INTRODUCTION. Lumbar total disc replacement (TDR) is an alternative treatment to avoid fusion related adverse events, specifically adjacent segment disease. New generation of elastomeric non-articulating devices have been developed to more effectively replicate the shock absorption and flexural stiffness of native disc. This study reports 5 years clinical and radiographic outcomes, range of motion and position of the center of rotation after a viscoelastic TDR. Material and methods. This prospective observational cohort study included 61 consecutive patients with monosegmental TDR. We selected patients with intermediate functional activity according to Baecke score. Hybrid constructs had been excluded. Only cases with complete clinical and radiological follow-up at 3, 6, 12, 24 and 60 months were included. Mean age at the time of surgery was 42.8 +7.7 years-old (27–60) and mean BMI was 24.2 kg/m² +3.4 (18–33). TDR level was L5-S1 in 39 cases and L4-L5 in 22 cases. The clinical evaluation was based on Visual Analog Scale (VAS) for pain, Oswestry Disability Index (ODI) score, Short Form-36 (SF36) including physical component summary (PCS) and mental component summary (MCS) and General Health Questionnaire GHQ28. The radiological outcomes were range of motion and position of the center of rotation at the index and the adjacent levels and the adjacent disc height changes. Results. There was a significant improvement in VAS (3.3±2.5 versus 6.6±1.7, p<0.001), in ODI (20±17.9 versus 51.2±14.6, p<0.001), GHQ28 (52.6±15.5 versus 64.2±15.6, p<0.001), SF 36 PCS (58.8±4.8 versus 32.4±3.4, p<0.001) and SF 36 MCS(60.7±6 versus 42.3±3.4, p<0.001). Additional surgeries were performed in 5 cases. 3 additional procedures were initially planified in the surgical program: one adjacent L3-L5 ligamentoplasty above a L5S1 TDR and two L5S1 TDR cases had additional laminectomies. Fusion at the index level was secondary performed in 2 L4L5 TDR cases but the secondary posterior fusion did not bring improvement. In the 56 remaining patients none experienced facet joint pain. One patient with sacroiliac pain needed local injections. Radiological outcomes were studied on 56 cases (exclusion of 5 cases with additional surgeries). The mean location centers of the index level and adjacent discs were comparable to those previously published in asymptomatic patients. According to the definition of Ziegler, all of our cases remained grade 0 for disc height (within 25% of normal). Discussion. The silent block design of LP-ESP provides an interesting specificity. It could be the key factor that makes the difference regarding facets problems and instability reported with other implants experimentally or clinically. Unfortunately no other comparative TDR series are available yet in the literature. Conclusion. This series reports significant improvement in mid-term follow up after TDR which is consistent with previously published studies but with a lower rate of revision surgery and no adjacent level disease pathologies. The radiographic assessment of the patients demonstrated the quality of functional reconstruction of the lumbar spine after LP ESP viscoelastic disc replacement

Introduction. Total disc replacement (TDR) provides an alternative to fusion that is designed to preserve motion at the treated level and restore disc height. The effects of TDR on spine biomechanics at the treated and adjacent levels are not fully understood. Thus, the present study investigated facet changes in contact pressure, peak contact pressure, force, peak force, and contact area at the facet joints after TDR. Methods. Seven fresh-frozen human cadaveric lumbar spines were potted at T12 and L5 and installed in a 6-DOF displacement-controlled testing system. Displacements of 15° flexion/extension, 10° right/left bending, and 10° right/left axial rotation were applied. Contact pressure, peak contact pressure, force, peak force and contact area for each facet joint were recorded at L2-L3 and L3-L4 before and after TDR at L3-L4 (ProDisc-L, Synthes Spine). The data were analysed with ANOVAs/t-tests. Results. Axial rotation had the most impact on contact pressure, peak contact pressure, force, peak force, and contact area in intact