The cadaveric anatomy of the distal radius: implications for the use of volar plates

Systematic review of nerves at risk at the wrist in common surgical approaches to the forearm: Anatomical variations and surgical implications

Three commonly used approaches to the forearm in orthopedic surgery are Henry's, Thompson's, and the ulnar approach, each of which has the potential to cause injury to nerves around the wrist. Preserving these nerves is important to prevent complications such as neuroma formation and motor and sensory changes to the hand. We conducted a review of the literature to assess the nerves at risk and whether 'safe zones' exist to avoid these nerves. An independent reviewer conducted searches in Embase and MEDLINE of the literature from 2010 to 2020. A total of 68 papers were identified, with 18 articles being included in the review. Multiple nerves were identified as being at risk for each of the approaches described. In the anterior approach, the palmar cutaneous branch of the median nerve (PCBMN) is most at risk of injury. An incision immediately radial to the flexor carpi radialis (FCR) or directly over the FCR is most likely to avoid injury to both superficial branch of the radial nerve (SBRN) and PCBMN. With Thompson's approach, the safest zone for an incision is directly over or slightly radial to Lister's tubercle to avoid injury to SBRN and lateral cutaneous nerve of the forearm. For the ulnar approach, a safe zone was shown to be on the ulnar side of the wrist around the ulnar styloid (US) when the forearm was in supination or a neutral position to avoid injury to the dorsal branch of the ulna nerve (DBUN). Care must be taken around the US due to the density of nerves and the proximity of the last motor branch of the posterior interosseous nerve to the ulnar head. This review highlighted the proximity of nerves to the three most common surgical incisions used to access the forearm. In addition, anatomical variations may exist, and each of the nerves identified as being at risk has multiple branches. Both factors increase the potential of intraoperative damage if the anatomy is not properly understood. The surgeon must adhere carefully to the established approaches to the wrist and distal forearm to minimize damage to nerves and optimize surgical outcomes for the patient.

Interpretations of the Term "Watershed Line" Used as Reference for Volar Plating

Objective  The objective of this systematic review is to provide an overview of all interpretations of the definition of the watershed line used in literature. Methods  The Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) guidelines were followed for this review. A comprehensive search was performed for definitions of the watershed line given in literature. A total of 32 studies giving an explicit interpretation of the definition of the watershed line or anatomical reference for plate positioning in writing and/or imaging were included. Results  In 32 studies, we found eight different landmarks used to refer to the watershed line or correct plate positioning. Five studies used two different soft tissue landmarks. Six different bony landmarks were described in 24 studies. These could further be subdivided into three anatomical interpretations, described in seven studies, in which the term "watershed line" is explained as a distinguishable anatomical line, and two surgical interpretations, described in 15 studies, which are purely reflecting the optimal location of the volar plate. One interpretation of the watershed line described in two studies combined both anatomical and surgical landmarks. Conclusion  The (mis)interpretation of the definition of the term "watershed line" as described by Orbay is subject to the type of landmarks and purpose used: soft tissue or bony landmarks and an anatomical or a surgical purpose. A clear distinction can be made between interpretations using bony landmarks, as the true watershed line is defined and definitions using soft tissue landmarks, which might represent the reference points surgeons use in clinical practice.

A retrospective comparison of clinical and radiological outcomes using palmar or dorsal plating to treat complex intraarticular distal radius fractures (AO 2R3 C3)

INTRODUCTION

Complex intraarticular distal radius fractures are common, and treatment with open reduction and internal fixation (ORIF) can be done through either the palmar or dorsal approach. There is scant evidence, however, indicating which approach is more suitable. We compared clinical and radiological outcomes of patients with AO 2R3 C3 fractures surgically treated with one of these approaches.

MATERIALS AND METHODS

From January 2015 to November 2018, 72 surgically treated patients with AO 2R3 C3 fractures were radiologically (12 months) and clinically (mean 26 months) evaluated. Forty-one patients underwent ORIF using the palmar approach (Group 1), and the dorsal approach was used in 31 patients (Group 2). Radiological parameters were measured using the AO scoring system immediately following surgery and 12 months later. Clinical assessments included the range of motion, PRWE and DASH scores.

RESULTS

At the immediate postoperative assessment, the median AO score was 5.5 (IQR 2-9.5, range 0-30.5) for Group 1 and 8 (IQR 5-15, range 0-27) for Group 2, and 12-month follow-up results were 4.5 (IQR 1.5-10, range 0-41) and 6.5 (IQR 5-11, range 0-29.5), respectively. Group 1 had more favorable results for the flexion, extension, radial abduction, PRWE and DASH parameters. The plate removal and reoperation rates were higher in Group 2.

