Aims. Metal particles detached from metal-on-metal hip prostheses (MoM-THA) have been shown to cause inflammation and destruction of tissues. To further explore this, we investigated the histopathology (aseptic lymphocyte-dominated vasculitis-associated lesions (ALVAL) score) and metal concentrations of the periprosthetic tissues obtained from patients who underwent revision knee arthroplasty. We also aimed to investigate whether accumulated metal debris was associated with ALVAL-type reactions in the synovium. Methods. Periprosthetic metal concentrations in the synovia and histopathological samples were analyzed from 230 patients from our institution from October 2016 to December 2019. An ordinal regression model was calculated to investigate the effect of the accumulated metals on the histopathological reaction of the synovia. Results. Median metal concentrations were as follows: cobalt: 0.69 μg/g (interquartile range (IQR) 0.10 to 6.10); chromium: 1.1 μg/g (IQR 0.27 to 4.10); and titanium: 1.6 μg/g (IQR 0.90 to 4.07). Moderate ALVAL scores were found in 30% (n = 39) of the revised knees. There were ten patients with an ALVAL score of 6 or more who were revised for suspected periprosthetic joint infection (PJI), aseptic loosening, or osteolysis. R2 varied between 0.269 and 0.369 for the ordinal regression models. The most important variables were model type, indication for revision, and cobalt and chromium in the ordinal regression models. Conclusion. We found that metal particles released from the knee prosthesis can accumulate in the periprosthetic tissues. Several patients revised for suspected culture-negative PJI had features of an ALVAL reaction, which is a novel finding. Therefore, ALVAL-type reactions can also be found around knee prostheses, but they are mostly mild and less common than those found around metal-on-metal prostheses. Cite this article: Bone Joint Res 2024;13(4):149–156

Aims. This study aimed to evaluate the association between the sagittal alignment of the femoral component in total knee arthroplasty (TKA) and new Knee Society Score (2011KSS), under the hypothesis that outliers such as the excessive extended or flexed femoral component were related to worse clinical outcomes. Methods. A group of 156 knees (134 F:22 M) in 133 patients with a mean age 75.8 years (SD 6.4) who underwent TKA with the cruciate-substituting Bi-Surface Knee prosthesis were retrospectively enrolled. On lateral radiographs, γ angle (the angle between the distal femoral axis and the line perpendicular to the distal rear surface of the femoral component) was measured, and the patients were divided into four groups according to the γ angle. The 2011KSSs among groups were compared using the Kruskal-Wallis test. A secondary regression analysis was used to investigate the association between the 2011KSS and γ angle. Results. According to the mean and SD of γ angle (γ, 4.0 SD 3.0°), four groups (Extended or minor flexed group, −0.5° ≤ γ < 2.5° (n = 54)), Mild flexed group (2.5° ≤ γ < 5.5° (n = 63)), Moderate flexed group (5.5° ≤ γ < 8.5° (n = 26)), and Excessive flexed group (8.5° ≤ γ (n = 13)) were defined. The Excessive flexed group showed worse 2011KSSs in all subdomains (Symptoms, Satisfaction, Expectations, and Functional activities) than the Mild flexed group. Secondary regression showed a convex upward function, and the scores were highest at γ = 3.0°, 4.0°, and 3.0° in Satisfaction, Expectations, and Functional activities, respectively. Conclusion. The groups with a sagittal alignment of the femoral component > 8.5° showed inferior clinical outcomes in 2011KSSs. Secondary regression analyses showed that mild flexion of the femoral component was associated with the highest score. When implanting the Bi-Surface Knee prosthesis surgeons should pay careful attention to avoiding flexing the femoral component extensively during TKA. Our findings may be applicable to other implant designs. Cite this article: Bone Joint J 2020;102-B(6 Supple A):36–42

