During a retrospective case note analysis, a significant difference was found in prosthesis survival, between two cohorts of patients who underwent different total knee replacements. The first cohort included 70 patients who underwent Kinemax Plus total knee replacement, the second cohort included 58 patients who underwent PFC Total Knee replacement. All patients were under the care of one Consultant Orthopaedic Surgeon. Interestingly, the Kinemax Plus cohort was found to have a higher rate of revision compared to the PFC cohort. A detailed comparison was carried out between the two groups to identify any obvious cause for the disparity. The two cohorts were found to be well matched with respect to age, sex, ASA grade, underlying pathology and operative technique. Median follow up being 6 years and 5 years for the Kinemax Plus and PFC groups respectively. There were 11 failed prostheses in the Kinemax Plus cohort, 7 undergoing revision with the remaining 4 patients offered revision but unwilling to have surgery. Wear of the polyethylene tibial insert was the most obvious finding at revision, present in six of the seven revisions. 97% of the Kinemax Plus Prostheses were intact at 5 years but by 8 years only 87% were intact. There were no revisions performed in the PFC cohort. Post-operative x-ray analysis was undertaken to rule out prosthesis malalignment as a cause for the increased failure rate. The coronal alignment of the prostheses (CAK) was calculated and all post operative x-rays were within the normal limits of 4-10 degrees. Analysis of the explanted Kinemax Plus polyethylene liners was undertaken. In six cases, the polyethylene bearing surfaces displayed severe surface and subsurface delamination. This suggests massive fatigue and fatigue wear. Only one implant showed localised delamination. These findings suggest the hypothesis of weak polyethylene particle interface strength

We aim to explain the significant difference in survivor-ship found between two cohorts of patients who underwent different total knee replacements. The first cohort included 70 patients who underwent Kinemax Plus total knee replacement, the second cohort included 58 patients who underwent PFC Total Knee replacement. All patients were under the care of one Consultant Orthopaedic Surgeon. Interestingly, the Kinemax Plus cohort was found to have a higher rate of revision as compared to the PFC cohort. A detailed comparison was then carried out between the two groups to identify any obvious cause for the disparity. The two cohorts were found to be well matched with respect to age, sex, ASA grade, underlying pathology and operative technique. Median follow up being 6 years and 5 years for the Kinemax and PFC groups respectively. There were 11 failed prostheses in the kinemax cohort, 7 undergoing revision with the remaining 4 patients offered revision but unwilling have surgery. Wear of the polyethylene tibial insert was the most obvious finding at revision, present in six out of the 7 revisions. 97% of the Kinemax Plus Prostheses were intact at 5 years but by 8 years only 87% were intact. There were no revisions performed in the PFC cohort. Post operative x-ray analysis was undertaken to rule out prosthesis misalignment as a cause for the increased failure rate. The coronal alignment of the prostheses (CAK) was calculated and all post operative x-rays were within the normal limits of 4–10 degrees. Analysis of the explanted Kinemax Plus polyethylene liners was undertaken. In six cases, the polyethylene bearing surfaces displayed severe surface and subsurface delamination at both medial and lateral sides. This suggests massive fatigue and fatigue wear. Only one inplant showed localised delamination. The surface characterisation suggests the hypothesis of weak UHMWPE particle interface strength

Background. There is a paucity of long term data concerning the pre and postoperative patient reported function of total knee replacement. The aim of this study was to determine the mortality, implant survivorship, patient reported function and satisfaction in a cohort of 114 patients, from a single centre, who received a Kinemax total knee replacement more than 15 years ago. Methods. Patients completed a questionnaire incorporating validated disease- and joint-specific scores, patient satisfaction and overall health preoperatively, at 3 months, 1 year, 2 years and a minimum of 15 years following surgery. NHS National Strategic Tracing Service, hospital and primary care records were used to establish mortality and for implant survivorship in deceased patients. Results. 45 patients were alive at final follow up. The survivorship of the cohort with revision of the TKR as the endpoint was 84%. Four cases were revised for wear, three for loosening and one for peri-prosthetic fracture. There was a significant improvement in WOMAC Pain, Function and Stiffness Scores, Oxford Knee Score and Self-Administered Patient Satisfaction Scale between pre-operative and all post-operative time points, although patient satisfaction had decreased significantly by the time of final follow up. Conclusion. In this cohort, the Kinemax TKR showed satisfactory long term survivorship with functional scores demonstrating a high level of patient satisfaction at all follow up time points. Level of Evidence. 2

