Coronal Plane Alignment of the Knee (CPAK) classification

Abstract

Aims A comprehensive classification for coronal lower limb alignment with predictive capabilities for knee balance would be beneficial in total knee arthroplasty (TKA). This paper describes the Coronal Plane Alignment of the Knee (CPAK) classification and examines its utility in preoperative soft tissue balance prediction, comparing kinematic alignment (KA) to mechanical alignment (MA). Methods A radiological analysis of 500 healthy and 500 osteoarthritic (OA) knees was used to assess the applicability of the CPAK classification. CPAK comprises nine phenotypes based on the arithmetic HKA (aHKA) that estimates constitutional limb alignment and joint line obliquity (JLO). Intraoperative balance was compared within each phenotype in a cohort of 138 computer-assisted TKAs randomized to KA or MA. Primary outcomes included descriptive analyses of healthy and OA groups per CPAK type, and comparison of balance at 10° of flexion within each type. Secondary outcomes assessed balance at 45° and 90° and bone recuts required to achieve final knee balance within each CPAK type. Results There was similar frequency distribution between healthy and arthritic groups across all CPAK types. The most common categories were Type II (39.2% healthy vs 32.2% OA), Type I (26.4% healthy vs 19.4% OA) and Type V (15.4% healthy vs 14.6% OA). CPAK Types VII, VIII, and IX were rare in both populations. Across all CPAK types, a greater proportion of KA TKAs achieved optimal balance compared to MA. This effect was largest, and statistically significant, in CPAK Types I (100% KA vs 15% MA; p < 0.001), Type II (78% KA vs 46% MA; p = 0.018). and Type IV (89% KA vs 0% MA; p < 0.001). Conclusion CPAK is a pragmatic, comprehensive classification for coronal knee alignment, based on constitutional alignment and JLO, that can be used in healthy and arthritic knees. CPAK identifies which knee phenotypes may benefit most from KA when optimization of soft tissue balance is prioritized. Further, it will allow for consistency of reporting in future studies. Cite this article: Bone Joint J 2021;103-B(2):329–337.

The dissatisfied total knee arthroplasty patient. New technologies-the white knight in shining armor coming to their rescue?

“…This starts at the hip (varus or valgus neck), goes to the diaphysis of femur and tibia and ends in the load-bearing position of the foot [20]. The authors of this editorial believe it is time to understand coronal deformity in a more profound way as Hirschmann et al and MacDessi et al did with their extensive coronal alignment classifications [21,22].…”

Tibiofemoral dynamic stressed gap laxities correlate with compartment load measurements in robotic arm-assisted total knee arthroplasty

“…Both surgeons followed a standardised operative protocol employing a restricted kinematic philosophy to reproduce functional alignment. As described in the coronal plane alignment of the knee (CPAK) classification, 15 the medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA) were measured from four-foot standing radiographs. From these values, the constitutional alignment (arithmetic hip-knee-ankle angle; aHKA) and the obliquity of the joint line (joint line obliquity; JLO) were calculated for each patient.…”

Restricted Kinematic Alignment in Total Knee Arthroplasty: Scientific Exploration Involving Detailed Planning, Precise execution, and Knowledge of When to Abort

“…This sort of imaging can quantify the 2 independent variables of joint line obliquity and prearthritic limb alignment (arithmetic hipknee-ankle angle) [19]. These parameters define each patient's Coronal Plane Alignment of the Knee phenotype [20], a critical categorization for understanding how knee soft-tissue laxities will behave once implants are positioned …in MA or KA. Furthermore, when target boundaries are imposed, these data allow predictions for when minor soft-tissue releases will be required.…”