Flexor Tendon Injuries

This article is currently under review and may not be up to date. Please come back soon to see the finished work! (12/09/2020)

Original Editor - Lucinda hampton Top Contributors - Wanda van Niekerk, Kim Jackson, Lucinda hampton, Rachael Lowe, Tarina van der Stockt, Admin and Jess Bell

Introduction

Flexor tendons can be injured, for example, by a deep cut, if severe the cut could also damage surrounding structures such as nerves and vessels. Many times, an injury that looks simple on the outside, like a cut, can be very complicated on the inside. A severe cut that injures the tendons will mean that flexing finger(s) will be not possible.

Clinically Relevant Anatomy

File:Interactive hand - hand - L17F1.jpg

The tendons that can be involved include:

• Flexor pollicis longus (flexion tip of thumb)
• Flexor digitorum profundus (flexion of the fingers)
• Flexor digitorum superficialis (flexes the middle joint of each finger)
• Flexor carpi ulnaris
• Flexor carpi radialis

For the purpose of this page, specific anatomy details will be provided on the major muscles and tendons involved in flexion of the fingers.

Flexors of the Fingers

Flexor Digitorum Superficialis

• lies in the anterior compartment of forearm, deep to pronator teres, palmaris lonus and flexors carpi ulnaris and radialis
• superficial to flexor digitorum profundus and flexor pollicis longus
• muscle has long linear origin, but considered to arise by two heads
• medial/ humeroulnar head origin:
  • medial epicondyle of humerus, via common flexor tendon, the anterior part of the ulnar collateral ligament and the sublime tubercle at the upper medial part of the coronoid process of the ulna
• lateral/radial head origin:
  • upper two thirds of the anterior border of the radius
• halfway down the forearm, the muscle narrows and forms four separate tendons passing deep to the flexor retinaculum, here they are arranged in two pairs to enter the hand
  • superficial pair pass to the middle and ring fingers
  • deep pair pass to the index and ring finger
• insertion:
  • palmar surface of the base of the middle phalanges
• action:
• flexion of the metacarpophalangeal and proximal interphalangeal joints
• also contributes to flexion of the wrist

Flexor Digitorum Profundus

• lies deep to flexor digitorum superficialis on medial side of forearm
• origin:
  • arises from medial side of the coronoid process of the ulna, the upper three quarters of the anterior and medial surfaces of the ulna, and the medial, middle-third of the adjacent interosseus membrane
  • also arises from the aponeurosis that attaches the flexor carpi ulnaris to the posterior border of the ulna
• part of muscle arising from interosseus membrane forms a separate tendon halfway down the forearm, this passes to the index finger
• remaining tendons formed just proximal to the the flexor retinaculum
• separate tendons pass below the flexor retinaculum, lying side by side, deep to the tendons of flexor digitorum superficialis, but in the same synovial sheath
• the four tendons pass to their respective fingers in the palm
• insertion:
  • base of the palmar surface of the distal phalanges
• action:
  • flexion of the distal interphalangeal joint
  • also aids in flexion of the proximal interphalangeal, metacarpophalangeal and wrist joints, as it crosses several other joints during its course

Flexor Pollicis Longus

• lies on lateral side of flexor digitorum profundus
• origin:
  • arises from anterior surface of the radius, between the radial tuberosity above and pronator quadratus below, and the adjacent anterior surface of the coronoid process of the ulna
• fibres pass almost to the wrist, before the tendon is formed
• tendon passes below flexor retinaculum
• insertion:
  • palmar surface of the base of the distal phalanx of the thumb
• action:
  • flexor of the interphalangeal joint of the thumb
  • vital for all gripping activities of the hand
  • also flexes the metacarpophalangeal joint of the thumb and the wrist joint

Pulley System in the Hand

• The pulley system is an important anatomical structure in understanding the tendon system in the hand. (ref course).
• The annular pulley system's function - keep the tendons close to the bone, so that tendons don't bowstring in active flexion
• The cruciform pulley system is flexible and collapsible to allow for digital flexion without deformation of the pulley system
• This is key to remember when treating people who had a tendon repair as patients can sometimes present with bowstringing after a tendon repair, knowing the anatomy and function of the pulley system will aid in the clinical reasoning of the therapists as to why this is occurring.

