Custom total knee arthroplasty combined with personalised alignment grants 94% patient satisfaction at minimum follow-up of 2 years.

PURPOSE: The purpose was to report detailed patient-reported outcome measures (PROMs) and satisfaction rates for computed tomography (CT)-based custom TKA at minimum follow-up of 2 years. The hypothesis was that custom TKA combined with 'personalised alignment' would yield equivalent or better PROMs compared to values reported in systematic reviews and meta-analyses on off-the-shelf (OTS) TKA. METHODS: Of an initial cohort of 150 custom TKAs, four died (unrelated to surgery), one required a revision, and five refused participation, leaving 140 patients for analysis. Patients completed pre- and post-operative PROMs (Oxford Knee Score (OKS), Forgotten Joint Score (FJS), Knee injury and Osteoarthritis Outcome Score (KOOS), Western Ontario and McMaster osteoarthritis index (WOMAC)) as well as overall level of satisfaction. Proportions that attained a patient acceptable symptom state (PASS) were calculated for OKS and FJS. Clinical findings were compared to the average scores reported for PROMs in recent systematic reviews and/or meta-analyses on OTS TKA. Descriptive statistics were used to summarise the clinical findings as means, standard deviations (SD) and ranges, or numbers and percentages. RESULTS: At mean follow-up 33.5 ± 4.5 months, 94% (135/143) were either satisfied or very satisfied. Proportions that achieved PASS were 89% for OKS (120/135), and 85% for FJS (118/139). Median OKS, WOMAC and KOOS Symptoms and Pain scores were all within the 4th quartile of medians reported in systematic reviews and/or meta-analyses. CONCLUSIONS: At a minimum follow-up of two years following custom TKA combined with 'personalised alignment', 94% of patients were either satisfied or very satisfied, and the PASS criteria were achieved in 89% for OKS and 85% for FJS, all of which compare favourably to published outcomes of OTS TKA. Direct comparisons to the literature may not be appropriate, however, considering the heterogeneity of patient demographics and alignment techniques. Randomised controlled trials with sufficient statistical power are needed to corroborate these findings and generalise them to unselected TKA patients. LEVEL OF EVIDENCE: IV, retrospective cohort study.

Comparison of clinical outcomes of VISIONAIRE patient-specific instrumentation with conventional instrumentation in total knee arthroplasty: a systematic literature review and meta-analysis.

INTRODUCTION: Malalignment and resulting complications are major challenges in total knee arthroplasty (TKA) which patient-specific instrumentation (PSI) is proposed to alleviate. Previous PSI meta-analyses of TKA outcomes typically do not differentiate between PSI systems and assess relatively few outcomes, so the value of their findings is limited. VISIONAIRE™ cutting guides (Smith + Nephew Inc., Memphis, TN, USA) is a PSI system based on preoperative magnetic resonance and X-ray imaging. A systematic literature review (SLR) and meta-analysis, focussed specifically on VISIONAIRE, were conducted to assess TKA accuracy, intraoperative outcomes, and postoperative outcomes, compared with conventional instrumentation (CI). MATERIALS AND METHODS: The SLR was performed using PubMed, Embase, and Google Scholar databases to identify relevant studies published until March 2022. Depending on statistical heterogeneity, meta-analyses were performed for outcome measures with fixed effect (I2 < 50%) or random-effects models (I2 ≥ 50%). Dichotomous outcomes were reported as odds ratios and continuous outcomes were reported as mean differences. Descriptive analyses were performed for outcomes not amenable to meta-analysis. RESULTS: Outcomes for VISIONAIRE versus CI were reported in 25 studies. Compared with CI, VISIONAIRE reduced odds of mechanical outliers by 40% (p < 0.0001), with no statistically significant differences in odds of overall coronal, sagittal, or rotational plane component outliers. VISIONAIRE improved surgical efficiency (operating room, turnover, and tourniquet times reduced by 7.3% (p = 0.02), 42% (p = 0.022), and 15.9% (p = 0.01), respectively), lowering the odds of blood transfusion by 53% (p = 0.01) and shortening patients' hospital stays (11.1% reduction; p < 0.0001). There were no significant differences between groups in incidence of postoperative complications and (descriptively analyzed) return-to-function outcomes. CONCLUSION: Options for PSI in TKA differ substantially, and it is important to assess the outcomes of individual systems. The current findings suggest that VISIONAIRE guides can lead to improved alignment accuracy and surgical efficiency compared with CI, without compromising postoperative safety and return-to-function outcomes.