DISCUSSION

When treating complex intraarticular distal radius fractures, we found the palmar approach was more advantageous for this fracture pattern. Nevertheless, a dorsal approach may still be suitable for intraarticular comminuted distal radius fractures with dorsally displaced joint fragments.

Intrarater and Interrater Reliability of the Soong Classification for Distal Radius Volar Locking Plate Placement

Background: The purpose of this study was to analyze the intrarater and interrater reliability of the Soong classification for volar locking plate placement on a randomly selected, consecutive series of radiographs. Our hypothesis was that the classification would be reliable. Methods: Six physicians of differing levels of training (orthopedic surgery intern to fellowship-trained upper extremity staff) were asked to review 40 radiographs in a random order on 2 separate occasions, 4 weeks apart. All observers graded each image (0, 1, or 2) based on the corresponding Soong grade. A weighted κ was used to determine the intrarater agreement. The interrater agreement was determined using an intraclass coefficient: Results: The intrarater reliability using a weighted κ ranged from 0.229 (95% confidence interval [CI]: 0.048-0.411) to 0.946 (95% CI: 0.840-1.051). The interrater intraclass coefficient for Randomization 1 was 0.944 (95% 0.912-0.967) and Randomization 2 was 0.877 (95% CI: 0.797-0.930). Conclusion: The Soong classification is a reliable tool, both interrater and intrarater, for assessing distal radius volar locking plate placement. The classification system remained reliable despite a randomly selected, consecutive series of images and physician observers of varying levels of training.

The Watershed Line of the Distal Radius: Cadaveric and Imaging Study of Anatomical Landmarks

Background  Placement of volar plates remains a challenge as the watershed line may not be an easy-identifiable distinct line intraoperatively. Objectives  The main objective of this article is to define how anatomical landmarks identifiable upon the volar surgical approach to the distal radius relate to the watershed line. Methods  We identified anatomical landmarks macroscopically upon standard volar approach to the distal radius in 10 cadaveric forearms and marked these with radiostereometric analysis (RSA) beads in cadaveric wrists. The RSA beads were then referenced against the volar osseous structures using quantification of three-dimensional computed tomography and advanced imaging software. Results  The mean measurements were the radial and ulnar prominences 11.1 mm and 2.1 mm proximal to the joint line of the distal radius, respectively. The interfossa sulcus was 0.3 mm proximal and 3 mm dorsal to the ulnar prominence. The watershed line was between 3.5 (minimal) and 7.6 (maximal) mm distal to the distal line of insertion of the pronator quadratus. Conclusion  The watershed line is situated distal to the pronator quadratus, but with a wide variability making it an impractical landmark for plate position. The osseous ulnar prominence is a good anatomical reference for safe plate positioning, as it is located on the watershed line and easily palpated at surgery. One should keep in mind the sulcus-the point on the watershed line where the flexor pollicis longus runs-can be situated just proximal to the ulnar prominence. Clinical Relevance  To provide anatomical landmarks that are easy to identify upon surgical approach without the direct need for intraoperative imaging.

Risk Assessment of Injury to Palmar Cutaneous Branch of the Median Nerve Using High-Resolution Ultrasound

OBJECTIVE

To evaluate the relationship between the palmar cutaneous branch of median nerve (PCBMN) and surrounding anatomical structures by using high-resolution ultrasound (HRUS) to assess the risk of PCBMN injury.

METHODS

The PCBMN course and the characteristics of bilateral distal forearms and wrists of 30 healthy volunteers were identified. The distance between PCBMN and other anatomical structures at three different levels along its course were measured using HRUS. Moreover, the depth of PCBMN from skin and its cross-sectional area (CSA) were measured.

RESULTS

HRUS showed the PCBMN in all subjects. PCBMN branched off from the radial aspect of the median nerve (MN) at 4.69±0.89 cm proximal to the bistyloid line (BSL) and extended radially toward the flexor carpi radialis (FCR) tendon. PCBMN was within the ulnar edge of FCR tendon sheath, and became more superficial and perforated the antebrachial fascia between the FCR tendon laterally and the palmaris longus (PL) tendon medially. PCBMN was located at 4.08±0.72 mm on the ulnar aspect of the FCR tendon and 4.78±0.36 mm radially on the PL tendon at BSL. At the distal wrist crease level, the PCBMN was located at 5.68±0.58 mm on the ulnar side of the FCR tendon. The PCBMN depth from skin at BSL and its branching point was 1.92±0.41 and 7.95±0.79 mm, respectively. The PCBMN CSA was 0.26±0.15 mm2 at BSL.

