Management of Flexor and Extensor Injuries

Educational Objectives

The goal of this program is to improve management of flexor and extensor injuries. After hearing and assimilating this program, the clinician will be better able to:

1. Use anatomical tests to diagnose extensor tendon injuries.
2. Choose a treatment for correction of Boutonnière deformities.
3. Recognize indications for surgical management of bony mallet injuries.

Summary

Extensor Tendon Injuries

Extensor apparatus: the common extensor tendon becomes the central slip, which extends to the middle phalanx and facilitates metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joint extension; the lateral bands (LB) are conjoined from the common extensor tendon and extrinsic muscles and extend the PIP and distal IP (DIP) joints; the transverse retinacular ligament (TRL) prevents dorsal migration of LB at the PIP joint; the triangular ligament (TL) prevents volar migration of LB; the spiral oblique retinacular ligament combines PIP and DIP joint actions; sagittal bands at the MCP joint provide a lifting effect for extension, which surpass the extensor tendon's contribution and centralize it for PIP joint extension

Repair principles: distal tendons are thinner than proximal tendons and are suitable for a running-type repair; proximal tendons are treated with a core strand repair; extensors retract less than flexors; repairs should be done in ≤10 days; tendons should not be repaired in the presence of gross contamination or inadequate soft tissue cover; staging reconstruction should be done

Rehabilitation principles: tendons take longer to heal than bones and require sustained support; early protected motion (relative motion orthosis or a yolk splint) is preferred to static immobilization; protected motion positions the repaired tendon at relative extension compared with the adjacent tendon and allows controlled movement while providing support

Zone-Specific Injuries

Zone 1 (mallet finger): may be a bony mallet (involving avulsion of a piece of bone with terminal tendon insertion) or a soft tissue mallet; bony mallets heal faster than soft tissue mallets and require 6 wk of extension splinting; soft tissue mallets require 8 to 10 wk of splinting with an additional 2 wk of nighttime splinting; foam-laminated aluminum splints (AlumaFoam) should be used on the dorsal aspect for better hyperextension; a mild lag up to 10 degrees is common; the PIP joint is kept free to reduce stiffness and prevent LB migration; bony mallets may be treated with operative reduction in cases with >30% to 50% joint involvement, volar subluxation of the distal phalanx, or in cases of patients unable to tolerate full-time splint wear; pinning may be an option, with buried pins for prolonged use; the extension block splinting technique should be used for very small fragments

Zone 2: involve sharp lacerations, are often open, and affect the LB; involvement of 1 LB does not require repair; >50% LB involvement requires a running repair; immobilization may be achieved with a K-wire or a splint (6 wk, strict full-time splinting plus 6 wk, nighttime splinting) in cases that are treated operatively

Zone 3: involves a central slip disruption and may be closed or open; presents with a PIP extension lag in the Elson Test (confirmatory for injuries to the central slip of the extensor tendon); treatment is closed with 6 wk of full-time immobilization; the DIP is kept free while full extension is maintained in the PIP; splinting may be effective in delayed presentations; open repair should be done in cases of acute injuries or sharp lacerations; primary repair may be attempted in cases with adequate tendon; LB centralization or central slip turn-down may be used in cases of tendon which are inadequate

Zone 4: less common and involve a central slip extensor hood disruption; open injuries are repaired with a running stitch; should be mobilized early to prevent adhesion formation

Zone 5: includes fight bite; finger flexion may obscure location of the laceration; finger extension during surgery helps locate the laceration; sagittal band injury is usually a closed injury and may cause extensor tendon subluxation, which leads to an inability to extend the MCP joint; extended finger position may stabilize the injury; initial treatment is 6 wk of relative motion splinting; other options include primary repair, using the junctura, or use of a central tendon slip looped around the lumbrical insertion or the radial collateral band

Zone 6 to 8: injuries in this location have less scarring and reduced tendon excursion because of increased padding and more subcutaneous fat; an independent tabletop lift test is useful for identification; the tubular nature of the tendon at this level favors core suture repair; injuries respond well to early range of motion (ROM) and dynamic splinting

Swan neck deformity: occurs after a chronic mallet deformity; results from LB contraction and dorsal migration due to loss of the central terminal tendon insertion; initial attempts may involve splinting for correctable cases; surgical options address multiple components, eg, DIP flexion through pinning or tightening, PIP hyperextension; collaborating with a therapist for full ROM before soft tissue repair is essential

