Upper Limb Biomechanics Revision

Question 1

What injuries are the biceps susceptible to and why?

Answer 1

They are susceptible to tears and tendinopathy

Commonly injured due to a mechanical disadvantage
- long lever arm
- large distance from load to axis of rotation
▶️ subsequently biceps tension is 7 times the load
- muscle attachments very close to axis of rotation

Also significant joint compression

Question 2

What is the dial overload of the elbow?

Answer 2

Valgus moments of 120Nm
MCL failure at 34 Nm
Radial capitellum compression 500 Nm
Dynamic stabilisers are vital
- flexor carpi ulnar is and flexor digitorum superficialis
- flexor pronator mass, biceps, medial triceps

Question 3

What is Valgus extension overload?

Answer 3

Valgus and hyper extension
Compression
- lateral and posterior medial joint
- microfractures, osteophytes, loose bodies

Question 4

What are the common elbow pathologies in the skeletally immature?

Answer 4

In the skeletally immature medial epicondyle is the first point of failure
- little leaguers elbow
▶️ medial apophysitis

• lateral side - radiocapitellar osteochondritis dissecans
  ▶️ pain in the joint
  ▶️ anconeus soft spot
  ▶️ if swollen and painful = refer immediately

Question 5

What are the functions of the coracohunoral ligament and superior glenohumoral ligament?

Answer 5

Ligaments crucial to stability
It is a dependent arm support
Limits external rotation below 60degrees of abduction
Restricts movements inferiorally

Question 6

What is the function of the medial glenohumoral ligament?

Answer 6

It is at 2-3o’clock on the capsule
Anterior stability at 45degrees
Limits external rotation

Question 7

What is the function of the inferior glenohumoral ligament complex?

Answer 7

It is the most important ligament
Critical for stability
Prevents dislocation at extreme ROM
Has 3 sections:
- anterior band
- axillary pouch
- posterior band

Question 8

What is the function of the posterior capsule?

Answer 8

It is thin but very important
It restricts medial rotation and horizontal flexion
Works with anterior/superior capsule to prevent posterior dislocation

Question 9

What contributes to Elbow Laxity?

Answer 9

Primary Constraints:
- Ulnohumoral articulation
- anterior medial collateral ligament
- lateral collateral ligament complex
▶️ primary constraints alone cause gross laxity

Secondary constraints:
- radiohumoral articulation
- common extensor tendon
- common flexor pronation tendon
- capsule
▶️ secondary constraints alone won’t cause gross laxity
▶️ together with primary constraints = grossly lax elbow