Limb alignment in computer-assisted minimally-invasive unicompartmental knee replacement

Twenty patients underwent simultaneous bilateral medial unicompartmental knee arthroplasty. Pre-operative hip-knee-ankle alignment and valgus stress radiographs were used to plan the desired post-operative alignment of the limb in accordance with established principles for unicompartmental arthroplasty. In each patient the planned alignment was the same for both knees. Overall, the mean planned post-operative alignment was to 2.3 degrees of varus (0 degrees to 5 degrees ).The side and starting order of surgery were randomised, using conventional instrumentation for one knee and computer-assisted surgery for the opposite side.The mean variation between the pre-operative plan and the achieved correction in the navigated and the non-navigated limb was 0.9 degrees (sd 1.1; 0 degrees to 4 degrees ) and 2.8 degrees (sd 1.4; 1 degrees to 7 degrees ), respectively. Using the Wilcoxon signed rank test, we found the difference in variation statistically significant (p < 0.001).Assessment of lower limb alignment in the non-navigated group revealed that 12 (60%) were within +/- 2 degrees of the pre-operative plan, compared to 17 (87%) of the navigated cases.Computer-assisted surgery significantly improves the post-operative alignment of medial unicompartmental knee arthroplasty compared to conventional techniques in patients undergoing bilateral simultaneous arthroplasty. Improved alignment after arthroplasty is associated with better function and increased longevity.     

Prosthetic alignment and sizing in computer-assisted total knee arthroplasty

We implanted 60 posterior stabilized total knee prostheses (P.F.C. Sigma, DePuy, Warsaw, USA). In 30 cases, we used a CT-free navigation system (Vector Vision, Brain LAB, Heimstetten, Germany), and in 30 matched-paired controls, we used a conventional manual implantation. We compared postoperative long-leg radiographs in the two groups. The results revealed a significant difference in favor of navigation. In addition, we compared the preoperative anteroposterior dimension of the femoral condyle with the postoperative value. While there were no significant differences in the preoperative anteroposterior dimension of the femoral condyle between the two groups, the postoperative value in the navigation group was significantly larger than that of the preoperative value. Therefore, surgeons using navigation systems should guard against the possibility of oversizing when determining the size of the femoral component.

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Résumé Nous avons implanté 60 prothèses totales postéro-stabilisées du genou (P.F.C. Sigma, DePuy). Dans 30 cas nous avons utilisé un système de navigation sans scanner (Vector vision R, Laboratoire du Cerveau, Heimstetten, Allemagne) et dans 30 contrôles appairés nous avons utilisé une implantation manuelle habituelle. Nous avons comparé les grandes radiographies postopératoires des membres inférieurs dans les deux groupes. Les résultats ont révélé une différence notable en faveur de la navigation. De plus nous avons comparé la dimension antéro-postérieure du condyle fémoral avant lintervention avec la valeur postopératoire. Tandis quil ny avait pas de différence notable dans la dimension antéro-postérieure préopératoire du condyle fémoral entre les deux groupes, la valeur postopératoire dans le groupe de la navigation était nettement plus grande que la valeur préopératoire. Par conséquent les chirurgiens qui utilisent des systèmes de navigation doivent prendre garde à ne pas implanter un composant fémoral sur-dimensionné.

     

Meta-analysis of alignment outcomes in computer-assisted total knee arthroplasty surgery

Computer-assisted surgery (CAS) has been advocated as a means to improve limb and prosthesis alignment and assist in ligament balancing in total knee arthroplasty (TKA). Thus, we sought to examine alignment outcomes in CAS vs conventional TKA. A systematic review of literature from 1990 to 2007 was performed. Direct comparison of alignment outcomes was performed using random effects meta-analyses. Twenty-nine studies of CAS vs conventional TKA were identified, and included mechanical axis malalignment of greater than 3 degrees occurred in 9.0% of CAS vs 31.8% of conventional TKA patients. The risk of greater than 3 degrees malalignment was significantly less with CAS than conventional techniques for mechanical axis and frontal plane femoral and tibial component alignment. Tibial and femoral slope both showed statistical significance in favor of CAS at greater than 2 degrees malalignment. Meta-analysis of alignment outcomes for CAS vs conventional TKA indicates significant improvement in component orientation and mechanical axis when CAS is used.     

