Summary Statement. This 3-dimensional CT study on cadaveric proximal ulna provides further insight into the size and geometry of the proximal ulna intramedullary cavity with potential applications to design and sizing of proximal ulna components. Introduction. Total elbow arthroplasty (TEA) is an established treatment for varying pathologies of the elbow with very good functional outcomes. Optimal fit of ulna components in TEA is predicated on a detailed appreciation of the 3-dimensional anatomy of the proximal ulna intra-medullary cavity, but literature remains scarce. Three-dimensional (3D) models of the proximal ulna have been constructed using computed tomography (CT) programs, accurately defining the angular relations with the cross-sectional extra-medullary dimensions. However, current CT-based thresholding techniques lack accuracy in differentiating cortical from cancellous bone in the metaphyseal region, and thus cannot properly define the intra-medullary region of uncored proximal ulnae. We investigate the geometric dimensions of the proximal ulna intra-medullary cavity using CT studies of cored cadaveric ulnae. Patients & Methods. Three-dimensional models based on CT data of 17 manually cored cadaveric proximal ulnae were created using Matlab program and analyzed. The cadaveric specimens were dissected to identify the medullary canal and coring of the canal of the proximal ulna to exclude the cancellous bone was performed as for ulna canal preparation during TEA. Using the center of a circle fitted over the trochlear ridge as the origin, the diameter, coronal and sagittal angulation of the canal were determined. The diameter, posterior and lateral offsets of the proximal medullary canal were plotted against the normalised axial distance from the origin which was represented in terms of R, the radius of the circle fitted to the trochlear ridge. The normalization of the axial distance was done to compensate for the varying individual ulna lengths. Results. The mean of the radius of the circle which was fitted to the trochlear ridge, R, was found to be 16.64 ± 2.71 mm. The minimum diameter of the canal increased from the origin and peak at 2.3R (just distal to the coronoid process) with a value of 7.08 ± 1.74 mm, decreasing in a linear fashion to 4.48 ± 0.91 mm at 6R. There was an increasing posterior offset which was linear in nature (R. 2. = 0.954) up to 6R (approximately 97mm from the origin). Likewise, the lateral offset increased in a linear fashion (R. 2. = 0.996). Discussion. The findings of our study most likely represent the effective minimum diameter for optimal implant placement, which are consistent with previously documented cadaveric dimensions. The findings also support the current tapered component design of the proximal ulna stemmed implants without the need for significant angulation. Conclusion. Our study provides further insight into the size and geometry of the proximal ulna intramedullary cavity with potential applications to design and sizing of proximal ulna components

We have investigated the anatomy of the proximal part of the ulna to assess its influence on the use of plates in the management of fractures at this site. We examined 54 specimens from cadavers. The mean varus angulation in the proximal third was 17.5° (11° to 23°) and the mean anterior deviation 4.5° (1° to 14°). These variations must be considered when applying plates to the dorsal surface of the ulna for Monteggia-type fractures. A pre-operative radiograph of the contralateral elbow may also be of value.

Coronoid fractures account for 2 to 15% of the cases with elbow dislocations and usually occur as part of complex injuries. Comminuted fractures and non-unions necessitate coronoid fixation, reconstruction or replacement. The aim of this biomechanical study was to compare the axial stability achieved via an individualized 3D printed prosthesis with curved cemented intramedullary stem to both radial head grafted reconstruction and coronoid fixation with 2 screws. It was hypothesized that the prosthetic replacement will provide superior stability over the grafted reconstruction and screw fixation. Following CT scanning, 18 human cadaveric proximal ulnas were osteotomized at 40% of the coronoid height and randomized to 3 groups (n = 6). The specimens in Group 1 were treated with an individually designed 3D printed stainless steel coronoid prosthesis with curved cemented intramedullary stem, individually designed based on the contralateral coronoid scan. The ulnas in Group 2 were reconstructed with an ipsilateral radial head autograft fixed with two anteroposterior screws, whereas the osteotomized coronoids in Group 3 were fixed in situ with two anteroposterior screws. All specimens were biomechanically tested under ramped quasi-static axial loading to failure at a rate of 10 mm/min. Construct stiffness and failure load were calculated. Statistical analysis was performed at a level of significance set at 0.05. Prosthetic treatment (Group 1) resulted in significantly higher stiffness and failure load compared to both radial head autograft reconstruction (Group 2) and coronoid screw fixation, p ≤ 0.002. Stiffness and failure load did not reveal any significant differences between Group 2 and Group 3, p ≥ 0.846. In cases of coronoid deficiency, replacement of the coronoid process with an anatomically shaped individually designed 3D printed prosthesis with a curved cemented intramedullary stem seems to be an effective method to restore the buttress function of the coronoid under axial loading. This method provides superior stability over both radial head graft reconstruction and coronoid screw fixation, while achieving anatomical articular congruity. Therefore, better load distribution with less stress at the bone-implant interface can be anticipated. In the clinical practice, implementation of this prosthesis type could allow for early patient mobilization with better short- and long-term treatment outcomes and may be beneficial for patients with irreparable comminuted coronoid fractures, severe arthritic changes or non-unions

