Dynamic swan neck deformity in a patient with Ehlers-Danlos syndrome

Development of an In Vitro Swan Neck Deformity Biomechanical Model

BACKGROUND

Injury to the finger's extensor mechanism is a common cause of swan neck deformity (SND). Progression of extensor and flexor tendon imbalance negatively affects laxity of the volar plate, resulting in the inhibition of proper finger motion. The complexity of finger anatomy, however, makes understanding the pathomechanics of these deformities challenging. Therefore, development of an SND model is imperative to understand its influence on finger biomechanics and to provide an in vitro model to evaluate the various treatment options.

METHODS

The index, middle, and ring fingers from 8 cadaveric specimens were used in an in vitro active motion simulator to replicate finger flexion/extension. An SND model was developed through sectioning of the terminal extensor tendon at the distal insertion (creating a mallet finger) and transverse retinacular ligament (TRL). A strain gauge inserted under the volar plate measured laxity of the plate, and electromagnetic trackers recorded proximal interphalangeal joint (PIPJ) angles.

RESULTS

Strain in the volar plate increased progressively with creation of the mallet and SND conditions (P = .015). Although not statistically significant, the mallet finger condition accounted for 26% of the increase, whereas sectioning of the TRL accounted for 74% (P = .031). As predicted, PIPJ hyperextension was not detectable by joint angle measurement; however, the PIPJ angle had a strong positive correlation with volar plate strain (R2 = 1.0, P < .001).

CONCLUSION

Volar plate strain measurement, in an in vitro model, can detect an induced SND. Moreover, as a surrogate for PIPJ hyperextension, volar plate strain may be useful to evaluate the time-zero effectiveness of various surgical interventions.

A novel surgical correction and innovative splint for swan neck deformity in hypermobility syndrome

Splinting is a great domain of occupational therapy profession. Making a splint for the patient would depend on the need or requirement of the problems and deformities. Swan neck deformity is an uncommon condition, and it can be seen in rheumatoid arthritis, cerebral palsy, and after trauma. Conservative treatment of the swan neck deformity is available by different static splints only. There are very few reports of surgical correction of swan-neck deformity in benign hypermobility syndrome. This case report describes the result of novel surgical intervention and an innovative hand splint in a 20-year-old female with a history of cardiovascular stroke with no residual neurological deficit. She presented with correctable swan neck deformity and failed to improve with static ring splints to correct the deformity. She underwent volar plate plication of the proximal interphalangeal joint of the left ring finger along with hemitenodesis of ulnar slip of flexor digitorum superficialis (FDS) tendon whereby, the ulnar slip of FDS was passed through a small surgically created rent in A2 pulley and sutured back to itself. Postoperatively, the patient was referred to occupational therapy for splinting with the instruction that the splint would work sometimes for as static and some time as dynamic for positional and correction of the finger. After occupational therapy intervention and splinting, the patient had a full correction of the swan-neck deformity with near full flexion of the operated finger and can work independently.

Arthroscopic Glenoid Labrum Repair of Left Shoulder in a Male With Ehlers-Danlos Syndrome

Ehlers-Danlos syndrome (EDS) is an inherited connective tissue disorder that has been classified into several primary types. The clinical characteristic of EDS is hypermobility of the joints, hyperextensibility and fragility of the skin, and hemorrhage tendency. For many patients, the hypermobile joints become a serious problem. We present the case of a 19-year-old male diagnosed with EDS, with recurrent dislocations of his left shoulder, hyperextensibility and fragility of the skin, and a carp-mouth–shaped scar of the forearm. After 4 years of nonoperative treatment, we performed an arthroscopic glenoid labrum repair of left shoulder. At a 6-year follow-up, the patient has no instability in the left shoulder. We believe that glenoid labrum repair is a viable method for treating recurrent dislocations for patients with EDS. It is strongly suggested to check coagulation function of patients to avoid substantial bleeding when decorticating the glenoid rim, to ensure a conservative postoperative rehabilitation.