For more information on the Pulley System in the Hand, read this Physiopedia Page: Hand Pulleys

Vincula Tendinum

The tendons of flexor digitorum superficialis provide attachments for the vincula tendinum, which convey blood vessels to the tendon. The flexor tendons are encapsulated in a sheath. The flexor digitorum superficialis and flexor digitorum profundus have two vinicula each. These tendons are not well-vascularised and there are some avascular areas that receive nutrition by diffusion. (course)

This mechanisms puts the tendons at risk for adhesions. When adhesions are present, the tendon can not glide freely and this leads to limited range of motion and limited functional capacity. (course)

Tendon Zones

It is important to know and have a good understanding of the different tendon zones as this will:

• inform treatment planning
• the type of splint design that patient will need

Tendon zones differ for the extensors and the flexors. For the finger flexors the zones are as follows:

• Zone I - distal to the flexor digitorum superficialis (FDS)
• Zone II - from the FDS insertion to to distal portion of the A1 pulley
• Zone III - from the A1 pulley to the transverse carpal ligament
• Zone IV - the carpal tunnel
• Zone V - proximal to carpal tunnel

The thumb has its own zone distrubution.

• Zone I - distal to the interphalangeal joint (IP) in the thumb
• Zone II - between the metacarpophalangeal (MCP) and interphalangeal (IP) joints
• Zone III - proximal to the metacarpophalangeal (MCP) volar/palmar flexion crease

• Basic concepts in repair are similar for different zones
• Location of laceration directly affects healing potential

The below 8 minute video nicely outlines the key features of Flexor tendon injuries treatment and anatomy

Epidemiology of Flexor Tendon Injuries

• Incidence rate of 33.2 injuries per 100 00 person-years
• Highest incidence of injury occurs at 20 -29 years of age, and average age is 35 years
• Higher incidence in males
• Significant association between injury and age
• Incidence is inversely related to age (injuries decrease with increase in age)
• Extensor tendon injuries occur more frequently than flexor tendon injuries
• Majority of cases involve a single tendon, extensor tendon injuries involved Zone III of the index finger and flexor tendons involved Zone II of the index finger
• Common injury in people working in physical construction jobs, using saws, glass or getting metal lacerations
• Also common in people working in food preparation with knife injuries
• In recent years, the media has highlighted the increase in tendon injuries as a result of poor avocado de-seeding technique. In research a rising increase in avocado-related knife injuries to the hand has been reported

Mechanism of Injury / Pathological Process

Flexor tendon injuries commonly result from volar/palmar lacerations. This can occur with an accompanying neurovascular injury. Patients often present directly at a hospital as they have most likely sustained a significant laceration.

Another mechanism of injury is a rupture rather than a laceration, for example the FDP tendon has ruptured from its insertion at the distal phalanx - usually this is caused by a closed mechanism of injury. This usually occurs as a result of forced extension during active flexion. This happens in ball sports where a finger is forced into extension while it is being flexed or where a player grabs an opponent's shirt (jersey finger).

Clinical Presentation

Depending on the area of injury symptoms may include:

• Loss of active flexion strength or motion of the involved digit(s)
• Pain when attempting to flex the digit
• Swelling
• Tenderness

Diagnostic Procedures

• Clinical tests:
  • Flexor Digitorum Profundus (FDP) tendon - patient is unable to flex the distal interphalangeal joint (DIP) in isolation
  • Flexor Digitorum Superficialis (FDS) tendon - isolate the involved/affected finger and ask the patient to flex the proximal interphalangeal joint (PIP)
  • Flexor Pollicis Longus tendon - flexing the interphalangeal joint (IP) joint of the thumb in isolation

• Radiographs - may have associated fracture

• Ultrasound - used to assess suspected lacerations
• MRI

Outcome Measures

• Grip strength
• DASH
• Goniometer measurement

Medical Management

Surgical Repair

Surgical repair is needed for cut or ruptured tendons. When a tendon ruptures, the ends separate as a result of the tension in the tendons. Sometimes this separation between the cut or ruptured ends of the tendon can be several centimetres. Surgical repair is necessary in order to regain function that has been lost. The repair may be performed under general anaesthetic or regional anaesthetic (injection of local anaesthetic at the shoulder).  During surgery the wound is enlarged so that the cut ends of the tendon can be found and held together with stitches. After the surgery the hand and forearm are immobilised in a splint that is placed over the bandages with the wrist and fingers in a slightly bent position, in order to protect the repair.

