Extensor Pollicis Longus Rupture Research Articles

Cause of Extensor Pollicis Longus Ruptures After Distal Radius Fracture Fixation Using a Volar Plate.

This research sought to analyze a cohort of patients with extensor pollicis longus (EPL) ruptures after volar locked plating of a distal radius fracture (DRF) to characterize the incidence of ruptures that are unlikely to be related to dorsal screw prominence. This is a retrospective, observational, descriptive cohort study of adults with operative fixation of a closed DRF and an EPL rupture between 2002 and 2022. Eighteen patients with operative fixation using a volar plate of a closed DRF had an EPL rupture. The cohort consisted of 66% women with an average age of 57.5 years. Median follow-up was 14.5 months. The incidence of EPL rupture was 0.4% (18/4768). The average time from DRF and DRF fixation to EPL rupture was 3.7 and 3.4 months, respectively. Based on the operative record, in 2 of the 18 patients (11%), the rupture was directly attributable to prominent hardware; however, in 4 of the 18 patients (22%), the rupture was not related to prominent hardware, and the cause was indeterminate in 12 patients (67%). Radiologic analysis of those in the indeterminate group demonstrated that 5 of the 12 patients had screws that had a high probability of being prominent. The incidence of EPL rupture after volar plating of DRF is between 0% and 1% and usually occurs about 3 months after fixation. Approximately 50% of EPL ruptures are attributable to prominent dorsal screws. Although screw prominence is an important cause of EPL rupture, it is not the sole cause of rupture.

Etiology of Traumatic Causes of Extensor Pollicis Longus Tendon Rupture: A Systematic Review

IntroductionThe extensor pollicis longus (EPL) is a muscle that follows a complex anatomical course in the hand to allow for thumb extension. Almost all manual activities require the use of the EPL; therefore, when ruptured it can be very disabling for patients. The etiologies behind traumatic EPL rupture were mostly attributed to distal radius fracture in the literature. However, EPL rupture remains uncommon, and other traumatic etiologies exist. Therefore, this systematic review aimed to provide a holistic view of the traumatic etiologies behind the EPL rupture and fill the global lack of knowledge regarding this rare injury. Materials and MethodsWe searched among Cochrane Central Register of Controlled Trials (CENTRAL) Embase, Medline, and Cochrane Database of systematic review register databases via Ovid, with no restriction on the date, including studies containing data about the etiology of traumatic causes of EPL tendon rupture with available full text, and excluding non-English and animal studies. ResultsA total of 37 articles with 371 cases constituted the basis of this review. We classified the etiology of the EPL rupture into three groups according to the affected anatomical structure that caused the EPL rupture (fracture-related, soft tissue-related, and mallet thumb). ConclusionDistal radius fractures remain the most common cause of EPL rupture; however, other causes, such as lacerations, blunt trauma, and direct cuts to the EPL tendon, should be considered.

Spontaneous Rupture of the Extensor Pollicis Longus Tendon: A Systematic Review.

Extensor pollicis longus (EPL) rupture and tenosynovitis of the third dorsal compartment is often described in association with a history of rheumatoid arthritis or in the setting of a distal radius fracture. However, the literature suggests multiple other potential factors that may lead to a seemingly spontaneous rupture. We performed a systematic review following guidelines set forth by the Preferred Reporting Items for Systematic Reviews and Meta-Analyses statement. The search consisted of headings and keywords related to tendon injuries, tendinopathy, hand surgery, tendon transfer, and injections, as published in reports and studies. Citations were screened by title and abstract against predetermined inclusion and exclusion criteria by 2 independent reviewers, with a third reviewer resolving discrepancies. To be eligible, articles had to meet the following inclusion criterion: describe cases of spontaneous EPL rupture or tenosynovitis of the third dorsal compartment. The exclusion criterion was any history of distal radius fracture or rheumatoid arthritis. We identified 29 articles that met the inclusion criterion. A myriad of prodromal events or predisposing factors ultimately led to EPL rupture or tenosynovitis of the third compartment. Methods of reconstruction described included primary repair, tendon grafting, and tendon transfer techniques; all with generally good outcomes. These results highlight the inherent fragility of this tendon and support the historical recommendation for early release of the EPL tendon in the setting of tenosynovitis of the third dorsal compartment.