The Kinemax Plus knee replacement has a reported 10 year survival of around 96%. However we found the survival rate of this implant in our cohort to be 75% at 9 years. No abnormalities were found for clinical and radiological parameters. At reoperation the most striking feature was that of significant ultra-high molecular weight polyethylene (UHMWPE) failure. Oxidative and structural analysis of the polyethylene components was therefore undertaken. Ten Kinemax Plus tibial inserts were analysed; one was a shelf-aged unused implant, the others were explants. An FTIR analysis of the data showed that oxidation is present in all samples. The degree of oxidation however varied with depth and location. Except for a sharp oxidative peak approximately half way into the sample, the shelf aged samples had a fairly constant level of oxidation. The retrieved implants had an overall higher level of oxidation in both bearing and non-bearing regions. The latter had less of a variation in oxidation which implies that in vivo loading exaggerates the degree of oxidation. In the non-articulating regions oxidation of the explants was found to peak often at the region of about 40% from the bottom surface in all retrieved samples. By contrast, most articulating region had two oxidative peaks; one occurring at approximately 1–1.5mm from the surface, which is consistent with findings on subsurface oxidation, and another occurring about 2–3mm from the bottom surface. SEM imaging provided evidence for the presence of fusion defects by indicating grain boundaries through-out the explants. This indicates a compromised material which is more susceptible to damage. Fatigue loading of the implant has also been seen to produce a subsurface stress maximum at approximately 1 to 2mm below the articulating surface. It is thought that maximum contact stresses within this region cause Type 1 and Type 2 defects to open or become more pronounced. This in turn will increase the local concentration of oxygenating material as it will be present in these defects and voids where surface areas are greater for oxidative reaction. We therefore hypothesise that these fusion defects are the cause for the early failure of the Kinemax implants

Purpose of the study. To compare the patellofemoral kinematics and patella stability of a new TKR, with a continuous radius versus an established J shaped knee system and the natural knee. It was hypothesised that the high performance new TKR would be a better match to the natural knee and anatomical patella tracking would provide a more stable patella. Methods. A cadaveric study using physiological loads examined the continuous kinematic behaviour (optical tracking system) of the tibiofemoral and patellofemoral compartments in 6 knees for the native, kinemax and new design triathlon knee systems. Results. In all knees the patella shifted laterally as flexion increased. There were significant differences between the natural knee and the Triathlon knee from 10-40 degrees of flexion (p<0.001). In patella spin the natural knee moved 7 degrees of adduction compared to 15 degrees for the Triathlon and 11 for the Kinemax. Both the prosthetic patellae were tilted at 5 degrees of flexion and continued to tilt laterally to 7 degrees at 50 degrees where they remained. The natural knee tilted medially by 3 degrees up to 30 degrees of flexion, then laterally to 4 degrees at 90 degrees. Both prostheses showed the patella to be flexed at full extension. Fully extended, all knees required 100N to displace the patella 10mm medially. At 90 degrees of flexion the intact knee and the Triathlon knee needed 155N compared to 130N for the Kinemax knee. Around 110N was required in all knees for lateral displacement throughout flexion. Discussion. Both TKRs were a good match to the natural knee patellofemoral joint kinematics and patella stability. There were no overall statistical differences

