High Fracture Rate of AVANTA Silicone Implant Following Arthroplasty of the Thumb MCP Joint of Rheumatoid Arthritis Patients with Boutonniere Deformities.

We retrospectively investigated the mid-term outcomes of arthroplasty using the AVANTA silicone implant for thumb metacarpophalangeal (MCP) joints with boutonniere deformity in patients with rheumatoid arthritis (RA). This study involved 36 thumbs of 33 RA patients with a mean follow-up period of 5.1 years (range, 2.0-13.3). Postoperatively, the mean extension was significantly increased and the mean flexion was significantly decreased (p<0.001, p<0.001, respectively), resulting in the mean arc of range of motion (ROM) shifting in the direction of extension after surgery. Implant fracture was observed in 10 thumbs (28%), and 4 of these (11%) underwent revision surgery. The survivorship with implant fracture and revision surgery as endpoints were 73.4% and 91.8% at 5 years, respectively. The preoperative arc of ROM and the postoperative flexion range of the implant-fracture group were significantly greater than those in the no-implant-fracture group (p=0.039, 0.034, respectively). These results suggest the importance of patient education and careful rehabilitation to prevent excessive flexion. Overall, the AVANTA silicone implant showed a relatively high rate of implant fracture at our institute.

Direct fixation of fracture fragment with modified double Kirschner wires for the treatment of old bony mallet finger.

BACKGROUND: The management of old bony mallet fingers is complicated. The purpose of this study was to describe direct fixation of fracture fragment with modified double Kirschner wires (K-wires) for treatment of old bony mallet finger, and to evaluate the functional outcomes during long-term follow-up. METHODS: Forty-nine patients with old bony mallet finger were enrolled and underwent surgical treatment from August 2014 to January 2021 in our hospital. Patients were divided into two groups according to whether they had undergone triple K-wires fixation or modified double K-wires with a dorsal brace fixation. The operation time, mean number of intraoperative fluoroscopy, bone union time, functional recovery and incidence of complications were monitored. RESULTS: Neither QuickDASH nor visual analogue scale measurement found statistically significant difference between the two groups (P > 0.05). However, the patients that underwent fixation with double K-wires and a dorsal brace required a shorter operation time and fewer intraoperative fluoroscopy, and exhibited a significantly greater mean final active range of the distal interphalangeal joint flexion, compared to those treated with triple K-wires (P < 0.01). CONCLUSION: Direct fixation of fracture fragment with modified double K-wires was an easy and feasible procedure which could achieve anatomical reduction and stable fixation of the dorsal fracture block of old bony mallet finger with relatively few complications.

Flexor Digitorum Superficialis Excision for Trigger Finger - A Systematic Literature Review.

Background: Division of one or more slips of the flexor digitorum superficialis (FDS) tendon has been posited as an effective surgical modality for advanced or recurrent trigger finger. This may be an effective approach among patients with diabetes or rheumatoid arthritis, or in those with fixed flexion deformities who have poor outcomes from A1 pulley release alone. However, there is limited evidence regarding the effectiveness of this procedure. The role of this study was to systematically review the evidence on functional outcomes and safety of partial or complete FDS resection in the management of trigger finger. Methods: A systematic review was performed according to PRISMA guidelines. PubMed, Cochrane CENTRAL and Ovid Medline databases were electronically queried from their inception until February 2022. English language papers were included if they reported original data on postoperative outcomes and complications following resection of one or more slips of FDS for adult trigger finger. Results: Seven articles were eligible for inclusion, encompassing 420 fingers in 290 patients. All included studies were retrospective. Isolated ulnar slip FDS resection was the most described surgery. Mean postoperative fixed flexion deformity at the proximal interphalangeal joint was 6.0° compared to 31.5° preoperatively, and the proportion of patients with fixed flexion deformity reduced by 58%. Mean postoperative total active motion was 228.7°. Recurrence was seen in 4.7% of digits, and complications occurred in 11.2% of cases. No post-surgical ulnar drift or swan neck deformities were observed. Conclusions: FDS resection for long-standing trigger finger, or in diabetic or rheumatoid populations, is an effective and safe technique with low rates of recurrence. Prospective and comparative studies of this technique would be beneficial. Level of Evidence: Level III (Therapeutic).

