Small Joint Denervation of the Hand and Thumb Base: History, Anatomy, Technique, and Outcomes.

Painful arthritis of the small joints of the hand is a common condition affecting older adults, with distal interphalangeal joint and thumb carpometacarpal joint being the two most common locations. Younger adults may also develop painful arthritis after trauma and with inflammatory arthropathy. Traditional surgical approaches address the structure of the joints with either arthrodesis or arthroplasty with or without an implant. In recent decades, denervation has been reported as an alternative treatment for painful small joints that are mobile and stable. Publications on denervation often report faster surgery and recovery times than traditional surgeries that manipulate the small joint bony structures. This article reviews the history, anatomy, surgical techniques, and outcomes of denervation of the small joints of the hand.

Denervation of the Joints of the Hand and Wrist: Surgical Techniques and a Systematic Review with Meta-Analysis.

BACKGROUND: Joint denervation of the wrist, basal joint of the thumb, and the finger is an option for patients with chronic pain. Compared with other surgical treatment options, function is preserved and the rehabilitation time is limited. A systematic review and meta-analysis were performed for each joint to determine whether the choice of technique and choice of denervation of specific articular sensory branches lead to a different outcome. METHODS: Embase, MEDLINE (OvidSP), Web of Science, Scopus, PubMed publisher, Cochrane, and Google Scholar database searches yielded 17 studies with reported outcome on denervation of the wrist, eight on the basal joint of the thumb, and five on finger joints. RESULTS: Overall, the level of evidence was low; only two studies included a control group, and none was randomized. Meta-analysis for pain showed a 3.3 decrease in visual analogue scale score for wrist pain. No difference was found between techniques (total versus partial denervation), nor did different approaches influence outcome. The first carpometacarpal joint showed a decrease for visual analogue scale score for pain of 5.4. Patient satisfaction with the treatment result was 83 percent and 82 percent, respectively. Reported pain in finger joints decreased 96 percent in the metacarpophalangeal joints, 81 percent in the proximal interphalangeal joint, and 100 percent in the distal interphalangeal joint. The only reported case in the metacarpophalangeal joint of the thumb reported an increase of 37 percent. CONCLUSIONS: Only denervation of the metacarpophalangeal joint of the thumb reported an increase in pain; however, this was a single patient. Wrist and first carpometacarpal joint and finger joint denervation have a high satisfaction rate and decrease the pain. There was no difference between techniques.

Innervation of digital joints: an anatomical overview.

INTRODUCTION: The innervation of the digital joints as well as the anatomical relationships of the articular branches is present in this anatomical work to determine the technical feasibility of a selective and efficient denervation of the digital joints. MATERIALS AND METHODS: A study of 40 distal interphalangeal (DIP), 40 proximal interphalangeal (PIP), 50 metacarpophalangeal (MCP), 10 interphalangeal (IP) of the thumb, and 10 trapezo-metacarpophalangeal (TMC) joints was performed on ten hands. Under magnification and a proper surgical approach, we collected the course, the source origin, the number of articular nerve branches, and their caliber. RESULTS: In total, 118 nerve branches arising from the proper palmar digital nerves were found on 10 DIP of each dissected long finger (n = 40). A total of 226 nerve branches were found on 10 PIPs of each long finger (n = 40), of which 204 branches (90.3%) had a palmar origin. Dorsal innervation was found for the ring and little finger, originating from the dorso-ulnar digital nerve. 212 branches were found on 10 MCP of long fingers (n = 40), including 87 branches of palmar origin (41.1%), 107 branches of dorsal origin (50.4%), and 18 branches of the motor branch of the ulnar nerve (8.5%). 42 articular branches directed to the TMC joint (n = 10) were found. 13 branches (31%) originated from the anterior sensory branch of the radial nerve, 13 branches (31%) originated from the lateral cutaneous nerve of the forearm, 5 branches (12%) originated from the palmar cutaneous branch of the median nerve, and 11 (26%) branches originated from the thenar branch of the median nerve. The involvement of the sensory anterior branch of the radial nerve was always present for the innervation of each TMC. DISCUSSION AND CONCLUSION: Our research shows that finger joints receive their primary innervation from small branches of the digital nerves with the exception of the MCP joint and the TMC joint. To obtain an efficient and a selective digital denervation for articular pain relief, it is necessary to plan the best surgical approach and it is crucial to recognize the articular nervous branch localization and source.

Finger joint denervation in hand osteoarthritis: Indications, surgical techniques and outcomes. A systematic review of published cases.

