Morrisey Zachary, Cruse Jordan, Barra Matthew, Carroll Thomas, Drinkwater Christopher
University of Rochester School of Medicine, 601 Elmwood Ave, Rochester, NY, 14642, United States.
University of Rochester Department of Orthopedics and Physical Performance at Highland Hospital, 1000 South Ave, Rochester, NY, 14620, United States.
J Orthop. 2024 Jan 14;51:54-59. doi: 10.1016/j.jor.2024.01.008. eCollection 2024 May.
Coronal Plane Alignment of the Knee (CPAK), is an informative way to classify native knee alignment types, but does not consider posterior tibial slope, an important variable in knee kinematics. We hypothesized that tibial slope would have a significant effect on knee kinematics and warrant consideration in addition to the CPAK system.
We examined 335 adult patients with osteoarthritis receiving total knee arthroplasty. We measured the lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), and posterior tibial slope angle (PTS). Knees were categorized into CPAK classes and subdivided into types 'A' (PTS 8°) or 'B' (PTS >8°). We recorded pre-and-post operative knee flexion, and extension/flexion gaps in all subjects.
CPAK classes VII-IX were not seen. Classes I and II comprised a plurality of all knees. One-third of all knees were type B. CPAK classes III, IV, and VI had greater type B proportions, but this was not statistically significant. Type B knees had greater flexion both pre-op () and post-op (); type A knees had greater flexion improvement pre-to-post operatively (). Type A knees had greater medial and lateral flexion-extension gap change pre-operatively () and (), respectively. Type B knees had greater medial-lateral gap imbalance preoperatively in both flexion and extension.
DISCUSSION/CONCLUSION: Our results suggest that there are important pre and post-operative differences in medial and lateral femorotibial gap balance between type A and B knees that require consideration for intra-operative balancing. Differences in knee flexion further solidify that PTS is an important variable that affects kinematics before and after TKA. We propose the addition of PTS types A and B to the existing CPAK classes. This is an easy and logical way to create a comprehensive classification system in both coronal and sagittal planes that captures further differences in knee kinematics.
膝关节冠状面排列（CPAK）是对自然膝关节排列类型进行分类的一种有效方法，但未考虑胫骨后倾，而胫骨后倾是膝关节运动学中的一个重要变量。我们假设胫骨后倾会对膝关节运动学产生显著影响，除CPAK系统外还值得考虑。
我们检查了335例接受全膝关节置换术的成年骨关节炎患者。我们测量了股骨远端外侧角（LDFA）、胫骨近端内侧角（MPTA）和胫骨后倾角度（PTS）。膝关节被归类为CPAK等级，并细分为“A”型（PTS≤8°）或“B”型（PTS>8°）。我们记录了所有受试者术前和术后的膝关节屈曲以及屈伸间隙。
未观察到CPAK VII - IX级。I级和II级占所有膝关节的多数。所有膝关节中有三分之一为B型。CPAK III级、IV级和VI级中B型比例更高，但无统计学意义。B型膝关节术前（ ）和术后（ ）的屈曲角度更大；A型膝关节术前至术后的屈曲改善更大（ ）。A型膝关节术前内侧和外侧屈伸间隙变化更大（ ）和（ ）。B型膝关节术前在屈曲和伸展时的内外侧间隙不平衡更大。
讨论/结论：我们的结果表明，A型和B型膝关节在股骨胫侧间隙平衡方面存在重要的术前和术后差异，术中平衡时需要考虑。膝关节屈曲的差异进一步证实，胫骨后倾是影响全膝关节置换术前后运动学的一个重要变量。我们建议在现有的CPAK等级中增加A、B型胫骨后倾类型。这是一种简单且合理的方法，可在冠状面和矢状面创建一个全面的分类系统，以捕捉膝关节运动学中的更多差异。
