Longitudinal Radioulnar Dissociation Research Articles

Radiographic Comparison of Forearm Symmetry in Healthy Individuals and its Importance in the Diagnosis of Longitudinal Radioulnar Dissociation.

Longitudinal radioulnar dissociation (LRD) is an injury often missed upon initial presentation. A recent study examined a radiographic screening test in cadavers that showed increased interosseous distance when the interosseous ligament (IOL) was divided. For this test to be clinically useful, it is necessary for uninjured forearms to have similar interosseous spaces. The purpose of this study was to determine the typical differences between right and left interosseous spaces of healthy individuals. Anterior-posterior x-rays of bilateral forearms in maximum supination of 28 surgical residents with no history of injury were obtained. These images were uploaded into a picture archiving and communication system and then digitized. The length of the radius was measured (Xr). The maximum interosseous distance (Dmax) between the radius and ulna as well as the interosseous distance at a location 0.3 Xr from the distal radioulnar joint was measured. The right and left arm distances were compared. Also, an outlier analysis was used to evaluate forearm rotational asymmetry between right and left arms. The outlier analysis revealed two sets of forearm x-rays were rotationally different compared to the rest of the group due to asymmetric arm positioning; these data were excluded from the analysis. The average difference in Dmax was 1.7 mm (standard deviation [SD] 1.5) between right and left arms, and this was found at a position of 0.28 Xr on average. The difference in interosseous distance measured at a fixed location 0.3 Xr was 1.6 mm (SD 1.5). No significant difference was found between the paired right and left arms for Dmax or at 0.3 Xr. There does not appear to be any significant difference between the maximum interosseous distance of right and left arms in healthy individuals. Therefore, analyzing bilateral forearm x-rays may be a simple LRD screening test. Understanding the degree of normal variation in the forearm bone spacing might inform evaluation of abnormal forearm bone alignment resulting from LRD.

Defining acute Essex-Lopresti injuries is problematic and variable: a systematic review.

The aim of this study was to systematically review clinical studies on the employed definitions of longitudinal forearm instabilities referred to as Essex-Lopresti (EL) injuries, interosseous membrane (IOM) injuries or longitudinal radioulnar dissociation. A systematic literature search was performed in MEDLINE, Embase, CINAHL, Web of Science and Cochrane databases, adhering to PRISMA guidelines. All data on diagnosis and treatment were collected. In total, 47 clinical studies involving 266 patients were included. Thirty-nine of 47 studies did not mention an IOM lesion as part of the EL injury. The amount of preoperative positive ulnar variance varied from >1 to >12 mm. Nine studies used some form of dynamic pre-operative or intraoperative test of longitudinal radioulnar instability. There is no accepted definition of EL injury in the literature. In order to prevent underdetection of acute EL injury, a radial head fracture in a patient with wrist and/or forearm pain should raise awareness of the possibility of an EL injury. In this case, comparative radiographic studies and some form of dynamic assessment of longitudinal radioulnar stability should be performed.

Essex-Lopresti injuries: an update.

Reconstruction of the central band of the interosseous membrane is an emerging procedure implemented in the treatment of longitudinal radioulnar dissociation (LRUD), usually in its chronic setting, after Essex-Lopresti injuries of the forearm.There are no sufficient clinical data to support reconstruction of the central band of the interosseous membrane in acute LRUD injuries.Clinical and cadaveric studies comparing autografts (palmaris longus, flexor carpi radialis and bone-patellar-bone), allografts (Achilles tendon) and synthetic ligaments have not shown superiority of one technique versus another; however, they have shown special concerns with respect to the use of synthetic grafts.Latrogenic fracture, decrease of rotational range of movement, iatrogenic nerve injury (superficial radial and median nerve), donor site morbidity with autografts and recurrent instability are the complications reported in literature after interosseous membrane reconstruction.Cite this article: EFORT Open Rev 2019;4:143-150. DOI: 10.1302/2058-5241.4.180072

Anatomic Interosseus Membrane Reconstruction Utilizing the Biceps Button and Screw Tenodesis for Essex-Lopresti Injuries

Longitudinal radioulnar dissociation, also known as the Essex-Lopresti lesion, is a potentially debilitating condition causing painful instability of the forearm that often results from high-injury trauma with compromise of the proximal radius, triangular fibrocartilage complex, and the interosseous membrane. Indications for reconstruction of the interosseous membrane primarily include chronic instability of the forearm. Our reconstructive technique utilizes an anatomic allograft reconstruction with intraosseous fixation, in an effort to biologically reconstruct and anatomically tension the central band of the interosseus membrane.

