The effect of loop size on loop security and elongation of a knot

While repairing a teared rotator cuff tendon with suture anchors and horizontal mattress suture configurations, knots should be secure at time zero while approximating the tendon to the bone, otherwise any failure in loop security may cause undesired clinical results. Optimum distance between suture limbs passed through the tendon, in other words the bite size, is still not clear in the literature. The aim of this study was to test the effect of loop size, which is directly related to the bite size, on loop security and elongation of a knot.

We hypothesized that a knot with a smaller loop size would be more secure. We asked if a knot with shorter circumference (1) would offer a better knot security; (2) would produce less elongation following repeated traction cycles.

Two parallel metal rods in 3.0mm diameter were fixed to load cells of dynamic testing machine. Four groups, from A to D, had the initial rod to rod distances of 2-4-6-8mm respectively (n=10). Surgeon's knots were prepared with 2/0 Ultrabraid® sutures around the rods. A tension meter was used for tying each half hitch under equal tension. Crosshead distances were recorded after 7N pre-load and subsequent 1000 repetitive cyclic loads between 7-30N.

Elongations after a 7N preload for groups A to D were 0.107mm (±0.006), 0.143mm (±0.018), 0,16mm (±0.025), 0.185mm (±0.018) respectively. This increase was significant (p<0.05, power>0.95) between each group except between groups B and C. Maximum elongations after 1000^th cycle for groups A to D were 0.32mm (±0.124), 1.12mm (±0.333), 1.162mm (±0.211), 1.292mm (±0.241) respectively. Only samples in group A (0.732mm±0.124) elongated significantly less than others (p<0.05, power >0.95). No knots unravelled or ruptured.

This study basically reports that a knot with a shorter loop circumference has superior properties regarding loop security and resistance to elongation. From the perspective of clinical importance, shorter distance between suture limbs of mattress configuration may provide a more secure fixation of the rotator cuff tendon to the bone.

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