mapped automatically to all individual femora in the database with measurements taken in the plane of the linea aspera.

The linea aspera was found to be internally rotated as compared to the sagittal plane referenced off the posterior femoral condyles. An age related change in the posterior/anterior cortical thickness ratio was demonstrated. The >80 year old cohort shows a significantly disproportional posterior/anterior ratio increase of 70.0% from 25–50% bone length as compared to 48.1% for the <40 year old cohort (p<0.05).

This study has shown that assessment in the sagittal plane may be inaccurate because of rotational changes in the linea aspera. The centering influence of the corticies is lost with age with a relative thinning of the anterior cortex and thickening of the posterior cortex moving distally in the femur. This has a direct influence on the positioning of intramedullary implants explaining the preponderance of anterior malpositioning of intramedullary implants in the elderly.

Summary Statement. Prophylactic vertebroplasty treatment of ‘at-risk’ vertebrae may reduce fracture risk, however which areas weaken, thus providing surgical targets? Direct spatial 3D mapping of ReTm overcomes the constraints of 2D histology, and by application may provide insight into specific regional atrophy. Introduction. Insidious bone loss with age makes the skeleton fracture-prone in the rapidly expanding elderly population. Diagnosis of osteoporosis is often made after irreversible damage has occurred. There are over 300,000 new fragility fractures annually in the UK, more than 120,000 of these being vertebral compression fractures (VCF). Some VCFs cause life-altering pain, requiring surgical intervention. Vertebroplasty is a minimally invasive procedure whereby bone cement is injected into the damaged vertebral body with the aim of stabilisation and pain alleviation. However, vertebroplasty can alter the biomechanics of the spine, apparently leaving adjacent vertebrae with an increased VCF risk. Prophylactic augmentation of intact, though ‘at-risk’, vertebrae may reduce the risk of adverse effects. The question therefore arises as to which areas of a non-fractured vertebral body, structurally weakened with age, and thus should be targeted. Frequent reports of an overlap in BMD (bone mineral density) between fracture and non-fracture subjects suggest the combination of bone quantity and its ‘quality’ (microarchitectural strength) may be a more reliable fracture predictor than BMD alone. Providing a reliable method of cancellous connectivity measurement (a highly significant bone strength factor) is challenging. Traditional histological methods for microarchitectural interconnection are limited as they usually indirectly extrapolate 3D structure from thin (8 µm) 2D undecalcified sections. To address this difficulty, Aaron et al (2000) developed a novel, thick (300 µm) slicing and superficial staining procedure, whereby unstained real (not stained planar artifactual) trabecular termini (ReTm) are identified directly within their 3D context. The aim of this study was to automate a method of identifying trabecular regions of weakness in vertebral bodies from ageing spines. Patients and methods. 27 Embalmed cadaveric vertebral bodies (T10-L3) from 5 women (93.2±8.6 years) and 3 men (90±4.4 years) were scanned by µCT (micro-computerised tomography; µCT80, Scanco Medical, Switzerland, 74 µm voxel size), before plastic-embedding, slicing (300µm thick), and surface-staining with the von Kossa (2% silver nitrate) stain. The ReTm were mapped using light microscopy, recording their coordinates using the integrated stage, mapping them within nine defined sectors to demonstrate any apparent loci of structural disconnectivity that may cause weakness disproportionate to the bone loss. A transparent 3D envelope corresponding to the cortex, was constructed using code developed in-house (Matlab 7.3, Mathworks, USA), and was modulated and validated by overlay of the previous µCT scan and the coordinate data. Results. The ReTm distribution was found to be remarkably heterogeneous (p<0.05) and independent of the bone volume (p<0.05). For example, there was preliminary evidence of central endplate disconnection predominantly in the selected preparations. Discussion/Conclusion. Such automated spatial mapping of the ReTm within a 3D framework overcomes the constraints of 2D histology. By application of this new automated method, patterns of trabecular disconnection in the spine may now provide insight into specific regional atrophy, perhaps explaining why some vertebrae fracture while others with the same BMD do not, and indicating better targets for prophylactic vertebroplasty

The June 2014 Children’s orthopaedics Roundup³⁶⁰ looks at: plaster wedging in paediatric forearm fractures; the medial approach for DDH; Ponseti – but not as he knew it?; Salter osteotomy more accurate than Pemberton in DDH; is the open paediatric fracture an emergency?; bang up-to-date with femoral external fixation; indomethacin, heterotopic ossification and cerebral palsy hips; lengthening nails for congenital femoral deformities, and is MRI the answer to imaging of the physis?

The June 2013 Shoulder & Elbow Roundup³⁶⁰ looks at: whether suture anchors are still the gold standard; infection and revision elbow arthroplasty; the variable success of elbow replacements; sliding knots; neurologic cuff pain and the suprascapular nerve; lies, damn lies and statistics; osteoarthritis; and one- or two-stage treatment for the infected shoulder revision.

