Metallic radial head arthroplasty improves valgus stability of the elbow

The stabilizing influence of radial head arthroplasty was studied in eight medial collateral ligament deficient anatomic specimen elbows. An elbow testing apparatus, which used computer controlled pneumatic actuators to apply tendon loading, was used to simulate active elbow flexion. The motion pathways of the elbow were measured using an electromagnetic tracking device, with the forearm in supination and pronation. As a measure of stability, the maximum varus to valgus laxity over the range of elbow flexion was determined from the difference between varus and valgus gravity loaded motion pathways. After transection of the medial collateral ligament, the radial head was excised and replaced with either a silicone or one of three metallic radial head prostheses. Medial collateral ligament transection caused a significant increase in the maximum varus to valgus laxity to 18.0 degrees +/- 3.2 degrees. After radial head excision, this laxity increased to 35.6 degrees +/- 10.3 degrees. The silicone implant conferred no increase in elbow stability, with a maximum varus to valgus laxity of 32.5 degrees +/- 15.5 degrees. All three metallic implants improved the valgus stability of the medial collateral ligament deficient elbow, providing stability similar to the intact radial head. The use of silicone arthroplasty to replace the radial head in the medial collateral ligament deficient elbow must be questioned. Metallic radial head arthroplasty provides improved valgus stability, approaching that of an intact radial head.     

The effect of the radial head and prosthetic radial head replacement on resisting valgus stress at the elbow

Five fresh nonembalmed elbows were tested for resistance to valgus stress in their anatomic state, after radial head resection, and after insertion of Silastic and polymethylmethacrylate (PMMA) radial head replacements. The resistance to valgus stress was found to be reduced an average of 28% after radial head resection. The PMMA and Silastic implants restored valgus stiffness an average of 86% and 78% respectively, as compared to intact elbow values for corresponding flexion angles. Testing in pronation, supination and neutral forearm rotation demonstrated no difference in valgus stiffness. For each elbow, resistance to valgus stress was greatest at full extension and dropped approximately 30% at all other flexion angles as compared to corresponding full extension value. These data support the concept of the radial head as a stabilizer to valgus stress in the in vitro elbow. Further, this data demonstrated the ineffectiveness of current radial head replacement systems in restoring this biomechanical function and suggest that the use of a stiffer implant material may be beneficial in resisting valgus stress. Additional testing is indicated to determine the performance of a stiffer implant at the clinical and biological levels.     

The contribution of the coronoid and radial head to the stability of the elbow

We undertook this study to determine the minimum amount of coronoid necessary to stabilise an otherwise intact elbow joint. Regan-Morrey types II and III, plus medial and lateral oblique coronoid fractures, collectively termed type IV fractures, were simulated in nine fresh cadavers. An electromagnetic tracking system defined the three-dimensional stability of the ulna relative to the humerus. The coronoid surface area accounts for 59% of the anterior articulation. Alteration in valgus, internal and external rotation occurred only with a type III coronoid fracture, accounting for 68% of the coronoid and 40% of the entire articular surface. A type II fracture removed 42% of the coronoid articulation and 25% of the entire articular surface but was associated with valgus and external rotational changes only when the radial head was removed, thereby removing 67% of the articular surface. We conclude that all type III fractures, as defined here, are unstable, even with intact ligaments and a radial head. However, a type II deficiency is stable unless the radial head is removed. Our study suggests that isolated medial-oblique or lateral-oblique fractures, and even a type II fracture with intact ligaments and a functional radial head, can be clinically stable, which is consistent with clinical observation.     

