Morphometric parameters of the radial neck: an anatomical study

Avoiding Articular Breakthrough in Screw Fixation of Radial Head Fractures

Background

Methods

Results

Conclusion

Long-Term Outcomes of Radial Head Arthroplasty in Complex Elbow Fracture Dislocation

The purpose of the current study was to investigate the long-term outcomes of radial head arthroplasty in complex elbow injuries through radiographic analysis and functional correlation. We evaluated 24 radial head arthroplasties in 24 consecutive patients with complex elbow fracture dislocation. All patients were treated with a single type of modular monopolar prosthesis containing smooth stem in press-fit implantation. Clinical survey using the Mayo Elbow Performance Score (MEPS), self-reported scales of shortened Disabilities of the Arm, Shoulder, and Hand (QuickDASH) and the visual analog scale (VAS) at more than 10-year follow-up were reported and compared to 2-year outcomes. Periprosthetic osteolysis was measured in the 10 zones of prosthesis-cortical interface with a modified radiolucency score, which was calibrated by each prosthesis size. Pearson correlation analysis was performed to detect the association between periprosthetic radiolucency and clinical assessment. At the final follow-up, MEPS, QuickDASH score and VAS score averaged 82.5 ± 15, 14.1 ± 14.3 and 1.6 ± 1.2 respectively. A decline in functional status was noted, with decreased mean MEPS and increased mean QuickDASH and VAS scores as compared to the 2-year results while the difference was insignificant. Periprosthetic osteolysis was more prevalent around stem tip of zone 3 and zone 8. The final and 2-year radiolucency scores averaged 7.4 ± 4.2 and 2.6 ± 2.3 respectively with significant difference. Pearson correlation analysis indicated that the difference between radiolucency scores and clinical outcomes in MEPS/QuickDASH/VAS was -0.836, 0.517 and 0.464. Progression of periprosthetic osteolysis after postoperative 10 years is more prevalent around the stem tip with moderate to high correlation to clinical outcomes. Sustained follow-up is warranted to justify subsequent surgery for revision or implant removal.

Clinical anatomy and biomechanics of the elbow

The anatomy of the elbow joint had been studied extensively over the last 2 decades. The increased understanding of the anatomy and contribution of the anatomical structures to the elbow biomechanics had enabled surgeons to improve the results of surgical reconstruction and fracture fixation. This review articles intend to summarise the salient functional and clinical anatomical and relevant biomechanical data that had been published recently.

Stem Length and Neck Resection on Fixation Strength of Press-Fit Radial Head Prosthesis: An In Vitro Model

PURPOSE

Various radial head prosthesis designs are currently in use. Few studies compare different prosthetic designs. We hypothesized that increasing a cementless implant stem's length would reduce stem-bone micromotion, with both short and long neck cuts. We also hypothesized that a minimum stem length might be required for the initial fixation strength of a press-fit implant.

METHODS

In 16 fresh-frozen cadaveric elbows (8 pairs), the radial head and neck were cut either 10 or 21 mm below the top of the head. Modular cementless stems were inserted and sequentially lengthened in 5-mm increments. Micromotion under eccentric loading was tested after each incremental change.

RESULTS

Incremental lengthening of the prosthetic stem and the amount of neck resection (10-mm cut vs 21-mm cut) both had a significant effect on micromotion. After a 10-mm radial head-neck resection, we observed a significant decrease in micromotion with stem lengths of 25 mm or greater, whereas with 21 mm of neck resection there was no further reduction in micromotion with increased stem length. These differences can be explained, at least in part, by the concept of the cantilever quotient: the ratio of the head-neck length outside the bone to the total length of the implant.

CONCLUSIONS

The length of the stem affects the initial stability of press-fit radial head prostheses when the level of head and neck resection is at the minimum (ie, 10 mm) for currently available prosthetic designs. At this resection level, stems 25 mm or greater had significantly higher initial stability, but all stem lengths tested had mean micromotion values within the threshold for bone ingrowth.

CLINICAL RELEVANCE

The length of a radial head prosthetic stem affects the initial stability of press-fit radial head prostheses when the level of head and neck resection is at the minimum (ie, 10 mm) for currently available prosthetic designs.

Morphometry of the radiocapitellar joint: is humeral condyle diameter a reliable predictor of the size of the radial head prosthesis?

