Radiocapitellar stability: the effect of soft tissue integrity on bipolar versus monopolar radial head prostheses

Radial head arthroplasty: state of the art

Radial head arthroplasty has joined the armamentarium of options for the treatment of complex radial head fractures, elbow instability, and arthritic conditions. A variety of implants has been introduced in the past decade; these differ in metallic composition, design, and method of fixation. Good short- and intermediate-term outcomes have been reported with the use of loose-fitting prostheses. Press-fit devices restore stability and improve pain and motion but are associated with a greater likelihood of implant loosening, leading to revision surgery. Postoperative elbow stiffness, pain, ulnar nerve palsy, posterior interosseous nerve palsy, and heterotopic ossification have all been reported following radial head surgery, but these complications are likely related to the trauma sustained by the elbow. Adequate knowledge of the surgical indications, types of implants, and surgical technique are essential for a satisfactory outcome when a radial head prosthesis is used for the treatment of nonreconstructable radial head fractures.

Radial head reconstruction in elbow fracture-dislocation: monopolar or bipolar prosthesis?

BACKGROUND

Monopolar and bipolar radial head prosthetic arthroplasties have been used successfully to treat elbow fracture-dislocation with unsalvageable radial head fractures. The relative stability of these two designs in different clinical situations is a topic of ongoing investigation.

QUESTIONS/PURPOSES

We tested the effects of monopolar and bipolar fixed-neck prosthetic radial head implants on improvement in elbow coronal and axial plane laxity in a terrible triad biomechanical model that accounted for lateral collateral ligament integrity and the presence of a transverse coronoid fracture.

METHODS

Kinematic data were collected on six fresh-frozen cadaveric upper extremities tested with passive motion throughout the flexion arc. Varus and valgus gravity stress were applied with the wrist in neutral position. A lateral collateral ligament reconstruction was simulated. We assessed instability after radial head resection and reconstruction with either a monopolar or bipolar implant in the presence of a transversely fractured (Regan and Morrey Type 2) or fixed coronoid process.

RESULTS

With collateral ligament integrity, no difference was detected, with the numbers available, in valgus laxity between implants under valgus stress (p = 1.0). Laxity improvement with each prosthesis was higher when the coronoid was fractured (mean ± SD: monopolar: 7.4° ± 1.6°, p < 0.001; bipolar: 6.4° ± 1.6°, p = 0.003) than when it was fixed (monopolar: 4.0° ± 1.6°, p = 0.02; bipolar: 4.2° ± 1.6°, p = 0.01). With the numbers available, there was no difference in external rotation laxity between implants under valgus stress (p = 1.0). The greatest stabilizing effect of the prostheses occurred when the coronoid was fractured (monopolar: 3.3° ± 1.2°, p = 0.15; bipolar: 3.3° ± 1.2°, p = 0.17). Radial head arthroplasty offered no substantial stability under varus stress for varus or internal rotation laxity.

CONCLUSIONS

In our terrible triad cadaveric model, coronoid fixation was effective in improving varus laxity with a monopolar or bipolar prosthesis in place. Also, both types of prostheses were effective in improving valgus and external rotation laxity to the elbow, regardless of coronoid status. With collateral ligaments reconstructed, no large kinematic differences were noted between implants regardless of the varus-valgus position or whether the coronoid was fractured or fixed.

CLINICAL RELEVANCE

The data from our cadaveric model support the use of either implant type in terrible triad injuries if the collateral ligaments are intact or reconstructed.

Radial head, radiocapitellar and total elbow arthroplasties: a review of recent literature

The outcome of prosthetic elbow surgery is continually evolving. We thoroughly reviewed the literature on this issue to analyse the indications, outcomes and complications of the numerous types of implants currently in use. Radial head replacement is recommended in comminuted fractures of the radial head and in post-traumatic conditions. Medium- and long-term results prove to be satisfactory in the majority of cases, with no evidence to indicate that some prostheses (monopolar vs. bipolar; cemented vs. press-fit) are more effective than others; nonetheless, the bipolar-cemented implant was found to be associated with a lower revision rate than other prostheses. Unicompartmental arthroplasty has recently been used for the treatment of osteoarthritis and rheumatoid arthritis when the lateral compartment is prevalently involved; the results reported to date have been encouraging, although further studies are warranted to confirm the validity of these implants. Total elbow arthroplasty is performed in a range of conditions, including distal humerus fractures in the elderly and elbow arthritis. In the former condition, linked elbow replacement yields excellent results with few complications and a low revision rate. In elbow arthritis, total elbow arthroplasty is indicated when patients suffer from disabling pain, stiffness and/or instability that prevent them from performing daily activities. Unlinked elbow arthroplasty, which is used above all in rheumatoid arthritis, also yields satisfactory results, although the risk of instability persists. The use of linked elbow arthroplasty, which yields similar results but lower revision rates, has consequently increased. Lastly, the results yielded by linked elbow prosthesis in post-traumatic conditions are good, although not quite as good as those obtained in rheumatoid arthritis. Early mechanical failure may occur in younger and more active patients after elbow arthroplasty. However, the careful selection of patients who are prepared to accept functional limitations imposed by elbow implants will enable indications for elbow arthroplasty to be extended to young subjects, particularly when no other therapeutic options are available.

