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abstractFull article available online at Healio.com/Orthopedics. Search: 20121217-18

Operative treatment of displaced and comminuted radial head fractures involves in-ternal fixation with plates and screws in cases where reconstruction is possible and replacement with a radial head prosthesis when comminution renders the radial head unreconstructable. The purposes of this study were to evaluate the morphometry of the radial head using a modern technique and to compare the findings with several com-mercially available radial head prostheses.

Computed tomography scans of 30 cadaveric elbows and 3-dimensional reconstruc-tions were used to analyze the morphometry of the proximal radius. Results were com-pared with the manufacturer data of several radial head prostheses. Mean diameter of the radial head at the level of the fovea was 1961.58 mm (range, 15.82-21.81 mm) in the anteroposterior plane and 18.6261.78 mm (range, 15.48-22.21 mm) in the ra-dioulnar plane. Mean diameter of the radial head at its widest part was 23.1561.94 mm (range, 19.45-26.49 mm) in the anteroposterior plane and 22.4461.73 mm (range, 19.64-25.44 mm) in the radioulnar plane. Mean diameter of the radial head at the level of the head–neck junction was 15.4261.59 mm (range, 11.80-18.46 mm) in the antero-posterior plane and 14.7561.39 mm (range, 12.32-17.31 mm) in the radioulnar plane. Statistically significant sex differences existed in the maximum diameter of the radial head, the diameter at the level of the head–neck junction, and the length of the radial head. Currently available radial head prostheses cover the range of sizes encountered. Products with a choice of head and stem sizes in any combination are preferable. In unstable elbow fractures, correct implant size is an important factor to avoid subluxation of the radial head (Mason type IV fractures) if collateral ligaments are sufficient.

The authors are from the Department of Traumatology (PP, LS, WP) and the Department of Radiology (KD), Medical University of Graz, Graz, Austria; and from the Specialist Registrar Royal London Rotation (NH), Royal London Hospital, London, United Kingdom.

The authors have no relevant financial relationships to disclose.Correspondence should be addressed to: Paul Puchwein, MD, Department of Traumatology, Medical

University of Graz, Auenbruggerplatz 7a, A-8036 Graz, Austria (paul.puchwein@medunigraz.at).doi: 10.3928/01477447-20121217-18

Computer-aided Analysis of Radial Head MorphometryPaul Puchwein, MD; niMa heiDari, MD; Katrin Dorr, MD; luKas struger; wolfgang Pichler, MD

Figure: Screenshot of Mimics 3-dimensional software (Materialise, Leuven, Belgium) showing a circle quantifying the flexion between the radial head and neck in the sagittal plane.

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Fractures of the radial head and neck are one of the most common fractures about the elbow, compris-

ing 33% of all elbow fractures and 1.5% to 4% of all fractures in adults.1 A com-mon mechanism of injury is a fall on an outstretched hand with an extended and pronated forearm.2 Operative treatment of displaced and comminuted radial head fractures involves open reduction and in-ternal fixation with plates and screws in cases where reconstruction is possible and replacement with a radial head prosthe-sis when comminution renders the radial head unreconstructable.3

In 1954, Mason4 classified the dis-placement of radial head fractures. This classification was subsequently modi-fied by Broberg and Morrey5 in 1987 and Hotchkiss6 in 1997. In Hotchkiss type III fractures, resection or replacement of the radial head with a prosthesis may be nec-essary. However, these implants may not always precisely recreate the complex anatomy of the proximal radius.7,8

The purpose of this study was to evalu-ate the morphometry of the radial head us-ing a modern technique and compare the findings with several commercially avail-able radial head prostheses.

Materials and MethodsThirty cadaveric elbows preserved

using Thiel’s embalming method were examined in the supine position using a 64-slice Siemens Somatom Sensation computed tomography system (0.6 mm contiguous axial slices) (Siemens Medical Solutions USA, Inc, Malvern, Pennsylvania). Digital Imaging and Communications in Medicine raw data sets were reconstructed using Mimics 3-dimensional software (Materialise, Leuven, Belgium). Extremities with se-vere arthrosis, evidence of trauma, or other pathological changes were excluded from the study. Mean age of the donors at death was 72.5 years (range, 59-98 years). Fourteen elbows were from male donors and 16 were from female donors. Sixteen

elbows were right elbows and 14 were left elbows. The results were recorded on Excel 2003 software (Microsoft Corp, Redmond, Washington). Two-sample t test was used for calculating sex differ-ences. A P value of .05 or less was consid-ered statistically significant.

