The MR arthrographic anatomy of the biceps labral insertion and its morphological significance with labral tears in patients with shoulder instability

Introduction: Most of the fibres of the long head of biceps tendon attach on the superior labrum just posterior to the supraglenoid tubercle.

Aim: Our hypothesis was that posteriorly attached biceps tendons predispose to posterior superior labral tears and SLAP lesions.

Methods and materials: A prospective analysis of all MR shoulder arthrograms for shoulder instability referred from the shoulder specialist clinics, performed during a one year period were reviewed by two independent observers who were blinded to clinical history. The biceps attachment was classified into four groups according to the method described in an earlier cadaveric study into four groups; posterior-type 1, predominantly posterior-type 2, equal contributions to both anterior and posterior labrum-type 3 and predominantly anterior labral attachment-type 4. Data was analysed using Kappa statistics and Fischer's exact test.

Results: 48 patients (33 males and 15 females) were included in this study with a mean age of 32 years. Majority, 22 patients (46%) had a type 1 attachment of the biceps on the superior labrum. There was moderate intra-observer and good interobserver agreement with a Kappa of 0.58 and 0.63 respectively. There was a significant association between a type 2 attachment and posterior tears (p≤0.04) and also between a type 2 attachment and SLAP tears (p≤0.04).

Conclusion: Our results suggest that variation in anatomy of biceps origin influences the type of labral tears that occur in patients with shoulder instability. The importance of these findings could influence selection of individuals in throwing sports like cricket and baseball.