7. Biomechanics Flashcards
hallux interphalangeal angle:
normal range
normal is 0-10 degrees
distal articular set angle (DASA):
normal range
normal: 7.5 degrees
proximal articular set angle (PASA):
normal range
normal: 7.5 degrees
Types of joint deformities
(hint: 3 types)
- Congruent – joint lines are parallel
- Deviated – joint lines intersect outside joint
- Subluxed – joint lines intersect inside joint
3 types of bunion deformities
- Structural
- Positional
- Combined
structural bunion deformities:
characteristics
- Bony deformity
- Abnormal PASA and DASA
- PASA + DASA = HA
positional bunion deformities
characteristics
- Soft tissue deformity with subluxed or deviated joint
- Normal PASA and DASA
- PASA + DASA < HA
combined bunion deformities:
characteristics
- Elements of both structural and positional with subluxed or deviated joint
- Abnormal PASA and DASA
- PASA + DASA < HA
hallux abductus angle:
normal range
normal: 10-15 degrees
true intermetatarsal (IM) angle:
normal range
Normal: 8-12°
mild increase (10-13°) in IM angle:
type of procedure
Head procedure if mild 10-13°
moderate increase (14-17°) in IM angle:
type of procedure
Shaft procedure if moderate 14-17°
severe increase (18-21°) in IM angle:
type of procedure
Base procedure if severe 18-21°
procedure for hypermobile 1st ray
Lapidus procedure if hypermobile 1st ray
(recall: involves fusing the joint between the first metatarsal bone and the medial cuneiform)
metatarsus adductus angle:
normal range
normal: <20 degrees
(recall: bisect tarsus; distal MC, proximal MC, base of 4th Met, tip of CC joint)
true IM angle:
calculation
True IM angle = (metatarsus adductus angle - 15) + IM angle
1st Metatarsal protrusion distance:
normal range
Normal +/- 2 mm compared to the 2nd metatarsal
tibial sesamoid position:
normal range
normal: 1-3
* (recall: tibial sesamoid in relation to line that bisects 1st metatarsal)*
1st MPJ: normal ROM
- 65-75° dorsiflexion and
- 40° plantarflexion
1st Metatarsal-medial cuneiform angle:
normal range
Normal: 22°
1st ray:
normal ROM
- 5 mm dorsiflexion + 5 mm plantarflexion = 1 cm total ROM
Engel’s angle:
normal range
Normal: <24 degrees
(recall: bisect intermediate cuneiform, bisect 2nd ray)
Meary’s angle:
normal range
Normal: up to 15 degrees
(recall: angle b/w line drawn from the centers of longitudinal axes of talus and 1st metatarsal)
1st MPJ condition:
how to determine, and the 3 types
- draw line parallel to articular surface of MT and base of PP
- types:
- congruous: lines are parallel and do not intersect
- deviated: lines intersect OUTSIDE joint
- subluxed: lines intersect WITHIN the joint
1st MPJ joint space:
normal value
2 mm width, uniform
1st and 2nd MT shaft comparison:
normal
should be parallel
(recall: look at shaft of 1st metatarsal and compare it to shaft of 2nd metatarsal)
Seiberg index:
calculation
-
distal – proximal = Seiberg’s index
- Positive with dorsal angulation → elevatus
- (recall: perpendicular distance [mm] from the dorsal aspect of the 2nd met shaft to the dorsal aspect of the 1st met.*
- 2 points = one at the neck, and the other at 1.5 cm from the 1st met base)
Fallat & Buckholz 4th IM angle
(aka 4-5 IM angle):
normal range
- Normal: 6°
- Pathologic: 8.7°
(recall: angle between bisection of 4th metatarsal and proximal-medial cortical border of 5th metatarsal)
Fallat & Buckholz Lateral Deviation angle (lateral bowing):
normal range
- Normal 2.64°
- Pathologic >8°
(recall: Angle of line bisecting head and neck of 5th met and line adjacent to proximal-medial cortex)
metatarsal length:
longest → shortest
Longest 2 > 3 > 5 > 4 > 1 shortest
metatarsal protrusion:
longest → shortest
Longest 2 > 3 > 1 > 4 > 5 shortest