RESEARCH A Biomechanical and Clinical Comparison of Midshaft Clavicle Fixation Performed with Either Two or Three Screws on Each Side of the Fracture

Displaced midshaft clavicle fractures are relatively common injuries and studies
have shown that surgical plate fixation results in superior patient satisfaction and lower non-union rates than non-operative management.1 In recent studies, the rate of non-union after plate fixation is 2.2 percent, whereas it is as high as 15.1 percent when treated non-operatively.2 Surgical plate fixation with six cortices of purchase (three screws) on each side of the fracture has been the standard of care for plating displaced midshaft clavicle fractures.3 However, the use of locking plates and screws may afford equivalent biomechanical strength and clinical outcomes with only four cortices of purchase (two screws) on each side of the fracture. The purpose of this study is to compare the biomechanical and clinical performance of three-screw versus two-screw constructs for plating displaced midshaft clavicle fractures.

Biomechanically, there were no significant differences in cyclic displacement (p=0.17),
stiffness (p=0.94), yield load (p=0.65), or ultimate load (p=0.622) between the two groups [Table 1]. Clinically, there were no significant differences in ASES score (p=0.35), Constant score (p=0.34), VAS pain score (p=0.34), SANE score (p=0.99), or average time to union (p=0.74) [Table 1].

We found that the length of plates used were consistently shorter in the two-screw group overall (p<0.005) and when broken down by comminuted (p<0.005) and non-comminuted (p=0.039) fractures, although for both the two-screw and three-screw groups larger plates were used for fixation of comminuted fractures. Complication rates trended toward being higher in the three-screw group with three cases of painful hardware requiring removal and one case of hardware failure (19%) and two cases of painful hardware requiring removal in the two-screw group (10%) (p=0.20).

RESEARCH Fixing a Midshaft Clavicle Fracture-A Biomechanical Study

Operative plate fixation of displaced mid-shaft clavicle fractures has been shown to improve the functional outcomes and decrease the likelihood of non-union over non-surgical techniques. The purpose of the study was to biomechanically compare the pull-out strength of two locking bicortical screws versus three non-locking bicortical screws used in plate fixation of midshaft clavicle fractures. We hypothesized there would be no significant difference in pull-out strength between the experimental groups and the load to failure of the two fixation methods would both exceed the reported load to failure in other more physiologic cantilever bending midshaft clavicle fracture-plate biomechanical models.

There was no significant difference in stiffness, cyclic displacement, yield or ultimate load between the constructs. Three non-locking screws demonstrated an average ultimate load of 2496 +/-1102 N, while the two locking screws had an ultimate load of 2715 +/-1150 N. This remained true when examining the data with the removal of outliers, as well as when examining only the desired method of failure (screw pullout).

Despite not demonstrating significant differences between our two experimental groups, the absolute values for pull-out strength of both groups exceed the reported load to failure in other more physiologic cantilever bending midshaft clavicle fracture-plate biomechanical models. This demonstrates that using either two locking bicortical, or three non-locking bicortical screws on both sides of the fracture site, is not the limiting factor in midclavicular fracture fixation strength and therefore, our study supports the use of two locking bicortical screws on each side of the fracture site rather than three screws for plating of midshaft clavicle fractures. The clinical implications include decreased cost, surgical time, incision length, periosteal exposure, plate length, number of screws and drill holes, and the ability to use shorter, simpler, and easier to apply standard straight plates along the straight segment of the mid-shaft clavicle.

RESEARCH Morphologic Study of the Midshaft Clavicle

Clavicle fractures occur relatively frequently, representing up to five percent of all fractures and 44 percent of those in the shoulder girdle. Eighty percent of clavicular fractures in adults occur in the middle one-third of the bone.5

Operative plate fixation of displaced midshaft clavicle fractures has been shown to improve the functional outcomes and decrease the likelihood of non-union over non-surgical techniques. One study showed that the risk of nonunion after plating was 2.5 percent, which was significantly lower compared to 5.9 percent for the non-operative treatment. For displaced fractures, the risk of nonunion after plating was 2.2 percent, which was significantly lower compared to 15.1 percent for non-operative treatment.6

Recent studies have demonstrated that precontoured anatomic plates have not been as conforming in certain patients.2,3 The use of shorter and straighter plates with less cortices (two on each side of the fracture instead of three) seem to have better outcomes in midshaft clavicle fracture repair. However, no studies have been conducted to investigate the average length and subtle contours of this segment of the clavicle in order to design the ideal plate.

The purpose of this study was to characterize the morphology of the straight midshaft segment of the clavicle to examine the potential for using shorter, straight superior plates that could ultimately improve treatment, reduce surgical morbidity and cost.

Recent studies have shown that operative plate fixation of displaced midshaft clavicular fractures demonstrate better functional outcomes than those that are treated nonoperatively. Furthermore, the use of shorter plates with fewer screws has the potential to decrease surgical morbidity, time and cost as it relates to less surgical exposure and drill holes, as well as potentially allowing for a smaller plate inventory and less technical difficulty in applying a shorter straight plate to the midshaft clavicle fracture.

Understanding clavicular anatomy is important for better plate design and fixation. Using 3-D modeling we were able to characterize the length and radius of curvature of the clavicle straight segment. Our data provides potentially important information for the design of shorter, more anatomic plates that could decrease the length of surgical exposure, cost and morbidity associated with superior plating of midshaft fractures of the clavicle.

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