Page 8 - Arthroscopic Knot Tying: An Instruction Manual

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Introduction

An increasing number of surgeons are performing arthroscopic surgery in the knee to repair meniscal tears
and in the shoulder to repair rotator cuff or labral tears. Many are also performing capsular shifts to treat
instability. Essential to these procedures is the ability to tie arthroscopic knots to approximate
intraarticular tissues and thereby avoid the need for large arthrotomies. Arthroscopic knot tying is more
difficult than manual knot tying because the surgeon must sequentially construct the knot outside the
joint and then pass the knot into the joint through small cannulas. Tying arthroscopic knots is technically
demanding and requires considerable practice. With the heightened popularity of arthroscopic surgery,
the number of commonly used arthroscopic knots and the number of surgeons using these knots has
increased. It is our intention to provide instruction on how to tie all of the arthroscopic knots that have
been described in the literature.

Knot Tying Principles

The goal of knot tying is to approximate tissue under tension and maintain the tissue in apposition until
biologic repair and healing can occur. It is imperative for all surgeons to learn and use knot-tying
techniques that minimize the chance of knot failure. Knot failure can occur through four different
processes: 1) knot slippage and loosening, 2) suture breakage, 3) tissue failure, and 4) suture anchor
pullout from bone.

Knot security is a term that describes the ability of a knot to resist slippage once tying is completed and a
load is applied (4 ,6 ,7 ). There are three factors that determine knot security: friction, internal
interference, and slack between throws. Friction is inherent to the suture material. For example, braided
suture has a higher coefficient of friction than does monofilament. Internal interference is determined by
the configuration of the knot and increased by the length of the contact between the loop limb and the
post limb. Reversing the direction of half hitches and alternating posts increases the internal interference
of a knot. Lastly, the surgeon should minimize the slack between the individual throws in each knot to
maximize loop security (5 ). This can be done by removing twists in the suture between throws to ensure
the knots lie flat and by past pointing to cinch the suture down tightly to reduce internal knot looseness.
If an individual loop slips during the process of knot tying, the tissue will lose its apposition, which is
necessary to ensure biologic healing and repair. It has been suggested that more than two to three
millimeters of knot slippage can lead to failure of tissue apposition (3 ,24 , 25 , 26 ,38 ,39 ). Knots that
fail through slippage have been shown to have less strength (i.e., knot-holding capacity) than knots that
fail through suture rupture (10 ).

In addition to slippage, knot failure can occur through suture breakage. Suture rupture is usually due to
shear forces rather than tensile forces because the tensile strength of a suture is larger than its shear
strength. The most common shear point is at the knot where the suture bends into the body of the knot
and the tensile forces are converted to shear forces (10 ). Suture breakage can occur at other sites as
well if there is a weakness in the suture. This may occur if the suture is weakened by instrument
manipulation or if the suture becomes frayed by repeated sliding of one suture limb over the other,
especially with materials that have a high coefficient of friction (e.g., uncoated, braided polyester).
The third mechanism of knot failure is tissue failure. The suture can pull through the tissue being apposed.
This may happen in atrophic tissue or in normal tissue that is damaged by the suture. Suture-derived
tissue damage occurs when the suture “saws” through the tissue leading to tissue failure and suture
pullout. This situation may be minimized by using a suture with a lower coefficient of friction such as a
monofilament suture.