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A biomechanical comparison of repair techniques in posterior type II superior labral anterior and posterior (SLAP) lesions
A biomechanical comparison of repair techniques in posterior type II superior labral anterior and posterior (SLAP) lesions Jae Chul Yoo, MD,a Jin Hwan Ahn, MD,a Sang Hak Lee, MD,a Hong Chul Lim, MD,b Kui Won Choi, PhD,c Tae Soo Bae, PhD,c and Chang Yang Lee,c Seoul, Korea
The purpose of this study was to compare the 3 different fixation methods of posterior type superior labral anterior posterior (SLAP) II lesion. Fifteen cadavers were randomly divided into 3 groups to compare the initial strength of 3 different fixation methods in posterior type II SLAP lesions. Group I used 1 anchor for 1-point fixation with a conventional simple suture; group II used 1 anchor passing both limbs through the posterior-superior labrum in a mattress fashion; and group III used 2 anchors for 2-point fixation with conventional simple sutures. Repair failure (2 mm permanent displacement of repaired site) and ultimate failure were measured. The mean load to (clinical) failure was 156 6 22 N in group I, 117 6 33 N in group II, and 161 6 44 N in group III. The mean load to ultimate failure was 198 6 6 N in group I, 189 6 23 N in group II, and 179 6 22 N in group III. The specimen stiffness was equivalent among groups. In mode of failure, clinical failure (more than 2 mm separations) first occurred between the markers on the biceps tendon just above (A) and below (B) compared to other markers, and ultimate failure occurred at the labral-implant interface. A single simple suture anchor repair in posterior type II SLAP seems sufficient to withstand the initial load without clinical failure. A mattress suture, although it anchors the biceps root, seems to be inferior than simple suture technique. (J Shoulder Elbow Surg 2008;17:144-149.)
T
he superior portion of the labrum and long head of the biceps anchor are considered to have some contribution From the aDepartment of Orthopaedic Surgery, Sungkyunkwan University School of Medicine, Samsung Medical Center, bDepartment of Orthopaedic Surgery, Korea University School of Medicine, Korea University Medical Center Guro Hospital, and cKorea Institute of Science and Technology, Biomedical Research Center. Reprint requests: Sang Hak Lee, MD, Department of Orthopaedic Surgery, Sungkyunkwan University School of Medicine, Samsung Medical Center, 50 Ilwon-Dong, Kangnam-Ku, Seoul, Korea 135710 (E-mail: [email protected]; [email protected]). Copyright ª 2008 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2008/$34.00 doi:10.1016/j.jse.2007.03.025
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to the glenohumeral joint stability.14 Andrews et al1 originally described the detachment of the superior labrum in a subset of throwing athletes in 1985. Later, Snyder et al19 described 4 distinct types of injury to the superior glenoid labrum and coined the term superior labral anterior posterior (SLAP) lesion for superior labrum, anterior, and posterior. Three additional types were later included,9 yet the type II SLAP lesion, which is defined as an injury involving the concurrent detachment of the labrum and the long head of the biceps from the superior glenoid, was the most common type and comprised of approximately 50% of all SLAP lesions.15,18 The type II SLAP lesion was later differentiated into 3 distinct subcategories based on the main location of the detachment: anterior, posterior, or combined anterior-posterior.10 Type II SLAP lesions with a posterior component represented 62% of all SLAP lesions and were 3 times more common in throwing athletes, as previously described by Huber and Putz7 and Vangsness et al.20 They can cause extreme dysfunction in the throwing athletes and produce significant symptoms with the activities of daily living in the nonthrowers. In recent years, it has become clear that symptomatic SLAP lesions can be treated effectively with either arthroscopic debridement or repair, depending on the specific type of pathology present.5,6,8,12,13,16,17,21 However, there still remains the question of how many sutures or what kind of technique is needed to withstand the initial load before bone to soft-tissue healing occurs. Most surgeons perform 2 sutures for fixation of SLAP II lesions, regardless of its type. However, we have been performing only 1 suture fixation, but for posterior type II SLAP lesions. We questioned whether this common practice would be sufficient to deal with the initial load before healing in posterior type II SLAP lesion. The purpose of this study was to compare the biomechanical properties after different repair techniques of posterior type II SLAP lesions using 1 or 2 suture anchors. MATERIALS AND METHODS Specimen preparation and group designation Fifteen unmatched fresh-frozen human cadaveric shoulders with a mean age of 52 years (range, 38-60; standard
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to the glenoid surface. A suture anchor was inserted into the predrilled hole according to each design group. An empty needle loaded with a suture limb was used to penetration the labrum. Group I repair was made with one anchor screw by a simple suture technique at the 11 o’clock position in right shoulders and the 1 o’clock position in left shoulders. In group II, repair was made with one anchor screw using a horizontal mattress technique. The anchor was inserted at the same position as in group I, but one limb was passed at 12 o’clock (biceps anchor) and the other limb was passed approximately at the 10:30 or 1:30 position in the midportion of the labrum. The knot was tied on the posterior aspect (capsular side) of the labrum. A 5-mm tissue bridge was maintained between suture arms. In group III, the lesions were repaired with 2 anchor screws using the simple suture technique at 11:30 and 10 o’clock in right shoulders and 12:30 and 2 o’clock position in left shoulder (Figure 2, A-C). All knots were made with a knot pusher.
