Biometry of the radial head: biomechanical implications in pronation and supination

Anatomical features of the proximal end of the radius and its implications for implant design

PURPOSE

The proximal radio-ulnar joint allows supination and pronation of the forearm and the humeroradial joint allows flexion and extension movements at the elbow joint. Although the proximal end of the radius is less common than other fractures, it is more common nowadays due to the prolongation of life expectancy, increased incidence of osteoporosis. There have been reports in the literature that success has not been achieved due to the lack of anatomical fit of the prosthesis. Knowledge of the morphometric features of the proximal end of the radius is important for the design of anatomically and biomechanically appropriate prostheses.

METHODS

In this study, measurements of head and neck of radius, and radial tuberosity were measured in 80 dry radii. Parameters important for prosthesis design were analysed and their correlations examined.

RESULTS

The shapes of radial head was found 36% oval and 64% circular. The mean heights of the radial head at anterior, posterior, medial, and lateral sides were 8.52 ± 1.32 mm, 9.02 ± 1.23 mm, 9.20 ± 1.59 mm, 8.05 ± 1.13 mm, respectively. The mean depth of articular facet were 1.85 ± 0.37 mm. It was determined that there was no high correlation between the parameters affecting the prosthesis design.

CONCLUSIONS

Morphological and morphometric features of the proximal radius are important for prosthesis design and implantation. The ideal radial head prosthesis design is challenging due to numerous parameters, wide ranges and low correlation, although modular designs facilitate compatibility. The widespread use of 3D printing technologies is expected to reduce the potential complications associated with prosthesis applications.

Posterior Translation of the Radial Head in Magnetic Resonance Imaging of Lateral Epicondylitis

Background

Posterolateral rotatory instability is produced by disruption of the lateral collateral ligament complex (LCLC); it is commonly induced by trauma, with few cases reported due to lateral epicondylitis. We examined the amount of posterior transition of the radial head with or without LCLC injury, common extensor tendon (CET) injury, and Baker classification in lateral epicondylitis.

Methods

We retrospectively studied patients with lateral epicondylitis of the humerus who underwent surgery between April 2016 and July 2021. Fifteen elbows with coronal and sagittal images on preoperative magnetic resonance imaging (MRI) were included. We investigated the amount of posterior transition of the radial head in sagittal MRI images of the elbow, which were compared based on LCLC and CET lesion.

Results

The mean age of patients was 49 years. The lesions in four, nine, and two patients were classified as LCLC0, LCLC1, and LCLC2, respectively. The mean radio-humeral distance values among the LCLC lesions were 0.65, 2.46, and 2.22 mm in LCLC0, LCLC1, and LCLC2, respectively, with the RHD between LCLC0 and LCLC1 differing significantly. In five, six, and four patients, the lesions were classified as CET1, CET2, and CET3, respectively. The mean RHD values among the CET lesions were 1.33, 2.68, and 1.48 mm in CET1, CET2, and CET3, respectively.

Conclusions

Our results showed that posterior transition of the radial head is greater in patients with lateral epicondylitis with LCLC lesions on MRI than those with normal findings of LCLC.

The Relationship between the Bevel of the Radial Head Epiphysis and the Posterior Synovial Fringe During Rotation of the Elbow: An Ultrasonography Study with Possible Implications Regarding the Pathophysiology of Nursemaid's Elbow

BACKGROUND

Nursemaid's elbow is the most common upper extremity injury in children under 5 years of age. However, the exact pathomechanism underlying the nursemaid's elbow remains elusive, and approximate one-third of patients present with a nonclassical history. Using a high-frequency ultrasound probe, we attempted to determine the relationship between the anterior edge of the posterior synovial fringe and the peripheral rim of the radial head epiphysis during rotation. It is possible that the primary reason for the nursemaid's elbow is due to the pronator position.

METHODS

Twenty-one patients had a history of nursemaid's elbow and had a successful reduction before enrollment in this study. A high-frequency linear array 6 to 24 MHz hockey stick transducer was used to detect small morphologic changes in the peripheral rim of the radial head epiphysis and the posterior synovial fringe during rotation of the capitellum-radial joint.

RESULTS

In complete pronation, the anterior edge of the posterior synovial fringe contacts the beveled articular surface of the radial head peripheral rim in all 21 patients. In neutral and complete supination, the anterior edge of the posterior synovial fringe contacts the convexly nonarticular surface of the radial head peripheral rim and extends deep into the foveal radius. The posterior synovial fringe and the capsule-aponeurotic membrane were tightened in passive pronation in all 21 cases. The posterior synovial fringe and the capsule-aponeurosis membrane were all loose in the neutral and supination positions.

CONCLUSION

The anterior edge of the posterior synovial fringe touches the beveled peripheral rim of the radial head epiphysis during complete pronation, and the tension of the lateral collateral ligament complex during pronation may further cause unstable conditions of the anterior edge of the posterior synovial fringe. We hypothesized that the beveled peripheral rim of the radial epiphysis and its relationship with the anterior edge of the posterior synovial fringe could be the reason why nursemaid's elbow only occurs while the elbow is in the pronator position.

Radial head distalisation with an external ring fixator as a therapy option in children with chronic posttraumatic radiocapitellar dislocations

PURPOSE

Missed monteggia-type injuries in children can result in chronic radial head dislocation with anatomic changes and osteoarticular remodeling of the radial head. In later stages, joint reconstruction is impossible and a functional radial head distalization can be a therapy option in symptomatic patients.

METHODS

From 2010 to 2018, 46 patients (18 female and 28 male, mean age 11.8 (4-20)) with chronic radius head dislocation treated in our institution were retrospectively analyzed. A radial head distalization was performed in symptomatic patients at the time of ulna lengthening and angulation by use of an external ring fixator. We analyzed the surgical and radiographic data as well as the clinical outcome of the patients measured by DASH and Mayo Elbow score.

RESULTS

16 patients (6 female, 10 male) fulfilled the criteria for functional radial head distalization. Main reason was Monteggia injury in 11 cases, and radial head fracture in 5 cases. Average follow-up was 5.1 years (range 1-9, SD 2.1). Mean time from injury was 4.14 years (range: 4 months to 12 years, SD 3.5 years). Mean duration of external fixation was 106 days (range 56-182, SD 31.2), lengthening was 21.3 mm (range 12-42, SD 8.8). Average degree of sagittal angulation 14.8° (0-32°, SD 10.7°), coronal angulation 4.4° (0-25°, SD 7.3°). DASH score showed a good result with 2.4, and the MAYO Elbow Score was excellent (95/100). No secondary luxation of the radius head was detected.