Introduction. Post cam structure, which is the main structure of posterior-stabilized design (PS), is useful to realize the intrinsic stability of a knee prosthesis replaced for a case with the severe degeneration. A large size post might, however, shorten the range of knee motion. On the other hand, retrieval studies sometimes reveal the ultrahigh molecular weight polyethylene (UHMWPE) deformation or severe failure of the tibial post of PS knee. Strength of a tibial post of available design is obviously insufficient to prevent the severe deformation. Therefore, minimally required size of the post should be clarified for polyethylene inserts. In the present study, we performed finite element (FE) analysis assumed the mechanical conditions of a tibial post in a PS knee and aimed to design criterion of a post of polyethylene insert of a knee prosthesis. Method. The shape of one commercially available knee prosthesis was referred as a posterior-stabilized knee prosthesis. The contour of the metallic femoral component was traced and digitized by hand. The contour of the UHMWPE insert was digitized by a micro computed tomography apparatus. Three dimensional finite elements were generated by a modeling software (Simpleware, Ltd. UK) as total 83000 four-noded tetrahedral elements. The bottom of the tibial insert was fully constrained. Load on femoral component was assumed to realize the tibial post impingement under several kinds of knee motions. Posterior load 100 N or 500N at the 10 degree hyperextension, anterior load 500N or 1000N during 120 degree flexion were applied (Fig. 1). The software of FE analysis was LS-DYNA ver.971 (Livemore Software Technology Corp. USA). The hardware was Endeaver Pro-4500 (EPSON Corp. Japan). The distributed values of von Mises stress and plastic strain of the tibial post were shown as the results of the analysis. Results. At the 10 degree hyperextension, the maximum values of von Mises stress and plastic strain of anterior aspect of tibial post were 26.0 MPa, 0.054 at posterior load 100 N., 35.3 MPa, 0.383 at posterior load 500N, respectively (Fig. 2). At 120 degree flexion, these values of posterior aspect of tibial post were 27.6 MPa, 0.086 at anterior load 500 N, 32.1 MPa, 0.208 at anterior load 1000N, respectively (Fig. 3). Plastic deformation has occurred on the contact area, as shown in Fig. 2, 3. Discussion. Our results showed that large plastic deformation may occur in the anterior or the posterior aspect of a tibial post by impingement during common exercises like running, climbing up, or squatting. In the femoro-tibial articulation, the true-stress decreases with increase in load because the compressive deformation can widen the contact area on the UHMWPE. The true-stress in the tibial post, however, increases with increase in load because bending and tensile deformation reduces the section area. Therefore, the design criterion of tibial post of PS knee prosthesis including the size of the post must be revised the safety coefficient that realize the sufficiently lower stress generated in the tibial post than the yield stress of UHMWPE

Introduction and Objectives: There are knee prostheses that are specifically designed for the treatment of extreme cases of surgical revision of cases with large bone losses. These are hinged systems that provide greater stability and have a wide range of components to reconstruct bone defects Experience with this type of prosthesis is usually limited, due to the fact that it is used in complex and sporadic cases. Our aim is to review the results obtained with the implant of this prosthesis in our unit. Materials and Methods: From June 2000 until March 2008 we implanted 10 salvage knee prostheses (5 TKR OSS, 5 TKR FINN). These procedures were carried out in 6 women and 4 men of 33 to 77 years of age. Indications for these procedures were many, with predominance of revision surgery of septic knee, bone tumors and failure of an infected osteosynthesis. Results: We achieved pain relief in 7 patients: Mean morbidity > 45° in 7 cases. And 90% of the patients were satisfied. Discussion and Conclusions: Large bone defects are difficult to reconstruct, especially when a joint is affected. Revision surgery is difficult and has poor results. Knee salvage prostheses are capable of providing a stable non-painful knee in severely incapacitated patients. We had few complications and we hope to have more cases and be able to carry out a longer follow-up of the ones we had. We are optimistic and we have named this prosthesis ‘the third knee prosthesis’