Biomechanical testing Figure 1 Scapular specimen potted in the square box container with denture acrylic material. The specimen is tilted slightly anterior for posterior pull of biceps anchor.
deviation, 7.0) were prepared for the experiment. Each shoulder was thawed for 24 hours at room temperature before dissection. All soft tissues were carefully dissected free from the humerus of each specimen with preservation of only the scapula, labrum, and entire length of the long head of the biceps tendon. The scapular was potted in a square container with denture acrylic (Vertex, Dentimex, The Netherlands) (Figure 1). The acromion was then removed at its neck for freedom of applying traction vertically to the biceps tendon. The square container was later secured in a custom made jig. The specimens were kept moist with normal saline at room temperature. No anatomic variations were found in any of the specimens. Specimens were separated randomly into 3 groups of 5 shoulders: group I used 1 anchor for 1-point fixation with a conventional simple suture; group II used 1 anchor passing both limbs through the posterior-superior labrum in a mattress fashion; and group III used 2 anchors for 2-point fixation with conventional simple sutures (Figure 2). Since the sizes of the glenoid and its labrum were slightly different from one specimen to another, instead of extending 7 mm from the posterior border of the biceps tendon as described in the literature, we used clock position to create the posterior type II lesions.4 The posterior type II SLAP lesions were created at the 12 o’clock to 10 o’clock positions in right shoulders and the 12 o’clock to 2 o’clock position in left shoulders. A no. 15 scalpel blade was used to create each lesion by detaching the superior labrum and the biceps tendon origin from the glenoid and dissecting at least 5 mm medially along the glenoid until the tissue was free.
Repair technique A pilot hole was made using a bone punch made for MiniRevo (loaded with Herculine; Linvatec, Largo, FL) screw insertion. Each hole was located at the articular margin of the posterior-superior glenoid rim and angled 45 in relation
Specimens were mounted on a servohydraulic testing machine (Instron 8511, MTS, Minneapolis, MN). A custom-made jig was used to hold the denture acrylic potted scapulae. The potted scapulae was then securely bolted within the jig. A custom made rod type jig was used for biceps tendon fixation. The biceps tendon was looped around the rod and sutured with number 2 Ethibond (Ethicon, Somerville, NJ). Tensile loading was applied to the biceps tendon in a 20 posterior and 20 dorsal (capsular) direction from the vertical axis of the glenoid to simulate a posteriorly directed force (Figure 3, A, B). When the specimen was mounted securely, a 4 mm circular marker was prepared with a bonding agent on the biceps tendon, superior labrum, and glenoid. Eight 4-mm reflective markers were attached to the glenoid, labrum, and biceps to measure displacement of the posterior-superior labral/biceps complex from the glenoid (Figure 4). Four Eagle Digital Cameras (Motion Analysis Corp. Santa Rosa, CA) were used to measure the displacement of the labral-biceps complex from the glenoid, as well as record the spatial coordinates of each marker at 50 frames (50 Hz) per second. All data were recorded on a computer for analysis with EVaRT 4.6 (Motion Analysis Corp., Santa Rosa, CA) and EVaRT Analysis tool. For convenience, the marker was labeled with letters (Figure 4). The markers can identify any change from any point distance. In other words, it can simultaneously measure distance A-B, A-B1, A1-B, A1-B1, C1-A , etc. The focus is on the A-B, A-B1, A1-B, A1-B1, A2-B, and A2-B1 marker distances. The rest is for reference. Clinical failure occurs where there is change of more than 2 mm in any of these distances. The distance from the A-B is more prone to displace where the load is directly above. We considered that any marker distance change among the above 5 to be significant if more than 2 mm displacement was seen. To negate slack from all specimens, a 10 N preload was applied. Afterward, each specimen was loaded in 10 N increments at a rate of 10 N/sec. This was continued for a maximum of 200 N load or until soft-tissue or implant failure occurred. The maximum load of 200 N was chosen, because it has been described in the literature to represent the force that could be transmitted maximally across the superior labrum/biceps complex.
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Figure 2 A, Group 1 configuration, simple one anchor suture repair of posterior type II SLAP repair. B, Group 2 configuration, one anchor suture repair in mattress fashion where one limb anchor the biceps root and the other limb suture the labrum. C, Group 3 configuration, two suture anchors fixation with simple suture repair.
Figure 3 Direction of the load vector applied to the specimen. A, Slight posterior (20 ) direction in reference to the vertical axis of glenoid. B, Slight dorsal or capsular side (20 ) direction for mechanical pull.
