determining the relative effects of single- and double - row suture anchor repairs of the rotator cuff will allow physicians to be better equipped to treat patients with rotator cuff disease .
the prevalence of full and partial thickness defects increases linearly with age after 50 years , and by the age of 80 years , they exist in 80% of the population .
the influence of rotator cuff pathology on glenohumeral kinematics is not well documented in the literature , although several authors have speculated on the wide disparity of functional abilities of patients with grossly similar pathology .  
a number of cadaveric studies have examined the effects of rotator cuff pathology on shoulder kinematics . collectively , these studies suggest that increasing the size of the rotator cuff tear will result in an increased alteration of kinematics . currently , there is little information available on the effect of rotator cuff tears on active kinematics in - vitro .
examined the effects of sequential one , two , and three cm rotator cuff tears that were created in the supraspinatus tendon and extended into the subscapularis tendon .
the humeral head was displaced posteriorly with progressively larger tears of the rotator cuff during active shoulder elevation .
the authors concluded that increasing the size of the rotator cuff tear resulted in greater alterations in glenohumeral kinematics .
the goals of surgical repair of rotator cuff tears are to restore the anatomic relationship between the tendons and their osseous footprints on the humerus .
common open and arthroscopic techniques include transosseous suture repair or the use of suture anchors in either a single- or double - row repair configuration .
several recent studies have examined the biomechanical properties and clinical outcomes of the different repair techniques .
biomechanical studies have found double - row constructs to be stronger than single - row constructs in both cadaveric and animal models .
in addition , double - row repairs can restore the tendon footprint more accurately and are associated with higher rates of tendon healing than single - row repairs .
it has also been suggested that double - row repairs are preferable for cases with retracted tendons . despite the biomechanical advantage ,
clinical studies have failed to show a distinct advantage favoring the double - row repair technique .  
in addition to ensuring mechanical integrity of these reconstructions , the resulting glenohumeral joint motion is also important . however , we are unaware of any studies that have examined the effect of different suture anchor repairs on shoulder translations . hence , the purpose of this study was to determine active glenohumeral kinematics with simulated 2 cm - sized rotator cuff tears .
in addition , the ability of single- and double - row suture anchor repair to restore intact glenohumeral kinematics was also compared .
we hypothesized that ( 1 ) two cm defects in the rotator cuff would have a minor effect on simulated active glenohumeral kinematics and that ( 2 ) both single- and double - row suture anchor fixation would restore normal active intact motion .
eight pairs of fresh - frozen cadaveric upper forequarters ( mean age : 66  9 years ; range : 46 - 74 years ; 5 male ) were used .
all specimens had no evidence of previous surgery , trauma , glenohumeral arthritis , or rotator cuff tendonopathy .
specimens were thawed to room temperature ( mean 23c ( 2c ) ) and were kept moist with 0.9% saline throughout testing . a shoulder testing simulator that creates active unconstrained glenohumeral elevation was employed .
specimens were prepared by osteotomy of the distal humerus at mid - shaft , exposure of the anterior deltoid , and exposure of the inferior border of the scapula . a 316 stainless - steel rod , with weights added to be equivalent to the intact arm , was cemented into the distal humeral canal .
equivalence between the intact arm and the weighted rod was verified with a spring scale .
each specimen was mounted to the simulator by securing the inferior pole of the scapula into a custom pot with polymethylmethacrylate .
muscle simulation was achieved by suturing pneumatically actuated cables to the tendons of the rotator cuff muscles 
supraspinatus , subscapularis , and infraspinatus / teres minor , and attaching three cables to the deltoid tuberosity to simulate the three heads of the deltoid muscle .
forces were applied to the individual cables using a previously described set of loading ratios .
these were based upon electromyographic ( emg ) data and the relative physiological cross - sectional areas of the muscles .
the forces varied according to the angle of elevation of the humerus and were different for each specimen .
the relative motion of the humerus with respect to the scapula was collected with an electromagnetic tracking device ( flock of birds , ascension technologies , burlington , usa ) .
the receivers for the tracking system were fixed to the superior border of the scapula and the rod that replaced the distal humerus .