Introduction. Post cam is useful to realize the intrinsic stability of a posterior-stabilized (PS) knee prosthesis replaced for a case with the severe degeneration. Some retrieval studies reveal the ultrahigh molecular weight polyethylene (UHMWPE) deformation or severe failure of the tibial post of PS knee. Strength of the tibial post of available design is obviously insufficient to prevent the severe deformation. The large size post might, however, shorten the range of knee motion. Therefore, minimally required size of the post should be clarified for polyethylene inserts. In the present study, we performed finite element (FE) analysis assumed the mechanical conditions of a tibial post in a PS knee and aimed to design criterion of a post of polyethylene insert of a knee prosthesis. Method. The shape of three commercially available knee prostheses, product A, B, and C was referred as PS knee prosthesis. The contour of the metallic femoral component and the UHMWPE insert were digitized by a computed tomography apparatus. Three dimensional finite elements were generated by modeling software (Simpleware, Ltd. UK) as four-node tetrahedral elements. In FE analysis, we used LS-DYNA ver.971 (Livemore Software Technology Corp. USA) as the software and Endeaver Pro-4500 (EPSON Corp. Japan) as the hardware. These bottoms of the tibial insert were fully constrained. The value of 30MPa was defined as yield stress of UHMWPE. 500N posterior load was applied to each femoral component at 10 degree hyperextension. Then, 1000N anterior load at 120 degree flexion, after tibial insert was located 10 degree internal rotation (Fig. 1). These loads were assumed to realize the two types of tibial post impingement under several kinds of knee motions. The distributed values of von Mises stress and plastic strain on the tibial post were shown as the results of the analysis. Results. At the 10 degree hyperextension, these maximum values of von Mises stress were 24.5, 3.23, 27.09MPa on anterior aspect of tibial post of the product A, B, and C, respectively (Fig. 2). These plastic strains were 0.045, 0.001, 0.064. At the 120 degree flexion, these maximum values of von Mises stress were 33.67, 4.53, 27.03MPa on posterior aspect of the product A, B, and C, respectively (Fig. 3). These plastic strains were 0.28, 0.004, 0.061. The stress of product A was higher than yield stress of UHMWPE. The strain was obviously higher than that of product B and C. Discussion. Our results showed that plastic deformation may occur in the posterior aspect of a tibial post by impingement during common exercises like climbing up, or squatting. In the femoro-tibial articulation, the true-stress decreases with increase in load because the compressive deformation can widen the contact area on the UHMWPE. The true-stress in the tibial post, however, increases with increase in load because bending and tensile deformation reduces the section area. Therefore, the design criterion including the post size must be revised the safety coefficient which realizes that the generated stress in the tibial post is sufficiently lower than the yield stress of UHMWPE

Aim. Analysis of the effect of administration of antibiotics before collection of microbiology samples in patients with septic arthritis of the native and prosthetic knee. Method and Results. A retrospective analysis of patients admitted to the unit with a diagnosis of septic arthritis of the knee. There were 27 infections in 26 native knees and 27 infections in 26 prosthetic knees. Sixty-three percent of the native knees had received antibiotics prior to collection of microbiology samples. Fifty-three percent of these grew an organism from at least one of their aspirate, washout fluid or swab. Of the 37% that did not have antibiotics 100% grew an organism. There was no difference in the type or length of treatment required between the groups. Forty-one percent of the prosthetic knees had received antibiotics prior to collection of microbiology samples. Forty-five percent of these had an organism identified. Of the 59% that did not have antibiotics 81% had an organism identified. Overall 67% had an organism isolated, fifty-six percent of these retained their implant. Thirty-three percent of those with no organism identified retained their implant. Conclusion. Administration of antibiotics before samples have been collected for microbiology has a significant effect on the likelihood of isolating a responsible organism in both native and prosthetic knees. This does not have an effect on the outcome in the native knee but does have a significant effect in the prosthetic knee

The range of motion (ROM) after total knee arthroplasty (TKA) is one of the most important factors for patient satisfaction, especially in Asian countries. To enhance the knee flexion angle, “high-flexion” designs have been introduced in total knee prostheses. One of such design was a new design of femoral prosthesis, which increased the posterior cut on the bone by 2 mm and thickened the posterior condyle, allowing the posterior condylar radius to continue further. There were several reports on postoperative ROM of such “high-flexion” posterior-stabilized (PS) total knee prosthesis. However, there was no report on the postoperative ROM of “high-flexion” cruciate ligament retaining (CR) total knee prosthesis. The purpose of this study was to compare the ROM associated with standard and high-flexion posterior CR total knee prostheses. One hundred and fifty-one consecutive patients (176 knees) had CR total knee prosthesis. 89 knees had standard CR TKA (NexGen CR, Zimmer, Warsaw, IL), and 87 knees had high-flexion CR knee prostheses (NexGen CR-Flex, Zimmer, Warsaw, IL). Differences in the age, diagnosis, preoperative Knee Society Score (KSS), and preoperative ROM of the knee between two groups were not significant. At one year postoperatively, the patients were assessed clinically and radiographically. The mean postoperative KSS knee score was 96.2 points for the standard CR prosthesis group and 96.7 points for the high-flexion CR prosthesis group (p=0.464). The mean postoperative KSS function score was 83.4 points for the standard CR prosthesis group and 84.8 points for the high-flexion CR prosthesis group (p=0.446). The mean postoperative ROM was 110.8 degrees in the standard CR prosthesis group, and 114.0 degrees in high-flexion prosthesis group (p=0.236). No knee had aseptic loosening, revision, or osteolysis. Previous report showed that “high-flexion” PS design did not increase postoperative ROM compared to standard design. However, there was no report on the postoperative ROM of “high-flexion” CR total knee prosthesis. We found no significant differences between the standard CR group and “high-flexion” CR group with regard to ROM or clinical and radiographic parameters. However, in the cases which achieved high flexion, “high-flexion” design, which chamfered posterior femoral edge, can reduce the possibility of deformation from posterior contacts under lord. Therefore, the results of the current study suggested that “high-flexion” CR design is not the design that increase ROM significantly, but might be the safe design even when the knee achieved deep flexion

