Download a biomechanical analysis of supraspinatus rotator cuff tear and repair

A BIOMECHANICAL ANALYSIS OF SUPRASPINATUS ROTATOR CUFF TEAR AND REPAIR
*Bissell, J L; *McGarry, M H; *Yang, B Y; *Gupta, R; +*Lee, T Q
+*Orthopaedic Biomechancis Laboratory, VA Healthcare System and University of California, Irvine, Long Beach, CA. 562-494-2611x5319, Fax: 562-4942611x5675, [email protected]
Methods
Six fresh frozen shoulder specimens with intact rotator cuff tendons and
five fresh frozen shoulder specimens with full-thickness, 50-100% width
supraspinatus tears were dissected leaving the tendons of the rotator cuff,
deltoid, latissimus dorsi, and pectoralis major. A custom shoulder testing
device (2) simulating the muscle forces of the humerothoracic muscles was
used. The muscles loaded included the individual rotator cuff muscles,
deltoid, latissimus dorsi, and pectoralis major. (Figure 1) The glenohumeral
joint forces were measured using a six degrees-of-freedom load cell. All joint
force measurements were resolved into three orthogonal components directed
perpendicular (compression force), anterior, and superior to the glenoid. The
GHJ forces in specimens with intact rotator cuff and simulated supraspinatus
tear (unloaded supraspinatus), as well as specimens with supraspinatus tears
both before and after tendon repair were measured. Testing of each shoulder
was performed in 90° abduction, 90° external rotation, and varying degrees of
horizontal abduction, neutral (scapular plane), 20° anterior to neutral and 20°
posterior. ANOVA with a p-value of 0.05 was used for statistical analysis.
Results
The GHJ force was resolved into three orthogonal components: 1)
anterior/posterior force (x), 2) superior/inferior force (y), and 3) compressive
force (z). The force data was analyzed and compared by calculating the
percentage of each force component of the resultant force vector (Fr) using the
formula Fr = (x2 + y2 + z2)0.5 a method described by Lee et al. (3).
Comparisons were made between intact specimens (I) with supraspinatus
loaded (SSL) and supraspinatus unloaded (SSuL) versus supraspinatus tear
specimens (T) both before and after tendon repair. No significant differences
were noted in force components between SSuL (I) versus SSuL (T) or
between SSL (I) and SSL before repair (T) in all positions of abduction. This
suggests that the partial supraspinatus tear does not significantly affect the
glenohumeral joint forces. There was a significant difference between SSL (I)
and SSL after repair (T) in superior/inferior force in all three positions of
abduction and compressive force in anterior and neutral positions (p<0.010.05) (Figure 2). In the supraspinatus tear specimens, a significant difference
was noted between supraspinatus unloaded (SSuL) and supraspinatus loaded
before repair (T) in both inferior and compressive force (p<0.005-0.02). No
significant differences were noted between supraspinatus loaded before and
after repair except in compressive force in the anterior position only (p<0.05).
Discussion
The cadaveric model used in this study is unique for simulating the force
environment in the glenohumeral joint because of the inclusion of the
humerothoracic muscles. The latissimus dorsi and pectoralis major muscles
act as a force vector couple counteracting the superior pull of the deltoid
muscle. The results from this study suggest that the intact specimen actually
resembled the supraspinatus specimen before repair, and the supraspinatus
repair introduced a more inferiorly directed force as well as decreased
compressive force. The implication is that the supraspinatus force was still
transmitted in the specimens prior to repair via the intact cable of the rotator
cuff as described by Burkhart (1) as the supraspinatus tears were all less than
100%.
Supraspinatus
Deltoid
Subscapularis
◆
Infraspinatus
/Teres Minor Pectoralis
Major
Latissimus
Dorsi
◆
Figure 1. A schematic drawing illustrating the force vectors applied to
simulate glenohumeral joint forces.
Ant
Neu
*
*
SSuL
SSL Before
Post
0.00
-10.00
% Force
Introduction
Rotator cuff tears are common injuries seen by orthopaedic surgeons.
Management may vary depending on patient factors, size and location of tear,
and severity of symptoms. Treatment for symptomatic rotator cuff tear often
includes subacromial decompression, debridement, and/or repair. The
objective of this study was to determine the change in glenohumeral joint
(GHJ) forces after repair of pathologic supraspinatus tears.
-20.00
-30.00
-40.00
*
SSL After
Figure 2. Histogram showing magnitude of superior/inferior force component
in supraspinatus tear specimens with supraspinatus unloaded, loaded before
repair, and loaded after repair. (-) =inferior
References:
1. Burkhart, SS, Reconciling the Paradox of Rotator Cuff Repair versus
Debridement: A Unified Biomechanical Rationale for the Treatment of
Rotator Cuff Tears. Arthroscopy, 10(1): 4-19, 1994.
2. Eberly V, Yang B, McMahon P, Lee TQ: Effects of Shoulder Muscle
Forces on the Glenohumeral Joint Force and Translation. Trans ORS, 1999.
3. Lee SB, Kim KJ, O'Driscoll SW, Morrey BF, An KN: Dynamic
glenohumeral stability provided by the rotator cuff muscles in the mid-range
and end-range of motion. A study in cadavera. J Bone Joint Surg 82A(6): 84957, 2000.
Acknowlegements:
VA Rehab R&D Grant and California Orthopaedic Research Institute
48th Annual Meeting of the Orthopaedic Research Society
Poster No: 0832