The issue of preservation or sacrifice of the posterior cruciate ligament in total knee arthroplasty remains unresolved. We report the results of 200 consecutive total knee arthroplasties performed at our hospital under the direction of the senior author. Pre-operatively, patients were randomly chosen to receive either a Kinemax (posterior cruciate retaining) or a Press-Fit-Condylar (posterior cruciate sacrificing) prosthesis. We implanted 97 Kinemax and 103 Press-Fit-Condylar prostheses which were prospectively followed-up by clinical and radiographic assessment. Review at mean follow-up of 2.7 years showed a satisfactory clinical result in both groups [Surace, et al., 1994]. We present the results of our further review, with maximum follow-up of over nine years (mean: 5.9 years). Revision of the implant has been performed in five knees (three Kinemax and two Press-Fit-Condylar). The polythene spacer had to be replaced in one patient with a Press-Fit-Condylar implant. Patients were assessed with the Hospital for Special Surgery Knee Score and radiologically assessed with the Knee Society Roentgenographic Evaluation and Scoring System. Pre-operative demographics and disease states of the patients were similar, with an average Hospital for Special Surgery Knee Score of 63. At the latest assessment the average knee score was good (85). Remarkably, the mean knee score for the posterior cruciate sacrifice and the PCL groups remains similar (mean: 85). Radiographic evaluation demonstrated that the prosthetic components of both groups were in comparable alignment. The posterior cruciate ligament retained (Kinemax) patient group showed a mean 5.9 degrees of the valgus angle at the knee. The angle in the posterior cruciate ligament sacrifice (PFC implant) group was 6.2 degrees. Evaluation of the radiolucent depths below the femoral, tibial and any patella component showed a mean total depth of 1.5 mm (pcl retaining) and 1.7 mm (pcl sacrificing). Our study presents a quantitative perspective of the results of total knee replacement with proven implant systems and performed in a general orthopaedic unit by both consultants and surgeons in training. The Kinemax (Howmedica) and Press-Fit-Condylar (DePuy Johnson and Johnson) implant systems have both previously demonstrated good results and continue to be available with little subsequent modification. To our knowledge, there have been no other large prospectively randomised studies of posterior cruciate ligament preservation or sacrifice in total knee replacement

Modular knee bearings typically consist of a femoral component, a tibial base-plate and a polyethylene insert, which is located in the tibial base-plate using some sort of locking mechanism. Although modular knee bearings offer many advantages there is the potential for micro-motion between the tibial insert and the base-plate. Tests were performed on six large Kinemax Plus knee bearings (snap-fit design) to evaluate the amount of movement between the tibial inserts and the tibial base-plates. The knee bearings were tested up to one million cycles on the Durham Six-Station Knee Wear Simulator which subjected the bearings to similar motion and loading profiles that would be experienced by the natural knee during walking. The movement of the tibial inserts was measured with dial gauges (accuracy of ±0.01 mm) before and after the bearings were tested on the simulator, when unloaded, and throughout the tests whilst the bearings were being dynamically loaded in the simulator. Movement occurred between the tibial insert and the tibial base-plate after initial assembly due to the snap-fit mechanism used to locate the tibial insert within the tibial base-plate. However, this decreased appreciably when the bearings were loaded in the simulator. The amount of movement did not change with time when the bearings were continuously loaded in the simulator. However, after each test the amount of movement of the tibial inserts, when unloaded, was less than before the test. This was thought to be due to creep of the UHMWPE inserts. The movement between the tibial insert and tibial base-plate in-situ is likely to be much less than that observed by a surgeon at the time of assembly due to loading of the knee bearing in the body. However, the amount of movement when the tibial inserts are loaded may still be great enough to produce a second interface where wear of the tibial insert may take place

224 patients from the Cardiff and Vale NHS Trust who had total knee replacements at the NHS Treatment Centre in Weston-Super-Mare by surgeons from overseas appeared to have significantly worse results than those recorded in the published literature. We wished to establish whether a group of patients treated in the same hospital with the same prosthesis at a similar time by local NHS orthopaedic surgeons in substantive posts would have a similar outcome.

Follow-up of all 214 patients (223 knee replacements) treated in 2004 was conducted with questionnaires, clinical review and x-ray assessment. In cases of no response, contact was made with GPs to establish the outcome of the surgery.

