The 3D muscle morphology and intramuscular innervation of the digital bellies of flexor digitorum profundus: Clinical implications for botulinum toxin injection sites.

Spasticity of flexor digitorum profundus is frequently managed with botulinum toxin injections. Knowledge of the 3D morphology and intramuscular innervation of the digital bellies of flexor digitorum profundus is necessary to optimize the injections. The purpose of this study was to digitize and model in 3D the contractile and connective tissue elements of flexor digitorum profundus to determine muscle morphology, model and map the intramuscular innervation and propose sites for botulinum toxin injection. Fiber bundles (FBs)/aponeuroses and intramuscular nerve branches were dissected and digitized in 12 formalin embalmed cadaveric specimens. Cartesian coordinate data were reconstructed into 3D models as in situ to visualize and compare the muscle morphology and intramuscular innervation patterns of the bellies of flexor digitorum profundus. The 3rd, 4th and 5th digital bellies were superficial to the 2nd digital belly and located adjacent to each other in all specimens. Each digital belly had distinct intramuscular innervation patterns. The 2nd digital belly received intramuscular branches from the anterior interosseus nerve (AIN). The superior half of the 3rd digital belly was innervated intramuscularly by the ulnar nerve (n = 4) or by both the anterior interosseus and ulnar nerves (n = 1). The inferior half of the belly received dual innervation from the anterior interosseus and ulnar nerves in 2 specimens, or exclusively from the AIN (n = 2) or the ulnar nerve (n = 1). The 4th digital belly was innervated by intramuscular branches of the ulnar nerve. One main branch, after coursing through the 4th digital belly, entered the lateral aspect of the 5th digital belly and arborized intramuscularly. The morphology of the FBs, aponeuroses and intramuscular innervation of the digital bellies of FDP were mapped and modelled volumetrically in 3D as in situ. Previous studies were not volumetric nor identified the course of the intramuscular nerve branches within each digital belly. Based on the intramuscular innervation of each of the digital bellies, one possible optimized botulinum toxin injection location was proposed. This injection location, at the junction of the superior and middle thirds of the forearm, would be located in dense nerve terminal zones of the anterior interosseus and ulnar nerves. Future anatomical and clinical investigations are necessary to evaluate the efficacy of these anatomical findings in the management of spasticity.

Anatomical design and production of a novel three-dimensional co-culture system replicating the human flexor digitorum profundus enthesis.

The enthesis, the specialized junction between tendon and bone, is a common site of injury. Although notoriously difficult to repair, advances in interfacial tissue engineering techniques are being developed for restorative function. Most notably are 3D in vitro co-culture models, built to recreate the complex heterogeneity of the native enthesis. While cell and matrix properties are often considered, there has been little attention given to native enthesis anatomical morphometrics and replicating these to enhance clinical relevance. This study focuses on the flexor digitorum profundus (FDP) tendon enthesis and, by combining anatomical morphometrics with computer-aided design, demonstrates the design and construction of an accurate and scalable model of the FDP enthesis. Bespoke 3D-printed mould inserts were fabricated based on the size, shape and insertion angle of the FDP enthesis. Then, silicone culture moulds were created, enabling the production of bespoke anatomical culture zones for an in vitro FDP enthesis model. The validity of the model has been confirmed using brushite cement scaffolds seeded with osteoblasts (bone) and fibrin hydrogel scaffolds seeded with fibroblasts (tendon) in individual studies with cells from either human or rat origin. This novel approach allows a bespoke anatomical design for enthesis repair and should be applied to future studies in this area.

The Effect of Forearm Shortening on Finger Flexion: A Biomechanical Study.

