Distal Clavicle Osteolysis after Modified Weaver-Dunn's Procedure for Chronic Acromioclavicular Dislocation: A Case Report and Review of Complications

Distal clavicle osteolysis after acromioclavicular joint stabilization has only been described after the use of hardware for clavicle stabilization or synthetic graft causing a foreign body reaction. This paper reports a very rare case of distal clavicle osteolysis after modified Weaver-Dunn procedure for the treatment of chronic acromioclavicular joint dislocation. The paper also provides a comprehensive review of complications of this surgical technique and discusses a potential vascular etiology and preventive strategies aimed at avoiding clavicle osteolysis.

Well-known causes of clavicle osteolysis are acute trauma or chronic overuse [9,10]. Specifically, it has been reported that direct traumatism over the AC joint [10] or overuse due to weight lifting [9,10] can cause distal clavicle osteolysis. To the best of our knowledge, the development of clavicle osteolysis after AC joint stabilization has only been reported related to the use of hardware or Gore-Tex (W. L. Gore Associates, Flagstaff, AZ) graft fixation [11,12] but not the use of the modified Weaver-Dunn's technique. The purpose of this paper is to report a rare case of clavicle osteolysis after AC joint stabilization using the modified Weaver-Dunn's technique in a chronic painful AC joint dislocation.

Case Presentation
A 49-year-old man, with unremarkable past medical history, came to our clinic in 2009 after falling onto his right shoulder. The patient's chief complaints consisted of right shoulder pain upon movements and deformity. Physical examination revealed tenderness and deformity at the AC joint, exacerbated with arm abduction in the coronal plane and forced adduction in the transverse plane. Plain radiographs showed a superior displacement of the clavicle of more than 50% compared to the normal side, corresponding to a type III AC joint dislocation according to Rockwood's classification [13]. He was recommended to be initially treated conservatively with a sling in internal rotation for three weeks. Then, the patients followed a rehabilitation program to gain shoulder range of motion and strength. After 6 months, the patient was scheduled for surgery because of persistent pain despite rehabilitation. A modified Weaver-Dunn's technique was planned to address this chronic type III AC joint dislocation. Standard patient positioning and surgical approach were employed. Distal clavicle excision and transposition of the coracoacromial ligament to the clavicle were performed. An absorbable anchor using the Panalok system (DePuy Mitek, Inc., Raynham, Massachusetts, USA) was placed at the base of the coracoid process and sutures were passed through drill holes in the clavicle to ensure primary stabilization of the AC joint.
Plain radiographs 2 weeks and 2 months after surgery demonstrated correct reduction of the AC joint, adequate bone appearance of the clavicle, and no signs of hematoma and infection. In the follow-up visit 6 months after surgery, the patient complained of AC joint pain on palpation but demonstrated full active range of motion. One year after surgery, shoulder function was also complete, but pain was still present on palpation. Plain radiograph at that time showed initial osteolysis of the clavicle. Two years after surgery, the patient's shoulder symptoms and function did not change, but radiographs demonstrated progression of osteolysis ( Figure 1). A CT scan confirmed the lateral third clavicle osteolysis and found no associated bone injuries ( Figure 2). MRI study confirmed the osteolysis with no bone edema or soft tissue reaction ( Figure 3). Despite image findings, the patient currently refers no clinical symptoms except a minimum loss of strength in specific movements over the head. However, the patient is pain free and declines further surgery.
The knowledge of the blood supply of the clavicle may help understand the occurrence of nonunion and osteolysis. Knudsen et al. found that the suprascapular, the thoracoacromial, and the internal thoracic arteries provided blood to the clavicle [26]. The authors reported that the main blood supply was primarily periosteal and that no nutrient artery was found. Therefore, any injury to the periosteal vascularity during the surgical procedure may cause clavicle osteolysis or nonunion [5,26]. Considering that important branches reach the posteroinferior part of the clavicle, care must be taken to not perform a wide deperiostization of the lower rim of clavicle. In fact, the thoracoacromial artery was found to constantly supply the lateral 4/5 of the clavicle through its clavicular and acromial branches, with an inferoanterior relation to the bone approximately 2 cm medial to the distal end [26]. One step of the modified Weaver-Dunn's technique is the oblique resection of 2 cm of the distal clavicle. This step may explain the development of osteolysis or nonunion.
Although most common vascular injuries following AC joint stabilization may involve the great subclavian vessels [5,6,8], disruption of small vessels may also occur after modified Weaver-Dunn's procedure leading to osteolysis of the clavicle. Special care must be taken when performing modified Weaver-Dunn's technique not to elevate too much of periosteum from the lateral clavicle, since its main blood supply is provided by the periosteum, and also to avoid damage of clavicular and acromial branches of the thoracoacromial artery.