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DOI: 10.1016/J.JHSB.2005.02.003
The Porcine Forelimb as a Model for Human Flexor Tendon SurgeryFrom the Department of Orthopaedic Surgery, The Royal Sussex County Hospital, Brighton, UK, The Department of Orthopaedic Surgery, Conquest Hospital, St. Leonards on Sea, East Sussex, UK and The Departments of Mechanical Engineering and Musculoskeletal Surgery, Imperial College, London, UK Correspondence: Mr. Andrew Smith, Christine M Kleinert Institute for Hand and Microsurgery, 225 Abraham Flexner Way, Suite 850, Louisville, Kentucky 402023840, USA. E-mail: asmithfrcs{at}aol.com
Technical skills have been shown to transfer very well from bench models to practical use. The central two rays of 30 forelimbs of pigs were dissected and anatomical observations were made. The rays contained deep and superficial flexor tendons enclosed in a fibro-osseous tunnel and these were present in all 60 specimens. The fibrous part of the tunnel had specific constant condensations in annular and oblique directions which were present in all 60 rays. The anatomy of the porcine forelimb digital flexor tendon system is sufficiently similar to the human system to be used as a model for surgeons wishing to master the technical aspects of zone II flexor tendon repair. This paper proposes the porcine forelimb as a bench model for zone II flexor tendon repair.
Key Words: porcine forelimb • flexor tendon surgery • model • the porcine forelimb
Flexor tendon injuries can cause significant morbidity and repair of such injuries in zone II is technically demanding (Verdan, 1979). Technical skills have been shown to transfer very well from bench models to practical use. This has been shown in both general and ophthalmic surgery (Anastakis et al., 1999, Helveston and Coffey, 1986). To date, only mechanical simulators have been developed for practicing flexor tendon repair (Rhodes et al., 2001) and no adequate animal model for training surgeons in the repair of zone II flexor tendons has been proposed. Embalmed cadavers have previously been used to allow surgeons to practice surgical approaches in the hand. However, tissue properties are markedly different after the embalming process. Fresh human tissue is becoming increasingly difficult to obtain due to public concern over the handling of tissue removed from cadavers (Gupte et al., 2002). Pig tendons have previously been used to allow basic repair and mechanical testing of suture techniques (Smith and Evans, 2001). The general anatomy of the porcine forelimb has been documented in veterinary textbooks (Sack, 1982) but the detailed anatomy of the pulley system and vincula is not well described. This paper details the anatomy of the central two rays of the porcine forelimb flexor tendon system and assesses its suitability as a model for human zone II flexor tendon repair.
Thirty porcine forelimbs were collected from commercially slaughtered animals and were refrigerated, but not frozen, prior to dissection. The foot has two prominent central rays that are weight bearing and two subsidiary rays that are shorter, one on each side (Fig 1). The central two rays were dissected in 20 specimens and general anatomical observations were made.
The presence of deep and superficial flexor tendons and their sites of insertion were noted. The presence of the superficial tendon decussation and whether a vinculum was present at this site was noted, as was the presence and number of pulleys. Ten further forelimbs were dissected in more detail to assess the insertion sites of the different pulleys. The length of the flexor pulley system and the maximum excursion of the tendons in response to traction on the proximal tendons were measured with vernier callipers in 20 specimens. Measurements were taken from the mouth of the most proximal annular pulley (Fig 2).
The two central rays of the porcine forelimb each contained a deep and a superficial flexor tendon enclosed in a fibro-osseous tunnel. These were present in all 60 dissected rays. The deep flexor tendon inserted into the proximal palmar aspect of the distal phalanx in all 60 rays. The superficial flexor tendon decussated and inserted into the middle phalanx deep to the deep flexor tendon in all 60 rays. At the point of this decussation there was a vinculum attached to the dorsal surface of the deep flexor tendon in all 60 rays (Fig 3).
The fibrous part of the tunnel had specific constant condensations in annular and oblique directions in all 60 rays (Fig 1). The attachments of these different pulleys were recorded in the last 10 specimens, amounting to 20 pulley systems. The first annular pulley (A1) formed the proximal mouth of the fibro-osseous tunnel and attached dorsally to a sesamoid bone just proximal to the metacarpophalangeal joint (Fig 1). The second annular pulley (A2) was attached to the proximal part of the proximal phalanx in 12 rays and to the metacarpophalangeal joint in eight. The third annular pulley (A3) was attached to the proximal interphalangeal joint in 18 rays and to the distal part of the proximal phalanx in two. The fourth annular pulley (A4) was attached to the middle phalanx in all 20 rays. There was one oblique condensation in the fibrous tunnel that ran between the third and fourth annular pulleys. This was present in all 60 rays (Fig 1). The mean length of the fibro-osseous tunnel was 37 mm (S.D. 3 mm). The superficial and deep flexors had mean excursions of 10 mm (S.D. 3 mm) and 20 mm (S.D. 3 mm), respectively. Table 1 outlines the porcine structures and their human equivalents.
There are a number of problems associated with zone II flexor tendon repair, including complicated anatomy, difficult suture placement with minimal tendon handling and repair with minimal gap formation, sufficient strength for early mobilization and without bunching leading to sticking and triggering. An accurate model for repair would thus greatly aid the surgical trainee. The flexor tendons, their pulleys and vincula were found to have a constant arrangement in the digits of the porcine forelimb. The excursions of human flexor digitorum profundus and flexor digitorum superficialis tendons to produce full finger flexion at the metacarpophalangeal joint are 23 and 26 mm, respectively (Strickland, 1999). In the porcine forelimb the deep flexor had a mean excursion of 20 mm (S.D. 3 mm) and the superficial flexor had a mean excursion of 10 mm (S.D. 3 mm). Although the porcine specimens all had a system of four annular pulleys and one oblique, these were not as large and dense as in the human finger (Fig 1). This may reflect the comparatively smaller range of flexion of the porcine joints and that they are most frequently loaded in an extended posture. However, the porcine pulleys are applied closely to the tendons, as in human fingers (Amis and Jones, 1988) and so provide a realistic scenario for practicing surgery in zone II. These dissections show that the anatomy of the porcine forelimb digital flexor tendon system is sufficiently similar to the human digital flexor tendon system to be used as a model for surgeons wishing to master the technical aspects of zone II flexor tendon repair.
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Abstract
INTRODUCTION
