The most important finding of the present study was that it is possible to excise the distal end of the clavicle with accurate amount and shape using our technique involving two K-wires. In previous reports, needle insertion techniques to identify the exact location of the AC joint [12, 17, 23, 26] and viewing portals to evaluate the amount of distal clavicle resection [28, 29] were described. However, there are few reports on specialized arthroscopic techniques for distal clavicle resection. We penetrated two K-wires perpendicular to the clavicular axis and parallel to the inserted needles until they penetrated the lower surface of the distal clavicle at the planned excision site and excised the distal clavicle to the penetration points of the K-wires arthroscopically. It was possible to excise the distal clavicle vertically, meaning that there was no risk of insufficient resection or residual superior cortex at the distal clavicle, which can lead to a risk of reoperation. The originality of our procedure is the insertion of two K-wires at the resection margin to allow the distal clavicle resection as planned preoperatively.
Open and arthroscopic distal clavicle resection techniques have been performed for symptomatic AC joint osteoarthritis that does not respond to several months of non-surgical treatment [2–4]. Insufficient resection can result in persistent pain caused by residual impingement between the distal clavicle and the acromion. Excessive resection can lead to instability of the scapular girdle resulting from injury to the coracoclavicular ligament . In a cadaveric study, Stein et al.  reported that the mean distance from the end of the lateral clavicle to the beginning of the trapezoid ligament was 14.7 mm. Harris et al.  reported that the mean distance between the end of the clavicle and the most lateral fibers of the trapezoid ligament was 15.3 mm. Therefore, we judged that the amount of distal clavicle resection should be up to approximately 15 mm to avoid damage to the trapezoid ligament. Several authors have suggested that the critical resection length of the distal clavicle ranges from 5 to 15 mm, but there is still no consensus on the amount required to maintain AC joint stability and prevent contact between the distal clavicle and the acromion . Gartsman et al.  reported that 1.5 cm was an appropriate resection amount. Kay et al.  resected 1 cm in 10 patients with satisfactory results. Meanwhile, Eskola et al.  found that patients with resections of less than 10 mm had significantly better outcomes and less pain than patients with resections exceeding 10 mm. However, Rabalais et al.  commented that the study by Eskola et al. included a variety of patients with AC joint separations and fractures, making it difficult to generalize their conclusions on the association between pain and the amount of AC joint resection. Previous cadaver studies showed that a 5-mm resection was adequate to prevent bony abutment in both rotationally and axially loaded shoulders [32, 33]. However, two cases (8.2%) with insufficient excision of the superior part or posteroinferior part of the distal clavicle were reported in a study with a mean distal clavicle resection length of 5.4 mm . In addition, Elhassan et al.  reported that a reoperation was required in 5 of 81 cases (6.2%) because of persistent or recurrent pain resulting from inadequate distal clavicle resection or bony regrowth of the distal clavicle, despite a mean AC joint space of 9.5 mm after resection. In a long-term study with a mean follow-up of 6 years, Kay et al.  reported that the traditional clavicle resection of 1.0–1.5 cm may be more appropriate to prevent long-term impingement, because 25% of the postoperative radiographs showed evidence of calcified density at the distal clavicle. In our study, a 15-mm excision of the distal clavicle was performed as the maximum excision possible without damaging the trapezoid ligament and without impingement between the distal clavicle and the acromion. In postoperative measurements, the mean amount of bone resection at the distal clavicle was 14.1 ± 2.4 mm, which matched the amount determined in the preoperative planning.
AC joint arthritis mainly results from overuse and aging in manual workers. Under similar conditions, rotator cuff tears can develop as concomitant lesions. In recent years, distal clavicle resection for AC joint arthritis has been performed arthroscopically, and it is possible to simultaneously treat rotator cuff lesions. Kim et al.  reported good results for arthroscopic distal clavicle resection combined with rotator cuff repair. Arthroscopic distal clavicle resection is a useful method that can simultaneously treat concomitant rotator cuff lesions.
Excellent outcomes have been reported after arthroscopic distal clavicle resection [1, 14, 18–20, 26, 31]. However, Strauss et al.  reported postoperative instability of the AC joint that required additional ligament reconstruction. In our method, the orientation of the distal clavicle is determined using the landmarks of the two needles during the bursal side arthroscopy. The distal clavicle undersurface is removed to expose the tips of the two K-wires, which are located at the most medial position of the resection area where the lateral edge of the trapezoid ligament is attached. The distal undersurface of the clavicle is resected via the ALP. The distal upper surface of the clavicle can be resected accurately via Flatow’s portal based on the plane created by the two K-wires. The K-wires are recognized as landmarks for the amount of the distal clavicle resection. This not only allows for a correct plane and amount of the distal clavicle resection, but also avoids excessive ablation of the inferior surface of the clavicle where there is a risk of damaging the trapezoid ligament. In addition, an advantage of our technique is that fluoroscopy is only used for the initial insertion of the needles and K-wires during surgery, and this can reduce the operators’ radiation exposure and use of frequent fluoroscopic imaging to confirm the resection volume. In our study, there was no significant difference in preoperative versus postoperative coracoclavicular distances and no cases had postoperative AC joint instability.
Arthroscopic distal clavicle resection may have several advantages over the open procedure. The former reduces injury and weakness of the deltoid and trapezius muscles and minimizes postoperative pain. These advantages result in a shorter rehabilitation period, which enables a quicker return to work [23, 36]. In our study, there were no significant differences in the strengths of elevation, external rotation, or internal rotation between the affected and unaffected sides after surgery. Postoperatively, muscle strengths for elevation and internal rotation showed greater improvements than those for external rotation. These findings may have resulted from decreased AC joint pain. Usually, patients with AC joint osteoarthritis experience pain when they elevate or internally rotate their shoulder. These motions increase the compression force on the AC joint. In contrast, during external rotation, traction force is applied to the AC joint, which causes less pain, both before and after surgery. This may explain why there was no significant difference in external rotation strength before versus after surgery.
Arthroscopic distal clavicle resection is minimally invasive, but technically demanding. Therefore, it is necessary to establish a simple and reproducible surgical method, and such a procedure can promise good clinical outcomes and reduced complications. Although our technique may not be necessary for skilled arthroscopists, we believe that it is a useful aid for resident-level arthroscopists who have difficulty in accurately determining the orientation of the distal clavicle and resecting a precise volume and shape. We believe that this method can promote accurate surgery and may save time.
Our study has several limitations. First, this was a retrospective study with a relatively small sample size and short follow-up period. Second, the muscle strengths were not measured preoperatively and postoperatively in all patients. Third, we did not consider the trapezoid ligament attachment area because of sex-related differences and physique differences among patients . Thus, the resection amount was based on the mean attachment range of the trapezoid ligament in a previous anatomical study . In our study, the amount of resection was larger than that reported in previous studies [15–17, 19, 26, 29, 32, 33]. However, we were extremely worried that the additional resection could have been required because of AC joint impingement that resulted in remaining oblique or occurring regrowth. We believe that this amount of resection is acceptable, because excellent clinical outcomes were obtained, no revision surgery was needed, and no postoperative radiographs showed AC joint instability.