CPAK oversimplifies the complex 3D anatomy of the bony knee: Role of 3D CT for improved analysis - a schematic...

Knee osteoarthritis (OA) is a prevalent condition impacting approximately 30 % of individuals over the age of 60, highlighting the importance of effective assessment and treatment options. Traditional assessments of knee OA focus on biological and mechanical factors, with lower limb malalignment identified as a significant contributor to the condition's progression and symptom severity. Total knee arthroplasty (TKA) serves as the primary intervention for severe cases, aimed at providing pain relief and improving range of motion, yet dissatisfaction rates post-surgery remains concerningly high, reported at 15 %-25 %. Accurate implant positioning and optimal limb alignment are critical for successful surgical outcomes and overall patient satisfaction following TKA. Current practices predominantly rely on two-dimensional (2D) radiographic parameters to evaluate knee alignment; however, these methods may oversimplify the complex three-dimensional (3D) anatomy of the knee joint, potentially leading to inadequate surgical planning. The recently developed Coronal Plane Alignment of the Knee (CPAK) classification offers a valuable framework, categorizing knee alignment into nine phenotypes based on 2D measurements of key anatomical angles. Nonetheless, existing research mainly utilizes 2D assessments, neglecting the impact of tibial rotation and knee flexion, which are crucial for understanding true alignment characteristics in patients with advanced OA. Thus, the purpose of this review is to critically analyse the limitations of the CPAK system and 2D imaging in assessing joint orientation and alignment, and to highlight the importance and potential of 3D imaging, particularly upright weight-bearing computed tomography (CT) for improved preoperative planning and functional outcomes in TKA.