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal articulating surface wear has focussed attention on the trunnion / taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in form and surface finish of the head taper as well as quantitative assessment of wear volume. This study aimed to assess and compare qualitatively tapers from small and large diameter MOMTHR's. Tapers from 3 retrieval groups were analysed. Group 1: 28mm CoCr heads from MOMTHRs (n=5); Group 2: Large diameter CoCr heads from LHMOMTHRs (n=5); Gp 3 (control): 28mm heads from metal on polyethylene (MOP) THRs; n=3). Clinical data on the retrievals was collated. RedLux profiling of tapers produced a taper angle and 3D surface maps. The taper angles were compared to those obtained using CMM measurements. There was no difference between groups in mean 12/14 taper angles or bearing surface volumetric and linear wear. Only LHMOMs showed transfer of pattern from stem trunnion to head taper, with clear demarcation of contact and damaged areas.3D surface mapping demonstrated wear patterns compatible with motion or deformations between taper and trunnion in the LHMOM group. These appearances were not seen in tapers from small diameter MOM and MOP THRs. Differences in appearance of the taper surface between poorly functioning LHMOMTHRs and well functioning MOP or MOM small diameter devices highlight an area of concern and potential contributor to the mode of early failure

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal wear at the articulating surfaces has focussed attention on the trunnion / taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in the form and surface finish of the head taper as well as a quantitative assessment of wear volume. This study aimed to assess and compare qualitatively the tapers from well functioning small diameter, with poorly functioning LHMOMTHR's using the above technique. Method. 3 groups of retrieval tapers were analysed (Group 1: 28 mm CoCr heads from well functioning MOMTHRs (n=5); Group 2: Large diameter CoCr heads from LHMOMTHRs revised for failure secondary to adverse reaction to metal debris (n=5); Gp 3 (control): 28 mm heads from well functioning metal on Polyethylene (MOP) THRs; n=3). Clinical data on the retrievals was collated. The Redlux profiling of modular head tapers involves a non direct method whereby an imprint of the inside surface of a modular head is taken, and this is subsequently scanned by an optical non contact sensor using dedicated equipment [1]. The wear was also measured on the bearing surface [1]. RedLux profiling of the tapers produced a taper angle and 3D surface maps. The taper angles obtained with the Redlux method were compared to those obtained using CMM measurement on 3 parts. The Redlux profiling, including imprints, was also repeated 3 times to gauge potential errors. Results. There was no difference in mean 12/14 taper angles between groups. There was no difference in volumetric and linear wear at the bearing surface between groups. Only the LHMOMs showed transfer of pattern from the stem to the internal head taper, with clear demarcation of the contact and damaged area between head taper and stem trunnion (see figure 1 – interpretation of head taper surface features demonstrated using Redlux optical imaging). 3D surface mapping demonstrated wear patterns compatible with motion or deformations between taper and trunnion in the LHMOM group. These appearances were not seen in tapers from small diameter MOM and MOP THRs (see Figure 2). Discussion. Differences in appearance of the taper surface between poorly functioning LHMOMTHRs and well functioning MOP or MOM small diameter devices highlight an area of concern and potential contributor to the mode of early failure. Further work is required to fully qualify the Redlux method capabilities, and to understand the origin of the damage seen on those tapers, and the possible partial contribution of damage caused during retrieval

The poor outcome of large head metal on metal total hip replacements (LHMOMTHR) in the absence of abnormal wear at the articulating surfaces has focussed attention on the trunnion/taper interface. The RedLux ultra-precision 3D form profiler provides a novel indirect optical method to detect small changes in form and surface finish of the head taper as well as a quantitative assessment of wear volume. This study aimed to assess and compare qualitatively the tapers from small diameter with LHMOMTHR's. 3 groups of retrieval tapers were analysed (Group 1: 28mm CoCr heads from MOMTHRs (n=5); Group 2: Large diameter CoCr heads from LHMOMTHRs (n=5); Group 3: 28mm heads from metal on polyethylene (MOP) THRs; n=3). Clinical data on the retrievals was collated. Both bearing surfaces and head tapers were measured for wear using the Redlux profiling non contact measurement system. Measurements included taper angle and 3D surface maps. Taper angles obtained with the Redlux method were compared to those obtained using CMM measurement on 3 parts. The Redlux profiling, including imprints, was also repeated 3 times to gauge potential errors. There was no difference in mean 12/14 taper angles between groups. There was no difference in volumetric and linear wear at the bearing surface between groups. Only the LHMOMs showed transfer of pattern from the stem to the internal head taper, with clear demarcation of the contact and damaged area between head taper and stem trunnion. 3D surface mapping demonstrated wear patterns compatible with motion or deformations between taper and trunnion in the LHMOM group alone. Discussion: Differences in appearance of the taper surface between LHMOMTHRs and MOP or MOM small diameter devices highlight an area of concern and potential contributor to the mode of early failure. Further work is required to fully qualify the Redlux method capabilities

