Aims. The aim of this study was to investigate the difference in functional outcome after repair and non-repair of the pronator quadratus muscle in patients undergoing surgical treatment for a distal radial fracture with volar plating. Patients and Methods. A total of 72 patients with a distal radial fracture were included in this randomized clinical trial. They were allocated to have the pronator quadratus muscle repaired or not, after volar locked plating of a distal radial fracture. The patients, the assessor, the primary investigator, and the statistician were blinded to the allocation. Randomization was irreversibly performed using a web application that guaranteed a secure and tamper-free assignment. The primary outcome measure was the Patient Rated Wrist Evaluation (PRWE) after 12 months. Secondary outcomes included the Disabilities of the Arm, Shoulder and Hand (DASH) score, pronation strength, grip strength, the range of pronation and supination, complications, and the operating time. Results. Of the 72 patients, 63 (87.5%) completed follow-up for the primary outcome measure: 31 (86.1%) from the non-repair group and 32 (88.9%) from the repair group. At the 12-month follow-up, the mean difference in PRWE of 5.47 (95% confidence interval (CI) -4.02 to 14.96) between the repair (mean 18.38 (95% CI 10.34 to 26.41)) and non-repair group (mean 12.90 (95% CI 7.55 to 18.25)) was not statistically significant (p = 0.253). There was a statistically significant difference between pronation strength, favouring non-repair. We found no difference in the other secondary outcomes. Conclusion. We found that repairing pronator quadratus made no difference to the clinical outcome, 12 months after volar plating of a distal radial fracture. We conclude that there is no functional advantage in repairing this muscle under these circumstances and advise against it. Cite this article: Bone Joint J 2019;101-B:1498–1505

We have performed a form of lunate replacement arthroplasty, which included excision of the lunate and insertion of a vascularised radial bone flap wrapped in pronator quadratus, for stage IIIB or stage IV Kienböck’s disease, in 41 patients who have been followed up for more than three years. All patients reported an improvement in their symptoms, and 20 of the 41 became free of pain after the operation. Extension and flexion of the wrist were increased by a mean of 9° and 6°, respectively (p < 0.05). The radioscaphoid angle and the carpal height ratio were not significantly changed and only minimal deterioration was observed due to degenerative change. The size, density or location of the inserted bone did not change with time. A vascularised radial bone flap wrapped in pronator quadratus can be a reliable treatment option for advanced Kienböck’s disease, when the pedicled bone and muscle envelope acts as a stable spacer for the excised lunate

Delayed union or non-union of the scaphoid was treated by a bone graft on a pronator quadratus pedicle in eight cases. This produced earlier union than the Russe procedure. The procedure is simple and is recommended for old un-united scaphoid fractures

Increased use of locking volar plates for distal radius fractures led to a number of reports in literature of flexor tendon injuries from impingement and attrition against hardware. Repair of the pronator quadratus is critical in preventing tendon injury. We present a pronator quadratus sparing approach to the distal radius. The senior author has used a pronator quadratus sparing lateral pillar approach for for the past five years. A lateral incision is used over the radial styloid. The first dorsal compartment is released and APL and EPB tendons retracted. The underlying brachio-radialis tendon and insertion fascia is split and the palmar portion elevated off the distal radius with the pronator quadratus as a single contiguous sheet. The distal edge of the pronator quadratus is elevated from the wrist capsule by sharp dissection. The radial artery is protected by the retracted tissue. Repair of the brachio-radialis tendon and insertion fascia is much more robust than that of the pronator quadratus covering the entire plate. Since 2004, the senior author has used the pronator quadratus sparing approach for volar plating of the distal radius, in 183 cases. At last follow-up there were no instances of flexor tendon injury, which was considered to be one of the outcome measures and end-points. There was no impingement in the first dorsal compartment, except in two cases of lateral pillar hardware impingement from additional lateral pillar plate fixation through the same approach. Nine cases had minor persistent superficial radial nerve parasthesia. One case had a superficial wound infection requiring drainage. The repaired pronator quadratus formed a barrier protecting the plate. The infection was aggressively treated and the plate left in situ for three months till fracture union. Cultures from the retrieved plate showed no organisms. Another implant had two of the locking screws back out. The pronator quadratus fascia was tented with an underlying haematoma. The fascia however only showed minimum screw penetration and no flexor tendon injury. Average wrist dorsiflexion was 72 deg and palmar flexion 65 deg. Average pronation was 81 deg and average supination 69 deg. Supination range was slow to recover in younger patients. One explanation could be the tight pronator quadratus repair. Average PRWE and DASH scores were 19. The quadratus sparing approach to the volar distal radius is easy to perform and protects the flexor tendons at the wrist. Cases demonstrated that an intact pronator quadratus can act as an effective barrier to prominent hardware and superficial infection. Supination range may be reduced by this approach due to a tight repair, though a palmar DRUJ capsule contracture may also be an explanation

