Bilateral total knee arthroplasty: One mobile-bearing and one fixed-bearing

We compared the early results of mobile-bearing knee prosthesis with fixed-bearing knee prosthesis in 16 patients who had one-stage, sequential, bilateral replacements. In each patient, a Low Contact Stress (LCS, Depuy) rotating-platform prosthesis was inserted in one side, and an Anatomic Modular Knee (AMK, Depuy) posterior-stabilised prosthesis was inserted in the other side. The same surgical routines were adopted for both sides in each patient. There were significant improvements in the Knee Society knee score and functional score, as well as the Oxford Knee score after both mobile-bearing and fixed-bearing knee replacements (p<0.001). However, we could not find any significant difference between the clinical results of the two prostheses. The authors early experience with the mobile-bearing total knee prosthesis was as favourable as the medium-term experience of the fixed-bearing total knee prosthesis in this prospective, match-pair study.     

Long-term results of low contact stress mobile-bearing total knee replacements

Five hundred ninety-eight consecutive primary low contact stress total knee replacements were done in 502 patients between 1985 and 1990. Clinical review was available for 495 knees (406 patients), 228 knees with meniscal-bearing prostheses and 267 knees with rotating-platform prostheses. The average followup was 12 years (range, 10-15 years). The average postoperative knee and functional scores were 87 points and 75 points, respectively. The average postoperative range of motion was 110 degrees. Fifty-six knees (11%) required revision for excessive wear of the tibial insert (41), dislocation (10), patellar polyethylene breakage (one), component loosening (one patellar, one tibial), and infection (two). During revision, osteolysis (20 knees), patellar polyethylene failure (33), and femoral component fracture (one) were seen. The overall survivorship was 88.1% at 15 years using Kaplan-Meier analysis. The survival rate was 83% for the meniscal-bearing prostheses and 92.1% for the rotating-platform prostheses. The Low Contact Stress mobile-bearing knee prosthesis has no superiority over that of fixed-bearing knees, especially for the meniscal-bearing design in prevention of polyethylene failure or revision. Based on the results of this study, the use of the LCS meniscal-bearing prosthesis does not appear to be justified.     

Mobile-bearing knee replacement: clinical results: a review of the literature.

Mobile-bearing knee replacements have been implanted for more than 20 years. The Oxford unicompartmental replacement and the LCS (low contact stress) total knee system have been studied extensively. Ninety-five to 97% 10-year survivorship rates of the Oxford unicompartmental replacement have been reported. Low contact stress meniscal-bearing survivorship rates of 98% at 6 years and 94.6% at 8 years have been reported. Ninety-five to 100% survivorship rates at the 11- and 12-year followup have been reported for low contact stress rotating platform knee replacements. Complications with the Oxford unicompartmental replacement include an increase in bearing dislocation and an increase in loosening rate when the components were placed in knees that had anterior cruciate ligament deficiency. Complications with the low contact stress total knee system include bearing dislocation (meniscal, rotating platform, and patellar), bearing breakage, and polyethylene wear. If mobile-bearing knee replacements are inserted with the same precision as fixed-bearing knee replacements, the results should at least be comparable. There may be some potential for an increase in durability, compared with fixed-bearing knee replacements, especially those of a modular design.     

Comparison of anterior-posterior-glide and rotating-platform low contact stress mobile-bearing total knee arthroplasties