passive glenohumeral elevation in the plane of the scapula was conducted to ensure no impingement occurred as a result of fixation .
small tone loads of between 20n and 30n were applied to the rotator cuff muscles at the start of each cycle of motion .
these loads were selected to ensure that the humeral head was centered in the glenoid socket when the motion began .
five trials of both passive and active motions were conducted to allow quantification of repeatability .
elevation was defined as movement in the scapular plane from approximately 0 to 90 of glenohumeral elevation .
following intact testing , a deltoid splitting technique was used to expose the rotator cuff for creation of a 1 cm ( mediolateral ) by 2 cm ( anteroposterior ) defect in the anterior supraspinatus , which began at the rotator interval and propagated posteriorly .
one centimeter of the supraspinatus tendon was resected to simulate the clinical scenario of tendon retraction .
the deltoid muscle and skin incisions were closed with a running suture prior to recording the simulated active motion of the new torn state .
following testing , one shoulder from each of the eight pairs was randomized to undergo rotator cuff repair using a single - row suture anchor technique , while the contralateral shoulder was repaired using a double - row suture anchor technique .
all repairs were performed with 5.5 mm threaded metal anchors double - loaded with # 2 high strength suture ( arthrex , naples , usa ) .
the single row repair was performed by placing one anchor into the midportion of the greater tuberosity footprint .
the rotator cuff was repaired with simple sutures placed into the lateral edge of the tendon .
the double - row repair was performed by placing one anchor adjacent to the articular margin , and a second anchor was placed at the lateral edge of the greater tuberosity .
the medial row was repaired using two mattress sutures , and the lateral row was repaired with two simple sutures .
an overview of the experimental procedure repeatability of the trials was quantified by using the standard deviation of the five trials at each position .
a segment - fixed co - ordinate system was created on each of the scapula and humerus to allow calculation of the glenohumeral joint kinematics .
the plane of abduction and the position of the humeral head relative to the fixed scapula were analyzed at every 10 of glenohumeral elevation .
the relative motion of the humeral head with respect to the scapula was also quantified .
statistical analyses were performed using a friedman repeated measures analysis of variance ( anova ) on ranks .
the dependent variables considered were the angle of abduction and the torn or repaired state .
specimens were prepared by osteotomy of the distal humerus at mid - shaft , exposure of the anterior deltoid , and exposure of the inferior border of the scapula .
a 316 stainless - steel rod , with weights added to be equivalent to the intact arm , was cemented into the distal humeral canal .
equivalence between the intact arm and the weighted rod was verified with a spring scale .
each specimen was mounted to the simulator by securing the inferior pole of the scapula into a custom pot with polymethylmethacrylate .
muscle simulation was achieved by suturing pneumatically actuated cables to the tendons of the rotator cuff muscles 
supraspinatus , subscapularis , and infraspinatus / teres minor , and attaching three cables to the deltoid tuberosity to simulate the three heads of the deltoid muscle .
forces were applied to the individual cables using a previously described set of loading ratios .
these were based upon electromyographic ( emg ) data and the relative physiological cross - sectional areas of the muscles .
the forces varied according to the angle of elevation of the humerus and were different for each specimen .
the relative motion of the humerus with respect to the scapula was collected with an electromagnetic tracking device ( flock of birds , ascension technologies , burlington , usa ) .
the receivers for the tracking system were fixed to the superior border of the scapula and the rod that replaced the distal humerus .
passive glenohumeral elevation in the plane of the scapula was conducted to ensure no impingement occurred as a result of fixation .
small tone loads of between 20n and 30n were applied to the rotator cuff muscles at the start of each cycle of motion .
these loads were selected to ensure that the humeral head was centered in the glenoid socket when the motion began .
five trials of both passive and active motions were conducted to allow quantification of repeatability .
elevation was defined as movement in the scapular plane from approximately 0 to 90 of glenohumeral elevation .
following intact testing , a deltoid splitting technique was used to expose the rotator cuff for creation of a 1 cm ( mediolateral ) by 2 cm ( anteroposterior ) defect in the anterior supraspinatus , which began at the rotator interval and propagated posteriorly .
