Ulnar Head Implant Arthroplasty
DEFINITION
As with any synovial joint, the distal radioulnar joint (DRUJ) can degenerate due to osteoarthritis, inflammatory arthritis, chronic instability, infection, and trauma.4
Standard treatments such as partial (“matched resection”) or complete (Darrach procedure) distal ulnar resection have the potential to destabilize the forearm axis and cause painful forearm rotation.
The normal compressive muscle forces acting between the radius and ulna help stabilize the DRUJ.1
When the distal ulna has been resected and the forearm is rotated under such a compressive load, a palpable grinding between the ulnar stump and the radius may develop; this is referred to as ulnar
impingement.6 This may progress from minor irritation to painful erosion of the radius. These patients present with pain on stress loading of the upper extremity, weakness in grip strength, decreased
forearm rotation, and difficulty with lifting.2
Ulnar head implant arthroplasty is designed to maintain the DRUJ, thereby avoiding ulnar impingement. An adequate soft tissue envelope repaired over the implant provides stability.
The first prosthesis used was a silicone cap designed to provide a soft end to the ulnar stump. These prostheses understandably failed under loading.
Newer designs aim to restore the ulnar head using a metallic prosthesis to articulate with the sigmoid notch.
ANATOMY
See Chapters 26, 63, 64, 65, 111, 112, and 115.
PATHOGENESIS
See Chapters 111 and 112.
NATURAL HISTORY
See Chapters 111 and 112.
PATIENT HISTORY AND PHYSICAL FINDINGS
Patients who have had an ulnar head resection complain of painful forearm rotation, often associated with instability of the forearm axis, decreased strength, and joint grinding.
In addition to recording the range and fluidity of DRUJ motion, the examiner must determine the stability of the joint and the contribution of ulnar impingement to the patient's pain.
Radioulnar compression creates radioulnar impingement by external passive compression.
The examiner should encircle the patient's distal forearm with his or her hands and apply firm compression. A positive sign is reproduction of the patient's pain.
Active radioulnar impingement is reproduced by active muscle contraction, specifically the brachialis.
The patient has pain lifting a load of 2 pounds with the forearm in neutral position.
Ulnar stump instability results from compromised soft tissue stabilizers of the distal stump, which tends to fall away from the radius as the forearm is rotated.
The patient is asked to actively rotate the forearm. Dorsal and palmar subluxation of the ulnar stump is visible.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Standard posteroanterior, lateral, and oblique radiographs of the wrist
These x-rays demonstrate scalloping of the ulnar cortex of the radial metaphysis and some corresponding pencilling of the distal ulnar stump.
Posteroanterior stress-loaded radiographs
May demonstrate impingement between the radius and ulna
The patient stands with the involved forearm facing the x-ray tube. The wrist is stress-loaded by asking the patient to hold a 2.2-kg lead cylinder with the shoulder adducted, the elbow flexed to 90 degrees, and the forearm in the position of neutral rotation.
The forearm rests on the x-ray cassette and the radiograph is then taken with the beam aligned in the coronal plane, creating a posteroanterior view of the neutral forearm.
Radiographs are obtained before and after stress-loading.
Computed tomography (CT) scanning
In patients with osteoarthritis of the DRUJ, axial scans are essential for evaluation of the extent of degenerative changes in the ulnar head and the need for total or partial replacement.
CT scanning is also essential for evaluation of the sigmoid notch for osteophytes and erosion in patients with painful ulnar head replacement.
CT scanning with forearm in pronation and supination is also useful in detecting radioulnar instability if clinical examination is equivocal.
DIFFERENTIAL DIAGNOSIS
In addition to radioulnar impingement, a patient who has pain at the DRUJ after resection of the ulnar head may have pain due to the following conditions:
Ulnar neuropathy
Painful surgical scar due to sensory nerve injury or scarring Radiocarpal or midcarpal arthritis
NONOPERATIVE MANAGEMENT
Activity modification to minimize forearm rotatory movements will diminish pain.
A Russe splint is partially helpful for patients with instability of the distal ulnar stump but is of no help in preventing radioulnar impingement pain.
SURGICAL MANAGEMENT
The most common indication for distal ulnar implant arthroplasty is to relieve impingement symptoms in patients who have undergone previous ulnar head resection.
