Biomechanical effect of latissimus dorsi tendon transfer for irreparable massive cuff tear

J Shoulder Elbow Surg (2013) 22, 150-157

www.elsevier.com/locate/ymse

BASIC SCIENCE

Biomechanical effect of latissimus dorsi tendon transfer for irreparable massive cuff tear Joo Han Oh, MD, PhDa,b, Justin Tilan, MSb, Yu-Jen Chen, PhDb, Kyung Chil Chung, MD, PhDb, Michelle H. McGarry, MSb, Thay Q. Lee, PhDb,* a

Department of Orthopedic Surgery, Seoul National University College of Medicine, Seoul National University Bundang Hospital, Seoul, South Korea b Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System and University of California, Irvine, CA, USA Background: The purpose of this study was to determine the biomechanical effects of latissimus dorsi transfer in a cadaveric model of massive posterosuperior rotator cuff tear. Methods: Eight cadaveric shoulders were tested at 0
, 30
, and 60
of abduction in the scapular plane with anatomically based muscle loading. Humeral rotational range of motion and the amount of humeral rotation due to muscle loading were measured. Glenohumeral kinematics and contact characteristics were measured throughout the range of motion. After testing in the intact condition, the supraspinatus and infraspinatus were resected. The cuff tear was then repaired by latissimus dorsi transfer. Two muscle loading conditions were applied after latissimus transfer to simulate increased tension that may occur due to limited muscle excursion. A repeated-measures analysis of variance was used for statistical analysis. Results: The amount of internal rotation due to muscle loading and maximum internal rotation increased with massive cuff tear and was restored with latissimus transfer (P < .05). At maximum internal rotation, the humeral head apex shifted anteriorly, superiorly, and laterally at 0
of abduction after massive cuff tear (P < .05); this abnormal shift was corrected with latissimus transfer (P < .05). However, at 30
and 60
of abduction, latissimus transfer significantly altered kinematics (P < .05) and latissimus transfer with increased muscle loading increased contact pressure, especially at 60
of abduction. Conclusion: Latissimus dorsi transfer is beneficial in restoring humeral internal/external rotational range of motion, the internal/external rotational balance of the humerus, and glenohumeral kinematics at 0
of abduction. However, latissimus dorsi transfer with simulated limited excursion may lead to an overcompensation that can further deteriorate normal biomechanics, especially at higher abduction angles. Level of evidence: Basic Science Study, Biomechanical, Cadaveric model. Ó 2013 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Massive cuff tear; latissimus dorsi transfer; range of motion; glenohumeral kinematics; contact pressure

Institutional review board approval: not applicable (basic science study). *Reprint requests: Thay Q. Lee, PhD, Orthopaedic Biomechanics Laboratory, VA Long Beach Healthcare System (09/151), 5901 E 7th St, Long Beach, CA 90822, USA. E-mail address: [email protected] (T.Q. Lee).

A massive rotator cuff tear is defined as a tear involving more than two cuff tendons or as a tear with a length of at least 5 cm.4 Some patients with massive tears have no symptoms; however, most individuals with massive rotator cuff tears show impaired function in their activities of daily living due

1058-2746/$ - see front matter Ó 2013 Journal of Shoulder and Elbow Surgery Board of Trustees. doi:10.1016/j.jse.2012.01.022