CONCLUSION

HRUS can be used to identify PCBMN and its relationship with other anatomical structures. Our data can be used to predict PCBMN location, and prevent complications associated with invasive procedures involving the wrist.

Minimal invasive plating of distal radius fractures. A safe procedure?

BACKGROUND

Minimal invasive plate osteosynthesis (MIPO) with preservation of the pronator quadratus (PQ) muscle represents a new technique for stabilization of distal radius fractures. However, the complex anatomy of the distal radius metaphysis requires implants with features that address all morphologic specifics of this area to avoid complications, which are still reported with this technique. It was the aim of our anatomic investigation to evaluate the feasibility of plate insertion via a minimal transverse approach as well as the risk of soft- tissues compromise with the use of an implant, which is only partially adapted to the characteristics of distal radius metaphysis.

METHODS

Twenty forearm specimens, conservated with Thiels method, have been used for this study. The majority (n = 19/20) of implants (2.4 mm small fragment juxta-articular locking compression/ LCP T-plate -5-hole; Depuy - Synthes^®, Solothurn, Switzerland) could be inserted easily and all were seated proximal to the so called "watershed line" (n = 20/20).

RESULTS

In a total of 8/20 specimens close contacts or potential compromise to neighboring soft- tissues was seen: perforation of the PQ muscle by the plate occurred in 2/20 specimens and was related to an extreme muscle morphology. In 7/20 specimens close contacts between the T-plate and other soft tissues were observed, which were exclusively located at the radial edge of the distal transverse bar. They affected the brachio-radialis tendon (elevation: 2/20, side-to-side contact: 3/20, overriding: 1/20) and the radial artery (elevation: 4/20, side-to-side contact: 2/20, overriding: 1/20). No significant differences of morphologic types of PQ muscle and the difficulty of plate insertion, adjustment on the bone, PQ muscle damage and contact to neighboring soft-tissues could be evaluated.

CONCLUSIONS

Insertion of volar radius plates through a MIPO approach can be easily accomplished without detachment and damage to the PQ muscle even with grossly adapted implants. However, perfectly pre-shaped plates which are adapted to all anatomic aspects of the distal radius metaphysis are required to achieve optimal contact with the metaphyseal bone and to avoid potential complications.

A Cadaveric Study of the Mean Distance of the Radial Artery During the Approach to the First Carpometacarpal Joint

Multiple surgical procedures have been described to treat first carpometacarpal (CMC) arthritis. Although the superiority of one procedure over the others continues to be a controversial topic, they all approach the trapezium and require careful attention to the surrounding structures. One potential complication is injury to the radial artery, which lies in close proximity to the trapezium and is often encountered during surgical approach. Using cadaveric specimens, the authors dissected to identify and isolate the radial artery as it travels in the forearm, wrist, and hand while being careful not to disturb its native course. The authors then measured the shortest distance interval from the radial artery to the first CMC joint and from the radial artery to the scaphotrapeziotrapezoidal joint. Descriptive statistics were calculated from these measurements and averaged over the various specimens. The mean distance of the radial artery to the closest segment of the volar CMC joint was 11.6±2.5 mm. The mean distance of the radial artery to the closest segment of the volar scaphotrapeziotrapezoidal joint was 1.6±1.8 mm. A precise understanding of nearby anatomy is paramount to a successful surgical treatment for first CMC arthritis and to avoid iatrogenic complications. The authors describe the mean distance from the radial artery to 2 major landmarks used during surgical treatment and provide insight to surgeons who perform these CMC reconstruction procedures to decrease the risk of intraoperative radial artery injury. [Orthopedics. 2018; 41(4):e541-e544.].

[Descriptive, radiographic, topographic and functional anatomy applied to distal radius fractures]

Extensive anatomical knowledge is needed in order to correctly treat distal radius fractures: normal and pathological osteology of the distal radius, distal radio-ulnar joint and radiocarpal joint-both on the descriptive and functional level-the neurovascular and muscular environments of the distal radius-which are essential to the surgical approaches-and the angles that need to be restored during the reduction. All of these concepts are broached in this article.

[Nerve injuries associated with distal radius fractures]

Nerve damage is a common complication of distal radius fractures. It may be a result of the injury event or be iatrogenic. It is the source of disability and potential handicap. There is little published data on this topic and no study has validated the strategies needed to prevent or manage these nerve-related complications. There is no consensus on treatment. Prevention requires a good knowledge of the various surgical approaches and rigorous fracture fixation technique. The objective of this article is to take stock of recent data from the scientific literature.

Anatomic considerations when performing the modified Henry approach for exposure of distal radius fractures

BACKGROUND

Identify the proximity of anatomic structures during the modified Henry approach (MHA).

