Clinical History: A 16 year-old male presents with loss of flexion at the distal interphalangeal joint (DIP) of the ring finger, following an injury playing flag football 2 weeks before. T1-weighted axial (1a), fat-suppressed proton density-weighted axial (1b), and T2-weighted sagittal (1c) images are provided. What are the findings? What is your diagnosis?
Type 2 avulsion of the flexor digitorum profundus tendon of the ring finger.
Flexor tendon ruptures of the fingers can lead to significant functional impairment. The diagnosis of tendon rupture is typically made clinically, but at times the physical findings are indeterminate, especially in the acute setting or with partial tendon tears. Flexor tendon injuries can occur within the finger, hand, wrist, or forearm. While the treatment of some flexor tendon injuries is considered relatively straightforward, other injuries are more complex. The most challenging injuries are those in zone II of the finger where both the flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) are found in close apposition within the confines of the fibro-osseous flexor tunnel. An accurate depiction of the location of the tendon tear, the amount of cross-sectional involvement of the tendon, the amount of retraction, and associated injuries provides critical information used in formulating a treatment strategy.
Flexor Tendon Anatomy
The flexor tendons of the digits enter the carpal tunnel in a generally consistent anatomic relationship. The FDS tendons are the most palmar, and the FDS tendons to the long and ring fingers are most superficial. The FDP and FPL tendons are found in the deepest level of the carpal tunnel.
Each finger receives attachment from a FDS and FDP tendon. The thumb only receives the flexor pollicis longus (FPL). The FDS remains palmar to the FDP at the level of the metacarpal. At the proximal third of the proximal phalanx the FDS divides into medial and lateral tendon slips, which spiral deep to the FDP and form a thin bridging plate of crisscrossing fibers known as the tendinous (Camper’s) chiasm1,2. Distal to the chiasm, radial and ulnar tendon slips insert on either side of the middle phalanx in close proximity to the A4 pulley3. The FDP passes through the resulting hiatus formed by the divided FDS tendon at the midlevel of the proximal phalanx becoming superficial and continuing distally to insert on the volar base of the distal phalanx.
The vincula tendinum are thin bands of synovial tissue that attach the tendons to the dorsal portions of the fibro-osseous tunnel near the tendon attachment. There are two vincula brevia. One attaches the FDS to the distal portion of the proximal phalanx and proximal interphalangeal (PIP) joint. The second attaches the FDP to the distal aspect of the middle phalanx and distal interphalangeal (DIP) joint. Three vincula longa are found in each finger: two vincula longa connect the bifurcated FDS tendon slips attaching to the proximal end of the proximal phalanx, one vincula longa attaches to the FDP just distal to the point where the FDP passes through the FDS fenestration and blends with the vincula brevia of the FDS at the PIP and distal aspect of the proximal phalanx. Delivery of nutrients to the tendons is accomplished by blood supply via the vinculae and from the synovial fluid in the tendon sheath.
The flexor tendons are closely fixed to the phalanges by a fibro-osseous tunnel that is lined by a synovial sheath. The fibro-osseous tunnel is formed by the palmar surface of the phalanges and their joint capsules and an overlying network of fibrous arches representing thickening of the flexor tendon sheaths referred to as the finger pulley system. The fibro-osseous tunnel provides biomechanical stability to the flexor tendons and facilitates finger flexion by keeping the tendons closely apposed to the phalanges. Five annular and three cruciate pulleys extend from the metacarpophalangeal joint to the DIP joint. Additional details may be found at MRI Web Clinic December 2005.
Numerous variations in the flexor tendon sheath and palmar bursae are encountered. The most common pattern demonstrates continuity between the flexor tendon sheath of the thumb with the radial palmar bursae and continuity of the flexor tendon sheath of the little finger with the ulnar bursa. Communication between the radial and ulnar bursae by an intermediate bursa is commonly seen. The flexor tendon sheaths of the index, middle, and ring fingers are typically separate from the palmar bursae.
Sagittal and axial images are the most helpful in evaluating the flexor tendons of the fingers and hand. The normal tendon demonstrates low signal intensity on all pulse sequences. At the level of the metacarpal the FDP is deep to the FDS. At the proximal phalanx the FDS splits into two fascicles and fuses deep to the FDP before inserting as separate slips on the middle phalanx (5a,6a). The proximal and distal margins of the annular pulleys may be identified as subtle step-offs of the volar surface contour of the flexor tendon on sagittal images, and the phalangeal attachments of the pulleys are seen on axial views.