Extensor indicis proprius to extensor pollicis longus transfer in spontaneous rupture of extensor pollicis longus following non displaced fracture distal end radius

Exact incidence of extensor pollicis longus (EPL) ruptures following distal radius fracture is not known. Peculiarly it’s common in nondisplaced fracture of the distal radius with an incidence of EPL rupture of 0.2-5%. Cortical irregularities from distal radius fractures or osteophytes easily abrade the tendon, causing gradual attrition and ultimately rupture. Compromised blood supply is also related to EPL rupture which is supported by microcirculatory anatomic studies. We present a case of 49 year old female who presented with spontaneous rupture of the EPL following a nondisplaced fracture of the distal radius managed by extensor indicis proprius (EIP) transfer. EIP transfer gives promising outcome. Optimum tension of the tendon is crucial for good functional outcome. We recommend suturing the tendon with thumb in extension and wrist in neutral position for optimum tension of tendon to avoid extensor lag and to prevent loss of IP flexion.

Dynamic Ultrasound Examination for Extensor Pollicis Longus Tendon Rupture after Palpation-Guided Corticosteroid Injection.

This report aimed to present a case of wrist-tendon rupture and to discuss a rare complication after corticosteroid injection. A 67-year-old woman had difficulty extending her left-thumb interphalangeal joint several weeks after a palpation-guided local corticosteroid injection. Passive motions remained intact without sensory abnormalities. Ultrasound examination showed hyperechoic tissues at the site of the extensor pollicis longus (EPL) tendon at the wrist level and an atrophic EPL muscle stump at the forearm level. Dynamic imaging demonstrated no motion in the EPL muscle during passive thumb flexion/extension. The diagnosis of complete EPL rupture, possibly due to inadvertent intratendinous corticosteroid injection, was therefore confirmed.

TENDON INJURIES AFTER DISTAL RADIUS FRACTURES

Tendon injuries after distal radius fractures Introduction: Tendon injuries after distal radius fractures are a well-documented complication that can occur in fractures managed both operatively and non-operatively. The extensor tendons, in particular the extensor pollicis longus (EPL) tendon, can be damaged and present late after initial management in a cast, or by long prominent screws that penetrate the dorsal cortex and cause attrition. Similarly, a prominent or distally placed volar plate can damage the flexor pollicis longus tendon (FPL). The aim of our study was to evaluate the incidence of tendon injuries associated with distal radius fractures.We conducted a single centre prospective observational study. Patients aged 18-99 who presented with a distal radius fracture between May 2018 to April 2020 were enrolled and followed-up for 24 months. Tendon injuries in the group were prospectively evaluated. Results: 199 patients with distal radius fractures were enrolled. 119 fractures (59.8%) had fixation and 80 (40.2%) were managed incast. In the non-operative group, 2 (2.5%) had EPL ruptures at approximately 4 weeks post injury. There were no extensor tendon ruptures in the operative group. In the operative group, there were 6 (5%) patients that required removal of metalware for FPL irritation. At the time of operation, there were no tendon ruptures noted. Within the operative group we evaluated plate prominence using a previously described classification (Soong et al.). 5 of the 6 patients (83%) with FPL irritation had Grade 3 prominence.The incidence of both flexor and extensor tendon injury in our cohort was 4%, extensor tendon rupture was 1% and flexor tendon rupture was avoided by early metalware removal. This study demonstrates tendon injuries are not uncommon after distal radius fractures, and close examination and follow-up are necessary to prevent eventual rupture. Plate prominence at the time of fixation should be minimised to reduce the risk of rupture.

Ultrasound assistance in treatment with elastic stable intramedullary nail fixation in radial and ulnar fractures in children.

Radial and ulnar fractures are one of the most common fractures in children. When closed reduction of fractures fails, elastic stable intramedullary nail (ESIN) fixation can mostly be used under the guidance of fluoroscopy. In this study, we evaluated the effect of ultrasound (US) as assistance for radial and ulnar fracture reduction and the insertion of ESINs. There were 56 patients with midshaft radial and ulnar fractures included in our hospital from March 2019 to August 2021. After applying the inclusion and exclusion criteria and according to the treatment method, they were divided into the US group (patients treated with US assistance) and the conventional group (C-group, patients treated with fluoroscopy guidance). All patients' clinical data were collected. Operation time, fluoroscopy times, radiation dose, and post-operative complications were analyzed. The elbow function was evaluated using the Mayo Elbow Performance Index. There were 26 patients in the US group and 30 in the C-group. The average operation time was 44.5±19.4 min in the US group and 65.1±16.2 min in the C-group. There were significant differences regarding the surgery time, fluoroscopy time, and radiation dose between the groups (all p = 0.001). The average follow-up time was 13.5±3.1 months. No significant difference was found regarding radial nerve injury, extensor pollicis longus rupture, non-union or delayed union, ulnar nerve injury, or acute compartment syndrome. There was no difference in elbow function at the final follow-up. US guidance can be adopted for the treatment of displaced radial and ulnar fracture reduction and the insertion of ESINs. It can significantly decrease fluoroscopy times, radiation doses, and duration of surgery.

