Cementless Oxford Unicompartmental Knee Replacement Research Articles

THE TEN-YEAR RADIOLOGICAL RESULTS OF THE UNCEMENTED OXFORD MEDIAL COMPARTMENT KNEE ARTHROPLASTY

IntroductionThe Oxford Unicompartmental Knee Replacement (OUKA) is the most popular unicompartmental knee replacement (UKR) in the New Zealand Joint Registry with the majority utilising cementless fixation. We report the 10-year radiological outcomes.MethodsThis is a prospective observational study. All patients undergoing a cementless OUKA between May 2005 and April 2011 were enrolled. There were no exclusions due to age, gender, body mass index or reduced bone density.All knees underwent fluoroscopic screening achieving true anteroposterior (AP) and lateral images for radiographic assessment. AP assessment for the presence of radiolucent lines and coronal alignment of the tibial and femoral components used Inteliviewer radiographic software. The lateral view was assessed for lucencies as well as sagittal alignment.Results687 OUKAs were performed in 641 patients. Mean age at surgery was 66 years (39–90yrs), 382 in males and 194 right sided. 413 radiographs were available for analysis; 92 patients had died, 30 UKRs had been revised and 19 radiographs were too rotated to be analysed the remainder were lost to follow-up. Mean radiograph to surgery interval was 10.2 years (7.1–16.2yrs).RLLs were identified in zone 1 (3 knees), zone 2 (2 knees), zone 3 (3 knees), zone 5 (3 knees), zone 6 (2 knees) and zone 7 (42 knees). No RLL had progressed, and no case had any osteolysis or prosthesis subsidence.Alignment in the coronal plane: mean 2.90° varus (9.30° varus - 4.49° valgus) of the tibial component to the tibial anatomic axis and the femoral component in mean 4.57° varus (17.02° varus - 9.3° valgus). Sagittal plane posterior tibial slope was a mean 6.30° (0.44° -13.60° degrees) and mean femoral component flexion of 8.11° (23.70° flexion – 16.43° extension).ConclusionThe cementless OUKA demonstrates stable fixation with low revision rates at our centre supporting results earlier published by the design centre.

Microporous titanium and hydroxyapatite improve fixation of the tibial wall in unicompartmental knee replacement.

Cementless Oxford unicompartmental knee replacement (OUKR) is associated with less pain than cemented OUKR 5 years postoperatively. This may be due to improved fixation at the tibial wall, which transmits tension and reduces stress in the bone below the tibial component. This study compares tibial wall fixation with three different types of fixation: cemented, cementless with hydroxyapatite (HA)and cementless with a microporous titanium coat and HA (HA + MPC). Three consecutive cohorts were identified (n = 221 cemented in 2005-2007, n = 118 HA in 2014-2015, n = 125 HA + MPC in 2016-2017). Analysis was performed on anterior-posterior radiographs aligned on the tibial component taken 1-2 years postoperatively. Aligned radiographs are needed to see narrow radiolucencies adjacent to the wall. Alignment was assessed with rotation ratio (RR = wall width/internal wall height). Perfect RR is 0.3, and a maximum threshold of 0.5 was used. Quality of fixation to the wall was assessed with fixation ratio (FR = bone wall contact height/total wall height). Notable radiographic features at the tibial wall were also recorded. A total of 33knees with cement, 37 knees with cementless with HAand 57 knees cementless with HA + MPC had adequately aligned radiographs. Fixation was significantly better with HA compared with cement (55% vs. 25%, p = 0.0016). The microporous coat further improved fixation (81% vs. 55%, p < 0.0001). FR > 80% was achieved in 3% of the cemented implants, 32% of HAand 68% of HA + MPC. In cementless cohorts, features suggestive of a layer of bone that had delaminated from the wall were seen in 8 (22%) HA and 3 (5%) HA + MPC knees. Radiographic tibial wall fixation in OUKR is poor with cement. It improves with an HA coating and improves further with an intermediary MPC. Improved tibial wall fixation may explain the lower levels of pain observed with cementless rather than cemented fixation described in the literature, but further clinical correlation is needed. Level III, retrospective cohort study.