CONCLUSION

Radial head distalization with external ring fixator can be a therapy option for chronic radius head dislocations in symptomatic patients without losing stability of the elbow joint in contrast to radial head resection.

Early aseptic loosening of a press-fit radial head prosthesis - A case series of 6 patients

OBJECTIVE

Radial head arthroplasty (RHA) is the principal treatment option for comminuted radial head (RH) fractures. Here, we present six cases of failed RHA using a modular monopolar press-fit RHA that was subsequently withdrawn from the market because it was associated with a high incidence of loosening.

METHODS

We retrospectively collected data from six patients who had received Radial Head Prothesis System^TM at our centre between July 2015 and June 2016. The average follow-up was 40 months.

RESULTS

Aseptic loosening of the stem affected five (83%) of the six RHA. Four of these were symptomatic and RHA removal was performed. For these patients, the pain subsided and their elbow range of motion (ROM) improved.

CONCLUSION

While the ideal design for an RHA is still debatable, RHA is an efficient treatment option that restores elbow stability and function after a comminuted RH fracture. Importantly, removal of the prosthesis is an effective remedy following RHA associated elbow pain and decreased ROM.

Treatment of comminuted radial head fractures with personalized radial head prosthesis produced with 3-dimensional printing technology

BACKGROUND

The radial head is the forearm's pivot point for supination-pronation. Although radial head resection can be performed in comminuted radial head fractures, radial head prosthesis has gained popularity in order to prevent possible complications such as progressive valgus instability in the elbow and secondary ulnocarpal impaction that may develop due to proximal displacement of the radius. As for radial head prostheses, standard prosthetic designs do not provide the same results in everyone, and the alignment of the radial head and radial neck angle cannot be fully achieved. We believe that the radial head must be reconstructed with a complete anatomical implant. We designed and applied personalized prostheses to our patients, and in this study, we wished to share the 2-year results of these patients.

METHODS

In this study, 23 patients who had comminuted radial head fractures had personalized radial head prostheses inserted. Preoperative variables such as type of injury, age, side, additional ligament injury, operation time, number of radial head parts, neck angle of individual prosthesis, stem length, and stem diameter were noted. The mean operating time was 26 ± 9 minutes. One month postoperatively, after physical therapy, elbow range of motion, loss of strength compared to the opposite joint, Mayo elbow scores, QuickDASH scores, and patient satisfaction were evaluated. Patients were evaluated 2 years postoperatively.

RESULTS

QuickDASH and Mayo elbow scores were satisfactorily good (mean QuickDASH score: 9.091, mean Mayo score: 91.08). According to the results of the patient satisfaction questionnaire, 16 of the 23 patients reported excellent satisfaction, 5 patients good satisfaction, and 2 patients moderate satisfaction. None of the patients reported poor results.

DISCUSSION

Since personalized radial head prosthesis consists of a single monoblock, its surgical application consists of a single step and has a short operating time. As the applications in the literature increase and more studies are conducted, this subject will be better understood. Our study demonstrated that these patients, whose anatomies were individually replicated, achieved good range of motion and patient satisfaction. In fact, none of the patients reported negative results. In comminuted radial head fractures, surgical implantation of personalized radial head prosthesis is a treatment modality with easy application, short operating time, and good functional results.

Anthropometric Study of Proximal Radius in Below-Average Height Thai Women and Its Correlation with Commercially Available Radial Head Prostheses

Background: Most radial head prostheses were designed in Western countries based on the anatomical characteristics of Western populations. We hypothesised that these prostheses are too large for below-average height Thai women. The objective of this study is to evaluate the anthropometric parameters of the proximal radius in such a population and its correlation with commercially available prostheses.

Methods: Dominant elbows of 124 Thai women whose height was <155 cm were studied. Using the standard anteroposterior and lateral radiographic images, the head diameter and thickness, the distance between the articular surface and radial tuberosity, the narrowest intra-medullary canal diameter and the narrowest outer diameter of the radial neck were measured. Correlations between body height and each radiographic parameter were assessed using the Pearson correlation coefficient (PCC). The specifications of the commercial metallic radial head implants were reviewed and used to evaluate the relevant radiographic parameters.

Results: Mean of the minimum and maximum head diameter was 18.54 ± 1.11 mm and 19.13 ± 1.17 mm, respectively; the thickness was 7.43 ± 0.69 mm, the distance between the articular surface and tuberosity was 19.05 ± 1.45 mm, the intra-medullary canal diameter was 7.63 ± 1.2 mm and the outer diameter of the radial neck was 11.13 ± 1.26 mm. There is a poor correlation between the participant’s height and each parameter (PCC ≤ 0.50). In 24.2% of the participants, the smallest size of prosthetic designs with a head diameter of 20 mm is larger than +2 mm in reference to minor diameter. The minimum prosthetic head thickness is greater than the average value of the participants in 12 out of 15 designs. One participant has an outer neck diameter smaller than the smallest stem diameter of three designs.

Conclusions: Surgeons must be aware that commercially available radial head replacement implants may be too large for below-average height Thai women.

Level of Evidence: Level IV (Prognostic)

Radial head fractures: a quantitative analysis

Several classification systems for radial head fractures discuss the number of fragments and their displacement, but not the exact location. This study aimed to evaluate the location of the radial head fracture fragments and the influence of the Mason type on the size of the fracture fragment. Forty-one radial head fractures (31 Mason type I and 10 type II) with an elliptical radial head were included in this retrospective study and 3D reconstructed. First, the fragments were repositioned to their original location. Next, the orientation of the scanned forearm was evaluated using the position of the longest axis relative to the proximal radio-ulnar joint, and all radial heads were rotated to the neutral rotation. The radial head was divided into 4 quadrants (anteromedial, anterolateral, posteromedial, and posterolateral). The location of the fracture line in correlation with these 4 quadrants was evaluated. All fracture fragments were located in the anteromedial quadrant. Thirty-eight (93%) were located in the anterolateral quadrant. The posterolateral quadrant was involved in 32%. At last, the average fracture fragment size was evaluated according to the Mason classification. A significant difference was found in the average fracture fragment size between Mason type I (38% of the radial head surface) and type II (48% of the radial head surface). It was concluded that there is an important involvement of the anterior quadrants of the fracture. The mean size of the fracture is significantly larger in Mason type II compared to type I.