Anomalous Extensor Indicis Proprius Muscle Extending Beyond the Extensor Retinaculum: A Case Report.

During dissection of the upper limb of a cadaver in preparation for a first-year anatomy course, an extensor indicis proprius (EIP) variant was discovered with its muscle belly extending distal to the extensor retinaculum and beyond what has been previously described in the literature. EIP is commonly used as a tendon transfer for extensor pollicis longus rupture. Few anatomic variants of EIP have been reported in the literature, but such variants should be considered because of their consequences to the success of tendon transfer and potential implications for diagnosis of an otherwise unexplained mass of the wrist.

'Hook' Shape Lister Tubercle Is Associated with a Greater Incidence of Extensor Pollicis Longus Tendon Rupture after Distal Radius Fracture.

Background: A rupture of the extensor pollicis longus (EPL) tendon located close to the Lister tubercle is an uncommon complication of distal radius fractures. This study aimed to determine whether the size and shape of Lister tubercle in patients with EPL rupture differs from a matched group of patients with distal radius fractures without EPL rupture. Methods: We identified 15 patients with EPL rupture (3.5%) out of 426 with distal radius fractures treated conservatively at our hospital over 4 years. Out of the remaining 411 patients with distal radius fractures without EPL rupture, we selected patients using simple random sampling and pseudo-randomised them such that their age, sex and fracture type were matched with patients exhibiting EPL rupture. The size and shape of the Lister tubercle and the size of the EPL groove were measured in both groups using computed tomographic scans and compared. Results: There was no difference in the size of the Lister tubercle or the EPL groove between both groups. A 'hook'-shaped Lister tubercle was noted in 8 out of 15 patients with EPL rupture but in only 1 out of 15 matched patients without EPL rupture. Conclusions: A 'hook'-shaped Lister tubercle was seen more often in patients with EPL rupture following distal radius fracture. Level of Evidence: Level III (Therapeutic).

Radial vs. Dorsal Approach for Elastic Stable Internal Nailing in Pediatric Radius Fractures-A 10 Year Review.

Background: Forearm fractures are one of the most common fractures in children. Over the last years, a tendency towards surgical treatment was seen, especially closed reduction and internal fixation with elastic stable internal nailing (ESIN). Despite an overall low complication rate being described, a risk of intraoperative complications remains. Material and Methods: A total of 237 patients (mean age 8.3 ± 3.4 (1–16) years) with forearm or radius fractures treated with ESIN between 2010 and 2020 were included in the study. The retrospective review of 245 focused on fracture pattern, pre- and postoperative fracture angulation, intra- and postoperative complications, and surgical approach for nail implant. The fracture pattern and pre- and postoperative angulation were measured radiographically. Complications such as ruptures of the extensor pollicis longus (EPL) tendon and sensibility disorders of the superficial radial nerve were further analyzed. Results: In 201 cases (82%), we performed a dorsal approach; 44 fractures (17.9%) were treated with a radial approach. In total, we found 25 (10%) surgery-related complications, of which 21 (8.6%) needed further surgical treatment. In total, we had 14 EPL ruptures (5.7%), 4 sensibility disorders of the superficial radial nerve (1.6%), 2 refractures after implant removal (0.8%), 2 superficial wound infections (0.8%), and 1 child with limited range of motion after surgery (0.4%). No statistical significance between pre- and postoperative angulation correlated to fracture patterns or diameter of the elastic nail was seen. As expected, there was a significant improvement of postoperative angulation. Using radial approach in distal radial fractures showed a lower rate of surgical related complications, 2.3% of which need further surgical treatment as well as better postoperative angulations compared to the dorsal approach (8.5%). Conclusion: Especially due to the low risk of damaging the EPL tendon, the radial approach showed a lower complication rate which needed further surgical treatment. The risk of lesions of the superficial radial nerve remains.