Posttraumatic Osteoarthritis of the Distal Interphalangeal Joint: A Follow-Up Study of 12 Years After Nonsurgical Treatment of Mallet Finger Fractures.

PURPOSE: In treatment of mallet finger fractures (MFFs), the aim is to minimize residual extension lag, reduce subluxation, and restore congruency of the distal interphalangeal (DIP) joint. Failure to do so may increase the risk of secondary osteoarthritis (OA). However, long-term follow-up studies focusing on OA of the DIP joint after an MFF are scarce. The purpose of this study was to assess OA, functional outcomes, and patient-reported outcome measures (PROMs) after an MFF. METHODS: A cohort study was performed with 52 patients who sustained an MFF at a mean of 12.1 years (range, 9.9-15.5 years) previously and who were treated nonsurgically. A healthy contralateral DIP joint was used as the control. Outcomes were radiographic OA, using the Kellgren and Lawrence and Osteoarthritis Research Society International classifications, range of motion, pinch strength, and PROMs (Patient-Rated Wrist Hand Evaluation, Quick Disabilities of the Arm, Shoulder, and Hand, Michigan Hand Outcome Questionnaire, 12-item Short Form Health Survey). Radiographic OA was correlated with PROMs and functional outcomes. RESULTS: At follow-up, there was an increase in OA in 41% to 44% of the MFFs. Of all the MFFs, 23% to 25% showed a higher degree of OA than the healthy control DIP joint. Range of motion (mean difference ranging from -6° to -14°) and Michigan Hand Outcome Questionnaire score (median difference, -1.3) were decreased after MFFs but not to a clinically relevant extent. Radiographic OA was weakly to moderately correlated with functional outcomes and PROMs. CONCLUSIONS: Radiological OA after an MFF is similar to the natural degenerative process in the DIP joint and is accompanied by a decrease in range of motion of the DIP joint, which does not clinically affect PROMs. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic IV.

The relative motion concept in acute and chronic boutonniere deformity: Invited commentary.

STUDY DESIGN: Retrospective. INTRODUCTION: Boutonniere deformity (BD) is a troublesome injury occurring from rupture of tissue connecting the extrinsic to intrinsic tendon systems. This causes loss of interphalangeal joint balance, and immobilization often results in adherence and difficulty restoring balance. PURPOSES: Review of relative motion flexion (RMF) orthotic use for safe healing during functional activity in 23 patients, and explanation of the rationale. METHODS: Anatomic rationale and clinical experience is reviewed in 8 acute BD patients utilizing RMF orthoses for 6 weeks, and for chronic BD patients, 3 months after serial casting. RESULTS: All patients met the Strickland and Steichen criteria for "excellent" results following treatment, with an average of 35° increase in ROM. DISCUSSION: The anatomic rationale for relative motion recognizes that altering relative positioning between adjacent metacarpophalangeal (MCP) joints produces a protective favorable impact on interphalangeal forces during hand function using 15°-20° greater MCP joint flexion. This provides dorsal and volar protective benefits because the extensor digitorum communis (EDC), a single-muscle-four-tendon system, attaches to the intrinsic lateral band (LB) tendons. With greater MCP flexion, dorsal EDC force is increased, pulling lateral bands medially, while on the volar surface the downward pull of the lumbrical on LB is relaxed due to origin from the flexor digitorum profundus tendon of the injured digit, also a single-muscle-four-tendon system. The RMF orthosis permits protected active motion during functional activity with acute BD. In patients with chronic BD and adequate passive extension, an RMF orthosis for 3 months also produced encouraging results. CONCLUSION: Management of acute BD with RMF orthoses provided earlier recovery of motion and hand function. Similar results occurred for chronic BD using serial casting for adequate extension followed by 3 months of RMF orthotic use and should be attempted prior to surgical intervention, with surgery remaining an alternative.

An in-depth look at zone III and IV anatomy of the finger extensor mechanism and some clinical implications for use of the relative motion flexion orthosis.