Boutonnière deformity: occurs with chronic central slip disruption or TL attenuation; the LB drift volarly, which results in PIP extension loss and associated DIP hyperextension; central slip repair, LB centralization, or a turn-down approach may be used for supple joints and deformities which are potentially correctable; static progressive extension splinting is an option for stiff joints; correction through surgery may be impossible for fixed joints; patient counseling is crucial for addressing poor outcomes and high recurrence rates

Flexors

Anatomy: the flexor digitorum profundus (FDP) inserts at the distal phalanx base and flexes the DIP joint; the flexor digitorum superficialis (FDS) splits at carpus chiasm and inserts at the middle phalanx base for PIP flexion; the FDS has a unique blood supply by vincula which aids tendon healing; each tendon has a hypovascular zone located between the vincula; disruption in the hypovascular zone impacts overall tendon healing and strength

Pulley system: consists of 5 pulleys; A1, A3, A5 overlie the joints; A2 and A4 overlie the proximal and middle phalanx; A2 and A4 were formerly considered crucial to prevent bowstringing, but recent literature has questioned their clinical importance; venting or dividing the pulleys is acceptable for optimal repair, according to Cox et al (2021); thumb pulleys (A1, oblique, A2) prevent bowstringing, increasing moment arm and FDP excursion; the oblique pulley is crucial for the thumb

Tendon repair principles: early ROM should be prioritized; sutures must be sufficient to ensure strength and early mobilization; shortening and bulkiness should be minimized; full impingement should be avoided and glide enhanced; repair gapping should be prevented; flexor tendon repairs should be performed within 7 days; strength is influenced by factors such as core suture strand passes (6 core for greater strength), suture caliber (commonly 3/0 or 4/0), and 7 to 10 mm purchase length; locking sutures are preferred over grasping; knot location (eg, inside versus outside, volar versus dorsal) may impact repair strength and bulkiness; epitendinous sutures enhance tendon glide and strength up to 30% and are recommended; core suture repairs typically use a 4- or 6-strand 3/0 or 4/0 loop supramid suture in a modified Kessler technique; the repair should be tested through full ROM to rule out gapping

Management

Zone 1 (“Jersey finger”): an isolated FDP injury which may result from forced extension during maximal flexion; the tendon alone may be affected or in combination with a small avulsion fracture; Leddy classification categorizes degree of retraction; prompt treatment is advised, except in cases of type 2 (bony fragment) injuries; zone 1 injuries without bony fragments may require fixation to the bone using, eg, Mitek anchors, button repairs with pull-out sutures; recent literature questions the necessity of fixation and suggests comparable long-term outcomes without operative intervention

Zone 2: known as “no man's land” due to poor injury outcomes and significant tendon excursion; partial lacerations (involving 0% to 25% of tendon structure) require trimming; lacerations between 25% and 50% benefit from an epitendinous repair; lacerations involving >50% of tendon structure require a core suture with an epitendinous repair; adequate exposure to fully locate the retracted tendon may require additional proximal skip incisions; FDP repair may involve a single or double slip of the FDS to prioritize optimal tendon glide

Zone 3 to 5: tendon injuries are less severe due to more soft tissue and subcutaneous fat; a Pulvertaft weave may be considered for repair because of the larger size of the tendons; Pulvertaft weaves may produce bulkier outcomes

Rehabilitation principles: a dorsal blocking orthosis is used to restrict full extension during surgery; the patient collaborates with the therapist on an active or passive ROM protocol; recent consensus acknowledges the risk for rupture and complications with early active motion

Complications of repair: lumbrical plus deformity — results from distal FDP tendon disruption and causes paradoxical extension of the PIP joint during digit flexion due to the lumbrical's extensor hood insertion; treatment options include FDP repair or lumbrical muscle release; quadriga effect — occurs during attempts to repair a gap >1 cm in the common FDP muscle belly, which reduces excursion on other tendons; repair rupture — risk ranges from 4% to 30%; vulnerability is in the first 6 to 12 days after surgery when core sutures lose strength but the tendon has not adequately healed; the risk for rupture continues up to 4 wk; the highest risk is seen in the second week, coinciding with the initiation of therapy; re-repair may be considered; inadequate sheath/pulley may require staged reconstruction with a Hunter rod; good tendon quality allows repeat repair; poor tendon quality may require primary tendon interposition grafting; single-stage grafting requires an adequate pulley/sheath system, well-healed wound, good soft tissue, and passive ROM