Custom total knee arthroplasty facilitates restoration of constitutional coronal alignment.

PURPOSE: To describe a strategy for coronal alignment using a computed tomography (CT) based custom total knee arthroplasty (TKA) system, and to evaluate the agreement between the planned and postoperative Hip-Knee-Ankle (HKA) angle, Femoral Mechanical Angle (FMA) and Tibial Mechanical Angle (TMA). METHODS: From a consecutive series of 918 primary TKAs, 266 (29%) knees received CT-based posterior-stabilized cemented custom TKA. In addition to a preoperative CT-scan, pre- and post-operative radiographs of weight-bearing long leg, anterior-posterior and lateral views of the knee were obtained, on which the FMA, TMA and HKA angles were measured. CT-based three-dimensional (3D) models enabled to correct for cases with bony wear by referring to the non-worn areas and to estimate the native pre-arthritic angles. The alignment technique aimed to preserve or restore constitutional alignment (CA) within predetermined limits, by defining a 'target zone' based on three criteria: 1) a ± 3° (range 87°-93°) primary tolerance for the femoral and tibial resections; 2) a ± 2° secondary tolerance for component obliquity, extending the bounds for FMA and TMA (range 85°-95°); 3) a planned HKA angle range of 175°-183°. Agreement between preoperative, planned and postoperative measurements of FMA, TMA and HKA angle were calculated using intra-class correlation coefficients (ICC). RESULTS: Preoperative radiograph and CT-scan measurements revealed that, respectively, 73 (28%) and 103 (40%) knees were in the 'target zone', whereas postoperative radiographs revealed that 217 (84%) TKAs were in the 'target zone'. Deviation from the planned angles were - 0.5° ± 1.8° for FMA, - 0.5° ± 1.8° for TMA, and - 1.1° ± 2.1° for HKA angle. Finally, the agreement between the planned and achieved targets, indicated by ICC, were good for FMA (0.701), fair for TMA (0.462) and fair for HKA angle (0.472). CONCLUSION: Using this strategy for coronal alignment, 84% of custom TKAs were within the 'target zone' for FMA, TMA and HKA angles. These findings support the concepts of emerging personalized medicine technologies, and emphasise the importance of accurate strategies for preoperative planning, which are key to achieving satisfactory 'personalised alignment' that can further be improved by customisation of implant components. LEVEL OF EVIDENCE: IV.

Custom TKA combined with personalised coronal alignment yield improvements that exceed KSS substantial clinical benefits.