The objective of this study is to determine the in-vivo knee joint kinematics of patients having specially designed knee prosthesis (Bi-surface) at sitting sedentary (seiza) state. An increase in the demand for TKA has required improvement in the durability and flexibility of knee prostheses. One of the representative cases which have improved knee flexion is Bi-surface knee. Bi-surface knee has two joint surfaces; one for weight bearing and the other for flexion motion which has a unique ball-and-socket joint. This knee prosthesis, having been applied for two decades, has not yet been precisely analyzed how the femoral and tibial components are articulating at deep knee flexion. Since there is no practical method to measure directly prosthetic kinematics in-vivo; we applied indirect techniques, pattern matching method to the Bi-surface patients. The method has been originated by Banks and Hodge (1964), and we have improved it in order to obtain higher and more reliable accuracies. The number of subjects examined by X-ray apparatus was 18 knees of 14 patients (3 male and 11 female) who could attain the seiza. Patients were asked to sit at seiza state and their Bi-surface knees were X-ray photographed from lateral side. We focused if the internal rotation was shown at maximum flexion as commonly shown for a normal knee. We also represented the CAD models with the same position/orientation as the data from the pattern matching, thereby investigating the contact states between the ball and socket by viewing them from the desired direction. The following results were introduced. The mean maximum flexion angle was 144.1° (SD=5.3°), and the mean internal rotation angle at maximum flexion was 15.2° (SD=6.6). The maximum flexion angle among all subjects was 153.3° and internal rotation was 19.5° at that flexion angle. The number of subjects which had (a) contact point(s) on the tibio-femoral and/or ball-socket surface(s) was 5 knees (2 knees had contact point on both the ball-and-socket and the tibio-femoral lateral surfaces, 3 knees had only on either surface) and the other 13 knees had a slight gap between two components. Correlation was found between the value of the maximum flexion angle and the value of internal rotation angle at that flexion; the subjects of larger maximum flexion angle also demonstrated larger internal rotation angle. This suggests that at deep knee flexion, the tibial internal rotation may play an important role after TKA as a normal knee does. By checking the CAD representations, we found that the tibio-femoral and ball-socket surfaces were separate for most subjects at seiza state. Although serious impingements were not found, it was suggested the risk of subluxation when a patient rises up. The limitation of our study is that we used simple still X-ray pictures. In order to assess kinematics for ascending from seiza state, kinematic analyses from fluoroscopic images are needed

The wear phenomenon of ultra-high molecular weight polyethylene (UHMWPE) in knee and hip prostheses is one of the major restriction factors on the longevity of theses implants. Despite quite a number of studies on the wear of UHMWPE, the wear mechanism is not clear yet. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear mechanism of UHMWPE. Especially for the artificial knee joint with anatomical design, the contact stresses in the UHMWPE tibial insert are generally higher than the yield stress of the material during normal gait. In addition, the predominant types of wear on reported simulator-tested and retrieved UHMWPE tibial inserts are delamination and pitting. These facts suggest that the fatigue fracture that causes micro-cracks both on and below the surface of the UHMWPE tibial insert and the generation of wear particles as fatigue type are closely related to the repeated plastic deformation. On the metallic femoral components of the retrieved knee prostheses with anatomical design, a number of microscopic scratches caused by various factors were observed. It is thought that microscopic surface asperities caused by this surface damage contribute to increasing and/or accelerating wear of the UHMWPE tibial insert. The primary objective of this study was to investigate the factors influencing the wear mechanism of UHMWPE tibial insert in knee prosthesis. In this study, macroscopic and microscopic elasto-plastic contact analyses of the UHMWPE tibial insert based on macroscopic and microscopic geometrical measurements from retrieved knee prosthesis were performed using finite element method (FEM) in order to investigate the mechanical state, plastic deformation behavior in the UHMWPE tibial insert and microscopic wear of the polyethylene caused by microscopic surface asperity. For this purpose, the determinative method of the contact position between the femoral component and the UHMWPE tibial insert for the retrieved knee prosthesis was developed. The three-dimensional FEM model of the retrieved knee prosthesis with worn contact surfaces was produced. Three-dimensional microscopic surface profile measurements of damaged surface of a retrieved metallic femoral component by using a laser microscope and reproduction of the femoral component surface by using 3D CAD software were performed in order to produce the 3D FEM models of the microscopic asperity based on actual measurement data. The analytical findings of this study suggest that maximum plastic strain below the surface is closely related to subsurface crack initiation and delamination of the retrieved UHMWPE tibial insert. The worn surface whose macroscopic geometrical congruity had been improved due to wear after joint replacement showed lower contact stress at the macroscopic level. The aspect ratio, shape ratio and indentation depth of the microscopic asperity have a significant effect on increasing and/or accelerating wear on the UHMWPE. Higher aspect ratios, shape ratios and indentation depths cause higher contact stresses and plastic strains in the UHMWPE. These are therefore significant factors influencing the wear mechanism of UHMWPE