Avoiding Articular Breakthrough in Screw Fixation of Radial Head Fractures

Background

Methods

Results

Conclusion

Regional differences in the three-dimensional bone microstructure of the radial head: implications for observed fracture patterns

INTRODUCTION

A characterization of the internal bone microstructure of the radial head could provide a better understanding of commonly occurring fracture patterns frequently involving the (antero)lateral quadrant, for which a clear explanation is still lacking. The aim of this study is to describe the radial head bone microstructure using micro-computed tomography (micro-CT) and to relate it to gross morphology, function and possible fracture patterns.

MATERIALS AND METHODS

Dry cadaveric human radii were scanned by micro-CT (17 μm/pixel, isotropic). The trabecular bone microstructure was quantified on axial image stacks in four quadrants: the anterolateral (AL), posterolateral (PL), posteromedial (PM) and anteromedial (AM) quadrant.

RESULTS

The AL and PL quadrants displayed the significantly lowest bone volume fraction and trabecular number (BV/TV range 12.3-25.1%, Tb.N range 0.73-1.16 mm^-1) and highest trabecular separation (Tb.Sp range 0.59-0.82 mm), compared to the PM and AM quadrants (BV/TV range 19.9-36.9%, Tb.N range 0.96-1.61 mm^-1, Tb.Sp range 0.45-0.74 mm) (p = 0.03).

CONCLUSIONS

Our microstructural results suggest that the lateral side is the "weaker side", exhibiting lower bone volume faction, less trabeculae and higher trabecular separation, compared to the medial side. As the forearm is pronated during most falls, the underlying bone microstructure could explain commonly observed fracture patterns of the radial head, particularly more often involving the AL quadrant. If screw fixation in radial head fractures is considered, surgeons should take advantage of the "stronger" bone microstructure of the medial side of the radial head, should the fracture line allow this.

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.

Positioning of longest axis of the radial head in neutral forearm rotation

INTRODUCTION

The radial head has an ellipsoid shape so that a longest and a shortest axis can be defined. The aim of this study is to evaluate the position of the longest axis of the radial head (LARH) in relation to proximal radioulnar joint (PRUJ) and to the forearm in neutral position using 3D computed tomography (CT).

MATERIALS AND METHODS

3D CT reconstructions of the distal humerus, the radius and the ulna of 27 healthy volunteers (average age 27.65 ± 9.25; 24 males, 3 females) were created. First an evaluation of the elliptic form of the radial head and the location of its longest axis was performed. Next, three planes were defined: the PRUJ plane, the forearm plane and a neutral plane. Based on the angle between the forearm plane and the neutral plane, the rotation of the scanned forearm was measured. Taking this rotation into account, the position of the LARH compared to PRUJ plane and forearm plane in neutral position is recalculated.

RESULTS

The shape of the radial head is determined to be non-circular based on this study population (p < .001). In neutral position, the angle between the LARH and the forearm plane is 5.28° (SD: 15.09) and between the LARH and the PRUJ is 33.46° (SD: 13.91).

CONCLUSIONS

The position of the LARH is found to be approximately perpendicular to the forearm plane when the forearm is in neutral position and perpendicular to the PRUJ plane when the forearm is on average in 30° of pronation.

Fracture Pattern Influences Radial Head Replacement Size Determination Among Experienced Elbow Surgeons

BACKGROUND

Correct sizing is challenging in radial head replacement and no consensus exists on the implant's optimal height and width to avoid elbow stiffness and instability. Studies exists, suggesting how to appropriately choose the implant size, but the manner by which the fracture pattern influences the surgeons' operative choices was not investigated.

METHODS

The radial heads of four fresh-frozen cadaveric specimens were excised, measured, and fractured to simulate four patterns: three fragments (A); four fragments (B); comminuted (C); comminuted with bone loss (D). Nine examiners were asked to indicate first the maximum diameter of the radial heads with the help of dedicated sizing dishes and then the appropriate implant size with trial implants. Accuracy and precision were determined. A coefficient of variation was calculated and agreement was evaluated with the Bland-Altman method.

RESULTS

Accuracy and precision of radial head diameter estimation with dedicated sizing dish were 96.73% and 93.64%, (best pattern, D; worst, C). Accuracy and precision of radial head diameter estimation with trial implants were 99.71% and 90.66% (best pattern, A; worst, D). Frequent modifications occurred between the initial radial head size proposal based on the sizing dish and the radial head size chosen after use of the trial implants (47.2%).

CONCLUSIONS

Diameter estimation of radial heads with dedicated sizing dishes may be underestimated in comminuted fractures; when bone loss is present, this may lead to an overestimation, especially when using trial implants. Care is essential to determine the optimal size of the implant and to avoid overlenghtening and oversizing, which can be responsible for implant failure.

LEVEL OF EVIDENCE

Basic Science Study.

CLINICAL RELEVANCE

Knowledge of the manner by which the fracture pattern influences radial head replacement size estimation can help preventing overlenghtening and oversizing during this procedure.

Joint contact areas after radial head arthroplasty: a comparative study of 3 prostheses

BACKGROUND

Contact stresses of radial head prostheses remain a concern, potentially leading to early capitellar cartilage wear and erosion. In particular, point contact or edge loading could have a detrimental effect. The purpose of this study was to compare 3 different types of radial head prostheses in terms of joint contact areas with each other and with the native situation. The hypothesis was that the joint contact areas would be lower after monopolar arthroplasty.

METHODS

Seven fresh-frozen cadaveric upper limbs were used. Radiocapitellar contact areas of a monopolar design, a straight-neck bipolar design, and an angled-neck bipolar design were compared with each other and with the native joint. After standardized preparation, polysiloxane was injected into the loaded radiocapitellar joint to create a cast from which the joint contact area was measured. Measurements were performed at 3 angles of elbow flexion and in 3 different forearm positions.

RESULTS

In the native elbow, contact areas were highest in supination. Elbow flexion had no significant effect on native and prosthetic joint contact areas. Contact areas were decreased for all types of arthroplasties compared with the native joint (from 11% to 53%). No significant contact area difference was found between the 3 designs. However, bipolar prostheses showed lateral subluxation in neutral forearm rotation, resulting in a significant decrease in the contact areas from pronation to the neutral position.

CONCLUSIONS

All types of radial head prostheses tested showed a significant decrease in radiocapitellar contact area compared with the native joint. Bipolar designs led to subluxation of the radial head, further decreasing radiocapitellar contact.

