Passive strain distribution in the interosseous ligament of the forearm: implications for injury reconstruction

PURPOSE: For severe forearm injuries such as an Essex-Lopresti fracture-dislocation, functional reconstruction necessitates repair of the interosseous ligament (IOL) to restore normal load sharing between the radius and ulna. Locating or tensioning such a reconstruction improperly can lead to abnormal load sharing and/or restriction of forearm rotation. The normal IOL strains should indicate the proper location of reconstruction grafts and the proper forearm rotation for tensioning the grafts. The objective of this study was to quantify the passive strain distribution of the IOL of the forearm with passive rotation of the forearm throughout the range of motion. METHODS: The 3-dimensional motions of the radius with respect to the ulna were measured throughout forearm rotation in 10 cadaveric forearms by using an instrumented spatial linkage. From the bone motions and ligament insertion site geometry from dissection and computed tomographic scanning, insertion site motions were determined and used to calculate changes in ligament fiber lengths. RESULTS: The measured strain distribution in the IOL was nonuniform and varied with forearm rotation. The overall magnitude of IOL strain was found to be greatest in supination and smallest in pronation. In supination the strains varied across fibers with strains being greatest in the distal fibers and lowest in the proximal fibers. Strains in neutral rotation were uniform across fibers. Although fibers were generally slack in pronation proximal fibers were less slack than distal fibers. CONCLUSIONS: The results of this study indicate that fiber strains in the IOL vary from proximal to distal and depend on forearm rotation. Our data suggest that to prevent restriction of forearm rotation all grafts should be tensioned in supination, where measured strains were generally highest. Our data also suggest that a 2-bundle IOL reconstruction may be necessary for proper load transfer between the radius and ulna in both supination and pronation.     

Electromyographic activity and strength during maximum isometric pronation and supination efforts in healthy adults.

There exists a lack of quantitative data in the literature related to the torque produced during axial forearm rotation and the electromyographic (EMG) activity of the muscles involved. Therefore, the purpose of this study was to compare the relative EMG activity of four forearm muscles during resisted forearm rotation. A custom-built device capable of measuring torque in the absence of grip was employed. Fourteen healthy volunteers performed maximum isometric voluntary contractions in five positions of axial forearm rotation for both pronation and supination. EMG data were collected simultaneously from the supinator, biceps, pronator quadratus (deep and superficial heads), and pronator teres muscles using fine-wire bipolar electrodes. Data were analyzed to determine the contributions of each muscle to pronation and supination torque over five positions of forearm rotation. In the absence of grip no significant difference was found between supination and pronation torque in neutral position. Supination torque generation was greater in the pronated forearm positions, and pronation torque was greater in the supinated positions (p<0.05). A root-mean-square EMG analysis verified the major contributions of the pronator teres and both heads of the pronator quadratus muscle to pronation torque, and supinator and biceps to supination torque. The deep head of the pronator quadratus was active during both pronation and supination, lending support to the theory that it may act primarily as a dynamic distal radioulnar joint stabilizer. This information may be helpful in upper extremity modeling, surgical treatments, and rehabilitation strategies.     

Effects of forearm rotation on the clinical evaluation of ulnar variance

Neutral rotation radiographs of the wrist are recommended to standardize the measurement of ulnar variance because it is known that changes in forearm rotation result in changes of this measurement. The purpose of this study was to examine whether there are clinically measurable differences in ulnar variance between radiographs in various degrees of forearm rotation in human subjects. Forty-five wrist radiographs of 15 normal adults were obtained in 3 positions: maximum forearm pronation, neutral rotation, and maximum supination. The ulnar variance on each view was measured by 3 independent observers using a standard millimeter ruler. The average absolute difference in ulnar variance was 0.4 mm between pronation, 0.6 mm between pronation and supination, and 0.2 mm between neutral and supination. Although we found a statistically significant difference in ulnar variance between the pronated and neutral positions, this difference may not be clinically significant and may not justify concerns of forearm position during the radiographic evaluation of ulnar variance.     

