The article describes the special surgical anatomy of the extensor carpi ulnaris tendon (ECU) and the sixth extensor compartment, including the most common pathological conditions. The sixth extensor compartment is only loosely covered and not connected by the extensor retinaculum. The ECU has its own retinaculum at the ulnar head, for which the Latin name "retinaculum privatum" (English: subsheath) is proposed. Dislocation of the extensor tendon (ECU), first described by Schlesinger in 1907, can be treated using various techniques for reconstructing the retinaculum privatum (from the extensor retinaculum, transosseous with a free tendon graft, or using fibers from the Linea jugata).1 Tendovaginosis of the extensor compartment was first surgically treated by Stein in 1927; the first detailed description was provided by Pfeiffer in 1969 in Volume 1 of this journal.2 , 3 The sixth extensor compartment is frequently affected in rheumatic diseases. In these cases, significant structural damage is found in the ECU tendon and tendon sheath due to aggressive inflammatory synovitis and instability of the ulnar head (caput ulnae syndrome).

The ulnar nerve runs at the level of the ulnar carpus through Guyon's canal. Due to the proximity to very rigid ligamentous and bony structures, space-occupying processes or fractures can easily cause compression of the ulnar nerve and its two distal branches. Pathologies of the adjacent ulnar artery can also irritate the nerve.

Glomus tumors are benign neoplasms typically found in the fingers and usually present with localized pain, swelling, and cold sensitivity. Extradigital glomus tumors are rare, and their diagnosis is often delayed due to atypical location and lack of cold sensitivity. In this article, we report a unique case of an extradigital glomangioma, a subset of glomus tumors, masquerading as more common ulnar-sided wrist pathology, such as a triangular fibrocartilage complex tear or extensor carpi ulnaris tendinitis. The patient presented with a two-year history of gradually worsening ulnar-sided wrist pain with no history of trauma. Examination revealed localized tenderness on the ulnar wrist without a palpable mass. X-rays were normal, and the pain was unresponsive to nonsteroidal anti-inflammatory medication and cortisone injection. Magnetic resonance imaging revealed a subcentimeter mass in the subcutaneous fat on the ulnar side of the wrist. The lesion was bright on T2-weighted and IV gadolinium-enhanced sequences. Excisional biopsy allowed the pathological diagnosis of benign glomangioma to be established. The patient reported immediate, complete resolution of pain postoperatively. This case underscores the importance of advanced imaging, clinical vigilance, and surgical excision for this rare tumor.

Giant cell tumor of bone is a locally aggressive tumor that usually affects the epiphyseal region of long bones in young adults. Involvement of the distal ulna is rare, and the diagnosis in elderly patients with end-stage chronic kidney disease may be difficult because brown tumors related to secondary hyperparathyroidism can mimic giant cell tumor radiologically and histologically. We report the case of a 69-year-old woman with end-stage chronic kidney disease on hemodialysis who was admitted for a painful and progressively enlarging mass on the ulnar border of the left wrist that had been present for six months. Standard radiographs showed a well-defined, expansile osteolytic lesion of the distal ulna involving the epiphysis and metaphysis, with cortical thinning and no obvious periosteal reaction. Surgical biopsy demonstrated a proliferation of mononuclear stromal cells associated with numerous osteoclast-like multinucleated giant cells, compatible with a giant cell tumor. Given the hemodialysis background, a brown tumor was discussed; however, serum calcium, phosphate, and parathyroid hormone levels were within normal limits, and histology favored a giant cell tumor. The extension workup showed no secondary localization. The patient underwent en bloc resection of the distal ulna according to a Darrach-type procedure, associated with flexor carpi ulnaris tenodesis to improve the stability of the ulnar stump. Histopathological examination of the surgical specimen confirmed the diagnosis. At eight months of follow-up, the outcome was favorable, with satisfactory wrist function, a stable radiographic appearance, and no clinical or radiological recurrence. This case highlights the importance of clinicobiological and histopathological correlation when evaluating a giant-cell-rich bone lesion in a dialysis patient. It also supports the value of distal ulna resection associated with soft-tissue stabilization as a pragmatic option in selected elderly patients.