Summary. Increased lateral ulnotrochlear joint space due to improper sizing in radial head arthroplasty may result in medial collateral ligament laxity, leading to increased osteophytes and arthritis. Introduction. Radial head (RH) arthroplasty is a common response to comminuted RH fractures. Typical complications include improper sizing, leading to changes in joint kinematics. Evidence of these changes should be visible through fluoroscopic images of affected joints. The two examined changes in this study are the ulnar deviation from distal radial translation (DRT), and the widening of the lateral ulnotrochlear joint space (LUT). Methods. Eight fresh-frozen cadaver arms were used. Initial images were taken with the native RH intact. The Kocher approach exposed the radiocapitellar (RC) joint capsule, preserving all ligaments. The RH was excised and Integra Katalyst CoCr (Plainsboro, NJ) telescoping, bipolar, RH inserted. Images were taken with implant sizings: −2mm, 0mm, +2mm, and +4mm, (from native) using 1mm washers preventing implant bipolarity. AP fluoroscopic images of the elbow were taken at full extension. Joint spaces were measured using image analysis, normalised using known radio-opaque lengths. Four LUT measurements were made, two medially and two laterally, and normalised by measuring the RH implant diameter. Each set (medial and lateral) were averaged together and the resulting value used for all comparisons. Images of distal ulnar deviation at the wrist were taken with the wrist in supination, the hand rotated medially. Measurements were from the distal medial radial tip to the distal lateral ulnar tip. Images were normalised by placing a scalpel in the same plane as measurement. Results. DRT values were difference paired for each arm using the 0mm values as baselines. One-way ANOVA of the paired values resulted in significant DT with sizing increases (p<0.01). The quotient of DRT and sizing determined comparative impact with the LUT increase. LUT joint gap measurements were percentage paired, with natives as the baseline, and One-way ANOVA used. A significant increase in LUT spacing occurred with increased sizings (p<0.01). Discussion. Increased ulnar deviation can increase loading on the TFCC, leading to possible TFCC tear, increased articular cartilage wear from carpal misalignment, and eventual wrist instability and arthritis. The percentage of the radial lengthening is represented in DRT. Over-sizing results in small percentages of increased radial length at the wrist, therefore deviation at the elbow must take place, either through rotation of the ulna, or translation. Either of these can be seen through LUT measurements. Previous measurements of the LUT space were made by Frank (2009), with similar results. This was being used as a method of improper sizing detection using radiographs. The percentage difference of LUT space for corresponding sizing: there is an increase in LUT space for every sizing; maybe due to loosening of the soft tissue from arthroplasty. Increased LUT space indicates the medial translation of proximal ulna. This can result in Medial Collateral Ligament laxity, leading to increased osteophytes, and arthritis. Use and non-treatment, can create a chronic, painful, disorder

Using an osteotomy of the olecranon as a model of a transverse fracture in 22 cadaver elbows we determined the ability of three different types of suture and stainless steel wire to maintain reduction when using a tension-band technique to stabilise the bone. Physiological cyclical loading simulating passive elbow movement (15 N) and using the arms to push up from a chair (450 N) were applied using an Instron materials testing machine whilst monitoring the osteotomy site with a video extensometer. Each osteotomy was repaired by one of four materials, namely, Stainless Steel Wire (7), No 2 Ethibond (3), No 5 Ethibond (5), or No 2 FiberWire (7).

There were no failures (movement of > 2 mm) with stainless steel wire or FiberWire and no significant difference in the movements measured across the site of the osteotomy (p = 0.99). The No. 2 Ethibond failed at 450 N and two of the five of No. 5 Ethibond sutures had a separation of > 2 mm at 450 N.

FiberWire as the tension band in this model held the reduction as effectively as stainless steel wire and may reduce the incidence of discomfort from the hardware. On the basis of our findings we suggest that a clinical trial should be undertaken

We undertook a study on eight arms from fresh cadavers to define the clinical usefulness of the lesser sigmoid notch as a landmark when reconstructing the length of the neck of the radius in replacement of the head with a prosthesis. The head was resected and its height measured, along with several control measurements. This was compared with in situ measurements from the stump of the neck to the proximal edge of the lesser sigmoid notch of the ulna. All the measurements were performed three times by three observers acting independently.

The results were highly reproducible with intra- and interclass correlations of > 0.99. The mean difference between the measurement on the excised head and the distance from the stump of the neck and the lesser sigmoid notch was −0.02 mm (−1.24 to +0.97). This difference was not statistically significant (p = 0.78).

The proximal edge of the lesser sigmoid notch provides a reliable landmark for positioning a replacement of the radial head and may have clinical application.