Effects of radioulnar instability on the radiocarpal joint: a biomechanical study

Five fresh cadaver upper extremities were studied with use of a static positioning frame, pressure-sensitive film and a microcomputer-based videodigitizing system to assess the effect of increasing radioulnar instability on the load distribution within the proximal carpal joint. Three stages of radioulnar instability were studied: (1) an avulsion fracture at the base of the ulna styloid; (2) an avulsion fracture at the base of the ulna styloid plus disruption of the dorsal portion of the distal radioulnar joint capsule; and (3) an avulsion fracture at the base of the ulna styloid, disruption of the dorsal portion of the distal radioulnar joint capsule, and disruption of the radioulnar interosseous membrane. All stages of radioulnar instability demonstrated a decrease in the lunate contact area in positions with the forearm in supination. In stage 3 instability there was also less lunate contact area in positions with the forearm in neutral pronation/supination. In stage 3 instability the lunate high pressure area centroid was abnormally palmar in all positions and the scaphoid high pressure area centroid was abnormally palmar in positions with the forearm in pronation or supination.     

Biomechanical analysis of two ulnar head prostheses

The biomechanical effectiveness of 2 ulnar head prostheses was evaluated in 5 fresh-frozen cadaver arms. By using electromagnetic sensors, the amount of forearm rotation, diastasis, and dorsal/palmar subluxation of the radius at the level of the sigmoid notch was measured with the forearm in neutral rotation, pronation, and supination with and without dorsal/palmar loading. Testing was done in the intact specimens and after insertion of 2 types of ulnar head prostheses. Dynamic forearm rotation was also achieved by applying loads in the line of action of the appropriate pronator or supinator muscles to obtain a centroidal path of the radius relative to the ulna. Overall after ulnar head replacement forearm rotation lessened in pronation, diastasis decreased in most forearm positions, and subluxation increased in supination compared with the intact specimen. Despite these changes, both prostheses maintained near-normal biomechanics of the distal radioulnar joint when compared with the irregular behavior occurring after distal ulna resection. Therefore these prostheses are suggested for restoration of distal radioulnar joint function.     

Influence of distal radioulnar joint subluxation on restricted forearm rotation after distal radius fracture

PURPOSE: To analyze the influence of subluxation of the distal radioulnar joint (DRUJ) on restricted forearm rotation after distal radius fracture. METHODS: Twenty-two cases of healed unilateral distal radial fracture with restricted forearm rotation were included in the study. The subluxation of the DRUJ was evaluated using helical computed tomography scan at neutral, maximum pronation, and maximum supination and presented as the percent displacement of the ulnar head in both the injured and uninjured sides. The radiographic parameters of palmar tilt, radial inclination, dorsal shift, radial shift, and ulnar variance were measured on plain x-ray films and the rotational deformity of the distal radius was evaluated from the computed tomography scan. The differences of each radiographic parameter from the uninjured side were calculated. The relationships between the restricted forearm rotation and the percent displacement of the ulnar head and each of the radiographic parameters were analyzed statistically. RESULTS: When forearm pronation was restricted the ulnar head was located palmarly at neutral, maximum supination, and maximum pronation with severe dorsal tilt of the distal radius. When supination was restricted the ulnar head was located dorsally at maximum supination with severe ulnar-positive variance. CONCLUSIONS: The subluxation of the DRUJ was related to restricted forearm rotation. The radiographic parameters of palmar tilt and ulnar variance showed an adverse influence on the position of the ulnar head at the DRUJ, which might lead to restricted forearm rotation after distal radial fracture.     

