Ulnar variance: its relationship to ulnar foveal morphology and forearm kinematics

Covariation between wrist bone morphology and maximal range of motion during ulnar deviation and supination in extant nonhuman primate taxa

This study investigates the maximal range of motion (ROM) during wrist deviation and forearm rotation for five different primate genera and the possible correlation with the shape of the distal ulna, triquetrum and hamate. A two-block phylogenetic partial least square analysis was performed to test this covariation in a phylogenetic context, using shape coordinates and a matrix of maximal ROM data as input data. The results show that gibbons have the highest ROM for both ulnar deviation and supination, whereas Macaca exhibited the lowest ROM for supination, and Pan had the lowest ROM for ulnar deviation. These results can be attributed to differences in locomotor behaviour, as gibbons need a large wrist mobility in all directions for their highly arboreal lifestyle, whereas Macaca and Pan need a stable wrist during terrestrial locomotion. However, we found no correlation between distal ulna/triquetrum/hamate shape and maximal ROM during ulnar deviation and supination in the different primate taxa. A larger dataset, in combination with behavioural and biomechanical studies, is needed to establish form-function relationships of the primate hand, which will aid the functional interpretation of primate fossil remains.

Malunion deformity of the forearm: Three-dimensional length variation of interosseous membrane and bone collision

It remains unclear to what extent the interosseous membrane (IOM) is affected through the whole range of motion (ROM) in posttraumatic deformities of the forearm. The purpose of this study is to describe the ligament- and bone-related factors involved in rotational deficit of the forearm. Through three-dimensional (3D) kinematic simulations on one cadaveric forearm, angular deformities of 5° in four directions (flexion, extension, valgus, varus) were produced at two locations of the radius and the ulna (proximal and distal third). The occurrence of bone collision in pronation and the linear length variation of six parts of the IOM through the whole ROM were compared between the 32 types of forearm deformities. Similar patterns could be observed among four groups: 12 types of deformity presented increased bone collision in pronation, 8 presented an improvement of bone collision with an increase of the mean linear lengthening of the IOM in neutral rotation, 6 had an increased linear lengthening of the IOM in supination with nearly unchanged bone collision in pronation and 6 types presented nearly unchanged bone collision in pronation with a shortening of the mean linear length of IOM in supination or neutral rotation. This kinematic analysis provides a better understanding of the ligament- and bone-related factors expected to cause rotational deficit in forearm deformity and may help to refine the surgical indications of patient-specific corrective osteotomy.

Bone Morphology in Ulnar Impaction Syndrome: A Radiographic Evaluation

Background: Positive ulnar variance (UV) may be associated with a higher incidence of ulnar impaction syndrome (UIS). However, neutral and/or negative UV has also been associated with the development of UIS; therefore, other risk factors may be involved. The purpose of this study was to compare radiological bone morphology in patients with UIS and asymptomatic controls. Methods: Between 2009 and 2018, posteroanterior wrist radiographs of 47 wrists in 45 patients diagnosed with UIS were compared with those of 163 wrists in 93 asymptomatic patients from the control group. The following parameters were obtained: ulnar variance (UV); ulnar head top-fovea distance (UTFD); capitate-triquetrum distance (CTD); radio-lunate distance (RLD) and lunate coverage ratio (LCR). The morphology of the lunate was classified based on the absence (type I) or presence (type II) of a medial facet that articulates with the hamate. The radiographic parameters and lunate types were compared between the two groups. We then divided the groups into two subgroups: the positive UV subgroup and the neutral/negative UV subgroup. In each subgroup, the radiographic parameters and lunate types were compared between the UIS and control groups. Results: In the UIS group, the UV and UTFD were significantly increased compared to those in the control group. The proportion of type II lunates was significantly higher in the UIS group than in the control group. In addition, the type II lunate was more common in the UIS group in both the positive UV and negative UV groups. Conclusions: Our study suggests that in addition to positive UV, ulnar head morphology with an increased UTFD and type II lunate morphology may be associated with the development of ulnar impaction syndrome. Level of Evidence: Level III (Diagnostic).

Load-Bearing Radioulnar Distances to Evaluate an Unstable Distal Radioulnar Joint in Patients With Triangular Fibrocartilage Complex Tears

PURPOSE

Tears of the proximal component of the triangular fibrocartilage complex (pc-TFCC) lead to instability in the distal radioulnar joint. The aim of this study was to measure the load-bearing radioulnar distances (RaUls) and to evaluate its diagnostic suitability in patients with pc-TFCC tears.

METHODS

We retrospectively assessed and compared the lateral wrist radiographs of 61 adult patients with arthroscopically confirmed tears of pc-TFCC with those of a control group of 64 healthy participants. The RaUl was measured on lateral radiographs, and the difference in RaUl (D-value) between load-bearing and nonloading conditions was calculated in the 2 groups. Receiver operator characteristic curves were plotted to determine the diagnostic accuracy and optimal cutoff-score of load-bearing RaUl and RaUl D-value. The diagnostic performance was verified in a validation sample of patients (30 wrists) with pc-TFCC tears and a control group of healthy individuals (30 wrists).

