Lecture 7: Engineering the Musculoskeletal System Flashcards
What are the largest shoulder muscles?
the three most superficial shoulder muscles which are the deltoid, latissimus dorsi and pecs (prime movers)
What is the role of the rotator cuff muscles?
prevent shoulder joint dislocation
What is the role of force couples in the shoulder?
keeps the humerus pressed up against the shoulder joint at all times
What are examples of force couples in the shoulder joint?
transverse plane: the subscapularis and infraspinatus force couple
scapular plane: the deltoid and the infraspinatus / subscapularis / teres minor force couple
What is anatomic shoulder arthroplasty used to treat?
end-stage osteoarthritis, severe pain, reduced range of motion, and loss of muscle strength
How many people will experience a rotator cuff tear?
50% of people in their seventh decade, and over 80% of people over the age of 80 will suffer a full-thickness rotator cuff tear
What are the symptoms of a rotator cuff tear?
pain, shoulder instability, shoulder dislocation, loss of shoulder movement and inability to perform activities of daily living
What is reverse total shoulder arthroplasty used in the treatment of?
rotator cuff tear arthropathy (when the glenohumeral joint is unstable), but also trauma and tumour resection
How is muscle and joint function quantified after reverse total shoulder arthroplasty?
muscle moment arms, muscle lines of action, muscle forces and joint forces
What is the muscle moment arm?
the perpendicular distance between a muscle’s line of action and the joint centre of rotation in which it spans -> muscle leverage
Which muscle has the largest muscle moment arm in early elevation?
the supraspinatus
Which muscle has the largest muscle moment arm in mid-late elevation?
the deltoid
Which muscle has a large negative muscle moment arm? What makes it negative?
the latissimus dorsi
negative because it is involved in adduction as opposed to the other muscles which have positive muscle moment arms and are involved in abduction
How does reverse total shoulder arthroplasty affect muscle moment arms?
significant increase in the mean abduction moment arm of anterior deltoid and middle deltoid
What is the muscle line of action? What does the muscle line of action confer?
the unit vector direction of the force produced by a muscle
it confers muscle stabilising or destabilising potential
How does reverse total shoulder arthroplasty affect muscle line of action?
the rotator cuff muscles are less inferiorly inclined and the deltoid muscles are more superiorly inclined
How can muscle forces be estimated?
cannot be measured (non-invasively)
patient-specific musculoskeletal models can estimate muscle forces using physiological cost functions and constraints
How are muscle force models derived and validated?
using experimental data e.g. cadaveric testing, instrumented implants etc.
How does reverse total shoulder arthroplasty affect muscle forces in the deltoids and rotator cuff muscles and why? Where do muscle force peaks occur?
significantly smaller muscle forces (due to larger lever arms)
muscle force peaks occur at different joint positions
What is the overall effect of RTSA?
⬆ in muscle moment arms reduces muscle forces (greater range of motion, improved joint function)
this ultimately ⬇ joint compression, which may lead to dislocation
more superior joint shear compression occurs
What are the issues associated with TMJ prosthetics?
only two implant suppliers
three sizes fit all?
risk of nerve damage
poor fit in cases of complex anatomy
What is the strategy for developing a TMJ prosthetic?
problem definition -> musculoskeletal model development -> design of prosthetic TMJ -> evaluate / iterate design using musculoskeletal model -> cadaveric testing -> 1st prosthesis recipient
What is an important factor that must be determined before a prosthetic can be used in patients?
implant loading
How is implant loading determined?
need to solve a mathematical problem: input is bite force, outputs are muscle forces and TMJ force
then, use calculated forces to drive finite element model simulation of implant loading
How is bite force determined?
subject bites a rubber measuring device -> development of a subject-specific musculoskeletal model -> decomposing bite force into individual muscle forces -> musculotendon parameters scaled from a previous dataset
Why is reverse shoulder arthroplasty performed?
to restore shoulder function in cases of rotator cuff tears and end-stage OA (i.e. rotator cuff tear arthropathy), improves joint stability but can present risk of superior subluxation
In this lecture what does computational modelling and 3D printing facilitate?
personalised implant development for the jaw, with cost and practical benefits
