Flexor Tenolysis 

Updated: Sep 13, 2021
Author: Cato T Laurencin, MD, PhD; Chief Editor: Harris Gellman, MD 



Flexor tenolysis is a surgical procedure used to remove adhesions that inhibit active flexion of digits.[1, 2, 3]  Normal active tendon function requires that flexor tendons be able to glide smoothly within their tendon sheath. Damage to these tendons can necessitate surgical repair, and tendon adhesions can develop despite successful surgical tendon repair, appropriate postoperative management, and compliance with physical therapy.[4]

The exact etiology of tendon adhesions following surgery is unclear, but it appears to be due to scarring between the damaged surfaces of both the tendon and the tendon sheath when the tendon is immobilized.[5]

The classical paradigm including inflammation, proliferation, synthesis, and apoptosis appears to be at work, but cellular activity has been shown to be greater in the surrounding tendon sheath.[3]  Initially, the adhesions were thought to be the source of reparative cells, nutrients, and blood supply to the tendon, but that opinion fell out of favor.[6]  Subsequent investigations revealed that healing of tendons could occur in the absence of tendon adhesions and thereby helped to elucidate the presence of a population of cells inside the tendon capable of repair.[7]

As far back as the 1960s, tendon immobilization was shown to be critical to adhesion formation.[8, 9]  Subsequent investigations mapped out the phases of repair that occur separately in both the tendon and surrounding synovial sheath and showed that the healing phases are more robust and prompt in the sheath than in the tendon body.[3]


Any surgery of the flexor tendon anatomy should only be undertaken if the patient is willing to commit to a rigorous course of physical therapy. In addition, the patient must have the following:

  • Intact alignment of skeletal structures, including bones, ligaments, and tendons, with no underlying arthrosis
  • Stable, mature scarring evident over all wound areas
  • Good strength in flexor and extensor muscles of the hand, as well as intact nerves to flexor muscles
  • Good passive range of motion (ROM) of affected tendons

Clinically, tenolysis is frequently offered if after a prolonged period of immobilization, passive flexion noticeably exceeds active flexion or if the patient exhibits a fixed contracture at a proximal interphalangeal (PIP) joint.[4] The exact period prior to undergoing tenolysis is up for debate, and every patient is unique, but it is generally accepted that flexor tenolysis is recommended after the patient has concluded passive and active ROM exercises for at least 3 months and has reached a plateau of progress.[3]


Tenolysis is absolutely contraindicated in patients with active infection, motor-tendon problems secondary to denervation, and unstable underlying fractures requiring fixation and immobilization.

Relative contraindications include extensive adhesions, immature previous scars, and severe posttraumatic underlining arthrosis.

Technical Considerations


Two tendons contribute to active flexion of a finger: the tendon from the flexor digitorum profundus (FDP) muscle and the tendon from the flexor digitorum superficialis (FDS) muscle (see the image below). Both tendons attach to each finger. Both are enclosed within an enclosed tendon sheath called a theca. The tendons connect the muscle bodies in the forearm with the fingers in the hand, passing through the carpal tunnel at the wrist.

Flexor tendons with attached vincula. FDS, flexor Flexor tendons with attached vincula. FDS, flexor digitorum superficialis; FDP, flexor digitorum profundus.

Tendons from the FDS insert on the base of the middle phalanx of each finger to flex the finger at the metacarpophalangeal (MCP) and PIP joints. The FDP inserts into the base of the distal phalanx and flexes the finger at the MCP, PIP, and distal interphalangeal (DIP) joints. Not all fingers are capable of independent movement in every individual, because the tendons from the FDP are usually connected proximal to the individual fingers, the only common exception being the tendon to the index finger.

An elaborate system of pulleys is in place to prevent “bowstringing” or elevation of the tendon away from the palmar surface of the wrist during active flexion. The tough membrane that prevents this at the wrist is called the flexor retinaculum of the hand, and the tunnel for the tendons beneath is called the carpal tunnel.

At the fingers, there are various anular or cruciate ligaments that perform a similar task by preventing the tendons from elevating. The precise number of anular or cruciate ligaments in each finger can potentially vary from individual to individual, but commonly, there are three or four cruciate ligaments (C1-C4, proximal to distal) and four or five anular ligaments (A1-A5, proximal to distal).

The first anular pulley, A1, lies at the head of the metacarpal bones, whereas the second through fifth anular ligaments, A2-A5, all attach to the bones on the finger. The cruciate ligaments generally are smaller than anular ligaments and are found between anular ligaments. Together, the cruciate and anular ligaments make a tunnel through which normally the flexor tendons pass.