The outcome of all patients was known and of the 125 knee replacements available for clinical review at six years (mean), 119 cases (96%) achieved satisfactory coronal alignment with reference to the published literature. There were six revisions, five for loosening and one for malalignment. The cumulative survival rate for re-operation at six years was 97.2% (95% confidence interval 95.2 to 99.1).

This study shows that the results of total knee replacement performed by a group of NHS orthopaedic surgeons were comparable with other institutions and were significantly better than those reported from the NHS Treatment Centre in Weston-Super-Mare, using the same facilities and implant over the same period of time. This work supports previous recommendations for single surgeon supervision of the patient pathway and appropriate follow-up procedures.

Aims. The aims were to assess whether joint-specific outcome after total knee arthroplasty (TKA) was influenced by implant design over a 12-year follow-up period, and whether patient-related factors were associated with loss to follow-up and mortality risk. Methods. Long-term follow-up of a randomized controlled trial was undertaken. A total of 212 patients were allocated a Triathlon or a Kinemax TKA. Patients were assessed preoperatively, and one, three, eight, and 12 years postoperatively using the Oxford Knee Score (OKS). Reasons for patient lost to follow-up, mortality, and revision were recorded. Results. A total of 94 patients completed 12-year functional follow-up (62 females, mean age 66 years (43 to 82) at index surgery). There was a clinically significantly greater improvement in the OKS at one year (mean difference (MD) 3.0 (95% CI 0.4 to 5.7); p = 0.027) and three years (MD 4.7 (95% CI 1.9 to 7.5); p = 0.001) for the Triathlon group, but no differences were observed at eight (p = 0.331) or 12 years’ (p = 0.181) follow-up. When assessing the OKS in the patients surviving to 12 years, the Triathlon group had a clinically significantly greater improvement in the OKS (marginal mean 3.8 (95% CI 0.2 to 7.4); p = 0.040). Loss to functional follow-up (53%, n = 109/204) was independently associated with older age (p = 0.001). Patient mortality was the major reason (56.4%, n = 62/110) for loss to follow-up. Older age (p < 0.001) and worse preoperative OKS (p = 0.043) were independently associated with increased mortality risk. An age at time of surgery of ≥ 72 years was 75% sensitive and 74% specific for predicting mortality with an area under the curve of 78.1% (95% CI 70.9 to 85.3; p < 0.001). Conclusion. The Triathlon TKA was associated with clinically meaningful greater improvement in knee-specific outcome when compared to the Kinemax TKA. Loss to follow-up at 12 years was a limitation, and studies planning longer-term functional assessment could limit their cohort to patients aged under 72 years. Cite this article: Bone Jt Open 2024;5(10):911–919

Aims. There are comparatively few randomized studies evaluating knee arthroplasty prostheses, and fewer still that report longer-term functional outcomes. The aim of this study was to evaluate mid-term outcomes of an existing implant trial cohort to document changing patient function over time following total knee arthroplasty using longitudinal analytical techniques and to determine whether implant design chosen at time of surgery influenced these outcomes. Methods. A mid-term follow-up of the remaining 125 patients from a randomized cohort of total knee arthroplasty patients (initially comprising 212 recruited patients), comparing modern (Triathlon) and traditional (Kinemax) prostheses was undertaken. Functional outcomes were assessed with the Oxford Knee Score (OKS), knee range of movement, pain numerical rating scales, lower limb power output, timed functional assessment battery, and satisfaction survey. Data were linked to earlier assessment timepoints, and analyzed by repeated measures analysis of variance (ANOVA) mixed models, incorporating longitudinal change over all assessment timepoints. Results. The mean follow-up of the 125 patients was 8.12 years (7.3 to 9.4). There was a reduction in all assessment parameters relative to earlier assessments. Longitudinal models highlight changes over time in all parameters and demonstrate large effect sizes. Significant between-group differences were seen in measures of knee flexion (medium-effect size), lower limb power output (large-effect size), and report of worst daily pain experienced (large-effect size) favouring the Triathlon group. No longitudinal between-group differences were observed in mean OKS, average daily pain report, or timed performance test. Satisfaction with outcome in surviving patients at eight years was 90.5% (57/63) in the Triathlon group and 82.8% (48/58) in the Kinemax group, with no statistical difference between groups (p = 0.321). Conclusion. At a mean 8.12 years, this mid-term follow-up of a randomized controlled trial cohort highlights a general reduction in measures of patient function with patient age and follow-up duration, and a comparative preservation of function based on implant received at time of surgery. Cite this article: Bone Joint J 2020;102-B(4):434–441