Primary repair of extensor pollicis longus rupture after volar locking plating for distal radial fracture

We presumed that primary repair would be possible if the extensor pollicis longus (EPL) rupture after volar locking plating (VLP) for distal radius fracture (DRF) was diagnosed earlier. Thus, five cases of EPL ruptures were resolved via primary repair rather than extensor indicis proprius (EIP) transfer, so we reported the clinical outcomes of at least 2 years follow-up since EPL repair. Of 588 consecutive patients with the fractures treated between January 2016 and December 2019, 501 who met out inclusion/exclusion criteria were initially investigated. We informed patients of: (1) the ordinary range of motion of thumb at full wrist flexion/extension; (2) the proper tone of thumb extension compared to the contralateral thumb; and (3) the degree of pain/discomfort during thumb exercise. After discharge, we called each patient monthly commencing at 8 weeks postoperatively to enquire if any of those had worsened, by telephone. Five patients had ruptured EPLs diagnosed at a mean of postoperative-12.8 weeks. Three came to outpatient department for suspected tendon rupture just after telephone survey with the authors. The other two visited after detecting insufficiency in the three items, during the period between telephone inquiries. In four, the torn EPL were encapsulated by tendon sheathes. Extension lag at interphalangeal joint was absent and other clinical outcomes associated with DRF were all satisfactory at final follow-up. Primary repair of EPL rupture (rather than EIP transfer) is possible if patients are properly followed up after VLP for DRF. Level of evidenceLevel IV, retrospective case series.

Extensor Pollicis Brevis Transfer to Extensor Pollicis Longus for Delay Spontaneous Ruptures: A Case Series and Functional Outcomes at One Year Follow Up

Introduction: When Extensor Pollicis Longus (EPL) spontaneously ruptures, two major risk factors are present: rheumatoid arthritis and distal radius fracture. The gold standard treatment is the transfer of Extensor Indicis Proprius (EIP) to restore the functionality of the thumb. Utilization of Extensor Pollicis Brevis (EPB) was used initially, in patients with rheumatoid arthritis. The aim of this study is to ascertain if the EPB transfer technique is the most competent and efficient surgical method for rupture of EPL, analyzing functional outcomes, complications and final patient`s satisfaction. Material & Methods: Eighteen patients (14 female and 4 men) with an average age of 43 years old were introduced in this study. All cases reported no history of trauma. From the derived clinical history, 8 cases suffered from rheumatoid arthritis, 4 patients reported initial corticosteroid injection in radial side of wrist, one case was revised surgery and in rest cases the etiology was unknown. Radiographic investigation was normal in all cases, while magnetic resonance studies detect EPL ruptures. All patients were operated in a mean time of 3, 4 weeks (ranging from 2 to 6 weeks) after the diagnosis and in all cases the tendon applied was the EPB. After surgery all patients followed the same rehabilitation program. Results: The mean follow-up was 20,5 months (range from 15 months to 36 months). None of patients missed the last re-examination. Results were evaluated according to complications, range of motion of the thumb (elevation deficit, opposition distance, difference flexion-extension deficit), Quick Dash Score, EQ-5D-5L, and satisfaction of the patients. No intra-or extra-operative complications or re-ruptures were noted. At the final follow up the mean range of elevation deficit was0,7(from 0,5 to 1,5), opposition distance was 0,8(range from 0,5 to 1,8) and difference flexion-extension deficit was 1,6˚ (from 0˚ to 5˚). The Quick Dash score was 1.38 (varied from 0.0- 6.8) and the EQ-5D-5L was 92. Finally, the majority of patients appeared to be very satisfied (66,7%) or satisfied (27,8%). Conclusion: Extensor Pollicis Longus tendon spontaneously ruptures due to specific factors. Restore of thumb functionality is achieved only with tendon transfer technique and the use of Extensor Indicis Proprius tendon has been described as the gold standard. Extensor Pollicis Brevis tendon transfer is an alternative technique with significant advantages which preserves good functionality of the thumb and excellent patient satisfaction.

Simple surgical technique for minimizing the risk of extensor pollicis longus rupture following volar plate fixation of distal radial fracture: A case report.