Flexor tenolysis is a highly individualized procedure; consequently, reports of how much active flexor ROM increases after tenolysis vary widely. It has been reported that active ROM increases for between 59% and 90% of all patients.[10]

Breton et al evaluated the increase in active ROM and the incidence of complications in 60 patients (75 fingers) who underwent flexor tenolysis in zone 2, with or without dorsal tenolysis or PIP arthrolysis.[11]  The mean increase in total active motion for patients undergoing tenolysis only was 60°, compared with 90° in those undergoing tenolysis with arthrolysis. At 6 weeks, 23% of cases had excellent functional outcomes, 47% had good outcomes, 20% had average outcomes, and 10% had poor outcomes. 





Periprocedural Care

Preprocedural Planning

Imaging studies

The major utility of imaging studies prior to flexor tenolysis is to evaluate whether the patient has a failure of tendon reconstruction, elongated callus, or tendon adhesions that lead to the clinical presentation.[12]

Initially, radiographs should be taken to ensure proper anatomic alignment of the skeletal elements.[3]  Ultrasonography (US) has proved effective for assessing both the presence and the location of a ruptured tendon repair.[13, 14]  Additionally, the mechanism of US allows dynamic assessment of flexor tendon injuries; accordingly, this modality is recommended for evaluation of zone 1 (distal interphalangeal [DIP] joint) tendon injuries.

US is not, however, effective for distinguishing pure adherence from elongated callus and thus for determining the type of surgical intervention required.[12]  Additionally, US of the ligaments in zone 2 (metacarpophalangeal [MCP] and proximal interphalangeal [PIP] joints) is a difficult endeavor and is strongly operator-dependent.[12]

Magnetic resonance imaging (MRI) has proved to be effective as a noninvasive imaging procedure to differentiate between tendon rupture and tendon adhesions in zone 2.[12]  Imaging artifacts from implanted devices, including metal plates or screws, can limit the effectiveness of MRI in evaluating tendon injuries.

Histologic findings

In a rabbit model of tendon repair, once a tendon is injured, within 24 hours a noticeable increase in cellularity, predominantly from neutrophils, is seen. In the same model, cells in the tendon sheath are seen to migrate into the tendon, and cells from the periphery of the tendon are seen to migrate to the interior of the tendon core within 7 days.[5]

By 7 days, alpha smooth-muscle actin expression is high, which marks the presence of myofibroblasts and pericytes in the wound area.[5] From 7 to 21 days, cells are both depositing and remodeling collagen bundles, which correlate with a peak in heat shock protein 47 around day 21. As intrinsic healing of affected tendons progresses, alignment of collagen fibers along the axis of contraction, as well as a decrease in inflammatory cellularity, is usually seen, with a peak in apoptosis around 84 days in rabbits.[5, 12]

In human subjects, studies that closely track cell origin and type are lacking, but when histologic sections of adhesions are examined, noninflammatory cells resemble myofibroblasts and secrete types I and III collagen, and epitenon cells are also involved in the process of both collagen production and collagen debris clearance.

Patient Preparation

Since the 1970s, flexor tenolysis has been popularly performed with local anesthesia alone.[15]  One benefit of this approach is that the surgeon may engage actively with the patient to ensure that the tendon is free from adhesions and can glide easily in the tendon canal. Active participation from the patient also establishes whether the musculature for digit flexion is strong enough to power tendon contraction. There is increasing interest in performing flexor tenolysis via the WALANT (wide awake, local anesthesia, no tourniquet) approach.[16, 17, 18]

General anesthesia can still be considered for patient-specific factors, including irritability, anxiety, or a complicated surgical plan owing to multiple affected tendons. Under circumstances of general anesthesia, active flexion can be ascertained by opening a surgical window proximal to the affected tendon as described by Whitaker et al.[19]  Using this opened window, surgeons can pull on the tendons to simulate muscular contraction.



Approach Considerations

Flexor tenolysis is a surgical procedure used to remove adhesions that inhibit active flexion of digits. Candidates for this procedure typically present with decreased active range of motion (ROM) after surgical repair of flexor tendons. The average time from flexor repair to flexor tenolysis has been indicated to be around 8 months, but the length of this interval varies widely, ranging from 2 to almost 25 months.[4]  Developments in primary tendon repair (eg, stronger core tendon repair techniques, as well as judicious and adequate venting of critical pulleys, followed by a combination of passive and active digital flexion and extension) may lead to lower rates of tenolysis.[20]

A 2012 study looked at a population of New York State dwellers who had flexor tendon reconstruction and found that 6% of patients required a subsequent surgical correction. Tenolysis was performed in 186 (3.6%) of 5229 patients, and tenolysis in combination with tendon re-repair was performed in 11 (0.2%).[10]  In that particular population, patients who underwent concomitant nerve repair during the initial tendon repair were 26% less likely to undergo a reoperation.