spines. During lateral bending and axial rotation, TDR resulted in a significant increase in facet forces at the level of treatment and a decrease in contact pressure, peak contact pressure, and peak force at the level superior to the TDR. With flexion/extension, there was a decrease in peak contact pressure and peak contact force at the superior level. Conclusion. Our study demonstrates that rotation is the most demanding motion for the spine. We also found an increase in facet forces at the treated level after TDR. To our knowledge, we are the first to show a decrease in several biomechanical parameters after TDR at the adjacent superior level in a cadaveric model. In general, our findings suggest there is an increase in loading of the facet joints at the level of disc implantation and an overall unloading effect at the level above

The emerging of non-fusion surgery is aimed to solve the long-term complication of fusion surgery that may bring the adjacent disc degeneration. Among several kinds of artificial discs developed in these years, the majority in the market is Prodisc-L (Synthes Inc.) which is designed with the purpose to restore the motions including anteroposterior translation, lateral bending, and axial rotation. These is also one artificial disc called Physio-L (Nexgen Spine) which were hyper-elastic material (Polycarbonate Polyurethanes) and is designed to restore the motions maintioned above plus axial loading. The concept of using hyper-elastic material as disc is to mimic the material properties of intervetebral discs so that this disc both absorb the axial loading and also restore the physiological range of motion. Few studies focused on the biomechanical behavior of hyper-elastic artificial discs have yet been reported. Therefore, the purpose of this study is to compare the biomechanical behavior between Prodisc-L and Physio-L. A validated three-dimensional finite element model of the L1-L5 lumbar intact spine was used in this study with ANSYS software [Fig.1]. Total disc replacement surgery, partial discectomy, total nuclectomy and removal of the anterior longitudinal ligament were performed at the L3/L4 segment of this intact model, and the Prodisc-L and Physio-L was implanted into L3/L4 segment, respectively. In addition, hyper-elastic materials adopted by Physio-L are usually categorized by their hardness into soft and hard [Fig.2]. Therefore, two kinds of Physio-L were studied. A 400 N follower load and a 10 N-m moment were applied to the intact model to obtain four physiological motions as comparison baseline. The implanted models were subjected to 400 N follower load and specific moments in accordance with the hybrid test method. For the Prodisc-L model in the surgical segment, the range of motion (ROM) varied by -26%, +17%, -0.01%, and -0.04% in flexion, extension, lateral bending, and axial rotation, respectively, as compared to intact model [Fig.3]. For the Physio-L (soft) model, ROM varied by +10%, +8%, +3%, and +19% in four physiological motions, respectively. For the physio-L (hard) model, ROM varied by +1%, +8%, +1%, and +11% in four physiological motions, respectively. For the Prodisc-L model in the adjacent segments, ROM varied by +4% ∼ +10%, -2% ∼ -5%, -1% ∼ -4%, and +1% ∼ -2% in four physiological motions, respectively. For the Physio-L (soft) model, ROM varied by 0% ∼ -5%, -2% ∼ -5%, -0% ∼ -5%, and -9% ∼ -11% in four physiological motions, respectively. For the physio-L (hard) model, ROM varied by +4% ∼ -2%, +8% ∼ -5%, +1 ∼ -5%, and +11% ∼ -6% in four physiological motions, respectively. As seemed in the simulation, the behavior of Physio-L (both soft and hard) is similar to that of intact model under flexion and extension, but not in axial rotation. In addition, Physio-L (hard) model is more similar to intact model as compared to Physio-L (soft) model