Biomechanics of latissimus dorsi tendon transfer to pain, decreased range of motion, and decreased power of abduction and external rotation. Imaging studies show that in patients with rotator cuff tears, the humeral head can elevate superiorly, resulting in a decreased acromiohumeral distance; fatty infiltration is also a common finding on magnetic resonance images of patients with massive cuff tears.3,10,21 The treatment plan for patients with massive rotator cuff tears is challenging because it must be tailored to meet the patients’ desired activity level, as well as appropriately address the severity of the rotator cuff pathology. Latissimus dorsi tendon transfer, introduced by Gerber et al9 in 1988, is one of the surgical options available for irreparable massive cuff tears, especially in young patients who require a higher activity level in their daily lives. Currently, several studies support the latissimus dorsi transfer procedure as a salvage procedure,2,7,8,11,12,18,23 although clinical outcomes have varied among patients. Warner24 reported that late rupture of the transferred latissimus dorsi tendon and poor function were due to the relatively small size of the latissimus dorsi and suggested autogenous iliotibial band augmentation for a better outcome. At present, latissimus dorsi transfer is often performed with a reverse total shoulder arthroplasty in patients with cuff tear arthropathy whose active external rotation is deficient.6 Few cadaveric studies have been reported in the literature regarding the biomechanical influence of latissimus dorsi transfer using a massive rotator cuff tear model. Therefore, the purpose of this study was to determine the biomechanical influence of latissimus dorsi transfer using a cadaveric model of massive posterosuperior rotator cuff tear. Our hypotheses were that latissimus tendon transfer would restore abnormal glenohumeral joint kinematics created by massive cuff tear and that latissimus dorsi transfer would increase glenohumeral joint contact pressure.

Methods Eight fresh-frozen human cadaveric shoulders with a mean age of 56.5 years (range, 45-65 years) were used. Specimens found on dissection to have pre-existing pathology, such as acromial fracture, limited range of motion, osteoarthritis, or rotator cuff tear, were excluded from the study. The specimens were stored at -20
C until the day before testing and thawed overnight at room temperature in preparation for dissection and testing. The specimens were kept moistened with physiologic saline solution to prevent dehydration. All soft tissues were removed except the glenohumeral joint capsule, coracoacromial ligament, coracohumeral ligament, and shoulder muscles. The supraspinatus, infraspinatus, teres minor, subscapularis, deltoid, and pectoralis major muscles were released from their origins, but their original insertions on the humerus were retained. The remaining portion of the latissimus dorsi was preserved for later use in the tendon transfer procedure. The glenohumeral joint was vented by a small incision through the rotator interval to isolate the influence of the negative intra-articular pressure, as well as to serve as an opening for insertion of the pressure measurement sensor. Suture loops were made with a modified Kessler stitch at the insertion of each

151 muscle with No. 2 FiberWire (Arthrex, Naples, FL, USA). One line of action for the teres minor, two lines of action for the supraspinatus and infraspinatus, and three lines of action for the remaining muscles were used to load anatomically based on muscle fiber orientation. Three reference screws were inserted on the scapula (coracoid, anterior acromion, and posterior acromion) and the humerus (proximal bicipital groove, distal bicipital groove, and greater tuberosity) to provide consistent digitization markers to define local coordinate systems on each bone for kinematic measurements. The local coordinate systems were digitized during testing to measure the 3-dimensional position of each bone at all positions and in all conditions. An aluminum rod was inserted into the medullary canal of the humeral shaft and secured with several screws. The scapula was mounted in the anatomic resting position with 20
of anterior tilt in the sagittal plane on a multi-axis load cell (Assurance Technologies, Garner, NC, USA).5,13 The aluminum rod inserted into the humerus was placed in a custom device that allows frictionless axial rotation of the humerus. The humeral rod was then attached to the arc of the testing system, which allows the specimen to be secured in different degrees of shoulder abduction (Fig. 1). Humeral axial rotation was defined based on the anatomic relationship between the bicipital groove and the anterolateral corner of the acromion as determined from a previous study.14 When the bicipital groove was aligned with the anterolateral corner of the acromion at 90
of shoulder abduction, the humeral rotation was defined as 20
of external rotation. The amount of muscle loading was determined based on physiologic muscle cross-sectional area ratios.1,22,25 Specifically, the supraspinatus was loaded with 10 N; subscapularis, 24 N; infraspinatus/teres minor, 24 N; deltoid, 48 N; pectoralis major, 24 N; and latissimus dorsi, 24 N. A second, increased load condition (48 N) for the latissimus dorsi transfer was used to simulate increased muscle tension due to limited tendon excursion. Testing was performed in the scapular plane (30
anterior to the coronal plane) at 0
, 30
, and 60
of shoulder abduction, considering a 2:1 ratio of glenohumeral-to-scapulothoracic abduction. First, we measured the amount of humeral head rotation due to muscle loading by holding the humerus at neutral rotation (0
) while loading all muscles simultaneously. After muscle loading, the humerus was allowed to rotate and the amount of internal rotation due to muscle loading was measured. Next, maximum internal rotation and external rotation were measured with 2.2 Nm of torque applied with a torque wrench after preconditioning for 5 cycles in each direction. Then, glenohumeral kinematics throughout the rotational range of motion were measured by digitizing the local coordinate systems of the glenoid and humerus by use of a MicroScribe 3DLX device (Revware, Raleigh, NC, USA) from maximum internal to maximum external rotation in 30
increments. Finally, glenohumeral contact area, pressure, and peak pressure were measured throughout the rotational range of motion with a Tekscan Pressure Measurement System (saturation pressure, 10.3 MPa) (Sensor 4000; Tekscan, South Boston, MA, USA). The Tekscan sensor was trimmed peripherally to insert into the glenohumeral joint through the rotator interval. Once the Tekscan sensor was inserted, muscle loading was applied and several trials of internal and external rotation were performed to ensure that the sensor covered the glenoid surface. Once the muscle loading was applied, the Tekscan sensor was calibrated by use of the resultant glenohumeral joint force measured from the multi-axis load cell with the spec-