BACKGROUND AND HYPOTHESIS

Radial head arthroplasty (RHA) is a reliable procedure to manage complex injuries of the elbow, but complications due to inadequate sizing have been observed. Radiocapitellar morphometry has been studied widely, but RHA preoperative planning is not yet well defined. We hypothesized that specific morphologic parameters of the radiocapitellar joint measured with simple clinical software for radiographic analysis could be useful tools for clinical practice to predict RHA size preoperatively.

METHODS

Radiologic radiocapitellar joint dimensions (humeral condyle diameter [HCDi], radial head diameter [RHDi], and radial head height) were analyzed on true anteroposterior and lateral radiographs, using commercial picture archiving and communication system software, in 43 patients with non-osseous pathology of the elbow and 24 patients with RHA. Interobserver concordance was studied, and a regression model to relate different parameters was developed.

RESULTS

Interobserver concordance was greater than 0.8 for HCDi and RHDi on the lateral view and RHDi on the anteroposterior view for the general population. The parameter with the best correlation with the radial head arthroplasty diameter (RHADi) size was HCDi on the lateral view. A regression model was calculated and defined as follows: RHADi = 6.99 + 0.733 × HCDi on lateral view. This model allows prediction of RHADi in 67% of cases.

CONCLUSION

Radiologic radiocapitellar parameters show good interobserver reliability. RHADi can be calculated preoperatively from HCDi on the lateral view in 67% of cases.

Contribution of cartilage to size and shape of radial head circumference: magnetic resonance imaging analysis of 78 elbows

BACKGROUND

The aims of our study were to quantify cartilage thickness at the minimum and maximum diameters of the radial head circumference and to investigate its influence on the size and shape of the proximal radius.

METHODS

We analyzed high-definition magnetic resonance imaging scans of 78 healthy elbows in 19 men and 20 women, with a mean age of 28 (21-32) years. All measurements were estimated in the axial plane just distal to the fovea radialis. Maximum and minimum bone diameters, maximum and minimum total diameters (including cartilage thickness), and cartilage thickness were calculated. Cartilage thickness was measured at 4 different points: (1) at the articular side of the maximum diameter (point A), (2) at the nonarticular side of the maximum diameter (point B), (3) at the medial side of the minimum diameter (point C), and (4) at the lateral side of the minimum diameter (point D). Pearson correlation and t test were used for the statistical analysis.

RESULTS

Mean maximum and minimum bone diameters and maximum and minimum total diameters were 22.2, 21.5, 24.0, and 23.2 mm, respectively. All differences between diameters were statistically significant. Mean cartilage thickness at points A, C, and D was 1.7, 0.8, and 0.8 mm, respectively. No measurable cartilage thickness was found at point B. No significant correlation was found between bone diameters and cartilage thickness.

CONCLUSIONS

Cartilage surface significantly increases and modifies the size and shape of the radial head. The observation that cartilage thickness varies between subjects and does not correlate with bone parameters suggests that the diameters of the radial head cannot be inferred from indirect measurements of dry bones or radiographs.

Fractures of the radial head and neck

The majority of simple fractures of the radial head are stable, even when displaced 2 mm. Articular fragmentation and comminution can be seen in stable fracture patterns and are not absolute indications for operative treatment. Preservation and/or restoration of radiocapitellar contact is critical to coronal plane and longitudinal stability of the elbow and forearm. Partial and complete articular fractures of the radial head should be differentiated. Important fracture characteristics impacting treatment include fragment number, fragment size (percentage of articular disc), fragment comminution, fragment stability, displacement and corresponding block to motion, osteopenia, articular impaction, radiocapitellar malalignment, and radial neck and metaphyseal comminution and/or bone loss. Open reduction and internal fixation of displaced radial head fractures should only be attempted when anatomic reduction, restoration of articular congruity, and initiation of early motion can be achieved. If these goals are not obtainable, open reduction and internal fixation may lead to early fixation failure, nonunion, and loss of elbow and forearm motion and stability. Radial head replacement is preferred for displaced radial head fractures with more than three fragments, unstable partial articular fractures in which stable fixation cannot be achieved, and fractures occurring in association with complex elbow injury patterns if stable fixation cannot be ensured.

The anatomy of the proximal radius: implications on fracture implant design

BACKGROUND

The proximal radius features a complex anatomy. Several studies have been published on the anatomy using different technical approaches; however, most of these studies were conducted with a special focus on parameters relevant to radial prosthetic design. The purpose of our study was to explore the complex geometry of the proximal radius with regard to fracture implant design.