one centimeter of the supraspinatus tendon was resected to simulate the clinical scenario of tendon retraction .
the deltoid muscle and skin incisions were closed with a running suture prior to recording the simulated active motion of the new torn state .
following testing , one shoulder from each of the eight pairs was randomized to undergo rotator cuff repair using a single - row suture anchor technique , while the contralateral shoulder was repaired using a double - row suture anchor technique .
all repairs were performed with 5.5 mm threaded metal anchors double - loaded with # 2 high strength suture ( arthrex , naples , usa ) .
the single row repair was performed by placing one anchor into the midportion of the greater tuberosity footprint .
the rotator cuff was repaired with simple sutures placed into the lateral edge of the tendon .
the double - row repair was performed by placing one anchor adjacent to the articular margin , and a second anchor was placed at the lateral edge of the greater tuberosity .
the medial row was repaired using two mattress sutures , and the lateral row was repaired with two simple sutures .
repeatability of the trials was quantified by using the standard deviation of the five trials at each position .
a segment - fixed co - ordinate system was created on each of the scapula and humerus to allow calculation of the glenohumeral joint kinematics .
the plane of abduction and the position of the humeral head relative to the fixed scapula were analyzed at every 10 of glenohumeral elevation .
the relative motion of the humeral head with respect to the scapula was also quantified .
statistical analyses were performed using a friedman repeated measures analysis of variance ( anova ) on ranks .
the dependent variables considered were the angle of abduction and the torn or repaired state .
within all pairs of intact specimens , no statistically significant side - to - side differences were observed .
therefore , the measurements for the left and right cases were averaged and included in the friedman repeated measures anova as one entity .
in addition , no significant differences were found between passive and active intact glenohumeral elevation of the specimens through the range of motion .
statistical analyses were performed at every 10 of elevation , through an arc of 20 to 80 of glenohumeral elevation .
the plane of elevation exhibited was altered between the intact and the simulated tear states ( p = 0.01 ) [ figure 2 ] .
the 2 cm defect resulted in posterior angulation of the plane of elevation through the arc of abduction .
this was greatest at the mid - portion of abduction ( 40-60 ) with an overall average of 8 posterior shift when compared to the intact kinematic state .
the angle of internal - external rotation of the humerus was not affected by the simulated tear [ figure 3 ] .
similarly , no differences in the position of the humeral head were observed as a result of the simulated defect [ figure 4 ] .
change in plane of glenohumeral elevation from the intact state as a function of elevation angle for all states .
mean ( 1 sd ) for all specimens presented for 30 to 80 of elevation change in internal - external rotation angle from the intact state as a function of elevation angle for all states .
mean ( 1 sd ) for all specimens presented for 30 to 80 of elevation change in ( a ) superior - inferior and ( b ) anterior - posterior position of the humeral head from the intact state as a function of elevation angle for all states .
mean ( 1 sd ) for all specimens presented for 30 to 80 of elevation once repaired , a significantly different plane of elevation was achieved [ figure 2 ] .
this was true of both the single row suture anchor repair ( p < 0.001 ) and the double - row suture anchor repair ( p = 0.001 ) .
the internal - external rotation angle and position of the humeral head were not altered by the repair [ figures 3 and 4 ] .
single- and double - row suture anchor repairs were able to restore the intact kinematic state of the glenohumeral joint for 2 cm rotator cuff defects ( p = 0.10 ) [ figure 2 ] .
single row suture anchor repair resulted in a slightly anterior angulation of the plane of elevation on average when compared to the intact kinematic state .
double - row suture anchor repair resulted in a similar plane of elevation as that observed in the intact state ( p = 1.00 ) .
no differences in the plane of elevation were observed between the two repairs ( p = 0.10 ) .
both single- and double - row repairs resulted in increased variability in the change of the internal - external rotation angle of the humerus [ figure 3 ] , but no statistically significant differences were observed .
likewise , the position of the humeral head was not altered as a result of the repairs .
differences in the plane of glenohumeral elevation summarized for all specimens in all angles of elevation .
no differences were observed in the internal - external rotation angle , superior - inferior position , and anterior - posterior position
the plane of elevation exhibited was altered between the intact and the simulated tear states ( p = 0.01 ) [ figure 2 ] .