Total disc replacement (TDR) is the gold standard for lumbar degenerative disc disease in selected patient groups. Traditional TDR designs benefit from a wealth of literature and use a polyethylene inlay pseudo-disc between two metal endplates. There is scarce literature for novel monomodular implants that form an artificial construct of woven annulus and central nucleus, providing physiological motion preservation. The aim was to compare the evolving changes to radiological position between monomodular and traditional implants and assess the relationship of migration with bone densitometry. This retrospective series of consecutive patients undergoing TDR under a single surgeon recorded demographics, co-morbidities, previous surgery and clinical outcomes. Measurements of endplate subsidence, lordosis and spondylolisthesis taken from weight-bearing erect x-rays at 0, 3, 6 and 12 months. Radiological outcomes were compared against CT bone densitometry. 33 monomodular and 13 traditional implants. Mean age 40 years. All patients had degenerative disc disease. Monomodular and traditional implants were as likely to develop lordosis (p=0.32), endplate subsidence (p=0.78) or spondylolisthesis (p=0.98). Comparison between endplate subsidence and low bone densitometry were insignificant (p=0.47). Developing lordosis in the monomodular implant was related to low bone density; mean 134vs.184mg/cm. 3. (p=0.018). Three monomodular implants developed a posterior hinge after migrating into lordosis. One traditional implant dislocated, requiring emergency fusion. Radiological outcomes are comparable between traditional and monomodular implants. The larger endplate-footprint of the monomodular implant did reduce subsidence. Monomodular implants pivoting on a posterior hinge may fail early. Bone densitometry may identify patients who will drift into lordosis

Introduction. The majority of spine patients present with discogenic low back pain, originating from either degenerative disc disease (DDD) or internal disc disruption (IDD). Successful treatment of this patient population relies on obtaining precision diagnosis and careful patient selection, as well as matching the pathology with reliable technology. Total disc replacement (TDR), as an alternative to spinal fusion in the treatment of DDD or IDD, has been studied and reported for several decades in long-term follow-up studies and in several randomized control trials. This prospective study presents a single surgeon experience with two-level CHARITÉ® TDR in 84 consecutive patients, with minimum follow-up of 5 years. The aims of the study were to assess the clinical outcomes of two-level TDR in patients with DDD/IDD. Based on the literature review conducted, this study is considered the largest single surgeon series experience with the two-level CHARITÉ® TDR in the treatment of lumbar DDD, with a minimum follow-up of 5 years reported to date. Materials and Methods. Between January 1997 and March 2006, n=84 consecutive patients underwent two-level TDR for the treatment of two-level DDD or IDD discogenic axial low back pain with or without radicular pain. All patients completed self-assessment outcome questionnaires pre and postoperatively (3, 6, 12 months, and yearly thereafter), including Oswestry Disability Index (ODI), Roland-Morris Disability Questionnaire (RMDQ) and Visual Analogue Score (VAS) for back and leg pain. Results. For the n=84 patients, the mean follow-up was 94.34±2.19 months (range = 62–150). The mean age was 49.6±0.94. The mean surgical time was 91±3.16 minutes and the mean blood loss was 207.5±30.62 mls. The main diagnosis was two-level DDD in 63 (76.8%) patients, followed by one-level disc herniation and one-level DDD. Seventy-three (89%) patients underwent L4-5 L5-S1 TDR and 9 (11%) patients underwent L3-4 L4-5 TDR. At all follow-up points, patients demonstrated significant improvement in ODI, RMDQ, and VAS back and leg pain scores compared to pre-operative scores (p < 0.001). The mean improvement between pre-op and last follow-up was 33.3 (66.8%) and 13.23 (74%) for ODI and RMDQ, respectively. Similarly, that was 54.8 (69 %%) and 34.8 (65%) for VAS back and VAS leg pain, respectively. At least 87.8% of the patients rated their satisfaction as good/excellent at any follow-up point. At 5 years follow-up, 54 patients (65.9%) rated their satisfaction as excellent, 19 (23.2%) as good, 7 (8.5%) as satisfactory and 2 (2.4%) as poor. Two patients (2 out of 84, 2.38%) required early revision of one of the prostheses due to failure of indication and/or failure of technique. There has been no device failure. One patient required surgery for adjacent segment disease (1.19%). Conclusion. This study has shown that statistically significant reductions in pain and functional outcomes can be obtained in patients at a minimum follow-up of 5-years following 2-level TDR for the treatment of multilevel DDD or IDD. The clinical benefits of this procedure is supported by the data, with the outcomes reflecting a precision diagnosis, stringent patient selection criteria, and a standardised surgical technique