BACKGROUND: For hand therapists and hand surgeons acute and chronic injuries of the extensor mechanism (EM) in zones III-IV are challenging to treat with satisfying results. INTRODUCTION: Early active motion combined with relative motion flexion (RMF) orthoses to manage EM zone III injuries and boutonnière deformity has renewed interest in the complex anatomy and biomechanics of the EM. PURPOSE: To provide an in-depth discussion of EM zones III-IV anatomy with emphasis on inter-tendinous structures, often omitted in simplified, model-wise illustrations which focus mostly on the tendinous structures. METHOD: In collaboration the authors combined on the one hand extensive clinical experience and knowledge of the EM literature and on the other hand decades of anatomical, biomechanical and kinesiology research of the EM with special interest for the spiral fibers, through gross anatomy and microdissection anatomy laboratory work, MRI and ultrasonography studies. RESULTS: The inter-tendinous tissues (i.e., spiral fibers) in zone III are of imminent importance for proper functioning of the EM and to prevent boutonnière deformity to develop after EM surgery or injury. DISCUSSION: Inter-tendinous links between the tendinous structures of the EM are necessary for balanced finger motion. The spiral fibers are described in more detail because of their role in controlling volar migration of the conjoined lateral bands and because their disruption makes development of boutonnière deformity more likely. Understanding the anatomy and biomechanics of the EM may assist in progress toward 'proof of concept' for use of RMF orthoses and controlled early active motion after EM injury or surgery. CONCLUSION: Hand surgery and hand therapy practice interventions, including use of RMF orthoses for management of non-surgical and surgical EM injuries may benefit from an in-depth look at the EM zone III and IV anatomy and biomechanics.

Boutonniere Versus Pseudoboutonniere Deformities: Pathoanatomy, Diagnosis, and Treatment.

Finger injuries involving the proximal interphalangeal (PIP) joint are common, particularly among athletes. Injury severity is often underappreciated at initial presentation and may be dismissed broadly as a "jammed finger" injury. Delayed diagnosis and treatment of certain injuries can have an important impact on the patient's chance of regaining full function. Central slip and PIP volar plate injuries are frequently encountered injuries that, if left untreated, can lead to the permanent loss of function of the proximal interphalangeal joint. Despite the differing mechanisms of these 2 pathologies, volar plate hyperextension injuries often present with a PIP joint flexion contracture and mild distal interphalangeal joint hyperextension deformity. This is similar to a boutonniere deformity seen after an injury to the central slip, and thus, has been referred to as a "pseudo-boutonnière" deformity. Distinguishing these 2 diagnoses is important, as treatment differs, and highlights the importance of thoroughly understanding the anatomy and relevant clinical applications when evaluating PIP joint injuries.

Effect of a Flexor Digitorum Superficialis Hemitenodesis on Reducing Volar Plate Strains for Swan Neck Deformities.

BACKGROUND: Flexor digitorum superficialis (FDS) hemitenodesis is a common procedure to treat swan neck deformity (SND). We hypothesize that this surgical technique is a biomechanically effective way to reduce strain in the volar plate at the proximal interphalangeal joint (PIPJ). METHODS: Fifteen digits from 5 cadaveric specimens were tested using a novel in vitro active finger motion simulator under 4 finger conditions: intact, SND, FDS hemitenodesis, and FDS hemitenodesis with distal interphalangeal (DIP) joint fusion. Tensile loads in FDS and flexor digitorum profundus (FDP) and joint ranges of motion were measured by electromagnetic tracking. In addition, strain gauges were inserted under the volar plate to measure strain during PIPJ hyperextension. Results were analyzed using 1-way repeated-measures analysis of variance tests. RESULTS: The SND condition increased volar plate strain by 176% ± 25% (P < .001) compared with the intact condition. The FDS hemitenodesis repair relieved more than 50% of the SND strain, restoring it to within no statistical difference from intact. The DIP fusion further reduced strain with no further statistical significance. At full flexion, FDS and FDP tendon loads diverged as a function of the test condition (P < .001). With the FDS hemitenodesis, the FDP load increased by 2.1 ± 1.5 N from the SND condition (P < .001), whereas the FDS load decreased by 1.3 ± 1.3 N (P = .012). CONCLUSION: The FDS hemitenodesis repair restored strains to within 3.0 milli-strain of the intact condition with no significant difference. Application of DIP fusion did not further protect the PIPJ from increased hyperextension and further exacerbated the imbalance of flexor tendon loads.

Management of chronic mallet finger: Indications and long-term results of Fowler central slip tenotomy and distal interphalangeal joint arthrodesis.