Introduction. The exact action of the Peroneus Longus muscle on the foot is not fully understood. It is involved in a number of pathological processes like tendonitis, tenosynovitis, chronic rupture and neurological conditions. It is described as having a consistent insertion to the base of the first metatarsal, but there have also been reports of significant variations and additional slips. Our aim was to further clarify the anatomy of the main insertion of the Peroneus Longus tendon and to describe the site and frequency of other variable insertion slips. Methods and Materials. The course of the distal peroneus longus tendon and its variable insertion was dissected in 12 embalmed, cadaveric specimens. The surface area of the main insertion footprint and angle of insertion was measured using an Immersion Digital Microscribe and 3D mapping software. The site and frequency of the other insertion slips is also presented. Results. There was a consistent, main insertion to the infero-lateral aspect of the first metatarsal in all specimens. The only additional slip was to the medial cuneiform. This did not increase the total footprint. Discussion. The main footprint of the Peroneus Longus tendon is on the first metatarsal. There was an additional slip to the medial cuneiform in 33% of our specimens. Although we are unsure about the significance of this additional slip, we hope it will lead to a better understanding of the mechanism of action of this muscle and its role both in the normal and pathological foot

Peroneal tendon subluxation although rare, is a commonly misdiagnosed cause of lateral ankle pain and instability. The orientation and depth of the lateral retromalleolar groove is a major contributor to peroneal stability, but is little understood. We attempt to quantify the groove using three directional mapping techniques.

Eight age and sex matched embalmed cadaveric feet were dissected to expose the peroneal tendons and the retromalleolar groove. A hand held digitiser was used to map the version and inclination of the groove in a 3D virtual environment. The length and depth of the groove and its orientation were calculated using the cartilage boundary and the centroid of the curved surface.

Four male and four female specimens (mean age 80 Yrs) were studied. The groove was noted to be concave in 62%, flat in 25 % and concave in 12.5 %. Flatter groove were more commonly noted in (2/4) females. There was a significant difference in length and width of the groove between male and female feet. The mean length of the groove in male specimens was 6.2cm (5.4–6.7cm), and in female specimens 5.5cm (4.4–5.9cm). The mean width in males was 5.3mm (5.0–6.1mm) and in females 4.5mm (3.7–5.3mm). There was no significant difference noted in the depth of the groove between male and female feet. The mean depth in males was 2.3mm (0.8–3.1) and in female 2.2mm (0–2.4mm).

Knowledge of peroneal groove geometry in treatment of peroneal tendon instability is important. There appears to be a consistent difference in the anatomy of the groove between the sexes. Although men have longer and wider grooves than woman, the depth is the same in both sexes.

The exact action of the Peroneus Longus muscle on the foot is not fully understood. It is involved in a number of pathological processes like tendonitis, tenosynovitis, chronic rupture and neurological conditions. It is described as having a consistent insertion to the base of the first metatarsal, but there have also been reports of significant variations and additional slips. Our aim was to further clarify the anatomy of the main insertion of the Peroneus Longus tendon and to describe the site and frequency of other variable insertion slips. The course of the distal peroneus longus tendon and its variable insertion was dissected in 20 embalmed, cadaveric specimens. The surface area of the main insertion footprint was measured using an Immersion Digital Microscibe and 3D mapping software. The site and frequency of the other variable insertion slips is presented. There was a consistent, main insertion to the infero-lateral aspect of the first metatarsal in all specimens. The surface area of this insertion was found to be proportional to the length of the foot. The insertion in males was found to be significantly larger than females. The most frequent additional slip was to the medial cuneiform. Other less frequent insertion slips were present to the lesser metatarsals. The main footprint of the Peroneus Longus tendon is on the first metatarsal. There appears to an additional slip to the medial cuneiform frequently. Although we are unsure about the significance of these additional slips, we hope it will lead to a better understanding of the mechanism of action of this muscle and its role both in the normal and pathological foot