Relationships between tibial rim alignment and joint space width measurement reproducibility in non-fluoroscopic radiographs of osteoarthritic knees

RATIONALE: Superimposition of the rims of the medial tibial plateau to within 1mm is an aim of fluoroscopic knee positioning protocols for osteoarthritic (OA) knee radiography and has also been proposed as a measure of quality for non-fluoroscopic methods. OBJECTIVE: To evaluate the effect of tibial rim alignment (TRA) on reproducibility of joint space width (JSW) measurement, both were measured from radiographs taken with each tibial plateau at a range of angles determined by different non-fluoroscopic views. METHODS: TRA and JSW measurements were taken from both knees of 100 OA patients each radiographed in fully extended, schuss/tunnel, and MTP views. Degree of TRA was compared with JSW reproducibility using correlation, and between groups defined both by the 1mm threshold and by TRA-defined quartiles. RESULTS: JSW reproducibility was dependent on the degree of TRA in the fully extended and schuss/tunnel flexed knee views, although the use of the specific TRA threshold of 1mm was not supported. In the MTP view, JSW measurement was found to be highly reproducible across the full range of TRA values. CONCLUSION: These results contradict claims that TRA to within 1mm is essential for useful measurement of JSW. It is an arbitrary threshold, of use in quality control (QC) for protocols which explicitly require such alignment, and the choice of QC criteria for other protocols should be evaluated on a view-by-view basis. The results confirm previous studies showing the MTP view to afford highly reproducible JSW measurement.     

Assessing short-term functional outcomes and knee alignment of computer-assisted navigated total knee arthroplasty

This retrospective study examined the relationship between the mechanical axis of the knee throughout its functional arc and functional outcomes in patients with computer-assisted navigation total knee arthroplasty. Data on final intraoperative functional arc alignment were obtained on 76 patients who had computer-assisted navigation total knee arthroplasty over a 2-year period and correlated with scores from postoperative Short Form 12 and Western Ontario and McMaster Universities functional outcome surveys. No correlation was found between functional arc alignment and outcomes from Western Ontario and McMaster Universities or Short Form 12 surveys; however, subgroup analysis of patients with more than 3° average final intraoperative alignment throughout the functional arc of motion demonstrated increased difficulty with daily activities (P = .05). The results indicate that patients with more than 3° average alignment throughout the functional arc of motion perform more poorly with daily activities postoperatively.     

Image-based computer-assisted total knee arthroplasty leads to lower variability in coronal alignment

In a prospective randomized controlled trial, one group of 50 patients had total knee arthroplasty using conventional instruments; another group of 50 patients had total knee arthroplasty using a fluoroscopy-based computer navigation system. The variability of postoperative alignment of the lower limb in the coronal and saggital plane, early clinical outcome scores, and morbidity of the procedure were compared. In addition, the image-based computer navigation system was used to assess the following presumptions: the accuracy of the calculation of the kinematic center of rotation of the hip and the reliability of full-leg standing xrays in determining overall coronal alignment of the lower limb. Variability in the coronal plane was significantly reduced in the computer-assisted surgery group compared with the conventional group (p < 0.0001). Early clinical outcome and complication rates were similar for both groups. The correlation between full-leg standing xrays and the computer navigation system for determining the mechanical alignment of the lower limb in the coronal plane was high (r = 0.987). The maximum deviation between the calculated kinematic center of rotation of the hip and the fluoroscopically determined anatomic center of the hip was 5 mm (mean, 1.6 mm). An image based computer-assisted system can be safely used and leads to a consistent and perfect postoperative alignment in the coronal plane.     