METHODS

Our computed tomography-based measurements of 78 multiplanar reformatted radii allow for exact assessment of its geometry and offer a scientific rationale towards the design of fracture implants. We conducted measurements on the radial head, the radial neck, the radial tuberosity, the radial head-to-neck angle, and the safe zone.

RESULTS

A wide range of normal anatomy has been demonstrated for all parameters. Sex differences are statistically significant in all registered parameters, except the radial head-to-neck angle. Although measurements of maximum vs minimum radial head, neck, and tuberosity diameters show close correlation, diameter-to-length correlations, such as radial head diameter vs radial head height and radial neck diameter vs radial neck length, are low.

CONCLUSIONS

Besides the wide range in size, intraindividual parameter variations have to be taken into account in the design of anatomically precontoured plates. The results of this study indicate that these plates will still need to offer the ability of "bend to match."

Anatomical variations of the proximal radius and their effects on osteosynthesis

PURPOSE

In fractures of the radial head and neck requiring open reduction and internal fixation, osteosynthesis may be safely applied in a limited zone. We conducted a morphometric study of the proximal radius at the level of the safe zone to identify different morphologic types of this anatomical region.

METHODS

We analyzed 44 dried cadaveric radii. We measured the whole length of the radius, the length of the neck and head, and the minimum and maximum diameter of the radial head. The morphologic aspect of the neck-head curvature of the safe zone was evaluated qualitatively and quantitatively.

RESULTS

The proximal radius at the level of the safe zone exhibited different radii of bending. In particular, we identified a morphologic type A, which showed a flat profile (25% of cases), morphologic types B and C, which showed a low concave curvature (64%), and a marked concave curvature (11%), respectively, of the safe zone.

CONCLUSIONS

The profile of the proximal radius in the safe zone shows substantial morphologic variations that should be taken into account when operating on fractures of the proximal radius, to avoid malunions, pain, and stiffness of the elbow joint. A preoperative radiograph of the contralateral uninjured radius may be helpful in selecting the most appropriate internal fixation device to reconstruct the proximal radius after comminuted fractures.

CLINICAL RELEVANCE

Knowledge of the proper bending radius of the safe zone allows the surgeon to select the most appropriate plate, and to achieve good fracture reduction and anatomical restoration of the proximal radius.

Radial head translation measurement in healthy individuals: the radiocapitellar ratio

HYPOTHESIS

We hypothesized that the radiocapitellar ratio (RCR) is a valid and reproducible method to assess radial head translation in healthy individuals and that the normal RCR of healthy individuals is 0%.

MATERIALS AND METHODS

Lateral radiographs of the elbow were examined in 40 healthy patients. The measurement method of the RCR was the displacement of the radial head (minimal distance between the right bisector of the radial head and the center of the capitellum) divided by the diameter of the capitellum. Intraobserver and interobserver reliability was evaluated using intraclass correlation (ICC).

RESULTS

The RCR was 4% ± 4% (range, -7% to 19%). The mean RCR of 4% measured in this cohort represents an anterior displacement of 1 mm in a capitellum of 25 mm. Intraobserver reliability was good (ICC, 0.72) and interobserver reliability was fair (ICC, 0.52). A significant side-to-side correlation was observed (r = 0.4, P = .009). No difference was identified between men and women, and no correlation was identified between age and the RCR. The standard deviation of the centered RCR measurements was 3%, which represented the variability of RCR measurements.

CONCLUSIONS

The results of this study confirm the traditional belief that in the normal elbow, the radial head is generally aligned towards the capitellum on lateral radiographs. Accordingly, a RCR observed outside the ranges of 1 mm posterior (-5%) to 3 mm anterior (13%) in a 25 mm capitellum suggests a misalignment at the RC joint of the elbow. The RCR method to assess RC joint translations has demonstrated a normal distribution in healthy individuals and good reliability.

Influence of prosthetic design on radiocapitellar concavity-compression stability

BACKGROUND

Radial head prostheses are available with multiple geometric properties. The effect of design features on radiocapitellar stability has not been investigated.

HYPOTHESIS

The shape (depth and radius of curvature) of the articulating dish of a radial head prosthesis affects radiocapitellar stability.

MATERIALS AND METHODS

Radiocapitellar stability due to concavity-compression was evaluated in 8 fresh frozen elbows before and after radial head replacement with 2 different designs of radial head implants (RH 1 and RH 2). Both functioned as monopolar implants. Peak forces resisting subluxation and force-displacement characteristics were compared between the 2 and to the native radial head.