PURPOSE: The purpose of this study was to report Knee Society Scores (KSS) at 12-month follow-up in a series of 266 knees that received custom TKA. The hypothesis was that custom TKA combined with personalised alignment would yield improvements greater than substantial clinical benefits (SCB) of KSS Knee and Function. METHODS: From a consecutive series of 905 patients (918 knees) that received primary TKAs, 261 (29%) patients (266 knees) received computed tomography (CT)-based posterior-stabilised cemented custom TKA. Knees were aligned aiming to preserve or restore constitutional alignment within predetermined limits of 85°-95° for femoral mechanical angle (FMA) and tibial mechanical angle (TMA), and 175°-183° for hip knee ankle (HKA) angle. The KSS Knee and Function were collected preoperatively and 12 months postoperatively, to determine if patients achieved SCB. Uni- and multivariable analyses were performed to determine associations between KSS scores (Knee and Function) and patient demographics as well as pre- and postoperative radiographic alignments. RESULTS: Of the initial cohort of 261 patients, 4 (1.8%) were reoperated for patellar resurfacing, 1 (0.4%) for lavage to treat infection, and 1 (0.4%) had arthroscopy to treat a stiff knee with < 90° range of motion. Complete clinical records were available for 227 patients (232 knees, 87%) that comprised 102 men (5 bilateral) and 125 women. At 12-month follow-up, mean improvements in KSS Knee and Function scores were, respectively, 61.0 ± 13.0 and 42.7 ± 16.7, which exceeded the SCB of KSS. Comparison of knees inside versus outside the target zone revealed no differences in KSS Knee (94.1 ± 9.1 versus 94.3 ± 9.0, n.s.) and Function (96.1 ± 9.2 versus 96.3 ± 8.9, n.s.). Multivariable analysis revealed worse KSS Knee in knees with preoperative FMA > 95° (ß = - 6.21; p = 0.023), but no association between KSS Function and patient demographics or pre- and postoperative radiographic alignments. CONCLUSIONS: Custom TKA combined with personalised alignment yielded improvements that exceeded substantial clinical benefits of KSS Knee and Function scores. These findings demonstrate the feasibility of custom TKA with 'personalised alignment' and encourage further investigations using comparative studies at longer follow-up. LEVEL OF EVIDENCE: IV, case series.

Improved tibial component rotation in TKA using patient-specific instrumentation.

INTRODUCTION: Patient-specific instrumentation (PSI) was introduced in an attempt to reduce positional outliers of components in total knee arthroplasty (TKA). It was hypothesized that PSI could help with the positioning of tibial components in optimal rotational alignment. METHODS: A magnetic resonance imaging (MRI) analysis of 58 patients following TKA was conducted. Of these, 30 operations were performed using PSI and 28 using conventional instrumentation. The rotation of the tibial components was determined in MRI using three different reference lines: a tangent to the dorsal tibial condyles, the tibial epicondylar line, and the tibial tubercle. Deviations >9° were considered outliers. Also internal rotation >1° was considered an outlier. Data were analyzed statistically for positional outliers using the Chi-squared test. RESULTS: There was excellent inter- and intraobserver reliability with low standard deviations for the determination of tibial component rotation using the tangent to the dorsal condyles and the tibial epicondylar line as reference. Using the dorsal tangent as reference, there were eight components in excessive external rotation (28.6 %) and one component being in relative internal rotation (5.4°) in the conventional group, while there were two components in excessive external rotation in the PSI group (6.7 %). Using the tibial epicondyles as reference, there were seven components in excessive external rotation (21.4 %) and one component being in relative internal rotation (4.4°) in the conventional group; while there were two components in excessive external rotation in the PSI group (6.7 %). These differences were statistically significant (p < 0.05). Measurements based on the tibial tubercle showed poor reproducibility in terms of intra- and interobserver reliability and was of little use in the context of the research question. DISCUSSION AND CONCLUSION: In this setup, PSI was effective in significantly reducing outliers of optimal rotational tibial component alignment during TKA. Anatomy of the proximal tibia does not deliver clear landmarks that are prominent and consistent. This makes both, MRI analysis as well as cutting jig production and intraoperative placement a challenge.

A comparison of conventional and patient-specific instruments in total knee arthroplasty.