The April 2024 Wrist & Hand Roundup. 360. looks at: Lunocapitate versus four-corner fusion in scapholunate or scaphoid nonunion advanced collapse: a randomized controlled trial; Postoperative scaphoid alignment, smoking, and avascular necrosis determine outcomes; Grip strength signals broader health concerns in females with distal radius fractures; Clearing the smoke: how smoking status influences recovery from open carpal tunnel release surgery; Age matters: assessing the likelihood of corrective surgery after distal radius fractures; Is pronator quadratus muscle repair required after anterior plate fixation for distal radius fractures?; Efficacy of total wrist arthroplasty: a comparative analysis of inflammatory and non-inflammatory arthritis outcomes; A comprehensive review of the one-bone forearm as a salvage technique

Aims. The aim of this study was to investigate surgeons’ reported change of treatment preference in response to the results and conclusion from a randomized contolled trial (RCT) and to study patterns of change between subspecialties and nationalities. Methods. Two questionnaires were developed through the Delphi process for this cross-sectional survey of surgical preference. The first questionnaire was sent out before the publication of a RCT and the second questionnaire was sent out after publication. The RCT investigated repair or non-repair of the pronator quadratus (PQ) muscle during volar locked plating of distal radial fractures (DRFs). Overall, 380 orthopaedic surgeons were invited to participate in the first questionnaire, of whom 115 replied. One hundred surgeons were invited to participate in the second questionnaire. The primary outcome was the proportion of surgeons for whom a treatment change was warranted, who then reported a change of treatment preference following the RCT. Secondary outcomes included the reasons for repair or non-repair, reasons for and against following the RCT results, and difference of preferred treatment of the PQ muscle between surgeons of different nationalities, qualifications, years of training, and number of procedures performed per year. Results. Of the 100 surgeons invited for the second questionnaire, 74 replied. For the primary outcome, six of 32 surgeons (19%), who usually repaired the PQ muscle and therefore a change of treatment preference was warranted, reported a change of treatment preference based on the RCT publication. Of the secondary outcomes, restoring anatomy was the most common response for repairing the PQ muscle. Conclusion. The majority of the orthopaedic surgeons, where a change of treatment preference was warranted based on the results and conclusion of a RCT, did not report willingness to change their treatment preference. Cite this article: Bone Joint Open 2020;1-9:549–555

The December 2013 Wrist & Hand Roundup. 360 . looks at: Scapholunate instability; three-ligament tenodesis; Pronator quadratus; Proximal row carpectomy; FPL dysfunction after volar plate fixation; Locating the thenar branch of the median nerve; Metallosis CMCJ arthroplasties; and timing of flap reconstruction

We conducted an anatomical study to determine the best technique for transfer of the anterior interosseous nerve (AIN) for the treatment of proximal ulnar nerve injuries. The AIN, ulnar nerve, and associated branches were dissected in 24 cadaver arms. The number of branches of the AIN and length available for transfer were measured. The nerve was divided just proximal to its termination in pronator quadratus and transferred to the ulnar nerve through the shortest available route. Separation of the deep and superficial branches of the ulnar nerve by blunt dissection alone, was also assessed. The mean number of AIN branches was 4.8 (3 to 8) and the mean length of the nerve available for transfer was 72 mm (41 to 106). The transferred nerve reached the ulnar nerve most distally when placed dorsal to flexor digitorum profundus (FDP). We therefore conclude that the AIN should be passed dorsal to FDP, and that the deep and superficial branches of the ulnar nerve require approximately 30 mm of blunt dissection and 20 mm of sharp dissection from the point of bifurcation to the site of the anastomosis. The use of this technique for transfer of the AIN should improve the outcome for patients with proximal ulnar nerve injuries. Cite this article: Bone Joint J 2014;96-B:789–94