The original distance between the superior labrum/biceps complex and glenoid margin was defined as the initial distance between these markers before testing began. Clinical or strain failure was defined as 2 mm or more permanent separation between the posterior-superior labrum and the
glenoid rim following completion of the loading force. Ultimate failure was defined as the maximum load tolerated before the implant broke or pulled out of the labrum or biceps anchor tore. Stiffness was also determined to compare the different cadaveric shoulder. The slope of the length tension
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Mean Specimen Stiffness 90
Stiffness (N/mm)
80 70
60.774
60
54.304
57.558
50 40 30 20 10 0
Mattress suture Group
Simple suture
Simple double suture
Figure 5 The mean specimen stiffness of each group summarized by graph configuration.
Mean clinical failure 250
200 161.092
Figure 4 Four-millimeter markers are attached to the posterior labrum, glenoid, and biceps tendon for testing.
curve obtained during the specific point of the loading cycle, at which 2 mm of permanent diastases occurred, was used to calculate the stiffness of each individual specimen.4
Statistical analysis The Kruskal-Wallis test was used to compare the biomechanical properties of the 3 different groups. All statistical analyses were performed with SPSS software (SPSS for Windows Release 11.0, SPSS Inc, Chicago, IL). All analyses were set at a 95% confidence interval for statistical significance.
Load (N)
156.84 150 117.52 100
50
0 Simple suture
Mattress suture Group
Two Simple suture
Figure 6 Graphical comparison between groups of mean tensile load at 2 mm displacement.
tically, there was no significant difference among the groups (P ¼ .114) (Figure 6). Ultimate failure strength
RESULTS Specimen characteristics
Forty-nine years was the mean age for group I, 51 years for group II, and 54 for group III 54. Among individual groups, the mean stiffness is summarized in Figure 5. None of the differences was statistically significant for each individual group (P > .05). Clinical failure strength
Two milimeters permanent glenolabral separation was observed as follows: in group I, mean load to failure was 156 N (range, 137-191 N; standard deviation, 22N); in group II, 117 N (range, 60-142 N; standard deviation, 33 N); and in group III, 161 N (range, 96-200 N; standard deviation, 44 N). Statis-
The mean ultimate failure occurred in group I, 198 N (range, 194-200 N; standard deviation, 6 N); group II, 189 N (range, 146-200 N; standard deviation, 23 N); and group III, 179 N (range, 143-200; standard deviation, 22 N). Statistically, ultimate failure load showed no significant difference among the groups (P ¼ .209) (Figure 7). Mode of failure
Clinical failure, defined as 2 mm permanent separation between the glenoid and the labrum, occurred initially at a point localized under the origin of the biceps tendon in all specimens. The marker between biceps tendon just above (Figure 4, A) and below (Figure 4, B) showed the earliest 2 mm separation prior to other markers. All specimen failed by cutting through the labrum of the suture materials, a new generation
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Mean load at ultimate failure 250
Load (N)
200
198.014 189.37
179.45
150
100
50
0 Simple suture
Mattress suture Group
Two simple suture
Figure 7 Graphical comparison between groups of mean tensile load at ultimate failure.
suture material, ‘‘Herculine,’’ leaving the biceps labral complex separated from the glenoid and implants. Thus the ultimate failure occurred at the labral-implant interface. DISCUSSION This study showed that single suture anchor fixation with a simple suture technique is sufficient to hold against initial loading after a posterior type II SLAP repair. Furthermore, a mattress-type suture, although it looks more ideal since it anchors the biceps root, does not seem to be better than the conventional simple suture. Considering the potential for labral-glenoid healing, this study backs up the rationale for a simple 1 anchor suture in posterior type II SLAP lesions. With the advance of arthroscopic instruments and surgical techniques, arthroscopic repair of symptomatic type II SLAP lesions has become common.3,8,1012,16,21 A variety of techniques and suture configurations have been described, but there is a lack of biomechanical data to support the use of one over another. It has been difficult to determine the clinical features or surgical results, despite many relevant biomechanical and clinical studies over the past decade, because it frequently accompanies other abnormalities.2,6,8,11,16,18 Most of type II SLAP lesions deal with anterior and posterior type repair. Nam and Snyder11 reported their technique of SLAP lesion repair with a single anchor-double suture technique. They recommended an additional single-suture anchor inserted at the posterosuperior corner for additional fixation, if necessary. To our knowledge, there is only one study reporting biomechanical data comparing the initial strength of the various repairs. DiRaimondo et al4 compared the initial strength of fixation for type II SLAP lesions in three cadaveric shoulder groups using suture anchors
Figure 8 Arthroscopic view of peelback position (maximum abduction and external rotation, cocking phase shoulder) and biceps figure in relation with glenoid.
