Prosthetic Radial Head Research Articles

The impact of anatomic alignment on radiocapitellar pressure following radial head arthroplasty

BackgroundThe incidence of radial head fractures is increasing, and radial head arthroplasty (RHA) is being more frequently utilized as treatment for irreparable fractures. Our objective was to compare radiocapitellar pressure between the native joint and two radial head prosthesis conditions - (1) a prosthetic head that was aligned to the forearm axis of rotation and (2) the same prosthesis with an axisymmetric nonaligned head. MethodsTen cadaveric specimens received a pressfit radial head prosthesis (Align, Skeletal Dynamics, Miami, FL) for both prosthetic testing conditions. Anatomic alignment (AL) was defined as the prosthetic head aligned to the forearm axis of rotation. Axisymmetric alignment (NA) was defined as the prosthetic radial head aligned to the axis of the prosthetic stem. Axial load was applied with the elbow in extension and the forearm pronated. Data was collected using a Tekscan 4000 sensor. ResultsThe mean pressure in the AL and AX groups were significantly higher than the mean pressure in the native joint. Compared to the native joint, the mean pressure was 19% higher in the AL group and 56% higher in the AX group. Peak pressure beyond 5 MPa occurred in zero specimens in the native joint group, in one specimen (10%) in the AL group, and in five specimens (50%) in the AX group. DiscussionOur results demonstrated that a pressfit radial head prosthesis aligned with the forearm axis of rotation yields capitellar pressures that were more similar to the native condition than a non-aligned pressfit prosthesis. These findings suggest that anatomic alignment may optimize capitellar wear properties, improving the long-term durability of radial head arthroplasty.

Giant cell tumour of proximal radius – A rare case report of treatment, with resection & custom- made radial head prosthesis

Giant cell tumour is locally aggressive benign lesion arising from epiphysis of long bones, common in 2 and 3 decade of life. The most commonest sites being, lower end radius, upper end tibia, and lower end femur. Treatment depends upon stage of disease Presenting here with a case of 36-yrs old male presented with pain and swelling at rt elbow. Patient having GCT arising from upper end radius, was treated with excision of lesion and reconstruction of 4-cm defect with custom-made radial head prosthesis. A literature review of GCT upper end radius is very scanty, hardly any reports available, however for a lesion involving head and around 3-cm of neck with pathological #, treatment remains excision of tumour and reconstruction with prosthetic radial head.

Relationship between measurements of ipsilateral capitellum and prosthetic radial head size

BackgroundSelecting the correct size of head component is challenging in radial head arthroplasty, particularly in comminuted fractures. This study aimed to investigate the relationship between measurements of the ipsilateral capitellum and the prosthetic radial head size, which may be used to predict the size of the radial head prosthesis preoperatively.MethodsOur study enrolled all patients who underwent radial head arthroplasty at Beijing Jishuitan Hospital. Demographic, injury-related and radiographic data were collected. The prosthetic radial head size was recorded from the surgical notes. Three-dimensional models of preoperative CT scans were reconstructed, on which the lateral capitellar diameter, the capitellar width and the width between the capitellum and trochlea were measured. The correlations between measurements of the ipsilateral capitellum and the prosthetic radial head size were evaluated, and linear regression equations were established.ResultsThe study enrolled 37 patients, with an average age of 42.8 ± 11.5 years and a male–female ratio of 20:17. The median diameter of the radial head prostheses was 22 (20, 22) mm. The average lateral capitellar diameter was 20.71 ± 1.93 mm, the mean capitellar width was 14.90 ± 1.40 mm, and the mean width between the capitellum and trochlea was 19.29 ± 1.78 mm. The lateral capitellar diameter (R = 0.820, P < 0.001), the capitellar width (R = 0.726, P < 0.001) and the width between the capitellum and trochlea (R = 0.626, P < 0.001) were significantly positively correlated with the size of the radial head prosthesis. The linear regression equation between the lateral capitellar diameter and the size of the radial head prosthesis was calculated and defined as follows: D = 7.44 + 0.67*d (D: diameter of radial head prosthesis; d: lateral capitellar diameter; and adjusted R2 = 0.719, P < 0.001).ConclusionsThere are positive correlations between the anatomical parameters of the ipsilateral capitellum and the prosthetic radial head size. The lateral capitellar diameter can be measured on three-dimensional CT preoperatively to predict the size of the radial head prosthesis intraoperatively.