Introduction: The prosthetic replacement of the infected knee is conditioned by the bone stock according with the A.O.R.I. We classified the bone defects on the infected knee following the Windsor protocol. When we find ourselves on a situation with T2-3 F2-3 and/or post-infection prosthetic replacements, we use tumoral knee prosthesis (“third prosthesis”). The main causes of segmentary bone defects at the knee, appear after high energy injuries, tumoral resections and after infected total knee arthroplasties. Nowadays the treatment of these lesions, supposes a challenge to the orthopaedic surgeons due to the difficulty of the bone and soft tissue lesions. Material and Methods: We present our first 35 cases involving tumoral knee prosthesis replacements after infected conminutive fractures around the knee, infected replacements and infections after tumoral resections. Initially we used the prosthesis FINN model (BIOMET©) on 11 cases, while we have used the RHK model (BIOMET©) on the remaining 24. We followed the two-stage reimplantation using antibiotic PMMA spacers either manual or preformed depending on the defect’s size. Exposure of the stiff or ankylosed knee can be especially difficult when preoperative flexion is limited, so in these situations we use the Whitesides technique (tibial tubercle osteotomy). We used platelet derivated growth factors (inductors) associated with hydroxiapatite (conductors) with the goal to obtain the best possible osteo-integration. Results: Our results are satisfying, considering we are confronting severe bone defects with a poor situation of soft tissues around the knee. We have not observed major complications involving the use of the inductors and conductors mentioned above. Conclusions: We consider the use of tumoral knee prosthesis (“third prosthesis”) a useful technique which allows us to avoid the disability promoted by the knee arthrodesis, obtaining satisfactory results according to the severe lesions observed

Purpose: To study the functional outcome and survivorship of custom designed knee implants for revision and primary total knee replacement surgery where off-the-shelf prosthesis were unsuitable. Methods: We prospectively reviewed the clinical and radiological results of 20 patients with 23 custom designed total knee prosthesis from 1991 to 2000. The indications were bone loss due to multiple revisions of total knee prosthesis and debridement for infection; peri-prosthetic fractures; bone deformity with rickets and small bones of patients with juvenile chronic arthritis. All the patients had their knee designed and manufactured in the Centre for Biomedical Engineering, University College London Medical School, Stanmore, UK. There were 4 different designs of knee prosthesis used: Condylar knee of miniature size, CAD-CAM knee, Superstabiliser and Rotating Hinges. Patients were operated upon by one senior surgeon and the Hospital for Special Surgery score taken pre-operatively, at three months, and yearly by an independent research physiotherapist. Results: Clinical and radiological results after an average of 62.5 months (range 22 to 118 months) showed that the average Hospital for Special Surgery Score improved significantly (p=0.025) from 13.5 points (range 0–48) pre-operatively to 86.5 points (range 62–96 points). Average maximum flexion post operatively measured 86.4 degrees (range 60–122 degrees). 16 knees had excellent, 5 good and 2 poor results. Three patients had an extension lag ranging from 15–25 degrees. Only one patient with juvenile chronic arthritis needed revision at five years after the index arthroplasty. Conclusion: The clinical and radiological results compare favorably with those who had standard knee prosthesis with similar indications. Our results support the use of a custom designed knee implant as a salvage prosthesis and an alternative to arthrodesis or amputation