In cases of osteoarthritis with preserved motion, joint denervation can be an effective alternative to arthroplasty or arthrodesis to reduce joint-related pain. Although denervation is a standardized procedure for wrist osteoarthritis, it is used sparingly for finger joints. We conducted a systematic review to summarize reported cases of finger joint denervation in hand osteoarthritis with a specific focus on surgical procedures and postoperative outcomes. PubMed, Cochrane and Science Direct databases were searched from 1998 to 2019 and 13 relevant articles were selected. Three hundred and twenty-five denervations were conducted on 291 patients. Distal interphalangeal (DIP) joint denervation was performed through a dorsal approach; 83% of patients were satisfied with the surgery and complications occurred in 58%. Proximal interphalangeal (PIP) joint denervation was performed through a palmar approach; 90% of patients were satisfied with the surgery; complications were observed in 14%. Good results were observed in 95% of patients who underwent metacarpophalangeal (MCP) joint denervation; complications were observed in 26%; denervation was carried out with dorsal and palmar approaches in all cases. Denervation of the trapeziometacarpal (TMC) joint was achieved through the Wagner approach (61%), multiple incisions (26%), or dorsal approach (13%); satisfaction rate was 91%, with a 6% complication rate. Finger joint denervation in hand osteoarthritis is a simple and effective procedure, providing satisfactory pain relief. Good results are reported in all studies, especially for PIP and TMC joint denervation. Further investigations should be conducted on DIP and MCP joint denervation.

Innervation of the Proximal Interphalangeal Joint: An Anatomical Study.

PURPOSE: To describe the innervation of the proximal interphalangeal (PIP) joint of the fingers as well as the anatomical relations of the articular branches. METHODS: In this anatomical study, 52 fresh-frozen index, long, ring, and little fingers of 6 male and 4 female cadavers were dissected after injection of a colored latex composite. The anatomical dissections were performed under ×3.5 and ×6.0 magnifications. The numbers of articular nerve branches that penetrated the PIP joint on both sides of the fingers were quantified and patterns of innervation were established. We also measured the origin of the branches regarding the PIP articular line, the angle of emergence, and the diameter of the nerves. RESULTS: The PIP joint was innervated by one articular branch of the proper palmar digital nerve at each side of the finger (pattern 1). Less frequently, an additional distal branch from the same proper palmar digital nerve was found (pattern 2). Dorsal articular branches were identified innervating only the little finger. CONCLUSIONS: The findings suggest that PIP joints of the fingers have a consistent articular nerve anatomy predominantly provided at the palmar aspect of the joint. These findings provide an anatomical basis for procedures to denervate the PIP joint. CLINICAL RELEVANCE: An accurate understanding of peripheral nerve anatomy of the PIP joint is essential to improve outcomes in denervation techniques.

Innervation of the interphalangeal joint of the thumb: anatomical study.

We dissected 30 cadaveric thumb interphalangeal joints to delineate the sensory nerve anatomy of its capsule. Four articular branches supplying the interphalangeal joint capsule of the thumb were found in all specimens. Ulnar and radial proper digital nerves provide one palmar capsular nerve branch on their respective sides. Of the two dorsal branches of the radial nerve at the dorsum of the thumb, we observed that each nerve provided one branch to the interphalangeal dorsal capsule. Our findings demonstrate a consistent pattern of innervation and may provide the anatomical basis to the treating surgeon for an effective and safe denervation of the interphalangeal joint of the thumb.

Joint Denervation in the Digits: Technique and Patient Satisfaction.

BACKGROUND: Traditional approaches to treating painful osteoarthritis of the fingers include arthrodesis and arthroplasty. Although highly effective for pain control, arthrodesis sacrifices joint motion and can be complicated by nonunion, malunion, and infection.Implant arthroplasty preserves motion but is likewise subject to complications-particularly at the level of the proximal interphalangeal joint. In contrast, finger joint denervation is a simple outpatient procedure that maintains joint motion. In this study, we describe our surgical techniques for joint denervation and review our survey of patient satisfaction. METHODS: A retrospective review was performed of all patients undergoing finger joint denervation for osteoarthritis at our institution from 2012 to 2014. Each patient was contacted by phone and asked to rate their pre- and postoperative pain and function.Patients were also asked about any complications experienced and if they would choose to undergo the operation again. RESULTS: Over the 2-year period, 12 patients underwent denervation of 23 joints. Of the 12 patients in the study, 11 undergoing 22 joint denervations were available for our survey. Patient-reported pain scores fell from a median of 5/5 preoperatively to 0/5 after recovery (P < 0.001). Perceived hand function improved from a preoperative reported median of 2/5 to a postoperative median of 5/5 (P < 0.001). Complications were few, and 9 of 11 patients said they would choose to have the operation again. CONCLUSIONS: Joint denervation is a safe and effective treatment modality for osteoarthritis of the digits, resulting in good pain relief and high patient satisfaction with low complication rates.

