Objective To compare and analyze the biomechanical differences of different anchor nail placement methods in the repair of rotator cuff injury complicated with osteoporosis using the finite element method.

Methods An eligible elderly patient with rotator cuff injury was selected, and five sets of three-dimensional models with different nailing methods were established according to the thin-slice CT and anchor data of shoulder joint, followed by the traditional suture bridge model (A model), internal 90° naddling model (B model), four-anchor single-locking model (C model), four-anchor double-locking model (D model), and three-anchor single-locking model (E model). 50N load was applied to the five groups of models, and the stress distribution changes of the five groups of models were compared and analyzed. Finally, the ultimate load of the five groups of models was compared.

Results The maximum stress of humerus and anchor in the 90° pinning model and interlocking anchor model were lower than those in the traditional suture bridge model, and the ultimate load of three models was significantly higher than that in traditional suture bridge model (P ＞ 0.05). The maximum humeral stress of three-anchor model was similar to that of the suture bridge model, but the maximum stress of anchor was significantly higher than that of suture bridge model, and the ultimate load of three-anchor model was lower than that of traditional suture bridge model (P ＞ 0.05).

Conclusions For elderly patients with rotator cuff injurycomplicated with osteoporosis, the 90° bolt placement method can effectively reduce the stress on the humerus and anchor bolts compared with the traditional 45° bolt placement method when using threaded anchor bolts for rotator cuff repair, and increase the uplift resistance of anchor bolts. The interlocking method of inner and outer row of anchor bolts can further enhance the uplift resistance of the anchor bolts on this basis, and improve the stability of rotator cuff repair. Among them, the method of double interlocking with anchor nails has the greatest improvement.