A finite element model for investigating the influence of keel design and position on unicompartmental knee replacement cementless tibial component fixation

ObjectivesThe cementless Oxford Unicompartmental Knee Replacement (OUKR) tibial component relies on an interference fit to achieve initial fixation. The behaviour at the implant-bone interface is not fully understood and hence modelling of implants using Finite Element (FE) software is challenging. With a goal of exploring alternative implant designs with lower fracture risk and adequate fixation, this study aims to investigate whether optimisation of FE model parameters could accurately reproduce experimental results of a pull-out test which assesses fixation. Materials and methodsFinite element models of implants with three methods of fixation (standard keel, small keel, and peg) in a bone analogue foam block were created, in which implants were modelled using an analytical rigid definition and the foam block was modelled as a homogenous linear isotropic material. The total interference and elastic slip were varied in these models and optimised by comparing simulated and experimental results of pull-out tests for two (standard and peg) implant geometries. Then the optimised interference and elastic slip were validated by comparing simulated and experimental data of a third (small keel) implant geometry. ResultsThe optimisation of parameters established an interference of 0.16 mm and an elastic slip of 0.20 mm as most suitable for modelling the experimental force–displacement plots during pull-out. This combination of parameters accurately reproduced the experimental results of the small keel geometry. The maximum pull-out forces from the FE models were consistent with experimental data for each implant design. ConclusionsThis study shows that experimental pull-out tests can be accurately modelled using adjusted interference values and non-linear friction and outlines a method for determining these parameters. This study demonstrates that complex problems in modelling implant behaviour can be addressed with relatively simple models. This can potentially lead to the development of implants with reduced risk of failure.

OPTIMIZING THE TIBIAL KEEL SLOT FOR THE OXFORD UNICOMPARTMENTAL KNEE ARTHROPLASTY

Tibial periprosthetic fracture is an important complication of the Oxford Unicompartmental Knee Replacement (OUKR). Primary fixation of cementless OUKR tibial components relies on the interference-fit of the ‘keel’ and a slot in the proximal tibia. Clinically used double blade keel saws (DKS) create slots with two grooves, generating stress concentrations where fractures may initiate. This study aimed to investigate slot factors that may influence incidence of tibial periprosthetic fractures.Slots were made in PCF20 polyurethane foam using the DKS plus/minus adjuvant rasping, single blade keel saw (SKS), and rasp-only. Round and square slots were machined with milling cutters. Compact tensile tests were conducted per ASTM E399 to determine tensile load to fracture (TLTF) and results were validated using bovine tibia. Cementless OUKR components were implanted into slots in custom polyurethane blocks and compressed to failure to determine anatomical load to fracture (ALTF). A custom MATLAB program calculated slot roundness from cross-sectional images.Round slots had higher TLTF (29.5N, SD=2.7) than square (25.2N, SD=1.7, p&lt;0.05) and DKS slots (23.3N, SD=2.7, p&lt;0.0001). Fractures occurred at the round slot apices, square slot corners, and deepest DKS slot grooves. ALTF was not significantly different between square and round slots. Adjuvant rasping made DKS slots significantly rounder, resulting in significantly higher TLTF, but rasping did not increase ALTF. ALTF was significantly higher for SKS (850N, SD=133, p&lt;0.01) and rasp-only (912N, SD=100, p&lt;0.001) slots compared to standard DKS slots (703N, SD=81).Round keel slots minimise stress concentrations and increase TLTF but do not increase ALTF. The SKS and rasp-only slots retain material at slot ends and have significantly higher ALTF. Future studies should assess saw blades that retain material and round slot ends to evaluate if their use may significantly reduce the incidence of tibial periprosthetic fracture.

Less pain reported 5 years after cementless compared to cemented unicompartmental knee replacement: an analysis of pain, neuropathy, and co-morbidity scores

