Tendon-to-Bone Interface Augmentation Using a Marrow Wicking System for Primary Rotator Cuff Repair in a
Sheep Model
Kirk McGilvray1, Eileen S. Hackett1, Michael Hawes2, Patrick St. Pierre3, Dean Cummings4, Mark Frankle5, Robert Tashjian6, Joseph Abboud7, Charles
Getz7, Kevin Nason8, Derek J. Harper8, Christian M. Puttlitz1, Jeremiah T. Easley1
1
Colorado State University, Fort Collins CO, 2Charter Preclinical Services, Hudson, MA, 3Eisenhower Medical Center, Palm Desert, CA, 4The Orthopedic
Clinic Association, Pheonix, AZ, 5Florida Orthopaedic Institute, Tampa, FL, 6University of Utah, Salt Lake City, UT, 7Rothman Institute, Philadelphia, PA,
8
Cayenne Medical, Inc., Scottsdale, AZ
Disclosures: Kirk McGilvray (5-Cayenne Medical), Eileen S. Hackett (5-Cayenne Medical), Michael Hawes (3B-Cayenne Medical), Patrick St. Pierre
(1,3B-Cayenne Medical), Dean Cummings (1,3B-Cayenne Medial), Mark Frankle (1,3B-Cayenne Medial), Robert Tashjian (1,3B-Cayenne Medial), Joseph
Abboud (1,3B-Cayenne Medial), Charles Getz (1,3B-Cayenne Medial), Kevin Nason (3A-Cayenne Medical) , Derek J. Harper (3A-Cayenne Medical),
Christian M. Puttlitz (5-Cayenne Medical), Jeremiah T. Easley (5-Cayenne Medical)
INTRODUCTION: Healing rates in rotator cuff repair range from 91% healing in small tears1, to only 10% in the largest tears2. Various techniques have
been employed to improve interface healing, including bone marrow venting, mesenchymal stem cells, xenograft, allograft, and acellular scaffolds. Bone
marrow vents may hold promise in improving the bone-tissue interface healing of many soft tissue injuries by allowing autologous marrow derived cells to
reach the repair site. Bone marrow venting is a comparatively expeditious surgical procedure, has no issue of cellular incompatibility, and may be
accomplished through vented tissue anchors or through separate bone puncture holes3. It was theorized that a PLGA (Poly (L-lactide-co-Glycolide)) core
designed to function as a wick to improve marrow egress to the bone-tendon interface would be advantageous to bone-tendon healing. In this process,
autologous marrow elements travel along the absorbable wick by cellular diffusion, thus the cellular elements would be transported to the repair site. A
PLGA wick could enhance the egress of autologous marrow elements from the bone to the surface interface, but without the risk of tuberosity fracture or
additional steps required in separate bone marrow venting punctures. This study aimed to test the hypothesis that a novel PLGA “wick” would enhance (as
compared to a currently-approved device) the egress of autologous marrow elements from the bone to the surface interface in an ovine acute rotator cuff tear
model.
MATERIALS AND METHODS: This study was performed according to a Colorado State University IACUC approved protocol and utilized an
established acute rotator cuff tear model4. Fifty-six (n=56) skeletally mature sheep underwent right-sided detachment of the infraspinatus tendon followed by
immediate repair/reattachment to the humeral footprint utilizing a total of two (n=2) suture anchors with a PLGA “wick” (Treatment Group) or without a
PLGA ‘wick” (Control Group) and two (n=2) anchors in a bridging fashion (SureLockTM All-Suture Cayenne Medical, AZ). The animals were divided into 2
sacrificial time points; 7 weeks (n=28 sheep) and 12 weeks (n=28 sheep). Thirteen (n=13) contralateral untreated shoulders served as controls. Sixteen (n =
16) samples (Treatment group n = 8; Control group n = 8) were used for destructive biomechanical testing for each sacrifice time point; these data provided
information on both the structural and material properties of the tendon-to-bone construct. Twelve (n = 12) samples (Treatment group n = 6; Control group n
= 6) were allocated for decalcified histological analysis for each sacrificial time point. Quantitative morphometry was performed on two distinct regions
within the PLGA-tendon-bone footprint area for presence of tendon/bone healing, new bone formation, fibrocartilage and collagen. Statistical significance
in the biomechanical output parameters between groups was performed using a standard one-way ANOVA test for multiple comparisons (p<0.05; Sigma
Stat, Systat Software Inc., San Jose, CA).