Muscle contribution to elbow joint valgus stability

Repetitive valgus stress of the elbow can result in excessive strain or rupture of the native medial ulnar collateral ligament (MUCL). The flexor-pronator mass (FPM) may be particularly important for elbow valgus stability in overhead-throwing athletes. The aim of this study was to identify the relative contribution of each muscle of the FPM--that is, the flexor carpi ulnaris (FCU), flexor digitorum superficialis (FDS), flexor carpi radialis (FCR), and pronator teres (PT)--and of the extensor-supinator mass, including the extensor carpi ulnaris (ECU), extensor digitorum communis (EDC), extensor carpi radialis longus and brevus, and brachioradialis, to elbow valgus stability at 45 degrees and 90 degrees of elbow flexion angles. Eight fresh-frozen elbow specimens (mean age at death, 73.75 +/- 14.07 years) were tested. With the skin and subcutaneous tissue removed but all muscles left intact, each individual muscle of the FPM and extensor-supinator mass was loaded at 3 levels of force. During loading, strain on the MUCL and the kinematics of the elbow were measured simultaneously. Kinematic measurements were later repeated when the MUCL was fully cut. At 45 degrees and 90 degrees of elbow flexion, individual loading of the FCU, FDS, and FCR caused significant relief to the MUCL whereas the PT produced no significant change. Furthermore, of these flexor muscles, the FCU provided the greatest MUCL relief at both 45 degrees and 90 degrees . In contrast, loading of the ECU at 45 degrees of elbow flexion produced a significant increase in MUCL strain. All FPM muscles caused significant elbow varus movement at both 45 degrees and 90 degrees when loaded individually. At 90 degrees , the FCU created more motion than both the FCR and PT but not the FDS, and the FDS created more motion than the PT. The EDC and ECU created significant valgus movement at 45 degrees and 90 degrees , which became insignificant when the MUCL was transected. Our study suggested that the FCU, FDS, and FCR may function as dynamic stabilizers, with the FCU being the primary stabilizer for elbow valgus stability, incorporating with the MUCL for all tested joint configurations. Our findings also suggest that the ECU and EDC increased MUCL strain and elbow valgus movement at both 45 degrees and 90 degrees .     

The effect of radial head fracture size on elbow kinematics and stability.

This study determined the effect of radial head fracture size and ligament injury on elbow kinematics. Eight cadaveric upper extremities were studied in an in vitro elbow simulator. Testing was performed with ligaments intact, with the medial collateral (MCL) or lateral collateral (LCL) ligament detached, and with both the MCL and LCL detached. Thirty degree wedges were sequentially removed from the anterolateral radial head up to 120 degrees . Valgus angulation and external rotation of the ulna relative to the humerus were determined for passive motion, active motion, and pivot shift testing with the arm in a vertical (dependent) orientation. Maximum varus-valgus laxity was calculated from measurements of varus and valgus angulation with the arm in horizontal gravity-loaded positions. No effect of increasing radial head fracture size was observed on valgus angulation during passive and active motion in the dependent position. In supination, external rotation increased with increasing fracture size during passive motion with LCL deficiency and both MCL and LCL deficiency. With intact ligaments, maximum varus-valgus laxity increased with increasing radial head fracture size. With ligament disruption, elbows were grossly unstable, and no effect of increasing radial head fracture size occurred. During pivot shift testing, performed with the ligaments intact, subtle instability was noted after resection of one-third of the radial head. In this in vitro biomechanical study, small subtle effects of radial head fracture size on elbow kinematics and stability were seen in both the ligament intact and ligament deficient elbows. These data suggest that fixation of displaced radial head fractures less than or equal to one-third of the articular diameter may have some biomechanical advantages; however, clinical correlation is required.     

Dynamic contributions of the flexor-pronator mass to elbow valgus stability

BACKGROUND: Previous studies have indicated that the demands placed on the medial ulnar collateral ligament of the elbow when it is subjected to valgus torque during throwing exceed its failure strength, which suggests the necessary dynamic contribution of muscle forces. We hypothesized that the flexor-pronator mass assists the medial ulnar collateral ligament in stabilizing the elbow against valgus torque. METHODS: Six cadaveric elbows were tested at 30 degrees and 90 degrees of flexion with no other constraints to motion. A full medial ulnar collateral ligament tear was simulated in each elbow. Muscle forces were simulated on the basis of the centroids and physiological cross-sectional areas of individual muscles. The biceps, brachialis, and triceps were simulated during flexor carpi ulnaris, flexor digitorum superficialis, flexor digitorum superficialis and flexor carpi ulnaris, and pronator teres-loading conditions. Kinematic data were obtained at each flexion angle with use of a three-dimensional digitizer. RESULTS: Release of the medial ulnar collateral ligament caused a significant increase in valgus instability of 5.9 degrees +/- 2.4 degrees at 30 degrees of elbow flexion and of 4.8 degrees +/- 2.0 degrees at 90 degrees of elbow flexion (p < 0.05). The differences in valgus angulation between each muscle-simulation condition and the medial ulnar collateral ligament-intact condition were significantly different from each other (p < 0.05), except for the difference between the flexor carpi ulnaris contraction condition and the flexor digitorum superficialis-flexor carpi ulnaris co-contraction condition. This co-contraction provided the most correction of the valgus angle in comparison with the intact condition at both 30 degrees and 90 degrees of elbow flexion (1.1 degrees +/- 1.8 degrees and 0.38 degrees +/- 2.3 degrees , respectively). Simulation of the flexor carpi ulnaris alone provided the greatest reduction of the valgus angle among all individual flexor-pronator mass muscles tested (p < 0.05), whereas simulation of the pronator teres alone provided the least reduction of the valgus angle (p < 0.05). CONCLUSIONS: The flexor-pronator mass dynamically stabilizes the elbow against valgus torque. The flexor carpi ulnaris is the primary stabilizer, and the flexor digitorum superficialis is a secondary stabilizer. The pronator teres provides the least dynamic stability.     

