Results from a small study show no difference in hormone receptors in male/female, diseased/healthy samples

It’s no secret that posterior tibial tendon disease (PTTD) occurs more frequently in women than in men (See “PTTD: More prevalent in women,” AAOS Now, March 2009). The question is why?

During the 2010 annual meeting of the American Orthopaedic Foot & Ankle Society, Allison Muia Wade, MD, and coauthors presented the results of their investigation into the role of estrogen in the pathophysiology of PTTD, a major cause of acquired flat foot syndrome. Noting that exogenous oxygen has also been shown to influence collagen synthesis of the tendon, and working with the idea that estrogen receptors (ERɑ and ERß) could be identified indirectly by measuring receptor gene expression, the authors reasoned that identifying ER gene expression in the fibroblast (tenocyte) might shed insight on whether estrogen influences the tenocyte.

The influence of estrogen on fibroblasts has been studied in other musculoskeletal tissues.

Studies of sex-related differences in anterior cruciate ligament (ACL) injuries have demonstrated the expression of both estrogen and progesterone receptors in the ACL. The expression of ERɑ and ERß has been detected in dermal fibroblasts, and exogenous estrogen has been shown to affect the mechanical behavior of the Achilles tendon.

In part because the incidence of PTTD is higher among perimenopausal and menopausal women (the overall female–male ratio of clinical presentation is 3:1), the authors hypothesized that diseased posterior tibial tendons (PTTs) of women would express ERɑ and ERß, but that diseased PTTs of men would not. They also speculated that samples harvested from healthy flexor digitorum longus tendons (FDLs) would not express the receptors. But no significant sex-related difference in the PTT tissue was detected, and no differences were seen in ER expression in the diseased PTT versus the controls of healthy PTT and FDL tissue.

The study group was small: five women and three men, with an age range of 17 to 73 years (mean age 52.4). All eight patients had PTT dysfunction requiring surgery.

Tendon samples were harvested both from the distal aspect of the PTT—representing the most diseased portion of the tendon—and from the more proximal aspect, exemplifying a healthy-appearing tendon. A portion of transferred FDL tendons was used as controls.

Tendon samples were processed using specific protocols for total RNA isolation from hypocellular, dense connective tissues. ERɑ and ERß transcripts were quantified using real-time reverse transcription-polymerase chain reaction (RT-PCR) assays. Transcripts of both ERɑ and ERß were reproducibly detected in RNA samples isolated from the tendon samples.

Although ERɑ and ERß messenger RNA levels were higher in female diseased samples relative to female control samples, the difference did not reach statistical significance.

Weaknesses in the study, said Dr. Wade, included the small number of patients, a nonhomogeneous patient group, possible prednisone use, age, sex distribution, and possible microcontamination of white blood cells.

Looking ahead
In this study of PTT dysfunction, the expression of estrogen receptors was detected in the tenocytes of normal and diseased tendons in both women and men, with no difference in receptor expresson found in diseased samples versus controls or in men versus women. According to the authors, this study was the first to demonstrate ER expression for the tenocyte and represents an initial step toward discovering whether tenocytes are targets for estrogen function.

The authors noted that further research is needed to better understand PTT pathology. Current theories suggest that PTTD is caused by spontaneous degeneration of the tendon; histologic changes of the diseased tendon have been described as consistent with degenerative change and not inflammation. An association has also been made with a decreased vascular supply, although the authors noted that this link has been challenged. PTTD has also been associated with obesity, hypertension, and diabetes.

Dr. Wade said that “future studies with more patients are needed to identify trends in gene expression versus controls. Differences in estrogen receptor expression in diseased tendon may identify estrogen as a factor in tendon health.”

Noting that future study results may show that tenocytes “are influenced by estrogen and may change with hormone levels,” an effect that has been studied in other musculoskeletal disorders, the authors conclude that “the mechanism remains to be elucidated.”

Dr. Wade’s coauthors are Jay Bridgeman, MD, Yue Zhang, Henry Donahue, PhD, and Paul J. Juliano, MD.

Disclosure information: Dr. Juliano—EBI/Biomet. Drs. Bridgeman, Donahue, and Juliano and Mr. Zhang—no conflicts.

Terry Stanton is senior science writer for AAOS Now. He can be reached at tstanton@aaos.org

Bottom line

• The pathophysiology of PTTD is poorly understood.
• Changes in hormone physiology may be a factor in influencing tendon health.
• Detection of estrogen receptor expression in the fibroblast is an initial step in discovering whether estrogen influences the tenocyte.
• This small, initial study detected no differences in ER levels in diseased versus control or male versus female samples.