PURPOSE: Surgeons may shorten the forearm for many indications. We quantified the impact of shortening on finger flexion with a cadaver model. METHODS: Ten fresh cadaver proximal forearms were pinned to a static block. We pinned each distal forearm/hand to a block that could unlock, slide, and relock on a mounting track. This block allowed wrist-neutral or 30-degree extension. With the sliding block locked, we removed the central 10 cm of the radius/ulna. We placed sutures in the proximal end of each flexor digitorum profundus (FDP). After pretensioning, we simulated near-maximum baseline FDP muscle-generating force by applying 100 N via a load cell at the proximal sutures. We then anchored the load cell system proximally to set the initial length-tension relationship for simulating near-maximum baseline muscle-generating force. We called subsequent load cell readings the simulated muscle force (SMF) and pressure sensor readings between fingertips and the palm the tip-to-palm force (TPF). We shortened the forearm in 1 cm increments with the distal sliding-locking block. At each increment, we recorded SMF and TPF in the wrist-neutral position. Once a specimen lost measurable TPF, we applied 30 degrees wrist extension until again losing TPF. RESULTS: Incremental forearm shortening was associated with exponential decreases in each FDP's SMF and TPF. In wrist-neutral, 3 cm mean shortening had a loss of 99% and 98% SMF and TPF, respectively. Wrist extension marginally improved SMF and TPF up to 4 cm mean shortening, where both lost 99%. Loss of any fingertip touchdown occurred after a mean shortening of 4.9 cm in wrist-neutral and 5.3 cm in 30 degrees wrist extension. CONCLUSIONS: Mean forearm shortening of 3 or 4 cm had a near-complete loss of FDP SMF and TPF in wrist-neutral/wrist extension, respectively. With ∼5 cm shortening, there was a complete loss of fingertip touchdown. CLINICAL RELEVANCE: Surgeons should consider the influence of forearm shortening on the FDPs and contemplate flexor tendon shortening or alternative reconstructions as indicated.

All-Suture Anchor Repair of the Flexor Digitorum Profundus Insertion: A Biomechanical Comparison of 2 Suturing Techniques.

PURPOSE: We compared 2 suturing techniques for reattachment of the flexor digitorum profundus (FDP) via all-suture anchor. METHODS: We used fresh, matched-pair, cadaveric hands. We disarticulated the fingers at the proximal interphalangeal joints, preserving the proximal FDP. We released the FDPs at their distal insertion and placed an all-suture, 1.0-mm anchor at the center of each FDP footprint. Each anchor's sutures were used to reattach each FDP using 1 of 2 techniques: group H (n = 14) via horizontal mattress; group H + K (n = 12) via horizontal mattress with knots thrown and, with each suture tail, 3 proximal, running-locking, Krackow-type passes on the radial and ulnar FDP sides with the suture ends tied together. We excluded 2 specimens from the H + K group because of improper anchor placement. All other fingers in both groups were individually mounted in an MTS machine for FDP loading in the following sequence for 500 cycles each: (1) to 15 N to simulate passive motion forces; (2) to 19 N for short-arc active motion forces; and (3) to 28 N for full active motion forces. Specimens that had not failed during cyclic testing were then loaded to failure. We measured FDP-to-bone gapping via a digital transducer. We defined failure as >3-mm gapping. RESULTS: The H + K group had significantly less gapping during cyclic loading up to 19 N and significantly higher load to failure. The H + K group failed exclusively at the anchor-bone level; the H group failed mostly by suture-tendon pullout. CONCLUSIONS: The H + K group performed significantly better regarding cyclic and load-to-failure testing after FDP reattachment. CLINICAL RELEVANCE: The H + K technique combines the benefits of horizontal-mattress tendon-to-bone apposition and Krackow-tendon locking. It converts the point of failure to the bone level rather than the suture-tendon level.

Congenital Contracture of the Ulnar Digits and Its Differentiation From Ischemic Contracture.