The December 2012 Wrist & Hand Roundup. 360. looks at: the imaging of scaphoid fractures; splinting to help Dupuytren’s disease; quality of life after nerve transfers; early failure of Moje thumbs; electra CMCJ arthroplasty; proximal interphalangeal joint replacement; pronator quadratus repair in distal radius fractures; and osteoporosis and wrist fractures

The aim of this study was to investigate surgeons’ reported change of treatment preference in response to the results and conclusion from a randomized controlled trial (RCT) and to study patterns of change between subspecialties and nationalities. Two questionnaires were developed through the Delphi process for this cross-sectional survey of surgical preference. The first questionnaire was sent out before the publication of a RCT and the second questionnaire was sent out after publication. The RCT investigated repair or non-repair of the pronator quadratus (PQ) muscle during volar locked plating of distal radial fractures (DRFs). Overall, 380 orthopaedic surgeons were invited to participate in the first questionnaire, of whom 115 replied. One hundred surgeons were invited to participate in the second questionnaire. The primary outcome was the proportion of surgeons for whom a treatment change was warranted, who then reported a change of treatment preference following the RCT. Secondary outcomes included the reasons for repair or non-repair, reasons for and against following the RCT results, and difference of preferred treatment of the PQ muscle between surgeons of different nationalities, qualifications, years of training, and number of procedures performed per year. Of the 100 surgeons invited for the second questionnaire, 74 replied. For the primary outcome, 6 of 32 surgeons (19%), who usually repaired the PQ muscle and therefore a change of treatment preference was warranted, reported a change of treatment preference based on the RCT publication. Of the secondary outcomes, restoring anatomy was the most common response for repairing the PQ muscle. The majority of the orthopaedic surgeons, where a change of treatment preference was warranted based on the results and conclusion of a RCT, did not report willingness to change their treatment preference

Introduction: Distal radius metaphyseal fractures in children are not uncommon, but when they occur proximal to the insertion of the pronator quadratus muscle, reduction and maintenance of reduction can be challenging. The deforming forces at the fracture site result in pronation and shortening of the distal fragment. Manual manipulation of this fracture often results in tearing of the dorsal periosteum and hence renders this fracture highly unstable. Aim: We present a novel easily reproducible mini-open surgical technique and functionally and radiologically evaluate a series of eleven patients who have undergone this technique. Materials and Methods: The surgical technique consists of a mini-open intrafocal image intensifier guided reduction technique with percutaneous k-wiring fixation. Five males and six females with an average age of 8.8 years (range 5 to 13 years), who sustained a pronator quadratus distal radius fracture and subsequently underwent this surgical technique from 2005 to 2007, were evaluated both radiologically in terms of radial length, radial tilt and volar tilt compared with the contralateral limb and functionally using the Mayo Modified wrist score and the patient related wrist evaluation questionnaire. Results: Patients were followed up for an average of 18 months (range 2–31 months). All patients achieved clinical and radiological union. No patient required remanipulation for loss of reduction. Radiological outcome measures similar to contralateral limb with good functional scores. No complications were noted. All patients returned to preoperative level of function. Conclusion: This minimally invasive technique has been shown to be technically easy, reliable and reproducible with excellent results and low risk of displacement compared to other techniques used to treat this potentially challenging fracture

This study quantified the joint reaction forces in the distal radioulnar joint using an instrumented ulnar head replacement implant. Muscle activity was simulated in-vitro to determine the effects on joint reaction force. Forces were found to linearly increase with simulated muscle load in all forearm positions for the biceps and pronator teres muscles. However, this did not occur for simulations of the supinator and pronator quadratus muscles, likely due to their broader insertion, smaller size and non-linear lines-of-action. This work has important implications in forearm biomechanical modelling, implant design, fixation and rehabilitation protocols following arthroplasty. To determine the relationship between forearm muscle activity and joint reaction force (JRF) in the distal radioulnar joint (DRUJ). The DRUJ reaction force is linearly related to the muscle activity of the PT and biceps, but not necessarily to the activity of the supinator and PQ. This work has implications for biomechanical modelling, implant design, fixation and rehabilitation protocols following DRUJ arthroplasty. JRFs were found to increase linearly with muscle load for all muscles simulated (biceps, pronator teres (PT), pronator quadratus (PQ), supinator) in all forearm positions tested (supination, neutral and pronation) (correlation coefficient r> 0.85, p< 0.01) with two exceptions; simulation of the PQ in the neutral position (r=−0.65, p=0.2), and the supinator in the pronated position (r=0.72, p=0.2). Biceps simulation generated larger JRF magnitudes in all positions compared to other muscles (p< 0.001), and the PQ generated larger JRF magnitudes compared to the supinator (p=0.05). Ulnar head arthroplasty was performed with a replacement ulnar head implant instrumented with strain gauges to allow measurement of the DRUJ reaction force. An upper extremity joint simulator applied muscle loads in seven fresh frozen cadaveric upper extremities through computer-controlled pneumatic actuators. Load was varied in 10N increments from 10-80N (biceps and PT) and from 10-50N (PQ and supinator). A hand clamp was used to restrain the forearm in varying positions. The results illustrate that broad insertion and non-linear muscles may not be linearly correlated to joint reaction force in the DRUJ. Please contact author for diagrams and graphs

