Soft Tissue to Bone Healing in Rotator Cuff Repair - Structural Interfaces and Attachments in Biology - page 252

Experiments in animal models have demonstrated that the healing tendon-to-bone
insertion remains biomechanically inferior to the uninjured tissue, even in the long
term [ 14 - 18 ]. Structural properties reach approximately one half of normal between
8 and 16weeks, depending on themodel utilized. This gain in strength is due primarily
to an increase in the quantity of tissue produced at the healing site. The cross sectional
area of the healing tissue at the tendon-to-bone junction largely exceeds that of the
native insertion, accounting for the increase in pullout strength. However, when
normalizing the structural properties by the amount of tissue present in order to
determine tissue material properties, it is clear that the quality of the material produced
is vastly inferior to normal tendon. This outcome is characteristic of the scar-like
response that typifies early tendon healing.
Importantly, the graded fibrocartilaginous insertion site which characterizes the
uninjured rotator cuff attachment to bone is not recreated in the healing scenario.
The tendinous tissue that is generated does, with time, form a functional attach-
ment, but the fibrocartilage and mineralized fibrocartilage tissues characteristic of
the natural insertion are not reliably recreated. Some fibrocartilage cells may be
found at later healing time points, but they are typically few in number and lack the
distinct and organized morphology characteristic of the normal insertion site.
12.4 Patient-Specific Factors Affecting Rotator
Cuff Tendon Healing
In every published study that has evaluated the anatomic outcome after rotator cuff
repair using imaging modalities, a high percentage of unhealed tendons has been
reported. Failure rates range from 20 to 94% [ 3 - 5 , 19 ]. Multiple factors, including
patient-related and technique-related factors, influence tendon healing.
12.4.1 Age
Age is likely the strongest biologic factor influencing rotator cuff healing. Most
studies that have stratified patients for age have revealed a significant relationship
between increased age and failure of healing [ 3 , 4 , 20 - 24 ]. The average age of the
patients who heal are in their mid-to-late 50s and the average age of the patients
who fail to heal is in the mid 60s. This information suggests that somewhere in the
early seventh decade of life, changes in biology and/or physiology are such that the
likelihood of healing even a small tear decreases dramatically.
This information has significant clinical implications. Surgical decision-making
is influenced by patient age. Older patients who are less likely to heal may be better
candidates for nonoperative treatment compared to younger patients, who are more
likely to heal and also have higher functional demands. These younger individuals
will benefit to a greater extent from operative repair.