INTRODUCTION: Many surgical techniques have been described to correct the sequelae of chronic mallet fingers (MF), but no clear therapeutic strategy has been defined. We have reported the choice of their management according to the severity of the deformities. Two procedures were compared: Fowler's central slip tenotomy (CST) and arthrodesis of the distal interphalangeal joint (DIP). HYPOTHESIS: The use of our decision tree, based on the severity of deformity (flexion deformity at the DIP and recurvatum at the proximal interphalangeal joint), allows good long-term clinical results to be obtained. MATERIAL AND METHODS: Thirty-three patients (34 fingers) were operated on for sequelae of chronic MF either by CST or by DIP arthrodesis. Patients with ≤35° DIP flexion deformity and <25° proximal interphalangeal (PIP) recurvatum, without DIP joint involvement (osteoarthritis, subluxation, stiffness), were treated with CST. For the others, arthrodesis of the DIP joint was performed. RESULTS: Thirteen patients (13 fingers) were evaluated in the CST group with a mean follow-up of 13 years. There were no postoperative complications and no failures. The mean DIP residual extension lag was 4.23° with complete correction of the PIP recurvatum. All patients would redo the intervention in hindsight. The improvement in Quick-DASH was statistically significant (p=0.01). Twenty patients (21 fingers) were included in the DIP arthrodesis group with a mean follow-up of 10 years. Two failures (9.5%) occurred due to failed correction of the PIP recurvatum. No worsening of the deformities was reported, and they were corrected in 90% of cases. The absence of correction of the PIP recurvatum was more frequent in MF bone (p=0.01). All except 1 (95%) patient, who reported a lack of mobility of the DIP joint, would repeat the procedure. Quick-DASH was improved for all patients. DISCUSSION: CST is effective in correcting deformities in chronic MFs for ≤35° DIP flexion deformity and <25° PIP recurvatum without DIP joint involvement. In other cases, it is preferable to perform a DIP arthrodesis by combining, if necessary, a complementary procedure to correct the PIP recurvatum. LEVEL OF EVIDENCE: IV, retrospective study.

Clarification of Extensor Tenotomy for Finger Deformities.

This article clarifies the terminology and different applications of proximal Fowler extensor tenotomy and distal Dolphin extensor tenotomy. Although Fowler is a popular eponym for all finger extensor tenotomies, proximal Fowler tenotomy is specifically indicated for swan neck deformities, whereas distal Dolphin tenotomy is indicated for boutonniere deformities. For swan neck deformities with a distal interphalangeal joint extensor lag of greater than 40°, central slip tenotomy can be combined with terminal tendon imbrication or reinsertion. More distal Dolphin tenotomy of the lateral conjoined bands is complemented by centralization of the lateral bands or central slip reconstruction to correct hyperflexion of the proximal interphalangeal joint. The pertinent anatomic structures, mechanisms of release, and biomechanical principles have been demonstrated using intraoperative and animated videos of the surgical techniques.

Dynamic Rather than Static Procedures in Correcting Claw Deformities Due to Ulnar Nerve Palsy.

The theoretic disadvantage of dynamic tendon transfers is the perception that they are "more complex" than static procedures. The latter may provide a simple solution to claw deformity in a subset of patients; however, they completely disregard the disability associated with loss of the intrinsic musculature. Dynamic procedures reconstruct in part the deficient intrinsic forces and are thus capable of correcting the deformity and some disabilities associated with ulnar nerve palsy. In our practice, we have consistently achieved reasonable correction of claw deformity and improvement in tendon synchrony and grip strength with a modified Stiles-Bunnell, flexor digitorum superficialis tendon transfer.

Dynamic correction of ulnar claw hand deformity with a simple insertion into the lumbrical muscle.

Numerous methods of tendon transfers are available to correct claw hand deformity. In this article, we describe a simple insertion of the transferred flexor digitorum superficialis tendon, into the lumbrical muscle and proximal tendon. Sixty patients underwent surgery for claw hand correction. These were equally divided into three groups undergoing; modified Stiles Bunnell procedure; 'lasso' insertion into A1 pulley and the lumbrical insertion procedure. Evaluation was done with proximal interphalangeal joint angle measurements, grip strength and using the Brand's criteria, 1 year after surgery. The improvements were comparable among the three groups. Insertion into the lateral bands has been a standard method of claw correction. In addition to correcting the hyperextension of the metacarpophalangeal joint, it transmits force for interphalangeal joint extension and restores the sequence of flexion of fingers, thus making the grasp effective. Insertion into the lumbrical muscle belly and proximal tendon shows similar results. It can be performed via a single incision in the palm, reducing operative time.

