OR2: THE PRODIGY OF THE MARRIAGE OF LOAD AND RADIOSTEREOMETRIC ANALYSIS, DLRSA – A TOOL TO MONITOR FRACTURE STIFFNESS IN-VIVO”

Abstract

Differentially loaded radiostereometric analysis (DLRSA) uses RSA whilst simultaneously applying load to the bones under investigation. This technique allows measurement of interfragmentary translations and rotations under measured amounts of weight bearing. The aim of this paper was to measure the mechanical stiffness of distal femoral fractures during healing.

Six patients with a 33A2, 33A3, 33B2 and 33C2 fracture were treated with open reduction, internal fixation using a long bridging plate. All patients had a DLRSA examination at 6, 12, 18 and 26 weeks postoperatively. Each DLRSA examination consisted of RSA radiographs taken without load (pre-load), under different increments of load, and finally, without load (post-load). The direction and magnitude of the interfragmentary displacements in six degrees of freedom were recorded at each examination.

DLRSA examinations were able to monitor the inter-fragmentary displacements of the distal femoral fragment relative to the femoral shaft. The interfragmentary displacement recorded, progressively increased as more load was applied in all patients, at all follow-up time points. The two dimensional (2D) translations under maximum tolerated load, progressively decreased over time in three patients. The 2D translations recorded under 60 kg of load at 26 weeks for these patients was 0.18, 0.21 and 0.27mm. The 2D translations of two patients did not decrease progressively between 6 and 18 weeks but did decrease at 26 weeks to 0.47 and 0.75mm. One patient recorded 2D translations of 4.11, 3.48 and 4.53mm under 30kg at 12, 18 and 26 weeks respectively. In the majority of examinations, post-load radiographs enabled the interfragmentary displacements under load to be identified as elastic in nature.

The DLRSA stiffness data confirmed that at 26 weeks three patients had united; two were delayed but improving; and one was a clear non-union without progression. DLRSA examinations may be used as a clinical research tool. to monitor in vivo the stiffness of healing femoral fractures fixed with “relative stability”.