Hydroxyapatite deposition disease (HADD) is a relatively common disorder characterised by periarticular deposition of calcium hydroxyapatite, most frequently involving tendons of the glenohumeral joint. Although calcific deposits typically produce a self-limiting inflammatory response, mass-like presentations at atypical sites can mimic trauma, infection or soft tissue neoplasia, posing a significant diagnostic challenge. We report an unusual presentation of mass-like calcific tendinitis within the flexor carpi ulnaris (FCU) tendon of the distal forearm-an atypical location for HADD presenting as a painful soft tissue swelling. Multimodality imaging, including radiography, MRI and CT, was instrumental in characterising the deposit and excluding alternative diagnoses. The patient was treated with ultrasound-guided barbotage using a large bore needle system, with significant reduction in deposit volume and symptom relief. This case highlights the importance of considering HADD in the differential diagnosis of painful soft tissue masses at atypical sites, where multimodal imaging is essential for accurate characterisation and ultrasound-guided barbotage represents an effective minimally invasive treatment alternative to surgery.

A 1-year-and-9-month-old Golden Retriever presented with a 9-month history of right thoracic limb lameness. Radiographs revealed a monostotic, expansile lesion of the right accessory carpal bone (ACB). A computed tomography (CT) confirmed the aggressive nature of the lesion, demonstrating multifocal moth-eaten osteolysis, sclerosis, periosteal reaction, and flexor carpi ulnaris tendinopathy. Differential diagnoses included the ischemic necrosis of the ACB, osteomyelitis, and primary bone neoplasia. Histopathology confirmed osteonecrosis. This case highlights the value of CT in evaluating aggressive carpal lesions and identifies ischemic necrosis as an important differential diagnosis. This case represents the first CT description of this disease in dogs.

Unstable extensor carpi ulnaris (ECU) tendons with longitudinal interfascicular separation and loss of concentric integrity (LIS-Loci) are rare and not previously reported in the literature. Seven cases were identified in a retrospective study over a 4-year period.

Background: Muscle strength, endurance, and muscle quality are important determinants of upper-limb function. Although surface electromyography (sEMG) characterizes muscle activation and fatigue, its integration with bioelectrical impedance analysis (BIA) for muscle quality assessment remains limited. Objective: This study investigated neuromuscular responses during graded handgrip contractions and evaluated an exploratory muscle quality (MQ) index integrating sEMG and BIA measures in healthy adults. Methods: Fifty-three healthy adults (35 males and 18 females) performed maximal voluntary contraction (MVC) followed by graded handgrip contractions at 0%, 20%, 40%, 60%, 80%, and 100% MVC. Surface EMG was recorded from the biceps brachii, triceps brachii, brachioradialis, and flexor carpi ulnaris. Root mean square (RMS) and frequency-domain features were extracted, with median frequency (fmedian) selected as the representative frequency-domain outcome for nonparametric analyses and linear mixed-effects analysis. The MQ index integrated grip strength, muscle mass, body fat, and RMS and was evaluated using Spearman correlation. Results: RMS increased with contraction intensity, whereas fmedian increased to a peak at 60% MVC and then gradually declined with the lowest values at 100% MVC. Significant fixed effect and interaction indicated that neuromuscular responses varied by gender, muscle, contraction stage, and muscle mass. The MQ index correlated moderately with right-arm muscle mass and phase angle but weakly with the conventional muscle quality index. Conclusion: Integrating sEMG and BIA provides complementary information on muscle activation, fatigue, and tissue characteristics beyond conventional strength-based measures, supporting assessment of upper-limb neuromuscular function and muscle quality.

Total distal radioulnar joint (DRUJ) arthroplasty with the Aptis prosthesis is an increasingly used salvage procedure for refractory DRUJ pathology, though prior studies often rely on mean rather than minimum follow-up, limiting assessment of true mid- to long-term durability. This systematic review evaluated implant survivorship, complications, and functional outcomes following total DRUJ arthroplasty with a minimum follow-up of 60 months. A systematic review of PubMed, Embase, and Cochrane databases was performed, including patients who underwent total DRUJ arthroplasty with reported survivorship or complication data and a minimum of 60-month follow-up. Seven studies met the inclusion criteria, comprising 66 implants meeting the follow-up threshold. Implant survivorship at final follow-up was 96.0%, with an overall complication rate of 51.0% and reoperation rate of 44.9%; the most common complications were extensor carpi ulnaris tendonitis, heterotopic ossification, and hardware loosening. Weighted mean postoperative supination and pronation were 74° and 78°, respectively, with mean grip strength of 29 kg. Outcome scores demonstrated meaningful improvement. Total DRUJ arthroplasty shows appropriate mid- to long-term implant survivorship and satisfactory functional gains, though complication and reoperation rates warrant cautious interpretation. It remains a viable salvage option in appropriately selected patients, underscoring the need for thorough preoperative counseling.