Morphometric scrutiny of the radial head: A foundation for prosthesis crafting

Background: Radius is one of the two constituent bones of the forearm. It is frequently fractured or dislocated due to trauma, pathology, etc. Prosthetic radial head may be indicated in the management of comminuted fractures of the radial head. Aims and Objectives: This study was undertaken with the aim to measure various dimensions of the head of the radius bone and to collate these dimensions between right-sided and left-sided bones. Materials and Methods: Three hundred bones, collected from the Department of Anatomy of Jawaharlal Nehru Medical College, Belagavi, Karnataka, were systematically investigated using digital Vernier caliper, normal ruler, and inelastic thread. The data recorded were then analyzed to obtain the results. Results: The mean length, diameter, and circumference of the head of the radius bones were 9.47 ± 1.49 mm, 19.92 ± 2.03 mm, and 6.42 ± 0.63 cm, respectively (irrespective of the side). For only one aspect, the length of the radial head, a statistically significant difference was obtained between the values of bones of both sides. Conclusion: Numerous studies have shown an extensively varied range of values for several parameters. Utmost care and precision are required by the orthopedic surgeons, prosthetists, etc. while treating patients or prosthesis making, to avoid untoward outcomes like soreness, etc. This study strives to underline this need for precision by highlighting the varied range of parameters in the regional population.

Optimal Prosthesis Sizing for Radial Head Arthroplasty: A Review of Current Evidence and Guidelines.

Radial head arthroplasty is a viable surgical option when a radial head fracture cannot be reconstructed. Radial head arthroplasty provides a load-bearing articular structure against the capitellum in unstable fractured elbows. Studies have emphasized the importance of choosing the correct implant size to replicate the native radial head anatomy, citing various consequences of improperly sized radial head prostheses. Overstuffing of the radiocapitellar joint, or lengthening of the radius, has been extensively studied because of its detrimental effects on elbow biomechanics, but other types of improper sizing also have negative consequences. In the setting of severe fracture-dislocation or revision surgery, anatomic landmarks that are useful for prosthesis sizing often are missing. Various methods have been described to provide guidance for the accurate sizing of a prosthetic radial head; a retrieved radial head, the proximal edge of the lesser sigmoid notch, the radiocapitellar synovial fold, and the ulnohumeral joint space all represent useful references. Intraoperative radiographic examination is an important step while assessing implant size, including the height of the prosthetic radial head. Since no single method is perfect on its own, the surgeon should combine as many reference measures as possible, both before and during the procedure, for accurate prosthesis sizing in order to achieve successful outcomes.

Radial head fractures : Epidemiology, diagnosis, treatment and outcome

Radial head fractures account for the majority of bony injuries to the elbow. The usual clinical signs include hemarthrosis, pain and limitations in movement. The standard diagnostic tool is radiological imaging using X‑rays and for more complex fractures, computed tomography (CT). Concomitant ligamentous injuries occur more frequently than expected and must be reliably excluded. The classification is based on the modified Mason classification. Mason typeI fractures are usually treated conservatively with immobilization and early functional aftercare. Mason typeII fractures can be well-addressed by screw osteosynthesis but higher grade fractures (Mason typesIII-IV) can necessitate a prosthetic radial head replacement. In this case, prosthesis implantation is to be preferred to aradial head resection. The outcome after treatment of radial head fractures can be described as good to very good if all accompanying injuries are adequately addressed.

Joint Contact Changes with Under-Sized Prosthetic Radial Heads

Joint Contact Changes with Under-Sized Prosthetic Radial Heads

Joint Contact Changes With Undersized Prosthetic Radial Heads.

