gms | German Medical Science

Objectives: Posterolateral rotatory instability (PLRI) is the most common type of elbow instability. It is caused by an insufficiency of the lateral ligamentous complex, which consists mainly of the radial collateral ligament (RCL) and the lateral ulnar collateral ligament (LUCL). The objectives were to investigate the influence of serial sectioning of the lateral ligamentous complex on elbow stability in a cadaveric model of PLRI.

Methods: Kinematics of six fresh frozen cadaveric elbow specimens were measured by digitizing anatomical marks with a Microscribe 3DLX digitizing system (Revware Inc, Raleigh, NC). Each specimen was tested under four conditions: Intact, LUCL tear, LUCL and RCL tear, and complete Tear (LUCL, RCL and capsule tear). Each specimen was tested in 30°, 60° and 90° elbow flexion angles. Varus- laxity was measured in supination, pronation, and neutral forearm rotation positions and total forearm rotation was measured with 0.3 Nm of torque. Statistical significant differences between the conditions were detected using a two-way ANOVA with Tukey's post-hoc test.

Results and Conclusion: The radial head dislocated in all specimens in LUCL and RCL tear and Comp but not in LUCL tear. Total forearm ROM did not increase form intact to LUCL tear (p>0.05) but significantly increased in LUCL and RCL tear (p=0.0002) and complete tear (p<0.0001) in all flexion angles. Additionally, ROM in LUCL tear significantly differed from LUCL and RCL tear and complete tear (p=0.0027 and p=0.0002). A similar trend was seen with the varus angle. While there was a significant difference when the intact condition was compared to both the LUCLand RCL tear and complete tear conditions (p<0.0001 and p<0.0001), there was no difference between the intact and LUCL tear conditions.

PLRI is a complex injury of the elbow so far defined as radial head dislocation and increase in varus laxity. In accordance with previous literature, LUCL tear alone is not sufficient to cause PLRI; additional RCL tear is needed to cause subluxation of the radial head and increase varus laxity. Capsular tear had no additional effect. Our study found that PLRI not only increases radial head dislocation and varus laxity but also leads to an increase in forearm ROM. The increase of forearm ROM is a so far unknown symptom in PLRI and might be used as an additional diagnostic feature in the clinical evaluation of the complex syndrome.