Deviation of femoral intramedullary alignment rod influences coronal and sagittal alignment during total knee arthroplasty

Background

An intramedullary (IM) rod is used to resect the distal femur vertically to the femoral mechanical axis in the coronal plane in many cases of total knee arthroplasties (TKA). The valgus angle between the mechanical axis and the anatomical axis of the distal femur is estimated preoperatively. It is known the deviation of the IM rod in the femoral canal could influence the femoral component alignment. However, there is no published data regarding how many degrees of deviation to make with the IM rod. The purpose of this study is to measure each deviation of the IM rod using three-dimensional (3D) computer simulations.

Accuracy of intramedullary femoral alignment in total knee replacement: intraoperative assessment of alignment rod position

Current knee replacement techniques favour intramedullary (IM) alignment instrumentation for the guidance of distal femoral resection. Accurate femoral resection depends on the IM alignment guide lying along the line of the anatomical femoral axis, any discrepancy will affect the placement of the femoral cutting jig causing an inaccuracy of the femoral component position in the coronal plane. This study recorded the intra-operative alignment rod position prior to femoral resection. A variation of 5.3° (1.6° varus to 3.7° valgus) was found in relation to the true femoral anatomical axis. This study reveals that IM femoral alignment techniques often place the femoral resection jig in 1–2° more valgus than anticipated which reflects distal femoral anatomy.     

Relative positions of the contacts on the cartilage surfaces of the knee joint

The goal of this project was to determine the centers of contacts (points of closest approach of the articular surfaces) for the tibio-femoral and patello-femoral joints throughout the flexion range, with a focus on high flexion where there is potential overlap between the contacts. The purpose was to determine the implications to the design of joint replacements and tissue engineered implants. Eight cadaveric knees were mounted in a rig with different loading combinations applied to the femur, including axial load, anterior/posterior shear, and internal/external torque. The range of flexion was 0 degrees to 155 degrees . Reference points on the bones measured during the experiments were used to later reconstruct an accurate 3D computer model of the multiple joint positions and determine the centers of contact between the opposing bearing surfaces. The tibio-femoral contact at 0 degrees flexion was displaced 5 mm anterior to the notch (the end point of the articular cartilage on the mid-line of the femoral sulcus) on the medial side, while remaining level with the notch on the lateral side. The patella contacts on the femur extended 15 mm posterior to the intercondylar notch with a centerline between the lateral and medial paths being several millimeters lateral to the center of the femur. The centers of the patella contacts were close to the inner margin of the medial condyle and did not directly overlap with the centers of the tibial contacts. On the lateral side the patella contacts ended where the tibial contacts began. For applications to medial unicondylar knee replacement design it was shown that patellar impingement on the anterior of the femoral component would occur at 110 degrees flexion. For TKR design, a continuous patella contact up to high flexion could be obtained by extending the trochlea 15 mm posterior to the intercondylar notch.     

The effect of component alignment on clinical outcomes in fixed bearing unicompartmental knee arthroplasty

BackgroundThe aim of this study is to report component alignment in a series of ZUK fixed bearing unicompartmental knee arthroplasty (UKA) implants and compare this to clinical outcomes.MethodsThe radiographs, Knee Society Scores (KSS) and knee flexion of 223 medial UKAs were evaluated. The following alignment parameters were assessed; coronal and sagittal femoral component angle (c-FCA and s-FCA), coronal and sagittal tibia component angle (c-TCA and s-TCA) and the coronal tibiofemoral angle (c-TFA). Each alignment parameter was grouped at consecutive 2.5° intervals, mean KSS and knee flexion was then compared between the interval groups.Results96.4% of femoral components were between 7.5° of varus and valgus and 95.1% between 7.5° extension and 5° flexion. 89.6% of tibial components were between 7.5° of varus and 2.5° valgus and 97.3% between 2.5° and 15° flexion. There was no significant difference between the KSS or knee flexion between any of the incremental groups of component alignment. Mean c-TFA was 0.2 ± 3.0°, 92.4% were between −5° (varus) and 5° (valgus). KSS were significantly greater for two of the increments with slightly more varus. Linear regression analysis showed there was very weak correlation (R² = 0.1933) between c-TFA and c-TCA.ConclusionsThe results of this study show that fixed bearing UKA components are forgiving to accommodate some variation in tibial and femoral component position without effecting clinical outcome scores or knee flexion. Limb alignment matters more than component position and knees with slight varus tibiofemoral alignment have better clinical scores than those with valgus.     

