Does Joint-line Obliquity Explain OA Onset Better Than CPAK Type?

Q: Which clinical question does this address?

Continuous measures of aHKA=MPTA−LDFA and JLO=MPTA+LDFA should be retained. The findings suggest possible refinement of classification boundaries, but do not validate preventive osteotomy or TKA alignment targets.

Over 5 years, 480 knees (18.9%) developed KL ≥2. CPAK type itself was not significantly associated with onset.

Among 2,541 knees without baseline OA, 480 developed OA over five years. The study examined continuous JLO measures and OA onset, beyond categorical alignment types.
The Bone & Joint Journal (2026). DOI: 10.1302/0301-620X.108B7.BJJ-2025-0687.R2 · Original explanatory chart based on reported data
Evidence & Original Source Image use terms

The research question

Does Joint-line Obliquity Explain OA Onset Better Than CPAK Type?

Participants and Methods

CPAK types and continuous aHKA and JLO values were compared. Covariate-adjusted logistic regression assessed associations with the development of KL ≥2, and linear regression was used for changes in JLCA. 2,541 MOST knees with KL <2 at baseline, followed for 5 years. Alignment-change analysis included 2,314 knees with follow-up full-length radiographs.

Main Findings

Over 5 years, 480 knees (18.9%) developed KL ≥2. CPAK type itself was not significantly associated with its development. Lower JLO was associated with its development (OR 1.048 per 1° decrease, 95% CI 1.001–1.098). The odds at JLO <171.6° were 1.36 times those at or above that threshold (95% CI 1.053–1.770). The regression coefficient for aHKA and change in JLCA was −0.139 (95% CI −0.241 to −0.036).

Implications for clinical and surgical practice

Continuous measures of aHKA=MPTA−LDFA and JLO=MPTA+LDFA should be retained. The findings suggest possible refinement of classification boundaries, but do not validate preventive osteotomy or TKA alignment targets.

Limitations

This observational association does not prove alignment correction prevents OA. The 171.6° cutoff was derived from these data, not a universal surgical target or diagnostic risk threshold. Consider 5-year observation, MOST’s high-risk population and image selection/attrition.

Let's put it briefly.

Which clinical question does this address?

Keywords

Osteoarthritis, Knee
Knee Joint
Bone Malalignment
Alignment
CPAK
Osteoarthritis
MOST

Abstract · Original text

Ji-Sahn Kim, Samuel J MacDessi, Do Weon Lee, Du Hyun Ro. Coronal alignment parameters of the knee predict osteoarthritis development : a Coronal Plane Alignment of the Knee classification-based analysis using the Multicenter Osteoarthritis Study data. The bone & joint journal. 2026;108-B(7):889-897. doi:10.1302/0301-620X.108B7.BJJ-2025-0687.R2.

AIMS

Mechanical varus or valgus alignment measures have been demonstrated to be closely related to knee osteoarthritis (KOA) development, but few attempts have been made to correlate the Coronal Plane Alignment of the Knee (CPAK) classification and disease development. This study hypothesized that certain CPAK types or deviations in CPAK parameters might enhance the risk of KOA development.

METHODS

KOA was defined as a Kellgren-Lawrence grade of 2 or higher. Data from 2,541 knees without KOA at baseline from the Multicenter Osteoarthritis Study (MOST) over five years of follow-up were examined. Differences in baseline CPAK types and parameters were analyzed between knees that developed KOA and those that did not. The association of CPAK type, arithmetic hip-knee-ankle angle (aHKA), and joint line obliquity (JLO) with the risk of disease development and joint line convergence angle (JLCA) changes were assessed.

RESULTS

Knees that developed KOA (480 knees; 18.9%) had significantly lower JLO (p = 0.022) and aHKA (p = 0.008) values than those that did not (2,061 knees; 81.1%). JLO was significantly associated with KOA development (odds ratio 1.048 (95% CI 1.001 to 1.098)). For knees with JLO values under the cut-off value of 171.6°, the risk of KOA development was 1.36 times higher than for those with values over the cut-off value (95% CI 1.053 to 1.770). aHKA showed a significant negative correlation with JLCA change (regression coefficient -0.139 (95% CI -0.241 to -0.036); p = 0.008). However, CPAK type itself showed no significant correlation with KOA development.

CONCLUSION

CPAK parameters, rather than types, were significantly associated with KOA development. Importantly, significant obliquity to the constitutional joint line might be as impactful as lower limb alignment. By potentially adjusting cut-off values, CPAK classification might be applied for predicting KOA development and investigating alignment-related aspects of KOA pathophysiology.

Read abstract on PubMed

The original paper.

Coronal alignment parameters of the knee predict osteoarthritis development: A Coronal Plane Alignment of the Knee classification-based analysis using the Multicenter Osteoarthritis Study data

J-S. Kim, S. J. MacDessi, D. W. Lee, D. H. Ro
The Bone & Joint Journal · 2026

DOI · 10.1302/0301-620X.108B7.BJJ-2025-0687.R2 Based data

Academic Discussion

Results explained with study numbers