Comparison of 2 Forearm Reconstructions for Longitudinal Radioulnar Dissociation: A Cadaver Study

We present the results of a cadaveric study of 2 forearm reconstructions with radial head replacement for longitudinal radioulnar dissociation injuries. We created a simulated longitudinal radioulnar dissociation injury in 8 cadaver forearms. Two reconstructions were performed alternately on each arm: patellar tendon interosseous ligament complex reconstruction and the Herbert sling extensor retinaculum plication. We performed mechanical testing in a materials testing machine with and without a radial head replacement, and measured ulnocarpal impaction force through 2 distal ulna strain gauges. We determined relative radioulnar displacement using live fluoroscopic analysis of implanted stainless-steel beads. Relative radioulnar longitudinal displacement in the destabilized forearms was 10.7 compared with 0.7 mm before creating the injury. A prosthetic radial head replacement alone decreased the displacement by 75% to 2.7 mm. Interosseous ligament reconstruction alone reduced the displacement to 5.1 mm and to 1.3 mm when combined with a radial head implant. The Herbert sling alone did not improve longitudinal stability. The distal ulna force in the native arm was 17 N, or 17% of the force across the wrist. The interosseous ligament reconstruction restored the force to 21 N, whereas the Herbert sling only marginally decreased the ulna impaction force to 45 N. Adding a radial head decreased the distal ulna force to 7 N for the patellar tendon interosseous ligament reconstruction, and 2 N for the Herbert sling. In longitudinal radioulnar dissociation injuries, the radial head is an important stabilizer and should be repaired or replaced to minimize radial shortening and ulnar impaction force. Patellar tendon interosseous ligament reconstruction effectively restores the ulnocarpal force distribution and markedly reduces longitudinal instability at the distal radioulnar joint. Combined with radial head arthroplasty, the construct has stability similar to an intact forearm. The Herbert sling did not improve longitudinal stability in this testing construct. Treatment of longitudinal radioulnar dissociation may benefit from radial head replacement and interosseous ligament reconstruction using a patellar tendon graft.

Suture-Button Construct for Interosseous Ligament Reconstruction in Longitudinal Radioulnar Dissociations: A Biomechanical Study

Longitudinal radioulnar dissociation is a triad of injuries consisting of distal radioulnar joint disruption, interosseous ligament complex (IOLC) tear, and radial head fracture. This renders the forearm longitudinally unstable, resulting in proximal migration of the radius and ulnar-sided wrist degeneration. We hypothesized that reconstruction of the central band of the IOLC in cadaver forearms using a Mini-TightRope suture-button construct would restore native forearm stability. We implanted 8 fresh-frozen cadaver arms with steel beads into the distal radius and ulna, mounted them on an MTS machine, and cyclically loaded them from 13 N distraction to 130 N compression. Bead motion was recorded fluoroscopically and analyzed using Image-Pro Express software. We measured distal ulnar forces using strain gauge transducers. Longitudinal radioulnar dissociation injuries were created by radial head excision and complete IOLC and triangular fibrocartilage complex disruption. At each stage, arms were tested with and without a radial head implant. We reconstructed the central band of the IOLC using a Mini-TightRope and tightened until the distal radioulnar joint was reduced fluoroscopically. We used multiple-comparison analysis of variance with Tukey's Honestly Significant Difference test for statistical analysis. The intact arms had an average radioulnar axial displacement of 0.7 ± 0.8 mm and distal ulnar impaction force of 16.7 ± 11.1 N (per 100 N of axial load on the forearm). After destabilization, the radioulnar displacement increased to 10.7 ± 3.9 mm (p < .001) and ulnar load increased 312%, to an average of 52.2 ± 25.7 N (p < .001). After IOLC reconstruction, average displacement decreased to 2.2 ± 0.9 mm with a distal ulnar load of 19.05 ± 13.5 N (not significantly different from intact arms). In this cadaveric study, Mini-TightRope IOLC reconstruction with or without a radial head prosthesis significantly reduced distal ulnar impaction forces to that of the native forearm, while limiting radioulnar displacement to near-anatomic levels.