Reproducibility of goniometric measurement of the knee in the in-hospital phase following total knee arthroplasty

Background  

The objective of the present study was to assess interobserver reproducibility (in terms of reliability and agreement) of active and passive measurements of knee RoM using a long arm goniometer, performed by trained physical therapists in a clinical setting in total knee arthroplasty patients, within the first four days after surgery.     

Accuracy and reproducibility of computer-assisted measurement of polyethylene wear in knee arthroplasty

When using computer-assisted methods to evaluate polyethylene wear in knee arthroplasty (TKA), variations in the inclination of the X-ray beam and lack of standard calibration may affect accuracy and reproducibility. To address these issues, we evaluated the polyethylene thickness of unimplanted specimens of known dimensions using the Imagika software. Radiographs were taken with small controlled variations in the inclination of the X-ray beam. Reproducibility was studied based on triplicate measurement of 132 fluoroscopic images by three observers. Calibration was tested against a reference based on a spherical metal ball with a known diameter. The mean differences between the measured and true values ranged from 0.6 mm to 0.8 mm. The repeatability coefficient revealed a maximum variation of 0.43 mm for the same observer, and 0.39 mm between observers. There were significant differences between the measurements of polyethylene thickness performed using two different calibration methods. The variance of measurements was lower with digitized images than with fluoroscopic images. Imagika was not efficient to measure wear in TKA.     

Comparison of radiographic alignment of imageless computer-assisted surgery vs conventional instrumentation in primary total knee arthroplasty

A total of 208 patients were enrolled in a multicenter, prospective randomized, institutional review board-approved study that compared preoperative surgical plan to postoperative 2-dimensional radiographic alignment measured by a blinded reviewer for primary total knee arthroplasty (TKA) implanted using computer-assisted surgery (CAS) compared with conventional TKA instrumentation. The results demonstrated a statistically significant improvement in the coronal tibial component alignment (P < .03) and failed to demonstrate a statistically significant improvement in the mechanical axis, femoral coronal/sagittal, and tibial sagittal alignment. Knee Society Score knee and function scores and 6-minute walk test were equivalent between the 2 treatment groups at all postoperative intervals. There was a statistically significant increase in the skin-skin time (P < .0001) and the time until first bone cut (P < .0001) for the CAS knees compared with those implanted with conventional instrumentation. The use of CAS in this randomized clinical trial conducted at high-volume centers did not offer a clinically meaningful improvement in postoperative alignment, clinical, functional, or safety outcomes compared with conventional TKA.     

Standing radiographs underestimate joint widthComparison before and after resection of the joint in 34 total knee arthroplasties

Background?Measurement or estimation of joint width is routinely used in the preoperative evaluation of gonarthrosis. To our knowledge, the validity and reproducibility of this procedure has not been adequately studied.Patients and methods?We measured joint width in 34 knees (medial arthrosis: n?=?22, lateral arthrosis: n?=?12) on preoperative weight-bearing radiographs and on radiographs of the corresponding part of the joint after knee arthroplasty. The bone/cartilage pieces were placed in anatomical positions and loaded in a jig made of perspex. High-density film was used to obtain maximum resolution.Results?In medial and lateral arthrosis, the minimum joint widths were median 0.3 and 0.2?mm smaller on the radiographs of the specimens (p?=?0.05, 0.04). In lateral arthrosis the differences were more scattered (95% CI: lateral: 0.1 to ?1.2?mm; medial: 0 to ?0.5?mm), suggesting less precise determination.Interpretation?In medial arthrosis, the degree of underestimation is usually small and acceptable. More pronounced discrepancies could be found in lateral arthrosis, calling for the use of further diagnostic measures.     

Inconsistencies between navigation data and radiographs in total knee arthroplasty are system-dependent and affect coronal alignment

Background

Few studies have compared the effect of different computer navigation systems on postoperative alignment in patients who have had total knee arthroplasty (TKA). We examined 2 computed tomography (CT)–free computer navigation systems by comparing the accuracy of intraoperative measurements to postoperative alignment.