and tissue tacks. Their study dealt with anterior and posterior type II SLAP lesions. Their mattress sutures did not incorporate the biceps anchor but were adjacent to it. They recommend that the 2 suture anchor configurations were equivalent, and both provided better fixation as compared to the tissue tack, despite the lack of statistical differences between techniques. Their study also produced slightly lower load to clinical and ultimate failure than ours. The mean clinical failure was 111N-123N, and mean ultimate failure was 157N-163N for suture anchor repair. However, in our study, the mean clinical failure ranged from 117 to 161 N and mean ultimate failure ranged from 179 to 198N. Although the 2 experiments cannot be compared directly due to different setups and force vectors, we presume that this is because a posterior type II SLAP will be more resistant to a force load than the anterior-posterior type SLAP II. The mattress sutures, with which we anchored the biceps root, showed no additional benefit over the conventional repair. However, we feel that anchoring the biceps root is a logical option because it directly addresses the pathophysiology of the lesion. The possible explanation for this result is that more dorsal (capsular) side suture knot configuration might be weaker in divergence to the labral-glenoid complex. If the force is directed more posteriorly and dorsally, the labral-glenoid complex is more prone to diastasis, as the mean clinical failure load was weak (without statistically significant difference) but ultimate failure was equivalent to the other constructs. Our loading vector was different from the previous study4 because the peelback mechanism (abduction and external rotation, cocking phase) is the main force causing posterior type II SLAP lesion. To generate such force, it would be more a torsional and posteriorly
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directed force (Figure 8). However, due to the limitation of the mechanical construct, we used a slight posterior and dorsal surface direction (more capsular side instead of glenoid surface side) in reference to the vertical axis of glenoid to imitate the force. Although this vector does not truly represent the late cocking phase of throwing, it was closer than the usual perpendicular force against the glenoid. Several limitations of our study should be acknowledged. First, it is a cadaveric in vitro, time-zero study; therefore, we are unable to determine the effects of biologic processes on the suture anchor fixation and glenolabral healing in vivo. Second, as mentioned, loading of the biceps anchor may not accurately reflect strains in vivo. Third, 5 shoulder specimens in each individual group may not be sufficient power for statistical analysis. Fourth, we tested in older cadaveric shoulder specimens than the majority of arthroscopic labral repairs. Cadavers have more osteoporotic bone and weaker tendons. Fifth, we did not perform cyclic loading; instead, we performed incremental loading of 10N/sec. Sixth, the stiffness of group III was lower than group I or II in mean load to failure; this might imply that there be some specimen bias in terms of their tissue quality or repair technique. A possible explanation might be that since we only created a posterior type SLAP II lesion, the detachment of the labrum was smaller than the conventional anterior-posterior type. Thus repair stiffness might have been less affected by load than the tissue quality itself. Although we randomized the specimens and used no paired specimens from single cadaver in one group, we cannot completely rule out the possibility that a grouping of 5 specimens might have had less healthy or older biceps-labral tissues. However, since the results from clinical failure are more important than ultimate failure, we felt that the data support the scientific information. Finally, the orientation of the normal biceps tendon, with respect to the glenoid, varies with shoulder position. However, our specific orientation was chosen to simulate biceps loading during the peel-back mechanism without cyclic loading. In conclusion, a single simple suture anchor repair in posterior type II SLAP seems sufficient to withstand the initial load without clinical failure. A mattress suture, although it anchors the biceps root, seems to be inferior to the simple suture technique. REFERENCES
1. Andrews JR, Carson WG Jr, McLeod WD. Glenoid labrum tears related to the long head of the biceps. Am J Sports Med 1985; 13:337-41.
