Morphologic analysis of the proximal ulna with special interest in elbow implant sizing and alignment

Computed Tomography-Based Humeral Templating for Uncemented Elbow Arthroplasty

BACKGROUND

Intramedullary (IM) screw insertion into the distal humerus provides fixation for a novel, uncemented elbow arthroplasty. A multitude of screw sizes is required to accommodate variable humeral morphology. The goal of this study was to use computed tomography (CT) for IM screw sizing and to validate this templating by inserting screws into three-dimensionally (3D) printed models.

METHODS

Computed tomography humerus scans for 30 patients were reformatted in the plane of the distal IM canal. Screw size was templated by measuring the canal diameter at 3 locations corresponding to the lengths of the screws being tested. Interrater and intrarater reliabilities of the measurements were assessed. Three-dimensional models of 5 humeri were printed, and IM screws were placed to achieve a secure endosteal fit.

RESULTS

We identified combinations of body components and IM screw length and diameter for all patients to seat this uncemented elbow arthroplasty. The measurements and screw width determinations were reliable. Canal diameter correlated with age but was unrelated to sex. Screws were inserted into five 3D-printed models which matched the templates and demonstrated mechanical and radiographic evidence of secure fit.

CONCLUSIONS

This study characterizes distal humerus anatomy in the context of IM screw fixation. Humerus CT scans of 30 patients were able to be templated, and validation via implantation of IM screws into 3D models was successful. Computed tomography templating will allow surgeons to predict the optimal screw size prior to implantation. A broad range of screw lengths and diameters is critical for implantation of this novel elbow arthroplasty.

Demographic heterogeneity in valgus angulation of the proximal ulnar canal in relation to the flexion-extension axis

BACKGROUND

The long-term outcome of total elbow arthroplasty remains unsatisfactory because of loosening and polyethylene wear, which could be caused by malpositioning of the ulnar component. When introducing an ulnar component, 2 different angles should be considered in the coronal plane: the valgus angulation of the proximal ulna in relation to the flexion-extension axis (FE-axis) and the intramedullary varus angulation in relation to the FE-axis. Currently, available TEA designs may not always be able to reconstruct the FE-axis because of the morphologic variability of the ulna.

HYPOTHESIS

This study aimed to determine the demographic variability of the ulna and the relation between the 2 angulations in the frontal plane based on 3-dimentional computed tomography (CT) reconstructions of the elbow joint of healthy volunteers.

METHODS

Computed tomography scans of 36 left elbows of healthy volunteers were obtained (20 men and 16 women). The scans were segmented and analyzed using the Mimics Research 20.0 software. A local coordinate system was created based on the FE-axis of the elbow and the ulna's longitudinal axis. The measurements were conducted using the 3-Matic Research 12.0 software.

RESULTS

The valgus angulation of the proximal medullary canal was on average 16° in men but 12° in women and ranged between 5° and 21°. The varus angulation of the medullary cavity could be determined at 57 mm in men and 64 mm in women from the FE-axis. This angulation was on average 10° in men and 7° in women. There was no significant correlation between this angle and the length of the ulna or the point of varus angulation.

CONCLUSION

This study found a wide range of valgus angulation of the proximal ulnar canal in relation to the FE-axis. The available elbow implant designs are discordant with the mean valgus angulation of the proximal ulna found in this study, and the valgus laxity of the implants does not cover the variability in the population.

Optimal K-Wire Placement for Indirect Cannulated Screw Fixation of Coronoid Process Fractures: A Radiology-Based Guide

PURPOSE

Indirect fixation of coronoid process fractures of the ulna, especially arthroscopically, offers the possibility to avoid extensive medial surgical approaches. However, optimal placement of K-wires for cannulated screw fixation is technically challenging. The aim of the present study was to present guide values for K-wire placement for indirect screw fixation of coronoid tip (COT) and anteromedial facet (AMF) fractures of the ulna.

