Chen Shi-Chang, Zeng Yi-Ming, Yan Meng-Ning, Yue Bing, Zhang Jun, Wang You
Department of Orthopaedic Surgery, Shanghai Key Laboratory of Orthopaedic Implants, Shanghai Ninth People's Hospital, Shanghai Jiaotong University School of Medicine, Shanghai, China.
Orthop Surg. 2017 Feb;9(1):91-96. doi: 10.1111/os.12319.
Femoral component overhang in total knee arthroplasty (TKA) has been reported in previous studies. The purpose of this study was to evaluate the effect of femoral component flexion implantation on mediolateral bone-prosthetic fit in TKA.
Virtual prosthesis implantations were performed on computed tomographic models of 10 Chinese knees with femoral prostheses of the Advance Medial-Pivot knee system (MicroPort Orthopedics, Arlington, TN, USA), with the femoral component positioned at 0°, 3°, or 6° of flexion in the sagittal plane. For each degree of flexion implantation, the differences between the knee and femoral component models on the lateral and medial sides at trochlea (zone 1), anterior-distal condyle (zone 2), posterior-distal condyle (zone 3), and posterior condyle (zone 4) were measured. Positive difference values indicate component overhang, and negative difference values indicate component underhang. The values of component overhang (underhang) in each zone were statistically analyzed across the 3° of flexion implantation.
With a greater degree of flexion implantation, overhang was reduced and even changed to underhang. With 0° of flexion implantation, an overhang exceeding 3 mm existed mainly on the medial side of zone 1 (5.81 mm) and the lateral side of zone 2 (3.39 mm). With 3° of flexion, overhang exceeding 3 mm was observed only on the medial side of zone 1 (3.10 mm), and underhang was observed only on the medial side of zone 4 (-0.32 mm). No overhang exceeding 3 mm was observed for 6° of flexion, while underhang was observed except on the lateral sides of zone 2 (1.32 mm) and zone 4 (1.10 mm) and on the medial side of zone 1 (1.54 mm). A significant difference in overhang values on the lateral and medial sides of zone 1 was observed between 0 and 6° of flexion (P < 0.05).
The present study demonstrated that femoral component flexion implantation by 3° can reduce excessive overhang, although 3.10 mm of overhang remained at the medial side of zone 1. Conversely, 6° of flexion implantation can avoid 3 mm of overhang for any zone, but increases the risk of underhang. Slight flexion implantation may be an effective alternative technique to prevent excessive component overhang, especially in the trochlea and anterior region of the distal condyle, in Chinese patients with standard TKA prostheses.
以往研究报道了全膝关节置换术（TKA）中股骨假体的悬垂情况。本研究的目的是评估股骨假体在矢状面以不同屈曲角度植入对TKA中外侧和内侧骨-假体适配性的影响。
在中国10例膝关节的计算机断层扫描模型上进行虚拟假体植入，使用的是Advance Medial-Pivot膝关节系统（美国美敦力公司，田纳西州阿灵顿）的股骨假体，股骨假体在矢状面分别处于0°、3°或6°的屈曲位。对于每个屈曲角度的植入，测量在滑车（区域1）、髁前远端（区域2）、髁后远端（区域3）和髁后（区域4）的外侧和内侧，膝关节与股骨假体模型之间的差异。正值表示假体悬垂，负值表示假体覆盖不足。对3°屈曲植入范围内每个区域的假体悬垂（覆盖不足）值进行统计学分析。
随着屈曲植入角度的增加，悬垂减少，甚至变为覆盖不足。在0°屈曲植入时，超过3 mm的悬垂主要存在于区域1的内侧（5.81 mm）和区域2的外侧（3.39 mm）。在3°屈曲时，仅在区域1的内侧观察到超过3 mm的悬垂（3.10 mm），而仅在区域4的内侧观察到覆盖不足（-0.32 mm）。在6°屈曲时，未观察到超过3 mm的悬垂，而除了区域2的外侧（1.32 mm）、区域4的外侧（1.10 mm）和区域1的内侧（1.54 mm）外，均观察到覆盖不足。在0°和6°屈曲之间，区域1的外侧和内侧悬垂值存在显著差异（P < 0.05）。
本研究表明，股骨假体屈曲3°植入可减少过度悬垂，尽管区域1内侧仍有3.10 mm的悬垂。相反，屈曲6°植入可避免任何区域出现3 mm的悬垂，但增加了覆盖不足的风险。对于使用标准TKA假体的中国患者，轻微屈曲植入可能是一种有效的替代技术，可防止假体过度悬垂，尤其是在滑车和髁远端前部区域。