Monobloc radial head prostheses in complex elbow injuries: results after primary and secondary implantation

Purpose

Dislocations of components, loosening of the stem, overstuffing and removal in up to 24 % of common radial head prostheses (RHP) after implantation in complex elbow injuries signal the need for improvement. The latest biomechanical evidence shows advantages for monopolar designs. Clinical results after primary and secondary implantation of the newly designed press-fit monobloc monopolar RHP in cases of complex elbow injury are evaluated.

Methods

Twenty-nine patients [median age 60 years (29–86)] were followed up retrospectively for a median of 25 months (7–54) post-operatively. Subjective parameters, the Mayo Elbow Performance Score (MEPS), the Broberg and Morrey score (BMS), latest radiographs and complications were evaluated.

Results

MEPS and BMS averaged 87.2 ± 12.9 and 81.1 ± 11.9 points, respectively. No case of implant loosening was observed; the RHP had to be removed in one case (3 %). The overall complication and revision rate was higher after secondary (53 %) than after primary (19 %) implantation.

Conclusions

Satisfactory clinical results and low short-term removal rates emphasise the practicality of monobloc monopolar RHP. Differentiated treatment of complex elbow fracture-dislocations is compulsory to avoid the need for secondary RHP implantation which carries a higher complication rate.     

The effect of radial head excision and arthroplasty on elbow kinematics and stability

BACKGROUND: Radial head fractures are common injuries. Comminuted radial head fractures often are treated with radial head excision with or without radial head arthroplasty. The purpose of the present study was to determine the effect of radial head excision and arthroplasty on the kinematics and stability of elbows with intact and disrupted ligaments. We hypothesized that elbow kinematics and stability would be (1) altered after radial head excision in elbows with intact and disrupted ligaments, (2) restored after radial head arthroplasty in elbows with intact ligaments, and (3) partially restored after radial head arthroplasty in elbows with disrupted ligaments. METHODS: Eight cadaveric upper extremities were studied in an in vitro elbow simulator that employed computer-controlled actuators to govern tendon-loading. Testing was performed in stable, medial collateral ligament-deficient, and lateral collateral ligament-deficient elbows with the radial head intact, with the radial head excised, and after radial head arthroplasty. Valgus angulation and rotational kinematics were determined during passive and simulated active motion with the arm dependent. Maximum varus-valgus laxity was measured with the arm in a gravity-loaded position. RESULTS: In specimens with intact ligaments, elbow kinematics were altered and varus-valgus laxity was increased after radial head excision and both were corrected after radial head arthroplasty. In specimens with disrupted ligaments, elbow kinematics were altered after radial head excision and were similar to those observed in specimens with a native radial head after radial head arthroplasty. Varus-valgus laxity was increased after ligament disruption and was further increased after radial head excision. Varus-valgus laxity was corrected after radial head arthroplasty and ligament repair; however, it was not corrected after radial head arthroplasty without ligament repair. CONCLUSIONS: Radial head excision causes altered elbow kinematics and increased laxity. The kinematics and laxity of stable elbows after radial head arthroplasty are similar to those of elbows with a native radial head. However, radial head arthroplasty alone may be insufficient for the treatment of complex fractures that are associated with damage to the collateral ligaments as arthroplasty alone does not restore stability to elbows with ligament injuries.     