Extension Block Pinning Vs Single Kirshner Wiring To Treat Bony Mallet Finger. A Retrospective Study.

BACKGROUND AND AIM: Bony Mallet Finger or Mallet Fracture is a common injury of the hand, which follows a forced flexion of the extended distal interphalangeal joint, that leads to a bony avulsion of the distal phalanx. Depending on fracture extension and dislocation, those lesions can either be treated conservatively or surgically. Several surgical options have been described in the literature. The aim of this study is to compare retrospectively two percutaneous pinning techniques: the extension block technique according to Ishiguro vs an original single Kirshner wiring (Umbrella technique). METHODS: Between January 1998 and December 2019, among all patients treated surgically for a Mallet Fracture with either the Ishiguro' and the Umbrella technique, 98 have been included in this study. All patients have been assessed one year after surgery using the Crawford method. RESULTS: With both techniques better results have been achieved in younger patients and for those treated early. The umbrella technique seems to have better results in patients with fracture classified as 2b or 2c (Wehbe and Schneider classification), whereas the Ishiguro technique seems more appropriate for patients with a 1b fracture. Complication rate and typology vary depending on the used technique. CONCLUSIONS: The Ishiguro' and the Umbrella technique both lead to good results for the treatment of surgical Mallet Fractures. The choice of the best type of pinning should mainly depend on fracture extension and time elapsed from trauma.

[Treatment of Wehbe-Schneider typesâ B and â ¡B bony mallet fingers with one-stage closed reduction and elastic compression fixation with double Kirschner wires].

Objective: To investigate the effectiveness of one-stage closed reduction and elastic compression fixation with double Kirschner wires for Wehbe-Schneider types ⅠB and ⅡB bony mallet fingers. Methods: Between May 2017 and June 2020, 21 patients with Wehbe-Schneider type ⅠB and ⅡB bony mallet fingers were treated with one-stage closed reduction and elastic compression fixation using double Kirschner wires. There were 15 males and 6 females with an average age of 39.2 years (range, 19-62 years). The causes of injury were sports injury in 9 cases, puncture injury in 7 cases, and sprain in 5 cases. The time from injury to admission was 5-72 hours (mean, 21.0 hours). There were 2 cases of index finger injury, 8 cases of middle finger injury, 9 cases of ring finger injury, and 2 cases of little finger injury. The angle of active dorsiflexion loss of distal interphalangeal joint (DIPJ) was (40.04±4.02)°. According to the Wehbe-Schneider classification standard, there were 10 cases of typeⅠB and 11 cases of type ⅡB. The Kirschner wire was removed at 6 weeks after operation when X-ray film reexamination showed bony union of the avulsion fracture, and the functional exercise of the affected finger was started. Results: The operation time was 35-55 minutes (mean, 43.9 minutes). The length of hospital stay was 2-5 days (mean, 3.4 days). No postoperative complications occurred. All patients were followed up 6-12 months (mean, 8.8 months). X-ray films reexamination showed that all avulsion fractures achieved bony union after 4-6 weeks (mean, 5.3 weeks). Kirschner wire was removed at 6 weeks after operation. After Kirschner removal, the visual analogue scale (VAS) score of pain during active flexion of the DIPJ was 1-3 (mean, 1.6); the VAS score of pain was 2-5 (mean, 3.1) when the DIPJ was passively flexed to the maximum range of motion. The angle of active dorsiflexion loss of affected finger was (2.14±2.54)°, showing significant difference when compared with preoperative angle (t=52.186, P<0.001). There was no significant difference in the active flexion angle between the affected finger (79.52±6.31)° and the corresponding healthy finger (81.90±5.36)° (t=1.319, P=0.195). At 6 months after operation, according to Crawford functional evaluation criteria, the effectiveness was rated as excellent in 11 cases, good in 9, and fair in 1, with an excellent and good rate of 95.24%. Conclusion: For Wehbe-Schneider typesⅠB and ⅡB bony mallet fingers, one-stage closed reduction and elastic compression fixation with double Kirschner wires can effectively correct the deformity and has the advantages of simple surgery, no incision, and no influence on the appearance of the affected finger.