To the authors’ knowledge, no pub-lished standardized methods for measur-ing the radial head exist. Therefore, the following points of reference were used to describe the geometry of the radial head and neck for the purposes of this study.

The first 4 points were set on the most proximal projections of the fovea of the radial head to measure the anteroposte-rior (AP) and radioulnar (RU) diameters (Figure 1). The radial head is slightly barrel shaped and widens before nar-rowing again to join the radial neck. Measurements were performed in the AP and RU planes between points set at the widest part of the radial head to quantify its maximum diameters (Figure 2). Four more points were set at the head–neck junction as determined by the vertex of the curve of the neck as it joins the shaft in the AP and RU planes. The vertex was defined by the point of the curve that is

farthest from a line between the beginning and end of the curve (Figure 3).

Two pairs of points 5 mm distal to those at the head–neck junction on the periosteal surface of the radial shaft in the AP and RU planes were chosen and labeled shaft (Figure 3). The head–shaft angle was calculated between the points max head, junction, and shaft at each of the measure-ment points for the anterior, posterior, ul-nar, and radial sides (Figure 3).

To determine the lengths of the ante-rior, posterior, radial, and ulnar aspects of the radial head, the distance between each of the 4 fovea points and the correspond-ing junction point was measured (Figure 3). To quantify the flexion between the radial head and neck in the sagittal plane, a circle was constructed using 3 points on the coverture. The radius of this con-structed circle was measured (Figure 4). The dimensions of various radial head prostheses are shown in Table 1.

results Mean diameter of the radial head at

the level of the fovea was 1961.58 mm (range, 15.82-21.81 mm) in the AP plane and 18.6261.78 mm (range, 15.48-

Figure 1: Screenshots of Mimics 3-dimensional software (Materialise, Leuven, Belgium) showing measure-ments of the most proximal projections of the fovea. Coronal (A), transverse (B), and sagittal (C) views of the radial head of the left elbow (A). Anteroposterior 3-dimensional reconstruction of the elbow (D).

1A 1B

1D1C

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22.21 mm) in RU plane. Mean diameter of the radial head at its widest part was 23.1561.94 mm (range, 19.45-26.49 mm) in the AP plane and 22.4461.73 mm (range, 19.64-25.44 mm) in the RU plane. Mean diameter at the level of the head–neck junction was 15.4261.59 mm (range, 11.80-18.46 mm) in the AP plane and 14.7561.39 mm (range, 12.32-17.31 mm) in the RU plane.

Because the differences between the mean AP and RU diameters were mar-ginal, the radial head was assumed to be circular, mean AP and RU measure-ments at each level (labeled diameter) were used. Mean diameter of the fovea was 19.1561.54 mm in male donors and 18.5061.66 mm in female donors. This difference did not reach statistical signifi-cance (P5.28). However, for the widest part of the radial head, sex-dependent dif-ferences were observed (men, 23.8161.58 mm; women, 21.9061.37 mm; P,.01). Similar results were observed at the head–neck junction (men, 15.7661.39 mm; women, 14.4961.12 mm; P5.01). No statistically significant difference ex-isted between the right and left radial head measurements (P5.49).

Mean radial head length on each side (anterior, 11.8161.57 mm; posterior, 11.7761.41 mm; radial, 11.8961.52 mm; ulnar, 11.7261.42 mm) was compared between male and female donors, re-sulting in significant differences (men, 12.4161.7 mm; women, 11.2660.83 mm; P,.01). Mean radius of the curvature was 8.7662.50 mm, with no significant differ-ence between the sexes (P5.59). Mean angle between the radial head and shaft was 158.8° (Table 2).

Comparing this study’s results with the dimensions of commercially avail-able radial head prostheses is demanding because different controversial concepts exist regarding radial head displacement.

The Acumed Anatomical Radial Head System (Acumed, Hillsboro, Oregon) is a metal implant with a free combinable head and cementless stem components.

