Patella: luxation in Horses (Equis) | Vetlexicon
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Patella: luxation

ISSN 2398-2977


Introduction

  • Cause: uncommon congenital or rare acquired (secondary to joint disease Musculoskeletal: osteoarthritis (joint disease) or trauma to stifle) disorder.
  • Signs: hindlimb lameness, may be uni- or bilateral, stifle swelling, abnormal gait.
  • Diagnosis: manual examination, radiography.
  • Treatment: surgery.
  • Prognosis: poor to guarded for athletic career.

Presenting signs

  • Hindlimb lameness or abnormal gait; uni- or bilateral.

Acute presentation

  • Acute onset severe lameness in traumatic cases.

Age predisposition

  • Foals (congenital).
  • Adults (acquired).

Breed/Species predisposition

Cost considerations

  • Costs of diagnosis and treatment.
  • Loss of use of animal.

Pathogenesis

Etiology

  • Luxation of the patella is usually lateral due to the larger medial trochlear ridge of the distal femur. Medial displacement is normally only seen following trauma to the region.
  • Congenital malformation and hypoplasia of the femoral trochlea, particularly the lateral ridge, is commonly associated with lateral luxation, although the condition can occur in foals with apparently normal conformation.
    • In some breeds it is an inherited condition caused by a monogenic autosomal recessive gene.
    • Usually presents in the young foal.
  • In the adult horse, luxation of the patella is much less common and usually related to a traumatic incident. In traumatic cases, luxation can be medial, lateral or even distal.
  • Rarely, severe osteochondrosis Bone: osteochondrosis lesions of the lateral trochlear ridge can lead to loss of the bone structure and secondary lateral luxation. This has been seen in older foals and yearlings, often with very straight hindlimb conformation.

Predisposing factors

General

  • Breed.
  • Previous stifle injury/disease.

Specific

  • Abnormal conformation of the femoropatellar joint.

Pathophysiology

  • Congenital abnormality in the topography of the femoropatellar joint, eg shallow trochlea groove / hypoplastic trochlear ridges → quadriceps flexion pulls patella laterally.
  • Femoropatellar joint disease: osteoarthritis Musculoskeletal: osteoarthritis (joint disease), osteochondrosis Bone: osteochondrosis → remodeling of the trochlea ridges → loss of normal tracking for patella → luxation.
  • Trauma to patella ligaments → patella instability → luxation.

Diagnosis

Presenting problems

  • Hindlimb lameness.

Client history

  • Abnormal gait.
  • Reluctance to move.
  • Inability to stand (foals).

Clinical signs

  • Condition can be unilateral or bilateral.
  • Lateral luxation is the most common in the congenital form, but medial cases are occasionally reported.
  • Graded as follows:
    • Grade 1: patella can be manually luxated but readily reduces itself.
    • Grade 2: patella usually in place but luxates intermittently.
    • Grade 3: patella is usually luxated but can be manually relocated.
    • Grade 4: patella is continuously luxated and cannot be relocated.
  • Severely affected foals are unable to extend the stifle and stand in a characteristic crouching position.
  • Less severe cases may not show obvious signs but are often reluctant to flex the stifle, may have a moderate lameness, or have a stiff gait in the affected limb. Mild distension of the femoropatellar joint may be present.
  • In some cases, there are minimal clinical signs until degenerative joint disease Musculoskeletal: osteoarthritis (joint disease) occurs in the femoropatellar joint/s secondary to the low-grade luxation and instability in the joint.
  • Foals with severe lateral ridge osteochondrosis lesions and secondary lateral luxation are often lame, with distended femoropatellar joints.
  • Manual examination → luxation of patella.
  • Gait evaluation Musculoskeletal: gait evaluation.
  • Traumatic injuries of the stifle leading to patellar luxation are usually unilateral and may have signs of soft tissue injury and lameness. Lameness is variable but often acute onset and severe.
  • Luxation can be lateral , medial or distal.

Diagnostic investigation

Radiography

  • Radiography of the stifle Hindlimb: radiography.
  • Lateromedial, cranioproximal-craniodistal oblique, and caudocranial views are required to ascertain the position of the patella, evaluate the trochlear ridges, and the presence of any bony abnormalities.

Ultrasonography

  • Can be used to assess the position of the patella, shape and size of the trochlear ridges, the patellar ligaments, and soft tissue injuries Ultrasonography: bone/joints.

Confirmation of diagnosis

Discriminatory diagnostic features

  • Signs.

Definitive diagnostic features

  • Manual examination/palpation.
  • Radiography.
  • Ultrasonography.

Differential diagnosis

Treatment

Initial symptomatic treatment

Standard treatment

Surgery

  • Medial imbrication combined with a lateral release incision of the joint capsule; or medial imbrication of peripatellar fascia to the tendon of the sartorius muscle - to counter lateral pull of quadriceps and biceps fascia.
  • Recession wedge sulcoplasty or trochleoplasty - to deepen the trochlear groove in the presence of hypoplastic trochlear ridges.
  • A medial traumatic luxation in a pony was treated by transection of the medial femoropatellar ligament allowing patella release, followed by a prosthetic suture to replace the lateral femoropatellar ligament and reinforcement of the lateral retinaculum with a mesh implant.

Monitoring

  • Standard post-anesthetic and surgery monitoring.

Subsequent management

Treatment

Monitoring

  • Gradual return to normal management and exercise as determined by specific surgery carried out.

Prevention

Group eradication

  • Do not breed from affected animals.

Outcomes

Prognosis

  • Poor for cases with joint osteoarthritis, severe osteochondrosis or in larger horses.
  • Guarded in miniature breeds kept as pets with conservative treatment.
  • Guarded to fair for an athletic career with surgery as a foal.

Expected response to treatment

  • Improvement in gait.

Reasons for treatment failure

  • Complications associated with surgery, eg wound infection, incision dehiscence, septic arthritis, osteoarthritis.
  • Development of luxation in contralateral limb.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Hall M S, Jalim S L & Russell T M (2010) Distal luxation of the patella in a horse. Aust Vet J 88 (10), 396-398 PubMed.
  • O'Meara B & Lischer C J (2009) Surgical management of a pony with a traumatic medial luxation of the patella. Equine Vet Educ 21 (9), 458-463 VetMedResource.
  • Busschers E (2009) Patellar luxation in horses: Treatment and prognosis. Equine Vet Educ 21 (9), 464-466 Wiley Online Library.
  • Milner P (2009) Lateral patellar luxation associated with severe osteochondritis dissecans (OCD) of the lateral trochlear ridge. UK Vet 14 (7), 5-6 VetMedResource.
  • Hart J C A, Jann H W & Moorman V J (2009) Surgical correction of a medial patellar luxation in a foal using a modified recession trochleoplasty technique. Equine Vet Educ 21 (6), 307-311 VetMedResource.
  • Talbot A M & Singer E R (2009) Luxation of the patella in foals. Equine Vet Educ 21 (6), 313-314 VetMedResource.
  • Englebert T A et al (1998) Lateral patellar luxation in miniature horses. Vet Surg 22 (4)293-297 PubMed.
  • Kobluk C N (1998) Correction of patellar luxation by recession sulcoplasty in three foals. Vet Surg 22 (4)298-300 PubMed.
  • Hermans W A, Kersjes A W, van der Mey G J & Dik K J (1987) Investigation into the heredity of congenital lateral patellar (sub)luxation in the Shetland pony. Vet Q (1), 1-8 PubMed.