the 2 cm defect resulted in posterior angulation of the plane of elevation through the arc of abduction .
this was greatest at the mid - portion of abduction ( 40-60 ) with an overall average of 8 posterior shift when compared to the intact kinematic state .
the angle of internal - external rotation of the humerus was not affected by the simulated tear [ figure 3 ] .
similarly , no differences in the position of the humeral head were observed as a result of the simulated defect [ figure 4 ] .
change in plane of glenohumeral elevation from the intact state as a function of elevation angle for all states .
mean ( 1 sd ) for all specimens presented for 30 to 80 of elevation change in internal - external rotation angle from the intact state as a function of elevation angle for all states .
mean ( 1 sd ) for all specimens presented for 30 to 80 of elevation change in ( a ) superior - inferior and ( b ) anterior - posterior position of the humeral head from the intact state as a function of elevation angle for all states .
once repaired , a significantly different plane of elevation was achieved [ figure 2 ] .
this was true of both the single row suture anchor repair ( p < 0.001 ) and the double - row suture anchor repair ( p = 0.001 ) .
the internal - external rotation angle and position of the humeral head were not altered by the repair [ figures 3 and 4 ] .
single- and double - row suture anchor repairs were able to restore the intact kinematic state of the glenohumeral joint for 2 cm rotator cuff defects ( p = 0.10 ) [ figure 2 ] .
single row suture anchor repair resulted in a slightly anterior angulation of the plane of elevation on average when compared to the intact kinematic state .
double - row suture anchor repair resulted in a similar plane of elevation as that observed in the intact state ( p = 1.00 ) .
no differences in the plane of elevation were observed between the two repairs ( p = 0.10 ) .
both single- and double - row repairs resulted in increased variability in the change of the internal - external rotation angle of the humerus [ figure 3 ] , but no statistically significant differences were observed .
likewise , the position of the humeral head was not altered as a result of the repairs .
differences in the plane of glenohumeral elevation summarized for all specimens in all angles of elevation .
no differences were observed in the internal - external rotation angle , superior - inferior position , and anterior - posterior position
over the last decade , arthroscopic shoulder techniques and equipment have improved the ability to perform minimally invasive repairs to the rotator cuff tendons .
the literature has demonstrated that single- and double - row repairs are safe and effective .
the purpose of this study , unlike prior biomechanical studies that examined the relative strength double - row cuff repair , was to illustrate the kinematic effects of single- and double - row suture anchor repairs of 2 cm supraspinatus tears on simulated active glenohumeral joint kinematics .
the effects of a simulated 2 cm defect in the supraspinatus tendon in this study were similar to the results found previously by kedgley et al .
as theorized , no changes were found in the internal - external rotation of the humerus or the position of the humeral head with elevation , though the 2 cm defect did result in an alteration in the plane of elevation with a mean change of 8 posteriorly .
these results would perhaps be expected ; however , compensation likely occurs in - vivo with a medium - sized tear such as this .
our observations did not demonstrate any significant differences in the plane of elevation between single- and double - row repairs .
sugaya et al . , in a retrospective cohort study , compared the functional and structural outcomes of single - row versus double - row rotator cuff repair . at
a follow - up 35 months , no statistically significant differences in clinical outcome could be appreciated between the two different repair techniques .
franceschi et al . , in a randomized controlled clinical trial , compared 30 patients who received a single - row repair and 30 patients who received a double - row repair . at two years
follow - up , there was no clinically significant difference between the two different repair techniques . in this study , there are a number of possible reasons that may account for the results .
first , all rotator cuff repairs were performed with suture anchors that create focal sites of tendon reattachment to the greater tuberosity . in an in - vitro study ,
integration of the tendon to the tuberosity does not occur , and restoration of normal force distribution from a pennate muscle across the tendon - bone interface is unlikely . in both repair conditions ,
in - vivo repair studies may be capable of identifying kinematic differences among repair techniques that result in proportionately different rates of healing at the bone - tendon interface .