The tendon repair is a surgeon-dependant process and surgeons will decide on the most appropriate technique for the specific tendon repair. Common repairs are four-strand or six-strand repairs. This review article, Flexion Tendon Injuries provide a good oversight of the various tendon repair techniques.

Post-surgical Tendon Healing

The healing stages of tendons includes three phases:

Inflammatory phase

• this is the first phase
• lasts from day one to day seven post-operatively
• in this stage fibroblasts produce type III collagen and macrophages help initiate healing and remodelling

Proliferative phase

• this is the second phase
• this runs from day 8 to about three weeks post-operatively
• tissue modelling via large amounts of disorganised collagen happens during this stage
• angiogenesis also happens during this stage

Remodelling phase

• this is the third stage
• occurs up until about 18 months post-operatively
• in this stage, tensile forces lead to tissue remodelling, and type III collagen is replaced with type I collagen
• this happens in a more linear fashion, and this creates cross-linking to build strength in the tendon

Post-Surgical Physiotherapy Management

Wound Management

After surgery wound management is the first step to address. The post-surgical wound may be dressed with a basic silicone dressing(products such as Mepitel may be used). The finger is wrapped with breathable handy gauze material. Other products that therapists may use include Coban, but a good, comfortable, clean and dry dressing is acceptable as well.

Compression bandaging is used to control oedema.

Orthoses

FDP and FDS Tendon Repair

• Forearm-based metacarpophalangeal joint (MCP) extension blocking splint with wrist in neutral and MCP's in around 30° of flexion.
  • Zone I, II and III injuries of the flexor digitorum profundus and/or the flexor digitorum superficialis
  • This promotes the arc of flexion to be activated by the long flexors, rather than the intrinsics.
  • It allows differential glide between the FDP and FDS tendon, as flexion is inititated by the FDP tendon in this position.
  • If therapists splint patients in greater degree of MCP joint flexion, flexion will be initiated by the intrinsics rather than the long flexors.
• Manchester short splint
  • hand-based splint
  • allows maximal wrist flexion, blocks wrist extension at 45°
  • MCP joints - 30° flexion
  • IP joints - neutral
  • The use of the Manchester sport splint appears to enhance the digital arc of flexion in the early phase. This results in improvements in DIP joint flexion and differential glide
  • Use of this type of splint showed improved outcomes, while still preserving repair integrity.

FPL Repair

• Dorsal forearm-based orthosis
  • goes to the tip of the thumb up to three quarters of the metacarpal length on the dorsum of the hand
  • wrist in neutral
  • thumb slightly palmar-flexed into eased opposition with the MCP in about 20° of flexion and IP joint in neutral

The type of orthosis/splint that will be used in a patient is often prescribed by the surgeon and therapists will need to discuss the appropriate choice of splint with the surgeons that they work with.

Rehabilitation Exercises

The goal of the rehabilitation exercises after a flexor tendon repair is to:

• keep the tendons gliding and promote differential tendon glide
• control early collagen deposition
• facilitate strengthening of the repair site
• prevent adhesions, tendon gapping or re-rupture
• provide patients with the best possible outcome after surgery

Various different protocols have been developed for the rehabilitation of flexion tendon repairs. These programs usually make use of combinations of active and passive range of motion.

Post-Operative Exercises FDS and FDP Repairs (first 6 weeks)

Place-and-hold Flexion Exercises

Many flexor tendon rehabilitation protocols include place-and-hold flexion exercises. However, recent research shows that this causes gapping and forces through the tendon when the tendon is suddenly required to activate after passive flexion. Hand therapists are moving away from this exercise and instead prescribe active flexion to a half fist with active extension into the back of the splint. (course)

This open source article with videos included, provides a good overview of why true active movement is preferred over full fist place-and-hold flexion exercises: Flexor Tendon Repair Postoperative Rehabilitation: The Saint John Protocol

Passive Flexion and Active Extension

• The patient can perform passive flexion of the fingers and then actively extend the fingers into the back of the splint.
• A way to prevent any PIP joint flexion adhesions is to put a ruler down the back of the splint for the patient to actively extend against. (course)

Exercise Frequency and Precautions

• Patients should perform these exercises for 10 repetitions, five times a day.
• Patients always do their exercises with the splint, so that there is no risk of extending the fingers and rupturing or putting the tendon at risk.