Two knee arthroplasty implants with very different design principles were previously available in our region. Kinemax is PCL retaining with a fixed bearing and cemented components. LCS is PCL sacrificing, fully uncemented and incorporates a rotating bearing. The aim of this study was to compare the outcome of these two radically different knee designs. Between 1994 and 2004, 300 consecutive patients were recruited and underwent a knee replacement performed by the senior author. Each patient was randomised via sealed envelopes to receive either LCS or Kinemax implants. All patients were followed up by an audit nurse and patient satisfaction and Knee Society Scores (KSSs) were recorded. By 2012, 135 patients had complete data at a minimum of 10-years of follow-up. The remaining 165 had either died before 10-year review or had not reached the 10-year mark. No patient was lost to follow-up. There were 69 patients in the Kinemax group and 68 in the LCS group. The pre-operative demographics were not significantly different between the two groups. At 10-years of follow-up, each implant design demonstrated significant improvements in the KSS (p=0.001 kinemax, p=0.001 LCS) over pre-operative values. No significant difference could be identified between the two designs at 10 years. There were only two revisions in the whole study population and both were for kinemax implants at less than five years post-operatively. In conclusion, there was no statistically significant difference in outcome between the two radically different knee designs at ten years with both designs performing equally well

Aim: The Low Contact Stress (LCS) Total Knee Replacements (TKR) is a well-established mobile bearing prosthesis with more than 25 year experience, while the Kinemax Plus is a well established fixed bearing prosthesis. We examined whether reproducing the joint line height to within 5 mm of the pre-operative joint line height had any impact on the clinical outcome in the two different types of Total Knee Replacements. Method: 48 consecutive LCS knee replacements with a minimum of 2 years follow up had their pre and postoperative joint line (using Figgie’s method) and range of movement (ROM) measured. We used the Oxford Knee Score as a clinical outcome measurement tool. A cohort group of 53 CR Kinemax plus TKR from the Bristol Knee group was matched for age and sex. They had the same parameters measured. Results: Accurate joint line restoration was achieved significantly more frequently (P< 0.05) in the Kinemax group. Better post-operative ROM also occurred in the Kinemax group than the LCS, p = 0.03 and the former produced a bigger gain in ROM p < 0.01. However, no difference in the Oxford Knee Score existed between the two prostheses, p = 0.28. Joint line: elevation K+ LCS. 0–2 mm (16/48) = 33% (26/53) = 49% 2–5 mm (14/48) = 29% (14/53) = 26%> 5 mm (18/48) = 38% (12/53) = 25%. There was no significant difference in the ROM or Oxford Knee Score when the joint line was not elevated versus elevated for each prosthesis. However, there was suggestion that the ROM in LCS might be more sensitive to joint line changes, although this was not significant. ROM. K+ LCS. Normal joint line 116° 105°. Elevated joint line 108° 101°. Conclusion: Accurate joint line restoration could not be shown to correlate with either improved ROM or Oxford knee score; probably because of the small mount of elevation encountered and the small study size. There was a significantly greater post-operative increase in ROM with the Kinemax Plus relative to the LCS, and a significantly closer restoration of the joint line with the Kinemax Plus, both with respect to the actual measurement and with respect to the proportion of cases in which the joint line was accurately reproduced. This is surprising since in most K+ cases additional distal femur had been resected to avoid a tight knee. While in the LCS group special efforts had been made to achieve accurate restoration of the joint level

