Hypothesis One: Trauma

Trauma is evident in the past history as a fall from the bed.  Trauma could damage 
muscle, nerves, bone, or ligaments.  
The muscle groups we are concerned with in this case are the hamstrings and 
quadriceps.  Possible muscle damage includes tears, strains or pressure necrosis.  The 
type of injury depends on the type of trauma.  We can likely rule out muscle trauma due 
to the long duration of time between the fall and the current presentation.  Muscle damage 
should usually heal in approximately six weeks.  
The nerves vulnerable in the stifle are the ischiatic (which branches into the tibial) 
and the saphenous.  Nerve damage can be classified in three ways: complete nerve 
division (neurotmesis) in which you would see complete paralysis, damage to axons 
(axonotmesis) leading to peripheral degeneration, and simple contusion which causes a 
temporary loss of function recovering in two weeks.  The clinical signs do not point to 
nerve damage.  However, a further neurological exam is necessary to rule out this option.
The proximal tibia, distal femur and the patella are bones in the stifle that are 
susceptible to trauma.  Although no fracture was diagnosed or treated immediately after 
the fall, improper healing of an undiagnosed fracture could result in mal-alignment.  A 
common sequela is abnormal stress on the joint leading to arthritis changes.  
There are many ligaments in the stifle area.  Ligament rupture as a direct result of 
trauma will cause joint laxity.  This can lead to osteoarthritic changes and subsequent 
pain.  As the joint architecture changes ligaments undergo hyalinization, reducing tensile 
strength and leaving the joint vulnerable to further injury.  After a long-standing rupture 
of a ligament, chronic proliferative changes of the menisci, joint capsule, and supporting 
structures may stabilize the joint.  Therefore, the free sliding movements of the tibia the 
meniscus damage may be harder to palpate or demonstrate during the initial physical 
exam.