The influence of the supinator and pronator quadratus (PQ) muscles on distal radioulnar joint stability were evaluated using a joint simulator capable of producing forearm rotation, before and after ulnar head excision. Multiple pronation trials were conducted with incremental loading of the PQ relative to the pronator teres; supination trials were similarly conducted with the supinator and biceps. Incremental supinator muscle loading did not alter forearm kinematics. Increased PQ loading did not affect intact kinematics, but did alter joint motion following ulnar head excision. PQ activation will likely aggravate forearm instability following ulnar head excision; suggesting rehabilitation should incorporate immobilization in supination. The purpose of this study was to study the effect of pronator quadratus (PQ) and supinator loads on forearm kinematics in both an intact distal radioulnar joint (DRUJ) and following ulnar head excision. The PQ muscle appears to aggravate instability of the DRUJ following ulnar head excision, while incremental loading of the supinator muscle had no effect. Patients with DRUJ instability and/or who have undergone surgical removal of the ulnar head should be rehabilitated in supination to limit the influence of the PQ muscle. Eight cadaveric upper extremities were tested in a custom joint simulator employing motion and load-controlled tendon loading to produce forearm rotation. Pronation was achieved via loading of the pronator teres and PQ muscles. Repeated trials were conducted in which the ratio of the PQ load was increased incrementally relative to the pronator teres load. Supination trials were similarly conducted using the biceps and supinator muscles. Testing was conducted in the intact forearm and following ulnar head excision. An electromagnetic tracking device was used to record motion of the radius and ulna. Kinematic data was analyzed with a planar analysis that measured dorsal palmar displacements and diastasis of the DRUJ. Greater diastasis and dorsal translation of the radius relative to the ulna were noted under increased PQ loading following ulnar head excision (p< 0.05). Increased supinator load had no effect on kinematics before or after ulnar head excision. This effect is likely due to the location of the two muscles. The effect of PQ muscle loading was only noted in neutral to full pronation. These results suggest that rehabilitation of the forearm following ulnar head excision should be conducted with the forearm in supination to minimize joint instability. Funding: Natural Sciences and Engineering Research Council of Canada, The Arthritis Society (Canada)

Purpose: The Sauvé-Kapandji procedure is often performed for the treatment of posttraumatic degeneration of the distal radioulnar joint. Few studies have been devoted specifically to the proximal stump of the ulnar after this procedure. The aim of our study was to conduct a radioclinical evaluation of the dynamics of the proximal ulnar stump. Material and methods: This retrospective analysis involved fourteen patients (four women and ten men), mean age 48 years who underwent the procedure between January 1991 and March 2002. All presented posttraumatic degradation of the distal radioulnar joint. The operation took place twelve months after trauma on average. Mean ulnar resection was 11 mm, performed as distally as possible. The pronator quadratus was not advanced into the false joint. Pronation-supination rehabilitation exercises were instituted shortly after surgery. A static and dynamic x-rays protocol was designed for analysis. Results: Patients were reviewed at five years two months on average. There were two complications: fusion of the intentional ulnar pseudarthrosis and one pseudarthrosis of the distal radioulnar joint. Time to resumption of former activity was nine months on average. Two patients could not resume their former activity. Seven patients complained of mechanical pain at the ulnar resection. Three patients reported cracking sounds along the ulnar border of the wrist and two patients presented an objective snap during pronosupination. Clinically, the ulnar stump was unstable in the sagittal plan in all cases. Radiographs confirmed this instability. Clinically, there was also an instability in the frontal plane in three patients. The dynamic films did not confirm frontal instability. Discussion: Although less so than after the Darrach procedure, the proximal ulnar stump is the principle complication of the Savué-Kapandji procedure. Preservation of the structures stabilising the distal ulnar stump is crucial: periosteum, interosseous membrane, ulnar extensor of the carpus, pronator quadratus. Our use of a shorter resection made as distally as possible was only able to avoid a certain degree of instability which was nevertheless well tolerated. Conclusion: The Sauvé-Kapandji procedure provides very satisfactory results for pain and motion. All patients appeared to have some degree of distal ulnar stump instability which was as a rule well tolerated. Nevertheless, one patient required a revision for stabilisation. This instability remains an unsolved problem which apparently cannot be prevented even with a very rigorous technique