METHODS

Distances between median nerve (MN), palmar cutaneous branch (PCB), radial artery (RA) and the flexor carpi radialis (FCR) were measured at the wrist crease (WC), 5 and 10 cm proximal in 16 fresh frozen cadavers. The FPL origin and innervation was measured.

RESULTS

Most at risk was the MN proximally and the PCB distally while the RA was safe. Innervation occurred at the proximal third of the FPL's origin along the ulnar aspect.

CONCLUSION

The MHA is safe when understanding the proximity of structures.

Incidence of an Anomalous Course of the Palmar Cutaneous Branch of the Median Nerve During Volar Plate Fixation of Distal Radius Fractures

PURPOSE

Volar plating of distal radius fractures using an approach through the flexor carpi radialis (FCR) sheath is commonplace. The palmar cutaneous branch of the median nerve (PCB) is considered to run in a position adjacent to, but outside, the ulnar FCR sheath. Anatomic studies have not identified anatomic abnormalities relevant to volar plating. The purpose of this study was to determine the frequency of anomalous PCB branches entering the FCR sheath during volar plating.

METHODS

This observational study involved 10 attending hand surgeons during a 7-month period (July 2015-January 2016). Surgeons assessed, documented, and reported any PCB anomalies that were encountered during volar plating through a trans-FCR approach.

RESULTS

There were 182 volar plates applied that made up the study group. There were 10 cases (5.5%) of anomalous PCBs entering the FCR sheath. In 4 cases, the PCB pierced the radial FCR sheath proximally, crossed beneath the tendon, and traveled distally on the ulnar side. In 4 other cases, the PCB entered the FCR sheath proximally on the ulnar or central aspect of the sheath and remained within the sheath, staying along the ulnar or dorsal side of the tendon. In 1 case, the PCB pierced the ulnar distal aspect of the sheath and split into 2 branches. In 1 case, the PCB ran within the sheath along the radial aspect of the FCR.

CONCLUSIONS

Anomalies in the course of the PCB are more common than often considered. These variants are at risk during volar surgical approaches to the wrist that proceed through the FCR sheath.

CLINICAL RELEVANCE

Although dissecting along the radial side of the FCR sheath may protect the PCB in most cases, care must be taken to identify anomalous branches (if present) and protect them during surgery.

Flexor carpi radialis tendon ultrasound pictorial essay

Disorders of the flexor carpi radialis tendon (FCRt) are often missed even though they are a relatively frequent cause of volar radial wrist pain. They can manifest as tenosynovitis, tendinopathy, synovial sheath cysts with or without scaphoid-trapezoid-trapezium (STT) joint pathology, and partial or complete rupture. Because FCRt disorders often present with non-specific symptoms and a non-diagnostic clinical examination, imaging is often necessary for accurate evaluation and therapeutic planning. Conventional radiography provides good visualization of the neighboring bones and joints, as well as rare intratendinous calcifications. MRI enables evaluation of the FCRt and adjacent anatomical structures with excellent tissue resolution. In comparison, ultrasound (US) evaluation of the FCRt is less commonly described in the radiology literature, despite its affordability, exquisite soft tissue resolution, and the advantages of quick, dynamic diagnostic imaging. This pictorial essay describes and demonstrates the normal anatomy of the FCRt, its US examination technique and normal US appearance, and US findings of clinically relevant FCRt disorders.

Distal volar radial plates: how anatomical are they?

BACKGROUND

Fractures of the distal radius are common, with volar locking plates being increasingly used in their treatment. They aim to provide stable internal fixation and are designed to mirror the natural anatomy. Current volar plate designs incorporate a volar cortical angle (VCA) of 25 degrees.

HYPOTHESIS

The aim of this study is to determine whether the VCA in uninjured distal radii corresponds accurately with modern volar plate designs.

MATERIALS AND METHODS

A retrospective radiological analysis utilizing Computed Tomography scans to assess the VCA of 100 distal radii. Each distal radius was subjected to 3 measurements of the VCA in the sagittal plane.

RESULTS

One hundred patients were identified (67 male, 33 female; mean age 37.4 years). The mean VCA was 32.9 degrees (S.D.±5.14 degrees). The VCA in male patients was significantly greater than in females (33.6 vs 31.5 degrees; P=0.04). There was a statistically significant difference between the lateral VCA and medial VCA (32.2 vs 34.3 degrees, P=0.02).

DISCUSSION

Our study clearly demonstrates that the VCA measured in the distal radius is significantly greater than the volar angulation incorporated within modern plate design. Given that the aim of ORIF is to anatomically reconstruct the distal radius, our study highlights that this may not be possible with current plates.

LEVELS OF EVIDENCE

Level IV Retrospective case series.