There is a paucity of published Canadian literature comparing lumbar total disc arthroplasty (LDA) to fusion on patient outcomes in degenerative spondylosis. The purpose of this study is to quantify and compare the long-term patient reported outcomes following LDA and matched-fusion procedures. We conducted a matched-cohort study comparing consecutive patients enrolled by CSORN who underwent standalone primary LDA or hybrid techniques for degenerative disk disease between 2015–2019. Fusion patients were included by a primary diagnosis of degenerative disk disease, chief complaint of back pain, who received a primary fusion irrespective of technique. Fusion patients were matched by number of involved levels of surgery to LDA counterparts. Outcome scores and patient satisfaction were assessed preoperatively and 2-years postoperatively. 97 patients (39-female, 58-male) underwent LDA or hybrid construct up to 4 levels. 94 patients (52-female, 42-male) underwent a lumbar fusion were selected based on inclusion criteria. 36 LDA and 57 Fusion patients underwent a 1-level surgery. 39 LDA and 25 Fusion patients underwent 2-level surgery. 18 LDA and 7 Fusion patients underwent 3-level surgery. 4 LDA and 5 Fusion patients underwent a 4-level procedure. Slight differences in average cohort age were found (LDA-43.4yrs, Fusion-49.8yrs, p<0.01). Cohort preoperative-BMI (LDA-27.0kg/m. 2. , Fusion-27.9kg/m. 2. , p=0.29) and total comorbidities (LDA-2.6, Fusion-2.1, p=0.05) demonstrated no clinically significant differences. At 2 year follow-up, no differences were found in ODI improvement (LDA-20.32pts, Fusion-17.02pts, p=0.36), numerical back-pain improvement (LDA-3.5pts, Fusion-3.06pts, p=0.40), numerical leg-pain improvement (LDA-1.67pts, Fusion-1.87pts, p=0.76), and Health Scale improvement (LDA-17.12, Fusion-10.73, p=0.20) between cohorts. Similar positive findings were found in subgroups stratified by number of surgical levels. Satisfaction rate at 2 years was 86.7% and 82.4% for LDA and Fusion patients respectively. There didn't appear to be significant differences in outcomes or satisfaction through 2 years comparing patients who underwent LDA (whether used in isolation or as part of a hybrid construct) for debilitating degenerative disk disease and isolated spinal fusion for back dominant pain

Cervical total disc replacement has been in practice for years now as a viable alternative to cervical fusion in suitable cases, aspiring to preserve spinal motion and prevent adjacent segment disease. Reports are rife that neck pain emerges as an annoying feature in the early postoperative period. The facet joint appears to be the most likely source of pain. 50 patients were prospectively followed up through 5 years after having received disc replacement surgery, indicated for symptomatic soft disc herniation of the cervical spine presenting with radiculopathy. • All were skeletally mature and aged between 22 to 50. • All had failed a minimum of 6 months conservative therapy. • Up to 2 disc levels were addressed. C3 till C7 levels. • Single surgeon (first author). • NDI > 30% (15/50). • Deteriorating radicular neurology. We excluded those with degenerative trophic changes of the cervical spine, focal instability, trauma, osteoporosis, previous cervical spine surgery, previous infection, ossifying axial skeletal disease and inflammatory spondyloarthritides. The device used was an unconstrained implant with stabilizing teeth. Over the 5 years, we studied their postoperative comfort level via the Neck Disability Index (NDI) and Visual Analogue Score (VAS). Pre-operative and post-operative analysis of the sagittal axis and of involved facet joints were done. 22 patients suffered postoperative