Post- Operative Exercises FPL Repair (first 6 weeks)

• Passive IP joint flexion exercises
• Passive thumb composite flexion
• Active flexion to about half of the patient's active range of motion
• 10 repetitions, 5 times a day

Post-Operative Exercises after 6 weeks

For all post-surgical tendon repairs - the splints are worn for 6 weeks

After the initial 6 weeks, the patient is weaned out of the splint to commence light functional use

Slowly increase and grade the patient's full active and full passive range of motion

Strengthening can usually commence at about 8 weeks post-operatively

Strengthening exercises can include activities such as:

Squeezing Theraputty, Play-doh or a sponge in hot water

If a patient has significantly reduced grip strength, can pr

The goal of any rehabilitation program is to provide incremental, controlled stress to promote differential tendon glide and control early collagen deposition; to facilitate strengthening of the repair site; and to avoid adhesion formation, gapping, or re-rupture. Animal models have shown that motion and tension improve eventual strength. Specific programs have evolved using combinations of active and passive range of motion (ROM). These are described below.

Early physical therapy and splinting after flexor tendon repair is very important to

• Improve tendon healing,
• Increase tensile strength,
• Decrease adhesion formation,
• Early return of function and less stiffness and deformity.

After optimizing the repair, the therapist team works with the surgeon to select a rehabilitation plan that protects the repair but helps to maintain tendon gliding. There are 3 types of rehabilitation programs for flexor tendon repairs: delayed mobilization, early passive mobilization, or an early active mobilization. The first part of the process is to ensure a thorough assessment is undertaken.

Objective Examination

• Observe the resting posture of the hand and assess the digital cascade
• Observe evidence of malalignment or malrotation may indicate an underlying fracture
• Assess skin integrity to help localize potential sites of tendon injury
• Look for evidence of traumatic arthrotomy

Assess Range of Movement

• Passive wrist flexion and extension allows for assessment of the tenodesis effect
• Normally wrist extension causes passive flexion of the digits at the MCP, PIP, and DIP joints
• Maintenance of extension at the PIP or DIP joints with wrist extension indicates flexor tendon discontinuity
• Active PIP and DIP flexion is tested in isolation for each digit

Neurovascular Assessment

This is an important aspect of the assessment given the close proximity of flexor tendons to the digital neurovascular bundles

Physiotherapy Protocols

1. Immobilization
   1. Indicated for children and non-compliant patients
   2. Casts/splints are applied with the wrist and MCP joints positioned in flexion and the IP joints in extension
2. Early passive motion
   1. Duran protocol: low force and low excursion; active finger extension with patient-assisted passive finger flexion and static splint
   2. Kleinert protocol: low force and low excursion; active finger extension with dynamic splint-assisted passive finger flexion
   3. Mayo synergistic splint: low force and high tendon excursion; adds active wrist motion which increases flexor tendon excursion the most
3. Early active motion
   1. Moderate force and potentially high excursion
   2. Dorsal blocking splint limiting wrist extension
   3. Perform “place and hold” exercises with digits

No guidelines for rehabilitation should be followed exactly. Many factors influence therapy decisions, including repair technique, associated tendon healing, passive versus active range of motion, edema, and tendon adhesions. These factors can assist in guiding rehabilitation progression and promote functional range of motion, safely mobilize the repaired tendon(s) and prevent gapping, rupture, and adhesions.

Hand Therapy

The hand therapist will usually replace the plaster splint with a light plastic splint and start a protected exercise programme within a few days of the operation. The therapy programme after tendon repair is crucial and at least as important as the operation itself, so it is vital to follow the instructions of the therapist closely.   The objective is to keep the tendon moving gently in the tunnel, to prevent it from sticking to the walls of the tunnel, but to avoid breaking the repair.

The splint is usually worn for five or six weeks, after which a gradual return to hand use is allowed.  However, the tendon does not regain its full strength until three months after the repair and the movement may improve slowly for up to six months.

Complications

• The repair breaks.  It usually happens early on as the tendon is at its softest at this stage of healing. The patient may feel a "ping" as the repair snaps or simply notices that the finger isn't bending in the way it has been.
• The tendon sticks to its surroundings and does not slide in its tunnel. The finger(s) can be moved with help from the other hand (passive movement) but will not move on its own (active movement).  Additional hand therapy may help.  In some cases, an operation to release the tendon from the scar tissue (tenolysis) may improve the movement, but full movement may not be regained.