PURPOSE: To describe the clinical features, radiologic findings, differential diagnosis, and surgical treatment of a congenital flexion deformity of the middle, ring, and little fingers. The cause of the condition is the aberrant origin of the flexor digitorum profundus, leading to a congenital contracture of the ulnar digits. METHODS: We reviewed 8 patients with congenital contracture of the ulnar digits. The mean age at the time of surgery was 14 years. An examination revealed a flexion contracture of the middle, ring, and small fingers. Plain radiographs, 3-dimensional computed tomography, magnetic resonance imaging, and ultrasound were used to characterize bony and soft tissue pathology. Surgical treatments included resection of the aberrant origin and a muscle-sliding procedure. RESULTS: Bony prominence on the proximal ulna was seen in the plain radiographs and/or 3-dimensional computed tomography. A cord that extended from this bony prominence to the tendons of flexor digitorum profundus was revealed in the magnetic resonance imaging. The bony prominence and the cord were also seen using ultrasound. The median time of patient follow-up was 1.7 years. A simple resection of the tendinous origin only resulted in a release in 2 patients who were 4 years old. Older patients required a further muscle-sliding procedure. The average grip strength ratio on the contralateral side was 82%. CONCLUSIONS: Congenital contracture of the ulnar digits is a new congenital flexion deformity involving the middle, ring, and small fingers. Bony prominence on the proximal ulna is the key finding for establishing its diagnosis and distinguishing it from an ischemic contracture. We recommend treating this surgically at 12 years of age or older after the phase of rapid growth of the extremities. We recommend the resection of the aberrant origin, combined with a muscle-sliding procedure, as the treatment of choice, even for young patients. TYPE OF STUDY/LEVEL OF EVIDENCE: Diagnostic V.

An Analysis of Profundus Tendon Repairs After Distal Phalanx Amputation in a Cadaveric Model of Little Finger Superficialis Deficiency.

PURPOSE: The flexor digitorum superficialis tendon to the little finger (FDS-5) has been observed to have a higher degree of functional and structural variation than the FDS of other digits. FDS-5-deficient individuals necessarily rely on the flexor digitorum profundus tendon to the little finger (FDP-5) for flexion in their little fingers. FDS-5 deficient patients who experience a considerable injury to their FDP-5 are therefore at a risk of losing substantial little finger flexion. The purpose of this study was to evaluate the degree of flexion of the little finger at the metacarpophalangeal and proximal interphalangeal (PIP) joints in a cadaveric model of FDS-5 deficiency following amputation of the distal phalanx. METHODS: Ten fresh-frozen cadaveric upper extremities with no prior trauma were used. Loads were applied to the FDP-5. Flexion at the PIP and metacarpophalangeal joints was measured in degrees with a goniometer. Little finger flexion testing was conducted under 5 different conditions: "baseline," "FDS-deficient," "no repair," "bone anchor" repair, and "A4 pulley" repair. RESULTS: The results were as follows: (1) no significant differences in the flexion between baseline and FDS-deficient conditions; (2) a significant decline in PIP flexion in the no repair condition after FDP-5 division compared with the FDS-deficient condition; (3) a significant restoration in PIP flexion in both surgical repair groups compared with the no repair group; and (4) no significant differences in PIP flexion between the A4 pulley and bone anchor groups. CONCLUSIONS: The bone anchor repair and the A4 pulley repair demonstrate similar abilities to restore flexion of the little finger at the PIP joint to baseline levels in this cadaveric model. CLINICAL RELEVANCE: A clinical protocol is yet to be established for the surgical treatment in FDS-5-deficient patients requiring amputation of the distal phalanx of the little finger. This study aims to address this area of uncertainty by comparing the little finger flexion after 2 different approaches to profundus tendon reattachment that may be applicable in this clinical scenario.

The muscular branching patterns of the ulnar nerve in fetal forearms.