BACKGROUND: The anterior-posterior-glide Low Contact Stress mobile-bearing knee prosthesis was developed to approximate the natural kinematics of the knee more closely than the rotating-platform Low Contact Stress mobile-bearing knee prosthesis does. The purpose of the present study was to compare the results associated with these two prostheses in patients managed with simultaneous bilateral total knee replacement. METHODS: One hundred and ninety patients received an anterior-posterior-glide Low Contact Stress mobile-bearing prosthesis in one knee and a rotating-platform Low Contact Stress mobile-bearing prosthesis in the contralateral knee. The mean age of the patients at the time of the index procedure was sixty-four years. Eleven patients were men, and 179 patients were women. The mean duration of follow-up was 6.4 years (range, five to seven years). The patients were followed clinically and radiographically with use of the knee-rating systems of the Knee Society and the Hospital for Special Surgery. RESULTS: The mean postoperative Hospital for Special Surgery knee score was 89.4 points for the knees treated with the anterior-posterior-glide mobile-bearing prosthesis and 88.6 points for those treated with the rotating-platform mobile-bearing prosthesis. Three knees in each group had a poor result. Two knees in each group had persistent moderate pain. One knee with an anterior-posterior-glide prosthesis had permanent tibial and deep peroneal nerve palsies, and one knee with a rotating-platform prosthesis had a permanent deep peroneal nerve palsy. No knee had aseptic loosening, revision, measurable wear of the tibial or patellar polyethylene bearing, or osteolysis. CONCLUSIONS: After a minimum duration of follow-up of five years, the results associated with the anterior-posterior-glide and rotating-platform Low Contact Stress mobile-bearing total knee replacements were favorable and comparable.     

活动平台与固定平台全膝关节置换的比较研究

目的评价人工全膝关节置换术中使用活动平台和固定平台假体治疗膝骨关节炎的早期疗效。方法对2009年3月至2011年3月收治的诊断为膝骨关节炎的患者,随机应用活动平台型假体和固定平台型假体行全膝关节置换（total knee arthroplasty,TKA）手术。记录术前及随访时术膝的膝关节评分、疼痛评分、功能评分、髌骨评分和膝关节活动度,以及股骨角、胫骨角、膝外翻角、胫骨平台后倾角、截骨高度。结果术前活动平台组和固定平台组的年龄、体重指数、患膝内翻畸形、最大屈曲角度及屈曲挛缩度均无统计学差异（P〉0.05）。术后平均随访26个月,活动平台组和固定平台组的术前术后膝关节评分、疼痛评分、功能评分、髌骨评分均无统计学差异（P〉0.05）,都明显地改善了患膝的症状和功能。活动平台组和固定平台组的术后最大屈曲度间存在显著性差异（P〈0.05）。两组的股骨角、胫骨角、膝外翻角、胫骨平台后倾角、截骨高度和术前术后髌骨高度无显著性差异（P〉0.05）。结论活动平台型假体和固定平台型假体TKA均明显改善了患膝的症状和功能,两组的膝关节评分、功能评分、疼痛评分、髌骨评分及X线检查评价差异均无统计学意义。固定平台组的术后最大屈曲度大于活动平台组的最大屈曲度。     

In vivo kinematics for fixed and mobile-bearing posterior stabilized knee prostheses

This is the first in vivo kinematic study to compare mobile-bearing with fixed-bearing prostheses in patients who had total knee arthroplasties. Femorotibial contact positions for 40 patients implanted with either a fixed-bearing or mobile-bearing prosthesis were analyzed using videofluoroscopy. Femorotibial contact paths were determined using a computer automated model-fitting technique. Nineteen of 20 patients in each group experienced posterior femoral rollback of their lateral condyles, with a mean of 3.6 and 3.7 mm for fixed-bearing and mobile-bearing prostheses respectively. Eighteen patients who had mobile-bearing prostheses and 17 patients with fixed-bearing knee prostheses experienced a normal pattern of axial rotation of 7.3 degrees and 4.1 degrees respectively. Eleven of 20 (55%) patients who had mobile-bearing prostheses implanted and eight of 20 (40%) patients who had fixed-bearing prostheses implanted did not experience femoral condylar lift-off. The remaining knees had condylar lift-off less than 2.4 mm for fixed-bearing prostheses and 1.7 mm for mobile-bearing prostheses, respectively. Patients who had mobile-bearing prostheses implanted experienced greater axial rotation and less condylar lift-off than patients who had fixed-bearing prostheses implanted. Both cruciate ligaments are sacrificed for the mobile and fixed-bearing total knee replacements. The results from the current study showed that, in both groups, the majority of patients experienced kinematics similar to those of a normal knee. However, the extent of lateral femoral condyle posterior rollback and the extent of axial rotation were less.     