Other less common indications include the following:
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Treatment of patients with primary degenerative arthritis of the DRUJ who have failed to respond to splinting and steroid injections
Reconstruction of the ulna after excision of a tumor involving the ulnar head
After unreconstructable fractures of the ulnar head as either a primary or delayed procedure Relative indication: patients with well-controlled inflammatory arthritis but well-preserved bone stock
The amount of the DRUJ that is replaced may vary for any given case.
Partial ulnar head replacement
Unconstrained replacement of the entire distal ulna with or without sigmoid notch resurfacing Constrained total DRUJ replacement, including the sigmoid fossa of the distal radius
Partial ulnar head replacement preserves the styloid process and the attachment of the triangular fibrocartilage.
This procedure is indicated when the disease process, typically arthritis, is limited to the distal ulnar articular surface.
Contraindications include active infection, inadequate soft tissue coverage or poor bone stock, instability of the distal ulna, excessive ulnar positive variance, and degeneration at the sigmoid notch.
Two types of implants are available: a one-piece stemmed metal prosthesis and a two-piece prosthesis with a titanium stem and an articulating pyrolytic carbon disc that replaces the head (FIG 1).5
Long-term results of partial ulnar head replacement are not known. The articulating two-piece prosthesis has the theoretical advantage of less radius erosion from articulation with the pyrocarbon head.
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FIG 1 • The Eclypse partial ulnar head replacement (Tornier Surgical Implants, Tornier, Inc., Rodborough Road, FR) consists of an expandable titanium stem with a mobile pyrocarbon spacer (A). When implanted, the prosthesis preserves the ulnar styloid and attachment of the TFCC (B).
Unconstrained complete ulnar head replacement is indicated for reconstruction of ulnar impingement after resection or replacement of an arthritic DRUJ associated with instability of the distal ulna. With mild instability, repair of the soft tissue envelope is adequate to restore stability. In cases with more obvious instability, an additional soft tissue procedure is indicated along with ulnar head replacement.
Ulnar head prostheses are generally spherical and made of metal or ceramic. An eccentric-shaped metallic head has been designed to more closely approximate the shape of the normal head. However, biomechanical studies have demonstrated normal tracking patterns of the distal ulna around the radius,
closely simulating the normal joint, even with the use of spherical heads.8
Ulnar head prostheses may articulate with a metal-backed polyethylene resurfacing of the sigmoid notch in an unconstrained manner (FIG 2).
An adequate soft tissue envelope is essential to prevent subluxation of a complete ulnar head replacement. The triangular fibrocartilage complex (TFCC) is no longer attached to the distal ulna, making the prosthesis prone to dislocation. Thus, an essential part of the surgical technique is reconstructing the capsuloligamentous envelope surrounding the ulnar prosthesis.
Other contraindications include previous open fracture, infection in or around the joint, skeletal immaturity, and known sensitivity to the implant materials.
In cases of marked instability, with lack of an adequate soft tissue stabilizing envelope and ablation of the DRUJ
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after trauma or tumor resection, a constrained total DRUJ replacement should be used (FIG 3).
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FIG 2 • The Stability total ulnar head arthroplasty system (Small Bone Innovations, Inc., Morrisville, PA ) consists of a metal ulnar head component that articulates with a metal-backed polyethylene sigmoid notch. The ulnar head component can be used individually as a hemiarthroplasty.
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FIG 3 • The Aptis system (Aptis Medical, Louisville, KY) replaces the entire DRUJ with a constrained
articulation. The components include (a) radial plate with socket, (b) polyethylene ball, (c) hemisocket with screws, and (d) ulnar stem with peg.
The radial component consists of a plate with a polyethylene-lined metal sphere affixed to the interosseous surface of the radius.
The ulnar stem has a protruding peg that is captured and rotates within the polyethylene liner. The stem has limited freedom of proximodistal and limited dorsopalmar motion, simulating normal DRUJ mechanics.
Preoperative Planning
Preoperative radiographs of both sides are used for templating (FIG 4).
Normal anatomy and ulnar variance are reproduced to the extent possible. The appropriate implant size is chosen.
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FIG 4 • Preoperative templating for the Aptis system is done in the frontal and lateral planes to determine the appropriate size of implants to be used at surgery.
Positioning
Standard positioning and tourniquet application are used.
Approach
An incision is made along the ulnar border of the shaft of the distal ulna in line with the ulnar styloid. The interval between the flexor carpi ulnaris (FCU) and extensor carpi ulnaris (ECU) tendons is developed for access to the ulna.