OBJECTIVE: We aimed to present our findings systematically by examining the muscular branching patterns of the ulnar nerve (UN) in the forearms of fetuses. METHODS: This study was conducted on the 52 forearms of 26 formalin-fixed fetal cadavers with gestational ages varying between 19 and 37 weeks. The anatomical dissection was performed by using stereomicroscope with × 8 magnification. The numbers of muscular branches leaving UN and their order of leaving main nerve were noted down. The findings were classified according to the muscles they reached, and branching typing was done. RESULTS: It was found that a total of 2-6 muscular branches left UN to reach flexor carpi ulnaris (FCU) and flexor digitorum profundus (FDP). UN was classified by separating into five main types according to the number of muscular branches, and these types were classified into 16 different branching patterns according to the order of branches leaving from the main trunk and going to FCU and FDP. The pattern where two branches left UN was classified as Type I (n = 6), three branches left was classified as Type II (n = 18), four branches left was classified as Type III (n = 24), five branches left was classified as Type IV (n = 3), and six branches left was classified as Type V (n = 1). Martin-Gruber connection occurred in 17 (32.7%) fetal forearms. CONCLUSION: We believe that the information that UN can demonstrate different branching patterns on the forearm can help the surgeons to prevent complications that may develop in potential nerve injury during the selection and transfer of relevant branch.

A reverse form of Linburg-Comstock variation with comments on its etiology and demonstration of interactive 3D portable document format.

PURPOSE: Two most common variations of flexor pollicis longus include its accessory head and its connection with the flexor digitorum profundus of the index (Linburg-Comstock variation). In addition, while three-dimensional (3D) screening has widely been used in anatomical education, its use as reporting tool in anatomical research is still limited. The objective of this study is to report a previously unrecognized form of the accessory head of flexor pollicis longus, discuss the potential etiology of Linburg-Comstock variation, and pilot the 3D scanning of a large-scale anatomical structure. METHODS: An unusual tendon slip was discovered during a routine dissection in the anterior compartment of the right forearm of a 54-year-old male cadaver. A 3D scanner was used to capture the surface topography of the specimen and an interactive portable document format (PDF) was created. RESULTS: An anomalous tendon was found originating from the lateral aspect of the flexor digitorum profundus muscle. This variant tendon then inserted onto the medial surface of the flexor pollicis longus tendon before entering the carpal tunnel. The variation resembles a reverse form of Linburg-Comstock variation, because pulling this variant tendon resulted in simultaneous flexion of the interphalangeal joint of thumb. CONCLUSION: Surgeons should be aware of the reverse Linburg-Comstock variation, because it may not be detectable by the conventional provocative testing. Linburg-Comstock variation may be classified as an anatomical variant or a secondarily acquired condition depending on its type. Our demonstration of interactive 3D-PDF file highlights its potential use for delivering anatomical information in future cadaveric studies.

The accessory heads of the muscles flexor pollicis longus and flexor digitorum profundus (Gantzer muscle) - An anatomical study in Brazilian cadavers.

An important accessory anatomical variation, exclusively human, and related to the muscular ventres of the flexor pollicis longus and flexor digitorum profundus is frequently denominated Gantzer. These variations have close relations with the anterior interosseous nerve (AIN), which provides, for many authors, by direct compression, one of the rare neuropathic syndromes. In this work, thirty-four forearms were dissected from the collections of the Medical School of the Federal University of Minas Gerais and the Department of Basic Sciences of the Federal University of Juiz de Fora, with a prevalence of 50% of the 34 forearms studied for the Gantzer muscle. The muscle relationship was mainly with the flexor pollicis longus muscle and only one occurrence related to the flexor digitorum profundus muscle, described as a rare occurrence of unilateral double formation of Gantzer muscle. Bilaterality was observed in 88.23% of the findings and the dominant innervation for this muscle variation occurred in 82.35% by the anterior interosseous nerve (AIN). The type morphological in all forms found was the fusiform, with 10.5cm of total length and an average of 0.3cm in diameter and all related, as origin, in the medial aspect of the coronoid process of the ulna, next to the origin of the flexor digitorum superficialis muscle. Our work largely reflected the findings of most publications and, considering the controversy of the occurrence of a compressive neuropathy, the data were not sufficient, from a strictly anatomical point of view, to confirm or refute the hypothesis.

Anatomy and histomorphology of the flexor digitorum profundus enthesis: functional implications for tissue engineering and surgery.