Superficialis Sling (Flexor Digitorum Superficialis Tenodesis) for Swan Neck Reconstruction

Swan neck deformity, or hyperextension of the proximal interphalangeal joint, may occur secondary to trauma, rheumatoid arthritis, cerebral palsy, or Ehlers-Danlos syndrome, and can be treated with tenodesis of one slip of the flexor digitorum sublimis tendon. This technique has several variations, differing primarily in the specific location and method that a single slip of the flexor digitorum sublimis tendon is secured, but they all serve to create a static volar restraint against hyperextension. Options include tunneling the tendon through the bone of the proximal phalanx, attaching the tendon to the A1 or A2 pulley, or securing the tendon with bone anchors in the proximal phalanx.

Kinematic evaluation of the finger's interphalangeal joints coupling mechanism--variability, flexion-extension differences, triggers, locking swanneck deformities, anthropometric correlations

The human finger contains tendon/ligament mechanisms essential for proper control. One mechanism couples the movements of the interphalangeal joints when the (unloaded) finger is flexed with active deep flexor. This study's aim was to accurately determine in a large finger sample the kinematics and variability of the coupled interphalangeal joint motions, for potential clinical and finger model validation applications. The data could also be applied to humanoid robotic hands. Sixty-eight fingers were measured in seventeen hands in nine subjects. Fingers exhibited great joint mobility variability, with passive proximal interphalangeal hyperextension ranging from zero to almost fifty degrees. Increased measurement accuracy was obtained by using marker frames to amplify finger segment motions. Gravitational forces on the marker frames were not found to invalidate measurements. The recorded interphalangeal joint trajectories were highly consistent, demonstrating the underlying coupling mechanism. The increased accuracy and large sample size allowed for evaluation of detailed trajectory variability, systematic differences between flexion and extension trajectories, and three trigger types, distinct from flexor tendon triggers, involving initial flexion deficits in either proximal or distal interphalangeal joint. The experimental methods, data and analysis should advance insight into normal and pathological finger biomechanics (e.g., swanneck deformities), and could help improve clinical differential diagnostics of trigger finger causes. The marker frame measuring method may be useful to quantify interphalangeal joints trajectories in surgical/rehabilitative outcome studies. The data as a whole provide the most comprehensive collection of interphalangeal joint trajectories for clinical reference and model validation known to us to date.

Correction of bilateral congenital swan-neck deformity by use of Mitek mini anchor: a new technique

Congenital swan neck deformity is a rare condition, secondary to congenital laxity of the palmar plate of the proximal interphalangeal joint. Here, we describe a new surgical method which is based on the palmar plate reinforcement using the Mitek mini anchor system (Mitek Surgical Products Inc., Norwood, MA, USA). Four fingers of a patient with congenital swan neck deformities were corrected with this technique at two stages. First, the anchor was inserted into the volar surface of the proximal phalanx. The two sutures of the anchor system were then crossed the PIP joint in a V fashion. Two holes, 5mm apart from each other, were created through the middle phalanx distal to both insertion points of superficial flexor tendon. The suture ends of the anchor were passed through these holes from the volar to the dorsal side of the middle phalanx and then turned around the edges of the bone to the volar surface. They were tied to each other as the PIP joint was stabilised at 20 degrees flexion by use of a K-wire. The K-wire was removed 21 days later and a rehabilitation program was then initiated. A second operation for the two fingers of the opposite hand was performed 2 months after the first operation. No postoperative complications were encountered. At 2 years follow-up, the active range of motion was within normal limits at PIP and DIP joints of all four fingers without any recurrence of hyperextension or hyperflexion. The final result was satisfactory regarding both the functional and cosmetic aspects. The Mitek mini anchor offers a practical, reliable and functional reconstruction of the volar plate in the management of congenital swan neck deformities. We believe that it may also be used for the acquired deformities.