Change in the temporal coordination of the finger joints with ulnar nerve block during different power grips analyzed with a sensor glove.

Ulnar nerve injuries can cause deficient hand movement patterns. Their assessment is important for diagnosis and rehabilitation in hand surgery cases. The purpose of this study was to quantify the changes in temporal coordination of the finger joints during different power grips with an ulnar nerve block by means of a sensor glove. In 21 healthy subjects, the onset and end of the active flexion of the 14 finger joints when gripping objects of different diameters was recorded by a sensor glove. The measurement was repeated after an ulnar nerve block was applied in a standardized setting. The change in the temporal coordination of the metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints with and without the nerve block was calculated within the same subject. In healthy subjects, the MCP joints started their movement prior to the PIP joints in the middle and ring finger, whereas this occurred in the reverse order at the index and little finger. The DIP joint onset was significantly delayed (P<0.01). With the ulnar nerve block, this coordination shifted towards simultaneous onset of all joints, independent of the grip diameter. The thumb and index finger were affected the least. With an ulnar nerve block, the PIP joints completed their movement prior to the MCP joints when gripping small objects (G1 and G2), whereas the order was reversed with larger objects (G3 and G4). The alterations with ulnar nerve block affected mainly the little finger when gripping small objects. With larger diameter objects, all fingers had a significant delay at the end of the PIP joint movement relative to the MCP and DIP joints, and the PIP and DIP joint sequence was reversed (P<0.01). Based on the significant changes in temporal coordination of finger flexion during different power grips, there are biomechanical effects of loss of function of the intrinsic muscles caused by an ulnar nerve block on the fine motor skills of the hand. This can be important for the diagnosis and rehabilitation of ulnar nerve lesions of the hand.

A Neuromuscular Electrical Stimulation (NMES) and robot hybrid system for multi-joint coordinated upper limb rehabilitation after stroke.

BACKGROUND: It is a challenge to reduce the muscular discoordination in the paretic upper limb after stroke in the traditional rehabilitation programs. METHOD: In this study, a neuromuscular electrical stimulation (NMES) and robot hybrid system was developed for multi-joint coordinated upper limb physical training. The system could assist the elbow, wrist and fingers to conduct arm reaching out, hand opening/grasping and arm withdrawing by tracking an indicative moving cursor on the screen of a computer, with the support from the joint motors and electrical stimulations on target muscles, under the voluntary intention control by electromyography (EMG). Subjects with chronic stroke (n = 11) were recruited for the investigation on the assistive capability of the NMES-robot and the evaluation of the rehabilitation effectiveness through a 20-session device assisted upper limb training. RESULTS: In the evaluation, the movement accuracy measured by the root mean squared error (RMSE) during the tracking was significantly improved with the support from both the robot and NMES, in comparison with those without the assistance from the system (P < 0.05). The intra-joint and inter-joint muscular co-contractions measured by EMG were significantly released when the NMES was applied to the agonist muscles in the different phases of the limb motion (P < 0.05). After the physical training, significant improvements (P < 0.05) were captured by the clinical scores, i.e., Modified Ashworth Score (MAS, the elbow and the wrist), Fugl-Meyer Assessment (FMA), Action Research Arm Test (ARAT), and Wolf Motor Function Test (WMFT). CONCLUSIONS: The EMG-driven NMES-robotic system could improve the muscular coordination at the elbow, wrist and fingers. TRIAL REGISTRATION: ClinicalTrials.gov. NCT02117089 ; date of registration: April 10, 2014.

Neurovascular Advancement Flap to Release Flexion Contracture of the Proximal Interphalangeal Joint.

Various methods have been described to surgically release posttraumatic flexion contracture of the proximal interphalangeal joint. Extension of the distal digit often creates a soft tissue defect on the volar aspect of the finger. Although various flaps and skin grafting have been utilized for coverage of this defect, they can be associated with morbidity. We present our experience with a volar neurovascular advancement flap to achieve soft tissue release in proximal interphalangeal joint flexion contracture. This advancement flap is designed to include both digital neurovascular bundles and eliminates the need for a secondary procedure as it allows primary closure of the subsequent defect. It is indicated for contracture lengthening of 10 to 14 mm. Surgical considerations of flap design are discussed.

