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

ISSN 2398-2977


Introduction

Presenting signs

  • Hindlimb lameness, usually unilateral and acute onset.
  • Evidence of trauma in stifle region and possible soft tissue injuries.
  • Swelling of stifle region and/or femoropatellar joint.

Acute presentation

  • Acute onset, hindlimb lameness, usually unilateral and severe.

Breed/Species predisposition

Cost considerations

  • Costs of diagnosis and treatment.
  • Costs of loss of use.

Pathogenesis

Etiology

  • Usually, the consequence of direct trauma including kicks or impact from hitting a hard object during jumping.

Predisposing factors

General

  • Eventing.
  • Hunting.

Specific

  • Direct trauma to cranial stifle region.

Pathophysiology

  • Jumping fence → stifle fully flexed, patella held against femoral trochlea → direct trauma, eg stifle strikes fence → fracture of patella Musculoskeletal: fracture.
  • Most common fracture after this incident is a parasagittal fracture of the medial part of the patella. Possibly related to the more prominent medial trochlear ridge of the distal femur cleaving off the medial side of the patella. The fracture line may occur anywhere from the midline medially, but smaller more medial fragments are the most common.
  • Transverse fractures are much less common and arise from direct trauma plus increased tension through the quadriceps apparatus at the time of impact – stifle partially flexed. They are usually horizontal and in the middle of the patella. These fractures are more likely to distract.
  • Chip fractures are also uncommon but are usually due to direct trauma. They can be medial, lateral, or proximal.
  • Distal osteochondral patellar fragmentation may be a degenerative disorder rather than a direct fracture and has been most regularly recognized as a consequence of medial patellar desmotomy Medial patellar ligament: desmotomy.
  • All fractures can trigger off osteoarthritis of the femoropatellar joint if inadequately treated Musculoskeletal: osteoarthritis (joint disease).

Timecourse

  • Acute - for direct trauma.
  • Chronic - for degenerative joint disease post-undiagnosed or untreated fracture.

Diagnosis

Presenting problems

  • Hindlimb lameness of acute onset.
  • Soft tissue trauma in the stifle region.
  • Swelling in the stifle region or of the femoropatellar joint.

Client history

  • Hit fence while jumping.
  • Kicked.
  • Pulled up lame after competition.

Clinical signs

  • Hindlimb lameness Musculoskeletal: gait evaluation:
    • At the walk.
    • Moderate to severe.
    • Partial weightbearing.
    • Heel elevated.
    • Stifle partly flexed and will not extend the stifle and lock the patella and stifle.
    • Usually unilateral.
  • Evidence of peripatellar soft tissue swelling and/or injury.
  • Femoropatellar effusion Stifle: effusion - osteochondrosis.
  • Crepitus and pain on direct palpation of the stifle regions and patella itself. In displaced fractures it may be possible to palpate the fracture gap through the dense cranial fascia.
  • Very positive to stifle flexion or resistant and resentful.
  • Lameness improves on intrasynovial analgesia Hindlimb: joint anesthesia. If the horse is very lame, diagnostic analgesia techniques should be used with caution.
  • Lameness is most severe in the complete sagittal or transverse fractures which are usually more unstable.  
  • Lameness may moderate with time in chip fractures.
  • With distal patellar fragmentation, the lameness is usually mild to moderate with no evidence of soft tissue trauma but often the presence of a previous medial patellar desmotomy Medial patellar ligament: desmotomy incision or scar.

Diagnostic investigation

Radiography

  • Full set of views is essential Hindlimb: radiography.
  • Lateral, craniocaudal, both oblique and flexed dorsoventral skyline (cranioproximal-craniodistal oblique) views.
  • The flexed skyline view is essential to characterize sagittal fractures and define degree of separation. Flexion of the stifle may be resented by the horse with patellar fractures and heavy sedation Anesthesia: standing chemical restraint may be necessary in such cases.
  • Single or multiple fragments, displaced or non-displaced, articular or non-articular.
  • May be concurrent fracture of distal end of femur Femur: physeal fracture.
  • Transverse fracture Patella: fracture 05 - LM radiograph.
  • Sagittal fracture Patella: fracture 01 - radiograph skyline.
  • Avulsion fracture Patella: fracture 04 - CrPrCrDiO radiograph.
  • Normal views - lateromedial Stifle: normal 04 - LCaMCrO radiograph, skyline Stifle: normal 03 - CrPCrDO radiograph.

Nuclear imaging

  • Scintigraphy Bone: scintigraphy may be used to identify chronic smaller fractures where localizing clinical signs are less obvious.

Ultrasonography

  • To assess soft tissue structures of the stifle Ultrasonography: musculoskeletal such as patellar ligament desmitis. Fractures of the medial aspect of the patella have been recognized as a concurrent injury to avulsion of the femoral origin of the lateral collateral ligament of the femorotibial joint.
  • Allows localization of fragments and assessment of the fracture gap.

Confirmation of diagnosis

Discriminatory diagnostic features

Definitive diagnostic features

  • Diagnostic imaging.