RESULTS

In the training sample, load-bearing RaUls of the affected wrists were higher than the same side of the controls (12.0 mm vs 7.1 mm). The TFCC-injury group showed a significantly higher RaUl D-value than the control group (8.5 mm vs 3.4 mm). Using a receiver operator characteristic curve, the cutoff value of load-bearing RaUl was 10 mm (sensitivity = 97.6%, specificity = 85.7%) and that of RaUl D-value was 6.5 mm (sensitivity = 90.2%, specificity = 78.5%). The areas under the curve of load-bearing RaUl and RaUl D-value were 0.96 and 0.88, respectively. In the test sample, the sensitivity, specificity, and accuracy of RaUl were 0.93, 0.70, and 0.82 and those of RaUl D-value were 0.77, 0.83, and 0.80 respectively.

CONCLUSIONS

Load-bearing RaUl measurement is a simple method to diagnose an unstable distal radioulnar joint in patients with TFCC injury. The load bearing RaUl of >10 mm or RaUl D-value of >6.5 mm can be used to differentiate TFCC injuries and showed acceptable accuracy.

TYPE OF STUDY/LEVEL OF EVIDENCE

Diagnostic II.

The Critical Size of Ulnar Styloid Fragment for the DRUJ Stability

Background  Ulnar styloid fractures can be associated with clinically significant instability of the distal radioulnar joint (DRUJ). However, the exact fragment size that results in DRUJ instability is unknown. Purpose  The objective of this study was to determine the critical size of an ulnar styloid fracture that would result in a significant increase in DRUJ translation and forearm rotation. Methods  Eight cadaveric specimens were used to investigate the effects of three different ulnar styloid fracture sizes on DRUJ instability: tip fracture, base fracture, and a fracture including the fovea. Forearm rotation and dorsopalmar DRUJ translation were measured after each sequential increase in fracture size. Results  Relative to the uninjured state, a significant increase in forearm rotation and dorsopalmar translation was found for all three fractures. However, the fovea fracture showed a statistically significant increase in forearm rotation compared with all other fracture types and a statistically significant increase in total dorsopalmar translation compared with the tip fracture. Conclusion  In this study, ulnar styloid fractures involving the fovea resulted in significantly greater DRUJ instability comparted to tip and base fractures alone. This study provides important biomechanical data regarding the critical size of ulnar styloid fractures that result in DRUJ instability and may aid in the surgical decision-making algorithm in these patients.

Morphology of the Ulnar Insertion of the Triangular Fibrocartilage Complex and Related Osseous Landmarks

PURPOSE

In triangular fibrocartilage complex (TFCC) injuries, a foveal tear of the radioulnar ligament often requires surgery. Previous studies have suggested that surgeons should attach the TFCC to the center of the fovea. The TFCC and its insertion points are small structures, and few studies have reported details of the foveal insertion. This study aimed to clarify the morphology of the ulnar insertion of the TFCC and related osseous landmarks with 3-dimensional imaging.

METHODS

This study used 26 formalin-fixed cadavers. At the ulna, the TFCC was inserted from the fovea to the middle part of the ulnar styloid. After gross observation of the TFCC, the ulnar insertion was outlined using a 1.0-mm drill. We then created 3-dimensional images of the ulna using computed tomography and marked (with software) an outline of the foveal insertion of the TFCC. We measured the area and the long and short diameters of the TFCC insertion.

RESULTS

The area of the TFCC insertion was 34 mm² and positively correlated with the height of the ulnar styloid and the area of the ulnar head. The TFCC's highest point was 58% of the ulnar styloid height. The center of the TFCC insertion was 1.3 mm ulnar and 0.6 mm dorsal from the lowest point of the ulnar surface.

CONCLUSIONS

The center of the TFCC insertion was slightly ulnar of the lowest point of the ulnar surface. This study revealed the center, the area, and the osseous relation of the ulnar insertion of the TFCC.

CLINICAL RELEVANCE

When surgeons repair a TFCC foveal tear, they can find the anatomical center of the ulnar insertion efficiently and easily based on its osseous relationship.

Ulnar footprints of the distal radioulnar ligaments: a detailed topographical study in 21 cadaveric wrists

Understanding of the exact topography of the distal radioulnar ligaments insertions remains limited. An anatomical study was performed in 21 fresh frozen cadaveric wrists, where the superficial and deep ligaments were sequentially transected sharply at their ulnar insertions. The relationships between the distal radioulnar ligament footprints relative to the bony landmarks of the ulnar styloid were digitized. Our study demonstrated that in the coronal plane, the superficial distal radioulnar ligaments inserted at an average of 87% of the styloid height proximally to the styloid tip distally. The deep distal radioulnar ligaments inserted at an average of 81% of the styloid height distally to the fovea proximally. The superficial footprint had an area of 10.6 mm² on the ulnar styloid. The deep distal radioulnar ligaments attachment was asymmetric and generally had two separate footprints. This study adds important topographical knowledge about the footprint of the distal radioulnar ligaments and may contribute to understanding the consequences of ulnar styloid fractures and distal radioulnar ligaments lesions.