Total knee arthroplasty (TKA) is an established and successful procedure. However, the design of prostheses continues to be modified in an attempt to optimise the functional outcome of the patient. . The aim of this study was to determine if patient outcome after TKA was influenced by the design of the prosthesis used. A total of 212 patients (mean age 69; 43 to 92; 131 female (62%), 81 male (32%)) were enrolled in a single centre double-blind trial and randomised to receive either a Kinemax (group 1) or a Triathlon (group 2) TKA. . Patients were assessed pre-operatively, at six weeks, six months, one year and three years after surgery. The outcome assessments used were the Oxford Knee Score; range of movement; pain numerical rating scales; lower limb power output; timed functional assessment battery and a satisfaction survey. Data were assessed incorporating change over all assessment time points, using repeated measures analysis of variance longitudinal mixed models. Implant group 2 showed a significantly greater range of movement (p = 0.009), greater lower limb power output (p = 0.026) and reduced report of ‘worst daily pain’ (p = 0.003) over the three years of follow-up. Differences in Oxford Knee Score (p = 0.09), report of ‘average daily pain’ (p = 0.57) and timed functional performance tasks (p = 0.23) did not reach statistical significance. Satisfaction with outcome was significantly better in group 2 (p = 0.001). These results suggest that patient outcome after TKA can be influenced by the prosthesis used. Cite this article: Bone Joint J 2015;97-B:64–70

Summary Statement. Using current analysis/methodology, new implant technology is unlikely to demonstrate a large enough change in patient function to impact on the cost-effectiveness of the procedure. Purpose. Cost effectiveness is an increasingly important metric in today's healthcare environment, and decisions surrounding which arthroplasty prosthesis to implant are not exempt from such health economic concerns. Quality adjusted life years (QALYs) are the typical assessment tool for this type of evaluation. Using this methodology, joint arthroplasty has been shown to be cost effective, however studies directly comparing the QALY achieved by differing prostheses are lacking. Methods. Data was gathered in a single centre prospective double-blind randomised controlled trial comparing the outcome a modern implant, the Triathlon total knee replacement, with its traditionally designed predecessor the Kinemax, using the Short Form 6 dimensional (SF-6D) score and quality adjusted life year (QALY) methodology. The study cohort consisted of 64 patients that were randomised to a Triathlon and 60 randomised to a Kinemax. Results. There was a significant improvement in the SF-6D score for both groups at one year compared with pre-operative scores (p<0.0001). The calculated overall life expectancy for the study cohort was 15.1 years, which resulted in an overall QALY gain of 2.144 (95% CI 1.752–2.507). The modern implant group demonstrated only a small improvement in the SF-6D score compared to the traditional design at one year (0.141 versus 0.143, p=0.94). This difference in health gain resulted in the modern implant costing £298 less per QALY at one year, however this saving diminished to less than £30 per year over the lifetime of the cohort. Discussion. This study demonstrates that despite comparing 2nd and 4th generation design, modern implant technology does not influence the cost-effectiveness of TKA using the SF-6D and QALY methodology. As most implants demonstrate similar longevity, differences in patient function will likely carry the greatest influence on QALY. This type of analysis however assesses health status, and is not sensitive to joint specific function. Dramatic differences in patient outcome would be required to influence QALY score. Evolutionary design changes in implant technology are thus unlikely to influence QALY analysis following joint replacement, which has important implication for implant procurement

Templating of preoperative radiographs is routinely recommended prior to knee arthroplasty. We performed this study to assess the reproducibility and accuracy of the templates for three commonly used knee implants (PFC, Kinemax, Scorpio). Six lower limb surgeons templated 10 patients for each of the three designs. The inter and intra-observer reliability and accuracy was calculated. There was marked variation in the reliability of the templating with the tibial insert scoring better than the femoral and the Kinemax being the most reproducible of the three. In general, the intra-observer scores (κ= 0.57–0.81) were better than the inter-observer ones (κ= 0.21–0.60). The Scorpio was the most accurately templated of the three implants, with the percentage correlating with what was actually implanted ranging from 55–62% for the femur and 72–75% for the tibia, with no templated sizes more than 1 size different from the actual implant. The other implants ranged from 38–42% for the femur and 53–58% for the tibia with both having up to 3% more than 1 size difference from the actual implant. We believe that the use of templating in total knee arthroplasty should be interpreted with caution and we urge the development of more accurate prosthesis sizing techniques