Lesions of the anterior interosseous nerve in the forearm are rare and often misdiagnosed as tendon injuries. A consecutive series of 13 patients with this condition referred for electrodiagnosis is reviewed. Only three had originally a correct clinical diagnosis and three were initially considered to have tendon ruptures. Five cases were of mechanical origin and seven due to ‘neuritis’. All showed electrophysiological abnormalities, most commonly involving the pronator quadratus. Late spontaneous recovery was common, and only one case had surgical exploration

Distal radius fractures are typical and frequent fracture of elderly woman with reduced bone density. Thus implant fixation is more difficult. Dorsal and radial comminution are frequent in these patients and so reduction and angle stable osteosynthesis needed. The angle stable plate, often also multidirectional is today the most common stabilisation device. Because of the introduction of bulky and bended implants as the Micronail or Targon DR wich require difficult opening of the bone with awles we decided to test the XS radius nail witch is a 4,5mm or 3,5mm straight nail and witch is introduced after guide wire placement and over drilling with a canulated drill of the same diameter. It is locked parallel to the joint in 3 different directions with angular stability with threaded wires. Methods 16 radius sawbones were osteotomised corresponding to a A3 Fracture and stabilised with a angle stable plate (8) and XS nail (8). 1000 alternating load cycles from 20–200N were performed and the deformation was registered. Also a FE analysis with the MSC Patran/Marc softwere were performed. Also the calculated deformation in the FE study was 20% lower. Also deformation amplitude was lower with 0.31mm compared to 0.42mm in the plate group. The differences however were not significant. Both devices show good biomechanical results. The XS nail has the advantage of mainly intraosseus position, simple operation technique with introduction over a guide wire from the proc. Styloideus radii and over drilling with a canulated drill of the same size. The exposure of the N rad. superf. must be performed. First clinical evaluation is presented. Due to the results we developed a anatomically adapted XS radius nail. The results of the first 100 patients are presented. Conclusions. Both angular stable plate and XSR nail can be used in unstable distal radius fracture fixation. The mainly intraosseus position of the nail and saving of the pronator quadratus as well as lower deformation are in favour of the XSR nail. However frontal plane fractures and very comminuted fractures are better treated with a multidirectional locking plate due to technical reasones so that we use the XSR nail mainly in A3 and C1 fractures

Purpose of the study: Defective reduction and secondary displacement after osteosynthesis of distal radius fractures can compromise wrist function. Volar locking plates enable solid fixation which remains stable over time but section of the pronator quadrates necessary for the anterior approach raises the risks of destabilising the distal radioulnar joint and loss of pronation force. Our study was designed to evaluate recovery of grip, pronation and supination force after volar locking plate fixation. Material and methods: This was a prospective study of 29 fractures of the distal radius with dorsal displacement fixed with a volar locking plate in 28 patients (17 men, 11 women, mean age 48.75 years) from January 2007 to May 2008. The quality of the pronator quadrates suture was assessed at the end of the operation. The assessment included the classical parameters of wrist movement, the Herzberg and Dumontier score, radial slope and ulnar variance on the ap and lateral views of the wrist, and recovery of grip, pronation and supination force compared with the opposite side using an ambulatory device. Results: The pronator quadratus suture was considered solid in eight cases, precarious in seven. Complete suture was not possible in 14 cases. At mean follow-up of 10 months, patients had on average recovered 77% of the grip force, 74% of the pronation force, and 76% of supination force, compared with the opposite side. Complications included one defective reduction, one secondary displacement (by defective plate position), two dystrophy syndromes, and four posttrauma carpal tunnel syndromes. Discussion: The literature shows that volar plate fixation enables recovery of 74% to 84% of grip force. Few studies have examined the recovery of pronosupination and none have described results after osteosynthesis for fracture. Our study did not find that section of the pronator quadrates, a muscle difficult to suture, had a deleterious effect. Conclusion: Osteosynthesis using a volar locking plate for distal fractures of the radius remains a controversial issue. Study of recovery of the grip, pronation and supination force did not reveal any prejudice attributable to this technique

