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

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

Methods: 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.

Results: 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.

Conclusions: 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.

Clinical Relevance: 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.