PURPOSE: Several authors have observed that standard instrumentation (SI) may be insufficient for addressing component malalignment. Patient-matched cutting blocks (PMCB) technology was introduced to improve surgeons' ability to achieve a neutral postoperative mechanical axis following total knee arthroplasty (TKA). The current retrospective study was designed to compare the ability of SI and PMCB to achieve a hip-knee-ankle angle (HKA) within ±3° of the ideal alignment of 180°. METHODS: Between October 2009 and December 2012, 170 TKAs in 166 patients (four bilateral) using VISIONAIRE (Smith & Nephew) PMCB technology were performed. Additionally, 160 TKAs in 160 consecutive patients that had received a total knee arthroplasty using SI during the same time period were used as a control group, All surgeries were performed by the same surgeon. Standardized pre- and postoperative long-leg standing x-rays were retrospectively evaluated to compare the two patient cohorts. RESULTS: X-rays were available for analysis for 156 knees in the SI group and 150 in the PMCB group. The average post-surgical HKA was 178.7 ± 2.5 in the SI group and 178.4 ± 1.5 in the PMCB group. However, the rate of ± 3° outliers was 21.2 % in the SI group and 9.3 % in the PMCB group. There were no intraoperative complications with the use of PMCB technology or SI. CONCLUSIONS: PMCB technology proved superior to conventional instrumentation in achieving a neutral mechanical axis following TKA. Further follow-up will be needed to ascertain the long-term impact of these findings.

Femoro-tibial kinematics after TKA in fixed- and mobile-bearing knees in the sagittal plane.

PURPOSE: Lack of the anterior cruciate ligament in total knee arthroplasty results in paradoxical movement of the femur as opposed to the tibia under deep flexion. Total knee arthroplasty with mobile-bearing inlays has been developed to provide increased physiological movement of the knee joint and to reduce polyethylene abrasion. The aim of this study was to perform an in vitro analysis of the kinematic movement in the sagittal plane in order to show differences between fixed- and mobile-bearing TKA in comparison with the natural knee joint. METHODS: Seven knee joints of human cadaver material were used in a laboratory experiment. Fixed- and mobile-bearing inlays were tested in sequences under isokinetic extension in so-called kinemator for knee joints, which can simulate muscular traction power by the use of hydraulic cylinders, which crossover the knee joint. As a target parameter, the a.p. translation of the tibio-femoral relative movement was measured in the sagittal plane under ultrasound (Zebris) control. RESULTS: The results show a reduced tibial a.p. translation in relation to the femur in the bearing group compared to the natural joint. In the Z-axis, between 110° and 50° of flexion, linear movement decreases towards caudal movement under extension. Admittedly, the study did not show differences in the movement pattern between "mobile-bearing" and "fixed-bearing" prostheses. CONCLUSION: Results of this study cannot prove functional advantages of mobile-bearing prostheses for the knee joint kinematic after TKA. Both types of prostheses show typical kinematics of an anterior instability, hence they were incapable of performing physiological movement.

Frontal plane alignment after total knee arthroplasty using patient-specific instruments.

PURPOSE: Although total knee arthroplasty (TKA) is regularly associated with favorable outcomes, considerable research efforts are still underway to improve its ability to achieve a neutral postoperative mechanical axis. Patient-specific instrumentation (PSI) was introduced with this and other goals in mind. The current retrospective study was designed to determine whether PSI would lead to a hip-knee-ankle angle (HKA) within ±3° of the ideal alignment of 180°. METHODS: A long-leg x-ray of the knee was performed after an average of 3.5 months (SD, three to four months), following 124 TKAs performed by a single surgeon using PSI technology (VISIONAIRE; Smith & Nephew). In addition to HKA, the zone of the mechanical axis (ZMA; zone of the tibial base plate where the mechanical axis of the limb intersects with the tibial base plate) was analysed, with the ideal intersection occurring centrally. RESULTS: There were 100 knees (average age, 66.8 years) with follow-up data available. The average HKA changed from 175.5±5.6° preoperatively to 178.5±1.7° postoperatively. The rate of ±3° and ±5° HKA outliers was 11 % and 3 %, respectively. In terms of ZMA, the mechanical axis passed through the central third of the knee in the majority of cases (93 knees, 93 %). There were no intra-operative complications with the use of PSI. CONCLUSIONS: The use of PSI technology was able to achieve a neutral mechanical axis on average in patients undergoing TKA. Further follow-up will be needed to ascertain the long-term impact of these findings.

Benefits of using customized instrumentation in total knee arthroplasty: results from an activity-based costing model.