膝关节置换时股骨髓内定位对假体排列的影响

BACKGROUND: The femoral intramedullary guides in total knee arthroplasty require high precision, complex operation, it is very important for prosthesis and joint function to choose more precise positioning method and determine the correct needle point. OBJECTIVE: To study the effect of needle point position on prosthesis arrangement when applying different femoral intramedullary guides methods in total knee arthroplasty. METHODS: Totally 80 patients who received the treatment of total knee arthroplasty in Changshu No.1 People’s Hospital from January 2012 to July 2015 were selected and divided into test and control groups according to random number table (n=40/group). The patients in the test group accepted CT scan for femoral   intramedullary guides. The theoretical position of femoral intramedullary guides entry point was marked using radiographic parameters. In the control group, the traditional total knee arthroplasty technology was used to mark the entry point of femoral intramedullary guides. The needle point position when applying different femoral intramedullary guide methods was observed. The effect of femoral intramedullary guides on prosthesis arrangement in total knee arthroplasty was discussed. RESULTS AND CONCLUSION: Compared with the control group, the distance from entry point to femoral anatomic line on positive and lateral X-ray film in the test group was shorter, femoral prosthesis lateral angle and physiological valgus angle were closer to the theoretical value, distance from intersection of femur axis and femoral condyle to block center was shorter; the differences were statistically significant (P < 0.05). These results demonstrate that compared with the traditional two-dimensional intramedullary positioning, the needle point position of three-dimensional CT scan stimulative positioning is more accurate. The location more concentrates on within intercondylar fossa 2-5 mm, more front of intercondylar fossa 3-10 mm, three-dimensional CT scan stimulative positioning is a reliable choice for femoral intramedullary guides.      

Surgical epicondylar axis is not orthogonal to the femoral mechanical knee axis in valgus knees with primary osteoarthritis: Three-dimensional analysis according to knee coronal alignment in 112 patients

BackgroundDuring total knee arthroplasty (TKA), most surgeons align the femoral component along the surgical epicondylar axis (SEA) considering it as orthogonal to the femoral mechanical axis. However, it is still unclear how SEA coronal alignment varies according to the native coronal knee alignment. The main goal of this study was to analyze the SEA orientation according to the native coronal knee morphotype.MethodsA total of 112 patients underwent a three-dimensional (3D) -planning-based TKA. The SEA was then determined by locating the epicondyles on 3D models. The 3D femoral and tibial mechanical axes were marked and the femoral (FMA) and tibial (TMA) mechanical angles were measured. The native HKA angle was measured as FMA + TMA. The SEA orientation angles were measured in the coronal (SEA-α) and axial (SEA-β) plane. SEA orientation was compared between the valgus, neutral, and varus knees.ResultsThe mean SEA-α angle was 90.2 ± 3° and the mean axial SEA-β angle was 92.2 ± 1.3°. The SEA-α angle was significantly higher in the valgus group compared with the neutral group (92.3 ± 2.9°, 90 ± 2.9°, P = 0.0009) whereas there was no significant difference in the SEA-α angle between the varus and the neutral group (89.7 ± 2.3°, 90 ± 2.9°, P = 0.32).ConclusionsIn contrast to the neutral and varus knees, the SEA was not orthogonal to the femoral mechanical axis in patients undergoing TKA for primary osteoarthritis. Our results suggest adapting the coronal alignment of the femoral component during TKA, while maintaining an average 2° valgus in valgus knees. By contrast, with varus and neutral knees, our data support the use of a mechanical alignment.     