The Patient-Specific Implant Created with 3D Printing Technology in Treatment of the Irreparable Radial Head in Chronic Persistent Elbow Instability

Successful treatment of the chronic persistent elbow instability is a challenge for orthopedic surgeons. In this form, it is important to recognize and restore the osseous stabilizer in order to obtain the concentric reduction. In the present report, we describe a case of such injury with irreparable radial head treated with patient-specific radial head prosthesis which was created with 3D printing technology. To our knowledge, this is the first report in clinical use of this kind of prosthesis for the radial head fracture. At a 24-month follow-up visit, the patient was satisfied with the functional outcomes. The Mayo Elbow Performance Index (MEPI) increased from 20 points at the preoperative day to 85 points, and the patient-based Disabilities of the Arm, Shoulder, and Hand (DASH) was reduced from 88.33 points to 28.33 points. Due to the favorable result, replacement of the radial head with the patient-specific implant could be a useful treatment for the irreparable radial head in chronic persistent elbow instability.

Complications after radial head arthroplasty: a comparison between short-stemmed bipolar and monopolar long-stemmed osteointegrative rigidly fixed prostheses

INTRODUCTION

To date, only a few studies have compared radial head prostheses (RHP) and their different anchoring principles. The aim of this study was to characterize concomitant injuries, necessary adjuvant procedures, complications, and radiological findings after implantation of two different types of RHP.

METHODS

Sixty-six patients with radial head fractures were treated with MoPyC (Tornier/France, 50 mm stem, monopolar) or SBI rHead prostheses (Small Bone Innovations/USA, 22-mm stem, bipolar) and followed up over 42 months (16-64 months). Primary objective was the detection of different loosening and explantation rates. In addition to the revision rate and the reasons for revision, we also used radiological findings to assess the dynamics of lysis phenomena.

RESULTS

Thirty-five patients (mean age 48 years; 22-73 years) were treated with the MoPyC, and 31 patients (mean age 47 years, 19-69 years) with the rHead prosthesis. Of these, 98% had a Mason 3 or 4 type of radial head fracture, and 94% showed concomitant injuries, which were addressed in 89% of cases by adjuvant procedures. The surgical revision rate was 20% (rHead 23%; MoPyC 18%). Significantly more of the rHead prostheses had to be explanted compared to MoPyC prostheses because of painful loosening (16% vs. 3%; p = 0.029). Predictors of subsequent loosening were significant radiolucent lines in the RHP over the first six months and an increase in width by two and a half times within the first 50 days after implantation.

CONCLUSION

Complex radial head fractures are frequent and difficult to treat. The monopolar long-stemmed prosthesis showed significantly lower rates of painful loosening and explanation rates than the bipolar short-stemmed prosthesis.

A new method to locate the radial head "safe zone" on computed tomography axial views

PURPOSE

Direct location of the "safe zone" on a CT axial view is impossible because the radial head is circular in shape. Previous "safe zone" location methods are not appropriate if the physician is unable to visualize the actual radial head. This study aims to introduce a new method to locate the "safe zone" on CT.

METHODS

CT scans were performed on 20 intact cadaveric upper limbs from 20 different corpses in full pronation and supination. The DICOM-format raw data were then re-sliced and analyzed in Mimics 17.0 (Materialise, Belgium). The radial interosseous border (IB) is shaped like a droplet on the axial view; its axis was selected as our reference line (RL). A parallel line in the radial head axial slice was created, and its position relative to the "safe zone" was studied. Deviation in RL direction was evaluated.

RESULTS

Safe-zone scope was 114.41°±11.99. The rotation angle from the RL to the safe-zone's anterior and posterior border was 215.03°±5.99 and 100.62°±8.12, respectively. Rotation direction (clockwise or anti-clockwise) depended on relative radius-ulna position. The safe zone was located by determining these two borders. The reference line's direction was stable in the upper half of the IB; its distance to the radial head fovea was 77.33° mm±6.24.

CONCLUSIONS

The radial head "safe zone" can be located on CT axial view based on the upper half of the IB using this new method. The method is clinically applicable to determine whether postoperative elbow malrotation results from plate impingement.

Design of Anatomical Population-Based and Patient-Specific Radial Head Implants

PURPOSE

The objective of this study was to characterize the morphology of the radial head and design population-based anatomical and patient-specific radial head implants.

METHODS

Computed tomography (CT) images of 50 normal cadaveric upper extremities (34 male, 16 female) were obtained using a 64-slice CT scanner. Surface models were ellipse-fitted and characterized. Using an intersurface distance mapping approach, the surface geometry of the population-based anatomical design (PB-An), 3 distinct patient-specific designs, and an existing axisymmetrical implant (Com-Axi) were compared with the native radial head and the overall surface mismatch was measured.

RESULTS

Morphological analysis indicated that the diameters of the outer and rim ellipses were correlated. The mean mismatch for the existing commercially available axisymmetrical implants was 0.5 ± 0.1 mm.The PB-An implants showed significantly reduced surface mismatch (0.4 ± 0.2 mm). The PS-An implant using 82 parameters in its design (0.1 ± 0.0 mm), had the lowest mean surface mismatch of any of the implants investigated.

CONCLUSIONS

The mean surface mismatch of radial head implants may be reduced using reverse engineering techniques to determine the required parameters for both population-based and patient-specific implant designs. Whether there is a significant clinical advantage of a more anatomically shaped radial head implant requires additional study. More anatomical implant shapes rely on a surgical technique to accurately position these implants during surgery. It is unclear if this can be achieved clinically using conventional techniques or whether computer-assisted surgery will be required to realize the potential advantages of a more anatomical implant.

CLINICAL RELEVANCE

This study characterized the morphology of the radial head with implications for population-based anatomical implants and patient-specific implants. The overall design of each implant was quantitatively compared with the native radial head. This study has implications for the design of patient-specific/anatomical implants and compares their use with commercially available generic implants.

Tight-fitting radial head prosthesis: does stem size help prevent painful loosening?

INTRODUCTION

The most common reason for removal of well-fixed radial head prostheses is painful loosening. We hypothesised that short-stemmed prostheses, used for radial head arthroplasty, are not associated with an increased risk of implant loosening.

METHODS

From 2002 to 2014, 65 patients were enrolled in a retrospective single-centre study. The radial head prostheses were classified as having either a long (30-mm) or short (16- to 22-mm) stem. The long-stemmed implants comprised 30 GUEPAR® DePuy Synthes (West Chester, PA, USA) and 20 Evolutive® Aston Medical (Saint-Etienne, France) devices; the short-stemmed implants comprised nine RECON and six STANDARD rHead® SBI-Stryker (Morrisville, PA, USA) devices. At last follow-up, clinical (range of motion, Disabilities of the Arm, Shoulder, and Hand score, Mayo Elbow Performance score) and radiographic (osteolysis) outcomes were assessed.

