Suture Anchor Fixation in Osteoporotic Bone: A Biomechanical Study in an Ovine Model

To evaluate the load to failure strength of anchor techniques suitable for osteoporotic bone.

Using an osteoporotic ovine model in 72 humeri, 6 fixation techniques were tested. Group 1: two interlocking 5-mm anchors with fewer, wider threads; group 2: one 5-mm anchor; group 3: one 5-mm anchor reinforced laterally by a 6.5-mm cancellous screw; group 4: one 5-mm anchor in an area reinforced with a cancellous plug; group 5: two interlocking 5-mm anchors with smaller threads; group 6: one 5-mm smaller threaded anchor. After a 10-N preload, the specimens were cyclically loaded between 10 N and 30 N for 50 cycles and then destructively tested. Peak-to-peak displacement, cyclic elongation, ultimate load, stiffness, and failure mode were recorded.

Group 1 had lower peak-to-peak displacement than group 3 (P = .001), group 5 (P = .001), and group 6 (P = .033). In addition, group 1 showed lower cyclic elongation than group 3 (P = .001), group 5 (P = .035), and group 6 (P = .001). Group 1 had a higher ultimate load than group 2 (P = .002), group 3 (P = .019), and group 6 (P = .006). Group 1 also showed higher stiffness than group 2 (P = .007) and group 3 (P = .022). Mode of failure was predominantly caused by anchor pullout for all of the groups except group 3, which mainly failed by suture rupture.

Two interlocking suture anchors are stronger than a single anchor in osteoporotic bone. The anchor with fewer, wider threads and a smaller core diameter showed greater strength and less elongation than the other constructs. Reinforcement by cancellous autografting increased suture anchor strength.

Considering concerns about suture anchor pullout from osteoporotic bone, interlocking a second suture anchor with the first increases load to failure resistance. Anchors with small core diameters and fewer but wider threads are more efficient in osteoporotic bone.