a Departamento de Ortopedia, Santa Casa de São Paulo, São Paulo, SP, Brasil
b Serviço de Ortopedia e Traumatologia, Hospital Israelita Albert Einstein, Universidade Federal de São Paulo (Unifesp), São Paulo, SP,Brasil
c Instituto de Ortopedia, Hospital das Clínicas, Faculdade de Medicina, Universidade de São Paulo (USP), São Paulo, SP, Brasil
d Escola Paulista de Medicina, Universidade Federal de São Paulo (Unifesp), São Paulo, SP, Brasil
Introduction
Suturing of rotator cuff injuries (RCIs) is one of the biggestchallenges for shoulder surgeons. There are high dehiscencerates, especially in relation to extensive injuries, and the inci-dence can range from 13% to 94% of the cases.
The aim of surgical treatment is to mechanically producea firm and secure suture of the tendon at its insertion site sothat healing can take place. The surgical materials used aretoday highly reliable and for this reason, according to Cum-mins, the major cause of repair failure is the interface of thesuture thread with the tendon.3Gerber et al.4suggested thatthe ideal repair should withstand a high traction force duringthe initial period of fixation, enable formation of the minimumspace between the tendon and bone and maintain mechani-cal stability until healing takes place. The type of stitch usedfor the suture is a crucial part of the success or failure of thesurgical procedure.
Arthroscopic RCI repairs require a refined operative tech-nique and knowledge and skill on the part of the surgeon inorder to pass the thread through the tendon. The suturing canbe performed using different types of stitches, which weredeveloped to withstand traction forces without undoing thetendon repair.5The Mason-Allen stitch is the most resistanttype.4It can be performed arthroscopically and is then knownas the modified Mason-Allen stitch, as described by Scheibeland Habermeyer.
With regard to tendon suturing performed as an open pro-cedure, the technique developed by Krackow et al.7is generallyrecognized as the most resistant and secure method, but itis almost impossible to perform it arthroscopically. Moreover,because it involves stitches that are transverse to the directionof the tendon, it may compromise the vascularization of thetendon and thus the healing of the injury.
Based on the Lasso-Loop stitch described by Lafosse et al.,8the senior member of our group (SLC) sought to develop atechnique that could be combined with the resistance of thesuture developed by Krackow et al.7and which could be per-formed arthroscopically while only minimally compromisingthe vascularization. This new technique is performed usingdoubly locked longitudinal stitches, which we have namelocked double-tie (LDT) stitches.
In addition to describing the technique for constructingLDT stitches, done on the tendon of the infraspinatus muscleof sheep, we compare it biomechanically with the modifiedMason-Allen stitch, which is considered to be the most resis-tant method performed arthroscopically.
This study using animals was approved by our institution'sethics committee.
Materials and methods
Surgical technique
The LDT stitch is simples, but like all techniques, it needs tobe practiced and assistants need to be trained. Use of knotlessanchors facilitates construction of these stitches but is notessential. The six steps in making these stitches are as follows:
First: After placing the suture anchor in the appropriateposition, using an arthroscopic suturing needle, one of theends of the thread is passed through the tendon from the artic-ular to the subacromial face, approximately 20 mm mediallyto the lateral border of the tendon, close to the muscle-tendontransition. The thread should run through the anchor and notbe trapped (Fig. 1A).
Second: The length of the thread is equalized and then thesuturing needle is used to make another partial passage of
the same thread, leaving a loop from the articular face to thesubacromial face (Fig. 1B).
Third: The end of the thread that is in the subacromial spaceis passed through this loop. At this time, the lower thread istensioned, which thus locks the first part of the suture (Fig. 1Cand D).
Fourth: A new loop is made approximately 10 mm from thelateral extremity of the tendon (Fig. 1E).
Fifth: The end of this thread is passed through this new loop(Fig. 1F).
Sixth: The stitch is then tightened using nonslip knots andthe lesion is closed (Fig. 1G).
With a suturing anchor loaded with two thread, twostitches can be constructed and the suture resistance can befurther increased (Fig. 1H and I).
Biomechanical evaluation
In previous experimental studies, it was established anddemonstrated that the tendon of the infraspinatus muscle ofsheep has characteristics similar to those of the supraspinatusof the human shoulder and serves as a model for studies onrotator cuff diseases.
Twenty tendons of the infraspinatus muscle of male Texelsheep aged 1.5-2 years were used in this study. These wererandomly divided into two groups: LDT, in which the stitchdescribed above was constructed (Fig. 2A); and MA, in whichthe modified Mason-Allen stitch6was constructed (Fig. 2B).In removing the tendons from the animals, only the tendonpart of the infraspinatus muscle was preserved. Tenotomywas performed on the humeral insertion, without any bonestructure continuing to adhere to the tendon. The samplesdid not undergo any freezing process and were kept in salinesolution at -5?C. Before the stitch was constructed, the thick-ness and width of the tendons were measured. The stitcheswere constructed using arthroscopic instruments (Bird-Beak®and Tendon-Grasper®, from Arthrex) and the thread used wasFiber-wire®no. 2 (Arthrex). The proximal extremity of the ten-don was to a clamping device and the threads were fixed in acomponent of a traction device that had an opening throughwhich the threads were passed and tied to a fixed bar, usingnonslip stitches and an arthroscopic knot pusher. The sample
was subjected to an initial load of 30 N for 60 s to pretension thesuture. The traction device had a scale marked in millimetersand this was used to observe the force needed to form dis-placements of 5 mm and 10 mm and the maximum force thatthe sample withstood. The causes of the failures were alsonoted (Fig. 3).
