Acromial spur formation in patients with rotator cuff tears

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Abstract

In this study we analyzed the acromial spurs of 15 patients with impingement syndrome undergoing open rotator cuff repair. Mineral apposition analysis and quantitative cytochemical techniques for glucose-6-phosphate dehydrogenase (G6PD) activity (pentose phosphate pathway), alkaline phosphatase (ALP) activity (osteoblast activity), and tartrate-resistant acid phosphatase (TRAP) activity (osteoclast phenotype) were used to examine the distribution and level of activity of selected marker enzymes within the acromial spur insertion into the coracoacromial ligament in order to establish whether local behavior of bone cells is consistent with the proposed secondary development of the acromial spur. Our results indicate that G6PD and ALP activity was higher in osteoblasts on the inferior surface compared with the superior surface of the acromial spur in all patients (P < .001). This area correlated to the most intense area of mineral apposition shown by dual tetracycline labeling. TRAP activity revealed a heterogeneous distribution within the samples. A greater G6PD activity per cell (mean increase of 87%) was seen at the tip compared with that in post- and pre-tip zones within the coronal plane (P < .0002). The qualitative and quantitative enzyme analyses show that the acromial insertion of the coracoacromial ligament is actively involved in bone turnover. The spatial distribution patterns of metabolically active bone-forming osteoblastic cells compared with a heterogeneous distribution of TRAP-positive osteoclasts provide evidence of bone remodeling consistent with the morphologic contours of the acromial enthesis. The sites of oxytetracycline labeling appear to correlate with the sites of high ALP and G6PD activity, which supports the concept of spur formation being a secondary phenomenon in the presence of established rotator cuff tears.

Section snippets

Methods

Acromial samples were taken from 15 consecutive patients undergoing modified open acromioplasty and rotator cuff repair. All had medium-sized cuff tears. The mean age was 62.2 ± 1.75 years, with a male-to-female ratio of 11:4. Ethical committee approval was obtained before the study was undertaken. Informed consent was obtained with regard to the reason for this study and the collection of suitable acromial samples. Patients also gave their permission to be given oxytetracycline tablets

G6PD activity

The mean G6PD activity per cell in osteoblasts on the inferior aspect of the tip of the acromial enthesis (0.92 ± 0.04 [mean ± SEM]) (Figure 1, A) was statistically significantly higher (P < .001, paired t test) than on the superior aspect (0.80 ± 0.03) (Figure 1, B). This increased level of G6PD activity on the acromion’s inferior aspect was also evident, within any single patient, when the activity of these two sites were compared (Figure 2), and this was also reflected in a significant

Discussion

This study concentrated on the coracoacromial ligament’s insertion onto the acromion, namely the enthesis, and thus bone growth at the ligament insertion is described as an enthesophyte.4 Therefore, the commonly used term spur in this text refers to an acromial enthesophyte at the coracoacromial ligament’s insertion.

G6PD activity is a rate-limiting step of the pentose phosphate shunt, which is used during energy metabolism for the production of reducing equivalents that contribute to many

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