Biomechanical evaluation of chronic boutonnière reconstructions

Y-Shaped Tendon Graft-A Technique in the Reconstruction of Posttraumatic Chronic Boutonniere Deformity

PURPOSE

Current reconstruction strategies for chronic posttraumatic boutonniere deformities have variable outcomes and are prone to complications. This study aimed to describe the clinical outcomes of a Y-shaped tendon graft technique.

METHODS

In this retrospective case study, we reviewed the files of 18 patients treated with the Y-shaped tendon graft between January 2010 and January 2017. The technique involves release of the central slip, lateral bands, and transverse retinacular ligaments at the proximal interphalangeal (PIP) joint, total excision of scar tissue in the central slip and at the insertion site, and construction of 3 1.5-mm unicortical holes at the base of the middle phalanx, through which a Y-shaped graft of the palmaris longus is inserted to reconstruct the central slip and stabilize the lateral bands in a dorsal position. Clinical evaluations included measuring the active range of motion in the PIP joint and distal interphalangeal (DIP) joint, grip strength, Souter score, and the Quick Disabilities of the Arm, Shoulder, and Hand (QuickDASH) score.

RESULTS

The mean age of patients was 36.1 years, and 12 of the 18 patients were men. The average follow-up period was 23 months (range, 13-38 months). The preoperative PIP joint extension deficit was 48.0° ± 5.0° compared with 10.9° ± 9.3° after surgery. The preoperative DIP joint active flexion was 34.4° ± 8.0° compared with 71.4° ± 8.6° after surgery The outcomes based on the Souter score were 11 excellent, 5 good, and 2 poor. The QuickDASH score was 17.7 ± 6.4 before surgery and 11.2 ± 7.2 after surgery.

CONCLUSIONS

The Y-shaped tendon graft can be a useful procedure for the correction of chronic boutonniere deformity; in our patient series, this provided good or excellent results in 16 of 18 patients.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic IV.

Biomechanics of the Acute Boutonniere Deformity

PURPOSE

To demonstrate which structures of the extensor mechanism create a boutonniere deformity, when damaged, in a cadaver model. An analysis of how damage to these anatomical structures affects the biomechanical performance of the extensor mechanism was also performed.

METHODS

We secured 18 fresh cadaveric hands onto an apparatus consisting of a computer-controlled motor and tensiometer attached in series to the extensor communis tendon of the ring and middle digits. The central slip, transverse, and oblique fibers of the interosseous hood and the triangular ligament were sequentially divided. After each structure was divided, the motors were activated to provide a constant tendon displacement force. The angular displacement at the proximal interphalangeal (PIP) and distal interphalangeal joints was recorded.

RESULTS

In all digits, detachment of the central slip from the middle phalanx produced a decrease in extension of the PIP joint. When the transverse and oblique fibers of the interosseous hood were also divided, extension at the PIP joint was further decreased. A boutonniere deformity occurred only when all 3 structures were damaged.

CONCLUSIONS

The boutonniere deformity requires subluxation of the lateral bands volar to the axis of rotation of the PIP joint. This study demonstrates that damage to the central slip alone does not cause the deformity. Combined injury of the central slip, triangular ligament, and transverse and oblique fibers of the interosseous hood causes a boutonniere deformity.

CLINICAL RELEVANCE

Division of the central slip leads to loss of extension at the PIP joint. A more substantial loss of extension after injury or development of a boutonniere deformity should alert clinicians that other structures of the extensor mechanism are also damaged.

Combinatorial roles of extrinsic and intrinsic muscles in extension strength of the distal interphalangeal joint

In this study, we observed a combinatorial relationship between intrinsic and extrinsic muscles to extend the distal phalanx via the terminal tendon of the finger extensor. Eleven fresh-frozen human cadaver digit rays were used in these experiments (four index, four middle, three ring digits). All fingers had full joint motion without degenerative diseases. Fingers were individually mounted in a custom built jig fixed by a 1-mm Kirschner wire that was driven into the rotational center of the distal interphalangeal (DIP) and proximal interphalangeal joints. Loads were applied to the extensor digit and dorsal interosseous tendons without flexor tendons, via sutures attached over low-friction pulleys. Extension forces that crossed the DIP joint were measured by a force transducer coupled with a materials-testing machine. We observed a steep inclination of the extensor forces produced by the intrinsic muscles, and there were no significant differences in comparisons among loads (200, 400, 600, and 800 g). The inclination slope increased with an increase of load (p < 0.001). Additionally, the inclinations of the non-linear phases among all finger types were not statistically different. Thus, the contribution between the extrinsic and intrinsic muscles in providing extensor forces to the distal phalanx was similar.

Monopolar radiofrequency energy application to the dorsal extensor tendon apparatus in a canine model of tendon injury

PURPOSE

To evaluate the use of monopolar radiofrequency energy (MRFE) to shorten stretched dorsal extensor tendon apparatus (DETA) tissues in a canine model.

METHODS

Eleven adult canine forelimbs were used in this in vitro investigation. The DETA tissue was isolated between the metacarpophalangeal and proximal interphalangeal joints in the third and fourth digits of each limb. Isolated tissue was stretched in all but 2 of the digits (control group). After tissue stretching, monopular radiofrequency energy (MRFE) was applied to 18 of the digits at 1 of 3 temperatures: 50 degrees C, 60 degrees C, or 70 degrees C (stretch-treatment group). Two digits were treated identically, but MRFE was not applied (stretch-only group). Tissue length was measured before and after stretching and after treatment. Percent stretch, percent shortening, and percent original length were compared among the 3 stretch-treatment groups. All DETA specimens were examined with light microscopy.

RESULTS

Histologic changes were apparent in the stretch-treatment and stretch-only specimens compared with controls. Percent stretch was not significantly different between groups. Percent shortening and percent original length were significantly lower and higher, respectively, in the 50 degrees C group than in the 60 degrees C and 70 degrees C stretch-treatment groups, which were not significantly different from each other. There was a significant linear correspondence between percent shortening and treatment temperature.

CONCLUSIONS

The application of MRFE at a temperature of 60 degrees C and a power of 10 W appears to shorten stretched DETA tissue to approximately the prestretched length in an in vitro canine model. Further investigation is necessary to determine the effect of treatment on the tissue's mechanical properties.

Staged extensor tendon reconstruction in the finger

Staged extensor tendon reconstruction using a silicone implant followed by tendon grafting was done to restore proximal interphalangeal (PIP) joint extension in 6 fingers with severe injuries to the dorsal skin and extensor mechanism. Abrasions to the joint capsule and cortical surfaces were also present. To avoid finger stiffness, the reconstruction was delayed and range of motion exercises were initiated early. The skin injury was managed by split-thickness skin grafting or allowed to heal by secondary intention to avoid prolonged immobilization. During surgery, the peritendinous fascia of the extensor tendon is used to guide insertion of the implant, and it serves as a premade tunnel that appears to aid the gliding and stability of the implant and subsequent tendon graft. Active extension of the PIP joint was restored in all fingers; there was an average extension lag of 15 degrees. PIP joint flexion averaged 95 degrees. On the basis of this experience, the author believes the technique to be a reliable treatment alternative for severely injured fingers with extensor mechanism loss.