Methods

Patients underwent unilateral TKA performed by a single surgeon using 1 of 2 CT-free navigation systems. We compared final intraoperative tibial and femoral coronal angles and mechanical axis with the same angles measured on standing postoperative radiographs.

Results

Groups of 31 and 50 patients underwent TKA with the 2 systems, respectively. We noted a significant difference in the coronal tibial implant angle (1.29º ± 1.35º) and in the mechanical axis (1.59º ± 2.36º) for one navigation system (both p < 0.001), while only the coronal tibial implant angle showed a significant difference (1.17º ± 1.65º, p < 0.001) for the second system. The number of radiographic outliers also significantly differed. A significantly higher proportion (32%; p < 0.01) of patients in the second cohort exhibited unacceptable malalignment compared with the first cohort (24%).

Conclusion

Navigation systems for TKA continue to increase in sophistication and popularity. Owing to the significant difference in the proportion of alignment outliers in the 2 navigation systems tested in this study, orthopedic surgeons should not consider all TKA navigation systems equivalent. Additional investigations are needed to compare the accuracy of a variety of CT-free and CT-based navigation systems and to confirm our finding that accuracy is system-dependent.     

轻度OA膝关节有限元解剖模型的构建及其力学分析

[目的]构建轻度OA膝关节的有限元解剖模型,并用于研究在OA膝关节关节软骨和半月板上的应力分布特征。[方法]基于MRI和CT影像数据构建具有骨性结构和非骨性结构的轻度OA膝关节有限元解剖模型,定义材料属性并确定边界条件和轴向载荷,以胫股关节间软骨接触的Mises应力和接触压强为研究指标,分析关节内的应力分布特征。[结果]构建了轻度OA膝关节三维有限元解剖模型,有限元分析结果表明内侧胫骨近端关节软骨接触压强大于外侧室,外侧半月板接触压强峰值大于内侧室;股骨远端与胫骨近端关节软骨边缘处Mises应力峰值大于胫股关节间软骨接触部分,外侧半月板最大Mises应力位于半月板中部,而内侧半月板最大Mises应力位于半月板后部。[结论] OA膝关节内应力分布特征不同于正常膝关节,内侧半月板半脱位和关节软骨退变的特征促进了膝OA的进一步发展。     

Influence of femoral malrotation on knee joint alignment and intra-articular contract pressures

Introduction  

The standard treatment of femoral diaphyseal fractures is intramedullary nailing. Torsion error remains a largely unsolved problem. We hypothesized that femoral malrotation would change the coronal alignment of the lower extremity and the center of force (COF) in the tibiofemoral joint as compared to the native state.     

Standing radiographs underestimate joint width: comparison before and after resection of the joint in 34 total knee arthroplasties

BACKGROUND: Measurement or estimation of joint width is routinely used in the preoperative evaluation of gonarthrosis. To our knowledge, the validity and reproducibility of this procedure has not been adequately studied. PATIENTS AND METHODS: We measured joint width in 34 knees (medial arthrosis: n = 22, lateral arthrosis: n = 12) on preoperative weight-bearing radiographs and on radiographs of the corresponding part of the joint after knee arthroplasty. The bone/cartilage pieces were placed in anatomical positions and loaded in a jig made of perspex. High-density film was used to obtain maximum resolution. RESULTS: In medial and lateral arthrosis, the minimum joint widths were median 0.3 and 0.2 mm smaller on the radiographs of the specimens (p = 0.05, 0.04). In lateral arthrosis the differences were more scattered (95% CI: lateral: 0.1 to -1.2 mm; medial: 0 to -0.5 mm), suggesting less precise determination. INTERPRETATION: In medial arthrosis, the degree of underestimation is usually small and acceptable. More pronounced discrepancies could be found in lateral arthrosis, calling for the use of further diagnostic measures.     

Routine radiographs in acute knee distortions

The value of primary knee radiographs was examined in 144 cases with acute anterior cruciate ligament rupture to determine the ability of the films to reveal or confirm the correct diagnosis. In 15% of the patients, the radiographs were found to give significant diagnostic help by revealing typical avulsion fractures associated with injury to the ligament. Primary knee radiographs are recommended in every major knee ligament injury.     

