Central slip repair is the treatment, either surgical or conservative, of a torn or disrupted central slip tendon in the finger, aimed at restoring the ability to straighten the middle joint and preventing a permanent deformity known as boutonnière. Because the central slip is a small but mechanically critical part of the finger’s extensor system, getting the timing and approach right matters enormously: a missed or delayed diagnosis can turn a straightforward splinting problem into a complex reconstruction. The picture is further complicated by the fact that no randomized controlled trials directly compare surgical and nonsurgical approaches, leaving surgeons and therapists to rely on case series and biomechanical studies.
What the Central Slip Actually Does
The central slip is the middle portion of the extensor tendon that crosses the back of the finger and attaches to the base of the middle phalanx, the middle bone of the finger. Its job is to straighten the proximal interphalangeal (PIP) joint, the finger’s middle knuckle. On either side of the central slip sit two lateral bands, which continue distally to straighten the fingertip joint. These structures are held in place by a web of small ligaments, collectively called the extensor hood.
When the central slip tears or detaches, the lateral bands gradually slide toward the palm side of the finger. Over time, this repositioning means the lateral bands start pulling in the wrong direction: instead of helping extend the middle joint, they flex it, while simultaneously hyperextending the fingertip. This is the boutonnière deformity, so named because the head of the middle phalanx pokes through the torn extensor mechanism like a button through a buttonhole. A cadaveric study found that cutting the central slip alone was not enough to produce a boutonnière deformity; the deformity only appeared after additional damage to the triangular ligament and the transverse and oblique fibers of the interosseous hood, meaning all the surrounding stabilizing structures had to fail before the lateral bands could fully subluxate below the joint’s axis of rotation.1Journal of Hand Surgery. Biomechanical Analysis of the Extensor Mechanism and Boutonniere Deformity That finding has real clinical significance: it explains why a fresh central slip injury can look deceptively normal at first, since the remaining structures temporarily hold everything in place.
How Central Slip Injuries Are Diagnosed
The most widely used bedside test is Elson’s test. The patient places the injured finger over the edge of a table with the middle joint bent at 90 degrees and tries to push the finger straight against resistance. In a healthy finger, the central slip tenses and the fingertip stays floppy. When the central slip is torn, force is rerouted through the lateral bands, and the fingertip becomes rigid instead. A cadaveric analysis found this was the only clinical maneuver that could reliably detect central slip disruption across different simulated injury patterns.2PubMed. Diagnosis of closed central slip injuries. A cadaveric analysis of non-invasive tests
That said, Elson’s test has limits. A controlled experimental study showed that the difference in resistance at the fingertip between an intact and disrupted central slip, while measurable in a laboratory setting, is so small that it can be imperceptible during a clinical exam, especially in a swollen, painful finger soon after injury. The researchers recommended considering delayed testing or repeat examination once swelling and pain have subsided to improve the test’s sensitivity.3PubMed Central. Experimental Evaluation of the Elson Test Efficiency Following Central Slip Injury Another important gap: when both the central slip and the lateral bands are lacerated, Elson’s test and its modifications lose their usefulness entirely, because the lateral bands can no longer transmit extension forces to produce the telltale fingertip rigidity.4PubMed Central. Central slip and bilateral lateral band laceration with negative Elson’s and modified Elson’s tests In those cases, a false-negative test can lead to a missed diagnosis. MRI and ultrasound can help confirm the injury, but in practice the diagnosis often relies on a combination of clinical suspicion, mechanism of injury, and repeated examination.
A computational model of the finger validated against cadaveric testing was able to replicate the positive Elson’s test by tensioning the extensor tendon after dividing the central slip while holding the PIP at 90 degrees: the fingertip joint extended, confirming the mechanism behind the clinical finding.5PubMed Central. Assessment of the ligamentous stress distribution in the pathomechanics of the boutonniere deformity through a computational 3D model This kind of modeling work helps surgeons understand which structures contribute most to different stages of the deformity, which in turn guides surgical decision-making about what needs to be repaired and what can be left alone.