Anatomic considerations regarding the posterior interosseous nerve at the elbow

The relationship of the posterior interosseous nerve (PIN) to the radius was studied to determine the change in position associated with forearm motion because of the risk of injury during surgical exposure of the lateral elbow. The distance from the PIN to the radiocapitellar joint (RCJ) was measured in 24 cadaveric specimens in pronation, neutral rotation, and supination. The mean distance from the PIN to the RCJ was 4.6 +/- 0.5 cm, 5.3 +/- 0.6 cm, and 5.7 +/- 0.7 cm in supination, neutral rotation, and pronation, respectively. In pronation, there was substantial variation of this distance, with a minimum distance of 4.3 cm. In supination, the minimum distance was 4.0 cm. On the basis of limited PIN distal translation, noted with pronation, as well as the variation between individuals, we recommend limiting dissection to 4.0 cm from the RCJ during a lateral approach without formal identification of the PIN. This safe zone is recommended regardless of forearm rotation, in contrast to the recommendation of prior authors, as pronation does not reliably increase the distance of the PIN to the RCJ.     

An analysis of symmetry of torque strength of the forearm under resisted forearm rotation in normal subjects

PURPOSE: To establish normative pronation and supination torque values in right-handed adults without evidence of upper-extremity dysfunction or impairment in the forearm positions of neutral, pronation, and supination. METHODS: Fifty-one normal right-handed participants ages 22 to 45 years were enrolled and tested in this study using a custom device that incorporated a torque cell and a grip system that produced a digital recording of the peak torque during maximal resisted pronation and supination in positions of neutral forearm rotation, 60 degrees pronation, and 60 degrees supination. RESULTS: The greatest peak torque strength for both male and female participants was found during resisted pronation in the supinated position. The peak torque values averaged 11.9 +/- 3.7 N.m on the right side and 10.4 +/- 3.3 N.m on the left side for men, and 6.0 +/- 1.4 N.m on the right side and 5.0 +/- 1.2 N.m on the left side for women. The weakest torque strengths were resisted pronation in the pronated position and resisted supination in the supinated position. CONCLUSIONS: Torque strength measurements are reliable and should be collected when treating patients with forearm dysfunction. Maximal torque follows the same pattern related to hand dominance as grip strength. Men generate average torque strengths that are approximately twice the magnitude of those generated by women.     

Forearm rotational profile in obstetric brachial plexus injury

Children with obstetric brachial plexus palsy (OBPP) most commonly have weakness of supination. There is little previous information on later progress of forearm rotation movements, although severe supination contracture has been reported in a small proportion of children. The aims of this study were to evaluate forearm rotation after initial recovery from OBPP, to define the relationship with the severity of disease, and to assess which factors might limit rotation. Measurements of active and passive pronation and supination were recorded in 56 children (37 boys and 19 girls) who had had OBPP and did not have full recovery. The mean age was 8 years (minimum, 2.5 years). Care was taken to measure forearm rotation in isolation from shoulder movements. According to the Narakas classification for severity of the original brachial plexus lesion, there were 23 group I cases, 16 group II cases, 11 group III cases, and 6 group IV cases. Twenty-one children underwent reconstructive procedures for shoulder deformity. Mallet scores for shoulder function were available for all patients. Overall pronation was more limited than supination. Active movements were more limited than passive movements. Active pronation was less than normal in 48 children, active supination was less than normal in 36, passive pronation was less than normal in 22, and passive supination was less than normal in 9. Active pronation and active and passive supination were significantly limited in children with worse Mallet scores and in Narakas group IV children. Both active supination and passive supination were decreased in children with more severe elbow flexion contractures. No significant relationship was found between forearm rotation movements and the time of biceps recovery. Many children have persisting limitation of forearm rotation after OBPP. Despite the initial weakness of supination, pronation is more often reduced in the longer term. Patients with more severe OBPP and poorer recovery of shoulder function have greater limitation of forearm rotation.     