BACKGROUND: The enthesis possesses morphological adaptations across the soft-hard tissue junction which are not fully restored during surgical avulsion repairs. This loss of anatomical structure, highly related to function, contributes to poor clinical outcomes. Investigating the native macro- and micro-structure of a specific enthesis can provide functional and biomechanical insights to develop specialised, novel tissue-engineered therapeutic options and potentially improve current surgical treatments for avulsion injuries. METHODS: This study examines the anatomy and histomorphology of the flexor digitorum profundus (FDP) enthesis in 96 fresh-frozen human cadaveric fingers, quantitatively and qualitatively analyzing the shape, size, angle of tendon fibres and histological architecture, and explores differences in sex, finger and distance along the enthesis using linear mixed effects models. RESULTS: Macroscopically, results showed a consistent trapezoidal insertion shape of 29.29 ± 2.35 mm2 mean surface area, but with significant morphometric size differences influenced primarily by the smaller dimensions of the little finger. Microscopically, a fibrocartilaginous enthesis was apparent with a 30.05 ± 0.72o mean angle of inserting tendon fibres, although regional variation in fibrocartilage and the angle change of tendon fibres before insertion existed. CONCLUSIONS: The implication of these findings on native and specific FDP enthesis function is discussed whilst providing recommendations for optimal FDP enthesis recreation for interfacial tissue engineers and hand surgeons. The study emphasizes the importance of region-specific knowledge whilst also describing methods applicable to assessing any soft tissue insertion.

The Ideal Insertion Site for the Flexor Digitorum Profundus Tendon in Jersey Finger Repair: A Biomechanical Analysis.

PURPOSE: Most jersey finger repair techniques involve reattaching the tendon to an approximate location corresponding to the tendon's native attachment. This study aimed to determine the biomechanical effect on the distal interphalangeal joint flexion forces and range of motion when the flexor digitorum profundus (FDP) tendon attachment site on the distal phalanx is altered within its broad footprint. METHODS: We fixed 14 fresh-frozen cadaveric fingers to a wooden block with an attached pulley and weights system. A pressure mapping sensor placed under the fingertip measured the contact force and area in response to FDP tendon loading for the intact tendon and 3 repair sites along the FDP footprint. Two-way repeated-measures analysis of variance test using mixed-effect model was performed to test the influences of attachment location (intact, proximal, central, and distal) and digit (index, middle, and ring) on the outcomes. RESULTS: Mean ± SD contact force under 45 N tendon loading force was 43.5 ± 7.2 N for the intact tendon, 34.6 ± 7.4 N for the proximal insertion, 38.0 ± 7.1 N for the central insertion, and 43.1 ± 6.3 N for the distal insertion. Compared with the intact tendon, the proximal group generated notably less contact force. No significant difference was detected between the intact tendon and the central or distal repairs. Comparisons among the 3 repair groups show that the distal group generated significantly higher force than the proximal group. There was no difference between contact areas across all groups. CONCLUSIONS: The FDP tendon inserted at the distal edge of its footprint conferred significantly greater distal interphalangeal joint flexion force compared with the proximal insertion site and most closely resembled the intact FDP tendon. CLINICAL RELEVANCE: Biomechanically, distal reattachment of the FDP most closely approximates the contact force of the native anatomy and may help guide intraoperative placement of the repair footprint.

Tensile load on the flexor digitorum profundus tendon during palmar and lateral blocking exercises: Influence on blocking force and distal interphalangeal joint flexion angle.

STUDY DESIGN: This is a basic science research. INTRODUCTION: Isolating excursion of the flexor digitorum profundus (FDP) in zones I and II is common practice in the current management after flexor tendon repair. During this procedure, the proximal interphalangeal joint is sometimes fully extended with unmeasured external forces at the middle phalanx when the distal interphalangeal joint is actively flexed. PURPOSE OF THE STUDY: The purpose of the study was to investigate the incremental effect of external force with palmar blocking versus lateral blocking and increased angles of flexion on internal tendon forces at the repair site for a safer application of force by the treating therapist. METHODS: Eight human cadaveric fingers were studied. To simulate palmar or lateral finger blocking, a compression force of blocking was applied from 5N (510 grams) to 25N (2,550 grams) on the skin surface of the palmar or the lateral aspect of each of these middle phalanges in 5N increments. The tensile load on the FDP tendon during distal interphalangeal joint flexion from 0° to 60° was measured in 10° increments. RESULTS: During palmar blocking, the tensile load was significantly increased with increases in palmar blocking force. However, no significant increase in the tensile load on the FDP tendon was observed at any lateral blocking. DISCUSSION: Lateral blocking exercise can be performed with less tensile force on the FDP tendon when performing blocking exercise after flexor tendon injury repair. CONCLUSIONS: This study supports the concept that lateral blocking with incremental joint angles allows a safer application of force for the healing tendon.