Other studies showed that approximately 28% of flexor tendon repairs have a suboptimal recovery period, likely due in large part to tendon adhesions.[21]

Although steroid injections to augment tendon repair are notable in the literature,[19, 22, 23]  they are not universal, and by the time tendon adhesions occur, there is no currently accepted medical therapy to treat the condition.[3]

Various barrier materials have been studied as potential means of preventing postoperative tendon adhesion, including Seprafilm and other hydrogels.[24, 25, 26]

A mini-invasive approach to flexor tenolysis has been described for adhesions in zones 1 and 2.[27]

Surgical Lysis of Flexor Tendon Adhesions

Care must be taken to ensure that the patient meets all indications for surgery to proceed, including a rigorous examination of the external anatomy to check for mature scarring and good passive ROM.

The procedure begins with exposure of the full length of the flexor tendon through either a zigzag or a midlateral incision. A zigzag incision, championed by Schneider, provides the best operative window to the flexor tendon and pulley system.[28, 29] The midlateral incision is believed to diminish the presence of scarring directly over the affected flexor tendon and puts the neural and vascular structures at less risk.[30]

After exposure, both flexor tendons (ie, flexor digitorum profundus [FDP] and flexor digitorum superficialis [FDS]) are raised from underlying structures, and all tendon adhesions are lysed. After adhesions are removed between the tendons and the sheath, it is usually recommended to remove adhesions between the FDP and the FDS, with sacrifice of the FDS being necessary if free tendon gliding cannot be accomplished otherwise.[29]

During the process of removing adhesions, the participation of the patient can be critical, especially when one is trying to differentiate between scar tissue and the pulley system. Although adhesion removal using lasers has been described in rabbits, the practice has not gained a wide clinical following in the human population, and most surgeons still use traditional hand instruments modified for the procedure.[31]

A crucial aspect of flexor tenolysis is to respect the pulley system for the flexor tendons. Preservation of this system, especially the A2 and A4 pulleys, is vital for normal flexor tendon activity. Less commonly, the pulley structures are compromised and a pulley reconstruction may be indicated.[3, 29]  A safer way to reconstruct the pulley system using natural or synthetic materials could potentially improve the prognosis for this procedure.[32]  Usually, the procedure continues and adhesions are removed until full active flexion can be achieved.

The final stage of the surgery is to assess whether the tendon is robust enough to progress through the rigorous physical therapy necessitated by this complex procedure. Both scarring and substantial tendon tissue loss (>30% width lost) can put the patient at risk, and in such situations it is generally recommended that the patient undergo a two-stage tendon reconstruction.[12, 28, 29, 30, 33]

Some physicians treat patients with steroids at this point in order to abrogate the formation of new adhesions during recovery, but given that steroids have a well-described capability to limit the healing response, many abstain from their use altogether.

Since the 1930s, physicians have described the use of various other natural or synthetic materials to prevent subsequent formation of tendon adhesions,[34, 24, 25, 26] but these techniques have not yet been universally accepted.

Postoperative Care

Physical therapy is absolutely necessary for healthy tendon function to return, and poorly controlled pain can hamper the recovery effort. To reduce postoperative pain, most physicians recommend oral analgesia, but every patient is different, and severe cases of pain may necessitate more extreme measures, including indwelling catheters capable of dispensing local anesthesia.[30]

When to start physical therapy in an issue up for debate. As immobilization is necessary for the tendon adhesions to form, some physicians recommend immediate hand exercises, whereas others recommend waiting for a period of days until the effects of the surgical approach (eg, inflammation and scarring) have diminished.

The level and rigor of physical therapy should take the individual surgery of the patient into consideration. If, upon surgical exposure of the flexor tendon, the surgeon notices significant impairment in the health and quality of the tendon, this important information should be relayed to the physical therapist, who may then appropriately modify a treatment plan. Protocols for patients with poor tendon quality are well documented and have shown improved results in comparison with a protocol for a healthier tendon.[35]

A common protocol for patients with a healthy tendon is to undergo physical therapy 3-5 days per week at first and then to decrease the frequency of physical therapy slowly over a period of weeks to months, with the goal of decreasing pain and increasing ROM and strength.


Some studies have shown that as many as 20% of patients who undergo this procedure do not benefit from the operation; 8% of patients experience frank tendon rupture, with some studies reporting rates as high as 15%.[10, 35, 36]

Although flexor tenolysis has proved to be effective in the majority of cases, the complication rate is still very high, and much research is needed into protocols, surgical techniques, or materials that can restore active ROM to patients.

One way to combat the formation of adhesions after flexor tendon repair would be to find a therapy that could decrease the immunologic response to the surgery.[37, 38]  As mentioned before, corticosteroids have been tried, but their limitations are too severe for widespread acceptance.