A comparison of fixed-bearing and mobile-bearing total knee arthroplasty at a minimum follow-up of 4.5 years

BACKGROUND: Durable long-term independent results with the Low Contact Stress rotating-platform (mobile-bearing) and the Insall Burstein-II (fixed-bearing) total knee prostheses have been reported, but no studies describing either the mid-term or long-term results and comparing the two prostheses are available, to our knowledge. METHODS: Thirty-two patients who had bilateral arthritis of the knee with similar deformity and preoperative range of motion on both sides and who agreed to have one knee replaced with a mobile-bearing total knee design and the other with a fixed-bearing design were prospectively evaluated. Comparative analysis of both designs was done at a mean follow-up period of six years, minimizing patient, surgeon, and observer-related bias. Clinical and radiographic outcome, survival, and complication rates were compared. RESULTS: Patients with osteoarthritis had better function scores and range of motion compared with patients with rheumatoid arthritis. However, with the numbers available, no benefit of mobile-bearing over fixed-bearing designs could be demonstrated with respect to Knee Society scores, range of flexion, subject preference, or patellofemoral complication rates. Radiographs showed no difference in prosthetic alignment. Two knees with a mobile-bearing prosthesis required a reoperation: one had an early revision because of bearing dislocation and another required conversion to an arthrodesis to treat a deep infection. CONCLUSIONS: We found no advantage of the mobile-bearing arthroplasty over the fixed-bearing arthroplasty with regard to the clinical results at mid-term follow-up. The risk of bearing subluxation and dislocation in knees with the mobile-bearing prosthesis is a cause for concern and may necessitate early revision. LEVEL OF EVIDENCE: Therapeutic Level II.     

Natural history and pathogenesis of the patella clunk syndrome

Introduction The current study aims to test the importance of the design of total knee prostheses in the 'patella clunk syndrome', which is one of the possible patellofemoral complications that can occur after total knee replacement.Materials and methods Three patient cohorts consisting of 75 consecutive patients with 80 Insall-Burstein II (IB II) total knee replacements; 57 patients with 60 Anatomic Modular Knee (AMK) total knee replacements; and 103 patients with 106 Low Contact Stress Rotating Platform (LCS) total knee replacements were studied during the period from 1995 to 2001. This was an unselected series of elderly patients with knee arthritis of comparable demographics; we excluded only those patients receiving revision surgery. We recorded the preoperative and postoperative Knee Society scores, and the patient subgroups with postoperative patellofemoral complications were analysed in detail and were serially followed up. Radiological analysis followed the recommendation of the Knee Society, and the degree of pain was recorded on a visual analogue scale. Also, since the majority of patients with patella clunk syndrome had refused operation and were followed up for several years, an idea of the natural history of this condition was obtained.Results The relative frequency of occurrence of patella clunk syndrome among patients with the IB II, AMK, and LCS prostheses was 8.8%, 3.3%, and 0%, respectively. The calculated p value is strongly significant when comparing the IB II group with the LCS group (p<0.01); and of borderline significance when comparing the AMK with the LCS group (p=0.05); and not statistically significant between the IB II and AMK groups (p=0.19). Analysis of the results also showed that about half of the patients who underwent conservative treatment still had incapacitating symptoms after several years of follow-up, while the other half showed progressive improvement over time. Conclusion Given a good surgical technique in component placement and debridement of the peripatella synovium, the design of a total knee prosthesis has a strong bearing on the incidence of the patella clunk syndrome. The natural history of the patella clunk syndrome reveals that for as yet uncertain reasons about 50% will improve with time even when given conservative treatment.     