152

J.H. Oh et al.

Figure 1 Custom shoulder testing system with specimen mounted in 0
of shoulder abduction in scapular plane. imen in neutral rotation. The glenohumeral contact area and pressure were then recorded at each position. The peak pressure was defined as the average pressure of a 2  2–pixel area on the Tekscan image. After testing in the intact cuff condition, a massive rotator cuff tear was created and the same testing procedures were repeated. The massive rotator cuff tear was created by complete resection of the supraspinatus and infraspinatus tendons just proximal to the footprint along the greater tuberosity. The tendinous part of the rotator cuff was also removed to simulate an irreparable tear (Fig. 2, A). The massive rotator cuff tear was repaired by latissimus dorsi transfer as described by Gerber et al.9 The latissimus dorsi tendon was released as close to its insertion site as possible, and the tendon was then positioned in a superior-posterior manner along the humeral head to cover the entire footprint of both the supraspinatus and infraspinatus. The lateral edge of the tendon was secured to the humerus by use of 3 transosseous tunnels to pass No. 2 FiberWire over the anterior, middle, and posterior footprint. A total of 3 simple sutures were used to secure the latissimus dorsi tendon to the remaining supraspinatus and infraspinatus muscle, and 2 simple sutures were used to attach the latissimus dorsi tendon covering the anterior insertion site to the superior edge of the subscapularis tendon (Fig. 2, B). After testing of the latissimus dorsi transfer by use of muscle loading based on physiologic cross-sectional area, the second loading condition (48 N) for the latissimus dorsi transfer was tested to simulate increased muscle tension due to limited tendon excursion. After all testing procedures, the specimens were carefully disarticulated and the humeral head and glenoid geometry were digitized relative to the local coordinate systems of each bone by use of the MicroScribe 3DLX device to calculate the position of the humeral head apex with respect to the geometric center of the glenoid (Fig. 3).15 The humeral head apex was defined as the farthest point on the articular surface of the humeral head from a plane defined by the articular margin. The geometric center of the glenoid was defined as the center of the superior-inferior and anterior-posterior glenoid axes at the level of the articular surface. During testing, all measurements were performed twice to ensure reproducibility and the averages were used for data

Figure 2 (A) Massive rotator cuff tear. (B) Latissimus dorsi tendon transfer. analysis. A repeated-measures analysis of variance with a Tukey post hoc test (Statistica; StatSoft, Tulsa, OK, USA) was used to determine significant differences. The level of significance was set at P < .05.