基于CT数据的股骨轴线的获取

目的　提出一种利用CT影像数据自动获取股骨轴线的方法,利用该方法可以在计算机上获取精准的股骨三维解剖轴线与机械轴线。方法　对人体下肢进行CT扫描,然后对CT图像进行二维阈值分割、三维数据体重建、骨骼分组、数据平滑填充及三维数据体旋转等预处理,获得三维股骨表面模型;通过对股骨头与股骨远端形态特征的分析,根据股骨头近似球形的特点,对判断断层扫描数据梯度变化来计算股骨头中心位置,另外,逐层搜索膝关节断层图像上闭环区域的方法自动求得股骨远端中心的坐标,从而获得股骨长轴。结果　建立了一种基于CT图像简便快捷的自动获取股骨头中心与膝关节骨中心三维空间坐标的方法。结论　通过此方法可较为精确获得人体下肢的三维股骨机械轴线和股骨解剖轴线。     

Preoperative tibiofemoral rotational alignment is a risk factor for component rotational mismatch in total knee arthroplasty

BackgroundRotational mismatch between the femoral and tibial components is reported to be a risk factor for unsuccessful total knee arthroplasty (TKA). However, the rotational mismatch can still occur even when each component is aligned within the desired angle. Therefore, there may be other unknown factors. This study aims to investigate a risk factor for component rotational mismatch in TKA. The authors hypothesized a significant correlation between the rotational mismatch angle and not only the rotational alignments of components, but also the preoperative tibiofemoral rotation angle.MethodThis retrospective cohort study included 79 knees who underwent TKA. Computed tomography images were obtained preoperatively and 2 weeks after surgery for the component positional measurement. The postoperative component rotational mismatch angle between the tibial and femoral components and the rotational alignment of each tibial and femoral component to anatomical axes was evaluated. In addition, the preoperative rotational angle between the tibia and femur bones and patients’ demographics were also investigated. The correlation between the postoperative component rotational mismatch angle and perioperative variables was analyzed to identify risk factors for component rotational mismatch.ResultsThe mean component rotational mismatch angle was 1.8° of internal rotation of the tibial component relative to the femoral component, and the angle ranged from 11.3° of internal rotation to 7.3° of external rotation of the tibial component. Multivariate regression analysis showed that the preoperative rotational alignment between the tibia and femur and the rotational alignment of each component were influential factors in the postoperative component rotational mismatch angle.ConclusionThe preoperative tibiofemoral rotational alignment and the rotational alignment of each tibial and femoral component and are risk factors for the postoperative component rotational mismatch in TKA.     

Differences in impact on adjacent compartments in medial unicompartmental knee arthroplasty versus high tibial osteotomy with identical valgus alignment

BackgroundIt is unclear why medial unicompartmental knee arthroplasty (UKA) with postoperative valgus alignment causes adjacent compartment osteoarthritis more often than high tibial osteotomy (HTO) for moderate medial osteoarthritis of the knee with varus deformity. This study used a computer simulation to evaluate differences in knee conditions between UKA and HTO with identical valgus alignment.MethodsDynamic musculoskeletal computer analyses of gait were performed. The hip–knee–ankle angle in fixed-bearing UKA was changed from neutral to 7° valgus by changing the tibial insert thickness. The hip–knee–ankle angle in open-wedge HTO was also changed from neutral to 7° valgus by opening the osteotomy gap.ResultsThe lateral tibiofemoral contact forces in HTO were larger than those in UKA until moderate valgus alignments. However, the impact of valgus alignment on increasing lateral forces was more pronounced in UKA, which ultimately demonstrated a larger lateral force than HTO. Valgus alignment in UKA caused progressive ligamentous tightness, including that of the anterior cruciate ligament, resulting in compression of the lateral tibiofemoral compartment. Simultaneously, patellofemoral shear forces were slightly increased and excessive external femoral rotation against the tibia occurred due to the flat medial tibial insert surface and decreased lateral compartment congruency. By contrast, only lateral femoral slide against the tibia occurred in excessively valgus-aligned HTO.ConclusionsIn contrast to extra-articular correction in HTO, which results from opening the osteotomy gap, intra-articular valgus correction in UKA with thicker tibial inserts caused progressive ligamentous tightness and kinematic abnormalities, resulting in early osteoarthritis progression into adjacent compartments.     