Background/Objectives: The extramuscular branching pattern of the ulnar nerve shows substantial interindividual variability, limiting the value of single-pattern anatomical descriptions. It remains unclear whether the origins of its motor branches are spatially random or retain reproducible relationships with the neural, anthropometric, and musculotendinous organization of the forearm. This study characterized the normalized spatial distribution of the origins of the main ulnar motor branches supplying the flexor carpi ulnaris (FCU) and the ulnar portion of the flexor digitorum profundus (FDP), and examined their relationships with anatomical reference variables measured during dissection. Methods: A cross-sectional cadaveric study was conducted on 16 adult right upper limbs. Fifteen specimens were dissected fresh on the day they were received by the Body Donation Programme; one specimen was frozen at -80 °C, thawed overnight, and dissected the following morning. Standardized anatomical dissection identified 54 main motor branches arising from the ulnar nerve and confirmed their target muscles by direct anatomical continuity (36 FCU and 18 FDP branches). For quantitative mapping, only the origin of each branch on the parent ulnar nerve was recorded using a laser-guided Cartesian coordinate system. Anthropometric dimensions and topographical landmarks were normalized to the corresponding forearm dimensions. Spatial organization was characterized using centroids, 95% data ellipses, Euclidean centroid distances, and a specimen-level cluster bootstrap. Generalized estimating equations (GEE) were used for cluster-aware group comparisons and exploratory multivariable association analysis, while ROC analysis and leave-one-cadaver-out cross-validation quantified internal separation and stability within the cadaveric dataset. Results: FCU and FDP branch origins occupied reproducible but partially overlapping normalized spatial territories. Their centroids differed in location, and specimen-level bootstrap resampling supported the stability of the observed separation. Cluster-aware analyses confirmed differences in the proximodistal branch-origin coordinate and in the tendon-crossing landmark. In the multivariable GEE model, the normalized tendon-crossing landmark showed the strongest adjusted association with group membership, while the proximodistal coordinate also remained associated. Conclusions: Despite marked interindividual variation in ulnar nerve branching, the origins of its main motor branches exhibit reproducible population-level spatial organization. Their distributions are related to the anatomically confirmed target muscle and to normalized neural, anthropometric, and musculotendinous landmarks measured during dissection. This integrated reference framework supports interpretation of peripheral motor innervation as an organized spatial system rather than a collection of isolated variants. The findings provide an anatomical basis for future imaging and image-guided research; however, the exploratory regression and ROC analyses do not constitute a clinically validated diagnostic model.

The olecranon medial flip osteotomy offers adequate exposure to the posterior elbow, while preserving the continuity of the triceps extensor complex and sparing the innervation of the anconeus muscle. It avoids soft-tissue injury due to strain and aids in protecting the ulnar nerve by medially reflecting the long head of triceps.

The presence of anomalous muscles in the hand are present in around 22-35% of individuals, leading to potential clinical implications. During a routine cadaveric dissection of a 72 year old male, a unique hypothenar muscle variant was identified: the pisi-palmaris muscle. Detailed dissection and literature review determined the origin, insertion, and relationships of the muscle. The pisi-palmaris originated from the pisiform bone, deep to the tendon of the flexor carpi ulnaris and the volar carpal ligament, and inserted onto the transverse carpal ligament, merging with fibers of the abductor and flexor digiti minimi muscles. Based on its distinguishing anatomical features, we believe this muscle represents a previously unreported anatomical variant. Given its proximity to the ulnar nerve within Guyon's canal, this variant may contribute to ulnar nerve compression. Recognizing its presence may decrease the risk of diagnostic error or iatrogenic injury during nonoperative interventions or surgical decompression and improve patient outcomes and guide treatment. LEVEL OF EVIDENCE: V.