Mid-term survivorship results for a rotating-platform knee prosthesis

Interest in mobile-bearing knee prostheses is increasing in the US market. We studied results at 2 to 5 years with a mobile-bearing system that includes a cobalt-chrome tibial tray and femoral component with a polyethylene cruciate-retaining tibial component insert that allows rotation around a central axis and can be used with cruciate-retaining or posterior-stabilized femoral components. The inserts used in this study were cruciate retaining and did not include the posterior-stabilized design. The goal of this study was to demonstrate the function and safety of this prosthesis along with the lack of spinout, which is a major concern in the mobile-bearing knee. Four hundred thirty-five knees constituted the study cohort and underwent survivorship analysis and complication reporting. Routine clinic evaluations included pre- and postoperative radiographs and Knee Society knee and function scores at 6 and 12 weeks and every 2 years. The most recent follow-up data within 2 to 5 years was included for the study along with survey data. Flexion at most recent follow-up averaged 125°. Knee Society score at most recent visit averaged 88 of 100. Knee Society function score averaged 83 of 100. Radiographic results were available for 226 knees, with 97.3% assessed as normal and 6 with these issues: patella stress fracture (3), aseptic tibial loosening (1), patellar osteolysis (1), and patella aseptic loosening (1). In comparison with the fixed-bearing knee equivalent, this mobile-bearing knee demonstrated at least equivalent results in terms of survivorship, function, and patient satisfaction in the short- and mid-term.     

Long-term followup after mobile-bearing total knee replacement

Clinical and radiographic analyses and survivorship were done on the initial cementless series of 309 posterior cruciate-retaining meniscal-bearing and rotating-platform New Jersey LCS total knee replacements followed up for 10 to 20 years (mean, 12.4 years). Clinical results in patients surviving at least 10 years using a strict knee scoring scale were similar for posterior cruciate ligament-retaining and posterior cruciate ligament-sacrificing designs. Good to excellent results were seen in 97.9% of primary posterior cruciate-retaining-bearing prostheses and in 97.9% of primary rotating-platform prostheses. Radiographic analysis of minimum 10-year followup radiographs showed generally stable fixation of all components with gross migration seen in one tibial component (0.6%) in a patient with a failed high tibial osteotomy. Significant osteolysis was present requiring bearing exchange and bone grating in three patients with cementless rotating-platform prostheses (1.8%) who had multiple knee surgeries at an average of 10.2 years from the index surgery. Survivorship of the primary cementless posterior cruciate-retaining meniscal-bearing prostheses with an end point of revision for any mechanical reason was 97.4% at 10 years and 83% at 16 years; using an end point of a poor clinical knee score, the survivorship was 98.9% at 10 and 16 years, respectively. Survivorship of the primary cementless rotating-platform prostheses with end points of revision for any mechanical reason or a poor clinical knee score was 98.3% survivorship at 10 and 18 years, respectively. In the current study, no cementless rotating-bearing patella loosened, fractured, or dissociated in patients without prior knee surgery although one cementless rotating-bearing patella (0.6%) in a patient who had multiple knee surgeries wore through the inferior marker wire after 10.8 years, causing metallosis that required revision.     

Lateral unicompartmental knee replacements: early results from a District General Hospital

Lateral unicompartment knee replacements are performed infrequently in the United Kingdom. This study evaluates the experience of two knee surgeons in a District General Hospital for all lateral unicompartmental arthroplasties performed between October 2007 and August 2011. Two different implants were used in this time period, the Oxford domed and the Zimmer fixed-bearing system. Twenty-seven procedures were completed in this time span (15 Oxford domed and 12 Zimmer fixed bearing), all of which once completed were followed up and 21 patients completed an Oxford knee score. Average Oxford knee scores were 36.6 (95 % CI 29.0–44.2) for the Oxford domed prosthesis and 28.6 (19.8–37.5) for the Zimmer fixed-bearing prosthesis (p = 0.15). One patient with an Oxford domed prosthesis required revision for bearing dislocation. The follow-up Oxford knee scores support the use of this technique as an alternative to total knee replacement but with no significant difference in functional outcome. Our results, however, may encourage a more cautious approach to the use of a mobile-bearing prosthesis in favour of a fixed-bearing prosthesis.     