RESULTS

Radial head design significantly affected radiocapitellar stability. RH 1, which had a deeper dish than RH 2, required significantly higher peak forces to subluxate the radiocapitellar joint. The peak subluxation forces and the slopes of the force-displacement curves were not significantly different from the native radial head for RH 1, but they were for RH 2.

CONCLUSION

The shape of the articular dish (depth, radius of curvature) of a monopolar radial head implant affects its contribution to radiocapitellar stability. An implant that mimics normal anatomy is more effective than a shallow radial head implant with a radius of curvature that is longer than normal.

Radial head prosthesis micromotion characteristics: Partial versus fully grit-blasted stems

BACKGROUND

Compared to fully textured prosthetic stems, partial texturing lessens bone loss due to stress shielding and makes removal easier. However, initial press-fit stability is necessary for bone ingrowth.

HYPOTHESIS

There is no significant difference in the initial stability of radial head prostheses that are partially grit-blasted compared to those that are fully grit-blasted.

MATERIALS AND METHODS

Cadaveric radii were implanted with partial or fully grit-blasted radial head prostheses. Micromotion of the stem at the isthmus of the canal and stem tip were measured under circumstances simulating eccentric loads.

RESULTS

Micromotion was not significantly different in the fully grit-blasted stems (isthmus, 11 ± 1 μm; tip, 21 ± 2 μm) and partially grit-blasted stems (isthmus, 13 ± 2 μm; tip, 25 ± 2 μm) (P = 0.4). The direction of loading had no effect on micromotion characteristics in either the fully or partially grit-blasted stems (P = .07).

DISCUSSION

Micromotion is comparable in partially and fully grit-blasted radial head prosthetic stems. For both stem surfaces, micromotion was well within the range that is conducive for bone ingrowth. A partially textured stem might have less bone loss due to stress shielding, making it easier to remove without destroying bone.

CONCLUSION

The initial stability of a radial head stem that is partially grit-blasted only at the proximal end is comparable to that of a radial head stem that is grit-blasted along its entire length.

Nasal, sellar, and sphenoid sinus measurements in relation to pituitary surgery

A study of 24 adult Caucasian cadavers was undertaken to assess and document the anatomical measurements within the nasal cavity and sphenoid sinus as routes of instrumentation utilized in sublabial transsphenoidal and endonasal endoscopic approaches. Five measurements were performed. The mean thickness of the anterior sellar wall was 0.8 +/- 0.3 mm for both the sellar and presellar types of sinuses, respectively. Also, the mean thickness of the bony floor of the sellar type of sinus was 0.9 +/- 0.4 mm. In addition, the mean depth of the sphenoid sinus was 13.6 +/- 5.1 mm for the sellar type and 13.2 +/- 3.9 mm for the presellar type of sinus. Furthermore, the mean distance between the suspinale (inferior-posterior edge of the anterior nasal spine) and the anterior sphenoid wall was 62.3 +/- 4.6 mm for the sellar type of sinus (P < 0.05) and 60.6 +/- 2.9 mm for the presellar type of sinus, while the distance between the subspinale and the anterior sellar wall had a mean value of 75.9 +/- 6.3 mm for the sellar type of sinus (P < 0.05) and 73.8 +/- 4.2 mm for the presellar type of sinus, with the distance of the sellar type sinus being greater for male specimens. Sphenoid sinus pneumatization was of a conchal type in 4%, presellar type in 28%, and sellar type in 68% of subjects examined. The results of the current study expand upon current anatomical knowledge and may be beneficial in the future refinement of surgical instrument design.

Simple overlay device for determining radial head and neck height

BACKGROUND

The purpose of this study was to test the hypothesis that a simple overlay device can be used on radiographs to measure radial head and neck height.

MATERIALS AND METHODS

Thirty anteroposterior elbow radiographs from 30 patients with a clinical diagnosis of lateral epicondylitis were examined to measure radial head and neck height. Three methods using different points along the bicipital tuberosity as a landmark were used. Method 1 used the proximal end of the bicipital tuberosity, method 2 used the most prominent point of the bicipital tuberosity, and method 3 used a simple overlay device (SOD) template that was aligned with anatomic reference points. All measurements were performed three times by three observers to determine interobserver and intraobserver reliability.

RESULTS

Intraclass correlation coefficients revealed higher interobserver and intraobserver correlations for the SOD template method than for the other two methods. The 95% limits of agreement between observers were markedly better (-1.8 mm to +1.0 mm) for the SOD template method than for the proximal point method (-3.8 mm to +3.4 mm) or the prominent point method (-5.9 mm to +4.9 mm).