An investigation into the reliability and methodology of the Linburg-Comstock anomaly clinical test.

STUDY DESIGN: This is a cross-sectional study. INTRODUCTION: An intertendinous connection between the flexor pollicis longus (FPL) and index flexor digitorum profundus (IFDP) tendons causes involuntary index flexion during active thumb flexion and has been named the Linburg-Comstock anomaly (LCA). It may become symptomatic or cause functional limitations. Literature has documented the prevalence to range from 13% to 70%. Cadaver studies have reported an anatomical connection in 5% to 25%. PURPOSE: This study aimed to examine the methodology and reliability of the LCA clinical diagnostic test and to explore the wide range of reported incidence and the discrepancy between cadaver and subject prevalence. METHODS: Two examiners observed for the presence of involuntary index flexion during 3 separate variations of thumb flexion in 67 subjects (134 limbs); results were considered positive if involuntary flexion occurred at either index interphalangeal joint. Intertester reliability was assessed using Cohen's kappa coefficient. The volar forearm and wrist of 53 cadavers (106 limbs) were dissected and assessed for an observable and mechanical tendinous connection between the FPL and IFDP tendons. RESULTS: Prevalence for subjects (5%-32%) was at the lower end of the range of previously reported values; results differed with altering thumb flexion motion. Observation for the presence of an intertendinous connection between the FPL and IFDP tendons in cadaver specimens (23%) fell within previously reported ranges. Intertester reliability coefficients ranged from no to weak agreement and varied according to specific thumb flexion motion performed during the test. CONCLUSIONS: The identification of index finger flexion during thumb flexion varied both with thumb flexion motions and with whether flexion was assessed at the index proximal interphalangeal or distal interphalangeal joint. Intertester reliability was low for all variations of the LCA clinical test performed. The wide range in previously reported LCA incidence may be due to variability in testing procedure, and there is a need to establish a reliable and valid clinical test for this potentially symptomatic anatomic anomaly.

Complications Following Transosseous Repair of Zone I Flexor Tendon Injuries.

PURPOSE: Multiple techniques are described for repair of zone I flexor tendon injuries, many of which are fraught with complications. This study evaluated the clinical complications after a transosseous repair technique. METHODS: A retrospective review of a single institutional database identified all zone I flexor digitorum profundus (FDP) injuries repaired using a transosseous technique. In this technique, 2 nonabsorbable sutures were passed from volar to dorsal through transosseous tunnels and tied dorsally over the distal phalanx proximal to the germinal matrix. Demographics, injury characteristics, operative details, and complications were reviewed. RESULTS: Eight patients met the inclusion criteria. Average age was 31 years (range, 15-66 years) and all patients were male. Eight fingers were included: ring (4), small (3), and middle (1). Seven injuries were closed and one was open. Average time between injury and surgery was 13 days (range, 4-34 days). Five patients experienced complications, including osteomyelitis, chronic draining granuloma, and abnormal nail growth. Three patients required an additional operative procedure for management of complications. CONCLUSIONS: Transosseous repair of zone I flexor digitorum profundus injuries with a buried dorsal suture is associated with a high rate of clinical complications. TYPE OF STUDY/LEVEL OF EVIDENCE: Therapeutic V.

Absence of flexor digitorum profundus muscle and variation of flexor digitorum superficialis muscle in a little finger: two case reports.

