Mullaji Arun
Breach Candy Hospital, Mumbai, India.
Mullaji Knee Clinic, Mumbai, 400036 India.
Indian J Orthop. 2022 Jan 19;56(5):902-907. doi: 10.1007/s43465-022-00601-y. eCollection 2022 May.
Placement of prosthetic components and limb alignment can be adversely impacted by errors in identification of registration points in digitally assisted knee arthroplasty. The purpose of this study was to trigonometrically analyze the impact on the accuracy of coronal tibial component and limb alignment of discrepancy between the registered midpoint of the proximal bony tibia the radiographic medio-lateral center of the lateralized final tibial implant in certain varus-deformed knees.
We analyzed trigonometrically the angular difference in coronal alignment of tibial component and hip-knee-ankle angle resulting from lateral translation of the medio-lateral center of the final tibial implant, with respect to the initial registered midpoint of the proximal bony tibia. was calculated using the equation tan( ) = /, where is the numerical distance between the registered point and the center of the final tibial tray position and t is the length of tibia distal to the resection.
One degree of varus malpositioning of the tibial component and the limb can occur for every 6.3 mm of lateral translation of the tibial implant with respect to the midpoint of the proximal bony tibia of average reported length (372 mm). The magnitude of this error is inversely proportional to tibial length and the patient's height.
Coronal malalignment of the tibial component and the limb is directly proportional to the amount of lateral translation of the tibial tray with respect to the registered midpoint of the proximal bony tibia and inversely proportional to the patient's height. This may occur in cases with tibial extra-articular deformity, those undergoing reduction osteotomy, downsizing of the tray, or inadvertently during tibial preparation. The error can be avoided by initial registration of the tibial midpoint more laterally by templating, re-registering the new center of the resected tibial surface or osteotomy for extra-articular deformity.
在数字辅助膝关节置换术中，注册点识别错误可能会对假体组件的放置和肢体对线产生不利影响。本研究的目的是通过三角学分析在某些内翻畸形膝关节中，近端胫骨注册中点与最终胫骨假体外侧化后的影像学中外侧中心之间的差异对冠状位胫骨组件准确性和肢体对线的影响。
我们通过三角学分析了最终胫骨假体中外侧中心相对于近端胫骨初始注册中点的横向平移所导致的胫骨组件冠状位对线和髋-膝-踝角的角度差异。使用公式tan(θ) = d / t计算θ，其中d是注册点与最终胫骨托位置中心之间的数值距离，t是切除平面远端的胫骨长度。
对于平均报告长度（372 mm）的近端胫骨，胫骨假体相对于近端胫骨中点每横向平移6.3 mm，胫骨组件和肢体就可能出现1°的内翻错位。这种误差的大小与胫骨长度和患者身高成反比。
胫骨组件和肢体的冠状位对线不良与胫骨托相对于近端胫骨注册中点的横向平移量成正比，与患者身高成反比。这可能发生在胫骨关节外畸形、接受截骨矫形、托盘尺寸缩小或在胫骨准备过程中意外发生的情况下。通过模板法将胫骨中点初始注册点更偏向外侧、重新注册切除的胫骨表面新中心或针对关节外畸形进行截骨术，可以避免该误差。