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2. Barthel T, Konig U, Bohm D, Loehr JF, Gohlke F. Anatomy of the glenoid labrum. Orthopade 2003;32:578-85. 3. Burkart A, Debski RE, Musahl V, McMahon PJ. Glenohumeral translations are only partially restored after repair of a simulated type II superior labral lesion. Am J Sports Med 2003;31: 56-63. 4. DiRaimondo CA, Alexander JW, Noble PC, Lowe WR, Lintner DM. A biomechanical comparison of repair techniques for type II SLAP lesions. Am J Sports Med 2004;32: 727-33. 5. Field LD, Savoie FH III. Arthroscopic suture repair of superior labral detachment lesions of the shoulder. Am J Sports Med 1993;21: 783-90. 6. Handelberg F, Willems S, Shahabpour M, Huskin JP, Kuta J. SLAP lesions: a retrospective multicenter study. Arthroscopy 1998;14: 856-62. 7. Huber WP, Putz RV. Periarticular fiber system of the shoulder joint. Arthroscopy 1997;13:680-91. 8. Kim SH, Ha KI, Kim SH, Choi HJ. Results of arthroscopic treatment of superior labral lesions. J Bone Joint Surg Am 2002; 84-A:981-5. 9. Maffet MW, Gartsman GM, Moseley B. Superior labrum-biceps tendon complex lesions of the shoulder. Am J Sports Med 1995; 23:93-8. 10. Morgan CD, Burkhart SS, Palmeri M, Gillespie M. Type II SLAP lesions: three subtypes and their relationships to superior instability and rotator cuff tears. Arthroscopy 1998;14:553-65. 11. Nam EK, Snyder SJ. The diagnosis and treatment of superior labrum, anterior and posterior (SLAP) lesions. Am J Sports Med 2003;31:798-810. 12. O’Brien SJ, Allen AA, Coleman SH, Drakos MC. The trans-rotator cuff approach to SLAP lesions: technical aspects for repair and a clinical follow-up of 31 patients at a minimum of 2 years. Arthroscopy 2002;18:372-7. 13. Pagnani MJ, Speer KP, Altchek DW, Warren RF, Dines DM. Arthroscopic fixation of superior labral lesions using a biodegradable implant: a preliminary report. Arthroscopy 1995;11:194-8. 14. Panossian VR, Mihata T, Tibone JE, Fitzpatrick MJ, McGarry MH, Lee TQ. Biomechanical analysis of isolated type II SLAP lesions and repair. J Shoulder Elbow Surg 2005;14:529-34. 15. Parentis MA, Mohr KJ, ElAttrache NS. Disorders of the superior labrum: review and treatment guidelines. Clin Orthop Relat Res 2002:77-87. 16. Rhee YG, Lee DH, Lim CT. Unstable isolated SLAP lesion: clinical presentation and outcome of arthroscopic fixation. Arthroscopy 2005;21:1099. 17. Samani JE, Marston SB, Buss DD. Arthroscopic stabilization of type II SLAP lesions using an absorbable tack. Arthroscopy 2001;17: 19-24. 18. Snyder SJ, Banas MP, Karzel RP. An analysis of 140 injuries to the superior glenoid labrum. J Shoulder Elbow Surg 1995;4:243-8. 19. Snyder SJ, Karzel RP, Del Pizzo W, Ferkel RD, Friedman MJ. SLAP lesions of the shoulder. Arthroscopy 1990;6:274-9. 20. Vangsness CT Jr, Jorgenson SS, Watson T, Johnson DL. The origin of the long head of the biceps from the scapula and glenoid labrum. An anatomical study of 100 shoulders. J Bone Joint Surg Br 1994;76:951-4. 21. Yoneda M, Hirooka A, Saito S, Yamamoto T, Ochi T, Shino K. Arthroscopic stapling for detached superior glenoid labrum. J Bone Joint Surg Br 1991;73:746-50.
The purpose of this study was to compare the 3 different fixation methods of posterior type superior labral anterior posterior (SLAP) II lesion. Fifteen cadavers were randomly divided into 3 groups to compare the initial strength of 3 different fixation methods in posterior type II SLAP lesions. Group I used 1 anchor for 1-point fixation with a conventional simple suture; group II used 1 anchor passing both limbs through the posterior-superior labrum in a mattress fashion; and group III used 2 anchors for 2-point fixation with conventional simple sutures. Repair failure (2 mm permanent displacement of repaired site) and ultimate failure were measured. The mean load to (clinical) failure was 156 6 22 N in group I, 117 6 33 N in group II, and 161 6 44 N in group III. The mean load to ultimate failure was 198 6 6 N in group I, 189 6 23 N in group II, and 179 6 22 N in group III. The specimen stiffness was equivalent among groups. In mode of failure, clinical failure (more than 2 mm separations) first occurred between the markers on the biceps tendon just above (A) and below (B) compared to other markers, and ultimate failure occurred at the labral-implant interface. A single simple suture anchor repair in posterior type II SLAP seems sufficient to withstand the initial load without clinical failure. A mattress suture, although it anchors the biceps root, seems to be inferior than simple suture technique. (J Shoulder Elbow Surg 2008;17:144-149.)