A dorsal approach is an alternative and is indicated for partial head replacement. Access to the articular portion of the ulnar head is gained through the floor of the fifth extensor compartment.
TECHNIQUES
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Partial Ulnar Head Replacement Arthroplasty
Evaluate preoperative radiographs (TECH FIG 1A).
Make a longitudinal skin incision over the DRUJ between the fifth and sixth extensor compartments (TECH FIG 1B).
Divide the extensor retinaculum of the fifth compartment (TECH FIG 1C). Retract the extensor digiti minimi tendon.
Create an ulnarly based combined retinaculum and DRUJ rectangular capsular flap, with care to make the distal limb of the capsulotomy just proximal to the dorsal radioulnar ligament.
Leave the ECU subsheath and ECU tendon in place.
Dorsally subluxate the ulnar head from sigmoid notch using a small Hohmann retractor placed under the head.
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TECH FIG 1 • A,B. Preoperative radiographs of a patient with rheumatoid arthritis and previous radiolunate fusion who treat with First Choice partial ulnar head arthroplasty (Integra LifeSciences, Plainsboro, NJ). (continued)
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TECH FIG 1 • (continued) C. Longitudinal dorsal incision made to expose ulnar head and elevate ulnar-based flap of capsule. D. Reflected extensor retinaculum with preserved ECU. E. Resected ulnar head measured to match partial ulnar head prosthesis. F,G. Intraoperative Fluoroscan demonstrating partial ulnar head resection. H,I. Intraoperative Fluoroscan images following placement of implant and soft tissue used to stabilize the prosthesis during closure. J. The ulnar medullary canal is reamed. K,L. Postoperative radiographs of partial ulnar head prosthesis.
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Resect the articular portion of the ulnar head using a customized jig specific to the implant system to be used (TECH FIG 1D,E).
Ream the ulnar medullary canal and place a trial prosthesis of the appropriate size (TECH FIG 1F). Obtain intraoperative radiographs to confirm correct sizing of head and ulnar variance.
Ascertain range of motion and stability and insert a definitive prosthesis. Repair the capsular flap and retinaculum together and imbricate it only if necessary for stability (TECH FIG 1G).
Confirm stability with postoperative radiographs (TECH FIG 1H).
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Ulnar Head Hemiarthroplasty (without Sigmoid Notch Resurfacing)
Make a longitudinal skin incision on the ulnar border of the distal forearm (TECH FIG 2A).
Incise the extensor retinaculum along the medial border of the distal ulna between the ECU and FCU.
Identify and protect the dorsal cutaneous branch of the ulnar nerve as it crosses from volar to dorsal across the most distal part of the incision.
Elevate the ECU tendon subsheath subperiosteally off the distal ulna along with the TFCC and ulnar collateral ligament distally.
Determine the resection level of the distal ulna using a template and mark it with a pen or osteotome (TECH FIG 2B).
The aim is to create ulnar neutral variance after the implant is in place.
When the distal ulna has been previously excised, use the distal end of the sigmoid fossa of the distal radius as a landmark to determine the ulnar osteotomy level.
With soft tissue retractors in place, use an oscillating saw to osteotomize the distal ulna (TECH FIG 2C).
Take care to ensure that the cut is perpendicular to the long axis of the ulna.
Remove and size the ulnar head.
To allow for easy identification for soft tissue repair, place a tagging suture into the TFCC attachment in the fovea before releasing it from the ulna.
Inspect the sigmoid notch of the distal radius for incongruity. Remove osteophytes.
Define the intramedullary canal of the distal ulna using an awl or sharp broach. Gently enlarge the canal to the appropriate stem size using broaches of increasing diameter (TECH FIG 2D).
Gently impact the appropriate trial stem into the shaft of the distal ulna (TECH FIG 2E). The collar should seat firmly against the resected surface of the distal ulna.
In cases with previous excessive ulnar resection, a prosthesis with an extended collar may be indicated.
To ascertain the need for an extended collar, place a trial spacer on the neck of the trial stem before placing the trial head.
