Anatomy of the flexor digitorum profundus insertion

Surgical anatomy of the nail

Knowledge of nail anatomy is a prerequisite for both diagnostic and therapeutic purposes. The nail apparatus is a highly specialized structure, but is in close relationship to the distal phalanx which supports it and to the pulp which carries the sensory receptors and is involved in pinching. It can be divided by the nail plate into the perionychium underneath, and the paronychium above. The perionychium includes, from proximal to distal: the nail matrix, the sole structure responsible for the growth of the nail plate; the nail bed, mostly responsible for adhesion of the plate; and the hyponychium, which is the most distal part, where the nail plate loses its adhesion. The paronychium comprises three nail folds, one proximal and two lateral, that embed the nail plate. The nail apparatus is richly vascularized, with three main sources, and richly innervated, which explains why trauma and surgery are so painful.

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.

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 ± 0.72^o 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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-021-04922-1.

Four Anchor Repair of Jersey Finger

BACKGROUND

Various surgical techniques for treating avulsions of the flexor digitorum profundus tendon at the distal phalanx have been published but no ideal technique has emerged. We introduce a new all-internal 4-anchor flexor tendon repair technique and evaluate outcomes in three clinical cases.

METHODS

In this retrospective case series, we reviewed three patients that sustained an avulsion of the flexor digitorum profundus tendon at the distal phalanx. All patients were surgically treated with the four-anchor repair technique. Two titanium anchors were inserted into the distal phalanx and two all-suture anchors were inserted distal to the first set of anchors. The tendon was then attached to these four anchors using a Krackow stitch pattern and the anchors were sown to each other. Active flexion and extension of the proximal and distal interphalangeal joint were measured at 3-month, 12-month, and 5-year follow-up. Postoperative complications were documented.

RESULTS

All patients achieved excellent clinical outcomes according to assessment criteria. At 3-month follow-up, all patients regained full flexion; two patients had full extension, while one patient was 3 degrees short of full extension. At 12-month follow-up, all patients had full flexion and extension. Five-year follow-up demonstrated the same results with no loss of function, sensation or grip strength. The repairs healed without rupture, and no complications were reported.

CONCLUSION

The 4-anchor flexor tendon repair is a viable surgical technique for zone 1 flexor digitorum profundus tendon repair or reconstruction. Further studies are needed to replicate these promising results and biomechanically validate this technique.Level of Evidence: IV.

Spiral Oblique Retinacular Ligament Procedure Using Flexor Digitorum Profundus Hemi-Tendon Transfer: Anatomical Basis and Clinical Application

PURPOSE

The spiral oblique retinacular ligament (SORL) procedure acts as a dynamic tenodesis to restore distal interphalangeal joint (DIP) extension and restrain proximal interphalangeal hyperextension. Despite the ingenious technique based on the oblique retinacular ligament anatomy, obtaining strong internal fixation remains an issue during the SORL procedure. We present a modified technique using the flexor digitorum profundus (FDP) hemi-tendon transfer.

METHODS

We dissected 5 fresh cadaveric specimens to evaluate morphometric parameters of the SORL procedure using the hemi-FDP. The volar groove of the FDP tendon was identified in zone I of the flexor sheath and the tendon was divided into radial and ulnar bundles. The selected hemi-tendon was divided at the proximal edge of the A1 pulley and a SORL procedure was performed through a transosseous tunnel in the distal phalanx. This technique was used in 3 patients with swan neck deformity.

RESULTS

The optimal distance between the DIP joint and the anterior drill hole of the transosseous tunnel was 7.6 mm (range, 6.8-8.5 mm). The relative loss of length of the tendon owing to the SORL path was 25.8 mm (range, 19.6-29.9 mm). In the clinical cases, the procedure improved DIP joint extension lag and prevented proximal interphalangeal joint hyperextension. Preserving one-half of the FDP allowed complete flexion of the DIP joint.

CONCLUSIONS

The procedure is technically feasible. Its main advantages are that a distal suture is not required and that the substantial length of the tendon allows sturdy proximal internal fixation.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic V.

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.

The Burden of Fingertip Trauma on the US Military

Fingertip injuries in the military are common and often hinder the fighting force and support personnel. Injuries range from small subungual hematomas to proximal finger amputations. Treatment modalities are dictated by injury patterns, anatomic considerations, and the need to return to duty. Nail bed injuries should be repaired when possible and exposed bone or tendon is treated with appropriate soft tissue coverage. If soft tissue coverage is unobtainable, revision amputation should be performed with attention given to maintaining as much finger length as possible. Antibiotics may not be required, however they are often utilized in the deployed setting.

