ISSN 2398-2977      

Palmar / plantar annular ligament syndrome

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Synonym(s): PAL syndrome


Introduction

  • Cause: damage to the palmar / plantar annular ligament (PAL) by direct or indirect trauma; secondary desmitis to non-infectious or infectious tenosynovitis, usually chronic causing enlargement of the flexor tendon sheath; tendonitis of the SDFT/DDFT within digital sheath.
  • Signs: lameness, pain on flexion, 'bulging' of tissues proximal and distal to annular ligament.
  • Diagnosis: history, signs, intrasynovial and regional analgesia, ultrasonography.
  • Treatment: as for primary cause, symptomatic, surgical transection of annular ligament.
  • Prognosis: good in acute cases and uncomplicated chronic cases.

Pathogenesis

Etiology

  • Damage to annular ligament, eg direct or indirect trauma (overextension) leads to a primary desmitis.
  • Secondary desmitis is caused by:
  • A combination of the above factors.

Predisposing factors

General

  • Local trauma.
  • Fetlock hyperextension.

Specific

Pathophysiology

  • The PAL is a focal thickening of the fascia or retinaculum that forms a thin, transverse inelastic band that restrains the digital flexor tendons on the palmar/plantar aspect of the fetlock during flexion.
  • It extends from the periosteum on the abaxial aspect of the proximal sesamoid bones and lies superficial to the digital sheath, which encloses the flexor tendons.
  • It normally measures <2 mm in thickness.
  • The role of PAL as a cause of lameness is subject to debate and controversy. Thickening of the PAL and distension of the digital flexor tendon sheath (DFTS) is associated with lameness in a number of different diseases of the sheath and associated structures. This has been termed palmar/plantar annular ligament (PAL) syndrome or constriction.
  • Direct external trauma to the PAL can occur in lacerations and or direct impact (overreach).
  • Overextension of the fetlock at high-speed gaits may lead to increased tension in the PAL and injury.
  • Excessive tendon swelling (uncommon) within the DFTS can lead to pressure on the PAL and inflammation.
  • Chronic inflammation of the DFTS due to infectious or non-infectious tenosynovitis leads to effusion of the sheath and fibrosis and thickening of the DFTS capsule, including the PAL. Additional sheath pathology such as hypertrophied synovial membrane, adhesions and synovial masses may restrict movement within the sheath.
  • In certain breeds or horses, there may be additional thickening and fibrosis of the subcutaneous connective tissue, which often includes the PAL.
  • Whatever the cause of the inflammation and thickening, the space within the annular or fetlock canal is decreased and restricts movement of the structures within.
  • Further trauma and inflammation to the PAL is induced by this restriction, perpetuating the cycle of events and leading to additional thickening of the PAL and pain.
  • Pathology at the insertion of the PAL onto the proximal sesamoid bone can lead to an insertional enthesopathy or small avulsion fractures which may contribute to relative stenosis and pain.

Timecourse

  • Acute tendinitis or tenosynovitis may lead to a rapid restriction of movement within the canal, but generally the onset is more chronic over weeks or months.

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.
  • Cender A N et al (2022) Diagnosis and outcome following tenoscopic surgery of the digital flexor tendon sheath in German sports and pleasure horses. Equine Vet J (Ahead of Print) WileyOnline.
  • Kent A V et al (2020) Improved diagnostic criteria for digital flexor tendon sheath pathology using contrast tenography. Equine Vet J 52 (2), 205-212 PubMed.
  • Espinosa P et al (2017) A novel ultrasonographic assisted technique for desmotomy of the palmar/plantar annular ligament in horses. Vet Surg 46 (5), 611-620 PubMed.
  • Garvican E R et al (2016) Mineralization of the equine palmar/plantar annular ligament treated by surgical resection. Vet Surg 45 (5), 602-608 PubMed.
  • Cohen J M et al (2008) Desmitis of the distal digital annular ligament in seven horses: MRI diagnosis and surgical treatment. Vet Surg 37 (4), 336-344 PubMed.
  • Owen K R et al (2008) Retrospective study of palmar/plantar annular ligament injury in 71 horses: 2001-2006. Equine Vet J 40 (3), 237-244 PubMed.
  • Smith M R W & Wright I M (2006) Non-infectious tenosynovitis of the digital flexor tendon sheath: a retrospective analysis of 76 cases. Equine Vet J 38 (2), 134-141 PubMed.  
  • McGhee J D, White N A & Goodrich L R (2005) Primary desmitis of the palmar and plantar annular ligaments in horses: 25 cases (1990-2003). J Am Vet Med Assoc 226 (1), 83-86 PubMed.
  • Wilderjans H et al (2003) Tenosynovitis of the digital flexor tendon sheath and annular ligament constriction syndrome caused by longitudinal tears in the deep digital flexor tendon: a clinical and surgical report of 17 cases in warmblood horses. Equine Vet J 35 (3), 270-275 PubMed.
  • Fortier L A et al (1999) Tenoscopic examination and proximal annular ligament desmotomy for treatment of equine "complex" digital sheath tenosynovitis. Vet Surg 28 (6), 429-435 PubMed.

Other sources of information

  • Kummerle J M, Theis F & Smith R KW (2019) Diagnosis and Management of Tendon and Ligament Disorders. In: Equine Surgery. 5th edn. Eds: Auer J A, Stick J, Kummerle J M & Prange T. Elsevier, USA. pp 1441-1445.
  • Schramme M C & Smith R K W (2011) Diseases of the Digital Flexor Tendon sheath, Palmar Annular Ligament, and Digital Annular Ligaments. In: Diagnosis and Management of Lameness in the Horse. 2nd edn. Eds: Ross M K & Dyson S J. Elsevier, USA. pp 764 -776.

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