Radial Head Arthroplasty Alone Provides Inadequate Treatment for Longitudinal Radio-ulnar Dissociation: A Cadaveric Study: Not a clinical study

Radial Head Arthroplasty Alone Provides Inadequate Treatment for Longitudinal Radio-ulnar Dissociation: A Cadaveric Study: Not a clinical study

Delayed treatment of elbow pain and dysfunction following Essex-Lopresti injury with metallic radial head replacement: A case series

Chronic longitudinal radioulnar dissociation has been associated with unpredictable and generally unfavorable outcomes. Metallic radial head replacement may address this treatment deficiency. Eight patients were treated with a metallic radial head replacement for chronic longitudinal radioulnar dissociation. The average treatment delay was 3.3 years. All eight patients were seen for a clinical and radiographic assessment. Five of the 8 failed after a mean of 3 years (range, 1-5.7). Revision to bipolar metallic radial head replacement was successful in the short term in 2 of 3 that failed from aseptic loosening. One of 2 failures due to painful radiocapitellar arthritis was salvaged with a capitellar replacement. Reconstruction for symptoms following an Essex-Lopresti injury remains problematic. A metallic radial head implant appears to be an effective adjunct, but not a perfect solution in all patients. Recognition of the negative impact of residual lateral ulnar collateral ligament laxity is an important observation and should be specifically addressed with the reconstructive procedure. Metallic monoblock radial head replacement did not reliably address the functional deficiency from chronic radioulnar dissociation primarily due to malalignment and implant loosening. A cemented bipolar radial head implant may provide a better alternative as a long-term solution. Regardless, ligamentous integrity at the elbow should also be addressed at the time of the reconstruction.

Reconstruction of the Interosseous Ligament Unloads Metallic Radial Head Arthroplasty and the Distal Ulna in Cadavers

Longitudinal radioulnar dissociation may result when a compressive load to the hand results in excessive proximal migration of the radius with interosseous ligament (IOL) disruption and radial head fracture. Interosseous ligament reconstruction has been proposed to restore more normal forearm mechanics. The objective of this study was to evaluate the effect of IOL reconstruction on compressive load transfer through the forearm after excision and metallic replacement of the radial head in cadavers. In 8 cadaveric forearms, 138 N of compressive load was applied to the hand in neutral forearm rotation and neutral elbow varus-valgus alignment. We measured proximal radial migration and 3-dimensional force vectors acting on the distal radius, distal ulna, IOL, proximal radius, and proximal ulna. The experiment was repeated in order for 5 conditions: (1) with the IOL intact, (2) with the IOL reconstructed with a double-bundle flexor carpi radialis construct, (3) with the radial head excised, (4) after metallic radial head arthroplasty, and (5) after cutting the IOL reconstruction. Analysis of variance was used for statistical comparisons. With the IOL intact the resultant load in the distal radius was 94% +/- 3% of hand load, with 75% +/- 2% transmitted to the proximal radius. Double-bundle flexor carpi radialis reconstruction effectively restored this relationship. After radial head excision the resultant distal radius load decreased whereas great increases were seen in the resultant distal ulna load, the resultant load in the IOL reconstruction, the resultant load in the proximal ulna, and proximal radial migration. Force continued to transfer through the proximal radius transversely, with a 400% increase in transverse force, a consequence of abutment of the radial stump caused by proximal radioulnar convergence (there was no contact at the capitellum). After radial head arthroplasty loads transferred across the wrist remained closer to intact but the resultant load on the distal ulna and proximal radius remained increased. With cutting of the IOL reconstruction transverse forces in the forearm became negligible, the resultant distal ulna load increased by 50%, and the resultant radial head load increased by 25%. Proximal migration of the radius was small and was increased by 4.6 mm with radial head excision and by 1 mm after radial head replacement compared with the IOL-reconstructed, radial head-intact state. Interosseous ligament reconstruction may help improve treatment of longitudinal radioulnar dissociation but remains an experimental procedure.