neck pain as reflected by the NDI and VAS scores. Of these, 10 reported of neck pain even 24 months after surgery. However, none were neurologically worse and all patients returned to their pre-morbid functions and were relieved of pain by 28 months. All 22 patients reported of rapid dissolution of neckache after peri-facetal injections of steroids were done under image guidance. We draw attention to the facet joint as the pain generator, triggered by inappropriate implant height, eccentric stresses via hybrid constructs, eccentric loading due to unconstrained devices and unaddressed Luschka joint degeneration. Such factors require careful selection of patients for surgery, necessitate proper pre-operative templating and call for appropriate technical solutions during surgery

Surgical interventions for the treatment of chronic neck pain, which affects 330 million people globally, include fusion and cervical total disc replacement (CTDR). Most of the currently clinically available CTDRs designs include a metal-on-polymer (MoP) bearing. Numerous studies suggest that MoP CTDRs are associated with issues similar to those affecting other MoP joint replacement devices, including excessive wear and wear particle-related inflammation and osteolysis. A standard ISO testing protocol was employed to investigate a device with a metal-on-metal (MoM) bearing. Moreover, with findings in the literature suggesting that the testing protocol specified by ISO-18192-1 may result in overestimated wear rates, additional tests with reduced kinematics were conducted. Six MoM CTDRs made from high carbon cobalt-chromium (CoCr) were tested in a six-axis spine simulator, under the ISO-18192-1 protocol for a duration of 4 million cycles (MC), followed by 2MC of modified testing conditions, which applied the same axial force as specified in ISO-18192-1 (50-150N), but reduced ranges of motion (ROM) i.e. ±3° flexion/extension (reduced from ±7.5°) and ±2° lateral bending (reduced from ±6°) and axial rotation (reduced from ±4°). Foetal bovine serum (25% v/v), used as a lubricant, was changed every 3.3×10. 5. cycles and stored at −20°C for particle analysis. Components were measured after each 1×10. 6. cycles; surface roughness, damage modes and gravimetric wear were assessed. The wear and roughness data was presented as mean ±95% confidence interval and was analysed by one-way analysis of variance (ANOVA) (p=0.05). The mean wear rate of the MoM CTDRs tested under the ISO protocol was 0.246 ± 0.054mm. 3. /MC, with the total volume of wear of 0.977 ± 0.102mm. 3. lost over the test duration (Fig. 1). The modified testing protocol resulted in a significantly lower mean volumetric wear rate of 0.039 ± 0.015mm. 3. /MC (p=0.002), with a total wear volume of 0.078 ± 0.036mm. 3. lost over the 2MC test duration. Under both test conditions, the volumetric wear was linear; with no significant bedding-in period observed (Fig. 1). The mean pre-test surface roughness decreased from 0.019 ± 0.03µm to 0.012 ± 0.002µm (p=0.001) after 4MC of testing, however surface roughness increased to 0.015 ± 0.002µm (p=0.009) after the additional 2MC of modified test conditions. Following 4MC of testing, polishing marks, observed prior to testing, had been removed. Consistently across all components, surface discolouration and multidirectional, criss-crossing, curvilinear and circular wear tracks, caused by abrasive wear, were observed. Reduced ROMs testing caused similar types of damage, however the circular wear tracks were smaller in size, compared to those produced during testing under the ISO protocol. The wear rates exhibited by MoM CTDRs tested under ISO-18192-1 testing protocol (0.246mm. 3. /MC) were lower, when compared to CTDR designs incorporating MoP bearings, as well as MoM lumbar CTDRs. Wear rates generated under a modified ISO testing protocol were reduced tenfold, similarly to findings that have previously been reported in the literature, and support the hypothesis that the testing protocol specified by ISO-18192-1 may overestimate wear rates. Characterisation of particles generated by MoM CTDRs and biological consequences of those remain to be determined. For figures/tables, please contact authors directly.

