Acromioclavicular Joint Depth and Angle in the Thai Population: Implications for Clavicle Hook Plate Design.

BACKGROUD: Subacromial erosion and impingement syndrome are frequently reported complications following clavicle hook plate (CHP) fixation in Thai orthopedic practice. These complications may result from CHP designs that do not adequately accommodate the acromioclavicular joint (ACJ) anatomy of the Thai population. Currently, only 2 CHP sizes (12 mm and 15 mm in depth) with a 0° angle are commercially available, potentially increasing the risk of osteolysis due to direct point contact with the acromion. This study aimed to determine the average depth and angle of the ACJ in the Thai population to optimize CHP design.

METHODS

This study analyzed 74 embalmed Thai cadavers (39 males and 35 females) donated for medical research. ACJ depth and inclination angle were measured bilaterally using 2 modified metric gauges constructed from stainless steel. The hanging hook of the depth measurement device was inserted close to the posterior ACJ before measuring the distance between the acromion process and the superior surface of the distal clavicle. The hypothetical ACJ angle was measured by reading at the scale on a standard protractor that complied with the matric tools.

RESULTS

The mean ACJ depth in Thai cadavers was 12.02 ± 4.11 mm (95% CI, 11.06-12.97 mm), while the mean inclination angle was 16.90° ± 6.76° (95% CI, 15.33°-18.46°). Males had significantly greater ACJ depth (14.06 ± 3.69 mm) compared to females (9.74 ± 3.31 mm, p < 0.01), but no significant difference was found between left and right clavicles. The ACJ inclination angle did not differ significantly between sexes. However, it was shown that the right ACJ angle (20.91° ± 6.94°) of Thais was significantly wider than the left side (14.05° ± 4.96°).

CONCLUSIONS

The optimal ACJ depth in the Thai population remains within the commercially available range of 12 to 15 mm. However, a CHP with an inclination angle of approximately 16° may help reduce postoperative complications such as subacromial erosion and impingement syndrome. The differences in ACJ depth between sexes and angle between sides should also be clinically considered before fixation.