A biomechanical evaluation of the relative load change in the joints of the wrist with ulnar shortening: a 'handbag' model

A finite element model to investigate the effect of ulnar variance on distal radioulnar joint mechanics

Ulnocarpal impaction syndrome involves excessive loading of the ulnocarpal joint. Ulnar shortening osteotomies are an effective way to reduce ulnocarpal loading but alter contact mechanics at the distal radioulnar joint (DRUJ). This study used a computational model to investigate the relationship between ulnar length and DRUJ mechanics. Detailed, finite element models of the radius and ulna bones were constructed from magnetic resonance imaging data. The length of the ulna bone model was increased and decreased up to 5 mm in 1 mm increments. A computational model was used to predict joint contact at the DRUJ for each ulnar length. Lengthening the ulna caused a slight decrease in DRUJ contact pressure, with a more substantial decrease in contact area. Shortening the ulna caused a substantial increase in contact area, with a smaller increase in DRUJ contact pressure. The location of contact on the radial sigmoid notch changed with 2 mm lengthening and 3 mm shortening. The results of this study demonstrate the sensitivity of DRUJ contact to ulnar length changes, which may explain the DRUJ cartilage degeneration that often follows ulnar osteotomies. The joint contact model implemented in this study allowed the relationship between ulnar length and DRUJ contact to be examined systematically, in a way that is difficult to achieve through cadaveric experimentation. The results confirmed published experimental data showing an increased DRUJ contact pressure with ulnar shortening. It is important that clinicians consider the influence of ulnar osteotomies, not only on ulnocarpal loading but also on DRUJ mechanics. Copyright © 2016 John Wiley & Sons, Ltd.

Examining the influence of distal radius orientation on distal radioulnar joint contact using a finite element model

Distal radius malunion is a problem that is common to distal radius fractures and can affect the contact mechanics of the distal radioulnar joint (DRUJ). The goal of this study was to use a computational model of the DRUJ to investigate the influence distal radius orientation has on its contact mechanics. Detailed, finite element models of the radius and ulna bones were constructed from magnetic resonance imaging data. The orientation of the distal radius was rotated in 2° increments about three orthogonal axes representing dorsal-palmar rotation, radial-ulnar rotation and anteversion-retroversion. A computational model was used to predict joint contact at the DRUJ in each condition. Joint contact was found to be most sensitive to dorsal rotation of the distal radius, while radial and ulnar rotation did not substantially affect joint contact pressure. Slight retroversion was found to lower joint contact pressure. In most cases, more than 6° rotation in a given direction resulted in dislocation of the DRUJ, so that adaptation at the joint would be required to maintain articular contact. The joint contact model implemented in this study allowed the relationship between distal radius orientation and DRUJ contact to be examined systematically, in a way that is difficult to achieve using a cadaver-based approach. The results demonstrated the distal radius displacements most critical for maintaining healthy joint mechanics at the DRUJ. It is important that clinicians consider the influence of distal radius malunion and its treatment on DRUJ mechanics, in addition to its consequences for wrist function and forearm rotation. Copyright © 2016 John Wiley & Sons, Ltd.

Distal Radioulnar Joint Reaction Force Following Ulnar Shortening: Diaphyseal Osteotomy Versus Wafer Resection

PURPOSE

To compare how ulnar diaphyseal shortening and wafer resection affect distal radioulnar joint (DRUJ) joint reaction force (JRF) using a nondestructive method of measurement. Our hypothesis was that ulnar shortening osteotomy would increase DRUJ JRF more than wafer resection.

METHODS

Eight fresh-frozen human cadaveric upper limbs were obtained. Under fluoroscopic guidance, a threaded pin was inserted into the lateral radius orthogonal to the DRUJ and a second pin was placed in the medial ulna coaxial to the radial pin. Each limb was mounted onto a mechanical tensile testing machine and a distracting force was applied across the DRUJ while force and displacement were simultaneously measured. Data sets were entered into a computer and a polynomial was generated and solved to determine the JRF. This process was repeated after ulnar diaphyseal osteotomy, ulnar re-lengthening, and ulnar wafer resection. The JRF was compared among the 4 conditions.

