Biomechanical properties of a suture anchor system from human allogenic mineralized cortical bone matrix for rotator cuff repair

Abstract

Background: Suture anchors (SAs) made of human allogenic mineralized cortical bone matrix are among the newest developments in orthopaedic and trauma surgery. Biomechanical properties of an allogenic mineralized suture anchor (AMSA) are not investigated until now. The primary objective was the biomechanical investigation of AMSA and comparing it to a metallic suture anchor (MSA) and a bioabsorbable suture anchor (BSA) placed at the greater tuberosity of the humeral head of cadaver humeri. Additionally, we assessed the biomechanical properties of the SAs with bone microarchitecture parameters.

Methods: First, bone microarchitecture of 12 fresh frozen human cadaver humeri from six donors was analyzed by high-resolution peripheral quantitative computed tomography. In total, 18 AMSAs, 9 MSAs, and 9 BSAs were implanted at a 60° angle. All three SA systems were systematically implanted alternating in three positions within the greater tuberosity (position 1: anterior, position 2: central, position 3: posterior) with a distance of 15 mm to each other. Biomechanical load to failure was measured in a uniaxial direction at 135°.

Results: Mean age of all specimens was 53.6 ± 9.1 years. For all bone microarchitecture measurements, linear regression slope estimates were negative which implies decreasing values with increasing age of specimens. Positioning of all three SA systems at the greater tuberosity was equally distributed (p = 0.827). Mean load to failure rates were higher for AMSA compared to MSA and BSA without reaching statistical significance between the groups (p = 0.427). Anchor displacement was comparable for all three SA systems, while there were significant differences regarding failure mode between all three SA systems (p < 0.001). Maximum load to failure was reached in all cases for AMSA, in 44.4% for MSA, and in 55.6% for BSA. Suture tear was observed in 55.6% for MSA and in 22.2% for BSA. Anchor breakage was solely seen for BSA (22.2%). No correlations were observed between bone microarchitecture parameters and load to failure rates of all three suture anchor systems.

Conclusions: The AMSA showed promising biomechanical properties for initial fixation strength for RCR. Since reduced BMD is an important issue for patients with chronic rotator cuff lesions, the AMSA is an interesting alternative to MSA and BSA. Also, the AMSA could improve healing of the enthesis.

Keywords: Allogenic mineralized suture anchor; Biomechanical analysis; High-resolution peripheral quantitative computed tomography; Rotator cuff reconstruction; Shoulder; Shoulder surgery; Suture anchor.

Fig. 1

Suture anchors and biomechanical setup. A Suture anchors tested in the study. 1: allogenic mineralized suture anchor (SharkScrew® suture), 2: metallic suture anchor (HEALIX TI™), 3: bioabsorbable suture anchor (BioComposite SwiveLock®). B The humerus is fixed in the uniaxial spindle-operated testing machine. The adjustable fixation device and the transversal bar (white star) prevent slipping and sliding of the specimen during biomechanical testing. The suture anchor is fixed at the greater tuberosity of the humeral head (black star) and the sutures of the anchor are knotted together and fixed on a hook for uniaxial testing at 135°

Fig. 2

Structure of the SharkScrew® suture, an allogenic mineralized suture anchor (AMSA). A The AMSA is armed with two FiberWire® #2 sutures and fixed on the implantation screwdriver. B Histological section of a sterile AMSA (toluidine blue staining) under fluorescent light. Decellularized and mineralized osteons with the surrounding lamellae and central Harversian canals are visible. C Electron microscopic image of the AMSA. Decellularized Harversian canals with surrounding bone lamellae are visible. D Animation of the AMSA after subtraction of bone tissue. The Harversian canal system is visible all along the suture anchor

Fig. 3

Relationships between bone microarchitecture measurements and age. Pairs of measurements of humeri from identical specimen (black dots) are connected by vertical black lines. Gray lines indicated linear regressions. Slope estimates are non-significant for all measurements

Fig. 4

Box plot diagram of load to failure. Load to failure rates are given according to the implanting position at the greater tuberosity of the humeral head (light grey: position 1 anterior; white: position 2 central; dark grey: position 3 posterior) of the allogenic mineralized suture anchor (AMSA), the metallic suture anchor (MSA), and the bioabsorbable suture anchor (BSA)