Methods of operative fixation of the acromio-clavicular joint: a biomechanical comparison.
OBJECTIVE
Three different methods of fixation used in acute disruption of the acromio-clavicular (AC) joint-namely, the coraco-clavicular Bosworth screw (CC Screw), a coraco-clavicular sling of Mersilene #5 tape (CC Sling), and a Hook Plate-were compared to baseline to see which could most closely replicate the stiffness of healthy cadaveric AC specimens (Intact).


OBJECTIVE
It is hypothesized that the Hook Plate method, as compared with the other reconstructions tested, will be most similar mechanically to the intact AC joint with respect to present outcome measures.


METHODS
Five matched pairs of fresh-frozen cadaveric specimens were tested. Stiffness was tested with superior cyclic loads to 70 N. The stiffness for each specimen was initially tested with all the ligaments in place (Intact). The AC and CC ligaments were then sectioned, and stiffness was tested, in varying order, with reconstructions using the CC Screw, the CC Sling, and the Hook Plate. Failure testing consisted of taking either the CC Screw or Hook Plate to failure within each matched pair.


RESULTS
The CC Screw and the CC Sling, respectively, showed stiffnesses of 46 +/- 23 N/mm and 15 +/- 8 N/mm, which was significantly different from the Intact specimen (P < 0.05). The Hook Plate had a stiffness of 26 +/- 17 N/mm, most comparable to the Intact joint stiffness of 25 +/- 8 N/mm (P = 0.785). With failure testing, the CC Screw failed at a significantly higher load than the Hook Plate (744 +/- 184 N vs 459 +/- 188 N) (P = 0.034).


CONCLUSIONS
The CC Screw demonstrated the greatest stiffness with repetitive loading to 70 N. The Hook Plate had a stiffness most similar to the normal physiologic state of the AC joint. The CC Sling was significantly less stiff than the Intact joint or the other methods of fixation.


CONCLUSIONS
Although the stiffest construct is the CC Screw, Hook Plate fixation allows physiologic motion without pathological deformation and most closely resembles the stiffness of the native AC joint for the current test procedure used.
McConnell
Alison J
AJ
Division of Orthopaedic Surgery, Department of Surgery, St. Michael's Hospital, Toronto, Canada.
Yoo
Daniel J
DJ
Zdero
Rad
R
Schemitsch
Emil H
EH
McKee
Michael D
MD
D000173:Acromioclavicular Joint / Q000293:injuries / Q000503:physiopathology / Q000601:surgery*; D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D005593:Fracture Fixation, Internal / Q000295:instrumentation*; D006801:Humans; D016268:Internal Fixators; D008875:Middle Aged; D008953:Models, Anatomic; D016059:Range of Motion, Articular