Retrieval analysis has been valuable in the assessment of in-vivo surface damage of orthopedic devices. Historically, subjective techniques were used to grade damage on the implant's surface. Microscopy improved the ability to localize and quantify damage, but cannot measure volumetric wear due to this damage. Laser scanning provides volumetric wear, but lacks image data. Recent techniques superimpose image data on laser scan data (photorendering) and combine the strengths of both methods. Our goal is to use such methods to improve our damage assessment and potentially correlate this assessment to volumetric wear. This project focused on two areas: image-stitching and photorendering. Image-stitching registers multiple images into large-scale high-resolution composites. Six total disc replacement components were imaged with a digital microscope (Moticam 2, Motic). Three sets were taken of each component: a single template at 10x zoom (1×1), a 4-image composite at 18x zoom (2×2), and a 9-image composite at 18x zoom (3×3). The 2×2 and 3×3 sets were image-stitched to resemble their template counterpart. Measurement error was defined using common pixels identified between the composite and template images for comparison with a semi-automated feature detection algorithm (Figure 1). For photorendering, a pilot study was performed on a single retrieved tibial bearing. The component was imaged with a digital microscope (VHX-2000, Keyence) under a 3D image-stitching setting, providing a high-resolution photo embedded with height values. MATLAB was used to convert the image into a photo-rendered point cloud approximating the surfaces. The component was then laser scanned, creating a 3D point cloud with resolution 0.127 mm. The photo-rendered point cloud data was registered to the laser scan data using an iterative closest point algorithm (Geomagic Studio, Geomagic). An analysis of all composite images showed a mean error of 0.221 mm. Figure 2 compares regions of images for the template, 2×2, and 3×3 composites. Zooming in shows the effect of the increased resolution contained in the composite. The 2×2 and 3×3 composites had mean errors of 0.231 mm and 0.209 mm, respectively; these were not significantly different. Comparisons among image types showed that components with less features exhibited larger errors during image-stitching. Figure 3 shows images resulting from each step of the photorendering process. The final image of the figure shows a qualitative result of our ability to photorender the tibial bearing surface of the component. While combining microscopy and laser scan data works anecdotally, further analyses must be performed to assure the robustness of the technique. The digital microscope's embedded image-stitching software is limited in its maximum field of view; we look to extend this by taking multiple scans and using in-house software to generate a composite of a whole implant. The improved resolution provided by microscopy offer an opportunity to automate damage assessment, yielding damage mapped images which can also be overlaid on laser scan data. This may provide a means to better quantify observed damage and yield meaningful correlations with volumetric loss due to wear

Purpopse. Few Cervical Total Disc Replacement (TDR) devices are engineered to address both the Center of Balance (COB) and the Center of Rotation (COR) of the cervical motion segments. The COB is the axis in the intervertebral disc through which the axial compressive load is transmitted. TDRs placed posterior of this point tend to fall into kyphosis while devices placed anterior of this point tend to fall into lordosis. Thus from a “balancing” point of view the ideal placement would be at the COB. However, the COR position has been shown to be posterior and inferior to the disc space. It has also been shown that constrained devices tend to lose motion when there is a mismatch between device and anatomic centers. Mobile core devices may be placed at the COB since their unconstrained rotations and translations allow for the device COR to follow the anatomic COR, but they rely heavily on the facet joints and other anatomic features to resist the paradoxiacal motion. The TriLobe cervical TDR (Figure 2) was engineered for both the COB and COR. The purpose of this study was to compare the 3D kinematic and biomechanical performance of the TriLobe to a ball and trough(BT) cervical TDR in an augmented pure moment cadaveric study to find the ideal AP implant placement. Materials and methods. Specimen were CT imaged for three-dimensional reconstruction. Visual, CT, and DEXA screening was utilized to verify that specimens are free from any defects. Specimens were prepared by resecting all nonligamentous soft tissue leaving the facet joint capsules and spinal ligaments intact. C2 and T1 were potted to facilitate mounting in the testing apparatus (7-axis Spine Tester, Univ. of Utah, Salt Lake City, UT). OptoTRAK motion tracking flags were attached to each vertebra including C2/C3 and T1 to track the 3D motion of each vertebra. •. Specimens C2–T1. •. Treatment Level C5–C6. •. Insertion of fixture pins under fluoro. •. Load Control Testing to 2.5Nm in FE, LB, AR at 0.5Hz. •. 