[Endoprosthetics of acute radial head fractures]

Radial head arthroplasty is the treatment of choice for non-reconstructble radial head fractures. Solid prostheses made of metal or pyocarbon can restore valgus stability of the elbow independent of design or stem fixation. Short-term and mid-term results show mostly good to excellent results without any evident differences between the different prosthesis philosophies. In order to obtain good results it is important to implant the prosthesis correctly without overfilling and to judge concomitant ligament injuries correctly. This article discusses the anatomical and biomechanical basis of radial head arthroplasty as well as the surgical technique and radiological diagnosis of overfilling.

Clinical and radiographic comparisons of two different radial head implant designs

BACKGROUND

There is little comparative data to guide implant choice for radial head replacements. The purpose of this study was to evaluate the clinical and radiographic results between patients who received a smooth-stemmed bipolar radial head implant and patients who received an in-growth monopolar prosthesis.

METHODS

Twenty-seven patients requiring a metallic radial head implant in the management of acute or chronic elbow trauma were evaluated. Fourteen patients received a smooth-stemmed bipolar prosthesis and 13 patients received a press-fit monopolar prosthesis. Patients returned for follow-up at an average of 33 months (range, 18-57). Outcome assessments included joint motion, elbow stability, grip strength, pain, the Mayo Elbow Performance Index, and the Disability of Arm, Shoulder and Hand questionnaire. Radiographs were reviewed for joint congruence, ectopic bone, periprosthetic osteolysis, degenerative arthritis, and capitellar wear, and selected patients were tested for inflammatory markers and metal ion levels.

RESULTS

The differences between patient groups for elbow flexion and forearm pronation averaged 10° or less. There were no other pertinent differences between groups for standardized patient and examiner-determined outcomes. There was a trend for ectopic bone to develop more commonly around the smooth-stemmed implants, while periprosthetic osteolysis was more pronounced in cases with the press-fit design. Inflammatory markers were normal, and metal ion levels did not exceed values reported for a well-functioning hip arthroplasty.

CONCLUSION

Outcomes at short- to mid-term follow-up were similar with either implant design. Loosening of a press-fit prosthesis may lead to extensive osteolysis, but of undetermined clinical consequence.

Avulsion fracture of the supinator crest of the proximal ulna in the context of elbow joint injuries

PURPOSE

While performing CT examinations of the elbow, we frequently observed a previously undescribed fracture fragment of the supinator crest of the ulna. According to the anatomy of the lateral collateral ligament complex, this fracture might be an avulsion fracture of the annular ligament and/or the lateral ulnar collateral ligament. The aim of this study was to further characterize these fragments and document their associated injuries.

METHODS

Retrospective evaluation of CT scans of the elbow was performed. Conventional X-ray and CT diagnoses were used to systematically document any associated injuries.

RESULTS

A total of 152 CT scans were evaluated. The fragment in question was discovered in 17 patients (11.2%). The average age of the patients was 40 years (±14.9; 9-71 years). The fragment size varied between a few millimetres and 2.4 cm. Multifragmented fractures were observed. In 82.3% of the cases, associated radial head fractures were diagnosed. In 29.4%, a coronoid process fracture was present. Distal humerus fractures were found in 23.5%. Instability in the medial collateral ligament and an Osborne-Cotterill lesion were found in 11.8% of the patients, respectively.

CONCLUSIONS

In a significant percentage of the population, a previously undescribed fracture fragment of the supinator crest of the ulna could be detected. The most frequently occurring associated injuries were fractures of the radial head, the coronoid process, and the distal humerus. The aetiology of these lesions is unknown; however, bony avulsion of the annular or the lateral ulnar collateral ligament seems to be the most likely cause. If this fragment is to be diagnosed by CT, the possibility of lateral or posterolateral instability should be considered.

