How Does the Subchondral Bone Density Distribution of the Distal Humerus Change Between Early and Advanced Stages of Osteoarthritis?
Authors: Hwang Ji Sup , Won Samuel Jaeyoon , Gong Hyun Sik 
Published: November 2023

Abstract

Background
The distribution of subchondral bone density in a joint represents stress that is applied to the joint. Knowing this information is important for understanding the pathophysiology of osteoarthritis (OA). In the elbow, however, this has not been studied before.

Questions/purposes
(1) Is advanced-stage elbow OA associated with more radially distributed subchondral bone density than earlier stages? (2) What demographic (age and sex) and radiographic (osteophyte location and carrying angle) factors are associated with increased radial shift in subchondral bone density?

Methods
Between March 2001 and December 2021, we treated 301 patients for elbow OA. We considered patients with plain radiographs and conventional CT scans as potentially eligible. Thus, 68% (206 patients) were eligible; a further 27% (80 patients) were excluded because of a history of any injury or surgery or known inflammatory joint disease, leaving 42% (126 patients) for analysis here. Their mean ± standard deviation age was 60 ± 10 years. Early OA with minimal joint space narrowing and osteophyte formation was found in 33% (42 of 126) of patients, and advanced OA was found in the remaining 67% (84 of 126). Three-dimensional distal humerus subchondral bone models were derived from CT images, and in the central intra-articulating portion, we measured the subchondral bone density in two different sites: where it articulates with the radius (SBDrad) and with the ulna (SBDulna). We further defined the SBDratio as the percent ratio of SBDrad to SBDulna. We also evaluated osteophyte severity based on its size at the radiocapitellar and ulnotrochlear joints, and alignment through measuring the carrying angle on radiographs. To assess interobserver reliability, two orthopaedic surgeons took measurements independently from each other. All measurements had excellent intraoberver and interobserver reliabilities. Then, we compared the subchondral bone parameters between early and advanced OA and performed a multivariable analysis of the factors associated with subchondral bone parameters, including age, sex, osteophyte location, and carrying angle.

Results
Radial versus ulna subchondral bone density (SBDratio) was modestly higher in patients with advanced OA (118% ± 17%) than in patients with early OA (109% ± 17%, mean difference 9% [95% CI 2.3% to 15.3%]; p = 0.01). With increasing radial deviation in subchondral bone density, cubitus valgus had a modest association (β = 0.46 ± 0.23; p = 0.04) and severe osteophytes at the radiocapitellar joint had a large association (β = 9.51 ± 3.06; p = 0.002).

Conclusion
According to subchondral bone density distribution, stress concentration was more radially deviated in patients with the advanced stages of elbow OA than in those with the early stages. We also found that an increase in carrying angle is associated with radial deviation of stress. A future study that examines longitudinal changes in the subchondral bone density might be required to confirm changes in stress concentration with OA progression.

Clinical Relevance
This study gives us insight into the potential pathophysiology of elbow OA in relation to elbow alignment. Although debridement of osteophytes in the ulnotrochlear joint is the most frequently performed procedure in patients with advanced elbow OA, our finding suggests that some patients with an increased carrying angle might benefit from management of the radiocapitellar joint as well, or from being informed of the future development of OA in the radiocapitellar joint, because stress at this site can be increased with the advancement of OA.