The purpose of this study was to determine the incidence of revision total knee replacement (TKR) within 5 years of the index procedure at a large multi-surgeon unit using a single prosthesis and to determine the cause of failure of those implants. This was a retrospective review of all primary Kine-max Plus TKR performed at the Avon Orthopaedic Center between 1.1.1990 and 1.1.2000. Cases were identified that required revision arthroplasty in any form within 5 years of the index procedure. Case notes and Xrays were reviewed to determine causes of failure. There were 2826 primary Kinemax Plus TKR performed during the study period. Of these 20 were known to have required revision surgery within 5 years. 8 were revised for deep infection of the prosthesis and 12 for aseptic causes. The overall incidence of premature failure of the Kinemax Plus TKR at 5 years was 0.71%. The incidence of aseptic premature failure at 5 years was 0.42%. Detailed examination of the clinical records indicated that some form of technical error at the time of the index arthroplasty was responsible for the early failure of 6 prostheses. This equates to 0.21% of the procedures performed. Aseptic loosening of the remaining 6 cases could not be attributed to a specific cause

Three cases of posterior dislocation of the Kinemax Posterior- Stabilized total knee replacement are reported, and predisposing factors, including operative technique and prosthesis design, are discussed. All three patients underwent posterior-stabilised knee replacement surgery at the Avon Orthopaedic Centre for osteoarthritis, between 1984 and 2000. In all cases the patient represented to the Emergency Department of a local hospital with posterior dislocation, at between 9 months and 6 years postoperatively. The mechanism for dislocation was hyperflexion of the knee. The dislocations could not be reduced under sedation because of obstruction by the protruding tibial insert, and required general anaesthesia to disengage the components. In all cases posterior dislocation became recurrent problem, and further surgery was required to address the instability. Two of the three patients underwent exchange of their stabilised tibial inserts for thicker versions of the same design, in order to reduce the excessive laxity present in flexion. The third patient underwent exploratory surgery and it was found that his patellar button had separated from the underlying bone. The patella was therefore resurfaced, restoring the integrity of his extensor mechanism. No further dislocations have occurred in any of the three patients. The causes of posterior dislocation of posterior-stabilized total knee replacements are multifactorial. They include malrotation of the tibial component, although this was not found to be the case in the three patients reported here. The design of the prosthesis may also contribute, and the upsloping and relatively shallow tibial spine of the Kinemax prosthesis (Howmedica) appears to be less forgiving than others. This is particularly the case if soft tissue lateral release or excessive resection of the posterior condyles has produced an increased flexiongap and therefore excessive flexion laxity. Our cases demonstrate the pitfalls that can produce this uncommon but serious complication, some of which can be predicted preoperatively, particularly in the patient with a valgus knee or deficiency of the extensor mechanism

The aim of this study was to examine causes of the failed knee arthroplasty. Since 1980 the Bristol Knee Replacement Registry has prospectively recorded data on 3024 patients. Complete original and 5 year follow up data was available on 999 knees. The surgery was judged a failure if there was no improvement in the American Knee Society score at 5 years or if there had been a revision within that time. The prosthesis used was Kinematic in 471 knees, the Medial Unicompartmental Sled in 258 knees, the Kinemax Plus in 134 knees and a variety of other designs. At 5 years, 79 (7. 9%) either showed no improvement in the American Knee Society score or had been revised. The failure rate was 7% for the Kinematic, 7% for the medial Sled and 5% for the Kinemax Plus. 20% of the less frequently used designs failed. Five (0. 5%) knee replacements failed because of infection. 22 knees (2. 2%) had significant comorbidity that precluded a satisfactory functional outcome. For 7 knees (0. 7%), the patient exhibited patterns of abnormal illness behaviour that were thought to explain the poor outcome. A further 27 knees (2. 7%) failed because of technical errors either at the time of surgery (13 cases, 1. 3%), or in selecting a prosthesis which failed prematurely (14 cases 1. 4%). No cause for failure could be identified in 12 cases (1. 2%). The high failure rate amongst infrequently used prosthesis emphasises the need to use established designs. No cause for failure could be identified in 12 cases and 5 were due to infection; such cases are hard to avoid. This study shows the importance of assessing both the overall physical and psychological state of the patient if disappointing results are to be avoided. The most frequent cause of an unsatisfactory outcome was a technical one, which should be avoidable