Effects of elbow flexion and forearm rotation on valgus laxity of the elbow

BACKGROUND: Clinical evaluation of valgus elbow laxity is difficult. The optimum position of elbow flexion and forearm rotation with which to identify valgus laxity in a patient with an injury of the ulnar collateral ligament of the elbow has not been determined. The purpose of the present study was to determine the effect of forearm rotation and elbow flexion on valgus elbow laxity. METHODS: Twelve intact cadaveric upper extremities were studied with a custom elbow-testing device. Laxity was measured with the forearm in pronation, supination, and neutral rotation at 30 degrees, 50 degrees, and 70 degrees of elbow flexion with use of 2 Nm of valgus torque. Testing was conducted with the ulnar collateral ligament intact, with the joint vented, after cutting of the anterior half (six specimens) or posterior half (six specimens) of the anterior oblique ligament of the ulnar collateral ligament, and after complete sectioning of the anterior oblique ligament. Laxity was measured in degrees of valgus angulation in different positions of elbow flexion and forearm rotation. RESULTS: There were no significant differences in valgus laxity with respect to elbow flexion within each condition. Overall, for both groups of specimens (i.e., specimens in which the anterior or posterior half of the anterior oblique ligament was cut), neutral forearm rotation resulted in greater valgus laxity than pronation or supination did (p < 0.05). Transection of the anterior half of the anterior oblique ligament did not significantly increase valgus laxity; however, transection of the posterior half resulted in increased valgus laxity in some positions. Full transection of the anterior oblique ligament significantly increased valgus laxity in all positions (p < 0.05). CONCLUSIONS: The results of this in vitro cadaveric study demonstrated that forearm rotation had a significant effect on varus-valgus laxity. Laxity was always greatest in neutral forearm rotation throughout the ranges of elbow flexion and the various surgical conditions. CLINICAL RELEVANCE: The information obtained from the present study suggests that forearm rotation affects varus-valgus elbow laxity. Additional investigation is warranted to determine if forearm rotation should be considered in the evaluation and treatment of ulnar collateral ligament injuries of the elbow joint.     

Distal radioulnar joint instability in distal radius fractures: the role of sigmoid notch and triangular fibrocartilage complex revisited

The stabilising effects of various structures of the distal radioulnar joint (DRUJ) have been heavily debated. This biomechanical cadaveric study examined the effects of the volar and dorsal lips of the sigmoid notch and the volar and dorsal aspects of the triangular fibrocartilage complex (TFCC) on DRUJ stability. Sequential fractures of the distal radius and sectioning of the TFCC were performed followed by measurements of ulnar translation with the forearm in pronation, neutral and supination. A dorsal lunate facet fracture created instability in pronation. Lunate facet fractures alone did not create instability in other forearm positions. Sectioning of the volar TFCC after loss of the dorsal TFCC by a dorsal lunate facet fracture caused DRUJ instability with the forearm in neutral position. Sectioning of the dorsal TFCC after loss of the volar TFCC due to a volar lunate facet fracture created instability in neutral and pronated positions.     

Scaphoid fracture displacement with forearm rotation in a short-arm thumb spica cast.

Three-dimensional motion between the fragments of an experimental scaphoid waist fracture was measured during dynamic forearm pronation and supination in a short-arm thumb spica cast with and without applied tendon loads. Metal markers placed in each fragment were tracked using high-speed biplane radiographic image sequences and stereophotogrammetric analysis. Peak displacements (from the intact state) exceeded 1 mm in all specimens, with the largest movements occurring in the radial direction during pronation (mean: 2.1 mm unloaded, 2.5 mm loaded). Total range of displacement motion between fragments exceeded 3 mm (mean ulnar/radial direction: 3.4 mm unloaded, 4.1 mm loaded). Dorsal/palmar and proximal/distal displacements were minimal except at the extremes of forearm pronation/supination. Rotations between fragments were small (within +/- 6 degrees) and varied considerably across specimens. No significant differences were found between loaded and unloaded trials. Thus, in the absence of long-arm thumb spica casting to limit forearm rotation, significant motion between the fragments of a scaphoid waist fracture is likely.     

Functional anatomy of the lateral collateral ligament complex of the elbow: morphology and strain

The anatomy of the lateral ulnar collateral ligament (LUCL) of the elbow was investigated in 26 fresh frozen cadavers. Two types of insertion of the LUCL were originally described but we found another type which is characterized by a broad single expansion along with a thin membranous fibre. Strain on the LUCL was measured in situ during extension and flexion with the forearm in supination, pronation and neutral. Strain in the proximal fibres started to occur at around 32 degrees flexion and peaked at between 50 degrees and 60 degrees flexion. Strains measured in the distal fibres were smaller in magnitude. Forearm rotation had little effect on strain during extension to flexion. Based on these results, we conclude that the LUCL functions in unison with the annular ligament.     

