The design of surface replacement arthroplasty has evolved over the past 20 years. From cemented prostheses such as the SCAN to cementless prostheses such as the Copeland, the basic concept and design of surface replacement favoring maximal bone preservation has remained constant. The indications and surgical technique have been refined over this period. The surface replacement prosthesis has demonstrated clinical results at least equal to those of conventional stemmed prostheses. The indications, surgical techniques, and results of surface replacement shoulder arthroplasty are presented.
Primary osteoarthritis of the shoulder (most common)
Inflammatory arthropathies (e.g., rheumatoid and other inflammatory arthritides)
Secondary osteoarthritis of the shoulder
Arthritis secondary to glenoid dysplasia and epiphysial dysplasia
Bone loss of the humeral head greater than 40% of the surface
Bone is too soft to support the prosthesis
Confirm that patient position allows arm to extend and adduct adequately on table.
Have a low threshold for an acromioplasty and acromioclavicular (AC) joint excision.
Expose the junction of the head and anatomic neck adequately, a crucial step requiring removal of all osteophytes on the humerus.
Accurately identify the center of the humeral head before proceeding.
If in doubt about the size, downsize.
Preserve as much of the bone reamings in the patient’s blood as possible to augment any bone loss in the humeral head; up to 40% bone loss can be reconstituted during a surface replacement.
Remember to perform soft tissue release/balancing as necessary.
Drill the glenoid surface to stimulate bleeding and fibrocartilage regeneration.
Reconstruct soft tissues carefully, including repair of the deltoid during closure.
|00.00–01.45||Exposure, acromioplasty, and AC joint excision|
|01.46–02.45||Soft tissue release|
|02.45–03.38||Dislocation of joint|
|03.39–04.02||Removal of osteophytes|
|04.03–04.44||Locating the center of the humeral head|
|04.44–05.02||Insertion of the central guide wire|
|05.30–05.42||Removal of remaining osteophytes|
|05.43–06.10||Use of central peg reamer and removal of guide wire|
|06.11–06.52||Trial implant insertion and soft tissue balancing|
|06.52–06.57||Checking the range of movement|
|06.58–06.27||Exposure and drilling of the glenoid|
|07.31–07.45||Drilling of the humeral head surface|
|07.46–08.34||Implantation of prosthesis and reduction of joint|
|08.35–09.05||Checking stability and closure|
OVERVIEW OF HUMERAL HEAD RESURFACING
When any prosthetic replacement for arthritis is considered, the only part of the prosthesis that is of use to the patient is the new, shiny interface surface. The patient is unaware of whether this surface is fixed by a stem or cement or by just a pure surface replacement.
The historical prostheses designed by Gluck and Pean had been developed for the late results of infection (tuberculosis); the original constrained joints in Europe, for the problems of tumor replacement ; Neer’s prosthesis, for proximal humeral fracture ; and Grammont’s design, for cuff arthropathy.
Zippel in Germany implanted two surface replacements that were fixed by a transosseous screw, but no follow-up is recorded for these cases. Steffee and Moore in the United States implanted a small hip-resurfacing prosthesis into the shoulder, and in Sweden, in greater numbers, a surface replacement SCAN (Scandinavian) cup was used as a cemented surface replacement.
Development of the Copeland Cementless Surface Replacement Arthroplasty (CSRA) began in 1979, with the first clinical use of the prosthesis occurring in 1986. Since 1993, the entire bony surfaces of the glenoid and humeral components have been hydroxyapatite-coated to allow transformation of the initial mechanical implant into a biologic fixation with bony ingrowth into the hydroxyapatite coating. Simple instruments allow anatomic placement of the humeral head by identifying the center of the sphere. Once this point has been identified, the prosthesis can be positioned to replicate the original anatomic bearing surface, including version, offset, and angulation.
The potential advantages of a cementless surface replacement include the following:
The head is anatomically seated, restoring anatomic variations of version, offset, and angulation in each individual patient.
There is no requirement for intramedullary canal reaming or cementation, making it a less traumatic and safer procedure in an elderly patient given the lowered risk of fat embolus or hypotension.
There are no complications or complications associated with an intramedulalry canal previously filled with cement, fracture fixation devices, or a stem from elbow arthroplasty. If there is a malunion at the proximal end of the humerus with secondary osteoarthritis, the malunion can be left undisturbed, the tuberosities intact, and just the humeral articulation resurfaced.