RESULTS

At a mean follow-up of 76.78 months (24-141), the rate of painful loosening [6 (40%) vs 8 (16%), p = 0.047] and osteolysis [12 (80%) vs 23 (46%), p = 0.02] were significantly higher in patients with short-stemmed versus long-stemmed implants. Despite the significant difference in loosening between stems as groups, individual stem length was not determined.

CONCLUSIONS

Tight-fitting implants with short stems are more prone to painful loosening.

Beveled posteromedial corner of the radial head: a three-dimensional micro-computed tomography modeling study

The posteromedial quadrant of the radial head is known to be different from the other quadrants. However, the explanation of this unique anatomical feature remains elusive. Hence, this study was designed to address this unique anatomical variance using three-dimensional μCT (micro-computed tomography) analysis. Nine fresh cadaveric radial heads were scanned using μCT. Three-dimensional subchondral bone and cartilage models were rendered. Both models were separated into the four quadrants at both the periphery (rim) and the articulating dish (fovea): anteromedial (AM), posteromedial (PM), posterolateral (PL), and anterolateral (AL). Each quadrant was analyzed in terms of (1) subchondral bone porosity (SBP), (2) mean subchondral bone thickness (MSBT), and (3) mean cartilage thickness (MCT). There was a significant difference between the fovea and the rim in terms of its microarchitectural features. Although within the fovea, the PM quadrant did not differ significantly from the other quadrants, a significant difference was found within the rim. In terms of SBP, PM, AM, PL and AL were calculated as 33, 37, 36 and 35%, respectively. In terms of MSBT, PM, AM, PL and AL were calculated as 0.11, 0.10, 0.09, and 0.09 mm, respectively. In terms of MCT, PM, AM, PL and AL were calculated 1.09, 0.81, 0.84 and 0.83 mm, respectively. The PM corner of the radial head between the 8 and 9 o'clock positions, was beveled. This might explain why the PM quadrant of the rim differed significantly from the other quadrants in terms of its microarchitectural features.

Intraoperative fluoroscopic assessment of proper prosthetic radial head height

BACKGROUND

Selecting a properly sized radial head prosthesis is imperative during radial head replacement. Although there has been much emphasis on avoiding overlengthening of the radius, little has been studied about how to avoid shortening. The purpose of this study was to characterize how a radial head replacement appears on intraoperative fluoroscopy depending on the height of the prosthetic radial head.

METHODS

Articular cartilage thickness of the radial head was measured in 9 cadaveric elbows. Radial head replacement was performed in each specimen with 4 different prosthetic head heights: 4 mm and 2 mm shortening, anatomic, and 2 mm overlengthening. Anteroposterior fluoroscopic images were obtained for each head height, and the prosthetic radial head height was measured at 3 forearm positions (supination, neutral, and pronation) using the subchondral bone of the lateral edge of the coronoid at the reference point.

RESULTS

The mean cartilage thickness of the radial head was 1.3 ± 0.4 mm. The prosthetic radial head appeared 2.2 ± 0.4 mm more proximal than the subchondral bone of the coronoid lateral edge in anteroposterior radiographs when the articular surface of the prosthesis was completely even with the coronoid articular surface. Unlike the native radial head, a prosthetic radial head showed a significant change of height with different forearm rotation (P < .001).

DISCUSSION

This study found that a perfectly anatomic radial head replacement appears overlengthened by approximately 2 mm in intraoperative radiographs. This finding can be useful in guiding the appropriate height of a prosthetic radial head.

Radial head replacement in adults with recent fractures

Radial head fractures are fairly common (20% of all traumatic elbow injuries). Non-operative treatment is indicated in non-displaced fractures, and direct stable internal fixation allowing early elbow mobilisation in most other cases. For severely comminuted fractures precluding stable fixation, replacement of the radial head was introduced in the 1970s as a better alternative to simple radial head resection, which can induce instability of the elbow and/or forearm, most notably in patients who have complex fractures with concomitant lesions to other structures. With contemporary implants (modular or monoblock, with or without a mobile cup), mechanical stability is close to that provided by the native radial head, although appropriate treatment of concomitant lesions remains crucial (e.g., re-attachment of the radial collateral ligament, or distal radio-ulnar stabilisation in patients with Essex-Lopresti fracture). The key technical points are selection of implant size and determination of the optimal implantation height. The two most common complications are capitellar overloading due to excessively high implantation of the prosthetic head, which causes stiffness and pain, and loosening of the stem. These complications may require removal of the implant at a distance from the injury. Studies have demonstrated satisfactory clinical outcomes in 60% to 80% of cases.

Validation of the contralateral side as reference for selecting radial head implant sizes

Purpose

In arthroplasty of comminuted radial head fractures, the contralateral radial head diameter can be used as reference for implant selection. However, potential bilateral asymmetry may result in a mismatch of the implant with the native bone. Therefore, our purpose was to evaluate anatomical right-to-left differences of radial head diameters. We also compared conventional two-dimensional (2D) with three-dimensional (3D) measurements.

Methods

We used bilateral CT-scans from 25 intact proximal radius pairs of right-handed adult subjects to obtain 50 3D radial head models. After contralateral matching, diameters were calculated using a 3D-based method using an automated circle-fit in standardized cross-sections at the widest level midway through the radial head. The 3D-based diameters were compared to orthogonal line measurements in standard axial CT-slices.

Results

Three-dimensional analysis yielded a radial head diameter of 23.0 ± 1.7 mm. The dominant right side was significantly wider, with right-to-left differences of 0.2 ± 0.4 mm, with a maximum of 0.9 mm. The 2D-based diameter was 22.9 ± 1.7 mm, which was 0.1 ± 0.3 mm smaller compared to corresponding 3D-based diameter.

Conclusions

In healthy radial heads, the diameter was biased to the dominant right side, but individual differences were not larger than 1 mm. Compared to implant designs, in which diameter increments are usually 2 mm, this right-bias is not clinically relevant, as it would not affect implant selection. Therefore, the contralateral side can be considered a suitable reference. In clinical practice, the surgeon could estimate this diameter using standard axial CT slices, since its difference with the 3D-based evaluation was also relatively small compared to implant sizing increments.

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.

Regional Variations in Cartilage Thickness of the Radial Head: Implications for Prosthesis Design

PURPOSE

To characterize the regional variations in cartilage thickness around the radial head.