Fractures of the radial head

Most fractures of the radial head are stable undisplaced or minimally displaced partial fractures without an associated fracture of the elbow or forearm or ligament injury, where stiffness following non-operative management is the primary concern. Displaced unstable fractures of the radial head are usually associated with other fractures or ligament injuries, and restoration of radiocapitellar contact by reconstruction or prosthetic replacement of the fractured head is necessary to prevent subluxation or dislocation of the elbow and forearm. In fractures with three or fewer fragments (two articular fragments and the neck) and little or no metaphyseal comminution, open reduction and internal fixation may give good results. However, fragmented unstable fractures of the radial head are prone to early failure of fixation and nonunion when fixed. Excision of the radial head is associated with good long-term results, but in patients with instability of the elbow or forearm, prosthetic replacement is preferred. This review considers the characteristics of stable and unstable fractures of the radial head, as well as discussing the debatable aspects of management, in light of the current best evidence.

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 biomechanical effect of prosthetic design on radiocapitellar stability in a terrible triad model

OBJECTIVES

The integrity of elbow soft tissues affects radiocapitellar joint stability in the presence of bipolar radial head (RH) prostheses. This study examined the effect on radiocapitellar stability of monopolar designs versus bipolar RH prostheses in an elbow model with a surgically controlled terrible triad injury.

METHODS

In each of 8 fresh-frozen elbow specimens (4 male and 4 female), a terrible triad fracture dislocation was created through soft tissue releases, coronoid fracture, and RH resection. Radiocapitellar stability was recorded under the following 3 sets of conditions: (1) surgical control (native RH), (2) RH replacement (circular monopolar or bipolar), (3) replacement with alternate circular RH not used in condition 2, and (4) replacement with the anatomic RH.

RESULTS

The type of RH used significantly impacted the mean peak force required to resist posterior subluxation (p = 0.0001). The mean peak subluxation force of the bipolar prosthesis (1 ± 1 N) was significantly less than both the anatomic (16 ± 1 N) and nonanatomic circular (12 ± 1 N) implants (p = 0.0002). The peak subluxation force of the native RH (18 ± 2 N) was not different than the anatomic implant (p = 0.09) but was greater than the nonanatomic circular design (p = 0.0006).

CONCLUSIONS

Monopolar RHs confer greater radiocapitellar stability than bipolar implants in the setting of terrible triad injuries. Of the 2 monopolar designs tested, the anatomic design provided more stability than the non-anatomic RH prosthesis.

Effect of radial head malunion on radiocapitellar stability

BACKGROUND

Management for Mason type II radial head fractures is controversial. We hypothesized that angulation or depression of a marginal radial head fragment would affect radiocapitellar stability similarly to fragment excision.

MATERIALS AND METHODS

A Mason type II radial head fracture was created in 6 cadaveric elbows by excising a segment from the anterolateral quadrant that was 30% of the diameter of the articular surface. Radiocapitellar stability was recorded under 5 sets of conditions: (1) intact radial head (intact), (2) 30% surface area fragment resected (partially excised), (3) anatomic fragment fixation with screws (fixed), (4) fragment fixation with 2 mm of depression relative to the articular surface (depressed), and (5) fragment fixation after a 30° wedge resection (angulated).

RESULTS

The forces required to subluxate the joint were greatly reduced after fragment excision (5 ± 1 N; P = .0001) and restored to normal (21 ± 1 N; P = .9) after anatomic fixation of the excised fragment. The peak forces were significantly reduced with fragment depression (4 ± 1 N) and angulation (4 ± 2 N; P = .0001).

CONCLUSION

A radial head fracture that is depressed 2 mm or angulated 30° may cause up to an 80% loss of concavity-compression stability of the radiocapitellar joint.

Alteration of the end-plane angle in press-fit cylindrical stem radial head prosthesis: an in vitro study

PURPOSE

Many studies comparing the morphology of native radial head with the prosthesis have been published. However, there is limited information regarding the postoperative alignment of the articular surface following the radial head replacement. The purpose of this study is to evaluate the alteration of the end-plane angle in the modular radial head prosthesis with a press-fit cementless cylindrical stem.

METHODS

The study used 36 cadaveric radii. The press-fit size prosthesis with cylindrical stem was inserted into each specimen. The end-plane angles of the radial head before and after prosthetic replacement, were measured in coronal and sagittal planes with a digital inclinometer. The data were analyzed by paired t-test.

RESULTS

From paired t-test, there were statistically symmetrical end-plane angles before and after radial head replacement in both coronal and sagittal planes (p-value < 0.01). The mean of radial head end-plane angle alteration in the coronal plane was 3.62° (SD, 2.76°) (range, 0.3°-8.9°). In the sagittal plane, the mean of alteration was 5.85° (SD, 3.56°) degrees (range, 0.3° - 14.2°).

CONCLUSION

The modular radial head prosthesis with cylindrical stem is in vitro able to restore the native end-plane angles of radial heads statistically when used in a press-fit fashion.

Influence of prosthetic design on radiocapitellar concavity-compression stability

BACKGROUND

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

HYPOTHESIS

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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