Graft reconstruction of the interosseous membrane in conjunction with metallic radial head replacement: A cadaveric study

Longitudinal radioulnar dissociation (Essex-Lopresti injury) occurs when traumatic axial loading through the wrist disrupts the interosseous membrane (IOM) of the forearm and fractures the radial head. Proximal migration of the radius results in an ulnar-positive wrist, which can lead to painful ulnar-sided wrist degeneration and distal radioulnar joint instability. The purpose of this study was to measure the ability of an IOM reconstruction used in combination with a metal prosthetic radial head implant to reduce distal ulnar forces in a cadaveric model. The effects of varying the initial graft pretension on distal ulnar force were also studied. Twelve fresh frozen and thawed cadaveric forearms had a miniature load cell installed to record force in the distal ulna as the wrist was loaded axially to 134 N of compression force in neutral rotation. Intact forearms were tested first with the elbow in valgus and varus alignments. Loading tests were repeated after (1) insertion of a metal radial head implant that restored radius anatomic length, (2) excision of the IOM (with a radial head implant), and (3) reconstruction of the IOM using a palmaris longus tendon autograft (with a radial head implant). The implant then was removed and loading tests were repeated using 3 levels of initial graft pretension. Mean distal ulnar forces with an intact forearm were 23% of applied wrist force in the varus alignment and 12% in the valgus alignment. Mean force levels after insertion of the implant were 18% (varus) and 13% (valgus); these were not significantly different from corresponding values for the intact forearm. Mean force levels after section of the IOM were 30% (varus) and 14% (valgus); these were not significantly different from corresponding values for the intact forearm (varus and valgus) but the mean for varus was significantly greater than the corresponding value with an implant. After IOM reconstruction with a palmaris longus tendon tensioned to 22 N mean distal ulnar forces were 8% (varus) and 7% (valgus); these means were significantly less than the corresponding values for all prior test conditions. With the radial head removed increasing the level of graft pretension reduced significantly mean distal ulnar force. With the IOM resected insertion of a metal radial head implant alone did not reduce distal ulnar forces to intact forearm levels. When an IOM reconstruction was performed in combination with the implant mean distal ulnar force was reduced significantly to a level below that for the intact forearm. Applying pretension to the graft displaced the radius distally thereby making the wrist more ulnar negative and reducing distal ulnar force. Our results suggest that an IOM reconstruction used in combination with a metal radial head implant theoretically could help reduce distal ulnar impaction in an Essex-Lopresti injury.

Reconstruction of the interosseous ligament restores normal forearm compressive load transfer in cadavers

Longitudinal radioulnar dissociation may result when compressive load to the hand causes excessive proximal migration of the radius with interosseous ligament (IOL) disruption and radial head fracture. Although radial head salvage or arthroplasty and temporary distal radioulnar joint pinning constitute the current treatment for this injury IOL reconstruction has been proposed to restore normal forearm mechanics. To help provide a biomechanical basis for IOL reconstruction we measured load transfer and proximal migration of the radius with the IOL intact, cut, and reconstructed while leaving the radial head intact. We dissected the central third of 12 normal cadaveric forearms to bone-IOL-bone. We applied 136 N of compressive load to the hand and measured proximal radial migration and 3-dimensional force vectors acting in the distal radius, distal ulna, IOL, proximal radius, and proximal ulna. Experiments were performed in neutral forearm rotation and neutral elbow varus-valgus. The protocol was repeated with the IOL intact, cut, and reconstructed with single and double flexor carpi radialis allografts. With the IOL intact 94% +/- 3 % of hand load was in the distal radius with 75% +/- 2% was transmitted to the proximal radius. With the IOL cut 92% +/- 2% of hand load was in the distal radius and this was unchanged at the proximal radius. With single flexor carpi radialis reconstruction 94% +/- 3% of hand load was in the distal radius and 80% +/- 2% was in the proximal radius; with double flexor carpi radialis reconstruction these numbers changed to 95% +/- 3% and 74% +/- 2%, respectively. Forces in the forearm were mainly in the longitudinal and transverse directions with negligible components in the dorsal-volar direction. Transverse force in the IOL was about half that of the longitudinal force in the intact and reconstructed states. When the IOL is cut and load is applied to the hand the unloading of the proximal radius and the transversely directed force that compresses normally across the proximal and distalradioulnar joints is lost. Reconstruction of the IOL can restore the normal load transfer characteristics. These data help provide a biomechanical basis for IOL reconstruction. Further research on the biomechanics of IOL reconstruction in the setting of radial head replacement along with clinical evaluation is needed.

