Biomechanical cadaveric study on displacement following AC Joint stabilisation: a comparison of three constructs

Design

Materials & Methods:

Constructs under investigation (chosen for ability to perform via mini op technique as per principal investigators preference, and ability to pass button through coracoid drill hole without additional exposure).

Three constructs – 10 samples of each:

1. Construct 1: ACJ Tightrope
2. Construct 2: Two individual ACJ Tightopes
3. Construct 3: Self loaded Tightrope variation with Pec button, open ABS tightrope II, Fibertape and Dog bone

Stage 1: Biomechanical testing set up

Material testing machine (model 8874; Instron, Norwood, MA) with a 250-N capacity load cell (Dynacell; Instron) with custom made mount to replicate Coracoid clavicular relationship

Under go Dynamic testing (70 N/500Hz)

Outcomes:

1. Dynamic creep (the difference in peak displacement between the first and last loading cycles was measured. Indication of Time-dependent gap formation).
2. Peak-to-peak displacement (the amplitude of the loading curve was recorded by averaging the axial displacement from trough to peak of the last 5 loading cycles. indication of Gap formation during cyclic loading).
3. Relaxed elongation (final length after resting period, indicative of Plastic deformation and Time-dependent gap formation)

Stage 2: Cadaveric Testing

18 shoulders will be dissected to remove soft tissue from the clavicle and scapular while preserving the ACJ capsule and CC ligaments. (12 already prepared and additional 6 in progress)

each construct will be tested with 6 samples.

Clavicle and scapula will be mounted in PMMA casing for testing, with care to insure correct alignment of the ACJ and mounted on the Material testing machine (model 8874; Instron, Norwood, MA) with a 250-N capacity load cell (Dynacell; Instron).

A base line dynamic testing of each specimen will be conducted at 70N and reduced cycles

Constructs will be inserted while specimen is loaded in machine to ensure replication of normal anatomy for each specimen. The ACJ capsule and CC ligaments will then be divided and Dynamic testing will be conducted.

Outcomes:

1. Superior Displacement of clavicle as measure by the material testing machine and surrogate for clinical displacement seen after fixation.
2. Dynamic Creep
3. Peak-to-peak displacement and;
4. relaxed elongation.

Outcomes of three groups will then compared for clinical significance via statistical methods

Ethics and Governance

Approved by Northern Sydney Local Health District Human Research Ethics Committee. HREC reference 2019/ETH08332.

Status

Data Analysis.