Overview of insertional achilles tendinopathy
Overuse injury of the Achilles tendon is becoming a more common problem in the United States as the younger population becomes more athletic and as elderly patients assume ever-increasing levels of physical activity. Thus, it is not surprising that the Achilles tendon, one of the largest tendons in the body, would be subjected to repetitive overuse injuries in both patient populations. This overuse phenomenon can ultimately lead to different forms of Achilles tendinopathy. It is important at the onset to emphasize that Achilles tendinopathy is not a single entity, but rather is made up of a large variety of pathophysiologic processes, all of which can result in pain production at the posterior heel and calf areas. It is useful, I believe, to divide Achilles tendinopathy into noninsertional and insertional disease processes since the location of the pain and the pathophysiology is so distinctly different. This chapter concentrates on the evaluation and diagnostic characteristics of insertional Achilles tendinopathy. The term insertional Achilles tendinosis was originally suggested by Clain and Baxter, who felt that this condition was an overuse phenomenon that resulted in enthesopathic changes occurring within the Achilles tendon. The theory was that repetitive mechanical stress from overuse would lead to microtears within the tendon itself. Given the low-oxygen environment seen in that anatomic area of the Achilles tendon, this subsequently would cause localized collagen degeneration, fibrosis, and, ultimately, calcification. Schepsis and Leach also noted that insertional tendinosis is frequently seen in combination with Haglund's deformity and symptomatic retrocalcaneal bursitis, which they believed would exacerbate the condition simply by mechanical bony impingement and chemical irritation. The result in any case is the production of posterior heel pain. The posterior heel is composed of the Achilles tendon insertion, the posterior superior calcaneal process, and the retrocalcaneal bursa. The Achilles fibers insert at the enthesis on the posterior-inferior aspect of the calcaneus by way of Sharpey's fibers. The insertion of the tendon is quite broad and extends very far distally on the calcaneus. In our study, the distance over which the Achilles inserts measured from superior to inferior is 19.8 mm (range, 13 to 25 mm) and the width measured at the superior insertion is 23.8 mm (range, 17 to 30 mm), while at the inferiormost insertion the distance averages 31.2 mm (range, 25 to 38 mm). The retrocalcaneal bursa is a horseshoe-shaped structure that is approximately 22 mm long, 8 mm wide, and 4 mm deep as established by Frye and colleagues, and its function is to lubricate the anterior surface of the Achilles tendon. The superior calcaneal process makes up the final component of the posterior heel region and is generally the superior border of the retrocalcaneal bursa. Since the space between the Achilles tendon and the calcaneus is occupied by the retrocalcaneal bursa-and the deep surface of the tendon is part of the bursa and the anterior part of the bursa is the calcaneus-during dorsiflexion of the ankle the Achilles tendon bends near its distal attachment and the bursa flattens as its walls become opposed. This allows the distal part of the Achilles tendon to be pressed against the calcaneus. This complex anatomic region, with an extremely important function, is designed to protect the tendon and the bone from excessive wear. It has been established by DePalma et al. that there are three different fibrocartilaginous surfaces that make up this complex interaction: fibrocartilage on the anterior or deep surface of the tendon, which some have referred to as the sesamoid fibrocartilage; periosteal fibrocartilage covering the superior calcaneal tuberosity; and fibrocartilage of the enthesis where the Achilles tendon inserts into bone. Recent investigations have implicated these fibrocartilaginous cells as a factor in the degenerative phenomenon that occurs with posterior heel pain. Posterior heel pain can certainly be caused by any disease process that affects any one or all three of these components, such as a prominent superior calcaneal process (Haglund's deformity), which has been associated with the retrocalcaneal bursitis that is frequently seen in long-distance runners. There can be mechanical causes for retrocalcaneal bursitis, such as a varus hindfoot and a cavus foot with the resultant increase in calcaneal pitch. Some patients simply have a prominent posterior lateral superior tuberosity, which aggravates the heel counter of the shoe and has been referred to as "pump bump." This is usually seen in women who wear high-heel shoes. Other causes of posterior heel pain that must be included in the differential diagnosis are inflammatory causes such as rheumatoid arthritis, seronegative spondyloarthropathies, and gout; even pseudogout or chondrocalcinosis has been associated with calcium pyrophosphate dehydrate deposition at the Achilles insertion. © Springer Science+Business Media, LLC 2009.
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