Head diameter options are 20, 22, 24, 26, and 28 mm, which is more than the aver-

age head diameter in the current study. With a preset 4° ventral and 4° ulnar

Figure 3: Screenshots of Mimics 3-dimensional software (Materialise, Leuven, Belgium) showing 1 of the 4 shaft–head angles (radial angle) and measurement of the head length (ulnar head length). Coronal view of the radial head of the left elbow showing the radial and ulnar shaft points measured 5 mm distal to cor-responding junction points (A). Sagittal view showing the anterior and posterior junction and shaft points (B). Oblique front view on the reconstructed elbow showing the radial shaft–head angle (C). Coronal view of the radial head showing the ulnar head length between the fovea point and the junction point (D).

3A 3B

3C 3D

2A 2B

Figure 2: Screenshots of Mimics 3-dimensional software (Materialise, Leuven, Belgium) showing mea-surements of the widest part of the radial head and junction area. Coronal view of the radial head of the left elbow (A). Transverse view of the proximal radial head (B). Coronal view of the radial head of the left elbow (C). Transverse view of the radial head at the level of the junction (D).

2C 2D

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angulation, right and left implants are needed.

Ascension Orthopedics (Austin, Texas) offers a metal modular radial head implant and a pyrocarbon radial head im-plant with 3 head sizes (20, 22, and 24 mm) and 4 stem sizes (each with a stan-dard or a long collar) that can be implant-ed without cement.

The Liverpool Radial Head Replacement (Biomet, Inc, Warsaw, Indiana) has a shaft angulation of 10°, two head diameters, and 13 different stems. The stems are bond-coated, which should provide a better fixation. The ExploR Radial Head by Biomet can be cemented or press-fit. Three different head sizes (20, 22, and 24 mm), 5 different head lengths, and 5 different stems are offered.

The Radial Head metal (CoCrMo) implant (Corin Group PLC, Cirencester, United Kingdom) is coated with hydroxy-apatite and titanium. Three head sizes (18, 21, and 25 mm) and 3 different stems are offered.

Another radial head prosthesis is the rHead implant (Small Bone Innovations, Inc, Morrisville, Pennsylvania), which is offered in a lateral version (head can be loaded from lateral using a less invasive approach) and a recon version (bipolar head with the ability of a free angulation up to 20°). The implants are made of met-al (CoCr) and feature a fully coated stem. The shaft angulation is 12°. Three head

Figure 4: Screenshot of Mimics 3-dimensional software (Materialise, Leuven, Belgium) showing a circle quantifying the flexion between the radial head and neck in the sagittal plane.

4

Table 1

Dimensions and Specifications of Radial Head Prostheses

Prosthesis

Diameter (Length), mm

Special FeaturesHead Stem

Anatomic Radial Head Systema

20 22 24 26 28

6 (25) 7 (25) 8 (25) 9 (25) 10 (25)

Chirality (different implants for right/left arms);

head-socket 10, 12, 14, 16, and 18

Carbon Modular Radial Headb

20 22 24

4 stem sizes each in long

version

Pyrocarbon

ExploR Radial Headc 20 22 24

(10, 12, 14, 16, 18)

5 stem sizes

Liverpool Radial Head Replacementc

16 18

(6-18, step 2) (14-24, step 2)

10° angulation; bond-coated stem

Radial Head metal (CoCrMo)d

18 (9, 13) 21 (11,15) 25 (12,17)

10 (28) 12 (31) 14 (33)

rHeade 18 (7.2) 21 (10.2) 24 (13.2)

6.4 (16) 7.2 (18) 8.0 (20) 8.8 (22)

Recon version

Solar Radial Headf Small Medium

8 9 11 12 15

CRF II Judetg 19 22

6.5 8

Bipolar

MoPyCg 18 (9) 20 (10) 22 (11)

7 (40) 8 (44) 9 (48) 10 (50)

Pyrocarbon neck; 15° angulation;

neck lengths: 5, 6.5, 8, 10 mm

Evolve Prolineh 18 20 22 24 26 28

4.5-9.5 Step 1

12 and 14

12 and 14 mm head

Swansonh 19 20 21 22

23 (10-13.5)

27-32 Not modular combinable

aAcumed, Hillsboro, Oregon. bAscencion Orthopedics Inc, Austin, Texas. cBiomet, Inc, Warsaw, Indiana. dCorin Group PLC, Cirencester, United Kingdom. eSmall Bone Innovations, Inc, Morrisville, Pennsylvania. fStryker, Kalamazoo, Michigan. gTornier, Saint-Ismier Cedex. France. hWright Medical Technology, Inc, Arlington, Tennessee.

