Longitudinal Tear of the Central Slip Causing Painful and Unusual Snapping of the Finger: A Case Report

Abstract

The most common cause for catching or snapping in the finger is stenosing tenosynovitis, that is, trigger finger. Although less common, snapping can also occur as a result of extensor mechanism injury. Among these injuries, sagittal band rupture is most common and leads to snapping at the metacarpophalangeal joint. Snapping at the proximal interphalangeal (PIP) joint is rare with only 4 reported cases; reported mechanisms of PIP joint snapping include retinacular ligament injury or tendon impingement. We present a unique case of painful finger snapping at the PIP joint as a result of longitudinal tear of the central slip, leading to sudden subluxation of one-half of the central slip and conjoint lateral band with flexion of the PIP joint.

Introduction

Finger catching, where the digit becomes temporarily stuck during flexion/extension before suddenly releasing, is a common problem seen by hand surgeons. The most common cause is stenosing tenosynovitis of the flexor tendon, that is, trigger finger. Injuries to the extensor mechanism can also cause catching, although they are substantially less common; in these cases, a chief complaint is snapping of the finger which is similar to catching, but with an accompanying audible clicking or snapping sound. The predominant cause for extensor mechanism snapping is sagittal band injury and the metacarpophalangeal (MCP) joint is most frequently affected.^1,2 Pathological snapping at the proximal interphalangeal (PIP) joint is extremely uncommon. Reported cases of PIP joint snapping have involved lateral band subluxation and impingement due to bony prominence. Herein, we describe a unique case of painful snapping at the PIP joint as a result of a longitudinal tear of the central slip, leading to radial-volar subluxation of one-half of the central slip and conjoint lateral band with flexion of the finger.

Methods and Case Report

The patient is a 67-year-old right hand-dominant woman who presented with painful snapping in the left index finger. Two months before, the patient fell and sustained blunt closed injuries to the left index finger and face. She was seen at a local hospital where plain films were negative for bone/joint abnormalities in the hand. The patient was diagnosed with a left index finger sprain and the finger was splinted in extension at the proximal and distal interphalangeal joints. The patient complied with full-time splinting of the finger for 2 months. However, the pain persisted.

On examination, the patient demonstrated full passive range of motion in all fingers on the left hand except for the index finger. The patient had mild swelling and tenderness over the index finger PIP joint dorsally, especially on the radial side. There was neither pain nor tenderness on the volar portion of the finger. The patient was able to achieve full active extension of the finger, but painful snapping occurred at the PIP joint with flexion from 0° to 30° (Supplemental Video 1). Active flexion of the finger was limited due to a combination of pain and stiffness secondary to splinting. The PIP joint was stable, including the collateral ligaments.

Common causes for snapping were eliminated. Trigger finger was eliminated as there was neither tenderness with palpation nor triggering at the A1 pulley. Sagittal band injury was eliminated as snapping was visible at the PIP joint rather than the MCP joint and the patient did not have tenderness or extensor tendon subluxation at the MCP joint. The patient did not present with Boutonnière deformity, which typically indicates complete rupture or avulsion of the central slip.

Radiographs of the left hand demonstrated normal bone and joint anatomy. A magnetic resonance imaging was not deemed necessary as examination ruled out common causes for snapping and the snapping was visible at the PIP joint through the skin.

Based on the clinical presentation, the patient was diagnosed with left index finger snapping/subluxation of the lateral band. Treatment options were discussed, and operative treatment was chosen.

Surgical exploration was undertaken through a dorsal approach over the PIP joint under local anesthesia. Exploration revealed a longitudinal tear in the fibers of the central slip. There was no disruption of the central slip attachment to the dorsal lip of the middle phalanx base. The longitudinal tear led to extensor mechanism instability and volar subluxation of the extensor mechanism when the PIP joint was flexed, both passively and actively. In a healthy finger, the lateral band on each side of the digit provides the force necessary to centralize the central slip over the PIP joint during flexion, preventing subluxation either radially or ulnarly. In our case, the longitudinal split in the central slip meant that the stabilizing force of the ulnar lateral band was not transmitted sufficiently to the radial half of the central slip. As such, there was no restraint to keep the radial half of the central slip dorsal to the PIP flexion axis (Figure 1, Supplemental Video 2).

Figure 1.

Simplified diagram of the extensor mechanism of the finger demonstrating the location of the longitudinal tear in the central slip, proximal to and without disruption of the central slip insertion.

At surgery, to remove the force displacing the radial half of the central slip, the conjoint lateral band was released from the central slip. The central slip split was then repaired in a side-to-side manner with vicryl suture.

Results

Intraoperatively after the surgical repair of the central slip, the snapping resolved. The patient retained full active PIP extension as demonstrated by dynamic assessment during the procedure. Postoperatively, the finger was not splinted.

Twelve days after surgery, the patient did not have snapping of the finger but lacked full active flexion at the PIP joint. She was prescribed hand therapy for range of motion and strengthening. At 6-week postoperative follow-up, the patient was able to achieve full active extension and 95° of active flexion at the PIP joint with no pain or snapping (Supplemental Video 3).