METHODS

We dissected 27 cadaveric radii and scanned them with computed tomography in neutral position. Three-dimensional cartilage and subchondral bone surface models were generated from computed tomography scans and 2 independent observers processed them through a computer program to obtain cartilage thickness measurements. These measurements were taken at 41 predetermined landmarks around the periphery of the radial head and within the articular dish.

RESULTS

At the periphery of the radial head, cartilage was thickest in the posteromedial region. Thickness values within the articular dish were similar but increased toward the rim. Regional variations within the rim (range, 0.76-1.73 mm) were also detected with the thickest region located anteriorly and thinnest region laterally. In addition, cartilage was significantly thicker in male relative to female specimens.

CONCLUSIONS

Regional variations in cartilage thickness are present around the periphery and rim and within the articular dish of the radial head.

CLINICAL RELEVANCE

Cartilage thickness across the articular dish may contribute to dish depth and the radius of curvature. This may be clinically important for the design of anatomic implants, because accounting for such subtle contours could help to restore radiocapitellar concavity-compression stability better.

Measurements of the ispilateral capitellum can reliably predict the diameter of the radial head

BACKGROUND

There is no validated method to determine the correct diameter of a radial head implant when the radial head is too comminuted to function as a template or during revision surgery when the radial head has been previously excised. The purpose of this study was to determine if ipsilateral capitellar dimensions could be used to predict the diameter of the radial head; and hence to assist with implant selection.

METHODS

Computer tomography scans of 50 normal elbows were used to generate 3D models. Measurements of the radial head included the maximum (Dmax) and minimum (Dmin) outer diameters and the maximum (Dishmax) and minimum (Dishmin) articular dish diameters. Measurements of the humerus included the width of the capitellum (CAPwidth), and the width from the lateral aspect of the capitellum to the lateral trochlear ridge (CAP-TROCHridge). Relationships were determined with Pearson bivariate coefficients.

RESULTS

The mean radial head dimensions were Dmax = 24.7 ± 2.3 mm, Dmin = 23.5 ± 2.3 mm, Dishmax = 18.2 ± 1.9 mm and Dishmin = 16.8 ± 1.7 mm. The mean capitellar measurements were CAPwidth (18.4 ± 1.4 mm) and CAP-TROCHridge (23.0 ± 2.1 mm). The most significant correlations were found between Dmax and CAP-TROCHridge (R = .90, P < .001) and Dmin and CAP-TROCHridge (R = .90, P < .001).

DISCUSSION

Radiologic measurements of the capitellum are useful in the estimation of native radial head diameter. The CAP-TROCHridge measurement was very strongly correlated with both the maximum and minimum diameters of the radial head. This suggests that CAP-TROCHridge may be useful to accurately predict the native radial head diameter. These morphological relationships were plotted to produce an implant selection chart for radial head sizing applicable to any implant system.

LEVEL OF EVIDENCE

Basic science, anatomy study, CT imaging.

Computer-aided analysis of radial head morphometry

Operative treatment of displaced and comminuted radial head fractures involves internal 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 commercially available radial head prostheses. Computed tomography scans of 30 cadaveric elbows and 3-dimensional reconstructions were used to analyze the morphometry of the proximal radius. Results were compared with the manufacturer data of several radial head prostheses. Mean diameter of the radial head at the level of the fovea was 19±1.58 mm (range, 15.82-21.81 mm) in the anteroposterior plane and 18.62±1.78 mm (range, 15.48-22.21 mm) in the radioulnar plane. Mean diameter of the radial head at its widest part was 23.15±1.94 mm (range, 19.45-26.49 mm) in the anteroposterior plane and 22.44±1.73 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 15.42±1.59 mm (range, 11.80-18.46 mm) in the anteroposterior plane and 14.75±1.39 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.

Terrible triad of the elbow

The terrible triad of the elbow is a difficult injury with historically poor outcomes. Improved experience, techniques, and implants have advanced to the point where restoration of elbow stability can be expected. Careful attention to each destabilizing element of the injury pattern is essential and places high demands on the surgeon's mastery of the anatomic complexity of the elbow. Technically, the surgeon must bring every skill to bear, as soft tissue techniques, fracture repair, and joint arthroplasty are routinely required to adequately treat these complex constellations of injury.

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.

The applicability of the Mayo Clinic congruent radial head plate: cadaveric study

In the last few years, several anatomical plates have been introduced to improve the results of ORIF in Mason Type II and III radial head fractures. However, no study analyzed whether currently used plates match adequately the profile of the proximal radius in the "safe zone". In the present investigation, we evaluate the congruence between the proximal radius and a currently used plate. Forty-four radial dried cadaveric bones were analyzed. The plate congruence was evaluated qualitatively and quantitatively. The congruence of the tested plate with the proximal radius was good in 27.3% of specimens, while it was moderate or poor in the remaining 43.2% and 29.5% of cases, respectively. The profile of the proximal radius in the "safe zone" shows substantial morphologic variations which should be taken into account to avoid a malunion of the proximal radius. A preoperative radiograph of the contralateral uninjured radius may be helpful in order to select the most appropriate plate profile in comminuted radial head and neck fractures.

Cementless fixation of radial head implants is affected by implant stem geometry: an in vitro study

BACKGROUND

Metal radial head implants are widely used for the management of unreconstructible fractures. However, the effect of implant stem design on initial fixation and stability is unknown. This study determined the effects of radial head stem geometry on the initial stability of the uncemented implant. It was hypothesized that cortical contact and hence increased fixation would be achieved with an increased stem diameter, stem length and a tapered shape.

METHODS

Eleven radii received five implants with differing stem geometries: short and long undersized, short and long optimally sized and short tapered. Inferiorly-directed compressive loads were applied successively to the anterior, posterior, medial and lateral edges of the implants. Maximum contralateral radial head "lift-off" was quantified by the distance between bone and implant surface markers.

FINDINGS

The short and long undersized implants experienced greater micromotion with approximately 100 microm and 160 microm more lift-off respectively (P<0.02). The remaining optimally sized and tapered implants averaged 50 microm. There was greater motion for the undersized implants loaded at the lateral position (P0.005).

INTERPRETATION

This study shows that filling the diameter of the medullary canal is more important than filling the length of the canal. The taper did not offer any additional advantages compared to the straight stem, suggesting that reaming of bone to accept the taper did not produce enhanced initial purchase. If rigid initial implant fixation is desired with an uncemented radial head implant, a canal-filling stem reduces initial implant micromotion to less than 50 microm which may enhance bone ingrowth.

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.

