Class of October 2010


Active stabilizers (muscles) are responsible for joint stability; passive stabilizers are loaded only when active structures fail in their function.
Yet, pathologies of passives structures (lesions of ligaments, capsule...) can lead to a disturbed proprioception (erroneous afferent signals), which induces in turn wrong efferent signals (incorrect pattern of muscular contractions).
A disturbed senso-motorical process is responsible for instability.


Improvement of stability = improvement of muscle control (not of strength)
Control is based upon slow twitch fibres (small motor units > finer movements)
Strength is based upon fast twitch fibres
Slow twitch fibres depolarization threshold lower than fast twitch threshold.

?Older people are more unstable because nerves get thinner and thus speed of conduction decreases (the higher the diameter, the faster the conduction)?

Testing of global stability of knee joint

Walk forward, walk backward, run, jump using both legs (no adjustment step allowed), jump using 1 leg (1 adjustment step allowed)

> Stand on one leg, stand on one leg and perform short flexion movements
> Push patient backward: expected response: 1st contraction of tibialis anterior, 2nd contraction of quadriceps
> Push patient forward: expected response: 1st contraction of calves, 2nd contraction of hamstrings

Standing: quadriceps must be relaxed > patella mobile, patella centred (no squinting or frog eyes), apex of patella at the altitude of joint space, contraction of quadriceps (must rise patella)


With eyes closed:
> PT moves healthy leg, patient performs simultaneously identical movement with unstable leg
> PT moves healthy leg to a given position, patient moves unstable leg to identical position (if necessary PT corrects error)
> Patient moves both legs in opposite directions with a precise timing, one leg must reach 90° of flexion when the other reach full extension (the slower the more difficult)

Testing of passive structures with related instability

MEDIAL instability = Medial Collateral Ligament (MCL)
> Valgus (ABD) test at 0° (locked) and at 30° (unlocked)

LATERAL instability = Lateral Collateral Ligament (LCL)
> Varus (ADD) test at 0° (locked) and at 30° (unlocked)

ANTERIOR instability = ACL
> Lachman test (or modifications) (ACL + POL)
> Anterior Drawer sign (ACL + Post. Capsule)

POSTERIOR instability = PCL
> Posterior Drawer sign (PCL + Arcuate-politeus complex)
> Posterior sag sign (Drawer gravity) (PCL + Arcuate-politeus complex)

ANTERIOR + MEDIAL instability = MCL + ACL
> Slocum test (= Drawer) with tibia in LATERAL rotation (MCL + ACL)

ANTERIOR + LATERAL instability = ACL
> Slocum test (= Drawer) with tibia in MEDIAL rotation (ACL + Post. Lat. Capsule)
> Lateral Pivot shift (ACL + Post. Lat. Capsule)
Based upon action of iliotibial band: extensor when knee extended, flexor when knee flexed from 30°
Knee in extension and medial rotation > flexion by examiner reduces subluxation by action of iliotibial band

> Hughston's postero-medial drawer sign (PCL + POL)
= Drawer with knee medially rotated

> Hughston's postero-lateral drawer sign (PCL + popliteus-arcuate complex)
= Drawer with knee laterally rotated

As a reminder about MENISCUS:
> Bounce home test = ventral part
> Apley's test = middle part (most frequently injured)
> Mac Murray's test = dorsal part