OBJECTIVE: The growing demand for total knee arthroplasty (TKA) associated with the efforts to contain healthcare expenditure by advanced economies necessitates the use of economically effective technologies in TKA. The present analysis based on activity-based costing (ABC) model was carried out to estimate the economic value of patient-matched instrumentation (PMI) compared to standard surgical instrumentation in TKA. METHODOLOGY: The costs of the two approaches, PMI and standard instrumentation in TKA, were determined by the use of ABC which measures the cost of a particular procedure by determining the activities involved and adding the cost of each activity. Improvement in productivity due to increased operating room (OR) turn-around times was determined and potential additional revenue to the hospital by the efficient utilization of gained OR time was estimated. RESULTS: Increased efficiency in the usage of OR and utilization of surgical trays were noted with patient-specific approach. Potential revenues to the hospital were estimated with the use of PMI by efficient utilization of time saved in OR. Additional revenues of 78,240 per year were estimated considering utilization of gained OR time to perform surgeries other than TKA. CONCLUSIONS: The analysis suggests that use of PMI in TKA is economically effective when compared to standard instrumentation.

Revision of tibial TKA components: bone loss is independent of cementing type and technique: an in vitro cadaver study.

BACKGROUND: Different bone cements and various cementation techniques can lead to different bone loss in revision surgery. We investigated the degree of tibial bone loss depending on different cements and techniques. METHODS: 30 tibia specimens were matched into three groups (10 each). In all cases Genesis II tibia component were implanted. In two groups, the tibia base plate alone was cemented with Palacos® R+G and Refobacin® Bone Cement R. In the third group, both tibial base plate and tibial stem were cemented with Palacos® R+G. Afterwards, the specimens were axial loaded with 2000 N for 10,000 cycles. Tibial components were explanted and the required time to explantation was recorded. Bone loss after explantation was measured by CT. RESULTS: On CT, there was no significant difference in bone loss between cementing techniques (p = 0.077; 95% CI -1.14 - 21.03) or the cements themselves (p = 0.345; 95% CI -6.05 - 16.70). The required time to explantation was 170.6 ± 54.89, 228.7 ± 84.5, and 145.7 ± 73.0 seconds in the first, second, and third groups, respectively. CONCLUSIONS: Cement technique and type do not influence tibial bone loss in simulated revision surgery of the tibial component in knee arthroplasty.

Sagittal plane kinematics of fixed- and mobile-bearing total knee replacements.

PURPOSE: The objective of this prospective, randomized, patient- and observer-blinded study was to analyze, in vivo, the knee joint kinematics in the sagittal plane in a patient population that had received either a fixed or a mobile TKA. METHODS: Thirty-one patients (57 knees) were evaluated by means of fluoroscopy during unloaded flexion and extension against gravity as well as during step up and step down with full weight bearing. In these 31 patients, 22 fixed-bearing TKAs, 16 mobile-bearing TKAs, and 19 natural knee joints were included. Fluoroscopic radiographs were evaluated by measuring the "patella tendon angle" in relation to the knee flexion angle, as a measure of anteroposterior translation, as well as the "kinematic index," as a measure of reproducibility. RESULTS: During unloaded movement, fluoroscopic analysis did not show a significant difference between both types of prosthesis design and the natural knee. In the weight-bearing movement, both types of TKA designs revealed a more linear patellar tendon angle curve, with a greater angle in extension and in flexion than in the natural knees. In the mobile-bearing group, interindividual deviations from the mean during weight-bearing movements were significantly less than in the fixed-bearing group. CONCLUSIONS: No functional advantage of mobile-bearing TKA over fixed-bearing devices could be found. Both TKA designs showed the typical kinematics of an anterior instability. These results only apply to cruciate retaining mobile-bearing TKA with a bearing that allows both rotation and anteroposterior translation, using a sagittal plane kinematics analysis evaluated by such methodology. A possible influence of less variability of the kinematic pattern on clinical results still needs to be confirmed.

Gait analysis and electromyography in fixed- and mobile-bearing total knee replacement: a prospective, comparative study.

