Overview of Lameness in Horses

Definition and Fundamental Nature

Clinical Definition: An abnormal stance or gait caused by structural or functional disorders of the locomotor system.
Core Symptom: The horse is either unwilling or unable to stand or move normally.
Significance: It is the most common cause of loss of use in horses.
Disease Status: It is not a disease itself, but a clinical sign of underlying pain, mechanical restrictions, or altered neuromuscular function.

Primary Classifications

Pain-Based Lameness:
- The most common cause of lameness in all horses.
- Weight-Bearing (Supporting Leg): Reduction in the amount of time or force applied to the limb while on the ground.
- Non-weight Bearing (Swinging Leg): Reduction in the "swing phase" of the stride.
- Treatment Indicator: Generally responds well to systemic or local analgesics and anti-inflammatory drugs.
Mechanical Lameness:
- Caused by physical restrictions or neuromuscular disorders rather than pain.
- Examples: Upward fixation of the patella, fibrotic myopathy, and stringhalt.
- Diagnostic Clue: Typically does not respond to analgesics.
- Characteristic Gaits:
  - Fibrotic Myopathy: Foot "slaps down" quickly at the walk.
  - Stringhalt: Affected limb is hyperflexed during the swing phase.

Clinical Indicators and Observation

- Forelimb Signs: Most easily recognized by a head nod.
- Hindlimb Signs: Characterized by a sacral rise (also known as a pelvic rise or hip hike).
- Visual Assessment Protocols:
  - Side View: Allows assessment of the arc of foot flight, duration of protraction/retraction, and length of weight-bearing.
  - Rear View: Best for observing the sacral rise.
  - Circular Movement: Lameness is often accentuated when the affected limb is on the inside of a circle.

Predisposing and Inciting Factors:

Predisposing Factors (Internal/Environmental):
- Physical immaturity (early training of foals).
- Preexisting developmental orthopedic diseases (e.g., osteochondrosis).
- Poor conformation or improper hoof balance/shoeing.
- Hard, slippery, or rocky surfaces.
Inciting Factors (Immediate Causes):
- Direct or indirect trauma.
- Fatigue leading to muscle incoordination.
- Inflammation and infection.
- Early Warning Signs: Failure to notice reduced training times or resistance to lead changes.

Secondary Lameness and Compensation:

The Chain Effect: Lameness in one area often leads to soreness in another part of the same limb or the contralateral limb due to compensation.
Holistic Evaluation: The entire horse must be assessed even when the primary cause seems obvious.
Severe Complication: Biomechanical laminitis can develop in the "normal" limb if it is forced to bear excessive weight due to a severe injury on the opposite side.

Overview of Lameness in Horses

Definition and Fundamental Nature

Clinical Definition: An abnormal stance or gait caused by structural or functional disorders of the locomotor system.

Core Symptom: The horse is either unwilling or unable to stand or move normally.

Significance: It is the most common cause of loss of use in horses.

Disease Status: It is not a disease itself, but a clinical sign of underlying pain, mechanical restrictions, or altered neuromuscular function.

Primary Classifications

Pain-Based Lameness:

The most common cause of lameness in all horses.

Weight-Bearing (Supporting Leg): Reduction in the amount of time or force applied to the limb while on the ground.

Non-weight Bearing (Swinging Leg): Reduction in the "swing phase" of the stride.

Treatment Indicator: Generally responds well to systemic or local analgesics and anti-inflammatory drugs.

Mechanical Lameness:

Caused by physical restrictions or neuromuscular disorders rather than pain.

Examples: Upward fixation of the patella, fibrotic myopathy, and stringhalt.

Diagnostic Clue: Typically does not respond to analgesics.

Characteristic Gaits:

Fibrotic Myopathy: Foot "slaps down" quickly at the walk.

Stringhalt: Affected limb is hyperflexed during the swing phase.

Clinical Indicators and Observation

Forelimb Signs: Most easily recognized by a head nod.

Hindlimb Signs: Characterized by a sacral rise (also known as a pelvic rise or hip hike).

Visual Assessment Protocols:

Side View: Allows assessment of the arc of foot flight, duration of protraction/retraction, and length of weight-bearing.

Rear View: Best for observing the sacral rise.

Circular Movement: Lameness is often accentuated when the affected limb is on the inside of a circle.

Predisposing and Inciting Factors:

Predisposing Factors (Internal/Environmental):

Physical immaturity (early training of foals).

Preexisting developmental orthopedic diseases (e.g., osteochondrosis).

Poor conformation or improper hoof balance/shoeing.

Hard, slippery, or rocky surfaces.

Inciting Factors (Immediate Causes):

Direct or indirect trauma.

Fatigue leading to muscle incoordination.

Inflammation and infection.

Early Warning Signs: Failure to notice reduced training times or resistance to lead changes.

Secondary Lameness and Compensation:

The Chain Effect: Lameness in one area often leads to soreness in another part of the same limb or the contralateral limb due to compensation.

Holistic Evaluation: The entire horse must be assessed even when the primary cause seems obvious.

Severe Complication: Biomechanical laminitis can develop in the "normal" limb if it is forced to bear excessive weight due to a severe injury on the opposite side.