Results of acute excision of the radial head in elbow radial head fracture-dislocations

OBJECTIVES: To evaluate the results of radial head excision for the treatment of elbow fracture-dislocations with an unsalvageable comminuted radial head fracture and no other associated fractures. DESIGN: Retrospective study. SETTING: University Hospital. PATIENTS AND INTERVENTION: Ten elbow fracture-dislocations with a comminuted radial head fracture treated with radial head excision in our institution between 1990 and 1996 and followed a mean of 4.62 years. MAIN OUTCOME MEASUREMENTS: Clinical results were graded using the Mayo index and the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire. Radiographs were evaluated for proximal radius migration, elbow angulation, degenerative changes, and ectopic bone. RESULTS: Final clinical results were excellent in four patients, good in five patients, and fair in one patient. Pain was absent in six patients, mild in three patients, and moderate in one patient. Mean flexion arc was 7.5 to 140 degrees, and mean pronation and supination were 85.5 and 83.5 degrees, respectively. Average strength loss was 15 percent. No elbow was unstable. The raw DASH score ranged from 39 to 62 points (normalized values, 0.66 to 15,79 points). On average, the carrying angle increased 5.4 degrees. Degenerative changes were absent in two, Grade I in four, and Grade II in four patients. Ectopic bone, mainly residual fracture fragments, was evident in four patients. Proximal migration of the radius averaged 1.6 millimeters; the two patients with over four millimeters of migration had mild wrist pain. CONCLUSIONS: Acute radial head excision for the treatment of elbow fracture-dislocations provides satisfactory short-term clinical results when there are no other associated intraarticular fractures. However, the long-term significance of the early degenerative changes is not known.     

The stability of the elbow following excision of the radial head and transection of the annular ligament

Summary The stabilizing role of the lateral ligament complex and the radial head were investigated in ten osteoligamentous elbow preparations. The annular ligament was the prime stabilizer of the lateral aspect of the elbow. Transection of the annular ligament caused maximal varus and external rotatory instability of 13.7° and 32.8° respectively, with an elbow flexion about 70°. Isolated excision of the radial head caused slight varus and external rotatory instability of 4.8° and 10.4° respectively, with an elbow flexion about 40°. The lateral collateral ligament had only a minor stabilizing function of the elbow. The stability of the elbow after excision of the radial head may be improved by proper preservation of the annular ligament.     

Vitallium radial head prosthesis for acute and chronic elbow fractures and fracture-dislocations involving the radial head

This retrospective study aims to evaluate the radiographic, functional, and patient-derived outcomes of 16 patients who each received a Vitallium radial head prosthesis for unreconstructable acute fractures of the radial head, as well as previously treated fractures of the radial head associated with residual instability, pain, and stiffness. Follow-up averaged 33 months. A trend toward greater disability and poorer motion was noted in the delayed treatment group compared with the acute replacement group. Overall, the results were excellent in 5 patients, good in 10, and poor in 1, as determined by the Mayo Elbow Performance Score. All elbows were stable at follow-up, and no patient reported wrist pain. Four required further operative treatment of their elbow injuries. Metallic radial head arthroplasty yields satisfactory results in acute unreconstructable radial head fractures or as a salvage procedure for previously treated radial head fractures.     

Short-term to medium-term outcomes of cemented Vitallium radial head prostheses after early excision for radial head fractures

Studies show that the radial head is a significant stabilizer to valgus and varus stresses and external rotatory stability. We review the outcomes of patients who had radial head replacement in our institution. Six patients with Mason-Johnston type III or IV radial head fractures underwent radial head replacement and were evaluated by radiologic and clinical assessment. The American Shoulder and Elbow Surgeons score, DASH (Disabilities Arm, Shoulder and Hand) score, and Broberg and Morrey Performance Index were calculated. Average follow-up was 29.7 months. The Broberg and Morrey score was excellent for 1 patient, good for 3, fair for 1, and poor for 1. Complications included prosthetic loosening in 4 patients and 1 patient each with ulnar neuropathy, heterotrophic ossification, and wrist pain. Outcomes did not necessarily correlate with the severity of the initial injury or the eventual range of motion. Longer follow-up is required to see if the radiologic loosening will lead to clinical instability.