A kinematic comparison of fixed- and mobile-bearing knee replacements

Mobile-bearing posterior-stabilised knee replacements have been developed as an alternative to the standard fixed- and mobile-bearing designs. However, little is known about the in vivo kinematics of this new group of implants. We investigated 31 patients who had undergone a total knee replacement with a similar prosthetic design but with three different options: fixed-bearing posterior cruciate ligament-retaining, fixed-bearing posterior-stabilised and mobile-bearing posterior-stabilised. To do this we used a three-dimensional to two-dimensional model registration technique. Both the fixed- and mobile-bearing posterior-stabilised configurations used the same femoral component. We found that fixed-bearing posterior stabilised and mobile-bearing posterior-stabilised knee replacements demonstrated similar kinematic patterns, with consistent femoral roll-back during flexion. Mobile-bearing posterior-stabilised knee replacements demonstrated greater and more natural internal rotation of the tibia during flexion than fixed-bearing posterior-stabilised designs. Such rotation occurred at the interface between the insert and tibial tray for mobile-bearing posterior-stabilised designs. However, for fixed-bearing posterior-stabilised designs, rotation occurred at the proximal surface of the bearing. Posterior cruciate ligament-retaining knee replacements demonstrated paradoxical sliding forward of the femur. We conclude that mobile-bearing posterior-stabilised knee replacements reproduce internal rotation of the tibia more closely during flexion than fixed-bearing posterior-stabilised designs. Furthermore, mobile-bearing posterior-stabilised knee replacements demonstrate a unidirectional movement which occurs at the upper and lower sides of the mobile insert. The femur moves in an anteroposterior direction on the upper surface of the insert, whereas the movement at the lower surface is pure rotation. Such unidirectional movement may lead to less wear when compared with the multidirectional movement seen in fixed-bearing posterior-stabilised knee replacements, and should be associated with more evenly applied cam-post stresses.     

Modular fixed-bearing total knee arthroplasty with retention of the posterior cruciate ligament. A study of patients followed for a minimum of fifteen years

BACKGROUND: There have been a limited number of studies of total knee arthroplasties with durations of follow-up of fifteen years, but we are not aware of any involving modular fixed-bearing posterior cruciate-retaining prostheses. METHODS: A consecutive series of 139 total knee arthroplasties in 109 patients (average age, sixty-seven years), performed by one surgeon using a nonconforming posterior cruciate-retaining prosthesis, was followed for fifteen years or longer. Forty-five patients (fifty-nine knees) were examined at a minimum of fifteen years postoperatively, fifty-seven patients (seventy knees) had died, five patients (eight knees) were too ill to return for assessment, and two patients (two knees) were considered lost to follow-up. The patients were assessed clinically with use of the Knee Society clinical rating system, and the knees were assessed radiographically. Survivorship analysis was performed with use of worst-case-scenario analysis and with failure defined as a reoperation for any reason. RESULTS: There were five reoperations, four of which were performed because of wear of the polyethylene insert. In addition, one loose cemented femoral component was revised at fifteen years. The survival rate without revision or a need for any reoperation was 92.6% at fifteen years. The mean Knee Society score and functional score at fifteen years were 96 and 78 points, respectively. The prevalence of radiolucent lines was 13%, with 2% around the femur, 11% around the tibia, and none around the patella. None of these lines were clinically relevant. There was no evidence of progressive radiolucent lines, and there was one case of asymptomatic femoral osteolysis. CONCLUSIONS: In this single-surgeon series, modular fixed-bearing posterior cruciate-retaining total knee arthroplasties had good clinical and radiographic results with excellent survivorship for up to fifteen years. These results are comparable with those in long-term studies of posterior stabilized implants and of prostheses with mobile-bearing and nonmodular tibial inserts.     

Tibiofemoral force following total knee arthroplasty: comparison of four prosthesis designs in vitro.