PurposeTo compare patient-reported pain scores and assess the influence of neuropathy and co-morbidity, on knee pain following cemented and cementless medial unicompartmental knee replacement (UKR) 5 years after surgery.MethodIn this longitudinal study, 262 cemented and 262 cementless Oxford UKR performed for the same indications and with the same techniques were recruited. Patients were reviewed at five years, evaluating patient-reported pain and association with clinical outcomes. Intermittent and Constant Osteoarthritis Pain (ICOAP), PainDETECT (PD), Charnley score, Oxford Knee Score (OKS) and American Knee Society Score (AKSS) were compared.ResultsIn both cohorts, intermittent pain was more common than constant pain (47% vs 21%). Cementless knees reported significantly less pain than cemented (ICOAP-Total 5/100 vs 11/100, p < 0.0001). A greater proportion of cementless knees experienced no pain at all (ICOAP = 0/100, 61% vs 43%, p < 0.0001) and 75% fewer experienced severe or extreme pain. Pain sub-scores in PD, OKS and AKSS follow this trend. Pain was unlikely to be neuropathic (PD positive: 5.26%), but patients reporting high levels of ‘strongest’ pain were three times more likely to be neuropathic. Patients with co-morbidities (Charnley C) experienced greater pain than those without (Charnley A+B) across all knee-specific scores, despite scores being knee specific.ConclusionBoth cemented and cementless UKR in this study had substantially less pain than that reported in literature following TKR. Cementless UKR had significantly less pain than cemented UKR in all scores. Two-thirds of patients with a cementless UKR had no pain at all at 5 years, and pain experienced was most likely to be mild and intermittent with no patients in severe or extreme pain. Patients with cementless UKR that had higher levels of pain were more likely to have co-morbidity or evidence or neuropathic pain. It is unclear why cementless UKR have less pain than cemented; further study is necessary.

SIXTEEN-YEAR SURVIVAL AND FUNCTIONAL RESULTS OF THE CEMENTLESS OXFORD UNICOMPARTMENTAL KNEE REPLACEMENT

Cementless fixation is an alternative to cemented unicompartmental knee replacement (UKR), with several advantages over cementation. This study reports on the 15-year survival and 10-year clinical outcomes of the cementless Oxford unicompartmental knee replacement (OUKR).This prospective study describes the clinical outcomes and survival of first 693 consecutive cementless medial OUKRs implanted in New Zealand.The sixteen-year survival was 89.2%, with forty-six knees being revised. The commonest reason for revision was progression of arthritis, which occurred in twenty-three knees, followed by primary dislocation of the bearing, which occurred in nine knees. There were two bearing dislocations secondary to trauma and a ruptured ACL, and two tibial plateau fractures. There were four revisions for polyethylene wear. There were four revisions for aseptic tibial loosening, and one revision for impingement secondary to overhang of the tibial component. There was only one revision for deep infection and one revision where the indication was not stated. The mean OKS improved from 23.3 (7.4 SD) to 40.59 (SD 6.8) at a mean follow-up of sixteen years.In conclusion, the cementless OUKR is a safe and reproducible procedure with excellent sixteen-year survival and clinical outcomes.

Five-year results of a randomised controlled trial comparing cemented and cementless Oxford unicompartmental knee replacement using radiostereometric analysis

BackgroundCementless fixation is an alternative to cemented unicompartmental knee replacement (UKR). The aim of this study was to determine if cementless UKR fixation is as good as cemented by comparing the five-year migration measured radiostereometric analysis (RSA) in a randomised controlled trial. MethodsThirty-nine patients were randomised to receive either a cemented or a cementless Oxford UKR and were studied at intervals up to five years to assess migration with RSA and radiolucencies with radiographs. ResultsDuring the first year there was a small and significant amount of migration, predominantly in an anterior direction, of both the cemented (0.24 mm, SD 0.32, p = 0.01) and cementless (0.26 mm, SD 0.31, p = 0.00) femoral components. Thereafter there was no significant migration in any direction. At no stage was there any significant difference between the migrations of the cemented or cementless femoral components. During the first year, particularly the first three months, the cementless tibial components subsided 0.28 mm (SD 0.19, p = 0.00). This was significantly (p = 0.00) greater than the subsidence of the cemented tibial component (0.09, SD 0.19, p = 0.28). Between the second and fifth years there was no significant migration of either cemented or cementless tibial components.At five years radiolucent lines occurred significantly less with cementless (one partial) compared to cemented (six partial and one complete) tibial components. ConclusionsAs, between two and five years, there was no significant migration of cemented or cementless components, and no significant difference between them, we conclude that cementless fixation is as reliable as cemented. It may be better as there are fewer radiolucent lines.

Cementless Oxford Medial Unicompartmental Knee Replacement-Clinical and Radiological Results of 228 Knees with a Minimum 2-Year Follow-Up.