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sizes (18, 21, and 24 mm) and 4 stems sizes with 2 collar lengths are available.

The Solar Radial Head implant by Stryker (Kalamazoo, Michigan) has a cemented stem and features 2 head sizes with 5 different stems.

Tornier (Saint-Ismier Cedex, France) offers different radial head prostheses. The commonly used CRF II implant was introduced approximately 2 decades ago. It features a shaft angulation of 15°, a head range of motion of 35°, and is made of metal (CrCo). Two head sizes (19 and 22 mm) and 2 cementable stems (6.5 and 8 mm) are available. The newer MoPyC implant is made of pyrocarbon and offers the same shaft angulation and a cement-less press-fit implantation. Its smaller head sizes (18, 20, and 22 mm) are com-parable with the sizes found in the current study. Four neck sizes and 4 shaft sizes are free combinable.

Wright Medical Technology, Inc (Arlington, Tennessee), offers 2 radial head implants. The Swanson Titanium Radial Head Implant is available in 5 head diameters (19-23 mm). The stem size de-pends on the head, and the components are not combinable. A Silicon Head version is also offered. The modular Evolve system is offered with 6 head diameters (18, 20, 22, 24, 26, and 28 mm), lengths of 11, 13, or 15 mm, and 6 stem sizes, each with a standard neck, a 2-mm neck, and a 4-mm neck. Many combinations are possible.

discussionOperative treatment of radial head and

neck fractures consists of open reduction and internal fixation when a stable, reli-able fixation can be achieved. In fractures where comminution renders the fracture unreconstructable, the fragments are ex-cised and a metal radial head prosthesis is inserted.

Some biomechanical studies have em-phasized the importance of correctly siz-ing the radial head prosthesis at the time of implantation.1 A short, small prosthesis can lead to valgus instability, whereas a

long implant has the po-tential to overstuff the ra-diocapitellar joint. Some authors have suggested that a difference of no more than 2 mm from the patient’s native anatomy is tolerated.9

In unstable elbow frac-tures, correct implant size is an important factor to avoid subluxation of the radial head (Mason type IV fractures) if collateral ligaments are sufficient. In the current authors’ opinion, posterior sublux-ation can occur in cases of insufficient medial collat-eral ligaments.

Tejwani and Mehta1 reported that 60% of the axial load from the forearm is transmitted through the radiocapi-tellar joint, particularly with the elbow flexed and the forearm pronated. The highest loads were recorded with the elbow extended and forearm pronated.1 Itamura et al10 reported discrepancies between the anatomy of the radial head and available radial head prostheses. Beredjiklian et al7 used magnetic reso-nance imaging to investigate the mor-phology of the radial head and reported results similar to those of the current study. They measured the minimum (22 mm) and maximum (23 mm) diameter of the radial head at the level of the convex-ity, comparable with the maximum diam-eter of the radial head in the AP (23.15 mm) and RU (22.44 mm) planes.7 Mean radial head length (12 mm) in the study by Beredjiklian et al7 was similar to the mean dorsal, ventral, radial, and ulnar length (11.861.19 mm) in the current study.

Using the Poli SKY II coordinate measur-ing machine (Quality Control Technology Ltd, Nottingham, United Kingdom) and ProENGINEER software (PTC, Needham, Massachusetts), Swieszkowski et al11 ex-amined 16 radial heads and reported a mean diameter of 23.3661.14 mm. In a biometric study, Captier et al12 measured 96 radial bones using a vernier caliper and goniometer and found the fovea to be ellip-tical (more than 1 mm difference between AP and RU diameters) in 57% of bones; mean AP diameter was 21.662.9 mm and mean RU diameter was 2162.7 mm. Compared with the current study’s re-sults, Captier et al12 measured a slightly smaller diameter in both planes. They