Results The average humeral head rotation due to muscle loading across all abduction angles with the intact rotator cuff condition was 7.1
 4.8
of internal rotation (Table I). Six specimens maintained 0
of rotation, whereas two specimens internally rotated 28.5
 4.3
. With massive rotator cuff tear, the humeral head rotated internally 42.1
 3.6
due to muscle loading. After the latissimus dorsi transfer was performed, all specimens maintained 0
of rotation and did not internally rotate. Maximum internal rotation significantly increased after massive rotator cuff tear at each abduction angle (P < .05). Latissimus dorsi transfer significantly decreased maximum internal rotation compared with massive cuff tear at all abduction angles (P < .05). At 30
and 60
of shoulder abduction, latissimus dorsi transfer also significantly

Biomechanics of latissimus dorsi tendon transfer

153 Table I Humeral head internal rotation due to muscle loading at each abduction angle Intact 0
of abduction 6.8
 4.4
30
of abduction 7.9
 5.4
60
of abduction 6.8
 4.4


Massive cuff tear

Latissimus dorsi transfer

44.1
 3.2
45.4
 3.8
36.9
 3.7


0
0
0


Figure 4 Maximum internal rotation at each abduction angle. At 30
and 60
of abduction, increased muscle loading after latissimus dorsi transfer significantly decreased maximum internal rotation compared with latissimus dorsi transfer with normal muscle loading. Asterisk, P < .05 versus intact condition; plus sign, P < .05 versus massive cuff tear; pound sign, P < .05 versus latissimus transfer. Bars indicate standard error.

Figure 3 After all testing procedures, the specimens were carefully disarticulated and the humeral head (A) and glenoid geometry (B) were digitized to calculate the position of the humeral head apex with respect to the geometric center of the glenoid.

decreased maximum internal rotation compared with the intact condition (P < .05). At 30
and 60
of abduction, increased muscle loading after latissimus dorsi transfer also significantly decreased maximum internal rotation compared with latissimus dorsi transfer with normal muscle loading (P < .05) (Fig. 4). There were no significant differences in maximum external rotation. At maximum internal rotation, with the massive cuff tear condition, the humeral head apex shifted superiorly and laterally at 0
of abduction (P < .05) (Figs. 5 and 6). Latissimus dorsi transfer shifted the humeral head

inferiorly-medially, restoring the normal humeral head kinematics (P < .05) (Fig. 5). However, in 30
and 60
of glenohumeral abduction, both latissimus dorsi transfer conditions significantly shifted the humeral head inferiorly and medially (P < .05). Because of the convexity of the glenoid, a lateral humeral head apex shift correlated with a humeral movement away from the center of the glenoid and a medial humeral head shift correlated with a humeral movement toward the center of the glenoid. Contact area was decreased with the massive rotator cuff tear condition but restored by latissimus dorsi transfer, especially at abduction angles of 0
and 30
(Table II). Latissimus dorsi transfer with increased muscle loading showed a pattern of increased contact pressure (Table III) and peak pressure (Table IV) during the mid range of motion, especially at abduction angles of 30
and 60
.

Discussion On the basis of this study, patients electing for latissimus dorsi tendon transfer may benefit because we have shown that latissimus dorsi transfer can restore the abnormal biomechanics caused by a massive rotator cuff tear. It should be noted that the potential for increased muscle tension resulting from the limited tendon excursion of the

154

Figure 5 Lateral-medial humeral head apex shift at maximum internal rotation compared with intact condition. Asterisk, P < .05 versus intact condition; plus sign, P < .05 versus massive cuff tear. Bars indicate standard error.