To evaluate the effect of intentional undersizing of prosthetic radial head implant diameters on joint contact pressures. Eight fresh-frozen cadaveric elbows were aligned in neutral extension and loaded with 100 N using a custom testing apparatus. Radiocapitellar contact pressures were recorded using a Tekscan thin-film pressure sensor. Prosthetic radial head replacement was performed with 2 prostheses: the Anatomic Radial Head and the Evolve Proline Radial Head prostheses. Each design was sized according to the manufacturer's recommendations and then again using 2-mm smaller radial heads. Average and peak pressures were significantly higher with the Evolve than the Anatomic prostheses (P < 0.03 and 0.02, respectively). Peak pressures decreased from 4.2 ± 0.5 MPa to 2.9 ± 0.3 MPa for the Anatomic Radial Heads and from 5.6 ± 0.5 MPa to 3.9 ± 0.6 MPa when the Evolve Radial Heads were undersized by 2 mm. The mean pressures of the Anatomic Radial Heads (1.4 ± 0.1 MPa) did not change significantly with undersizing (1.3 ± 0.1 MPa, P = 0.12), whereas the mean pressures of the Evolve Radial Heads (1.6 ± 0.1 MPa) were significantly reduced with undersizing (1.4 ± 0.1 MPa, P < 0.02). Both mean and peak pressures were initially high for the Evolve Radial Head sized based on the short axis diameter and were improved with further undersizing by 2 mm. Peak, but not mean, contact pressures were improved by undersizing the Anatomic prosthesis based on the long axis diameter. These findings support the clinical recommendation of some surgeons to undersize the Evolve prosthesis by 2-mm smaller diameter than the current manufacturer's suggestion and give reason to consider doing the same for the Anatomic prosthesis.

Clinical outcomes of anconeus interposition arthroplasty after radial head resection in native and prosthetic radial heads

Radiocapitellar pathology after traumatic injury to the elbow can be challenging to treat. The anconeus interposition arthroplasty has been proposed to treat radiocapitellar or proximal radioulnar joint dysfunction and pain, or both. This study evaluated whether radial head excision (native or prosthetic), followed by an anconeus interposition arthroplasty, relieves pain and improves subjective and objective elbow function in patients with post-traumatic radiocapitellar pathology. A retrospective comparative case series was performed of 50 consecutive patients who underwent a native radial head excision or radial head implant excision, followed by an anconeus interposition arthroplasty. Clinical outcome scores, range of motion, and proximal radius migration were evaluated in patients with at least 2 years of follow-up. Included were 23 patients (11 native and 12 prosthetic radial heads) with a mean age of 41 years. Average follow-up was 38 months. Overall, significant improvement was obtained in the Disabilities of the Arm, Shoulder and Hand and visual analog scale scores. Range of motion significantly improved from preoperatively to postoperatively. Patients with a native radial head excision scored better on the Single Assessment Numeric Evaluation (76.8 vs. 56.3, P = .037) and obtained significantly more flexion postoperatively (141° vs. 123°, P = .016). Mild wrist pain developed in 3 patients, but no further intervention was required. The overall complication rate was 13%, and 5 patients required reoperation. Anconeus interposition arthroplasty performed after radial head resection in native and prosthetic groups is a viable adjunct in the operative treatment of patients with post-traumatic radiocapitellar pathology. However, whether anconeus interposition arthroplasty alone produced the favorable clinical results of this study was difficult to determine.

Analysis of the predisposition factors for complications after artificial radial head replacement

Objective To analyze the predisposition factors for cubitus valgus and other complications following radial head prosthesis replacement in treating comminuted fractures of the radial head. Methods From August 2008 to November 2011, 21 cases of radial head comminuted fractures were treated with prosthetic radial head replacement. There was one case with combined distal humeral fracture, 5 cases with combined olecranon fractures and 6 cases with combined elbow dislocation. Based on Mason classification, there were 15 type Ⅲ fractures and 6 type Ⅳ fractures. All were closed injuries that were surgically treated 2 weeks after the injury. Results Postoperatively 19 cases were follow-up while two cases were reportedly lost for follow-up. The follow-up period ranged from 5 to 79 months (mean 39.9 months). According to the Mayo elbow performance scoring system, the results were assessed as excellent in 16 cases, good in 2 cases and fair in 1 case. Out of the 19 cases, 4 cases had an elbow carrying angle more than 10° greater than that of the contralateral side. Seven cases had varying degrees of radiolucent area around the radius stem. There was no wound infection, nerve damage, metallic foreign body reaction, or wrist deformities. Elbow stiffness occurred in one case that required arthrolysis. There were 5 cases that had mild heterotopic ossification in the elbow, which did not significantly impair the movement of the elbow and forearm. Conclusion Prosthetic radial head replacement for treatment of radial head fractures lead to satisfactory intermediate term results. The most common complications are cubitus valgus and loosening of the prosthesis which may be attributed to surgical skills, the lack of filler or prosthesis strength. Key words: Radius; Fractures, bone; Radial head replacement; Complications