Table 2

Measurement Results

Measurement Mean6SD Range

Diameter

AP 19.0061.58 mm 15.82-21.81 mm

RU 18.6261.78 mm 15.48-22.21 mm

Maximum head

AP 23.1561.94 mm 19.45-26.49 mm

RU 22.4461.73 mm 19.64-25.44 mm

Mean 22.7961.74 mm

Junction

AP 15.4261.59 mm 11.80-18.46 mm

RU 14.7561.39 mm 12.32-17.31 mm

Length

Ventral 11.8161.57 mm 9.09-15.44 mm

Dorsal 11.7761.41 mm 9.77-14.80 mm

Radial 11.8961.52 mm 8.34-15.04 mm

Ulnar 11.7261.42 mm 9.67-15.42 mm

Mean 11.8061.19 mm

Curvature radius 8.7662.50 mm 5.57-17.67 mm

Angle

Ventral 153.1°69.1° 134°-171.9°

Dorsal 164.8°63.8° 155.1°-170.3°

Radial 154°68.6° 136.4°-168.7°

Ulna 163.5°68.1° 147.4°-162.2°

Abbreviations: AP, anteroposterior; RU, radioulnar.

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also reported a mean radial head length of 15.3 mm,12 whereas in the current study it was 11.80 mm. This may be due to the use of dry bones as opposed to fresh. Captier et al12 detected a relationship between the an-gle of the axis of the radial neck and diaphy-sis and the shape of the fovea. They reported a mean angle of 166.75°63° in specimens with a circular fovea and 168.62°63.2° in specimens with an oval-shaped fovea. They postulated that pronation is facilitated due to deviation of the radial tuberosity by 2 mm from the incisura.12

Popovic et al8 scanned 51 proximal radii using computed tomography and compared their measurements with those of a commercially available radial head prosthesis. They reported results for radial head diameter (22.861.9 mm maximum and 21.861.9 mm minimum) comparable to the current study and described sex-dependent differences in radial head size. They showed that the smaller 19-mm im-plant is too small for most adults, whereas the 22-mm implant should fit in most cas-es. They also recommended that the shaft and head of the implant should be used in any combination because no correlation seemed to exist between head size and in-tramedullary neck diameter.8

Itamura et al10 examined 22 elbows us-ing computed tomography with the forearm placed in different positions and reported a maximum diameter of 22.362.4 mm

and a minimum diameter of 20.961.9 mm, comparable with the measurements in the current study (Table 3). However, their mean radial head length measurement (11.861.19 mm) differed from those of the current study because different mea-surement points were used.

Numerous radial head prostheses from a variety of manufacturers are available on the market (Table 1). Most implants come in several head sizes covering the anatomical range demonstrated by the current study’s measurements, but not all products offer the possibility of fully in-terchangeable head and shaft sizes.

New isoelastic (pyrocarbon) prostheses should offer better gliding ability without wear. First results from animal studies and retrospective clinical studies show advan-tages of pyrocarbon prostheses compared with metal prostheses.13-16 Recent case se-ries on the use of bipolar radial head pros-theses report good functional results.17,18 In a cadaveric study, Moon et al19 reported that a bipolar prosthesis was unable to re-sist subluxation as well as the native radial head or a monopolar prosthesis.

Summarizing the aforementioned stud-ies, reliable, comparable values were found for small and large radial head diameters, whereas radial head and neck length and head–diaphysis angle measurements are difficult to compare in the absence of well-defined landmarks.

In unstable elbow fractures, correct implant size is an important factor to avoid subluxation of the radial head (Mason type IV fractures) if collateral ligaments are sufficient. Measurement of the contralateral side is a valid option to determine the size of the fractured radial head and to choose the correct implant size. Currently available radial head pros-theses cover the range of sizes encoun-tered in the current study. Implants with a choice of head and stem sizes in any com-bination are preferable. Several prosthesis design features cannot be easily com-pared, but anatomic ovoid implants affect kinematics more physiologically.

references 1. Tejwani NC, Mehta H. Fractures of the ra-

dial head and neck: current concepts in man-agement. J Am Acad Orthop Surg. 2007; 15(7):380-387.

2. Gebauer M, Rücker AH, Barvencik F, Rueger JM. Therapie der Radiusköpfchenfraktur. Unfallchirurg. 2005; 108(8):657-667.