Malpositioning of radial head prostheses: an in vitro study

Nonanatomic insertion of radial head prostheses may result in maltracking and capitellar erosion. The purpose of this study was to analyze the ability to perform anatomic radial head replacement and to study radiocapitellar prosthetic subluxation under unstable conditions. In vitro measurements were performed in 10 intact elbows and after insertion of radial head prostheses (rigid uncemented, rigid cemented, bipolar). The diameter and length of the proximal radius were approximately restored. However, prosthesis-shaft malalignment, up to 21 degrees , was observed frequently. A posterolateral rotatory stress after resection of 50% of the coronoid caused a mean radiocapitellar subluxation of more than 30% for the rigid prostheses, whereas bipolar devices self-aligned with a mean subluxation similar to intact elbows. In conclusion, it was not possible to consistently insert radial head prostheses anatomically. Marked radiocapitellar subluxation occurred for the rigid but not for the bipolar implants. Clinical trials are needed to analyze these findings.

Computed tomography study of radial head morphology

Computed tomography scans of 22 cadaveric adult elbows were obtained in 3 forearm positions: full supination, neutral, and full pronation. The radial head dimensions, the radiocapitellar joints, and the proximal radioulnar joints were measured. Multivariate analysis of variance was used to determine which portions of each articulation were the most congruent. The results showed that the radial head tended to become uncovered at the radial lip (P < .001). The radiocapitellar joint was tighter in pronation than in supination (P = .001). The proximal radioulnar joint was most congruent at the middle proximal radioulnar joint, at the midportion and posterior aspects rather than the anterior aspect (P < .001). The proximal radioulnar joint coverage was between 69 degrees and 79 degrees . Prosthesis trial sizing should be judged by the articulations providing the most congruency: (1) the ulnar lip or trough of the radiocapitellar joint in pronation and (2) the posterior or midportion of the middle proximal radioulnar joint.

The effect of the annular ligament on kinematics of the radial head

PURPOSE

There is evidence that the radial head translates during pronation and supination. This study measured radial head movement and the location of the pronation-supination axis of the forearm with and without the annular ligament.

METHODS

Thirteen cadaveric arms were attached to a custom-built frame. Pronation and supination were achieved by actuation of the pronator teres and biceps tendons, respectively. Motion was captured by video cameras via marker arrays attached to the distal radius, distal ulna, humerus, and radial head. Three pronation-supination trials were performed with the annular ligament intact and the elbow positioned at 90 degrees . The sequence was repeated after transection of the annular ligament.

RESULTS

The radial head traveled an average of 2.1 mm in the anteroposterior direction and 1.6 mm in the mediolateral direction during forearm rotation. After annular ligament resection, travel of the radial head increased by an average of 44% in the mediolateral direction and by 24% in the anteroposterior direction. On average, the mean pronation-supination axis (screw displacement axis) passed 1.4 mm +/- 1.9 medial to the center of the capitellum and through the center of the ulnar head. Loss of the annular ligament did not change the location of the pronation-supination axis.

CONCLUSIONS

During forearm rotation, the radial head travels to a greater extent in the anteroposterior direction than in the mediolateral direction. Loss of the stabilizing effect of the annular ligament increases the travel mediolaterally more than anteroposteriorly. The pronation-supination axis of the forearm is nearly constant and is not affected by annular ligament transection.

Morphometric parameters of the radial neck: an anatomical study

INTRODUCTION

The purpose of this study was to describe the anatomy of the intramedullary canal of the radial neck for stem design of radial head prostheses.

METHODS

Radial neck measurement was performed from the proximal edge of the radial tuberosity to the distal border of the articular surface on 40 macerated proximal radii using X-rays and Optosil imprints of the intramedullary canal. Radial neck to shaft angle was measured under image intensification.

RESULTS

The neck length was 13.3 mm (range 8.0-20.0 mm) measured on X-rays and 13.5 mm (range 9.9-18.8 mm) on Optosil imprints. Concerning the neck's intramedullary canal we obtained a minimum diameter of 9.7 mm (range 6.3-16.4 mm) on X-ray. Corresponding Optosil imprints had a mean diameter of 11.6 mm (range 6.6-18.6 mm) at their proximal end, 10.5 mm (range 5.5-16.3 mm) in the middle and a minimum of 9.8 mm (range 6.0-16.9 mm) at the distal end. Differences between left and right sides were not significant between X-ray and Optosil imprints, nor between left X-ray and right imprints and vice versa at a P-level of 0.001. Radial neck to shaft angle was 167.8 degrees (range 160.5-178 degrees ) measured under image intensification at a rotation angle of 58.6 degrees (range 50-70 degrees ) supination.

CONCLUSION

Geometry of the radial neck's intramedullary canal has been described for stem design. The minimum diameter was seen at the distal end, just proximal to the radial tuberosity. A forearm rotation of 58.6 degrees to full supination should be considered during implantation of monopolar prostheses. The wide variety of lengths and diameters complicates standard prosthetic design, but ipsilateral and contralateral X-rays can be useful for preoperative stem size calculation.

Morphometric parameters of the radial head: an anatomical study

INTRODUCTION

Exact anatomical description of the proximal radius is imperative for the development of radial head prostheses. The purpose of this study was to measure the anatomical parameters of the radial head.

METHODS

Optosil imprints of 18 pairs of proximal radii fixed with formalin were taken. All possessed their native cartilage joint surface free of any arthritic defects. After being cut into 3 mm slices, the diameter of each slice was measured in steps of 30 degrees of rotation with the margo interosseous acting as a reference point.

RESULTS

Maximum radial head diameter was seen from the 0 to the 9 mm slice at a rotation of 30 degrees to full supination perpendicular to the proximal radioulnar joint. The diameter increased from the radiocapitular joint surface to the 6 mm slice, and then it decreased (P < 0.001). At the level of 6 mm the maximum radial head diameter was 24.13 mm (range 21.2-27.3 mm). The minimum diameter was seen perpendicular to the maximum; it also increased from the radiocapitular joint surface to the 6 mm slice and then decreased. There was a significant difference between the minimum and maximum diameter of each slice at a P-level of P < 0.001. Left and right sides were not significantly different at a P-level of 0.01.

CONCLUSION

Our data show that the radial head is neither round nor conical. It has a complex shape with an increasing size from the radiocapitular joint surface to the middle of the proximal radioulnar joint surface. No statistically significant differences could be observed between right and left radii.

Reference points for radial head prosthesis size

PURPOSE

Metallic radial head implants are useful when the radial head cannot be repaired reliably and when either the elbow or the forearm is unstable. Problems arise when the radial head prosthesis is too thick, causing erosions of the capitellum and incongruity of the ulnohumeral joint. We used quantitative 3-dimensional computed tomography analysis to investigate the relative height of the radial head relative to the lateral edge and central ridge of the coronoid process as reference points for optimal insertion of a radial head prosthesis.