In vivo kinematic comparison before and after mobile-bearing unicompartmental knee arthroplasty during high-flexion activities

BackgroundMany patients who undergo unicompartmental knee arthroplasty (UKA) have an expectation that their knee flexion would increase following its replacement. Additionally, the survival rate of mobile-bearing UKA (MB-UKA) is high. However, the effect on the patient's kinematics remains unknown. This study aimed to clarify the kinematic effect of MB-UKA knees during high-flexion activities by comparing the in vivo kinematics before and after surgery.MethodsA squatting motion was performed under fluoroscopic surveillance in the sagittal plane before and after MB-UKA. To estimate the spatial position and orientation of the knee, a two-dimensional/three-dimensional registration technique was used. The femoral rotation and varus–valgus angle relative to the tibia and anteroposterior (AP) translation of the medial and lateral side of the femur on the plane perpendicular to the tibial mechanical axis in each flexion angle were evaluated.ResultsRegarding the varus–valgus angle, the preoperative knees indicated a significant varus alignment compared with the postoperative knees from 10° to 60° of flexion. There were no significant differences in the femoral rotation angle, AP translation, and kinematic pathway before and after MB-UKA in the mid-flexion of the range of motion.ConclusionThere were differences between the varus–valgus knee kinematics before and after MB-UKA, from 10 to 60° of flexion, but no difference from midrange of flexion to deep flexion. In addition, the rotational knee kinematics before and after MB-UKA was not significantly different.     

Three-dimensional assessment of lower limb alignment: Reference values and sex-related differences

BackgroundThree-dimensional (3D) preoperative planning and assisted surgery is increasingly popular in deformity surgery and arthroplasty. Reference ranges for 3D lower limb alignment are needed as a prerequisite for standardized analysis of alignment and preoperative planning in 3D, but are not yet established.MethodsOn 60 3D bone models of the lower limbs based on computed tomography data, fifteen parameters per leg were assessed by standardized validated 3D analysis. Distribution parameters and differences between sexes were evaluated. Reference values were generated by adding/subtracting one standard deviation from the mean.ResultsWomen had a significantly lower mean mechanical lateral distal femoral angle compared with men (86.4 ± 2.1° vs. 87.8 ± 2.0°; P < .05) and significantly lower mean joint line convergence angle (−2.5 ± 1.4° vs. -1.3 ± 1.2; P < .01), but higher mean hip knee ankle angle (178.9 ± 1.9° vs. 177.8 ± 2.3°; P < .05) and mean femoral torsion (18.2 ± 9.5° vs. 13.2 ± 6.4°; P < .05), resulting in a tendency towards valgus alignment and vice versa for men. Differences in mean medial proximal tibial angle were not significant. The mean mechanical axis deviation from the tibial knee joint center was 6.9 ± 7.3 mm medial and 1.4 ± 16.1 mm ventral without significant differences between sexes.ConclusionsWe describe total and sex-related reference ranges for all alignment relevant axes and joint angles of the lower limb. There are sex-related differences in certain alignment parameters, which should be considered in analysis and surgical planning.     

Comparative anatomical measurements of osseous structures in the ovine and human knee