Management of Tendon and Bony Injuries of the Distal Phalanx

Acute tendon and bony injuries of the distal phalanx are challenging injuries because they may result in chronic pain, hypersensitivity, stiffness, and deformity if they are not adequately treated. Flexor tendon avulsions require early surgical repair. Conversely, most extensor tendon injuries and fractures heal well with nonoperative treatment. However, surgery is indicated in selected patients, and meticulous technique is required to achieve good postoperative outcomes. In this article, we outline the pertinent clinical anatomy of the distal phalanx, review the current literature regarding treatment options, and highlight key management points to ensure good clinical outcomes while minimizing complications.

Fingertip Injuries in Athletes, Musicians, and Other Special Cases

Management of fingertip injuries in athletes is optimized by consideration of the sport, the playing position, the timing within the season, the level of competition, and the patient's goals. Mallet and jersey fingers are common injuries in athletes and may be treated in several different ways, based on the nature of the injury and the timing of presentation, as well as the athlete's demands. Management of fingertip injuries in musicians is optimized by consideration of how the musician handles his or her instrument and the specific requirements of the injured digit in the context of musical performance.

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.

Redefining Zone II: Anatomy of the Flexor Digitorum Superficialis Insertion

BACKGROUND

Flexor zone II is defined as the region spanning the proximal aspect of the A1 pulley to the insertion of the flexor digitorum superficialis (FDS) tendon. Descriptions of the FDS insertion are inconsistent in the literature, but zones of injury are frequently determined with reference to superficial landmarks. The purpose of this study was to describe the footprint of the FDS insertion and define its relationship to the proximal interphalangeal (PIP) skin crease.

METHODS

The FDS insertion on the index, middle, ring, and small fingers was dissected in 6 matched pairs of fresh-frozen cadaveric hands. A Kirschner wire was used to mark the level of the PIP skin crease on bone before measurements of the FDS footprint and its position relative to the PIP skin crease were made using digital calipers.

RESULTS

The radial and ulnar FDS slips inserted a mean distance of 3.22 mm from the distal aspect of the PIP skin crease and varied by digit. The mean distal extent of the FDS insertion was 8.29 mm. The mean length of the insertion of each FDS slip was 5.15 mm and the mean width was 1.9 mm.

CONCLUSIONS

The radial and ulnar FDS slips insert on average 3.22 mm distal to the PIP skin crease and vary by digit. Knowledge of the FDS insertion is clinically relevant when differentiating between flexor zone I and zone II injuries, planning surgical approaches to the finger, and in guiding patient expectations for surgery given the variability in outcome based on zone of injury.

Zone I Flexor Digitorum Profundus Repair: A Surgical Technique

We present an all-inside technique for zone I flexor tendon repair that combines suture anchor fixation with buried back-up fixation. The back-up fixation uses transosseous tunnels and a dorsal counterincision to allow a suture tied dorsal to the distal phalanx and buried. This technique is strong and permits early active range of motion. The dorsal tie-over does not require a suture button and, therefore, does not imperil the nail matrix. The surgical technique is herein described including the proposed anesthesia (wide awake), the incisions (midlateral), the exposures, and the repair itself.

The Effect of Distal Phalanx Bony Dimensions in Suture Anchor Fixations of Tendon Avulsion

Background: The terminal phalanx of the fingers carries the attachment of the Flexor Digitorum Profundus (FDP) on the volar surface and the extensor on the dorsal surface. Avulsion of these tendons has traditionally been repaired with pull-through sutures. Recently, bone anchor sutures have been found to be of comparable biomechanical strength but with the added advantage of technical ease and fewer complications. However, the dimensions of the bone, at the site of insertion of the anchors, have never been studied.

Methods: Following some cases of penetration of the dorsal cortex by the anchors, we measured the antero-posterior dimensions of the terminal phalanx in 251 digits from plain radiographs and compared these with the dimensions of the commonly used bone anchors. We also compared male and female digits.

Results: The anchors were oversized in 76% of index, 78% of ring and 100% of little fingers in the female population and in 49%, 44% and 97% of index, ring and little fingers respectively in the male population.

Conclusions: This analysis of bone dimensions can be a useful guide to surgeons in choosing the appropriate implant for flexor tendon avulsions.

Fingertip Winding Suture: Pull-out Suture Technique for Flexor Tendon Repair in Zone I

Injuries to flexor tendons in zone I has always been challenging during repair. Over the time several techniques were developed and modified to achieve the highest repair strength and thus the best functional outcome. These techniques vary from pull-out sutures with internal and external fixation to the use of bone anchors. All techniques were accompanied with advantages and disadvantages as well as postoperative morbidities related to certain techniques. In the present technique we introduce a subperiosteal pull-out suturing technique. It is a simple, strong, and cost-effective method for repair of flexor tendon injuries in zone I or in the context of tendon grafting.