3. Pike JM, Athwal GS, Faber KJ, King GJ. Ra-dial head fractures—an update. J Hand Surg Am. 2009; 34(3):557-565.

4. Mason ML. Some observations on fractures of the head of the radius with a review of one hundred cases. Br J Surg. 1954; 42(172):123-132.

5. Broberg MA, Morrey BF. Results of treat-ment of fracture-dislocations of the elbow. Clin Orthop Relat Res. 1987; (216):109-119.

6. Hotchkiss RN. Displaced fractures of the ra-dial head: internal fixation or excision? J Am Acad Orthop Surg. 1997; (5):1-10.

7. Beredjiklian PK, Nalbantoglu U, Potter HG, Hotchkiss RN. Prosthetic radial head com-ponents and proximal radial morphology: A mismatch. J Shoulder Elbow Surg. 1999; 8(5):471-475.

8. Popovic N, Djekic J, Lemaire R, Gillet P. A comparative study between proximal ra-dial morphology and the floating radial head prosthesis. J Shoulder Elbow Surg. 2005; 14(4):433-440.

9. Moghaddam A, Lennert A, Studier-Fischer S, Wentzensen A, Zimmermann G. Pros-thesis after comminuted radial head frac-tures Midterm results. Unfallchirurg. 2008; 111(12):997-1004.

10. Itamura JM, Roidis NT, Chong AK, Vaish-nav S, Papadakis SA, Zalavras C. Com-puted tomography study of radial head morphology. J Shoulder Elbow Surg. 2008; 17(2):347-354.

Table 3

Measurement Results in Comparable Studies

Range, mm

Study Head Size Length Head–Diaphysis Angle

Current study 23.15 22.44 11.89 11.72 153°-165°

Beredjiklian et al7 23 22 12 12 N/A

Popovic et al8 22.8 21.8 N/A 9.93 N/A

Itamura et al10 22.3 20.9 9.8 N/A N/A

Swieszkowski et al11 23.36 22.26 N/A N/A N/A

Captier et al12 21.6 21 15.3 N/A 167°-169°

Abbreviation: N/A, not available.

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11. Swieszkowski W, Skalski K, Pomianowski S, Kedzior K. The anatomic features of the ra-dial head and their implication for prosthesis design. Clin Biomech (Bristol, Avon). 2001; 16(10):880-887.

12. Captier G, Canovas F, Mercier N, Thomas E, Bonnel F. Biometry of the radial head: biome-chanical implications in pronation and supina-tion. Surg Radiol Anat. 2002; 24(5):295-301.

13. Cook SD, Beckenbaugh RD, Redondo J, Popich LS, Klawitter JJ, Linscheid RL. Long-term follow-up of pyrolytic carbon metacarpophalangeal implants. J Bone Joint Surg Am. 1999; 81(5):635-648.

14. Cook SD, Thomas KA, Kester MA. Wear characteristics of the canine acetabulum against different femoral prostheses. J Bone Joint Surg Br. 1989; 71(2):189-197.

15. Sarris IK, Kyrkos MJ, Galanis NN, Papavasi-liou KA, Sayegh FE, Kapetanos GA. Radial head replacement with the MoPyC pyrocar-bon prosthesis. J Shoulder Elbow Surg. 2012; 21(9):1222-1228.

16. Lamas C, Castellanos J, Proubasta I, Dominguez E. Comminuted radial head fractures treated with pyrocarbon prosthet-ic replacement. Hand (N Y). 2011; 6(1):27-33.

17. Burkhart KJ, Mattyasovszky SG, Runkel M, et al. Mid- to long-term results after bipolar radial head arthroplasty. J Shoulder Elbow Surg. 2010; 19(7):965-972.

18. Celli A, Modena F, Celli L. The acute bipo-lar radial head replacement for isolated un-reconstructable fractures of the radial head. Musculoskelet Surg. 2010; 94(suppl 1):S3-S9.

19. Moon JG, Berglund LJ, Zachary D, An KN, O’Driscoll SW. Radiocapitellar joint stability with bipolar versus monopolar radial head prostheses. J Shoulder Elbow Surg. 2009; 18(5):779-784.

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