Purpose: Open reduction internal fixation with a volar plate is a popular surgical option for distal radius fractures. The pronator quadratus (PQ) must be stripped from the distal radius in this procedure. PQ is an important pronator of the forearm and stabilizer of the distal radioulnar joint. The purpose of this study was to investigate pronation torque in healthy volunteers before and after temporary paralysis of the PQ with lidocaine under EMG guidance. Method: A custom-made apparatus was built to allow isometric testing of pronation torque at 5 positions of rotation: 90° of supination, 45° of supination, neutral, 45° of pronation and 80° of pronation. It was validated using a test-retest design with 10 subjects. For the study, 17 (9 male, 8 female) right hand dominant volunteers were recruited. They were tested at all 5 positions in random order and then had their PQs paralyzed with lidocaine. Repeat testing was performed in the same random order 30 minutes after injection. Three subjects underwent unblinded testing with saline injected instead of lidocaine. Results: After paralysis of PQ with lidocaine, pronation torque decreased by 23.2% (p=0.0010) at 90° of supination, 16.7% (p=0.0001) at 45° of supination, 22.9% (p=0.0002) in the neutral position, 20.4% (p=0.0066) at 45° of pronation and 22.2% (p=0.0754) at 80° of pronation. All were statistically significant except 80° of pronation. Peak torque values before and after injection were highest in the supinated positions (8.2 Nm at 45° supination) and decreased gradually as the subjects were in more pronated positions (1.8 Nm at 80° pronation). The test-retest trial demonstrated no evidence of fatigue with repeated testing. The subjects who underwent injection of saline demonstrated no evidence of pronation torque loss secondary to pain or a pressure effect of the injectate. Conclusion: This study demonstrated a significant decrease in pronation torque with controlled elimination of PQ function. Open reduction internal fixation of distal radius fractures damages the PQ. This may result in a pronation torque deficit. Functional significance of this loss should be shown. Pronation torque measurement may add to postoperative outcome analysis of surgical procedures about the wrist

Change in forearm muscle length can be used to predict muscle function during pronosupination. In ten fresh cadaveric specimens, markers were placed at fifteen muscle origins and insertions. The forearm was positioned at 10° increments from 80° of pronation to 90° of supination with the elbow flexed at 90°. An electromagnetic tracking system was used to digitally collect 3D origin and insertion coordinates. These coordinates were used to create a vector representing muscle length as a straight line from the muscle origin to the muscle insertion. To normalize the data, all lengths were normalized as a percentage of the maximum muscle length for each specimen. Differences in the data were determined through paired t-test analysis. The muscles which exhibited a significant decrease in length from pronation to supination throughout the entire range were the biceps brachii and the palmaris longus. Muscles exhibiting a significant increase over the range were the pronator teres at both the humeral and ulnar origins as well as the pronator quadratus. The brachialis also exhibited an increase, though not as pronounced. The supinator, extensor indicis and the extensor carpi ulnaris all exhibited maximum length at the neutral position while length decreased in both pronation and supination directions. The only muscle to exhibit minimal length at neutral with increasing length in each direction was the brachioradialis. The extensor carpi radialis longus kept a consistent length during pronation and increased during supination. Muscles that remained consistent during pronation but decreased their length during supination included the extensor policis longus, the flexor carpi ulnaris, and the radial and ulnar origins of the abductor policis longus. The extensor carpi radialis brevis and the flexor carpi radialis exhibited no significant change in muscle length during forearm rotation. Forearm Rotation involves a complex interaction between the Radius and Ulna. Multiple muscles traverse the forearm en route to the hand. Many muscles change significantly in length during pronosupination. These muscles. Must adapt to this change in length to allow coordinated Upper Extremity function. Produce a force vector stressing the Distal and Proximal Radioulnar joints. Assist with Forearm Motion. Clinical Relevance- Rehabilitation following Injury needs to take into account the effect of forearm rotation, Splint position may vary depending on which Muscle or Tendon is injured, Surgical Procedures and Implants need to be designed to take into account transverse and longitudinal forces on the forearm