The proximal ligamentous component of the triangular fibrocartilage complex

The proximal ligamentous component of the triangular fibrocartilage complex (TFCC) was studied anatomically using 15 fresh-frozen cadaver hand forearm specimens. Changes in the length of either side of this component were analysed during forearm rotation with the complete three-dimensional structure of the TFCC preserved. The proximal ligamentous component consists of three portions: dorsal, central and palmar. The dorsal and palmar portions connect the radius and ulna directly. These were recognized in all specimens whereas the central portion was not constant. The morphology of the proximal component was categorized into three types: fan-shaped, V-shaped, and funnel-shaped in five wrists each. Changes in ligament length during forearm rotation were measured using fine wires under slight tension that paralleled the ligaments from origin to insertion. The dorsal and palmar portions demonstrated three trends: the dorsal portion increased in length from supination to pronation whereas the palmar portion increased in length from pronation to supination; the length of the dorsal portion remained almost constant as the palmar portion increased in length from pronation to supination; the length of the palmar portion remained almost constant while the dorsal portion lengthened from supination to pronation. These variations appear to be related to which portion of the ligament was attached nearest to the centre of the ulnar fovea, where the rotational axis of the forearm passes. The portion attaching nearest to the fovea demonstrated a nearly isometric length pattern, whereas the portion which attached at a distance showed greater extensibility. These findings suggest that the proximal component of the TFCC corresponds to a true radioulnar ligament, and the isometric and eccentric fibres act mutually during forearm rotation.     

The role of the distal radioulnar ligaments, interosseous membrane, and joint capsule in distal radioulnar joint stability

The individual contribution of the distal radioulnar ligaments to dorsal and palmar translational stability during forearm rotation remains controversial. Furthermore, the role of the distal radioulnar joint capsule as a restraint and contributor to stability has not been investigated. A biomechanical study was performed in 11 fresh cadaver specimens to simultaneously measure dorsal and palmar radioulnar ligament tension. Joint rotation and radial translation were measured after sequential excision of the disk, interosseous membrane, joint capsule, and radioulnar ligaments. Results confirmed that the dorsal ligament tightens during pronation while the palmar ligament becomes progressively lax; the converse occurred during supination. Translational stability remained intact at all positions throughout the sectioning sequence until one of the radioulnar ligaments was sectioned. The most significant increases in translation occurred after sectioning the dorsal radioulnar ligament in pronation and after sectioning the palmar radioulnar ligament in supination. Forearm rotation increased significantly after excising either hemicapsule.     

Contribution of the interosseous membrane to distal radioulnar joint constraint

PURPOSE: Although forearm injuries are accompanied frequently by rupture to the interosseous membrane (IOM) diagnosis of the extent of IOM injury is difficult. In this study we evaluated distal radioulnar joint (DRUJ) laxity caused by both partial and complete IOM disruption and compared these quantitative measurements with the common clinical manual evaluation of DRUJ laxity and dislocatability. METHODS: Human cadaveric forearms (n = 8) were used in this study. Skin, muscles, and tendons were removed. The specimens were mounted on an experimental apparatus that allowed the radius to move freely about the fixed ulna. Tests were performed in neutral rotation, 60 degrees pronation, and 60 degrees supination. Under various conditions of IOM sectioning testing was performed by volary and dorsally translating the radius relative to the ulna in the coronal plane of the radius. Testing was performed both qualitatively as would be performed in the clinic and quantitatively with an instrumented probe. RESULTS: Our results show that dorsal dislocation of the radius relative to the ulna strongly suggests distal IOM rupture. Disengagement of the radius from the DRUJ indicated injury to the distal and middle IOM. The distal IOM constrained volar and dorsal laxity of the radius at the DRUJ in all forearm rotation positions. The midportion of the IOM constrained laxity except in the volar direction of the pronated forearm. The proximal IOM did not constrain the proximal radius except dorsally for the pronated forearm position. CONCLUSIONS: The IOM, in particular the distal IOM, plays an important role in constraining dorsal dislocation of the radius at the DRUJ.     