(1) Background: Studies show several advantages of unicompartmental knee replacement (UKR) over total knee replacements (TKR), whereas registry based revision rates of UKR are significantly higher than for TKA. Registry data report lower revision rates for cementless UKR compared to cemented UKR. The aim of this study was to assess clinical and radiological results of cementless Oxford UKR (OUKR) in an independent cohort. (2) Methods: This retrospective cohort study examines a consecutive series of 228 cementless OUKR. Clinical outcome was measured using functional scores (Oxford Knee Score (OKS), American Knee Society Score (AKSS), Hannover Functional Ability Questionnaire for Osteoarthritis (FFbH-OA), range of motion (ROM)), pain and satisfaction. Radiographs were analyzed regarding the incidence of radiolucent lines (RL), implant positioning, and their possible impact on clinical outcome. (3) Results: At a mean follow-up of 37.1 months, the two and three year revision free survival-rates were 97.5% and 96.9%. Reasons for revision surgery were progression of osteoarthritis, inlay dislocation and pain. All clinical outcome scores showed a significant improvement from pre- to postoperative. The incidence of RL around the implant was highest within the first year postoperatively (36%), and decreased (5%) within the second year. Their presence was not correlated with inferior clinical outcome. Implant positioning showed no influence on clinical outcome. (4) Conclusion: Cementless OUKR showed excellent clinical outcome and survival rates, with reliable osteointegration. Neither the incidence of radiolucent lines nor implant positioning were associated with inferior clinical outcome.

Fast Return to Sports and High Level of Activity after Cementless Oxford Unicompartmental Knee Arthroplasty.

Physical activity is essential for overall health. For patients undergoing knee arthroplasty, questions about the implant's suitability for sports arise. The general recommendations for physical activity with knee replacements are often based upon experts' opinions, with a lack of scientific data. This study was performed at an independent high-volume center and aimed to investigate what level of activity patients can achieve and how they perform with a well-functioning cementless unicompartmental knee replacement (UKR). Possible differences in outcome in regards to patients' body mass index (BMI) were also examined. A total of 228 knees treated with cementless Oxford UKR (OUKR) were followed up after a mean of 37.1 months. Tegner's and UCLA (University of California, Los Angeles) scores were obtained to assess the level of physical activity. The Schulthess Clinical Activity Questionnaire was assessed for detailed information on practiced sports, and the SF-36 questionnaire was evaluated to analyze patients' quality of life. The return to activity rate was 92.9%. In total, 64% of the physically active patients had already taken up sports within 3 months after surgery. Mean Tegner's score was at 3.5, and mean UCLA score was at 6.3. High impact sports were not performed very often after surgery. Higher BMI showed a negative correlation with the numbers of sports (rsp = -0.289) as well as Tegner's (rsp = -0.222) and UCLA (rsp = -0.383) scores. The SF-36 scores were comparably good to those in an age-equivalent standard reference group. In conclusion, cementless OUKR allows a fast return to activity with a high level of physical exercise. Patients with increased BMI tend to practice less types of sports with decreased activity scores.

Comparison of the 10-year outcomes of cemented and cementless unicompartmental knee replacements: data from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man

Background and purpose — Unicompartmental knee replacement (UKR) offers advantages over total replacement but has higher revision rates, particularly for aseptic loosening. The cementless Oxford UKR was introduced to address this. We undertook a registry-based matched comparison of cementless and cemented UKRs.Patients and methods — From 40,552 Oxford UKRs identified by the National Joint Registry for England, Wales, Northern Ireland and Isle of Man (NJR) we propensity score matched, based on patient, surgical, and implant factors, 7,407 cemented and 7,407 cementless UKRs (total = 14,814).Results — The 10-year cumulative implant survival rates for cementless and cemented UKRs was 93% (95% CI 90–96) and 90% (CI 88–92) respectively, with this difference being significant (HR 0.76; p = 0.002). The risk of revision for aseptic loosening was less than half (p < 0.001) in the cementless (0.42%) compared with the cemented group (1.00%), and the risk of revision also decreased for unexplained pain (to 0.46% from 0.74%; p = 0.03) and lysis (to 0.04% from 0.15%; p = 0.03). However, the risk of revision for periprosthetic fracture increased significantly (p = 0.01) in the cementless (0.26%) compared with the cemented group (0.09%). 10-year patient survival rates were similar (HR 1.2; p = 0.1).Interpretation — The cementless UKR has improved 10-year implant survival compared with the cemented UKR, independent of patient, implant, and surgical factors. This improved survival in the cementless group was primarily the result of lower revision rate for aseptic loosening, unexplained pain, and lysis, suggesting the fixation of the cementless was superior. However, there was a small increased risk of revision for periprosthetic fracture with the cementless implant.