Background. Talar neck fractures occur infrequently and are associated with high complication rates. Anatomical restoration of articular congruity is important. Adequate exposure and stable internal fixation of these fractures are challenging. Aims. We investigate the use of an anterior extensile approach for exposure of these fractures and their fixation by screws introduced through the talo-navicular articulation. We also compare the quality and quantity of exposure of the talar neck obtained by this approach with the commonly described combined medial/lateral approaches. Materials and Methods. An anterior approach to the talus between the tibialis anterior and the extensor hallucis longus tendons protecting both the superficial and deep peroneal nerves was performed on 5 fresh frozen cadaveric ankles . The surface area of talar neck accessible was measured using an Immersion Digital Microscibe and analysed with Rhinoceros 3D graphics package. Standard antero-medial and antero –lateral approaches were also carried out on the same ankles, and similar measurements taken. Seven patients with talar neck fractures (4 Hawkins Type II and 3 Hawkins Type III) who underwent operative fixation using this approach with parallel cannulated screws through the talo-navicular joint were followed and the clinical radiological outcomes were recorded. Results. 3D mapping demonstrated that talar surface area visible by the anterior approach (mean 1200sqmm) is consistently superior to that visible by either the medial or lateral approaches in isolation or in combination (mean medial 350sqmm, mean lateral 600sqmm). Medial malleolar osteotomy does not offer any additional visualisation of the talar neck. 3D reconstruction of the area visualised by the three approaches confirms that the anterior approach provides superior access to the entirety of the talar neck. 5 male and 2 female patients (mean age -) were reviewed at a mean follow up period of 6 months. All had anatomical articular restoration, and no wound problems. None developed non or AVN. There were no symptoms referable to the talo-navicular joints which showed no evidence of any secondary changes on the radiographs. Discussion. The anterior extensile approach offers superior visualisation of the talar neck in comparison to other approaches for anatomical articular restoration. Surgical morbidity with this approach is low, and introduction of screws through the talo-navicular joint allows stable fixation of talar neck fractures along the axis of the bone. We argue that this approach is safe, adequate and has the potential to cause least vascular disruption

Talar neck fractures are associated with high complication rates with significant associated morbidity. Adequate exposure and stable internal fixation remains challenging. We investigated the anterior extensile approach for exposure of these fractures and their fixation by screws introduced through the talo-navicular articulation. We also compared the quality and quantity of exposure of the talar neck obtained by this approach, with the classically described medial/lateral approaches. An anterior approach to the talus between the tibialis anterior and the extensor hallucis tendons protecting both the superficial and deep peroneal nerves was performed on 5 fresh frozen cadaveric ankles . The surface area of talar neck accessible was measured using an Immersion Digital Microscribe and analysed with Rhinoceros 3D graphics package. Standard antero-medial and antero –lateral approaches were also carried out on the same ankles, and similar measurements taken. Seven talar neck fractures underwent operative fixation using the anterior approach with parallel cannulated screws inserted through the talo-navicular joint. 3D mapping demonstrated that the talar surface area visible by the anterior approach (mean 1200sqmm) is consistently superior to that visible by either the medial or lateral approaches in isolation or in combination. Medial malleolar osteotomy does not offer any additional visualisation of the talar neck. 3D reconstruction of the area visualised by the three approaches confirms that the anterior approach provides superior access to the entirety of the talar neck. 5 male and 2 female patients were reviewed. All had anatomical articular restoration, and no wound problems. None developed non union or AVN. The anterior extensile approach offers superior visualisation of the talar neck in comparison to other approaches for anatomical articular restoration. We argue that this approach is safe, adequate and causes less vascular disruption

Retrieval analysis offers a direct insight into in vivo wear mechanisms. However, the 3D measurement of wear patch characteristics on spherical highly reflective bearings has been difficult. An instrument based on an optical technique has been developed over the past 3 years. It is capable of scanning metallic head and cup in a single measurement, within minutes, at a resolution of 20 nm. From the cloud of 3D points obtained during scanning (typically 35,000 To 1,000,000), a 3D image of the measured part can be obtained. The associated computer program allows for sphericity, roughness, radius and local radius to be calculated, and surface maps of the 3D model can easily be plotted. Both head and cup of two failed MoM resurfacing devices, a wear simulator test couple and intact components were analysed using the new technique. A successful McKee Farrar head (20 years in vivo) was also scanned. Results were compared with traces obtained on a Mitutoyo RA 300 roundness machine (resolution 0.01 microns). 3D maps of the bearing surfaces of MoM devices were obtained. The maximum linear wear values on heads were 2.5 microns, 99 microns 53.5 microns and 298 microns for the simulator sample, the McKee Farrar head and the two failed resurfacing devices respectively. The corresponding maximum linear wear values on cups were 11 microns, 529 microns and 645 microns for the simulator sample and the two failed resurfacing devices respectively. These results were in good agreement with results obtained on the Mitutoyo machine. Contrary to other worn samples, the two latter cups showed that the cup had worn on the edge of the bearing surface. This resulted in an oval shaped wear patch on the head. For the McKee Farrar device and the simulator device, the wear patch was away from the edge and the outline of the wear patch was circular in shape. This novel technique has allowed for high resolution 3D mapping of the full bearing surfaces on successful McKee Farrar device and on more recent resurfacing devices. Further studies are required. However, the results suggest that component positioning is paramount to wear performance of metal on metal devices