PURPOSE: The theoretical superiority of mobile-bearing total knee arthroplasties (TKAs) has not yet been proven in clinical studies. The aim of the current study was to compare and to analyse in a patient population that had received either a fixed or a mobile TKA differences in gait analysis electromyography and clinical scores. METHODS: In a prospective, randomized, patient- and observer-blinded clinical study, 33 patients with primary osteoarthritis of the knee were included. All patients received a Genesis II total knee replacement. Sixteen patients received a mobile and 17 a fixed-bearing cruciate retaining Genesis II TKA. Clinical and quality-of-life scores, electromyography and gait analysis were applied preoperatively and postoperatively with a follow-up of 24 months. RESULTS: In both groups, improvements from pre- to postoperative were detected. whereas the results of gait analysis and electromyography did not show any differences. The results from the clinical and the quality-of-life scores improved from pre- to postoperative, while the Knee Society Score showed a superiority of the mobile-bearing group (mean 159 ± 28) over the fixed-bearing group (mean 134 ± 41). CONCLUSION: No functional advantage of mobile over fixed-bearing TKA was detected, although the mobile-bearing group had better clinical results for which a reason could not be found. These results only apply to cruciate retaining mobile-bearing TKA with a bearing which allows both rotation and anteroposterior translation.

Influence of hepatocyte growth factor on autologous osteochondral transplants in an animal model.

PURPOSE: Several studies have investigated the influence of different growth factors on hyaline cartilage regeneration. In a rabbit model, hepatocyte growth factor (HGF) was proven to increase the amount of hyaline-like chondrocytes in a mixed fibro-cartilaginous regenerate of small defects. The aim of the current study was to evaluate whether intra-articular administration of HGF influences the ingrowth of osteochondral grafts in a sheep model. TYPE OF STUDY: Animal experiment. METHODS: Both knee joints of eight sheep were opened surgically and osteochondral grafts were harvested and simultaneously transplanted to the opposite condyle of the same joint. The sheep were divided into two groups of four sheep, resulting in 16 grafts per group. In one group, HGF was administered by bilateral intra-articular injections given three times a week for 4 weeks. The control group received isotonic sodium chloride injections. The animals were killed after 3 months. RESULTS: Histological evaluation showed a complete ingrowth of the osseous part of the osteochondral grafts. A healing or ingrowth at the level of the cartilage could not be observed. Histological evaluation of the transplanted grafts according to the modified Mankin score revealed less degeneration in the cartilage of the HGF group, as compared to the control group. In the HGF group, less cloning of chondrocytes and less irregularities of the articular surface were observed. Importantly, no deleterious effects, such as osteophyte formation, cartilage thickening or synovial proliferation, were found. CONCLUSION: HGF positively influenced the cellularity of the transplanted osteochondral graft, but could not diminish the fissures in the marginal zone of the grafts. CLINICAL RELEVANCE: Marginal zone fissures and degeneration in the absence of HGF may undermine long-term results of autologous osteochondral grafts.

Initial stability of tibial components in primary knee arthroplasty. A cadaver study comparing cemented and cementless fixation techniques.

The purpose of this roentgen stereophotogrammetric analysis (RSA) study was to evaluate the initial stability of cemented and cementless tibial components in vitro. Twenty tibia specimens were matched into two groups. In the first group, the tibial trays were cemented superficially and in the second group cementless fixation with stem and screws was performed. An axial load of 2000 N for 1000 and 10,000 cycles was applied onto the specimens and RSA was performed. The experimental results after 1000 cycles showed a higher migration with significant differences for the parameters maximum lift off (p = 0.011) and maximum total point motion (p = 0.002) in the cementless group. After 10,000 cycles, the migration in the cementless group increased significantly for maximum lift off (p = 0.043), maximum subsidence (p = 0.045) and maximum total point motion (p = 0.013). The higher migration rates in the cementless group demonstrate a lower initial mechanical stability of cementless tibial components which can cause an early component loosening.