Radiocapitellar contact characteristics during prosthetic radial head subluxation

Metallic radial head prostheses are often used in the management of comminuted radial head fractures and elbow instability. We hypothesized that during radiocapitellar subluxation, the contact pressure characteristics of an anatomic radial head prosthesis will more closely mimic those of the native radial head compared with a monopolar circular or a bipolar circular radial head design. With use of 6 fresh frozen cadaver elbows, mean radiocapitellar contact pressures, contact areas, and peak pressures of the native radial head were assessed at 0, 2, 4, and 6 mm of posterior subluxation. These assessments were repeated after the native radial head was replaced with anatomic, monopolar circular and bipolar circular prostheses. The joint contact pressures increased with the native and the prosthetic radial head subluxation. The mean contact pressures for the native radial head and anatomic prosthesis increased progressively and significantly from 0 to 6 mm of subluxation (native, 0.6 ± 0.0 MPa to 1.9 ± 0.2 MPa; anatomic, 0.7 ± 0.0 MPa to 2.1 ± 0.3 MPa; P < .0001). The contact pressures with the monopolar and bipolar prostheses were significantly higher at baseline and did not change significantly further with subluxation (monopolar, 2.0 ± 0.1 MPa to 2.2 ± 0.2 MPa [P = .31]; bipolar, 1.7 ± 0.1 MPa to 1.9 ± 0.1 MPa [P = .12]). The pattern of increase in contact pressures with the anatomic prosthesis mimicked that of the native radial head. Conversely, the circular prostheses started out with higher contact pressures that stayed elevated. The articular surface design of a radial head prosthesis is an important determinant of joint contact pressures.

Intraoperative fluoroscopic assessment of proper prosthetic radial head height

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. 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. 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). 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.

Influence of radial head prosthetic design on radiocapitellar joint contact mechanics

Our aim was to test whether anatomically designed metallic radial head implants could better reproduce native radiocapitellar contact pressure and areas than nonanatomic implants. The distal humerus and proximal radius from 6 cadaveric upper extremities were serially tested in supination with 100 N of compression force at 4 angles of flexion (0°, 30°, 60°, and 90°). By use of a thin flexible pressure transducer, contact pressures and areas were measured for the native radial head, an anatomic implant, a nonanatomic circular monopolar implant, and a bipolar nonanatomic implant. The data (mean contact pressure and mean contact area) were modeled using a 2-factor repeated-measures analysis of variance with P ≤ .05 considered to be significant. The mean contact areas for the prosthetic radial heads were significantly less than those seen with the intact radial heads at every angle tested (P < .01). The mean contact pressures increased significantly with all prosthetic radial head types as compared with the native head. The mean contact pressures increased by 29% with the anatomic prosthesis, 230% with the monopolar prosthesis, and 220% with the bipolar prosthesis. Peak pressures of more than 5 MPa were more commonly observed with both the monopolar and bipolar prostheses than with the anatomic or native radial heads. The geometry of radial head implants strongly influences their contact characteristics. In a direct radius-to-capitellum axial loading experiment, an anatomically designed radial head prosthesis had lower and more evenly distributed contact pressures than the nonanatomic implants that were tested.

Prosthetic radial head stem pull-out as a mode of failure: a biomechanical study

Press-fit cementless radial head implant longevity relies on adequate bone ingrowth. Failed implant osseointegration remains a clinical concern and has been shown to lead to prosthetic failure. The purpose of this study was to test the hypothesis that implants with sufficient initial press-fit stability would be less likely to fail due to implant pull-out, as demonstrated by an increasing amount of energy required to remove the prosthesis from the canal. Ten cadaveric radii were implanted with five sizes (6-10mm in 1-mm increments) of grit-blasted, cementless radial head stems. A customised slap hammer was used to measure the energy required to remove each stem. Stem-bone micromotion was also measured. The suboptimally sized stem (Max - 1) (i.e. 1mm undersized) required less energy (0.5 ± 0J) to pull out than the optimally sized stem (Max) (1.7 ± 0.3J) (p = 0.008). The optimally sized stem demonstrated greater initial stability (45 ± 7μm) than the suboptimally sized stem (79 ± 12μm) (p = 0.004). This investigation demonstrates the importance of obtaining adequate press-fit stability for the prevention of radial head stem pull-out failure. These data add to the relatively scant knowledge in the literature regarding radial head biomechanics. The energy required to remove a prosthetic radial head ingrowth stem decreases in conjunction with diameter. The use of an inadequately sized stem increases the stem's micromotion as well as the risk of prosthetic loosening due to pull-out.