latissimus dorsi muscle may lead to an over-compensation phenomenon that increases contact pressure and may further deteriorate normal kinematics of the shoulder joint. Although there are several clinical studies regarding latissimus dorsi tendon transfer, studies examining the biomechanical changes with this procedure have been lacking. A cadaveric study by Werner et al25 reported the importance of the subscapularis muscle function for latissimus dorsi tendon transfer in latissimus dorsi tendon transfer with subscapularis loading to latissimus dorsi tendon transfer without subscapularis loading. However, they did not compare their results with a normal control group or massive cuff tear group. Finite element studies4,17 and a computer simulation study16 have also evaluated latissimus dorsi tendon transfer, but their results are difficult to apply to a clinical surgery setting. Another cadaveric study, by Favre et al,6 showed that latissimus dorsi tendon transfer may improve active external rotation after reverse total shoulder arthroplasty and that the posterior greater tuberosity serves as the proper insertion to produce an effective moment arm. However, this result is difficult to apply to the joint-preserving latissimus dorsi tendon transfer in patients with irreparable massive cuff tears. No study has reported on the biomechanical changes after latissimus dorsi tendon transfer or compared the biomechanical variables among the normal, massive cuff tear, and latissimus dorsi tendon transfer conditions. We defined the internal/external rotational balance of the humeral head as the amount of humeral head rotation when the specimen was fully loaded and 0 Nm of torque was applied. In the intact cuff condition, the humeral head was well balanced between the internal and external rotators of the shoulder. However, the humeral head rotated internally because of the loss of external rotators in the massive tear condition, because the internal rotators (ie, subscapularis, pectoralis major, and latissimus dorsi muscles) were much stronger than the remaining external rotator muscle (ie, teres minor). This rotational imbalance in massive cuff

J.H. Oh et al.

Figure 6 Superior-inferior humeral head apex shift at maximum internal rotation compared with intact condition. Asterisk, P < .05 versus intact condition; plus sign, P < .05 versus massive cuff tear. Bars indicate standard error.

tears could be restored by latissimus dorsi tendon transfer to the posterosuperior footprint of the humeral head. Patients with massive cuff tears may compensate for this rotational muscle imbalance with over-firing of the remaining external rotators, such as the teres minor or posterior deltoid muscle. These muscles may be subject to fatigue and strengthening exercises should be considered if surgery is not indicated. The results of the internal and external rotational range of motion assessment showed that the abnormally increased maximum internal rotation seen in massive cuff tears was reversed as a result of latissimus dorsi tendon transfer. However, increased shoulder abduction angle, especially with increased muscle tension (latissimus dorsi transfer with limited excursion), may cause a further decrease in internal rotation, lower than the intact state. Having a short tendon to cover the whole footprint and the resultant higher tension after latissimus dorsi tendon transfer may limit the rotational range of motion, and teres major tendon transfer should be considered to solve this problem. In a previous biomechanical cadaveric study using the same shoulder testing system with anatomically based muscle loading, we found that the humeral head apex shifted superiorly and laterally at maximum internal rotation with a massive cuff tear model.20 The current data confirmed this abnormal shift of the humeral head apex at maximum internal rotation; latissimus dorsi tendon transfer improved the abnormal kinematics found with massive rotator cuff tear. These data also suggested that latissimus dorsi tendon transfer may act as a humeral head depressor and compressor at maximum internal rotation. However, an increased shoulder abduction angle and increased tendon tension may result in overcompensation and abnormal humeral head kinematics. The pattern of increased glenohumeral contact pressure and peak pressure may also suggest negative effects of latissimus dorsi tendon transfer, specifically in patients with shorter tendon lengths. Increased glenohumeral contact pressure along with the

Biomechanics of latissimus dorsi tendon transfer Table II

155

Contact area for each condition and abduction angle Contact area (mm2) Maximum IR

30
of IR

0


30
of ER

Maximum ER




0 of abduction Intact Massive cuff tear Latissimus transfer Latissimus transfer with limited excursion 30
of abduction Intact Massive cuff tear Latissimus transfer Latissimus transfer with limited excursion 60
of abduction Intact Massive cuff tear Latissimus transfer Latissimus transfer with limited excursion