计算机导航辅助下与传统全膝关节置换术后下肢力线和假体位置的比较

目的 比较计算机导航辅助下和传统方法进行全膝关节置换(TKA)术后膝关节下肢力线和假体位置. 方法 对2007年5月至2009年12月收治的60例膝骨关节炎患者进行前瞻性研究,随机分为计算机导航组(导航组)和传统方法组(传统组),每组 30例.导航组:男11例,女19例;平均年龄(69.2±8.3)岁,术前患者下肢力线平均偏差9.4°±5.3°;膝关节骨关节炎分级:Ⅲ级12例,Ⅳ级18例.传统组:男17例,女13例;平均年龄(71.9±8.1)岁;术前患者下肢力线平均偏差8.9°±4.8°.膝关节骨关节炎分级:Ⅲ级17例,Ⅳ级13例.均采用同种产品的TKA,所有手术均由同一组医生完成.比较两组患者膝外翻角、冠面和矢状面的假体组件角度和手术时间. 结果 导航组髋-膝-踝角平均偏差角度(0.7°±0.2°)小于常规组(1.2°±0.3°),差异有统计学意义(t=3.972,P=0.000).导航组额面股骨部分角平均偏差角度(1.5°±0.4°)小于传统组(2.1°±0.5°),差异有统计学意义(t=2.433,P=0.017).导航组额而胫骨部分角(1.4°±0.5°)平均偏差角度小于传统组(1.5°±0.6°)差异无统计学意义(t=0.326、P=0.116).导航组侧面股骨部分角(7.3°±0.4°)和侧面胫骨部分角(2.5°±0.2°)平均偏差角度均小于传统组(9.5°±0.4°、4.5°±0.6°),差异均有统计学意义(P＜0.05).导航组平均手术时间比传统组延长15～28min,差异有统计学意义(t=2.553,P=0.008).结论 计算机导航辅助下TKA与传统方法相比,下肢力线和假体组件的位置更准确.     

Partially loaded plain radiographic measurement to evaluate rotational alignment in total knee arthroplasty

Purpose

Rotational alignment of prosthetic components after total knee arthroplasty (TKA) is predominantly monitored with computer tomography (CT), for example by relating the anatomical transepicondylar axis (a-TEA) of the native femur to the posterior bicondylar axis of the prosthetic component (PBCA). The purpose of the present study was to portray a reliable, novel plain radiographic method that likewise enables the evaluation of rotational positioning of prosthetic components in TKA. Furthermore, it was intended to evaluate the prosthetic femoro-tibial functional behavior under loaded conditions.

Methods

Modified plain axial radiographs under partial weight bearing (20 kg) were performed in 63 patients (63 knees) after TKA. On the obtained radiographs, all established, relevant anatomic, and prosthetic axis and angles reflecting the rotational position of the femoral (i.e., a-TEA/PBCA angle) and tibial component were detected twice by two independent examiners with an interval of one month. Additionally, in 14 cases with anterior knee pain after surgery, radiographic results were compared to obtained computer tomography images; intraclass coefficients (ICC’s) for intra- and inter-rater reliability were calculated.

Results

All pre-assigned axis and angles could be identified doubtlessly by both examiners in all investigated knees. For all measurements, ICC’s for intra-rater and inter-rater reliability ranged from 0.75 to 0.96. The comparison of the radiographic measurements with corresponding CT results (n?=?14) revealed no significant differences (p?>?0.05). Rotational alignment of the tibial tray in relation to the native tibial bone was not measurable due to display overlaying. Femoro-tibial behaviour of the prosthetic components under partial loading showed a high variability.

Conclusion

We were able to establish a new reliable radiographic technique that is able to show the most established and relevant anatomic landmarks and prosthetic axis after TKA to assess the rotational alignment of the prosthetic components in TKA in relation to the distal femur. The evaluation of the femoro-tibal behaviour instead shows a high variability and so far does not allow valid explanatory conclusions.