Differential diagnosis

Other causes of stifle effusion

Treatment

Initial symptomatic treatment

Standard treatment

Conservative management

  • Complete patellar fractures, sagittal or horizontal, may be managed conservatively where there is minimal separation along the fracture plane.
  • Careful palpation and radiography can help establish whether fracture stabilization is required.
  • Where there is an intact overlying fascia and minimal displacement, then strict box rest for up to 2-4 months and initial analgesics may allow fracture healing.  
  • Regular clinical examination and follow-up radiographs are important to assess progress.
  • Most sagittal fractures heal by fibrous union in this situation.
  • Stable transverse and comminuted fractures of the patella can heal by bony union.
  • Controlled walking exercise is started once there is evidence of fracture healing.
  • Further distraction of the fracture during stall rest indicates the need for surgical repair by internal fixation.

Surgery

  • Delay until the acute inflammatory response of soft tissues has subsided.
  • Ultrasound examination Ultrasonography: bone / joints prior to arthrotomy to locate precise site of fracture may reduce periarticular soft tissue damage.
  • Distracted (>5 mm gap), malaligned or unstable articular fractures of the patella require repair by open reduction and internal fixation under general anesthesia Anesthesia: general - overview and radiographic control.
  • Occasionally arthroscopic assisted control is possible Joint: arthroscopy - overview.
  • Repair is usually using two to four, 4.5 mm or 5.5 mm cortical lag screws placed perpendicular to the fracture line.
  • Congruity of the articular surface of the patella is confirmed ideally with arthroscopy Joint: arthroscopy - overview.

​Arthroscopy

  • Removal of distracted small intra-articular chip or bone fragments and debridement of lesion(s) plus joint lavage Joint: arthroscopy - overview. The most common site is medially and up to one-third of the patella has been removed successfully. Dissection and removal from the overlying fascia can be difficult and time consuming. The fracture bed and any remaining damaged soft tissue then requires debridement
  • Larger fractures may be alternatively removed via an arthrotomy and partial patellectomy.
  • Chip fractures of the proximal aspect of the patella are the most difficult to access and may require a variety of special arthroscope and instrument portals.
  • Concurrent damage to the medial or lateral trochlear ridge/s may be encountered and require debridement.

Monitoring

Subsequent management

Treatment post-surgery

  • Peri-operative antibiotics Therapeutics: antimicrobials, sodium penicillin Penicillin G (IV TID) or procaine penicillin Penicillin G (IM BID) continued for 24 h.
  • Postoperative phenylbutazone Phenylbutazone first few days and then as required.
  • +/- butorphanol Butorphanol for additional anti-inflammatory/analgesic effect.
  • Stall or box rest for 14 days.
  • Begin in-hand walking exercise increasing in small increments of 5-10 min.
  • Turnout in 4-6 weeks depending on specifics of surgery.
  • Return to work at 3-6 months.

Monitoring

Prevention

Outcomes

Prognosis

  • Good for partial patellectomy for small and large chip fractures with no concurrent degenerative joint disease. Up to one-third of the patella can be removed with a successful outcome. Involvement of the lateral femorotibial joint collateral ligament complicates the outcome.
  • Minimally displaced sagittal, transverse, or comminuted complete fractures of the patella have a good chance of return to athletic function with conservative treatment.
  • No retrospective studies of surgical stabilization of these fractures but case reports suggest their use and successful results.
  • Poor if osteoarthritis develops.

Reasons for treatment failure

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Vautravers G et al (2018) Articular sagittal and medial parasagittal patellar fracture repair using lag screws in two adult horses. Equine Vet. Educ. 30 (1), 31-36 WileyOnline.
  • McLellan J, Plevin S & Taylor E (2012) Concurrent patellar fracture and lateral collateral ligament avulsion as a result of trauma in three horses. JAVMA 240 (10), 1218-1222 PubMed.
  • Marble G P & Sullins K E (2000) Arthroscopic removal of patellar fracture fragents in horses - five cases (1989-1998). JAVMA 216 (11), 1799-1801 PubMed.
  • Dyson S et al (1992) Clinical and radiographic features, treatment and outcome in 15 horses with fracture of the medial aspect of the patella. Equine Vet J 24 (4), 264-268 PubMed.
  • McIlwraith C W (1990) Osteochondral fragmentation of the distal aspect of the patella in horses. Equine Vet J 22, 157-163 PubMed.
  • Parks A H & Wyn-Jones G (1988) Traumatic injuries of the patella in five horses. Equine Vet J 20, 25-28 PubMed.

Other sources of information

  • McIlwraith C W, Nixon A J & Wright I M (2015) Diagnostic and Surgical Arthroscopy in the Horse. 4th edn. Mosby Elsevier, USA.
  • Fowlie J G, Stick J A & Nickels F A (2012) Patellar Fractures. In: Equine Surgery. 4th edn. Eds: Auer J A & Stick J A. Elsevier Saunders, USA. pp 1434-1436.


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