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TECH FIG 2 • A. A longitudinal incision is made between the FCU and ECU tendons on the ulnar border of the distal forearm and wrist. B. The cutting guide helps determine the level of resection of the ulnar head. The distal notches are for use with the three head sizes and standard stem, and the proximal notches are for use with a collared stem in cases of previous resection or resorption of the distal ulna. C. An oscillating saw is used to resect the ulnar head at the determined level. D. The ulnar medullary cavity is reamed using broaches. (continued)
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TECH FIG 2 • (continued) E. The appropriate trial stem is inserted into the ulnar shaft using an impactor and gentle taps with a mallet. F. Soft tissue-stabilizing sutures are placed in holes in the definitive head implant before impaction onto the stem (inset). The TFCC sutures are passed through holes in the deeper distal row of holes corresponding to the fovea of the native head. Sutures from the ECU subsheath are passed through the proximal superficial row of holes. The sutures are left untied until final closure. G. Because the head does not freely rotate on the stem, it is essential to align the head before impaction onto the stem. The holes on the head are lined up with the subcutaneous border of the ulna. H. After the pull-through sutures of the prosthesis are tied down, the remaining soft tissue envelope deep to the extensor retinaculum is approximated with the forearm in neutral position. I. Preoperative radiographs of an unstable and incongruous ulnar head after comminuted fracture of the distal radius and ulna. J. Ulnar head replacement and soft tissue imbrication restored congruity and stability to the articulation.
Place the trial head of the appropriate size onto the neck of the trial stem and reduce the DRUJ. Supination and pronation should be full and smooth, with no instability at the articulation.
Obtain intraoperative radiographs to evaluate the size of the ulnar head and the ulnar variance.
If the prosthesis is too distal, resection of more distal ulna is necessary.
Remove the trial implant by gently applying anteriorly directed pressure on the distal ulna to dislodge the ulnar head from the sigmoid notch.
If a firm fit is obtained with the trial, a press-fit technique may be used with the final implant. In patients
with osteopenia or previous wrist fusion, use cement to secure the ulnar stem.
Prepare the appropriately sized head for soft tissue stabilization before the stem is fully impacted. Pass two 3-0 nonabsorbable sutures with curved double needles through each row of holes in the prosthesis head. Pass the needles from the deeper suture through the TFCC at its previous foveal insertion, and insert the needles from the superficial suture into the ECU subsheath. Leave the sutures untied (TECH FIG 2F).
Insert and impact the final stem (with or without cement) using the stem impactor.
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Align the head of the prosthesis such that the two rows of suture holes are along the subcutaneous border of the ulna (TECH FIG 2G). Then place it onto the tapered neck of the stem and gently impact it.
Advance the soft tissues ulnarly over the head of the prosthesis as it is reduced into the sigmoid notch. With the forearm in midrotation, tie down the sutures placed in the head, closing the ECU subsheath over the top of the prosthesis.
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TECH FIG 3 • A,B. Preoperative posteroanterior (PA) and oblique radiographs demonstrating previous
Darrach procedure and distal radius plate for a distal radius fracture treated 1.5 years prior to presentation. C,D. Intraoperative Fluoroscan images status post ulnar head prosthesis insertion. E,F. Six-week postoperative radiographs of ulnar head prosthesis demonstrating stability of implant.
Imbricate the remaining soft tissue envelope over the distal ulna while approximating the FCU-ECU interface (TECH FIG 2H).
Check the stability of the prosthesis in supination and pronation. Close the extensor retinaculum over the capsule.
Obtain final radiographs (TECH FIG 2I,J).
Obtain hemostasis after the tourniquet is deflated.
Obtain repeat radiographs at the first postoperative followup to confirm stability of prosthesis within the sigmoid notch (TECH FIG 3A-C).
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Constrained Distal Radioulnar Joint Arthroplasty
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Make an 8-cm longitudinal incision in the shape of a hockey stick along the ulnar border of the distal forearm between the fifth and sixth dorsal extensor compartments (TECH FIG 4A).
Create a rectangular ulnarly based fascia flap (TECH FIG 4B). Use the flap to create a barrier between the prosthesis and the ECU at closure.
The width of the flap should cover the head of the implant and may include the most proximal part of the extensor retinaculum.
Expose the distal ulna through the floor of the fifth extensor compartment and mobilize the tendons of the extensor digiti minimi proximally for a distance of 8 cm.
Divide the sensory branch of the posterior interosseous nerve to avoid avulsion of the nerve from the thumb extensors when placing an elevator between the extensor mass and the radius.
Incise the ECU sheath to its insertion at the base of the fifth metacarpal.
This is to avoid pressure against the distal end of the implant.