Conservative Management With Splinting
Not every central slip injury requires surgery. Closed injuries, where the skin is intact and the tendon is stretched, partially torn, or avulsed from bone without displacement, are commonly treated with splinting. The standard approach holds the PIP joint in full extension (zero degrees) while leaving the fingertip joint free to move. Keeping the middle joint straight allows the torn central slip to heal at its proper length, while flexing and extending the fingertip encourages the lateral bands to glide back into their normal dorsal position rather than migrating palmward.
A retrospective study of patients with acute central slip lacerations treated with initial immobilization in full extension for an average of three and a half weeks, followed by active bending in a finger-based dynamic extension-assist splint, reported excellent results. Patients achieved an average PIP extension of +1 degree and average PIP flexion of 109 degrees, with a combined total active motion of about 175 degrees across the PIP and fingertip joints.6PubMed. Dynamic extension assist splinting of acute central slip lacerations These numbers compare favorably to surgical outcomes, which is part of the reason conservative management remains a first-line option for suitable injuries. The protocol also required less frequent therapy visits and used only a small finger-based splint, making it practical for patients to wear during daily activities.
The catch is compliance. If the splint slips or the patient bends the joint before the tendon has healed, the repair fails and a chronic deformity develops. Some hand therapists use a thermoplastic splint molded directly to the finger, while others prefer a figure-of-eight design or a prefabricated sleeve. Regardless of the style, the goal is uninterrupted extension for a period that typically runs four to six weeks before graded flexion exercises begin.
Surgical Repair Techniques
Surgery is generally indicated when the injury is open (a laceration has cut through the tendon), when the central slip has avulsed a bone fragment that needs fixation, or when conservative management has failed and a fixed deformity has developed. Several techniques exist, and no single method has proven clearly superior.
Direct suture repair is the most straightforward approach when enough tendon tissue remains on both sides of the tear. One group described a four-strand core double-looped suture technique using braided polyester, augmented with a small bone anchor at the insertion site on the middle phalanx.7PubMed Central. Anatomic Repair of the Central Slip with Anchor Suture Augmentation for Treatment of Established Boutonniere Deformity The anchor gives the repair a secure bony attachment point, which is especially useful when the tendon has pulled away from bone rather than torn in its midsubstance.
Bone anchor fixation has been studied as a standalone method as well. A case series of eight digits repaired with a miniature bone anchor for central slip avulsion injuries concluded that the technique was reliable for soft-tissue-to-bone fixation and recommended it as a treatment option for patients needing surgical repair.8PubMed. Surgical repair of central slip avulsion injuries with Mitek bone anchor–retrospective analysis of a case series A separate biomechanical study tested the anchor repair against the traditional horizontal mattress stitch in 40 cadaver fingers and found no statistically significant difference in the force required to pull the repair apart, with the anchor group averaging about 22 newtons and the mattress group about 25 newtons.9PubMed. Repair of central slip avulsions using Mitek Micro Arc bone anchors. An in vitro biomechanical assessment In other words, the two methods hold up about equally well under load, and the choice between them is often guided by the surgeon’s preference and the specific injury pattern.
Reconstruction for Chronic Deformities
When the central slip injury is missed or undertreated and a fixed boutonnière deformity sets in, a simple direct repair is usually not enough. The surrounding soft tissues have contracted and remodeled: the volar plate has shortened, the lateral bands are stuck below the joint axis, and the oblique retinacular ligaments may be taut on the palm side while the dorsal structures have stretched out. Addressing the chronic deformity requires a more elaborate reconstruction that deals with all of these secondary changes.
One approach involves releasing the extensor expansion proximal to the distal insertion of the oblique retinacular ligaments, recessing the extensor tendon proximally, and then lifting the lateral bands back up onto the dorsal side of the PIP joint after separating the transverse retinacular ligaments from their volar insertion.10PubMed. Surgical management of chronic boutonniere deformity The idea is to restore the normal dorsal positioning of the lateral bands so they once again contribute to extension rather than flexion at the PIP joint.
