With rotator cuff pain, the importance of the acromioclavicular joint is often overlooked.
If the role of osteophytes is well understood, P. Wagner showed that in almost half of acromioclavicular arthropathies, an inferior instability increases the agressiveness of the clavicle against the rotator cuff. He described a dynamic ultrasound test showing this inferior instability of the clavicle. This inferior instability is correlated to the severity of the injury to the rotator cuff.
Degenerative acromioclavicular osteophytes and synovites
In the two tiers of rotator cuff pathology, Wagner found osteophytosis (Fig. 1) at the upper part of the acromioclavicular joints. In these cases of acromioclavicular osteoarthritis (Fig. 2), it is probable that an inferior osteophytosis could be aggressive against the rotary cuff. Radiological assessment with Lamy incidence must be demonstrated. This arthrosis is often accompanied by synovitis, sometimes very inflammatory either with or without effusion. The acromioclavicular joint space may be in communication with the BSAD. An infiltration permits visualization of the passage of liquid from one compartment to the other. A subcutaneous synovial cyst (Fig. 3), from a acromioclavicular point of view, is also a manifestation of this effusion.
(Video in French)
Acromioclavicular instability
In 1/3 of acromioclavicular instabilities, Wagner found a dynamic instability (Fig. 4, 5), which has never been described before, and which seems to potentiate the risk of conflict. Indeed, we find this dysfunction 1 in 2 times in the case of a complete tear of the cuff. This instability is linked with a hyper-laxity, which adds to the arthrosis of the joint. During the abduction, it is as if the clavicle were pulled downwards at the same time as the acromion follows the motion of the humerus. This phenomenon appears to be cased by a retraction of the anterior fascia and especially by a contraction of the subclavicle muscle, which is painful when put under pressure. Manual de-contracting manipulation can be proposed.
Fig.4. Inferior instability of the clavicle. Due to the subclavicle muscle, sometimes associated with scapular dyskinesia, the clavicle does not follow the rocking motion of the scapula, creating an ultrasound impression of the lower discrepancy.
We understand that lower osteophytosis attacks the cuff, particularly:
– supraspinatus at neutral rotation
– infra-spinous at forced medial rotation
– sub-scapular at forced lateral rotation
Surgical resection (Fig. 6) of the distal end of the clavicle is often ineffective, as it aggravates the instability (Fig. 7, 8).
Acromioclavicular atypia (Fig. 9, 10)