METHODS

Seventeen computed tomography scans of the elbow were analyzed. The anatomic coronal plane of the forearm was determined using 3-dimensional images and a 2-dimensional image bisecting the articular surface of the radial head was created in this plane. The distance between the plane of the articular surface of the radial head and parallel planes at the most proximal aspect of the coronoid (the central ridge) and the lateral edge of the coronoid articular surface were measured. Negative values indicate the radial head is proximal to the coronoid.

RESULTS

The average distance between the planes defined by the radial head articular surface and the coronoid central ridge was -0.8 mm. The average distance between the planes defined by the radial head articular surface and the lateral edge of the coronoid articular surface was -0.9 mm.

CONCLUSIONS

Because the radial head was on average only 0.9 mm more proximal than the lateral edge of the coronoid process and because the key is to not overstuff the joint a useful general guideline would be to place the plane of the articular surface of the radial head even with or just slightly more proximal than the lateral edge of the coronoid articular surface. Considering the substantial variability of the normal height of the articular surface of the radial head with respect to that of the coronoid, preoperative radiographs of the opposite elbow may be useful to avoid overstuffing the elbow.

Morphology of the radial head: A reverse engineering based evaluation using three-dimensional anatomical data of radial bone

The proximal part of the radius has a complex shape and dimension that cannot be precisely determined by standard roentgenogram for real three-dimensional anatomical shape which is important for prosthesis design. This study presents a method by which computer tomography (CT) images are combined with the reverse engineering technique to obtain and analyse the three-dimensional inner and outer geometry of the proximal radius. The three-dimensional models were reconstructed from CT images obtained from 40 radial bones and approximated with two- and three-dimensional fitting algorithms based on reverse engineering methods. The mean total length of the radius was 240.0mm [standard deviation (SD) = 17.3]. The radial head in this study is more likely to be circular with an average diameter of 20.5 mm (SD = 1.9). The outer diameter of the radial neck averages 14.7 mm (SD = 1.0). The thickness of the radial head averages 12.9 mm (SD = 1.4). The intramedullary canal diameter of the radial neck averages 7.4 mm (SD = 1.4). The depth of the fossa at the articular surface averages 1.5 mm (SD = 0.4).

Fractures récentes de la tête radiale associées à une instabilité du coude traitées par prothèse à cupule mobile de Judet

PURPOSE OF THE STUDY

Fracture of the radial head associated with elbow instability is infrequent. We report a retrospective series of floating Judet prostheses implanted for comminutive fractures of the radial head associated with elbow laxity caused either by dislocation or rupture of the medial collateral ligaments.

MATERIAL AND METHODS

The series included ten patients who underwent surgery from October 1996 to September 2002 at the Amiens University Hospital. The indication for radial head prosthesis was established in the emergency setting for fracture unamendable by osteosyntheis and elbow laxity. Mean age was 48.2 years (25-69). All patients were seen at mean follow-up of 31.7 months (18-48). According to the Mason classification as modified by Johnson, all patients had type 4 fracture. A Judet radial head prosthesis with a floating metallic cup was implanted in all patients. An investigator other than the operators evaluated outcome using the Mayo Clinic criteria.

RESULTS

Joint motion as measured by goniometry was: mean flexion 121degrees (90-140 degrees), mean extension deficit 20 degrees (5-60 degrees), mean pronation 45 degrees (0-85 degrees), mean supination 42.5 degrees (0-90 degrees). The Mayo clinic score was excellent in 3, good in 2, fair in 3, and poor in 2 (prosthesis dislocation in one and hung prosthesis requiring removal in one). Four patients developed periarticular ossifications compromising the final result.

DISCUSSION

The floating Judet prosthesis allows optimal adaptation of the implant to anatomy and function. For us, these implants are indispensable when the radial head fracture is associated with elbow instability. The indication for prosthesis may be questionable if the non-fixed fracture is free of associated ligament injury, as suggested by the good long-term reported after simple resection. Rigorous operative technique is crucial, with careful restitution of the radial height. The quality of the result is related to the degree of capsule and ligament injury even after optimal implant positioning. Preventive treatment against periarticular ossification should be systematic.

A comparative study between proximal radial morphology and the floating radial head prosthesis

A morphometric study of the proximal radius was performed with computed tomography scanning in 51 healthy adults. These dimensions were then compared with those of a commercially available floating radial head prosthesis. Results were expressed as mean values, SD, and minimum and maximum values. The minimum and maximum diameters of the radial head were 21.9 +/- 1.9 mm and 22.9 +/- 1.9 mm, respectively. The minimum and maximum intramedullary diameters of the radial neck were 8.3 +/- 1.3 mm and 9.3 +/- 1.5 mm, respectively. The combined length of the radial head and neck was 22.47 +/- 2.84 mm. The implications for prosthetic design are as follows: the small floating cup (19 mm in diameter) is too small for the large majority of adults, the large floating cup (22 mm in diameter) is closer to the radial anatomy, the mean values are significantly different between male and female patients, and a single component would suffice for right and left elbows.

Anatomical considerations of the radius

Most radial head prostheses do not seem to be based on anatomic data. This may be due partly to the great variation of radial morphology. More importantly, few articles report on the dimensions of the radius. Authors have mainly studied dimensions of the radial head, with less emphasis to the relationship with the rest of the radius. Dimensions of, and relationship between, the proximal and the rest of the radius were measured on 27 fresh-frozen cadaveric upper extremities. Radial head, articulating surface, diaphysis, and distal radius were measured. Angles between the radial neck and diaphysis were defined and calculated. Axes of the distal and proximal radius were defined and radial torsion was calculated. Repeated measures were done by two observers in ten specimens. Inter- and intra-class correlation coefficients were very acceptable. Radial dimensions were found to be highly variable. Calculation of radial torsion showed the largest range. The average torsion was 54 degrees (range = 23-78 degrees). Radial length was 235 mm (range = 207-269 mm). Radial neck length was 13 mm (range = 9-19 mm). We found an average proximal diaphysis-neck angle of 17 degrees (range = 6-28 degrees). End to end-neck angle was 13 degrees (range = 4-22 degrees). Our findings indicate that even with a perfectly anatomical prosthesis, restoration of the anatomical situation can only be achieved when the implant is placed in the correct position. Instrumentation should be developed to allow accurate and reproducible implantation. The measurements we provide may aid this development.