RESULTS: All fifty-six (56) sheep survived to the 7 and 12-week time points. No abnormalities were noted throughout the study period. No significant
differences were noted between the Treatment and Control groups at the 7 or 12-week time points in regards to ultimate load, yield failure, yield
displacement, stiffness, ultimate stress, yield stress, yield strain, elastic modulus, ultimate strain at the repair site, and ultimate strain in the middle and distal
tendon. Histology did not reveal any adverse reactions/immune response in either group. Histologic tendon repair progressed in an expected fashion from 7weeks to 12-weeks in both groups. Inflammation scores for the Treatment group at both 7- and 12-weeks was modestly reduced compared to the Control
groups. No significant differences were noted between Treatment and Control group at any time points based on Movin5 total sum scores (histological
scoring of repaired tendon compared to “normal” tendon). The area of new fibrocartilage, area of new bone formation, and tendon/bone repair distance at
the tendon-bone interface increased over time in the Treatment groups compared to the Control groups, but these differences were not statistically
significant. A significant increase in the percentage of tendon-bone integration distance, where repair tissue fibers were oriented perpendicular to the bone at
the surgical site, was noted in the Treatment ROI2 compared to the Control groups at 12-weeks (p<0.05) (Figure 1). There was a statistically significant
increase in collagen type III deposition in the Treatment group as compared to the Control group at 12-weeks (p<0.05). A correlation analyses between
histology and biomechanical results showed a statistically significant, positive, linear correlation in the Treatment group between increased failure loads at
12 weeks and the following histological parameters: increased levels of % perpendicular fibers, new bone formation, % tendon/bone integration, and
collagen type III.
DISCUSSION: This study successfully evaluated a novel suture anchor with a PLGA “wick” core designed to improve marrow egress to the tendon-bone
interface in an ovine rotator cuff model. Inflammation scores, Movin scores, area of new fibrocartilage, area of new bone formation, and total tendon-bone
repair distance at the tendon-bone interface tended to be higher in the Treatment group, while percentage of tendon-bone integration distance was
significantly higher in the Treatment group at 12 weeks. This finding implies that the PLGA wick imparts a long-term benefit to the quality of tendon repair.
However, it is unclear whether the benefit is a direct result of marrow at the healing site or the morphology of the wick itself.
SIGNIFICANCE: To our knowledge, this is the first suture anchor with an engineered wicking mechanism for egress of marrow in rotator cuff repair. The
results indicate that the PLGA core of the novel suture anchor is safe and could improve the quality of rotator cuff repairs. Further analysis is warranted to
fully understand this novel technology’s potential in rotator cuff healing.
REFERENCES:
[1] Lafosse L et al. Bone Joint Surg Am. 2007; 89:1533-1541 [2] Galatz LM et al. Bone Joint Surg Am. 2004; 89:219-224 [3] Yokoya S et al. Am J Sports
Med. 2008; 36:1298-1309 [4] Turner AS. J Shoulder Elbow Surg. 2007; 16:158-163 [5]Movin et al. Acta Ortho. 1997; 68:170-175
FIGURES:
Figure 1. Representative Control and Treated infraspinatus tendon repair sites showing tissue integration at the tnedon/bone
interface at 12-weeks (%tendon/bone integration with any tissue). Black brackets denote areas where repair tissue is not
well-integrated with bone. Safranin-O stain; 40x magnification.
ORS 2017 Annual Meeting Poster No.1112