Background: In the UK 80% unicompartmental knee replacements(UKRs) and 10% of total knee replacements(TKRs) use mobile bearings. It is suggested that mobile bearings are more physiological and wear less, however it is still unclear whether patients tolerate mobile bearing knee replacements as well. Patients and methods: We report four prospective studies,. Two compared fixed with mobile bearings in TKR and two in UKR. The prostheses involved were fixed and mobile variants of the Rotaglide (TKR), Kinemax (TKR) and Uniglide (UKR). In addition the Oxford and St. George Sled UKRs were compared. All except the Uniglide study were randomized prospective trials (RCTs). 611 patients were involved with a mean age of 68 years. Residual pain following surgery was assessed with either the Oxford Knee Score (OKS) or the WOMAC score. The patients were followed up at one and two years postoperatively by a Research nurse and the findings recorded prospectively on the Bristol Knee database. Results:. Study 1:. Rotaglide. Prospective RCT. 171 patients. Mean pain score (OKS) Fixed bearing 15.4 v Mobile bearing 13.2. P= 0.012. Fixed bearing prosthesis caused significantly less pain. Study 2:. Kinemax. Prospective RCT. 198 patients. Mean pain score (WOMAC) Fixed bearing 8.9 v Mobile bearing 8.3. P = 0.443. Trend favouring fixed bearing. Study 3:. Uniglide Non-randomised trial. 184 patients. Mean pain score (WOMAC) Fixed bearing 7.6 v Mobile bearing 10.1. P < 0.001. Fixed bearing caused significantly less pain. Study 4:. St. George Sled v Oxford. Prospective RCT. 94 patients. Mean pain score (OKS) 15.8 v 13.9 . P= 0.058. Strong trend suggesting the Sled caused less pain. Conclusion: Our data suggests that the fixed bearing knee replacements result in less residual pain than their mobile bearing counterparts, at least in the first two years following surgery

One of the main surgical goals when performing a total knee replacement (TKR) is to ensure the implants are properly aligned and correctly sized; however, understanding the effect of alignment and rotation on the biomechanics of the knee during functional activities is limited. Cardiff University has unique access to a group of local patients who have relatively high frequency of poor alignment, and early failure. This provides a rare insight into how malalignment of TKR's can affect patients from a clinical and biomechanical point of view to determine how to best align a TKR. This study aims to explore relationship clinical surgical measurements of Implant alignment with in-vivo joint kinematics. 28 patient volunteers (with 32 Kinemax (Stryker) TKR's were recruited. Patients undertook single plane video fluoroscopy of the knee during a step-up and step-down task to determine TKR in-vivo kinematics and centre of rotation (COR). Joint Track image registration software (University of Florida, USA) was used to match CAD models of the implant to the x-ray images. Hip-Knee-Ankle (HKA) was measured using long-leg radiographs to determine frontal plane alignment. Posterior tibial slope angle was calculated using radiographs. An independent sample t-test was used to explore differences between neutral (HKA:-2° to 2°), varus (≥2°) and valgus alignment (≤-2°) groups. Other measures were explored across the whole cohort using Pearson's correlations (SPSS V23). There was found to be no statistical difference between groups or correlations for HKA. The exploratory analysis found that tibial slope correlated with Superior/Inferior translation ROM during step up (r=−0.601, p<0.001) and step down (r=−.512, p=0.03) the position of the COR heading towards the lateral (r=−.479, p=0.006) during step down. Initial results suggest no relationship between frontal plane alignment and in-vivo. Exploratory analyses have found other relationships that are worthy of further research and may be important in optimizing function