Canal preparation for prosthetic radial head replacement: rasping versus reaming

While many design-specific features of radial head prostheses have been studied (ie, geometry and surface coating), the optimum technique for canal preparation has not been determined. We hypothesized that preparation of the radial canal with a reamer would allow for the accommodation of a larger stem diameter versus following canal preparation with a rasp, and would provide acceptable stem-bone micromotion. Paired proximal radii from 7 cadavers were prepared by a rasp on one side and a reamer on the contralateral side. Cementless radial head stems of increasing diameter were sequentially implanted up to the maximum size or until a fracture occurred and the micromotion between the stem and bone was recorded. In 3 of 5 pairs, at least a 1mm larger stem size fit into the canal after reaming versus after rasping (P=.04). 5 of 7 radii fractured secondary to intentional stem oversizing. For the optimally-sized stems, similar micromotion values were observed whether the canal was rasped (41±6μm) or reamed (44±6μm) (P=.72). This study investigated an aspect of radial head arthroplasty technique about which little has currently been published. It is possible that use of a reamer rather than a rasp, while providing similar initial stability, might expand the stem size options for initial press-fit stability, and decrease the risk of fracture. Radial canal preparation with a reamer allows for implantation of a 1mm larger stem diameter versus rasping, while providing comparable initial stability to that achieved after rasping.

Effect of stem length on prosthetic radial head micromotion

Osteointegration of press-fit radial head implants is achieved by limiting micromotion between the stem and bone. Aspects of stem design that contribute to the enhancement of initial stability (ie, stem diameter and surface coating) have been investigated. The importance of total prosthesis length and level of the neck cut has not been examined. Cadaveric radii were implanted with cementless, porous-coated radial head stems. We resected 10, 12, 15, 20, and 25 mm of radial neck in each specimen. Stem-bone micromotion was measured after each cut. Values were expressed in terms of quotients (cantilever quotient). A threshold effect was observed at 15 mm of neck resection (cantilever quotient, 0.4), with a significant increase in micromotion observed between 12 mm (40 ± 10 μm) and 15 mm (80 ± 25 μm). A cantilever quotient of 0.35 or less predicted implant stability, whereas implants with a cantilever quotient of 0.6 or more were unstable. In between, the stems were "at risk" of instability. Initial stem stability of a porous-coated, cementless radial head implant is dependent on length of the implant stem within bone and the level of the cut (amount of bone resected). Stability may be compromised by an implant with a combined head and neck length that is too long compared with the stem length within the canal. We found a critical ratio of exposed prosthesis to total implant length (cantilever quotient of 0.4), which puts the prosthesis at risk of inadequate initial stability. These data carry important implications for implant design and use.

Comparison of 2 Forearm Reconstructions for Longitudinal Radioulnar Dissociation: A Cadaver Study

We present the results of a cadaveric study of 2 forearm reconstructions with radial head replacement for longitudinal radioulnar dissociation injuries. We created a simulated longitudinal radioulnar dissociation injury in 8 cadaver forearms. Two reconstructions were performed alternately on each arm: patellar tendon interosseous ligament complex reconstruction and the Herbert sling extensor retinaculum plication. We performed mechanical testing in a materials testing machine with and without a radial head replacement, and measured ulnocarpal impaction force through 2 distal ulna strain gauges. We determined relative radioulnar displacement using live fluoroscopic analysis of implanted stainless-steel beads. Relative radioulnar longitudinal displacement in the destabilized forearms was 10.7 compared with 0.7 mm before creating the injury. A prosthetic radial head replacement alone decreased the displacement by 75% to 2.7 mm. Interosseous ligament reconstruction alone reduced the displacement to 5.1 mm and to 1.3 mm when combined with a radial head implant. The Herbert sling alone did not improve longitudinal stability. The distal ulna force in the native arm was 17 N, or 17% of the force across the wrist. The interosseous ligament reconstruction restored the force to 21 N, whereas the Herbert sling only marginally decreased the ulna impaction force to 45 N. Adding a radial head decreased the distal ulna force to 7 N for the patellar tendon interosseous ligament reconstruction, and 2 N for the Herbert sling. In longitudinal radioulnar dissociation injuries, the radial head is an important stabilizer and should be repaired or replaced to minimize radial shortening and ulnar impaction force. Patellar tendon interosseous ligament reconstruction effectively restores the ulnocarpal force distribution and markedly reduces longitudinal instability at the distal radioulnar joint. Combined with radial head arthroplasty, the construct has stability similar to an intact forearm. The Herbert sling did not improve longitudinal stability in this testing construct. Treatment of longitudinal radioulnar dissociation may benefit from radial head replacement and interosseous ligament reconstruction using a patellar tendon graft.