METHODS

Computed tomography scans of the elbows of 197 patients with an uninjured ulna were identified and evaluated following a standard measuring protocol. Optimal placement of K-wires was defined as the bisector between the anterior and articular cortex while respecting a 1.6-mm safe zone for each placement. This placement of the K-wires in the COT and the AMF was analyzed by measuring the wire angulation in relation to the posterior ulnar cortex (AUC), the distance from the entry point to the posterior olecranon edge (DPE), and the intraosseous length (IOL). Because the coronoid has a curved shape, measurements of the COT and AMF were expected to differ significantly. Sex was also expected to influence measurements. To determine whether this optimal placement of K-wires can be reliably identified, interobserver and intraobserver reliabilities were evaluated.

RESULTS

To address tip fragments, we determined a mean AUC of 64°, DPE of 36 mm, and IOL of 38 mm. Regarding wire placement toward the AMF, the means for the AUC, DPE, and IOL were 79°, 27 mm, and 33 mm, respectively. Statistically significant differences were found between the COT and the AMF for the AUC, DPE, and IOL. Our measuring protocol showed good interobserver and intraobserver reliability.

CONCLUSIONS

K-wire placement toward the COT demands a smaller angle, a longer IOL, and a more distal entry point than wires placed toward AMF. These differences reflect the curved and complex anatomy of the coronoid.

CLINICAL RELEVANCE

This measuring algorithm can be used to plan osteosynthesis, and the obtained reference values can help understand the coronoid's complex anatomy.

Rotational Anatomy of the Radius and Ulna: Surgical Implications

PURPOSE

The rotational anatomy of the forearm bones is not well defined. This study aims to further the understanding of the torsion of the radius and ulna to better guide treatment.

METHODS

Computed tomography images of 98 cadaveric forearms were obtained and 3-dimensional models of the radius and ulna were generated and analyzed. The rotation of the radius was evaluated by comparing the orientation of the distal radius central axis (DRCA) with the volar cortex of the distal radius (DR) and biceps tuberosity (BT). The rotation of the ulna was evaluated by assessing the orientation of the ulnar head with respect to the proximal ulna.

RESULTS

The DR volar cortex pronates from distal to proximal. The BT was 43.8° ± 16.9° supinated from the DRCA (range, 2.7°-86.5°). The mean difference in rotation between contralateral biceps tuberosities was 7.0° ± 7.1°. The volar cortex of the DR was 12.6° ± 5.4° supinated compared with the DRCA. The ulnar head was pronated 8.4° ± 14.9° with respect to the greater sigmoid notch (range, 50.3° pronation-22.0° supination).

CONCLUSIONS

The BT has a variable orientation relative to the DR, but it is generally located anteromedially in a supinated arm or 136° opposite the radial styloid. Understanding the rotational anatomy of the radius and ulna can play an important role in surgical planning and implant design. The rotational anatomy of the radius and ulna varies significantly between individuals, but is similar in contralateral limbs.

CLINICAL RELEVANCE

Distal radius volar cortex rotational anatomy can help guide treatment of DR fractures and malunions as well as assist in positioning of wrist arthroplasty implants, particularly in the presence of bone loss. The side-to-side similarities demonstrated in this study should be helpful in managing patients with segmental bone loss or fracture malunion and those requiring joint reconstruction.

Computer tomographic analysis of anatomic characteristics of the ulna - essential parameters for preshaped implants

Purpose

Anatomically preshaped implants are needed for exact restoration of the anatomy after fractures of the proximal ulna and ulnar shaft, which enables a good functional outcome. Aim of this computed tomographic analysis was to identify specific characteristics of the ulna. The data serve for the development of a new intramedullary implant for stabilisation of proximal and diaphyseal ulna fractures.

Methods

With a standardized research method 100 CT scans of the ulna were evaluated regarding anatomic parameters like width of the medullary canal, proximal ulna dorsal angulation and varus angulation. Also, correlations of these parameters were analyzed statistically.