Despite ongoing evolution in total knee arthroplasty (TKA) prosthesis design, restricted flexion continues to be common postoperatively. Compressive tibiofemoral force during flexion is generated through the interaction between soft tissues and prosthesis geometry. In this study, we compared the compressive tibiofemoral force in vitro of four commonly used prostheses: fixed-bearing PCL (posterior cruciate ligament)-retaining (PFC), mobile-bearing posterior-stabilized (PS), posterior-stabilized with a High Flex femoral component (HF), and mobile-bearing PCL-sacrificing (LCS). Fourteen fresh-frozen cadaver knee joints were tested in a passive motion rig, and tibiofemoral force measured using a modified tibial baseplate instrumented with six load cells. The implants without posterior stabilization displayed an exponential increase in force after 90 degrees of flexion, while PS implants maintained low force throughout the range of motion. The fixed-bearing PFC prosthesis displayed the highest peak force (214 +/- 68 N at 150 degrees flexion). Sacrifice of the PCL decreased the peak force to a level comparable with the LCS implant. The use of a PCL-substituting post and cam system reduced the peak force up to 78%, irrespective of whether it was a high-flex or a standard PS knee. However, other factors such as preoperative range of motion, knee joint kinematics, soft tissue impingement, and implantation technique play a role in postoperative knee function. The present study suggests that a posterior-stabilized TKA design might be advantageous in reducing soft tissue tension in deep flexion. Further research is necessary to fully understand all factors affecting knee flexion after TKA.     

Prevalence of osteolysis after simultaneous bilateral fixed- and mobile-bearing total knee arthroplasties in young patients

This study aimed to evaluate the clinical and radiographic results and to document the prevalence of osteolysis associated with fixed-bearing (anatomic modular knee) and mobile-bearing (low contact stress) total knee arthroplasties (TKAs) in 61 patients younger than 55 years who had bilateral simultaneous primary TKAs. Forty-five patients were female and 16 patients were male. The mean age of the patients was 48.3 years (range, 34-55 years). The mean postoperative Knee Society knee and functional score were similar in both groups (91 and 90 points and 85 and 86 points, respectively). Three knees (5%) in each group were revised for wear of the tibial bearing, and 1 knee (2%) in the mobile-bearing TKA was revised for dislocation of the meniscal bearing. Osteolysis was identified in both radiographs and computed tomography scans in 6 knees (10%) in the anatomic-modular-knee group and 4 knees (7%) in the low-contact-stress group.     

Simultaneous mobile- and fixed-bearing total knee replacement in the same patients. A prospective comparison of mid-term outcomes using a similar design of prosthesis

We conducted a randomised prospective study to evaluate the clinical and radiological results of a mobile- and fixed-bearing total knee replacement of similar design in 174 patients who had bilateral simultaneous knee replacement. The mean follow-up was for 5.6 years (5.2 to 6.1). The total knee score, pain score, functional score and range of movement were not statistically different (p > 0.05) between the two groups. Osteolysis was not seen in any knee in either group. Two knees (1%) in the mobile-bearing group required revision because of infection; none in the fixed-bearing group needed revision. Excellent results can be achieved with both mobile- and fixed-bearing prostheses of similar design at mid-term follow-up. We could demonstrate no significant clinical advantage for a mobile bearing.     

An analysis of rotating-platform total knee replacements

Rotating-platform, mobile-bearing total knee replacements have been developed to improve knee kinematics, lower contact stresses on the polyethylene tibial component, minimize constraint, and allow implant self-alignment. The purpose of the current study was to examine some of these parameters. Gait studies during normal gait showed that the stance phase was associated with knee flexion between 8 degrees and 15 degrees. Contact area studies have shown two types of rotating-platform total knee replacements, namely gait congruous (congruous only during the stance phase of gait) and totally congruous (congruous up to 90 degrees knee flexion) implants. Knee simulator studies have shown increased gravimetric wear with rotating-platform total knee replacements compared with their fixed-bearing counterparts. Rotate-only implants had less gravimetric wear than rotate and translate rotating-platform total knee replacements. Clinical studies show similar outcomes (knee scores, range of motion, and complications) when rotating-platform and fixed-bearing total knee replacements are compared. Although attractive, the benefits of rotating-platform total knee replacements still need to be proven.     