Instruments to reduce the risk of tibial fracture following cementless unicompartmental knee replacement

BackgroundTibial plateau fracture is an important complication of cementless Oxford unicompartmental knee replacement. The press fit between the keel and the bone's keel slot is responsible for primary fixation and also contributes to fracture risk. This study investigates whether the fracture risk could be reduced without compromising primary fixation, by using different instruments to widen the keel slot. MethodsKeel slots were made in polyurethane blocks (n = 60) using the standard keel cut saw blade or a new blade that was 0.2 mm wider, with adjuvant use of the cemented pick or a prototype rasp. A tibial component was pushed into and pulled out of the slots using a Dartec materials testing machine. It was assumed that the ‘push-in’ force was related to the risk of fracture and ‘pull-out’ force was related to fixation. Reproducibility studies with 10 different tibial components were undertaken. ResultsThe new blade required significantly lower push-in forces than the standard blade (789 N SD 130, 1411 N SD 180; P < 0.001), but the pull-out forces were not different (240 N SD 47, 230 N SD 56; P > 0.999). With the standard blade the pick decreased the push-in (818 N SD 318; P < 0.001) and pull-out (128 N SD 58; P < 0.001) forces, but the rasp had no effect. With the new blade the pick had no effect, but the rasp increased the push-in force (1390 N SD 202; P < 0.001). ConclusionsThis study suggests the fracture risk will be reduced with the new blades, with no compromise in fixation. If the new blades are used routine use of the cemented pick appears to be of no benefit.

Ten-year survival and seven-year functional results of cementless Oxford unicompartmental knee replacement: A prospective consecutive series of our first 1000 cases

BackgroundCementless fixation is an alternative to cemented unicompartmental knee replacement (UKR), with several advantages over cementation.This study reports the ten-year survival and seven-year clinical outcome of cementless Oxford unicompartmental knee replacement (OUKR). MethodsThis prospective study describes the clinical outcome and survival of the first 1000 consecutive cementless medial OUKRs implanted at two centres for recommended indications. ResultsThe 10-year survival was 97% (CI 95%: 92–100%), with 25 knees being revised. The commonest reason for revision was progression of arthritis laterally, which occurred in nine knees, followed by primary dislocation of the bearing, which occurred in six knees. There were two dislocations secondary to trauma and a ruptured ACL, and two tibial plateau fractures. Although there were no definite cases of aseptic loosening, two early revisions were related to tibial fixation: one for pain and a radiolucent line and one for incomplete seating of the component with a radiolucent line. There were four revisions for pain, but the cause of the pain was uncertain: in one there was tibial overhang and in two there was patellofemoral degeneration, which possibly contributed to the pain. There were no deep infections. The mean OKS improved from 23 (SD 8) to 42 (SD 7) at a mean follow-up of 7.0 years (p < 0.001). There was no significant difference in survival or clinical outcome between the designer and independent centre. ConclusionsThe cementless OUKR is a safe and reproducible procedure with excellent 10-year survival and clinical results in the hands of both designer and independent surgeons.

Optimal interference of the tibial component of the cementless Oxford Unicompartmental Knee Replacement.

