Flexion test

A flexion test is a preliminary veterinary procedure performed on a horse, generally during a prepurchase or a lameness exam. The animal's leg is held in a flexed position for 30 seconds to up to 3 minutes (although most veterinarians do not go longer than a minute), and then the horse is immediately trotted off and its gait is analyzed for abnormalities and uneveness.^[1] The flexion places stress on the joint capsule and soft tissue of the joint, and sometimes the cartilage and bone, usually accentuating any lameness that is present, such as arthritis. The horse may take a few uneven steps, or may be lame for several minutes following the procedure.^[2]

Specificity

Flexion tests are rather nonspecific, as each test flexes multiple joints (such as the stifle and the hock, or the pastern and the navicular area). So while they can help localize a lameness issue to one particular leg, or even to a few joints in the leg, they can not pinpoint it.^[3] In lameness exams, the next step is usually to perform nerve blocks to help localize, confirm, or rule out a suspected source of lameness. A local anesthetic is injected in a specific joint and sensation is temporarily inhibited.^[4] Once the area is sufficiently numbed, another flexion test is performed. If the horse is no longer lame, the joint or area where the block was performed is the likely site of the problem. If the horse is still lame, another site may be blocked and more flexion tests performed.

False positives may occur, however, especially if excessive force was placed on the joint, and many horses can continue to perform their jobs quite well despite having "failed" a flexion test. It is therefore important for owners to continue to perform diagnostics if they suspect there is a problem. Additionally, a veterinarian may flex both fore or hindlimbs separately for comparison, to determine which limb is experiencing an unknown lameness, or if the few uneven steps are "normal" for the horse.^[5]

Gait evaluation

A horse's walk and trot are most useful in gait analysis. The veterinarian looks for signs, such as shortening of the stride, irregular foot placement, head bobbing, stiffness, weight shifting, etc. The walk makes it easier to observe slight deviations that aren't readily apparent at a faster pace. However, the trot is perhaps most useful for evaluating lameness because it is the simplest gait, consisting of a two-beat stride pattern, and because the horse's weight is distributed evenly between diagonal pairs of legs. In some cases the speed and concussion of a faster pace (i.e. canter, gallop) is needed to help demonstrate the lameness.^[6]

Grading lameness

A grading system that accurately describes and categorizes the severity of lameness helps veterinarians, owners, and trainers communicate effectively. "Severe" lameness to one person may only be "moderate" to another. The system also makes it easier to refer back to earlier findings when performing a repeat examination. A scale from 0 to 5 (see example below) is most commonly used to grade the lameness, though some veterinarians may use others (using halves or a 1 to 10 scale). The surface a horse is worked on can also affect the perceived grade of lameness, with harder surfaces such as asphalt making it worse or more apparent. These two factors make it important to provide the context in which the lameness was graded, such as: grade 2 out of 5 or 2/5 on sand and grade 3/5 on pavement.^[7]

Degrees of lameness

• Grade 0 - Lameness not perceptible under any circumstances.

• Grade 1 - Lameness is difficult to observe and is not consistently apparent, regardless of circumstances (e.g. under saddle, circling, inclines, hard surface, etc.).

• Grade 2 - Lameness is difficult to observe at a walk or when trotting in a straight line but consistently apparent under certain circumstances (e.g. weight-carrying, circling, hard surface, etc.).

• Grade 3 - Lameness is consistently observable at a trot under all circumstances.

• Grade 4 - Lameness is obvious at a walk.

• Grade 5 - Lameness produces minimal weight bearing in motion and/or at rest or a complete inability to move.^[8]

Usefulness

Though flexion tests are a rather common veterinary procedure, the exact duration has not been widely agreed upon by veterinarians. Multiple studies have been done on the length and force applied during the test and devices have even been created to measure the force applied. Such tools are not commonly used in practice though which affects consistency. Unfortunately, a positive response to forelimb flexion tests, meaning lameness was evident after the limb was released and the horse trotted away, is one reason horses may be deemed unsuitable for purchase during the prepurchase exam. The wide range of significance attributed to these tests varies according to opinion and the experience of the examiner. While there have been many purchase exams discontinued solely because a positive response to a flexion test in one or both forelimbs, there’s really nothing in the veterinary literature to support such an action. Due to the variable response to the test depending on such things as the force applied, duration of the test, age of the horse and the day of examination, discontinuation of a prepurchase examination based solely on a failed forelimb flexion test is probably unwarranted.^[9]

Notes

References

• King, Christine, BVSc, MACVSc, and Mansmann, Richard, VDM, PhD. (1997). Equine Lameness. Equine Research, Inc.
• Ramey, David. "Flex Test", (2008, May). Retrieved from American Association of Equine Practitioners: http://www.aaep.org/health_articles_view.php?id=88
• Ramey, David. (1997). "Prospective Evaluation of the Forelimb Flexion Tests in Practice: Clinical Response, Radiographic Correlations, and Predictive Value for Future Lameness". AAEP Proceedings. Vol 43, p. 116-120.
• "Lameness Exams: Evaluating the Lame Horse", (2005, June). Retrieved from American Association of Equine Practitioners: http://www.aaep.org/health_articles_view.php?print_friendly=true&id=280