Flexor Tendon Injuries
Clinically Relevant Anatomy
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.
Flexor tendon injuries are a traumatic condition classified by the zone of injury ( zone 1 distal to FDS insertion, zone 2FDS insertion to distal palmar crease, zone 3 palm , zone 4 carpal tunnel, zone 5 carpal tunnel to forearm)
- basic concepts in repair are similar for different zones
- location of laceration directly affects healing potential
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
The below 8 minute video nicely outlines the key features of Flexor tendon injuries treatment and anatomy
Mechanism of Injury / Pathological Process
Commonly results from volar lacerations and may have concomitant neurovascular injury
- loss of active flexion strength or motion of the involved digit(s)
- Physical exam
- observe 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
- 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
important given the close proximity of flexor tendons to the digital neurovascular bundles
Radiographs - may have associated fracture
Management / Interventions
Tendon repair. Cut tendons do not heal by themselves; the tension in the tendon causes its cut ends to separate, sometimes by several centimetres. Without surgical repair, there is no prospect of regaining the movement that has been lost. The repair may be performed under general anaesthetic or regional anaesthetic (injection of local anaesthetic at the shoulder). The wound is enlarged so that the cut ends of the tendon can be found and held together with stitches. At the end of the operation the hand and forearm are immobilised in a plaster splint that is placed over the bandages with the wrist and fingers in a slightly bent position, in order to protect the repair.
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 rerupture. 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.
indicated for children and non-compliant patients
casts/splints are applied with the wrist and MCP joints positioned in flexion and the IP joints in extension
2.Early passive motion
- Duran protocol: low force and low excursion; active finger extension with patient-assisted passive finger flexion and static splint
- Kleinert protocol: low force and low excursion; active finger extension with dynamic splint-assisted passive finger flexion
- Mayo synergistic splint: low force and high tendon excursion; adds active wrist motion which increases flexor tendon excursion the most
3.Early active motion
- moderate force and potentially high excursion
- dorsal blocking splint limiting wrist extension
- perform “place and hold” exercises with digits
No guideline 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 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.
- 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.
- Ortho bullets Flexion tendon injuries Available from: https://www.orthobullets.com/hand/6031/flexor-tendon-injuries (last accessed 8.12.2019)
- J Knight Flexor tendon surgery Available from: https://www.youtube.com/watch?v=nrZdYJdrSCo&app=desktop (last accessed 8.12.2019)
- BSHH Flexor tendon injuries Available from: https://www.bssh.ac.uk/patients/conditions/26/flexor_tendon_injury#What_is_the_treatment_ (last accessed 8.12.2019)
- Klifto CS, Bookman J, Paksima N. Postsurgical Rehabilitation of Flexor Tendon Injuries. The Journal of hand surgery. 2019 May 18. Available from: https://www.sciencedirect.com/science/article/pii/S0363502317322049#sec3 (last accessed 9.12.2019)
- Rrecaj S, Martinaj M, Murtezani A, Ibrahimi-Kaçuri D, Haxhiu B, Zatriqi V. Physical therapy and splinting after flexor tendon repair in zone II. Medical Archives. 2014 Apr;68(2):128. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4272500/ (last accessed 8.12.2019)
- Kannas S, Jeardeau TA, Bishop AT. Rehabilitation following zone II flexor tendon repairs. Techniques in hand & upper extremity surgery. 2015 Mar 1;19(1):2-10. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25700105 (last accessed 9.12.2019)