The ovine stifle has been increasingly used as a large animal model for the human knee. Still, comparative anatomical measurements of the knee in sheep and humans are missing. Thus, the purpose of this study was to describe and measure the osseous anatomy of the ovine stifle in comparison to the human knee. Twenty-four stifles of skeletal-mature merino-sheep and 24 human cadaver knees were obtained and distances between selected anatomical structures of the distal femur, the proximal tibia, and the patella were measured digitally and documented. Based on these, intercondylar ratio, tibial aspect ratio, patella aspect ratio and the cortical index were calculated. Regarding epicondylar width, lateral condylar width, medial condylar width and the tibial dimensions, the ovine stifle can be considered as a human knee scaled down by one third. However, sheep have a smaller trochlear width and a narrower femoral intercondylar notch than humans resulting in lower relative values for intercondylar width and intercondylar height. The distal femur's cortical index is the same in both species. In contrast, sheep have a massive bone stock below their tibial plateau and a proximal tibial shaft with remarkably thick cortical bone. The ovine stifle can be regarded as a useful model for the human knee. However, future studies should consider the differences in the femoral intercondylar notch width, the patellofemoral joint's biomechanics and the proximal tibia's cortical bone stock.     

Differences in three intercondylar notch geometry indices between males and females: a cadaver study

The primary purpose of this unique evaluation of cadaveric skeletal geometry was to compare intercondylar notch geometry between males and females. One hundred male skeletons and 100 female skeletons were evaluated. Three indices of notch geometry were calculated from digital photographs of the distal femur: notch width index, notch area index, and notch shape index. Notch shape index for males exceeded that for females (P<0.004). The intercondylar notch appears less round in females and may play a role in causing ACL injuries. Future studies are required to confirm any link between notch geometry and ACL injury.     

The effect of medial condylar bone loss of the knee on coronal plane stability--a cadaveric study

IntroductionThe quantitative effects of medial bone loss of the knee on both leg alignment and coronal plane stability are poorly understood.Materials and methodsUtilizing computer navigation, 5 mm bone defects of the medial distal femur (MDF), medial posterior femoral condyle (MPF), and medial tibial plateau (MT) were simulated in 10 cadaveric limbs, and alignment of the knee at various degrees of flexion were analyzed when applying standardized varus and valgus loads.ResultsThe 5 mm MPF defect significantly increased varus laxity at 90° of flexion by 3.3° ± 1.2° (p = 0.019), a 5 mm MDF defect resulted in a 2.2° ± 1.7° (p = 0.037) and a 2.1° ± 1.3° (p = 0.023) increase in laxity at 0° and 30° of flexion, respectively, and a 5 mm MT defect increased varus laxity at all flexion angles by 4.0° to 7.0°, but was only statistically significant at 30° (p = 0.026).DiscussionThis study confirms and quantifies the theories of flexion and extension gap balancing, and pseudolaxity of the medial collateral ligament in the varus knee, the results of which can be used in preoperative planning and intraoperative decision making for both total knee and unicondylar arthroplasty.     

Knee rotation associated with dynamic knee valgus and toe direction

BackgroundDynamic knee valgus contributes to injuries of the anterior cruciate ligament (ACL). However, it is unclear how the knee rotates during dynamic knee valgus. Knee rotation significantly affects ACL strain. To understand knee rotation during dynamic knee valgus should help the clinician evaluate dynamic alignment. The purpose of this study was to determine how the knee rotates during dynamic knee valgus and whether the knee rotation is affected by toe direction (foot rotation).MethodsSixteen females performed dynamic knee valgus in three toe directions (neutral, toe-out, and toe-in) while maintaining the knee flexion angle at 30°. The knee rotation angle was evaluated using a 7-camera motion analysis system. Knee rotation was compared between the start position and the dynamic knee valgus position, as well as among the three toe directions, using repeated measures ANOVA models.ResultsThe knee significantly rotated externally in the dynamic knee valgus position compared with the start position in two toe directions (neutral and toe-out). A similar tendency was observed with the toe-in condition. Toe direction significantly affected the knee rotation angle. For toe-out and toe-in conditions, external and internal shifts of knee rotation compared with neutral were observed.ConclusionsThe knee rotates externally during dynamic knee valgus, and the knee rotation is affected by toe direction.Clinical RelevanceBecause of knee abduction and external rotation, the ACL may impinge on the femoral condyle in the case of dynamic valgus, especially in the toe-out position.     