Results

The mean proximal ulna dorsal angulation (PUDA) was 6.4° (SD 2.8°), while the mean varus angulation of the proximal ulna was 12.4° (SD 3.3°). The length of the ulna bone was 253.6 mm (SD 19.9 mm) on average. The average minimum diameter of the medullary canal was 4.2 mm (SD 1.1 mm) located at 141.3 mm (SD 19.7 mm) from the olecranon tip. There is a positive correlation between age and minimum diameter in our patient cohort (p< 0.001).

Conclusion

Our study described the anatomy of the proximal ulna and the ulna shaft with a reproducible research method in a representative patient cohort. The knowledge of the evaluated anatomic parameters can lead to an improvement of any implant design for the fixation of proximal and diaphyseal ulna fractures.

The impact of varus angulation on proximal fractures of the ulna

Background

We studied anteromedial varus angulation (VA) in the proximal third of the ulna. The importance of restoration of the anatomical orientation of the ulnar after a proximal fracture is unclear. The purpose of this study was to evaluate the impact of minimal proximal ulna malunion on elbow function after a proximal ulna fracture.

Methods

We reviewed the follow-up of 60 patients who had undergone open reduction with internal fixation (ORIF) of a proximal fracture of the ulna. Patients were divided into two groups, defined as either more or less than 5° of the difference between the VA of the fractured and contralateral ulna. The range of motion(ROM)of elbow flexion, extension and forearm rotation on both sides, Mayo Elbow Performance Score (MEPS) and Visual Analogue Scale (VAS) were measured.

Results

The average postoperative time was 3.1 years (1–5 years). Mean VA of the fractured arm was different from the normal side (7.8 ± 3.0 vs 12.7 ± 3.0). Compared to the unfractured arm there was a loss in mean elbow flexion (14.2 ± 4.9 vs 18.0 ± 5.9), extension ROM (7.1 ± 2.5 vs 9.3 ± 1.9, p < 0.05) and forearm rotation ROM (15.6 ± 8.6 vs 21.8 ± 9.5) that were statistically significant (p < 0.05). There were no statistically significant differences in the MEPS and VAS score results between the two groups (p > 0.05).

Conclusions

The function of the elbow and forearm was restricted after VA malunion in the proximal ulna, but the quality of life of these patients had not been significantly affected. We suggest that orthopedic surgeons should assess whether the specialized structures of the proximal ulna are damaged or not before surgery. If the anatomy of the fractured bone cannot be restored through manipulation of the connected end directly, it is better to image the anatomical structure of the healthy side from using an elbow X-ray before surgery, and then reset using a pre-shaped plate to prevent malunion.

Osseous Anatomy of the Distal Radioulnar Joint: An Assessment Using 3-Dimensional Modeling and Clinical Implications

PURPOSE

Using a novel technique, we assess and describe the distal radioulnar joint (DRUJ) anatomy. The purpose of this study was to provide the anatomic dimensions of the DRUJ and to evaluate contralateral symmetry.

METHODS

Computed tomography images of 100 cadaveric forearms were obtained. Three-dimensional models of the radius and ulna were generated and evaluated using 3-dimensional modeling software. Measurements of the radius of curvature of the sigmoid notch (SN) and ulnar head (UH), as well as the length of the SN and volar and dorsal lips were performed in the axial and coronal sequences. In addition, mid-coronal angular measurements were made of the SN and UH to quantify the obliquity of the DRUJ. All coronal measurements were performed with the forearm set to neutral rotation.

RESULTS

The average ulnar variance was -0.9 ± 1.8 mm. The radius of curvature of the UH (8.2 ± 1.3 mm) was markedly smaller than that of the SN (18.2 ± 8.5 mm). The length of the SN in coronal sequences increased from volar to dorsal by 65%. The mid-coronal angle (DRUJ obliquity) of the SN and UH measured 6.0 ± 9.9° and 18.0 ± 9.9°, respectively. A direct inverse correlation was demonstrated in the obliquity of the DRUJ and ulnar variance. All anatomic measurements were similar when comparing bilateral specimens.

