The displaced lateral clavicle fracture is an uncommon fracture. Although 15% of all clavicle fractures consist of lateral clavicle fractures, only a third of these fractures are displaced (Neer Type 2/Edinburgh Type 3B1)[12].
Due to the rarity of this fracture, literature consists mainly of retrospective case series with small number of patients, some with inclusion of heterogeneous patient population, usually with a short and sometimes incomplete follow up.
Neer described this type of clavicle fracture as an unstable clavicle fracture requiring operative treatment due to the high rate of observed non union and the even higher rate of delayed union. He explained this by the deforming forces around the fracture, causing displacement and interpositioning between the fracture fragments, with continuous motion at the fracture ends [13–15].
Treatment of the displaced lateral clavicle fracture in the literature
Conservative management has been advocated by several authors. Rokito et al [15] retrospectively compared results of 16 conservatively and 14 operatively treated patients with displaced lateral clavicle fractures. They reported a high percentage of non union in the conservatively treated group (7/16) while the shoulder function was comparable in both groups after approximately 4.5 years. Robinson and Cairns [16], retrospectively followed up on 101 patients. According to their policy, the treatment was conservative during the first six months. If still symptomatic after six months, patients were treated operatively. They reported a non union of 37%. Only 35% of these patients required an operation because of symptoms. Only 14 of the 101 (14%) patients were operated on because of persisting symptoms after 6 months. The functional results at follow up of the different groups were similar.
Operative treatment of these fractures can be a challenge because of the small and soft metaphyseal and usually comminuted distal fragment and the proximity to the AC joint. Several methods have been described.
Transacromial wire fixation was popularized by Neer [14] and is a commonly used method. Kona et al [17] reported an unacceptably high complication rate (47%) with the use of K-wires and advised against its use. Flinkkila et al [1] compared K-wire fixation to hook plate fixation. Although the functional results were similar, they advised hook plates because of migration and infection in the K-wire group. Lee et al [2] compared K-wire fixation with tension band wiring to hook plate fixation. Their results showed that the group with the hook plate had earlier regain of pre-injury activities. The K-wire fixation group had 30% complications related to hardware failure.
Another operative treatment option is indirectly reducing the fracture by coracoclavicular fixation. Using this method, several techniques have been described. Ballmer and Yamaguchi reported good results with the Bosworth screw fixation [18, 19]. Similarly several methods have been described where a PDS suture, a Dacron patch or an Endobutton© device through bore holes is used to perform the fixation [20–22]. The indirect reduction method requires extensive dissection around the fracture and bore holes through the clavicle and the coracoid process. Erosion of these structures and fracture of the clavicle and the coracoid are well recognized complications [17, 23, 24]. Especially in case of the rigid fixation with the Bosworth screw, and in lesser extent with the other devices, the rotation of the clavicle is disabled requiring partial immobilization of the shoulder until fracture consolidation with the potential of implant breakage and a longer revalidation period.
Despite the small, soft and sometimes comminuted metaphyseal fragment, Regazzoni et al [11] described extra articular double plating of this fracture, using mini AO plates with similar results and complications to other operative treatments.
Treatment with the clavicle hook plate
The clavicle hook plate is an easy to handle solid plate that withstands forces that are applied to the fracture fragments. By design it keeps the lateral end of the clavicle reduced, hereby aligning the clavicle with the ligaments and minimizing movement at the fracture ends while it does not interfere with the rotational movement of the clavicle [25]. The results published in several studies [1–10] show good results in terms of bony union and in terms of shoulder function. Shoulder function is measured most frequently by the DASH and Constant-Murley scores. The DASH score is usually below 5 and the Constant-Murley score averages around 90. Non union occurs only seldom, below 10% in most series. Compared to the K-wire fixation and the Bosworth screw fixation, it facilitates earlier regain of previous activities [1, 2, 24].
Complications of the clavicle hook plate
Although the types of fractures included, mean follow up time, postoperative mobilization and plate removal policy varies in different publications, several typical complications are associated with the hook plate.
The first category is related to the freely movable hook of the plate that is placed posterior to the AC joint, below the acromion, and above the supraspinatus tendon. Even though the design of the hook plate promotes fracture healing by keeping the fracture fragments reduced without interfering with the rotational movement of the clavicle, this design also leads to complaints due to mismatch between the hook of the plate and the diverse anatomy of the acromion.
El Maraghy et al [26] demonstrated the mismatch between the plate and the subacromial space leading to several well described short term complications in an anatomic study. In 89% of the specimens the hook perforated the subacromial bursa, in 60% the tip had contact with the supraspinatus tendon and in 60% contact with the acromion was concentrated at the tip of the plate. These findings clarify the subacromial bursitis, the impingement complaints and the subacromial osteolysis respectively. They concluded that the anatomy of the acromion is too diverse to accommodate a single hook plate and when necessary the hook and the tip of the plate needs bending and smaller depths of the hook should be selected if necessary, especially for women.