Structural properties of reconstruction constructs for the interosseous ligament of the forearm

The Essex-Lopresti fracture-dislocation, also termed longitudinal radioulnar dissociation (LRUD), results in major functional impairment from pain and limitation of motion at the wrist and elbow. Interosseous ligament (IOL) reconstruction has been proposed to help treat LRUD and restore forearm stability. The objective of this study was to evaluate the biomechanical structural properties of 3 different IOL reconstruction constructs and of the intact IOL for comparison. Structural tensile testing was performed on 24 fresh-frozen cadaveric forearms with 4 different forearm conditions: IOL intact and IOL reconstructed with Achilles tendon, flexor carpi radialis (FCR) tendon, and bone-patellar tendon-bone. Isolated radius-IOL-ulna constructs were loaded to failure in a materials testing machine with force applied along the local fiber direction. Stiffness in the intact IOL was 129 +/- 31 N/mm, which was significantly stiffer than any of the constructs tested. The intact IOL was 8 times stiffer than the Achilles tendon construct, 7 times stiffer than the FCR construct, and 3 times stiffer than the bone-patellar tendon-bone construct. The Achilles tendon and FCR constructs were similar to each other biomechanically but the bone-patellar tendon-bone construct was slightly stiffer than the Achilles tendon and FCR constructs. All graft constructs tested were inferior structurally to the intact IOL. The results of this study provide a biomechanical basis for graft selection for reconstruction of the IOL.

Reconstruction of the interosseous membrane of the forearm with a graft substitute: A cadaveric study

Longitudinal radioulnar dissociation occurs when traumatic axial loading through the wrist disrupts the interosseous membrane (IOM) of the forearm and fractures the radial head (Essex-Lopresti injury). Proximal migration of the radius results in a wrist with a positive ulnar variance, which leads ultimately to painful ulnar-sided wrist degeneration and wrist pain during grasping activities that involve axial loading or ulnar deviation of the wrist. In theory reconstruction of the IOM with a graft substitute can limit proximal migration of the radius, thereby preserving wrist function. The objective of this study was to measure the abilities of 3 graft tissues to limit proximal radial displacement compared with the native IOM in a radial head-deficient cadaver model. Sixteen fresh-frozen cadaveric forearms were loaded axially to 134 N through the potted central 3 metacarpals; the elbow was flexed to 90 degrees with the wrist in neutral rotation. Proximal displacement of the radius relative to the capitellum was measured. With the radial head excised specimens were first tested with the IOM intact. The IOM was then sectioned and central band IOM reconstructions were performed on each specimen using the following tissues: palmaris longus tendon, flexor carpi radialis (FCR) tendon, and a 1-cm- wide bone-patellar tendon-bone (BPTB) onlay allograft. Ten loading cycles were performed with each test configuration. Proximal radial displacement between 13.4 N and 134 N of applied wrist force was analyzed for the 10th loading cycle. The increase in proximal displacement between the first and 10th loading cycles (recorded at 134 N of wrist force) represented permanent elongation of the graft. Mean cross-sectional areas were 5.11 mm2 for the palmaris longus tendon, 15.23 mm2 for the FCR tendon, and 51.59 mm2 for the BPTB allograft. Mean proximal radial displacements were 3.04 mm (intact IOM), 4.37 mm (BPTB), 4.92 mm (FCR tendon), and 6.43 mm (palmaris tendon); all means were significantly different from each other. Mean permanent graft elongations were 0.06 mm (IOM), 0.36 mm (BPTB), 1.25 mm (FCR tendon), and 1.80 mm (palmaris tendon); all means were significantly different from each other with the exception of means for palmaris longus vs FCR and BPTB vs IOM. No graft reconstruction limited proximal radial displacement as effectively as the native IOM. Of the 3 graft tissues tested the BPTB allograft had the greatest cross-sectional area, allowed the least proximal radial displacement, and displayed the least permanent elongation after 10 cycles of loading. The relatively thin and narrow palmaris longus tendon appears to be the least desirable choice for IOM reconstruction because of its relatively low stiffness and tendency to elongate permanently after cyclic loading. When the radial head is absent rupture of the IOM allows unopposed proximal displacement of the radius relative to the ulna as the wrist is loaded axially. In the present tests all 3 graft tissues used to reconstruct the IOM limited proximal radial displacement. The choice of graft material is an important variable if IOM reconstruction is considered for treatment of an Essex-Lopresti injury.