Introduction and importanceExtensor pollicis longus (EPL) tendon injury is a major complication in distal radial fracture repair. The risk factors for EPL tendon injury are prominent dorsal screws, direct intraoperative damage through drilling, and/or dorsal roof fragments. Herein, we introduce a simple technique to minimize the risk of EPL tendon rupture after volar plate fixation of distal radial fracture.Case presentationThe patient was a 67-year-old woman with an intra-articular unstable distal radial fracture treated by volar locking plate fixation. Intraoperatively, we opened the third compartment after screw fixation. Because the screw had penetrated the floor of the third compartment, we moved the EPL tendon out of its groove and closed the third compartment by suturing the retinaculum. We confirmed that the EPL tendon was intact 7 years postoperatively, even though the screw was prominent in the third compartment.Clinical discussionAfter volar plate fixation of the distal radial fracture, we partially open the third compartment through an approximately 2-cm-long incision on the ulnar side of Lister's tubercle. If the screw is prominent in the third compartment, we completely open the third compartment, take the EPL tendon out of its groove, and close the compartment by suturing the retinaculum. Our method was proved useful because the EPL tendon has remained intact for 7 years with the screw protruding into the third compartment.ConclusionOur surgical technique is useful to prevent secondary EPL tendon rupture after distal radial plate fixation.

Diagnostic ultrasound of tendon injuries in the setting of distal radius fractures.

Describe tendon injuries and their structural causes seen on ultrasound in wrists with distal radius fractures and estimate the accuracy of ultrasound and its impact on clinical management. Ultrasounds of 226 wrists (221 patients) with distal radius fractures were retrospectively reviewed. Ultrasound findings of tendon injuries and their structural causes were correlated with surgery and clinical outcome. Accuracy and inter- and intra-observer reproducibilities were calculated. Twenty-five wrists were treated non-operatively while 201 underwent surgery. Ultrasound demonstrated hardware contact with flexor pollicis longus (FPL) in 76 wrists, extensor pollicis longus (EPL) in 21, and other tendons in 94. Ultrasound identified tendon ruptures in 23 wrists (13 EPL/8 FPL/2 extensor indicis proprius (EIP)), most of which were surgically confirmed. Among 12 wrists with confirmed EPL ruptures, distal radius fracture had been treated with volar plating in 6 and non-operatively in 6, and ultrasound showed osseous irregularity at the rupture site in 8. All FPL ruptures occurred in wrists with volar plating. Ultrasound findings were concordant with subsequent clinical management in most. In 2, ultrasound findings led to the decision to remove hardware despite lack of symptoms. Ultrasound had sensitivity/specificity/accuracy of 88/99/98% for identifying a specific tendon as ruptured and 88/87/88% for tendon abnormalities in general. Inter- and intra-observer reproducibilities were excellent (kappa = 0.85 ~ 1.0). Certain wrist tendons, particularly EPL and FPL, are vulnerable after distal radius fractures. Ultrasound is accurate and useful for detecting tendon injury and sources of tendon irritation and can guide clinical management.

What’s New in Hand and Wrist Surgery

What’s New in Hand and Wrist Surgery

Subcutaneous rupture of extensor pollicis longus with extension impairment of thumb metacarpohalangeal joint: A case report

Subcutaneous rupture of extensor pollicis longus with extension impairment of thumb metacarpohalangeal joint: A case report

Effect of Downsized Screw Selection on Bone Healing and Postoperative Complications in Volar Plating of Distal Radius Fractures.

When performing volar plating of distal radius fractures, selecting downsized subchondral screws may prevent dorsal screw penetration (DSP), which is a risk factor for extensor tendon rupture. However, downsizing may cause loss of reduction or poor bone healing. This prospective study investigated the effect of downsized screw selection on bone healing and postoperative complications. A total of 115 patients with postoperative follow-up longer than 6 months comprised the study population. Using a depth gauge, screws that were 2-mm shorter than the measured value were selected. The DSP then was checked using dorsal tangential view (DTV) radiographs during surgery and at final follow-up. Baseline data included bone healing, loss of reduction of radiological parameters, DSP location, and postoperative complications. To assess DSP on DTV radiographs, the dorsal surface of the radius was divided into the radial and ulnar sides at the Lister tubercle, and each was further divided into 2 equal regions. These 4 regions were defined as zones 1 to 4 from the radial side. A total of 114 patients (99%) showed bone healing. Mean loss of reduction was approximately 1° and within 1 mm in radiological parameters. Eleven patients (9.6%) showed DSP during surgery or at final follow-up despite using 2-mm downsized screws. The most common site of DSP was zone 3. Extensor pollicis longus rupture occurred in 2 patients (1.7%) despite no DSP. Downsized screw selection provided a high rate of bone healing with minimum loss of reduction and a low complication rate. The extensor tendon can be torn regardless of DSP. [Orthopedics. 2021;44(2):e259-e265.].

Spontaneous Rupture of Extensor Pollicis Longus Tendon: Clinical and Occupational Implications, Treatment Approaches and Prognostic Outcome in Non-Rheumatoid Arthritis Patients: A Retrospective Study.

