Introduction

Triggering or snapping of the fingers is a prevalent hand condition primarily caused by stenosing tenovaginitis at the first annular pulley (A1) [1]. Also, snapping of the fingers at metacarpophalangeal joins has been frequently reported [2].
Lateral band snapping of the extensor tendon at the proximal interphalangeal joint (PIPJ) is a rare chronic disorder consisting of a painful volar snapping of one lateral band of the extensor tendon at the PIPJ due to retinacular ligament rupture [3–5].
The retinacular ligament, first described by Landsmeer, is a portion of the dorsal aponeurosis at the level of the PIPJ composed of two layers [6]. The deep one is the oblique retinacular ligament, extending laterally and palmary between the distal part of the first phalanx to the proximal part of the distal phalanx, involved in connecting the PIPJ to the distal interphalangeal joint (DIPJ) during movement. The superficial one, called the transverse retinacular ligament is involved in maintaining a steady relationship between the central slip and the lateral bands of the extensor tendon. The transverse retinacular ligament is the main site of tear in a lateral band-snapping syndrome.
Diagnosis is based on meticulous analysis of the patient history, clinical examination and dynamic US imaging, where possible [7]. The most common clinical symptoms are pain, discomfort, and snapping [3,4]. Knowledge of this pathology can lead to an early assessment and full recovery after surgical treatment with satisfactory results.

Case report

A 15-year-old girl was referred to our clinic with chronic pain for 2 years at the dorsum of the PIPJ of the fifth finger on the left side, with exacerbation of the symptoms in the last 6 months. The symptoms were connected with clicking and snapping in the finger. The pain started after a sprain of the finger while playing volleyball, and the symptoms gradually intensified over time. As someone who plays the guitar and piano, the symptoms above made playing uncomfortable and resulted in pain after exercise or performances. She was diagnosed with trigger finger and operated on one year before at another hospital without any improvement.
During the clinical examination, full active range of motion was attainable; however, pain and clicking were detected at the dorsoradial aspect of the PIPJ during active and passive flexion. Instability and volar subluxation of the radial lateral band during flexion was visible only with careful observation, which was initially distracted by previous treatment, history and evaluation of the previous surgical zone (Fig. 1).
Upon observation, snapping was confirmed with ultrasonography and possible bony deformities were excluded by X-ray. An experienced radiologist described the snapping and change in the tissue structure between the lateral band and central slip.
After analysis of published cases similar to those proposed by other authors, surgical treatment was planned and performed with dorsal approach over the PIPJ with a curved incision. The injured area is approached to evaluate the snapping lateral band and scar tissue.. The scar is excised, and the retinacular ligament between the central and radial lateral band of the extensor apparatus is directly repaired using single absorbable monofilament 5-0 sutures (Fig. 2). The passive range of motion was checked to confirm the repair and lateral band stability. The finger was immobilized with a splint for 2 weeks in 30° of PIPJ flexion. A supervised program of gradually increasing range of motion exercises was initiated by an experienced hand therapist and continued for 12 weeks.
Full range of motion with complete pain relief was recovered after 12 weeks; the patient successfully returned to playing the violin and guitar without discomfort (Fig. 3).

Discussion

The primary cause of finger snapping or triggering is stenosing tenosynovitis, commonly known as trigger finger. This condition causes discomfort and finger clicking, resulting from an inflammation-induced difficulty in sliding the flexor tendon through its pulleys, usually A1 [1,8]. This condition is typically seen in adults, but can also occur in young children, often referred to as pediatric trigger thumb. It may also affect adolescents and other fingers. [9] Given the various presentations, it is easy to diagnose finger clicking and locking as a pathology, and treatment options include steroid injection or surgical release of A1 pulley [10,11].
At the metacarpophalangeal joint (MPJ), along with the volar trigger finger, snapping at the dorsal part of the joint due to a palmar subluxation of the extensor tendon is frequently associated with the sagittal band rupture, known as boxer’s knuckle [2,3].
True tendon snapping is an infrequent occurrence at the PIPJ, primarily associated with palmar subluxation of the lateral extensor tendon slip. This condition is caused by retinacular ligament rupture, referred to as lateral band-snapping syndrome. A longitudinal tear of the central slip can also lead to tendon snapping, but only one case has been reported in the literature [12].
The case we present is 5th reported in the literature, meaning that symptomatic snapping at this area is uncommon and does not belong to standard evaluation when examination is performed even by an experienced hand surgeon. Special care must be taken when evaluating the patient’s medical history, assessing previous traumas and arthritis, to identify any potential joint defect that may lead to a misinterpreted clicking.
Specific points in our case demand attention for accurate diagnosis, namely previous injury, unsuccessful surgical treatment, snapping and pain at the PIP joint reported by the patient, and visible as well as palpable symptoms.
In the report of Lee et al., a 24-year-old male was described with snapping at the PIP joint after a previous sport-related sprain injury. He did not report pain but discomfort due to a snapping sound and had undergone A1 pulley release treatment a few years ago without any improvement. He recovered full motion without snapping after 6 months post-op, which was longer than in our case, possibly due to the age difference [3].
In their report, Lim et al. detailed the case of a 74-year-old man who may have sustained an injury 6 months prior and was experiencing triggering or locking of his middle finger. The proper diagnosis was based on eliminating more common causes: no pain and nodule over A1 pulley, stable extensor at MP joint. Next inspection of the radial aspect of the PIPJ showed the radial lateral band subluxing volarly over the radial proximal phalangeal condyle on flexion. Following a similar surgical treatment and postoperative protocol, the patient regained full function within 3 months [5].
The surgical technique is not complicated and intuitional but requires experienced intraoperative assessment of extensor apparatus structures, scar tissue to excise and amount of lateral band relocation to provide stability, proper function and non-limited active range of motion without any deformity (as before the surgery). Moreover, it is crucial to incorporate appropriate exercises that protect the repaired site while gradually increasing range of motion. This requires the assistance of a cooperative hand therapist.
While not applicable to all cases, we consider ultrasonography to be the primary diagnostic test for analyzing tendon snapping and confirming a lateral band-snapping syndrome, after a clinical examination [7]. In cases where symptoms are apparent, the use of US may not always seem necessary; however, due to the high incidence of misdiagnosis and mistreatment, it can be an important tool in providing objective pathology confirmation and exclusion of other problems.
If there is any uncertainty about the pathology, XR imaging and CT scan can help identify or rule out any defects that could cause joint clicking or tendon snapping, such as chondroma or other bone deformities, including congenital ones [4,13].

Conclusion

Lateral band-snapping syndrome can be misdiagnosed and mistreated due to its rarity and symptoms that may mimic finger triggering in stenosing tenosynovitis. It can be diagnosed clinically and confirmed by ultrasonography. The treatment, when appropriate, is successful. To the best of our knowledge, only 4 cases of lateral band-snapping syndrome have been reported (5-8), and we believe that raising the awareness of this pathology can help with early identification and proper treatment.

References

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