Excise the remaining head of the ulna at a level just proximal to the cartilage or where the DRUJ would have been.
Leave the radial attachment of the TFCC undisturbed to provide a barrier between the prosthesis and the carpal bones.
Displace the ulnar shaft in a volar direction to expose the radius and sigmoid notch (TECH FIG 4C). Elevate the interosseous membrane along the distal 8 cm of the radius.
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TECH FIG 4 • A. Intraoperative photograph of implantation with the Aptis system. The dorsoulnar skin incision is placed between the fifth and sixth extensor compartments. B. A large ulnar-based flap of retinaculum is raised for later interposition between the ECU tendon and the implant. C. The ulna is displaced volarly with retractors to expose the interosseous surface of the radius and the sigmoid notch.
D. The radial plate template is positioned and temporarily fixed to the radius. The plate's position is checked with radiographs (inset). E. Operative photograph demonstrating completion of fixation of the radial component. Radiographs confirm correct placement of implant and screw length (inset). F. A sizer with an attached ball is used to determine the level of ulnar resection. This ensures that the ulnar implant with seated polyethylene ball will be level with the radial socket. (continued)
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TECH FIG 4 • (continued) G. Medullary broaches are used to enlarge the medullary canal of the distal ulna. H-J. Steps for final assembly of the system. After the ulnar stem is inserted, the polyethylene ball is placed over the peg. The ball is then aligned with the radial socket and the cap is placed over it and secured with two screws. K. Final radiographs demonstrate correct placement of the implant. L. The previously raised retinacular flap (marked by asterisks) is then placed over the prosthesis and beneath the ECU tendon.
Place the radial trial plate over the interosseous crest of the radius with the volar border aligned with the volar surface of the radius (TECH FIG 4D).
The plate should lie at least 3 mm proximal to the distal end of the sigmoid notch of the radius to avoid impaction with the carpus.
Use a burr to contour the distal radius as necessary to accommodate the plate. Position the plate and hold it temporarily with Kirschner wires passed through the plate.
Use intraoperative imaging to check the position of the plate.
After drilling the hole for the radial peg, remove the trial and gently impact the final radial component in place. Insert fixation screws into the radius to secure the implant and take radiographs (TECH FIG 4E). Remove the Kirschner wires.
With the forearm fully pronated, seat a sizer with attached ball into the hemisocket of the radius and align
it with the ulna (TECH FIG 4F). Determine the level of ulnar resection.
After resecting the distal ulna, insert a 1.6-mm guidewire into the medullary canal and use a cannulated drill to ream the canal.
Insert a medullary broach of the appropriate size into the canal to bevel the distal ulna and plane its distal end (TECH FIG 4G).
Irrigate the medullary canal and insert the stem of the ulnar component (TECH FIG 4H). Place the ultra-high-molecular-weight polyethylene ball over the distal peg and position the ulnar component within the hemisocket of the radial component (TECH FIG 4I).
Position the cover of the socket over the ball and secure it with two small screws (TECH FIG 4J). Obtain radiographs to confirm satisfactory positioning of the prosthesis (TECH FIG 4K).
Position the fascia and retinacular flap between the prosthesis and the ECU tendon and suture them to the radius before doing a layered closure (TECH FIG 4L).
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PEARLS AND PITFALLS
Scar
sensitivity or tenderness
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Identify and protect the sensory branch of the ulnar nerve.
Intraoperative ▪ Broach the distal ulna with caution. In hard cortical bone, use a drill to enlarge
fracture of the cavity before impacting a broach in the ulna. the distal
ulna
Incorrect
ulnar variance
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Before making the ulnar osteotomy, identify the correct level of the DRUJ using
radiographs or along the distal edge of the sigmoid notch.
Loosening of
prosthesis
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Rule out metal allergy, infection.
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Revision options include (1) explanting prosthesis, (2) conversion to interposition arthroplasty with Achilles tendon allograft, (3) conversion to total linked distal DRUJ arthroplasty, or (4) conversion to a one-bone forearm.
Instability of
the prosthesis
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Correct soft tissue insufficiency prior to prosthesis implantation.
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Raise a thick and large flap of soft tissue when exposing the distal ulna. This tissue can be imbricated to stabilize the prosthesis if needed. Alternatively, a distally based strip of the FCU can be wound around the prosthesis to provide volar stability.
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Stability of the implant may not be to demonstrate intraoperatively until the soft tissue envelope is closed over the prosthesis.