Micromotion of plasma spray versus grit-blasted radial head prosthetic stem surfaces

Initial stability of a textured surface prosthetic stem is necessary for bone in-growth. Surfaces currently used for radial head prostheses include titanium plasma spray and grit-blasted titanium. Plasma spray radial head prosthetic stems are less dependent than grit-blasted stems on a tight press fit. Good initial press-fit stability, with acceptable micro-motion, can be achieved with a greater range of stem sizes using a plasma spray than grit-blasted surface. Paired cadaveric radii were implanted with plasma spray or grit-blasted radial head prosthetic stems. Micromotion at the stem tip was measured under circumstances simulating eccentric loads. Micromotion in the plasma spray (PS) stems (49 ± 37) μm was not better than that in the grit-blasted (GB) stems (28 ± 10) μm (P = .13). Micromotion of less than 100 μm was measured in all 12 GB stems that were maximum or 1 mm less than maximum size, versus 5/6, and 4/6 PS stems, respectively. Micromotion in plasma spray prosthetic radial head stems was not better than that seen in grit-blasted stems, contrary to our initial hypothesis. Grit-blasted prosthetic radial head stems confer initial press-fit stability that is as good as, or slightly better than, corresponding plasma spray stems. Acceptable amounts of micromotion can be achieved with 2 grit-blasted stem sizes and probably with 2 plasma spray stem sizes.

Dialyse (Groupe A)

Our aim was to test whether anatomically designed metallic radial head implants could better reproduce native radiocapitellar contact pressure and areas than nonanatomic implants.The distal humerus and proximal radius from 6 cadaveric upper extremities were serially tested in supination with 100 N of compression force at 4 angles of flexion (0°, 30°, 60°, and 90°). By use of a thin flexible pressure transducer, contact pressures and areas were measured for the native radial head, an anatomic implant, a nonanatomic circular monopolar implant, and a bipolar nonanatomic implant. The data (mean contact pressure and mean contact area) were modeled using a 2-factor repeated-measures analysis of variance with P ≤ .05 considered to be significant.The mean contact areas for the prosthetic radial heads were significantly less than those seen with the intact radial heads at every angle tested (P < .01). The mean contact pressures increased significantly with all prosthetic radial head types as compared with the native head. The mean contact pressures increased by 29% with the anatomic prosthesis, 230% with the monopolar prosthesis, and 220% with the bipolar prosthesis. Peak pressures of more than 5 MPa were more commonly observed with both the monopolar and bipolar prostheses than with the anatomic or native radial heads.The geometry of radial head implants strongly influences their contact characteristics. In a direct radius-to-capitellum axial loading experiment, an anatomically designed radial head prosthesis had lower and more evenly distributed contact pressures than the nonanatomic implants that were tested.

Radiocapitellar joint contacts after bipolar radial head arthroplasty

The purpose of this study was to determine radiocapitellar contacts before and after radial head replacement, using the bipolar design of Judet. Joint contacts were measured by moulding the joint surfaces of 6 fresh-frozen cadaveric specimens, in various positions of elbow flexion and forearm rotation. Expressed as function of the radial cup, contact areas averaged 44% in the normal elbow, decreasing with flexion and increasing with supination (P < .05). After prosthetic implantation, contact areas averaged 33% and remained quite similar, irrespective of elbow position. Subluxation of the prosthetic head over the lateral margin of the trochlea was seen systematically with supination. Because of intraprosthetic mobility, contact areas were not dependant on elbow position. This adaptability, however, also led to abnormal positioning of the prosthetic radial head with supination, subluxing over the trochlea lateral margin.