T
he superior portion of the labrum and long head of the biceps anchor are considered to have some contribution From the aDepartment of Orthopaedic Surgery, Sungkyunkwan University School of Medicine, Samsung Medical Center, bDepartment of Orthopaedic Surgery, Korea University School of Medicine, Korea University Medical Center Guro Hospital, and cKorea Institute of Science and Technology, Biomedical Research Center. Reprint requests: Sang Hak Lee, MD, Department of Orthopaedic Surgery, Sungkyunkwan University School of Medicine, Samsung Medical Center, 50 Ilwon-Dong, Kangnam-Ku, Seoul, Korea 135710 (E-mail: [email protected]; [email protected]). Copyright ª 2008 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2008/$34.00 doi:10.1016/j.jse.2007.03.025
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to the glenohumeral joint stability.14 Andrews et al1 originally described the detachment of the superior labrum in a subset of throwing athletes in 1985. Later, Snyder et al19 described 4 distinct types of injury to the superior glenoid labrum and coined the term superior labral anterior posterior (SLAP) lesion for superior labrum, anterior, and posterior. Three additional types were later included,9 yet the type II SLAP lesion, which is defined as an injury involving the concurrent detachment of the labrum and the long head of the biceps from the superior glenoid, was the most common type and comprised of approximately 50% of all SLAP lesions.15,18 The type II SLAP lesion was later differentiated into 3 distinct subcategories based on the main location of the detachment: anterior, posterior, or combined anterior-posterior.10 Type II SLAP lesions with a posterior component represented 62% of all SLAP lesions and were 3 times more common in throwing athletes, as previously described by Huber and Putz7 and Vangsness et al.20 They can cause extreme dysfunction in the throwing athletes and produce significant symptoms with the activities of daily living in the nonthrowers. In recent years, it has become clear that symptomatic SLAP lesions can be treated effectively with either arthroscopic debridement or repair, depending on the specific type of pathology present.5,6,8,12,13,16,17,21 However, there still remains the question of how many sutures or what kind of technique is needed to withstand the initial load before bone to soft-tissue healing occurs. Most surgeons perform 2 sutures for fixation of SLAP II lesions, regardless of its type. However, we have been performing only 1 suture fixation, but for posterior type II SLAP lesions. We questioned whether this common practice would be sufficient to deal with the initial load before healing in posterior type II SLAP lesion. The purpose of this study was to compare the biomechanical properties after different repair techniques of posterior type II SLAP lesions using 1 or 2 suture anchors. MATERIALS AND METHODS Specimen preparation and group designation Fifteen unmatched fresh-frozen human cadaveric shoulders with a mean age of 52 years (range, 38-60; standard
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to the glenoid surface. A suture anchor was inserted into the predrilled hole according to each design group. An empty needle loaded with a suture limb was used to penetration the labrum. Group I repair was made with one anchor screw by a simple suture technique at the 11 o’clock position in right shoulders and the 1 o’clock position in left shoulders. In group II, repair was made with one anchor screw using a horizontal mattress technique. The anchor was inserted at the same position as in group I, but one limb was passed at 12 o’clock (biceps anchor) and the other limb was passed approximately at the 10:30 or 1:30 position in the midportion of the labrum. The knot was tied on the posterior aspect (capsular side) of the labrum. A 5-mm tissue bridge was maintained between suture arms. In group III, the lesions were repaired with 2 anchor screws using the simple suture technique at 11:30 and 10 o’clock in right shoulders and 12:30 and 2 o’clock position in left shoulder (Figure 2, A-C). All knots were made with a knot pusher.
Biomechanical testing Figure 1 Scapular specimen potted in the square box container with denture acrylic material. The specimen is tilted slightly anterior for posterior pull of biceps anchor.
deviation, 7.0) were prepared for the experiment. Each shoulder was thawed for 24 hours at room temperature before dissection. All soft tissues were carefully dissected free from the humerus of each specimen with preservation of only the scapula, labrum, and entire length of the long head of the biceps tendon. The scapular was potted in a square container with denture acrylic (Vertex, Dentimex, The Netherlands) (Figure 1). The acromion was then removed at its neck for freedom of applying traction vertically to the biceps tendon. The square container was later secured in a custom made jig. The specimens were kept moist with normal saline at room temperature. No anatomic variations were found in any of the specimens. Specimens were separated randomly into 3 groups of 5 shoulders: group I used 1 anchor for 1-point fixation with a conventional simple suture; group II used 1 anchor passing both limbs through the posterior-superior labrum in a mattress fashion; and group III used 2 anchors for 2-point fixation with conventional simple sutures (Figure 2). Since the sizes of the glenoid and its labrum were slightly different from one specimen to another, instead of extending 7 mm from the posterior border of the biceps tendon as described in the literature, we used clock position to create the posterior type II lesions.4 The posterior type II SLAP lesions were created at the 12 o’clock to 10 o’clock positions in right shoulders and the 12 o’clock to 2 o’clock position in left shoulders. A no. 15 scalpel blade was used to create each lesion by detaching the superior labrum and the biceps tendon origin from the glenoid and dissecting at least 5 mm medially along the glenoid until the tissue was free.
Repair technique A pilot hole was made using a bone punch made for MiniRevo (loaded with Herculine; Linvatec, Largo, FL) screw insertion. Each hole was located at the articular margin of the posterior-superior glenoid rim and angled 45 in relation
Specimens were mounted on a servohydraulic testing machine (Instron 8511, MTS, Minneapolis, MN). A custom-made jig was used to hold the denture acrylic potted scapulae. The potted scapulae was then securely bolted within the jig. A custom made rod type jig was used for biceps tendon fixation. The biceps tendon was looped around the rod and sutured with number 2 Ethibond (Ethicon, Somerville, NJ). Tensile loading was applied to the biceps tendon in a 20 posterior and 20 dorsal (capsular) direction from the vertical axis of the glenoid to simulate a posteriorly directed force (Figure 3, A, B). When the specimen was mounted securely, a 4 mm circular marker was prepared with a bonding agent on the biceps tendon, superior labrum, and glenoid. Eight 4-mm reflective markers were attached to the glenoid, labrum, and biceps to measure displacement of the posterior-superior labral/biceps complex from the glenoid (Figure 4). Four Eagle Digital Cameras (Motion Analysis Corp. Santa Rosa, CA) were used to measure the displacement of the labral-biceps complex from the glenoid, as well as record the spatial coordinates of each marker at 50 frames (50 Hz) per second. All data were recorded on a computer for analysis with EVaRT 4.6 (Motion Analysis Corp., Santa Rosa, CA) and EVaRT Analysis tool. For convenience, the marker was labeled with letters (Figure 4). The markers can identify any change from any point distance. In other words, it can simultaneously measure distance A-B, A-B1, A1-B, A1-B1, C1-A , etc. The focus is on the A-B, A-B1, A1-B, A1-B1, A2-B, and A2-B1 marker distances. The rest is for reference. Clinical failure occurs where there is change of more than 2 mm in any of these distances. The distance from the A-B is more prone to displace where the load is directly above. We considered that any marker distance change among the above 5 to be significant if more than 2 mm displacement was seen. To negate slack from all specimens, a 10 N preload was applied. Afterward, each specimen was loaded in 10 N increments at a rate of 10 N/sec. This was continued for a maximum of 200 N load or until soft-tissue or implant failure occurred. The maximum load of 200 N was chosen, because it has been described in the literature to represent the force that could be transmitted maximally across the superior labrum/biceps complex.