POSTOPERATIVE CARE
The forearm is immobilized in neutral rotation and held in a supportive long-arm or Muenster-type splint or cast for 3 weeks.
Active range of motion of the wrist and forearm is initiated at 3 weeks.
A removable splint is required between therapy sessions for 3 weeks.
Therapy is advanced as tolerated after 6 weeks, with strengthening starting only after functional wrist and forearm motion has been obtained.
For a patient with rheumatoid arthritis, poor-quality soft tissue coverage, or mild instability intraoperatively, immobilization in supination for up to 6 weeks must be considered.
Postoperative radiographs should be obtained at 6 weeks, 6 months, and then yearly.
OUTCOMES
Outcomes vary with the indication and type of prosthesis used.3
The pain of radioulnar impingement is relieved in patients with previous excision arthroplasty and stability is restored.9
The range of motion of the forearm after prosthetic replacement remains largely unchanged, as it depends on previous scarring.
Grip strength recovered depends on the underlying problem, but in patients with severe pain and weakness preoperatively, final grip averages about 60% of the opposite side.
Long-term results are limited and variable.
One study reported 6-year survival of implant as 83%.7
Implant failure was associated with a history of previous surgery, use of an extended collar, lucency greater than 2 mm around the implant stem, and pedestal formation at the tip of the implant.7
Continued pain relief and no deterioration or revision requirements were seen in other small, longer term followup studies.10,11
COMPLICATIONS
Immediate- or short-term complications
Infection and wound breakdown, especially in revision cases with poor soft tissue cover Injury to the dorsal sensory branch of the ulnar nerve, leading to tender neuroma Fracture of the distal ulna during reaming or impaction of the prosthesis
Dislocation of the prosthesis from the DRUJ postoperatively Long-term complications
Progressive degeneration of the sigmoid notch Implant loosening
Tenosynovitis of the ECU tendon
Erosion of the radius sigmoid notch with pain Ectopic bone formation around the distal ulna Stress shielding and resorption of distal ulna Prosthetic fracture
ACKNOWLEDGMENTS
The authors thank Small Bone Innovations for permission to use their illustrations for demonstration of operative technique, Dr. Luis Scheker for the images of the Aptis system and Dr. Marc Garcia-Elias for the images of the Eclypse prosthesis.
REFERENCES
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Berger RA. Implant arthroplasty for treatment of ulnar head resectionrelated instability. Hand Clin 2013;29:103-111.
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Berger RA, Cooney WP III. Use of an ulnar head endoprosthesis for treatment of an unstable distal ulnar resection: review of mechanics, indications, and surgical technique. Hand Clin 2005;21:603-620.
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Bizimungu R, Dodds S. Objective outcomes following semiconstrained total distal radioulnar joint arthroplasty. J Wrist Surg 2013;2:319-323.
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Conaway DA, Kuhl TL, Adams BD. Comparison of the native ulnar head and a partial ulnar head resurfacing implant. J Hand Surg Am 2009;34(6):1056-1062.
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Garcia-Elias M. Eclypse: partial ulnar head replacement for isolated DRUJ arthrosis. Tech Hand Upper Extrem Surg 2007;11:121-128.
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Gordon KD, Roth SE, Dunning CE, et al. An anthropometric study of the distal ulna: Implications for implant design. J Hand Surg Am 2002;27(1):57-60.
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Kakar S, Swann P, Perry KI, et al. Functional and radiographic outcomes following distal ulna implant arthroplasty. J Hand Surg Am 2012;37:1364-1371.
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Scheker LR, Babb BA, Killion PE. Distal ulnar prosthetic replacement. Orthop Clin North Am 2001;32:365-376.
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Van Schoonhoven J, Fernandez DL, Bowers WH, et al. Salvage of failed resection arthroplasties of the distal radioulnar joint using a new ulnar head prosthesis. J Hand Surg Am 2000;25(3):438-446.
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Van Schoonhoven J, Muhldorfer-Fodor M, Fernandez DL, et al. Salvage of failed resection arthroplasties of the distal radioulnar joint using an ulnar head prosthesis: long-term results. J Hand Surg Am 2012;37:1372-1380.
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Yen SN, Dion GR, Bowers WH. Ulnar head implant arthroplasty: an intermediate term review of 1 surgeon's experience. Tech Hand Up Extrem Surg 2009;13:160-164.