. a 2 cm defect may behave differently in a small specimen than in a large specimen and may have affected our ability to detect a change following the simulated tears .
simulating tears that are proportional to the size of the specimen rather than based on an absolute dimension may have resulted in more physiologically relevant results , although they should not have influenced the comparison of the repair types .
this supports the generalized trend toward more accurate restoration of the intact glenohumeral kinematics was seen in double - row suture anchor repair for a 2 cm defect of the supraspinatus .
third , rotator cuff pathology is often a chronic and progressive disorder that may occur in conjunction with adaptive changes in adjacent muscles .
in contrast , this study examined the kinematics of an acute lesion , and repair of the rotator cuff and may not accurately reflect the more common clinical scenario seen in patients with chronic rotator cuff disease .
the primary factors that contribute to shoulder stability remained functional , including the glenohumeral articular structures and capsulolabral complex . in a clinical situation
, this would likely not be the case , as some degree of degradation would have occurred throughout the cuff tissue .
however , had the specimens already exhibited pathology of the rotator cuff , we would have been unable to compare the repaired and intact states .
fourth , this study simulated a chronic clinical scenario by creating an acute defect in the rotator cuff to mimic tendon retraction .
shortening the tendon may have inadvertently created the anterior angulation seen in the plane of elevation with our suture anchor repairs .
however , there are also theories that a biochemical mediator may cause a damaged rotator cuff to retract .
similarly , the re - attachment of the tendon most likely imposed the observed increased variability in the internal - external rotation angle of the humerus .
unfortunately , the use of a deltoid split to produce the rotator cuff tear may not represent the same biomechanics , as that which would be observed had an arthroscopic approach been taken . however , no deltoid failures occurred during testing , and a previous study showed very little alteration of glenohumeral kinematics with a 1 cm rotator cuff tear created in the same way .  
the paired , randomized , and controlled nature of this study did generate results of significant merit .
furthermore , a unique , validated shoulder simulator capable of simulating active glenohumeral joint motion using a physiologically - based muscle loading protocol was employed .
in summary , a 2 cm defect in the supraspinatus alters the kinematics of the glenohumeral joint by moving the humeral plane of elevation posteriorly . both single- and
double - row repair techniques resulted in restoration of normal kinematics when compared to the intact state .
we did not find a significant difference in glenohumeral kinematics between the two repair techniques .
further studies are warranted to ascertain which repairs afford patients optimal functional and clinical results . with an improved understanding of the kinematics of the glenohumeral joint
 purpose : double - row suture anchor fixation of the rotator cuff was developed to reduce repair failure rates . 
 the purpose of this study was to determine the effects of simulated rotator cuff tears and subsequent repairs using single- and double - row suture anchor fixation on three - dimensional shoulder kinematics . 
 it was hypothesized that both single- and double - row repairs would be effective in restoring active intact kinematics of the shoulder.materials and methods : sixteen fresh - frozen cadaveric shoulder specimens ( eight matched pairs ) were tested using a custom loading apparatus designed to simulate unconstrained motion of the shoulder . in each specimen , the rotator cuff was sectioned to create a medium - sized ( 2 cm ) tear . within each pair , 
 one specimen was randomized to a single - row suture anchor repair , while the contralateral side underwent a double - row suture anchor repair . 
 joint kinematics were recorded for intact , torn , and repaired scenarios using an electromagnetic tracking device.results:active kinematics confirmed that a medium - sized rotator cuff tear affected glenohumeral kinematics when compared to the intact state . 
 single- and double - row suture anchor repairs restored the kinematics of the intact specimen.conclusions:this study illustrates the effects of medium - sized rotator cuff tears and their repairs on active glenohumeral kinematics . 
 no significant difference ( p  0.10 ) was found between the kinematics of single- and double - row techniques in medium - sized rotator cuff repairs.clinical relevance : determining the relative effects of single- and double - row suture anchor repairs of the rotator cuff will allow physicians to be better equipped to treat patients with rotator cuff disease . 
Clinical Relevance:
INTRODUCTION
MATERIALS AND METHODS
Testing procedure
Outcome variables and statistical analysis
RESULTS
Intact versus defect condition
Defect versus repair condition
Intact versus repair condition
DISCUSSION
CONCLUSIONS