固定平台与旋转平台假体用于外翻膝的早期疗效观察

目的:比较外翻膝人工全膝关节置换术应用旋转平台和固定平台两型假体的早期临床疗效。方法:选取2011年1月至2013年12月吉林大学第一医院骨关节外科由同一医师进行初次人工膝关节置换的17例(23膝)进行回顾性随访研究,其中男2例,女15例;年龄48～75岁,平均61.5岁。术前诊断为骨性关节炎14例(19膝),类风湿性关节炎3例(4膝),所有膝关节有外翻畸形。其中9例(12膝)使用固定平台型假体(PFC Sigma),8例(11膝)使用旋转平台型假体(PFC Sigma RP).术前和术后随访行KSS、HSS、WOMAC评分,测量关节活动度、胫股角等指标,进行统计学分析。结果:所有患者获随访,时间6～36个月,平均25个月。两组患者膝外翻畸形均得到矫正,术后末次随访的KSS、HSS、WOMAC评分及膝关节活动度、胫股角较术前明显改善(P<0.01).其中固定平台组和旋转平台组在术后KSS、HSS、WOMAC评分以及胫骨角、膝关节活范围改善度方面比较,差异无统计学意义(P>0.05);而术后末次随访膝关活动范围固定平台组(101.8±8.8)°与旋转平台组(108.4±7.2)°差异有统计学意义(P<0.05).旋转平台组没有发现垫片脱位,两组术后均无感染、腓总神经麻痹、脱位、膝关节不稳等并发症发生,X线检查未见假体骨溶解及松动发生。结论:外翻膝人工全膝关节置换术使用旋转平台和固定平台型假体均能获得满意的早期临床效果,两者的近期临床疗效比较无明显差异。     

The long-term results of simultaneous fixed-bearing and mobile-bearing total knee replacements performed in the same patient

We compared the results of 146 patients who received an anatomic modular knee fixed-bearing total knee replacement (TKR) in one knee and a low contact stress rotating platform mobile-bearing TKR in the other. There were 138 women and eight men with a mean age of 69.8 years (42 to 80). The mean follow-up was 13.2 years (11.0 to 14.5). The patients were assessed clinically and radiologically using the rating systems of the Hospital for Special Surgery and the Knee Society at three months, six months, one year, and annually thereafter. The assessment scores of both rating systems pre-operatively and at the final review did not show any statistically significant differences between the two designs of implant. In the anatomic modular knee group, one knee was revised because of aseptic loosening of the tibial component and one because of infection. In addition, three knees were revised because of wear of the polyethylene tibial bearing. In the low contact stress group, two knees were revised because of instability requiring exchange of the polyethylene insert and one because of infection. The radiological analysis found no statistical difference in the incidence of radiolucent lines at the final review (Student's t-test, p = 0.08), most of which occurred at tibial zone 1. The Kaplan-Meier survivorship for aseptic loosening of the anatomic modular knee and the low contact stress implants at 14.5 years was 99% and 100%, respectively, with a 95% confidence interval of 94% to 100% for both designs. We found no evidence of the superiority of one design over the other at long-term follow-up.     

A randomised controlled clinical trial and gait analysis of fixed- and mobile-bearing total knee replacements with a five-year follow-up

This study compared the outcome of total knee replacement (TKR) in adult patients with fixed- and mobile-bearing prostheses during the first post-operative year and at five years' follow-up, using gait parameters as a new objective measure. This double-blind randomised controlled clinical trial included 55 patients with mobile-bearing (n = 26) and fixed-bearing (n?= 29) prostheses of the same design, evaluated pre-operatively and post-operatively at six?weeks, three months, six months, one year and five years. Each participant undertook two walking trials of 30 m and completed the EuroQol questionnaire, Western Ontario and McMaster Universities osteoarthritis index, Knee Society score, and visual analogue scales for pain and stiffness. Gait analysis was performed using five miniature angular rate sensors mounted on the trunk (sacrum), each thigh and calf. The study population was divided into two groups according to age (≤ 70 years versus > 70 years). Improvements in most gait parameters at five years' follow-up were greater for fixed-bearing TKRs in older patients (> 70 years), and greater for mobile-bearing TKRs in younger patients (≤ 70 years). These findings should be confirmed by an extended age controlled study, as the ideal choice of prosthesis might depend on the age of the patient at the time of surgery.