When the central slip tissue itself is too damaged or scarred to be repaired directly, a tendon transfer can replace it. A commonly described technique uses a slip of the flexor digitorum superficialis (FDS) tendon, routed from the palm side of the finger through a drill hole in the base of the middle phalanx and woven into the extensor tendon on the back of the proximal phalanx.11PubMed. Central Slip Reconstruction With a Distally Based Flexor Digitorum Superficialis Slip: A Biomechanical Study In one case report, a patient treated with a partial FDS tendon reconstruction saw their range of motion at the PIP joint return to normal within two months and their disability score drop dramatically from 50 to about 4 on a standardized hand-function questionnaire.
A newer cadaveric technique called fractional dolphin tenotomy offers a graduated option for managing the fingertip hyperextension component of chronic boutonnière. By making partial transverse cuts across the terminal tendon, surgeons can reduce fingertip hyperextension in a controlled, stepwise fashion. In cadaver testing, one-third tenotomy reduced average fingertip hyperextension from about 15 degrees to 11 degrees, one-half tenotomy brought it to about 9 degrees, and two-thirds tenotomy brought it to about 5 degrees, while a complete tenotomy created an unacceptable 25-degree extension lag.12PubMed Central. Fractional Dolphin Tenotomy for Boutonniere Deformity: A Cadaveric Study The stepwise nature of the technique gives the surgeon fine control, which is appealing in a deformity where overcorrection at the fingertip is a known risk.
Rehabilitation After Repair
How the finger is managed in the weeks after surgery is arguably as important as the repair itself. Historically, the repaired finger was held completely still in extension for six weeks, but prolonged immobilization tends to produce stiff joints and adhesions that limit the final range of motion. The shift in recent decades has been toward earlier controlled movement.
The short arc motion (SAM) protocol is the most studied early-movement approach for central slip repairs. The principle is biomechanically grounded: the recommended tendon excursion for the extensor tendon in zone III during early healing is about 3.75 millimeters, which corresponds to roughly 30 degrees of PIP joint arc. The resistance applied to the central slip during active extension from 30 degrees back to full extension has been calculated at approximately 290 grams, a load the healing repair can safely tolerate. The fingertip joint is left free during PIP flexion to let the lateral bands slide normally, while isolated fingertip exercises with the PIP held at zero degrees create a distal glide of the extensor tendon that promotes healing without stressing the repair site.13Journal of Hand Therapy. An Analysis of Factors That Support Early Active Short Arc Motion of the Repaired Central Slip
The clinical results support this approach. Compared with static immobilization, the SAM protocol improved extension lag from about 8 degrees down to 3 degrees and increased PIP motion from about 72 degrees to about 88 degrees, without increasing complications.14The Journal of Hand Surgery. Early active short arc motion for the repaired central slip A subsequent study confirmed that early active short arc motion produces improved range of motion with shorter treatment time compared with static immobilization.15PubMed. Early active short arc motion following central slip repair In practice, the protocol begins within the first week after surgery. The patient actively bends and straightens the PIP joint through just 30 degrees while wearing a protective splint between exercise sessions. Over subsequent weeks, the arc is gradually increased as the tendon gains strength.
Wide-Awake Surgery and Intraoperative Testing
A development that has changed how some surgeons approach central slip repair is the use of wide-awake local anesthesia with no tourniquet, often abbreviated WALANT. Instead of putting the patient under general anesthesia or using a regional nerve block that paralyzes the hand, the surgeon injects local anesthetic with a small amount of epinephrine directly into the surgical area. The patient stays awake and can actively move the finger on command during the operation.