Lateral unicompartmental knee arthroplasty: a review.

Lateral unicondylar knee arthroplasty (UKA) has been utilized as a treatment for isolated lateral tibiofemoral osteoarthritis (OA) since the first description of UKA in the 1970s. To date, there remains some controversy on UKA procedures. As indications for lateral UKA are usually rare, surgeon experience seems to be the key factor for a successful intervention. Better understanding of biomechanics of the knee joint, recent developments in prosthesis design, surgical techniques and indications may add to improved outcomes of lateral UKA. Alternatives that are applied to treat lateral tibiofemoral OA include arthroscopic interventions, osteotomies and total knee arthroplasty (TKA). In comparison with TKA, potential advantages of UKA include a minimally or less invasive approach, less bone resection, preservation of the cruciate ligaments, preservation of the medial tibiofemoral and the patellofemoral compartments, shorter rehabilitation, and physiological knee kinematics. This review aims to summarize the current concepts of implant designs as well as indications and contraindications for lateral UKA. The literature will be presented and discussed as well as results and realistic expectations on both the surgeon's and the patient's side. Alternative treatments and future concepts for lateral UKA will be presented.

Quadriceps force in relation of intrinsic anteroposterior stability of TKA design.

PURPOSE: Decreased quadriceps strength and fatigue is suspected to be one of the contributing factors for anterior knee pain and malfunction after total knee arthroplasty (TKA). The purpose of this in vitro study was to investigate the amount of quadriceps force required to extend the knee isokinetically after TKA in dependence of different prosthesis designs and the state of the posterior cruciate ligament (PCL). MATERIALS AND METHODS: Eight fresh frozen human knee specimens underwent testing in a kinematic device simulating an isokinetic knee extension cycle from 120° of flexion to full extension. The quadriceps force was measured after implantation of a cruciate retaining (CR) TKA (Genesis II, Smith&Nephew, Memphis, TN, USA) applying a conventional CR (11 mm) and a highly conforming (deep dished, DD) polyethylene (PE) inlay consecutively before and after resection of the PCL. Finally, tests were repeated with a posterior-stabilized (PS) design. RESULTS: Simulating a physiological knee extension, no significant differences in the average quadriceps force were detected between the cruciate preserving inlays (CR 1,146.57 ± 88.04 N, DD 1,150.19 ± 97.54 N, P = 0.86) as long as the PCL was intact. After resection of the PCL, the required quadriceps force increased significantly for both designs (CR 1,203.17 ± 91.51 N, P < 0.01 and DD 1,191.88 ± 80.07 N, P < 0.03). After implantation of the posterior stabilized femoral component quad force decreased to its initial levels with forces significantly lower compared to the PCL deficient knees provided with a CR or DD (PS 1,130.91 ± 107.88 N, P < 0.01) inlay. With a deficient PCL there were no statistical differences for the DD design in comparison with CR in mean quad forces (CR 1,203.17 ± 91.51 N vs. DD 1,191.88 ± 80.07 N, P = 0.50) nor in peak forces (CR 1,729.44 ± 161.86 N, DD 1,688.66 ± 123.18 N, P = 0.17). DISCUSSION: At intact PCL peak quad forces and mean forces beyond 70° of flexion could be shown to be significantly lower with a PS TKA design in comparison with cruciate preserving designs such as CR and DD. In the PCL deficient knee quad forces with a highly conforming implant (DD) and CR were significantly higher than with a PS TKA. The use of PS implants in all PCL deficient knees seems to be advisable

Patellofemoral pressure after TKA in vitro: highly conforming vs. posterior stabilized inlays.