Radial Reference Points for Measuring Palmar Tilt and Ulnar Variance on Lateral Wrist Radiographs

Background: Palmar tilt and ulnar variance are crucial parameters for evaluating the distal radius. Identifying suitable reference points for these parameters on lateral wrist radiographs remains challenging. The purpose of this study was to establish reference points for measuring palmar tilt and ulnar variance on lateral wrist radiographs and to evaluate the reliability of these two parameters using the newly defined reference points. Methods: The distal articular surfaces of 25 cadaver radii were marked at four different locations using thin wires. These bones were radiographed and constant landmarks were recorded. The reliability of the palmar tilt and ulnar variance measurements was assessed using the new reference points and two serial measurements recorded by three observers on 27 standardized lateral wrist radiographs. Results: The reference points for palmar tilt on lateral radiograph were the dorsal and volar end points of the subchondral line. The subchondral line was connected to two of five metaphyseal cortical lines. The reference point for lateral ulnar variance was easily defined on the midpoint of the proximal aspect of the subchondral line. The corresponding posteroanterior central reference point for ulnar variance was at the ulnar corner of the subchondral line. Inter- and intra-observer reliabilities were overall good for the palmar tilt measurements, and excellent for the ulnar variance measurements. Conclusions: Palmar tilt can be determined accurately with a good understanding of the radiographic landmarks on lateral radiographs, and by addressing the problems caused by ulnar inclination of the articular surface of the distal radius. Lateral wrist radiographs can provide a complete picture of the ulnar border of the radius for measuring ulnar variance.

Ulnar Wrist Pain Revisited: Ultrasound Diagnosis and Guided Injection for Triangular Fibrocartilage Complex Injuries

The triangular fibrocartilage complex (TFCC) serves as the major stabilizer of the wrist. Its injuries can result from trauma or degeneration, both of which are strongly correlated with the loading stress on the ulnar shaft and carpal joints. The TFCC is made of the articular disc, meniscus homologue, ulnocarpal ligament, radioulnar ligament, ulnotriquetral ligament, ulnolunate ligament, and subsheath of the extensor carpi ulnaris tendon. Because of its complexity, it is challenging to confirm the exact component affected in TFCC injuries. The Palmer classification is widely used for investigation of TFCC lesions using magnetic resonance imaging. Recently, high-resolution ultrasound (US) has become more popular in diagnosing musculoskeletal disorders. However, the utility of US imaging in TFCC lesions is less common because its anatomy under US imaging is not described in the current literature. Accordingly, in this review, we aimed to propose a standard US scanning protocol for the TFCC, present relevant images for its pathologies, and illustrate appropriate US-guided injection techniques for their management.

Topographical Anatomy of the Distal Ulna Attachment of the Radioulnar Ligament

PURPOSE

The deep component of the distal radioulnar ligament provides translational stability and rotational guidance to the forearm. However, controversy exists regarding the importance of this structure as well as the nature of its attachment to the distal ulna. We aimed to evaluate the topographic anatomy of the distal ulna attachment of both the superficial and the deep components of the radioulnar ligament and to assess the relationship between its internal and its external morphometry.

METHODS

Thirteen human distal ulnae attached by ulnar part of the distal radioulnar ligament were scanned using micro-computed tomography and reconstructed in 3 dimensions. In addition, the distal radioulnar ligaments were examined under polarized light microscopy to determine the histological characteristics of collagen contained within the ligaments.

RESULTS

The deep limbs have broad marginal insertions at the fovea, whereas the superficial limbs have a circular and condensed insertion to the ulnar styloid. The center of the deep limb was separated from the base of the ulnar styloid by a mean of 2.0 ± 0.76 mm, and this distance was positively correlated with the width of the ulnar styloid. The mean distance between the center of the ulnar head and the center of the fovea was 2.4 ± 0.58 mm. The proportion of collagen type I was lower in the deep limb than in the superficial limb.

CONCLUSIONS

This new observation of the footprint of the radioulnar ligament in the distal ulna indicates that the deep limb may serve as an internal capsular ligament of the distal radioulnar joint, whereas the superficial limb as the external ligament.

CLINICAL RELEVANCE

Knowledge of the topographic anatomy of the radioulnar ligament's attachment to the distal ulna may provide a better understanding of distal radioulnar ligament-related pathologies.

Palmar reconstruction of the triangular fibrocartilage complex for static instability of the distal radioulnar joint

This study describes a new technique that can be used for reconstructing the triangular fibrocartilage complex to correct the static palmar radius instability of the distal radioulnar joint. In the abovementioned condition, the radius is extremely unstable with respect to the ulna and dislocates palmarly in the resting position. Using a palmar approach, a palmaris longus tendon graft was sutured to the remnant of the disrupted palmar radioulnar and ulnocarpal ligaments and then anchored to the bone tunnel that was created at the ulnar fovea. This technique predominantly reinforces the palmar structure of triangular fibrocartilage complex because the palmar radioulnar ligament is the most critical stabilizer of palmar radius instability.