MRI has proven invaluable in assessing the severity of flexor tendon tears, capably differentiating low-grade from high-grade partial tears and complete ruptures4. Fluid filled partial or complete tendon defects are best seen on T2-weighted, STIR, or fat-suppressed proton density-weighted images while T1-weighted images allows a more detailed evaluation of the anatomy. In partial thickness tears the smooth contour of the low signal tendon is interrupted. Axial images in particular are helpful in determining the amount of tendon disrupted(7a,8a). Lacerations result in tendon margins that are sharp and linear (9a), often with a visible overlying soft tissue defect (11a). With complete tendon disruption MRI accurately determines the extent of tendon retraction (14a).
Flexor Tendon Injuries
Kleinert et al.5 and Verdan6 classified tendon injuries into five anatomic zones. Zone V extends from the musculotendinous junction to the proximal aspect of the carpal tunnel. Zone IV is comprised of the flexor tendons within the carpal tunnel. Zone III extends from the distal part of the flexor retinaculum at the carpal tunnel to the proximal part of the A1 pulley and contains the lumbrical origins from the FDP tendons. Zone II extends from the A1 pulley to the distal insertion of the FDS. Zone II was coined as “no man’s land” by Bunnell based on the belief that primary repairs should not be done in this zone because of the frequency of complications. Zone I includes the FDP extending from the distal insertion of the FDS on the middle phalanx to the distal insertion of the FDP on the distal phalanx. For the thumb, zone III incorporates the level of the thenar muscles, zone II extends from the neck of the metacarpal to the neck of the proximal phalanx, and zone I includes the FPL insertion.
Flexor tendon injuries are divided into open and closed injuries. Open injuries are the result of lacerations and penetrating trauma in which the skin and soft tissues overlying the flexor tendons are violated. Closed injuries occur when the overlying soft tissues are intact. Closed ruptures are less common and most often the result of trauma, although closed ruptures may be found in tendons that are weakened by other conditions such as rheumatoid arthritis, osteoarthritis, or previous trauma.
Lacerations are the most common cause of flexor tendon ruptures, and typically affect the midsubstance of the tendon rather than the sites of insertion7. Injuries in Zone I are isolated lacerations of the FDP, and the patients demonstrate loss of active flexion at the DIP joint (11a,12a). Trauma more proximally subjects both the FDS and FDP to potential injury. If both are ruptured, loss of flexion at the PIP and DIP joints is the typical clinical finding. However, in some instances, complete tendon rupture can mimic a partial laceration when an intact vinculum preserves some degree of active flexion. Lacerations in Zone II are the most common and carry the most severe prognosis with high incidences of adhesions, entrapment or triggering of the flexor tendons. Lacerations in Zones III, IV, and V often have associated injuries of the neurovascular structures and lumbrical muscles in addition to the flexor tendons(13a,14a).
Acute traumatic avulsion of the FDP is the most frequent type of closed rupture. As in the introductory case, FDP avulsion is the result of sudden hyperextension of the DIP during active flexion and usually occurs while grasping the jersey of an opposing player, hence the name “jersey finger”8. This is most commonly encountered in football, rugby and flag football and most commonly affects the ring finger9. This injury is often overlooked in the acute setting, since there is no alignment abnormality or deformity on physical exam and loss of active flexion at the DIP may be masked by pain and soft tissue swelling. These factors often lead to a delay in diagnosis. Leddy described 3 types of FDP avulsions: Type 1 results in tendon retraction into the palm (15a-17a); Type 2 results in tendon retraction to the PIP level (2a-4a); Type 3 is seen with a bone fragment avulsion with the FDP. Type 3 injuries are further categorized as 3B when a fragment is present but the tendon has been avulsed from the fragment10.
Isolated FDS avulsion is rare. The FDS is most often injured in conjunction with FDP injuries and such injuries are often delayed in diagnosis11. With an isolated FDS avulsion there is loss of active flexion at the PIP. There may be palmar tenderness or a palpable palmar mass accompanying tendon retraction(18a-20a).
Closed FPL rupture is frequently seen at the level of tendon contact with the distal scaphoid (21a-23a) and can occur in the clinical setting of rheumatoid arthritis or volar carpal subluxation. When tears occur at the level of the phalanges, the torn FPL tendon may freely retract because of the lack of an anchoring vincula.
Treatment of flexor tendon injuries is dependent on the type, location, and chronicity of injury. In order to restore active flexion to a finger with lacerated flexors, surgery with tendon repair is necessary. The goal of flexor tendon surgery is to create a repair that allows early motion, will not fail, and minimizes the development of adhesions. Balancing a strong repair with minimal resistance to tendon gliding requires meticulous surgical technique including incision placement, suture placement and technique. Early repair is critical to successful outcomes12. In general, repair is less challenging when performed early as there is less proximal tendon retraction necessitating fewer incisions. Muscle shortening and tendon retraction may complicate delayed repairs and result in greater tension across the repair site, tendon repair gapping, and an increased failure rate. Additionally, in an effort to relieve tension at the repair, the digits or wrist may be splinted in excessive flexion leading to joint contractures. Primary repair is often attempted in injuries up to 4 weeks old. Beyond this time, other options including no surgery, tendon grafting, and staged repairs may be necessary13.