Unlike stemmed prostheses, there is no stress riser effect that could result in a shaft fracture at the tip of the prosthesis.
Resurfacing can be used in congenital abnormalities of the humerus that do not permit the passage of standard intramedullary stemmed prostheses.
Revision surgery to a stemmed prosthesis or arthrodesis can be performed easily because there is no loss of bone stock and no cement to retrieve from within the humeral shaft.
INDICATIONS AND CONTRAINDICATIONS
Primary and secondary arthritis of the shoulder is the most common indication for humeral head resurfacing. This type of prosthesis has also been used successfully for rheumatoid and other inflammatory arthritides, avascular necrosis, cuff-tear arthropathy, instability arthropathy, posttrauma arthritis, postinfective arthritis, and arthritis secondary to glenoid dysplasia or epiphysis dysplasia.
The results of surface replacement, as in any other shoulder replacement, depend on achieving the appropriate and accurate diagnoses that coincide with the indications. The best results are achieved in cases of osteoarthritis in which the rotator cuff is intact. Conversely, suboptimal results are seen in individuals with cuff-tear arthropathy and also in instances of posttraumatic arthritis. The surface replacement arthroplasty can even be used in circumstances of moderate to severe erosion of the humeral head, in conjunction with bone graft. If there is more than 60% contact between the undersurface of the trial prosthesis and humeral head, after it has been milled, then it would be suitable for surface replacement. In other words, up to 40% of the humeral head may be replaced by bone graft.
The contraindications for surface replacement arthroplasty include active infection, bone loss of the humeral head exceeding 40% of the surface, and acute fractures.
Approximately 92% of our cases requiring shoulder arthroplasty receive a surface replacement. It is our opinion that surface replacement should be the standard prosthesis of choice for all cases, unless specifically contraindicated. The question now is not when to use a surface replacement, but what are the limited residual indications for a stemmed implant?
This operation can be performed under general or regional anesthesia, according to site preferences. We favor a light total intravenous anesthetic in combination with an interscalene block for effective analgesia.
The patient is placed in the beach-chair position with a sandbag underneath the medial scapular border to thrust the shoulder forward. An arm board is attached to the table at the level of the elbow to support the forearm. The arm should be draped free to allow full movement at the shoulder and confirm that it can be adequately extended and adducted.
Either a standard anterior deltopectoral approach or the anterosuperior approach as described by Neviaser and Neviaser and Mackenzie can be used to insert the prosthesis. The advantages of the Mackenzie incision include a smaller and neater scar, easier and more direct access via the rotator interval to the glenoid, and better access to the posterior and superior rotator cuff for reconstruction. It also allows for excision arthroplasty of the acromioclavicular joint and acromioplasty if these are indicated. The acromioclavicular joint excision can be a useful source of bone graft.
The anterosuperior approach leads you onto the rotator cuff. If the cuff is intact or there is a repairable tear, an anterior acromioplasty with partial resection of the coracoacromial ligament should be performed. The coracoacromial arch should be left undisturbed if the rotator cuff is extensively torn or nonfunctional. If preoperative radiographs have shown arthritic changes of the acromioclavicular joint and symptoms suggest this as an origin of pain, then performance of an excision arthroplasty at this stage is indicated. This further improves the surgical exposure. We excise the acromioclavicular joint in almost all patients with osteoarthritis because they usually do not have adequate preoperative range of motion to demonstrate symptoms arising from this joint. At least 80 degrees of forward flexion is required to induce pain at this site, and once range of movement has been restored, this joint can become irritable and impede function of the shoulder. Once the rotator interval at the base of the coracoid is identified, the coracohumeral ligament is released to gain external rotation. A longitudinal incision along the line of the long head of biceps and the rotator interval defines the insertion of the subscapularis. The subscapularis is detached with an osteoperiosteal flap from the medial border of the biceps groove. By extending and adducting the shoulder, the humeral head can be delivered through the wound. If the long head of biceps is intact, it should be displaced posteriorly over the humeral head.
The key landmark for determining the ideal position of the humeral component is the line-of-junction of the head and the anatomic neck of the humerus. One can demonstrate this by removing osteophytes around the neck. The humeral drill guide is placed over the head with its free edge parallel to the junction of the anatomic neck and the humeral head ( Fig. 5-1 ).