Lee et al [10] performed arthroscopy during the procedure to verify the position and fit of the hook and tip besides intra-operative fluoroscopy verification. If necessary the tip and the plate was bent according to the required anatomy of the patient. They also had access to the new LCP plate which comes in a smaller depth of 12 mm. In this case series none of the patients suffered impingement. However they still encountered subacromial osteolysis (17%) and subacromial bursitis (22%).
Muramatsu et al [8] found it necessary to bend the hook in 77% of their patients, and found in most of their patients, migration of the hook after fixation. Their operative technique describes however, forcefully reducing the fracture using the plate as a lever.
Impingement, subacromial bursitis and subacromial osteolysis on x-ray are signs of a mismatch between the plate and the anatomy of the patient. These complications can be minimized by performing an anatomic fit of the plate during the procedure.
However, the plate design is such, that the vertical part of the hook and the tip must have contact with the underside of the acromion hereby maintaining reduction of the fracture and withstanding forces applied to the fracture ends. Pressure concentration at the tip of the plate that leads to subacromial erosion due to the rotation of the clavicle when the implant is retained for a longer period, becomes unavoidable in part of the patients. Similarly, contact with the supraspinatus tendon in some cases is unavoidable, even though there is no contact during the operation, the contact may happen when abducting the arm during the rehabilitation period.
Even though aforementioned short term complications have the potential of acromion fracture, and supraspinatus tendon rupture, these complications have never been reported with this plate in the literature [8].
In our patient group, we used the surgical technique as described above. We had impingement complaints in 32% and subacromial osteolysis in 25% of our patients [Figure 1]. These complaints were mild and all patients could complete their rehabilitation program. None of these patients developed a frozen shoulder or required early plate removal. The impingement complaints as well as subacromial osteolysis resolved after plate removal and had no mid term consequences.
Another complication is a fracture medial to the plate that can be seen with a minimal trauma. This complication has only been described with a retained implant after fracture healing [27, 28].
The last category of complications are typical complications of plate osteosynthesis such as fixation failure due to osteoporotic bone and deep infection of the plate [27–29].
Several long term complications associated to the lateral clavicle fracture have also been described in relation to the use of this plate. These are ACJ arthrosis and extra articular ossifications. Due to the proximity of this plate to the ACJ, several authors discourage use of this plate [11, 22]. When placed correctly, the plate does not violate the ACJ. However the vertical part of the hook passes behind the ACJ. This part of the plate could violate the joint if the plate migrates anteriorly but this is almost impossible when secured rigidly on the shaft.
ACJ arthrosis and extra articular ossification have been described in all types of lateral clavicle fractures in studies where there was longer term follow up.
Nordqvist et al. [30] described a cohort of conservatively treated lateral clavicle fractures with a mean follow up of 15 years. They reported 7 ACJ arthrosis in 89 patients. Five of these occurred after a type I fracture, 1 after a type2 and 1 after a type 3 fracture. Extra articular ossification was observed in 8 cases. Robinson et al [12, 16] described a prevalence of 9% up to 15% of ACJ arthrosis in patients with conservatively treated lateral clavicle fractures. Flinkkila et al [5] described 63 patients with displaced lateral clavicle fractures treated with the clavicle hook plate. Fifty percent of the patients were clinically re-evaluated with a mean follow up of 3.6 years. Ten of 31 followed up patients (32%) had mild asymptomatic ACJ arthrosis.
We analysed our patient population to find a relation between occurrence of ACJ arthrosis and extra articular ossification detected at mid term follow up and and signs of a mismatch between the plate and the subacromial space such as impingement and subacromial osteolysis.
In our study, 4 patients (14%) had ACJ arthrosis [Figure 2], of which one was symptomatic. Only one patient with ACJ arthrosis had suffered impingement without signs of subacromial osteolysis. Three patients (11%) had extra articular ossification [Figure 3] of which one was symptomatic. Only one of the patients with extra articular ossification had suffered impingement and had no signs of subacromial osteolysis.
Even though the numbers are small to perform statistical analysis, we found no relation between ACJ arthrosis, extra articular ossifications at mid term follow up and the typical short term complications occurring due to mismatch of the plate tip and the acromion. In light of previous publications [5, 12, 16, 30] about the lateral clavicle fracture, ACJ arthrosis as well as extra articular ossification is more likely to be caused by the initial trauma to the joint and the ligaments rather than a complication that can be addressed to the hook plate.
The strength of this study is in its high rate of follow up duration, the uniformity of the included fractures and the number of included patients for such a rare fracture. To our knowledge, this study has the longest mean time of follow up in the literature concerning primary operative treatment of acutely displaced lateral clavicle fractures with the clavicle hook plate. Our study is retrospective with limitations of this design. Even though we operated on all displaced lateral clavicle fractures, a possible selection bias is the age of our patient population since our series is younger than some described series. Younger patients have fewer complications due to better bone quality and better circulation of tissues which could explain the low percentage of infection and the high percentage of union in our report.