Lacerations in zone II are the most frequently encountered flexor tendon injury. Up until the 1960’s, primary repair in this zone was not considered a viable option, because of the high incidence of complications including adhesions, entrapment, or triggering of the flexor tendons14. Advances in the understanding of intrasynovial flexor tendon anatomy, responses to injury, and methods of repair have made primary repair the preferred operative treatment for acutely lacerated tendons in zone II, followed by tenolysis to release adhesions if needed. Many authors recommend repairing only one slip of the FDS to allow improved gliding of the tendon and to minimize adhesions15. For late zone II injuries of both the FDP and FDS, staged tendon reconstruction may be an option.
In general, the indications for single-stage free tendon grafting include: injuries that result in segmental tendon loss, delayed presentation that allows tendon fraying or retraction into the muscle belly, and delayed presentation of some retracted FDP avulsions. Tendon reconstruction is more amenable in zones III, IV, and V than zone II because of the lack of a restrictive fibro-osseous tunnel. In more significantly damaged fingers where the pulley system requires reconstruction, the fibro-osseous canal is severely scarred, or there are significant joint contractures, a two-stage reconstruction may be appropriate. In this type repair, silicone rods are placed to facilitate the formation of a pseudosheath with the second-stage tendon graft performed 3-4 months later16. Tendon grafts are most commonly fashioned from the palmaris longus and plantaris tendons.
Management of partial tendon tears remains controversial. Controlled animal studies have shown that suturing of partial tendon tears actually results in weaker tendons and an increased rate of rupture in contrast to partial tendon tears managed by early mobilization17,18. Conservative treatment plans recommend that tears involving 60% or less of the tendon cross-section may be treated without surgical repair19. However, there are reports of successful treatment of partial tendon tears involving up to 95% of the cross-sectional area of the tendon20.
Closed ruptures of the flexor tendons are most commonly avulsions of the FDP at its insertion on the distal phalanx. In type 1 injuries of the FDP, the tendon is retracted into the palm, and there is significant loss of blood supply to the tendon. Repair in these instances should be undertaken within 7-10 days, before the tendon becomes scarred. In type 2 injuries where the torn tendon is retracted to the PIP level, a portion of the nutritional supply is intact. Most surgeons favor early repair with this injury, however treatment may be delayed up to 6-8 weeks in some cases. An athlete may choose to complete his season with this type of injury, even though delay may result in a suboptimal result or further tendon retraction. In type 3 injuries, the bony fragment is tethered at the A-4 pulley. Delayed repair may be possible, unless the 3B variant is found in which the tendon is retracted from the bony fragment. If presenting with a chronic FDP avulsion in which delayed primary repair is not possible, treatment options include nonrepair, flexor tendon graft through the intact FDS, and arthrodesis if the DIP is unstable. In most cases nonrepair is recommended. Flexor tendon grafts of the FDP remain controversial as they can interfere with FDS function21.
Following primary tendon repair, intermediate signal on the T1-weighted and T2-weighted images at the repair site is termed tendon callus and represents healing at the tendon repair. This is best evaluated on axial images with mature tissue with new collagen fibers demonstrating low signal and immature connective tissue as intermediate signal intensity(24a)22. Adhesions, elongation of tendon callus at the repair site, and recurrent rupture (24a) are frequent complications of tendon repair and may be difficult to differentiate clinically. MRI can help differentiate these complications in the face of an inconclusive physical examination. Tendon adhesions are the most common complication of tendon repair. On MRI adhesions appear as regions of intermediate to low signal soft tissue thickening surrounding and within the flexor tendon sheath (25a). Recurrent rupture demonstrates fluid signal within the tendon defect (26a). Elongation of the callus region beyond 10mm is associated with a poor surgical outcome and tendon grafting may be necessary23.
Flexor tendon lacerations and ruptures of the fingers are a frequently encountered injury that may result in significant loss of function. Flexor tendon lacerations frequently involve both the FDP and FDS tendons. Lacerations in zone II pose a significant challenge because of the high rate of postsurgical complications. Closed flexor tendon injuries most commonly result in avulsion of the FDP from the distal phalanx. In these cases, treatment is guided by the degree of retraction and the presence of associated fractures. Successful outcomes depend on careful preoperative planning, meticulous surgical technique, and careful rehabilitation. In both the preoperative and postoperative settings MRI can provide valuable information about the extent of tendon injury and retraction, serving as a valuable guide to surgical planning and postoperative care.
