Posterior wall acetabular fracture fixation: A mechanical analysis of fixation methods

Abstract

Stable, anatomical fixation of acetabular fractures gives the best chance of successful outcome, while penetration of the acetabular articular surface with screws is associated with poor outcomes. Spring plates are an alternative to interfragmentary lag screws when penetration is a concern. A mechanical study comparing fracture stability and construct stiffness of three fixation methods for posterior wall acetabular fractures with transverse comminutions was performed. The three fixation methods tested were a posterior wall rim plate, a posterior wall buttress plate with separate lag screws and a posterior wall plate with two spring plates. Nine samples were tested, three for each fixation method. Twodimensional motion analysis was used to measure fracture fragment displacement and construct stiffness. After two 6000 cycle-loading protocols, to a maximum 1.5 kN, the mean fracture displacement was 0.154 mm for the rim plate model, 0.326 mm for the buttress plate and 0.254 mm for the spring plate model. Mean maximum displacement was significantly less for the rim plate fixation than the buttress plate (p ¼ 0.015) and spring plate fixation (p ¼ 0.02). The rim plate was the stiffest construct 10,962 N/mm, followed by the spring plate model 5637 N/mm and the buttress plate model 4882 N/mm. Based on data obtained in this study, where possible a rim plate with interfragmentary lag screws should be used for isolated posterior wall fractures as this is the stiffest and most stable construct. When this method is not possible, spring plate fixation is a safe and a superior alternative to a posterior buttress plate method.

Biomechanical analysis of fixation methods in acetabular fractures: a systematic review of test setups

“…For biomechanical tests, research groups could choose between human cadaveric pelves prepared in various ways, or synthetic pelvis models, which consisted of bone substitutes intended to reflect the biomechanics of physiological bone. Most research groups investigating fixation methods for acetabular fractures used synthetic pelves models (25 test setups) [ 28 – 32 , 35 – 44 , 49 – 51 , 54 – 56 , 60 – 63 ]. These models consisted of a whole pelvis or a hemipelvis model fixed in different ways to enable particular loading directions.…”

“…Pease et al mounted a synthetic pelvis so that the anterior superior iliac spine and symphysis pubis were vertical, and the joint surface of the symphysis was vertical at 90° to this plane. Additionally, flexion of the pelvis in the hip joint was simulated with the pelvis loaded axially by an artificial femoral head [ 54 ]. Olson et al used a single-leg stance protocol, in which a linear actuator applied the loading force via a simulated abductor mechanism to a cadaveric pelvis rigidly mounted at the sacrum and moveably connected to the femur [ 59 ].…”

“…A few experiments measured the subluxation of the load transmitting femoral head with integrated displacement sensors of the biomechanical testing machine (5 of 34 biomechanical test setups) [ 34 , 43 , 47 , 52 , 53 ]. Most studies that determined the fracture displacement also calculated the construct stiffness, defined as the force per unit length in N/mm, by means of a linear regression (22 of 36 biomechanical tests) [ 29 – 35 , 37 , 39 , 41 , 43 , 45 – 49 , 52 , 54 – 57 , 63 ].…”

Outcome of Open Reduction and Internal Fixation of Posterior Acetabular Fractures

“…In 35% of acetabular fractures, the posterior wall had been involved, being is the most common affected, with about 76% of these injuries had complex fractures [2] .…”

“…In general, isolated posterior wall fractures are considered to have a good prognosis, but recent reviews have shown that 21% and 32% of patients have a poor prognosis [2] .…”