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Figure 2 A, Group 1 configuration, simple one anchor suture repair of posterior type II SLAP repair. B, Group 2 configuration, one anchor suture repair in mattress fashion where one limb anchor the biceps root and the other limb suture the labrum. C, Group 3 configuration, two suture anchors fixation with simple suture repair.
Figure 3 Direction of the load vector applied to the specimen. A, Slight posterior (20 ) direction in reference to the vertical axis of glenoid. B, Slight dorsal or capsular side (20 ) direction for mechanical pull.
The original distance between the superior labrum/biceps complex and glenoid margin was defined as the initial distance between these markers before testing began. Clinical or strain failure was defined as 2 mm or more permanent separation between the posterior-superior labrum and the
glenoid rim following completion of the loading force. Ultimate failure was defined as the maximum load tolerated before the implant broke or pulled out of the labrum or biceps anchor tore. Stiffness was also determined to compare the different cadaveric shoulder. The slope of the length tension
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Mean Specimen Stiffness 90
Stiffness (N/mm)
80 70
60.774
60
54.304
57.558
50 40 30 20 10 0
Mattress suture Group
Simple suture
Simple double suture
Figure 5 The mean specimen stiffness of each group summarized by graph configuration.
Mean clinical failure 250
200 161.092
Figure 4 Four-millimeter markers are attached to the posterior labrum, glenoid, and biceps tendon for testing.
curve obtained during the specific point of the loading cycle, at which 2 mm of permanent diastases occurred, was used to calculate the stiffness of each individual specimen.4
Statistical analysis The Kruskal-Wallis test was used to compare the biomechanical properties of the 3 different groups. All statistical analyses were performed with SPSS software (SPSS for Windows Release 11.0, SPSS Inc, Chicago, IL). All analyses were set at a 95% confidence interval for statistical significance.
Load (N)
156.84 150 117.52 100
50
0 Simple suture
Mattress suture Group
Two Simple suture
Figure 6 Graphical comparison between groups of mean tensile load at 2 mm displacement.
tically, there was no significant difference among the groups (P ¼ .114) (Figure 6). Ultimate failure strength
RESULTS Specimen characteristics
Forty-nine years was the mean age for group I, 51 years for group II, and 54 for group III 54. Among individual groups, the mean stiffness is summarized in Figure 5. None of the differences was statistically significant for each individual group (P > .05). Clinical failure strength
Two milimeters permanent glenolabral separation was observed as follows: in group I, mean load to failure was 156 N (range, 137-191 N; standard deviation, 22N); in group II, 117 N (range, 60-142 N; standard deviation, 33 N); and in group III, 161 N (range, 96-200 N; standard deviation, 44 N). Statis-
The mean ultimate failure occurred in group I, 198 N (range, 194-200 N; standard deviation, 6 N); group II, 189 N (range, 146-200 N; standard deviation, 23 N); and group III, 179 N (range, 143-200; standard deviation, 22 N). Statistically, ultimate failure load showed no significant difference among the groups (P ¼ .209) (Figure 7). Mode of failure
Clinical failure, defined as 2 mm permanent separation between the glenoid and the labrum, occurred initially at a point localized under the origin of the biceps tendon in all specimens. The marker between biceps tendon just above (Figure 4, A) and below (Figure 4, B) showed the earliest 2 mm separation prior to other markers. All specimen failed by cutting through the labrum of the suture materials, a new generation
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Mean load at ultimate failure 250
Load (N)
200
198.014 189.37
179.45
150
100
50
0 Simple suture
Mattress suture Group
Two simple suture
Figure 7 Graphical comparison between groups of mean tensile load at ultimate failure.