86.8 58.9 77.8 84.3

   

13.0 12.1) 16.0y 11.3y

75.6 33.8 66.4 80.1

   

8.5 6.4) 11.4y 10.8y

87.0 43.4 47.9 76.6

   

11.2 8.2) 8.2 11.5

108.4 70.6 78.0 69.6

   

9.1 9.2 10.5 11.9)

128.8 93.9 71.8 104.5

   

10.4 13.0 11.1 16.1

86.8 64.6 90.5 107.9

   

15.9 8.3 12.8 9.7y

75.1 46.8 55.4 93.5

   

10.0 7.9 8.9 8.7y

89.4 53.5 51.1 91.0

   

10.5 9.7) 6.7) 5.4y,z

105.6 62.4 63.0 95.1

   

9.1 13.4) 7.2) 9.2

110.8 91.1 89.0 100.6

   

13.4 11.9 15.4 17.0

74.9 75.6 76.0 93.1

   

7.4 9.4 11.1 6.0

74.9 61.0 71.9 84.4

   

9.1 11.1 9.2 8.3

93.0 67.0 59.6 91.5

   

15.3 13.8 10.1 5.1

95.6 74.0 74.3 97.8

   

10.2 12.3 10.2 6.7

96.3 84.9 73.5 87.3

   

8.6 11.4 10.2 9.2

ER, external rotation; IR, internal rotation. Data are given as mean  standard error. ) P < .05 versus intact condition. y P < .05 versus massive cuff tear. z P < .05 versus latissimus transfer.

Table III

Contact pressure for each condition and abduction angle Contact pressure (MPa) Maximum IR

30
of IR

0


30
of ER

Maximum ER




0 of abduction Intact Massive cuff tear Latissimus transfer Latissimus transfer with limited excursion 30
of abduction Intact Massive cuff tear Latissimus transfer Latissimus transfer with limited excursion 60
of abduction Intact Massive cuff tear Latissimus transfer Latissimus transfer with limited excursion

0.61 0.94 0.62 0.78

   

0.07 0.08 0.09 0.08

0.57 0.61 0.57 0.70

   

0.02 0.07 0.08 0.08

0.50 0.52 0.50 0.55

   

0.03 0.05 0.06 0.07

0.61 0.54 0.54 0.59

   

0.06 0.04 0.07 0.10

0.82 0.67 0.60 0.68

   

0.07 0.05 0.06) 0.09

0.90 0.99 0.66 0.76

   

0.12 0.10 0.05 0.06

0.62 0.61 0.56 0.77

   

0.09 0.05 0.04 0.06

0.56 0.55 0.52 0.67

   

0.04 0.03 0.03 0.06z

0.62 0.60 0.55 0.64

   

0.05 0.03 0.03 0.06

0.79 0.82 0.64 0.65

   

0.11 0.11 0.06 0.06

0.96 1.11 0.68 0.94

   

0.17 0.10 0.03y 0.11

0.70 0.63 0.65 0.97

   

0.09 0.04 0.04 0.09),y,z

0.65 0.70 0.60 0.78

   

0.05 0.04 0.04 0.05z

0.68 0.74 0.62 0.78

   

0.05 0.07 0.03 0.06z

0.75 0.82 0.65 0.74

   

0.04 0.06 0.03y 0.08

ER, external rotation; IR, internal rotation. Data are given as mean  standard error. ) P < .05 versus intact condition. y P < .05 versus massive cuff tear. z P < .05 versus latissimus transfer.

abnormal humeral head kinematics caused by massive rotator cuff tear and by latissimus dorsi tendon transfer may contribute to patients’ pain and long-term consequences, such as osteoarthritis. Aoki et al2 observed progression of glenohumeral osteoarthritis in 41% of their cases, and Gerber et al8 observed it in 30%. These observations were confirmed in a recent study by Moursy et al19 with

a progression rate of osteoarthritis of 29%, independent of the surgical technique that had been used. Considering that most patients in whom latissimus dorsi tendon transfer is indicated are relatively young, complicated osteoarthritis of the shoulder due to latissimus dorsi transfer is concerning. There are several limitations to our study. First, this was a cadaveric study, so paindwhich may have a significant