PURPOSE: Knowledge of rare variants of the FDP is of high clinical importance for physicians examining patients for tendon lacerations and especially for hand surgeons operating tendon injuries. METHODS: During routine dissection at our Department of Anatomy both cases were observed. RESULTS: Variations of flexor digitorum superficialis and flexor digitorum profundus muscles of the little finger were observed in two cadavers. In both cases, the flexor digitorum profundus muscle for the little finger was absent. Moreover, in the first case, the flexor digitorum superficialis muscle for the little finger was hypoplastic and in the second case it featured variable insertion. CONCLUSION: There were found only four cases in previous literature describing absent flexor digitorum profundus tendon without any muscle attachment to the base of the distal phalanx. Furthermore, all previously described cases were observed in living patients. To our best knowledge, a case report in cadaver has yet not been reported and is of high importance for hand surgeons examining the hand for tendon injuries.

Mapping of finger fascicles within the flexor digitorum superficialis and profundus muscles.

INTRODUCTION: In this study we aimed to systematically investigate and map localization of the individual finger fascicles within the flexor digitorum superficialis (FDS) and the flexor digitorum profundus (FDP) muscles. METHODS: Using B-mode ultrasonographic assessments, the right forearms of ten healthy participants (five males and five females) were examined during active and passive finger movements. RESULTS: A topographical map indicating clear core areas of fascicle activation within the FDS and FDP muscles was created. Borders that could, to some degree, define individual differences were also indicated. DISCUSSION: Our findings offer a detailed image of fascicle distributions within the FDS and FDP muscles. Various challenges, such as managing individual muscular profiles or the existence of the palmaris longus muscle, are discussed and should always be taken into consideration. The current map can serve as a general orientation for future measurements or injection therapies.

The Accommodation of Bone Anchors Within the Distal Phalanx for Repair of Flexor Digitorum Profundus Avulsions.

PURPOSE: Avulsion injury of the flexor digitorum profundus (FDP) tendon has been traditionally repaired with a pull-out suture over the nail plate. Complication rates with this method and improvements in anchor design have led to the increased use of bone anchors to give a rigid all-inside repair. However, the dimensions of the distal phalanx may limit their use. The primary hypothesis was that 2 micro bone anchors could fit in either perpendicular or 45° proximally angled positions within each distal phalanx. A further hypothesis was that 1 mini bone anchor could fit in similar positions in the distal phalanx. METHODS: Thirty-two fresh frozen fingers were dissected, and the FDP tendon was removed from the distal phalanx footprint. Two bone anchor types were used, mini and micro sizes, and inserted at 2 angles, perpendicular and 45° proximally angled. Observations of dorsal cortex and joint space penetration were recorded. Distal phalanx dimensions were measured for each finger. RESULTS: The micro anchors penetrated the dorsal cortex in perpendicular tests in little fingers only. The micro anchor did not penetrate the joint in any angled tests. The mini bone anchor penetrated the dorsal cortex in 100% of perpendicular tests and the joint in 63% of angled tests, although none of these included the middle finger. CONCLUSIONS: Two micro bone anchors fit within the distal phalanx in all fingers tested, except the little finger, when placed in the perpendicular position. At a 45° angle, the distal phalanx of the little finger can also accommodate micro bone anchors without any evidence of complication when placed 4 mm from the joint. The mini anchors were too large to fit in a perpendicular position within the distal phalanx. In the 45° angled position, the joint was not penetrated by the mini anchor in only middle fingers. CLINICAL RELEVANCE: The study provides anatomical evidence of the accommodation of micro bone anchors within the distal phalanx in perpendicular or 45° angled positions for the repair of FDP tendon avulsion injury.

Prevalence of the Linburg-Comstock variation through clinical evaluation.