Whereas thermography has already been used as an assessment of disease activity in some kinds of inflammatory arthritis, it is a new method for objektive pain evaluation in patients with joint prosthesis. To our knowledge, no study has tested the correlation between increase of temperature and anterior knee pain with total knee prosthesis yet. Thirteen patients were included in this study who suffered from anterior knee pain of the retinaculum patellae with total knee prosthesis. The patients were asked to walk 3 km before entering a room which was cooled down to 20 degrees Celsius. A black 1 cm times 4.5 cm square stripe was attached on the diameter of the patella and the patients rested for 20 minutes to cool down before thermographic fotos were taken from 90 degrees, 45 degrees, frontal medial and lateral. The evaluation of temperature difference of each side was performed by marking a 1cm times 2cm square field rectangular around the black stripe and comparing it with a reference point of the same size 3 cm distal of the field. The patients were compared with thirteen others, not suffering from anterior knee pain. Statistical analysis was performed using a t- test and a p value < 0.05 was considered to be significant. The temperature differences between the rectangular field and the reference point increased significantly on the medial (p= 0.00037) or lateral (p= 0.000002) pain side of the knee. The thirteen knees with knee pain had significantly higher temperature differences between medial and lateral temperature differences, than the knees without knee pain. We demonstrate a significant correlation between anterior knee pain and an increase of superficial skin temperature around the retinaculum patellae. To our knowledge, this is the first report of an objective assessment of pain of the retinaculum patellae with total knee prosthesis

A new generation of knee prostheses has been introduced with the intention of improving post-operative knee flexion. In order to evaluate whether this goal has been achieved we performed a systematic review and meta-analysis. Systematic literature searches were conducted on MEDLINE and EMBASE from their inception to December 2007, and proceedings of scientific meetings were also searched. Only randomised, clinical trials were included in the meta-analysis. The mean difference in the maximum post-operative flexion between the ‘high-flex’ and conventional types of prosthesis was defined as the primary outcome measure. A total of five relevant articles was identified. Analysis of these trials suggested that no clinically relevant or statistically significant improvement was obtained in flexion with the ‘high-flex’ prostheses. The weighted mean difference was 2.1° (95% confidence interval −0.2 to +4.3; p = 0.07)

Introduction Osteoarthritis of the knee is a very common disease.In 80 to 90% of the cases it starts in the medial compartment and tends to remain there.Therefore, the Oxford Unicondylar Knee Prosthesis (OUKP) is a attractive device as it only replaces the diseased parts of the knee.For the past 15 years, the results of the OUKP, especially those achieved by the designer’s group, have mostly been very good. However, reports about long-term follow-up are scarce. For the designer group, Murray reported a 98% ten year survival. The only independent research bij Svard an Price and by Lewold of the Swedish Arthroplasty Study showed a good survival of 95% at 10 years and a poor survival of 87% at 8 years respectively.Our independent study reviews a ten year follow up of 149 OUKP’s. Methods and Results One hundred forty-nine medial prostheses were implanted in 140 patients between 1988 and 1996. After a mean of 67 months 28 patients had died, without the need for revision. Seventeen prostheses were lost to follow-up. Revision surgery using a total knee prosthesis was performed in 16 cases. In 4 others, a lateral prosthesis was implanted subsequently to a medial one. One of these 4 was revised to a total knee prosthesis 6 years later. In another 4 cases, late complications of the meniscal bearing were treated with replacement of this bearing. In the group af patients older than 75 years, no revisions were recorded. The surviving prostheses were seen back after a mean of 126 months. The cumulative survival rate at 10 years was 82% for the whole population and 84% when knees with a previous high tibial osteotomy were excluded. This difference is significant (p=0,0000). Conclusion These results are in line with those of the Swedish arthroplasty register and compare poorly to the survival of total knee arthroplasty, therefore this prosthesis is not the first choice for most cases. Because it preserves a maximum of bone stock and is revised to a total prosthesis almost without difficulty, it is the first-choice implant for medial unicompartmental osteoarthritis in the relatively young patient.The survival rate in the group of patients older than 75 years is as good as or better than that for total knee arthroplasty.Since the OUKP can now be placed minimally invasive, it might have its place in this subgroup. It should not be used in osteotomized knees