Evaluation of tautening method in repair of advanced mallet finger without bone fracture.

Many different repair methods have been described in the frequently seen mallet finger deformity, but without consensus. The present study aimed to present an alternative tautening technique in mallet finger repair and to compare it versus classical direct repair. Patients with untreated chronic mallet finger of more than three months' progression, treated surgically between March 2017 and October 2020, were included. Two surgical methods were applied to restore extensor function of the distal interphalangeal joints. In the first group, the granulation tissue was excised and the extensor tendon was repaired directly. In the second group, granulation tissue was not excised, and the extensor tendon was tautened by plication. Outcomes were evaluated according to Miller's criteria. Fort-six patients were included: group 1, 25 patients; group 2, 21 patients. Mean age in group 1 was 36.2 years and 33.4 years in group 2. Mean follow-up in group 1 was 14.8 months and 13.9 in group 2. Extensor lag was similar (5.6°) in both groups at the end of the sixth month. On Miller's mallet finger criteria, group 1 scored 3.4 points and group 2 3.4 points (p > 0.05). The tendon tautening method helps to start physiotherapy early, the learning curve is short, and it provides functionally positive results and a low complications rate. We think that this method should be evaluated in chronic mallet finger deformities without bone fracture.

Central Slip Reconstruction With a Distally Based Flexor Digitorum Superficialis Slip: A Biomechanical Study.

PURPOSE: The ideal method of central slip reconstruction is difficult to determine due to the multitude of techniques, nonstandardized outcome reporting, and small patient series in the literature. Although most boutonniere deformities may be treated with nonsurgical measures, chronic, subacute, or open injuries may require operative intervention. To aid surgeons in the choice of the ideal central slip reconstruction method, this biomechanical study compared the 3 most common methods performed at our institution: direct repair, lateral band centralization, and distally-based flexor digitorum superficialis (FDS) slip repair. METHODS: A boutonniere deformity was induced in 35 fresh-frozen cadaver digits. The central slip was repaired in 9 digits using a primary suture repair, in 9 digits using a lateral band centralization technique, and in 9 digits using a distally-based FDS slip reconstruction. A control group without injury was tested in 8 digits. Following repair or reconstruction, each digit was tested for load to failure, strain, and stiffness at the repair. RESULTS: The average load to failure after central slip reconstruction was significantly greater for a distally based FDS slip method at 82.1 ± 14.6 N (95% CI, 62.2-101.9 N) than all other repair types. Although the FDS slip reconstruction was not as strong as the intact state (82.1 N vs 156.2 N, respectively), it was 2.6 times stronger than the lateral band centralization (82.1 N vs 31.6 N, respectively) and 3 times stronger than a primary repair (82.1 N vs 27.6 N, respectively). CONCLUSIONS: Reconstruction of the central slip using a distally-based FDS slip provided the greatest biomechanical strength compared with the direct repair or lateral band centralization. CLINICAL RELEVANCE: The use of a distally based reconstruction using FDS may allow for safer early motion.

The treatment of Doyle types II and III mallet finger with the encircling fixation of a transplanted palmaris longus tendon.

OBJECTIVE: This study aimed to investigate the clinical effect of the encircling fixation of a transplanted palmaris longus tendon in the treatment of Doyle types II and III mallet finger. METHODS: There were 115 cases of mallet finger deformity with Zone 1 extensor tendon rupture and defect. After debridement by first intention, the tendon bundles of the palmaris longus tendon were used to pass through the subcutaneous tunnel on the volar side of the base of distal phalanx, forming an encircling binding, crossing on the dorsal side. The tail of the tendon was then overlapped with the proximal extensor tendon and sutured. The finger extension position was fixed with plaster for four weeks. If the skin defect could not be closed directly, depending on the size of the skin defect, either a local turndown flap or a pedicled flap was used to cover the wound. RESULTS: The patients were followed up for 3-12 months after the operation. According to Total Active Motion criteria, the clinical effect was excellent in 89 cases, good in 16 cases, acceptable in 7 cases, poor in 2 cases and inferior in 1 case. CONCLUSION: The treatment of Doyle types II and type III mallet finger with the encircling fixation of a transplanted palmaris longus tendon is simple and effective, with a low recurrence rate, few complications, and satisfactory results.

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.