A cortically-inspired model for inverse kinematics computation of a humanoid finger with mechanically coupled joints.

The human hand's versatility allows for robust and flexible grasping. To obtain such efficiency, many robotic hands include human biomechanical features such as fingers having their two last joints mechanically coupled. Although such coupling enables human-like grasping, controlling the inverse kinematics of such mechanical systems is challenging. Here we propose a cortical model for fine motor control of a humanoid finger, having its two last joints coupled, that learns the inverse kinematics of the effector. This neural model functionally mimics the population vector coding as well as sensorimotor prediction processes of the brain's motor/premotor and parietal regions, respectively. After learning, this neural architecture could both overtly (actual execution) and covertly (mental execution or motor imagery) perform accurate, robust and flexible finger movements while reproducing the main human finger kinematic states. This work contributes to developing neuro-mimetic controllers for dexterous humanoid robotic/prosthetic upper-extremities, and has the potential to promote human-robot interactions.

Anatomy of the direct small branches of the proper digital nerve of the fingers: a cadaveric study.

BACKGROUND AND AIM: The purpose of this study was to evaluate the anatomical constancy of the direct small branches of the proper digital nerve. METHODS: A total of 208 digital nerves of the index, long, ring, and little fingers from 13 cadavers were studied. For each digital nerve, the number of direct small branches was counted at the proximal and middle phalanx levels. In addition, the diameter of these branches was measured at the level of the branch bifurcation. We also measured the diameter of the proper digital nerve at the level of the distal interphalangeal (DIP) joint. RESULTS: The direct small branches of the proper digital nerve were anatomically constant among the index, long, and ring fingers. The average number of direct small branches was 2.7 at the proximal phalanx level and 2.3 at the middle phalanx level. At the level of the DIP joint, the average thickness of the proper digital nerve was 0.85 mm in the index finger, 0.84 mm in the long finger, 0.72 mm in the ring finger, and 0.49 mm in the little finger. CONCLUSION: In this study, we verified the anatomical constancy of the direct small branches of the proper digital nerve. The size of these branches at the proximal phalanx level was similar to that of the corresponding proper digital nerve at the level of the DIP joint. Therefore, these nerve branches at the proximal phalanx could be applied to the creation of various sensate flaps for the reconstruction of the fingertip injuries.

A biomechanical and evolutionary perspective on the function of the lumbrical muscle.

The lumbrical muscles of the hand originate from the flexor digitorum profundus tendons and insert onto the lateral band of the extensor tendons. Owing to these movable attachments, the function of this muscle is difficult to visualize. To better determine the function of this muscle, we considered its relative anatomy, biomechanical characteristics, and evolution. With the smallest physiological cross-sectional area in the upper extremity, the lumbrical muscles have weak motor function, which is only 1/10 of the interosseous muscle. Because they are spindle rich, the lumbrical muscles play an important role in the sensory feedback of the distal interphalangeal, proximal interphalangeal, and metacarpophalangeal joints of the fingers. The first 2 lumbrical muscles have lower variation in anatomy and higher density of muscle spindles compared to the ulnar 2 lumbricals. In addition, the index and middle finger lumbrical muscles are innervated by the median nerve, which also innervates the thenar muscles of the thumb. Therefore, it is possible that the first 2 lumbricals are functionally more important than the 2 ulnar lumbricals, specifically for precision pinch movements.

An unusual case of common digital nerve compression caused by a lipoma arising from the flexor tenosynovium.

Lipoma of the hand is a common lesion, but lipoma arising from the flexor tenosynovium is a very rare tumor that induces peripheral nerve disorders. Only four cases of synovial lesions that comprised mature fat at the wrist and imitated carpal tunnel syndrome have been described in the literature. We herein report an unusual case of a lipoma arising from the flexor tenosynovium at the level of the ring finger just proximal to the A1 pulley that was responsible for a sensory disturbance of the ring and middle fingers secondary to compression of the common digital nerve at the palm. The patient was completely relieved of the symptoms after lipoma excision.

The middle finger flexion test to locate the thenar motor branch of the median nerve.