CONCLUSIONS

We found that the SOD template method was reliable for assessing radial head and neck height. It had less variability than other methods, its 95% limit of agreement being less than 2 mm. This method could be helpful for assessing whether or not the insertion of a radial head prosthesis has resulted in over-lengthening of the radius.

Quantitative measurements of the volume and surface area of the radial head

PURPOSE

We investigated the hypothesis that a quantitative 3-dimensional computed tomography (Q3DCT) modeling technique based on anatomical and demographic data that can measure size, shape, and proximal articular surface area can be used to develop formulas that could predict the volume and proximal surface area of the intact radial head in patients with fractures of the radial head.

METHODS

We used a consecutive series of 50 computed tomography scans with a slice thickness of 1.25 mm or less obtained in patients with fracture of the distal humerus, but no injury to the radial head, to create 3-dimensional models. The volume and proximal articular surface area of the radial head were measured, and predictive formulas based on anatomical measurements and gender were calculated using multiple linear regression.

RESULTS

There were significant correlations between total radial head volume and proximal radial head articular surface area for height, weight, radial head diameter, radial neck diameter, coronoid diameter, and gender. Multiple linear regression modeling resulted in formulas that could account for 89% of the variation in radial head volume and 75% of the variation in proximal articular surface area.

CONCLUSIONS

The volume and proximal articular surface area of the radial head can be estimated based on anatomical measurements and gender. This may lead to better estimates of lost fragments when it is not possible to directly model the fractured radial head and computed tomography scan of the opposite limb is not available.

Stem diameter and micromotion of press fit radial head prosthesis: a biomechanical study

BACKGROUND

Aseptic loosening of the stem, ranging from mild periprosthetic lucency to symptomatic loosening leading to implant removal, has been reported in press fit radial head prostheses.

HYPOTHESIS

The purpose of this study was to determine the effect of the stem diameter and insertion force on initial stability with a press fit radial head prosthesis designed for bone ingrowth.

MATERIALS AND METHODS

Cadaveric radii were implanted with radial head prostheses of increasing stem diameter. The insertion forces for each rasp and stem were measured. Micromotion of the stem at the isthmus of the canal and stem tip were measured under circumstances simulating eccentric loads.

RESULTS

Insertion forces for all submaximum-sized rasps were similar. However, the insertion force for the maximum-sized rasp was approximately twice as large, and the insertion force for the oversized rasp was twice as large again, potentially indicating that the insertion force may be useful as a guide for determining appropriate stem size. Micromotions of the maximum diameter stem (isthmus, 41 microm; tip, 64 microm) were near the threshold for bone ingrowth, whereas the micromotions of the submaximum stem (isthmus, 253 microm; tip, 394 microm) were above this threshold.

DISCUSSION

The maximum diameter stem achieved greater stability (minimum micromotion) compared with the submaximum diameter stem.

CONCLUSION

The best fixation strength in the press fit radial head prosthesis was achieved by maximum sizing in the neck canal.

Intra-articular compressive stress of the elbow joint in extension: an experimental study using Fuji films

The use of Fuji films is simple but their manipulation and result interpretation seem to be difficult in the framework of medical research. The reliability and reproducibility of Fuji films have been proved by many previous studies. This study was undertaken to know precisely the articular zones of the elbow and to determine the compressive stress these areas undergo during different activities, in order to assess the importance of different articular contact areas. These data indicate the need for better-adapted elbow prosthesis and can be eventually used to design more durable prosthesis for the elbow. The compressive stress on the radial head was less than 25% in extension. The stress on the radial head varied from the neutral position (23% of the stress), to full pronation (11% of the stress) and to full supination (6% of the stress). The Humero-ulnar compartment had the maximum impact. Coronoid process seemed to be a fundamental element of the elbow joint in extension (60% of total compressive stress). The Medial humero-ulnar compartment was less stressed than the lateral compartment. The radial head does not seem to play a major role in the stability of the elbow in extension if the ulnar collateral ligament exists. The ulnar collateral ligament is essential to the elbow joint stability. The lifespan of a non-constrained prosthesis would depend on the existence of the couple: radial head/ulnar collateral ligament; the absence of radial head could compromise the humero-ulnar stability. This work paved the way for the designing of new non-constrained elbow prosthesis with the reconstruction of the radial head.