CONCLUSIONS

The SN length tends to increase in size from volar to dorsal. Bilateral specimens from the same individual demonstrate similarities and can be cautiously used for comparison.

CLINICAL RELEVANCE

The relationships and measurements demonstrated in this study can be a guide when considering reconstructive procedures or dealing with complex fractures involving the DRUJ.

Triceps-sparing ulnar approach for total elbow arthroplasty

To prevent insufficiency of the triceps after total elbow arthroplasty, we have, since 2008, used a triceps-sparing ulnar approach. This study evaluates the clinical results and post-operative alignment of the prosthesis using this approach.

We reviewed 25 elbows in 23 patients. There were five men and 18 women with a mean age of 69 years (54 to 83). There were 18 elbows with rheumatoid arthritis, six with a fracture or pseudoarthrosis and one elbow with osteoarthritis.

Post-operative complications included one intra-operative fracture, one elbow with heterotopic ossification, one transient ulnar nerve palsy, and one elbow with skin necrosis, but no elbow was affected by insufficiency of the triceps.

Patients were followed for a mean of 42 months (24 to 77). The mean post-operative Japanese Orthopaedic Association Elbow Score was 90.8 (51 to 100) and the mean Mayo Elbow Performance score 93.8 (65 to 100). The mean post-operative flexion/extension of the elbow was 135°/-8°. The Manual Muscle Testing score of the triceps was 5 in 23 elbows and 2 in two elbows (one patient). The mean alignment of the implants examined by 3D-CT was 2.8° pronation (standard deviation (sd) 5.5), 0.3° valgus (sd 2.7), and 0.7° extension (sd 3.2) for the humeral component, and 9.3° pronation (sd 9.7), 0.3° valgus (sd 4.0), and 8.6° extension (sd 3.1) for the ulnar component. There was no radiolucent line or loosening of the implants on the final radiographs.

The triceps-sparing ulnar approach allows satisfactory alignment of the implants, is effective in preventing post-operative triceps insufficiency, and gives satisfactory short-term results.

Cite this article: 2015;97-B:1096–1101.

Reliability and validity in measurement of true humeral retroversion by a three-dimensional cylinder fitting method

HYPOTHESIS AND BACKGROUND

Humeral retroversion is defined as the orientation of the humeral head relative to the distal humerus. Because none of the previous methods used to measure humeral retroversion strictly follow this definition, values obtained by these techniques vary and may be biased by morphologic variations of the humerus. The purpose of this study was 2-fold: to validate a method to define the axis of the distal humerus with a virtual cylinder and to establish the reliability of 3-dimensional (3D) measurement of humeral retroversion by this cylinder fitting method.

METHODS

Humeral retroversion in 14 baseball players (28 humeri) was measured by the 3D cylinder fitting method. The root mean square error was calculated to compare values obtained by a single tester and by 2 different testers using the embedded coordinate system. To establish the reliability, intraclass correlation coefficient (ICC) and precision (standard error of measurement [SEM]) were calculated.

RESULTS

The root mean square errors for the humeral coordinate system were <1.0 mm/1.0° for comparison of all translations/rotations obtained by a single tester and <1.0 mm/2.0° for comparison obtained by 2 different testers. Assessment of reliability and precision of the 3D measurement of retroversion yielded an intratester ICC of 0.99 (SEM, 1.0°) and intertester ICC of 0.96 (SEM, 2.8°).

DISCUSSION AND CONCLUSION

The error in measurements obtained by a distal humerus cylinder fitting method was small enough not to affect retroversion measurement. The 3D measurement of retroversion by this method provides excellent intratester and intertester reliability.

Proximal ulna morphometry: which are the "true" anatomical preshaped olecranon plates?

PURPOSE

To define the optimum design of the anatomical preshaped olecranon plate.