PURPOSE: To assess the accuracy of a physical examination maneuver, the middle finger flexion test, in locating the thenar branch of the median nerve (TBMN). METHODS: Forty-one cadaveric hands were studied. The TBMN was dissected and identified as it emerged from the median nerve. The middle finger was then passively flexed to 90° at both the metacarpophalangeal and the proximal interphalangeal joints with the distal interphalangeal joint at neutral, which allowed the fingertip to contact the thenar eminence. The distance of the TBMN in millimeters with respect to the position of the center of the tip of the middle finger was measured. Two measurements were obtained from each specimen: the distance from the origin of the TBMN to the tip of the finger (+ distal to fingertip, - proximal to fingertip), and the radioulnar distance from the center of the middle fingertip (+ radial, - ulnar). RESULTS: The average location of the TBMN was 1.9 mm ulnar and 0.9 mm proximal to the tip of the flexed middle finger. There were 2 transligamentous median nerve thenar branches. CONCLUSIONS: This physical examination method accurately located the TBMN. This method is simple to perform, does not require secondary landmarks to derive vectors, and may more closely approximate the position of the TBMN than the previously described methods. CLINICAL RELEVANCE: Understanding the location of the TBMN in the palm will aid in accurate identification of this structure and prevent damage to it during surgery.

Comparison of bilateral force deficit in proximal and distal joints in upper extremities.

Bilateral force deficit refers to the phenomenon that maximal generated force during simultaneous bilateral muscle contractions is lower than the sum of forces generated unilaterally. Based on the notion that neural inhibition is the main source for bilateral force deficit and existing differences in neural inhibiting interhemispheric organization of proximal and distal muscles, we expected differences in bilateral deficit in proximal and distal joints. The aim of the current behavioral experiment was to compare bilateral force deficit in proximal compared to distal upper extremity joints. Ten young adults performed single-joint maximal voluntary contractions in isometric flexions of the shoulder and index finger unilaterally and bilaterally. The results showed a significant absolute bilateral force deficit for both proximal (140.01 ± 86.99 N) and distal muscles (4.64 ± 4.86 N). More importantly, relative bilateral force deficit for shoulder flexion was significantly larger than for index finger flexion, -20.51 ± 7.8% and -5.07 ± 3.84% respectively. The hypothesis of a more pronounced bilateral force deficit for proximal compared to distal muscles was confirmed in our results. Thus, our findings, in combination with the neuroanatomical differences for proximal and distal muscles, make it worthwhile to further explore the hypothesis that the commissural fibers provide differences in interhemispheric inhibitory interactions during bimanual actions for proximal and distal muscles.

The prevalence of functional absence of flexor digitorum superficialis to the little finger: a study in a Turkish population.

This prospective study was conducted to determine the prevalence of absence of flexor digitorum superficialis (FDS)-V tendon and to investigate the clinical usefulness of symmetry patterns, differences between sex, laterality, and dexterity in a Turkish population. Four hundred randomly-selected adult patients were examined for the absence of FDS-V function. The absence of FDS-V on both sides, results of the examination tests, age, sex, and dexterity were recorded and analysed statistically. The overall prevalence of absence of FDS-V was 18.5% in the Turkish population. The prevalence of functional absence of FDS-V was statistically similar between the body sides and sex (p = 0.258 and p = 0.333). The prevalence of symmetric occurrence of the variations in both hands was 87.2%. If a functional FDS is demonstrated in one hand, the probability of having a functional FDS-V in the contralateral hand is 91.8%. However, when the FDS-V is absent in one hand, the probability of having an absent FDS-V in the contralateral hand is 51.1%. The symmetric occurrence of variations was equally distributed in both sex and dexterity (p = 0.223 and p = 0.201). Prediction of FDS-V function in one hand through examining the opposite hand may cause false negative or false positive results. However, if the uninjured hand has independent FDS-V function, the inability to flex the PIP joint in the injured hand can be accepted as an injury to the FDS and surgical exploration should be performed. However, if the uninjured hand has an absent function, assumption of symmetric distribution should not be used.

Innervation patterns of thumb trapeziometacarpal joint ligaments.

