Initial stability of the acetabular fragment after periacetabular osteotomy: a biomechanical study.
BACKGROUND
Periacetabular osteotomy (PAO) has become the treatment of choice for skeletally mature patients with symptomatic acetabular dysplasia. Coincident with increasing use of PAO worldwide has been the introduction of various techniques for fixation of the acetabular fragment. Owing to the expanding indications for PAO, such as acetabular retroversion and femoroacetabular impingement, there is an increased interest in biomechanical data supporting the use of the varied acetabular fragment fixation techniques. Our study investigated the biomechanical strength of several PAO fixation techniques in vitro, including a novel plating technique.


METHODS
PAO was performed on 17 artificial hemi-pelves with standardized biomechanical properties. Specimens were instrumented with the following constructs-3 screws from the iliac crest into the fragment (IS), 3 screws from the iliac crest and 1 transverse screw from the anterior inferior iliac spine into the sciatic buttress (IT), or 1 transverse screw with a contoured 3-hole plate across the iliac osteotomy (PT). The specimens were then loaded cyclically under compression and tension and to failure under tension in an material testing system through the anterior-inferior iliac spine.


RESULTS
Data analysis with a single factor analysis of variance yielded mean loads-to-failure of 462 N for IS, 714 N for IT, and 817 N for PT (P=0.005). Further analysis using 2-sample t tests revealed that both IT and PT provided significantly higher loads-to-failure than IS (P=0.016 and P=0.0007, respectively). Under cyclic compression loading, the IT construct demonstrated decreased overall displacement when compared with IS (P=0.003). Under cyclic tension loading, PT achieved significantly smaller overall displacement than IS (P=0.007), as did IT when compared with IS (P=0.018). However, no significant difference was found between PT and IT (P=0.165) groups in cyclic loading or failure testing.


CONCLUSIONS
Prior results showing improved performance of the IT construct have been replicated in a novel tension model. The novel plating technique provides greater load-to-failure than IS and is not inferior to IT. Both PT and IT allow significantly less displacement than IS in tensile and compressive cyclic loading. This novel technique may be easier to perform by surgeons in training or those new to the procedure. The results suggest a move beyond fixation solely with 3 antegrade screws.


METHODS
Biomechanical study.
Widmer
Benjamin J
BJ
Department of Orthopaedics, The University of Utah, Salt Lake City, UT, USA.
Peters
Christopher L
CL
Bachus
Kent N
KN
Stevens
Peter M
PM
D000077:Acetabulum / Q000503:physiopathology / Q000601:surgery*; D000704:Analysis of Variance; D001696:Biomechanical Phenomena; D001860:Bone Plates; D001863:Bone Screws; D050723:Fractures, Bone / Q000000981:diagnostic imaging / Q000601:surgery*; D006801:Humans; D007593:Joint Instability / Q000517:prevention & control; D008953:Models, Anatomic; D010027:Osteotomy / Q000295:instrumentation / Q000379:methods*; D011859:Radiography; D012680:Sensitivity and Specificity; D013314:Stress, Mechanical