Poster 190: Utilization of Distal Clavicle Bone Grafting in the Treatment of a Mobile Mesoacromion: Rationale and Technique

Abstract

Objectives: The treatment of symptomatic unstable os acromiale can be fraught with challenges. It is estimated that between 3-5% of the population has an unfused mesoacromion, but only a small fraction of those shoulders develop a painful, mobile mesoacromion that requires treatment. The variety of concomitant shoulder pathology and overlapping symptoms can make diagnosis and treatment difficult. Furthermore, there remains no consensus for the optimal surgical treatment when conservative methods fail. Surgical options include fragment excision, acromioplasty, and open reduction internal fixation (ORIF) with or without bone grafting. A variety of arthroscopic and open techniques have been described with a large amount of heterogeneity in the literature making comparison of these techniques difficult. Biomechanical forces through the clavicle and acromioclavicular (AC) joint throughout shoulder range of motion have been described in the literature. These forces have theoretical implications on the relationship between the distal clavicle and mesoacromion. Shear, rotational, translational and compression forces imparted against the acromion, by the clavicle and the acromioclavicular ligaments, impart those same forces on the mesoacromial defect via the linkage of the AC joint. There are currently no studies describing the utility in using the distal clavicle as a bone graft source during ORIF of symptomatic mesoacromion. The cross sectional shape and surface area of the distal clavicle is remarkably similar to that of the acromial process. We describe a surgical technique utilizing the distal clavicle as a bone grafting source and present a case series of 8 patients with 100% union rate. Methods: A retrospective analysis was done on 8 patients from 2001-2016 who underwent open reduction internal fixation (ORIF) with distal clavicle bone grafting of a symptomatic, mobile mesoacromion by a single surgeon. The technique utilizes a saber type incision for exposure of the acromion, AC joint, and distal clavicle. Small splits in the anterior and posterior deltoid are utilized to palpate the anterior and posterior aspect of the acromion. Two parallel Kirschner wires (K wires) are placed from anterior to posterior through the acromion crossing the mesoacromion site. The proximal and distal aspects of the site are prepared and rasped. The distal clavicle is skeletonized and 9mm of distal clavicle is removed using a micro saw. The distal clavicle is sliced to 2-3 mm thickness creating a "wafer" of local bone graft. Two narrow slots are placed into the wafer using a small rongeur. These slots are spaced at the exact distance of the parallel K wires. The wafer of bone graft is then placed into the prepared mesoacromion defect and allowed to straddle the K wires via the slots. The acromion is then clamped from front to back using a bone clamp and cannulated screws are placed over the K-wires. Supplemental tension band fixation was used for the earlier portion of the senior author’s practice. Over the course of the technique, with the development of modern screws, the supplemental tension band was felt to be unnecessary. Soft tissues were closed in a standard fashion. Results: The median patient age was 52.5 (range, 41-59) with 75% male and 87.5% Caucasian. The median body mass index (BMI) was 29.4 (range, 23.9-39.2), 62.5% were non-smokers, 25% were type 2 diabetics, 37.5% had hypertension and 25% had no comorbidities. The patients who underwent this procedure with a median follow-up of 6 years (range 2-18). All procedures were done utilizing the distal clavicle bone graft technique described above with fixation reinforced by tension band in 6 of the 8 patients. Seven of 8 patients had concomitant shoulder pathology which included either partial or full rotator cuff tears (n=6), AC arthritis (n=4), glenohumeral (GH) arthritis (n=2) and biceps injury (n=2). Six of 8 patients underwent additional procedures during the index mesoacromion ORIF including rotator cuff repair (n=3), biceps tenodesis (n=4), and AC or GH debridement (n=5). One patient had an acute superficial postoperative infection successfully treated with irrigation and debridement. Otherwise, there were no complications related to the index procedure. Postoperatively all patients had symptomatic relief and went on to radiographic union of the mesoacromion. Conclusions: There remains a paucity of literature to help guide surgical treatment of symptomatic mesoacromion. Studies are largely limited to retrospective reviews and case series with various surgical techniques utilized. Therefore, the importance of relying on surgical experience and expert opinion cannot be overemphasized. This is the first study describing the use of the distal clavicle as bone graft for ORIF of the mesoacromion. Use of a distal clavicle bone graft obviates the need for a separate bone graft harvest site. Furthermore, it reduces abutment, translational and rotational forces on the mobile mesoacromion, maintains acromion length, and increases surface area for bony union. This evolved technique resulted in 100% union rate in our series of 8 patients with a median 6 year follow-up.