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.

IV.

No abstract

Level IV, case series.

We assessed the impact of a minimal medial soft-tissue release with complete peripheral osteophyte removal on the ability to attain manual preresection deformity correction during navigation-assisted total knee arthroplasty (TKA) for varus osteoarthritis. We included 131 TKAs for 109 patients with medial compartment predominant osteoarthritis. The steps for achieving minimal medial soft-tissue release were performed as follows: (1) elevation of a periosteal sleeve to 5-mm distal to the joint line and (2) complete removal of peripheral osteophytes. The evaluation criteria of this study were as follows: (1) age, (2) height, (3) weight, (4) body mass index (BMI), (5) sex, (6) the preoperative femorotibial mechanical angle in the neutral position before medial release and (7) the mechanical angle in maximum manual valgus stress after the two-step medial-release procedure (measured on the navigation screens). Multiple regression analysis of the criteria was performed to determine the degree of varus deformity that allowed neutral alignment but required extensive medial release. The femorotibial mechanical angle in the neutral position before medial release and sex correlated with the mechanical angle in maximum manual valgus stress on the navigation screen after medial release (r = 0.72, p < 0.001). Based on the regression formula, the maximum degree of preoperative varus deformity that allowed neutral alignment by the minimum medial-release procedure was 5.3 degrees for males and 9.1 degrees for females. The magnitude of deformity which has an impact on the ability to correct varus deformity (by minimal soft-tissue release and complete osteophyte removal) was clarified. If the preoperative degree of varus deformity was within 5.3 degrees for males and 9.1 degrees for females, an extensive medial release was not required to obtain neutral alignment.