Tensile strength of modified 4-strand cruciate technique for transversely or obliquely lacerated tendons

Journal of Orthopaedic Surgery, Apr 2007 by Yuen, M H, Ip, W Y

ABSTRACT

Purposes. To assess the tensile strength of the modified 4-strand cruciate technique for obliquely lacerated tendons, and to compare the findings with the strength of transversely lacerated tendons repaired at various grasping depths.

Methods. 60 porcine front foot tendons were evenly divided into 4 groups. In groups 1 to 3, tendons were transversely lacerated and repaired with grasping points at both ends away from the laceration by 5 mm, 10 mm, and 15 mm respectively. In group 4, tendons were obliquely lacerated and repaired with a grasping point 5 mm away from the laceration on one end and 15 mm on the other. All tendons were repaired with a modified 4-strand core suture and continuous epitendinous suture, and then tested to failure in a tensile machine.

Results. The tensile strength in group 1 was significantly lower than that in the other 3 groups (p

Conclusion. The tensile strength of modified 4-strand cruciate repair configuration is not weakened in obliquely lacerated tendons; the grasping point at one end of the tendon being 15 mm away from laceration provides sufficient strength to compensate for the relatively weak 5-mm end. So long as one grasping point is away from the laceration site by 10 mm, the ultimate tensile strength of the transversely lacerated tendons appears acceptable. The modified 4-strand cruciate repair is safe to use for repairing obliquely lacerated tendons.

Key words: animals; biomechanics; suture techniques; tendon injuries; tensile strength

INTRODUCTION

Hand injuries in the forms of bone fractures, tendons injuries, neurovascular injuries, or a combination of all these are commonly seen. The reported incidence of hand injuries in Hong Kong was 600 per 100 000 annually, accounting for 3.2% of all accident and emergency attendance.1 Other countries reported such injuries ranging from 3.7 per 100 000 annually in Denmark, 475 per 100 000 annually in the United Kingdom, to 1981 per 100 000 annually in Russia.1

Tendons used to be considered avascular structures and primary flexor tendon repair was abandoned. In recent years, studies on tendon healing and physiology have led to many advances in their treatment and rehabilitation. Primary flexor tendon repair followed by early tendon movement is now considered standard, though the strength of such rectified tendons needs to be increased.

Numerous in vivo and in vitro studies have examined the effect of different suture techniques. A flexor tendon repair technique should satisfy 6 criteria2 prior to clinical application. They are: (1) easy placement of sutures in the tendon, (2) secure suture knots, (3) smooth junction of tendon ends, (4) minimal gap formation at the repair site, (5) minimal interference with tendon vascularity, and (6) sufficient strength throughout the healing to allow application of early motion stress to the tendon. Although many repair techniques have been proposed, few satisfy all 6 criteria.

The cruciate 4-strand flexor tendon repair technique3 showed a significantly stronger repair than the Kessler, Strickland, or Savage repairs, whilst providing better ultimate tensile strength and being easy to perform. It conferred the ease and speed of a 2-strand technique and the tensile strength that exceeded other 4-strand techniques.

Most flexor tendon repair techniques were based on studies that used transversely lacerated tendons. Tendon lacerations can be oblique or incomplete. Few publications on the tensile strength of the tendon repair techniques were based on obliquely lacerated tendons.

The direction of tendon lacerations affected the strength of certain repair configurations.4 The nonlocking modified Kessler or the 4-strand cruciate tendon repairs were weakened considerably when the tendon was obliquely lacerated. Nonetheless, re-orienting the repair strands to lie parallel to the laceration strengthened their mechanical performance.

The tensile properties of oblique partial tendon lacerations and the effects of peripheral sutures on their strength were evaluated.5 Obliquity of the laceration affected the strength of partially lacerated tendons. Tendons with 45° or 60° oblique lacerations had significantly lower ultimate strengths than those with transverse, or 15° or 30° oblique lacerations.4-6 Running peripheral sutures significantly increased both the gap formation forces and the ultimate strength of the tendons with oblique partial lacerations.

Elongating the repairs improved the strength in obliquely lacerated tendons.6 When the grasping point was moved farther away from the level of the laceration, the suture-tendon interface and grasping power of the sutures on the collagen bundles increased.

We assessed the tensile strengths of the modified 4-strand cruciate technique for obliquely lacerated tendons, and compared the findings with the strength of transversely lacerated tendons repaired at various grasping depths (ranging from 5 mm to 15 mm).

MATERIALS AND METHODS

60 flexor tendons of 30 adult pig front feet were harvested for the experiment. Such tendons are readily available, easy to handle, long enough for fixation in clamps for mechanical testing, and have a similar structure to human tendons. The 6-cm long flexor profundus tendons were exposed completely through an incision at the metatarsophalangeal joint. The site of transection was marked, so were the sites at 5 mm, 10 mm and 15 mm away from the transection site of both ends. The tendons were then transected either transversely or obliquely (45°).