Bi-directional mechanical properties of the human forearm interosseous ligament

Interest in reconstruction of the interosseous ligament (IOL) of the forearm in the setting of longitudinal radio-ulnar dissociation has increased in recent years with hopes of improving clinical outcomes. This increased interest has been accompanied by research on biomechanics of the IOL. However, little is known about stress and strain in the IOL under externally applied forearm loads. This information is needed to help guide reconstruction. Mechanical properties of the IOL are needed to properly model the IOL for analyses such as finite element models. The objective of this study was to document the bi-directional mechanical properties along the fiber direction (longitudinal) and perpendicular to the fiber direction (transverse). Twenty specimens were mounted in a materials testing machine to perform preconditioning and a load to failure tensile test in each direction. Strain markers on the surface of the specimens were tracked with a video system. Data analysis provided stress–strain curves for each specimen. The elastic moduli of longitudinal and transverse specimens were 515 ± 277 and 1.82 ± 2.93 MPa, respectively. The tensile strength and ultimate strain of longitudinal and transverse specimens were 54.1 ± 25.2 and 0.18 ± 0.20 and 16 ± 5% and 34 ± 32%, respectively. The bi-directional mechanical properties of the IOL compared well with those published for the medial collateral ligament of the knee. The mechanical properties in the longitudinal direction were much greater than those in the transverse direction, which is indicative of the IOL's role in resisting longitudinal loading. The results of this study can be used to generate mathematical models of stress and strain in the IOL.

Anatomic parameters for planning of interosseous ligament reconstruction using computer-assisted techniques

Purpose: Longitudinal radioulnar dissociation may result when both interosseous ligament (IOL) disruption and radial head fracture occur. Although radial head salvage or arthroplasty and temporary distal radioulnar joint pinning constitute the standard treatment for this injury, IOL reconstruction has been proposed to restore more normal forearm axis mechanics. To help provide an anatomic basis for IOL reconstruction, the purpose of this study was to characterize the geometry of the central band of the IOL and simulated IOL reconstructions. Methods: Twenty forearms free of pathology were dissected to bone-IOL-bone and computed tomography scans were taken. Computer models of radius-IOL-ulna were created from the computed tomography CT images, and computer-aided design software was used to measure key parameters for IOL reconstruction and simulate anatomic IOL reconstructions. Results: The insertion site locations of the IOL central band along the radius and ulna from the wrist were 57 ± 3% and 34 ± 4% of bone length, respectively. The angle at which the IOL central band inserts with the ulna was 24 ± 4 degrees, which agrees with previously reported values. We found that the minimum graft length needed to anatomically span both cortices through tunnels was 112 ± 14 mm. Conclusions: These data will help to provide a basis for planning and performing IOL reconstruction in cases of longitudinal radioulnar dissociation. (J Hand Surg 2003;28A:111–116. Copyright © 2003 by the American Society for Surgery of the Hand.)

Longitudinal radioulnar dissociation.

Proximal translation of the radius is a complication of radial head fractures that occurs in association with disruption of the longitudinal soft-tissue stabilizers of the forearm. The sequelae of this process include debilitating wrist and elbow pain secondary to ulnocarpal and radiocapitellar abutment as well as loss of grip strength. When radioulnar dissociation is recognized early, treatment involves prevention of proximal radial migration by preservation of the radial head and stabilization of the distal radioulnar joint. When primary bony repair of the radial head is not feasible, prosthetic replacement of the radial head is necessary to prevent proximal radial migration. Management is complex in chronic cases in which longitudinal radioulnar dissociation is diagnosed after radial migration has occurred. Treatment goals include normalization of the radioulnar relationship and prevention of further migration. Although several reconstructive treatment options are available, no clear solutions exist, and long-term prognosis is guarded. Therefore, early recognition of longitudinal forearm instability is critically important.

Attritional rupture of flexor tendons by the head of the ulna associated with a chronic longitudinal radioulnar dissociation

A 62-year-old woman sustained multiple attritional ruptures of the flexor tendons at the wrist caused by displacement of the head of the ulna. She had had injuries of the wrist and elbow when she was young, which were thought to have caused chronic longitudinal radioulnar dissociation with palmar dislocation of the head of the ulna. Attrition of the flexor tendons by the dislocated ulnar head during pronation and supination was the major mechanism for the ruptures in this case. She was successfully treated with tendon transfer and resection of the ulnar head.