Discussion

Snapping and catching in the finger are common problems seen by surgeons. The most common cause is stenosing tenosynovitis of the flexor tendon, that is, trigger finger, where tendon movement is hindered within the flexor sheath, most often at the A1 pulley. ³ The cause of snapping or catching can also be within the extensor mechanism, although it is substantially less common. Among these injuries, sagittal band rupture is the most frequent and results in subluxation of the extensor tendon over the metacarpal head with flexion.^1,2 Snapping at the PIP joint is even more uncommon and only 4 cases have been described.^4-7

Hsieh et al reported a case of lateral band snapping at the PIP joint due to rupture of the transverse retinacular ligament (TRL) with no traumatic injury. ⁴ The authors sutured the lateral band to the TRL, which resolved snapping. Lee et al described a case of post-traumatic lateral band snapping at the PIP joint due to injury to the retinacular ligament complex, specifically the lamina intertendineum between the central slip and the lateral band. ⁵ The authors repaired the retinacular ligament complex via suture, which resolved snapping. Ikeda et al reported a case of lateral band snapping at the PIP joint due to both congenital ulnar declination of the proximal phalanx and partial-thickness injury to the TRL. ⁶ The authors cut the remaining TRL and sutured it to the central slip to resolve the snapping. Yamamuchi et al described a case of PIP joint snapping due to a periosteal chondroma, which detached due to a finger sprain and impinged between the basal phalanx and extensor tendon. ⁷

Our case is unique from the existing literature in 2 main aspects. First, our patient had snapping of both the central slip and the conjoint lateral band, rather than just the conjoint lateral band alone. Second, the cause of snapping was subluxation of the central slip secondary to longitudinal split in the tendon, neither retinacular ligament injury nor impingement of the extensor tendon. In our case, the longitudinal tear of the central slip led to dynamic instability of the extensor mechanism. In a healthy finger, the radial lateral band exerts a force on the entirety of the central slip to prevent ulnar subluxation during flexion; similarly, the ulnar lateral band exerts the opposite force, preventing radial subluxation with flexion. The longitudinal tear meant that the radial half of the central slip was subjected to the force from the conjoint lateral band on the radial side, while the ulnar lateral band’s balancing force was not sufficiently transmitted. As a result, the radial half of the central slip subluxated volarly and snapped on PIP joint flexion.

Further, our case demonstrates a unique location and orientation of rupture of the central slip—specifically the longitudinal splitting of the fibers. The most common central slip injury is traumatic rupture from the dorsal base of the middle phalanx, resulting in the development of Boutonnière deformity. ⁸ With traumatic rupture, the central slip is injured transversely across the tendon fibers, avulsing it from the middle phalanx. In our case, the patient experienced a longitudinal tear in the central slip from blunt force mechanism without complete transverse disruption. Instead, the central slip insertion remained intact, effectively dividing the central slip into radial and ulnar portions with both tethered at the insertion and origin. With PIP joint flexion, the radial half of the central slip subluxated, leading to the snapping.

For more common central slip injuries, including avulsion or rupture, nonoperative management is preferred. The primary indication for surgical treatment is complete laceration of the tendon. Although our patient’s symptoms did not indicate complete laceration of the central slip, we chose operative treatment for 2 reasons. First, the patient had undergone 2 months of extension splinting, which did not resolve pain or restriction of motion. Second, we identified the snapping at the PIP joint by clinical examination; all reported cases of PIP joint snapping have been successfully treated surgically.^4-7

Orthopedists and hand surgeons should be cognizant that painful snapping in the fingers may be the result of extensor mechanism injury and not due to the more common stenosing tenosynovitis. Surgeons should progress through an appropriate differential diagnosis to identify the true cause of snapping/catching. Trigger finger commonly presents with tenderness and triggering of the A1 pulley near maximal finger flexion. ³ Sagittal band rupture typically presents with extensor tendon subluxation over the MCP joint and tenderness at the radial sagittal band.^1,2 If these diagnoses are eliminated, surgeons should consider injury to either the central slip or retinacular ligament complex.

Finally, our case highlights both the importance of confirming the mechanism of subluxation intraoperatively and the value of performing reparative surgery under local anesthesia. Our patient’s snapping was visible through the skin and the area of subluxation initially suggested lateral band displacement; however, surgical exploration revealed the true mechanism of subluxation to be an intact radial lateral band displacing an unstable central slip. Given the complex nature of the hand, it is important for surgeons to confirm the cause of snapping for other presentations as well. Further, the use of local anesthesia allowed for the authors to confirm that snapping during active flexion was resolved before termination of surgery. Local anesthesia enables the patient to be awake during the procedure, allowing for dynamic, active evaluation of the flexor and extensor mechanisms. Notably, the use of local anesthesia also has benefits in other hand surgeries, and the Wide-Awake, Local Anesthesia, No Tourniquet technique has recently risen in popularity. ⁹

Conclusions

We present a rare case of snapping at the PIP joint secondary to longitudinal tear of the central slip. Hand surgeons should be aware that injury to the extensor mechanism and specifically the central slip can lead to snapping or catching at the PIP joint in the finger.