INTRODUCTION: When highly conforming polyethylene inlays were introduced into total knee arthroplasty (TKA), they were characterized as adding anteroposterior stability to the reconstructed knee. The aim of this study was to examine the patellofemoral pressure with the designs of a highly conforming and a posterior stabilized inlay. The patellofemoral pressure depends among other factors on the anteroposterior stability of the knee joint. MATERIALS AND METHODS: Eight fresh frozen human knee specimens underwent testing in a kinematic device. Knee motion was driven by a hydraulic cylinder at an extension moment of 31 Nm. The patellofemoral contact pressure was measured using a pressure sensitive film (Tekscan((R)), Inc., Boston, USA). First, this was assessed after implantation of a cruciate retaining (CR) TKA with a highly conforming polyethylene insert before and after resection of the posterior cruciate ligament. After that, the same measurements were performed with a similar posterior stabilized prosthesis. RESULTS: Patellofemoral contact pressures in the CR prosthesis using the highly conforming inlay were not significantly different before and after resection of the posterior cruciate ligament. However, after implantation of a posterior stabilized prosthesis peak pressure was significantly lower [Mean: 6.12, (SD 2.37) MPa] in comparison to the highly conforming type [7.12, (SD 2.53) MPa, P < 0.01] at a preserved posterior cruciate ligament. Further to that, the mean contact pressure turned out to be lower with the posterior stabilized design (P < 0.006). CONCLUSION: The results of this study suggest that a posterior stabilized prosthesis design reduces the patellofemoral peak and mean pressure in comparison with a high conforming design. The better reproducible femoral rollback with a posterior stabilized model at a tibial ventral shift could serve as a possible explanation.

No effect of PMMA bone cement on thrombocyte levels after total hip arthroplasty.

Thrombocytopenia has been reported to occur after total hip arthroplasty (THA). Several in vitro studies have investigated whether polymethylmethacrylate (PMMA) bone cement could be a possible origin for toxic agents that interfere with platelet function and survival. The aim of this study was to screen patient data for postoperative thrombocytopenia and the level of platelet concentrations in relation with the fixation method of THA. A consecutive series of 499 THAs was studied (24.6% fully cemented, 45.5% hybrid and 29.9% uncemented). Pre- and postoperative thrombocyte levels were recorded. Patient data were reviewed for age, indication, BMI, blood cell count, and thromboembolic events. Patients in the noncemented group were significantly younger and their thrombocyte levels were higher. There were no statistically significant differences in platelet loss between groups at any point in time following THA. Platelet concentrations had fully recovered at the time of discharge from hospital. Power analysis revealed that the cohort was large enough to show even small effect sizes. The use of PMMA cement in THA does not appear to affect postoperative platelet concentrations to any significant extent.

Posterior stabilized TKA reduce patellofemoral contact pressure compared with cruciate retaining TKA in vitro.

Increased patellofemoral contact pressure was described after total knee arthroplasty (TKA). Aim of this in vitro study was to compare the influence of a posterior stabilized (PS) design in comparison to a cruciate retaining (CR) design on patellofemoral contact pressure. Patellofemoral area contact pressure, peak contact pressure and the centre of pressure motion were determined in eight fresh frozen human cadaveric specimens using a Tekscan sensor (K-Scan 4000). A robotic knee simulator was used simulating an isokinetic knee extension cycle from 120 degrees of flexion to full extension. All knees were tested in a first test cycle after implantation of a CR design and in a second test cycle after replacement by a PS design, both using a 11 mm PE inlay (Genesis II, Smith & Nephew, Memphis, TN, USA). The patella remained unresurfaced. A paired sampled t test to compare mean values (significance, P < or = 0.05) was used for statistical analysis. After implantation of the PS design, average patellofemoral area contact pressure was significantly lower (P < or = 0.006) compared with the CR design (PS: 3.58 +/- 1.25 MPa; CR: 4.31 +/- 1.40 MPa). Accordingly, average patellofemoral peak contact pressure decreased significantly (P < or = 0.02) with the PS design (6.12 +/- 2.37 MPa) in comparison with the CR design (7.17 +/- 2.41 MPa). On average, the centre of pressure motion was more physiological with the PS design compared to the CR design over the complete extension cycle. However, this was not significant. In conclusion, the data suggest less patellofemoral contact pressure of a posterior stabilized TKA design in comparison to a cruciate retaining design.