suture material, ‘‘Herculine,’’ leaving the biceps labral complex separated from the glenoid and implants. Thus the ultimate failure occurred at the labral-implant interface. DISCUSSION This study showed that single suture anchor fixation with a simple suture technique is sufficient to hold against initial loading after a posterior type II SLAP repair. Furthermore, a mattress-type suture, although it looks more ideal since it anchors the biceps root, does not seem to be better than the conventional simple suture. Considering the potential for labral-glenoid healing, this study backs up the rationale for a simple 1 anchor suture in posterior type II SLAP lesions. With the advance of arthroscopic instruments and surgical techniques, arthroscopic repair of symptomatic type II SLAP lesions has become common.3,8,1012,16,21 A variety of techniques and suture configurations have been described, but there is a lack of biomechanical data to support the use of one over another. It has been difficult to determine the clinical features or surgical results, despite many relevant biomechanical and clinical studies over the past decade, because it frequently accompanies other abnormalities.2,6,8,11,16,18 Most of type II SLAP lesions deal with anterior and posterior type repair. Nam and Snyder11 reported their technique of SLAP lesion repair with a single anchor-double suture technique. They recommended an additional single-suture anchor inserted at the posterosuperior corner for additional fixation, if necessary. To our knowledge, there is only one study reporting biomechanical data comparing the initial strength of the various repairs. DiRaimondo et al4 compared the initial strength of fixation for type II SLAP lesions in three cadaveric shoulder groups using suture anchors
Figure 8 Arthroscopic view of peelback position (maximum abduction and external rotation, cocking phase shoulder) and biceps figure in relation with glenoid.
and tissue tacks. Their study dealt with anterior and posterior type II SLAP lesions. Their mattress sutures did not incorporate the biceps anchor but were adjacent to it. They recommend that the 2 suture anchor configurations were equivalent, and both provided better fixation as compared to the tissue tack, despite the lack of statistical differences between techniques. Their study also produced slightly lower load to clinical and ultimate failure than ours. The mean clinical failure was 111N-123N, and mean ultimate failure was 157N-163N for suture anchor repair. However, in our study, the mean clinical failure ranged from 117 to 161 N and mean ultimate failure ranged from 179 to 198N. Although the 2 experiments cannot be compared directly due to different setups and force vectors, we presume that this is because a posterior type II SLAP will be more resistant to a force load than the anterior-posterior type SLAP II. The mattress sutures, with which we anchored the biceps root, showed no additional benefit over the conventional repair. However, we feel that anchoring the biceps root is a logical option because it directly addresses the pathophysiology of the lesion. The possible explanation for this result is that more dorsal (capsular) side suture knot configuration might be weaker in divergence to the labral-glenoid complex. If the force is directed more posteriorly and dorsally, the labral-glenoid complex is more prone to diastasis, as the mean clinical failure load was weak (without statistically significant difference) but ultimate failure was equivalent to the other constructs. Our loading vector was different from the previous study4 because the peelback mechanism (abduction and external rotation, cocking phase) is the main force causing posterior type II SLAP lesion. To generate such force, it would be more a torsional and posteriorly
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directed force (Figure 8). However, due to the limitation of the mechanical construct, we used a slight posterior and dorsal surface direction (more capsular side instead of glenoid surface side) in reference to the vertical axis of glenoid to imitate the force. Although this vector does not truly represent the late cocking phase of throwing, it was closer than the usual perpendicular force against the glenoid. Several limitations of our study should be acknowledged. First, it is a cadaveric in vitro, time-zero study; therefore, we are unable to determine the effects of biologic processes on the suture anchor fixation and glenolabral healing in vivo. Second, as mentioned, loading of the biceps anchor may not accurately reflect strains in vivo. Third, 5 shoulder specimens in each individual group may not be sufficient power for statistical analysis. Fourth, we tested in older cadaveric shoulder specimens than the majority of arthroscopic labral repairs. Cadavers have more osteoporotic bone and weaker tendons. Fifth, we did not perform cyclic loading; instead, we performed incremental loading of 10N/sec. Sixth, the stiffness of group III was lower than group I or II in mean load to failure; this might imply that there be some specimen bias in terms of their tissue quality or repair technique. A possible explanation might be that since we only created a posterior type SLAP II lesion, the detachment of the labrum was smaller than the conventional anterior-posterior type. Thus repair stiffness might have been less affected by load than the tissue quality itself. Although we randomized the specimens and used no paired specimens from single cadaver in one group, we cannot completely rule out the possibility that a grouping of 5 specimens might have had less healthy or older biceps-labral tissues. However, since the results from clinical failure are more important than ultimate failure, we felt that the data support the scientific information. Finally, the orientation of the normal biceps tendon, with respect to the glenoid, varies with shoulder position. However, our specific orientation was chosen to simulate biceps loading during the peel-back mechanism without cyclic loading. In conclusion, a single simple suture anchor repair in posterior type II SLAP seems sufficient to withstand the initial load without clinical failure. A mattress suture, although it anchors the biceps root, seems to be inferior to the simple suture technique. REFERENCES
1. Andrews JR, Carson WG Jr, McLeod WD. Glenoid labrum tears related to the long head of the biceps. Am J Sports Med 1985; 13:337-41.
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