PURPOSE: The human thumb trapeziometacarpal (TM) joint is a unique articulation that allows stability during pinch and grip and great degrees of mobility. Because the saddle-shaped articulating surfaces of the TM joint are inherently unstable, joint congruity depends on the action of restraining ligaments and periarticular muscles. From other joints, it is known that proprioceptive and neuromuscular joint stability depend on afferent information from nerve endings within ligaments. We hypothesize that the TM joint ligaments may similarly be innervated, indicating a possible proprioceptive function of the joint. METHODS: We harvested 5 TM joint ligaments in entirety from 10 fresh-frozen cadaver hands with no or only minor signs of osteoarthritis and suture-marked them for proximal-distal orientation. The ligaments harvested were the dorsal radial, dorsal central, posterior oblique, ulnar collateral, and anterior oblique ligaments. After paraffin-sectioning, we stained the ligaments using a triple-antibody immunofluorescent technique and analyzed them using immunofluorescence microscopy. RESULTS: Using the triple-stain technique, mechanoreceptors could be classified as Pacinian corpuscles, Ruffini endings, or Golgi-like endings. The 3 dorsal ligaments had significantly more nerve endings than the 2 volar ligaments. Most of the nerve endings were close to the bony attachments and significantly closer (P = .010) to the metacarpal insertion of each ligament. The anterior oblique ligament had little to no innervation in any of the specimens analyzed. DISCUSSION: The TM joint ligaments had an abundance of nerve endings in the dorsal ligaments but little to no innervation in the anterior oblique ligament. The Ruffini ending was the predominant mechanoreceptor type, with a greater density in the mobile metacarpal portion of each ligament. CLINICAL RELEVANCE: Presence of mechanoreceptors in the dorsal TM joint ligaments infers a proprioceptive function of these ligaments in addition to their biomechanical importance in TM joint stability.

The outcome of direct-flow neurovascular island flaps in pulp defects.

OBJECTIVE: In this study we aimed to evaluate the results of the direct-flow neurovascular island flap (NIF) transfers in pulp defects. METHODS: We reviewed the records of 96 patients with 115 NIF transfers performed for pulp defect reconstruction. The injury mechanism was crush type injury in 70 patients (72.9%). Ninety-three patients (97%) were emergency cases. Pulp reconstruction was performed by means of pedicled island flap transfer. The results were evaluated with proximal interphalangeal joint range of motion, the Semmes Weinstein monofilament test, static two-point discrimination and cold intolerance assessments. The relations between the injury mechanism, patient satisfaction, cold intolerance and scar problems were analyzed. Also, the association between skin grafting and hook nail deformity was investigated. The level of significance was set at p<0.05. RESULTS: All flaps survived. The mean follow-up time was 41±20.3 (range: 12-108) months. We observed proximal interphalangeal joint flexion contracture in 11 (9.5%) cases. In seven of these, the limitation was less than 10 degrees. Hook nail deformity was seen in 8 fingers (7%). Cold intolerance was found in 16 (17%) cases. Semmes Weinstein monofilament and static-two point discrimination tests of flaps revealed satisfactory results. There was no relation between the injury mechanism and cold intolerance, patient satisfaction and scar problems (p>0.05). Among patients, 91.7% were satisfied with their results. CONCLUSION: The transfer of direct-flow island flaps, from the same finger, causes minimal morbidity on the donor site and appears to be a safe method, providing satisfactory functional and aesthetic results in the reconstruction of pulp defects.

Distribution of nerve endings in human distal interphalangeal joint and surrounding structures.

PURPOSE: To examine the distribution of encapsulated nerve endings called mechanoreceptors in the human distal interphalangeal (DIP) joint and surrounding structures. METHODS: We processed 12 right index finger DIP joints and surrounding structures from fresh cadavers for immunohistochemistry of the anti-protein gene product 9.5 (PGP9.5) and silver staining to detect encapsulated nerve endings. Serial transverse sections were cut throughout the whole specimen and divided into 3 regions along the longitudinal axis: distal, middle, and proximal. Each of the transverse sections was partitioned into dorsal capsule (DC), radial capsule (RC), ulnar capsule (UC), volar plate (VP), and radial and ulnar assemblage nuclei (RAN and UAN); the RAN and UAN are located on both the radial and ulnar side of the VP. The C3 pulley contained the proximal region of the RAN and UAN, whereas the A5 pulley contained the middle and distal. The accessory collateral ligament contained all the regions of the RAN and UAN. We analyzed and compared the density of encapsulated nerve endings among the 18 different regions. RESULTS: According to the modified Freeman and Wyke classification, we identified type I (eg, Ruffini-like endings) and type II (eg, Pacini-like endings) nerve endings. The density of type II nerve endings in the proximal region of the RAN and UAN was considerably higher than that in the proximal region of the VP, RC, UC and DC, and that in the proximal region of the VP, RC, UC, and DC, respectively. CONCLUSIONS: Our examination of the distribution of type I and type II nerve endings provides new information on the sensory systems of the DIP joints and surrounding structures.