In vivo measurement of subacromial space width during shoulder elevation: Technique and preliminary results in patients following unilateral rotator cuff repair
Introduction
Rotator cuff tears are a common shoulder injury, affecting approximately 30–40% of individuals over age 60, having a significant impact on function, comfort, and quality of life. A decrease in the subacromial space – i.e., the space between the humerus and the acromion occupied by the rotator cuff’s supraspinatus tendon – may result in pathologic contact between the supraspinatus tendon and acromion. This phenomenon, known as subacromial impingement, is widely believed to be an etiologic factor in the development of rotator cuff tears (Bigliani and Levine, 1997, Neer, 1972, Neer, 1983). This concept has led to the development of surgical procedures designed to increase the subacromial space. These procedures – commonly referred to as acromioplasty or subacromial decompression – involve the removal of any projection or bone spurs from the anterior, inferior or anterolateral portion of the acromion to create a flat undersurface of the acromion, and are often performed in conjunction with surgical repair of a rotator cuff tear. However, the role of acromioplasty and its effect on the subacromial space have been questioned, with alternative approaches advocated that include rotator cuff repair without acromioplasty (Budoff et al., 1998, Goldberg et al., 2001) as well as acromioplasty alone without rotator cuff repair (Cordasco et al., 2002).
Given the clinical importance of the subacromial space, previous research efforts have measured the subacromial space in humans under a wide variety of testing conditions. These previous studies have measured the subacromial space under in vivo conditions with various imaging modalities, including three-dimensional (3D) computed tomography (Lochmuller et al., 1997), clinical radiographs (van de Sande and Rozing, 2006, van de Sande et al., 2006, Lehtinen et al., 2000, Petersson and Redlund-Johnell, 1984), ultrasound imaging (Girometti et al., 2006, Azzoni et al., 2004), and MRI (Pappas et al., 2006, Graichen et al., 1998, Graichen et al., 1999b, Graichen et al., 1999a, Graichen et al., 2001, Graichen et al., 2005, Hinterwimmer et al., 2003, Roberts et al., 2002, Solem-Bertoft et al., 1993). Additional studies have estimated the subacromial space width based on shoulder kinematics as measured using skin-mounted sensors (Tsai et al., 2003, Thigpen et al., 2006, Ludewig and Cook, 2002, Nawoczenski et al., 2003). In addition, measurements of the subacromial space have also been recorded during operative procedures (Tillander and Norlin, 2002) and in various experiments using cadaveric shoulder specimens (Karduna et al., 2005, De Wilde et al., 2003, Flatow et al., 1994). The previous in vivo studies have reported the subacromial space width to range from approximately 2 to 17 mm. This wide range of subacromial space width measurements reflects differences in age, gender, shoulder position, shoulder pathology, and the measurement technique and its associated accuracy. It has also been shown that muscle activity (in particular, adducting and abducting muscle activity) has a significant effect on subacromial space width (Graichen et al., 2005, Hinterwimmer et al., 2003). For example, Hinterwimmer and colleagues reported that adducting muscle forces increased the subacromial space from 32% to 138% over 30° to 150° of shoulder elevation when compared with abducting muscle forces (Hinterwimmer et al., 2003). Similarly, Graichen and colleagues reported a significant decrease in average subacromial space width from 6.7 mm to 4.9 mm in male subjects when 90° abduction was combined with abducting muscle activity (Graichen et al., 2001). These data clearly indicate that muscle forces have a significant effect on the subacromial space width. Unfortunately, many of the previous studies reported subacromial space width under passive (i.e., without any apparent muscle activity) and static conditions. The authors are unaware of any previous study that has accurately measured the 3D, in vivo subacromial space width during dynamic shoulder motion. Thus, the purpose of this study was to measure the 3D subacromial space width during shoulder elevation using a novel, accurate in vivo measurement technique.
Section snippets
Methods
Following IRB approval and informed consent, 11 subjects – 9 male, 2 female, average (standard deviation) age: 63.2 (10.7) – enrolled in the study. Each subject had been diagnosed by ultrasound with an isolated supraspinatus tear and had failed conservative treatment. To minimize subject variability, patients with partial-thickness tears, multi-tendon tears, or significant labral or glenohumeral joint pathology were excluded. All subjects had an asymptomatic contralateral shoulder and denied
Results
Average subacromial space width ranged from 2.3 to 7.4 mm in the repaired shoulders, and ranged from 1.2 to 7.1 mm in the contralateral shoulders (Fig. 3). Subacromial space width decreased with elevation angle in both the repaired and contralateral shoulders, with elevation angle having a statistically significant effect upon subacromial space width (P < 0.001). The average (standard deviation) elevation angle where the minimum distance between the humerus and acromion passed through the
Discussion
By applying accurate, state-of-the-art motion measurement techniques, we were able to report the subacromial space width during dynamic shoulder motion. Specifically, this study demonstrated a decrease in subacromial space width with increasing elevation angle. The study also found significant differences in the subacromial space width between the repaired and contralateral shoulders of patients who have had rotator cuff repair surgery. Given that the rotator cuff repair surgery included an
Conclusions
This study used a state-of-the-art biplane X-ray system to provide accurate, in vivo measurements of subacromial space width during shoulder elevation. These measurements were made in both the repaired and asymptomatic, contralateral shoulders of patients at 3–4 months after rotator cuff repair. The subacromial space width in the repaired shoulder (in which approximately 2–5 mm of the acromion had been removed by acromioplasty) was only 0.5 mm less than the asymptomatic, contralateral shoulder
Acknowledgement
The project described was supported by Grant Number AR051912 from NIH/NIAMS.
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