METHODS

The geometry of the proximal ulna was studied in 200 paired Caucasian ulnae, using a digital caliper and goniometer. Gender and side differences were analyzed. Results were compared with the corresponding geometrical parameters of three olecranon plates with different contour. All three plates were placed on the dorsal surface of a "model" ulna, i.e., a right dried ulna having osteometric parameters similar to the averages of our sample, and plate-to-bone fit was examined in two planes.

RESULTS

The proximal ulna had an 8.48° (2.1°-15.7°) mean varus angulation and an 8.49° (1.70°-14.10°) mean anterior angulation, located on average 8.19 cm (5.68-11.66 cm) and 8.63 cm (5.28-11.92 cm) distal to the bone's most proximal point, respectively. The mean olecranon angle was 110.34° (98.70°-125.80°) and the olecranon length was 1.58 cm on average (1.20-2.12 cm). Only the plate having both varus and anterior angulation presented a good plate-to-bone fit in both planes.

CONCLUSIONS

A "true" anatomical preshaped olecranon plate should have both varus and anterior angulation close to the average angulations of the normal ulna and located in a certain distance from its proximal edge. The olecranon part of the plate should primarily not exceed the olecranon length and secondarily be close to the average olecranon angle. We believe that such a plate may facilitate intraoperative restoration of the proximal ulna complex anatomy, when dealing with comminuted or Monteggia fractures, thus leading to better postoperative results.

Morphometric analysis of the proximal ulna using three-dimensional computed tomography and computer-aided design: varus, dorsal, and torsion angulation

PURPOSE

The proximal ulna, particularly the course of the posterior border, has a complex three-dimensional (3D) morphology which has been highlighted recently due to its clinical relevance in relation to surgical treatments. 3D computed tomography (CT) reconstruction and computer-aided design (CAD) based software can help to visualize the complex anatomy and thus aid the investigation of the more detailed morphology of the proximal ulna.

METHODS

In our current study, 3D CT reconstruction images of 20 cadavers were imported into the 3D CAD program. Three morphologic angle parameters of the proximal ulna were measured including the dorsal, varus and torsion angulation. The torsion angulation was measured using the flat spot of olecranon dorsal aspect. We measured the total length of the ulna and the distance between the olecranon tip and the apex of dorsal and varus angulation. Furthermore, the thickness of olecranon was also measured for all the specimens.

RESULTS

The results showed that the mean dorsal, varus, and torsion angulation was 4.3° (range 2.6°-5.9°), 12.1° (range 7.9°-17.6°), and 22.5° (range 16.6°-30.5°), respectively. The average length ratio of the dorsal and varus angulation apex to the total ulnar length was 26.4 % (range 19.8-30.7 %) and 32.7 % (range 27.5-37.5 %), respectively. The average of olecranon thickness at the proximal tip, mid-olecranon fossa, and at coronoid tip level was 17.8 mm (range 14.1-22.8 mm), 19.7 mm (range 15.8-23.1 mm), and 35.1 mm (range 27.9-41.8 mm), respectively.

CONCLUSION

In conclusion, variations in the proximal ulna have to be considered when anatomically contoured dorsal plates are applied. Knowledge of the 3D morphologic anatomy of the proximal ulna would provide important information on fracture reductions, and the design of a precontoured dorsal plate or a prosthetic ulnar stem.

Three-dimensional suitability assessment of three types of osteochondral autograft for ulnar coronoid process reconstruction

BACKGROUND

Osteochondral autografts with use of the olecranon tip, lateral radial head, or proximal radial head have been employed for coronoid process reconstruction. However, it is unclear which autograft is most suitable for coronoid articular configuration. We assessed 3-dimensional articular facet suitability of 3 osteochondral autografts for coronoid process reconstruction.

METHODS

We performed 3-dimensional computed tomography of 20 elbows to compare the articular facet configuration between the coronoid process and the ipsilateral olecranon tip, lateral radial head, and proximal radial head. We measured the area of the proximity region (≤2.0 mm) between the articular facets of the coronoid process and 3 osteochondral autografts, the covering rate defined as the percentage area of the coronoid articular facet occupied by the proximity region, the location of the proximity region center, and the percentage of the removed ulnohumeral articular facet.