The evaluation was done in the mechanics laboratory,using a standard test machine with unidirectional traction(MTS; Qtest model), at a constant velocity of 20 mm per sec-ond, with a load cell of 500 N and without cycling of the forceapplied.
Statistical assessment
Descriptive analysis was performed in relation to the spacesof 5 mm and 10 mm and the maximum force measured in eachtype of stitch. After all of the adherences had been checked,their equality of variance was tested for each pair of variables(measured in both types of stitch), by means of the Fisher Ftest.
The Student t test was then used on the variables of weight,width and thickness to ascertain the equality between theirmeans, and on the variables of 5 mm space, 10 mm space andmaximum force, to investigate whether the means obtainedfrom using the LDT stitch were superior to those obtained fromusing the MA stitch.
For all the tests, the significance level used was 5%. Thus,the hypotheses in which the descriptive levels (p-values) were<0.05 were rejected.
Results
Table 1 presents the mean, standard deviation (SD) andminimum, median and maximum values obtained for eachvariable and for each type of stitch used.
To compare the 5 mm space, 10 mm space and maximumforce of the two groups, an F test was firstly performed tocollate the variances. The hypothesis that the means for thevariables of 5 mm, 10 mm and maximum force in the LDTstitch group were at most equal to the means in the MA stitchgroup was then tested using the Student t test. From this, itwas concluded that the means for these variables in the LDTstitch group were superior to those of the MA group, at thesignificance level of 5% (Figs. 4-6).
Discussion
Competent suturing of RCIs should resist the initial tractionforce of the tendon, allow as little separation as possible
between the tendon edges and the bone bed and maintain sta-bility until the injury has healed.4Through stable and resistantsuturing, muscle-tendon-bone union will again be achievedafter healing.
After large numbers of cases of repeated tearing had beenobserved, especially in situations of extensive injury, inter-est in developing new techniques to improve the results fromthese operations increased.11-13Recent studies have shownthat the key point in maintaining these mechanical propertiesis the interface between the suture and the tendon.
Consequently, several types of arthroscopic stitches havebeen described, going from very simple ones to U-shapedstitches, modified Mason-Allen stitches,4Mac-Stitch14andLasso-Loop,8all with the aim of increasing the resistance ofthe fixation.
We believe that better healing is directly related to bettervascularization of the rotator cuff that is to be repaired, andconsequently to less area of ischemia. As shown by anatomicalstudies, the microvascularization of this structure is orientedparallel to its tendon fibers and progresses from medial to lat-eral, with a less vascularized area in the region of the tendon ofthe supraspinatus muscle (Codman's critical area).15,16Thus,stitches constructed transversally to the direction of vascu-larization will result in greater ischemic area and thereforeincrease the chance of repeated tearing. This does not occurwith LDT stitches, because they are parallel and respect thevascularization of the tendon (Fig. 1I).
With the aim of comparing the new stitch that wedeveloped (LDT) with the Mason-Allen stitch modified byHabermeyer, other factors that could alter the results fromthe samples were excluded, for example failure relating to thetendon-bone interface (poor bone quality, positioning errors,directionality, loosening and even cutting of the suture threadat the openings of the anchors). Thus, with the sheep tendonmodel, we were able to isolate and individually evaluateeach stitch with regard to the force required to produce
displacements of 5 mm and 10 mm and the maximum loadneeded for the sample to fail.
Unlike Ponce et al.,17we did not cut the tendons longitudi-nally, because their physical conformity was more consistentin the more proximal part of the spine of the scapula,but we obtained a smaller number of samples. We dis-tributed the stitches on our samples and imagined using ananchor. Thus, two LDT stitches were constructed for every MAstitch.
Our results showed that the LDT was superior to the MAstitch, both regarding the force required to form spaces of5 mm and 10 mm and regarding the maximum traction resis-tance. This confirmed our hypothesis and makes this stitch anoption for suturing in rotator cuff surgery. We observed duringthe test that the MA stitches resulted in "strangulation" of thetendon, which is bad in relation to its vascularization. This didnot occur with the LDT stitches.
In comparing our maximum load results with the resultsfrom other biomechanical studies on sheep, we observed thatthe LDT stitches withstood greater force before sample failureoccurred. However, we did not perform cycling of the forceapplied, as described by Burkhart et al.,18which is an impor-tant limitation of our study and impedes more trustworthycomparisons.
It is evident that biological factors are fundamentallyimportant in repairing rotator cuff injuries, but these were notan objective of the present study.
Conclusion
We confirmed our hypothesis that LDT stitches are supe-rior to MA stitches from a biomechanical point of view.LDT stitches are an additional option for surgeons whenfragile tendons with poor vascularization need to besutured. They improve the quality of the fixation withoutincreasing the strangulation and consequently the area ofischemia.
Conflicts of interest
The authors declare no conflicts of interest.
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