1 Schmidt, H.-M., S.-X. Zhang and K. Zieseniss: Clinical anatomy of the chiasma tendinum (Camper) in the fingers. Clin. Anat. 7 (1994) 65-71
2 Camper, P.: Demonstrationum anatomico-pathologicarum liber primus. Continens brachii humani fabricum et morbos. Amstelaedami, 4, 19, 1760. (zit. in Kaplan’s functional and surgical anatomy of the hand. 3rd ed. Ed. M. Spinner. J.B. Lippincott, Philadelphia, 1984) Caplan, H.S., J.M. Hunter and R.J. Merklin: Intrinsic vascularization of flexor tendons. Amer. Acad. Orthop. Surg. (AAOS) Symposion on tendon surgery in the hand. (pp. 48-58) C.V. Mosby, St. Louis 1975
3 Schmidt, Hans-Martin; Lanz, Ulrich (2004-02-20). Surgical Anatomy of the Hand. Thieme Medical Pub.
4 Rubin DA, Kneeland JB, Kitay GS, Naranja RJ. Flexor Tendon Tears in the Hand: Use of MR Imaging to Diagnose Degree of Injury in a Cadaver Model. AJR 1996;166:615-620.
5 Kleinert H, Kutz J, Ashbell T, et al. Primary repair of lacerated flexor tendons in “no man’s land,”. J Bone Joint Surg Am. 1967;49:577.
6 Verdan CE. Half a century of flexor-tendon surgery: current status and changing philosophies. J Bone Joint Surg Am. 1972;54:472-491.
7 Folmar RC, Nelson CL, Phalen GS. Ruptures of flexor tendons in hands of nonrheumatoid patients. J Bone Joint Surg Am 1972; 54:579-584.
8 Leddy JP, Packer JW: Avulsion of the profundus tendon insertion in athletes. J Hand Surg 2: 66, 1977.
9 Manske PR, Lesker PA: Avulsion of the ring finger flexor digitorumprofundus tendon: An experimental study. Hand 10: 52, 1978.
10 Leddy JP: Flexor tendons-acute injuries, in Green DP (ed): Operative Hand Surgery. Volume 3, second edition. New York, Churchill Livingstone, 1988, pp 1935-1968.
11 Drape J, et al. Closed ruptures of the flexor digitorum tendons: MRI evaluation. Skeletal Radiology 19??;27:617-624.
12 Tang J, Shi D, Gu Y. Flexor tendon repair: timing of surgery and sheath management. Zhonghua Wai Ke Za Zhi 1995;33:532-535.
13 Hunt, Thomas R, III, MD; Wiesel, Sam W. (2011-01-01). Operative Techniques in Hand, Wrist, and Forearm Surgery. Lippincott Williams & Wilkins.
14 Schlenker JD, Lister GD, Kleinert HE. Three complications of untreated partial laceration of flexor tendon-entrapment, rupture, and triggering. J Hand Surg 1981;6:392-396.
15 Zhao C, Amadio PC, Zobitz ME, et al. Resection of the flexor digitorum superficialis reduces gliding resistance after zone II flexor digitorum profundus repair in vitro. J Hand Surg Am 2002;27A: 316-321. Hunt, Thomas R, III, MD; Wiesel, Sam W. (2011-01-01). Operative Techniques in Hand, Wrist, and Forearm Surgery (Kindle Locations 21448-21450). Lippincott Williams & Wilkins. Kindle Edition.
16 Derby BM, et. al. Flexor Tendon Reconstruction. Clin Plastic Surg 2011; 38:607-619.
17 Wray RC Jr, Ollinger H, Weeks PM. Effects of mobilization on .tensile strength of partial tendon lacerations. Surg Forum 1975;26:557-558.
18 Bishop AT, Cooney WP Ill, Wood MB. Treatment of partial.tendon lacerations: the effect of tenorrhaphy and early protected mobilization. J Trauma 1986;26:301-312.
19 McGeorge DD, Stilwell JH. Partial flexor tendon injuries: to repair or not. J Hand Surg(BrJ1992;1 7-B:1 76-177.
20 Wray RC Jr, Weeks PM. Treatment of partial tendon lacerations. Hand 1980; 12:163-166.
21 Rettig AC: Athletic Injuries of the Wrist and Hand. The American Journal of Sports Medicine 32: 262-273, 2004.
22 Drape JL, et. al. Complications of Flexor Tendon Repair in the Hand: MR Imaging Assessment. Radiology 1996; 198:219-224.
23 Ejeskar A, Instam L. Elongation in profundus tendon repair: a clinical and radiological study. Scand J Plast Reconstr Surg 1981; 15:61-68.