INTRODUCTION: Linburg-Comstock variation, the tendinous interconnection between flexor pollicis longus and flexor digitorum profundus, is known to have a wide frequency range. Its prevalence is reported with a range of 13-66%. The aim of the study was to assess this variation in general population and to correlate it with gender and side. MATERIAL AND METHODS: This prospective study included 215 subjects (82 males and 133 females). Two clinical tests were conducted to diagnose the variation and to detect any related symptomatology. The primary outcome was set to be the prevalence of Linburg-Comstock variation. Secondary outcomes were defined as gender-based prevalence, side-based prevalence, and Linburg-Comstock variation prevalence association with gender and side. RESULTS: Linburg-Comstock variation was clinically diagnosed in 130 (60.47%) participants. Unilateral and bilateral prevalence were of 17.21% and 43.26%, respectively, yielding a statistically significant difference. Right-sided and left-sided presence were calculated at 7.44% and 9.77%. Bilateral prevalence was statistically more common in females. Right-sided variation was found to be more frequent in males while left-sided variation was more prevalent in females. The index finger was the most commonly involved with prevalence of 91.03%. Symmetry was noted in 67.74% of subjects. CONCLUSION: The results of our study demonstrated a relatively high prevalence of the Linburg-Comstock variation in Serbian population. We noted a few unusual cases and this finding point to the existence of the broader spectrum of Linburg-Comstock variation, and complexity of the flexor apparatus of the hand, so, further investigations about this topic are needed to improve our knowledge. Due to the possibility of false-positive result during clinical testing we suggest to use expanded clinical method.

Factors Accounting for Variation in the Biomechanical Properties of Flexor Tendon Repairs.

PURPOSE: To investigate factors that cause variation in the mechanical properties of flexor tendon repairs. METHODS: One surgeon repaired 50 homogeneous absorbent sticks and 40 porcine flexor tendons with a simple loop, an Adelaide repair, a peripheral over-and-over repair, or a combination of the latter 2 repairs. Ten hand surgeons repaired 1 porcine flexor tendon with the combined Adelaide core and over-and-over peripheral repair. We loaded the samples statically until failure and calculated the variations caused by the testing process, tendon substance, and surgical performance in terms of yield and ultimate load. RESULTS: Tendon material and surgical performance both caused about half of the variation in the yield load of the combined repair. Surgical performance caused all variations observed in the ultimate load of the combined, peripheral-only, and core repairs. The effect of the tendon material was negligible in ultimate load. The intersurgeon variation was present only in yield load, and it represented one-tenth of the total variation. CONCLUSIONS: The effect of tendon substance on variation of the ultimate load is minimal. In yield load, both tendon and surgical performance are responsible for the variation. CLINICAL RELEVANCE: In clinical realm, variation caused by testing is not present, but intersurgeon variation may cause additional variation in yield load. A hand surgeon cannot change the variation due to tendon properties, but with a more meticulous surgical technique, the variation related to the surgical performance can probably be diminished.

Gap Formation During Cyclic Testing of Flexor Tendon Repair.

PURPOSE: Substantial gap formation of a repaired finger flexor tendon is assumed to be harmful for tendon healing. The purpose of this study was to investigate the relationship between gap formation and the failure of the repair during cyclic loading. METHODS: Thirty-five porcine flexor tendons were repaired and tested cyclically using variable forces until failure or a maximum of 500 cycles. Depending on the biomechanical behavior during cyclic testing, specimens were divided into 3 groups: Sustained (no failure), Fatigued (failure after 50 cycles), and Disrupted (failure before 50 cycles). The relationships between the gap formations, time-extension curves, and group assignments of the samples were investigated. RESULTS: The time-extension curves of the Fatigued specimens showed a sudden onset of repair elongation-a fatigue point-which preluded the subsequent failure of the repair. This point coincides with the start of plastic deformation and, thereafter, cumulative injury of the repair consistently led to failure of the repair during subsequent cycles. None of the sustained repairs showed a fatigue point or substantial gapping during loading. CONCLUSIONS: We conclude that the emergence of a fatigue point and subsequent gap formation during loading will lead to failure of the repair if loading is continued. CLINICAL RELEVANCE: The results of this experimental study imply that an inadequate flexor tendon repair that is susceptible to gap formation is under risk of failure.