ObjectivesThe primary stability of the cementless Oxford Unicompartmental Knee Replacement (OUKR) relies on interference fit (or press fit). Insufficient interference may cause implant loosening, whilst excessive interference could cause bone damage and fracture.The aim of this study was to identify the optimal interference fit by measuring the force required to seat the tibial component of the cementless OUKR (push-in force) and the force required to remove the component (pull-out force).Materials and MethodsSix cementless OUKR tibial components were implanted in 12 new slots prepared on blocks of solid polyurethane foam (20 pounds per cubic foot (PCF), Sawbones, Malmo, Sweden) with a range of interference of 0.1 mm to 1.9 mm using a Dartec materials testing machine HC10 (Zwick Ltd, Herefordshire, United Kingdom) . The experiment was repeated with cellular polyurethane foam (15 PCF), which is a more porous analogue for trabecular bone.ResultsThe push-in force progressively increased with increasing interference. The pull-out force was related in a non-linear fashion to interference, decreasing with higher interference. Compared with the current nominal interference, a lower interference would reduce the push-in forces by up to 45% (p < 0.001 One way ANOVA) ensuring comparable (or improved) pull-out forces (p > 0.05 Bonferroni post hoc test). With the more porous bone analogue, although the forces were lower, the relationship between interference and push-in and pull-out force were similar.ConclusionsThis study suggests that decreasing the interference fit of the tibial component of the cementless OUKR reduces the push-in force and can increase the pull-out force. An optimal interference fit may both improve primary fixation and decrease the risk of fracture.Cite this article: S. Campi, S. J. Mellon, D. Ridley, B. Foulke, C. A. F. Dodd, H. G. Pandit, D. W. Murray. Optimal interference of the tibial component of the cementless Oxford Unicompartmental Knee Replacement. Bone Joint Res 2018;7:226–231. DOI: 10.1302/2046-3758.73.BJR-2017-0193.R1.

Cementless Oxford medial unicompartimental knee replacement: an independent series with a 5-year-follow-up.

Cemented unicompartmental knee replacement (UKR) has proven excellent long-term survival rates and functional scores in Price et al. (Clin Orthop Relat Res 435:171-180, 2005), Price and Svard (Clin Orthop Relat Res 469(1):174-179, 2011) and Murray et al. (Bone Joint Surg Br 80(6):983-989, 1998). The main causes for revision, aseptic loosening and pain of unknown origin might be addressed by cementless UKR in Liddle et al. (Bone Joint J 95-B(2):181-187, 2013), Pandit et al. (J Bone Joint Surg Am 95(15):1365-1372, 2013), National Joint Registry for England, Wales and Northern Ireland: 10th Annual Report 2013 ( http://www.njrcentre.org.uk/njrcentre/Portals/0/Documents/England/Reports/10th_annual_report/NJR%2010th%20Annual%20Report%202013%20B.pdf , 2013), Swedish Knee Arthroplasty Register: Annual Report 2013 ( http://www.myknee.se/pdf/SKAR2013_Eng.pdf , 2013). This single-centre retrospective cohort study reports the 5-year follow-up results of our first 30 consecutively implanted cementless Oxford UKR (OUKR). Clinical outcome was measured using the OKS, AKSS, range of movement and level of pain (visual analogue scale). The results were compared to cemented OUKR in a matched-pair analysis. Implant survival was 89.7%. One revision each was performed due to tibial fracture, progression of osteoarthritis (OA) and inlay dislocation. The 5-year survival rate of the cementless group was 89.7% and of the cemented group 94.1%. Both groups showed excellent postoperative clinical scores. Cementless fixation shows good survival rates and clinical outcome compared to cemented fixation.

Results after Cementless Medial Oxford Unicompartmental Knee Replacement - Incidence of Radiolucent Lines.

PurposeTibial radiolucent lines (RL) are commonly seen in cemented unicompartmental knee replacement (UKR). In the postoperative course, they can be misinterpreted as signs of loosening, thus leading to unnecessary revision. Since 2004, a cementless OUKR is available. First studies and registry data have shown equally good clinical results of cementless OUKR compared to the cemented version and a significantly reduced incidence of RL in cementless implants.MethodsThis single-centre retrospective cohort study includes the first 30 UKR (27 patients) implanted between 2007 and 2009 with a mean follow-up of 5 years. Clinical outcome was evaluated using the OKS, AKS, range of movement (ROM) and level of pain (VAS). Standard radiologic evaluation was performed at three months, one and five years after surgery. The results five years after implantation were compared to a group of 27 cemented Oxford UKR (OUKR) in a matched-pair-analysis.ResultsTibial RL were seen in 10 implants three months after operation, which significantly decreased to five after one year and to three after five years (p = 0.02). RL did not have a significant influence on revision (p = 1.0) or clinical outcome after five years. RL were always partial, never progressive and strictly limited to the tibia. There was no significant difference in the incidence of tibial RL five years after implantation between cemented and cementless implants (cemented: 4, cementless: 3, p = 1.0).ConclusionsAfter cementless implantation RL were limited to the tibia, partial and never progressive. During short term follow-up the incidence of RL decreased significantly. RL seem to have no influence on clinical outcome and revision.