Purpose: The quality of implantation of single-compartment knee prostheses is a recognised prognostic factor. Acceptable reproducibility can be achieved with traditional instrumentations, although the rate of error can be significant. Computer-assisted implantation might improve results. Most of the currently proposed techniques require supplementary preoperative imaging or implantation of metallic material for guidance. The Orthopilot® system is a purely peroperative system and could thus provide better cost-effectiveness. Material and methods: We implanted 30 single-compartment knee prostheses using the Orthopilot® computerised system (Aesculap, Chaumont, Group A) and compared the radiographic quality of the implant on telemetric AP and lateral views with those from a control group of 30 single-compartment prostheses implanted with a traditional instrumentation with a femoral centromedullary aiming device (group B). All patients underwent surgery for primary degeneration and were operated on by the same surgeon using the same implant (Search®, Aesculap, Chaumont). The control group was selected among a consecutive series of 250 implants to match the study group for age, gender, importance of the degeneration and frontal femorotibial mechanical angle. Results: The mechanical femorotibial angle was within desired limits (177±3°) in 26 patients in group A and in 20 patients in group B. Frontal orientation of the femoral component was within desired limits (90±2°) in 27 patients in group A and in 19 in group B (p< 0.05). Frontal orientation of the tibial piece was within desired limits (90±2°) in 27 patients in group A and in 19 patients in group B (p < 0.02). The original level of the joint line was reconstructed with a 2 mm margin in 30 patients in group A and in 24 patients in group B (p < 0.05). Eighteen patients in group A and four patients in group B had optimal implantation for all criteria studied (p < 0.001). There were no system-related complications. Discussion, conclusion: Computer-assisted implantation is more reliable and more reproducible than traditional instrumentation for the implantation of a single-compartment knee prosthesis. Follow-up results with these prostheses may be better. Systematic preoperative imaging, or preoperative implantation of metallic guide pins is not necessary with this system. The system appears to offer a better cost-effectiveness

Purpose of the study: The Alpina unicompartimen-tal knee prosthesis (Biomet) is an anatomic prosthesis inserted with a femoral cut, a tibial base plate made of titanium and a flat modular polyethylene insert. Cemented and non-cemented versions are available with hydroxyapatite ceramic (HAC) coating. Material and methods: We retrospectively reviewed the radiological outcome at more than five years (fie to eight years follow-up) in a consecutive series of patients who had an Alpina HAC prosthesis with tibial fixation completed with a titanium screw. Clinical and radiological findings were recorded. Radiologically: pre- and postoperative angles, implant position, reliability of the instrument set. At last follow-up, we studied the presence of lucent lines, polyethylene wear easily measured on the flat insert, and bone remodeling around the tibial fixation screw. Results: At last follow-up (5 to 8 years), three patients were lost to follow-up and three had died. Radiological outcome was thus assessed for 44 implants (41 medial and 3 lateral). One patient required an early total knee prosthesis (diagnostic error). Three patients underwent revision at 5–7 years (for rupture of the polyethylene insert in two very active patients, and for significant polyethylene wear in the third). Two had a revision procedure for a partial knee prosthesis and the third for a total knee prosthesis. For the 40 other patients, the following observations were made: partial lucent line along the tibial polyethylene plate with no functional impact (n=1), polyethylene wear visible but measuring less than 1 mm (n=12), remodeling around the tibial fixation screw probably corresponding to a granuloma but not threatening the implant (n=10). Discussion: The clinical results of partial knee prostheses are well known. Mid-term radiographic results of non-cemented unicompartmental prostheses with a flat tibial plateau producing a minimal contact surface has shown: good reliability of the instrument set, excellent bony integration of the HAC-coated implants, but measurable polyethylene wear on more than one quarter of the prostheses, with two ruptures of the polyethylene insert at 5 and 6 years. Conclusion: A study currently under way will examine finished pieces on a simulator to study wear and failure as a function of several parameters: polyethylene thickness, lateral restraint with a metal rim, presence of a basal stem fixing the polyethylene on the metal base, importance of the femur-polyethylene surface contact

Purpose: Loss of cutaneous tissue during knee prosthesis procedures raises the risk of implant exposure and infection with subsequent removal and poor functional outcome. The clinical course of the tissue loss is unpredictable leading to retarded curative treatment. Material and methods: We report a consecutive retrospective series of 39 knee prostheses implanted from 1990 to 2000 where cutaneous tissue loss was covered with a flap. We studied time to onset of tissue loss, wound border vitality, presence or absence of implant exposure, type of cover flap distinguishing faciocutaneous and muscle flaps, retention or not of the implant, and time of secondary reconstruction. Results: In 38 of the 39 prostheses, the implant use of the cover flap enabled saving the implant and proper wound healing. The joint remained functional but only 18 knees recovered flexion greater than 90°. In one case, the implant had to be removed due to infection with resistant Serratia. Prognositic factors identified included: time from tissue loss to its treatment, usefulness of a cover flap to save the implant, or usefulness of two-procedure reconstruction in case of implant infection. Discussion: We compared our therapeutic methods with the propositions in the Laing classification and preferred to distinguish a simplified three-step tactic based on time of exposure for determining the theraputic strategy for cutaneous tissue loss in knee prosthesis patients