Preventing recurrence of radioulnar synostosis with pedicled adipofascial flaps

The surgical treatment of post-traumatic radioulnar synostosis is difficult. Recurrence after resection alone is a concern with poor long-term maintenance of forearm rotation. We report on the use of pedicled adipofascial flaps to prevent recurrence and facilitate maintenance of movement in six adult patients with radioulnar synostosis. Five involved the proximal radioulnar joint and one the distal radioulnar joint. In four the flap was based on the radial artery and in two on the posterior interosseous artery. Mean intraoperative supination was 78° and pronation was 76°. Mean follow up was 32 months. At follow-up, mean supination was 71° and pronation was 70°. No patient had radiological recurrence of synostosis. The only complication was a transient posterior interosseous nerve palsy. Pedicled adipofascial flaps are a safe addition to resection alone which may prevent recurrence and maintain the range of forearm rotation achieved at operation.     

A mechanical study of the moment-forces of the supinators and pronators of the forearm

We determined the torque generated by the muscles rotating the forearm at varying degrees of pronation and supination. We used 8 human cadaveric upper extremity specimens with the humerus and ulna rigidly fixed with the elbow in 90 degrees of flexion, while free rotation of the radius around the ulna was allowed. The tendons of the flexor carpi ulnaris (FCU), extensor carpi ulnaris (ECU), supinator, biceps, pronator teres (PT), and the pronator quadratus' (PQ) superficial and deep heads were isolated. After locking the forearm at intervals of 10 degrees from 90 degrees of pronation to 90 degrees of supination, we loaded each muscle/tendon with a ramp profile. We found that the biceps and supinator are both active supinators, the biceps generating four times more torque with the forearm in a pronated position. As for pronation, the PT and both heads of the PQ are active throughout the whole rotation, being most efficient around the neutral position of the forearm. The ECU and FCU contribute significantly less to pronation and supination torque. However, they do generate potential pronating torque while the forearm is positioned maximally in supination and, to a lesser extent, potential supination torque while the forearm is positioned maximally in pronation.     

Salvage of the unstable Sauvé-Kapandji procedure: a new technique

The Sauvé-Kapandji procedure has been commonly performed in the setting of posttraumatic osteoarthritis of the distal radioulnar joint. A recognized complication is instability of the proximal ulnar stump, which may occur in up to 33% of cases. Salvage of the failed Sauvé-Kapandji procedure in this setting is difficult and can sometimes involve sacrifice of forearm rotation. We report the results of 3 cases of a new salvage procedure in this setting. The radioulnar pseudarthrosis was taken down; ulnar continuity was restored with an intercalary graft; and forearm rotation was restored with matched hemiresection and interposition arthroplasty at the site of previous radioulnar fusion. Postoperatively, all patients achieved good forearm rotation (mean supination, 60 degrees; mean pronation, 65 degrees), had no symptoms of instability, and were satisfied with the results of the procedure. Disabilities of the Arm, Shoulder and Hand scores improved from preoperative mean of 55 to postoperative mean of 18.     

Forearm rotation in healthy adults of all ages and both sexes

Factors such as sex, age, or hand dominance are supposed to influence forearm rotation; however, available data are scarce. This study therefore analyzed range of active supination and pronation bilaterally in 752 healthy white adults (age range, 20-95 years) of both sexes. Range of supination was higher than pronation. Range of forearm rotation was comparable between both sides, but it was higher in women than in men and inversely correlated with age. In contrast with women, where range started to decrease during the fifth decade of life, onset was later in men (seventh decade). No influence was observed with respect to hand dominance or constitutional variations. Thus, the contralateral side serves for clinical comparison independent from age, sex, hand dominance, or constitutional variances. The fact that several patients with a major limitation of pronation considered themselves healthy, but only 1 patient with limited supination did so, indirectly underlines the importance of restoring deficits of supination rather than pronation.