The study was conducted in accord with the Helsinki Declaration of 1975 and subsequent updates [5]. All enrolled participants provided written consent from a parent or legal guardian. In addition, written consent was obtained from patients or parent/guardian in regards to publication of the patient images. Due to the nature of the study no formal ethical approval was deemed necessary. Tennis players were invited to take part in the study during their practice sessions at their club. To be included in the study, each athlete was required to be a member of the Italian Tennis Federation. To be considered “non-elite” the player had to be an Italian Ranking below 2.8 and not to be involved in National Representatives [18]. The age had to be below 18 years.
For each athlete body mass index, dominant hand (the side on which they held the racquet for the forehand), the number of years playing tennis, the number of hours training per week, and what type of backhand stroke (with one or two hands), racket weight, grip (Eastern, Western and semi-Western), and string stiffness were registered.
From August 2009 to September 2010 both shoulder of n = 90 a-symptomatic non-elite junior tennis players (mean age ± standard deviation: 15 ± 3 years) were evaluated bilaterally by mean of high-resolution ultrasound using a 17–5 MHz broadband linear array transducer (iU22, Philips Medical System, the Netherlands). Ultrasonographic evaluation included complete shoulder assessment with a standardized protocol suggested by the European Society of Musculoskeletal Radiology [9] and coracohumaral thickness measurement (Figure 1) as described in literature [19]. All players included in the study had no history of trauma or treatment involving either shoulder. No player had a history of systemic inflammatory disease.
A control group of 60 subjects was constituted by 33 boy and 27 girls (mean age ± standard deviation: 15 ± 3 years). All of them were not involved in overhead recreational or sporting activities and had no history of trauma or treatment involving the shoulder. None of the controls had a history of systemic inflammatory disease. An accurate physical examination was performed before high-resolution ultrasound examination of the shoulder. US scans were performed by two musculoskeletal sonographers (each with more than 5 years of scanning experience): both static images and cine clips were recorded. Recording of static images and cine clips was previously used to analyze US evaluations [20]. The sonographer who performed the scan was blinded to the subject’s dominant side. Both shoulders were scanned. This protocol includes evaluation of the rotator cuff tendons, the tendon of the long head of the biceps brachii muscle in the long and short axes and of the subacromial-subdeltoid bursa, acromioclavicular joint, and posterior recess. Dynamic assessment for subacromial impingement and subluxation and dislocation of the long head of the biceps brachii was also performed. US static images and cine clips were retrospectively reviewed by three musculoskeletal radiologists (3, 4 and 2 years of experience respectively). Only definitive sonographic abnormalities agreed on by the three musculoskeletal radiologists in consensus were included in the study. The ultrasound diagnoses of pathologic findings were based on established criteria and according to the technical guidelines of the European Society of Musculoskeletal Radiology [3, 9]. To increase specificity and eliminate false-positive diagnoses, questionable findings were excluded from analysis as suggested by other studies [4].
Concerning the grip we registered the four basic single-handed grips used to hit the forehand: Continental, Eastern, Semi-western and Full Western. For each grip, the player places the base knuckle of the index finger and the heel pad of the palm on the grip bevel of the racquet. Different grips are defined on the base of the location of the base knuckle of the index finger on the eight faces of the racket grip (Figure 2). Grip types were defined according to the International Tennis Federation definitions [1, 21] and checked for accuracy by two tennis instructor in consensus who observed the players holding the racket at rest and during the game.
Continental grip
In the Continental grip the base knuckle is placed on the face number 2 and the heel pad between 1 and 2. This grip was once the universal grip used to hit almost all strokes: forehands, backhands, special shots, volleys and the serve. It originated on the soft, low bouncing clay courts of Europe. Nowadays it is usually employed only for serves and volleys.
Eastern grip
In the Eastern grip the base knuckle is on face 3 and the heel pad between 2 and 3. This grip arose on the medium-bouncing courts in the Eastern United States. It represents the classic forehand grip. The eastern grip is appropriate for different styles of play, comfortable for beginners, and adaptable for all surfaces. The advantages of the eastern grip are that it is easy for beginners to learn, it is easy to generate power, it is ideal for waist high balls, and you can hit a variety of topspin, under-spin and flat drive. The disadvantage is that it is difficult to powerfully hit very high balls.
Semi-western grip
The Semi-western forehand grip has the base knuckle and the heel pad on the face 4. Strength and control to the forehand are guaranteed by this grip, moreover beginners feel comfortable since the palm of the hand supports the racquet providing additional stability at contact. Powerful topspin forehands are the strokes facilitated by this grip. Advantage to this grip is that high balls are easy to hit, however low balls are difficult, back-spin is difficult and grip changes are necessary to hit volleys and overheads.
Western grip
In the Western grip both base knuckle and heel pad are located on face 5. This grip originated on the high-bouncing cement courts of the Western United States. The drawback of this grip is that it closes the racquet face too soon before contact. This is an excellent grip for high balls and topspin but is awkward for low balls and under-spin. It is widely accepted in the popular media that this grip is the most dangerous for the wrist and that a strong wrist and perfect timing are essential to avoid wrist injuries.
Statistical analysis
Statistical analysis included descriptive statistic and coracohumeral thickness was assessed to compare left and right side (dominant and non dominant arm). Fisher’s test was used to compare the presence of lesions in the players and in the control group. The presence of associations between the qualitative variables was evaluated using multivariate analysis. The significance level of 0.05 was adopted. The SPSS software package (release 13.0 for Windows, SPSS) was used. A post hoc power analysis was performed to be sure that the sample size was sufficient to make a meaningful statement. An error level or confidence level of 5% and a ß error level or statistical power (1–ß) of 80% was used and considered acceptable for medical purposes. A sample size of 40 enabled confidence within the required confidence ranges.