This has specific advantages for central slip repair. The surgeon can ask the patient to extend the finger after completing the repair and directly observe whether the PIP joint reaches full extension, whether the repair feels too tight (which would limit flexion later), and whether the lateral bands are tracking properly. One group reported that WALANT allowed them to check the stability of the repair, predict postoperative range of motion, and apply a pencil test to verify tendon glide, all while the repair was still accessible for adjustment. The ability to fine-tune the tightness of the repair during surgery means the surgeon can aim for minimal extension lag without overcorrecting into flexion stiffness, and can start early active motion postoperatively with greater confidence.16Journal of Hand Surgery Global Online. Successful Boutonniere Reconstruction With Wide-Awake Local Anesthesia No Tourniquet Intraoperative patient education is another practical benefit: when the patient sees their own finger moving during surgery, they tend to better understand the rehabilitation exercises they will need to do afterward.
Boutonnière in Rheumatoid Arthritis
The boutonnière deformity that develops in rheumatoid arthritis has a different origin than a traumatic central slip tear, though the end result looks similar. In rheumatoid disease, chronic inflammation of the joint lining (synovitis) gradually stretches and weakens the central slip from the inside out, rather than a single forceful event tearing it. The progression tends to be slower and more predictable but is also harder to reverse, because the underlying disease continues to damage the joint surfaces and soft tissues even after a repair.
Treatment options in rheumatoid arthritis span a wide range depending on how far the deformity has progressed. Early, flexible deformities may respond to corrective splinting or corticosteroid injections into the joint. When the joint lining is thickened but the deformity is still passively correctable, synovectomy, the surgical removal of the inflamed tissue, can be combined with extensor tendon reconstruction. For stiffer deformities, a terminal tenotomy at the fingertip can rebalance the forces across the finger. When the joint surfaces themselves are destroyed, salvage procedures such as joint fusion (arthrodesis) or joint replacement (arthroplasty) become the remaining options.17PubMed. Treatment of boutonniere finger deformity in rheumatoid arthritis The key difference from traumatic cases is that the underlying inflammatory disease needs to be well controlled medically before any surgical reconstruction has a reasonable chance of lasting.
The State of the Evidence
One of the most striking things about central slip repair is how thin the evidence base actually is. A systematic review of treatments for central slip extensor tendon injuries screened thousands of studies and found only nine that evaluated treatment modalities in adult cohorts with acute central slip injuries. No randomized controlled trials were identified, and no studies directly compared operative with nonoperative management. The review concluded that the roles of different treatment strategies for both open and closed injuries are not well supported by evidence.18PubMed Central. Central slip extensor tendon injuries: a systematic review of treatments
This gap matters for patients. In practice, the choice between splinting and surgery is often guided by the injury pattern (open versus closed, acute versus chronic, avulsion versus midsubstance tear) and the surgeon’s experience rather than by head-to-head trial data. The rehabilitation literature is further ahead: the SAM protocol has at least been compared to static immobilization and shown measurable benefit. But for the fundamental question of whether a given acute central slip injury should be operated on or splinted, the honest answer is that no high-quality comparative data exist. Given how common hand injuries are, this is a surprisingly underresearched corner of orthopedic surgery.
When a Finger Still Will Not Straighten
Even with a well-executed repair and diligent rehabilitation, some patients are left with a residual extension lag at the PIP joint, a persistent inability to fully straighten the middle knuckle. Small lags of a few degrees are common and often functionally insignificant. Larger lags may require a secondary procedure, whether that is a repeat central slip tightening, lateral band repositioning, or, in severe cases, a salvage fusion of the PIP joint in a functional position. The fingertip can also be a problem after repair: overcorrection of the lateral bands can produce a swan-neck posture, the reverse deformity in which the PIP hyperextends and the fingertip drops into flexion. Balancing these competing forces is part of what makes boutonnière reconstruction one of the more humbling problems in hand surgery.
Patients with occupational demands that involve sustained gripping or repetitive finger flexion, such as musicians, mechanics, and climbers, often have the hardest time tolerating the prolonged splinting and restricted activity that central slip healing requires. For these individuals, establishing realistic expectations early and tailoring the rehabilitation timeline to the specific demands they plan to return to are as important as the technical details of the repair itself.