Accuracy of implantation during computer-assisted minimally invasive Oxford unicompartmental knee arthroplasty: A comparison with a conventional instrumented technique

The prognosis of unicompartmental knee arthroplasty (UKA) is strongly associated with the accuracy of the component alignment. To determine the accuracy of navigated UKA during primary minimally invasive Oxford UKA, twenty-nine knees of 29 consecutive patients (Group A) implanted using conventional instrumented UKA were followed by 23 knees of 17 consecutive patients (Group B) implanted by navigation assisted UKA and radiological results regarding alignments of the femorotibial mechanical axis, femur, and tibial component were compared in the two groups. Assessments of mechanical limb alignment revealed statistically significant increases in mechanical limb alignment post-operatively in both groups (p = 0.0 for both). In terms of component alignment, Group B had more prostheses implanted in the satisfactory range (> ± 3° from the targeted values) for the femoral and tibial components than Group A. There were no significant differences in the rate of prosthesis implanted within the range of radiographic alignment variations for the coronal implantation of either femoral or tibial components in both groups. (Radiographic alignment variation; coronal orientation of femoral components 90 ± 10°, sagittal orientation of femoral components 90 ± 5°, coronal orientation of tibial components from 10° varus to 5° valgus, sagittal orientation of tibial components from 7° of posterior tibial flexion to 5° of anterior tibial flexion). However, significant increases in the accuracies of sagittal implantation of femoral and tibial components were observed in Group B versus Group A. Our data suggest that navigated implantation improves the accuracy of the radiological implantation of the Oxford UKA prosthesis without increasing complications versus conventional UKA.     

膝关节前交叉韧带后外束股骨止点位置的解剖

目的 通过对膝关节前交叉韧带后外束股骨止点的解剖测量,找到确定前交叉韧带后外束股骨止点的简单可行的方法,为双束重建前交叉韧带手术中的骨道定位提供理论依据。方法 解剖20例新鲜膝关节标本（25~45岁）。在屈膝90°位,测量前交叉韧带后外束股骨止点中心点距股骨髁间窝外侧壁前方、后方和下方软骨缘的距离,再对测量数据进行评估和对比。结果前交叉韧带后外束股骨止点中心点距离股骨前方软骨缘(8.74±1.39)mm,距离后方软骨缘(8.69±1.57)mm（P =0.926）。后外束止点中心点距离股骨下方软骨缘(5.06±0.77)mm。结论膝关节屈膝90°位时,前交叉韧带后外束的股骨止点中心点位于股骨髁间窝外侧壁,距离下方软骨缘5mm,距离前方和后方软骨缘的距离相等。在前交叉韧带双束重建的手术中,应用本研究的结果能够简单、快捷地确定前交叉韧带后外束股骨骨道位置。     

Influence of the distal femoral resection angle on the principal stresses in ceramic total knee components

PurposeA certain failure mode using a newly developed cemented ceramic femoral component in total knee replacement was observed in clinical application, i.e. fracture of the femoral component during intraoperative impaction. This may be caused by unintentional deflection of the saw blades during cutting with consecutive higher resection angle of the distal femur than desired, leading to bending of the femoral component during implantation. A finite-element-analysis was carried out to simulate implantation of the femoral component and to evaluate the influence of distal femur preparation on implant stress.ScopeWe developed and validated a numerical model of the ceramic femoral component including a contact formulation which allowed calculating the principal stresses of the implant during implantation onto the resected femur. The analysis considered different anterior and posterior resection angles with a total of 17 variations. By increasing the femoral resection angle in the finite-element-model it could be shown that a deviation of three degrees from the intended resection angle can cause critical stress amounts during implantation.ConclusionsWhen implanting the ceramic component in total knee arthroplasty, the femoral resection angles should be prepared very precisely, in particular anterior saw blade deflection has to be avoided. The implant manufacturer increased implant safety through an additional resection template. Moreover, the impaction of the ceramic femoral component during cementing was not further recommended by using a hammer.     