RESULTS

Average baseline DRUJ JRF for the 8 arms increased significantly after diaphyseal ulnar shortening osteotomy (7.2 vs 10.3 N). Average JRF after re-lengthening the ulna and wafer resection was 6.9 and 6.7 N, respectively. There were no differences in JRF among baseline, re-lengthened, and wafer resection conditions.

CONCLUSIONS

Distal radioulnar joint JRF increased significantly after ulnar diaphyseal shortening osteotomy and did not increase after ulnar wafer resection.

CLINICAL RELEVANCE

Diaphyseal ulnar shortening osteotomy increases DRUJ JRF, which may lead to DRUJ arthrosis.

Distal radius malunion increases risk of persistent disability 2 years after fracture: a prospective cohort study

BACKGROUND

Studies concerning the relationship between distal radius fracture malunion and a persistent arm-related disability have produced conflicting results.

QUESTIONS/PURPOSES

We investigated (1) how arm-related disability changes during the first 2 years after a fracture and (2) whether fracture malunion causes persistent disability.

METHODS

One hundred twenty-three patients with distal radius fractures, treated with closed reduction and casts or external or percutaneous pin fixations, completed the DASH questionnaire at baseline, 3 months, 6 months, 1 year, and 2 years after fracture. Radiographic measurements were made at 1 year. Using a definition of malunion as ulnar variance of 1 mm or more and dorsal tilt greater than 10°, the patients were classified into three groups: no malunion (n = 35), malunion involving either ulnar variance or dorsal tilt (n = 65), and malunion involving ulnar variance and dorsal tilt (n = 23). The changes in the DASH scores with time (baseline to 2 years), in relation to malunion, were analyzed using generalized estimating equations adjusted for age, sex, fracture type (extraarticular or intraarticular), and treatment method.

RESULTS

The mean change in DASH scores from baseline to 2 years was worse for patients with malunions involving ulnar variance and dorsal tilt than for patients with no malunions (mean difference, 13; 95% CI, 1.4-25) and for patients with malunions involving either ulnar variance or dorsal tilt (mean difference, 13; 95% CI, 2.2-24).

CONCLUSION

After distal radius fracture, arm-related disabilities are more likely to persist at least 2 years in patients with fractures that healed with shortening and dorsal angulation than in patients with only shortening or dorsal angulation or without malunion.

Management of forearm deformities with ulnar shortening more than 15 mm caused by hereditary multiple osteochondromas

BACKGROUND

Treatment for forearm deformities caused by hereditary multiple osteochondromas is still controversial. The purpose of the study was to describe the outcome of treatment with the combined use of ulnar lengthening and excision of osteochondromas.

METHODS

Fourteen patients with hereditary multiple osteochondromas had forearm deformities which belongs to type I Masada deformity. The mean relative ulnar shortening was 19.9 mm (range, 16-23). All patients ranging from 4 to 15 years old had operative treatment. Clinical evaluation involving the assessment of pain, activities of daily living, and range of motion of the wrist and forearm was performed. The radiographic evaluation was relative ulnar shortening (RUS), radial articular angle (RAA), carpal slip (CS), and radial bowing. Besides, we also evaluated the amount of ulnar lengthening, external fixation time, and external fixation index.

RESULTS

The mean EFT was 101 days (range, 84-133), and the mean external fixation index was 44.4 days/cm (range, 33.6-51.2). During the mean 43.1 months follow-up, four patients had mild pain and two patients had mild restriction of daily activities. The rotation of forearm and motion of wrist had increased except in Case 3. The RAA, CS, and radial bowing had been improved except in Case 6 and 7. In all patients, relative ulnar shortening had been corrected. According to the functional evaluation criteria recommended by Krimmer, there were ten excellent and four good.

CONCLUSIONS

The combined use of ulna lengthening and excision of osteochondromas is a proper and effective treatment method to the type I Masada deformity with the relative ulnar shortening more than 15 mm.