Canis ISSN: 2398-2942

Patella: medial luxation

Contributor(s): Joseph Harari, Gareth Arthurs

Introduction

  • Much more common than lateral luxation Patella: lateral luxation.
  • Degree of patellar instability is classified into 4 grades of increasing severity and complexity. According to the simplified patellar luxation grading system:
    • Grade 1: subclinical. The patella does not luxate through a normal range of stifle movement unless it is directly luxated by the examiner; as soon as manipulation is finished, it returns to the trochlear sulcus.
    • Grade 2: the patella luxates when the stifle is placed through a normal range of movement, usually on flexion from full extension. Severity of luxation frequency may range from only occasionally to very frequent.
    • Grade 3: permanent luxation but the patella can be manually returned (reduced) to the femoral trochlear sulcus by the examiner, but as soon as the examiner finishes manipulation, the patella luxates again.
    • Grade 4: permanent luxation and the patella cannot be returned to the femoral trochlear sulcus.
  • Signs: acute/intermittent unilateral/bilateral hindlimb lameness, usually non-painful.
  • Cause: developmental (common); trauma (rare).
  • Diagnosis: clinical (primary) and radiographic examinations (secondary).
  • Treatment: conservative or surgical correction.
  • Prognosis: overall good. Higher grades (3 and 4) are more challenging surgically with a higher rate of complications including patella relaxation. 
    Print off the owner factsheet Luxating patella Luxating patella to give to your client.
Use the interactive tool from ROYAL CANIN® UK  to explain dog anatomy and disease conditions to your client. Visit ROYAL CANIN Natom Explorer to find out more.​

Pathogenesis

Pathophysiology

1. Developmental - most common

  • Developmental abnormality leads to patella deviating from normal plane of tracking in the femoral trochlear sulcus. Contributary factors include:
    • Femoral varus = medial bowing.
    • Abnormal development of femoral trochlea whereby medial trochlear ridge is poorly developed, or the sulcus is too shallow.
    • Torsion of the proximal tibia with medial position of the tibial tuberosity.
    • These can all lead to:
      • Abnormal alignment of the quadriceps mechanism (quadriceps, patella, patella ligament and tibial tuberosity) relative to the trochlea sulcus.
      • Intermittent or permanent luxation of the patella.
      • In severe cases a new shallow "pseudo" sulcus can develop on the medial aspect of the femoral trochlea.
      • Abnormal medial-lateral movement of the patella can cause full thickness cartilage erosion, particularly on the articular caudal aspect of the patella.
      • Degenerative joint disease/arthritis Arthritis: osteoarthritis, but in most cases this is mild.

2. Concurrent cruciate rupture - uncommon

  • Severe stifle instability associated with cranial cruciate ligament rupture and patellar luxation.
  • Some dogs have pre-existing patellar luxation, but others seem to develop patellar luxation secondary to cruciate rupture. In some dogs it can be difficult to know which condition was present first, or which exacerbates the other.
These are all challenging cases to manage with a potentially high complication rate.

3. Traumatic - rare

Timecourse

  • Chronic/insiduous onset - majority of cases (common).
  • Progressively deteriorating lameness may be seen with patellar luxation of progressively increasing severity in puppies 6-12 months of age (infrequent).
  • Acute onset may be seen with traumatic luxation (rare) or concurrent cruciate rupture (uncommon).

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Bosio F, Bufalari A, Perione B, Petazzoni M, Vezzoni A (2017) Prevalence, treatment and outcome of patellar luxation in dogs in Italy. A retrospective multicentre study. Vet Comp Orthop Traumatol 30 (5), 364-370 PubMed.
  • Brower B E, Kowaleski M P, Peruski A M, Pozzi A, Dyce J, Jonson K A, Boudrieau R J (2017) Distal femoral lateral closing wedge osteotomy as a component of comprehensive treatment of medial patellar luxation and distal femoral varus in dogs. Vet Comp Orthop Traumatol 30 (1), 20-27 PubMed.
  • Newman M, Voss K (2017) Computed tomographic evaluation of femoral and tibial conformation in English Staffordshire Bull Terriers with and without congenital medial patellar luxation. Vet Comp Orthop Traumatol 30 (3), 191-199 PubMed.
  • Dunlap A E, Kim S E, Lewis D D, Christopher S A, Pozzi A (2016) Outcomes and complications following surgical correction of grade IV medial patellar luxation in dogs: 24 cases (2008-2014). JAVMA 249 (2), 208-213 PubMed.
  • Leonard K C, Kowaleski M P, Saunders W B, McCarthy R J, Boudrieau R J (2016) Combined tibial plateau levelling osteotomy and tibial tuberosity transposition for treatment of cranial cruciate ligament insufficiency with concomitant medial patellar luxation. Vet Comp Orthop Traumatol 29 (6), 536-540 PubMed.
  • Cashmore R G, Haveliceck M, Perkins N R, James D R, Fearnside S M, Marchevsky A M, Black A P (2014) Major complications and risk factors associated with surgical correction of congenital medial patellar luxation in 124 dogs. Vet Comp Orthop Traumatol 27 (4), 263-270 PubMed.
  • Arthurs G I, Langley-Hobbs S J (2006) Complications associated with corrective surgery for patellar luxation in 109 dogs. Vet Surg 35 (6), 559-566 PubMed.
  • Gibbons S E, Macias C, Tonzing M A, Pinchbeck G L, McKee W M (2006) Patellar luxation in 70 large breed dogs. JSAP 47 (1), 3-9 PubMed.
  • Johnson A L, Probst C E, Decamp C E, Rosenstein D S, Hauptman J G, Weaver B T, Kern T L (2001) Comparison of trochlear block recession and trochlear wedge recession for canine patellar luxation using a cadaver model. Vet Surg 30 (2), 140-150 PubMed.
  • Hayes A G, Boudrieau R J & Hungerford L L (1994) Frequency and distribution of medial and lateral patellar luxation in dogs - 124 cases (1982-1992). JAVMA 205 (5), 716-720 PubMed.
  • Remedios A M, Basher A W, Runyan C L & Fries C L (1992) Medial patellar luxation in 16 large dogs - a retrospective study. Vet Surg 21 (1), 5-9 PubMed.

Other sources of information

  • (2016) The Stifle Joint. In: Brinker Piermattei & Flos' Small Animal Orthopedics and Fracture Repair. Eds DeCamp, Johnston, Dejardin, Schaefer. Elsevier. Chapter 18, pp 597-669.
  • Kowalski M P, Boudrieau R J, Pozzi A (2012) Stifle Joint. In: Veterinary Surgery Small Animal. Eds Tobias & Johnston. Elsevier Saunders. Chapter 62, pp 906-998.
  • McKee W M & Cook J M (2006) The Stifle. In: BSAVA Manual of Canine and Feline Musculoskeletal Disease. Eds Houlton, Cook, Innes & Langley-Hobbs. Chapter 22, pp 350-395.
  • Roush (1993) Canine patellar luxation. Vet Clin North Am 23, 855-868.


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