Readings

Alla SR, Deal ND, Dempsey IJ. Current concepts: mallet finger. Hand (N Y). 2014;9(2):138-144. doi:10.1007/s11552-014-9609-y; Colzani G, Tos P, Battiston B, Merolla G, Porcellini G, Artiaco S. Traumatic extensor tendon injuries to the hand: Clinical anatomy, biomechanics, and surgical procedure review. J Hand Microsurg. 2016;8(1):2-12. doi:10.1055/s-0036-1572534; Cox HG, Hill JB, Colon AF, et al. The impact of dividing the flexor tendon pulleys on tendon excursion and work of flexion in a cadaveric model. J Hand Surg Am. 2021;46(12):1064-1070. doi:10.1016/j.jhsa.2021.05.013; Dubois E, Teboul F, Bihel T, Goubier JN. Chronic boutonniere deformities, supple, or stiff: A new surgical technique with early mobilization in 11 cases. Tech Hand Up Extrem Surg. 2017;21(2):37-40. doi:10.1097/BTH.0000000000000152; Elzinga K, Chung KC. Managing swan neck and Boutonniere deformities. Clin Plast Surg. 2019;46(3):329-337. doi:10.1016/j.cps.2019.02.006; Janssen P, Melamed E. Central slip and bilateral lateral band laceration with negative Elson's and modified Elson's tests. Trauma Case Rep. 2022;40:100671. Published 2022 Jun 28. doi:10.1016/j.tcr.2022.100671; Lamaris GA, Matthew MK. The diagnosis and management of mallet finger injuries. Hand (N Y). 2017;12(3):223-228. doi:10.1177/1558944716642763; Lee JK, Lee S, Kim M, et al. Anatomic repair of the central slip with anchor suture augmentation for treatment of established Boutonniere deformity. Clin Orthop Surg. 2021;13(2):243-251. doi:10.4055/cios20170; Marshall TG, Sivakumar B, Smith BJ, et al. Mechanics of metacarpophalangeal joint extension. J Hand Surg Am. 2018;43(7):681.e1-681.e5. doi:10.1016/j.jhsa.2017.12.010; Tolkien Z, Potter S, Burr N, et al. Conservative management of mallet injuries: A national survey of current practice in the UK. J Plast Reconstr Aesthet Surg. 2017;70(7):901-907. doi:10.1016/j.bjps.2017.04.009.

Disclosures

For this program, the following relevant financial relationships were disclosed and mitigated to ensure that no commercial bias has been inserted into this content: Dr. McCullough has received grants or research support from MTF Biologics. Members of the planning committee reported nothing relevant to disclose.

Acknowledgements

Dr. McCullough was recorded at the 1st Annual Cedars-Sinai Hand and Upper Extremity Symposium, held December 9, 2023, in Los Angeles, CA, and presented by Cedars-Sinai Medical Center. For information on upcoming CME activities from this presenter, please visit cedars-sinai.edu/education/continuing-medical.html. Audio Digest thanks the speakers and Cedars-Sinai Medical Center for their cooperation in the production of this program.

CME/CE INFO

Accreditation:

The Audio- Digest Foundation is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.

The Audio- Digest Foundation designates this enduring material for a maximum of 1.00 AMA PRA Category 1 Credits™. Physicians should claim only the credit commensurate with the extent of their participation in the activity.

Audio Digest Foundation is accredited as a provider of continuing nursing education by the American Nurses Credentialing Center's (ANCC's) Commission on Accreditation. Audio Digest Foundation designates this activity for 1.00 CE contact hours.

Lecture ID:

OR470601

Expiration:

This CME course qualifies for AMA PRA Category 1 Credits™ for 3 years from the date of publication.

Instructions:

To earn CME/CE credit for this course, you must complete all the following components in the order recommended: (1) Review introductory course content, including Educational Objectives and Faculty/Planner Disclosures; (2) Listen to the audio program and review accompanying learning materials; (3) Complete posttest (only after completing Step 2) and earn a passing score of at least 80%. Taking the course Pretest and completing the Evaluation Survey are strongly recommended (but not mandatory) components of completing this CME/CE course.

Estimated time to complete this CME/CE course:

Approximately 2x the length of the recorded lecture to account for time spent studying accompanying learning materials and completing tests.