Five-year experience of cementless Oxford unicompartmental knee replacement.

Cementless unicompartmental knee replacement (UKR) was introduced to address someof the problems that can occur following cemented UKR. The aim of this study was to report the 5-year experience of the first 512 medial cementless Oxford UKR implanted by two surgeons for the recommended indications. The first consecutive 512 cementless Phase 3 Oxford UKRs implanted by two surgeons for the recommended indications between June 2004 and October 2013 were prospectively identified and followed up independently. All the procedures were carried out through a minimally invasive approach without eversion or dislocation of the patella. Patients were assessed clinically pre-operatively and at 1, 2, 5, 7 and 10years after surgery with functional outcome scores and radiographs. There were eight reoperations of which six were revisions giving a 5-year survival of 98% (95% CI 94-100%). At a mean follow-up of 3.4years (1.0-10.2), the mean OKS was 43 (SD 7), AKSS (objective) was 81 (SD 13), and AKSS (functional) was 86 (SD 17). The first 120 cases had a minimum follow-up of 5years (mean 5.9; range 5-10.2). In these patients, the mean OKS was 41 (SD 8), AKSS (objective) was 81 (SD 14), and AKSS (functional) was 82 (SD 18). There were no femoral radiolucencies and no complete tibial radiolucencies. 11% of tibial components had partial radiolucent lines; the remaining 89% had no radiolucencies. The clinical results are as good as or better than those previously reported for cemented fixation. The radiographic results are better with secure bony attachment to the implants in every case. IV.

Valgus subsidence of the tibial component in cementless Oxford unicompartmental knee replacement

The cementless Oxford unicompartmental knee replacement has been demonstrated to have superior fixation on radiographs and a similar early complication rate compared with the cemented version. However, a small number of cases have come to our attention where, after an apparently successful procedure, the tibial component subsides into a valgus position with an increased posterior slope, before becoming well-fixed. We present the clinical and radiological findings of these six patients and describe their natural history and the likely causes. Two underwent revision in the early post-operative period, and in four the implant stabilised and became well-fixed radiologically with a good functional outcome. This situation appears to be avoidable by minor modifications to the operative technique, and it appears that it can be treated conservatively in most patients.Cite this article: Bone Joint J 2014;96-B:345–9.

Cementless fixation in Oxford unicompartmental knee replacement

The Cementless Oxford Unicompartmental Knee Replacement (OUKR) was developed to address problems related to cementation, and has been demonstrated in a randomised study to have similar clinical outcomes with fewer radiolucencies than observed with the cemented device. However, before its widespread use it is necessary to clarify contraindications and assess the complications. This requires a larger study than any previously published. We present a prospective multicentre series of 1000 cementless OUKRs in 881 patients at a minimum follow-up of one year. All patients had radiological assessment aligned to the bone-implant interfaces and clinical scores. Analysis was performed at a mean of 38.2 months (19 to 88) following surgery. A total of 17 patients died (comprising 19 knees (1.9%)), none as a result of surgery; there were no tibial or femoral loosenings. A total of 19 knees (1.9%) had significant implant-related complications or required revision. Implant survival at six years was 97.2%, and there was a partial radiolucency at the bone-implant interface in 72 knees (8.9%), with no complete radiolucencies. There was no significant increase in complication rate compared with cemented fixation (p = 0.87), and no specific contraindications to cementless fixation were identified. Cementless OUKR appears to be safe and reproducible in patients with end-stage anteromedial osteoarthritis of the knee, with radiological evidence of improved fixation compared with previous reports using cemented fixation.

Cementless Oxford unicompartmental knee replacement shows reduced radiolucency at one year

We randomised 62 knees to receive either cemented or cementless versions of the Oxford unicompartmental knee replacement. The implants used in both arms of the study were similar, except that the cementless components were coated with porous titanium and hydroxyapatite. The tibial interfaces were studied with fluoroscopically-aligned radiographs. At one year there was no difference in clinical outcome between the two groups. Narrow radiolucent lines were seen at the bone-implant interfaces in 75% of cemented tibial components. These were partial in 43%, and complete in 32%. In the cementless implants, partial radiolucencies were seen in 7% and complete radiolucencies in none. These differences are statistically significant (p < 0.0001) and imply satisfactory bone ingrowth into the cementless implants.