Aims: To study functional outcome and survivorship of custom designed knee implants for primary and revision TKR where off-the-shelf prostheses were unsuitable. Methods: Clinical and radiological results of twenty-three custom-designed total knee prosthesis in twenty patients were prospectively reviewed. The indications were bone loss following multiple revisions of total knee prosthesis and debridement for infection, periprosthetic fractures, bone deformity with rickets and small bones with juvenile chronic arthritis. All implants designed and manufactured at Centre for Biomedical Engineering, Stanmore, U.K. Four different designs of knee prosthesis used: Condylar knee of miniature size, CAD-CAM knee, Superstabiliser and Rotating Hinges. Hospital for Special Surgery (HSS) score taken preoperatively, at 3 months, and yearly by an independent research physiotherapist. Duration of follow up: 62.5 months (28–126 months) Results: Average HSS score improved from 13.5 points (range 0–48) pre-operatively to 86.5 points postoperatively (range 62–96) (p=0.025). Average maximum flexion post operatively: 86.4° (range 60°–122°). Sixteen knees had excellent, five good and two poor results. Extension lag of 15°–25° in three patients. One patient with juvenile chronic arthritis needed revision at five years after index arthroplasty. Conclusions: Clinical and radiological results for custom designed prostheses compare favourably with standard knee prosthesis for similar indications. Our results support the use of a custom designed knee implant as salvage prosthesis and also as an alternative to arthrodesis or amputation

Purpose: The design of the contact surfaces of total knee prostheses is a recognised factor affecting polyethylene wear and thus prosthesis survival. Flat-on-flat prostheses have a limited surface area of contact and are thought to favour polyethylene wear. They are not currently recommended for implantation. Nevertheless, several series have reported similar survival with other more congruent prostheses. We studied a series followed for eight years. Material and methods: We implanted 223 flat-on-flat design total knee prostheses between 1992 and 1996 (Search®, Aesculap, Chaumont). All patients were followed prospectively and seen at regular intervals for physical examination and x-rays. We noted any intervention for implant revision and recorded time to any such procedures as well as the underlying cause. Kaplan-Meier survival curves were plotted taking revision for any cause other than infection as the endpoint. Results: Ninety-four percent of the patients were reexamined or questioned by phone for this study conducted during 2001. Six percent of the patients were lost to follow-up after a mean 24 months. Seventy-four percent of the prostheses were still in situ at the time of this study at a mean 78 months follow-up. Ten percent of the patients died with their initial implant in place at a mean 50 months. Ten percent of the patients underwent revision surgery at a mean 37 months, half of them for infection and one quarter for a mechanical cause. The overall rate of revision at eight years was 11%; The rate of revision, infection excluded, at eight years was 6%. Discussion: Survival of this prosthesis in non-infected patients is similar to that of other more congruent implants. This study confirms earlier clinical findings.The undesirable effect of the linear contact surfaces is proven in the laboratory but must not be considered to be automatically transferable to the clinical level. Polyethylene wear is a multifactorial phenomenon which cannot be reduced to a simple question of prosthesis design

We evaluated the long-term fixation of 64 press-fit cemented stems of constrained total knee prostheses in 32 young patients with primary malignant bone tumours. Initial stable fixation, especially in rotation, was achieved by precise fit of the stem into the reamed endosteum, before cementation. Complementary fixation, especially in migration and rotation, was obtained by pressurised antibiotic-loaded cement. The mean age at operation was 33 years (13 to 61). No patient was lost to follow-up; 13 patients died and the 19 survivors were examined at a mean follow-up of 12.5 years (4 to 21). Standard revision press-fit cemented stems were used on the side of the joint which was not involved with tumour (26 tibial and six femoral), on this side there was no loosening or osteolysis and stem survival was 100%. On the reconstruction side, custom-made press-fit stems were used and the survival rate, with any cause for revision as an end point, was 88%, but 97% for loosening or osteolysis. This longevity is similar to that achieved at 20 years with the Charnley-Kerboull primary total hip replacement with press-fit cemented femoral components. We recommend this type of fixation when extensive reconstruction of the knee is required. It may also be suitable for older patients requiring revision of a total knee replacement or in difficult situations such as severe deformity and complex articular fractures