BackgroundSpontaneous rupture of extensor pollicis longus (EPL) tendon is a rare condition often found in patients actively having regular extensive use of hands and fingers especially the thumb. In this article, we report 7 cases of spontaneous rupture of EPL tendon and investigate the associated factors and treatment outcome.MethodsRetrospectively, the databases for the 7 cases were retrieved and studied. These cases represent all cases of spontaneous rupture of EPL in our institution. Demographic data, clinical presentation, any history of trauma or steroid injection, laboratory and clinical findings suggestive for rheumatoid arthritis, co-morbidities and imaging findings were obtained. In addition, the operative technique and findings were retrieved. Moreover, histopathological studies and follow-up assessment were included.ResultsSix males and one female were included. The mean age was 45.2 years. No prior history of trauma, rheumatological disease or steroid use was detected in any patient. All patients experienced prodromal pain in the radial side. Clinical examination was the most effective diagnostic measure. Magnetic resonance imaging (MRI) was used to confirm the diagnosis and to look for other abnormalities that may predispose to rupture. Five patients underwent extensor indicis proprius to EPL tendon transfer employing Pulvertaft weave technique and one patient underwent primary repair as there was a little gap in the tendon ends. In this study, one patient refused any treatment. All patients achieved a favorable outcome at the last follow-up.ConclusionDiagnosis of spontaneous ruptures of EPL tendon can be confirmed through clinical examination and MRI for patients with restricted thumb movement even with the absence of any identifiable predisposing risk factor. During surgery, detailed attention must be drawn towards the tendon ends which can have unusual gaps and bone abnormalities.

Delayed presentation of extensor pollicis longus tendon injury treated using extensor indicis proprius tendon transfer

Spontaneous closed rupture of EPL tendon are frequently associated with rheumatoid arthritis, Colles fracture, sports related injury. In cases of delayed presentation direct tendon repair is not feasible and a tendon transfer is usually recommended. In this study we evaluated the results of extensor indicis proprius (EIP) to extensor pollicis longus (EPL) transfers for EPL ruptures. Four patients, (two male and two females); mean age 32 years (range 20 to 45 years) with EPL tendon rupture underwent EIP to EPL tendon transfer. The mean duration from rupture to surgery was 4.5 weeks (range 4 to 6 weeks). Range of motion of the metacarpophalangeal (MCP), interphalangeal joints (IP) of the thumb and index finger of the operated side was compared with the normal side. The results were scored using geldmacher scheme, for the thumb four functions were scored, the radial abduction angle, the elevation deficit, the opposition distance and flexion extension deficit of MP and IP joints. The mean follow-up period was 5 months. All the four patients were able extend the thumb at MCP joint and oppose the thumb to the MCP of little finger after mean follow up of 5 months. Based on the questionnaire, the results of tendon transfer scored by three (75%) patients was excellent and by one (25%) patient was good. Independent extension of the index finger of operated hand was possible in all 4 patients. The procedure of EIP to EPL tendon transfer provides excellent result for extension of thumb. It is a safe procedure.

Anatomy of the extensor mechanism of the thumb in relation to the clinical presentation of extensor pollicis longus rupture

Extensor pollicis longus (EPL) tendon rupture is a debilitating condition that presents with impaired interphalangeal joint (IPJ) extension. Standard descriptions of EPL function state that it is the sole thumb IPJ extensor. It has been suggested that the intrinsic muscles of the thumb, acting through a dorsal extensor expansion (DEE), are also capable of producing IPJ extension which can result in a missed diagnosis of EPL rupture. It remains controversial whether the thumb possesses a DEE analogous to the DEE of the fingers. The aim of this study was to determine if a DEE of the thumb exists and to establish if intrinsic hand muscles insert into it to produce IPJ movement. Nine cadaveric hands were dissected, and muscle function was assessed. A DEE was observed in all thumbs and its structure closely resembled the DEE of the fingers. The DEEs had clear margins that received contributions from intrinsic muscles of the thumb and EPB. Applying traction to the intrinsic muscle attachment consistently resulted in IPJ extension. A DEE is present in the thumb that structurally and functionally resembles that of the fingers. Traction on the EPL tendon produced a compound movement including IPJ and metacarpophalangeal joint extension and supination of the entire first ray around the carpometacarpal joint. This compound movement is, in effect, the antagonistic movement to thumb opposition. This explains the profound loss of function associated with EPL rupture and suggests a more accurate test for EPL function than simply assessing for active IPJ extension. Level of evidence: Level IV, diagnostic study.