RESULTS

The covering rate was significantly higher with an olecranon graft than with radial head grafts. The regional center of a proximal radial head graft was significantly medial compared with that of olecranon and lateral radial head grafts. The olecranon graft used an average of 13.8% of the ulnohumeral articular facet.

CONCLUSIONS

An olecranon graft was most suitable for defects of the coronoid process involving the tip, and a proximal radial head graft was most suitable for defects of the coronoid process involving the anteromedial rim. The use of an olecranon graft for reconstruction of 50% of the height of the coronoid process does not cause concern for gross elbow instability.

Does cubitus varus cause morphologic and alignment changes in the elbow joint?

BACKGROUND

In cubitus varus after pediatric supracondylar fracture, late development of trochlear deformity causing additional varus angulation and joint misalignment relating to late complications of the tardy ulnar nerve palsy or posterolateral rotatory instability have been suggested. However, it is unclear whether these morphologic and alignment changes of the elbow joint occur in cubitus varus. The object of this study was to investigate morphologic changes of the bones and alignment changes of the elbow joint in longstanding cubitus varus using 3-dimensional computer bone models created from computed tomography data.

MATERIALS AND METHODS

We studied 14 patients with longstanding cubitus varus after pediatric supracondylar fractures. Three-dimensional bone models of the bilateral humerus, radius, and ulna were created from computed tomography data. We compared the morphology and alignment of the elbow joint between the affected side and contralateral unaffected side.

RESULTS

The posterior trochlea, distal part of the lateral capitellum, diameters of the radial head, and articular surface of the ulna in cubitus varus were larger than those of the contralateral elbow. In the ulna, the convex portion of the trochlear notch shifted laterally in cubitus varus. Joint alignment in cubitus varus was affected by a shift of the ulna to a more distal and medial position with external rotation and flexion.

CONCLUSIONS

In longstanding cubitus varus, the morphology and alignment of the elbow joint are observed to differ from those of the normal side.

Design of an implant for first metatarsophalangeal hemi-arthroplasty

This study was designed to examine the three-dimensional geometry of the head of the first metatarsal bone of the foot. Ninety-seven adult first metatarsal head (MTH1) bones were scanned using a laser scanner at 400 dpi. A best-fit ellipsoid was obtained from the articular surfaces of MTH1 for each size group using nonlinear unconstrained optimisation. Average root mean square errors between the articulating surfaces and the optimal fit surfaces of the bone specimens were between 0.29 and 0.42 mm. After classification based on sex and size groups, the profile provided a good fit to individual bones. Consideration of the thickness of cartilage overlying the metatarsal head (MTH) may further improve the fit. The proposed approach provides the basis for a design of an MTH hemi-arthroplasty that has good anatomical congruence with the native joint.

Kinematics and laxity of a linked total elbow arthroplasty following computer navigated implant positioning

Aseptic loosening in total elbow arthroplasty (TEA) remains the most common cause of long-term failure. While several different mechanisms of implant loosening have been suggested, it is likely that one important underlying cause is implant malpositioning, resulting in changes in joint kinematics and loading. Although use of computer navigation has been shown to improve component positioning in other joints, no such system currently exists for the elbow. This study used real-time computer feedback for humeral, ulnar, and radial component positioning in 11 cadaveric extremities. An elbow motion simulator evaluated joint kinematics. Endosteal abutment of the stems of the humeral and ulnar components precluded optimal positioning in 5 and 6 specimens, respectively. Loss of the normal valgus angulation following elbow arthroplasty (p < 0.05) suggests that errors in humeral component positioning translate directly into changes in joint kinematics during active motion. These findings suggest that although computer navigation can reproduce normal joint kinematics, optimal implant positioning may require a TEA system which allows for some modularity to accommodate the normal variations in osseous morphology of the elbow.