15 Pre-cycles in load control in FE / LB / AR (2.5Nm). •. Test implants in load control in FE / LB / AR to 2.5Nm for 4 cycles with data recorded for all cycles. Results. [Results Table - Figure 1]. Discussion. This study showed that the TriLobe had better control of motion compared to the ball and trough both in ROM and varibility for FE, LB, and AR. The TriLobe had better control of limiting kyphosis over the ball and trough by 41% of the flexion motion. The neutral zone slope, an measure for device stability, showed that the TriLobe was 51% more stable than the BT. AP placement of devices showed there was a general trend of decreasing stability from anterior to posterior placement; however, statistical significance was not established

Purpose. Total disc replacement (TDR) devices have been restricted to designs with large, congruent articulations due to the limited wear properties of available materials. TDRs with more natural motion could be designed if materials were available which could resist the higher wear conditions. A novel TriLobe TDR design is self-centering and energetically stable, emulating the natural motion of the intact motion segment, but is not feasible using traditional materials due to small incongruent articulating surfaces. The objective of this study was to compare the wear properties of a medical grade polycrystalline diamond with wear properties of cobalt chrome (CoCr) and ultrahigh molecular weight polyethylene (UHMWPE) in aggressive high wear conditions. Methods. A modified pin-on-disc, crossing-path wear test was used to measure the wear rates of PCD-on-PCD, CoCr-on-CoCr, and CoCr-on-UHMWPE. The discs were placed in the inferior position on an oscillating plate, moving in a 10mm by 5mm figure-eight pattern. Pins had an initial 11.5mm radius and were loaded at 133N normal to the disc. In a typical pin-on-disc test, a wear flat develops on the pin and the wear rate is reduced as the contact area increases. The TriLobe design uses three lobes sliding in three non-conforming lenses which prevents wear flats from developing. To approximate this condition, the fixture holding the disc was placed on an air bearing and was allowed to rock in concert with movement of the load. The test was conducted in 25% bovine serum at a speed of less than two Hertz. Two sets of each material were tested, one set to 2.0 million cycles and the other set to 14.0 million cycles. Wear rates on the rocking-discs were measured using a high resolution coordinate measuring machine because the wear in the PCD specimens was not detectable gravimetrically. Results. The diamond specimen averaged 0.0036mm. 3. /MC of wear over the first 2 million cycles. The CoCr-on-CoCr specimens averaged 1.4mm. 3. /MC and the CoCr-on-UHMWPE averaged 4.7mm. 3. /MC over 2 million cycles. The PCD specimen taken to 14 million cycles had and average wear of 0.0022mm. 3. /MC compared to 2.4mm. 3. /MC and 9.5mm. 3. /MC for CoCr-on-CoCr and CoCr-on-UHMWPE respectively. Conclusions. Using the pin-on-rocking-disc test to approximate small, non-congruent articulating surface wear, both CoCr-on-CoCr and CoCr-on-UHMWPE wore at rates that were orders of magnitude greater than medical grade PCD. At two million cycles, CoCr-on-CoCr had worn nearly 400 times more than PCD and CoCr-on-UHMWPE wore more than 1300 times greater. During the last 12 million cycles the wear in non-diamond specimen accelerated, while the diamond wear rate decreased. At the end of 14 million cycles CoCr on itself and on UHMWPE specimens had worn at more than 1100 times and nearly 4300 times greater than PCD, respectively. Coupled with the inherent biocompatibility, high strength and toughness, and ultra low friction of diamond, the performance of PCD makes it an attractive material for TDR applications. PCD could be used in current designs to alleviate concern over wear debris and ion release and to increase the space for the next generation of TDR devices