156 Table IV

J.H. Oh et al. Peak contact pressure for each condition and abduction angle Peak contact pressure (MPa) Maximum IR

30
of IR

0


30
of ER

Maximum ER




0 of abduction Intact Massive cuff tear Latissimus transfer Latissimus transfer with limited excursion 30
of abduction Intact Massive cuff tear Latissimus transfer Latissimus transfer with limited excursion 60
of abduction Intact Massive cuff tear Latissimus transfer Latissimus transfer with limited excursion

1.02 1.41 0.98 1.37

   

0.16 0.13 0.17 0.15

0.93 0.80 0.82 1.18

   

0.04 0.13 0.13 0.17y

0.73 0.63 0.59 0.74

   

0.07 0.10 0.08 0.10

0.88 0.74 0.68 0.87

   

0.11 0.08 0.09 0.18

1.28 1.09 0.92 1.05

   

0.10 0.12 0.09) 0.14

1.51 1.62 1.01 1.25

   

0.21 0.15 0.10) 0.10

0.86 0.83 0.70 1.29

   

0.13 0.10 0.07 0.10),y,z

0.75 0.67 0.61 1.00

   

0.08 0.06 0.04 0.10),y,z

0.86 0.69 0.72 0.94

   

0.10 0.06 0.07 0.12

1.27 1.31 0.92 0.98

   

0.19 0.19 0.10 0.11

1.59 1.88 0.96 1.51

   

0.32 0.19 0.09) 0.20

0.93 0.79 0.94 1.67

   

0.14 0.11 0.09 0.15),y,z

0.87 0.89 0.77 1.19

   

0.09 0.09 0.08 0.10),y,z

0.92 1.09 0.82 1.20

   

0.10 0.19 0.06 0.09z

1.10 1.33 0.90 1.10

   

0.09 0.17 0.10) 0.15

ER, external rotation; IR, internal rotation. Data are given as mean  standard error. ) P < .05 versus intact condition. y P < .05 versus massive cuff tear. z P < .05 versus latissimus transfer.

effect on glenohumeral kinematics or rotational range of motiondcannot be considered. Second, in this time-zero study, physiologic adaptation of the transferred latissimus dorsi cannot be evaluated, and complete physiologic adaptation of transferred muscle after long-term rehabilitation might result in proper tension restoring the biomechanics of the shoulder joint. Finally, the exact physiologic muscle loads were not produced, and the muscle forces may be more complex than our model. In addition, a limited excursion length of the transferred latissimus dorsi tendon was simulated by increasing the loading weight (24 N to 48 N). Future studies should be performed to correlate the tendon length and muscle tension and to determine when significant changes in biomechanical parameters occur.

Conclusion Latissimus dorsi tendon transfer can be beneficial because it can reverse the abnormal biomechanics caused by massive rotator cuff tear, restoring the internal/external rotational balance of the humeral head, range of motion, and path of the humeral head apex. However, the increased abduction angle and muscle tension due to the possibility of limiting muscle excursion by latissimus dorsi tendon transfer can lead to an overcompensation that can further alter normal kinematics of the shoulder, limit rotational range of motion, cause abnormal displacement of the humeral head, and increase glenohumeral joint pressure. Therefore, the clinical assessment of latissimus dorsi tendon length is

critical for a successful procedure, and surgeons should optimize the tension in the tendon for each patient by maintaining proper tension of the transferred latissimus dorsi using Z-plasty tendon lengthening or teres major transfer simultaneously.

Disclaimer Funding was provided in part by the VA Rehabilitation Research and Development and Merit Review program. The funding source had no role in the outcome of the study. The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.

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