Abstract
Coronal plane alignment of the knee (CPAK) has recently been proposed as a simple
and universal classification system to determine the suitability of a particular phenotype
of the knee to a specific alignment strategy for knee replacement surgery. Although
racial differences may affect knee alignment, there are no reports on the racial distribution
of this classification system. We aimed to clarify the distribution of CPAK classification
in patients with osteoarthritis who underwent total knee arthroplasty (TKA) in Japan.
Consecutive patients who underwent primary TKA were analyzed retrospectively. The
knees were categorized according to the CPAK classification system which comprised
of two independent variables (arithmetic hip–knee–ankle [aHKA] angle and joint-line
obliquity [JLO]) with three respective subgroups to create the following nine phenotypes
of the knee: type I (varus aHKA and apex distal JLO), type II (neutral aHKA and apex
distal JLO), type III (valgus aHKA and apex distal JLO), type IV (varus aHKA and neutral
JLO), type V (neutral aHKA and neutral JLO), and type VI (valgus aHKA and neutral
JLO), type VII (varus aHKA and apex proximal), type VIII (neutral aHKA and apex proximal),
and type IX (valgus aHKA and apex proximal). The distribution of the phenotypes in
the Japanese population was investigated as a primary outcome. To accurately compare
the results with previous studies conducted on non-Japanese patients, a sex-matched
distribution was investigated as a secondary outcome. A total of 570 knees were investigated
of which 500 knees were examined after exclusions. The most common distribution was
type I (53.8%), followed by type II (25.4%), type III (8.2%), type IV (7.2%), type
V (4.4%), and type VI (1.0%). Types VII, VIII, and IX were not distributed. The sex-matched
distribution was nearly identical to the overall distribution in Japan. The majority
of patients with knee osteoarthritis in Japan had medially tilted joints with constitutional
varus alignment.
Keywords
coronal plane alignment of the knee - osteoarthritis - constitutional varus - kinematic
alignment - mechanical alignment