股骨近端假体周围骨折锁定加压接骨板的设计

目的 探索适用于国人全髋关节置换术(THA)术后股骨近端假体周围骨折(PPFF)内固定的锁定加压接骨板(LCP)的设计。方法 (1)回顾性分析2012年9月—2013年12月南京中医药大学附属常州市中医医院骨科收治首次行THA治疗的90例患者的影像学资料。在90例患者术后髋关节侧位X线片上测量股骨假体近端1/2假体柄后边缘与股骨后方外皮质、远端1/2股骨假体柄前边缘与股骨前方外皮质的最小和最大垂直距离。(2)选取20具股骨标本,测量股骨标本长度和周径。将20具股骨标本植入股骨假体,建立股骨假体模型;对其中5具标本模型进行宝石能谱CT扫描和三维重建,测量股骨假体近端1/2假体柄后边缘与后方股骨外皮质、远端1/2假体柄前边缘与前方股骨外皮质间垂直距离,测量股骨假体近端1/2和远端1/2垂直距离＞6 mm的股骨长度,测量股骨中段侧方的弧度。(3)依据90例患者和5具股骨假体模型的测量数据设计并数字化定制LCP。采用定制LCP固定5具股骨假体模型,通过大体和影像学观察LCP近段锁定螺钉与假体的关系,调整可能与假体接触的锁定螺钉的角度;再采用调整后的LCP固定10具股骨假体模型,观察LCP近段锁定螺钉与假体的关系,确定LCP的设计方案。结果 (1)90例患者术后髋关节侧位X线片测量结果:股骨假体近端1/2假体柄后边缘与股骨后方外皮质的垂直距离,最小(11.26±3.58)mm,最大(17.97±6.94)mm;远端1/2假体柄前边缘与股骨前方外皮质之间的垂直距离,最小(9.18±2.32)mm,最大(14.22±3.10)mm。(2)20具股骨标本的股骨长度为(41.67±0.24)cm,周径为(9.19±0.74)cm。股骨假体模型CT测量结果:假体近端1/2假体柄后边缘与股骨后方外皮质的垂直距离为(12.36±3.24 )mm;假体远端1/2假体柄前边缘和股骨前方外皮质的垂直距离为(8.14±1.21)mm。假体近、远端1/2与股骨外皮质垂直距离＞6 mm的股骨长度分别为(69.20±4.53)mm 和(57.31±3.82)mm。(3)LCP设计方案:LCP与假体近端1/2对应的部分设计3枚向后内成一定角度的锁定螺钉,对应3个锁定孔,分布于LCP中轴线偏后,向后内方向;与假体远端1/2对应的部分设计3枚向前内成一定角度的锁定螺钉,对应的3个锁定孔,分布于LCP中轴线偏前,向前内方向。采用设计、定制LCP固定股骨假体模型,LCP与股骨侧方弧度一致,锁定螺钉在股骨假体的后方或前方均实现双层皮质固定,角度合适。结论 根据国人资料设计、定制LCP,在股骨假体模型上获得有效的固定空间,为THA后PPFF的处理提供可行方案,但临床应用效果有待进一步验证。     

5° to 6° of distal femoral cut for uncomplicated primary total knee arthroplasty : Is it safe?

The angle formed between the anatomical axis and mechanical axis of the femur determines the angle of resection of distal femur in total knee arthroplasty. The objective of this study was to analyse the safety of the routine practice of selecting 5-6 degrees of valgus for distal femoral cut during uncomplicated primary total knee arthroplasty. A retrospective study was undertaken involving a review of pre-operative CT scout films of osteoarthritic knees in 83 consecutive patients (44 males and 39 females; mean age 70 years) who presented for total knee arthroplasty. The anatomical and mechanical axis of femur were plotted on CT scout films and the angle between the two femoral axes were measured. Mean femoral axes angle was 5.4 degrees (range 3.3-7.6 degrees, SD 0.9 degrees). Estimated 95% confidence interval of the mean for the population was 5.2-5.6 degrees. There were no significant differences for age, gender or laterality of the limb. The routine practice of selecting 5 degrees to 6 degrees of the distal femoral cut for an uncomplicated primary total knee arthroplasty is safe.